INTRODUCTION
To make a satellite phone call today from a location that does not offer terrestrial wireline or wireless coverage requires the use of a large, costly terminal, and entails very high per minute charges. Further, the quality of service is relatively poor because of annoying echoes, large transmission delays, overtalk associated with satellite communications using geostationary satellites. The next generation of satellite communication systems will use advances in satellite systems, wireless technologies, and miniaturization, to provide global mobile satellite services that will make calls between any two locations on earth much easier, much more affordable and much more user friendly.
Even in the year 2000, the terrestrial cellular coverage is available to less than 60% of the world’s population and only about 15% of the earth’s total surface. More than 3 billion of the world’s population have no phone service. The waiting list of landline telephone service has over 50 million names with the average wait greater than 1.5 years. Rural areas, regions, that are sparsely populated in developed countries and large parts of the developing world are destined to be underserved or to remain out of reach of terrestrial mobile services altogether. Thus, in many parts of the world, the demand for communications mobility can be met effectively only through global mobile satellite services. Handheld satellite phones are therefore forecast as the emerging mobile communications frontier with growth that could parallel recent growth in cellular mobile industry. Regardless of how you look at the numbers, there is a significant amount of people without phone service throughout the world. Mobile Satellite communication services will solve the need of worldwide travelers and provide phone services to many areas of the world that currently do not have phone service. The emerging next generating mobile systems are generally referred as GMPCS, for Global Mobile Personal Communication by Satellites.
Until now Communication Satellites have operated using Geo-Stationery Orbits (GEO), lying above 36,000 kilometers above the earth’s surface. From this Orbit the satellite appears to be stationery (fixed) above a specific location from earth, thereby ensuring continuous, uninterrupted coverage to that location. The primary role of a geostationary communications satellite is to act as a wireless repeater station in space that operates in a broadcast mode and provides a microwave link between two remote locations on earth. The key components of a communication satellite include various transponders, transceivers, and antennas that are tuned to the allocated frequency channels. Although the Geostationary Satellites have a large footprint, so that the entire surface of the earth can be covered by few such satellites, their high altitude leads to very long roundtrip signal delays and resultant degradation in service quality.
There is a trend for mobile satellite system architectures aimed at the deployment of multi-satellite constellations in Non-Geostationary Earth Orbits (NGEOs).This allows the user terminals to be small size, low cost and having low power demand.To enhance the coverage and quality of service, Low Earth Orbiting (LEO) constellations are usually selected. To supports a wide range of services and to provide superior service quality comparable to that available from terrestrial wireless and wireline networks, constellations of satellites operating in Low Earth Orbits (LEO) or Medium Earth Orbits (MEO) are considered more suitable.
A number of various global mobile satellite communications systems have already been in development stages. With the first global mobile satellite services initiated in 1998. The four such systems that are in advanced stages of planning or early implementations are Iridium, Globalstar, ICO and Teledesic.
The era of satellite-based mobile communications systems started with the first MARISAT satellite which was launched into a geostationary orbit over the Pacific Ocean in 1976 to provide communications between ships and shore stations. The combination of high cost and unacceptably large equipment has kept mobile satellite communications (MSC) systems from appealing to the wider market of personal mobile communications. However, the progress made over the last ten years in digital voice processing, satellite technology, and component miniaturization has resulted in the viability of MSC systems in responding to the growing market in personal mobile
Communications.The system architectures of each system are presented along with a description of the satellite and user handset designs, the multi-access techniques employed, and an analysis of their respective cost structures.It is concluded that the technical feasibility of satellite-based mobile communications systems seems to be secure. It will be challenging however, for the vendors to actually develop and deploy these systems in a cost effective, timely, and reliable way that meets a continually evolving set of requirements driven by user expectations fueled by a rapidly changing technology base.
In order to guarantee the service quality and reliability for mobile satellite communication systems, we have to take into account outages due to obstruction of the line-of-sight path between a satellite and a mobile terminal as well as the signal fluctuation caused by interference from multipath radio waves. Thus, we need a good characterization for the satellite propagation channel. It is commonly accepted that satellite communications systems (in particular,low earth orbit LEO systems) are the de facto solution for providing the real personal communications services (PCS’s) to the users either stationary or on the move anywhere, anytime and in any format (voice, data,and multimedia).Satellite communication systems have provided international telecommunications services since the 1960’s. These systems were augmented in the 1970’s and 1980’s with regional satellite systems, national systems, and private network-based very small aperture terminals (VSAT’s). Throughout this period, systems have been based exclusively on satellites in geosynchronous orbit communicating with earth stations using high gain fixed antennas. As the systems have evolved, the original 30-m-diameter Intelsat earth stations have evolved into 1.2-m -band VSAT’s for business and home TV usage, but the basic system architecture explaining a geosynchronous spacecraft has not changed during this period. With the launch of the first Iridium spacecraft in 1997 and 1998, a significant new architecture has been introduced into the field of satellite communications. These systems are based upon the use of LEO and medium earth orbiting (MEO) systems. hese LEO and MEO systems have several advantages over geosynchronous systems. The most significant advantages are:
1) The reduction in range provides a large decrease in path loss resulting in much small receiving antennas and
2) The reduction in range provides a significant reduction in propagation delay making voice conversation more pleasing to the user and increasing the throughput of most data communication protocols. These systems can and will serve mobile and portable users
With small near omni antennas.
However, the use of the small antennas as well as the motion of the transmitter and the receiver introduces the possibility of multipath and path blockage into the link budget of these satellite systems. Moreover, the propagation channel will be time varying due to different shadowing and scattering phenomena, so traditional channel models may
not work well.This is concerned with the statistical modeling of the propagation characteristics of LEO and MEO systems. Since in these systems, satellites and mobile users are all allowed to move during communication sessions, the channel characteristics
will be different from the geostationary systems (GEO’s). Due to the movement of receivers or transmitters, the received signals may fluctuate very rapidly from time to time. This fluctuation results from the combining effects of random multipath signals and obstruction of the line-of-sight path, which induces various fading phenomena. The communication quality of service(QoS) parameters such as the word-error rate will be affected in great deal in such communication environment. For effective mobile satellite communications system design, we must quantitatively know the propagation characteristics such as signal fading due to reflection; shadowing from trees, buildings,utility poles, and terrain; Doppler effects due to movement of mobile terminals, mobile satellites, or the communication effects; and other effects such as the rainfall. Such characteristics can be studied by the statistical distribution of the received
signal envelope or received power in mobile communication systems.
Friday, August 27, 2010
MOBILE SATELLITE COMMUNICATION SYSTEM CAN BE BROADLY CLASSIFIED BY ORBIT PERIOD
MOBILE SATELLITE COMMUNICATION SYSTEM CAN BE BROADLY CLASSIFIED BY ORBIT PERIOD
1. Mobile Satellite Communication System by the Geostationary Satellite
The geostationary satellite is the artificial satellite which looks stationary from the ground. 3-4 geostationary satellites can cover almost the entire surface of the earth. Most of the artificial satellites actually used for communications or broadcasting are geostationary satellites.
• i. Altitude: about 36,000km
• ii. Orbit: the circle orbit cycle on the equator is the same as the earth's autorotation time.
• iii. Number of Satellites: four (service areas are duplicated.)
• iv. Principle Satellite System: Inmarsat Communication System, N-STAR Communication System, Omunitrucks Communication System
2. Mobile Satellite Communication System by the Quasi-Zenith Satellite
The quasi-zenith satellite is an artificial satellite of the satellite system where one satellite always stays near the zenith in Japan by positioning at least three satellites synchronously on the orbit inclined at 45 degrees from the geostationary orbit. As the ground surface orbit draws the shape of number 8, it's also called "Number 8 Orbit Satellite". It can obtain a high elevation angle to reduce the influence of buildings and so forth (blocking.)
• i. Altitude: about 36,000km
• ii. Orbit: circle orbit crossing with the equator by the angle of 45 degrees
• iii. 3 as the minimum
• iv. The research and development of the satellite communication system is in progress
3. Mobile Satellite Communication System by the Non-Geostationary Satellite
This is roughly divided into three kinds of orbits: highly elliptic orbit, medium earth orbit, and low earth orbit. The medium and low earth orbits have lower satellite altitudes to shorten the radio transmission delay, enabling more speedy and smooth communication. Specifically, the highly elliptic orbit can obtain a higher elevation angle. It is currently being researched and developed.
i. Highly Elliptic Orbit (HEO)
1. Altitude: about 40,000km
2. Orbit: about 5-6 hours
3. Number of Satellites: 2-3 as the minimum
4. The system planning is in progress.
ii. Medium Earth Orbit (MEO)
1. Altitude: several thousand - 20,000km (about 10,000km)
2. Orbit: about 5-6 hours
3. Number of Satellites: 8-10 (for the entire world)
4. The system planning is in progress.
iii. Low Earth Orbit (LEO)
1. Altitude: 500km - several thousand km (about 1,000km)
2. Orbit: about 5-6 hours
3. Number of Satellites: several dozen (for the entire world)
4. Principle Satellite System: Globalstar Mobile Satellite Communication System, Orbcomm Mobile Satellite Communication System (IRIDIUM Mobile Satellite System (abolished))
Satellites in GSO
GSO satellites orbit the Earth in the equatorial plane with the same angular velocity as the Earth at a height of about 36 000 km above the equator. Geostationary satellites therefore appear stationary to an earth-bound observer and a single satellite can provide continuous service to roughly one third of the Earth's surface (but excluding
polar regions above ± 75 degrees of latitude). The maximum distance the satellite can "see" on the Earth's surface is about 42 000 km and means the propagation delay for a single hop via the satellite (once up and down) can be up to 280 ms. Geostationary satellites also move about their nominal positions causing a small but noticeable Doppler shift on both the feeder and mobile links.For personal and vehicle terminals, handover during a call between GSO satellites is unnecessary because the coverage is static and wide. However handover might be contemplated for aircraft terminals between different spot beams of the same satellite. In the latter case there is practically no difference in path length to consider. Within Europe, GSO satellites appear at low elevation angles. For the geographical latitude of 50°North (e.g.Luxembourg), the satellites reach approximately 31° elevation as a maximum when the satellite is due South: either East or West of this position the elevation slowly reduces. Frequent blocking of the line-of-sight signal therefore occurs from trees, buildings and hills. GSO satellites can work in such a shadowed environment but the satellite Equivalent Isotropic Radiated Power (EIRP) would have to be increased by 15 dB to 20 dB or more depending on the coverage required.This could be achieved but has a serious impact on the size and cost of the satellite. In addition, assuming that the mobile EIRP is limited, the satellite receive sensitivity also has to increase and this can only be done with very large spacecraft dish antennas. For this reason, only very low bit rate services (i.e. paging, alerting, etc.) might be viable under such circumstances until the user moves to a more favourable position to receive a voice call.
Satellites in HEO
Satellites in HEO constellations orbit the Earth in planes that are inclined nominally 63,4° against the equatorial plane.This is necessary in order to keep the apogees in the most northern (southern) positions within their elliptical orbits.Typically HEO orbital periods are between 8 and 24 hours. HEO satellites are normally active only about their apogees where they appear nearly stationary to an earth observer for about eight hours, and then have to hand over to a following satellite.The satellites belonging to one particular system appear in time shift in the same celestial region. In the HEO track is sketched in profile showing at every point the true distance to the Earth's surface. In this specially depicted case, the orbital period is 12 hours and the satellites appear
alternatively at the opposite sides of the rotating globe. Therefore the illustrated HEO track reaches a maximum height at both ends above the geographical latitude of 63,4° North. At both upper ends (solid line), the satellite payloads are active. The dotted line constitutes the part where the satellite payloads are (typically) switched off. For comparison, see figure 2, where two HEO loops are indicated corresponding
to the two ends in profile in figure 1.Under the above conditions, the HEO apogee (maximum height above the Earth's surface) can be up to 42 000 km.However the maximum range to the Earth's surface is in the order of 47 000 km resulting in a maximum propagation delay of the order of 310 ms. HEO satellites reach high relative speeds during their active phase (order of magnitude:2 km/s), so that the Doppler shift (1.3 x 10-5 of radio frequency and bit rate) cannot be neglected: the radio frequency
shift is mainly due to the microwave feeder link and is of the order of 50 kHz for C-band feeder links. The satellite motion is mainly radial relative to the user community, so that common compensation of the Doppler main component is feasible.Irrespective of any user roaming, HEO systems require handover from the descending to the ascending satellite typically every eight hours. Depending on the specific system design, the distance to the two satellites at handover could be significant and a jump in path length cannot be excluded. However, a large Doppler jump will always happen.Within Europe HEO satellites can appear near the zenith. Therefore the user can work under vertical line-of-sight condition for most of the time, with blockage only being experienced in tunnels or under bridges, trees, etc. However vertical propagation is not very good within multi-storey buildings and hence paging, alerting, etc. may not be satisfactory.
Because vertical propagation can be in principle multipath-free, high data rate services are possible for outdoor operation.A number of HEO orbits have been studied extensively and given names such as "Molnya", "Tundra", and "Loopus".
Satellites in MEO
MEO satellites are in principle the same as LEO satellites. The differences are that MEO systems cause more propagation delay (80 ms to 120 ms), their Doppler shift is smaller, and handover happens less frequently and is less problematic. MEOs also need to work in a multipath environment as the number of satellites is usually smaller than for LEO but the average margins can be lower since many calls will be at a continuously high
elevation angle.The typical MEO altitude is between 10 000 km and 20 000 km, just outside the Van Allen belts with an orbital period of around 6 to 12 hours. A complete MEO constellation would probably require between 10 to 15 satellites. MEO satellites are used to provide current global radio navigation services and are optimum for such services.
Satellites in LEO
LEOs are typically circular orbits where satellites fly low above the Earth's atmosphere typically 700 to 1 500 km, bounded by outer atmospheric drag and the Van Allen radiation belts with an orbit time of about 90 minutes. For orbits near 1 500 km, inclinations near 50 degrees reduce the risk of debris collisions. Whereas polar orbits provide a whole Earth coverage including the poles themselves, inclined orbits can provide improved coverage over the populated areas located between latitudes -75 to +75 degrees. One proposed system is known to stay 700 km above the surface (see figure 1; LEO) where the coverage area at any point in time may measure up to 3 000 km in radius for about 10 degree elevation. This implies a maximum propagation delay of 20 ms and while higher altitude LEO systems would have higher propagation delays, they will never approach the values associated with GSO or HEO systems for a single satellite hop. However, on-board processing and Inter-Satellite Links (ISL) can increase delays considerably.LEO satellites move at very high speeds relative to the Earth's surface (7 km/s) and produce large Doppler frequency shifts (4,7x10-5 of radio frequency and bit rate). As the velocity is tangential to the Earth, Doppler compensation may need to be applied individually for each user.LEO systems, in common with HEO systems, also require to handover between adjacent satellites, but at a much more frequent rate of about ten minutes. Although the two LEO satellites are widely spaced, the individual path lengths can be similar and it is possible to minimise any path length jump. However, the Doppler shift jump will still always happen. As LEO satellites orbit very close to Earth, they can be considered as moving base stations. For the user the satellites appear most of the time below 30 degree elevation. Therefore LEO satellites work much of the time in a multipath environment. The additional satellite EIRP and receive sensitivity to compensate for multipath losses are achieved witha much smaller antenna on a LEO spacecraft (compared to GSO) because of the much shorter range (roughly 1/12th).
Diversity techniques may offset some of these multipath effects.The total number of satellites required to give total global coverage depends on many factors including quality of service and system capacity but the total could be as high as 70. Lower numbers are possible using special orbits or by using a mixture of LEO and GSO (for example). The cost for large numbers of LEO satellites is offset to some extent by their lower complexity and easier launch requirements. However their orbital life tends to be half that of typical GSO satellites (10 - 13 years). Another factor in LEO design is the required battery capacity and solar panel size to allow operation for nearly 50% of time in eclipse.
1. Mobile Satellite Communication System by the Geostationary Satellite
The geostationary satellite is the artificial satellite which looks stationary from the ground. 3-4 geostationary satellites can cover almost the entire surface of the earth. Most of the artificial satellites actually used for communications or broadcasting are geostationary satellites.
• i. Altitude: about 36,000km
• ii. Orbit: the circle orbit cycle on the equator is the same as the earth's autorotation time.
• iii. Number of Satellites: four (service areas are duplicated.)
• iv. Principle Satellite System: Inmarsat Communication System, N-STAR Communication System, Omunitrucks Communication System
2. Mobile Satellite Communication System by the Quasi-Zenith Satellite
The quasi-zenith satellite is an artificial satellite of the satellite system where one satellite always stays near the zenith in Japan by positioning at least three satellites synchronously on the orbit inclined at 45 degrees from the geostationary orbit. As the ground surface orbit draws the shape of number 8, it's also called "Number 8 Orbit Satellite". It can obtain a high elevation angle to reduce the influence of buildings and so forth (blocking.)
• i. Altitude: about 36,000km
• ii. Orbit: circle orbit crossing with the equator by the angle of 45 degrees
• iii. 3 as the minimum
• iv. The research and development of the satellite communication system is in progress
3. Mobile Satellite Communication System by the Non-Geostationary Satellite
This is roughly divided into three kinds of orbits: highly elliptic orbit, medium earth orbit, and low earth orbit. The medium and low earth orbits have lower satellite altitudes to shorten the radio transmission delay, enabling more speedy and smooth communication. Specifically, the highly elliptic orbit can obtain a higher elevation angle. It is currently being researched and developed.
i. Highly Elliptic Orbit (HEO)
1. Altitude: about 40,000km
2. Orbit: about 5-6 hours
3. Number of Satellites: 2-3 as the minimum
4. The system planning is in progress.
ii. Medium Earth Orbit (MEO)
1. Altitude: several thousand - 20,000km (about 10,000km)
2. Orbit: about 5-6 hours
3. Number of Satellites: 8-10 (for the entire world)
4. The system planning is in progress.
iii. Low Earth Orbit (LEO)
1. Altitude: 500km - several thousand km (about 1,000km)
2. Orbit: about 5-6 hours
3. Number of Satellites: several dozen (for the entire world)
4. Principle Satellite System: Globalstar Mobile Satellite Communication System, Orbcomm Mobile Satellite Communication System (IRIDIUM Mobile Satellite System (abolished))
Satellites in GSO
GSO satellites orbit the Earth in the equatorial plane with the same angular velocity as the Earth at a height of about 36 000 km above the equator. Geostationary satellites therefore appear stationary to an earth-bound observer and a single satellite can provide continuous service to roughly one third of the Earth's surface (but excluding
polar regions above ± 75 degrees of latitude). The maximum distance the satellite can "see" on the Earth's surface is about 42 000 km and means the propagation delay for a single hop via the satellite (once up and down) can be up to 280 ms. Geostationary satellites also move about their nominal positions causing a small but noticeable Doppler shift on both the feeder and mobile links.For personal and vehicle terminals, handover during a call between GSO satellites is unnecessary because the coverage is static and wide. However handover might be contemplated for aircraft terminals between different spot beams of the same satellite. In the latter case there is practically no difference in path length to consider. Within Europe, GSO satellites appear at low elevation angles. For the geographical latitude of 50°North (e.g.Luxembourg), the satellites reach approximately 31° elevation as a maximum when the satellite is due South: either East or West of this position the elevation slowly reduces. Frequent blocking of the line-of-sight signal therefore occurs from trees, buildings and hills. GSO satellites can work in such a shadowed environment but the satellite Equivalent Isotropic Radiated Power (EIRP) would have to be increased by 15 dB to 20 dB or more depending on the coverage required.This could be achieved but has a serious impact on the size and cost of the satellite. In addition, assuming that the mobile EIRP is limited, the satellite receive sensitivity also has to increase and this can only be done with very large spacecraft dish antennas. For this reason, only very low bit rate services (i.e. paging, alerting, etc.) might be viable under such circumstances until the user moves to a more favourable position to receive a voice call.
Satellites in HEO
Satellites in HEO constellations orbit the Earth in planes that are inclined nominally 63,4° against the equatorial plane.This is necessary in order to keep the apogees in the most northern (southern) positions within their elliptical orbits.Typically HEO orbital periods are between 8 and 24 hours. HEO satellites are normally active only about their apogees where they appear nearly stationary to an earth observer for about eight hours, and then have to hand over to a following satellite.The satellites belonging to one particular system appear in time shift in the same celestial region. In the HEO track is sketched in profile showing at every point the true distance to the Earth's surface. In this specially depicted case, the orbital period is 12 hours and the satellites appear
alternatively at the opposite sides of the rotating globe. Therefore the illustrated HEO track reaches a maximum height at both ends above the geographical latitude of 63,4° North. At both upper ends (solid line), the satellite payloads are active. The dotted line constitutes the part where the satellite payloads are (typically) switched off. For comparison, see figure 2, where two HEO loops are indicated corresponding
to the two ends in profile in figure 1.Under the above conditions, the HEO apogee (maximum height above the Earth's surface) can be up to 42 000 km.However the maximum range to the Earth's surface is in the order of 47 000 km resulting in a maximum propagation delay of the order of 310 ms. HEO satellites reach high relative speeds during their active phase (order of magnitude:2 km/s), so that the Doppler shift (1.3 x 10-5 of radio frequency and bit rate) cannot be neglected: the radio frequency
shift is mainly due to the microwave feeder link and is of the order of 50 kHz for C-band feeder links. The satellite motion is mainly radial relative to the user community, so that common compensation of the Doppler main component is feasible.Irrespective of any user roaming, HEO systems require handover from the descending to the ascending satellite typically every eight hours. Depending on the specific system design, the distance to the two satellites at handover could be significant and a jump in path length cannot be excluded. However, a large Doppler jump will always happen.Within Europe HEO satellites can appear near the zenith. Therefore the user can work under vertical line-of-sight condition for most of the time, with blockage only being experienced in tunnels or under bridges, trees, etc. However vertical propagation is not very good within multi-storey buildings and hence paging, alerting, etc. may not be satisfactory.
Because vertical propagation can be in principle multipath-free, high data rate services are possible for outdoor operation.A number of HEO orbits have been studied extensively and given names such as "Molnya", "Tundra", and "Loopus".
Satellites in MEO
MEO satellites are in principle the same as LEO satellites. The differences are that MEO systems cause more propagation delay (80 ms to 120 ms), their Doppler shift is smaller, and handover happens less frequently and is less problematic. MEOs also need to work in a multipath environment as the number of satellites is usually smaller than for LEO but the average margins can be lower since many calls will be at a continuously high
elevation angle.The typical MEO altitude is between 10 000 km and 20 000 km, just outside the Van Allen belts with an orbital period of around 6 to 12 hours. A complete MEO constellation would probably require between 10 to 15 satellites. MEO satellites are used to provide current global radio navigation services and are optimum for such services.
Satellites in LEO
LEOs are typically circular orbits where satellites fly low above the Earth's atmosphere typically 700 to 1 500 km, bounded by outer atmospheric drag and the Van Allen radiation belts with an orbit time of about 90 minutes. For orbits near 1 500 km, inclinations near 50 degrees reduce the risk of debris collisions. Whereas polar orbits provide a whole Earth coverage including the poles themselves, inclined orbits can provide improved coverage over the populated areas located between latitudes -75 to +75 degrees. One proposed system is known to stay 700 km above the surface (see figure 1; LEO) where the coverage area at any point in time may measure up to 3 000 km in radius for about 10 degree elevation. This implies a maximum propagation delay of 20 ms and while higher altitude LEO systems would have higher propagation delays, they will never approach the values associated with GSO or HEO systems for a single satellite hop. However, on-board processing and Inter-Satellite Links (ISL) can increase delays considerably.LEO satellites move at very high speeds relative to the Earth's surface (7 km/s) and produce large Doppler frequency shifts (4,7x10-5 of radio frequency and bit rate). As the velocity is tangential to the Earth, Doppler compensation may need to be applied individually for each user.LEO systems, in common with HEO systems, also require to handover between adjacent satellites, but at a much more frequent rate of about ten minutes. Although the two LEO satellites are widely spaced, the individual path lengths can be similar and it is possible to minimise any path length jump. However, the Doppler shift jump will still always happen. As LEO satellites orbit very close to Earth, they can be considered as moving base stations. For the user the satellites appear most of the time below 30 degree elevation. Therefore LEO satellites work much of the time in a multipath environment. The additional satellite EIRP and receive sensitivity to compensate for multipath losses are achieved witha much smaller antenna on a LEO spacecraft (compared to GSO) because of the much shorter range (roughly 1/12th).
Diversity techniques may offset some of these multipath effects.The total number of satellites required to give total global coverage depends on many factors including quality of service and system capacity but the total could be as high as 70. Lower numbers are possible using special orbits or by using a mixture of LEO and GSO (for example). The cost for large numbers of LEO satellites is offset to some extent by their lower complexity and easier launch requirements. However their orbital life tends to be half that of typical GSO satellites (10 - 13 years). Another factor in LEO design is the required battery capacity and solar panel size to allow operation for nearly 50% of time in eclipse.
SOME LEO SATELLITE SYSTEM
SOME LEO SATELLITE SYSTEM
1. THE IRIDIUM SYSTEM
The Iridium System is not proposed to be a replacement for existing terrestrial cellular systems, but rather as an extension of existing wireless systems to provide mobile services to remote and sparsely populated areas that are not covered by terrestrial cellular services. It provides more capacity (large no of channels) and better quality of service (shorter transmission delays) to areas that currently receive mobile services from geostationary satellites. It can also provide emergency service in the event that terrestrial cellular services are disabled in disaster situations(earthquakes,fires,floods,etc.).
The concept of using a constellation of low earth orbit satellites to provide global telecommunication services to mobile users. Because the initial proposal called for 77 satellites in the constellation, the system was called IRIDIUM after the element, which has 77 electrons in its orbit.later studies indicated that only 66 satellite would be adequate to provide the targeted services and performance. The 66 satellites are are grouped in six orbital planes; there are 11 active satellites in each plane with uniform nominal spacing of 32.7”. the satellites have circular orbits at an altitude of 783 km, and for each plane an in-orbit satellite is provided.
Satellites in one plane are placed to travel out of phase with those in the adjacent planes. Except for the first and last planes, which are counterrotating where they are adjacent, all remaining planes are corotating, The distance between corotating planes is 31.6, and the distance between the counterrotating planes is 22. The reduced seperation between counterrotating planes is needed to compensate for the reduced coverage provided by satellites on counterrotating planes. In the Iridium system, each satellite is equipped with four two-way communication links(intersatellite links, or ISLs), one each with its neighbors in the same plane and with those in the adjacent planes.
Each Iridium satellite uses a 48-beam antenna pattern, and each beam, which has a minimum diameter of 600 km, can be individually switched. For example, only about two-thirds of the beams will be active at any given time because some the beams will be switched off when the satellites are in the vicinity of the poles, where beam patterns tend to overlap, or when the satellites are over countries or regions in which, Iridium does not have regulatory arrangements to operate. The switched of beams is referred a cell management. In a LEO-based system like Iridium, the beams are equivalent to cells associated with terrestrial mobile systems. However, in case of the Iridium system, it is the beams that move rapidly relative to the subscriber, who is considered to be stationary with respect to the satellite. Thus, switching of beams or cell management to provide continuity of an existing call is equivalent to handoff in terrestrial cellular mobile systems. This requirement for cell management is, of course, and additional complexity associated with LEO- based systems compared with MEO or GEO systems.
The Iridium system supports links of three types:up- and downlinks from the space vehicle (SV) to the gateway (GW) [or to the telemetry, tracking, and control (TT & C) center], using the ka band; up- and downlinks between the SV and the Iridium subscriber unit (ISU), using the L band; and two-way inter-satellite links between the SVs using the Ka band.
2. THE GLOBALSTAR SYSTEM
Globalstar is a global mobile satellite system based on a constellation of 48 LEO satellites. Unlike the Iridium system, Globalstar system does not use intersatellite links but rather depends on a large number of interconnected earth stations or gateways for efficient call routing and delivery over the terrestrial network. It is designed to complement the terrestrial cellular mobile networks to provide telephony and messaging services to subscribers in locations that are not covered, or inadequately covered, by conventional wireline or wireless networks.
Globalstar’s constellation of 48 LEO satellites is designed t orbit at an altitude of 1414 km above earth’s surface in eight orbital plans inclined at 52. With each plane to be occupied by six satellited with a provision for one in-orbit spare satellite in each plane. The nominal weight of each satellite is 450 kg, with a deployed span of 7 meters and working life of 7.5 years. Since Globalstar satellites do not employ intersatellite communication, they essentially provide only transponder functions, making their design and operation less complex and perhaps more reliable. Each satellite supports a 16-beam antenna pattern with an average beam diameter of 2250 km. To mitigate blocking and shadowing, Globalstar will deploy path diversity, whereby multiple satellites may be used to complete a call.
In the absence of intersatellite links, the Globalstar system makes maximum use of the international terrestrial networks (wireline and wireless). Calls from a subscriber are routed via a satellite to the nearest earth station/gateway, and from there they will be routed over the existing terrestrial network. To provide the interface between the ground segment (terrestrial networks) and space segment (Globalstar satellites) Globalstar design deploys 100 or more gateway stations distributed around the world with each station equipped with three or five antennas that can track the trajectories of the satellites. A Globalstar gateway is designed to serve an area 3000 km in diameter and will be designed to take into account the technical and administrative requirements of the coverage area. These requirements may include such factors as coverage, quality of service, and satellite visibility, as well as regulatory and contractual factors associated with national boundaries.
Globalstar uses two types of communication links: service links in the L/S band for communication between the terminals and the space vehicle, and the gateway links in the C band for communication between the earth stations and the space vehicle.
]3. THE TELEDESIC SYSTEM
Currently the high bandwidth, high quality fiber connectivity needed to support Internet access, computer internetworking, video conferencing, and so on is restricted to major commercial and population centers. Outside these application areas, such facilities are either too expensive or simply not available. The aim of the Teledesic network is to extend the existing terrestrial, fiber-based infrastructure to provide advanced information and communication services anywhere on earth. Whereas the target application for Iridium, Globalstar, and ICO is voice, with support of low bit rate data for facsimile and messaging for mobile subscribers, the primary target application for the Teledesic system is the provide worldwide, seamless, fiber like connectivity to support multimedia, video, and high bit rate data services. In a strict sense, Teledesic does not fall in the category of global mobile satellite systems or GMPCS because its focus is not on worldwide terminal mobility, but rather on providing the so-called Internet in the sky function. The planned target for Teledesic service availability is end of year 2002. Rather than individual end users, primary customers for the Teledesic system will be service providers in countries around the world wishing to extend their network capabilities in terms of geographic scope and the range of services, and also multinational corporations needing to extend the capabilities of their enterprise networks.
The design of the Teledesic system has not been finalized. According to the original plans, the Teledesic satellite segment was to use 840 LEO satellites in 21 planes at altitudes of 700 km. The Teledesic system now intends to deploy only 288 active LEO satellites placed in 12 planes (24 satellites per plane) at altitudes around 1350 km. Each satellite in the Teledesic constellation will have connections to eight of its neighboring satellites through intersatellite links operating in the connectionless packet mode, with each satellite in this interconnected mesh network providing necessary switching functions. The Teledesic network is designed for dual-satellite visibility with at lest one insight satellite at a minimum elevation of 40. This high elevation angle ensures an unobstructed and omnidirectional view of the sky from most building tops where Teledesic terminals may be located. Besides eliminating shadowing effects from neighboring buildings and terrain, the high elevation angel greatly reduces the fading effects of rain at high frequencies.
1. THE IRIDIUM SYSTEM
The Iridium System is not proposed to be a replacement for existing terrestrial cellular systems, but rather as an extension of existing wireless systems to provide mobile services to remote and sparsely populated areas that are not covered by terrestrial cellular services. It provides more capacity (large no of channels) and better quality of service (shorter transmission delays) to areas that currently receive mobile services from geostationary satellites. It can also provide emergency service in the event that terrestrial cellular services are disabled in disaster situations(earthquakes,fires,floods,etc.).
The concept of using a constellation of low earth orbit satellites to provide global telecommunication services to mobile users. Because the initial proposal called for 77 satellites in the constellation, the system was called IRIDIUM after the element, which has 77 electrons in its orbit.later studies indicated that only 66 satellite would be adequate to provide the targeted services and performance. The 66 satellites are are grouped in six orbital planes; there are 11 active satellites in each plane with uniform nominal spacing of 32.7”. the satellites have circular orbits at an altitude of 783 km, and for each plane an in-orbit satellite is provided.
Satellites in one plane are placed to travel out of phase with those in the adjacent planes. Except for the first and last planes, which are counterrotating where they are adjacent, all remaining planes are corotating, The distance between corotating planes is 31.6, and the distance between the counterrotating planes is 22. The reduced seperation between counterrotating planes is needed to compensate for the reduced coverage provided by satellites on counterrotating planes. In the Iridium system, each satellite is equipped with four two-way communication links(intersatellite links, or ISLs), one each with its neighbors in the same plane and with those in the adjacent planes.
Each Iridium satellite uses a 48-beam antenna pattern, and each beam, which has a minimum diameter of 600 km, can be individually switched. For example, only about two-thirds of the beams will be active at any given time because some the beams will be switched off when the satellites are in the vicinity of the poles, where beam patterns tend to overlap, or when the satellites are over countries or regions in which, Iridium does not have regulatory arrangements to operate. The switched of beams is referred a cell management. In a LEO-based system like Iridium, the beams are equivalent to cells associated with terrestrial mobile systems. However, in case of the Iridium system, it is the beams that move rapidly relative to the subscriber, who is considered to be stationary with respect to the satellite. Thus, switching of beams or cell management to provide continuity of an existing call is equivalent to handoff in terrestrial cellular mobile systems. This requirement for cell management is, of course, and additional complexity associated with LEO- based systems compared with MEO or GEO systems.
The Iridium system supports links of three types:up- and downlinks from the space vehicle (SV) to the gateway (GW) [or to the telemetry, tracking, and control (TT & C) center], using the ka band; up- and downlinks between the SV and the Iridium subscriber unit (ISU), using the L band; and two-way inter-satellite links between the SVs using the Ka band.
2. THE GLOBALSTAR SYSTEM
Globalstar is a global mobile satellite system based on a constellation of 48 LEO satellites. Unlike the Iridium system, Globalstar system does not use intersatellite links but rather depends on a large number of interconnected earth stations or gateways for efficient call routing and delivery over the terrestrial network. It is designed to complement the terrestrial cellular mobile networks to provide telephony and messaging services to subscribers in locations that are not covered, or inadequately covered, by conventional wireline or wireless networks.
Globalstar’s constellation of 48 LEO satellites is designed t orbit at an altitude of 1414 km above earth’s surface in eight orbital plans inclined at 52. With each plane to be occupied by six satellited with a provision for one in-orbit spare satellite in each plane. The nominal weight of each satellite is 450 kg, with a deployed span of 7 meters and working life of 7.5 years. Since Globalstar satellites do not employ intersatellite communication, they essentially provide only transponder functions, making their design and operation less complex and perhaps more reliable. Each satellite supports a 16-beam antenna pattern with an average beam diameter of 2250 km. To mitigate blocking and shadowing, Globalstar will deploy path diversity, whereby multiple satellites may be used to complete a call.
In the absence of intersatellite links, the Globalstar system makes maximum use of the international terrestrial networks (wireline and wireless). Calls from a subscriber are routed via a satellite to the nearest earth station/gateway, and from there they will be routed over the existing terrestrial network. To provide the interface between the ground segment (terrestrial networks) and space segment (Globalstar satellites) Globalstar design deploys 100 or more gateway stations distributed around the world with each station equipped with three or five antennas that can track the trajectories of the satellites. A Globalstar gateway is designed to serve an area 3000 km in diameter and will be designed to take into account the technical and administrative requirements of the coverage area. These requirements may include such factors as coverage, quality of service, and satellite visibility, as well as regulatory and contractual factors associated with national boundaries.
Globalstar uses two types of communication links: service links in the L/S band for communication between the terminals and the space vehicle, and the gateway links in the C band for communication between the earth stations and the space vehicle.
]3. THE TELEDESIC SYSTEM
Currently the high bandwidth, high quality fiber connectivity needed to support Internet access, computer internetworking, video conferencing, and so on is restricted to major commercial and population centers. Outside these application areas, such facilities are either too expensive or simply not available. The aim of the Teledesic network is to extend the existing terrestrial, fiber-based infrastructure to provide advanced information and communication services anywhere on earth. Whereas the target application for Iridium, Globalstar, and ICO is voice, with support of low bit rate data for facsimile and messaging for mobile subscribers, the primary target application for the Teledesic system is the provide worldwide, seamless, fiber like connectivity to support multimedia, video, and high bit rate data services. In a strict sense, Teledesic does not fall in the category of global mobile satellite systems or GMPCS because its focus is not on worldwide terminal mobility, but rather on providing the so-called Internet in the sky function. The planned target for Teledesic service availability is end of year 2002. Rather than individual end users, primary customers for the Teledesic system will be service providers in countries around the world wishing to extend their network capabilities in terms of geographic scope and the range of services, and also multinational corporations needing to extend the capabilities of their enterprise networks.
The design of the Teledesic system has not been finalized. According to the original plans, the Teledesic satellite segment was to use 840 LEO satellites in 21 planes at altitudes of 700 km. The Teledesic system now intends to deploy only 288 active LEO satellites placed in 12 planes (24 satellites per plane) at altitudes around 1350 km. Each satellite in the Teledesic constellation will have connections to eight of its neighboring satellites through intersatellite links operating in the connectionless packet mode, with each satellite in this interconnected mesh network providing necessary switching functions. The Teledesic network is designed for dual-satellite visibility with at lest one insight satellite at a minimum elevation of 40. This high elevation angle ensures an unobstructed and omnidirectional view of the sky from most building tops where Teledesic terminals may be located. Besides eliminating shadowing effects from neighboring buildings and terrain, the high elevation angel greatly reduces the fading effects of rain at high frequencies.
MEO SATELLITE SYSTEM
MEO SATELLITE SYSTEM
1. THE ICO SYSTEM
The ICO is a medium earth orbit (MEO) mobile satellite system, which is designed primarily to provide services to handheld phones. ICO will use TDMA as the radio transmission technology. The system is designed to offer digital voice, data, facsimile, and short-targeted messaging services to its subscribers. ICO’s primary target customers are users from the existing terrestrial cellular systems who expect to travel to locations in which coverage is unavailable or inadequate. Other customer groups potentially served by ICO include road transport, maritime, and aeronautical users, as well as users of semifixed terminals in rural areas and develo0ping countries, where conventions terrestrial wireline or wireless mobile satellite communications capability with the public land mobile networks like GSM, D-AMPS, and PDC and their PCS variants.
ICO system is designed to use a constellation of 10 MEO satellites in intermediate circular orbit (ICO), at an altitude of 10,355 km above the earth’s surface. The nominal weight of these satellites at launch is less than 2000 kg. The satellites, with an expected life of 12 years, are arranged in two planes with five satellites (and one spare) in each plane: orbital planes inclined at 45 relative to the equator. Each satellite has antennas to provide 163 transmit and receive service link beams. The orbital configuration provides coverage of earth’s entire surface at all times and ensures significant overlap so that two or more satellites are visible to the user and the satellite access node (SAN) at any time. Further, at least one of the satellites appears at the high elevation angle, thereby minimizing the probability of blocking due to shadowing effects.
The ground segment in the ICO system, which will link the ICO satellites to the terrestrial networks, will consist of the 12 interconnected SANs located in various parts of the world. Each SAN consists of earth stations with multiple antennas for communication with the satellites, switching equipment, and databases to facilitate interconnection with public telephone, data, and mobile networks. The interconnection to the public networks is through appropriate gateways. Whereas each SAN supports VLR functions, the HLR function can reside in one (or more) of the SANs. A SAN tracks the satellites within its sight and will direct communication traffic to the satellite, which can provide reliable, uninterrupted link for a given call, in terms of angle of elevation and duration of satellite visibility. SANs also have the capability to execute handoffs from an area covered by one satellite to another satellite’s coverage. Such handoffs are expected to be very infrequent in ICO’s MEO-based system. Besides the SANs, the ICO system deploys TT & C stations connected to a satellite control center (SCC) for monitoring and controlling the satellites, as well as one or more network control centers (NCC) for overall management and control of the ICO system. The TT & C functions are associated with 6 of the 12 interconnected SANs.
A broad overview how a mobile satellite system works
A satellite system consists of a satellite segment, ground segment, and end-user segment.
Satellite Segment
The satellite segment is a network of GEO or LEO satellites arranged in orbital planes (i.e. different parts of the sky) in such a way that they have a communications link with end-user equipment, ground gateways and other satellites. The satellites transmit a continuous signal to earth which enables the satellites, end-user equipment and
gateways to be linked together. The links allow end-users to be transferred between satellites as the satellites move overhead (LEO systems). On the ground, there is a ground control facility (or facilities) which manage the performance of the satellites and the transfer of information from the satellites to the gateways.
Ground segment - gateways
The gateway connects the satellites to the local telephone network. The gateway also transmits signals to the satellites and receives transmission from the satellites. The gateway tends to have switching capabilities along with software that allows the system provider to keep track of billing information and route calls.
End-user
The end user terminals, pagers and phones communicate with the gateway equipment, satellites, satellite and cellular phones along with the cellular base station equipment. For the Iridium and Globalstar systems, the endusers will use a phone slightly larger than the average cellular phone. Both Iridium and Globalstar plan to offer dual mode handsets which will allow users to connect to the existing cellular systems or their own satellite system.Other systems from such companies as American Mobile Satellite and Intelsat, use phones which are the size of a briefcase and must be unpacked before use. The paging equipment from Iridium, the only satellite company who currently has a paging system in place, is your normal run of the mill pager. A few satellite systems (Globalstar included) plan to offer fixed satellite terminals which are a telephone booth in rural areas. The phone booth will include one or more phones and will not look much different than a phone booth you may find on the streets of New York City.
1. THE ICO SYSTEM
The ICO is a medium earth orbit (MEO) mobile satellite system, which is designed primarily to provide services to handheld phones. ICO will use TDMA as the radio transmission technology. The system is designed to offer digital voice, data, facsimile, and short-targeted messaging services to its subscribers. ICO’s primary target customers are users from the existing terrestrial cellular systems who expect to travel to locations in which coverage is unavailable or inadequate. Other customer groups potentially served by ICO include road transport, maritime, and aeronautical users, as well as users of semifixed terminals in rural areas and develo0ping countries, where conventions terrestrial wireline or wireless mobile satellite communications capability with the public land mobile networks like GSM, D-AMPS, and PDC and their PCS variants.
ICO system is designed to use a constellation of 10 MEO satellites in intermediate circular orbit (ICO), at an altitude of 10,355 km above the earth’s surface. The nominal weight of these satellites at launch is less than 2000 kg. The satellites, with an expected life of 12 years, are arranged in two planes with five satellites (and one spare) in each plane: orbital planes inclined at 45 relative to the equator. Each satellite has antennas to provide 163 transmit and receive service link beams. The orbital configuration provides coverage of earth’s entire surface at all times and ensures significant overlap so that two or more satellites are visible to the user and the satellite access node (SAN) at any time. Further, at least one of the satellites appears at the high elevation angle, thereby minimizing the probability of blocking due to shadowing effects.
The ground segment in the ICO system, which will link the ICO satellites to the terrestrial networks, will consist of the 12 interconnected SANs located in various parts of the world. Each SAN consists of earth stations with multiple antennas for communication with the satellites, switching equipment, and databases to facilitate interconnection with public telephone, data, and mobile networks. The interconnection to the public networks is through appropriate gateways. Whereas each SAN supports VLR functions, the HLR function can reside in one (or more) of the SANs. A SAN tracks the satellites within its sight and will direct communication traffic to the satellite, which can provide reliable, uninterrupted link for a given call, in terms of angle of elevation and duration of satellite visibility. SANs also have the capability to execute handoffs from an area covered by one satellite to another satellite’s coverage. Such handoffs are expected to be very infrequent in ICO’s MEO-based system. Besides the SANs, the ICO system deploys TT & C stations connected to a satellite control center (SCC) for monitoring and controlling the satellites, as well as one or more network control centers (NCC) for overall management and control of the ICO system. The TT & C functions are associated with 6 of the 12 interconnected SANs.
A broad overview how a mobile satellite system works
A satellite system consists of a satellite segment, ground segment, and end-user segment.
Satellite Segment
The satellite segment is a network of GEO or LEO satellites arranged in orbital planes (i.e. different parts of the sky) in such a way that they have a communications link with end-user equipment, ground gateways and other satellites. The satellites transmit a continuous signal to earth which enables the satellites, end-user equipment and
gateways to be linked together. The links allow end-users to be transferred between satellites as the satellites move overhead (LEO systems). On the ground, there is a ground control facility (or facilities) which manage the performance of the satellites and the transfer of information from the satellites to the gateways.
Ground segment - gateways
The gateway connects the satellites to the local telephone network. The gateway also transmits signals to the satellites and receives transmission from the satellites. The gateway tends to have switching capabilities along with software that allows the system provider to keep track of billing information and route calls.
End-user
The end user terminals, pagers and phones communicate with the gateway equipment, satellites, satellite and cellular phones along with the cellular base station equipment. For the Iridium and Globalstar systems, the endusers will use a phone slightly larger than the average cellular phone. Both Iridium and Globalstar plan to offer dual mode handsets which will allow users to connect to the existing cellular systems or their own satellite system.Other systems from such companies as American Mobile Satellite and Intelsat, use phones which are the size of a briefcase and must be unpacked before use. The paging equipment from Iridium, the only satellite company who currently has a paging system in place, is your normal run of the mill pager. A few satellite systems (Globalstar included) plan to offer fixed satellite terminals which are a telephone booth in rural areas. The phone booth will include one or more phones and will not look much different than a phone booth you may find on the streets of New York City.
How a satellite call gets routed
How a satellite call gets routed
There are two types of satellite systems under development and each have a different approach to routing phone calls. The proposed satellite systems will use either a bent pipe or an intersatellite linked system.
Bent pipe
In a bent pipe system (Globalstar) a call is placed by a satellite user which is then beamed up to the nearest orbiting satellite. The satellite reflects the call to the nearest ground gateway. Once at the gateway, the call is routed through the public telephone network to the intended receiver of the call. The gateway must be in the line of sight of the satellite, so the system operator must have a significant number of ground gateways to provide direct satellite links. For the most part, a bent pipe system is less complex than an intersatellite linked system because the brains of the system (switching) are on the ground and the satellites are just reflectors in the sky. Bent pipe systems are easier to operate because most of the call is transferred over the public telephone network, this also reduces the cost of the system. Many of the technical features will be located at the gateway which will allows most technical problems to be fixed on the ground.
Intersatellite links
In an intersatellite linked system (Iridium) a user’s call is beamed up to the nearest orbiting satellite. When it reaches the satellite, the call enters the onboard satellite switching system and is routed between satellites up in space. The call is then downlinked to another satellite user or the closest local gateway to the end user. Upon
entering the gateway the call is directed to the intended receiver through the public telephone network. The major benefit of the intersatellite linked system is that it minimizes the cost of the ground segment (i.e. - the call is switched in the air therefore you do not need a ground gateway in the line of sight of each satellite) and it also
minimizes the long distance and interconnect fees (much of which is bypassed in the air). The intersatellite linked system operator is able to keep a larger dollar amount of each call as compared to the bent pipe system operator.However, there is added risk and higher costs because each satellite must have on-board switching capabilities.On-board switching also adds to the complexity of the system because repairs must be made to satellites.
There are two types of satellite systems under development and each have a different approach to routing phone calls. The proposed satellite systems will use either a bent pipe or an intersatellite linked system.
Bent pipe
In a bent pipe system (Globalstar) a call is placed by a satellite user which is then beamed up to the nearest orbiting satellite. The satellite reflects the call to the nearest ground gateway. Once at the gateway, the call is routed through the public telephone network to the intended receiver of the call. The gateway must be in the line of sight of the satellite, so the system operator must have a significant number of ground gateways to provide direct satellite links. For the most part, a bent pipe system is less complex than an intersatellite linked system because the brains of the system (switching) are on the ground and the satellites are just reflectors in the sky. Bent pipe systems are easier to operate because most of the call is transferred over the public telephone network, this also reduces the cost of the system. Many of the technical features will be located at the gateway which will allows most technical problems to be fixed on the ground.
Intersatellite links
In an intersatellite linked system (Iridium) a user’s call is beamed up to the nearest orbiting satellite. When it reaches the satellite, the call enters the onboard satellite switching system and is routed between satellites up in space. The call is then downlinked to another satellite user or the closest local gateway to the end user. Upon
entering the gateway the call is directed to the intended receiver through the public telephone network. The major benefit of the intersatellite linked system is that it minimizes the cost of the ground segment (i.e. - the call is switched in the air therefore you do not need a ground gateway in the line of sight of each satellite) and it also
minimizes the long distance and interconnect fees (much of which is bypassed in the air). The intersatellite linked system operator is able to keep a larger dollar amount of each call as compared to the bent pipe system operator.However, there is added risk and higher costs because each satellite must have on-board switching capabilities.On-board switching also adds to the complexity of the system because repairs must be made to satellites.
Handover Management in Mobile Satellite Systems
Handover Management in Mobile Satellite Systems
Due to the high mobility of low earth orbit (LEO) satellites, there is a significant number of handover attempts in a LEO-based mobile satellite communication system, causing a
high handover failure rate. This paper proposes to extend the period of which a handover request is valid, and thus rendering higher probability of successful handover. Satellite
communication service can be provided by geostationary earth orbit (GEO), medium earth orbit (MEO) or low earth orbit (LEO) satellites. Because of its much shorter distance from earth, lower power requirement and thus smaller mobile terminal (MT) size, LEO satellite system is a preferable choice. In this paper, only the LEO satellite system is considered. The satellite coverage area, or its footprint, is divided into a number of areas, each of which spotted by one of the satellite's multiple spotbeams, forming a cell. Since a LEO satellite is not located at a geosynchronous orbit, it is mobile with respect to a fixed point on earth. Hence an active MT may move from one cell to another and handover occurs. The ground velocity of the MT is ignored compared to the
much higher satellite velocity. Suppose the length of a cell is 400 km and the satellite moves at a velocity of 6.6 km/sec, the time taken for a MT to cross a cell, Tcell, is about 60 seconds. Thus handover is extremely frequent in this system. And it is probable that a call is dropped due to unsuccessful handover. Handover is prone to failure when the subsequent cell has no unused channel to offer. Drop call is a phenomenon where an ongoing call has to be discontinued, which the users find hard to tolerate with, making it a major technical issue.There have been some methods proposed to minimise handover failure. It is widely accepted that handover requests are to be prioritised over new call requests, either by allocating guard channels to the handover requests [1], or by queuing up the handover requests when all the channels in one cell are occupied [1] [2]. This is because dropping an ongoing call is less desirable than blocking a new call attempt. There are also proposals of making the handover request earlier, so that the request has longer time to wait for a free channel, thus reducing the handover failure rate [3] [4].
Gerard Maral et al. have proposed that a handover request is to be made to a cell as early as the MT enters the cell located right before the target cell [3]. In [4], the time of sending out a handover request during handover process was made available regardless of the location of MS in a cell. In all of these cases, a call somehow has to be terminated when the originating MT has crossed into the target cell and yet handover is not granted by the target cell. The termination is done since no service is provided by either the original cell or the target cell. In this paper it is proposed that in a similar situation, the call be only temporarily discontinued for a specific amount of time, before it is permanently terminated if there is still no available channel. Although no service is provided by both cells to the MT, its handover request which has been queued is ‘kept in view’ by the target cell. During this idle period, there is a chance that an originally occupied channel in the target cell is released. If this is the case, this channel is allocated to the suspended call and handover is completed. As a result, the handover failure rate is reduced.
Mathematical analysis has been carried out to verify the idea and the results are encouraging. For a user, he/she only experiences a short period of call discontinuity and is notified about the temporary discontinuity through a special tone. In terms of quality of service (QoS), this is more tolerable to the users compared to a drop call.
A handover management strategy is proposed to efficiently manage the channel resource of a cell in a multibeam mobile satellite system (MSS) and improves its service quality by reducing the interbeam handover failure rate (Phf) caused by limited number of communication channels. The Extended Queueing of Handover (EQH) technique extends the channel reservation time of a handover request into the adjacent cell that the user terminal (UT) is subsequently entering (destination cell). Both mathematical analysis and simulation show that EQH reduces Phf significantly, without compromising the new call
admission rate and efficiency of channel utilisation.
The footprint of a multibeam satellite is divided into cells where each cell is illuminated by a spotbeam. Interbeam handover is frequent in mobile satellite system (MSS) due to the high velocity of the satellite (about 7 km/h for a low earth orbit satellite). When a user terminal (UT) leaves from one cell and enters the adjacent one, a handover process must be completed for the sake of call continuity, where a
communication channel must be allocated to the UT by the adjacent cell (destination cell). In a channel resource limited system, handover is subject to failure when the destination cell has no idle channel to offer. In this case the call is dropped and this is intolerable to users. In order to provide higher handover quality, system operator has to allocate a larger portion of the channel resource to the ongoing call as compared to the new call. A method in use is by applying the blocked-calls-queued policy to the calls
requesting for handover (handover calls) [1]; and on the other hand sacrificing some new calls through the blocked-call-cleared policy. The longer a handover call stays in a queue, the higher chance of it being handed over successfully. Other methods that prioritise handover call over new call are: guard channelallocation [2], and channel reservation in advance [3] [4]. The compromise of new call causes inefficiency in channel utilisation because channels that are allocated to handover call cannot be taken up by new calls even though they are idle.
Due to the high mobility of low earth orbit (LEO) satellites, there is a significant number of handover attempts in a LEO-based mobile satellite communication system, causing a
high handover failure rate. This paper proposes to extend the period of which a handover request is valid, and thus rendering higher probability of successful handover. Satellite
communication service can be provided by geostationary earth orbit (GEO), medium earth orbit (MEO) or low earth orbit (LEO) satellites. Because of its much shorter distance from earth, lower power requirement and thus smaller mobile terminal (MT) size, LEO satellite system is a preferable choice. In this paper, only the LEO satellite system is considered. The satellite coverage area, or its footprint, is divided into a number of areas, each of which spotted by one of the satellite's multiple spotbeams, forming a cell. Since a LEO satellite is not located at a geosynchronous orbit, it is mobile with respect to a fixed point on earth. Hence an active MT may move from one cell to another and handover occurs. The ground velocity of the MT is ignored compared to the
much higher satellite velocity. Suppose the length of a cell is 400 km and the satellite moves at a velocity of 6.6 km/sec, the time taken for a MT to cross a cell, Tcell, is about 60 seconds. Thus handover is extremely frequent in this system. And it is probable that a call is dropped due to unsuccessful handover. Handover is prone to failure when the subsequent cell has no unused channel to offer. Drop call is a phenomenon where an ongoing call has to be discontinued, which the users find hard to tolerate with, making it a major technical issue.There have been some methods proposed to minimise handover failure. It is widely accepted that handover requests are to be prioritised over new call requests, either by allocating guard channels to the handover requests [1], or by queuing up the handover requests when all the channels in one cell are occupied [1] [2]. This is because dropping an ongoing call is less desirable than blocking a new call attempt. There are also proposals of making the handover request earlier, so that the request has longer time to wait for a free channel, thus reducing the handover failure rate [3] [4].
Gerard Maral et al. have proposed that a handover request is to be made to a cell as early as the MT enters the cell located right before the target cell [3]. In [4], the time of sending out a handover request during handover process was made available regardless of the location of MS in a cell. In all of these cases, a call somehow has to be terminated when the originating MT has crossed into the target cell and yet handover is not granted by the target cell. The termination is done since no service is provided by either the original cell or the target cell. In this paper it is proposed that in a similar situation, the call be only temporarily discontinued for a specific amount of time, before it is permanently terminated if there is still no available channel. Although no service is provided by both cells to the MT, its handover request which has been queued is ‘kept in view’ by the target cell. During this idle period, there is a chance that an originally occupied channel in the target cell is released. If this is the case, this channel is allocated to the suspended call and handover is completed. As a result, the handover failure rate is reduced.
Mathematical analysis has been carried out to verify the idea and the results are encouraging. For a user, he/she only experiences a short period of call discontinuity and is notified about the temporary discontinuity through a special tone. In terms of quality of service (QoS), this is more tolerable to the users compared to a drop call.
A handover management strategy is proposed to efficiently manage the channel resource of a cell in a multibeam mobile satellite system (MSS) and improves its service quality by reducing the interbeam handover failure rate (Phf) caused by limited number of communication channels. The Extended Queueing of Handover (EQH) technique extends the channel reservation time of a handover request into the adjacent cell that the user terminal (UT) is subsequently entering (destination cell). Both mathematical analysis and simulation show that EQH reduces Phf significantly, without compromising the new call
admission rate and efficiency of channel utilisation.
The footprint of a multibeam satellite is divided into cells where each cell is illuminated by a spotbeam. Interbeam handover is frequent in mobile satellite system (MSS) due to the high velocity of the satellite (about 7 km/h for a low earth orbit satellite). When a user terminal (UT) leaves from one cell and enters the adjacent one, a handover process must be completed for the sake of call continuity, where a
communication channel must be allocated to the UT by the adjacent cell (destination cell). In a channel resource limited system, handover is subject to failure when the destination cell has no idle channel to offer. In this case the call is dropped and this is intolerable to users. In order to provide higher handover quality, system operator has to allocate a larger portion of the channel resource to the ongoing call as compared to the new call. A method in use is by applying the blocked-calls-queued policy to the calls
requesting for handover (handover calls) [1]; and on the other hand sacrificing some new calls through the blocked-call-cleared policy. The longer a handover call stays in a queue, the higher chance of it being handed over successfully. Other methods that prioritise handover call over new call are: guard channelallocation [2], and channel reservation in advance [3] [4]. The compromise of new call causes inefficiency in channel utilisation because channels that are allocated to handover call cannot be taken up by new calls even though they are idle.
Friday, August 20, 2010
1 smartcard
5. Providing Value-Added Services
One of the most compelling benefits of smart cards is the potential for packaging and bundling various complementary services around basic mobile telephony services. These services can greatly reduce churn and increase usage and brand recognition (see Figure).
Figure Service Bundling with Smart Cards
The SIM card’s chip can be programmed to carry multiple applications. The activation of new applications can be downloaded to the card over the air, in real time, thereby reducing the time (and cost) to market.
Providing value-added services such as mobile banking, Web browsing, or travel services creates a high cost of exit for the customer. Long-distance companies have successfully used joint programs with airline companies to ensure the long-term loyalty of their customers. The more services a customer receives, the more difficult it is for the customer to leave the service provider. Smart cards provide an excellent vehicle for surrounding the core wireless service with these other valuable services, and packaging- and service-bundling opportunities are numerous. Examples of such opportunities are as follows:
• GSM Cellnet and Barclaycard, Europe’s largest credit-card issuer, developed a wireless, financial-services smart card. The SIM card activates the user’s Cellnet GSM phone and also provides a Barclays services menu. The services available via this alliance include the following:
o access to Barclays credit-card information
o access to Barclays checking-account information
o access to Barclays customer care
• Initially, the Barclaycard services will be provided via live customer service representatives who will answer calls from customers. Future enhancements will enable users to pay household bills, shop, and access financial information services while on the move.
• Swedish bank PostGirot implemented a utility bill–payment application in the Telia Mobitel SIM card. Mobile phone users accessed the service by simple menu navigation and keying information such as origin and destination bank-account numbers, date of payment, and amount, which enables them to pay their utility bills away from home.
One of the most compelling benefits of smart cards is the potential for packaging and bundling various complementary services around basic mobile telephony services. These services can greatly reduce churn and increase usage and brand recognition (see Figure).
Figure Service Bundling with Smart Cards
The SIM card’s chip can be programmed to carry multiple applications. The activation of new applications can be downloaded to the card over the air, in real time, thereby reducing the time (and cost) to market.
Providing value-added services such as mobile banking, Web browsing, or travel services creates a high cost of exit for the customer. Long-distance companies have successfully used joint programs with airline companies to ensure the long-term loyalty of their customers. The more services a customer receives, the more difficult it is for the customer to leave the service provider. Smart cards provide an excellent vehicle for surrounding the core wireless service with these other valuable services, and packaging- and service-bundling opportunities are numerous. Examples of such opportunities are as follows:
• GSM Cellnet and Barclaycard, Europe’s largest credit-card issuer, developed a wireless, financial-services smart card. The SIM card activates the user’s Cellnet GSM phone and also provides a Barclays services menu. The services available via this alliance include the following:
o access to Barclays credit-card information
o access to Barclays checking-account information
o access to Barclays customer care
• Initially, the Barclaycard services will be provided via live customer service representatives who will answer calls from customers. Future enhancements will enable users to pay household bills, shop, and access financial information services while on the move.
• Swedish bank PostGirot implemented a utility bill–payment application in the Telia Mobitel SIM card. Mobile phone users accessed the service by simple menu navigation and keying information such as origin and destination bank-account numbers, date of payment, and amount, which enables them to pay their utility bills away from home.
2 smartcard
6. Factors Driving Smart-Card Acceptance
6.1 Other Industries and Institutions
Certain industries, in particular information technology (IT), government, and financial services, will lead the way to mass-market acceptance of smart cards.
Large IT players are deploying public key infrastructure (PKI) to provide secure logical access to information. PKI is becoming the way to secure messaging and browsing of private information, leading the way to secure electronic commerce. Smart cards are the ideal vehicle to transport the digital certificate associated with the trusted third parties of PKI infrastructures. They provide secure certificate portability and can combine other security applications such as disk file encryption and secure computer log-on. The inclusion of smart-card readers in the equipment listed in the PC99 recommendation has already driven large computer manufacturers to integrate smart-card readers into their product offer (for example, Hewlett Packard and Compaq).
Government agencies around the world are relying on smart-card technology to secure off-line portable information, including identification documents and electronic benefit transfer systems. A Brazilian province has issued its drivers licenses on smart cards to allow the police to view securely stored ticket information immediately. The U.S. government is a major early adopter of smart cards. It has instituted numerous smart card identification programs for its defense department and recently announced that it will further explore the nationwide use of smart cards for electronic benefit transfers as a fraud reduction tool.
In the financial industry, large players such as Barclays and Citibank currently use SIM cards to provide banking information to mobile users via their GSM phones. Electronic purse systems based on VisaCash, Mondex, Proton, and other schemes are deployed around the world and account for tens of millions of cards in Asia, Europe, and Latin America. Major U.S. banks are considering or conducting trials of smart card-based systems. The push by these major financial services firms will serve to accelerate consumer acceptance.
6.2 Consumers Primed to Use Smart Cards
Research conducted by the Smart Card Forum, an interindustry association dedicated to advancing multiapplication smart cards, has generated the following statistics:
• 45 percent of consumers are favorably disposed to using smart cards
• 25 percent of households would actually obtain these smart cards
• 44 percent of consumers are likely to use identification-type smart cards (telephone cards, gas cards, automated teller machine [ATM] cards, etc.)
7 Smart Card?
A smart card is a credit-card sized plastic card embedded with an integrated circuit chip that makes it "smart". This marriage between a convenient plastic card and a microprocessor allows an immense amount of information to be stored, accessed and processed either online or offline. Smart cards can store several hundred times more data than a conventional card with a magnetic
stripe. The information or application stored in the IC chip is transferred through an electronic module that interconnects with a terminal or a card reader. A contactless smart card has an antenna coil which communicates with a receiving antenna to transfer information. Depending on the type of the embedded chip, smart cards can be either memory cards or processor cards.
6.1 Other Industries and Institutions
Certain industries, in particular information technology (IT), government, and financial services, will lead the way to mass-market acceptance of smart cards.
Large IT players are deploying public key infrastructure (PKI) to provide secure logical access to information. PKI is becoming the way to secure messaging and browsing of private information, leading the way to secure electronic commerce. Smart cards are the ideal vehicle to transport the digital certificate associated with the trusted third parties of PKI infrastructures. They provide secure certificate portability and can combine other security applications such as disk file encryption and secure computer log-on. The inclusion of smart-card readers in the equipment listed in the PC99 recommendation has already driven large computer manufacturers to integrate smart-card readers into their product offer (for example, Hewlett Packard and Compaq).
Government agencies around the world are relying on smart-card technology to secure off-line portable information, including identification documents and electronic benefit transfer systems. A Brazilian province has issued its drivers licenses on smart cards to allow the police to view securely stored ticket information immediately. The U.S. government is a major early adopter of smart cards. It has instituted numerous smart card identification programs for its defense department and recently announced that it will further explore the nationwide use of smart cards for electronic benefit transfers as a fraud reduction tool.
In the financial industry, large players such as Barclays and Citibank currently use SIM cards to provide banking information to mobile users via their GSM phones. Electronic purse systems based on VisaCash, Mondex, Proton, and other schemes are deployed around the world and account for tens of millions of cards in Asia, Europe, and Latin America. Major U.S. banks are considering or conducting trials of smart card-based systems. The push by these major financial services firms will serve to accelerate consumer acceptance.
6.2 Consumers Primed to Use Smart Cards
Research conducted by the Smart Card Forum, an interindustry association dedicated to advancing multiapplication smart cards, has generated the following statistics:
• 45 percent of consumers are favorably disposed to using smart cards
• 25 percent of households would actually obtain these smart cards
• 44 percent of consumers are likely to use identification-type smart cards (telephone cards, gas cards, automated teller machine [ATM] cards, etc.)
7 Smart Card?
A smart card is a credit-card sized plastic card embedded with an integrated circuit chip that makes it "smart". This marriage between a convenient plastic card and a microprocessor allows an immense amount of information to be stored, accessed and processed either online or offline. Smart cards can store several hundred times more data than a conventional card with a magnetic
stripe. The information or application stored in the IC chip is transferred through an electronic module that interconnects with a terminal or a card reader. A contactless smart card has an antenna coil which communicates with a receiving antenna to transfer information. Depending on the type of the embedded chip, smart cards can be either memory cards or processor cards.
4 smartcard
8. Classification of Smart Cards
Due to the communication with the reader and functionality of smart cards, they are classified differently.
8.1. Contact vs Contactless
As smart cards have embedded microprocessors, they need energy to function and some mechanism to communicate, receiving and sending the data. Some smart cards have golden plates, contact pads, at one corner of the card. This type of smart cards are called Contact Smart Cards. The plates are used to supply the necessary energy and to communicate via direct electrical contact with the reader. When you insert the card into the reader, the contacts in the reader sit on the plates. According to ISO7816 standards the PIN connections are below:
,----, ,----,
| C1 | | C5 | C1 : Vcc = 5V C5 : Gnd
'----' '----' C2 : Reset C6 : Vpp
,----, ,----, C3 : Clock C7 : I/O
| C2 | | C6 | C4 : RFU C8 : RFU
'----' '----'
,----, ,----,
| C3 | | C7 |
'----' '----'
,----, ,----,
| C4 | | C8 |
'----' '----'
• I/O : Input or Output for serial data to the integrated circuit inside the card.
• Vpp : Programing voltage input (optional use by the card).
• Gnd : Ground (reference voltage).
• CLK : Clocking or timing signal (optional use by the card).
• RST: Either used itself (reset signal supplied from the interface device) or in combination with an internal reset control circuit (optional use by the card). If internal reset is implemented, the voltage supply on Vcc is mandatory.
• Vcc : Power supply input (optional use by the card).
The readers for contact smart cards are generally a separate device plugged into serial or USB port. There are keyboards, PCs or PDAs which have built-in readers like GSM cell phones. They also have embedded readers for GSM style mini smart cards.
Some smart cards do not have a contact pad on their surface.The connection between the reader and the card is done via radio frequency (RF). But they have small wire loop embedded inside the card. This wire loop is used as an inductor to supply the energy to the card and communicate with the reader. When you insert the card into the readers RF field, an induced current is created in the wire loop and used as an energy source. With the modulation of the RF field, the current in the inductor, the communication takes place.
The readers of smart cards usually connected to the computer via USB or serial port. As the contactless cards are not needed to be inserted into the reader, usually they are only composed of a serial interface for the computer and an antenna to connect to the card. The readers for contactless smart cards may or may not have a slot. The reason is some smart cards can be read upto 1.5 meters away from the reader but some needs to be positioned a few millimeters from the reader to be read accurately.
There is one another type of smart card, combo card. A combo card has a contact pad for the transaction of large data, like PKI credentials, and a wire loop for mutual authentication. Contact smart cards are mainly used in electronic security whereas contactless cards are used in transportation and/or door locks.
8.2. Memory vs Microprocessor
The most common and least expensive smart cards are memory cards. This type of smart cards, contains EEPROM(Electrically Erasable Programmable Read-Only Memory), non-volatile memory. Because it is non-volatile when you remove the card from the reader, power is cut off, card stores the data. You can think of EEPROM, inside, just like a normal data storage device which has a file system and managed via a microcontroller (mostly 8 bit). This microcontroller is responsible for accessing the files and accepting the communication. The data can be locked with a PIN (Personal Identification Number), your password. PIN's are normally 3 to 8 digit numbers those are written to a special file on the card. Because this type is not capable of cryptography, memory cards are used in storing telephone credits, transportation tickets or electronic cash.
Microprocessor cards, are more like the computers we use on our desktops. They have RAM, ROM and EEPROM with a 8 or 16 bit microprocessor. In ROM there is an operating system to manage the file system in EEPROM and run desired functions in RAM.
----------------
| 8 or 16 bit |
Reader <===| microprocessor |-----+
---------------- |
|
|---> RAM
NON-CRYPTOGRAPHIC |
CARD |---> ROM
|
+---> EEPROM
As seen in the diagram above all communication is done over the microprocessor, There is no direct connection between the memory and the contacts. The operating system is responsible for the security of the data in memory because the access conditions are controlled by the OS.
---------------- --------
| 8 or 16 bit | | Crypto |
Reader <===| microprocessor |-----------| Module |
---------------- | --------
|
|---> RAM
CRYPTOGRAPHIC |
CARD |---> ROM
|
+---> EEPROM
With the addition of a crypto module our smart card can now handle complex mathematical computations regarding to PKI. Because the internal clock rate of microcontrollers are 3 to 5 MHz, there is a need to add a component, accelerator for the cryptographic functions. The crypto-cards are more expensive than non-crypto smart cards and so do microprocessor card than memory cards.
Depending on your application you should choose right card.
8.3. PC cards
While any IC-embedded card may be called a smart card, its distinguishing feature is its use for personal activities. For example, PC cards (also known as PCMCIA cards) have the same characteristics as a smart card but they are used as peripheral devices such as modems or game cartridges. These PC cards are seldom called smart cards since they are extension devices without personalization. In this sense, a smart card is a processor card that allows persons to interact with others digitally to conduct transactions and other personal activities.
Due to the communication with the reader and functionality of smart cards, they are classified differently.
8.1. Contact vs Contactless
As smart cards have embedded microprocessors, they need energy to function and some mechanism to communicate, receiving and sending the data. Some smart cards have golden plates, contact pads, at one corner of the card. This type of smart cards are called Contact Smart Cards. The plates are used to supply the necessary energy and to communicate via direct electrical contact with the reader. When you insert the card into the reader, the contacts in the reader sit on the plates. According to ISO7816 standards the PIN connections are below:
,----, ,----,
| C1 | | C5 | C1 : Vcc = 5V C5 : Gnd
'----' '----' C2 : Reset C6 : Vpp
,----, ,----, C3 : Clock C7 : I/O
| C2 | | C6 | C4 : RFU C8 : RFU
'----' '----'
,----, ,----,
| C3 | | C7 |
'----' '----'
,----, ,----,
| C4 | | C8 |
'----' '----'
• I/O : Input or Output for serial data to the integrated circuit inside the card.
• Vpp : Programing voltage input (optional use by the card).
• Gnd : Ground (reference voltage).
• CLK : Clocking or timing signal (optional use by the card).
• RST: Either used itself (reset signal supplied from the interface device) or in combination with an internal reset control circuit (optional use by the card). If internal reset is implemented, the voltage supply on Vcc is mandatory.
• Vcc : Power supply input (optional use by the card).
The readers for contact smart cards are generally a separate device plugged into serial or USB port. There are keyboards, PCs or PDAs which have built-in readers like GSM cell phones. They also have embedded readers for GSM style mini smart cards.
Some smart cards do not have a contact pad on their surface.The connection between the reader and the card is done via radio frequency (RF). But they have small wire loop embedded inside the card. This wire loop is used as an inductor to supply the energy to the card and communicate with the reader. When you insert the card into the readers RF field, an induced current is created in the wire loop and used as an energy source. With the modulation of the RF field, the current in the inductor, the communication takes place.
The readers of smart cards usually connected to the computer via USB or serial port. As the contactless cards are not needed to be inserted into the reader, usually they are only composed of a serial interface for the computer and an antenna to connect to the card. The readers for contactless smart cards may or may not have a slot. The reason is some smart cards can be read upto 1.5 meters away from the reader but some needs to be positioned a few millimeters from the reader to be read accurately.
There is one another type of smart card, combo card. A combo card has a contact pad for the transaction of large data, like PKI credentials, and a wire loop for mutual authentication. Contact smart cards are mainly used in electronic security whereas contactless cards are used in transportation and/or door locks.
8.2. Memory vs Microprocessor
The most common and least expensive smart cards are memory cards. This type of smart cards, contains EEPROM(Electrically Erasable Programmable Read-Only Memory), non-volatile memory. Because it is non-volatile when you remove the card from the reader, power is cut off, card stores the data. You can think of EEPROM, inside, just like a normal data storage device which has a file system and managed via a microcontroller (mostly 8 bit). This microcontroller is responsible for accessing the files and accepting the communication. The data can be locked with a PIN (Personal Identification Number), your password. PIN's are normally 3 to 8 digit numbers those are written to a special file on the card. Because this type is not capable of cryptography, memory cards are used in storing telephone credits, transportation tickets or electronic cash.
Microprocessor cards, are more like the computers we use on our desktops. They have RAM, ROM and EEPROM with a 8 or 16 bit microprocessor. In ROM there is an operating system to manage the file system in EEPROM and run desired functions in RAM.
----------------
| 8 or 16 bit |
Reader <===| microprocessor |-----+
---------------- |
|
|---> RAM
NON-CRYPTOGRAPHIC |
CARD |---> ROM
|
+---> EEPROM
As seen in the diagram above all communication is done over the microprocessor, There is no direct connection between the memory and the contacts. The operating system is responsible for the security of the data in memory because the access conditions are controlled by the OS.
---------------- --------
| 8 or 16 bit | | Crypto |
Reader <===| microprocessor |-----------| Module |
---------------- | --------
|
|---> RAM
CRYPTOGRAPHIC |
CARD |---> ROM
|
+---> EEPROM
With the addition of a crypto module our smart card can now handle complex mathematical computations regarding to PKI. Because the internal clock rate of microcontrollers are 3 to 5 MHz, there is a need to add a component, accelerator for the cryptographic functions. The crypto-cards are more expensive than non-crypto smart cards and so do microprocessor card than memory cards.
Depending on your application you should choose right card.
8.3. PC cards
While any IC-embedded card may be called a smart card, its distinguishing feature is its use for personal activities. For example, PC cards (also known as PCMCIA cards) have the same characteristics as a smart card but they are used as peripheral devices such as modems or game cartridges. These PC cards are seldom called smart cards since they are extension devices without personalization. In this sense, a smart card is a processor card that allows persons to interact with others digitally to conduct transactions and other personal activities.
5 smartcard
9. Operating Systems
New trend in smart card operating systems is JavaCard Operating System. JavaCard OS was developed by Sun Microsystems and than promoted to JavaCard Forum. Java Card OS is popular because it gives independence to the programmers over architecture. And Java OS based applications could be used on any vendor of smart card that support JavaCard OS.
Most of the smart cards today use their own OS for underlying communication and functions. But to give true support for the applications smart cards operating systems go beyond the simple functions supplied by ISO7816 standards. As a result porting your application, developed on one vendor, to another vendor of smart card becomes very hard work.Another advantage of JavaCard OS is, it allows the concept of post-issuance application loading. This allows you to upgrade the applications on smart card after delivering the card to the end-user. The importance is, when someone needs a smart card he/she is in need of a specific application to run. But later the demand can change and more applications could be necessary.
Another operating system for smart cards is MULTOS (Multi-application Operating System). As the name suggests MULTOS also supports multi-applications. But MULTOS was specifically designed for high-security needs. And in many countries MULTOS has achieved "ITSec E6 High" in many countries.
And also Microsoft is on the smart card highway with Smart Card for Windows.
In a point of view the above Operating Systems are Card-Side API's to develop cardlets or small programs that run on the card. Also there is Reader-Side API's like OpenCard Framework and GlobalPlatform.
New trend in smart card operating systems is JavaCard Operating System. JavaCard OS was developed by Sun Microsystems and than promoted to JavaCard Forum. Java Card OS is popular because it gives independence to the programmers over architecture. And Java OS based applications could be used on any vendor of smart card that support JavaCard OS.
Most of the smart cards today use their own OS for underlying communication and functions. But to give true support for the applications smart cards operating systems go beyond the simple functions supplied by ISO7816 standards. As a result porting your application, developed on one vendor, to another vendor of smart card becomes very hard work.Another advantage of JavaCard OS is, it allows the concept of post-issuance application loading. This allows you to upgrade the applications on smart card after delivering the card to the end-user. The importance is, when someone needs a smart card he/she is in need of a specific application to run. But later the demand can change and more applications could be necessary.
Another operating system for smart cards is MULTOS (Multi-application Operating System). As the name suggests MULTOS also supports multi-applications. But MULTOS was specifically designed for high-security needs. And in many countries MULTOS has achieved "ITSec E6 High" in many countries.
And also Microsoft is on the smart card highway with Smart Card for Windows.
In a point of view the above Operating Systems are Card-Side API's to develop cardlets or small programs that run on the card. Also there is Reader-Side API's like OpenCard Framework and GlobalPlatform.
Sunday, August 15, 2010
Introduction
Introduction
The term “BIOMETRICS” is derived from the Greek words “bio” (life) and “metrics” (to measure).Biometrics refers to methods for uniquely recognizing humans based upon one or more intrinsic physical or behavioral traits. In information technology, in particular, biometrics is used as a form of identity access management and access control.
OK, so what is biometrics and why should we be concerned with them?
Biometrics is best defined as measurable physiological and / or behavioral characteristics that can be utilized to verify the identity of an individual. They include fingerprints, retinal and iris scanning, hand geometry, voice patterns, facial recognition and other techniques. They are of interest in any area where it is important to verify the true identity of an individual. Initially, these techniques were employed primarily in specialist high security applications; however we are now seeing their use and proposed use in a much broader range of public facing situations.
So what was wrong with cards and PIN’s?
PIN’s (personal identification numbers) were one of the first identifiers to offer automated recognition. However, it should be understood that this means recognition of the PIN, not necessarily recognition of the person who has provided it. The same applies with cards and other tokens. We may easily recognize the token, but it could be presented by anybody. Using the two together provides a slightly higher confidence level, but this is still easily compromised if one is determined to do so.
A biometric however cannot be easily transferred between individuals and represents as a unique identifier as we are likely to see. If we can automate the verification procedure in a user friendly manner, there is considerable scope for integrating biometrics into a variety of processes.
What does this mean in practice?
It means that verifying an individuals identity can become both more streamlined (by the user interacting with the biometric reader) and considerably more accurate as biometric devices are not easily fooled.
In the context of travel and tourism for example, one immediately thinks of immigration control, boarding gate identity verification and other security related functions. However, there may be a raft of other potential applications in areas such as marketing, premium passenger services, online booking, and so on where a biometric may be usefully integrated into a given process at some stage. In addition, there are organization related applications such as workstation / LAN access, physical access control and other potential applications.
This does not mean that biometrics is a panacea for all our personal identification related issues. But they do represent an interesting new tool in our technology toolbox, which we might usefully consider as we march forward into the new millennium.
The term “BIOMETRICS” is derived from the Greek words “bio” (life) and “metrics” (to measure).Biometrics refers to methods for uniquely recognizing humans based upon one or more intrinsic physical or behavioral traits. In information technology, in particular, biometrics is used as a form of identity access management and access control.
OK, so what is biometrics and why should we be concerned with them?
Biometrics is best defined as measurable physiological and / or behavioral characteristics that can be utilized to verify the identity of an individual. They include fingerprints, retinal and iris scanning, hand geometry, voice patterns, facial recognition and other techniques. They are of interest in any area where it is important to verify the true identity of an individual. Initially, these techniques were employed primarily in specialist high security applications; however we are now seeing their use and proposed use in a much broader range of public facing situations.
So what was wrong with cards and PIN’s?
PIN’s (personal identification numbers) were one of the first identifiers to offer automated recognition. However, it should be understood that this means recognition of the PIN, not necessarily recognition of the person who has provided it. The same applies with cards and other tokens. We may easily recognize the token, but it could be presented by anybody. Using the two together provides a slightly higher confidence level, but this is still easily compromised if one is determined to do so.
A biometric however cannot be easily transferred between individuals and represents as a unique identifier as we are likely to see. If we can automate the verification procedure in a user friendly manner, there is considerable scope for integrating biometrics into a variety of processes.
What does this mean in practice?
It means that verifying an individuals identity can become both more streamlined (by the user interacting with the biometric reader) and considerably more accurate as biometric devices are not easily fooled.
In the context of travel and tourism for example, one immediately thinks of immigration control, boarding gate identity verification and other security related functions. However, there may be a raft of other potential applications in areas such as marketing, premium passenger services, online booking, and so on where a biometric may be usefully integrated into a given process at some stage. In addition, there are organization related applications such as workstation / LAN access, physical access control and other potential applications.
This does not mean that biometrics is a panacea for all our personal identification related issues. But they do represent an interesting new tool in our technology toolbox, which we might usefully consider as we march forward into the new millennium.
Popular Biometric Methodologies
Popular Biometric Methodologies
• Fingerprint Verification
• Hand Geometry
• Voice Verification
• Retinal Scanning
• Iris Recognition
• Facial Recognition
Fingerprint verification
The analysis of fingerprints for matching purposes generally requires the comparison of several features of the print pattern. These include patterns, which are aggregate characteristics of ridges, and minutia points, which are unique features found within the patterns.
Patterns
The three basic patterns of fingerprint ridges are the arch, loop, and whorl.
An arch is a pattern where the ridges enter from one side of the finger, rise in the center forming an arc, and then exit the other side of the finger.
The loop is a pattern where the ridges enter from one side of a finger, form a curve, and tend to exit from the same side they enter.
In the whorl pattern, ridges form circularly around a central point on the finger.
Minutia features
The major Minutia features of fingerprint ridges are: ridge ending, bifurcation, and short ridge (or dot).
The ridge ending is the point at which a ridge terminates.
Bifurcations are points at which a single ridge splits into two ridges.
Short ridges (or dots) are ridges which are significantly shorter than the average ridge length on the fingerprint.
Minutiae and patterns are very important in the analysis of fingerprints since no two fingers have been shown to be identical.
Hand geometry
As the name suggests, hand geometry is concerned with measuring the physical characteristics of the users hand and fingers, from a three dimensional perspective in the case of the leading product. Since hand geometry is not thought to be as unique as fingerprints or irises, fingerprinting and iris recognition remain the preferred technology for high-security applications. Hand geometry is very reliable when combined with other forms of identification, such as identification cards or personal identification numbers. In large populations, hand geometry is not suitable for so-called one-to-many applications, in which a user is identified from his biometric without any other identification.
• Fingerprint Verification
• Hand Geometry
• Voice Verification
• Retinal Scanning
• Iris Recognition
• Facial Recognition
Fingerprint verification
The analysis of fingerprints for matching purposes generally requires the comparison of several features of the print pattern. These include patterns, which are aggregate characteristics of ridges, and minutia points, which are unique features found within the patterns.
Patterns
The three basic patterns of fingerprint ridges are the arch, loop, and whorl.
An arch is a pattern where the ridges enter from one side of the finger, rise in the center forming an arc, and then exit the other side of the finger.
The loop is a pattern where the ridges enter from one side of a finger, form a curve, and tend to exit from the same side they enter.
In the whorl pattern, ridges form circularly around a central point on the finger.
Minutia features
The major Minutia features of fingerprint ridges are: ridge ending, bifurcation, and short ridge (or dot).
The ridge ending is the point at which a ridge terminates.
Bifurcations are points at which a single ridge splits into two ridges.
Short ridges (or dots) are ridges which are significantly shorter than the average ridge length on the fingerprint.
Minutiae and patterns are very important in the analysis of fingerprints since no two fingers have been shown to be identical.
Hand geometry
As the name suggests, hand geometry is concerned with measuring the physical characteristics of the users hand and fingers, from a three dimensional perspective in the case of the leading product. Since hand geometry is not thought to be as unique as fingerprints or irises, fingerprinting and iris recognition remain the preferred technology for high-security applications. Hand geometry is very reliable when combined with other forms of identification, such as identification cards or personal identification numbers. In large populations, hand geometry is not suitable for so-called one-to-many applications, in which a user is identified from his biometric without any other identification.
Voice verification
Voice verification
Voice biometrics works by digitizing a profile of a person's speech to produce a stored model voice print, or template. Biometric technology reduces each spoken word to segments composed of several dominant frequencies called formants. Each segment has several tones that can be captured in a digital format. The tones collectively identify the speaker's unique voice print. Voice prints are stored in databases in a manner similar to the storing of fingerprints or other biometric data.
To ensure a good-quality voice sample, a person usually recites some sort of text or pass phrase, which can be either a verbal phrase or a series of numbers. The phrase may be repeated several times before the sample is analyzed and accepted as a template in the database. When a person speaks the assigned pass phrase, certain words are extracted and compared with the stored template for that individual. When a user attempts to gain access to the system, his or her pass phrase is compared with the previously stored voice model. These systems are trained to recognize similarities between the voice patterns of individuals when the persons speak unfamiliar phrases and the stored templates.
A person's speech is subject to change depending on health and emotional state. Matching a voice print requires that the person speak in the normal voice that was used when the template was created at enrollment. If the person suffers from a physical ailment, such as a cold, or is unusually excited or depressed, the voice sample submitted may be different from the template and will not match. Other factors also affect voice recognition results. Background noise and the quality of the input device (the microphone) can create additional challenges for voice recognition systems. However, much work has been and continues to be undertaken in this context and it will be interesting to monitor progress accordingly.
Retinal scanning
A biometric identifier known as a retinal scan is used to map the unique patterns of a person's retina. The blood vessels within the retina absorb light more readily than the surrounding tissue and are easily identified with appropriate lighting. A retinal scan is performed by casting an unperceived beam of low-energy infrared light into a person’s eye as they look through the scanner's eyepiece. This beam of light traces a standardized path on the retina. Because retinal blood vessels are more absorbent of this light than the rest of the eye, the amount of reflection varies during the scan. The pattern of variations is converted to computer code and stored in a database.
Retinal scanners are typically used for authentication and identification purposes. Retinal scanning has been utilized by several government agencies including the FBI, CIA, and NASA. However, in recent years, retinal scanning has become more commercially popular. Retinal scanning has been used in prisons, for ATM identity verification and the prevention of welfare fraud.
Iris recognition
The iris is the colored ring of t issue surrounding the pupil of the eye. The iris is unique to an individual. To use the iris as a biometric it needs to be scanned by a device similar to a camera. An iris scan can then be matched against a library of templates to identify or authenticate an individual. It has been demonstrated to work with spectacles in place and with a variety of ethnic groups and is one of the few devices which can work well in identification mode.
Voice biometrics works by digitizing a profile of a person's speech to produce a stored model voice print, or template. Biometric technology reduces each spoken word to segments composed of several dominant frequencies called formants. Each segment has several tones that can be captured in a digital format. The tones collectively identify the speaker's unique voice print. Voice prints are stored in databases in a manner similar to the storing of fingerprints or other biometric data.
To ensure a good-quality voice sample, a person usually recites some sort of text or pass phrase, which can be either a verbal phrase or a series of numbers. The phrase may be repeated several times before the sample is analyzed and accepted as a template in the database. When a person speaks the assigned pass phrase, certain words are extracted and compared with the stored template for that individual. When a user attempts to gain access to the system, his or her pass phrase is compared with the previously stored voice model. These systems are trained to recognize similarities between the voice patterns of individuals when the persons speak unfamiliar phrases and the stored templates.
A person's speech is subject to change depending on health and emotional state. Matching a voice print requires that the person speak in the normal voice that was used when the template was created at enrollment. If the person suffers from a physical ailment, such as a cold, or is unusually excited or depressed, the voice sample submitted may be different from the template and will not match. Other factors also affect voice recognition results. Background noise and the quality of the input device (the microphone) can create additional challenges for voice recognition systems. However, much work has been and continues to be undertaken in this context and it will be interesting to monitor progress accordingly.
Retinal scanning
A biometric identifier known as a retinal scan is used to map the unique patterns of a person's retina. The blood vessels within the retina absorb light more readily than the surrounding tissue and are easily identified with appropriate lighting. A retinal scan is performed by casting an unperceived beam of low-energy infrared light into a person’s eye as they look through the scanner's eyepiece. This beam of light traces a standardized path on the retina. Because retinal blood vessels are more absorbent of this light than the rest of the eye, the amount of reflection varies during the scan. The pattern of variations is converted to computer code and stored in a database.
Retinal scanners are typically used for authentication and identification purposes. Retinal scanning has been utilized by several government agencies including the FBI, CIA, and NASA. However, in recent years, retinal scanning has become more commercially popular. Retinal scanning has been used in prisons, for ATM identity verification and the prevention of welfare fraud.
Iris recognition
The iris is the colored ring of t issue surrounding the pupil of the eye. The iris is unique to an individual. To use the iris as a biometric it needs to be scanned by a device similar to a camera. An iris scan can then be matched against a library of templates to identify or authenticate an individual. It has been demonstrated to work with spectacles in place and with a variety of ethnic groups and is one of the few devices which can work well in identification mode.
Facial recognition
Facial recognition
A facial recognition system is a computer application for automatically identifying or verifying a person from a digital image or a video frame from a video source. One of the ways to do this is by comparing selected facial features from the image and a facial database. It is typically used in security systems and can be compared to other biometrics such as fingerprint or eye iris recognition systems. Face recognition is not perfect and struggles to perform under certain conditions. It has been getting pretty good at full frontal faces and 20 degrees off, but as soon as you go towards profile, there've been problems. Other conditions where face recognition does not work well include poor lighting, sunglasses, long hair, or other objects partially covering the subject’s face, and low resolution images.
A facial recognition system is a computer application for automatically identifying or verifying a person from a digital image or a video frame from a video source. One of the ways to do this is by comparing selected facial features from the image and a facial database. It is typically used in security systems and can be compared to other biometrics such as fingerprint or eye iris recognition systems. Face recognition is not perfect and struggles to perform under certain conditions. It has been getting pretty good at full frontal faces and 20 degrees off, but as soon as you go towards profile, there've been problems. Other conditions where face recognition does not work well include poor lighting, sunglasses, long hair, or other objects partially covering the subject’s face, and low resolution images.
Applications
Applications
The bulk of biometric applications to date are probably in areas that you will never hear of. This is because there are a very large number of relatively small security related applications undertaken by specialist security systems suppliers.
The applications that you will here of are those in the public domain. These include:
Prison visitor systems, where visitors to inmates are subject to verification procedures in order that identities may not be swapped during the visit.
Drivers licensees, whereby some authorities found that drivers (particularly truck drivers) had multiple licenses or swapped licenses among themselves when crossing state lines or national borders.
Voting systems, where eligible politicians are required to verify their identity during a voting process. This is intended to stop ‘proxy’ voting where the vote may not go as expected.
In addition there are numerous applications in gold and diamond mines.
The bulk of biometric applications to date are probably in areas that you will never hear of. This is because there are a very large number of relatively small security related applications undertaken by specialist security systems suppliers.
The applications that you will here of are those in the public domain. These include:
Prison visitor systems, where visitors to inmates are subject to verification procedures in order that identities may not be swapped during the visit.
Drivers licensees, whereby some authorities found that drivers (particularly truck drivers) had multiple licenses or swapped licenses among themselves when crossing state lines or national borders.
Voting systems, where eligible politicians are required to verify their identity during a voting process. This is intended to stop ‘proxy’ voting where the vote may not go as expected.
In addition there are numerous applications in gold and diamond mines.
Future Applications
Future Applications
There are many views concerning potential biometric applications, some popular examples being;
Employee Recognition
There are many employee recognition systems available but Biometrics provides a cheaper alternative to most, very few people lose their fingers or eyes when compared with those who lose smartcards or forget passwords.
Time and Attendance Systems
Time and attendance has always been a problem in some industries. Biometrics can effectively eliminate problems with buddy clocking by ensuring that the employee in question is present.
Physical access control biometrics includes everything that requires identity authentication by scanning a person's unique physical characteristics. It is used where high security is a necessity due to its superiority compared with conventional access control methods. Hospitals, police, the military as well as the financial industry all use physical access biometrics for the purpose of greater security and efficiency.
The most common physical access control biometrics applications are in access control devices for doors and computers with highly confidential and important information or high level network access.
IT/Network Security
As more and more valuable information is made accessible to employees via LAN and WAN, the risks associated with unauthorized access to sensitive data grow larger. Protecting your network with passwords is problematic, as passwords are easily compromised, lost, or inappropriately shared. Whether driven by security, convenience, or cost-reduction, biometrics is proving to be an effective solution for IT/Network Security.
There are many views concerning potential biometric applications, some popular examples being;
Employee Recognition
There are many employee recognition systems available but Biometrics provides a cheaper alternative to most, very few people lose their fingers or eyes when compared with those who lose smartcards or forget passwords.
Time and Attendance Systems
Time and attendance has always been a problem in some industries. Biometrics can effectively eliminate problems with buddy clocking by ensuring that the employee in question is present.
Physical access control biometrics includes everything that requires identity authentication by scanning a person's unique physical characteristics. It is used where high security is a necessity due to its superiority compared with conventional access control methods. Hospitals, police, the military as well as the financial industry all use physical access biometrics for the purpose of greater security and efficiency.
The most common physical access control biometrics applications are in access control devices for doors and computers with highly confidential and important information or high level network access.
IT/Network Security
As more and more valuable information is made accessible to employees via LAN and WAN, the risks associated with unauthorized access to sensitive data grow larger. Protecting your network with passwords is problematic, as passwords are easily compromised, lost, or inappropriately shared. Whether driven by security, convenience, or cost-reduction, biometrics is proving to be an effective solution for IT/Network Security.
Advantages of Biometrics:
Advantages of Biometrics:
* Increase security - Provide a convenient and low-cost additional tier of security.
* Eliminate problems caused by lost IDs or forgotten passwords by using physiological attributes. For e.g. prevent unauthorized use of lost, stolen or "borrowed" ID cards.
* Reduce password administration costs.
* Replace hard-to-remember passwords which may be shared or observed.
* Make it possible, automatically, to know WHO did WHAT, WHERE and WHEN!
* Increase security - Provide a convenient and low-cost additional tier of security.
* Eliminate problems caused by lost IDs or forgotten passwords by using physiological attributes. For e.g. prevent unauthorized use of lost, stolen or "borrowed" ID cards.
* Reduce password administration costs.
* Replace hard-to-remember passwords which may be shared or observed.
* Make it possible, automatically, to know WHO did WHAT, WHERE and WHEN!
Subscribe to:
Posts (Atom)