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.