Inmarsat integrity channels for global navigation satellite systems

Abstract

It is pointed out that the transmission of integrity information using a signal format compatible with GPS (Global Positioning System) and relayed through a geostationary satellite repeater will be critical in achieving high integrity and availability of global navigation by satellite, along with self-contained consistency checking techniques such as receiver autonomous integrity monitoring. The next generation of Inmarsat spacecraft, Inmarsat-3, will contain navigation repeaters designed to fulfill this function. The global navigation satellite system integrity channel, will use pseudorandom codes in the same family as but distinct from the codes reserved by GPS. The data format of the basic integrity channel is designed to convey user range error information for 24 to 40 satellites. A closed-loop timing compensation technique will be used at the uplinking earth station, to make the signal's clock and carrier Doppler variations identical to those that would result from an on-board signal source. Therefore, the Inmarsat-3 satellites will increase the number of useful navigation satellites available to any user, and can also function as sources of precise tuning. There is also a possibility that wide-area differential corrections can be carried on the same signal. >