Studying On Multi-user Detection In LEO Satellite DS-CDMA Systems

Low earth orbit (LEO) satellite DS-CDMA communication systems combine the advantages of short transmission delay, small path loss, concealment of the signals,soft handover, global overlay by constellation made up of multi-satellites, and globality of personal communication. But, as the increasing of the users, multiple access interference becomes an unavoidable problem. The system performance including bit error rate and capacity suffers from the multiple access interference. Multiuser detection will be a key technology of the LEO Satellite DS-CDMA Systems.In this dissertation, relevant multiuser detectors are studied for the LEO satellite DS-CDMA systems.First, the sources of multiple access interference in the up-link and down-link of LEO satellite DS-CDMA systems are analyzed, and the effects of the multiple access interference in this communication system are simulated. The result declares that it is necessary to adopt multiuser detection in the LEO satellite DS-CDMA systems.Then, a threshold and its arithmetic is proposed for the PIC-MUD in the up-link of LEO satellite DS-CDMA systems based on the customary part PIC-MUD, and the performance is superior than the customary PIC-MUD. Then, the multiuser receiver in the up-link of LEO satellite DS-CDMA systems is designed, and the simulation results are given.Lastly, based on the customary blind Multiuser detection(BMUD), The formula of time-varying step size(TVSS) in BMUD is deducted, and the sato algorithm is used to TVSS based MOE BMUD, which resists the instability of tradition TVSS based MOE BMUD algorithm. The corresponding multiuser receiver in the down-link of LEO satellite DS-CDMA systems is designed and the performance of this system is given by simulation, and it indicates that this algorithm is more effective to restrain MAI.