Analyse de la capacité de systèmes de communications personnelles par satellites en orbites basses utilisant l'accès multiple par répartition de codes

Les communications personnelles à l'aube du 21ième siècle -- La téléphonie d'hier à aujourd'hui -- Les communications mobiles par satellites -- La téléphonie du 21ième siècle : les communications personnelles -- Les techniques d'accès multiple -- L'accès multiple par répartition des fréquences (AMRF) -- L'accès multiple de codes (AMRC) -- Définition d'un système de SCP par satellites en basse orbite utilisant l'AMRC -- Principes de base d'un système de communications utilisant l'AMRC -- Hypothèses de base d'un système de communication utilisant l'AMRC -- Modèle du canal satellite en basses orbites -- Modèle du système de contrôle de puissance -- Analyse de la capacité approche paramétrique -- Efficacité spectrale -- Calcul de l'interférence causée par les autres usagers -- Paramètres affectant l'interférence due aux autres usagers -- Valeurs typiques -- Calculs et analyse de la capacité -- Analyse de la capacité : approche probabiliste -- Analyse de la capacité : approche probabiliste sans codage -- Modèle probabiliste avec codage correcteur d'erreur -- Valeurs typiques -- Exemples de calculs et analyse des résultats obtenus -- Analyse de la capacité : combinaison des approches paramétrique et probabiliste -- Facteurs de l'approche paramétrique -- Calcul de la capacité : formules combinées

Analyse comparative des performances du MC-DS-CDMA dans un réseau cellulaire de troisième génération

L'évolution des systèmes de télécommunications mobiles -- Le canal radiomobile et ses corrections -- Le canal radiomobile CDMA2000 -- Étude de la capacité, approche paramétrique -- Le système multiporteuses MC-DS-CDMA -- Analyse des performances du MC-DS-CDMA

Band sharing and satellite diversity techniques for CDMA.

High levels of interference between satellite constellation systems, fading and shadowing are a major problem for the successful performance of communication systems using the allocated L/S frequency bands for Non-Geostationary Earth Orbit (NGEO) satellites. As free spectrum is nonexistent, new systems wishing to operate in this band must co-exist with other users, both satellite and terrestrial. This research is mainly concerned with two subjects. Firstly, band sharing between different systems Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA) has been evaluated for maximizing capacity and optimising efficiency of using the spectrum available. For the case of widened channel bandwidth of the CDMA channel, the overlapping was tested under different degrees of channel overlap and different orders of filters. The best result shows that at the optimum degree of channel overlap, capacity increases by up to 21%. For the case of fixed channel bandwidth, the optimum overlapping between CDMA systems depends on the filtering Roll-off factor and achieves an improvement of the spectrum efficiency of up to 13.4%. Also, for a number of narrowband signal users sharing a CDMA channel, the best location of narrowband signals to share spectrum with a CDMA system was found to be at the edge of the CDMA channel. Simulation models have been constructed and developed which show the combination of DS- CDMA techniques, forward error correction (FEC) code techniques and satellite diversity with Rake receiver for improving performance of interference, fading and shadowing under different environments. Voice activity factor has been considered to reduce the effect of multiple access interference (MAI). The results have shown that satellite diversity has a significant effect on the system performance and satellite diversity gain achieves an improvement up to 6dB. Further improvements have been achieved by including concatenated codes to provide different BER for different services. Sharing the frequency band between a number of Low Earth Orbit (LEO) satellite constellation systems is feasible and very useful but only for a limited number of LEOS satellite CDMA based constellations. Furthermore, satellite diversity is an essential factor to achieve a satisfactory level of service availability, especially for urban and suburban environments

Proceedings of the Fifth International Mobile Satellite Conference 1997

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments