Application of multi-frequency TDMA for satellite communications

Abstract

A Multi-Frequency Time Division Multiple Access (MFTDMA) system has been developed for a thin route satellite communication network which has most o f the desirable features o f both FDMA and TDMA systems. We show that when the network downlink is power limited (with negligible uplink noise) and consists o f mixed earth station sizes with dif ferent rain margin requirements, the MFTDMA and FDMA systems can have greater throughput capacity compared to TDMA. This improvement depends on the amount o f satellite transponder backoff required to keep the intermodulation e f fec ts small, and is the result o f the TDMA downlink having been sized for the smallest station and largest rain margin. In the case where the earth station must provide circuits to more than one station simultaneously, MFTDMA is advantageous over FDMA because fewer modems are required.Use of MFTDMA can lead to lower earth station costs by requiring lower transmitter power compared to TDMA, and fewer modems compared to FDMA. Even though the control algorithim for a MFTDMAm network is somewhat more complicated, a high degree o f flexibility in channel assignment is retained.