Wideband TDMA/CDMA terminal modem for broadband satellite multimedia

The time division multiplex/multiple access (TDM/TDMA) scheme has been until now the dominant multiplex/multiple access scheme in satellite communications while code division multiple access (CDMA) is still viewed as too complex and not sufficiently mature by many system designers, specially for high data rate systems. Nevertheless, the high flexibility of CDMA makes it attractive for future broadband satellite multimedia (BSM) systems. Realistic satellite communication systems require a careful system analysis to exploit the potential of CDMA at its best. In this paper, we describe a system concept for BSM relying on a hybrid code and time division multiple access technique and show that the fundamental argument against CDMA, namely receiver complexity, can be overcome. We describe how this system concept can be translated into an efficient modem architecture. We focus on the most critical part-the digital demodulator-that must be capable to sustain a user bit rate in excess of 20 Mbit/s. The main challenges of such demodulator design lie in fast synchronisation, operation at low E_b/N₀, low implementation loss and the complex rate conversion and buffering requirements