On the choice of TDMA or CDMA for a multimedia satellite system

The air interfaces of satellite systems envisage to use the multiple access frequency division multiple access (FDMA) scheme combined with time division multiple access (TDMA) or a further multiple access scheme, namely code division multiple access (CDMA). But how is the choice of CDMA or TDMA done? The design of a satellite system is a highly complex task. It might turn out that CDMA is a very good choice in some situations and a less advisable choice in others. We can find many papers debating on the comparison of TDMA and CDMA. In most of these papers, the comparison criterion is the system capacity. Here we give a comparison of TDMA and CDMA based on the terminal power amplifier specifications. Indeed, in general, the terminal must be low cost, because it is a consumer product. Thus, as the terminal power amplifier represents an important part of the terminal cost, it leads one to minimise the amplifier power. We describe the system taken into account, give the tool used to compare the transmitted power, and we test different waveforms used in CDMA and TDMA.