Binary modulations for digital satellite communications link with differential demodulation

The purpose of this study is the search for the best modulation and for the best filtering to use on the TDMA transmission system of Telecom 1. The simplest digital modulation-demodulation scheme can be used: binary PSK with differential demodulation. But it is demonstrated that offset binary modulation can offer a real improvement in a multichannel context, with the same modem simplicity. Offset binary modulation can be implemented in several ways (MSK, 2-4 PSK, 2-8 PSK), but it seems that 2-4 PSK (which is a simplified MSK) gives the best results in a multichannel transmission. For the I.F. filtering, the use of easy to implement, (flat filters of Butterworth type), seems to give better results than Nyquist filters.