Digital group demodulation system for multiple PSK carriers

TLDR: An adaptive rate conversion filter is proposed to resolve a new problem in demodulating an individual channel signal from the TMUX output, caused by a difference between a TMUX operation rate and each SCPC symbol rate.

Abstract: In the near future, the on-board regenerative repeating system will be employed to convert many low speed SCPC signals to a high speed TDM signal. Similar situation can be considered in a star-network, where many small earth stations communicate with terrestrial telephone stations through a large size central earth station. In both cases, many SCPC signals are concentrated and demodulated by a central station. Therefore, hardware and power consumption minimization is necessary. This demand resulted in a group modulator/demodulator concept. A group demodulator employs the same hardware effectively in common in demodulating multiple PSK/FDM carriers. Actually, a transmultiplexer(TMUX) is used as a combination of a filterbank and down converters. Although a TMUX usually markedly reduces hardware, it introduces a new problem in demodulating an individual channel signal from the TMUX output. This problem is caused by a difference between a TMUX operation rate and each SCPC symbol rate. In this paper, an adaptive rate conversion filter is proposed to resolve this problem. In addition, each channel clock timing difference and carrier frequency offset are compensated for by channel demodulators attached individually to each TMUX channel output. The channel demodulator has been actually developed for 64kbps QPSK signal and its performance has been evaluated. Using this technique, a 16 channel group demodulator has been manufactured.