A Fully Digital DPSK Burst Modem

Abstract

Burst modems are needed in point-to-multipoint radio networks. In this paper, a fully digital implementation of a burst modem that employs DPSK is proposed and analysed. Two algorithms are described for timing recovery. The choice of algorithm depends on the deviation of the actual IF carrier frequency from its design value. Both algorithms are equivalent in the absence of noise; however, one is shown to be better when noise is present. It is also shown that digital matched filtering performs as well as the conventional matched filter when noise is present, provided the sampling rate is chosen appropriately. Finally, it is shown that the probability of bit error for the differential-detection algorithm described here is identical to that of the conventional DPSK receiver. Some practical issues regardng the choise of the IF and RF in relation to the bit rate are briefly discussed.