The features and performances of one gigabits 4 PSK modem for a ultra-large TDMA system

Design of an ultrahigh-speed (1 gigabit/sec) PSK modulator/demodulator for use in PCM/PSK/TDMA satellite communication systems is investigated. The modem operates in burst mode with burst period varying from 131 to 1048 microsec and with a preamble word of 100 nsec. Modulation is 4 PSK at 6 GHz, and demodulation takes place via coherent detection at 4 GHz. The carrier can be extracted directly over the entire portion of the preamble word without remodulation so that recovery time is not affected by hunting phenomena at the start of remodulation. The symbol timing recovery circuit consists of a non-slave oscillator and a digital and an analog APC loop. Symbol timing recovery is completely established during the portion of the preamble word in which the symbol timing is densely contained on account of the construction of the preamble word.