Adaptive Coding for Coherent Detection of Digital Phase Modulation

Adaptive Coding for Coherent Detection of Digital Phase Modulation By C. L. RUTHROFF and W. F. BODTMANN (Manuscript received O c t o b e r 3, 1972) Although coherent phase-shift keying ( C P S K ) is an efficient means of transmitting digital signals over carrier systems, it has not enjoyed widespread use at microwave and millimeter wavelengths because of the difficulty of recovering an accurate reference carrier for coherent detection. In this paper, a system is described ivhich requires only a narrow-band phase-locked-oscillator filter for reference carrier recovery. This is accomplished by block-coding and decoding the pulse sequence at the terminals; the recovery of a baseband timing wave is also facilitated by the coding process. It is also shown that: (i) for an arbitrary random input sequence, accurate carrier recovery cannot be achieved with just a 7iarrowband filter, (ii) for the system described, any i?iput pulse sequence is acceptable, and (Hi) there is a maximum error in the phase of the recovered reference carrier which can be controlled by choosing the number of pulses in the coding block and the bandwidth of the recovery filter.