A reduced-complexity approach to iterative detection of coded MIL-STD SOQPSK

We develop a reduced-complexity approach to the detection of military-standard (MIL-STD) shaped-offset quadrature phase-shift keying (SOQPSK), a highly bandwidth-efficient constant-envelope waveform. The complexity savings result from viewing the signal as a continuous phase modulation (CPM). The proposed detector has a matched filter bank which is one-fourth as complex as previously reported designs. We establish that this reduced-complexity detector achieves optimal performance for uncoded MIL-STD SOQPSK. We also show a simple and convenient closed-form expression for a recursive precoder for SOQPSK, which is necessary in serially concatenated systems. Finally, we show that the proposed reduced-complexity detector achieves the large coding gains that have recently been reported for serially concatenated coded MIL-STD SOQPSK.