Simplified 2-State Detectors for SOQPSK

We study simple trellis-based detectors for SOQPSK that have a minimal level of complexity. In particular, we show that the state complexity can be cut in half relative to previous approaches¿from 4 states down to 2¿with asymptotically optimum performance. We give two possible means of achieving this: the pulse amplitude modulation (PAM) technique and the pulse truncation (PT) technique; both of these techniques make use of recent advances in SOQPSK technology based on a continuous phase modulation (CPM) interpretation of SOQPSK. The proposed simplifications are significant since trellis-based SOQPSK detectors are 1-2 dB superior to widely-deployed symbol-by-symbol detectors. These performance gains come at the expense of complexity, and the proposed 2-state detectors minimize this expense. Thus, these simple detection schemes are applicable in settings where high-performance and low complexity are needed to meet restrictions on power consumption and cost.