The pulse amplitude modulation (PAM) decomposition of continuous phase modulation (CPM) signals has been recently revamped to give another view of ternary shaped offset quadrature phase shift keying (SOQPSK) signals as duobinary CPMs. Taking advantage of this approach, we propose a new maximum likelihood sequence estimation (MLSE) OQPSK trellis-type detector which relies on the presence of a single main pulse unlike the detectors developed by Kaleh and Perrins. We show that the proposed solution has the best bit error rate (BER) performance/complexity trade-off among the state of the art detectors and we endorse by these results that SOQPSK modulation can be approximated as a linear modulation.

In this paper, we investigate the pulse amplitude modulation (PAM) decomposition and the spectral efficiency of duobinary continuous phase modulation (CPM), where duo- binary CPM represents a ternary CPM whose symbols are generated using a duobinary encoder. We show that this precoder ensures a higher spectral efficiency compared with binary CPM and we propose a PAM decomposition characterized by the presence of a single main pulse and by uncorrelated pseudo-symbols for a half integer modulation index value for this ternary CPM. We show that shaped offset quadrature phase shift keying belongs to this CPM family and we provide a new reduced complexity trellis detector capable of reaching identical performance as the one introduced by Perrins as well as new linear detectors.