Improving the bandwidth efficiency and of CPM signals via shaping and iterative detection

In this paper, we investigate the effects of shaping on the bandwidth efficiency and performance of continuous phase modulated (CPM) signals. We show that, theoretically, by properly shaping the unmodulated signal, better bandwidth efficiency and performance can be obtained. We then develop the soft-input soft-output (SISO) de-shaper for trellis shaping and block shaping schemes. For a coded, shaped CPM system, the SISO de-shaper enables joint decoding and de-shaping via iterative detection. We demonstrate that using the SISO deshaper, together with iterative decoding and de-shaping, the theoretical advantage of shaping can be realized with practical complexity.