Non-coherent iterative demodulation and decoding of serially concatenated continuous phase modulation

Abstract

In this work we consider the non-coherent iterative demodulation and decoding of serially concatenated continuous phase modulation (SCCPM) schemes. SCCPM is a special case of a serially concatenated convolutional code (SCCC), where a continuous phase modulator (CPM) is used instead of a regular inner convolutional encoder. SCCC schemes consist of two concatenated convolutional codes separated by an interleaver. Performance close to the Shannon limit can be attained by iteratively decoding a signal encoded by this scheme. Continuous phase modulation signals have code-like properties that enable their use in place of the recursive convolutional encoders in SCCC schemes. Synchronization of carrier phase and frequency is a major problem at low SNR (near Shannon limit). In this work we propose a non-coherent iterative receiver for an SCCC scheme with a CPM inner encoder, thereby circumventing the synchronization problem. The innovation proposed here is a non-coherent soft-input soft-output (SISO) inner CPM decoder.