Serially concatenated continuous phase modulation with symbol interleavers: Performance, properties and design principles

Serially concatenated continuous phase modulation (SCCPM) systems with symbol interleavers are investigated. The transmitted signals are disturbed by additive white Gaussian noise (AWGN). Iterative detection with extrinsic information is used at the receiver side. Compared to bit interleaved SCCPM systems, this scheme shows a substantial improvement in convergence threshold at the price of a higher error floor. In addition to showing this property, we also investigate the underlying reason by error event analysis. In order to estimate bit error rate performance, we generalize traditional union bounds for a bit interleaver to the non-binary interleaver. For the latter, both the order and the position of permuted non-zero symbols have to be considered. From the analysis, some principal properties are presented. Finally some design principles are proposed. The paper concentrates on SCCPM, but the proposed analysis methods and conclusions can be widely used in many other systems such as serially concatenated trellis coded modulation etcetera.