Some concatenated and iterative decoding approaches for continuous phase modulation

Several concatenated and iterative decoding approaches are used toimprove the power efficiency of continuous phase modulation (CPM).First a symbol interleaver is used for serially concatenated CPM(SCCPM). Convergence of iterative decoding for this scheme can beearlier (lower SNR: Signal-to-Noise-Ratio) compared to bitinterleaved SCCPM. Then a ring convolutional code (CC) is used asthe outer code in this symbol interleaved SCCPM. By setting thedenominator of the CPM modulation index equal to the alphabet sizeof the system (CPM, interleaver and ring CC), a naturalcombination of them is achieved. Further improvements on earlierconvergence or error floors are achieved with this scheme.Finally, irregular repeat accumulate (IRA) codes with CPM (IRCPM)are considered. CPM now takes the role of the accumulator. Thisscheme shows even earlier convergence than SCCPM. To analyze the error floor performance, we derive the union boundfor symbol interleaved SCCPM. In this bound analysis, we have toconsider the order of nonzero permuted difference symbols that arenot identical. We also derive the union bound for IRCPM from itsequivalent structure. This structure introduces a virtualinterleaver before CPM. Thus, the union bound analysis for SCCPMis now applicable