Design of serially concatenated continuous phase modulation with symbol-wise interleaving

In this letter we consider serially concatenated continuous phase modulation (SCCPM) schemes with symbolwise interleaving and an additional intra-symbol interleaving. We use extrinsic information transfer (EXIT) chart to optimize the outer code and intra-symbol interleaver. We show that, for various continuous phase modulation (CPM) parameters, the outer code with memory 2 may not always be the best choice. For CPM with modulation index h = 1/2, considerable improvements can be achieved by moderately increasing the outer code memory.