Reduced complexity iterative demodulation and decoding of serial concatenated continuous phase modulation

We present a structure for reduced complexity iterative demodulation and decoding of partial response continuous phase modulation (CPM) when serially concatenated with a convolutional code. The proposed receiver uses a single front-end filter and a 2 or 4 state trellis for decoding the inner CPM code. This can yield significant savings, as the complexity of the optimal demodulator increases exponentially with the length of the CPM frequency pulse. Simulations show that for GMSK with BT=1/6, the performance penalty for simplified iterative demodulation and decoding is less than 0.25 dB, compared to the receiver which performs optimal demodulation (which requires 64 filters and a 64 state inner trellis).