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 a 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 32 filters and a 64 state inner trellis).