Adjacent channel interference susceptibility of serial concatenated continuous phase modulation

Iterative decoding of a serially concatenated outer convolutional code and an inner Continuous Phase Modulation (CPM) separated by a random interleaver is examined. This scheme, which is known to produce high coding gain, is examined for various CPMs such as MSK, LRC, GMSK and TFM. CPM signals are constant envelope signals with very high bandwidth efficiency, providing good immunity to Adjacent Channel Interference (ACI). The susceptibility of the serial concatenated system to ACI is examined. Simulations show that this configuration can tolerate much stronger ACI than previous CPM schemes, including those detected with the Viterbi algorithm.