On iterative receivers with channel estimation for serially concatenated cpm

A novel iterative receiver for the highly energy and bandwidth efficient serially concatenated continuous phase modulation (SCCPM) is proposed. The receiver uses soft feedback information from a simplified demodulator to perform iterative equalization and estimation while also utilising iterative decoding. The Laurent signal model for CPM is exploited to reduce the complexity of all the receiver components. The proposed equalizer consists of interference cancellation followed by linear filtering under the MMSE criteria. Three well-known iterative channel impulse response (CIR) estimation techniques that use training symbols and soft information are compared for CPM, and the least squares (LS) algorithm is found to be the best practical choice. Iterative SNR estimation based on a simple averaging technique is also integrated into the receiver. Heuristic methods for switching between one-shot training based and iterative CIR and SNR estimation are proposed. These methods are shown to be effective through simulations based on randomly generated a-priori information. Numerical BER simulations show that the proposed receiver performs well compared to the case when the channel parameters are perfectly known.