Joint iterative noncoherent demodulation and MAP decoding algorithm for GMSK signal based on SCCC structure

Noncoherent demodulation is often used in many communication systems in which it is difficult to synchronize the carrier phase. It is generally acknowledged that iterative decoding technique plays an important role in improving performance. But at present, few researches on the iterative noncoherent detection for GMSK signals have been done. This paper proposes a novel noncoherent receiver for GMSK signals based on SCCC structure over an AWGN channel. At the transmitter, GMSK modulator can be made equivalent to a form of special recursive convolutional encoder. Then it is concatenated with the convolutional encoder and interleaver. At the receiver, GMSK modulation is viewed as the inner encoding of SCCC. And it is important to extend the received symbols for decoding the inner GMSK signals. Thus, based on MSDD(multiple symbol differential detectors) structure, the inner decoder implements GMSK noncoherent iterative detection by extending the virtual trellis structure. The simulation results show that this receiver has excellent performance and has ability against certain frequency offset.