Asymmetric modulation and multistage coding for multicasting with multi-level reception over fading channels

We investigate the application of joint iterative decoding and channel estimation for the transmission of multilevel coded signals using asymmetric QPSK modulation over flat Rayleigh fading channels. The goal is the transmission of multiresolution data streams to receivers with multi-level reception capabilities. We consider two types of receivers: the receivers in the first class can decode only the most significant bit (MSB) of the transmitted information; the receivers in the second class decode both the MSB and the LSB (least significant bit). Symbol aided demodulation (SAD) is used according to which known symbols are inserted in the encoded data stream to assist in the channel estimation process. Furthermore, an iterative algorithm is proposed that uses soft decoding information in addition to the information contained in the known symbols to improve the estimation of the fading channel. Simulation results show significant performance gains of the new scheme over both differential demodulation and conventional SAD.