Novel hybrid asymmetry modulation scheme for fountain codes

Fountain codes can be used to transmit information over different kinds of channels. The transmitter creates unlimited number of packets, once the receiver correctly receives enough packets, it can recover the original information. This property indicates that all the packets are with almost the same importance in recovering the original uncoded information. In this paper, we shall utilize this property and propose a novel hybrid BPSK/QPSK asymmetry modulation method for fountain codes, which can efficiently improve the system spectrum utilization, especially for relatively low SNR regime. The theoretical analysis on the symbol error rate and various simulation over AWGN channel has been given. It will show that when SNR is relatively low, it is necessary to adopt the hybrid BPSK/QPSK modulation scheme rather than regular QPSK and that there may exist some optimal constellations for hybrid BPSK/QPSK mode for different fountain coding parameter sets or transmission channel situations in practice. This result also provides some insight that when the channel is fading channel, hybrid modulation scheme may provide more performance gains since the system will have high probability falling in low SNR regime.