Convolutional Multi-Code Multiplexing for OFDM Systems

The paper proposes a new multiplexing scheme for the OFDM-based systems with significant coding gain and diversity gain, which is called convolutional multi-code multiplexing (CMM). In this scheme, the data symbols are spread onto orthogonal subcarriers by convolutional spreaders, and multiple data streams spread by different codes can be transmitted on the same frequency band simultaneously. The free Euclidean distance and the free Hamming distance are found to dominate the performance of the OFDM-CMM system in AWGN channel and frequency selective fading channel, respectively. Some codes with good performance are found by computer search. Compared to the conventional uncoded OFDM system with the same spectrum efficiency, the OFDM-CMM system can achieve significant diversity gain in frequency selective fading channel, and notable coding gain both in AWGN channel and fading channel.