Performance of sparse graph codes on a four-dimensional CDMA system in AWGN and multipath fading

This paper presents the uncoded and coded multiuser error performance results of a novel super-orthogonal (SO) 4D CDMA communication platform under AWGN and multi- path fading channel conditions. The communication platform employs a special class of root-of-unity filtered (RUF) constant- envelope (CE) complex spreading sequences (CSS) with zero cross-correlation (ZCC) properties. The uncoded communication platform employs multi-layered-modulation (MLM) to improve spectral efficiency compared with existing multi-level modulation techniques, and the coded system uses the multiple dimensions to transmit redundancy to improve error performance. Three classes of sparse graph coding schemes are evaluated and compared on the multi-dimensional (MD) communication platform. The channel codes include a 3D block-turbo-code (BTC) with extended Reed-Muller (RM) constituent codes, low- density parity-check (LDPC) codes and repeat-accumulate (RA) codes. It is shown that the three channel codes have comparable error performance results and approximately 6 dB performance improvement over BPSK is achieved at P_c(bit) = 1 x 10 ^-5.