A Novel Non-Orthogonal Multiple Access Based On Maximum Welch Bound Equality

A novel spreading non-orthogonal multiple access (NOMA) scheme is proposed for the future 5G communication system, which is called maximum Welch-bound spreading multiple access (MWSMA). In the transmitter, each user's modulated symbols are spread by a complex-valued short spreading sequence and then sent simultaneously on the same frequency spectrum. We design spreading sequences via maximum-Welch-bound-equality (MWBE) to minimize the maximum cross-correlation amplitude. Theoretical analysis on cross-correlation and average mutual information (AMI) proves that the proposed MWSMA scheme is much superior to the current orthogonal frequency division multiple access (OFDMA) and two key NOMA schemes, multi-user shared access (MUSA) and sparse code multiple access (SCMA), especially for high spectral efficiency (SE). Simulation results also verify that MWSMA can achieve significant 0.8dB, 0.8dB and 3.9dB signal-to-noise-ratio (SNR) gain at target block error rate (BLER) 10^-1 as compared with MUSA, SCMA and OFDMA, respectively.