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We have proposed a quasi-large random-sequence (QLRS) CDMA where K usersaccess a point through a common channel with spectral spreading factor N. Eachbit is extended by a temporal spreading factor B and hopped on a BN-chip randomsequence that is spread in time and frequency. Each user multiplexes andtransmits B extended bits and the total channel load is alpha = K/N bits/s/Hz.The linearly-complex LAS detectors detect the transmitted bits. We haveobtained that as B tends to infinity, if alpha < 1/2 - 1/(4ln2), eachtransmitted bit achieves the single-bit bound in BER in high SNR regime as ifthere was no interference bit. In simulation, when bit number BK >= 500, eachbit can approach the single-bit bound for alpha as high as 1 bit/s/Hz. In thispaper, we further propose the quasi-large sparse-sequence (QLSS) CDMA byreplacing the dense sequence in QLRS-CDMA with sparse sequence. Simulationresults show that when the nonzero chips are as few as 16, the BER is alreadynear that of QLRS-CDMA while the complexity is significantly reduced due tosequence sparsity.

Quasi-Large Sparse-Sequence CDMA: Approach to Single-User Bound by Linearly-Complex LAS Detectors