  We have proposed a quasi-large random-sequence (QLRS) CDMA where K users
access a point through a common channel with spectral spreading factor N. Each
bit is extended by a temporal spreading factor B and hopped on a BN-chip random
sequence that is spread in time and frequency. Each user multiplexes and
transmits 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 have
obtained that as B tends to infinity, if alpha < 1/2 - 1/(4ln2), each
transmitted bit achieves the single-bit bound in BER in high SNR regime as if
there was no interference bit. In simulation, when bit number BK >= 500, each
bit can approach the single-bit bound for alpha as high as 1 bit/s/Hz. In this
paper, we further propose the quasi-large sparse-sequence (QLSS) CDMA by
replacing the dense sequence in QLRS-CDMA with sparse sequence. Simulation
results show that when the nonzero chips are as few as 16, the BER is already
near that of QLRS-CDMA while the complexity is significantly reduced due to
sequence sparsity.
