Variable spreading and chip repetition factors (VSCRF)-CDMA in reverse link for broadband wireless access

This paper proposes variable spreading and chip repetition factors (VSCRF)-CDMA in the reverse link for broadband wireless access, which flexibility supports employing the same air interface both in multi-cell environments such as cellular systems and in isolated-cell environments such as hot-spot areas and indoor offices. In VSCRF-CDMA, the conventional CDMA feature, i.e., time-domain spreading using a combination of cell (or user)-specific scrambling and channelization codes, is applied in a multi-cell environment in order to suppress effectively other-cell interference to utilize one-cell frequency reuse. Meanwhile, in an isolated-cell environment, a chip repetition scheme is used in a part of the time-domain spreading by employing an orthogonal code in order to realize orthogonal multiple access by utilizing a comb-shaped frequency spectrum. Simulation results elucidate that the required average received signal energy per symbol-to-background noise power spectrum density ratio (E_s/N₀) using VSCRF-CDMA associated with the combination of spreading factor (SF_D) = 4 and chip repetition factor (CRF) = 4 at the average packet error rate of 10^-2 can be achieved by approximately 6 dB assuming four simultaneous users with the information bit rate of 6.4 Mbps each (the corresponding frequency efficiency becomes 0.62 bps/Hz) in an isolated-cell environment in a three-path Rayleigh fading channel with two-branch antenna diversity reception.