Variable Spreading and Chip Repetition Factors (VSCRF)-CDMA in Reverse Link for Broadband Packet Wireless Access

Abstract

This paper proposes Variable Spreading and Chip Repetition Factors (VSCRF)-Code Division Multiple Access (CDMA) broadband packet wireless access in the reverse link, which flexibly supports employing the same air interface in various radio environments such as a cellular system with a multi-cell configuration and local areas such as very-small cell, indoor, and isolated-cell environments. In VSCRF-CDMA, we propose two schemes: the first is a combination of time-domain spreading with an orthogonal code and chip repetition that achieves orthogonal multiple access in the frequency domain by utilizing a comb-shaped frequency spectrum, and the other is adaptive control of the spreading factor and chip repetition factor according to the cell configurations, number of simultaneously accessing users, propagation channel conditions, and major radio link parameters. Simulation results show that the proposed VSCRF-CDMA associated with the combination of the spreading factor, SF D , of four and the chip repetition factor, CRF, of four improves the required average received signal energy per bit-to-noise power spectrum density ratio (E b /N 0 ) for the average packet error rate of 10 -2 by approximately 2.0 dB compared to DS-CDMA only employing SF D = 16 assuming four simultaneously accessing users in an exponentially decaying six-path Rayleigh fading channel with two-branch diversity reception.