Downlink Space–Time Spreading Using Interference Rejection Codes

Abstract

In this paper, the authors will investigate the performance of a loosely synchronized (LS) code-based space–time spreading (STS) scheme in comparison to that of classic Walsh code and pseudonoise code-based STS when communicating over dispersive Nakagami-m multipath channels. Closed-form formulas are derived for characterizing the bit-error-rate performance as a function of the number of resolvable paths L and the number of users K. Our numerical results suggest that the employment of LS code-based STS scheme is beneficial in a low-user-load and low-dispersion channel scenario, where a near-single-user performance can be achieved without a multiuser detector. Index Terms—Code-division multiple access (CDMA), Gaussian approximation, interference-free window (IFW), large area synchronized (LAS) codes, loosely synchronized (LS) codes, Nakagami-m fading