Families of spreading sequences for multiuser asynchronous SS/CDMA communication

Abstract

This paper extends the DOVETAIL technique for construction of families of complex spreading sequences for use in multiuser asynchronous spread spectrum, SS/CDMA, communication, to extraction of derived real-valued spreading sequence families, intended for similar application. It is shown here that the preferred characteristics of the complex family, in terms of probability of error, are partially carried over to the real and imaginary components when considered to be real-valued sequences, and intermediate improvement in probability of error is retained. Clearly the use of real-valued sequences results in reduced complexity in implementation. The improvement in probability of error is gauged with reference to two Gaussian approximations from the literature for the interference limited case, as well as with reference to control experiment randomly drawn sequences constructed by cointossing and drawing from the Gaussian distribution. The focus on the interference limited case where noise is suppressed allows one to observe the improvement yielded by the technique. The major parameters of the system are N, the sequence length, and q, the family size. Results from simulations are presented, demonstrating enhanced performance. The Gaussian approximations used for comparison are shown to underestimate the probability of error for the control experiment sequences while the generated real sequences have augmented performance with the complex sequences superior