An efficient technique for deriving receiver filters in multiuser asynchronous DS/SSMA

It has been shown that the performance of sub-optimal multiuser receivers for synchronous DS/SSMA is improved by using a noise whitening matched filter (WMF) as a receiver filter. In the asynchronous case the performance is also improved through the use of a WMF. We present an efficient technique for deriving the WMF for an asynchronous DS/SSMA system. The WMF is determined as the Cholesky decomposition of X where X is the solution to X=R₀-R₁^TX^-1 R₁. A recursive algorithm for determining X is proposed. Constraints on the spreading codes that ensure convergence of the algorithm are derived and the efficiency of the technique is demonstrated by simulation