Optimal spreading sequences in large CDMA systems: A statistical mechanics approach

We discuss optimal spreading sequences for CDMA channels under assumption of an arbitrary data modulation. We evaluate, via replica method, capacity of a randomly spread, perfect power controlled CDMA channel in the large-system limit, under the assumption that the correlation matrix of random spreading sequences is orthogonally invariant. On the basis of the analytical result, we show that the capacity is maximized with orthogonally invariant random Welch bound equality spreading sequences in cases of non-Gaussian data modulation.