Spreading code construction for CDMA

In this letter, we use the well-known Walsh-Hadamard codes to construct larger sets of linearly dependent codes such that their matrix of correlations is band-diagonal. Optimal detection for systems employing these spreading codes can be efficiently accomplished by a trellis decoder. Analysis and simulation show that with a processing gain of N, up to 2N users can be accommodated without much performance degradation. This proposed approach is quite general and larger code set can be constructed analogously.