Optimal signature sets for oversaturated quasi-scalable direct-sequence spread-spectrum systems

Signature sets that maximize the sum capacity of an oversaturated code-division multiple-access (CDMA) system are derived, under the constraint that the signature sets have to be quasi-scalable. It turns out that the optimal signature set is composed of orthogonal signature sets, with at most one incomplete orthogonal set. As compared to the Gaussian multiple-access channel (GMAC), the loss in spectral efficiency for this multiple-orthogonal CDMA (OCDMA) system remains very low.