Channel overloading: improved OCDMA/OCDMA versus PN/OCDMA

The allowable load in oversaturated CDMA systems is investigated, with multistage successive interference cancellation (m-SIC) and optimum MUltiuser Detection (MUD). We compare the critical load of Pseudo Noise/Orthogonal CDMA (PN/O) and Orthogonal/Orthogonal CDMA (O/O). An extension to scrambled O/O (s-O/O) is introduced, labeled overall-permuted O/O (o-O/O), and its performance is evaluated as compared to s-O/O. Because of the special structure of the signatrue set with O/O, the intrinsic delay of SIC is reduced in O/O as compared to PN/O. For all systems, it is found that with m-SIC the achievable acceptable overload increases with the spreading factor, but O/O clearly outperforms PN/O. With optimum MUD, PN/O outperforms O/O.