For quasi-orthogonal multiplexing in an OFDMA system, multiple (M) sets of traffic channels are defined for each base station. The traffic channels in each set are orthogonal to one another and may be pseudo-random with respect to the traffic channels in each of the other sets. The minimum number of sets of traffic channels (L) is used to support a given number of (U) terminals selected for data transmission, where M≧L≧1 and U≧1. Each terminal transmits data and pilot symbols on its traffic channel. A base station receives data transmissions from all terminals and may perform receiver spatial processing on received symbols with spatial filter matrices to obtain detected data symbols. The spatial filter matrix for each subband may be derived based on channel response estimates for all terminals transmitting on that subband.