Combined TDMA/OCDMA with iterative multistage detection

We present a multiple access technique which accommodates more than N users on a channel whose bandwidth is N times the bandwidth of the individual user signals. It makes use of two sets of orthogonal signal waveforms, one for the first N users, and one for the additional users. An iterative multistage detection technique is used to cancel interference between the two sets of users. At each stage of the detection process, the best estimate of the multiuser interference (MUI) is synthesized using the decisions available from the previous stages, and this interference is subtracted from the user signals of interest before entering these signals to a threshold detector. The new concept is described using a combination of time-division multiple access (TDMA) and orthogonal code-division multiple access (OCDMA), but it is equally applicable to any other sets of orthogonal signal waveforms. Using a binary phase-shift keying modulation (BPSK), it is shown that the proposed technique supports an excess user rate of 40% at the expense of a very small degradation of the signal-to-noise ratio (SNR)