Multiple access using two sets of orthogonal signal waveforms

We present a new multiple access concept which allows to accommodate more than N users on a channel of NW Hz bandwidth, where W Hz is 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 is synthesized using the decisions available from the previous stages, and this interference is subtracted from the user signals of interest before entering them to a threshold detector. The new concept is described using orthogonal code-division multiple access and time-division multiple access as the two sets of signal waveforms, but we also briefly outline how it can be generalized to other orthogonal sets.