On a unified view of synchronous multiple-access schemes: a bandwidth efficiency perspective

Due to complexity considerations, synchronous multiple-access schemes, such as TDMA, CDMA, and OFDM, have been mainly based on orthogonal (unitary) transformations of the multiuser signal, which makes the receiver less complex, at the cost of bandwidth efficiency. In future systems, however, it seems that the limiting factor will not be processing power, but rather bandwidth. Therefore there is a need for redesigning multiple-access schemes, or rather unifying their design, in a multiple-access scheme that is bandwidth efficient. The efficiency in the bandwidth can he achieved by applying non-unitary transformations to the multiuser signal such that the multiuser interference can he handled by a reasonably complex receiver. In this paper we attempt to unify the design of the aforementioned multiple-access schemes to a scheme that efficiently utilities the bandwidth, given that receivers of reasonable complexity can be deployed.