A Comparison of Signal Design Methods for Correlated Waveform Multiple-Access Communications

There have been several recent papers in the literature that deal with the design of signature waveforms for use by the transmitters for up-link, single-cell, multiple-access communications. In particular, we consider the approach introduced in [1] and [2] where the signature waveforms are specifically designed for the centralized multiuser receiver at the base so that each transmitter can be guaranteed a pre-assigned Quality-of-Service (QoS) requirement in terms of the received Signal-to-Interference Ratio (SIR). The resulting strategy is called Bandwidth Efficient Multiple Access (BEMA) [2]. When all users employ Pulse Amplitude Modulation (PAM) and a common signaling rate, the key question in BEMA is how the waveforms must be designed to occupy as little bandwidth as possible and still meet the QoS objectives. For a strict measure of bandwidth, and for a given set of received powers, this question was addressed by the authors for the Maximum Signal-to-Interference Ratio-Decision Feedback (MSIR-DF) receiver in [3]. A similar question was addressed in [4] where, for a sum constraint on the received powers, optimal signature signals and transmit powers were obtained for the linear MSIR receiver (without decision feedback). A somewhat different but related non-QoS approach proposes the design of signature signals that maximize the total capacity of the multiple-access channel under a spreading gain constraint (cf. [5]-[6]). This pape