This project will explore the potential of a new multiple access technique called Bandwidth Efficient Multiple Access (BEMA) in offering higher spectral efficiencies than the well-known multiaccess strategies such as TDMA, FDMA, and CDMA. The primary emphasis is to realize BEMA with the use of only single-user codecs (and not multiuser codecs about which too little is known) as subsystems. Potential applications are in wireless indoor and personal communications. At the heart of BEMA will be signal processing algorithms that realize the functions of multiuser equalization and signal design by taking a combined approach to those two subjects. A systematic development of a theory of multiuser decision feeedback equalization for synchronous and asynchronous multiple-access channels will be undertaken. The achievement of vertices or near-optimal points in the capacity regions of Gaussian multiple-access channels with correlated waveforms will be sought under latency and complexity constraints on the multiuser equalizers. Generalizations of Rate-Splitting Multiple Access by combining equalization and successive decoding will be considered. Algorithms that determine the order in which users are to be equalized and decoded will be obtained, error propagation effects for multiuser decision feedback detection will be quantified, and a characterization of error exponents for decision feedback receivers for coded systems will be sought. The focus in signal design will be to obtain signature waveforms that shape the capacity region under power and rate (quality of service) constraints to be achieved for each user via decision feedback receivers so as to minimize bandwidth.
