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Network-assisted diversity multiple access (NDMA) is a novel random medium access method, which provides impressive throughput efficiency for multiplexing variable-bit-rate data sources. In this paper, we study the implementation of the NDMA scheme in the presence of multipath channels. A transceiver architecture and random access strategies are proposed, which are able to detect and resolve collisions in the presence of unknown propagation channels. The performance issues are studied both analytically and numerically. Index Terms--Network-assisted diversity, packet radio access, signal separation.

This paper deals with the multiuser medium access problem in the packet radio environment. Under the framework of network diversity multiple access (NDMA), a recently proposed medium access method, a blind collision resolution scheme is proposed employing rotational invariance and factor analysis techniques. The proposed approach (dubbed B-NDMA for Blind NDMA) overcomes the difficulty of orthogonal identification codes required by the original protocol, thereby improving channel utilization and system capacity, while being insensitive to multipath effects and synchronization errors. Performance issues of the proposed technique are addressed both analytically and numerically. Index Terms--Access protocols, blind signal separation, matrix decomposition, packet radio, rotational invariance.

Constrained optimization methods have received considerable attention as a means to derive blind multiuser receivers with low complexity. The receiver's output variance is minimized subject to appropriate constraints which depend on the multipath structure of the signal of interest. When multipath is present, the constraint equations can be written in parametric form, and the constraint parameters jointly optimized with the linear receiver's parameters. In this paper, we develop adaptive solutions for this joint, constrained optimization problem. Both stochastic gradient and recursive least-square-type algorithms are developed. The performance of the proposed methods is compared with other blind and trained methods and turns out to be close to the trained minimum mean-square-error receiver. Index Terms--Adaptive interference suppression, blind multiuser detection, code-division multiple access, constrained optimization.

Presents a study which dealt with the multiuser medium access problem in the packet radio environment under the framework of network diversity multiple access (NDMA). Associated drawbacks of NDMA; Discussion of a blind collision resolution method using rotational invariance and factor analysis techniques; Simulation results that corroborate the performance analysis conducted.

Presents information on a study which proposed a blind stochastic maximum-likelihood (SML) channel estimation algorithm for convolutionally coded signals transmitted through a multipath channel. Problem statement; Performance analysis of SML estimation technique; Simulation results.