On bandwidth-efficient multiuser-space-time signal design and detection

Abstract

Signals designed for transmission over multiple transmit antennas are capable for achieving significant capacity gain. Traditional approaches aim at improving the single-user link with a centralized control over the set of transmit antennas. In this paper, by considering a set of independent and synchronized users communicating with the base station on the up-link, the joint signal can be viewed as space-time coded signal without a centralized control. Co-channel/inter-antenna interference presents a major impairment that limits the capacity. We propose a novel multiuser signal structure called interference-resistant modulation (IRM) to improve performance without coding nor bandwidth expansion. IRM can also be combined with fading-resistant modulation or space-time coding to yield additional gain when each user employs multiple transmit antennas. We prove that, both analytically and by simulations, the IRM with maximum-likelihood (ML) detection achieves the single-user performance asymptotically. Furthermore, to reduce the prohibitive complexity posed by ML detection, we propose a simple minimum-mean-square-error based precombining group detector and an interference cancellation scheme. It is shown that the proposed detector combined with IRM provides significant improvement over previous approaches.

An iterative groupwise multiuser detector for overloaded MIMO applications

“…The problem of optimum grouping for a method based on ZF and hard cancellation was considered in [15]. An alternative in [10] is to assign users arbitrarily to groups, then to order the groups.…”

“…In a series of simulations, we compared the performances of IMUD, the group ML with MMSE suppression of [10] (denoted GD in the results), simple MMSE and MMSE V-BLAST [18]. Throughout this section, the notation ( ) …”

“…V-BLAST, modified to use MMSE suppression of undetected users per the suggestion in [4] (which we will term MMSE V-BLAST) is one candidate. Another is a variation of group detection, with MMSE suppression of undetected groups combined with hard cancellation of detected users [10], which we will term GD.…”

Detection of multiuser orthogonal space-time block coded signals via ordered successive interference cancellation

“…The established user-wise ordering property offers a potential advantage of computation reduction based on group-wise data processing; an associated low-complexity algorithm implementation which further exploits the OSTBC structure is derived in [7]. Recently it is reported that the uplink performance of MU-OSTBC systems can be further improved by incorporating the codeword rotation technique [14]. Our discussions below, however, will not take such a codeword mapping into account to better focus on the intrinsic properties introduced by OSTBC.…”

“…Our discussions below, however, will not take such a codeword mapping into account to better focus on the intrinsic properties introduced by OSTBC. It is noted that group-wise detectors are also proposed in [14] for multiuser signal separation. The MMSE based solution in [14, p-325] is basically a parallel interference suppression scheme but does not exploit the algebraic property of OSTBC; the associated refined version with signal ordering in [14, p-326] is however virtually similar to the one-step PIC method introduced in [13].…”