MMSE multiuser detection for array multicarrier DS-CDMA in fading channels

Abstract

Abstract-Reception of asynchronous, multicarrier direct-sequence-code division multiple access (DS-CDMA) in time-varying, multipath radio channels with use of a receiving antenna array is investigated. Interference reducing minimum mean squared error (MMSE) receivers are discussed, and by considering the time-variation of the channel, a modified structure is derived which is efficient for channels experiencing small-scale fading. A blind implementation of this receiver is then proposed. Subspace concepts are applied to formulate a tracking, composite channel vector estimator which operates effectively in fading situations, even when high levels of interference are present. Both the modified MMSE weight matrix and diversity combining weights are generated from these channel estimates. Simulations of the proposed receiver show it to have superior performance over a standard MMSE receiver which is periodically re-evaluated to permit it to follow the channel variations due to small-scale fading. Furthermore, a hybrid MMSE receiver is proposed which applies different processing methods depending on each transmitters mobility, resulting in improved performance.

Joint Timing and Channel Estimation for Bandlimited Long-Code-Based MC-DS-CDMA: A Low-Complexity Near-Optimal Algorithm and the CRLB

“…Although the amplitudes of the SW-CCGs remain the same as those of the CCGs, their phases are determined by the random DQPSK symbols. Fortunately, this symbol-induced ambiguity will not pose a problem for the Multi-User Detector (MUD) provided differential encoding and decoding are adopted, as advocated in many existing blind channel estimators [6]- [8] as well as in this work. The relationship between the differentially coded symbolsḃ …”

Arrayed MC‐CDMA reception in space‐time diffused multipath vector channels

“…Note that, in order to simplify the analysis, the path delay τ ij has been assumed to lie within the range [0, T cs ). The front-end of the MC-CDMA receiver for the i-th user is similar to that in [3] and consists of N tapped delay lines (TDLs) each of length 2N sc in order to ensure that (due to lack of synchronization) one whole data symbol of the desired user is captured within this 2N sc interval.…”

“…In the SIVO channel model, it is assumed that each multipath has distinct spatial and temporal signatures, with each multipath appearing at the receiver's antenna array as a point-like source [3]. In practical wireless channels, however, localized scattering of the multipaths invalidates the point-source assumption used by the conventional algorithms.…”

Bidirectional algorithms for interference suppression in multiuser systems

“…Low-complexity adaptive channel estimation can provide CSI but in highly dynamic channels tracking problems exist due to their finite adaptation rate [9]. An alternative statistical approach is to obtain the correlation structures required for optimal minimum mean-square error (MMSE) or least-squares (LS) filtering [10,11]. Although this relieves the tracking demands placed on the filtering process, in a Rayleigh fading channel, a zero correlator is the result due to the expectation of a Rayleigh fading coefficient, and therefore the crosscorrelation vector, equating to zero, i.e., E [h 1 [n] ] = 0 and E b * 1 [n] r[n] = 0.…”