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In iterative data-detection and channel-estimation algorithms, the channel estimator and the data detector recursively exchange information in order to improve the system performance. While a vast bulk of the available literature demonstrates the merits of iterative schemes through computer simulations, in this paper analytical results on the performance of an iterative detection/estimation scheme are presented. In particular, this paper focus is on uncoded systems and both the situations that the receiver and the transmitter are equlpped with either a single antenna or multiple antennas are considered. With regard to the channel estimator, the analysis considers both the minimum mean square error and the maximum likelihood channel estimate, while, with regard to the data detector, linear receiver interfaces are considered. Closed-form formulas are given for the channel-estimation mean-square error and for its Cramer-Rao bound, as well as for the error probability of the data detector. Moreover, the problem of the optimal choice of the length of the training sequence is also addressed. Overall, results show that the considered iterative strategy achieves excellent performance and permits, at the price of some complexity increase, the use of very short training sequences without incurring any performance loss. Finally, computer simulations reveal that the experimental results are in perfect agreement with those predicted by the theoretical analysis. Index Terms--Channel estimation, Cramer-Rao bound (CRB), data detection, multiantenna systems, wireless communication.

In this paper, the problem of subspace-based blind adaptive multi-user detection in multi-rate direct-sequence code-division multiple-access (DS.CDMA) systems adopting short (periodic) spreading codes is considered. The solution that we propose is based on the well-known formulation of the linear minimum mean-squared error and decorrelating detectors in terms of signal subspace parameters. Since in a multi-rate scenario the correlation properties of the observable (and, hence, the signal subspace parameters) are periodically time-varying, classical subspace tracking algorithms, which assume that the subspace to be tracked is time-invariant or slowly time-varying, are shown to be not useful in this situation. A new recursive cyclic subspace tracking algorithm is thus developed. This procedure, which is based on a generalization of the PASTd algorithm, is able to capture the periodical variations of the signal subspace, and thus enables subspace-based blind adaptive multi-user detection in multi-rate CDMA systems. The proposed algorithm has a smaller computational complexity than the recently developed cyclic recursive-least-squares procedure, and, as numerical results confirm, is capable of providing very satisfactory performance. Index Terms--Blind adaptive multi-user detection, cyclic algorithms, direct-sequence code-division multiple-access (DS-CDMA) systems, multi-rate CDMA, subspace tracking.

The problem of blind multiuser detection for direct-sequence code-division multiple-access systems operating over fading dispersive channels and in the presence of additive Gaussian noise with unknown temporal correlation function is considered. Such a problem has been addressed recently by Wang et al. and solved by employing a receiver with two well-separated antennas, such that the noise is spatially uncorrelated. A new method, which enables blind multiuser detection in correlated noise with just one antenna (and thus can be implemented in mobile transceivers), is proposed here. The effectiveness of the new procedure is tested through computer simulations, and its performance is compared to that of the algorithms developed by Wang et al.. Numerical results demonstrate that the newly proposed method, while relying on halved hardware resources, incurs a performance loss of only a few decibels with respect to the two-antenna based procedures. Index Terms--Blind multiuser detection, channel estimation, code-division multiple access (CDMA), correlated noise, group detection.

This paper addresses the problem of coordinated beamforming across a group of base stations (BSs) and frequency slots in the downlink of a multiple-input multiple-output (MIMO) orthogonal frequency-division multiple-access (OFDMA) cellular network. Three figures of merit are considered for system design under a per-BS power constraint: 1) the weighted sum of the rates (WSR) on the frequency slots of the coordinated BSs; 2) the global energy efficiency (GEE), defined as the ratio between the network sum rate and the corresponding consumed power; and 3) the weighted sum of the energy efficiencies (WSEE) on the frequency slots of the coordinated BSs. The Karush–Kuhn–Tucker (KKT) conditions of the considered optimization problems are first derived to gain insight into the structure of the optimal beamformers. Then, we propose a suboptimal design method that can be applied to all considered figures of merit. Numerical results are provided to assess the performance of the proposed beamforming strategies. [ABSTRACT FROM PUBLISHER]