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For space-division multiplexing (SDM) via block diagonalization on multiuser multiple-input multiple-output (MIMO) wireless downlink, it is shown that receive antenna selection (RAS) is necessary for maximizing the achievable sum rate. This is true even when all receive antennas are equipped with radio frequency (RF) chains and RAS reduces the upper bound on the broadcast sum capacity, and when the orthogonalized channels use optimal processing. Similarly, spatial-mode selection (SMS) is necessary for sum rate maximization when receive-weight matrices are used for spatial-mode allocation. RAS/SMS may release transmission resources that can fully be utilized via additional user scheduling to yield further sum rate gains. Optimal user selection for sum rate maximization is subsumed within an exhaustive RAS/SMS process for multiantenna terminals, and both selection processes become identical for single-antenna terminals. RAS/SMS thus helps reduce the performance gap from the optimal sum capacity even for small user pool sizes. A block antenna/mode selection approach is introduced to help overcome the drawbacks of existing algorithms. Since RAS/SMS involves antenna/mode ranking, a systematic method for resource allocation with sum rate loss minimization is inherently provided. This way, a streamlined process that combines user selection, RAS/SMS, and resource allocation is developed for sum rate maximization of block-diagonalized SDM. Index Terms--Block diagonalization, MIMO spatial multiplexing, multiuser MIMO downlink, receive-antenna selection, spatial-mode selection, sum rate maximization.

We consider a receive antenna selection multiple-input-multiple-output (MIMO) system, where only one out of [N.sub.r] receive antennas is selected. Spatial channel correlation will be considered at the receiver side only. Our goal is to investigate the capacity performance of this system. In particular, we will derive a closed-form expression for the outage probability and an upper bound for the ergodic (average) capacity. These quantities will be expressed using an infinite series representation. To do so, we will first derive the joint cumulative distribution function and the joint probability density function of the squared row norms of the channel matrix. This is enabled by taking advantage of the statistical properties of multivariate chi-squared random variables. Using the outage expression derived, we demonstrate that the considered antenna selection system achieves a full diversity order that is similar to a MIMO system without antenna selection. Next, we derive the probability density function of the maximum of the squared row norms of the channel matrix and its moments, which is straightly related to the system ergodic capacity. We also analyze the error rate performance of the aforementioned receive antenna selection MIMO system while using orthogonal space-time block codes (OSTBCs) at the transmitter. Our simulation results are shown to validate our analytical findings. Index Terms--Antenna selection, channel capacity, correlated channels, multiple-input-multiple-output (MIMO), multivariate chi-squared distribution.

In this paper, a narrowband interference (NBI) mitigation scheme for ultrawide bandwidth (UWB) signals using multiple receive antennas is examined. The low spatial fading of UWB signals compared to NBI signals is exploited to provide 'interference selection diversity (SD).' Whereas classical SD is designed to maximize the desired received signal power, the aim of interference SD is to minimize the effective NBI power. The resulting distribution of the signal-to-interference ratio at the receiver is derived for both Rayleigh and Ricean NBI fading scenarios. Expressions for the probability of error of the SD scheme are also derived for a perfect receiver (where the correlator template is matched to the received UWB pulse shape) as well as for a Rake receiver with a limited number of fingers. It is shown that doubling the number of antennas results in a 3-dB performance improvement for the Rayleigh fading case. Less substantial gains are observed under Ricean fading. The method provides a simple but effective technique to mitigate NBI effects in UWB systems. Index Terms--Multipath channel, multiple antennas, narrowband interference (NBI), ultrawide bandwidth (UWB).

Accurate characterization of multiple-input multiple-output (MIMO) fading channels is an important prerequisite for the design of multiantenna wireless-communication systems. In this paper, a single-bounce two-ring statistical model for the time-varying MIMO flat fading channels is proposed. In the model, both the base and mobile stations are surrounded by their own ring of scatterers. For the proposed model, a closed-form expression for the spatio-temporal cross-correlational function between any two subchannels is derived, assuming single-bounce scattering. The new analytical expression includes several key physical parameters of interest such as the mean angle-of-departure, the mean angle-of-arrival, the associated angle spreads, and the Doppler spread in a compact form. The model includes many existing correlation models as special cases. Its utility is demonstrated by a comparison with collected MIMO data in terms of the spatio-temporal correlations, level crossing rate, average fade duration, and the instantaneous mutual information. Index Terms--Average fade duration (AFD), channel modeling, instantaneous mutual information (IMI), level crossing rate (LCR), multiantenna systems, multiple input multiple output (MIMO), Rayleigh fading, spatio-temporal cross correlation (STCC).

In this paper, the maximum signal-to-interference-plus-noise ratio (MSINR) beamforming problem in antenna-array CDMA systems is considered. In this paper, a modified MSINR criterion presented in a previous paper is interpreted as an unconstrained scalar cost function. By applying recursive least squares (RLS) to minimize the cost function, a novel blind adaptive beamforming algorithm to estimate the beamforming vector, which optimally combines the desired signal contributions from different antenna elements while suppressing noise and interference, is derived. Neither the knowledge of the channel conditions (fading coefficients, signature sequences and timing of interferers, statistics of other noises, etc.) nor training sequence is required. Compared with previously published adaptive beamforming algorithms based on the stochastic-gradient method, it has faster convergence and better tracking capability in the time-varying environment. Simulation results in various signal environments are presented to show the performance of the proposed algorithm. Index Terms--Adaptive arrays, code division multiple access (CDMA), generalized eigenvector, maximum signal-to-interference-plus-noise ratio (MSINR) beamforming, multiple access interference (MAI).

Multi-input multi-output (MIMO) systems, with multiple antennas at both the transmitter and the receiver, are anticipated to be widely employed in future wireless networks due to their predicted tremendous system capacity. To protect the transmitted data against random channel impairment, it is desirable to consider link adaptation, such as rate adaptation and power control, to improve the system performance and guarantee certain quality of service. Based on the observation that link adaptation and antenna selection problems are often coupled, we propose a joint antenna subset selection and link adaptation study for MIMO systems. After the formulation of the multidimensional joint optimization problem, the main contribution of this paper lies in the design of efficient algorithms approaching the optimal solution for both uncorrelated and correlated MIMO channels. Specifically, we propose one simplified antenna selection and link adaptation rule based on the expected optimal number of active antennas for uncorrelated MIMO with Rayleigh fading and one for correlated MIMO channels only based on the slowly varying channel correlation information. Our proposed algorithms are verified through numerical results, demonstrating significant gains over traditional MIMO signaling, while feasible for practical implementation. Index Terms--Cholesky decomposition, multi-input multioutput (MIMO) systems, QR decomposition.

An automotive AM/FM hidden antenna using the slot between the body of the automobile and a metal solar heat-reduction film in the front windshield is described. Such solar heat-reduction metal films are becoming common and thus represent an opportunity to incorporate an antenna at only marginal cost. The radio frequency (RF) input impedance and gain patterns will be described, and techniques for impedance matching will be shown. Theoretical and experimental antenna patterns will be compared. A test range measurement system and experimental results will be described. A mobile on-road system to characterize the antenna in urban and suburban environments will be shown. The application of this mobile system to the measurement of calibrated gain patterns will be demonstrated. Index Terms - Antenna, automobile, conformal, on glass, solar film.

In the presence of pilot channels in the reverse-link, some approaches to compute the coherent beamforming vectors for the two-dimensional Rake (2-D Rake) combiner are considered. Since the beamforming vectors are computed using the despread signals, the computational complexity of the approaches is lower than that of the approach which uses the received signals before despreading. It has been shown that the beamforming performance depends on the accuracy of channel parameter estimation. The approach which provides better channel parameter estimates can give a better beamforming performance. The effect of the pilot power on the performance is also presented. Index Terms--Rake combining, smart antenna, spread spectrum.