The paper presents MIMO field performance results observed using a ultra mobile broadband (UMB) testbed network. We evaluate metrics such as antenna correlations and channel condition number to characterize the MIMO channel. Results show that low condition numbers, which are beneficial to MIMO, are prevalent for a majority of the coverage area in our network. We demonstrate that the use of MIMO provides gains of the order of 20-40% over SIMO transmissions. These gains are made possible by the use of cross-polarized transmit antennas and advanced UMB features that allow dynamic MIMO vs. SIMO transmission selection based on channel conditions. These results are obtained in a truly mobile, wireless wide-area deployment, which makes them unique. Our results point to the viability and value of MIMO in future mobile wireless networks.

The paper discusses antenna subset selection in MIMO wireless systems. The subsets of transmit and receive antennas are selected so as to maximise the channel capacity. First of all, we establish the relationship between the multiplexing gain and the diversity gain achievable with adaptive antenna subset selection. Second, we indicate a selection rule that allows a full diversity advantage to be achieved with a reduced computational effort, by decoupling the combined transmit/receive selection into the separate selection of transmit/receive subsets. Finally, we study the performance of practical systems with antenna selection in the context of high throughput MIMO-OFDM WLAN.

High data rate wireless communications, nearing 1 Gb/s transmission rates, is of interest in emerging wireless local area networks and home audio/visual networks. Designing very high speed wireless links that offer good quality-of-service and range capability in non-line-of-sight (NLOS) environments constitutes a significant research and engineering challenge. Ignoring fading in NLOS environments, we can, in principle, meet the 1 Gb/s data rate requirement with a single-transmit single-receive antenna wireless system if the product of bandwidth (measured in hertz) and spectral efficiency (measured in bits per second per hertz) is equal to 10/sup 9/. A variety of cost, technology and regulatory constraints make such a brute force solution unattractive, if not impossible. The use of multiple antennas at transmitter and receiver, popularly known as multiple-input multiple-output (MIMO) wireless, is an emerging cost-effective technology that offers substantial leverages in making 1 Gb/s wireless links a reality. The paper provides an overview of MIMO wireless technology covering channel models, performance limits, coding, and transceiver design.

Crosstalk is the major source of performance degradation in VDSL. A number of crosstalk cancellation techniques have been proposed to address this. Whilst these schemes lead to large performance increases they also have high run-time complexities, a problem which grows rapidly with the number of lines within a binder. Since the majority of crosstalk typically comes from only a few dominant crosstalkers, it is possible to do partial crosstalk cancellation. We present a low-complexity, partial crosstalk cancellation technique for VDSL based on line selection. We derive the optimal line selection technique, and several low-complexity selection algorithms which give near-optimal performance in most scenarios. These techniques lead to significant reductions in runtime complexity whilst giving similar performance to full crosstalk cancellation.

This paper discusses antenna sub-set selection in multiple-input multiple-output wireless systems. The antennas are selected so as to maximize the channel capacity. We present a near-optimal selection algorithm that enables tractable statistical analysis of the selection gain. We show that with antenna selection the capacity is statistically lower bounded by the capacity of the set of parallel independent SIMO channels each with selection diversity. We leverage this result to prove the equivalence in diversity order between the full system (all receive antennas) and the system with antenna selection. Simulations validating analysis and illustrating algorithm performance are also presented.

This correspondence discusses the problem of the receive antenna subset selection in multiple-element antenna (MEA) transmission systems. The antennas are selected so as to maximize the channel capacity. A set of near-optimal selection algorithms is presented. The first algorithm in particular allows statistical analysis of selection gains. We present tight analytic lower bounds on the outage capacity achievable through antenna selection. Extensive simulations validating analysis and illustrating performance of the selection algorithms are also presented.

Spatial multiplexing is a signaling strategy for achieving high spectral efficiencies in communication links that employ multiple transmit and multiple receive antennas. In such systems, it is desirable to use only a subset of the available transmit and/or receive antennas to reduce cost and complexity. We address the problem of optimal antenna subset selection in spatial multiplexing systems when only the second-order statistics of the channel are available. We derive selection criteria for both the maximum likelihood and zero forcing receivers, motivated by minimizing the average symbol error rate. We characterize the antenna selection gain and show that both coding gain and diversity gain is possible. We then use Monte Carlo simulations to validate our analysis.

Multiple input multiple output antenna subset selection is a low cost low complexity technique with the benefits of multiple antennas. This paper addresses the problem of statistical MIMO antenna sub-set selection with space-time coding. The antennas are chosen based on second order channel statistics, the goal being to minimize the average probability of error. We show that the optimal antenna set maximizes the determinant of the covariance of the vectorized channel. The derived selection rule allows simultaneous (joint) selection of optimal transmit and receive antennas. We discuss propagation scenarios in which the selection rule decouples so that joint selection can be carried out by performing transmit selection independent of the receive antennas and vice versa. The selection gain is quantified as the performance improvement due to transmission/reception on the optimal set instead of any other selection. We show the possibility of both coding gain as well as diversity gain. Finally, we support our analysis with simulations.

Space-time coding for the flat fading, quasi-static MIMO wireless channel has received widespread attention. This paper treats space-time code design for frequency selective channels from a single carrier modulation perspective. We present a general framework for analyzing space-time codes for delay spread channels based on PEP analysis. It is shown that as in the flat fading case, diversity gain is driven by the minimum rank of the pairwise codeword difference matrices. Delay spread, however, imposes a block Hankel structure on the codewords which may prevent certain codes designed for the flat fading case from exploiting full spatio-temporal diversity when used over frequency selective channels. We explicitly show this diversity loss for the delay diversity code. We show that a properly generalized delay diversity (GDD) code achieves full diversity over frequency selective channels. Finally we propose an extension to the GDD which fits naturally in a multi-carrier setting.

We present a new model for multiple-input-multiple-output (MIMO) outdoor wireless fading channels and their capacity performance. The proposed model is more general and realistic than the usual independent and identically distributed (i.i.d.) model, and allows us to investigate the behavior of channel capacity as a function of the scattering radii at transmitter and receiver, distance between the transmit and receive arrays, and antenna beamwidths and spacing. We show how the MIMO capacity is governed by spatial fading correlation and the condition number of the channel matrix through specific sets of propagation parameters. The proposed model explains the existence of "pinhole" channels which exhibit low spatial fading correlation at both ends of the link but still have poor rank properties, and hence, low ergodic capacity. In fact, the model suggests the existence of a more general family of channels spanning continuously from full rank i.i.d. to low-rank pinhole cases. We suggest guidelines for predicting high rank (and hence, high ergodic capacity) in MIMO channels, and show that even at long ranges, high channel rank can easily be sustained under mild scattering conditions. Finally, we validate our results by simulations using ray tracing techniques. Connections with basic antenna theory are made.

Space-time block codes provide maximal diversity advantage over a fading channel. This paper presents a novel technique that provides additional diversity gain by coupling antenna selection with a space-time block code. Specifically, we provide a choice of transmit antenna elements at the transmitter and transmit a space-time code over the optimal antenna pair. We present the optimal selection rule and quantify the improved performance in terms of gain in average SNR. The average SNR gain is calculated as a function of the number of transmit antenna elements and the number of receive antennas. We also investigate the improvement in outage capacity.

We present a new model for multiple-input multiple-output (MIMO) outdoor wireless fading channels which is more general and realistic than the usual i.i.d. model. We investigate the channel capacity as a function of parameters such as the local scattering radius at the transmitter and the receiver, the distance between the transmit (TX) and receive (RX) arrays, and the antenna beamwidths and spacing. We point out the existence of "pin-hole" channels which exhibit low fading correlation between antennas but still have poor rank properties and hence low capacity. Finally we show that even at long ranges high channel rank can easily be obtained under mild scattering conditions.

Previous work has shown that the use of multiple antennas in a fading environment results in a linear increase in capacity. This paper examines the capacity of a multiple antenna element array (MEA) in a quasi-static flat fading environment with a rank deficient channel. We assume that the channel is known at the receiver and the existence of a feedback path to the transmitter. For a particular channel realization, we show that the judicious use of fewer transmit antennas when the channel matrix is ill-conditioned can increase system capacity. We develop a criterion for selecting an optimum set of transmit antennas. This selection is optimal in the sense that the capacity of the resulting MEA system is greater than that for any other configuration with the same number of transmit antennas chosen from the original set. The resulting channel is full rank.