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ABSTRACT: Realizing antenna arrays that preserve channel capacity in multiple-input multiple-output (MIMO) radio communications is a challenge because of the detrimental effects of mutual coupling. The fact that mutual coupling becomes more pronounced as antenna spacing decreases is therefore a critical issue with compact arrays used in portable MIMO radios. The contributions made in this paper include the realization of compact MIMO arrays designed to preserve channel capacity and the characterization of these compact arrays' performance in field measurements using MIMO radios. A multiport metric is used to characterize the compact arrays in a way that more appropriately measures array performance under MIMO signalling conditions than the traditional scattering matrix characterization. Field measurements show the extent and proportion of the effect that correlation and radiation efficiency have on MIMO channel capacity. The compact arrays' strong performance in field measurements is explained by their ability to preserve the MIMO channel's eigenstructure. Results also show that mutual coupling prevents channel capacity from scaling linearly with the number of antennas. Guidelines for compact MIMO array design are given with supporting results from field measurements
IEEE Transactions on Antennas and Propagation 12/2006; · 2.15 Impact Factor
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ABSTRACT: Singular Value Decomposition (SVD) is a powerful tool for multivariate analysis. However, independent computation of the SVD for each sample taken from a bandlimited matrix random process will result in singular value sample paths whose tangled evolution is not consistent with the structure of the underlying random process. The solution to this problem is developed as follows: (i) a SVD with relaxed identification conditions is proposed, (ii) an approach is formulated for computing the SVD's of two adjacent matrices in the sample path with the objective of maximizing the correlation between corresponding singular vectors of the two matrices, and (iii) an efficient algorithm is given for untangling the singular value sample paths. The algorithm gives a unique solution conditioned on the seed matrix's SVD. Its effectiveness is demonstrated on bandlimited Gaussian random-matrix sample paths. Results are shown to be consistent with those predicted by random-matrix theory. A primary application of the algorithm is in multiple-antenna radio systems. The benefit promised by using SVD untangling in these systems is that the fading rate of the channel's SVD factors is greatly reduced so that the performance of channel estimation, channel feedback and channel prediction can be increased.
11/2006;
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ABSTRACT: STBC-MTCM scheme which achieves high rate, full diversity and large coding gains is an outstanding example of transmit diversity scheme for multiple-antenna system. In the case of time selective fast fading (TSFF) or frequency selective fading (FSF) channels, the performance of current existing STBC-MTCM decoder suffers from an irreducible error floor. In this paper, we present two computational efficient decoding algorithms: zero-forcing (ZF) detector and linear minimum mean square error (LMMSE) detector to combat the fast fading channels. The proposed decoding algorithms provide a robust performance across range of channel conditions from quasi-static (slow) fading to TSFF or FSF. Simulation results suggest that our proposed decoding algorithms have near Maximum-Likelihood (ML) performance while being computational more efficient.
Information Theory Workshop, 2006. ITW '06 Punta del Este. IEEE; 11/2006
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ABSTRACT: Iterative turbo processing between detection and decoding shows near-capacity performance on a multiple-antenna system. Combining iterative processing with optimum front-end detection is particularly challenging because the front-end maximum a posteriori (MAP) algorithm has a computational complexity that is exponential in the throughput. Sub-optimum detector such as the soft interference cancellation linear minimum mean square error (SIC-LMMSE) detector with near front-end MAP performance has been proposed. The asymptotic computational complexity of SIC-LMMSE remains O(nt2nr+ntnr3+ntMc2Mc) per detection-decoding cycle where nt is number of transmit antenna, nr is number of receive antenna, and Mc is modulation size. A lower complexity detector is the hard interference cancellation LMMSE (HIC-LMMSE) detector. HIC-LMMSE has asymptotic complexity of O(nt2nr+ntMc2Mc)but suffers exta performance degradation. In this paper, we introduce a frontend detection algorithm that achieves asymptotic computational complexity of O(ntMc2Mc). Simulation results demonstrate that the proposed low complexity detection algorithm offers exactly same performance as their full complexity counterpart in an iterative receiver while being computational more efficient.
Communications, 2006. ICC '06. IEEE International Conference on; 07/2006
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ABSTRACT: This paper presents a soft-output lattice detector algorithm for multiple-input multiple-output (MIMO) communications called layered orthogonal lattice detector (LORD). LORD adopts a new lattice formulation and relies on a channel orthogonalization process. Building on the optimality of LORD for two transmit antennas this paper is a generalization of the algorithm to any number of transmit antennas. The most interesting aspect of LORD is that for two transmit antennas max-log bit soft-output information can be simply generated and for greater than two antennas approximate max-log detection is achieved with reasonable complexity. LORD can be implemented in a parallel fashion, as desirable for VLSI. Extensive simulation results in different scenarios of interest for next generation WLANs (IEEE 802.11n) are reported. The simulations show that LORD is able to achieve very high signal-to-noise ratio (SNR) gains compared to current practical soft-output MIMO detectors.
Communications, 2006. ICC '06. IEEE International Conference on; 07/2006
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ABSTRACT: Iterative turbo processing between detection and decoding shows near-capacity performance on a multiple-antenna system. Combining iterative processing with optimum front-end detection is particularly challenging because the front-end maximum a posteriori (MAP) algorithm has a computational complexity that is exponential in the throughput. Sub-optimum detector such as the soft interference cancellation linear minimum mean square error (SIC-LMMSE) detector with near front-end MAP performance has been proposed. The asymptotic computational complexity of SIC-LMMSE remains O(nE2<sub>t</sub>n<sub>r</sub> + n<sub>t</sub>nE3 <sub>r</sub> + n<sub>t</sub>M<sub>c</sub>2<sup>M</sup> <sub>c</sub>) per detection-decoding cycle where n<sub>t</sub> is number of transmit antenna, n<sub>r</sub> is number of receive antenna, and mc is modulation size. A lower complexity detector is the hard interference cancellation LMMSE (HIC-LMMSE) detector. HIC-LMMSE has asymptotic complexity of O(nE2<sub>t</sub>n<sub>r</sub> + n<sub>t</sub>M<sub>c</sub>2<sup>M</sup> <sub>c</sub>) but suffers extra performance degradation. In this paper, we introduce a low complexity front-end detection algorithm that not only achieves asymptotic computational complexity of O(nE2<sub>t</sub>n<sub>r</sub> + n<sub>t </sub>nE3<sub>r</sub>[Gamma (beta)] + n<sub>t</sub>M<sub>c</sub>2 <sup>M</sup> <sub>c</sub>) where [Gamma (beta) is a function with discrete output {-1,2,3, ...,n<sub>t</sub>}. Simulation results demonstrate that the proposed low complexity detection algorithm offers exactly same performance as its full complexity counterpart in an iterative receiver while being computational more efficient
Wireless Communications and Networking Conference, 2006. WCNC 2006. IEEE; 05/2006
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ABSTRACT: In this correspondence, a new bound on the performance of multiuser receivers in fading channels is presented. The bound is based on a novel criterion for decomposability of error sequences. A constructive method to find the set of indecomposable error sequences under the new criterion is presented. Although the presentation is in the context of a narrow-band multiuser system, the improved bounds can be applied directly to code-division multiple-access (CDMA) multiuser systems over flat-fading channels. A modified bound is also developed for multipath-fading channels. Several examples demonstrate the improved tightness of the new bound, relative to previous results
IEEE Transactions on Information Theory 04/2006; · 3.01 Impact Factor
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ABSTRACT: In this paper, a new technique to design improved high-rate space-time (ST) codes is proposed based on the concept of concatenated ST block code (STBC) and outer trellis-coded modulation (M-TCM) encoder constructions. Unlike the conventional rate-lossy STBC-MTCM schemes, the proposed designs produce higher rate ST codes by expanding the codebook of the inner orthogonal STBC. The classic set partitioning concept is adopted to realize the STBC-MTCM designs with large coding gains. The proposed expanded STBC-MTCM designs for the two-, three-, and four-transmitter cases are illustrated. Simulation results show the proposed STBC-MTCM designs significantly outperform the traditional ST-TCM schemes. Furthermore, decoding complexity of the proposed scheme is low because signal orthogonality is exploited to ease data decoding.
IEEE Transactions on Information Theory 01/2006; · 3.01 Impact Factor
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Vehicular Technology Conference, 2005. VTC-2005-Fall. 2005 IEEE 62nd; 10/2005
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ABSTRACT: This paper provides details about experiments in realistic, urban, and frequency flat channels with space-time coding that specifically examines the impact of the number of receive antennas and the design criteria for code selection on the performance. Also the performance characteristics are examined of the coded modulations in the presence of finite size array geometries. This paper gives some insight into which of the theories are most useful in realistic deployments
Information Theory, 2005. ISIT 2005. Proceedings. International Symposium on; 10/2005
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ABSTRACT: This paper proposes a new peak-to-average power ratio (PAPR) reduction scheme in multiple transmit antenna environments. By applying a unitary rotation, overall PAPR of the multiple transmits antenna system is reduced. This scheme doesn't require any side information to decode the signal in the receiver, enabling throughput-lossless PAPR reduction. Furthermore, there is no increase in the complexity of the receiver.
Communications, 2005. ICC 2005. 2005 IEEE International Conference on; 06/2005
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ABSTRACT: This paper discusses the design of a packet detection algorithm for a burst mode continuous phase modulation (CPM) modem over flat Rayleigh fading channels in the 220 MHz frequency band. The modem design focuses on bandwidth efficiency while maintaining good synchronization performance and low complexity. The packet structure meets the Federal Communications Commission frequency emission mask for the 220 MHz frequency band. The packet detection algorithm uses a degraded maximum likelihood (ML) amplitude estimate to provide the initial timing needed for synchronization and demodulation. The ML amplitude estimate is shown to be a function of a one dimensional parameter search. The parameter search is degraded to reduce complexity while maintaining an accurate amplitude estimate.
Signals, Systems and Computers, 2004. Conference Record of the Thirty-Eighth Asilomar Conference on; 12/2004
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ABSTRACT: In this paper, we present an adaptive Wiener filtering channel estimation method in the context of pilot symbols assisted multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) communications in low mobility environment. Optimal Wiener filtering requires known channel statistics. When there exists channel model mismatch, performance could degrade significantly. We propose to quantize the channel model space into a set of hypothesized models with different delay spread and uniform multipath arrivals with equal power. A quasi maximum likelihood detector is developed to choose the hypothesized model that is closest to the actual channel. The Wiener coefficients associated with the selected model are then used for channel estimation. Simulation results show that the proposed adaptive Wiener filtering achieves significant gain over a pessimistic Wiener design and very robust performance with respect to model variations.
Signals, Systems and Computers, 2004. Conference Record of the Thirty-Eighth Asilomar Conference on; 12/2004
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ABSTRACT: This paper reports on some experiments with multiple antenna radios. Specifically this paper compares the performance between an experimental system with training and coherent demodulation and a system using noncoherent techniques of communication. The paper also examines robustness in performance across a variety of channel conditions.
Signals, Systems and Computers, 2004. Conference Record of the Thirty-Eighth Asilomar Conference on; 12/2004
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ABSTRACT: We present a radio telemetry solution for remote sensor networks that uses rotational actuation of directional antennas. The benefits of this solution over either omnidirectional or fixed directional antennas for intra-nodal communications include greater energy efficiency, sparse node deployment, and robustness to node failure. Four strategies for minimizing link acquisition time are presented. Each strategy uses a search algorithm tailored to a unique combination of radio hardware to provide nodes with coordination and/or geolocation capabilities. These strategies are implemented on a two-node testbed and their performance is measured in a realistic field trial. Results show that the use of secondary radios for search coordination and geolocation provide an order of magnitude reduction in search duration. In particular, the strategy using only search coordination yields performance that is independent of node separation while performance of the strategy using only geolocation is strongly dependent on range.
Vehicular Technology Conference, 2004. VTC2004-Fall. 2004 IEEE 60th; 10/2004
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ABSTRACT: The paper introduces a super-orthogonal space-time block coding scheme. The code construction is based on the expansion of an orthogonal block code via a unitary matrix transformation. By expanding the orthogonal block code, we can both increase the code rate and improve the performance in terms of E<sub>b</sub>/N<sub>0</sub>, with a moderate increase of the receiver complexity. The performance is compared with orthogonal and quasi-orthogonal block codes in computer simulation.
Vehicular Technology Conference, 2004. VTC2004-Fall. 2004 IEEE 60th; 10/2004
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ABSTRACT: In this work, we analyze the pairwise error probability (PEP) performance of space-time codes in the presence of transmit fading correlation. Unlike receive correlation, the effect of transmit correlation depends on the specific space-time code used. We show that at low SNR, depending on the code, transmit correlation can either improve or degrade the PEP performance. By analyzing the worst case scenario for asymptotically high or low SNR, we show that, to guarantee robust performance for arbitrary transmit correlation, the minimum eigenvalue of the codeword pair difference matrix should be maximized among all codeword pairs. Numerical and simulation results are given to corroborate the theoretical analysis.
Communications, 2004 IEEE International Conference on; 07/2004
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ABSTRACT: A two-dimensional space-time pilot-symbol assisted demodulation system is proposed in this paper. Since complex scattering environments can produce nontrivial space-time correlation characteristics, this paper proposes coherent demodulation by estimating the fading channel distortion using pilot observations across both space and time. The optimum interpolation filter takes in multiple signals from receiving antennas and exploiting the space-time channel correlation to produce multiple channel-estimate outputs corresponding to every antenna. The optimal channel-estimation filter, its mean-square error performance, and the pairwise symbol-error probability are derived for realistic scattering models to characterize the system performance. A design criterion is proposed for the pilot-symbol spacing and the filter length. Since the filter is a function of the statistical description of the channel, we investigate if this statistical description and the resulting optimal filters can be estimated simply from the pilot observations.
IEEE Transactions on Communications 07/2004; · 1.68 Impact Factor
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ABSTRACT: We derive the exact pairwise error probability (PEP) for space-time coding over quasi-static Rayleigh fading channels in the presence of spatial fading correlation. We show that receive correlation always degrades the PEP for all signal-to-noise ratios (SNRs). We quantify the effect of receive correlation by employing the notion of "majorization". We show that the stronger the receive correlation, the worse the PEP for all SNRs. We show that at low SNR, depending on the codes, transmit correlation can either improve or degrade the PEP performance. We show that to guarantee robust performance for arbitrary transmit correlation, the minimum eigenvalue of the codeword pair difference matrix should be maximized among all codeword pairs.
IEEE Transactions on Communications 07/2004; · 1.68 Impact Factor
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ABSTRACT: In this correspondence, we propose an algorithm for computing the distance spectrum of a space-time trellis code achieving maximal diversity gain in quasi-static fading channels. We further present a state reduction technique for trellis codes that can reduce the complexity of the distance spectrum computation. We provide numerical results supporting the empirical evidence that a truncated union bound obtained from the distance spectrum provides an accurate characterization of the relative performance ordering of different space-time trellis codes and, therefore, it offers a tool for better space-time trellis code design.
IEEE Transactions on Information Theory 01/2004; · 3.01 Impact Factor
