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Communications, IEEE Transactions on

Issue 4 • Date April 2006

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Displaying Results 1 - 25 of 32
  • Table of contents

    Page(s): c1 - c4
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    Freely Available from IEEE
  • IEEE Transactions on Communications publication information

    Page(s): c2
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  • LDPC-based channel coding of correlated sources with iterative joint decoding

    Page(s): 577 - 582
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    This letter considers low-density parity-check (LDPC) coding of correlated binary sources and a novel iterative joint channel decoding without communication of any side information. We demonstrate that depending on the extent of the source correlation, additional coding gains can be obtained. Two stages of iterative decoding are employed. During global iterations, updated estimates of the source correlation are obtained and passed on to the sum-product decoder that performs local iterations with a predefined stopping criterion and/or a maximum number of local decoding iterations. Simulation results indicate that very few global iterations (2-5) are sufficient to reap significant benefits from implicit knowledge of source correlation. Finally, we provide analytical performance bounds for our iterative joint decoder and comparisons with sample simulation results. View full abstract»

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  • Some interesting observations for certain line codes with application to RFID

    Page(s): 583 - 586
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    In this letter, we bring to the reader's attention some interesting properties of certain line codes that appear to not have been mentioned in the literature, that, in some cases, can be used to enhance their performance when used for digital communication with particular application to radio frequency identification. In addition, we correct a previously reported result pertaining to the performance of such codes. View full abstract»

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  • Approaching MIMO channel capacity with soft detection based on hard sphere decoding

    Page(s): 587 - 590
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    Hard sphere decoding (HSD) has well-appreciated merits for near-optimal demodulation of multiuser, block single-antenna or multi-antenna transmissions over multi-input multi-output (MIMO) channels. At increased complexity, a soft version of sphere decoding (SD), so-termed list SD (LSD), has been recently applied to coded layered space-time (LST) systems enabling them to approach the capacity of MIMO channels. By introducing a novel bit-level multi-stream coded LST transmitter along with a soft-to-hard conversion at the decoder, we show how to achieve the near-capacity performance of LSD, and even outperform it as the size of the block to be decoded (M) increases. Specifically, for binary real LST codes, we develop exact max-log-based SD schemes with M + 1 HSD steps, and an approximate alternative with only one HSD step to trade off performance for average complexity. These schemes apply directly to the real and imaginary parts of quaternary phase-shift keying signaling, and also to quadrature amplitude modulation signaling after incorporating an appropriate interference estimation and cancellation module. We corroborate our near-optimal soft detection (SoD) algorithms based on HSD (SoD-HSD) with simulations. View full abstract»

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  • Selective maximum-likelihood symbol-by-symbol detection for multidimensional multicode WCDMA with precoding

    Page(s): 591 - 595
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    To faciliate high-rate uplink transmission, a novel selective maximum-likelihood (SML) detection is realized on a set of parallel multicode (MC) channels as a result of MC wideband code-division multiple-access (WCDMA) signaling with precoding. Multidimensional (MD) signaling can be combined with MC to further increase the data rate with fixed spreading factor per symbol. In connection with this MDMC signaling, the proposed SML detection achieves significantly improved symbol-error probability, compared with other detection methods, both without soft sequential decoders for a tractable analysis. View full abstract»

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  • Throughput and delay analysis for the IEEE 802.11e enhanced distributed channel access

    Page(s): 596 - 603
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1000 KB) |  | HTML iconHTML  

    In this letter, we propose a three-dimensional Markov chain model for the 802.11e enhanced distributed channel access (EDCA) mode. This model can be used to compute the maximum sustainable throughput and service delay distribution for each priority class when under saturation load. The new framework models the performance impact of major quality-of-service (QoS)-specific features (e.g., CWMin, CWMax, AIFS, internal collision resolution) of the 802.11e EDCA mode, and hence can provide an analytical approach to pick the parameter values associated with EDCA to meet the QoS requirements of each priority. View full abstract»

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  • Performance of coherent DPSK free-space optical communication systems in K-distributed turbulence

    Page(s): 604 - 607
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    Closed-form solutions for the bit-error rate of a freespace, heterodyne optical communication system is derived when the optical beam is subjected to K-distributed optical turbulence. It is assumed that the scintillation index is confined to the range (2,3) or that the number of scatterers in the propagation path is a random variable. View full abstract»

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  • Performance study of the minimax robust phased array for wireless communications

    Page(s): 608 - 613
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    In this paper, new robust M-estimation techniques are developed for combating impulsive noise and multiple-access interference in communication systems. Power functions of the proposed robust estimators are obtained by minimizing a nonquadratic residual function derived from the Huber's minimax robust estimation theory. Maximum peaks of these power functions are used for estimation of communication signals as well as direction of arrival. A strong advantage of the proposed robust M-estimation algorithms is a decreased sensitivity of the estimates with respect to an actual unknown distribution of random noises and interferences. Simulation results demonstrate that the proposed robust algorithms, the robust median, and robust Huber estimators, offer significant performance gain over the conventional and minimum-variance distortionless-response estimators, with the best results given by the robust Huber estimator. View full abstract»

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  • Iterative vector channel estimation/MAP/PIC for CDMA systems in time-selective correlated multipath fading channels

    Page(s): 614 - 618
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    Recently, Gao et al. proposed the expectation-maximization (EM) vector channel estimation for single-user direct-sequence code-division multiple-access (DS-CDMA) systems to estimate the correlated fading channel coefficients of the paths of a user. They also used one D-lag decision-feedback maximum a posteriori (MAP) detector to detect the information bits. A straightforward extension (noniterative) to multiuser synchronous CDMA cases, i.e., adding the parallel interference cancellation (PIC) multiuser detector into their scheme, results in poor performance. Therefore, we propose an iterative scheme which combines vector channel estimation, decision-feedback MAP detection, and PIC. The partial PIC is applied in the sequence hypothesis stage of MAP in each iteration before the final MAP decision. The proposed scheme has twice the decision delay of the previous scheme for single-user cases. The performance of the proposed system in the time-selective, correlated multipath fading channel environment is investigated. Simulation results show that the proposed scheme significantly outperforms the noniterative scheme. Simulation results also show that the proposed scheme performs better than its scalar channel-estimation version. View full abstract»

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  • Interleaver design for turbo codes from convergence analysis

    Page(s): 619 - 624
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    In this letter, we present an analysis tool for the convergence of a turbo decoder using the min-sum algorithm. First of all, we classify cycles on a turbo code factor graph. We define and develop a quantity which characterizes the trellis convergence and a probability of a message round on a cycle. Our analysis is then applied to an interleaver design for a turbo decoder using the min-sum algorithm. Since the probability of a message round is closely related to the convergence property, the constructed interleaver optimizes the convergence property. The performance is compared with several referential interleavers. View full abstract»

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  • Comparative rate-distortion performance of multiple description coding for real-time audiovisual communication over the Internet

    Page(s): 625 - 636
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1000 KB) |  | HTML iconHTML  

    To facilitate real-time audiovisual communication through the Internet, forward error correction (FEC) and multiple description coding (MDC) can be used as low-delay packet-loss recovery techniques. We use both a Gilbert channel model and data obtained from real IP connections to compare the rate-distortion performance of different variants of FEC and MDC. Using identical overall rates with stringent delay constraints, we find that side-distortion optimized MDC generally performs better than Reed-Solomon-based FEC. If the channel condition is known from feedback, then channel-optimized MDC can be used to exploit this information, resulting in significantly improved performance. Our results confirm that two-independent-channel transmission is preferred to single-channel transmission, both for FEC and MDC. View full abstract»

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  • Precise analysis of bit-error probability for asynchronous multicode DS-CDMA systems

    Page(s): 637 - 647
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB) |  | HTML iconHTML  

    A precise bit-error probability (BEP) analysis method is derived for a multicode direct-sequence code-division multiple-access (DS-CDMA) system in an additive white Gaussian noise channel. The method is applicable to a multicode DS-CDMA system with an arbitrary number of multiple code sequences, and any selection of multiple code sequences. The precise method gives results that discriminate the effect of the selection of different multiple code sequences on the BEP, whereas Gaussian approximations (GAs) do not. Thus, the new method can be used to select the best multicode set for a given system, a task that cannot be achieved using GAs. A two-step analytical procedure enables deriving an explicit, compact form for the CF of the receiver decision statistic in a DS-CDMA system with an arbitrary number of multiple code sequences, and for any selection of multiple code sequences. View full abstract»

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  • Equalization algorithms in the frequency domain for continuous phase modulations

    Page(s): 648 - 658
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB) |  | HTML iconHTML  

    In this paper, novel equalization algorithms for continuous phase modulations (CPMs) are illustrated. Both conventional (linear and decision-feedback) and turbo equalization techniques are derived using the Laurent decomposition of CPM signals. All of them operate in the frequency domain and process two samples of the received signal per channel symbol. Numerical results show that on one hand, conventional equalization strategies offer good performance for binary partial response signaling over severely frequency-selective wireless channels at a moderate complexity. On the other hand, there is evidence that turbo techniques provide a small energy saving at the price of a substantial computational burden. View full abstract»

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  • Outage minimization with limited feedback for the fading relay channel

    Page(s): 659 - 669
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB) |  | HTML iconHTML  

    In this paper, we consider practical methods to approach the theoretical performance limits in the fading relay channel under different assumptions of transmitter channel knowledge. Specifically, we consider two degrees of transmitter channel knowledge: 1) perfect feedback is available and power control is employed and 2) no channel state knowledge is available at the transmitters and only spatial power allocation is possible. First, when perfect feedback is available, the optimal power control policy determines the ultimate limits of performance for constant rate transmission in the slow fading environment. However, in practice, perfect channel knowledge is not possible at the transmitters due to the finite capacity of the feedback links. We find practical methods to approach this performance limit through the use of power control with finite rate feedback. The finite-rate feedback results are shown for the low-complexity, full-diversity amplify-and-forward (AF) protocol. Interestingly, we see that only a few feedback bits are needed to achieve most of the gains of the optimal perfect feedback power control algorithm. Second, we consider the performance limit when the transmitters have no channel state knowledge and derive the optimal spatial power allocation between the source and relay for a given sum power constraint for the AF protocol. For most practical cases of interest, equal power allocation between the source and relay is shown to be nearly optimal. Our work suggests that there is minimal power savings from using spatial power allocation at the transmitters. To obtain large performance improvements over constant power transmission, it is imperative to have feedback for each realization of the channel state to allow for temporal power control. View full abstract»

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  • Joint data detection and channel estimation for OFDM systems

    Page(s): 670 - 679
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB) |  | HTML iconHTML  

    We develop new blind and semi-blind data detectors and channel estimators for orthogonal frequency-division multiplexing (OFDM) systems. Our data detectors require minimizing a complex, integer quadratic form in the data vector. The semi-blind detector uses both channel correlation and noise variance. The quadratic for the blind detector suffers from rank deficiency; for this, we give a low-complexity solution. Avoiding a computationally prohibitive exhaustive search, we solve our data detectors using sphere decoding (SD) and V-BLAST and provide simple adaptations of the SD algorithm. We consider how the blind detector performs under mismatch, generalize the basic data detectors to nonunitary constellations, and extend them to systems with pilots and virtual carriers. Simulations show that our data detectors perform well. View full abstract»

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  • Analysis and modeling of upstream throughput in multihop packet CDMA cellular networks

    Page(s): 680 - 692
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    We consider the problem of throughput modeling of wireless multihop packet CDMA networks with cellular overlay using simple forwarding strategies in the upstream. Considering the effect of shadowing and distance-dependent path loss, we approximate the probability density of interference at each base station (BS) and compare numerical and simulation results for different path-loss parameters. We derive the probability density of the received power at each BS due to transmission of one packet from a random node, as well as the probability distribution of the number of packets received at each node per time slot. Subsequently, we use the above results to approximate the probability density of the total received power at each BS based on calculations of moments. We observe that the probability density of intercell interference due to transmissions from terminals and routers may be approximated by normal and log-normal densities, respectively. We quantify the network performance based on throughput, total consumed power, and outage probability for different system parameters. For homogeneous link efficiencies, introducing routers into the network while reducing the transmission power increases the mean and variance of interference to the desired signal, hence higher outage probability. However, there are ample opportunities inherent to multihop structure, applicable to any of the physical, data link, and network layers, which help increase the overall achievable network throughput. View full abstract»

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  • Outage-based optimal power control for generalized multiuser fading channels

    Page(s): 693 - 703
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB) |  | HTML iconHTML  

    We address the problem of achieving outage probability constraints on the uplink of a code-division multiple-access (CDMA) system employing power control and linear multiuser detection, where we aim to minimize the total expended power. We propose a generalized framework for solving such problems under modest assumptions on the underlying channel fading distribution. Unlike previous work, which dealt with a Rayleigh fast-fading model, we allow each user to have a different fading distribution. We show how this problem can be formed as an optimization over user transmit powers and linear receivers, and, where the problem is feasible, we provide conceptually simple iterative algorithms that find the minimum power solution while achieving outage specifications with equality. We further generalize a mapping from outage probability specifications to average signal-to-interference-ratio constraints that was previously applicable only to Rayleigh-faded channels. This mapping allows us to develop suboptimal, computationally efficient algorithms to solve the original problem. Numerical results are provided that validate the iterative schemes, showing the closeness of the optimal and mapped solutions, even under circumstances where the map does not guarantee that constraints will be achieved. View full abstract»

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  • A new deterministic traffic model for core-stateless scheduling

    Page(s): 704 - 713
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    Core-stateless scheduling algorithms have been proposed in the literature to overcome the scalability problem of the stateful approach. Instead of maintaining per-How information or performing per-packet How classification at core routers, packets are scheduled according to the information (time stamps) carried in their headers. They can hence provision quality of service (QoS) and achieve high scalability. In this paper, which came from our observation that it is more convenient to evaluate a packet's delay in a core-stateless network with reference to its time stamp than to the real time, we propose a new traffic model and derive its properties. Based on this model, a novel time-stamp encoding scheme, which is theoretically proven to be able to minimize the end-to-end worst case delay in a core-stateless network, is presented. With our proposed traffic model, performance analysis in core-stateless networks becomes straightforward. View full abstract»

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  • Adaptive modulation in ad hoc DS/CDMA packet radio networks

    Page(s): 714 - 725
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB) |  | HTML iconHTML  

    This paper investigates the benefit of adaptive modulation based on channel state information (CSI) in direct-sequence/ code-division multiple-access (DS/CDMA) multihop packet radio networks. By exploiting varying channel conditions, adaptive modulation can be used in ad hoc networks to provide upper layers with higher capacity links over which to relay traffic. Using the α-stable interference model, the distribution of the signal-to-interference ratio (SIR) is obtained for a slotted system of randomly, uniformly distributed nodes using multilevel coherent modulation schemes. Performance is evaluated in terms of the information efficiency, which is a new progress-related measure for multihop networks. Three types of adaptivity are analyzed, differing in the level of CSI available: 1) full knowledge of the SIR at the receiver; 2) knowledge of only the signal attenuation due to fading; and 3) knowledge of only the slow fading component of the signal attenuation. The effect of imperfect channel information is also investigated. Sample results are given for interference-limited networks experiencing fourth-power path loss with distance, Ricean fading, and lognormal shadowing. View full abstract»

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  • Maximum-likelihood synchronization and channel estimation for OFDMA uplink transmissions

    Page(s): 726 - 736
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB) |  | HTML iconHTML  

    Maximum-likelihood estimation of the carrier frequency offset (CFO), timing error, and channel response of each active user in the uplink of an orthogonal frequency-division multiple-access system is investigated in this study, assuming that a training sequence is available. The exact solution to this problem turns out to be too complex for practical purposes as it involves a search over a multidimensional domain. However, making use of the alternating projection method, we replace the above search with a sequence of mono-dimensional searches. This results in an estimation algorithm of a reasonable complexity which is suitable for practical applications. As compared with other existing semi-blind methods, the proposed algorithm requires increased overhead but has more flexibility as it can be used with any subcarrier assignment scheme. Simulations indicate that the accuracy of the CFO estimates asymptotically achieves the Cramer-Rao bound. View full abstract»

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  • Performance analysis of multicarrier CDMA systems with frequency offsets and random spreading under optimum combining

    Page(s): 737 - 747
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    The carrier-frequency offset effect on the performance of asynchronous multicarrier direct-sequence code-division multiple-access (MC-DS-CDMA) systems with aperiodic random spreading and correlated Rayleigh fading is studied in this paper. We obtain the optimum combining filter that maximizes the signal-to-interference-plus-noise ratio (SINR) of the combined statistics and exploits correlated information among subchannels. A closed-form expression for the unconditional covariance matrix of the interference-plus-noise vector, which forms the basis of our theoretical analysis of the maximum SINR and the average bit error probability formula, is derived by averaging several random parameters including asynchronous delays, correlated Rayleigh fading, and signature sequences. The analytic results obtained are applicable to MC-CDMA with appropriate modifications. Furthermore, we show that the MC-CDMA system with a common random signature sequence over all subcarriers for a given user outperforms that with distinct sequences over different subcarriers. Finally, the performance of MC-CDMA systems using the optimum combining technique is compared with that of different combining filters in the simulation. View full abstract»

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  • Noncooperative iterative MMSE beamforming algorithms for ad hoc networks

    Page(s): 748 - 759
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB) |  | HTML iconHTML  

    An asynchronous unicast ad hoc network is considered, where each node i is equipped with a receive/transmit beam-former pair (Wi, gi) designed under a quality-of-service (QoS) SNR constraint. It is first shown that the minimum sum-power beamformers for the network satisfy a weak duality condition, in which the pairs ((giopt)*, (Wiopt)*) achieve the same sum power as the primal network. However, the optimum receive beamformer wiopt is not in general equal to (giopt)*, in contrast to the case of cellular and time-division duplexing networks. Iterative minimum mean-square error (IMMSE) beamforming algorithms are then proposed in which wi = gi* is enforced. These algorithms are shown to be instances of the Power Algorithm in which gi is the maximizing eigenvector of an SNR-related objective matrix. The IMMSE algorithm can also be viewed as a noncooperative beamforming game, in which the payoff includes normalized SNR, and the tax is related to interference caused at other nodes. The existence of fixed points (Nash equilibria) is proved for IMMSE. Furthermore, fixed points of IMMSE are shown to satisfy the first-order necessary conditions for optimization using a network Lagrangian. The IMMSE game is modified to yield a sequential distortionless-response beamforming algorithm, which is shown to be convergent using a Total Interference Function. Extensive simulation results illustrate that IMMSE yields better power efficiency than a greedy noncooperative SNR-maximizing game. View full abstract»

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  • Optimum DCT-Based Multicarrier Transceivers for Frequency-Selective Channels

    Page(s): 760
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    We derive on the impulse response and input signal of a frequency-selective finite impulse response channel to be diagonalized by the DCT into parallel, decoupled, and memoryless subchannels. We show how these conditions can be satisfied in a practical multicarrier transceiver through a novel design of the guard sequence and the front-end prefilter. This DCT-based design results in complete elimination of interblock and intercarrier interference without channel knowledge at the transmitter and at the same guard sequence overhead, compared with DFT-based multicarrier transceivers. Extensions to multi-input multi-output frequency-selective channels are also described. Finally, we present numerical examples from wireline and wireless communications scenarios to illustrate the viability and practicality of the DCT as a modulation/demodulation basis for baseband and passband signaling over frequency-selective channels. View full abstract»

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  • Benefit of Pattern Diversity via 2-Element Array of Circular Path Antennas in Indoor Clustered MIMO Channels

    Page(s): 760
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    In this paper, we analyze a MIMO array consisting of two circular microstrip antennas, designed to exploit pattern diversity. We analytically derive the spatial correlation coefficients of this array as a function of the mode excited for realistic clustered MIMO channel models. We compare the performance of the circular patch array (CPA) against an array of two space dipoles. In particular, we compute a theoretical tradeoff to predict when the pattern diversity provided by the CPA is more effective than space diversity from the uniform linear array (ULA), based on the eigenvalues of the spatial correlation matrix. Through simulations, we show that CPAs yield better performance or satisfy more restrictive size constraints than ULAs in clustered MIMO channels, depending on the element spacing of the ULA, These results make the CPA an attractive solution for miniaturized MIMO arrays for portable devices or access points. View full abstract»

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Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

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Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia