By Topic

Wireless Communications, IEEE Transactions on

Issue 7 • Date July 2007

Filter Results

Displaying Results 1 - 25 of 45
  • IEEE Transactions on Wireless Communications - Table of contents

    Publication Year: 2007 , Page(s): C1 - C3
    Save to Project icon | Request Permissions | PDF file iconPDF (65 KB)  
    Freely Available from IEEE
  • Transactions Letters - Outage Capacity and Optimal Power Allocation for Multiple Time-Scale Parallel Fading Channels

    Publication Year: 2007 , Page(s): 2369 - 2373
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (205 KB) |  | HTML iconHTML  

    In this paper, we address the optimal power allocation problem for minimizing capacity outage probability in multiple time-scale parallel fading channels. Extending ideas from the work of Dey and Evans (2005), we derive the optimal power allocation scheme for parallel fading channels with fast Rayleigh fading, as a function of the slow fading gains. Numerical results are presented to demonstrate the outage performance of this scheme for lognormal slow fading on two parallel channels. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Systematic Set Partitioning for Unitary Space-Time Signal Sets

    Publication Year: 2007 , Page(s): 2374 - 2378
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (189 KB) |  | HTML iconHTML  

    Proper partitioning of a unitary space-time (UST) signal set is essential for the optimal design of trellis coded unitary space-time modulation (TC-USTM). The unique properties of these UST signals have necessitated a different partitioning methodology from that of the conventional two dimensional constellations. In this letter, we propose a systematic set partitioning through a novel subset-pairing strategy, for an arbitrary UST signal set. This approach leads to a geometrically congruent partitioning, i.e., subsets of the same size (order) have identical intra-distance profiles. Based on this partitioning, the resulting TC-USTM can achieve a minimum bit error probability. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improvement in the Linearity of a LINC Transmitter using Genetic Algorithms

    Publication Year: 2007 , Page(s): 2379 - 2383
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    This paper proposes an automatically-adjusted linearization method based on the well-known linearization technique LINC (Linear amplification using Nonlinear Components) applied to the base station transmitter. A correction method of the gain and phase imbalances between both amplifying branches in a LINC transmitter is proposed to reduce the adjacent channel interference. A simple architecture is designed to compensate the unmatching between both branches being the adjusting coefficients calculated by means of a genetic algorithm. Several nonidealities are included in the analysis to deal with a realistic model, such as quadrature modulator imbalances, reconstruction filters and quantization error. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Gaussian Approximation Based Mixture Reduction for Joint Channel Estimation and Detection in MIMO Systems

    Publication Year: 2007 , Page(s): 2384 - 2389
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (157 KB) |  | HTML iconHTML  

    A novel Gaussian approximation based mixture reduction algorithm is proposed for semi-blind joint channel tracking and symbol detection for spatial multiplexing multiple-input multiple-output (MIMO) systems with frequency-flat time-selective channels. The proposed algorithm is based on a modified sequential Gaussian approximation detector (SGA) which takes into account channel uncertainty, and the first order generalized pseudo-Bayesian (GPB1) channel estimator. Simulation results show that the proposed algorithm performs better than the conventional and computationally expensive decision-directed method with Kalman filter based channel estimation and a posteriori probability (APP) symbol detection. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fade Statistics of Wireless Multi-User Systems

    Publication Year: 2007 , Page(s): 2390 - 2395
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    In this paper, we propose a new model named effective fade duration envelope to characterize the accumulative conditional fade durations of individual users or groups of users in wireless communication systems. The proposed model has the following novelties: (1) it introduces the statistical upper and lower bounds with the required degree of confidence for accumulative conditional fade durations during any given time interval; (2) it characterizes various conditional fading circumstances in wireless multi-user communication systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Robust Design of Spatial Tomlinson-Harashima Precoding in the Presence of Errors in the CSI

    Publication Year: 2007 , Page(s): 2396 - 2401
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (178 KB) |  | HTML iconHTML  

    In this letter, we study spatial Tomlinson-Harashima precoding (STHP) from an information theoretic point of view encompassing both the single and the multiuser scenarios. Since the performance of any communications preceding scheme relies on the quality of the channel state information (CSI) that is made available at the transmitter side, in this work we focus our attention on the analysis of the robustness of STHP in terms of rate loss when the CSI is imperfect. Precisely, we present a robust design of the set of moduli used in STHP and, consequently, of the corresponding power allocation, that maximizes the achievable rates for the worst-case errors in the CSI in the small errors regime. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hot Carrier Effects in Wireless Communication Systems Built on Short-Channel MOSFETs

    Publication Year: 2007 , Page(s): 2402 - 2406
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (306 KB) |  | HTML iconHTML  

    Phase noise is a critical factor that degrades the synchronization performance of a wireless communication receiver. Hot-carriers (HCs), found in the CMOS synchronization devices, are high-energy charge-carriers that can degrade the MOSFETs performance by damaging the internal device structure and lead to the phase noise increase therein. Such incremental phase noise can be related to the essential parameter, namely the MOSFET threshold voltage due to the HC effect, which is particularly evident in the short-channel MOSFET devices. In this letter, we analyze the impact of the phase noise arising from the HC effect on the wireless systems in terms of the bit-error-rate (BER) and the signal-to-interference-plus-noise ratio (SINR). View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Reduced-Complexity Near-Maximum-Likelihood Detection for Decision Feedback Assisted Space-Time Equalization

    Publication Year: 2007 , Page(s): 2407 - 2411
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    A novel decision-feedback (DF) aided reduced complexity maximum likelihood (ML) space-time equalizer (STE) designed for a single-carrier system is introduced. Two different methods of incorporating DF into the recursive tree search based receiver structure are proposed for allowing detection at a moderate computational cost. Additionally, a further complexity reduction scheme is proposed, which exploits the specific characteristics of both the wide-band channel and the proposed DF-STE. In comparison to the DF-STE not benefiting from this complexity reduction, the proposed detector is capable of reducing the complexity by several orders of magnitude. More quantitatively, for the specific rank-deficient system considered, which detected the signal transmitted from four transmit antennas with the aid of two receive antennas, the complexity might be reduced by a factor of 100 at low Signal-to-noise ratios (SNRs) without noticeable performance degradation. By contrast, at higher SNRs a complexity reduction of a factor of 10 might be achieved, depending on the tolerable performance degradation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Clustered ML Channel Estimation for Ultra-Wideband Signals

    Publication Year: 2007 , Page(s): 2412 - 2416
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (123 KB) |  | HTML iconHTML  

    The multipath capture of ultrawideband (UWB) communications systems can be dependent on the accuracy of channel estimation. Furthermore, inefficient modeling of the channel often leads to over-parametrization and increased channel estimation error. Relying on a channel model based on clusters, this letter proposes a maximum likelihood estimation strategy which exploits the properties of the UWB channel and offers performance improvement of about 2 dB over less parametric schemes. The robustness of the proposed algorithm in the presence of pulse distortion is investigated and the corresponding BER degradation is observed to be small even when experimental data are employed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cross Layer Design of Downlink Multi-Antenna OFDMA Systems with Imperfect CSIT for Slow Fading Channels

    Publication Year: 2007 , Page(s): 2417 - 2421
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (269 KB) |  | HTML iconHTML  

    In most existing works, perfect knowledge of channel state information at the transmitter (CSIT) is assumed to realize the potential benefit of cross-layer scheduling and spatial multiplexing gains of MIMO/OFDMA systems. However, perfect knowledge of CSIT is not easy to achieve in practice due to estimation noise or delay in feedback. In this paper, we shall focus on the cross-layer design of downlink multi-antenna OFDMA systems with imperfect CSIT for slow fading channels. We shall show that our proposed cross-layer scheduler can exploit the multiuser diversity and spatial multiplexing gain even in the presence of moderate CSIT error. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Threshold-Based Channel State Feedback Algorithm for Modern Cellular Systems

    Publication Year: 2007 , Page(s): 2422 - 2426
    Cited by:  Papers (22)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (134 KB) |  | HTML iconHTML  

    In this paper we propose a channel state feedback algorithm that uses multiple feedback thresholds to reduce the number of users transmitting feedback to a minimum. The users are polled with lower and lower threshold values and only the users that are above a threshold value transmit feedback to the base station. We show how this feedback algorithm can be used for any scheduling algorithm and show how closed-form expressions for the optimal threshold values can be obtained for two well-known scheduling algorithms. Finally, we propose a two-step optimization procedure for optimizing the feedback algorithm for real-life cellular standards. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance Comparison between Beamforming and Spatial Multiplexing for the Downlink in Wireless Cellular Systems

    Publication Year: 2007 , Page(s): 2427 - 2431
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (323 KB) |  | HTML iconHTML  

    We compare the performance between beamforming and spatial multiplexing showing in which downlink scenarios the higher performance of spatial multiplexing justify its complexity. We compute performance using readily measurable parameters such as angle spread (AS), antenna separation and signal to noise ratio (SKIR). Firstly, a semi-analytical approach relates these measurable parameters with parameters that theoretically characterize beamforming optimality such as the spatial correlation matrix first two eigenvalues and SNR. Secondly, the achieved spectral efficiency is given for beamforming and spatial multiplexing as a function of antenna separation, AS and SNR. Also, a "practical" region is given where beamforming achieves at least 90% of the spectral efficiency of spatial multiplexing. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On Trellis Coded Noncoherent Space-Time Modulation

    Publication Year: 2007 , Page(s): 2432 - 2437
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB) |  | HTML iconHTML  

    Unitary space-time modulation (USTM) is well-tailored for noncoherent space-time modulation. Trellis coded USTM (TC-USTM) can obtain significant coding gains over uncoded USTM for the noncoherent block fading channel. Conventional TC-USTM schemes expand the signal set of uncoded USTM by a factor of two. In this letter, we propose a new TC-USTM scheme in which the size of USTM set is not limited to be just double for uncoded USTM. However, in TC-USTM schemes, because signals of the same trellis branch are transmitted over the same fading coefficients, one trellis branch can only obtain one temporal diversity. In this letter, we also propose a new trellis coded noncoherent space-time modulation scheme by interleaving space-time signals. The proposed scheme can enlarge temporal diversity at the price of increased complexity and delay. Simulation results demonstrate the excellent error performances of codes found by computer searches for both schemes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimal Lattice-Reduction Aided Successive Interference Cancellation for MIMO Systems

    Publication Year: 2007 , Page(s): 2438 - 2443
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (147 KB) |  | HTML iconHTML  

    In this letter, we investigated the optimal minimum-mean-squared-error (MMSE) based successive interference cancellation (SIC) strategy designed for lattice-reduction aided multiple-input multiple-output (MIMO) detectors. For the sake of generating the MMSE-based MIMO symbol estimate at each SIC detection stage, we model the so-called effective symbols generated with the aid of lattice-reduction as joint Gaussian distributed random variables. However, after lattice-reduction, the effective symbols become correlated and exhibit a non-zero mean. Hence, we derive the optimal MMSE SIC detector, which updates the mean and variance of the effective symbols at each SIC detection stage. As a result, the proposed detector achieves a better performance compared to its counterpart dispensing with updating the mean and variance, and performs close to the maximum likelihood detector. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Transactions Papers - Device Placement for Heterogeneous Wireless Sensor Networks: Minimum Cost with Lifetime Constraints

    Publication Year: 2007 , Page(s): 2444 - 2453
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (582 KB) |  | HTML iconHTML  

    Device placement is a fundamental factor in determining the coverage, connectivity, cost and lifetime of a wireless sensor network (WSN). In this paper, we explore the problem of relay node placement in heterogeneous WSN. We formulate a generalized node placement optimization problem aimed at minimizing the network cost with constraints on lifetime and connectivity. Depending on the constraints, two representative scenarios of this problem are described. We characterize the first problem, where relay nodes are not energy constrained, as a minimum set covering problem. We further consider a more challenging scenario, where all nodes are energy limited. As an optimal solution to this problem is difficult to obtain, a two-phase approach is proposed, in which locally optimal design decisions are taken. The placement of the first phase relay nodes (FPRN), which are directly connected to sensor nodes (SN), is modeled as a minimum set covering problem. To ensure the relaying of the traffic from the FPRN to the base station, three heuristic schemes are proposed to place the second phase relay nodes (SPRN). Furthermore, a lower bound on the minimum number of SPRN required for connectivity is provided. The efficiency of our proposals is investigated by numerical examples. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Downlink Throughput Maximization for Interference Limited Multiuser Systems: TDMA versus CDMA

    Publication Year: 2007 , Page(s): 2454 - 2463
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (483 KB) |  | HTML iconHTML  

    We consider the downlink throughput maximization problem for interference limited multiuser systems. Our goal is to characterize the optimum base station transmission strategy, i.e., whether the base station transmits to one-user (TDMA) or multiple users (CDMA). Specifically, we aim at determining the optimum number of users to be scheduled and finding the corresponding power allocation. We model the interference by the aid of the orthogonality factor, and determine the throughput maximizing transmission strategy for a range of the values of the orthogonality factor, and the channel gains, subject to a total power constraint. Although the resulting optimization problem may turn out to be non-convex, we show that valuable observations regarding the structure of the optimum solution can be obtained by examining the performance metric from an individual user's point of view. We propose an exact and a near-exact algorithm to determine whether one-user-transmission is the optimum strategy, or more than one user should be transmitted to. Numerical results to support our analysis, as well as the modifications to the proposed algorithms in the presence of individual power constraints are presented. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ultrawideband Channel Modeling on the Basis of Information-Theoretic Criteria

    Publication Year: 2007 , Page(s): 2464 - 2475
    Cited by:  Papers (39)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (918 KB) |  | HTML iconHTML  

    We present results of two indoor ultrawideband channel measurement campaigns in the 2-5 GHz frequency band. In measurement campaign I (MC I), the channel is static and we sample it spatially, while in MCII the transmitting and receiving antennas are fixed and channel variation is induced by people moving in the environment. Transmitter and receiver are separated by up to 27 m in MC I and up to 20 m in MC II. To determine suitable small-scale fading distributions for the tap amplitudes of the discrete-time baseband-equivalent channel impulse response, we use Akaike's information criterion (AIC). Despite the large bandwidth, AIC supports the Rayleigh (MCI) or the Rice distribution (MC II). For data from MC II, we estimate the covariance matrix of the random channel impulse response and demonstrate that the number of corresponding significant eigenvalues, and hence the diversity order of the channel, scales approximately linearly with bandwidth. Contrary to the uncorrected scattering assumption, we find that the channel taps are weakly correlated. The ergodic capacity predicted by the Ricean channel model with parameters estimated from MC II shows good agreement with the ergodic capacity obtained by direct evaluation of the measurement results, while the corresponding outage capacities show a worse fit for low outage probabilities because of shadowing. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improving Wireless TCP Throughput by a Novel TCM-Based Hybrid ARQ

    Publication Year: 2007 , Page(s): 2476 - 2485
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (775 KB) |  | HTML iconHTML  

    A novel hybrid ARQ (HARQ) scheme using a concatenated two-state trellis-coded modulation (CT-TCM) code is proposed for improving wireless TCP throughput. A distinguished feature of the proposed scheme is that the heavily punctured TCM codes are used for retransmissions of the corrupted data block, which are combined at the receiver with the previously received sequences of the same data block for decoding. By this method, significantly improved coding gain and efficient spectrum utilization can be achieved with very low complexity. A Markov model is developed to evaluate TCP throughput over the proposed HARQ in wireless link. By both analysis and simulation, we demonstrate that compared with other existing TCM-based ARQ schemes, significant improvement of TCP throughput over wireless links is achieved by the proposed CT-TCM HARQ while smaller buffer size is required at the access point. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Simplified Soft-Output Detection of CPM Signals Over Coherent and Phase Noise Channels

    Publication Year: 2007 , Page(s): 2486 - 2496
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (323 KB) |  | HTML iconHTML  

    We consider continuous phase modulations (CPMs) in iteratively decoded serially concatenated schemes. Although the overall receiver complexity mainly depends on that of the CPM detector, almost all papers in the literature consider the optimal maximum a posteriori (MAP) symbol detection algorithm and only a few attempts have been made to design low-complexity suboptimal schemes. This problem is faced in this paper by first considering the case of an ideal coherent detection, then extending it to the more interesting case of a transmission over a typical satellite channel affected by phase noise. In both cases, we adopt a simplified representation of an M-ary CPM signal based on the principal pulses of its Laurent decomposition. Since it is not possible to derive the exact detection rule by means of a probabilistic reasoning, the framework of factor graphs (FGs) and the sum-product algorithm (SPA) is used. In the case of channels affected by phase noise, continuous random variables representing the phase samples are explicitly introduced in the FG. By pursuing the principal approach to manage continuous random variables in a FG, i.e., the canonical distribution approach, two algorithms are derived which do not require the presence of known (pilot) symbols, thanks to the intrinsic differential encoder embedded in the CPM modulator. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Rain Scatter Interference in mm-Wave Broadband Fixed Wireless Access Networks Caused by a 2-D Dynamic Rain Environment

    Publication Year: 2007 , Page(s): 2497 - 2507
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2918 KB) |  | HTML iconHTML  

    The classical Mie scattering theory together with the bistatic radar equation has been applied in this paper to quantify interference levels in broadband fixed wireless access (BFWA) for two different network topologies: mesh and cellular. The complete scattering analysis takes into account the realistic variations of rainfall along the propagation paths and inside the common volume. The interfering element is a rain cell model that follows closely the experimental characteristic dimension, decay and movement obtained in recent research by the authors. The signal-to-interference power ratios (S/I) for two different frequencies, 28 and 42 GHz, and several scattering angles have been calculated. They show that, when two beams cross each other, rain-induced interference must be taken into account for an efficient planning of radio communication systems operating at these millimeter-wave frequencies as well as for an adequate design and implementation of fade mitigation techniques. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An interference avoidance code assignment strategy for downlink multi-rate mc-ds-cdma with tf-domain spreading

    Publication Year: 2007 , Page(s): 2508 - 2518
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (653 KB) |  | HTML iconHTML  

    Frequency selective fading may affect the orthogonality of the spreading codes in the multi-carrier direct sequence code division multiple access (MC-DS-CDMA) systems. In this paper, we define a new performance metric called the multiple access interference (MAI) coefficient for the MC-DS-CDMA system to quantitatively predict the impact of inter-code interference with the time- and frequency-domain spreading in a frequency selective fading channel. With the help of MAI coefficient, a novel interference avoidance code assignment strategy is proposed. By jointly considering the incurred MAI effect and the blocking probability in the code tree structure, the proposed interference avoidance code assignment method can effectively reduce the MAI for the multi-rate MC-DS-CDMA system, while maintaining very good call blocking rate performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cooperative and Reliable ARQ Protocols for Energy Harvesting Wireless Sensor Nodes

    Publication Year: 2007 , Page(s): 2519 - 2529
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (893 KB) |  | HTML iconHTML  

    One class of wireless sensor networks makes use of sensor nodes that recharge their batteries by harvesting energy from the surrounding environment. Being continuously recharged, the battery does not need to be replaced regularly and the sensor node is maintenance-free. A key module in such sensor network solutions is the data link automatic repeat request (ARQ) protocol, which must be designed to reliably deliver sensor nodes data at the minimum energy cost. With this objective in mind, two ARQ protocol classes are compared. In one class, each sensor node operates individually. In the other, the concept of cooperative communications is adopted, whereby neighboring sensor nodes help each other during the retransmission process. It is shown that the use of cooperative ARQ protocols in energy harvesting sensor networks enables sensor nodes to balance their energy consumption to match their own battery recharge rate. In turn, a balanced energy consumption-to-recharge rate ratio has the potential to improve the network throughput. Both classes of ARQ protocols are analyzed and compared. Estimated throughput gains are discussed under various network scenarios. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Maximizing Cooperative Diversity Energy Gain for Wireless Networks

    Publication Year: 2007 , Page(s): 2530 - 2539
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (621 KB) |  | HTML iconHTML  

    We are concerned with optimally grouping active mobile users in a two-user-based cooperative diversity system to maximize the cooperative diversity energy gain in a radio cell. The optimization problem is formulated as a non-bipartite weighted-matching problem in a static network setting. The weighted-matching problem can be solved using maximum weighted (MW) matching algorithm in polynomial time O(n3). To reduce the implementation and computational complexity, we develop a Worst-Link-First (WLF) matching algorithm, which gives the user with the worse channel condition and the higher energy consumption rate a higher priority to choose its partner. The computational complexity of the proposed WLF algorithm is O(n) while the achieved average energy gain is only slightly lower than that of the optimal maximum weighted- matching algorithm and similar to that of the 1/2-approximation Greedy matching algorithm (with computational complexity of O(n2 log n)) for a static-user network. We further investigate the optimal matching problem in mobile networks. By intelligently applying user mobility information in the matching algorithm, high cooperative diversity energy gain with moderate overhead is possible. In mobile networks, the proposed WLF matching algorithm, being less complex than the MW and the Greedy matching algorithms, yields performance characteristics close to those of the MW matching algorithm and better than the Greedy matching algorithm. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Quantized UWB Transmitted Reference Systems

    Publication Year: 2007 , Page(s): 2540 - 2550
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (327 KB) |  | HTML iconHTML  

    Digital implementation of ultra-wideband receivers requires analog-to-digital conversion (ADC) at an extremely high speed, thereby limiting the available bit resolution. Herein, the effect of low bit resolution quantization on the performance of UWB transmitted reference receivers is investigated. It is verified that the gain of the automatic-gain-control (AGC) has a significant effect on the achievable performance. Because of the considerable performance loss of conventional transmitted reference receivers in the presence of a low resolution ADC a new family of receiver structures optimized and tailored to quantized observations is presented. In particular, the generalized- likelihood ratio test (GLRT) based on the quantized samples is derived and shown to provide modest performance gains relative to the infinite resolution GLRT rule employed on the quantized received signal suggesting that conventional receiver structures can also be employed in the presence of a low resolution ADC. Results reveal that four bits of resolution in combination with an optimal choice for the AGC gain are sufficient to closely approach the performance of an infinite resolution receiver. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

The IEEE Transactions on Wireless Communications publishes high-quality manuscripts on advances in the state-of-the-art of wireless communications.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Jeff Andrews
Cullen Trust for Higher Education Endowed Professor of Engineering