By Topic

Wireless Communications, IEEE Transactions on

Issue 4 • Date July 2005

Filter Results

Displaying Results 1 - 25 of 78
  • Table of contents

    Publication Year: 2005 , Page(s): c1 - 1278
    Save to Project icon | Request Permissions | PDF file iconPDF (58 KB)  
    Freely Available from IEEE
  • IEEE Transactions on Wireless Communications publication information

    Publication Year: 2005 , Page(s): c2
    Save to Project icon | Request Permissions | PDF file iconPDF (44 KB)  
    Freely Available from IEEE
  • Outage probability comparisons for diversity systems with cochannel interference in Rayleigh fading

    Publication Year: 2005 , Page(s): 1279 - 1284
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    Space diversity is an effective method to combat fading and cochannel interference (CCI) in wireless systems. In this paper, outage performances of several diversity schemes, including a practical variation of maximal-ratio combining that does not require signal-to-noise ratios at different antennas, equal-gain combining, and selection combining, are compared analytically for an interference-limited environment in a Rayleigh fading channel. Our analysis provides insight into the performance of diversity schemes in the presence of CCI as well as assesses the impact of cochannel interferer power distributions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Robust blind multiuser detection against signature waveform mismatch based on second-order cone programming

    Publication Year: 2005 , Page(s): 1285 - 1291
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    Blind signal detection in multiuser code division multiple access (CDMA) system is particularly attractive when only the desired user signature is known to a given receiver. A problem common to several existing blind multiuser CDMA detectors is that the detection performance is very sensitive to the signature waveform mismatch (SWM) which may be caused by channel distortion. In this paper, we consider the design of a blind multiuser CDMA detector that is robust to the SWM. We present a convex formulation for this problem by using the second-order cone (SOC) programming. The resulting SOC problem can be solved efficiently using the recently developed interior point methods. Computer simulations indicate that the performance of our new robust blind multiuser detector is superior to those of many existing methods. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimal placement of known symbols for slowly varying frequency-selective channels

    Publication Year: 2005 , Page(s): 1292 - 1296
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    The problem of placing known symbols in a data stream for a slowly varying frequency-selective channel is considered from an information-theoretic perspective. Given the amount of redundancy associated with known symbols, placement schemes that minimize the outage probability are derived by assuming that the transmitted codewords consist of packets that are constrained to have the same known symbol placement. Under the assumption that each known symbol cluster is at least as large as α ≥ 2L + 1 (where L is the channel order), we show that the optimal placement is obtained by arranging the known symbols into as many clusters as possible and placing them such that the unknown symbol blocks are as equal as possible. It is shown that the optimal placement of known symbol clusters does not depend on the probability density of the channel. Numerical examples are used to illustrate the ideas and potential gains of using optimal known symbol placement. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Soft handoff and uplink capacity in a two-tier CDMA system

    Publication Year: 2005 , Page(s): 1297 - 1301
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    This paper examines the effect of soft handoff on the uplink user capacity of a code division multiple access system consisting of a single macrocell in which a single hotspot microcell is embedded. The users of these two base stations operate over the same frequency band. In the soft-handoff scenario studied here, both macrocell and microcell base stations serve each system user, and the two received copies of a desired user's signal are summed using maximal ratio combining. Exact and approximate analytical methods are developed to compute uplink user capacity. Simulation results demonstrate a 20% increase in user capacity compared to hard handoff. In addition, simple approximate methods are presented for estimating soft-handoff capacity and are shown to be quite accurate. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Uplink throughput in a single-macrocell/single-microcell CDMA system with application to data access points

    Publication Year: 2005 , Page(s): 1302 - 1306
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    This paper studies a two-tier code-division multiple-access (CDMA) system in which the microcell base is converted into a data access point (DAP), i.e., is a limited-range base station that provides high-speed access to one user at a time. The microcell (or DAP) user operates on the same frequency as the macrocell users and has the same chip rate. However, it adapts its spreading factor, and thus its data rate, in accordance with interference conditions. By contrast, the macrocell serves multiple simultaneous data users, each with the same fixed rate. The achievable throughput for individual microcell users is examined and a simple accurate approximation for its probability distribution is presented. Computations for average throughputs, both per-user and total, are also presented. The numerical results highlight the impact of a desensitivity parameter used in the base-selection process. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Characterization of WSSUS channels: normalized mean square covariance and diversity combining

    Publication Year: 2005 , Page(s): 1307 - 1310
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    In this letter, we investigate the fundamental relationship between the performance of a maximum ratio diversity combining scheme and the normalized mean square covariance (NMSV) over wide-sense stationary uncorrelated scattering channels. In particular, we show that the reliability achieved by diversity combining is closely related to the value of NMSV of the channel under consideration. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Nonblind and semiblind space-time-frequency multiuser detection for space-time block-coded MC-CDMA

    Publication Year: 2005 , Page(s): 1311 - 1318
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    In this paper, a novel space-time-frequency minimum mean squared error (STF-MMSE)-based parallel interference cancellation receiver is proposed for space-time block-coded multicarrier code division multiple access systems in time-varying fading channels. The signal processing of this new detector is jointly implemented in space, time, and frequency domains, which leads to a powerful capability of combating interference coming from different sources. An adaptive implementation based on subspace estimation is proposed for slow-varying fading channels. Furthermore, based on the characteristic function of a complex Gaussian random vector, an analytical method to calculate the bit error probability of the proposed STF-MMSE receiver is presented. Representative examples of the detector are provided to demonstrate its superior performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Semiblind linear parallel interference cancellation multiuser detectors for DS-CDMA systems

    Publication Year: 2005 , Page(s): 1319 - 1324
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    Semiblind multiuser detection for the reverse link of a multicell code-division multiple-access (CDMA) system is considered. In such a system, although active users are present in the home cell and neighboring cells, the base station receiver only knows the signature information of the users in its own cell. Three new semiblind linear multiuser detectors are proposed based on parallel interference cancellation approach. Compared with some known semiblind detectors, the proposed detectors share a rather simple implementation structure and involve reduced latency for processing, which are of particular importance in a time-varying CDMA system. Numerical results are presented to compare the detection performance of the proposed detectors with that of some existing semiblind multiuser detectors. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Rapid slot synchronization in the presence of large frequency offset and Doppler spread in WCDMA systems

    Publication Year: 2005 , Page(s): 1325 - 1330
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    Slot synchronization is the most challenging step for rapid cell search in intercell asynchronous code division multiple access systems such as wide-band code division multiple access (WCDMA). For rapid cell search, it is desirable to design the receiver robust to initial frequency offset and Doppler spread. In this letter, we consider combining schemes for rapid slot synchronization of WCDMA signals in such channel impairments. We propose an inner-slot differential combining scheme that exploits partial correlation of slot synchronization code, making the receiver tolerable to a large amount of initial frequency offset and Doppler spread. Unlike conventional differential combining schemes, the proposed scheme is also applicable to the use of transmit antenna diversity. The detection performance of the proposed combining scheme is analyzed with the use of transmit antenna diversity. Finally, the analytic results are verified by computer simulation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fast differential unitary space-time demodulation via square orthogonal designs

    Publication Year: 2005 , Page(s): 1331 - 1336
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    This paper presents a natural concatenation between the real or complex square orthogonal designs and the differential unitary space-time modulation scheme for multiple transmit antennas. This concatenation renders the differential unitary space-time demodulator to detect in a decoupled way the information symbols and hence to have a very low decoding complexity. This fast differential demodulation method for multiple transmit antennas can be regarded as a generalization of the existing differential detection method proposed by Tarokh and Jafarkhani for two and four transmit antennas based on orthogonal designs. By using a systematic matrix-vector representation, a unified and simplified form of differential unitary demodulation via square orthogonal designs for any number of transmit antennas and any transmission rate in bits per channel use is provided. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Monobit digital receivers for ultrawideband communications

    Publication Year: 2005 , Page(s): 1337 - 1344
    Cited by:  Papers (56)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    Ultrawideband systems employ short low-power pulses. Analog receiver designs can accommodate the required bandwidths, but they come at a cost of reduced flexibility. Digital approaches, on the other hand, provide flexibility in receiver signal processing but are limited by analog-to-digital converter (ADC) resolution and power consumption. In this paper, we consider reduced complexity digital receivers, in which the ADC is limited to a single bit per sample. We study three one-bit ADC schemes: 1) fixed reference; 2) stochastic reference; and 3) sigma-delta modulation (SDM). These are compared for two types of receivers based on: 1) matched filtering; and 2) transmitted reference. Bit-error rate (BER) expressions are developed for these systems and compared to full-resolution implementations with negligible quantization error. The analysis includes the impact of quantization noise, filtering, and oversampling. In particular, for an additive white Gaussian noise channel, we show that the SDM scheme with oversampling can achieve the BER performance of a full-resolution digital receiver. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A factor graph approach to iterative channel estimation and LDPC decoding over fading channels

    Publication Year: 2005 , Page(s): 1345 - 1350
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    This letter provides a comparative study of joint channel estimation and low-density parity-check decoding algorithms for flat Rayleigh fading channels based on the receiver factor graphs. Two approaches for joint channel estimation and decoding are proposed. Intensive simulation studies are carried out to evaluate the receiver sensitivity to the choice of the factor graph. Results show that when channel statistical information is not available at the receiver, a low-pass filtering approach gives a more robust and simpler solution, and it is only 0.5 dB worse than the optimum Wiener filtering. All methods have about 2 dB improvements over the noniterative receivers. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Closed-form expressions for the correlation coefficient of directive antennas impinged by a multimodal truncated Laplacian PAS

    Publication Year: 2005 , Page(s): 1351 - 1359
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    This paper addresses the derivation of a closed-form expression for the correlation coefficient of a pair of antenna elements at the base station. The closed-form expression is derived for the case of a multimodal truncated Laplacian power azimuth spectrum that impinges on antenna elements exhibiting a directive radiation pattern that is widely used in standardization bodies. To avoid numerical instability, an approximation for small azimuth spreads is presented. The proposed closed-form expression, along with its approximation, is successfully validated against the numerical computation of the correlation coefficient. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Estimation of channel statistics for iterative detection of OFDM signals

    Publication Year: 2005 , Page(s): 1360 - 1365
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    Maximum likelihood sequence estimation for orthogonal frequency division multiplexing (OFDM) transmissions over unknown multipath fading channels is analytically infeasible for lack of efficient methods to maximize the likelihood function. A practical solution to this problem has been recently proposed in the context of space-time block-coded OFDM by resorting to the expectation-maximization (EM) algorithm. The resulting detector operates iteratively, exploiting knowledge of the channel statistics and the operating signal-to-noise ratio (SNR). In this work, we address the problem of estimating the above quantities and propose a recursive solution based on ad hoc reasoning. Simulations indicate that the EM detector employing the estimated SNR and channel statistics has better performance than other schemes operating in a mismatched mode. Also, the performance loss with respect to a system with perfect channel knowledge is negligible at SNR values of practical interest. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Average outage duration of multihop communication systems with regenerative relays

    Publication Year: 2005 , Page(s): 1366 - 1371
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    Closed-form expressions for the average outage duration (AOD) of multihop regenerative communication systems over generalized fading channels are presented. Both noise-limited and interference-limited systems are studied. To show the usefulness of the presented expressions, some specific fading scenarios are considered. In addition, some numerical examples of interest comparing direct versus relayed transmission and studying the effect of increasing the number of hops and/or cochannel interferers are plotted and discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The relationship between fading and bandwidth for multipath channels

    Publication Year: 2005 , Page(s): 1372 - 1376
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    A signal transmitted over a multipath channel experiences fading, the variability of which is a function of: 1) signal bandwidth; and 2) power delay profiles of the channel's specular and diffuse components. We analyze this general relationship and, for several important classes of multipath channel, we derive simple, closed-form approximations for what we call the stability bandwidth, W0. For signal bandwidths greater than W0, the local area variation in the received signal power is acceptably small, e.g., less than 1 dB standard deviation of decibel power. We demonstrate the accuracy of our W0 approximations for some representative cases. Moreover, we show that the root mean square delay spread-a statistic commonly used to characterize multipath channels-has limited utility in estimating W0. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Estimation of the output error statistics of space-time equalization in an antenna array EGPRS receiver with soft-decision decoding

    Publication Year: 2005 , Page(s): 1377 - 1382
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    The use of antenna arrays can help combat cochannel interference (CCI) in wireless cellular systems. In this paper, we consider an enhanced general packet radio service diversity receiver based on least squares spatio-temporal equalization and soft-decision decoding in the presence of decision feedback and/or asynchronous CCI. We compare known and novel estimators of the error mean and variance at the output of the deterministic space-time equalizer. The collected simulation data indicate that the estimation of the error mean and variance is critical to the performance of soft-in/hard-out Viterbi decoding in the presence of nonstationary input disturbance. Moreover, the use of short-term error statistics provides receiver performance gains of up to 15-20 dB in terms of signal-to-interference ratio, with respect to the use of burst statistics based on the training sequence midamble and tentative decisions on the payload symbols. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Bit loading with BER-constraint for multicarrier systems

    Publication Year: 2005 , Page(s): 1383 - 1387
    Cited by:  Papers (42)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    We present discrete adaptive bit loading algorithms for multicarrier systems with uniform (nonadaptive) power allocation operating in a frequency selective fading environment. The algorithms try to maximize the overall throughput of the system while guaranteeing that the mean bit error rate (BER) remains below a prescribed threshold. We also study the impact of imperfect subcarrier signal-to-noise ratio information on throughput performance. Results show that the proposed algorithms have approximately the same throughput and mean BER as the optimal allocation while having a significantly lower computational complexity relative to other algorithms with near-optimal allocations. Moreover, when compared with algorithms that employ approximations to water filling, the computational complexity is comparable while the overall throughput is closer to the optimum. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the macroscopic optimization of multicell wireless systems with multiuser detection and multiple antennas - uplink analysis

    Publication Year: 2005 , Page(s): 1388 - 1393
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    In this paper, we consider a system with K single-antenna client users, nB base stations (each base station has nR antennas), as well as a centralized controller. A client user could be associated with a single base station at any time. All the base stations operate at the same frequency and have optimal multiuser detection per base station which cancels intracell interference only. We consider a general problem of uplink macroscopic resource management where the centralized controller dynamically determines an appropriate association mapping of the K users with respect to the nB base stations over a macroscopic time scale. We propose a novel analytical framework for the above macroscopic scheduling problems. A simple rule is to associate a user with the strongest base station (camp-on-the-strongest-cell), and this has been widely employed in conventional cellular systems. However, based on the optimization framework, we found that this conventional approach is in fact not optimal when multiuser detection is employed at the base station. We show that the optimal macroscopic scheduling algorithm is of exponential complexity, and we propose a simple greedy algorithm as a feasible solution. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A bandwidth-on-demand strategy for GPRS

    Publication Year: 2005 , Page(s): 1394 - 1399
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    General packet radio service (GPRS) is a global system for mobile communications (GSM) packet data service. In order to efficiently accommodate GPRS traffic while maintaining the desired service quality of GSM calls, we propose a GPRS bandwidth-allocation strategy called the bandwidth-on-demand (BoD) strategy. The BoD strategy is adaptive to the change of traffic conditions, and thus can dynamically adjust the number of channels for GSM and GPRS traffic. Taking the effect of packet dropping due to movements of mobile stations into account, this paper develops an analytical model to study the BoD performance in terms of GSM-call-blocking probability and GPRS-packet-dropping probability. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Symbol/bit-error rate of LMMSE receiver for M-ary QAM in multipath faded CDMA channels

    Publication Year: 2005 , Page(s): 1400 - 1406
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    This letter investigates the performance analysis of a linear minimum mean square error receiver for M-ary quadratic-amplitude modulation in multipath fading channels. Both channel gain variances and instantaneous channel gains of the interferers are considered for receiver implementation. Approximate expressions for symbol and bit error rates are derived only when the receiver knows the channel gain variances of the interferers. In deriving the analytical expressions, we exploit large system analysis and results in single-user multipath combining. The receiver performance and the accuracy of the theoretical results are examined via simulations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Average output SINR of equal-gain diversity in correlated Nakagami-m fading with cochannel interference

    Publication Year: 2005 , Page(s): 1407 - 1411
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    In mobile radio systems, antenna diversity is used to combat fading and reduce the impact of cochannel interference. In this paper, we analyze the performance of L-branch equal-gain combining receivers over correlated nonidentically distributed Nakagami-m fading channels, in the presence of multiple identical cochannel interferers and additive white Gaussian noise. The performance criterion considered is the average output signal-to-interference-plus-noise ratio, which is obtained in closed form for both independent and correlative fading. Due to the simple form of the derived expressions, they readily allow numerical evaluation for cases of practical interest. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Decision-directed estimation of MIMO time-varying Rayleigh fading channels

    Publication Year: 2005 , Page(s): 1412 - 1417
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    This paper presents a decision-directed (DD) maximum a posteriori probability (MAP) channel-estimation scheme for multiple-input multiple-output (MIMO) time-varying fading channels. With the estimate of the channel matrix for the current symbol interval, a zero-forcing (ZF) receiver is applied to detect the spatially multiplexed data on a symbol-by-symbol basis. Symbol decisions are then fed to the channel predictor for estimation of channel coefficients in future symbol intervals. Simulated error performance of a ZF receiver with the DD MAP and perfect channel estimates is provided and compared. 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