By Topic

Communications Letters, IEEE

Issue 4 • Date April 2012

Filter Results

Displaying Results 1 - 25 of 44
  • Table of contents

    Page(s): c1 - c5
    Save to Project icon | Request Permissions | PDF file iconPDF (85 KB)  
    Freely Available from IEEE
  • [Staff List]

    Page(s): c2
    Save to Project icon | Request Permissions | PDF file iconPDF (44 KB)  
    Freely Available from IEEE
  • A Note on "A Novel ZCZ Code Based on m-Sequences and its Applications in CDMA Systems"

    Page(s): 425
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (56 KB) |  | HTML iconHTML  

    This short communication shows that zero correlation zone sequences could be generated by using any odd-length binary sequence with ideal two-level autocorrelation function in place of the m-sequence using the exact same procedure proposed in the original paper. This removes the restriction on the spreading factor of the m-ZCZ sequences which could assume only the form 2n for some integer n. The spreading factor can now be any N for which an ideal two-level autocorrelation sequence of period N - 1 exists. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Turbo Receiver for DS-SS Systems Employing Parity Bit Selected Spreading Codes

    Page(s): 426 - 428
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (813 KB) |  | HTML iconHTML  

    In this paper a turbo receiver for direct sequence spread spectrum (DS-SS) systems employing parity bit selected spreading code (SS-PB) is proposed where detection and decoding are performed iteratively for each detected bit in the receiver. In SS-PB systems, parity bits generated by a linear block encoder are used to select a spreading code from a set of orthogonal spreading sequences. Performance evaluation in both additive white Gaussian noise (AWGN) and fading channels show a significant reduction in bit error rates (BER) when a turbo receiver is used in these systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Polyphase Scrambled Walsh Codes for Zero-Correlation Zone Extension in QS-CDMA

    Page(s): 429 - 431
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (137 KB) |  | HTML iconHTML  

    Polyphase complex scrambling patterns are designed to extend the zero-correlation zone (ZCZ) of a family of user spreading sequences, called properly scrambled Walsh-Hadamard (PSW) codes, recently proposed for quasi-synchronous (QS) code-division multiple-access systems. The merits of the binary (ZCZ equals 2) and quadri-phase (ZCZ equals 4) PSW codes over the existing QS spreading codes are still retained in the proposed polyphase PSW codes. Scrambling patterns for the case of ZCZ of 8 are derived first. Then, the scrambling pattern design rules are generalized for greater ZCZs and a structured procedure to generate polyphase PSW codes for any ZCZ is developed. Finally, the cross-correlation properties of the proposed spreading codes are evaluated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hybrid Carrier CDMA Communication System Based on Weighted-Type Fractional Fourier Transform

    Page(s): 432 - 435
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (253 KB) |  | HTML iconHTML  

    Recently, an approach based on carrier scheme convergence was proposed based on the weighted-type fractional Fourier transform (WFRFT). Meanwhile, in the high-speed wireless communication systems, code division multiple access (CDMA) is an efficient technique for interference in the frequency-selective fading channels. In this letter, we combine the hybrid carrier (HC) scheme with CDMA and frequency domain linear equalization. The proposed system can not only provide the compatibility with single carrier (SC) CDMA and multi-carrier (MC) CDMA systems, but also achieve a smooth and seamless transition between the two. The proposed system can switch to single carrier or multi-carrier scheme under the specific conditions. Moreover, HC-CDMA outperforms SC-CDMA and MC-CDMA systems over the frequency-selective fading channel and single frequency jamming channel. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Spatial-Domain Joint-Nulling Method of Self-Interference in Full-Duplex Relays

    Page(s): 436 - 438
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (209 KB) |  | HTML iconHTML  

    In this letter, a spatial-domain joint-nulling method is proposed as a new means of suppressing the self-interference (or echo) occurring in full-duplex relays. Both amplify-and-forward (AF) and decode-and-forward (DF) type relays are considered. While the conventional method searches for the relay processing matrix from a discrete set of basis vectors obtained from the singular value decomposition (SVD) of the echo channel, the proposed method directly solves the optimal relay processing matrix over a continuous domain. As a result, it is shown that the proposed approach gives better performance than the conventional one in terms of the achievable rate. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Evolutionary Algorithm Based Power Coverage Optimization for Visible Light Communications

    Page(s): 439 - 441
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (463 KB) |  | HTML iconHTML  

    Inherent multipath diffuse channel characteristics inhibit visible light communications (VLC) system to provide uniform and satisfactory communication performance within the room domain. An evolutionary algorithm based optimization scheme is proposed to modify the optical intensity of LED transmitters for reducing the signal power fluctuation extent. Simulation results show that the proposed scheme can efficiently reduce the signal power dynamic range up to 26.5% while the SNR is still sufficient for keeping BER<;10-6 (using OOK-NRZ modulation format). View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Robust Peer-to-Peer Collaborative-Relay Beamforming with Ellipsoidal CSI Uncertainties

    Page(s): 442 - 445
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    This letter considers a multiuser peer-to-peer communication network using a number of shared relays for collaborative beamforming and aims to minimize the total transmitted power of the relays whilst satisfying the targets of the signal-to-interference and noise ratios (SINRs) at the destination nodes by optimizing the relaying coefficients with imperfect channel state information (CSI). By deriving an equivalent form for the SINR constraints and an upper bound for the relay power, the problem can be tackled by solving a semi-definite program (SDP). Results reveal that the proposed technique outperforms significantly a conventional robust approach in terms of the transmitted power, and has only a mild increase in power if compared to the non-robust optimum which fails to meet the SINR targets. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance Analysis of Optimum Zero-Forcing Beamforming with Greedy User Selection

    Page(s): 446 - 449
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (171 KB) |  | HTML iconHTML  

    In this letter, an exact performance analysis is presented on the sum rate of zero-forcing beamforming with a greedy user selection algorithm in a downlink system. Adopting water-filling power allocation, we derive a compact form for the joint probability density function of the scheduled users' squared subchannel gains when a transmitter with multiple antennas sends information to at most two scheduled users with each having a single antenna. The analysis is verified by numerical results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Energy-Efficient Cooperative Spectrum Sensing with Amplify-and-Forward Relaying

    Page(s): 450 - 453
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (161 KB) |  | HTML iconHTML  

    An energy-efficient cooperative spectrum sensing scheme with amplify-and-forward relaying is proposed in this letter. The goal is to minimize the total energy consumption while satisfying the sensing performance constraint. Toward this goal, a constrained optimization problem is formulated in terms of three sensing parameters (number of relays, relay amplifying gains, and number of samples). An approximate closed-form solution to the optimization problem is derived and is validated by simulations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multivariate η-μ Fading Distribution with Constant Correlation Model

    Page(s): 454 - 457
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    In this letter, we present formulas for the probability density, cumulative distribution, and moment generating functions of the multivariate η-μ fading distribution with the constant correlation model. We give examples of application of the derived results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An Analytical Expression for Performance of Optimum Combining with Multiple Correlated CCIs and Two Antennas

    Page(s): 458 - 461
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (141 KB) |  | HTML iconHTML  

    We derive an analytical expression for the average output signal-to-interference-plus-noise ratio (SINR) of optimum combining (OC) for spatially correlated signals from two antennas in the presence of correlated multiple co-channel interferers (CCIs) and Rayleigh fading. First, the moment generating function (MGF) of the output SINR is derived. Then we obtain the probability density function (PDF) by taking the Fourier transform of the characteristic function (c.f.) corresponding to the MGF. Using the derived expression, the average output SINR performance of OC is evaluated as the number of the correlated multiple CCIs increases. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the Design of Constant Modulus Sequences with Low Correlation Sidelobes Levels

    Page(s): 462 - 465
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    In many wireless communications/radar applications, constant modulus sequences with low correlation sidelobes levels are desired. In this letter, we present an efficient optimization method to design them. Firstly, we formulate a fourth-order polynomial, but unconstrained, minimization problem. And then, a customized LBFGS (Limited-Memory Broyden Fletcher Goldfarb and Shanno) iterative algorithm is proposed to solve it approximately. Numerical examples show that the proposed approach compares favorably with the state-of-the-art approach. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Symbol Error Rate of Rectangular QAM with Best-Relay Selection in Cooperative Systems over Rayleigh Fading Channels

    Page(s): 466 - 469
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (150 KB) |  | HTML iconHTML  

    An analytical expression for a lower bound of average symbol error rate (ASER) for Amplify and Forward cooperative systems with best-relay selection over Rayleigh fading channels is derived for general order rectangular quadrature amplitude modulation (QAM). A comparison of numerical values of the derived lower bound with Monte Carlo simulation results suggests that the obtained bound is suitable for less number of relays. Numerically evaluated ASER results are plotted and the effect of system parameters on the ASER is studied. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Sensor-Based Seamless Handover Solution for Express Train Access Networks (ETANs)

    Page(s): 470 - 472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    Express train transportation is becoming a major tool for carrying approximately one million passengers daily in China today. To provide broadband information services for train passengers, the greatest challenge is achieving a seamless handover solution to guarantee wireless service continuity. This motivates us to incorporate sensor technology into Radio over Fiber architecture to construct an Express Train Access Network (ETAN), where the deployed sensor network captures the train movement status, which can indicate the wireless signal strength. Since the train moves on a fixed rail with fixed direction, it is possible to form an intelligent handover decision system, in which a critical movement state can exactly trigger an optical switch unit in the central station to carry out the handover procedure. Theory analyses and simulation results demonstrate that the proposed architecture can perform handover within 22 ms at a train speed of 350 km/h, providing wireless services for users without disruption, even for a cell radius as small as 100 m. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analytical Model for Outage Probability of Interference-Limited Systems over Extended Generalized-K Fading Channels

    Page(s): 473 - 475
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (378 KB) |  | HTML iconHTML  

    In this letter, the novel analytical expressions for the probability density function, cumulative distribution function and moment generating function of the signal-to-interference ratio are derived for the interference-limited system operating over the extended generalized-K (EGK) fading channel. Since the EGK distribution can be used for modeling a great variety of fading channels, the new derived formulae have high level of generality and can be used for estimating the effects of interference and different composite fading channel conditions on system performance. The proposed analytical analysis is complemented by various outage performance results and confirmed by simulations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Joint Carrier Frequency Offset and Channel Estimation for MIMO-OFDM Systems Using Extended H_{∞} Filter

    Page(s): 476 - 478
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (118 KB) |  | HTML iconHTML  

    We address the problem of joint carrier frequency offset (CFO) and channel estimation for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems over time-varying channels. The CFOs between different pairs of transmit and receive antennas are considered to be different. The method is derived based on the extended H filter (EHF). Compared to the conventional extended Kalman filter (EKF)-based method, the EHF-based method does not require any knowledge of the noise distributions, so it is more flexible and robust to the unknown disturbances. Simulation results are provided to illustrate the performance of this method. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Joint Power and Bandwidth Allocation Algorithm with QoS Support in Heterogeneous Wireless Networks

    Page(s): 479 - 481
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    Heterogeneous wireless networks give rise to a multi-radio access environment which becomes crucial for load balancing to avoid network congestion and providing high quality services to maximize radio resource utilization. To this end, a joint power and bandwidth allocation with QoS support algorithm is proposed using convex optimization method in this letter. The algorithm achieves the goal of the total system capacity maximization, while efficiently satisfying the minimum rate constraint of delay-constraint service traffic and proportional fairness of best-effort service traffic. The simulation results show that the proposed algorithm significantly outperforms the existing scheme in QoS guarantee. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the Diversity-Multiplexing Tradeoff of an Improved Amplify-and-Forward Relaying Strategy

    Page(s): 482 - 485
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (147 KB) |  | HTML iconHTML  

    The diversity-multiplexing tradeoff (DMT) is one of the most important criteria to evaluate the performance of wireless relay networks. Previous work shows that, compared to decode-and-forward (DF) and estimate-and-forward (EF) relaying protocols, amplify-and-forward (AF) achieves the worst DMT and cannot reach the DMT upper bound. In this paper, we propose a new relaying protocol, called dynamic AF (DAF), which allows the relay to adapt the receiving and forwarding time durations to the channel conditions. We show that DAF achieves the DMT upper bound when the multiplexing gain r is between 0 and α, where 0 <; α <; 0.5 is a constant set according to the relaying channel conditions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • BEP Analysis for DF Cooperative Systems Combined with Signal Space Diversity

    Page(s): 486 - 489
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    In fading channels, increasing diversity gains can effectively improve the reliability of transmissions. This letter considers high-order diversity acquisition by incorporating signal space diversity (SSD) into a decode-and-forward (DF) cooperative system. Our focus is on the bit error probability (BEP) analysis for this cooperative system. In particular, a tight closed-form upper bound on the end-to-end BEP is derived. Moreover, an asymptotic approximation for the BEP is presented which reveals that both the signal space diversity and the spatial diversity gains are achieved when all channels are available. Simulation results validate the theoretical analysis and show that a significant BEP gain over the traditional DF-based system is obtained at no additional power or bandwidth expense. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ellipse Expanding Method for Minimum Distance-Based MIMO Precoder

    Page(s): 490 - 493
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (221 KB) |  | HTML iconHTML  

    This letter proposes a new MIMO precoding method for dual-stream data transmission based on the criterion of minimum Euclidean distance. The problem is optimally solved by expanding an ellipse within a 2-dimensional lattice to the maximum extent. A closed-form expression of minimum Euclidean distance is derived for square quadrature amplitude modulation (QAM) constellations. The ellipse expanding method (EEM) allows for very efficient implementation by checking a small lookup table with respect to the condition number of channel matrix. Illustrative examples validate the promising performance of the proposed method in comparison with existing schemes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improving Space-Time Code Performance in Slow Fading Channels using Reconfigurable Antennas

    Page(s): 494 - 497
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (287 KB) |  | HTML iconHTML  

    Space-time block codes typically only span a small number of time slots. However, error control coding spanning hundreds or thousands of symbol periods is often used with space-time coding. In this case, slow fading channels significantly degrade performance. In this letter, we show that performance can be significantly improved in slow fading conditions by using reconfigurable antennas. We propose switching the transmit antenna states during transmission so that the error control code experiences several different channel conditions over the transmission period. Hence, it can achieve higher diversity and the superior performance expected of a faster fading channel due to reconfigurable antenna state switching. If we also allow the receiver to select the reconfigurable receive antenna states based on channel energy, then an antenna state selection gain is also achieved. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • SNR Performance Analysis of Reconfigurable Antennas

    Page(s): 498 - 501
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    Reconfigurable antenna arrays offer advantages over traditional antenna selection in terms of requiring fewer physical antennas and the use of fixed antenna feeds. Hence, in this paper we analyze the signal to noise ratio (SNR) improvement offered by reconfigurable antennas and compare it to traditional selection. Both the distribution and the mean value of the link gains in a reconfigurable system are derived and used to gain insight into system performance, both for SNR gain and outage. Results demonstrate that for systems with up to four antennas and two radiation states, reconfiguration can provide at least 76% of the improvements offered by selection. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance Analysis of Energy Detection with Multiple Correlated Antenna Cognitive Radio in Nakagami-m Fading

    Page(s): 502 - 505
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    This letter analyzes the performance of energy- detection-based spectrum sensing in a cognitive radio (CR) possessing multiple correlated antennas when the channel from the primary user (PU) to the CR is Nakagami-m faded. The probability of detection of the CR by employing square law combining (SLC) is derived by using the MGF-based approach. Special cases of equally correlated, exponentially correlated and a linear array of 2, 3 and 4 arbitrarily correlated antennas are treated. Numerical and simulation results are used to quantify the detector performance as a function of antenna correlation across the branches, number of antennas, fading severity and the time-bandwidth product. View full abstract»

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

Aims & Scope

IEEE Communications Letters  is aimed at satisfying the need for rapid dissemination of information, offering a vehicle for authors to expose their results to be used in future developments. This ensures early recognition of work. 

 

 

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
George K. Karagiannidis
Aristotle University of Thessaloniki
Greece