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Communications Letters, IEEE

Issue 7 • Date July 2011

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Displaying Results 1 - 25 of 35
  • Table of contents

    Page(s): c1 - c4
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    Freely Available from IEEE
  • Staff List

    Page(s): c2
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    Freely Available from IEEE
  • Two-Way Writing on Dirty Paper

    Page(s): 689 - 691
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB) |  | HTML iconHTML  

    In this paper, the Two-Way Channel (TWC) with noncausal Channel State Information (CSI) is investigated. For the discrete memoryless channel an achievable rate region is derived. Then by extending the result to the Gaussian TWC with additive interference noise, it is shown that the capacity region of the latter channel is the same as the capacity when there is no interference, i.e., a two-way version of Costa's writing on dirty paper problem is established. View full abstract»

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  • An Algorithm for Computing Maximin of Mutual Informations

    Page(s): 692 - 694
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (197 KB) |  | HTML iconHTML  

    In this paper, we are concerned with the maximin of mutual informations, which usually occurs in the context of specifying the capacity of a compound channel or the maximum rate of broadcasting common messages to multiple receivers. Firstly, the analytical properties of the minimum mutual informations such as continuity, concavity and differentiability are analyzed. The necessary and sufficient conditions for the capacity-achieving input distributions are revealed by reformulating the original problem into an equivalent differentiable form. Also presented are bounds on the capacity. Secondly, an iterative method to compute the maximin value of two mutual informations is derived, which is almost the same as the Arimoto-Blahut algorithm except that a more complicated maximization algorithm is required at the second phase. Finally, the convergence of the proposed algorithm is proved. View full abstract»

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  • Spectral- and Power-Efficient Data Multiplexing Format Based on Code-Shift-Keying

    Page(s): 695 - 697
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (193 KB) |  | HTML iconHTML  

    This paper proposes a spectral- and power- efficient code division multiplexing (CDM) scheme based on code shift keying (CSK) for the down-link of a communication system subject to additive Gaussian noise (e.g., the forward link of a satellite communication system). In a CSK system, each active user is assigned a set of sequences taken from Gold codes and their cyclic shifts. Spectral efficiency can be achieved by multiplexing several CSK modulators. We first define the corresponding Maximum-Likelihood (ML) decoder, showing that it can be efficiently implemented through a Sphere Decoding (SD) algorithm. An approximate performance analysis of the proposed scheme is given, and validated through numerical simulations, showing that larger spectral efficiencies also lead to increased power efficiencies. View full abstract»

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  • A Population Based Incremental Learning for Network Coding Resources Minimization

    Page(s): 698 - 700
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (142 KB) |  | HTML iconHTML  

    In network coding based multicast, coding operations need to be minimized as they consume computational resources and increase data processing complexity at corresponding nodes in the network. To address the problem, we develop a population based incremental learning algorithm which shows to outperform existing algorithms in terms of both the solution obtained and computational time consumed on networks with various features. View full abstract»

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  • Energy-Efficient Power Control and Receiver Design in Relay-Assisted DS/CDMA Wireless Networks via Game Theory

    Page(s): 701 - 703
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (210 KB) |  | HTML iconHTML  

    Non-cooperative power control strategies for the uplink of relay-assisted DS/CDMA wireless networks are considered in this paper using game-theoretic tools. Assuming that each user is interested in maximizing his own energy efficiency, measured in bit/Joule and denoting the number of error-free delivered bits for each energy-unit used for transmission, several non-cooperative games are proposed and analyzed. Simulation results confirm the theoretical findings and show that the use of advanced data detection strategies has a huge and benefic impact on the energy efficiency of relay-assisted wireless networks. View full abstract»

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  • Cooperative Signal Constellation for LDPC-Coded Relay System

    Page(s): 704 - 706
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB) |  | HTML iconHTML  

    In this letter, we first develop the cooperative constellation design for the single relay LDPC-coded system; then we describe the associated iterative detection/decoding scheme at the destination node. Simulation results show that, with the cooperative constellation and an appropriate power allocation strategy, the relay system can achieve a performance gain of about 1.6 dB around BER = 10-4. View full abstract»

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  • Selective Decode-and-Forward Using Fixed Relays and Packet Accumulation

    Page(s): 707 - 709
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    We propose a cooperative scheme using a fixed relay based on the selective decode-and-forward (SDF) protocol. The relay accumulates Z source packets, concatenates them into a single packet, and forwards this single packet to the destination with an increased spectral efficiency. The proposed scheme can considerably outperform the conventional SDF protocol, at the cost of a moderate increased maximum delay. View full abstract»

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  • Outage Performance for Cognitive Relay Networks with Underlay Spectrum Sharing

    Page(s): 710 - 712
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (207 KB) |  | HTML iconHTML  

    The outage performance is investigated for a cognitive relay system with underlay spectrum sharing model. It is shown that the dependence among the received SNRs is introduced due to the interference power constraint. The joint probability of the received SNRs is derived. By considering the dependence for the case of null decoding set, a tight lower bound on the outage probability is obtained. Simulation results are presented to verify the theoretical analyses. View full abstract»

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  • Long Term Cluster-Based Channel Envelope and Phase Prediction for Dynamic Link Adaptation

    Page(s): 713 - 715
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (237 KB) |  | HTML iconHTML  

    A new cluster-based channel envelope and phase predictor is proposed for dynamic link adaptation in broadband wireless systems, based on our observation that each Multipath Cluster (MC) has its own variation characteristics, which can be identified and traced precisely. The proposed predictor consists of a channel envelope predictor and a phase slope detector. The performance of the proposed channel predictor has been verified through numerical simulations and field test measurement data. At a channel SNR of 6.05 dB and a prediction range of 240 Orthogonal Frequency Division Multiplexing (OFDM) symbols, the obtained normalized mean square error is less than -20 dB. View full abstract»

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  • Optimal Sensing Cardinality for Cognitive Radios

    Page(s): 716 - 718
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (247 KB) |  | HTML iconHTML  

    This letter puts forth a proactive approach for determining the sensing cardinality (the number of subchannels to sense) in a multiband cognitive radio network with limited available block energy. Specifically, we present the sensing cardinality that maximizes the achievable block rate of the cognitive user by optimally allocating available energy to the wideband spectrum sensing and data transmission. We further derive the closed-form expression for this optimal sensing cardinality when each subchannel has the identical primary spectrum occupancy statistics. View full abstract»

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  • On the Symbol Error Probability of Multihop Parallel Relay Networks

    Page(s): 719 - 721
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (355 KB) |  | HTML iconHTML  

    In this paper we analyze the symbol error probability (SEP) of a cooperative multihop parallel relay network in Rayleigh fading channels for M-ary Phase-shift keying (M-PSK) modulation. The general closed form expression of the SEP is derived. We present numerical results on the performance of the network. View full abstract»

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  • Resource Allocation in Multicast OFDM Systems: Lower/Upper Bounds and Suboptimal Algorithm

    Page(s): 722 - 724
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (199 KB) |  | HTML iconHTML  

    This letter studies generalized resource allocation in multiple description coding multicast (MDCM) orthogonal frequency division multiplexing (OFDM) systems, where many multicast groups are served simultaneously by base station (BS). Due to non-tractable nature, the problem is reformulated to weighted-capacity maximization by resource distribution among virtual multicast groups (VMGs). Then, the relaxation of exclusively-used constraints allows us to provide both upper and lower bounds for the original problem. A suboptimal algorithm is also proposed based on Newton's method to reduce the computational complexity. Simulation results show the proposed algorithm approximately reaches the optimal capacity within 2 iterations for multicast waterfilling, and MDCM is more bandwidth-efficient for multicast services than conventional multicast (CVM). View full abstract»

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  • Simplified Quantisation in a Reduced-Lattice MIMO Decoder

    Page(s): 725 - 727
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (193 KB) |  | HTML iconHTML  

    Symbol detection in a lattice-reduction aided MIMO receiver depends upon appropriate quantisation in the reduced lattice and this has previously been achieved using a shift-and-scale method. This paper describes a novel parity-based method that avoids the need to perform inversion of the reduction matrix and simplifies the computation involved in symbol estimation in MIMO receivers using QAM and PAM modulation schemes. The new algorithm is shown to be functionally identical to the shift-and-scale method. View full abstract»

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  • Queue Management Mechanism for 802.11 Base Stations

    Page(s): 728 - 730
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (315 KB) |  | HTML iconHTML  

    This paper presents a novel queue management mechanism for base stations in infrastructure IEEE 802.11 networks. The mechanism is transparent to high-level protocols and is compatible with the standard. Its effectiveness is illustrated by showing that it can ameliorate the RTT unfairness and the MAC anomaly problems in wired-cum-wireless networks. View full abstract»

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  • BER Analysis of Threshold Digital Relaying Schemes over Log-Normal Fading Channels

    Page(s): 731 - 733
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (193 KB) |  | HTML iconHTML  

    In this letter, an accurate analytical model is proposed to study the performance of threshold digital relaying schemes in cooperative systems over log-normal fading channels. The analytical expression for the average end-to-end bit error rate has been derived. Simulation results verify the accuracy of the proposed analytical model. View full abstract»

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  • An Auction Theory Based Algorithm for Throughput Maximizing Scheduling in Centralized Cognitive Radio Networks

    Page(s): 734 - 736
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (171 KB) |  | HTML iconHTML  

    In this letter we propose an auction theory based algorithm for throughput maximizing scheduling in centralized cognitive radio networks (CRN). In the considered CRN scheme, a centralized base station coordinates the assignment of frequencies and time slots to cognitive users with multiple antennas. Our proposed algorithm uses first-price sealed bid auction mechanism in which frequency and time slot pairs are considered as the auctioned resources and cognitive users are the bidders. The experimental results show that our computationally efficient algorithm yields very close throughput performance to the optimization software CPLEX values. View full abstract»

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  • Information Coupling in Cooperative Localization

    Page(s): 737 - 739
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    Cooperative network localization with high-accuracy and environment-independent reliability will enable a myriad of important applications. However, distributed implementations of cooperative algorithms currently do not account for the correlation of inferred nodes' positions. This letter investigates such correlation in cooperative localization in terms of Fisher information, leading to the concept of information coupling. To characterize its behavior, we focus on the simplest non-trivial case and derive the expressions for information coupling. View full abstract»

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  • Efficient Decision-Directed Channel Estimation for OFDM Systems with Transmit Diversity

    Page(s): 740 - 742
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (225 KB) |  | HTML iconHTML  

    To reduce the complexity involved in decision-directed channel estimation (DDCE) in orthogonal frequency-division multiplexing (OFDM) systems with transmit diversity, both data decoupling and direct cancellation of inter-antenna interference (IAI) suffer from residual IAI caused by channel frequency selectivity and time selectivity. In this paper, we propose a new algorithm to improve the performance of low complexity DDCE in OFDM systems with transmit diversity. The proposed algorithm includes a new data decoupling scheme with weaker assumptions regarding channel frequency response, and residual IAI cancellation using the results of the DDCE. Simulation results demonstrate that the proposed algorithm improves the performance of MSE and BER considerably. View full abstract»

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  • Parallel Concatenated Tree Hadamard Codes

    Page(s): 743 - 745
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (203 KB) |  | HTML iconHTML  

    In this letter, a new class of low-rate error-correcting codes named parallel concatenated tree Hadamard codes (CTrHC) are designed. Tree Hadamard codes consist of Hadamard segments which are connected by carefully chosen positions from a Hadamard codeword. With the same encoding and decoding complexity as the parallel concatenated zigzag Hadamard codes, CTrHC with short code length can achieve much better error floor performance illustrated by simulation results. View full abstract»

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  • Reduced Complexity MIMO Concatenated Code in Fading Channels

    Page(s): 746 - 748
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (173 KB) |  | HTML iconHTML  

    In conventional concatenations of Convolutional Codes (CC) and Space-Time Block Codes (STBC), the CC and STBC are utilized to provide coding gain and spatial diversity, respectively. We propose a concatenated code that achieves the full system diversity by appropriately selecting the outer CC with an inner reduced-rank STBC. The advantage of the lower rank STBC is that the number of RF chains can be reduced. For any number of RF chains, R, we show that a desirable diversity order Y can be easily achieved i.e., 1 ≤ R ≤ Y. Using trellis diagram, we formalize the method to determine the maximum diversity. View full abstract»

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  • Efficient Shortened Cyclic Codes Correcting Either Random Errors or Bursts

    Page(s): 749 - 751
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (143 KB) |  | HTML iconHTML  

    Efficient cyclic or shortened cyclic codes that can correct either up to t errors or a single burst of length up to b, where t <; b, are presented, as well as a search algorithm based on syndrome computation for each possible generator polynomial. Previously known results are improved by the new codes. View full abstract»

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  • Mixed Placement of 1R/2R/3R Regenerators in Translucent Optical Networks to Achieve Green and Cost-Effective Design

    Page(s): 752 - 754
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (478 KB) |  | HTML iconHTML  

    We develop a theoretical model to estimate the BER evolutions in optical translucent networks in a more accurate way. The model calculates the BER increment at each regeneration site with considerations of reshaping nonlinearity and jitter effect for 40 Gb/s signals. Based on the model, we propose a novel translucent optical network infrastructure that includes all-optical 2R regenerators and uses mixed operation of 1R/2R/3R regenerators for cost and power consumption savings. Simulation results show that our proposed infrastructure reduces the number of O/E/O 3R regenerators to less than 50% and achieves effective power saving. View full abstract»

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  • Evaluation of Optimum Threshold in OCDM/WDM Optical Packet Switches

    Page(s): 755 - 757
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (335 KB) |  | HTML iconHTML  

    In this paper we illustrate a procedure to evaluate the optimum receiver threshold in Optical Code Division Multiplexing (OCDM) systems using Gold Codes. The use of the optimum threshold allows for a higher number of optical codes carried on each wavelength. The increase in OCDM/WDM Optical Packet Switch performance is also evaluated when the threshold optimization is performed. We show that when the offered traffic is equal to p=0,7, the packet loss probability of the OCDM/WDM switch in saturation conditions, equals 1,28*10-6 in the case in which the optimal receiver threshold is used. On the contrary the performance reaches only 3,91*10-4 if a traditional threshold is chosen. View full abstract»

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George K. Karagiannidis
Aristotle University of Thessaloniki
Greece