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Communications Letters, IEEE

Issue 5 • Date May 2013

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Displaying Results 1 - 25 of 64
  • 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
  • Network Coded Modulation for Random Channel Class in WNC with HDF Relaying Strategy

    Page(s): 818 - 821
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (121 KB) |  | HTML iconHTML  

    A standard NCM (Network Coded Modulation) for WNC (Wireless Network Coding) with HDF (Hierarchical Decode & Forward) strategy requires that each node has full knowledge of the connectivity pattern to other nodes and this knowledge affects the design of NCM and HNC (Hierarchical Network Code) maps at each transmitting (source) and receiving (relay) node respectively. The final destination has to have full knowledge of all HNC maps used and the composite overall HNC map needs to be invertible to recover the source data. This approach collapses if nodes do not have a full knowledge of the connectivity pattern and thus cannot adjust their HNC maps properly. We design the NCM and HNC maps for WNC with HDF strategy that works regardless of this knowledge. It is based on a concept of a channel class which is a discrete (random) parameter describing the channel behavior and which becomes a part of HNC maps and the NCM hierarchical constellation. We analyze the rate regions for this design and compare it to the standard NCM and HNC map solution suffering from random channel outages. View full abstract»

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  • Delay Analysis of Orderly Reattempts in Retrial Queueing System with Phase Type Retrial Time

    Page(s): 822 - 825
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (201 KB) |  | HTML iconHTML  

    Retrial queueing systems play a major role in many communication systems. The delay analysis of such systems poses an interesting problem in communication engineering. This has motivated us to analyze the waiting time distribution of a multi-server retrial queueing system with phase type retrial time, impatience and Bernoulli abandonments. The impact of retrial time on waiting time and other system characteristics is analyzed by determining the waiting time distribution. Numerical examples are presented to reveal the impact of the parameters. View full abstract»

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  • Imperfect CSI Based Joint Bit Loading and Power Allocation for Deadline Constrained Transmission

    Page(s): 826 - 829
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB) |  | HTML iconHTML  

    This paper studies the imperfect channel state information (CSI) based joint resource scheduling problem for deadline constrained transmission. We present a holistic system model in terms of performance constraints of imperfect CSI, scheduling deadline and bit loading. By tackling channel estimation error, robust scheduling problems are formulated with the ellipsoidal approximation and transmission reliability constraints respectively. Dynamic programming (DP) based robust scheduling schemes are derived. The numerical results show that the proposed robust scheduling schemes are efficient in solving the jointly scheduling problem. It is also shown that the impact of imperfect CSI is non-negligible, thus highlighting the importance of robust design in time-sensitive communications. View full abstract»

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  • Tracking Performance of Two Constant Modulus Equalizers

    Page(s): 830 - 833
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB) |  | HTML iconHTML  

    Exploiting the error variance relation, this letter discusses the evaluation of excess mean square error (EMSE) of constant modulus equalizers in a noise-free non-stationary environment. The EMSE analyses are presented for two equalizers - the CMA22 and the βCMA. Simulation results show a close match in theoretical and simulated errors for both algorithms. View full abstract»

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  • Interleaver Design for Parallel Concatenated Chaos-Based Coded Modulations

    Page(s): 834 - 837
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (118 KB) |  | HTML iconHTML  

    It is a well known property that turbo-like systems owe their success to the principle of reducing error event multiplicities rather than just minimizing related error distances. It has also been shown that Parallel Concatenated Chaos-Based Coded Modulations exploit further this principle, and this article explains how to take advantage of their typical error event structure to heuristically build interleavers with improved error floor properties. Simulations will prove the validity of the approach, as well as its limits and trade-offs. View full abstract»

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  • Subset-Optimized Polarization-Multiplexed PSK for Fiber-Optic Communications

    Page(s): 838 - 840
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB) |  | HTML iconHTML  

    A more power-efficient modulation format than polarization-multiplexed quadrature phase-shift keying (PM-QPSK) can be obtained by optimizing the amplitude ratio between symbols with odd and even parity in the PM-QPSK constellation. The optimal amplitude ratio approaches the golden ratio at high signal-to-noise ratio (SNR), yielding a 0.44 dB increase in asymptotic power efficiency compared to PM-QPSK. Union bound expressions are derived for the bit and symbol error rate of the new format, which together with Monte Carlo simulations give the power efficiency at both low and high SNR. A similar optimization performed on PM-8PSK gains 1.25 dB. View full abstract»

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  • On Selfish Configuration in Wi-Fi Tethering

    Page(s): 841 - 843
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB) |  | HTML iconHTML  

    Due to the ease of setting up a Wi-Fi hotspot and the availability of readily configurable mobile operating systems, Wi-Fi tethering can be abused by misbehaving users to gain an unfair advantage in throughput performance. In this paper, we study the problem of detecting selfish nodes in Wi-Fi tethering environments. In particular, selfish nodes can manipulate carrier sensing thresholds to exploit recent advances in physical-layer concurrent transmission technologies as well as short link distance in a tethered network so as to achieve unfair throughput gains while evading detection. We propose a new MAC-layer detection algorithm based on frame sequence numbers that accurately detects selfish nodes. View full abstract»

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  • Optimal Selection of False Alarm Probability for Dynamic Spectrum Access

    Page(s): 844 - 847
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    This letter investigates the selection of false alarm (FA) probability for dynamic spectrum access (DSA). We suggest that the performance of DSA systems can be improved efficiently by properly selecting the value of FA probability. The problem of DSA process with imperfect sensing is modeled as a continuous-time Markov chain and based on which, an optimization problem is formulated to maximize the number of served secondary radios for long-run term. We also present a simple gradient-based algorithm to find the optimal FA probability. Numerical results show that the proposal has better performance than conventional constant false alarm ratio based scheme. View full abstract»

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  • Reduced Complexity Beamforming with Optimal Power Allocation in Two-Way Multi-Antenna Relay Systems

    Page(s): 848 - 851
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB) |  | HTML iconHTML  

    This paper introduces a new beamforming method for a two-way relay system, where two single-antenna terminals exchange messages via a multi-antenna amplify-and-forward (AF) relay operating in the half-duplex mode. The optimization problem under consideration is to design a relay beamforming matrix that maximizes the achievable weighted sum rate under the relay power constraint, given the channel state information. This problem is non-convex, and iterative optimization algorithms and suboptimal beamformers with reduced complexity have been developed in previous works. In this paper, we develop an alternative suboptimal scheme by converting the original non-convex optimization into convex optimization. This conversion is made possible through some changes of variables and an additional condition. The simulation results demonstrate that the proposed method performs almost as well as the optimal scheme and can yield larger achievable rates than conventional suboptimal beamformers. View full abstract»

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  • A Weighted First-Order Statistical Method for Time-Varying Channel and DC-offset Estimation Using Superimposed Training

    Page(s): 852 - 855
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (125 KB) |  | HTML iconHTML  

    Time-varying channel and dc-offset estimation using superimposed training and first-order statistics are considered. A weighted first-order statistics-based estimator using complex exponential basis expansion model (CE-BEM) is proposed, which explicitly exploits the cyclostationary characteristic of periodic training sequence and extends to time-varying channel estimation. By subtracting the cyclic mean from each data block, only partial unknown data interference is removed to make a tradeoff between interference cancellation and symbol recovery. A theoretical performance analysis is presented. Simulation results show that the proposed scheme has low computational complexity and exhibits good performance in terms of the symbol error rate. View full abstract»

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  • Recycling Polluted Packet at the Physical Layer in Wireless Network Coding

    Page(s): 856 - 859
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (165 KB) |  | HTML iconHTML  

    We take a physical-layer perspective in detecting the falsely injected packet (pollution attack) and removing it from the polluted packet to restore the true coded packet in wireless network coding system. The proposed scheme "recycles" the polluted packet by discarding only the falsely injected packet and uses the remaining part for recovering the message. By doing so, it avoids packet re-transmission and substantially improves the bandwidth efficiency as well as the reliability of decoding. View full abstract»

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  • PL Decoding in Double Differential Modulation Based Decode-and-Forward Cooperative System

    Page(s): 860 - 863
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (154 KB) |  | HTML iconHTML  

    In this letter, we derive a piecewise linear (PL) decoder of the double differentially modulated symbols in the decode-and-forward protocol based cooperative communication system. The analytical average bit error rate (BER) of the proposed PL decoder is derived. Based on this BER expression, diversity order of the PL decoder is obtained. View full abstract»

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  • Effects of Outdated CSI on the Secrecy Performance of MISO Wiretap Channels with Transmit Antenna Selection

    Page(s): 864 - 867
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    Multiple antennas at the transmitter enhance the diversity performance of multiple-input single-output (MISO) wiretap channels by selecting a single antenna that maximizes the instantaneous signal-to-noise ratio (SNR) at the intended receiver. However, the expected diversity performance may not be fully realized when channel state information (CSI) is outdated at the transmitter. Owing to this fact, in this letter we analyze the effects of outdated CSI on the secrecy outage performance of MISO wiretap channels with transmit antenna selection. More specifically, assuming Nakagami-m fading, a closed-form expression for the exact secrecy outage probability is derived, from which an asymptotic analysis is carried out. Our asymptotic results reveal that the expected diversity gain cannot be realized when CSI is outdated during the antenna selection process. The validity of our formulations is corroborated by Monte Carlo simulations. View full abstract»

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  • Proportional Resource Allocation with Subcarrier Grouping in OFDM Wireless Systems

    Page(s): 868 - 871
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    In practical orthogonal frequency division multiplexing (OFDM) wireless systems, such as long term evolution (LTE), the subcarriers assigned to one user in one scheduling determination always use the same modulation and coding schemes (MCS). Taking this implementation issue into consideration, multiuser resource allocation with subcarrier grouping is investigated in this paper. The resource allocation is modeled as an optimization problem, in which a set of proportional rate constraints ensures system fairness. Firstly, a preliminary subcarrier assignment is developed, and then, an optimal power allocation scheme is carried out to ensure the proportional rate constraints precisely. Furthermore, an entire iterative algorithm is proposed to utilize subcarrier as effectively as possible. Numerical results demonstrate that the proposed algorithm achieves sum-rate capacity which is close to optimum and distributes resource among users flexibly as well. View full abstract»

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  • Joint Power Allocation and Subcarrier Pairing for Cooperative OFDM AF Multi-Relay Networks

    Page(s): 872 - 875
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (129 KB) |  | HTML iconHTML  

    For conventional subcarrier pairing scheme in cooperative orthogonal frequency division multiplexing amplify-and-forward multi-relay networks, to avoid interference, each subcarrier pair (SP) is assigned to only one relay, over a specific subcarrier, the destination receives signals transmitted from only one relay. In this letter, we propose to assign each SP to all the relays. Thus, over a specific subcarrier, the destination receives signals transmitted from all the relays. We propose a joint power allocation and subcarrier pairing scheme which maximizes the transmission rate subject to total network power constraint. The problem is simplified and solved by using dual method. View full abstract»

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  • On the Performance of Underlay Cognitive Radio Networks Using M/G/1/K Queueing Model

    Page(s): 876 - 879
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    Motivated by a realistic scenario for cognitive radio systems, we model the underlay cognitive radio network (CRN) under interference power constraint imposed by the primary network as an M/G/1/K queueing system. The respective embedded Markov chain is provided to analyze several key queueing performance measures. In particular, the equilibrium probabilities of all states are derived and utilized to evaluate throughput, blocking probability, mean packet transmission time, mean number of packets in the system, and mean waiting time of an underlay CRN with Nakagami-m fading channels. View full abstract»

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  • Advanced Detection of Selfish Vehicles for Local File Sharing in Sparse Vehicular Networks

    Page(s): 880 - 883
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (133 KB) |  | HTML iconHTML  

    Recent advances in wireless technology provide interesting and effective solutions for vehicular applications. Due to the high deployment cost, implementing roadside units (RSUs) with low cost while maintaining high data throughput has become an important topic. This letter develops a selfishness detection mechanism for file sharing that addresses fairly use vehicle-to-vehicle communications. In locations where an RSU is not immediately available or cannot be directly used, the selfish behavior of not sharing with neighbors or not downloading from an RSU is difficult to detect. This letter proposes a novel selfishness detection mechanism, SDM, to force vehicles to stabilize at a socially optimal operating point incurring maximum total utility. The SDM along with our proposed hybrid self-history mechanism outperforms previous shared history mechanisms, even though the majority of users are selfish. View full abstract»

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  • Exact Capacity Analysis of Spectrum Sharing Systems: Average Received-Power Constraint

    Page(s): 884 - 887
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (174 KB) |  | HTML iconHTML  

    This letter presents an exact closed-form expression for the ergodic capacity of the secondary user in a spectrum sharing environment under an average received-power constraint, considering the effect of the interference from the primary user. Using capacity maximizing water-filling power allocation, we provide the closed-form expressions for the ergodic capacity and the average received-power assuming Rayleigh fading channels. Numerical results show that the primary user interference significantly affects the ergodic capacity of the secondary user. The obtained formulas can be used when predicting whether spectrum sharing is beneficial in a practical channel environment. View full abstract»

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  • On the Accuracy of Maximum Likelihood Estimation for Primary User Behavior in Cognitive Radio Networks

    Page(s): 888 - 891
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (210 KB) |  | HTML iconHTML  

    The primary user (PU)'s busy/idle behavior in a cognitive radio network is conventionally modeled using a two-state Markov chain. Maximum likelihood (ML) estimation is widely applied to estimate the state transition probabilities. This letter derives a precise expression of the probability mass function (PMF) for the ML estimator, which has not been reported in the literature. By leveraging the exact PMF expression, the essential relation among the number of samples, transition probabilities, and estimation accuracy is revealed. View full abstract»

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  • Achieving Secure Transmission with Equivalent Multiplicative Noise in MISO Wiretap Channels

    Page(s): 892 - 895
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (145 KB) |  | HTML iconHTML  

    In this letter, we verify that equivalent multiplicative noise, which is generally introduced by random beamforming security scheme, can also guarantee available secrecy rate in MISO wiretap channels. The multiplicative noise is transformed into additive one via a logarithmic operation which is further demonstrated to be information preserving. Then the achievable secrecy rate is quantitatively characterized when the amplitude and phase of the multiplicative noise are independently generated and follow lognormal and uniform distributions, respectively. Finally, power allocation between the multiplicative noise and the desired signal is optimized and discussed by numerical simulation when the eavesdropping channel is known. View full abstract»

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  • Orthogonal Pulse Design in Consideration of FCC and IEEE 802.15.4a Constraints

    Page(s): 896 - 899
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB) |  | HTML iconHTML  

    In Ultra-wideband (UWB) system mainly coexisting with other narrow band systems, a judicious pulse shape design is necessary, under the IEEE 802.15.4a standard and the Federal Communications Commission (FCC) spectral mask constraints. In this letter, a strategy to generate multiple orthogonal pulses while complying with both constraints is presented. The performance analysis is also presented with mathematical derivations and numerical simulations to show that the proposed pulses can be utilized for higher data rate or lower error rate. View full abstract»

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  • Inter-RAT Energy Saving for Multicast Services

    Page(s): 900 - 903
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    Green communication receives a growing number of concerns due to the consideration for energy and environment issues. On the other hand, the evolution of mobile and wireless communication also results in heterogeneous Radio Access Technologies (RATs), such as Wi-Fi, UMTS, LTE, CDMA2000 and so on. As a result, energy saving by inter-RAT cooperation has raised significant discussions in both industrial and academical worlds. In this paper, we concentrate on inter-RAT energy saving for multicast services. Moreover, we use Integer Linear Programming to model the problem and propose a distributed algorithm which can efficiently save the energy consumption. View full abstract»

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  • The Cost Efficient Location Management in the LTE Picocell/Macrocell Network

    Page(s): 904 - 907
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (275 KB) |  | HTML iconHTML  

    The discontinuous coverage of picocells causes the increased registration signaling overhead in the picocell/macrocell network where the dense picocells overlapped with a macrocell are partitioned into small Tracking Areas (TAs). The approach known as Delay Registration (DR) algorithm is proposed for overhead reduction with the expense of sacrificing the traffic offloading capability of the picocell in such case. However, its feasibility is greatly restricted because its effective implementation requires the accurate estimation of the mobile station (MS) information. We design a new scheme to enable both the low signaling cost location update without the complicated information estimation and the traffic offloading using the inter-cell handover. The theoretical analysis and the simulation experiments are conducted for the performance evaluation. The results show that our solution is superior to the DR algorithm in reducing the signaling cost while achieving the better adaptability to the high and diverse mobility environment. View full abstract»

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George K. Karagiannidis
Aristotle University of Thessaloniki
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