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Wireless Communications Letters, IEEE

Issue 1 • Date February 2013

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Displaying Results 1 - 25 of 36
  • Table of contents

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

    Page(s): c2
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  • Status of the Letters and Exemplary Reviewers

    Page(s): 1
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  • An Ordering Scheme Exploiting Modulation Information for Tree Search Based Detection in Interference-Limited MIMO Systems

    Page(s): 2 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (149 KB) |  | HTML iconHTML  

    The well-known vertical Bell Labs layered space-time (V-BLAST) ordering has been widely employed for tree search algorithms such as sphere decoder. The V-BLAST ordering was derived under the assumption that all transmitted symbols utilize the same modulation. In an interference-limited scenario, a cell-edge user probably receives serving and interfering signals with different modulations. In this case, the conventional V-BLAST ordering does not provide a satisfactory solution for complexity reduction. This letter shows how to incorporate the modulation information into the V-BLAST ordering to significantly reduce the complexity of the tree search algorithms. Simulation results show the new ordering based sphere decoder can provide a better trade-off between complexity (e.g., in terms of operations) and performance (e.g., in terms of throughput or error rate) in the interference-limited scenario. View full abstract»

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  • Enhanced Algorithm for Digital Mitigation of ICI Due to Phase Noise in OFDM Receivers

    Page(s): 6 - 9
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (211 KB) |  | HTML iconHTML  

    In this letter, an enhanced yet computationally efficient algorithm is proposed for suppressing ICI due to phase noise in OFDM receivers. The method is particularly targeted to improve the detection error rate performance when high-order constellation size and long cyclic prefix are used. The approach optimizes the interpolation of estimated excess phase between adjacent OFDM symbols and re-compensates for residual CPE after interpolation. The proposed enhancement is verified in OFDM system with 64-QAM subcarrier modulation and 1/4 cyclic prefix, and shown to outperform state-of-the-art. Implementation complexity and its optimization are also discussed. View full abstract»

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  • Channel Estimation with Optimal Power Controls in Amplify-and-Forward Relay Networks

    Page(s): 10 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (445 KB) |  | HTML iconHTML  

    In this paper, we present a power control method of relay for improving a channel estimation performance in amplify-and-forward (AF) relay networks over frequency-selective fading channel. We first analyze a channel mean-square error (MSE) by imposing a power control effect on a simple (LS) channel estimation. Then, we find that there is a trade-off between the amplitude of power control and MSE performance. Moreover, we propose the optimal and suboptimal power control methods in order to resolve such a trade-off. Finally, the superiority of the proposed channel estimation with optimal power controls is verified through numerical simulations. View full abstract»

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  • Power Amplifier Switching (PAS) for Energy Efficient Systems

    Page(s): 14 - 17
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (181 KB) |  | HTML iconHTML  

    We propose a power amplifier (PA) switching/selection (PAS) method to improve the energy efficiency (EE) of a transmit antenna selection and maximum ratio combining (TAS-MRC) system. A PAS transmitter has a PA bank consisting of multiple dissimilar PAs, which operate with different output power levels, and selects the most efficient PA and its power level that satisfies a target rate. If there is no PA supporting the target rate, the transmitter is set to an off-mode (i.e., all PAs are turned off). The receiver feeds back the choice of PA and its power level to the transmitter, similar to the feedback in a conventional power control system with a single PA. Numerical results show that the system EE can be improved by using the PAS. This letter is the first study to investigate and verify the potential capability of PAS for the system EE improvement in wireless communications. View full abstract»

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  • Performance Analysis of the Ordered V-BLAST Approach over Nakagami-m Fading Channels

    Page(s): 18 - 21
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (267 KB) |  | HTML iconHTML  

    The performance of the V-BLAST approach, which utilizes successive interference cancellation (SIC) with optimal ordering, over independent Nakagami-m fading channels is studied. Systems with two transmit and n receive antennas are employed whereas the potential erroneous decision of SIC is also considered. In particular, tight closed-form bound expressions are derived in terms of the average symbol error rate (ASER) and the outage probability, in case of binary and rectangular mathcal{M}-ary constellation alphabets. The mathematical analysis is accompanied with selected performance evaluation and numerical results, which demonstrate the usefulness of the proposed approach. View full abstract»

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  • Dynamic Power Allocation for Throughput Utility Maximization in Interference-Limited Networks

    Page(s): 22 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB) |  | HTML iconHTML  

    We present an algorithm to dynamically allocate transmission power to maximize the throughput-utility in an interference-limited network under an instantaneous sum power constraint with time-varying channels. We consider the equivalent problem of maximum admission with queue stability constraint through Lyapunov optimization. The resultant non-convex minimization problem is solved by an online algorithm consisting of two components: first, successive convex approximations to randomly choose a local minimum, and second, a modified pick-and-compare method for low-complexity convergence to a global minimum. We prove the optimality of this approach, derive its tradeoff between throughput-utility and delay, and demonstrate its performance advantage against existing methods. View full abstract»

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  • Cross-Layer Combining of Information-Guided Transmission with Network Coding Relaying for Multiuser Cognitive Radio Systems

    Page(s): 26 - 29
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (265 KB) |  | HTML iconHTML  

    For a cognitive radio relaying network, we propose a cross-layer design by combining information-gnided transmission at the physical layer and network coding at the network layer. With this design, a common relay is exploited to help the communications between multiple secondary source-destination pairs, which allows for a more efficient use of the radio resources, and moreover, generates less interference to primary licensees in the network. Considering the spectrum-sharing constraints on the relay and secondary sources, the achievable data rate of the proposed cross-layer design is derived and evaluated. Numerical results on average capacity and uniform capacity in the network under study substantiate the efficiency of our proposed design. View full abstract»

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  • Improved Throughput Physical-Layer Network Coding in Multi-Way Relay Channels with Binary Signaling

    Page(s): 30 - 33
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (229 KB) |  | HTML iconHTML  

    We consider the problem of full data exchange in multi-way relay channels. It is shown that a throughput of frac{1}{1.5N} symbol per node per channel use can be achieved using binary signaling, which is a 33% increase compared to plain routing. This is accomplished by providing common knowledge to all nodes and exploiting this knowledge to restrain some nodes from transmitting. The error performance of the proposed algorithm is evaluated analytically. Results are presented which provide insights into multi-node network coding. View full abstract»

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  • Jenga-Inspired Optimization Algorithm for Energy-Efficient Coverage of Unstructured WSNs

    Page(s): 34 - 37
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (251 KB) |  | HTML iconHTML  

    The Energy-Efficient Coverage (EEC) problem in unstructured Wireless Sensor Networks (WSNs) is an important issue because WSNs have limited energy. In this letter, we propose a novel stochastic optimization algorithm, called the Jenga-Inspired Optimization Algorithm (JOA), which overcomes some of the weaknesses of other optimization algorithms for solving the EEC problem. The JOA was inspired by Jenga which is a well-known board game. We also introduce the probabilistic sensor detection model, which leads to a more realistic approach to solving the EEC problem. Simulation results are conducted to verify the effectiveness of the JOA for solving the EEC problem in comparison with existing algorithms. View full abstract»

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  • Fastest-Known Maximum-Likelihood Decoding of Quasi-Orthogonal STBCs with QAM Signals

    Page(s): 38 - 41
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB) |  | HTML iconHTML  

    We present a maximum-likelihood (ML) decoder with the lowest computational complexity known to-date for full-diversity, arbitrary size Quasi-Orthogonal Space-Time Block Codes (QO-STBCs) with symbols from square or rectangular quadrature amplitude modulation (QAM) constellations. We start with the formulation of an explicit joint two-complex-symbol decoder for general QO-STBCs with arbitrary complex symbols and then derive the proposed ML decoder for QO-STBCs with QAM symbols. The complexity savings are made possible by a simplified quadratic ML decoding statistic that utilizes algebraically the structure of the signal points of the QAM constellation. Comparative computational complexity analysis with existing ML implementations and simulation studies are included herein for illustration and validation purposes. View full abstract»

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  • Joint Maximum Likelihood Estimation of CFO, Noise Power, and SNR in OFDM Systems

    Page(s): 42 - 45
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (141 KB) |  | HTML iconHTML  

    Estimation of noise power and signal-to-noise ratio (SNR) are fundamental tasks in wireless communications. Existing methods to recover these parameters in orthogonal frequency-division multiplexing (OFDM) are derived by following heuristic arguments and assuming perfect carrier frequency offset (CFO) synchronization. Hence, it is currently unknown how they compare with an optimum scheme performing joint maximum likelihood (ML) estimation of CFO, noise power and SNR. In the present work, the joint ML estimator of all these parameters is found by exploiting the repetitive structure of a training preamble composed of several identical parts. It turns out that CFO recovery is the first task that needs to be performed. After CFO compensation, the ML estimation of noise power and SNR reduces to a scheme that is available in the literature, but with a computational saving greater than 60% with respect to the original formulation. To assess the ultimate accuracy achievable by the ML scheme, novel expressions of the Cramer-Rao bound for the joint estimation of all unknown parameters are provided. View full abstract»

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  • Transmission Range Assignment for Backbone Connectivity in Clustered Wireless Networks

    Page(s): 46 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (211 KB) |  | HTML iconHTML  

    In this paper, a method is proposed to assign minimum transmission ranges to the backbone nodes of a hierarchically structured multihop network, while seeking an M% probability to have end-to-end connectivity to the network's data sink. The target scenario is data collection in which cluster head (CH) nodes collect packets from cluster members and then forward them over a CH-backbone towards the sink. The proposed method reduces the energy consumption of data transmissions made by CH nodes, and hence improves the efficiency of existing node clustering protocols, which select arbitrarily large ranges for backbone communications. View full abstract»

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  • Probability of Strictly Positive Secrecy Capacity of the Rician-Rician Fading Channel

    Page(s): 50 - 53
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (151 KB) |  | HTML iconHTML  

    Communication security is critical in the marine environment as information may be transmitted over large open areas like high seas. In this letter, an analysis is conducted on the probability of secrecy capacity for wireless communications over the Rician fading channels. In particular, a closed-form expression for the probability of strictly positive secrecy capacity is derived. The result is applicable to the scenarios of Rayleigh/Rayleigh, Rician/Rayleigh, Rayleigh/Rician, and Rician/Rician. View full abstract»

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  • Measuring Group Mobility: A Topology Based Approach

    Page(s): 54 - 57
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB) |  | HTML iconHTML  

    In highly mobile networks, mobility based clustering schemes exploit the group mobility of nodes to form stable communication structure by grouping nodes with similar mobility pattern together. However, existing group mobility metrics cannot assess quantitatively whether a mobility model can provide the necessary degree of group mobility. In this paper, we propose a novel metric, Degree of Node Reachability (DNR), to measure the degree of group mobility from the perspective of network topology. Based on DNR, we propose r-test to quantitatively assess whether a given mobility model will fail to satisfy the required network condition. The proposed metric is validated using common mobility models. The simulation results show that our metric can capture the network topology changes and reflect the impact of underlying node mobility. In addition, r-test is shown to provide a viable means to assess the level of group mobility of a given mobility model. View full abstract»

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  • On Approximating the Cognitive Radio Aggregate Interference} IEEEaftertitletextvspace{-1baselineskip

    Page(s): 58 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (150 KB) |  | HTML iconHTML  

    The aggregate interference caused on a primary receiver by Cognitive Radio (CR) nodes distrbuted uniformly in an annular region around it is investigated, assuming Rayleigh fading and path loss. By approximating the aggregate interference with that caused by the nearest CR interferer, the exact analytical moment generating function for the nearest interferer is derived for cases of no power control and distance based power control. The outage probability based on the approximation is derived, which is a tight lower bound under certain conditions. View full abstract»

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  • Distributed Network-Channel Codes Design with Short Cycles Removal

    Page(s): 62 - 65
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (314 KB) |  | HTML iconHTML  

    In this paper, we address short cycle effects in the distributed low density generator matrix (LDGM) codes. As a codeword is formed from various nodes, the decentralized code construction makes it difficult to eliminate short cycles, resulting in a degraded code performance. To mitigate this effect, we propose a distributed algorithm which can eliminate short cycles within the network. The complexity of the proposed algorithm is a linear function of the number of relay nodes in the network. The simulation results show that the code performance can lower the error floor of irregular LDGM codes significantly, when all short cycles have been removed. View full abstract»

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  • A Cooperative Positioning Algorithm in Cellular Networks with Hearability Problem

    Page(s): 66 - 69
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (243 KB) |  | HTML iconHTML  

    The letter presents a cooperative positioning algorithm in cellular networks. Due to hearability problem, the distance between a mobile terminal (MT) and only its home base station can be utilized for positioning. Moreover, several MTs belongs to 3 adjacent cells cooperate with their nearby MTs for positioning. The simulation results show that the proposed algorithm outperforms the existing algorithms in the literature. View full abstract»

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  • Clustered IEEE 802.15.4 Sensor Networks with Data Aggregation: Energy Consumption and Probability of Error

    Page(s): 70 - 73
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (138 KB) |  | HTML iconHTML  

    In this paper, we analyze an IEEE 802.15.4-compliant wireless sensor network, organized in clusters with fusion centers (FCs) acting as cluster heads. Sensors observe the same common binary phenomenon, decide on its status, and send their decisions to the FCs, which perform a majority fusion. FCs' decisions are then sent to an access point, where a final estimate is obtained. Data aggregation (DA) over consecutive observations can be also performed at sensors, with the aim of reducing the number of sensors simultaneously competing for the channel, while increasing the packet size. A novel mathematical framework for deriving the energy consumption in IEEE 802.15.4 networks is also proposed. The performance is evaluated in terms of energy consumption and probability of decision error, jointly accounting for decentralized detection, medium access, and DA. View full abstract»

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  • Frequency Packing and Multiuser Detection for CPMs: How to Improve the Spectral Efficiency of DVB-RCS2 Systems

    Page(s): 74 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (177 KB) |  | HTML iconHTML  

    We consider a frequency division multiplexed system where each user adopts a continuous phase modulation (CPM) and multiuser detection is employed at the receiver side. The spectral efficiency (SE) is used as a performance measure to compare, from an information-theoretic point of view, different modulation formats. More precisely, we consider the new CPM formats recently included in the DVB-RCS2 standard. We describe a framework for computing the information rate (IR) and the SE of such systems, and use it for optimizing the channel spacing between adjacent users and the CPM phase response. Our analysis reveals that modulation formats adopted in the DVB-RCS2 standard are suboptimal in terms of SE, while if we allow multiuser detection excellent performance can be achieved by using simple binary formats and highly frequency packed signals. Furthermore, we consider practical schemes, where CPMs are serially concatenated with an outer code, and a low-complexity multiuser receiver is employed, showing that the theoretical limits predicted by the IR analysis can be approached. View full abstract»

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  • Optimal Adaptive Modulation for QoS Constrained Wireless Networks with Renewable Energy Sources

    Page(s): 78 - 81
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (157 KB) |  | HTML iconHTML  

    In this paper we derive the optimal policy to minimize the average number of dropped packets for a delay constrained wireless node with a renewable energy source. The proposed framework employs adaptive modulation for transmission of the optimal number of packets towards satisfying the Quality of Service (QoS) constraints. This framework is formulated as a Markov Decision Process (MDP) which minimizes the long term packet drop rate. Further, we demonstrate that the optimal policy is monotone with respect to each of the joint state components of the MDP. Simulation results are presented to validate the monotone structure and superior performance of the proposed policy with respect to the existing schemes. View full abstract»

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  • Q-Learning Based Energy Management Policies for a Single Sensor Node with Finite Buffer

    Page(s): 82 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (145 KB) |  | HTML iconHTML  

    In this paper, we consider the problem of finding optimal energy management policies in the presence of energy harvesting sources to maximize network performance. We formulate this problem in the discounted cost Markov decision process framework and apply two reinforcement learning algorithms. Prior work obtains optimal policy in the case when the conversion function mapping energy to data transmitted is linear and provides heuristic policies in the case when the same is nonlinear. Our algorithms, however, provide optimal policies regardless of the form of the conversion function. Through simulations, our policies are seen to outperform those of in the nonlinear case. View full abstract»

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  • Error Probability of Opportunistic Decode-and-Forward Relaying in Nakagami-m Fading Channels with Arbitrary m

    Page(s): 86 - 89
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (189 KB) |  | HTML iconHTML  

    We investigate the error performance of opportunistic decode-and-forward (DF) relaying in Nakagami-m fading with arbitrary m≥ 0.5. In particular, we obtain exact moment generating function (MGF) expressions in terms of Lauricella hypergeometric function (LHF) for opportunistic DF relaying with maximal ratio combining (MRC) or selection combining (SC). In the case of SC, the cumulative density function (CDF) of the receive SNR is also derived and based on the CDF, two error probability expressions for opportunistic DF relaying with SC are provided. Further, we show that the MGF expressions can be greatly simplified when average SNRs become large. From asymptotic analysis, the diversity order of opportunistic DF relaying is identified. View full abstract»

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Aims & Scope

IEEE Wireless Communications Letters publishes shorter, high-quality manuscripts on advances in the state-of-the-art of wireless communications.

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Meet Our Editors

Editor-in-Chief
DONG IN KIM
Sungkyunkwan University (SKKU)