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Communications Letters, IEEE

Issue 12 • Date December 2012

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Displaying Results 1 - 25 of 52
  • Table of contents

    Page(s): c1 - c5
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  • Staff List

    Page(s): c2
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  • A Reduced Overhead OFDM Relay System with Clusterwise TMRC Beamforming

    Page(s): 1913 - 1916
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (154 KB) |  | HTML iconHTML  

    We consider a relay clustering system using decode and forward (DF) relaying, orthogonal frequency division multiplexing (OFDM), and transmit maximal ratio combining beamforming (TMRC-BF) at the relays. We address channel estimation at the destination for the above system. A cluster pairing scheme with corresponding pilot designs is proposed. It reduces both necessary pilot overhead and computational complexity by half. Simulation results show that if the signal to noise ratio (SNR) of pilots for channel estimation for TMRC-BF at the relays is kept above a threshold (5 dB below the SNR of the pilots sent to the destination by the cluster pairing strategy), nearly optimal channel estimation performance can be achieved. View full abstract»

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  • Novel Blind Encoder Parameter Estimation for Turbo Codes

    Page(s): 1917 - 1920
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    A novel blind parameter-estimation method, which identifies a turbo encoder, is proposed in this paper. The blind estimator is designed using an iterative expectation-maximization (EM) algorithm. To facilitate this innovative blind estimation scheme, we transform the recursive systematic convolutional (RSC) encoder into a non-systematic convolutional encoder preceded by a feedback encoder. The effect of the separate feedback encoder on the state sequence of the forward convolutional encoder will be studied. Besides, the effectiveness of our proposed new scheme will be evaluated by Monte Carlo simulations. View full abstract»

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  • On ARQ-Based Fast-Fading Channels

    Page(s): 1921 - 1924
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (131 KB) |  | HTML iconHTML  

    Automatic repeat request (ARQ) protocols are normally studied under slow-fading or quasi-static channel assumption where the fading coefficients are assumed to remain fixed during the transmission of a codeword or for the duration of all ARQ retransmission rounds, respectively. This letter investigates the performance of basic ARQ and incremental redundancy hybrid ARQ protocols in fast-fading channels where a number of channel realizations are experienced in each retransmission round. Long-term throughput, delay-limited throughput and outage probability of the ARQ schemes are obtained. Compared to slow-fading and quasi-static channels, a fast-fading channel results in a higher performance for both basic and incremental redundancy ARQ. The fast-fading channel, however, can be mapped to an equivalent slow-fading model at low signal-to-noise ratios. Finally, we show that the efficiency of ARQ protocols is overestimated if the fast-fading variations during a codeword transmission are approximated by their average value. View full abstract»

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  • On Correlated Generalized Rician Fading Based on Gaussian Class Multivariate Distributions with Generalized Correlation

    Page(s): 1925 - 1928
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB) |  | HTML iconHTML  

    Gaussian class multivariate distributions with single integral representations were recently proposed to obtain correlated fading channels with generalized correlation. In this letter, we focus on correlated generalized Rician fading channels, derived from Gaussian class multivariate distributions. We present a comprehensive investigation on the statistical properties of correlated generalized Rician fading channels. Specifically, closed-form expressions for joint probability density function (PDF), marginal PDF, power correlation, joint moment, and joint characteristic function are elaborated. These statistical characterizations help us have a better understanding of the correlated generalized Rician channels and allow for some new applications in performance analysis of diversity schemes and, particularly, maximal ratio combining over correlated fading channels with generalized correlation. View full abstract»

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  • Channel Shortening for Nonlinear Satellite Channels

    Page(s): 1929 - 1932
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (151 KB) |  | HTML iconHTML  

    We design of an efficient channel shortener for nonlinear satellite channels. When the memory of the channel is too large to be taken into account by a full complexity detector, excellent performance can be achieved by properly filtering the received signal followed by a reduced-state detector. This letter derives closed-form expressions for the front-end filter and the target response of the reduced-state detector. View full abstract»

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  • A Novel Association Control Strategy for Supporting Multiple Multicast Sessions in WLANs

    Page(s): 1933 - 1936
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    Multicast is an important service relied upon by many applications in Wireless Local Area Networks (WLANs), which unfortunately is limited by the subscribing station with the lowest data rate. A key approach to address this problem is to employ an association control strategy to ensure stations are organized in a manner that optimizes a given objective. To this end, this paper studies the NP-hard, Multiple Multicast Sessions (MMS) problem. It proposes a novel greedy algorithm that aims to minimize the average APs load. Simulation results show that our algorithm reduces the average APs load by up to 70.4% as compared to prior approaches. View full abstract»

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  • A Precoding Scheme for N-Continuous OFDM

    Page(s): 1937 - 1940
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (185 KB) |  | HTML iconHTML  

    In this letter, we present a novel, with-memory precoding scheme for N-continuous OFDM, which is based on the decomposition of a relevant matrix into its null space and orthogonal complement subspace. The transmitted data can be fully recovered by the proposed scheme, while the out-of-band emission performance is retained as other N-continuous OFDM signals. The data rate loss is reduced to half compared to the memory-less scheme. Bit-error-rate performance can be improved by exploiting the redundant information in the subsequent OFDM symbol. View full abstract»

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  • On Gaussian Interference Channels with Constellation-Based Transmitters

    Page(s): 1941 - 1943
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (209 KB) |  | HTML iconHTML  

    In this letter, we study a two-user Gaussian Interference Channel (GIC) with constellation-based transmitters where both transmitters utilize PSK signaling and both receivers treat interference as noise. It is verified that if one user rotates its constellation appropriately compared to the constellation of the other user, the achievable sum-rate in the network considerably increases. Due to the fact that the noise plus interference at each receiver is mixed-Gaussian, there is no closed formula for the sum-rate. Using Fano's inequality, a lower bound is developed on the sum-rate in the network. The lower bound is tight in the sense that it identifies the optimal value for the angle of rotation. Moreover, it is demonstrated that the proposed lower bound can be larger than the exact value of sum-rate achieved by random Gaussian codes or Time-Division-Multiplexing (TDM). View full abstract»

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  • Social Optimization Strategy in Unobserved Queueing Systems in Cognitive Radio Networks

    Page(s): 1944 - 1947
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    We study a noncooperative game problem for queueing control in the Cognitive Radio (CR) system where selfish Secondary User's (SU) data packets (a.k.a. "customers" in this work) are served by a CR base station (a.k.a. "server"). The scenario is modeled as an M/M/1 queueing game with server breakdowns where each customer wants to optimize their benefit in a selfish distributed manner. We first show that the game has an inefficient unique Nash Equilibrium (NE). In order to improve the outcome efficiency, we propose an appropriate admission fee that can be easily implemented at the server. We then show that the social welfare at the equilibrium point can be coincided the social welfare of the socially optimal strategy. View full abstract»

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  • Joint Optimal Sensing Time and Power Allocation for Amplify-and-Forward Cognitive Relay Networks

    Page(s): 1948 - 1951
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB) |  | HTML iconHTML  

    In this letter, we investigate the joint optimization of sensing time and power allocation for amplify-and-forward cognitive relay networks. By jointly considering the sensing slot and the data transmission slot, the optimization problems are respectively formulated to maximize the average network throughput and minimize the approximate outage probability of secondary transmission under the average transmit power constraint of secondary users and the average interference power constraint of primary user. The optimal algorithms are developed to acquire the optimal sensing time and power allocation. Simulation results demonstrate that significant improvements in the average throughput and outage behavior are achieved through the joint optimization. View full abstract»

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  • Green Communications with Network Cooperation: A Concurrent Transmission Approach

    Page(s): 1952 - 1955
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (665 KB) |  | HTML iconHTML  

    This letter investigates the benefits of concurrent transmission from the perspective of green communications. A concurrent transmission scheme under the metric of bit-per-joule, modeled as a constrained optimization problem, is proposed to split traffic flow among multiple networks. The threshold of the traffic splitting starting point and the optimal rate allocation of each flow are derived to maximize the system energy efficiency. The results demonstrate that our scheme can save significant power and improve the energy efficiency. View full abstract»

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  • Optimum Periodic Spectrum Sensing for CR Networks

    Page(s): 1 - 4
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (133 KB) |  | HTML iconHTML  

    In this article, we investigate joint sensing block length and detection threshold optimization to maximize the throughput of a cognitive radio (CR) network with limited interference to the primary user (PU). The CR network operates on a frame-by-frame basis, where the status of the PU can change at any time within one frame. Through theoretical analysis, optimal solution is derived, which is helpful to system design. Numerical results show that higher throughput can be obtained by considering the PU status change than the case without considering it. View full abstract»

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  • Modeling the Message Count of the Trickle Algorithm in a Steady-State, Static Wireless Sensor Network

    Page(s): 1960 - 1963
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (150 KB) |  | HTML iconHTML  

    Trickle is a transmission scheduling algorithm developed for wireless sensor networks. The Trickle algorithm determines whether (and when) a message can be transmitted. Therefore, Trickle operation is critical for performance parameters such as energy consumption and available bandwidth. This letter presents an analytical model for the message count of a static Trickle-based network under steady state conditions, as a function of a parameter called the redundancy constant and the average node degree. The model presented is validated by simulation results. View full abstract»

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  • Probabilistic Limited Feedback Precoding in MIMO Interference Channels

    Page(s): 1964 - 1967
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (130 KB) |  | HTML iconHTML  

    In this letter, we consider a probabilistic limited feedback precoding in MIMO interference channels. The probabilistic use of precoders in the codebook is modeled as a mixed strategy in a nonzero-sum game. The sum rate of mixed strategy Nash equilibrium (NE) and the maximum achievable sum rate of the probabilistic limited feedback precoding are derived in a two-user MIMO interference channel. For a distributed realization of probabilistic limited feedback precoding, we also propose a distributed limited feedback precoding scheme for use in K-user MIMO interference channels. View full abstract»

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  • Minimization of Transmission Duration of Data Packets over an Energy Harvesting Fading Channel

    Page(s): 1968 - 1971
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB) |  | HTML iconHTML  

    The offline problem of transmission completion time minimization for an energy harvesting transmitter under fading is extended to allow packet arrivals during transmission. A method for computing an optimal power and rate allocation (i.e., an optimal offline schedule) is developed and studied. View full abstract»

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  • Transmission Policies for Improving Physical Layer Secrecy Throughput in Wireless Networks

    Page(s): 1972 - 1975
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (134 KB) |  | HTML iconHTML  

    In this letter, we analyze the physical layer secrecy throughput in wireless fading networks with independent eavesdroppers that do not collude. We study the impacts of the total number of eavesdroppers on the secrecy throughput. In addition, we propose two channel-adaptive transmission policies for improving the secrecy throughput. The proposed transmission policies have low computational complexity and therefore are feasible in practice. We use analytical results and simulation results to justify the usage of the proposed schemes. View full abstract»

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  • Femtocell Operator Entry Decision with Spectrum Bargaining and Service Competition

    Page(s): 1976 - 1979
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (163 KB) |  | HTML iconHTML  

    This paper analyzes the effect of the entry of a femtocell operator into a mobile communications market where a macrocell operator exists. The analysis is conducted using a game-theory-based model, specifically a three-level multi leader-follower game, where different solution concepts are applied: Shapley value, Nash equilibrium and Wardrop equilibrium. It aims to answer the question of which benefit mobile communication users get from the entry of a femtocell operator into the market. The equilibrium is assessed from the point of view of each agent (e.g. profits and utilities), and of the whole (e.g. social welfare). A case for regulatory intervention is made. View full abstract»

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  • Performance Analysis of a Path Selection Scheme in Multi-Hop Decode-and-Forward Protocol

    Page(s): 1980 - 1983
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB) |  | HTML iconHTML  

    In this letter, we find cumulative distribution function (CDF) and probability density function (PDF) of the generalized max-min Exponential random variable (RV) in terms of converging power series. By using the PDF of this RV, the average bit error rate (BER) of the max-min criterion based best path selection scheme in multi-hop decode-and-forward (DF) cooperative communication system over Rayleigh fading channels is analyzed. It is demonstrated by the analysis and simulation that max-min criterion based path selection works very well in the multi-hop DF cooperative system. View full abstract»

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  • Proportional Fair Scheduling Gains for AMC-Aware Systems under Heterogeneous Radio Conditions

    Page(s): 1984 - 1987
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (230 KB) |  | HTML iconHTML  

    This letter provides exact analytical expressions and simpler, but still very effective, approximations for the multiuser diversity gains associated with Proportional Fair (PF) opportunistic scheduling. The impact of Adaptive Modulation & Coding (AMC) and of heterogeneous user populations with different radio conditions on the downlink are taken into account. The analysis is applicable to all major fading models and is based on the notion of the scheduling gain, a quantity that captures throughput and fairness aspects relevant to a user served under a considered scheduling policy as part of a heterogeneous group of users. Exploitation of relevant characteristics in the AMC rate function gives rise to two distinct regimes, corresponding to "regular" and "very high" average SNR conditions. All users in each of these regimes have approximately equal PF scheduling gains. View full abstract»

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  • Adaptive Adjacent-Frequency Interference Mitigation in Multi-Hop Point-To-Point FDD Wireless Backhaul Networks

    Page(s): 1988 - 1991
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (289 KB) |  | HTML iconHTML  

    Adjacent-frequency interference is a critical problem in point-to-point (PTP) frequency division duplex (FDD) wireless backhaul networks. It prevents existing methods from adaptively allocating frequencies to the PTP links, reducing spectrum utilization. We propose a new algorithm which mitigates the interference and enables the frequencies to be allocated adapting to changing traffic demands. Our algorithm is developed on a new recursive guard band adjusting technique. Simulations show that our algorithm is able to improve spectrum utilization by 33%, compared to the prior art, and enhance the network satisfaction regarding allocated bandwidth by over 173%. View full abstract»

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  • Iterative Compressive Estimation and Decoding for Network-Channel-Coded Two-Way Relay Sparse ISI Channels

    Page(s): 1992 - 1995
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (166 KB) |  | HTML iconHTML  

    We propose an iterative compressive channel estimation and decoding scheme for network-channel-coded two-way relay sparse intersymbol interference channels. The underlying system model comprises two source nodes and one relay node. In the first time slot, the two sources simultaneously transmit their independent training pilots along with the channel-coded data. In the second time slot, the relay applies analog network coding to the sum of the received signals and broadcasts the result to the two sources. Each source then uses iterative compressive sensing (CS) based estimation and decoding to estimate the composite channels and recover the transmitted signal. We analyze the performance of our proposed CS-based scheme and demonstrate its efficacy over existing ones. View full abstract»

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  • On the Combining of Correlated Random Measures with Application to Graph-Based Receivers

    Page(s): 1996 - 1999
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (150 KB) |  | HTML iconHTML  

    Nowadays, message combining is an essential component in most digital communication systems. Correlation between random measures has a significant impact on the combining process. In order to provide the best estimate after combining, correlation must be considered. In many applications correlation is obvious, e.g. correlation in the time, frequency, and/or spatial domain of a radio channel. In other cases, correlation is more concealed. In this paper, two methods to combine correlated random values are presented and applied to a graph-based iterative receiver. It is explained, why correlation in the message exchange arises and how it can be taken into account in the message combining step. Simulation results are provided showing the performance gains when correlation is considered. View full abstract»

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  • Dynamic Cooperative Retransmission Scheme for TDMA Systems

    Page(s): 2000 - 2003
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB) |  | HTML iconHTML  

    In this letter, we propose and analyze a dynamic cooperative retransmission scheme for TDMA systems in multi-hop networks. Our scheme cooperatively retransmits a failed packet during a neighbor node's idle slot, which is selected using a simple mechanism. If an idle slot is not available, cooperative retransmission is attempted during the source node's time slot. The throughput of TDMA can be significantly improved by cooperative retransmission. We formulate an analytical model for the proposed scheme that can be implemented over Rayleigh fading channels. The results showed that the throughput of TDMA systems was improved significantly if a sufficient number of idle slots were available for cooperative retransmission, although an overhead was introduced. View full abstract»

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Aristotle University of Thessaloniki
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