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Communications Letters, IEEE

Issue 11 • Date November 2012

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Displaying Results 1 - 25 of 52
  • Table of contents

    Page(s): c1 - c5
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    Freely Available from IEEE
  • Staff List

    Page(s): c2
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  • A Projected Parallel Interference Cancellation for Asynchronous Upstream OCDMA-PON

    Page(s): 1721 - 1724
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (183 KB) |  | HTML iconHTML  

    OCDMA is a promising candidate for next generation passive optical networks (NG-PON). OCDMA-PON can potentially provide all customers with a Gb/s-class BW upstream with inherent flexibility. Unfortunately OCDMA suffers from multiple access interference (MAI) and various detection noises. To mitigate MAI, we propose a novel parallel interference cancellation technique for incoherent DS-OCDMA that better exploits the non-negativity of the solution. The proposed PIC scheme incorporates this additional information into its structure. The proposed PIC detector is shown to outperform the conventional correlator detector, the decorrelator detector, the linear parallel interference Cancellation (LPIC) detector and even the linear minimum mean square error (LMMSE) detector. View full abstract»

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  • Unambiguous S-Curve Shaping Technique for Multipath Mitigation in Cosine-BOC Signals

    Page(s): 1725 - 1728
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB) |  | HTML iconHTML  

    This letter proposes a new multipath mitigation technique based on the concept of S-curve shaping for the new cosine phased binary offset carrier (cosine-BOC) modulated signals, which will most likely be used in both European Galileo system and Chinese Compass system. The definition of an optimum S-curve is employed to reduce the false lock points and to improve the multipath mitigation capability via determining the weights of the local linear combined code. The structure of the code tracking loop for cosine-BOC signals is quite simple and only requires one correlator. Results demonstrate that the proposed technique provides superior multipath mitigation performance and removes the ambiguity completely. View full abstract»

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  • Multi-Input Multi-Output Deletion Channel

    Page(s): 1729 - 1732
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (219 KB) |  | HTML iconHTML  

    We describe a new channel model suitable in certain applications, namely the multi-input multi-output (MIMO) deletion channel. This channel models the scenarios where multiple transmitters and receivers suffering from synchronization errors are employed. We then consider a coding scheme over such channels based on a serial concatenation of a low-density parity check (LDPC) code, a marker code and a layered space-time code. We design two detectors operating at the bit level which jointly achieve synchronization for the deletion channel (with the help of the marker code) and detection for the MIMO channel. Utilizing the proposed detector together with an LDPC code with powerful error-correction capabilities, we demonstrate that reliable transmission over a MIMO deletion channel is feasible. View full abstract»

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  • On the Transfer of Information and Energy in Multi-User Systems

    Page(s): 1733 - 1736
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (161 KB) |  | HTML iconHTML  

    The problem of joint transfer of information and energy for wireless links has been recently investigated in light of emerging applications such as RFID and body area networks. Specifically, recent work has shown that the additional requirements of providing sufficient energy to the receiver significantly affects the design of the optimal communication strategy. In contrast to most previous works, this letter focuses on baseline multi-user systems, namely multiple access and multi-hop channels, and demonstrates that energy transfer constraints call for additional coordination among distributed nodes of a wireless network. The analysis is carried out using information-theoretic tools, and specific examples are worked out to illustrate the main conclusions. View full abstract»

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  • Unambiguous Tracking Method for Alternative Binary Offset Carrier Modulated Signals Based on Dual Estimate Loop

    Page(s): 1737 - 1740
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (650 KB) |  | HTML iconHTML  

    We propose an unambiguous tracking method for Alternative Binary Offset Carrier (AltBOC) modulated signals based on the Dual Estimate Tracking (DET) loops. The proposed method employs a combined PRN code and a pure cosine signal which can be easily implemented in the hardware to make DET loops available to the complicated AltBOC signal structure. The two dimensional correlation function for AltBOC is derived, and an unambiguous delay estimate is deduced according to the correlation function. Simulation results reveal that the proposed method performed better in tracking performance than the traditional unambiguous tracking methods. View full abstract»

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  • Parallel Data Broadcasting for Optimal Client Service Ratio

    Page(s): 1741 - 1743
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB) |  | HTML iconHTML  

    This letter introduces service ratio-based optimization in multichannel data broadcast systems. The classic pursuit of data broadcast scheduling has revolved around QoS metrics, such as the minimization of the mean serving time or jitter. Recent studies in single channel systems have shown that this approach reduces the client service ratio, essentially forcing clients to abandon the system. Content discarding in single channel systems was then proven to maximize the service ratio. The present work introduces a novel algorithm for service-ratio-oriented assignment of data to multiple channels with different bandwidths. Comparison to related approaches demonstrates the superior scalability of the proposed algorithm. View full abstract»

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  • A Novel Group-Based Handover Authentication Scheme with Privacy Preservation for Mobile WiMAX Networks

    Page(s): 1744 - 1747
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    This letter proposes an efficient group-based handover authentication scheme for mobile WiMAX networks. When the first Mobile Station (MS) of the handover group moves from the service Base Station (BS) to a target BS, the service BS transmits all the handover group members security context to the target BS. Thus the rest of the MSs in the same handover group can bypass the Extensible Authentication Protocol (EAP) and the security context transfer phases to directly perform the handover authentication, which obviously reduces handover latency. Moreover, the proposed scheme not only meets the essential security requirements in handover authentication semantics (such as mutual authentication and resisting the domino effect) but also achieves privacy preservation. View full abstract»

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  • MSE Duality for Multi-User MIMO Relay System

    Page(s): 1748 - 1751
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (287 KB) |  | HTML iconHTML  

    This paper shows how uplink (UL)-downlink (DL) mean square error (MSE) duality holds in a single relay aided multi-user multiple-input multiple-output (MU-MIMO) system. Specifically, it is shown that the MSE duality holds for three levels of MSE which are sum-MSE (SMSE), per user MSE, and per stream MSE. For each case of duality level, we consider both total power constraint and separate power constraint. We also provide a conversion method which transforms a given transceiver and scale factor in DL to equivalent ones in UL for each case of duality level and each case of power constraint. View full abstract»

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  • Performance Analysis of an Opportunistic Relay Selection Protocol for Multi-Hop Networks

    Page(s): 1752 - 1755
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (214 KB) |  | HTML iconHTML  

    We analyze the performance of an interference-aware opportunistic relay selection protocol for multi-hop line networks which is based on the following simple rule: a node always transmits if it has a packet, except when its successive node on the line is transmitting. We derive analytically the saturation throughput and the end-to-end delay for two and three hop networks, and present simulation results for higher numbers of hops. In the case of three hops, we determine the throughput-optimal relay positions. View full abstract»

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  • Exact Outage Analysis of Dual-Hop Fixed-Gain AF Relaying with CCI under Dissimilar Nakagami-m Fading

    Page(s): 1756 - 1759
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (139 KB) |  | HTML iconHTML  

    This letter studies the outage probability of fixed-gain amplify-and-forward dual-hop relaying system in the presence of co-channel interference (CCI). Assuming that the relay and the destination terminals are subject to both CCI and additive white noise, and the envelopes of the channels follow dissimilar Nakagami-m distributions, an exact expression for the outage probability of the system is derived. The result is applicable for arbitrary numbers of interfering signals at receiving terminals and can be efficiently evaluated. In addition, it enables us to study the effect of CCI at either the relay or the destination as special cases. The analytical results are validated by simulations. The simulated results show that the outage performance of the system is less sensitive to the interference at the destination. View full abstract»

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  • New Simple Approximations for Error Probability and Outage in Fading

    Page(s): 1760 - 1763
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (154 KB) |  | HTML iconHTML  

    A new class of approximations for the bit error rate (BER), the symbol error rate (SER), and the outage of wireless digital communication systems impaired by fading and noise is derived. As compared to conventional high signal-to-noise ratio (SNR) approximations [1], these new approximations are better by an order of magnitude in the high SNR regime and retain their accuracy for a wider range of SNRs. They require the first two terms of the Taylor expansion of the channel probability density function (PDF). The resulting approximations for two diversity combiners, multiple-antenna eigenmode transmission and several important modulation schemes are developed. View full abstract»

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  • The Effect of Macrodiversity on the Performance of MLD in Flat Rayleigh/Rician Fading

    Page(s): 1764 - 1767
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (135 KB) |  | HTML iconHTML  

    In this letter, we consider the effect of macrodiversity on the performance of maximum likelihood detection in flat Rayleigh/Rician fading. Macrodiversity MIMO, where both the transmit antennas and receive antennas are widely separated, is becoming increasingly important with the advent of network MIMO, edge excited cells, base station cooperation, etc. The analysis builds on an exact evaluation of the pairwise error probability which leads to a union bound for symbol error rate (SER). SER results are shown, as well as a diversity analysis and an investigation of the impact of macrodiversity. View full abstract»

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  • Practical, Highly Efficient Algorithm for Generating κ-μ and η-μ Variates and a Near-100% Efficient Algorithm for Generating α-μ Variates

    Page(s): 1768 - 1771
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (218 KB) |  | HTML iconHTML  

    In this letter, we propose a simple and highly efficient random sequence generator for κ -μ and η -μ variates and a near-100% efficient algorithm for generating α -μ variates. The proposed algorithm may yield an efficiency higher than 80% for η -μ , 87.5% for κ -μ and almost 100% for α -μ . These generators are implemented via the rejection technique and allow for arbitrary fading parameters. The goodness-of-fit is objectively measured using the the p-value of the Kolmogorov-Smirnov test. View full abstract»

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  • RF Energy Transfer for Cooperative Networks: Data Relaying or Energy Harvesting?

    Page(s): 1772 - 1775
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (177 KB) |  | HTML iconHTML  

    This letter deals with a three-node cooperative network where the relay node harvests energy from radio frequency (RF) radiation. The source node is the only available RF generator and introduces a fundamental switching between energy harvesting and data relaying. A greedy switching (GS) policy where the relay node transmits when its residual energy ensures decoding at the destination is investigated. The GS policy is modeled as a Markov chain for a discretized battery; the stationary distribution and the outage probability of the system are derived in closed form expressions. In addition, an optimal switching policy that incorporates a-priori knowledge of the channel coefficients is proposed and solved by a mixed-integer linear programming formulation. View full abstract»

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  • The Ratio of Independent Arbitrary α-μ Random Variables and its Application in the Capacity Analysis of Spectrum Sharing Systems

    Page(s): 1776 - 1779
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    General, simple, exact, closed-form expressions for the ratio of independent non-identically distributed α-μ random variables are derived. These important results find applicability in several performance analysis of wireless communication systems, in particular those for which the ratio of signal powers is of relevance. One such application, currently of enormous interest, is the capacity analysis of spectrum sharing networks. Motivated by this, a comprehensive capacity study of spectrum sharing systems undergoing α-μ fading is performed, followed by insightful discussions. View full abstract»

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  • A Probabilistic Model of Spectrum Availability for OFDMA Based Cognitive Radio Systems

    Page(s): 1780 - 1783
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (141 KB) |  | HTML iconHTML  

    In this paper, the demands made by a set of spatially Poisson point distributed primary users on available channels in their proximity is considered and their effect on channel availability for secondary users under various channel requesting distributions is assessed. It is shown that for some "greedy" systems, providing more subcarriers will not increase the spectrum availability for a secondary network. The sustainable traffic of the system subject to a fixed spectrum outage probability is also investigated. It is shown that for a fixed spectrum outage probability, as long as the system is "greedy", providing more subcarriers does not help to support more primary users to successfully avoid spectrum outage. View full abstract»

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  • Rate Allocation for Transmission of Two Gaussian Sources over Multiple Access Fading Channels

    Page(s): 1784 - 1787
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (125 KB) |  | HTML iconHTML  

    We perform optimal rate allocation of two independent Gaussian sources on a two-user multiple access Rayleigh fading channel by minimizing the sum distortion at the common receiver. We first consider the case of fast fading, where we use the ergodic capacity region, and analytically solve for the optimal pair of rates. We then address the case of slow fading, where we determine the optimal pair of rates that minimizes the sum distortion, using outage probabilities. Results show that the sum distortion for slow fading is larger than for fast fading and that the use of individual outage probabilities outperforms the use of common outage probability. The higher variance source requires higher rates in both fast and slow fading. View full abstract»

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  • Seamless Handover for LTE Macro-Femto Networks Based on Reactive Data Bicasting

    Page(s): 1788 - 1791
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (149 KB) |  | HTML iconHTML  

    Seamless mobility support is a key technical requirement to motivate the market acceptance of the femtocells. The current 3GPP handover procedure may cause large downlink service interruption time when users move from a macrocell to a femtocell or vice versa due to the data forwarding operation. In this letter, a practical scheme is proposed to enable seamless handover by reactively bicasting the data to both the source cell and the target cell after the handover is actually initiated. Numerical results show that the proposed scheme can significantly reduce the downlink service interruption time while still avoiding the packet loss with only limited extra resource requirements compared to the standard 3GPP scheme. View full abstract»

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  • Effective Capacity of Cognitive Radio Systems with GSC Diversity under Imperfect Channel Knowledge

    Page(s): 1792 - 1795
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB) |  | HTML iconHTML  

    In this paper, we investigate the effective capacity of opportunistic spectrum sharing with generalized selection combining (GSC) diversity at the secondary receiver in fading environments. In particular, we study the impact of outdated channel information between the secondary transmitter and the primary receiver on the performance of the secondary user. An exact closed-form expression for the effective capacity of the secondary user with GSC diversity is derived under the peak interference constraint at the primary receiver. Comparisons done using simulations show the effect of the uncertainty of channel information on the effective capacity. Specially, the performance gap due to imperfect channel information becomes smaller with the increase of the number of selected antennas {k}. Theoretic analysis and simulations show that the system performance is robust against imperfect channel information and selection combining (SC) should be adopted under strict delay quality of service (QoS) requirements. View full abstract»

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  • DOD and DOA Estimation in Bistatic Non-Uniform Multiple-Input Multiple-Output Radar Systems

    Page(s): 1796 - 1799
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (138 KB) |  | HTML iconHTML  

    This letter investigates the joint estimation of the direction of departure (DOD) and direction of arrival (DOA) for multi-input multi-output (MIMO) radar systems. A novel estimation method based on non-uniform array configuration is proposed and the practical identifiability of the corresponding parameter is analyzed. The key idea is to use the Doppler diversity to construct a virtual MIMO array. Through the theoretical proof, we demonstrate that the proposed method can provide much stronger parameter identifiability than the conventional ones, and also can improve the parameter estimation performance. Numerical simulations verify the effectiveness of the proposed algorithm. View full abstract»

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  • Power Controlled Reverse Channel Training Achieves an Infinite Diversity Order in a TDD-SIMO System with Perfect CSIR

    Page(s): 1800 - 1803
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB) |  | HTML iconHTML  

    In this letter, we analyze the Diversity Multiplexing-gain Tradeoff (DMT) performance of a training-based reciprocal Single Input Multiple Output (SIMO) system. Assuming Channel State Information (CSI) is available at the Receiver (CSIR), we propose a channel-dependent power-controlled Reverse Channel Training (RCT) scheme that enables the transmitter to directly estimate the power control parameter to be used for the forward-link data transmission. We show that, with an RCT power of P̅γ, γ >; 0 and a forward data transmission power of P̅, our proposed scheme achieves an infinite diversity order for 0 ≤ gm <; Lc - LB,τ/Lc min(γ,1) and r >; 2, where gm is the multiplexing gain, Lc is the channel coherence time, LB,τ is the RCT duration and r is the number of receive antennas. We also derive an upper bound on the outage probability and show that it goes to zero asymptotically as exp (-P̅E), where E =Δ (γ-gmLc/Lc -LB,τ), at high P̅. Thus, the proposed scheme achieves a significantly better DMT performance compared to the finite diversity order achieved by channel-agnostic, fixed-power RCT schemes. View full abstract»

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  • Implementation-Oriented Model for Centralized Data-Fusion Cooperative Spectrum Sensing

    Page(s): 1804 - 1807
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (282 KB) |  | HTML iconHTML  

    We propose a new model for a cognitive radio in the scenario of centralized data-fusion cooperative spectrum sensing. The model is grounded on a direct-conversion receiver architecture and was applied to four detection methods: the eigenvalue-based generalized likelihood ratio test, the maximum-minimum eigenvalue detection, the maximum eigenvalue detection and the energy detection. It is shown that the sensing performance under the conventional model typically adopted in the above scenario is overestimated when compared with the proposed one, which suggests that our model better suits for the spectrum sensing design and its performance assessment. View full abstract»

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  • Achieving Maximum Weighted Sum-Rate in Multicell Downlink MISO Systems

    Page(s): 1808 - 1811
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (246 KB) |  | HTML iconHTML  

    This paper considers the maximization of the weighted sum-rate (WSR) in multicell downlink multiple-input single-output (MISO) systems. The problem is non-convex and thus cannot be solved directly via conventional convex optimization methods. To achieve global optimality, we propose a novel monotonic optimization approach where a sensible search scheme first checks the feasibility of a chosen point and then utilizes a sequential partition method at each iteration to reduce the total number of feasibility evaluations. Besides, another relocating procedure also accelerates the convergence. Simulation results verify the improved convergence performance of the proposed approach compared with the previously proposed outer polyblock approximation algorithm and the branch-reduce-and-bound algorithm. View full abstract»

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Aristotle University of Thessaloniki
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