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Communications Letters, IEEE

Issue 6 • Date June 2011

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Displaying Results 1 - 25 of 35
  • Table of contents

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

    Page(s): c2
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    Freely Available from IEEE
  • Compact Pulse Shaping for Efficient PAM/QAM Signaling

    Page(s): 593 - 595
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (267 KB) |  | HTML iconHTML  

    Compact pulse shaping (CPS) is considered with PAM/QAM signals to improve the performance/bandwidth tradeoff. CPS signals are constructed by targeting a finite impulse response of a pulse shaping filter as opposed to the traditional method of targeting a finite frequency response. CPS QAM signals can be optimally decoded using Viterbi decoding on I and Q channels independently. In the case of non-rectangular constellations, a simple adjustment is presented to correct any invalid QAM symbols that result from independent I and Q decoding. Minimum distance calculations indicate that CPS QAM provides between 2.04 and 5.4 dB of gain, depending on constellation size, over raised cosine filtering, when compared at a given value of the normalized bit bandwidth B99Tb. View full abstract»

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  • Fixed Point Optimization Algorithms for Network Bandwidth Allocation Problems with Compoundable Constraints

    Page(s): 596 - 598
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (251 KB) |  | HTML iconHTML  

    In this letter, we develop a novel computational approach for network bandwidth allocation problems in which the compoundable constraints about the preferable transmission rate fall in the infeasible region. The approach is based on an iterative technique for non-convex optimization over the fixed point set of a certain nonexpansive mapping. The realized allocation maximizes a predefined utility and is closest to the preferable transmission rate with respect to the norm. Numerical examples show that our approach is an efficient way to solve the non-concave utility maximization problem. View full abstract»

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  • Simplified MAP-MUD for Active User CDMA

    Page(s): 599 - 601
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (191 KB) |  | HTML iconHTML  

    In CDMA systems with variable number of users, the decoder consists of two stages. The first stage is the active user identification and the second one is the multi-user detection. Most of the proposed active user identification methods fail to work in overloaded CDMA systems (when the number of users is more than the spreading factor). In this paper we propose a joint active user identification and multi-user detection for binary input CDMA systems using the Viterbi algorithm. We will show that the proposed identification/detection method is Maximum A posteriori Probability (MAP) and outperforms the pervious results. In addition, some suboptimum decoders will be proposed that have lower computational complexities but lower performances. View full abstract»

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  • Adaptive Spatial Modulation for Wireless MIMO Transmission Systems

    Page(s): 602 - 604
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (361 KB) |  | HTML iconHTML  

    In this letter, an adaptive spatial modulation (ASM) transmission scheme is proposed to achieve better system performance under a fixed data rate. The proposed scheme is based on a developed modulation order selection criterion (MOSC), so as to minimize the conditioned pairwise error probability (PEP) for each channel realization. Furthermore, the special information-conveying mode of spatial modulation (SM) is utilized to reduce the complexity of the proposed algorithm. Simulation results show that the proposed adaptive SM scheme provides considerable system performance improvement compared to original SM system. View full abstract»

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  • Position Location in Ad-Hoc/Sensor Networks: A Linear Constrained Search

    Page(s): 605 - 607
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (266 KB) |  | HTML iconHTML  

    Position Location Information (PLI) is an enabler for a wide range of location based services. However, in ad hoc/sensor networks, PLI acquisition is difficult since conventional triangulation algorithms cannot be applied due to the lack of direct land fixed references. In this paper, a PLI acquisition algorithm suitable for multi-hop scenarios is formulated as a linear constrained search problem in a discretized space. Suitability is examined through analytic and simulation processes. View full abstract»

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  • Outage Probability of Two-Hop Fixed-Gain Relay with Interference at the Relay and Destination

    Page(s): 608 - 610
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    In this letter, we investigate the outage performance of a two-hop fixed-gain relay system in the presence of multiple unequal-power Rayleigh interference at both relay and destination. The closed-form expression for the outage probability is derived. We also show that the equal-power interference at the relay and destination leads to the worst outage performance. View full abstract»

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  • Low Complexity Data Decoding for SLM-Based OFDM Systems without Side Information

    Page(s): 611 - 613
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (513 KB) |  | HTML iconHTML  

    Selected mapping (SLM) scheme is a well-known technique for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. To recover data at receiver, the SLM scheme requires transmission of the selected phase sequence index, e.g., side information (SI). In this letter, a new pilot phase sequence enabling data recovery without SI and a low complexity decoding scheme are proposed. The BER performance of the proposed scheme is approximately the same in comparison with the SLM scheme with SI and considerably better than that of the Maximum Likelihood (ML) decoding scheme. In addition, the computational complexity of the proposed decoding scheme is much lower, as compared to the ML decoding scheme. View full abstract»

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  • Robust Weighted Non-Coherent Receiver for Impulse Radio UWB PPM Signals

    Page(s): 614 - 616
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    This letter proposes an energy detection based robust weight estimation scheme for pulse-position modulated (PPM) impulse radio ultra-wideband (IR-UWB) signals using weighted non-coherent receiver (WNCR). Conventional data-aided WNCR (DA-WNCR) scheme estimates the weighting coefficients, or channel state information (CSI), using a large number of training symbols over time-varying channels. In contrast, the proposed Robust WNCR (R-WNCR) scheme is non-data-aided (NDA), adaptive and robust to channel variations. The proposed R-WNCR estimates the weighting coefficients adaptively based on the received stochastic data, and the weight estimation process is refined using a decision directed approach. View full abstract»

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  • New Results on the Statistics and the Capacity of Dual-Branch MRC and EGC Diversity in Correlated Lognormal Channels

    Page(s): 617 - 619
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (245 KB) |  | HTML iconHTML  

    This letter addresses the performance analysis of dual diversity reception systems in correlated lognormal fading channels with not-necessarily-identical parameters. More specifically, novel results on the probability density function (PDF) and the ergodic capacity of dual-branch maximal ratio combining (MRC) and equal gain combining (EGC) diversity receivers are presented. The proposed expressions find application in cost-sensitive diversity receiver implementations and handover designs. View full abstract»

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  • Energy Efficient Wireless Multicasting

    Page(s): 620 - 622
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    This letter proposes an energy-efficient wireless multicasting scheme in which the base station (BS) and the mobile users cooperate to reduce the total power consumption in wireless multicasting. Minimizing the power consumption under the scheme is an NP-hard problem. The gradient guided approximation algorithm is thus proposed to achieve low computational complexity. The proposed energy-efficient wireless multicasting scheme consumes less energy than other multicasting schemes without cooperation. The energy savings are validated through well designed simulations. View full abstract»

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  • Obey or Play: Asymptotic Equivalence of Slotted Aloha with a Game Theoretic Contention Model

    Page(s): 623 - 625
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (158 KB) |  | HTML iconHTML  

    Contention control is an important means to mitigate adverse affects of multiple access interference on transmitted data packets in wireless communication networks. Most practical contention control mechanisms, e.g., IEEE 802.11 and slotted Aloha, rely on the assumption that all users abide with the rules of the protocol. There is also a growing body of work employing game theoretic techniques to gain new design insights for controlling contention when users act selfishly to maximize their perceived performance, as well as to reverse/forward engineer existing contention control protocols. In this paper, it is shown that the asymptotic behaviour of the slotted Aloha protocol when the number of contenders grows large coincides with a Nash equilibrium that is derived from a game theoretic contention model. Furthermore, the relationship between the design parameters in both approaches is established. In particular, it is shown that the back-off exponent in the slotted Aloha based contention control is linearly related to the cost of a collision in the game theoretic approach. View full abstract»

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  • On the Throughput of MIMO Relay Wireless Network with Receive Antenna Selection

    Page(s): 626 - 628
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (187 KB) |  | HTML iconHTML  

    In this letter, we consider a single-relay and K users multiple-input multiple-output (MIMO) system with the channel state information (CSI)-assisted amplify-and-forward (CAF) protocol, where each node is equipped with N antennas. We propose one antenna selection scheme for the multiuser wireless relay network. According to the order statistics, we derive the exact expressions for the probability density functions (PDF) and use them to evaluate the average throughput. The numerical results show that for a N = 2 and K = 3 relay channel the antenna selection scheme results about 2dB SNR loss compared to the full antenna case. View full abstract»

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  • Aggregate Interference in Secondary Access with Interference Protection

    Page(s): 629 - 631
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    This paper presents a derivation of the probability distribution function (pdf) of the aggregate interference in a secondary access network where multiple secondary users cause interference to a single primary user. The derivation considers a practical interference protection mechanism that the transmission of each secondary user is regulated by an interference threshold. Analytic pdf of the interference from a secondary user is obtained. Then, the distribution of the aggregate interference is approximated based on its cumulants. The derived pdf shows a good agreement with Monte Carlo simulation. View full abstract»

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  • Revisiting an RFID Identification-Free Batch Authentication Approach

    Page(s): 632 - 634
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (165 KB) |  | HTML iconHTML  

    SEBA is a recently proposed probabilistic identification-free batch authentication solution for RFID tags. It significantly differs from traditional RFID authentication approaches: rather than relying on authentication information delivered by the tags, it exploits the position of the tags' transmissions in response to an authentication challenge. This letter revisits, and meanwhile extends, SEBA. We show that SEBA is a particular case of a more general framework, called SEBA+, which envisions multiple tag responses in a frame. These are in turns interpreted as a Bloom filter, whose authenticity is verified against an authenticator Bloom filter comprising all the deployed tags' computed responses. Our proposed extension significantly improves SEBA's performance when more stringent counterfeit RFID tag detection capabilities are required. View full abstract»

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  • A Simple End-to-End Throughput Model for 802.11 Multi-Radio Multi-Rate Wireless Mesh Networks

    Page(s): 635 - 637
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (194 KB) |  | HTML iconHTML  

    We address the problem of estimating the end-to-end throughput of UDP flows in a multi-radio, multi-channel, and multi-rate 802.11 wireless mesh network (WMN). Estimates of the end-to-end throughput of flows in a WMN can facilitate the design of traffic-aware routing and channel assignment algorithms. We introduce a simple and intuitive model that captures key features of 802.11 WMNs such as contention, interference, and performance degradation due to links with low transmission rates. We use simulation to validate the accuracy of the proposed model in various scenarios for a network topology containing multiple transmitters and wired gateways. View full abstract»

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  • Symbol Error Rate of MIMO Broadcast Scheduling Systems with Partial Channel State Information

    Page(s): 638 - 640
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (201 KB) |  | HTML iconHTML  

    In this paper, we investigate the impact of partial channel state information (CSI) on the symbol error rate (SER) in a MIMO broadcast scheduling system. In this scheduling system, each transmit antenna is allocated based on scalar feedback information, which contains the largest effective signal to noise ratio (SNR) value with index for all user terminals. Exact closed-form expressions of the SER for the M-ary QAM and M-ary PSK modulations are presented. Using an asymptotic approach, we quantify the diversity order and SNR gain of the SER for the MIMO broadcast scheduling system employing scalar feedback information. From analysis results, we show insight into how the partial CSI affects the diversity order and SNR gain in the scheduling system. We verify the analytical results through simulation results. View full abstract»

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  • On the Optimality of the Selection Transmit Diversity for MIMO-FSO Links with Feedback

    Page(s): 641 - 643
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (206 KB) |  | HTML iconHTML  

    We propose an optimal power allocation strategy for Multiple-Input-Multiple-Output (MIMO) Free-Space Optical (FSO) links with Intensity Modulation (IM) and Direct Detection (DD). The optimization is performed for shot noise limited systems in the presence of complete feedback. The derived analytical solution turns out to be the same as the selection transmit diversity scheme proposed for MISO-FSO systems corrupted by Gaussian noise. We also propose and analyze a novel transmission strategy for the limited-feedback case. View full abstract»

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  • An Efficient Algorithm for Capacity and Outage Probability Estimation in MIMO Channels

    Page(s): 644 - 646
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (319 KB) |  | HTML iconHTML  

    An efficient algorithm based on a biased Monte Carlo method known as Transition Matrix Monte Carlo (TMMC) is proposed for capacity and outage probability estimation in multiple-input multiple-output (MIMO) communication systems. The algorithm is generally applicable to any fading scenario. A MIMO maximal ratio combining system operating over Nakagami-m fading is used to validate the algorithm. View full abstract»

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  • Performance of Analog Network Coding with Asymmetric Traffic Requirements

    Page(s): 647 - 649
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (202 KB) |  | HTML iconHTML  

    In this letter, we evaluate the outage performance of analog network coding (ANC) protocol for a two-way half-duplex relaying system with asymmetric traffic requirements at end terminals. We derive a simple and generalized expression for overall system outage probability in a Rayleigh flat-fading environment. We also deduce the optimal relay location and power allocation in order to minimize the overall system outage. Numerical and simulation results highlight the effect of optimal relay positioning and power allocation under various traffic requirements. View full abstract»

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  • On LLR Clipping in BICM-IDD Non-Coherent MIMO Communications

    Page(s): 650 - 652
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    In this letter a method is proposed for improving the performance of a BICM non-coherent MIMO communication system with iterative demapping and decoding. This method is based on adapting the clipping thresholds of the log-likelihood ratios of the demapper and the decoder to the channel realizations observed by each block. The method is particularly suited for systems in which the data blocks are relatively short and for systems in which list demapping is employed at the receiver. View full abstract»

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  • A Linear Precoding Scheme for Downlink Multiuser MIMO Precoding Systems

    Page(s): 653 - 655
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB) |  | HTML iconHTML  

    In this letter, we propose a low complexity linear precoding scheme for downlink multiuser MIMO precoding systems where there is no limit on the number of multiple antennas employed at both the base station and the users. In the proposed algorithm, we can achieve the precoder in two steps. In the first step, we balance the multiuser interference (MUI) and noise by carrying out a novel channel extension approach. In the second step, we further optimize the system performance assuming parallel SU MIMO channels. Simulation results show that the proposed algorithm can achieve elaborate performance while offering lower computational complexity. View full abstract»

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  • Effect of Channel Estimation Errors on Arbitrary Transmit Antenna Selection for Cognitive MISO Systems

    Page(s): 656 - 658
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (155 KB) |  | HTML iconHTML  

    This letter analyzes the effect of channel estimation errors on the performance of cognitive multiple input and single output (MISO) systems with arbitrary transmit antenna selection. In particular, the channel estimation errors are caused by the partial channel information between the cognitive transmitter and the primary receiver. Utilizing the derived probability density function (PDF) of the received signal-to-noise ratio (SNR), the effective capacity of the considered systems is numerically evaluated, and a new closed-form expression for the case of perfect channel estimation is also derived. Simulation results show that the system performance is not sensitive to the channel estimation error, especially for strict delay quality of service (QoS) requirement of the cognitive user (CU). View full abstract»

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  • Unequal Error Protection of JPEG2000 Images Using Short Block Length Turbo Codes

    Page(s): 659 - 661
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (275 KB) |  | HTML iconHTML  

    Examining the Bit Error Rate (BER) at various positions of a Turbo Coded data block reveals that Turbo Codes inherently possess Unequal Error Protection (UEP) properties. In this paper, we mainly investigate the impact of different puncturing patterns on the resulting UEP properties. And then we apply these properties to the JPEG2000 image transmission. The results indicate that a proper design of the system can bring substantial gain in decoded image quality. View full abstract»

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Aristotle University of Thessaloniki
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