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Communications, IET

Issue 10 • Date October 2009

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Displaying Results 1 - 13 of 13
  • Application of complex-network theories to the design of short-length low-density-paritycheck codes

    Publication Year: 2009 , Page(s): 1569 - 1577
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    Study of complex networks has been conducted across many fields of science, including computer networks, biological networks and social networks. Characteristics of different types of complex networks such as random networks, regular-coupled networks, small-world networks and scale-free networks have been discovered by researchers. Application of such network properties to solve engineering problems, however, is still at the infancy stage. In this study, we make one of the first attempts in applying complex network theories to communications engineering. In particular, inspired by the shortest-average-path-length property of scale-free networks, we design short-length low-density-parity-check (LDPC) codes with an aim to shortening the average distance between any two variable nodes. We will also compare the error performance, both theoretically and by simulations, of the proposed codes with those of other well-known LDPC codes. View full abstract»

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  • Handling node churn in decentralised network coordinate system

    Publication Year: 2009 , Page(s): 1578 - 1586
    Cited by:  Papers (1)  |  Patents (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (427 KB)  

    A Network Coordinate (NC) system is an efficient mechanism to predict Internet distance with scalable measurements. In this paper, we focus on the node churn problem - the continuous process of nodes arrival and departure - in distributed applications. Studies on Vivaldi, a representative distributed NC system, show that under node churn the prediction accuracy of the NC system will be seriously impaired. In this paper, we focus on how to handle the impact of node churn in Vivaldi. Firstly, we propose a simple solution by directly increasing the measurement frequency. Our experiments have demonstrated that this approach can reduce the harm of node churn. However, it increases the communication overhead as the measurement frequency grows. To avoid such expensive solution, we propose the design and implementation of Myth, a decentralised and fast convergence NC system. It introduces the merit of Landmark-based NC system to shorten convergence time in Vivaldi with slight extra overhead. Our experimental results show that Myth outperforms Vivaldi a lot under node churn, without compromising the performance under stable environment. Moreover, we have found that the use of Myth is a cost-effective way to achieve higher prediction accuracy; it will not only improve the prediction accuracy but also save the communication overhead. View full abstract»

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  • Ultra wideband powerline communication (PLC) above 30 MHz

    Publication Year: 2009 , Page(s): 1587 - 1596
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (921 KB)  

    A novel study of ultra wideband (UWB) communication over the indoor powerline channel, in a wide frequency range up to 1 GHz is presented. An exhaustive measurement campaign was conducted on a test bed that replicated the environment of an indoor powerline network. The aim of this study was to observe and analyse the transmission and noise properties of such a broadband powerline channel. A time domain channel model has been used to study the broadband channel response of the powerline. Measurement and modelling results show that the indoor powerline channel provides a communication link in the 50-550 MHz frequency range. Channel capacity is greatly enhanced by exploiting the 500 MHz bandwidth. The conclusions of this study indicate that gigabit per second data rate transmission are possible over the indoor powerline channel in 50-550 MHz. View full abstract»

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  • Analysis of the antenna array-aided multicarrier DS-CDMA RAKE system with synchronous uplink transmission

    Publication Year: 2009 , Page(s): 1597 - 1605
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (730 KB)  

    A multicarrier (MC) signalling was introduced as a means of reducing the effect of synchronisation offsets in a quasi-synchronous code division multiple access (CDMA) network. The incorporation of an antenna array (AA) into the multicarrier direct sequence (MC DS)-CDMA asynchronous uplink was considered to provide additional interference elimination capability. In addition, a combined AA and synchronous uplink transmission was proposed which results in more efficient estimation of covariance matrix to generate weights in the AA. However, the previous studies have considered each individual target, neglecting the comprehensive analysis of the system performances. Furthermore, the effects of diversity orders such as the number of branches in the RAKE receiver as well as the number of subcarriers transmitting the same data in the MC transmission have not been investigated. Against the background, the novel contribution of the study is that the performance of the AA-aided uplink synchronous MC DS-CDMA RAKE system is analysed under multipath Rayleigh fading channels in the context of the various shapes of multipath intensity profile (MIP) and the number of antenna elements. The resultant bit error rate performance and user capacity are compared to those of the corresponding AA-aided asynchronous uplink. View full abstract»

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  • A cooperative turbo coding scheme for wireless fading channels

    Publication Year: 2009 , Page(s): 1606 - 1615
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (402 KB)  

    A coded cooperative transmission scheme based on turbo encoding/decoding, in which only newly generated parity bits of the partner are sent if the user successfully decodes its partner's information in order to improve bandwidth efficiency is proposed. The proposed encoding structure introduces correlation between users' data over multiple frames, which offers effectively longer codes and facilitates high-performance iterative multi-user decoding at the destination. Additionally, the iterative decoding over multiple frames can provide time diversity besides spatial diversity inherent in user cooperation even for flat block fading channels. Simulation results show that the proposed scheme significantly outperforms direct transmission for the same transmitted power and bandwidth efficiency. View full abstract»

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  • Peak and leading edge detection for time-of-arrival estimation in band-limited positioning systems

    Publication Year: 2009 , Page(s): 1616 - 1627
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    The performance of the peak and leading edge detection methods for time-of-arrival (TOA) estimation in band-limited systems is examined. Analytical expressions for the detection performance in the presence of both random noise and multipath interference are derived. A dimensionless performance factor is presented that allows simple comparisons of the TOA estimation algorithms. These equations allow the performance tradeoff analysis to be undertaken without the need for simulations. It is shown that the leading edge detection method has significantly better multipath mitigation characteristics than the peak detection one, but at the expense of inferior noise performance. View full abstract»

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  • Providing scalable location service in wireless sensor networks with mobile sinks

    Publication Year: 2009 , Page(s): 1628 - 1637
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (433 KB)  

    Location-based routing has been considered as an efficient routing paradigm for wireless sensor networks (WSNs). The performance of location-based routing highly depends on the way the position information of mobile sinks are updated and managed, which is the typical function of location service. Frequent location updating can improve the location accuracy at the expense of additional communication overhead. In this study, the authors propose a scalable location service for supporting efficient location-based routing in WSNs with mobile sinks. The proposed location service enables each sensor node to locate its closest (mobile) sink with low overhead. Analytical and simulation results show that it can significantly reduce the communication overhead for providing location service while maintaining high routing performance. View full abstract»

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  • Receive maximal-ratio combining with outdated arbitrary transmit antenna selection in Nakagami-m fading

    Publication Year: 2009 , Page(s): 1638 - 1648
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (577 KB)  

    The use of transmit antenna selection algorithms in multiple-antenna systems enables significant reduction in implementation cost and complexity while maintaining acceptable performance. An attractive and quite flexible selection algorithm is to allow the receiver to pick any of the transmit antennas that can satisfy a predetermined performance target. Such an algorithm is referred to as the arbitrarily ordered transmit antenna selection algorithm. However, the effectiveness of transmit antenna selection is decreased by several propagation impairments over the feedback channel from the receiver to the transmitter. Of these impairments, the feedback channel time delay may impose a significant impact on the achieved performance. This paper aims to investigate the impact of this time delay on the performance of receive maximal-ratio combining (MRC) diversity employing the arbitrarily ordered transmit antenna selection algorithm. In order to obtain quantitative measures for this impact, new expressions for various performance criteria are obtained by using the new derived formulas for the probability density function (pdf) and the moment generating function (MGF) of the combined signal-to-noise ratio (SNR). Numerical and simulation results are presented to illustrate the effect of delayed (i.e. outdated) feedback information on the system performance for various transmit antenna selection scenarios. View full abstract»

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  • Error probability of direct sequence-code division multiple access systems with adaptive antenna minimum mean-square error multiuser receivers in Rayleigh-lognormal fading

    Publication Year: 2009 , Page(s): 1649 - 1658
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (418 KB)  

    In direct sequence-code division multiple access (DS-CDMA) cellular systems spreading codes, fading and positions of the users can be modelled as independent random variables and the corresponding multiuser interference (MUI) experienced by the base station is non-stationary. Here we evaluate in closed form the bit error probability for space-time linear minimum mean square error (MMSE) multiuser receivers for symbol-synchronous DS-CDMA system (bounds are provided for symbol-asynchronous system) by extending the known asymptotic results for random spreading sequences to non-stationary MUI. The analysis is based on the effective interference at the decision variable that is carried out to account for the non-stationary MUI that results from the multiuser beamforming that adapts each spatial filter to the randomness of the angle of arrivals of all the users. Propagation for each user is Rayleigh-lognormal faded channels as it is fairly general to model the imperfect power-control. The numerical validation proves that a simple geometrical model is accurate to evaluate the error probability for any arbitrary system loading. View full abstract»

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  • Analytical performance of orthogonal frequency division multiplexing systems impaired by a non-linear high-power amplifier with memory

    Publication Year: 2009 , Page(s): 1659 - 1666
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (346 KB)  

    The performance of modern communication transmitters utilising multi-carrier modulation techniques is highly sensitive to non-linear distortions arising mainly from the high-power amplifier (HPA). In addition, the wideband characteristics of multi-carrier signals result in frequency-dependent distortions, typically known as memory effects. This study aims to analytically evaluate the impact of the distortion induced by non-linear HPA with memory on a multi-carrier signal exemplified by orthogonal frequency division multiplexing (OFDM). The behavioural model of HPA considered for theoretical analysis is a memory polynomial model, which is a truncated form of the Volterra series. In the theoretical framework developed, this study shows that memory in HPA considerably degrades the performance of OFDM in terms of symbol error rate (SER), and the distortion itself can be canonically characterised by a complex attenuation component and a non-linear noise component. Closed-form expressions for SER in additive white Gaussian noise channel are derived and the SER for fading channel is approximated by the adaptive Gauss-Kronrod quadrature method. Simulation results are shown for a realistic HPA, based on the Wiener-Hammerstein model, and compared with the analytical results to validate the proposed analysis. View full abstract»

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  • Peak-to-average power ratio reduction in space-time block coded multi-input multi-output orthogonal frequency division multiplexing systems using a small overhead selective mapping scheme

    Publication Year: 2009 , Page(s): 1667 - 1674
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (622 KB)  

    The selective mapping (SLM) scheme is one of the most popular peak-to-average power ratio (PAPR) reduction techniques proposed for multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. One of the major disadvantages of this scheme is the need for the transmission of side information (SI) bits to enable the receiver to recover the transmitted data. The authors present a small overhead SLM (s-SLM) scheme for space-time block coded (STBC) MIMO-OFDM systems. This proposed scheme improves the system bandwidth efficiency and achieves a significantly lower bit error rate (BER) than the individual SLM (i-SLM) and direct SLM (d-SLM) schemes. In addition, approximate expressions for the complementary cumulative distribution function (CCDF) of the PAPR and the average BER of the proposed s-SLM scheme are derived. The simulation results show that the proposed s-SLM scheme improves the detection probability of the SI bits and hence gives a better performance than the i-SLM and the d-SLM schemes. View full abstract»

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  • Adaptive modulation for limited diversity fading channels

    Publication Year: 2009 , Page(s): 1675 - 1682
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    In this study, the authors propose a novel technique for adaptive modulation over limited diversity fading channels with channel state information at the transmitter. Limited diversity channels such as those encountered in indoor orthogonal frequency division multiplexing systems are characterised by the fact that achievable diversity orders are limited by the channel and not by code-free distances. The authors first propose a novel analysis technique for the performance of coded modulation on limited diversity block fading channels with different modulation sets on each block. The authors then propose adaptive modulation techniques for maximising the throughput at a fixed bit error probability and also for minimising the bit error probability at a fixed rate. Lastly, the authors show simulation results that support the arguments presented in the paper. View full abstract»

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  • Joint power allocation and relay positioning in multi-relay cooperative systems

    Publication Year: 2009 , Page(s): 1683 - 1692
    Cited by:  Papers (12)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    The authors consider a dual-hop multi-relay cooperative relay system in this study. Both decode-and-forward (DF) and amplify-and-forward (AF) protocols are considered. Under different relay selection strategies, the authors derive closed-form outage probability expressions. With the second-order channel statistics, the authors propose to jointly optimise power allocation (PA) and relay positions in order to minimise the system outage probability. Simulation results show that the proposed adaptive allocation algorithms significantly outperform fixed allocation algorithms. With the proposed joint optimisation algorithm, AF relaying outperforms DF relaying when multiple relays are selected to help. When only the best relay is selected to help, DF relaying is shown to have better performance. View full abstract»

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IET Communications covers the theory and practice of systems, networks and applications involving line, mobile radio, satellite and optical technologies for telecommunications, and Internet and multimedia communications.

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