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Communications, IET

Issue 13 • Date Sept. 5 2011

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Displaying Results 1 - 17 of 17
  • Efficient combining techniques for multi-input multi-output multi-user systems employing hybrid automatic repeat request

    Page(s): 1785 - 1796
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    The authors consider chase-combining hybrid automatic repeat request (HARQ) schemes over multiple antenna multi-user systems. The focus is on a multiple-access channel, where the users as well as the base-station are equipped with multiple antennas. In such chase-combining HARQ systems, the transmitters (users) re-transmit their codewords when requested by the receiver (base-station). The receiver may choose to enforce blanking, that is, it may choose to request only a subset of the transmitters to re-transmit and the remaining ones to be silent. Moreover, subject to the complexity and latency constraints, the receiver may be able to perform codeword cancellation wherein it can re-encode, re-modulate a subset of decoded codewords and subtract them from the received observations. A candidate combining technique is the conventional chase-combining, which in contrast to the optimal combining requires significantly less memory and processing capability at the receiver but can result in substantial performance degradation. The authors propose efficient combining techniques that cater to all the various scenarios that arise in such multi-codeword systems. The proposed techniques impose similar memory and complexity demands as the conventional combining but yield a significant performance improvement. The issue of limited feedback in multi-codeword multi-antenna chase-combining HARQ systems is also addressed and it can be used to further improve the system throughput. View full abstract»

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  • WSNHA-GAHR: a greedy and A* heuristic routing algorithm for wireless sensor networks in home automation

    Page(s): 1797 - 1805
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (367 KB)  

    The use of wireless sensor networks in home automation (WSNHA) is a growing trend, on account of their self-organisation, low cost and potential for rapid deployment. Routing in WSNHA is a challenging research topic, because of the requirements of low energy consumption, low storage, low computational complexity, fast response, self-adaptation to unpredictable topological changes and robustness with respect to discontinuous interference. With the development of localisation techniques, localised routing offers a number of attractive benefits, but not all are suitable for WSNHA. In this study, the authors propose a new routing algorithm for WSNHA, called WSNHA-GAHR (greedy and A* heuristic routing for WSNHA). The algorithm uses greedy forwarding, based on the smallest Euclidean distance, to minimise the number of hops for data packet transmission, and thus conserve energy. It also automatically adjusts the route, using the A* heuristic algorithm, when local minimum problems and unpredictable topological changes occur in WSNHA. In addition, link priority classification gives WSNHA-GAHR a greater tolerance than ZigBee routing algorithm for discontinuous interference. Simulation results show that this routing protocol dramatically improves reliability and reduces average packet delay, without introducing additional overhead. View full abstract»

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  • Reduced-complexity scheme using alpha-beta filtering for location tracking

    Page(s): 1806 - 1813
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (566 KB)  

    This study presents an efficient location tracking algorithm to reduce the computational complexity of the conventional Kalman filtering (KF) algorithm. In the proposed training and tracking scheme, the authors replace the decision mode of the KF algorithm with an alpha-beta (α-β) algorithm to avoid repeatedly calculating the Kalman gain. After the mode with α-β - tracking, the exact information of the state and measurement noise parameters used in the KF algorithm is not required. Using the inherent fixed-coefficient feature of α-β filtering, the location information between the prediction phase and correction phase is efficiently cycled, thus simplifying implementation of the KF approach. Under a stationary environment, numerical simulations show that the proposed training and tracking approach not only can achieve the location accuracy close to the KF scheme but has much lower computational complexity. View full abstract»

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  • Non-line-of-sight identification via phase difference statistics across two-antenna elements

    Page(s): 1814 - 1822
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (589 KB)  

    This study proposes and investigates the performance of a new non-line-of-sight (NLOS) identification technique for multiple antenna systems that is based on the phase difference across two antenna elements. In order to avoid any confusion in the position location process, NLOS identification techniques should be implemented in the localisation systems. A phase wrapping selection algorithm is proposed to calculate the phase difference variance across two-antenna elements. A theoretical relationship is maintained between the phase difference variance and the Rician K-factor. The proposed K estimator requires an uncorrelated phase across antenna elements. The validity of this assumption is verified via channel modelling simulations. Then, a hypothesis test on the K-factor is formed to identify NLOS situations. The prior distributions of K-factor under line-of-sight (LOS) and NLOS conditions, and the K-factor threshold that are used to distinguish LOS and NLOS situation are derived. The impact of shadowing on the performance of the proposed NLOS identification method is studied. The performance of the proposed phase difference K estimator technique is compared with the envelope-based K estimator. View full abstract»

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  • Improved markov predictor in wireless networks

    Page(s): 1823 - 1828
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (322 KB)  

    As wireless networks have been an integral part of our daily life, mobility prediction techniques have become one of the main topics in current research efforts. An accurate prediction of the next cell to which the mobile users are going can greatly improve the performance of wireless applications, such as map resource allocation, congestion control, quality of service and mobility management. It has been shown that the Markov predictor is a good mobility predictor in actual wireless local area network environments. However, from the standpoint of conditional entropy, the authors analyse that the Markov predictor has the disadvantage of performing worse when the location history is lacking or an approximate tie has happened. As a consequence, a novel improved Markov predictor is proposed, and simulations are conducted to evaluate the performance of the proposed scheme. The simulation results show that the improved Markov predictor solves not only the disadvantages of Markov predictor due to the lack of location history information, but also the expansion of state space in multiple-order Markov predictors. View full abstract»

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  • Second-order statistics of a maximum ratio combiner with unbalanced and unequally distributed nakagami branches

    Page(s): 1829 - 1835
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    In this study, exact closed-form expressions for the second-order statistics of the signal-to-noise ratio at a maximum ratio combiner (MRC) output for a Nakagami fading channel are derived. Using the joint characteristic function for the MRC output and its time derivative, the level crossing rate, average fading duration and autocorrelation function expressions are derived for the case of independent but unbalanced diversity branches, with unequal fading parameters and an arbitrary number of diversity branches. The analytical results are validated by simulations. View full abstract»

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  • (k, r)-Dominating set-based, weighted and adaptive clustering algorithms for mobile ad hoc networks

    Page(s): 1836 - 1853
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1450 KB)  

    The creation of stable, scalable and adaptive clusters with good performance, faster convergence rate and with minimal overhead is a challenging task in mobile ad hoc networks (MANETs). This study proposes two clustering techniques for MANETs, which are (k, r)-dominating set-based, weighted and adaptive to changes in the network topology. The set of dominating nodes functions as the clusterheads. The scenario-based clustering algorithm for MANETs (SCAM) is a greedy approximation algorithm, whereas the distributed-SCAM (DSCAM) selects the (k, r)-dominating set through a distributed election mechanism. These algorithms achieve variable degree of clusterhead redundancy through the parameter k which contributes to reliability. Similarly, flexibility in creating variable diameter clusters is achieved with the parameter r. To improve the stability of the created clusters, the affiliation of other nodes with the clusterhead is decided based on the quality of the clusterhead, which is a function of connectivity, stability, residual battery power and transmission range. Mechanisms are available for accounting the group mobility and load balancing. The performance of these algorithms are evaluated through simulation and the results show that these algorithms create stable, scalable and load-balanced clusters with relatively less control overhead in comparison with the existing popular algorithms. View full abstract»

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  • Power-saving mechanism with delay bound for Mobile WiMAX systems

    Page(s): 1854 - 1859
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (345 KB)  

    In Mobile World Interoperability for Microwave Access (WiMAX), the power-saving mechanism (PSM), which operates alternately in sleep and awake modes, works to extend the lifetime of mobile stations (MSs), although it concurrently induces a medium access control (MAC) service data unit (SDU) response delay. In this study, the authors derive the analytical models for two of the most important performance metrics: the average power consumption and the average MAC SDU response delay of an MS in sleep mode. These metrics are given as a function of the sleep mode system parameters: initial sleep window Tmin and final sleep window Tmax. Based on these models, the authors show that a tradeoff relationship exists between them. The authors then propose an optimised power-saving mechanism (OPSM) that jointly determines the optimal Tmin and Tmax to minimise the power consumption under a given MAC SDU response delay constraint. Through both numerical analyses and subsequent simulations, the authors show that the OPSM effectively minimises the power consumption of an MS in its sleep mode while guaranteeing the MAC SDU response delay constraint. View full abstract»

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  • Adjustable observation window length equalisation receiver based on H criterion for ultra-wideband in non-gaussian noise

    Page(s): 1860 - 1867
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (609 KB)  

    To suppress the effects of ultra-wideband receiver caused by non-Gaussian noise and difference of channel profile, an adjustable observation window length equalisation receiver based on H criterion is proposed. In contrast to the existing fixed observation window length (FOWL) equalisation receivers based on the minimum mean square error (MMSE) criterion, the proposed receiver is found on H criterion and can adaptively adjust the observation window length according to the specific channel profile. The proposed receiver so designed is shown to outperform the FOWL equalisation receivers based on the conventional MMSE criterion in a non-Gaussian noise environment. View full abstract»

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  • Research on low-complexity breadth-first detection for multiple-symbol differential unitary space-time modulation systems

    Page(s): 1868 - 1878
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1343 KB)  

    The breadth-first searching algorithms, typically represented by K-best algorithm, are widely studied for multiple-symbol differential detection in multiple-input multiple-output systems due to the advantages of fixed complexity and latency which are very attractive for hardware implementation. However, it needs a large K value to achieve near maximum likelihood performance, which results in large complexity. In this study, a dynamic K-best detection with reduced average K value is proposed. It reduces the complexity on path expanding, path updating and comparing and swapping (C&S) operations by 24.24, 25 and 43.46%, respectively, with less performance degradation. After that, two low-complexity sorting architectures, Batcher%s merge sort and K cycles sort, are presented and applied to the proposed dynamic K-best detection. The complexity analysis and simulation results show that, compared with the traditional Bubble sorting dynamic K-best detection, the K cycles sorting and the Batcher's merge sorting dynamic K-best detections can further save C%operations by 59.5 and 11.2%, respectively, while performance cost capable of being ignored. Moreover, the K cycles sorting dynamic K-best detection achieves best trade-off on throughput and required memory, and the architecture of the Batcher's merge sorting dynamic K-best detection is more beneficial to parallel processing and multiple-processor structure. View full abstract»

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  • Optimal power control of parallel orthogonalfrequency-division-multiplexing relaying networks

    Page(s): 1879 - 1888
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    This article studies the power allocation (PA) problem for dual-hop orthogonal-frequency-division-multiplexing (OFDM) relaying networks, in which a source communicates with a destination with the help of multiple amplify-and-forward relays that employ parallel transmission protocol. The objective is to maximise the system achievable rate, under which an aggregate power constraint is imposed on all relays, and an individual link rate constraint is imposed on each OFDM subchannel. Based on Zhao et al's prior work, the simpler PA problem without considering those rate constraints is firstly solved by optimally allocating the total power across all OFDM subchannels. Then, for the original problem with both power and rate constraints, an order structure is proposed such that in the optimal PA scheme, those subchannels that attain respective maximum link rates are determined one by one, that is the complexity to determine those subchannels is considerably reduced from exponential to linear order. View full abstract»

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  • Maximum flatness criterion based on extrinsic information transfer charts for symbol mapping design

    Page(s): 1889 - 1894
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    In bit-interleaved coded modulation with iterative decoding (BICM-ID), the extrinsic information transfer (EXIT) function of the demapper can be parameterised. Using this parameterisation, in conjunction with the EXIT function of the decoder, a symbol mapping design criterion based on the flatness of the gap between the two EXIT functions (called the maximum flatness criterion) is proposed in this study. Simulation results confirm that a good performance can be achieved in terms of convergence rate for fast fading channels and outage probability for slow fading channels. View full abstract»

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  • Load-balanced differentiated services support switch

    Page(s): 1895 - 1906
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (785 KB)  

    How to provide quality of service (QoS) guarantees in the routing and switching devices has become one of the key research topics in the areas of routing and switching technologies. Differentiated services architecture (DiffServ), which forwards packets based on their per-hop behaviours, is known as a promising way for supporting QoS in a high-speed backbone network scenario. Motivated by the load-balanced Birkhoff-von Neumann switch, which has received much attention recently because of its outstanding extensibility performance, in this study, the authors propose a new switch architecture called load-balanced DiffServ support switch (LBDS). LBDS consists of pipeline traffic bandwidth control, priority-based load balancing, and bandwidth-based priority scheduling to implement fast forwarding for expedited forwarding (EF) traffic and assured forwarding for AF classes of traffic. The authors evaluate LBDS by extensive theoretical analysis and comprehensive simulations. As expected, LBDS can provide bandwidth guarantees for both EF and AF traffic. We also show that under burst traffic arrivals, especially when the traffic arrival pattern is non-uniform and the load is above 0.6, LBDS performs much better delay performance than existing DiffServ support schemes. View full abstract»

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  • Layered space-time receiver for downlink multiple-input multiple-output multi-carrier code division multiple access systems

    Page(s): 1907 - 1917
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (641 KB)  

    Multi-carrier code division multiple access (MC-CDMA) allows multiuser communication with frequency diversity. To increase the system data rates, spatial multiplexing for multiple-input multiple-output (MIMO) MC-CDMA has been investigated. This study proposes a chip level layered space-time (LST) receiver architecture for coded downlink MIMO MC-CDMA systems. As the conventional chip level ordered successive interference cancellation (OSIC) receiver is unable to overcome multiple access interference and performs poorly in multiuser scenarios, the proposed receiver cancels both spatial and multiuser interference in an ordered LST detection process by requiring only the knowledge of the desired user-s spreading sequence. Simulation results show that the proposed receiver not only performs better than the existing linear detectors but also outperforms both the chip and symbol level OSIC receivers. In this study the authors also compare the error rate performance between the proposed system and MIMO orthogonal frequency division multiple access (MIMO OFDMA) system and they justify the comparisons by deriving and analysing the pairwise error probability (PEP) for both systems. MIMO MC-CDMA demonstrates a better performance over MIMO OFDMA under low system load. If all users- spreading sequences are known, multiuser interference can be reduced and MIMO MC-CDMA performs better than MIMO OFDMA at all system loads. View full abstract»

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  • Adaptive switching for multiple-input multiple-output multi-mode transmission in broadband wireless networks

    Page(s): 1918 - 1927
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    In this study, we propose a practical adaptive multiple-input multiple-output (MIMO) transmission approach for broadband wireless multiuser systems. The presented scheme adaptively switches between open-loop and closed-loop MIMO modes depending on the users' channel conditions and required rates as a means to enhance the system throughput and performance. Each mode is a combination of a transmission technique (space-time block coding and/or spatial multiplexing or beamforming) and a modulation/coding scheme. We first evaluate the spectral efficiency of each mode and provide a simple way to select adaptively the best combination of code rate and modulation scheme for open-loop and closed-loop transmission modes in a Rayleigh/composite fading environment. Based on these results, we propose a simple and practical switching criterion that is shown to yield significant spectral efficiency improvements over independent adaptive open-loop or closed-loop schemes for typical multiuser system scenarios. Simulations in an IEEE 802.16e framework are provided and illustrate significant improvements in throughput performance and service fairness. View full abstract»

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  • Robust decoder-based error control strategy for recovery of H.264/AVC video content

    Page(s): 1928 - 1938
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1188 KB)  

    Real-time wireless conversational and broadcasting multimedia applications offer particular transmission challenges as reliable content delivery cannot be guaranteed. The undelivered and erroneous content causes significant degradation in quality of experience. The H.264/AVC standard includes several error resilient tools to mitigate this effect on video quality. However, the methods implemented by the standard are based on a packet-loss scenario, where corrupted slices are dropped and the lost information concealed. Partially damaged slices still contain valuable information that can be used to enhance the quality of the recovered video. This study presents a novel error recovery solution that relies on a joint source-channel decoder to recover only feasible slices. A major advantage of this decoder-based strategy is that it grants additional robustness while keeping the same transmission data rate. Simulation results show that the proposed approach manages to completely recover 30.79% of the corrupted slices. This provides frame-by-frame peak signal-to-noise ratio (PSNR) gains of up to 18.1%dB, a result which, to the knowledge of the authors, is superior to all other joint source-channel decoding methods found in literature. Furthermore, this error resilient strategy can be combined with other error resilient tools adopted by the standard to enhance their performance. View full abstract»

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  • Performance of channel codes in wireless communication systems using efficient simulation

    Page(s): 1939 - 1946
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    With the widespread of new radio systems, it is essential that their performance is evaluated prior to auxiliary design and commercial development. Although there are many methods to model and estimate the performance of a given radio system with some accuracy, most of these methods require high computational resources or long simulation times. In this study, the authors present a general and efficient simulation method for estimating the performance of a wireless communication systems, with particular emphasis for its forward error correction sub-system when using block channel codes, for channels affected by additive white Gaussian noise, free space attenuation, shadowing, fading and interfering sources. Both soft-decision (SD) and hard-decision (HD) decoding are considered and the overall performance takes into account modulation, coding and channel conditions. This efficient simulation is compared with the Monte Carlo simulation method and its performance is assessed for the Tomlinson, Cercas and Hughes code family. This new simulation method has an temporal efficiency of two or three orders of magnitude for SD and HD and three or four orders, considering a bit-error-ratio of 0.01 and 0.001%, respectively. View full abstract»

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