Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 6, Issue 11, 24 July 2012
Volumes & issues:
Volume 6, Issue 11
24 July 2012
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- Author(s): P.R. Nair ; A.P. Vinod ; K.G. Smitha ; A.K. Krishna
- Source: IET Communications, Volume 6, Issue 11, p. 1341 –1348
- DOI: 10.1049/iet-com.2011.0751
- Type: Article
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An enormous influx of wireless services and devices coupled with inefficient usage of electromagnetic spectrum has led to an apparent scarcity of usable radio bandwidth. Cognitive radio is leading the trend for increasing the spectrum efficiency by utilising the vacancy in the radio spectrum created by absence of the licensed primary user. This paradigm shift can only take place if the means to detect the primary user are well established so that an ecosystem can be created where both primary and secondary users can co-exist without interfering with each other. In this study the authors propose a two-stage detection mechanism which gives an improved performance over conventional single-stage detectors yet optimises the usage of the second stage, thereby reducing the sensing time as compared to conventional two-stage spectrum sensing algorithms. A hardware implementation of the algorithm has also been done to quantify the area and power consumption values. By utilising the second-stage optimally, the algorithm presented in this study helps in reducing the sensing time by 86% as compared with the conventional two-stage detector. By not activating the second stage at high SNRs, the proposed algorithm saves 0.915 W of dynamic power out of a total of 1.09 W, thus effectively reducing the dynamic power consumption by 84%. - Author(s): Y. Park ; G. Hwang ; D.K. Sung
- Source: IET Communications, Volume 6, Issue 11, p. 1349 –1355
- DOI: 10.1049/iet-com.2011.0036
- Type: Article
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The authors propose a new power saving scheme based on a buffer-threshold and timer in wireless packet networks. In a standard sleep mode operation with a binary exponential algorithm, a mobile station (MS) can begin a wake period if it is aware of the existence of its own downlink packets during a listening interval. In a light traffic environment, this conventional standard operation consumes a considerable amount of power to switch modes (sleep/listen/wake). To solve this problem, a new power saving scheme based on joint control of buffer-threshold and timer (JCBT) is proposed. To see the performance behaviour of the JCBT scheme, the authors consider the total power consumption per unit time and the average packet transfer delay as performance measures. Based on the performance measures, the authors obtain the optimal solution for the proposed JCBT scheme that minimises the total power consumption per unit time with a given delay requirement. - Author(s): H. Xu
- Source: IET Communications, Volume 6, Issue 11, p. 1356 –1363
- DOI: 10.1049/iet-com.2011.0063
- Type: Article
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In this study, the authors propose a simplified maximum likelihood (ML)-based detection scheme for Nt×Nr M-ary quadrature amplitude modulation (M-QAM) spatial modulation (SM) that is computationally less complex than the conventional ML detection scheme. Instead of searching for the transmit antenna index and transmitted symbol pair among all possible NtM pairs as in the ML-based optimal detection, the proposed simplified ML-based detection scheme firstly searches for pairs of transmit antenna index and transmitted symbol in level-one subsets which the transmitted signal most probably belongs to, and secondly searches for pairs of transmit antenna index and transmitted symbol in level-two subsets among those pairs in level-one subsets. We also extend the simplified ML-based optimal detection into multistage detection. Simulation results validate that the bit error rate (BER) performance of the proposed simplified ML-based detection schemes is almost the same as that of conventional ML detection with significant complexity reduction until a BER of 10−6. - Author(s): E.S. Alikhani ; B. Mahboobi ; M. Ardebilipour
- Source: IET Communications, Volume 6, Issue 11, p. 1364 –1373
- DOI: 10.1049/iet-com.2011.0560
- Type: Article
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Adaptive radio resource allocation in a cellular and multiuser orthogonal frequency-division multiple access (OFDMA)-based relay network is studied here. The authors have considered a margin adaptive optimisation problem to minimise the total transmitted power of the base and relay stations subject to the requested data rates of the users. In this study, a novel algorithm is presented for subcarrier allocation to the users with frequency reusing in the network. The interference among users in non-adjacent cells has been considered in the proposed algorithm which results in interference aware power allocation. Tolerable bit error rate is satisfied as quality of service (QoS) factor for each subcarrier. Linear programming approach has been proposed to solve this problem, such that power allocation problem is isolated for each of the subcarriers and total transmitted power is minimised in the network. According to this technique, the cost of interference in the system in terms of the excess consumed power to satisfy QoS constraints can be computed. The gain achieved in the power consumption is demonstrated through the simulations and the results are compared with the previous works. - Author(s): R. Xu ; M. Chen ; J. Zhang ; B. Wu ; H. Wang
- Source: IET Communications, Volume 6, Issue 11, p. 1374 –1381
- DOI: 10.1049/iet-com.2011.0007
- Type: Article
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The large spectrum sidelobes of orthogonal frequency division multiplexing (OFDM) signal lead to the interference with the licensed user working on the adjacent band in spectrum pooling. The power spectral leakage of discrete Fourier transformation (DFT)-based OFDM systems can be divided into two parts, in-band–out-of-subband (IBOSB) spectral leakage and out-of-band (OOB) spectral leakage. A correlative coding technique is proposed to suppress the IBOSB leakage and redistribute the OOB leakage of DFT-based OFDM signal through the subcarrier coding in the frequency domain with appropriate weighting. The correlation is introduced between adjacent subcarriers and mutual cancellation of the spectrum sidelobes reshapes the spectrum of DFT-based OFDM signal. The optimum weighting factor is obtained through optimisation. Analytical results and simulation show that the proposed coding scheme significantly suppresses the IBOSB leakage in contrast with the common OFDM system and introduces least interference with the licensed user. Furthermore, the carrier–interference ratio (CIR) of OFDM system with correlative coding increases by 3 dB. At the same time, maximum likelihood sequence detection (MLSD) can mostly compensate the bit error rate (BER) degradation caused by error propagation at the expense of introducing a little computation complexity. - Author(s): M. Düngen ; A.G. Monsalve ; H. Rohling
- Source: IET Communications, Volume 6, Issue 11, p. 1382 –1387
- DOI: 10.1049/iet-com.2010.1000
- Type: Article
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Crosstalk (XT) is the main performance limiter in digital subscriber line (DSL) systems such as very-high-bit-rate digital subscriber line (VDSL) systems. In order to overcome these limitations various XT cancellation techniques have been proposed to mitigate this effect. While leading to very high performance gains, the computational complexity grows quadratically with the number of lines in a binder. This motivates partial cancellation schemes, maximising the capacity based on a given computational complexity. However, the data rate increase could still be very high above the quality of service (QoS) requirements that must be enforced for each user, leading to a ‘waste’ of computational resources. Therefore a QoS-based partial cancellation algorithm is presented in this study which selects the lines to be cancelled based on the desired data rates of the users. It relies on partial zero-forcing XT cancellation but the used selection algorithm [QoS-based joint tone-line selection (QoS-JTLS)] aims at QoS fulfilment instead of data rate maximisation. Simulation results show that compared with other QoS-based algorithms and conventional selection algorithms, QoS-JTLS leads to better fulfilment of QoS demands for the same given computational complexity. In other words, the computational complexity needed to achieve the target data rates of the users is reduced when applying QoS-JTLS. - Author(s): N. Pillay and H.J. Xu
- Source: IET Communications, Volume 6, Issue 11, p. 1388 –1396
- DOI: 10.1049/iet-com.2011.0506
- Type: Article
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Spectrum sensing for cognitive radio allows a secondary user to detect spectrum ‘holes’ and to opportunistically exploit this space for unlicensed communication. Blind spectrum sensing has the advantage that it does not require any knowledge of the transmitted signal, the channel or the noise-power, which are usually unknown at the receiver. In this study, the simulation and performance results for the maximum–minimum-eigenvalue and energy-minimum-eigenvalue sensing methods are presented for the Nakagami-m fading channel. The simulation and performance results are presented for the maximum-eigenvalue-to-trace method and the arithmetic-to-geometric-mean method together with the analytical expressions for the threshold, probability of detection and probability of false alarm. In addition, another algorithm, maximum-eigenvalue-geometric-mean is proposed and is investigated in terms of the analytical and simulation results for Nakagami-m fading channels. Improved performance is shown compared to the other schemes when the number of samples is decreased and when the number of cooperating users is increased such that the ratio of the latter to the former is positive and less than unity. Analytical expressions are also presented. The eigenvalue detection methods exhibit good performance in noisy environments and are matched by their bounds. - Author(s): B. Valluri and V. Bhaskar
- Source: IET Communications, Volume 6, Issue 11, p. 1397 –1406
- DOI: 10.1049/iet-com.2011.0753
- Type: Article
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In this study, a conceptual transmission scheme that adjusts rate and power of codewords which are sent over a slowly fading channel, when quantised and possibly erroneous channel state information (CSI) is available at the transmitter, is designed. Here, the goal is to maximise data throughput or the expected data rate using a two-way training protocol and temporal power control at the transmitter. The common models used in analysis either assume perfect CSI at the receiver or noiseless state feedback links. However, in practical systems, neither is the channel estimate known perfectly at the receiver nor is the feedback link perfect. Analytical expressions for the relationship between the average power and data transmission rate are obtained for various scenarios. The average spectral efficiency is analysed under various fading channels to evaluate the system performance. Here, the focus is on the average channel conditions to improve the system throughput. - Author(s): S.O. Park ; J.K. Lee ; J.H. Park ; S.J. Kim
- Source: IET Communications, Volume 6, Issue 11, p. 1407 –1415
- DOI: 10.1049/iet-com.2011.0727
- Type: Article
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Recently, methods that combine the concepts of dynamic voltage scaling (DVS) and dynamic power management (DPM) approaches have been proposed for a single task. This study proposes adaptive power management system (APMS), which utilises useful features of both DPM and DVS and an existing pattern analysis algorithm, and new break even time-based task partition scheduling (BET-BTPS). APMS splits tasks based on BET to reduce the total power consumption of multiple multimedia applications in a mobile embedded system environment and analyses their usage patterns of peripheral devices and apply the results to their scheduling for further reduction of power consumption. It also takes into account the additional time delay that may occur while invoking and executing a timeslot scheduler to guarantee real-time services for multimedia data streams when the scheduling of APMS is in effect. In order to determine the optimal processor speed that minimises power consumption, the extra consumption required by the scheduler is compared with that reduced by BTPS. The proposed approach demonstrates better performance compared to existing power management schemes not only for single task but multiple tasks. - Author(s): S.M. Karim and I. Chakrabarti
- Source: IET Communications, Volume 6, Issue 11, p. 1416 –1424
- DOI: 10.1049/iet-com.2011.0713
- Type: Article
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Novel high-throughput architecture for a turbo decoder, which has been conceived by combining the advantages of pipelining and parallel processing, is proposed. Increase in throughput has been achieved by pipelining the add compare select offset (ACSO) unit and advancing the normalisation process in the ACSO unit based on global overflow protection logic. The proposed turbo decoder also benefits from incorporating low-complexity contention-free interleaver. The present work has demonstrated that a 32 maximum a posteriori probability (MAP) decoder core achieves a data rate of 1.138 Gbps at a maximum clock frequency of 486 MHz when implemented in a 90 nm process technology. Thus, the proposed turbo decoder meets the throughput requirement of modern wireless communication standards like third-generation partnership project (3GPP) long-term evolution (LTE). - Author(s): W. Chee-Wah Tan ; S.K. Bose ; T.-H. Cheng
- Source: IET Communications, Volume 6, Issue 11, p. 1425 –1437
- DOI: 10.1049/iet-com.2011.0451
- Type: Article
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Nodes in a wireless ad hoc network have to support routing using their limited battery power resource. The routing protocol involved should use battery power efficiently for good system performance. For systems where node location information is available, this study proposes an on-demand routing protocol for choosing a route based on maximising the minimum node battery power and minimising the total transmission power required to reach the destination. In addition, the routing protocol proposed is able to restrict control packet flooding during route discovery and pre-empt link breakages because of node mobility. A power and mobility aware optimisation problem is first formulated. For an actual practical implementation, we present a heuristic scheme, Power and Mobility Aware Routing or PMAR protocol. PMAR performs almost as well as the proposed optimisation approach in static networks. In mobile networks, PMAR performs very well in terms of network lifetime, the number of data packets carried within the network lifetime and delay performance. It is shown to be energy efficient, effective in restricting control packet flooding and able to substantially reduce the network overheads caused by link breakages. - Author(s): M.F. Rabbi and C.C. Ko
- Source: IET Communications, Volume 6, Issue 11, p. 1438 –1446
- DOI: 10.1049/iet-com.2011.0633
- Type: Article
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In the use of orthogonal frequency division multiple access (OFDMA) in multiple access applications, symbols are transmitted in narrowband sub-channels, which are supposed to be orthogonal. However, the use of a practical oscillator, with its inherent drift because of temperature and other environmental changes, will result in clock jitter which destroys the orthogonality between subcarriers and introduces inter-carrier interference (ICI). To alleviate the problem, this study proposes a novel tracking-based estimation algorithm, using which the effect of clock jitter can be compensated. Instead of modelling the clock jitter as a white noise process, the authors present a more realistic coloured clock jitter model based on practical oscillators. Using the fact that the jitter is coloured and so the jitters in adjacent OFDMA symbols are very roughly related in a linear manner, the authors formulate a new algorithm that models the jitter in the most recent blocks as linearly time varying. The authors then make use of a new objective function based on this model to derive an iterative jitter tracking scheme, so that the jitter in the current block can be better tracked. Simulation results are presented to illustrate the improvement in performance that can be obtained. - Author(s): X. Yu ; P. Navaratnam ; K. Moessner
- Source: IET Communications, Volume 6, Issue 11, p. 1447 –1455
- DOI: 10.1049/iet-com.2011.0464
- Type: Article
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Guaranteeing quality of service (QoS) is one of the most critical challenges in IEEE 802.11-based wireless networks. This study proposes an analytical framework to evaluate hybrid medium access control (MAC) scheduling mechanisms with distributed resource reservation (RR), that was proposed for the IEEE 802.11e-enhanced distributed channel access protocol for guaranteeing QoS. The hybrid MAC scheduling mechanisms split the airtime into service intervals with contention-free period for QoS guaranteed real-time sessions (RTSNs), and contention access period for other traffic sessions. The distributed RR ensures that the resources are allocated to RTSNs without the support of a centralised controller–this makes it suitable for ad hoc networking applications. The proposed analytical framework models the QoS (i.e. delay and throughput) performance of RTSNs with dedicated resources in a distributed environment, and also estimates the overall capacity of the network. Moreover, the derived models can be used to investigate the impact of changes to individual system parameters, such as service interval or size of transmission opportunity. The simulation results show that the proposed analytical framework precisely models the QoS performance of RTSNs and predicts the optimum resource allocation for improved network capacity. - Author(s): J. Jiang ; J.S. Thompson ; H. Sun ; P.M. Grant
- Source: IET Communications, Volume 6, Issue 11, p. 1456 –1465
- DOI: 10.1049/iet-com.2011.0169
- Type: Article
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A cooperative virtual multiple-input multiple-output (MIMO) system using two transmit antennas that implements bit-interleaved coded modulation (BICM) transmission and compress-and-forward (CF) relay cooperation among two receiving nodes is presented here. To perform CF cooperation, we propose to use standard source-coding techniques for virtual MIMO detection, based on the analysis of its expected rate bound and the tightness of the bound. Since the relay and the destination are closely spaced, the authors first assume an error-free conference link between them, to focus on investigating the achievable gain from the CF cooperation. Then the system throughput expression and upper bounds on the system error probabilities over block fading channels are derived. The results show that the relay enables the proposed cooperative virtual-MIMO system to achieve almost ideal MIMO performance with low source-coding rates. Furthermore, when we consider a non-ideal cooperation link for practical considerations, a channel-aware adaptive CF scheme is proposed, so that the relay could always adapt its source-coding rate to meet the data rate on the non-ideal link. Owing to the short-range communication and the proposed scheme, the impact of the non-ideal link is too slight to impair the system performance significantly. - Author(s): S. Hussain and X. Fernando
- Source: IET Communications, Volume 6, Issue 11, p. 1466 –1474
- DOI: 10.1049/iet-com.2010.0510
- Type: Article
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In this study, the authors address the problem of bandwidth limitations of the reporting channels in cognitive radio (CR) networks. They propose a cluster-based spectrum-sensing approach that minimizes the bandwidth requirements by reducing the number of terminals reporting to the fusion centre to a minimal reporting set. The approach replaces the secondary base station by a local fusion centre and combats the destructive channel conditions by replacing the global reporting channels with local channels. They also propose a new approach to select the location of the local fusion centre using the general centre scheme in graph theory. The minimal dominating set (MDS) clustering algorithm is used to obtain the minimal set of clusters that keep the network connected. This study investigates how the sensing efficiency, the sensing accuracy, and the per-node throughput are affected by the cluster size, the number of clusters, and the reporting channels error. The results obtained reveal that the cluster-based cooperative sensing system outperforms the conventuional cooperative sensing system in terms of throughout capacity especially when the reporting channels are subjected to a high probability of error. A systematic way to find the optimal number of cooperative clusters that gives a minimum probability of false alarm is presented. - Author(s): H.-J. Lee and J.-T. Lim
- Source: IET Communications, Volume 6, Issue 11, p. 1475 –1482
- DOI: 10.1049/iet-com.2010.0658
- Type: Article
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Over wireless multihop networks, the conventional transmission control protocol (TCP) cannot allocate the bandwidth fairly to flows. This is because flows with different locations competing for the same wireless channel may have very different perceptions on congestion in terms of packet delay and packet loss rate. In this study, the authors introduce a new window control algorithm and a new estimation method of congestion, which is called a delay information-based fair congestion control protocol (DFCCP). A new window control algorithm not only supports starved flows, but also allows starved flows to share the bandwidth fairly. Furthermore, since congestion occurs at multiple nodes over wireless multihop networks, the authors detect the level of congestion based on the summation of the average window sizes of multiple flows. The simulation results show that the proposed algorithm supports the starved flows while providing fairness among flows over wireless multihop networks. - Author(s): H.-L. Hung and Y.-F. Huang
- Source: IET Communications, Volume 6, Issue 11, p. 1483 –1488
- DOI: 10.1049/iet-com.2010.0997
- Type: Article
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A differential evolution (DE)-based partial transmit sequence (PTS) scheme for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems has been proposed. PTS techniques can improve the PAPR statistics of an OFDM signals, but the considerable computational complexity for the required search through a high-dimensional vector space is a potential problem for the implementation in practical systems. The DE is an efficient and powerful population-based stochastic search technique for solving optimisation problems over continuous space, which has been widely applied in many scientific and engineering fields. Thus, to reduce the complexity for searching phase weight vector and to improve the PAPR statistics, the authors introduce DE, to search the optimal phase weight factors. The simulation results show that the proposed DE-based PTS obtains an excellent PAPR performance with a low computational complexity. - Author(s): Z. Ghassemlooy ; X. Tang ; S. Rajbhandari
- Source: IET Communications, Volume 6, Issue 11, p. 1489 –1494
- DOI: 10.1049/iet-com.2011.0780
- Type: Article
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Binary polarisation shift keying (BPOLSK) has been proposed to mitigate the atmospheric turbulence-induced fading in free space optical (FSO) communication systems. In this study, the Q-factors obtained for the BPOLSK-FSO system are verified in conjunction with theoretical results to confirm the validity of the proposed scheme. The analytical bit error rate (BER) for the BPOLSK and non-return-to-zero on–off keying (NRZ-OOK) schemes are presented. The authors show that the BPOLSK scheme with direct detection offers improved BER performances compared to NRZ-OOK in the presence of weak turbulence, which is inferred from the experimental Q-factor and theoretical BER. For a turbulence variance σ21 of 0.003 and the transmitted optical power of −16.8 dBm, values for Q-factor are ∼11 and ∼8.5 for BPOLSK and NRZ-OOK schemes, respectively. The authors show that the predicted signal-to-noise ratio (SNR) for BPOLSK and NRZ-OOK schemes are ∼13.5 and ∼15 dB, respectively, for a BER of 10−6 and σ21 of 0.01. When σ21 increases to 0.1, ∼8 dB lower values of SNR is required for BPOLSK compared with NRZ-OOK. - Author(s): O. Raoof and H.S. Al-Raweshidy
- Source: IET Communications, Volume 6, Issue 11, p. 1495 –1501
- DOI: 10.1049/iet-com.2010.0357
- Type: Article
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Throughout this study, an adaptive competitive second-price pay-to-bid sealed auction game is presented as a solution to the fairness problem of spectrum sharing among a number of users in a cognitive radio environment. First, a comparison among three main spectrum-sharing game models; optimal, cooperative and competitive game models is discussed to highlight the advantages and disadvantages of each model. The results prove that cooperative games aim to achieve Nash equilibrium between primary and secondary players and provide better revenue to them. Also, it proves that cooperative games are best when the number of secondary users changes dynamically, but only when the number is low. As in practical situations, the number of secondary users might increase dramatically and cooperative games will lose their powerful advantage once that happens. As a result, the proposed mechanism creates a competition between the bidders and offers better revenue to all players in terms of fairness. The proposed model ensures that users with better channel quality, higher traffic priority and fairer bids will get a better chance to share the offered spectrum. It is shown by numerical results that the proposed mechanism could reach the maximum total profit for all users with better fairness. - Author(s): Z. Andalibi ; H.H. Nguyen ; J.E. Salt
- Source: IET Communications, Volume 6, Issue 11, p. 1502 –1510
- DOI: 10.1049/iet-com.2010.0858
- Type: Article
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The performance of bit-interleaved coded modulation in multiple-input multiple-output (BICM-MIMO) systems using an iterative channel estimator is analysed. In a conventional iterative channel estimator, after initialisation with the training phase, the channel estimator switches to the data phase. However, such a conventional iterative channel estimator does not always improve the performance of the receiver. In order to guarantee the performance improvement, a condition on when the output of the decoder should be used by the estimator is determined. Such a condition is related to the reliability of the soft information utilised by the channel estimator. The key in establishing this relationship is to use the mutual information (MI) that the observation vector has about the channel gains given the output of the decoder at each iteration. In this switch-augmented conventional iterative channel estimator, referred to as SAICE, the condition is theoretically found and indicates the needed reliability of the soft information for the channel estimator at the switching time. The switch-augmented scheme guarantees performance improvement of the iterative receiver with each iteration, however, it might need many iterations to converge for moderate to low signal-to-noise ratios (SNRs). A less computationally intensive approach is to use both the training and data segments of the observation. This approach produces a combined iterative channel estimator (CICE) for BICM-MIMO systems. The performance behaviour of the BICM-MIMO system is illustrated through the extrinsic information transfer (EXIT) chart with imperfect channel state information (CSI). Analytical results are verified with computer simulations. - Author(s): M. Naeem ; U. Pareek ; D.C. Lee
- Source: IET Communications, Volume 6, Issue 11, p. 1511 –1518
- DOI: 10.1049/iet-com.2011.0247
- Type: Article
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The authors presented low-complexity schemes for jointly deciding subcarrier assignment, power allocation and relay assignment (JSPARA) for multiuser non-regenerative relaying in a multigroup, multicast cognitive radio system (MMCRS). The authors considered two different optimisation problems. In one optimisation problem, the authors studied the problem of maximising the sum-rate of an MMCRS. In another optimisation problem, the authors considered the problem of maximising the rate of the worst multicast group of users. And also the authors proposed low-complexity iterative algorithms for JSPARA. The proposed algorithms have low-computational complexity, and their effectiveness is verified through simulation results. - Author(s): R. Xie ; F.R. Yu ; H. Ji
- Source: IET Communications, Volume 6, Issue 11, p. 1519 –1528
- DOI: 10.1049/iet-com.2011.0343
- Type: Article
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Cognitive radio networks with cooperative communications can effectively improve spectrum efficiency and data rate. Under this network scenario, there are three possible transmission modes: direct transmission, multi-hop transmission and cooperative communication. To optimise the system performance, three issues should be carefully considered: whether or not and which relay is needed, which channel is selected and which transmission mode is used. Therefore in this study, the authors solve these three problems jointly to optimise the outage capacity for cognitive radio networks with cooperative communications. Particularly, they emphasise on the imperfect channel sensing situation. Under these setup and the constraints, the authors formulate the problem of relay determination, transmission channel and corresponding transmission mode selection to maximise the outage capacity as a discrete optimisation problem. Then a discrete stochastic optimisation algorithm is proposed to maximise the outage capacity to adaptively determine relay and select the optimal transmission channel and transmission mode. The proposed algorithm has fast convergence rate and low computation complexity. Moreover, the time-varying radio environment scenario is also considered, and they show that the proposed algorithm has good tracking capability for time-varying radio environment. Finally, simulation results are presented to demonstrate the performance of proposed scheme. - Author(s): H.L. Minh ; D. O'Brien ; G. Faulkner ; M. Wolf
- Source: IET Communications, Volume 6, Issue 11, p. 1529 –1536
- DOI: 10.1049/iet-com.2011.0322
- Type: Article
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The design, simulation and practical implementation for a bidirectional 1.25 Gbit/s indoor optical wireless communications system has been presented. It is a part of the European community funded hOME Gigabit Access project (OMEGA). The line-of-sight (LOS) system uses angle-diversity transceivers enabling discrete beam steering. Each transceiver uses three transmitting and receiving elements giving an overall field of view of ∼25×8° and a transmission range of 3 m. Measurement shows that the system can operate at a bit error rate below 10−9 without channel coding and the handover between cells is <400 ns. Detail of a demonstrator of high-definition (HD) video embedded in gigabit ethernet stream using this system is also reported. - Author(s): N. Souto ; R. Dinis ; J.C. Silva
- Source: IET Communications, Volume 6, Issue 11, p. 1537 –1543
- DOI: 10.1049/iet-com.2011.0905
- Type: Article
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The authors derive a lower bound on the performance of generalised multilevel quadrature amplitude modulations (M-QAM) in time-discrete multipath Rayleigh fading environments with imperfect channel estimation. The bound can be regarded as an extension of the well-known matched filter bound (MFB), taking into account the impact of imperfect channel knowledge. The analytical expressions derived allow the computation of the bit error rate for the different bit streams that can be mapped simultaneously onto M-QAM symbols using a hierarchical approach when unequal bit error protection is desired. - Author(s): F.H. Panahi and A. Falahati
- Source: IET Communications, Volume 6, Issue 11, p. 1544 –1554
- DOI: 10.1049/iet-com.2011.0030
- Type: Article
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This study investigates the spectrum shaping observed in ultra-wideband (UWB) communications. An auxiliary independent signal (AIS) to limit undesired spectral lines because of periodicity or unbalanced data sources (i.e. non-uniformly distributed) and or non-symmetric data modulation schemes are introduced. Each transmitted symbol is represented by a preamble AIS pulse followed by a set of transmitted data pulses that are weighted, delayed and summed in accordance with a predefined modulation. The use of the fifth derivative Gaussian pulse ensures that the UWB spectrum mask established by the Federal Communications Commission (FCC) is met, and a preamble signal is designed to eliminate spectral lines at specific frequencies that appear mainly by existing balanced or unbalanced binary data sources. A unified spectral analysis is adapted for general uncorrelated and correlated quaternary bi-orthogonal modulations. An optimisation problem is also introduced in the case of unbalanced data sources in order to minimise undesired spectral lines subject to comply with the FCC spectrum mask and maximise spectral utilisation. - Author(s): W.Y. Xu
- Source: IET Communications, Volume 6, Issue 11, p. 1555 –1561
- DOI: 10.1049/iet-com.2010.0884
- Type: Article
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This study presents a blind carrier frequency offset (CFO) tracking algorithm for orthogonal frequency division multiplexing systems with constant modulus signalling. Both single-input single-output and multiple-input multiple-output (MIMO) systems are considered. Based on the assumption that the channel frequency response (CFR) has been estimated by training symbols and keeps constant over one frame duration, we discover that the CFO can be estimated via minimising the power difference between the received signals and the CFR. The polynomial rooting method is exploited to derive a low complexity solution. The expectation and mean-square error of the proposed method are derived mathematically. Besides, the effect of channel estimation error on the performance of CFO tracking is addressed and it is shown that the proposed algorithm is robust to this error. At last, this blind scheme can be applied to a MIMO system with the aid of space time block codes. - Author(s): M. Coulon and D. Roviras
- Source: IET Communications, Volume 6, Issue 11, p. 1562 –1572
- DOI: 10.1049/iet-com.2011.0379
- Type: Article
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This study deals with a multiple-access transmission scheme based on random permutations, which allows one to obtain both spectrum spreading and time spreading. In particular, one is interested by the multi-user detection when the transmission is achieved in the context of asynchronous frequency-selective and time-varying channels. For this detection, it is assumed that the channel coefficients and delays are unknown at the receiver side. Instead, only rough estimates of the minimum and maximum delays are available. However, it is supposed that the transmitter sends pilot signals, that is, training bit sequences, which allow the receiver to perform an LMS (least-mean-square)-type detection. This study provides theoretical performance results. Moreover, this random permutation-based transmission scheme is compared with the DS-CDMA system, for which a similar LMS receiver is defined, under the same assumptions. It is then shown that, for time-varying channels, the permutation-based system presents lower bit-error rates than the DS-CDMA system, since the former provides time diversity. - Author(s): Y. Zhang
- Source: IET Communications, Volume 6, Issue 11, p. 1573 –1578
- DOI: 10.1049/iet-com.2011.0831
- Type: Article
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In linear multi-input multi-output channel systems, reduction process is employed to reduce the computational cost of sphere decoding (SD) algorithm. Usually a reduction process includes not only permutations but also unimodular transformations. However, owing to the box-constraint, the current reduction strategies are limited to only permutations, which makes SD algorithm still very time-consuming. In this study a theoretical complexity analysis on SD algorithm is first proposed to show what kind of criteria a reduction process should pursue. Then a new reduction strategy which combines permutations with unimodular transformations is presented to obtain a better reduced detection problem. Simulation results showed that this new reduction strategy can make SD algorithm much more efficient than those reduction strategies with only permutations. - Author(s): S.C. Nguyen and K. Sandrasegaran
- Source: IET Communications, Volume 6, Issue 11, p. 1579 –1586
- DOI: 10.1049/iet-com.2011.0863
- Type: Article
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Long-term evolution-advanced (LTE-A), the true 4G technology of third Generation Partnership Project family, has a new feature that aggregates multiple LTE carriers so that users can be served on multiple component carriers (CCs). This characteristic plays an important role to increase data rate multiple times for LTE-A users with corresponding multiple CCs. However, current proposed packet scheduling (PS) algorithms ignore this effect in the effort of providing new solution that increases system performance. The modified proportional fair algorithms proposed in this study can provide optimised algorithm for PS mechanism in LTE-A system as well as other technologies that use multiple carriers. - Author(s): A. Ijaz ; A.B. Awoseyila ; B.G. Evans
- Source: IET Communications, Volume 6, Issue 11, p. 1587 –1593
- DOI: 10.1049/iet-com.2010.0938
- Type: Article
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This paper presents a signal-to-noise ratio (SNR) estimation algorithm for advanced digital video broadcasting- return channel via satellite (DVB-RCS) systems using adaptive coding and modulation (ACM). Due to the absence of a repetitive pilot symbol structure, SNR estimation has to be performed using the fixed symbol preamble data. Moreover, sporadic nature of data traffic on the return link causes variation in interference level from slot to slot and, therefore, the estimation has to be done within one traffic slot duration. Hence, it becomes necessary to use a combination of data-aided and decision-directed (DD) algorithms so as to make use of traffic data. A non-data-aided estimator that was previously proposed by the authors for binary and quadrature phase shift keying schemes is extended to 8-PSK in a decision directed manner. The inherent bias of DD approach at low values of SNR is reduced by using a hybrid approach, that is, using the proposed estimator at moderate/high values of SNR and the moments-based estimator (M2M4) at low values of SNR. Overall improved performance of the proposed hybrid estimator, in terms of accuracy and complexity, makes it an attractive choice for implementing ACM in advanced DVB-RCS systems.
Fast two-stage spectrum detector for cognitive radios in uncertain noise channels
Power saving scheme based on joint control of buffer-threshold and timer in binary exponential sleep mode
Simplified maximum likelihood-based detection schemes for M-ary quadrature amplitude modulation spatial modulation
Interference aware resource allocation in orthogonal frequency-division multiple access-based relay networks
Spectrum sidelobe suppression for discrete Fourier transformation-based orthogonal frequency division multiplexing using adjacent subcarriers correlative coding
Quality-of-service-based interference cancellation in upstream very-high-bit-rate digital subscriber line systems
Blind eigenvalue-based spectrum sensing for cognitive radio networks
Performance measures over slowly fading multiple-input multiple-output channels using quantised and erroneous feedback
Adaptive power management system for mobile multimedia device
High-throughput turbo decoder using pipelined parallel architecture and collision-free interleaver
Power and mobility aware routing in wireless ad hoc networks
Timing jitter tracking for orthogonal frequency division multiple access system in high doppler spread
Performance analysis of distributed resource reservation in IEEE 802.11e-based wireless networks
Performance assessment of virtual multiple-input multiple-output systems with compress-and-forward cooperation
Approach for cluster-based spectrum sensing over band-limited reporting channels
Fair congestion control over wireless multihop networks
Peak-to-average power ratio reduction in orthogonal frequency division multiplexing system using differential evolution-based partial transmit sequences scheme
Experimental investigation of polarisation modulated free space optical communication with direct detection in a turbulence channel
Spectrum sharing in cognitive radio networks: an adaptive game approach
Analysing bit-interleaved coded modulation in multiple-input multiple-output systems with channel estimation error
Max–min fairness aware joint power, subcarrier allocation and relay assignment in multicast cognitive radio
Outage capacity optimisation for cognitive radio networks with cooperative communications
Bidirectional gigabit ethernet optical wireless communications system for home access networks
Performance bound for generalised multilevel-quadrature amplitude modulations constellations in multipath Rayleigh fading channels with imperfect channel estimation
Spectral efficient impulse radio-ultra-wideband transmission model in presence of pulse attenuation and timing jitter
Carrier frequency offset tracking for constant modulus signalling-based orthogonal frequency division multiplexing systems
Multi-user adaptive receivers for a multiple-access system based on random permutations on time-varying frequency-selective channels with unknown delays and coefficients
Effective reduction for sphere decoder in linear multi-input multi-output channel systems
Optimised proportional fair algorithm for long-term evolution-advanced system with multiple component carriers
Signal-to-noise ratio estimation algorithm for adaptive coding and modulation in advanced digital video broadcasting–radar cross section satellite systems
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