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Communications, IET

Issue 3 • Date Feb. 11 2011

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Displaying Results 1 - 14 of 14
  • Moment generating function-based performance evaluation of amplify-andforward relaying in n??nakagami fading channels

    Page(s): 253 - 263
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (965 KB)  

    In this study, the authors investigate the error rate performance of amplify-and-forward relaying over N*Nakagami fading channels. This is a recently introduced channel model that involves the product of N Nakagami-m-distributed random variables. Employing the moment generating function approach, the authors derive symbol error rate expressions for a single-relay system under instantaneous power scaling (IPS) and average power scaling (APS) factors at the relay node, that is, variable and fixed gains. The results achieved by the authors demonstrate that the achievable diversity order is a function of Nakagami fading parameter (m) and degree of cascading (N). An identical diversity order is obtained under both scaling factors when the relay is close to the destination. When the relay is close to the source, IPS becomes advantageous over APS. Monte-Carlo simulations are further provided to confirm the analytical results. View full abstract»

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  • Performance analysis of cooperative diversity systems with opportunistic relaying and adaptive transmission

    Page(s): 264 - 273
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (631 KB)  

    The system performance of the opportunistic relaying technique in amplify-and-forward cooperative systems with adaptive transmission over Rayleigh fading channels is analysed. Two rate-adaptive modulation techniques, continuous-rate and discrete-rate adaptive techniques, are considered. Closed-form expressions are derived for the average spectral efficiency, outage probability and the average bit error rate for two cases: independent and identically distributed (i.i.d.) fading links and independent and non-identically distributed (i.ni.d.) links. Using numerical evaluations, the performances of different cases are compared showing the advantages of each adaptive modulation technique in conjunction with the opportunistic relaying in a cooperative communication over both i.i.d. and i.ni.d. fading links. View full abstract»

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  • Efficient simulation of orthogonal frequency division multiplexing systems using importance sampling

    Page(s): 274 - 283
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (351 KB)  

    This study presents the importance sampling (IS) analysis for the efficient simulation of orthogonal frequency division multiplexing (OFDM) systems. Importance sampling is an efficient rare-event simulation technique that aims at reducing the simulation runtime by reducing the variance of the estimator. The efficiency of IS highly relies on the proper selection of the biased simulation density function. This paper considers the problem of biasing the simulation density function of OFDM systems for achieving higher variance reduction gains and computational efficiencies. In particular, the authors show how to bias the time domain noise density function and how to correct the biased error count at the receiver in the frequency domain of an OFDM system operating over multipath fading channels with minimum mean square error equalisation. Further, the authors obtain the optimum biasing parameters for variance scaling method and mean translation method applied to bias the noise density function. The presented results can easily be generalised to OFDM systems operating over additive white Gaussian noise (AWGN) channels. The simulation results demonstrate that extensive gains in estimator variance reduction can be achieved through the proposed analysis rather than by using conventional Monte-Carlo simulations. View full abstract»

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  • Quality of service provisioning in worldwide interoperability for microwave access networks based on cooperative game theory

    Page(s): 284 - 295
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (645 KB)  

    Quality of service (QoS) is a critical issue in the design and management of worldwide interoperability for microwave access (WIMAX) networks. In this study, the authors propose a novel two-tier QoS framework and a scheduling scheme for QoS provisioning in WiMAX networks based on the Nash bargaining solution (NBS) obtained from cooperative game theory. The framework cannot only offer Pareto optimality for the entire system, but also assure fairness for each service and connection. They apply the NBS into the issue of QoS service in WiMAX networks. They utilise the equivalent optimisation problem to obtain the bargaining point. The parameters of the optimisation model have been verified by analysing the characteristics of each service flow in the WiMAX networks. A heuristic scheduling algorithm has been designed to implement the optimised solution. The effectiveness of the proposal has been verified by experimental results, which can show much better performance in terms of delay, loss rate and throughput. View full abstract»

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  • Two-stage power allocation for amplify-andforward cooperative networks with distributed gabba space-time codes

    Page(s): 296 - 306
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (649 KB)  

    This study presents a two-stage power allocation for the amplify-and-forward (AF) cooperative networks with distributed generalised ABBA (GABBA) space-time codes. The new power allocation scheme first determines the transmit power between the source node and the relay nodes by maximising the instantaneous rate, and thereafter optimises the power distribution among the relay nodes via the water-filling. Also, a maximum-likelihood detection, which makes use of the encoding structure of the distributed GABBA space-time codes, is addressed to alleviate the computational overhead. Moreover, a performance analysis including the array gain and the diversity gain is also scrutinised to provide further insights into the cooperative networks considered, where the destination is equipped with multiple antennas. Conducted simulations show that the GABBA coded AF cooperative networks incorporated with the proposed two-stage power allocation can attain close or even superior performance compared with previous works but with substantially reduced computational complexity. View full abstract»

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  • High user capacity collaborative code-division multiple access

    Page(s): 307 - 319
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (546 KB)  

    In this study, the authors propose a novel collaborative multi-user transmission and detection scheme for the uplink of code-division multiple access (CDMA) that exploits the differences between users' fading channel signatures to increase the user capacity well beyond the spreading length in multiple access interference (MAI) limited environment. The authors show that it is possible to achieve this increase at a low complexity and high bit error rate (BER) performance in flat fading channels, which is a major research challenge for overloaded CDMA systems. In this approach, instead of using one sequence per user as in conventional CDMA, the authors group a small number of users to share the same spreading sequence and enable group spreading and despreading operations. The proposed collaborative multi-user receiver consists of two stages: group multi-user detection (MUD) stage to suppress the MAI between the groups and a low complexity maximum-likelihood detection stage to recover jointly the co-spread users' data using minimum Euclidean distance measure and users' channel gain coefficients. The scheme is investigated analytically and by extensive simulations and comparisons with conventional CDMA, overloaded CDMA using group pseudo-decorrelation (G-PD) and layered space'time (LAST) MUD. It is shown that the total number of full-rate users supported by the scheme is substantially higher than the available sequences. Moreover, it achieves much lower complexity and significantly improved BER for the same user capacity compared with G-PD. It is also shown that, with antenna diversity reception, collaborative CDMA considerably outperforms LAST scheme, particularly when more transmit antennas per group than available receive antennas are employed. View full abstract»

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  • Maximal ratio combining in independent identically distributed n nakagami fading channels

    Page(s): 320 - 326
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (394 KB)  

    Short-term fading in wireless systems can be described using a cascaded approach permitting the modelling of severely faded channels. A maximal ratio combining (MRC) diversity is implemented to study the performance improvement in such channels. While the probability density function (pdf) of the signal-to-noise ratio of the independent and identically distributed N*Nakagami cascade channels is available in terms of Meijer*s G functions, the pdf of the MRC output is not available. Because of this, the moment generating function of the MRC output is used to estimate the average bit error rates. The characteristic function is used to obtain the cumulative distribution (CDF) of the MRC output by applying the Gil-Pelaez approximation. The outage probabilities were then estimated using the CDF. Results showed that the wireless system performance improved with diversity even though the level of improvement declined as the number of cascaded components N increased. The analysis also suggests that additional mitigation such as combining signals from multiple base stations (macrodiversity) might be necessary to significantly improve the performances of cascaded channels. View full abstract»

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  • Quality of service-based multi-domain routing under multiple quality of service metrics

    Page(s): 327 - 336
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    Applications such as voice and video require network paths that satisfy several different quality of service (QoS) metrics, such as delay, jitter, packet loss rate and availability. The calculation of paths under multiple QoS metrics, such as the above four metrics, is a difficult problem since these metrics are in general incompatible. The authors propose a simple method for combining the above four QoS metrics into a single composite QoS metric which can be used as a link cost in Dijkstra's algorithm in order to calculate a path. The authors evaluated the proposed method in a multi-domain routing environment where domain reachability information is available through a service oriented architecture paradigm, and they show that it outperforms two commonly used methods. The results are also applicable to routing within a single domain. View full abstract»

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  • Performance analysis of incremental-relaying cooperative-diversity networks over rayleigh fading channels

    Page(s): 337 - 349
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (590 KB)  

    Cooperative-diversity has recently been proposed as an efficient technique to form virtual antenna arrays without using collocated multiple antennas at the transmitters or receivers. Cooperative-diversity networks use the neighbour nodes to assist the source by sending the source information to the destination for achieving spatial diversity. Regular cooperative-diversity networks make an inefficient use of the channels because relays forward the source signal to the destination every time regardless of the channel conditions. Incremental-relaying cooperative-diversity has been proposed to save the channels by restricting the relaying process to the bad channel conditions only. Incremental-relaying cooperative-diversity networks exploit limited feedback from the destination terminal, for example, a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback, in this case only, the relay retransmits the source signal in an attempt to exploit spatial diversity by combining the signals received at the destination from the source and the relay. In this study, the authors study the end-to-end performance of un-coded incremental-relaying cooperative-diversity networks using decode-and-forward and amplify-and-forward relaying over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate, the signal-to-noise ratio (SNR) outage probability and average achievable rate are determined. Results show that the un-coded incremental-relaying cooperative-diversity can achieve the maximum possible diversity, compared with the regular cooperative-diversity networks, with higher channel utilisation. View full abstract»

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  • Adaptive beamforming for large arrays in satellite communications systems with dispersed coverage

    Page(s): 350 - 361
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (683 KB)  

    Conventional multibeam satellite communications systems ensure coverage of wide areas through multiple fixed beams where all users inside a beam share the same bandwidth. The authors consider a new and more flexible system where each user is assigned his own beam, and the users can be very geographically dispersed. This is achieved through the use of a large direct radiating array coupled with adaptive beamforming so as to reject interferences and to provide a maximal gain to the user of interest. New fast-converging adaptive beamforming algorithms are presented, which allow one to obtain good signal to interference and noise ratio with a number of snapshots much lower than the number of antennas in the array. These beamformers are evaluated on reference scenarios. View full abstract»

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  • Power allocation in multiple-input multipleoutput orthogonal frequency division multiplexing-based cognitive radio networks

    Page(s): 362 - 370
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    Multi-carrier systems are one of the best candidates for applying in cognitive radio (CR) networks because of the spectrum shaping and high adaptive capabilities. Since secondary users (SUs) in this structure use a limited number of sub-carriers because of deactivation of the primary users' (PUs) band, the total capacity of CR networks is limited. On the other hand, multiple transmit antennas can be applied to orthogonal frequency division multiplexing (OFDM)-based CR in order to compensate this capacity leakage. This study aims to investigate multiple-input multiple-output (MIMO)-OFDM as one of the best hybrid multi-carrier systems, as a physical layer of CR networks. Considering different conditions to obtain maximum total capacity of CR networks, an optimal power allocation algorithm is scrutinised. Theoretically, it is shown that this proposed algorithm can maximise the total capacity and at the same time, keep the caused interference in PUs' bands in a tolerable range. To simplify the algorithm complexity, we also propose a sub-optimal scheme. The simulation results of the new algorithms are compared with previous methods, which present the enhancement and efficiency of the proposed algorithms. Furthermore, the simulation results show that our proposed schemes can load more power into the CR user's band in order to achieve higher transmission capacity for a given interference threshold. View full abstract»

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  • Cellular network bandwidth management scheme by using nash bargaining solution

    Page(s): 371 - 380
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (359 KB)  

    Bandwidth is an extremely valuable and scarce resource in wireless networks. Therefore efficient bandwidth management plays an important role in determining network performance. Adaptive bandwidth reservation and borrowing algorithms are proposed for multimedia cellular networks here. Based on the well known game-theoretic concept of bargaining, wireless bandwidth is controlled as efficiently as possible while ensuring quality-of-service (QoS) guarantees for higher-priority traffic services. Under dynamic network condition changes, control decisions in the proposed algorithms are made adaptively to strike a well-balanced network performance. This dynamic online approach can provide adaptability, feasibility and efficiency for real-world network operations. With a simulation study, the proposed scheme approximates an optimised solution under widely diverse traffic load intensities. View full abstract»

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  • Equalisation of non-linear time-varying channels using a pipelined decision feedback recurrent neural network filter in wireless communication systems

    Page(s): 381 - 395
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (878 KB)  

    To combat the linear and non-linear distortions for time-invariant and time-variant channels, a novel adaptive joint process equaliser based on a pipelined decision feedback recurrent neural network (JPDFRNN) is proposed in this paper. The JPDFRNN consists of a number of simple small-scale decision feedback recurrent neural network (DFRNN) modules and a linear combiner. The cascaded DFRNN provides pre-processing for the linear combiner. Moreover, each DFRNN can provide a local interpolation for M sample points; the final linear combiner presents a global interpolation with good localisation properties. Furthermore, since those modules of non-linear subsection can be performed simultaneously in a pipelined parallelism fashion, this would result in a significant improvement in the total computational efficiency. Simulation results show that the performance of the JPDFRNN using the modified real-time recurrent learning (RTRL) algorithm is superior to that of the DFRNN and RNN for the non-linear time-invariant and time-variant channels. View full abstract»

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  • Rate allocation games in multiuser multimedia communications

    Page(s): 396 - 407
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (358 KB)  

    In this study, the authors study a game-theoretic framework for the problem of multiuser rate allocation in multimedia communications. The authors consider the multimedia users to be autonomous, that is, they are selfish and behave strategically. The authors propose a rate allocation framework based on a pricing mechanism to prevent the selfish users from manipulating the network bandwidth by untruthfully representing their demands. The pricing mechanism is used for message exchange between the users and the network controller. The messages represent network-aware rate demands and corresponding prices. The authors show that a Nash equilibrium can be obtained, according to which the controller generates allocations that are efficient, budget balanced and satisfy voluntary participation. Simulation results demonstrate the validity of the proposed framework. 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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