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Communications, IET

Issue 12 • Date August 13 2010

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Displaying Results 1 - 12 of 12
  • Learning models for video quality prediction over wireless local area network and universal mobile telecommunication system networks

    Page(s): 1389 - 1403
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    Universal mobile telecommunication system (UMTS) is a third-generation mobile communications system that supports wireless wideband multimedia applications. The primary aim of this study is to present learning models based on neural networks for objective, non-intrusive prediction of video quality over wireless local area network (WLAN) and UMTS networks for video applications. The contributions of this study are two-fold: first, an investigation of the impact of parameters both in the application and physical layer on end-to-end video quality is presented. The parameters considered in the application layer are content type (CT), sender bitrate (SBR) and frame rate (FR), whereas in the physical layer block error rate (BLER) and link bandwidth (LBW) are considered. Secondly, learning models based on adaptive neural fuzzy inference system (ANFIS) are developed to predict the visual quality in terms of the mean opinion score for all contents over access networks of UMTS and WLAN. ANFIS is well suited for video quality prediction over error-prone and bandwidth restricted UMTS as it combines the advantages of neural networks and fuzzy systems. The ANFIS-based artificial neural network is trained using a combination of physical layer parameters such as BLER and LBW and application layer parameters of CT, SBR and FR. The proposed models are validated using unseen data set. The preliminary results show that good prediction accuracy was obtained from the models. This study should help in the development of a reference-free video prediction model and quality of service control methods for video over UMTS/WLAN networks. View full abstract»

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  • Distributed water-filling algorithm for direct-sequence ultra wideband cognitive radio network with limit on aggregate power emission

    Page(s): 1404 - 1414
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (434 KB)  

    Despite their near-noise power emission, ultra wideband (UWB) radios, particularly direct-sequence ultra wideband (DS-UWB), are still possible to cause harmful interference to legacy radio systems. When they participate in a large dense cognitive radio network (CRN) and transmit simultaneously, their joint power emission would be disastrous if without control. We address this problem by imposing a limit on the aggregate power emission of DS-UWB CRN. The limit is negotiable. It takes effect by letting each transmitter adapt to a spectrum void defined as the area below the limit itself and above the interference temperature experienced instantly by the transmitter. We propose a water-filling algorithm that maximises the sum capacity while enabling each transmitter to fit its power spectral density into, and thus to make the most of, the spectrum void. The algorithm is performed locally at the transmitter with low complexity. Numerical analysis based on a realistic office network shows that the algorithm can bring the aggregate power emission even down below the Federal Communications Commission limit for individual UWB device, but still guarantees a given bit-error performance to nearly 40 active users. View full abstract»

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  • Congestion control for streaming service in IEEE 802.11 multihop networks

    Page(s): 1415 - 1422
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    The existing congestion control algorithms for streaming service experience the performance degradation over IEEE 802.11 multihop network because they mainly focus on the prevention of the buffer overflow at the specific node. However, congestion collapse happens not because of the buffer overflow but because of the serious contention at multiple nodes. As the MAC layer contention becomes serious, the end-to-end delay and the packet loss rate due to collision increase while throughput smoothness is not guaranteed due to fluctuation of the queueing delay at each node. Here, the authors propose a TCP-friendly congestion control algorithm based on the MAC layer contention state to improve streaming service. Specifically, each flow controls its transmission rate based on the estimated contention state which each node notifies to each flow by marking packets. The simulation results show that the proposed algorithm utilises the channel bandwidth more efficiently with providing throughput smoothness compared with the existing algorithms. View full abstract»

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  • Outage analysis of relay-assisted free-space optical communications

    Page(s): 1423 - 1432
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (381 KB)  

    Despite their attractive features, free-space optical (FSO) communications suffer from several challenges in practical deployment; the major of them is fading or scintillation. To overcome such limitations, multiple input multiple output (MIMO) and cooperative techniques have been proposed. Although the promising effects of cooperative transmissions in radio frequency (RF) communications have greatly been investigated, there have not been remarkable researches on cooperative transmissions in FSO communications. In this study, the authors consider a relay-assisted FSO communication and investigate the outage performance of two well-known cooperative protocols, namely amplify-and-forward (AF) and decode-and-forward (DF), for this communication system. By a new definition of the order of diversity, the authors derive an analytical expression for the performance comparison of different cooperative and non-cooperative protocols. The authors also evaluate the performance of a FSO communication with two transmitter telescopes (MIMO systems) and compare its outage probability with those of cooperation strategies. The authors investigate the best place for the relay for both the AF and DF strategies and show that relay-assisted techniques can be used for FSO communication to achieve spatial diversity. Their performance can surpass that of the two-transmitter case by properly choosing the location of the relay. View full abstract»

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  • Reduction of out of band radiation using carrier-by-carrier partial response signalling in orthogonal frequency division multiplexing

    Page(s): 1433 - 1442
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (759 KB)  

    Orthogonal frequency division multiplexing (OFDM) is a mature and one of the most popular multicarrier modulation (MCM) techniques. Also, it is the main candidate for physical layer of cognitive radio (CR) networks. CR is a new method to satisfy ubiquitous demand for wireless services while there is no enough unlicensed spectrum. However, the most important shortcoming of OFDM-based CR systems is the high level of out of band (OOB) components that originate from simple fast Fourier transform (FFT)-based implementation. In this study, the authors propose a novel method to reduce side-lobes of OFDM spectrum. In this method proper carrier-by-carrier partial response signaling is used on the modulated symbols across the time. This method will allow for using other techniques for OOB radiation or peak-to-average power ratio (PAPR) reduction, while does not require high complexity at the transmitter, i.e. just the receiver should have either maximum likelihood sequence detector (MLSD) in case of no pre-coding or a simple slicer in case of pre-coding. Moreover, it will not affect the PAPR but will increase word error rate (WER). Simulation results show that about 7 dB reduction in OOB components can be expected by this method. View full abstract»

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  • Inter-subcarrier interference compensation in the frequency-hopped single-carrier frequency division multiple access communication system

    Page(s): 1443 - 1451
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (862 KB)  

    Single-carrier frequency division multiple access (SC-FDMA) system having very good characteristic on peak-to-average power ratio is promising in communication area. But the performance of SC-FDMA system is very sensitive to inter-subcarrier interference (ICI), and existing phase noise suppression algorithm has reduced just phase noise only. Therefore the authors propose effective method, phase noise and frequency offset suppression (PNFS) algorithm, using comb-type pilot. PNFS algorithm can suppress phase noise, carrier frequency offset and even Doppler effect simultaneously in frequency domain. Through PNFS algorithm, SC-FDMA system has robust characteristic against ICI of performance degradation. Moreover, in these days, most electronic communication systems are weak to jamming. So, frequency-hopped (FH) scheme, which is one kind of spread spectrum techniques as a means of making performance better to supplement a disadvantage of SC-FDMA system on jamming attack, is considered. The authors would like to analyse ICI and jamming in SC-FDMA system and employ FH technique in SC-FDMA system because existing studies have not considered the situation regarding ICI and jamming exist simultaneously in mobile channel. So, the authors analyse degradation factors in FH-SC-FDMA system about ICI and jamming signal categorised as partial band jamming and multi-tone jamming. Then, the proposed FH-SC-FDMA system using PNFS algorithm has strong performances about ICI and jamming. View full abstract»

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  • Block QR decomposition and near-optimal ordering in intercell cooperative multiple-input multiple-output-orthogonal frequency division multiplexing

    Page(s): 1452 - 1462
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (830 KB)  

    Here, the authors investigate dirty paper coding (DPC) in intercell cooperative multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM). Based on the multidimensional structure of intercell cooperative MIMO-OFDM, the DPC model has been modified by introducing a block QR decomposition (BQRD) algorithm which transforms the multiuser channel to a block lower triangular structure. The overall error performance of the proposed BQRD-based DPC is dominated by the error performance of the last precoded user. To improve the last user's performance, it was, first, shown that, in a system with U active users, the channel gain matrix remains unchanged for any user acting as the last user among all (U-1)! possible permutations of the other users. Then, a greedy algorithm that directly computes U channel gain matrices and obtains a near-optimal precoding order for the last user is proposed. The proposed greedy ordering scheme reduces the computational complexity by a factor of U!/2 compared with the brute force search. Our simulation results confirm that the performance of the greedy ordering scheme approaches that of the brute force search. Furthermore, the authors show that the proposed BQRD-based DPC expands the multiuser rate region and increases the sum rate over block diagonalisation based zero forcing method. View full abstract»

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  • Utility-based resource allocation in orthogonal frequency division multiple access networks

    Page(s): 1463 - 1470
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (399 KB)  

    The authors consider network utility maximisation problem in orthogonal frequency division multiple access (OFDMA) networks to study cross-layer, fair and efficient resource allocation. Assuming knowledge of the instantaneous channel gains, this problem is decomposed into rate control and scheduling problems at the transport and medium access control/physical layers, respectively. In contrast to the rate control problem that is solved using subgradient method, the scheduling problem has high computational complexity owing to optimising integer and continuous variables simultaneously. Based on the results from analysing the integer relaxed scheduling problem, computationally efficient adaptive scheduling (CEAS) and opportunistic time division multiple access (Opp-TDMA) scheduling schemes are proposed to joint subcarrier assignment and power allocation. Simulation results demonstrate that aggregate utility achieved in the network with the cooperation between rate control and proposed scheduling schemes outperforms those of previously proposed joint channel-aware and queue-aware scheduling schemes. Also, through comparison with the optimal solution, the authors conclude that CEAS is applicable for OFDMA real-time scheduling due to low computational complexity and high performance. View full abstract»

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  • Linear quadrature optimisation-based non-coherent time of arrival estimation scheme for impulse radio ultra-wideband systems

    Page(s): 1471 - 1483
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (506 KB)  

    Owing to the extremely high-time resolution of impulse radio ultra-wideband (IR-UWB), time of arrival (TOA) estimation has been an important and tempting issue of this technology ever since its emergence. Conventional TOA estimation (TOAE) schemes require prohibitively high sampling rate and a priori knowledge of the received signal, and hence render a practical implementation rigorous or even infeasible. To tackle these drawbacks, this paper proposes a low-complexity energy detection-based non-coherent TOAE scheme, which is composed of two processing stages: initial signal acquisition (ISA) and fine timing estimation (FTE). In the ISA stage, a linear quadrature optimisation (LQO)-based weighting scheme is proposed to coarsely capture the arrival of the IR-UWB signals. Capitalising on the acquisition of the IR-UWB signal in a relatively short time range, the authors then develop in the FTE stage, a double-threshold test (DTT) tailored for locating the leading edge of the IR-UWB signal. Simulations illustrate that the LQO algorithm yields a considerably increased probability of seizing the arrival of the IR-UWB signals in a blind manner, and the DTT strategy significantly ameliorates the TOAE accuracy in terms of mean absolute error, compared with the conventional energy detection-based TOAE methods. View full abstract»

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  • Multi-source multi-destination relay network: constrained optimisation for higher diversity

    Page(s): 1484 - 1494
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (482 KB)  

    The authors consider a cooperative communication system where multiple sources transmit data to multiple destinations, being helped by multiple half-duplex relay nodes: relay nodes perform `amplify and forward` as their cooperative technique, with the use of complex weights for forwarding; complex forwarding weights are optimised, based on the obtained channel information, to improve data transmission performance, especially its corresponding diversity order. In particular, the authors investigate the constrained optimisation on the forwarding weights, under the two constraints of interference-free data reception at all destinations and total forwarding power at all relays, to (i) maximise the signal-to-noise ratio (SNR) of any given source`destination pair; (ii) optimise (here maximise the minimum among) the SNRs of all source`destination pairs. Performance (especially diversity order) analysis and Monte-Carlo simulations show the achieved diversity order and the consistence between analytical and numerical results. View full abstract»

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  • Broadcast multicast capacity of network coding for random wireless networks

    Page(s): 1495 - 1503
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (359 KB)  

    The single-source multicast network coding (NC) capacity of random wireless networks was derived recently without incorporating broadcast property of the wireless medium. Here, capacity implications of the broadcast property are studied. It is shown that source cut (the cut that separates the source from all other nodes) still dominates the multicast NC capacity of random wireless networks incorporating broadcast property. It is also shown that, by capturing broadcast, the single-source multicast NC capacity result is increased inversely proportional to the connection probability among the nodes. Simulation results that verify the analysis are also presented. View full abstract»

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  • Alternative web caching design: a site-based approach

    Page(s): 1504 - 1515
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (366 KB)  

    The existing designs and solutions for web caching systems commonly make caching decisions based on document or uniform resource locator (URL) information. While this conventional approach works, the authors deliver insights into the alternative approach using site information for web caching design. This site-based approach makes caching decisions based on the website that an object belongs to, rather than the object itself. The authors show that this new approach can benefit different scopes of cache design, ranging from internal operation of a single proxy (host level), mapping of proxy array in a local area network (LAN level), to load reduction in the global cache hierarchy (wireless area network (WAN) level). Since disks are usually the performance bottleneck in a proxy, to overcome this, the authors design a site-based cache architecture that tries to store web objects belonging to the same site in nearby disk blocks. The simulation results show that it reduces disk access time by 21-50%, compared to the conventional URL-based cache architecture. Besides, in the LAN-level design, a site-based mapping scheme can be used to map all requests targeting the same website to the same proxy, resulting in up to 50% reduction in the total transmission control protocol connection overhead. On the other hand, in the WAN-level, upper-level proxies are usually overloaded. To solve it, site information is used in lower-level proxies to decide which requests to forward to the origin servers directly (instead of upper-level proxy). As a result, proxy load is reduced by 46-59% and a reduction of 9-25% in request compliance delay can be achieved. With the merits of these three levels, it is believed that the site-based approach would contribute to the future caching designs. 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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