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Online ISSN 1751-8636 Print ISSN 1751-8628

IET Communications

Volume 4, Issue 11, 23 July 2010

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Volume 4, Issue 11

23 July 2010

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  • Video communication over wireless networks

    • Editorial: Video communication over wireless networks
      Opportunistic spectrum access framework for video over ad hoc wireless networks
      • Author(s): J. Sun ; H.F. Rashvand ; H.-B. Zhu
      • Source: IET Communications, Volume 4, Issue 11, p. 1269 –1276
      • DOI:  10.1049/iet-com.2009.0410
      • Type: Article
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      • p. 1269 –1276 (8)
        The opportunistic spectrum access (OSA) over wireless networks, ad hoc wireless networks in particular, opens up use of licensed spectrum to unlicensed users for higher capacity and better commercial values enabling bandwidth-hungry content applications like video services. The existing solution's serious practical problems for the primary and secondary users include fairness, utilisation, collision and unfair spectrum access strategy. In this study the authors propose a new analytical framework for more effective implementing the OSA over ad hoc networks for which we integrate the spectrum access assignment with selective physical layer transmission characteristics enhanced with the service traffic information. For this we first define a distance-tree model to generate an available degree (AD) list for all primary and secondary users. Then, a new fairness-driven utility function is defined to control the spectrum efficiency and fairness for the secondary users. Finally, the authors propose some access strategies for the video applications using the cross-layer design.
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      Use of optimal wavelet packet decomposition for the long-term prediction of variable-bit-rate video traffic
      • Author(s): S. Zhang ; J. Chen ; L.-H. She ; X.-R. Bao
      • Source: IET Communications, Volume 4, Issue 11, p. 1277 –1287
      • DOI:  10.1049/iet-com.2009.0405
      • Type: Article
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      • p. 1277 –1287 (11)
        This study systematically investigates the long-term prediction of online, real-time variable-bit-rate (VBR) video traffic, which is a key and complicated component of advanced predictive dynamic bandwidth control for future networks such as multimedia satellite networks. As per the time variation, non-linearity and long-range dependence in the VBR video traffic trace, a novel method of feature extraction based on multi-scale decomposition is proposed. After an analysis of the time–frequency distribution characteristics of the video trace, the wavelet packets that have the trait of arbitrary distinction and decomposition are selected. After space partition of wavelet packets, the best wavelet packet basis for feature extraction is picked. Based on the best basis, fast arbitrary multi-scale wavelet packet transform (WPT) can be done and each higher dimension wavelet coefficient matrix can be obtained. Then, wavelet coefficients prediction is done based on normalised least mean square error (NLMS) or least mean-support vector machine (LS-SVM) algorithm. The long-term prediction of the VBR video traffic is obtained through reverse wavelet transforms on the predicted wavelet coefficients. Numerical and simulation results are provided to validate the claims.
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      Reliable multimedia multicast communications over wireless mesh networks
      • Author(s): M. Iqbal ; X. Wang ; D. Wertheim
      • Source: IET Communications, Volume 4, Issue 11, p. 1288 –1299
      • DOI:  10.1049/iet-com.2009.0134
      • Type: Article
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      • p. 1288 –1299 (12)
        Wireless mesh networks (WMNs) facilitate both data transfer and real-time applications over wireless medium. Owing to the shared nature of wireless frequencies, bandwidth limitation is a major challenge facing WMNs. If real-time multimedia applications, such as live video streaming, are shared among multiple clients using unicast communications, it could result in network resources starvation. Multicast transmission saves network resources by replicating live multimedia transmitted data from one source to multiple destinations using the same stream. The authors have developed a novel implementation of a multicast extension to ad hoc on-demand distance vector (MAODV) routing protocol in Linux kernel 2.6 user space, which is referred to as unidirectional link-aware MAODV (UDL-MAODV). Multicast video transmissions use user datagram protocol, which does not use implicit handshaking dialogues for guaranteeing reliability of data. Therefore the authors propose and have implemented modifications to the MAODV route discovery process to improve the reliability of multicast video transmissions. These modifications enable UDL-MAODV to ensure reliable route establishment for multimedia multicast communications over WMNs in the presence of UDLs. The authors describe in this study the software architecture of the UDL-MAODV implementation in the Linux kernel 2.6 user space, and also present multicast validation and results of performance tests using the SwanMesh WMN testbed. Furthermore, UDL-MAODV has been cross-compiled and tests are presented to compare the performance of the implementation using X86 and ARM architecture-based SwanMesh nodes. The test results show that the proposed algorithm is reliable and efficient.
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      Multi-source video streaming in a wireless vehicular ad hoc network
      • Author(s): N.N. Qadri ; M. Fleury ; M. Altaf ; M. Ghanbari
      • Source: IET Communications, Volume 4, Issue 11, p. 1300 –1311
      • DOI:  10.1049/iet-com.2009.0458
      • Type: Article
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      • p. 1300 –1311 (12)
        This study seeks to establish under what conditions (mobility, network size, wireless channel) multi-source video streaming is feasible across a wireless vehicular ad hoc network (VANET). Overlay networks with multiple sources have proven to be robust, distributed solutions to multimedia transport, including streaming. To achieve video streaming over a VANET overlay, this study introduces a spatial partition of a video stream based on flexible macroblock ordering. Tests show this can achieve a gain of over 5 dB in video quality (PSNR) depending on video content and packet loss rates. However, routing of streamed services over multiple hops and multiple paths may lead to significant packet losses, resulting in unacceptable quality of service. The paper examines the impact of differing traffic densities and road layouts upon an overlay network's performance. The work modelled the emerging IEEE 802.11p for wireless VANETs. The research demonstrates that the vehicles' mobility pattern and their drivers' behaviour need to be carefully modelled to determine signal reception. The study also considers the impact of the wireless channel, which also should be more realistically modelled.
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      QoS scheme for multimedia multicast communications over wireless mesh networks
      • Author(s): M. Iqbal ; X. Wang ; S. Li ; T. Ellis
      • Source: IET Communications, Volume 4, Issue 11, p. 1312 –1324
      • DOI:  10.1049/iet-com.2009.0413
      • Type: Article
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      • p. 1312 –1324 (13)
        A quality of service (QoS) scheme for multimedia multicast communications in wireless mesh networks (WMNs) is proposed in this study. It uses a new bandwidth calculation scheme to provide rate-adaptive admission control. It relies on information it receives from the network and application layers to calculate the network bandwidth consumption and operates independently of the media access control (MAC) layer. Using the proposed QoS scheme, the network layer provides feedback on network congestion to the application layer. The multimedia multicast sender adapts the real-time data transmission rate based on the network congestion feedback it receives. In this study, the authors describe the detailed architecture of the proposed QoS scheme. Furthermore, the authors have implemented the QoS scheme in our previously developed uni-directional link aware multicast extension to AODV (UDL-MAODV) routing protocol. The authors present validation tests to ensure the correct functionality of the QoS algorithm using our SwanMesh WMN testbed. The authors have also performed simulation tests to evaluate the performance of the proposed scheme. The simulation results show the effectiveness of the proposed QoS scheme.
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      Reliable transmission of wavelet-based scalable video over wireless networks using cross-layer approach
      • Author(s): M. Ayyub Khan ; A.A. Moinuddin ; E. Khan ; M. Ghanbari
      • Source: IET Communications, Volume 4, Issue 11, p. 1325 –1336
      • DOI:  10.1049/iet-com.2009.0412
      • Type: Article
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      • p. 1325 –1336 (12)
        The conventional network layers are mainly designed for fixed networks and are not suitable to cope the challenges offered by the modern wireless networks. Moreover, certain functionalities can be implemented simultaneously in more than one layer. For example, unequal error protection (UEP) can be performed at the application layer, using forward error correction (FEC), but it is bandwidth inefficient. On the other hand, UEP can also be performed at the physical layer using hierarchical modulation to protect higher priority bits more strongly without any additional bandwidth, but at the cost of increased errors in the lower priority bits. The authors propose a cross-layer UEP approach to enhance reliability of scalable video by combining adaptive FEC at the application layer and hierarchical quadrature amplitude modulation (HQAM) at the physical layer. The idea is to slightly reduce the FEC protection of higher priority bits and increase the FEC protection of low-priority bits in such a fashion that the overall data rate at the application layer remains unchanged. The higher priority bits are additionally protected using HQAM at the physical layer. Simulation results show significant improvements in performance when the proposed scheme is used.
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      Quality of experience-driven adaptation scheme for video applications over wireless networks
      • Author(s): A. Khan ; L. Sun ; E. Jammeh ; E. Ifeachor
      • Source: IET Communications, Volume 4, Issue 11, p. 1337 –1347
      • DOI:  10.1049/iet-com.2009.0422
      • Type: Article
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      • p. 1337 –1347 (11)
        User's perceived quality of service (QoS) or quality of experience (QoE) is likely to be the major determining factor in the success of new multimedia applications over wireless/mobile networks. The primary aim of this study is to present an adaptation scheme that is QoE-driven for optimising content provisioning and network resource utilisation for video applications over wireless networks. The proposed scheme encompasses the application of a QoE-driven model for optimising content provisioning and network resource utilisation. The content provisioning is optimised by the determination of initial content quality by adapting the video sender bitrate (SBR) according to users' QoE requirement. By finding the impact of the QoS parameters on end-to-end perceptual video quality, the optimum trade-off between SBR and frame rate is found and the benefits to network providers in maximising existing network resources are demonstrated. The QoE is measured in terms of the mean opinion score. The proposed scheme makes it possible for content providers to achieve optimum streaming (with an appropriate SBR) suitable for the network and content type for a requested QoE. The scheme is also beneficial for network providers for network resource provision and planning, and therefore maximising existing network infrastructure by providing service differentiation.
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      Delay controlled wireless video playout system
      • Author(s): C. Rui ; M. Zhengkun ; J. Liangbao ; H.F. Rashvand
      • Source: IET Communications, Volume 4, Issue 11, p. 1348 –1355
      • DOI:  10.1049/iet-com.2009.0467
      • Type: Article
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      • p. 1348 –1355 (8)
        Best-effort streamed video playout representing the most popular and cost-effective multimedia application today is unfortunately very sensitive to any fluctuations in packet loss and delay. There are always further problems for the provision of real-time playout applications over wireless links because of the complicated and highly variable nature of the channel and challenging quality issues for adopting the service in global scales, which necessitates adopting a new and effective buffer mechanism. As a solution to this problem, to smooth out the playout for quality viewing and improved overall systems’ performance, in this study the authors propose a new adaptive media playout (AMP) system that makes the most effective use of a packet-delay prediction algorithm. Here, as the prediction method makes decisions based on the delay interdependency of the adjacent packets the differential auto-regression delay prediction model is used for working out the estimation. The proposed algorithm also adopts more refinement changing steps in the adjustment process and takes into accounts any packet losses with deadline constraint. The simulation results show that the proposed method outperforms the AMP-live method in reducing the average buffer delays as well as enhancing package loss rates for both overflow and underflow.
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  • General articles

    • Throughput analysis of non-persistent carrier sense multiple access combined with time division multiple access and its implication for cognitive radio
      • Author(s): H. Li ; D. Grace ; P.D. Mitchell
      • Source: IET Communications, Volume 4, Issue 11, p. 1356 –1363
      • DOI:  10.1049/iet-com.2009.0430
      • Type: Article
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      • p. 1356 –1363 (8)
        This study analyses a cognitive radio scenario based on non-persistent carrier sense multiple access (CSMA) and time division multiple access (TDMA) systems sharing a single-channel wireless network. TDMA users are considered as primary users who can access the channel at any time, and non-persistent CSMA users are considered as secondary users who can share the channel when it is free. New expressions for the individual and aggregate throughput performance of this combined system have been developed, and the system performance is evaluated for a variety of proportions of non-persistent CSMA and TDMA traffic levels. Simulation and analytical results are presented and the ways in which both schemes suffer negative effects as a result of the interaction are shown, primarily caused by increased number of collisions arising from the other scheme.
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      Channel capacity and average error rates in generalised-K fading channels
      • Author(s): G.P. Efthymoglou ; N.Y. Ermolova ; V.A. Aalo
      • Source: IET Communications, Volume 4, Issue 11, p. 1364 –1372
      • DOI:  10.1049/iet-com.2009.0457
      • Type: Article
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      • p. 1364 –1372 (9)
        In the present study, the performance of digital communication systems operating over a composite fading channel modelled by the generalised-K distribution is analysed and evaluated. Novel closed-form expressions for the outage performance, the average bit error probabilities of several modulation schemes and the channel capacity under four different adaptive transmission schemes are derived. The analytical expressions are used to investigate the impact of different fading parameters of this composite fading channel model on the average bit error rate performance for a variety of digital modulation schemes and the spectral efficiency of different adaptive transmission policies.
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      Achievable rates with quantised channel state information in a multiple-access channel with one cognitive transmitter
      • Author(s): H. Charmchi  and  M. Nasiri-Kenari
      • Source: IET Communications, Volume 4, Issue 11, p. 1373 –1380
      • DOI:  10.1049/iet-com.2009.0437
      • Type: Article
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      • p. 1373 –1380 (8)
        The authors investigate the achievable rates of a multiple-access channel with one cognitive transmitter in a fading channel. The cognitive transmitter uses dirty-paper coding to mitigate the known interference. They assume partial transmit channel state information which is obtained through a quantised limited feedback. In this model, the receiver sends as feedback only a finite number of bits describing the fading coefficients. Numerical results show that different quantisation schemes must be used for different transmitters (cognitive and non-cognitive) in order to maximise their rates. Also, the number of quantisation bits allocated to each channel coefficient (i.e. the channels from the non-cognitive and cognitive transmitters to the receiver), for a fixed total feedback bits, can affect the achievable rates of the transmitters, and even for each channel coefficient, how to dedicate the considered quantisation bits between the coefficient magnitude and phase can have substantial effects on the rate.
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      Estimation scheme of the receiver IQ imbalance under carrier frequency offset in communication system
      • Author(s): Y.-J. Chiu  and  S.-P. Hung
      • Source: IET Communications, Volume 4, Issue 11, p. 1381 –1388
      • DOI:  10.1049/iet-com.2009.0392
      • Type: Article
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      • p. 1381 –1388 (8)
        IQ signal processing is widely utilised in today's communication systems. However, it usually faces a common problem of front-end distortion such as IQ imbalance and carrier frequency offset (CFO). Effective algorithms exist for estimating and compensating for IQ imbalance as well as CFO, when the two problems are treated separately. With both effects present, most of those algorithms suffer from degraded quality parameter estimates. In this study, the authors proposed a scheme to estimate and compensate for IQ imbalance in the presence of CFO by using a known preamble of a repeated training sequence. In addition, the authors present a modified algorithm to suit the particular case when CFO is small. The performance of our proposed scheme has been examined with computer simulations on IEEE 802.11a signals. It is shown that the proposed method is more robust and renders better performance than the existing method.
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