Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 3, Issue 12, December 2009
Volumes & issues:
Volume 3, Issue 12
December 2009
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- Author(s): W.-H. Liao ; K.-P. Shih ; W.-C. Chung
- Source: IET Communications, Volume 3, Issue 12, p. 1821 –1831
- DOI: 10.1049/iet-com.2008.0692
- Type: Article
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This study proposes a novel multi-channel medium access control protocol for mobile ad hoc networks that enables nodes to transmit packets in distributed channels. In our protocol, the ad hoc traffic indication message window is divided into two windows. The first window is called the deciding channel window (DCW). Source and destination nodes can negotiate with each other in deciding a channel that can be used to compete for the final data channel in the DCW. The second window is called the exchanging packet window (EPW). Pair source and destination nodes can compete to obtain a channel to transfer packets in the EPW. This mechanism can distribute pair source and destination nodes to compete for a data channel. Hence, because of this, collisions can be avoided greatly and throughput can be increased. The simulation results show that our protocol successfully exploits the use of the bandwidth of multiple channels effectively. - Author(s): A.M.A. Filho ; E.L. Pinto ; J.F. Galdino
- Source: IET Communications, Volume 3, Issue 12, p. 1832 –1842
- DOI: 10.1049/iet-com.2009.0038
- Type: Article
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A new variable step-size least mean squares (VSS-LMS) algorithm for the estimation of frequency-selective communications channels is herein presented. In contrast to previous works, in which the step-size adaptation is based on the instantaneous samples of the error signal, this algorithm is derived on the basis of analytical minimisation of the ensemble-averaged mean-square weight error. A very simple rule for step-size adaptation is obtained, using a small number of communication system parameters. This is another significant difference from other proposals, in which a large number of control parameters should be tuned for proper use. The algorithm here proposed is shown to be applicable to both time-varying and time-invariant scenarios. While the lack of a termination rule for step-size adaptation is a common characteristic of other schemes, the algorithm here presented adopts a criterion for stopping the step-size adaptation that assures optimal steady-state performance and leads to large computational savings. A simulation-based performance comparison with other VSS-LMS schemes is provided, including their application to maximum likelihood sequence estimation receivers using per survivor processing (MLSE/PSP). The results show that the algorithm proposed in this work has good performance characteristics and a very low computational cost, specially in the application to MLSE/PSP receivers. Besides, this algorithm is shown to be robust to changes in the signal-to-noise ratio (SNR). - Author(s): F. Xu ; F.C.M. Lau ; D.-W. Yue ; S.F. Hau
- Source: IET Communications, Volume 3, Issue 12, p. 1843 –1850
- DOI: 10.1049/iet-com.2008.0497
- Type: Article
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Cooperative communications has been recognised as an effective technique to combat multi-path fading impairment and to provide additional diversity advantage for small-size and low-power-consumption mobile terminals. A class of decode-and-forward (DF) relaying serial cooperative communications, in which each node is assumed to be able to determine whether the received signals can be successfully decoded or not, has recently been proposed and analysed over Rayleigh fading channels. Since the Nakagami fading channels represent a wide variety of realistic channels, such serial cooperative networks should be investigated over such channels before putting into real applications. In this paper, we analyse the performance of such serial cooperative transmission systems thoroughly over dissimilar Nakagami fading channels. We derive a closed-form symbol-error-rate expression for the case of M-ary phase shift keying (PSK) modulation. Moreover, we evaluate the system diversity property and investigate the achievable diversity order under two specific channel conditions. Finally, we perform simulations to verify the theoretical findings. - Author(s): K. Li ; W. Zhou ; S. Yu
- Source: IET Communications, Volume 3, Issue 12, p. 1851 –1860
- DOI: 10.1049/iet-com.2008.0586
- Type: Article
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In information theory, the relative entropy (or information divergence or information distance) quantifies the difference between information flows with various probability distributions. In this study, the authors first resolve the asymmetric property of Rényi divergence and Kullback–Leibler divergence and convert the divergence measures into proper metrics. Then the authors propose an effective metric to detect distributed denial-of-service attacks effectively using the Rényi divergence to measure the difference between legitimate flows and attack flows in a network. With the proposed metric, the authors can obtain the optimal detection sensitivity and the optimal information distance between attack flows and legitimate flows by adjusting the order's value of the Rényi divergence. The experimental results show that the proposed metric can clearly enlarge the adjudication distance, therefore it not only can detect attacks early but also can reduce the false positive rate sharply compared with the use of the traditional Kullback–Leibler divergence and distance approaches. - Author(s): Y.J. Lee ; D.W. Lee ; M. Atiquzzaman
- Source: IET Communications, Volume 3, Issue 12, p. 1861 –1869
- DOI: 10.1049/iet-com.2008.0710
- Type: Article
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In this study, the authors address a mobile web agent framework based on stream control transmission protocol (SCTP) to overcome the deficiencies, which the typical mobile web agent framework based on transmission control protocol (TCP) suffers from, such as performance degradation, head-of-line blocking and unsupported mobility in mobile wireless environment. The proposed SCTP-based mobile web agent framework supports seamless transport layer mobility in a ubiquitous environment. It consists of an application engine and a transport engine, to use the hypertext transfer protocol and to deploy SCTP with dynamic address reconfiguration, respectively. The authors explore and describe the components necessary to implement the proposed mobile web agent framework in an ubiquitous environment. The performance of the proposed SCTP-based mobile web agent is compared with that of a typical TCP-based mobile web agent using ns-2 simulator. The simulation results show that the proposed web agent based on SCTP has a remarkably lower mean response time than a typical web agent based on TCP. - Author(s): M. Beheshti ; M.J. Omidi ; A.M. Doost-Hoseini
- Source: IET Communications, Volume 3, Issue 12, p. 1870 –1882
- DOI: 10.1049/iet-com.2008.0659
- Type: Article
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Time variations of a doubly selective wireless channel and insufficient cyclic prefix (CP) length of an orthogonal frequency division multiplexing (OFDM) transmission system cause intercarrier interference (ICI) and interblock interference (IBI) as significant limitations. This paper investigates the problem of joint ICI and IBI mitigation in single-input multiple-output OFDM (SIMO-OFDM) systems. It is assumed, unlike most existing literature, that the channel delay spread is larger than the CP, and also the channel varies on each OFDM block. First, doubly selective channel is modelled using basis expansion model (BEM) and a closed-form expression for signal-to-interference-plus-noise ratio (SINR) is derived. Then, a time-domain equaliser is developed, which maximises the SINR for all subcarriers. Moreover, a frequency-domain equalisation approach is proposed which is based on the MSE minimisation per tone. A low-complexity implementation of the per-tone equaliser is also derived. An important feature of the proposed equalisers is that no bandwidth expansion or redundancy insertion is required except for the CP. Finally, complexity comparison and simulation results over Rayleigh fading channel are provided to illustrate the effectiveness of the proposed approaches. Since both equalisers are designed in the frequency domain, they provide significant interference cancellation. - Author(s): K. Salah and A. Kahtani
- Source: IET Communications, Volume 3, Issue 12, p. 1883 –1895
- DOI: 10.1049/iet-com.2009.0114
- Type: Article
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Network intrusion detection systems (NIDS) have become vital components in securing today's computer networks. To be highly effective, NIDS must perform packet inspection of incoming traffic at or near wire speed. Failing to do so will allow malicious packets to sneak through the network undetected, and thus jeopardising network security. Snort is one of the most popular IDS and intrusion prevention system (IPS) applications. Snort is a publicly available open-source NIDS application that typically runs on Linux. In this study, the authors present and discuss the essential software components of Snort and its underlying Linux support architecture. The authors characterise Snort execution and present an analytical queuing model to give insight into understanding the kernel and Snort behaviour as well as to identify key-dominating factors that strongly influence and impact Snort performance. The authors demonstrate that the current default configurations of the packet reception mechanism of the Linux networking subsystem (a.k.a. NAPI) are not suitable for Snort performance and show that the performance of Snort can be improved significantly by tuning certain configuration parameters, specifically by having a small NAPI budge value of 2. The performance is measured in terms of throughput and packet loss. The authors also measure the packet loss encountered at the kernel level as well as the interrupt rate of incoming traffic. Performance was measured when subjecting a PC host running Snort to both normal and malicious traffic, and with different traffic load conditions. - Author(s): M.S. Ab-Rahman ; B.C. Ng ; A. Premadi ; K. Jumari
- Source: IET Communications, Volume 3, Issue 12, p. 1896 –1906
- DOI: 10.1049/iet-com.2009.0017
- Type: Article
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This study proposes a practical transmission surveillance and self-protection scheme for time division multiplexing using passive optical network (TDM-PON) with centralised monitoring and self-restorable apparatus. Troubleshooting a TDM-PON involves locating and identifying the source of an optical problem in what may be a complex optical network topology that includes several optical line terminals (OLTs), optical splitters, fibres and optical network units (ONUs). Since most components in the network are passive, a large part of the issues are due to dirty/damaged/misaligned connectors or breaks/macrobends in optical fibre cables. These will affect one, some or all subscribers in the network, depending on the location of the problems. The proposed scheme is able to prevent and detect the occurrence of fibre faults in a network system through centralised monitoring and remotely operate from a central office via Ethernet connection. Even with fibre fault prevention mechanisms, failures will still occur. Therefore fibre fault detection is required in order to detect potential faults and precisely localise the exact failure location. Whenever any failure occurs on the primary entity, the proposed system can protect and switch the failure line to the protection line to ensure that traffic flows continuously. Meanwhile, the failure information will be delivered to field engineers for taking appropriate recovery action to treat the fibre fault and failure link. One suggestion in point-to-multipoint (P2PM) applications has been proposed with the experimental results as the feasibility approach. This approach has bright prospects for improving the survivability and reliability as well as increasing the efficiency and monitoring capabilities in TDM-PON. - Author(s): J.-C. Lin
- Source: IET Communications, Volume 3, Issue 12, p. 1907 –1918
- DOI: 10.1049/iet-com.2008.0558
- Type: Article
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A least-squares (LS) channel estimation (CE) technique is investigated to apply pseudo-random-postfix orthogonal-frequency-division multiplexing (PRP-OFDM) communications onto mobile applications, which often operate on a rapidly time-varying frequency-selective fading channel. Since conventional techniques exploiting a moving averager cannot function on a rapidly time-varying channel, the proposed technique takes advantage of several self-interference cancellation (SIC) methods to effectively and timely reduce inter-path interference, inter-symbol interference (ISI) and inter-block interference (IBI). The proposed technique can therefore overcome frequency selectivity caused by multipath fading and time selectivity caused by mobility; in particular, OFDM communication is often anticipated to operate in environments where both wide Doppler spread and long delay spread exist. Meanwhile, lower mean-square estimation errors, lower error probabilities and lower error floors can also be achieved using the proposed technique. Since conventional techniques based on minimum-mean-square-error (MMSE) CE usually highly require a priori channel information or many training preambles, a generic estimator assisted from LS CE is exploited as it can be performed serially, block by block, to reduce computational complexity. Extensive computer simulations in conjunction with strict statistical analysis are carried out to verify the improvements provided by the proposed technique. - Author(s): Z. Chen ; H. Yin ; C. Lin ; Y. Chen ; M. Feng
- Source: IET Communications, Volume 3, Issue 12, p. 1919 –1933
- DOI: 10.1049/iet-com.2008.0630
- Type: Article
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Peer-to-peer (P2P) paradigm has provided a disruptive market opportunity to define cost-effective multimedia streaming services, but at the same time network-oblivious P2P applications have been posing substantial technical and social challenges on network efficiency, operator economics and user performance. While end users are concerned with quality upgrade, Internet content provider (ICP) considers more on service scale and Internet service provider (ISP) focuses on operating cost. In taming P2P for a more friendly large-scale application, this paper provides a framework of evaluating the P2P media streaming application performance from perspectives of all entities involved, that is ISP, ICP and end users. Three-level performance metrics are defined, essential concerns of each party are theoretically quantified and bottlenecks in affecting quality service are identified. In handling tussles between P2P performance against ISP traffic, system scale against cost and user QoS against Security, the authors present proposals in defining an unprecedented friendly and cost-effective P2P streaming application to achieve the ideal philosophy of ‘more users=better performance+lower cost’. Based on the explorations in academy and industry, the authors envision that a large-scale streaming system will be built with a synergy of P2P and content distribution networks (CDN), and explore the feasibility of a general peer–server–peer (PSP) structure on the basis of our evaluation framework. With our analytical study and industrial deployment, this paper captures a certain essence of deploying large-scale P2P streaming application from a commercial and realistic point of view and suggests many avenues for addressing the emerging tensions between P2P application and network operators. - Author(s): S. Kim ; J. Cha ; J. Ma
- Source: IET Communications, Volume 3, Issue 12, p. 1934 –1947
- DOI: 10.1049/iet-com.2008.0498
- Type: Article
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The IEEE 802.11 distributed coordination function (DCF) employs a carrier sensing mechanism, a simple and effective mechanism to mitigate collisions in wireless networks. But the carrier sensing mechanism is inefficient in terms of shared channel use because an overcautious channel assessment approach is used to estimate interference at a receiver. A DCF node simply blocks its transmission when it senses that the channel is busy. However, in many cases this channel assessing node's own transmission may not generate enough interference to disrupt the ongoing transmission at the receiver. This overcautious channel assessment unnecessarily blocks transmission attempts, and thus degrades the overall network throughput. To avoid this unnecessary blocking, the authors propose a spatial reuse DCF (SRDCF), which utilises location information and transmission parameters to make accurate channel assessments and to permit concurrent transmissions by adjusting the transmission power. SRDCF also resolves the contention between opportunistic concurrent transmissions with a secondary backoff counter. Consequently, the proposed scheme improves the overall network throughput because of more concurrent transmissions. The authors theoretically analyse the performance enhancement of SRDCF over the original IEEE 802.11 DCF by using a Markov chain model and verify it through simulations. - Author(s): J.S. Chen and J.X. Wang
- Source: IET Communications, Volume 3, Issue 12, p. 1948 –1957
- DOI: 10.1049/iet-com.2009.0168
- Type: Article
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In this study, the authors develop a novel cooperative transmission scheme – distributed opportunistic incremental decode and forward (DOIDF) that employs the incremental relaying (IR) strategy in opportunistic relaying (OR) protocols. By exploiting limited feedback from the destination, the proposed scheme starts the OR plan only when outage event happens in direct transmission (DT). The outage probability of DOIDF is derived in detail, and the results show that DOIDF can achieve the same space diversity order as multiple input single output (MISO) and single input multiple output (SIMO) systems, which is the upper limit of cooperative diversity. By analysing and comparing the approximate expression of outage probability of various protocols in high-signal-to-noise ratio (SNR) regime, the concept of system overhead factor (SOF), which reveals the effects of channel allocation in cooperative protocols on system performance, is proposed. Subsequent analysis and simulation results show that DOIDF outperforms corresponding OR schemes in outage probability, spectral efficiency and SNR gain over DT.
Multi-channel medium access control protocol with channel distribution for mobile ad hoc networks
Simple and robust analytically derived variable step-size least mean squares algorithm for channel estimation
Error rate and diversity order of multinode cooperative communications in dissimilar Nakagami fading channels
Effective metric for detecting distributed denial-of-service attacks based on information divergence
Novel web agent framework to support seamless mobility for data networks
Equalisation of SIMO-OFDM systems with insufficient cyclic prefix in doubly selective channels
Improving Snort performance under Linux
Transmission surveillance and self-restoration against fibre fault for time division multiplexing using passive optical network
Least-squares channel estimation assisted by self-interference cancellation for mobile pseudo-random-postfix orthogonal-frequency-division multiplexing applications
Towards a universal friendly peer-to-peer media streaming: metrics, analysis and explorations
Design and theoretical analysis of throughput enhanced spatial reuse distributed coordination function for IEEE 802.11
Cooperative transmission in wireless networks using incremental opportunistic relaying strategy
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