Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 2, Issue 3, March 2008
Volumes & issues:
Volume 2, Issue 3
March 2008
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- Author(s): G. Androulidakis and S. Papavassiliou
- Source: IET Communications, Volume 2, Issue 3, p. 399 –409
- DOI: 10.1049/iet-com:20070231
- Type: Article
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p.
399
–409
(11)
Sampling has become an essential component of scalable Internet traffic monitoring and anomaly detection. A new flow-based sampling technique that focuses on the selection of small flows, which are usually the source of malicious traffic, is introduced and analysed. The proposed approach provides a flexible framework for preferential flow sampling that can effectively balance the tradeoff between the volume of the processed information and the anomaly detection accuracy. The performance evaluation of the impact of selective flow-based sampling on the anomaly detection process is achieved through the adoption and application of a sequential non-parametric change-point anomaly detection method on realistic data that have been collected from a real operational university campus network. The corresponding numerical results demonstrate that the proposed approach achieves to improve anomaly detection effectiveness and at the same time reduces the number of selected flows. - Author(s): W. Cao ; A. Nallanathan ; C.C. Chai
- Source: IET Communications, Volume 2, Issue 3, p. 410 –421
- DOI: 10.1049/iet-com:20070168
- Type: Article
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p.
410
–421
(12)
Exact BER analysis is carried out using the characteristic function (CF) method for direct sequence ultra-wide band (DS‐UWB) systems in lognormal multipath fading channels. Unlike the Gaussian approximation (GA) method, the CF method deals with exact probability density function (PDF) of the total noise [including multiple access interference, self interference and additive white gaussian noise (AWGN)] instead of making approximation on PDF of the total noise. Exact bit error rate (BER) formula is derived and verified by simulation results. It is shown that the CF method is more accurate than the GA method in BER calculation when SNR is large. Based on the BER formula, the performance of the DS pulse amplitude modulation UWB and DS pulse position modulation UWB systems is accurately compared. Discussions based on CFs provide further insight into the numerical results. - Author(s): M. Kousa
- Source: IET Communications, Volume 2, Issue 3, p. 422 –431
- DOI: 10.1049/iet-com:20070061
- Type: Article
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p.
422
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Ultra-wideband (UWB) is seen as a potential candidate for wireless communication and other applications as it possesses many attractive features. The multipath profile of UWB consists of resolvable components. However, unlike narrow-band pulses, the received components in different directions are fundamentally different from the transmitted signal. Traditionally, RAKE receivers work by correlating the received signal with the source signal. Although this proved sufficient in the narrowband transmission, it is not the case for the wideband. Some researchers showed that significant improvement in captured energy (CE) in the wideband reception could be achieved by correlating the received signal with multiple received templates. The author re-visits the issue to assess the amount of improvement resulting from multi-template reception of UWB signals and its relation to the number and type of templates. Moreover, the author studies the cost of the multi-template reception. Finally, a threshold-based capturing technique that reduces the cost of reception while maintaining most of the attainable gain in CE is proposed. - Author(s): W.-W. Ji and Z. Liu
- Source: IET Communications, Volume 2, Issue 3, p. 432 –439
- DOI: 10.1049/iet-com:20060044
- Type: Article
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p.
432
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Ineffective sensor node (InESN) in a wireless sensor network (WSN) is defined as one whose position cannot be estimated by traditional localisation methods. Incremental localisation method is investigated and the existence of the InESNs is confirmed. By analysing the existing characteristics, the InESNs are classified into three categories: InESNs connecting with one known node, InESNs connecting with two known nodes and InESNs standing alone. It is impossible to locate the InESNs of the third category because they cannot receive any information from the known nodes. With a moving target in the WSN, a constrained least-squares formulation is developed to estimate the InESNs of the first two categories. Numerical evaluations are carried out to examine the performance of the proposed method and show that it is indeed effective for locating the InESNs. By incorporating the InESNs in the tracking applications, the performance of the target tracking can be greatly enhanced. - Author(s): Y.-C. He ; D. Haccoun ; C. Cardinal
- Source: IET Communications, Volume 2, Issue 3, p. 440 –448
- DOI: 10.1049/iet-com:20070257
- Type: Article
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p.
440
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The complexities and latencies of iterative belief propagation (BP) and threshold decoding techniques for a new class of convolutional self-orthogonal codes are analysed using forward-only pipeline architectures. Computer simulation results show that over the additive white Gaussian noise channel at moderate signal-to-noise ratios, BP decoding yields one half the decoding delay when compared with threshold decoding at essentially the same error performances. However, the reduction in the decoding delay using BP is obtained at the cost of an increase of the implementation complexity. - Author(s): M.R.D. Rodrigues ; I. Chatzigeorgiou ; I.J. Wassell ; R. Carrasco
- Source: IET Communications, Volume 2, Issue 3, p. 449 –461
- DOI: 10.1049/iet-com:20060586
- Type: Article
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p.
449
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(13)
The performance of turbo codes in quasi-static fading channels both with and without antenna diversity is investigated. In particular, simple analytic techniques that relate the frame error rate of a turbo code to both its average distance spectrum as well as the iterative decoder convergence characteristics are developed. Both by analysis and simulation, the impact of the constituent recursive systematic convolutional (RSC) codes, the interleaver size and the number of decoding iterations on the performance of turbo codes are also investigated. In particular, it is shown that in systems with limited antenna diversity different constituent RSC codes or interleaver sizes do not affect the performance of turbo codes. In contrast, in systems with significant antenna diversity, particular constituent RSC codes and interleaver sizes have the potential to significantly enhance the performance of turbo codes. These results are attributed to the fact that in single transmit–single receive antenna systems, the performance primarily depends on the decoder convergence characteristics for Eb/N0 values of practical interest. However, in multiple transmit–multiple receive antenna systems, the performance depends on the code characteristics. - Author(s): W. Fang ; L.-L. Yang ; L. Hanzo
- Source: IET Communications, Volume 2, Issue 3, p. 462 –472
- DOI: 10.1049/iet-com:20070321
- Type: Article
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p.
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In this contribution, the authors investigate the single-user-bound performance of a direct-sequence code-division multiple-access (DS-CDMA) system, where one source mobile terminal (MT) communicates with its base-station (BS) with the assistance of multiple relays. The authors assume that the communications channels experience both propagation pathloss and fast fading, and that the channels from the source MT to the BS and relays as well as that from the relays to the BS may experience different fast fading modelled correspondingly by Nakagami-m distributions. In the study, they assume both the single-user combining using maximal ratio combining and the multiuser combining, which are derived based on the maximum signal-to-interference-plus-noise ratio criterion. The bit-error-rate (BER) performance of the DS-CDMA is investigated associated with considering the locations of the relays as well as the power-allocation among the source MT and relays. From the study and simulation results, it can be shown that the achievable BER performance of the DS-CDMA depends on the locations of the relays and also on the power-allocation among the source MT and relays. When the relays of a source MT are chosen from a different area, the power-allocation should also be adjusted correspondingly in order to achieve the minimum BER. Furthermore, when optimum power-allocation is assumed, the BER performance of the DS-CDMA can be significantly improved, when increasing the number of relays assisting the source MT. - Author(s): T. Nesimoglu ; S.C.J. Parker ; K.A. Morris ; J.P. McGeehan
- Source: IET Communications, Volume 2, Issue 3, p. 473 –483
- DOI: 10.1049/iet-com:20070171
- Type: Article
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p.
473
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The inefficiency of contemporary power amplifiers (PAs), when operating in their linear region, is a major obstacle to mobile operation of wireless local area networks (WLANs) based on IEEE 802.11n. Therefore the use of more efficient envelope elimination and restoration (EER) transmitter architectures is considered. In addition to high efficiency it is also necessary to satisfy the spectral mask and achieve satisfactory link-level performance. Link-level simulations of a contemporary WLAN PA show that, at the power back-offs necessary to achieve sufficient linearity, the power added efficiency (PAE) is only ∼1% for a system with four transmit antennas. In contrast, simulations of a phase feedback EER PA architecture show that it is possible to achieve an average PAE of 70%, while satisfying the spectral mask, with only a small degradation in link-level performance. - Author(s): K. Schneider and T. Kocak
- Source: IET Communications, Volume 2, Issue 3, p. 484 –492
- DOI: 10.1049/iet-com:20070331
- Type: Article
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p.
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As internet protocol (IP) networks in the enterprise space continue to mature, with regards to stability and availability, the desire for these networks to deliver multimedia content will grow. Although IP networks have long had enough bandwidth to support multimedia streams, the deployment of this content seems to have been somewhat limited in the enterprise. The control mechanisms for multicast traffic, both at the IP layer and the data link layer, are still the areas that have not been adopted as widely as their more common unicast counterparts. The authors examine the internet group messaging protocol (IGMP) snooping process that currently runs on enterprise switches and propose an offload hardware engine to accelerate it. Currently, many enterprise switches handle this task with a general-purpose processor within the switch. Although this process adds very little to the overall load of systems currently, as multicast transmissions become more commonplace, the need for this process to be offloaded onto specialised hardware will be a necessity, in order to maintain the stability of the switch and the surrounding network. The proposed hardware model simulations reveal significant increase in the number of packets per second that can be handled compared to software implementations. - Author(s): S. Punnoose ; X. Zhu ; A.K. Nandi
- Source: IET Communications, Volume 2, Issue 3, p. 493 –503
- DOI: 10.1049/iet-com:20070014
- Type: Article
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p.
493
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Single carrier (SC) code division multiple access (CDMA) with block transmission has been shown to be more effective while utilising a low-complexity equaliser to combat frequency-selective fading channels, when compared with conventional direct sequence CDMA technology. It also has lower peak-to-average power ratio and lower frequency sensitivity compared with multicarrier CDMA. The authors propose two blind channel estimation methods for uplink multiple input multiple output SC-CDMA systems with block transmisssion-one is the subspace-based method and the other is the so-called autocorrelation contribution method (ACM). Both the methods provide close performance to the case with perfect channel knowledge at high signal-to-noise ratio (SNR) without any training data required. It is shown that ACM yields a better performance than the subspace method at a lower SNR, and a similar performance at a high SNR, with the advantages of avoiding rank determination and noise power estimation as in the subspace method. In addition, the authors integrate layered space frequency equalisation with blind channel estimation, which provides improved performance over the conventional linear equalisation, by employing successive interference cancellation.
Improving network anomaly detection via selective flow-based sampling
Exact bit error rate analysis of direct sequence ultra-wide band multiple access systems in lognormal multipath fading channels
Enhancement of RAKE receivers for ultra-wideband reception
Locating ineffective sensor nodes in wireless sensor networks
Tradeoff of complexity and latency of iterative decoding for orthogonal convolutional codes
Performance analysis of turbo codes in quasi-static fading channels
Single-user performance of direct-sequence code-division multiple-access using relay diversity and power allocation
The performance and efficiency of envelope elimination and restoration transmitters for future multiple-input multiple-output wireless local area networks
Design and implementation of an offload engine for internet group messaging protocol multicast snooping
Blind channel estimation for multiple input multiple output uplink guard-band assisted code division multiple access systems with layered space frequency equalisation
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