IEE Proceedings - Communications
Volume 151, Issue 5, October 2004
Volumes & issues:
Volume 151, Issue 5
October 2004
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- Author(s): K. Ouahada and H.C. Ferreira
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 409 –414
- DOI: 10.1049/ip-com:20040674
- Type: Article
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The Viterbi decoding algorithm provides maximum likelihood decoding and has found widespread application since its introduction in 1967. It is currently the most widely used technique for the decoding of codes having a state system description, including the class of linear error correcting convolution codes. Contrary to this, it is still common practice to use combinational logic decoders for ternary line codes. These are nonlinear codes frequently used in metallic cable systems due to advantages such as efficient utilisation of bandwidth, and a DC-free power spectral density function. The authors investigate the behaviour of Viterbi decoding for the most important ternary line codes, and the coding gain that can be obtained by applying soft-decision decoding. The simplification of the Viterbi decoding implementation and the reduction in latency by shortening its survivor path length have also been investigated. - Author(s): P. Lusina ; M. Bossert ; S. Shavgulidze
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 415 –421
- DOI: 10.1049/ip-com:20040387
- Type: Article
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p.
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A solution for the design of space–time codes over a complex signal constellation is given. The Gaussian integer field is described and shown to produce a similar complex signal constellation as QAM for particular parameters. The mapping between the Galois field and the Gaussian integer field is shown to preserve the rank statistics of codeword matrices and thereby the diversity gain of the code. Factorisation space–time codes, which have similarities to BCH codes, are constructed over a Galois field and then mapped to a Gaussian integer constellation. This construction is one example of how classical coding theory can be directly applied to space–time code design. Statistical analysis of the Euclidean, geometric and rank metrics is performed. The codeword error performance for different dimensions is shown to give full rank and to perform marginally better than a similar delay diversity code for the parameters considered. - Author(s): A.O. Fapojuwo
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 422 –428
- DOI: 10.1049/ip-com:20040571
- Type: Article
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The delayed location updating (DLU), α-likelihood location updating (α-lLU) and delayed-α-likelihood location updating (D-α-lLU) schemes for throttling network-level registration traffic in personal communication network are proposed. The operational details of the proposed throttling schemes are described. The performance of the throttling schemes is evaluated analytically using the metrics of network-level registration delay, network-level registration load, and the probability that an incoming call cannot be delivered to an MS because its exact location is not known to the network. Numerical results are presented from which it is concluded that the DLU scheme provides up to 80% reduction in network-level registration load compared to when there is no throttling. The results are useful for efficient operation of personal communication networks. - Author(s): M.H. Kim and H.S. Park
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 429 –437
- DOI: 10.1049/ip-com:20040292
- Type: Article
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The authors address the short-term quality of service (QoS) issue caused by the unexpected nature of traffic and network operators' expectations of a high network utilisation. The authors develop a short-term QoS guaranteeing scheduler, called the short-term QoS deficit round robin (SQ-DRR), which adapts the allocated bandwidth to guarantee delay constraints. The key feature of the scheduler is that it guarantees the delay constraint for the short-term aggregate burst traffic violating pre-contracted descriptors without losing long-term fairness. The performance of the scheduler with and without an admission control scheme is evaluated for non-stationary long-range dependent traffic. The simulation results indicate that the SQ-DRR performs well in dynamic burst traffic conditions. - Author(s): C. Kodikara ; S.N. Fabri ; A.M. Kondoz
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 438 –444
- DOI: 10.1049/ip-com:20040115
- Type: Article
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The authors investigate deployment of link adaptation techniques to enhance the performance of real-time video communications over time-varying error-prone environments. A novel link adaptation algorithm is proposed and analysed. Two approaches for link adaptation are investigated. The first approach aims to optimise video quality for a fixed channel allocation. The design criterion of the second approach is to maximise the overall access network throughput while maintaining the required video quality. The effectiveness of the algorithms is demonstrated for MPEG-4 coded video transmissions over simulated EGPRS networks. In addition, the effects of feedback delay, a noisy feedback channel and bursty channel errors on algorithm performance are investigated.
Simulation study of the performance of ternary line codes under Viterbi decoding
Space – time block factorisation codes over Gaussian integers
Throttling schemes for location updating traffic in personal communications systems
Scheduling self-similar traffic in packet-switching systems with high utilisation
Link adaptation for real-time video communications in E-GPRS networks
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- Author(s): Axel Sikora
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 445 –446
- DOI: 10.1049/ip-com:20040918
- Type: Article
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- Author(s): G.T.F. de Abreu ; H. Ochiai ; R. Kohno
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 447 –459
- DOI: 10.1049/ip-com:20040663
- Type: Article
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A new linear decoder for space–time block codes is presented, which enables linear maximum-likelihood decoding in scenarios beyond those described by block-fading models. The new decoder employs linear combinations of received signals with weights designed so as to yield orthogonal estimates for all encoded symbols regardless of channel variations within the block transmission, provided that the channel is known. The combination weights are scalar functions of the channel estimates, obtained through systematic rotations over the decoding matrices of the linear maximum-likelihood decoder for the block-fading case. The proposed decoder yields good performance with low-complexity and is therefore suitable for low-cost portable receivers supporting space–time transmit diversity at the downlink of high data-rate wireless mobile communication systems. Combined with OFDM technology, the technique yields a low-complexity receiver that is effective in combating both time and frequency selectivities, and provides a tool to add flexibility to wireless local area network systems and to offer high data-rate services with support to mobility. - Author(s): S. Xu ; S. Papavassiliou ; S. Narayanan
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 460 –466
- DOI: 10.1049/ip-com:20040664
- Type: Article
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The problem of extending the network coverage in wireless local area networks has recently received significant research and industrial attention. IEEE 802.11 specifications allow only one hop communication between nodes. The authors propose and develop a layer-2 bridging architecture and solution to increase the range of an 802.11 access point using ad hoc networking. In the proposed framework, nodes are logically divided into levels based on their distance (hops) from the access point, and a layer-2 bridging tree is built based on the level concept. The specific mechanisms for the forwarding tree establishment as well as for the data propagation are introduced and discussed. An analytical model is also presented in order to analyse the saturation throughput of the proposed mechanism, while its applicability and effectiveness are evaluated via modelling and simulation. The corresponding numerical results demonstrate and confirm the significant area coverage extension that can be achieved by the author's solution, when compared with the conventional 802.11b scheme. - Author(s): Z. Li ; S. Nandi ; A.K. Gupta
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 467 –472
- DOI: 10.1049/ip-com:20040662
- Type: Article
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Fair access of the shared wireless medium among different contending stations is a very important issue, especially when quality of service needs to be provided. In the CSMA/CA-based IEEE 802.11 protocol, carrier sensing (CS), collision avoidance (CA) and contention resolution (CR), the three main components, affect its fairness. While the influences of CA and CR on the fairness have already been documented, to the best of the authors knowledge there is no research work taking into account CS's influence. The authors focus on the CS part to improve the fairness. In the current IEEE 802.11 standards, whenever a node detects a sensing range (SR) frame on the medium, it defers the transmission by a fixed duration. It is shown that this duration is sometimes smaller and sometimes larger than the desired period by which the transmission should be deferred, and it is the main cause of the unfairness in some cases. The authors propose an enhanced carrier sensing (ECS) scheme, which distinguishes among the SR frames based on their lengths and defers the transmission accordingly. Simulation results show that ECS improves the fairness substantially. - Author(s): A. Sikora
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 473 –479
- DOI: 10.1049/ip-com:20040742
- Type: Article
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p.
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The proliferation of mobile computing devices including laptops, personal digital assistants (PDAs) and wearable computers has created an enormous demand for wireless personal area networks (WPANs). WPANs originally enabled convenient interconnection of devices around an individual person or computer. From this starting point, a broad variety of new wireless appliances has been developed, allowing proximal devices to share information and resources. Major fields of application are industrial, scientific and medical (ISM), but also consumer electronics and smart home appliances. However, for this short-range wireless connectivity, some additional challenges must be resolved. They are: (i) topology issues, i.e. self-organising, ad hoc and mesh networking; (ii) device issues, i.e. efficient, modular, low-cost and power-saving implementation; and (iii) security issues. The paper gives an overview of the challenges and suggests different solutions, especially in the field of security. In addition, it reports on working experience with two protocols: Bluetooth and IEEE802.15.4. - Author(s): M. Biggs ; A. Henley ; T. Clarkson
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 481 –488
- DOI: 10.1049/ip-com:20040653
- Type: Article
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p.
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A survey and analysis of the 2.4 GHz ISM band has been carried out in order to assess the occupancy of this band by a range of services. Both the time-varying nature of usage and the density of users in the areas covered were assessed. The sites surveyed included private sector, public sector and city centre locations. The study concluded that the use of 2.4 GHz services appears to be very widespread. Generally, the recorded levels of activity were low. An instance of WLAN interference, due to microwave detectors operating legitimately in the 2.4 GHz band, was observed. This and subsequent studies will be used to inform the spectrum management process in this and other bands where WLANs are being deployed. - Author(s): S. Pack and Y. Choi
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 489 –495
- DOI: 10.1049/ip-com:20040834
- Type: Article
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p.
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Recently, wireless LAN systems have been widely deployed for public mobile Internet services. Public wireless LAN systems can provide high speed Internet connectivity using portable devices such as laptop computers, personal digital assistants (PDAs), etc. In public wireless LAN systems, reliable user authentication and mobility support are essential issues. However, re-authentication during handoff procedures causes long handoff latency and this affects the quality of service in real-time multimedia applications. A fast handoff scheme based on mobility prediction is proposed. In this scheme, a mobile host entering the area covered by an access point (AP) performs authentication procedures for multiple APs, rather than just the current AP. These multiple APs are selected by a prediction method called the frequent handoff region (FHR) selection algorithm, which takes into account users' mobility patterns, service classes, etc. Since a mobile host is registered and authenticated for an FHR in advance, handoff latency resulting from re-authentication can be significantly reduced. Simulation results show that the proposed scheme is more efficient than other schemes in terms of handoff delay and buffer requirements. - Author(s): M. Long ; C.-H. Wu ; J.D. Irwin
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 496 –500
- DOI: 10.1049/ip-com:20040661
- Type: Article
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Authentication for inter-network roaming across wireless LANs is an important issue for achieving the goal of pervasive access and computing. The technical challenge lies in the fact that a visited network does not initially have the authentication credentials of a roaming user. Previous proposals have suggested that a visited network obtain the credentials of a roaming user and then forward them to the user's home network for authentication. A public key certificate structure is proposed, tailored to the business model of wireless Internet service providers (ISPs). In this manner, the mutual authentication between a visited network and a roaming user can be performed locally without any contact with user's home network. As a result, the time overhead incurred by communication between the ISPs' authentication, authorisation and accounting (AAA) servers can be avoided. A concrete protocol is proposed for the initial roaming authentication, which modifies the secure socket layer (SSL) v3.0 handshake protocol in order to encrypt a roaming user's identity, thus preventing any leaks in the wireless medium. A visited network can a posteriori use a portion of the protocol execution transcript as evidence to obtain revenue from a roaming user's home network. As demonstrated, the proposed solution provides a high level of security and is computationally efficient. - Author(s): G. Kambourakis ; A. Rouskas ; G. Kormentzas ; S. Gritzalis
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 501 –506
- DOI: 10.1049/ip-com:20040835
- Type: Article
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Motivated by the fact that the SSL protocol has proved its effectiveness in wired IP networks, recent research work has examined the potential use of this protocol in various wireless technologies. Although Wi-Fi networks present security deficiencies, they manage to penetrate the wireless market to a great degree due to their low cost, easy administration, great capacity, IP-oriented nature, etc. Considering Wi-Fi networking settings, administrated by different operators, as parts of a common core 3G infrastructure, the author propose the potential application of enhanced SSL-based authentication mechanisms in integrated emerging-3G and Wi-Fi networks. Existing problems related to authentication and key agreement (AKA) procedures and the extensible authentication protocol (EAP)-AKA, as they appear in the latest 3G and integrated 3G/Wi-Fi specifications, are discussed. It is proposed how EAP-TLS, combined with public key infrastructure (PKI) elements, can be used to overcome these inefficiencies in a hybrid WLAN-3G heterogeneous environment, in order to provide strong authentication and end-to-end security to the mobile user. - Author(s): M. Lott ; M. Siebert ; S. Bonjour ; D. von Hugo ; M. Weckerle
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 507 –513
- DOI: 10.1049/ip-com:20040600
- Type: Article
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Interoperation of different fixed and mobile networks is one key feature of systems beyond 3G, specifically between wireless local area networks, covering hot-spots with high data rates, and mobile cellular systems with full coverage. This comprises the vertical handover, i.e. the handover between systems with different air-interfaces, which are investigated in the paper. In contrast to several approaches that investigate solutions for the IP layer, the focus of the paper is on mechanisms on the link layer to improve the handover, respectively scanning other air-interfaces, measurements and appropriate triggers from the link layer that are considered in the handover decision process. Finally, the benefits for the handover performance are indicated and the potential of the proposed new concepts is highlighted. - Author(s): D. Kouis ; P. Demestichas ; V. Stavroulaki ; G. Koundourakis ; N. Koutsouris ; L. Papadopoulou ; N. Mitrou
- Source: IEE Proceedings - Communications, Volume 151, Issue 5, p. 514 –520
- DOI: 10.1049/ip-com:20040665
- Type: Article
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Mobile multimedia services are expected to be in high demand from mobile wireless users on a worldwide scale. The research community and telecommunications industry have focused their efforts in providing suitable wireless networks for such services. The great advance achieved among wireless local area network (WLAN) technologies, combined with the current delays in deploying 3 G cellular networks, forces the network operators to investigate possible interworking mechanisms to exploit the broadband capabilities of WLANs jointly with currently deployed 2.5 G cellular networks, as well as other commercial broadband systems. The authors present a generic management platform, suitable for WLANs interworking with other wireless systems, targeting the implementation of a high-speed wireless environment and able to maintain multimedia services, especially at hot-spot locations. The main aim was to keep the functional layout of each individual wireless network as close as possible to its original form. Finally, the authors present examples of WLANs interworking with other wireless systems, using either real commercially deployed networks or laboratory testbeds.
Editorial: WLAN systems and interworking
Linear maximum likelihood decoding of space – time block coded OFDM systems for mobile communications
Layer-2 multi-hop IEEE 802.11 architecture: design and performance analysis
Improving fairness in IEEE 802.11 using enhanced carrier sensing
Design challenges for short-range wireless networks
Occupancy analysis of the 2.4 GHz ISM band
Fast handoff scheme based on mobility prediction in public wireless LAN systems
Localised authentication for inter-network roaming across wireless LANs
Advanced SSL/TLS-based authentication for secure WLAN-3G interworking
Interworking of WLAN and 3G systems
System for enhanced network management jointly exploiting WLANs and other wireless network infrastructures
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