IEE Proceedings - Communications
Volume 148, Issue 4, August 2001
Volumes & issues:
Volume 148, Issue 4
August 2001
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- Author(s): S.T. Worrall ; A.H. Sadka ; P. Sweeney ; A.M. Kondoz
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 197 –201
- DOI: 10.1049/ip-com:20010398
- Type: Article
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The introduction of third-generation wireless networks should result in real-time mobile video communications becoming a reality. Delivery of such video is likely to be facilitated by the real-time transport protocol (RTP). Careful packetisation of the video data is necessary to ensure the optimal trade-off between channel utilisation and error robustness. Theoretical analyses for two basic schemes of MPEG-4 data encapsulation within RTP packets are presented. Simulations over a GPRS (general packet radio service) network are used to validate the analysis of the most efficient scheme. Finally, a motion adaptive system for deriving MPEG-4 video packet sizes is presented. Further simulations demonstrate the benefits of the adaptive system. - Author(s): H. Cruickshank ; Z. Sun ; F. Carducci ; A. Sánchez
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 202 –206
- DOI: 10.1049/ip-com:20010392
- Type: Article
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202
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Satellites are foreseen to be complementary to future terrestrial networks in deploying multimedia communication systems. The use of geostationary multibeams and on-board processing provides a great opportunity for the speedy deployment of real time services such as IP telephony services over satellites. The effects of IP telephony transport over satellite channels have not been investigated in detail. The paper presents an overview of the VIP-TEN project architecture and the VoIP measurement campaign over the EuroSkyWay test-bed. The results show that geostationary satellites can carry VoIP traffic and offer a good quality service in terms of packet loss and jitter, and medium to poor quality in terms of packet delay. The paper also analyses the delays in setting/joining audio conferences and multicast group management over satellites. - Author(s): H. Cruickshank ; Z. Sun ; Z. Fan
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 207 –211
- DOI: 10.1049/ip-com:20010397
- Type: Article
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207
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The universal serial bus technology comes as a response to the increasing demands for unified interfaces and the need for flexible easy-to-use products for personal computers. Integrating this technology into PBXs and ISDN ICs can play an important role in the integration of telecommunications and computer technologies. The paper reports the findings of a research project called COPARIS for ISDN chip design with the additional USB interface. It also presents the software and hardware design approaches for implementing USB functions in the COPARIS chip. The research indicates that a balanced approach is the best, where the computationally intensive functions should be implemented in hardware and the rest in software. - Author(s): M.H. Habaebi and B.M. Ali
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 212 –216
- DOI: 10.1049/ip-com:20010360
- Type: Article
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212
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To enhance the throughput of the framed pseudo-Bayesian ALOHA (FPBA) algorithm used for reservation in wireless ATM, a scheme is described in which multiple power levels are used at the transmitters. One of the simultaneously sent packets can often be successfully received due to the power capture effect. The authors consider a capture model in which the transmitter captures the channel only if its signal-to-interference ratio is above some threshold when received at the central station. Rayleigh fading, shadowing and path loss all contribute to the capture effect in conjunction with the new physically induced random transmission power levels. Throughput equations of the algorithm are derived and the performance of the algorithm waiting time and throughput in the presence of the wireless channel is illustrated. Results show significant improvement in the throughput and low stable access delay for a wide range of traffic conditions. - Author(s): A. Raha ; W. Zhao ; S. Kamat ; W. Jia
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 217 –228
- DOI: 10.1049/ip-com:20010300
- Type: Article
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217
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A connection admission control (CAC) algorithm must efficiently determine if a new connection can be admitted by verifying that its QoS requirements can be met without violating those of previously admitted connections. In hard real-time systems, the QoS requirements are specified in terms of end-to-end cell deadlines and no cell loss due to buffer overflow. To achieve these objectives a CAC algorithm must account for the traffic characteristics of connections. Furthermore, arbitrary topology of the network may lead to cyclic dependencies among various connections. An efficient CAC algorithm is presented that addresses these issues. The algorithm uses a traffic descriptor called the ‘maximum traffic rate function’ to effectively compute bounds on end-to-end delays of connections and buffer requirements within the network. The work differs from most previous work in that it does not require traffic restoration inside the network. - Author(s): C.-H. Cho ; J.-J. Won ; H.-W. Lee
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 229 –233
- DOI: 10.1049/ip-com:20010399
- Type: Article
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p.
229
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To overcome the high level and bursty nature of bit errors in wireless channels a new data link control (DLC) frame structure for transmitting wireless ATM cells is proposed. The throughput, undetected error probability and error correcting probability of the proposed DLC frame structure employing a hybrid II ARQ (automatic repeat request) scheme with RS (Reed–Solomon) code are analysed for a fading channel that is characterised by a two-state Markov chain model. Using the analysis method, parameters of the proposed DLC structure can be determined so that throughput performance is optimised in a wireless channel with bursty errors. Numerical examples are presented to demonstrate the effects of burstiness and parameters of the proposed DLC frame format on performance. To verify the analytical model, analytical results and simulation results are compared. It is observed that the effect of channel fading on the throughput is not necessarily negative. - Author(s): S.-C. Lin
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 234 –242
- DOI: 10.1049/ip-com:20010270
- Type: Article
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The paper analyses the performance of optimum space combining diversity with finite-length decision-feedback equalisation operating in a mobile radio environment with frequency-selective fading and quadrature amplitude modulation transmission. Selection diversity, another very common diversity method, is also involved in the analysis. By analytic techniques and simulation, it is shown that for the same number of taps, generally, the improvement is greater with combining diversity structure. However, numerical results also indicate that combining diversity may be inferior to selection diversity in some cases where the channels are severely distorted and combining diversity may lead to noticeable amplitude dispersion which cannot be compensated for easily by using a finitely long postcombining equaliser. Estimates of average errors and outage probabilities as functions of length of equalisation are provided for different diversity structures. The required length of equalisation to approach the optimum performance (achievable with an infinitely long equaliser) for different values of relative delay spread is examined carefully. Admitting perfect elimination of intersymbol interference postcursors, considerably superior performance of decision feedback equalisation can be obtained in terms of a fairly smaller number of taps to achieve this best performance, in addition to a small minimum mean square error than linear equalisation if the channel suffers severe time-dispersive multipath fading, particularly in the combining diversity case. - Author(s): X. Dai
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 243 –248
- DOI: 10.1049/ip-com:20010269
- Type: Article
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p.
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Combining the ‘mixture of experts’ (ME) model with the expectation-maximisation (EM) algorithm, the author proposes a constant modulus algorithm-based (CMA-based) blind equalisation scheme for equalising the nonlinear channel. The equaliser considered in the paper is assumed as a two-layer feedforward neural network (FNN). The hidden units of the FNN equaliser are approximated with multiple linear systems around multiple points of its input space, and the FNN equaliser is then remodelled with an ME architecture. Based on the ME model, FNN equaliser parameters are estimated with the statistical EM algorithm in a faster convergence speed than the back-propagating algorithm, in which M-operation of the EM algorithm is in fact the CMA-based linear finite impulse response equalisation. - Author(s): Y. Gong ; T.J. Lim ; B. Farhang-Boroujeny
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 249 –254
- DOI: 10.1049/ip-com:20010274
- Type: Article
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p.
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The Gram–Schmidt (GS) orthogonalisation procedure has been used to improve the convergence speed of least mean square (LMS) adaptive code-division multiple-access (CDMA) detectors. However, this algorithm updates two sets of parameters, namely the GS transform coefficients and the tap weights, simultaneously. Because of the additional adaptation noise introduced by the former, it is impossible to achieve the same performance as the ideal orthogonalised LMS filter, unlike the result implied in an earlier paper. The authors provide a lower bound on the minimum achievable mean squared error (MSE) as a function of the forgetting factor λ used in finding the GS transform coefficients, and propose a variable-λ algorithm to balance the conflicting requirements of good tracking and low misadjustment. - Author(s): C.R. Iversen and T.E. Kolding
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 255 –259
- DOI: 10.1049/ip-com:20010396
- Type: Article
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p.
255
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The paper presents analytical expressions for determining noise and intercept points for cascaded radio receiver stages. The theory allows for active receiver stages with frequency selectivity and flexible impedance levels. This makes the method highly usable for planning of modern receivers where baseband stages significantly influence the overall performance. A simple homodyne receiver example is used to demonstrate the scope of applicability and to exemplify the proposed theory. - Author(s): J.-H. Wen ; J.-S. Sheu ; T.-S. Chen
- Source: IEE Proceedings - Communications, Volume 148, Issue 4, p. 260 –264
- DOI: 10.1049/ip-com:20010393
- Type: Article
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p.
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Based on the Newton interpolation method and a predefined one-way function, a cryptographic key assignment scheme, called the CHW scheme, in a user hierarchy was presented by Chang et al. in 1992. The CHW scheme did not need the large amount of storage needed in the Akl–Taylor scheme. However, two counter-examples have been presented to prove the incorrectness of the CHW scheme, and further two modified versions of the CHW scheme were also proven to be insecure. Owing to these problems, a simple scheme is proposed to overcome the incorrectness and to enhance the security of the CHW scheme.
Optimal packetisation of MPEG-4 using RTP over mobile networks
Analysis of IP voice conferencing over EuroSkyWay satellite system
Universal serial bus implementation in an integrated access chip for ISDN systems
Improving the performance of the FPBA algorithm using random transmitter power levels
Admission control for hard real-time connections in ATM LANs
Performance of hybrid II ARQ schemes using punctured RS code for wireless ATM
Finite-length decision-feedback equalisation for optimum combining diversity in digital cellular mobile radio
CMA-based nonlinear blind equaliser modelled by a two-layer feedforward neural network
Adaptive least mean square CDMA detection with Gram–Schmidt pre-processing
Noise and intercept point calculation for modern radio receiver planning
Cryptographic key assignment scheme for overcoming the incorrectness of the CHW scheme
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