IEE Proceedings - Communications
Volume 147, Issue 6, December 2000
Volumes & issues:
Volume 147, Issue 6
December 2000
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- Author(s): E. Rosdiana ; H. Azmoodeh ; M. Ghanbari
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 305 –310
- DOI: 10.1049/ip-com:20000772
- Type: Article
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p.
305
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In transmission of bursty traffic such as video and data, a network with a fixed capacity may have some unused bandwidth. The available bit rate (ABR) scheme in ATM networks can make use of this spare channel capacity as a lower priority service. ABR has been developed initially for delay-tolerant services such as data. The authors demonstrate how, with the help of a video transcoder, delay-sensitive services such as video may be transmitted over ABR. The transcoder further compresses the video bit stream according to the rates dictated by the network with minimum degradation to the picture quality. The video quality has been optimised by combining the classical minimum cell rate (MCR) with the subjectively acceptable minimum quality (SAMQ). The performance of two different coding formats for ABR sources, namely the constant bit rate (CBR) and variable bit rate (VBR) video input to the transcoder are compared. The authors also present techniques for further reduction of congestion at the multiplexing switches and report on the impact of the forward and backward link delays on the ABR performance with a video transcoder. - Author(s): V.K.N. Lau and Y.-K. Kwok
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 311 –316
- DOI: 10.1049/ip-com:20000728
- Type: Article
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p.
311
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A novel multiple access control (MAC) protocol (CHARISMA) is introduced for integrated wireless voice and data services on the uplink channel in a cellular wireless network. The CHARISMA protocol is motivated by the fact that previous protocols ignore the burst errors of the channel due to fading and shadowing. As such, the physical layer of the proposed system is a variable-rate adaptive channel encoder and modulator and thus the instantaneous offered throughput to the MAC layer is variable depending on the current channel state. Given the channel state information provided by the physical layer, priority is given to those mobile terminals with better channel states. Selection diversity is achieved through gathering a large set of new and queued requests such that requests with good channel states can be identified. The multiple access performance of the proposed MAC protocol is compared with traditional TDMA-based MAC algorithms and the RMAV protocol. Extensive simulation results indicate that significant improvements in terms of throughput, delay, and packet loss probability are achieved using the CHARISMA protocol. - Author(s): A. Holt
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 317 –321
- DOI: 10.1049/ip-com:20000779
- Type: Article
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The existence of long-range dependence and self-similarity properties within World Wide Web proxy cache references is reported. Fractional ARIMA processes were used to generate long-range dependent cache hit/miss sequences in order to model the growth in cache occupancy. This model was compared to a model using independent cache hit/miss sequences and it was found that the results predicted by these models differed significantly. However, the results of the fractional ARIMA model resembled the growth of an actual cache. Trace simulations were carried out in order to investigate the effects of long-range dependence and self-similarity on cache replacement and garbage collection policies. - Author(s): M. Esmaeili and A.K. Khandani
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 322 –332
- DOI: 10.1049/ip-com:20000663
- Type: Article
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The maximum-likelihood decoding of linear block codes by Wagner rule decoding is discussed. In this approach, the Wagner rule decoding, which has been primarily applied to single parity check codes, is employed on acyclic Tanner graphs. Accordingly, a coset decoding equipped with Wagner rule decoding is applied to the decoding of a code C having a Tanner graph with cycles. A subcode C1 of C with acyclic Tanner graph is chosen as the base subcode. All cosets of C1 have the same Tanner graph and are distinguished by their values of parity nodes in the graph. The acyclic Tanner graph of C1, together with a trellis representation of the space of the parity sequences, represent the code C. This graphical representation provides a unified and systematic approach to search for an efficient method for the maximum-likelihood decoding of a given linear block code. It is shown that the proposed method covers the most efficient techniques known for the decoding of some important block codes, including the hexacode H6, extended Golay codes, Reed–Muller codes, Hamming code and (32, 16, 8) quadratic residue codes. The generalisation to the decoding of lattices is briefly explained. - Author(s): I. Boyarinov ; I. Martin ; B. Honary
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 333 –336
- DOI: 10.1049/ip-com:20000823
- Type: Article
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p.
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A simple high-speed decoding algorithm for the [24, 12, 8] extended Golay code suitable for implementation in combinational circuits is described. The proposed decoding algorithm corrects all patterns of three or fewer errors and detects quadruple errors using the Turyn construction of the extended Golay code. It is proved that the [24, 12, 8] Golay code can correct all patterns of three or fewer random errors as well as certain patterns of quadruple errors such as four-bit cyclic single-burst and two-dimensional burst errors. - Author(s): F. Babich ; G. Montorsi ; F. Vatta
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 337 –344
- DOI: 10.1049/ip-com:20000826
- Type: Article
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An improved union bound on the performance of turbo codes is evaluated, extending the preliminary results presented by Viterbi and Viterbi (1998) in conjunction with the input-binary AWGN channel. Since, in an increasing number of important applications, the AWGN channel provides an entirely inappropriate model of the propagation environment, the analytical expression of the previously derived improved union bound is extended to provide a characterisation of turbo code performance in a more general case, namely when considering the multiplicative fast-fading fully-interleaved channel. A uniform interleaver is assumed; this strategy allows one to derive the average performance of the turbo coding scheme by analysis. Of interest is the improvement of the bound for values of Eb/N0 near and below R0 (i.e. the ‘computational cutoff rate’), a region where the conventional union bound becomes useless. This improvement allows a better estimate of turbo code performance in conjunction with the fast-fading fully-interleaved channel and with the AWGN channel, which can be treated as a particular case. Moreover, it allows one to determine a tighter bound to the actual code performance as far as the slow fading Rician channel is concerned. - Author(s): N. Zhang ; Q. Shi ; M. Merabti
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 345 –350
- DOI: 10.1049/ip-com:20000778
- Type: Article
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p.
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Two protocols are presented for the issuing and identity tracing of anonymous public-key certificates, used by different parties to engage in an anonymous and fair document exchange without revealing their real identities while still being held accountable for their activities. The certificate issuing protocol allows a party to apply to certificate authorities for anonymous public-key certificates using a certificate already issued. The identity tracing protocol enables a legal authority to trace the pseudonym in an anonymous certificate back to the real identity of the corresponding party. The protocols are also analysed with regard to anonymity and accountability. - Author(s): P. Moqvist and T. Aulin
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 351 –354
- DOI: 10.1049/ip-com:20000838
- Type: Article
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p.
351
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A lower bound on the symbol error probability obtained with maximum likelihood sequence detection on the intersymbol interference channel is derived. It is recognised that the bound can be substantially improved by considering every possible transmitted sequence and not only the ones generating the well-known dmin2. Also, a method is devised which finds the additive components of the bound using a trellis search. It is demonstrated that for many channels, using a truncated upper bound as a lower bound yields incorrect results. This might be the case even if the upper bound is truncated to its first term corresponding to dmin2. - Author(s): J. Iinatti
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 355 –360
- DOI: 10.1049/ip-com:20000754
- Type: Article
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p.
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The author introduces analytical results of a direct sequence (DS) spread spectrum code acquisition, which is performed using a matched filter in a multipath channel. The performance measure is the mean acquisition time, TMA. Equations for the mean acquisition times as a function of the number of propagation paths and the number of uncertainty cells are derived for a static channel. A novel approach to apply the equations to a slowly, Rayleigh fading channel is presented. Constant false alarm rate (CFAR) criteria are used as the threshold setting rule. Two cases are investigated: the effect of power difference of the multipaths and the effect of the number of multipaths. The results indicate that the worst performance in a static channel is obtained when the paths have equal power. The acquisition performance decreases as the number of paths increases. Also, the sensitivity to the threshold value is larger in the multipath case. In a slowly fading channel, the mean acquisition time in the multipath channel is shorter than in the one-path channel. The case of equal average power of the paths leads to the best result as opposite to a static channel. The advantage of selection diversity is therefore obtained in a frequency-selective fading channel. - Author(s): V.K.N. Lau
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 361 –364
- DOI: 10.1049/ip-com:20000685
- Type: Article
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p.
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Peak-to-average ratio (PAR) of a signal is an important parameter for a linear amplifier because it determines the backoff factor needed to be applied to the amplifier in order to avoid clipping and hence spectral regrowth. The author analyses and compares the PAR of the downlink signal for the IS-95 and the CDMA2000 single carrier systems. It is found that PAR of the signal depends on the Walsh code assignment. PAR control by Walsh code selection is proposed and its effectiveness is discussed. - Author(s): D.-W. Hsiung and J.-F. Chang
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 365 –370
- DOI: 10.1049/ip-com:20000686
- Type: Article
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p.
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The authors provide a general investigation on the performance of multi-code code division multiple access (MC-CDMA) over Rayleigh fading plus additive white Gaussian noise (AWGN) channels. In MC-CDMA, high speed data sources are serial-to-parallel converted to low speed streams, which are further spread by Hadamard–Walsh orthogonal sequences and random codes. Numerical results show that, in a multipath fading channel, MC-CDMA with properly assigned Hadamard–Walsh sequences outperforms conventional CDMA when signal to noise ratio (SNR) is low and shows comparable performance at high SNR. Furthermore, for the AWGN channel, the approximate formula developed by Lee et al. (1997) shows more variation than the authors' formula. The new approach is capable of telling the impact of code cross-correlation on system performance while the earlier approach does not. - Author(s): J.S. Thompson ; P.M. Grant ; B. Mulgrew
- Source: IEE Proceedings - Communications, Volume 147, Issue 6, p. 371 –380
- DOI: 10.1049/ip-com:20000689
- Type: Article
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p.
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Transmit diversity schemes that have been proposed for the downlink in CDMA networks are discussed. They provide diversity gain against Rayleigh fading at the mobile which can significantly improve performance. Theoretical error formulas for convolutional codes are shown to be useful in optimising the performance of some of these techniques. Performance results from a number of simulation studies are also presented. These can be used to determine the strengths and weaknesses of the algorithms and their effect on a typical CDMA network. The effects of Rician fading and fast downlink power control on transmit diversity are discussed.
Congestion reduction in transmission of video over ABR networks
Multiple access control protocol for integrated isochronous and bursty data services
Long-range dependence and self-similarity in World Wide Web proxy cache references
Acyclic Tanner graphs and maximum-likelihood decoding of linear block codes
High-speed decoding of extended Golay code
Improved union bounds on turbo codes performance
Anonymous public-key certificates for anonymous and fair document exchange
Improved lower bounds on the symbol error probability for ISI channels
Performance of DS code acquisition in static and fading multipath channels
Peak-to-average ratio (PAR) reduction by Walsh-code selection for IS-95 and CDMA2000 systems
Performance of multi-code CDMA in a multipath fading channel
Downlink transmit diversity schemes for CDMA networks
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