Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 1, Issue 4, August 2007
Volumes & issues:
Volume 1, Issue 4
August 2007
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- Author(s): B. Jovic and C.P. Unsworth
- Source: IET Communications, Volume 1, Issue 4, p. 549 –555
- DOI: 10.1049/iet-com:20060672
- Type: Article
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A chaos-based multi-user time division multiplexing (TDM) communication system has been proposed and its benchmark performance compared to that of the chaos-based direct sequence code division multiple access (DS-CDMA) system in the noisy and Rayleigh fading channels. The benchmark performance of the systems is investigated in terms of the bit error rate (BER) under the assumption of perfect synchronisation. The chaotic spreading signals, used to encrypt the binary messages, are generated using the logistic map. The degradation in performance of the systems in the Rayleigh fading channel when compared with the noisy channel is demonstrated. Furthermore, it is shown that in both noisy and Rayleigh fading channels, the chaos-based multi-user TDM system outperforms the chaos-based DS-CDMA system for a large number of users in the system, whereas the chaos-based DS-CDMA system yields better performance for low user numbers. The overall BER performance degradation for the chaos-based DS-CDMA multi-user system in noisy and Rayleigh fading channels is characterised by the flattening of the BER curves at low levels of noise due to the prevailing effects of the interuser interferences. - Author(s): J.-K. Lain and J.-J. Lai
- Source: IET Communications, Volume 1, Issue 4, p. 556 –561
- DOI: 10.1049/iet-com:20050456
- Type: Article
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An ant colony optimisation (ACO)-based multiuser detector assisted by spatial diversity reception using direct-sequence CDMA is proposed. By taking advantage of heuristic values and the collective intelligence of ACO, the proposed detector offers almost the same bit error rate (BER) performance as the full-search-based optimum multiuser detector does, while greatly reducing the computational complexity. The near–far resistance of the ACO-based multiuser detector is also examined. The BER performance for a ten-user system deteriorates scarcely when the interfering users’ energy is 12 dB higher than that of the desired user. - Author(s): Z. Li and R. Tafazolli
- Source: IET Communications, Volume 1, Issue 4, p. 562 –569
- DOI: 10.1049/iet-com:20060460
- Type: Article
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In order for third-generation partnership project (3GPP) networks to cope with the rapid growth of IP data traffic, the location management requires further enhancement to accommodate the burst data traffic characteristics of packet switched (PS) services. The universal mobile telecommunication system (UMTS) location management solutions for PS services in 3GPP networks has been investigated, and an inactivity counter mechanism in PS domain to reduce the location management cost of inactivate users has been proposed. An analytical model accommodating diverse call and mobility characteristics of user equipment to evaluate the performance of the inactivity counter mechanism has also been developed. Using the proposed model, the performance of the inactivity counter mechanism in UMTS terrestrial radio access network recommended by 3GPP is investigated, the cost reduction obtained by the proposed mechanism when compared with the original location strategy used in the PS domain is then analysed, which also shows the effect of system parameters and users' mobility and service patterns on the location management costs. - Author(s): E. Öztürk
- Source: IET Communications, Volume 1, Issue 4, p. 570 –576
- DOI: 10.1049/iet-com:20060272
- Type: Article
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The probability of error (Pe) performance of asynchronous direct sequence code division multiple access (DS-CDMA) signals over multi-path Rayleigh fading channels for general (i.e. time-limited and band-limited) chip waveforms is investigated. The numerical values of the Pe are calculated for DS-CDMA signals using conventional time-limited chip waveforms and a band-limited square root raised cosine (SRRC) chip waveform. Analytical calculations are verified by conducting simulations. In terms of the Pe, the SRRC-based system results in a worse performance value than those of the time-limited chip waveform-based systems. However, due to its compact bandwidth, the SRRC-based system provides the highest capacity defined as the number of users per Hertz for a same Pe performance level. - Author(s): R. de Renesse ; V. Friderikos ; H. Aghvami
- Source: IET Communications, Volume 1, Issue 4, p. 577 –586
- DOI: 10.1049/iet-com:20060243
- Type: Article
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Mobile ad hoc networks (MANETs) are unpredictable by nature. Providing any kind of reliability for quality of service (QoS) in such networks is challenging. Quantifying available resources accurately, avoiding interference with ongoing QoS traffic and adapting to QoS violations caused by nodes' mobility are the main concerns for the design of an efficient admission control protocol in MANETs. Adaptive admission control (AAC), a novel admission control protocol which uses robust and accurate resource estimation and prediction techniques for relevant admission decisions has been proposed. Furthermore, AAC uses statistical QoS provision to counteract the QoS threatening mobility. Through simulations, we show that our proposed scheme outperforms existing approaches in terms of correctness and overall performance. - Author(s): S.-I. Chu and S.-C. Chang
- Source: IET Communications, Volume 1, Issue 4, p. 587 –596
- DOI: 10.1049/iet-com:20060521
- Type: Article
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An empirical data-based design methodology is proposed for Internet-access management to improve congestion, uneven usage and fairness, especially during peak hours, over a free-of-charge or flat-rate network. The design methodology combines time-of-day pricing (TDP) with quota-based priority control (QPC). Core to the design methodology are the innovations in characterising user demand and quota-allocation behaviour with respect to time and pricing. In-depth analyses of empirical data reveal distinctive behaviour patterns of myopic and prudent quota allocations over time and both patterns indicate high preference for peak-hour access. The user models adopt general utility functions and capture how pricing affects user behaviour as prudent or myopic. Preference parameters of users' utility over time are then estimated by collecting easily measurable user volumes. The TDP design problem is formulated and solved as a Stackelberg game. Tested on the empirical data of a 5000-user network, the TDP design leads to significant improvements in peak-hour usage and fairness, peak shaving and load balancing over pure QPC. The methodology requires only two simple and short-period data collections from an operational network and takes about 1 min of CPU time for TDP calculation. Results demonstrate the effectiveness of our design methodology when applied to Internet-access environments with frequent changes. - Author(s): R. Liu and J. Elmirghani
- Source: IET Communications, Volume 1, Issue 4, p. 597 –603
- DOI: 10.1049/iet-com:20060387
- Type: Article
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An adaptive transmission scheme using variable-length spreading sequences (VLSS) is proposed. The system is based on an impulse direct sequence ultra-wideband (DS-UWB) approach for wireless communication where the number of active users is variable. In contrast to the conventional DS-UWB system, which employs a fixed length spreading code, the proposed system changes the length of spreading code according to the system load adaptively, which is proven to be able to reduce the inter-chip interference, inter-symbol interference and multiple-access interference and thus improve the system performance in terms of bit error rate. The proposed system is simulated in multipath channels with a high level of multipath fragments, modelled by the standard IEEE 802.15.3a indoor channel model 1 (CM1) and channel model 2 (CM2). Numerical results demonstrate that when RAKE receivers are employed, the proposed VLSS DS-UWB system outperforms the conventional system by appropriately allocating the spreading sequences. - Author(s): S. Attallah ; Y. Wu ; J.W.M. Bergmans
- Source: IET Communications, Volume 1, Issue 4, p. 604 –611
- DOI: 10.1049/iet-com:20060120
- Type: Article
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The presence of residual carrier frequency offset (CFO) in an orthogonal frequency division multiplexing (OFDM) system leads to a loss of orthogonality between the subcarriers. This introduces inter-subcarrier interference and degrades the system performance significantly. In the literature, Liu and Tureli proposed a blind CFO estimation method based on the observation that in a typical OFDM system not all the subcarriers are used for data transmission. However, the computational complexity of such a method is very high. Based on practical considerations, we propose an approximate closed-form solution for the blind estimation of CFO that is easily implementable at a very low cost. We also propose a successive CFO estimation and compensation procedure, which reduces the performance degradation of the proposed algorithm as compared with the method of Liu and Tureli when relatively large CFO values are assumed. In addition, a decision-directed extension of the successive algorithm, which further improves the CFO estimation at a slightly higher complexity, is also given. - Author(s): Z.C. Pereira ; M.E. Pellenz ; R.D. Souza ; M.A. Araújo Siqueira
- Source: IET Communications, Volume 1, Issue 4, p. 612 –617
- DOI: 10.1049/iet-com:20060530
- Type: Article
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An unequal error protection strategy for minimising the impact of error bursts in the storage or transmission of compressed data has been proposed. The strategy is designed for the LZSS algorithm, which is a dynamic dictionary compression method. Through extensive computer simulations we investigate which information classes within LZSS are more sensitive to burst errors. Based on these results, an unequal error protection strategy that greatly reduces the error propagation during the decompression process has been proposed. Numerical results using text files from a common database are presented. - Author(s): E.R. Pelet and J. Eric Salt
- Source: IET Communications, Volume 1, Issue 4, p. 618 –622
- DOI: 10.1049/iet-com:20060554
- Type: Article
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This paper deals with timing jitter reduction in the timing recovery loop of a digital QAM receiver. The main contribution, which is derived analytically, is an economical prefilter to reduce the timing jitter in timing recovery loops containing either the early–late or the Gardner timing-error detector (TED). The proposed prefilter has the advantage of being an infinite impulse response filter that is placed inside the TED and runs at the symbol rate. For small roll off factors, it is shown with a computer simulation that a single-pole filter placed inside either the early–late or the Gardner detector is quite effective in reducing the timing jitter. - Author(s): P. Moqvist and T. Aulin
- Source: IET Communications, Volume 1, Issue 4, p. 623 –627
- DOI: 10.1049/iet-com:20060346
- Type: Article
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Average performance bounds based on uniform interleaving are considered for a serial concatenation consisting of an outer code, an interleaver and an inner coded modulation system. The exact input–output weight spectrum is derived for the case when only the outer code has the uniform error property. Thereby, an upper bound to the bit error probability under maximum likelihood detection is obtained. However, numerous examples for serially concatenated continuous phase modulation show that neglecting the non-uniform error property of the inner system gives an accurate and less complex approximation. Other inner coded modulations may behave differently. - Author(s): D-F. Tseng and K-C. Lu
- Source: IET Communications, Volume 1, Issue 4, p. 628 –637
- DOI: 10.1049/iet-com:20060309
- Type: Article
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An uplink direct sequence spread spectrum communications systems employing a multi-sequence model over a quasi-static frequency-selective fading channel is considered. In analogy with bit-interleaved coded modulation (BICM) technique, a group of bits at the output of a bit-wise interleaver is mapped uniquely to a complex signalling vector belonging to an orthogonal plane sequence modulation signal space, which is constructed over a set of expanded signature sequences. This transmission system provides not only bandwidth efficiency offered by additional signal planes but also time diversity resulting from the BICM technique. It is observed that at high system traffic load error performance could degrade substantially due to user cross-correlations, multi-access asynchronism as well as channel frequency selectivity. The authors employ a ‘turbo principle’ receiver, consisting of a soft interference cancellation scheme, soft demappers and maximum a posteriori decoders, to avert this capacity loss by exploiting the serially concatenating structure at the transmitter. After simple mathematical manipulation, a soft space–time linear minimum mean-square error multi-user detector could even be explored on the basis of per signal plane per user. Both analytical performance-bound and computer simulation of the proposed framework in terms of bit-error rate (BER) are revealed. Further, performance comparisons with convolutionally coded and conventional bandwidth-efficient coded direct sequence code division multiple access systems under the same system conditions are illustrated. The authors have also investigated the impact of labelling maps on the BER performance. - Author(s): S. Zhu and A.G. Constantinides
- Source: IET Communications, Volume 1, Issue 4, p. 638 –646
- DOI: 10.1049/iet-com:20060022
- Type: Article
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The problem of blind linear data-symbol estimation and data detection for the air-interface adopting the wide-band direct sequence code division multiple access multiuser multiplexing technique with the promising short-code configurations has been addressed. The superior interference-suppression ability of the code-constrained minimum output energy multipath-component estimation is utilised to develop three code-aided quasi-maximum signal-to-interference and noise ratio (SINR) algorithms. These algorithms operate in such a way as to maximise approximate measures of the output SINR, each having variations, especially in the adaptive implementation, because of different criteria employed. The ‘quasi-maximum SINR’ nature is because of the approximations employed. Extensive simulations indicate that all of these algorithms significantly outperform the existing code-aided blind linear algorithms at considerably low computational complexity. Moreover their adaptive versions exhibit very high level of desirable trade-off between convergence speed and steady-state performance at further reduced computational complexity. - Author(s): V. Bhatia ; B. Mulgrew ; D.D. Falconer
- Source: IET Communications, Volume 1, Issue 4, p. 647 –654
- DOI: 10.1049/iet-com:20060067
- Type: Article
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A maximum-likelihood channel estimator for the orthogonal frequency division multiplexing communication environments, in the presence of interference is discussed here. In a training-based scenario, the channel is estimated based on pilots that precede the transmission of the information. To reduce the number of estimation parameters, the channel is estimated iteratively in time-domain. Since interference from other users provide no useful information, parameters of the interference are neither estimated nor the effect of the interference neglected, instead interference along with Gaussian noise is perceived as non-Gaussian noise process. The algorithm assumes no a priori knowledge about the interfering channel and signal at the receiver, further no assumption on the statistical properties of the interferer is assumed, which makes this algorithm robust. The estimated channel information along with the estimated distribution are then utilised to equalise the subsequent data blocks. The strength of the algorithm is in its robustness to both synchronous and asynchronous interference, which is confirmed by the simulation results for both flat and multipath fading channels in presence of synchronous and asynchronous interference. - Author(s): F. Xu ; D.-W. Yue ; F.C.M. Lau ; Q.F. Zhou
- Source: IET Communications, Volume 1, Issue 4, p. 655 –661
- DOI: 10.1049/iet-com:20060152
- Type: Article
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The performances of orthogonal space–time block codes (OSTBCs) over Rician–Nakagami channels are investigated. In particular, we derive closed-form symbol error probability (SEP) expressions for OSTBC systems in which M-ary phase-shift-keying modulation and M-ary quadrature-amplitude modulation are used. These SEP results are expressed in terms of Lauricella's multivariate hypergeometric functions, which can be easily evaluated numerically. When the Rician–Nakagami channel degenerates to the Rician–Rayleigh channel, or equivalently the Rayleigh fading channel, the closed-form SEP expressions are rewritten in terms of higher transcendental functions, that is, Gauss hypergeometric function and Appell hypergeometric function. - Author(s): S.H. Won and L. Hanzo
- Source: IET Communications, Volume 1, Issue 4, p. 662 –670
- DOI: 10.1049/iet-com:20060161
- Type: Article
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Both differentially coherent and non-coherent code acquisition schemes designed for the multiple-input multiple-output (MIMO)-aided multi-carrier (MC)-DS-CDMA downlink are analysed, when communicating over uncorrelated Rayleigh channels. The attainable mean acquisition time (MAT) performance is studied as a function of both the number of multiple transmit/multiple receive antennas and that of the number of subcarriers. It is demonstrated that in contrast to the expectations, when the number of multiple transmit antennas and/or that of the subcarriers is increased in both the differentially coherent and the non-coherent code acquisition scenarios, the achievable MAT deteriorates over the entire signal-to-interference plus noise ratio (SINR) per chip (Ec/Io) range considered, except for the scenario of single-carrier (SC)-DS-CDMA using P=2 transmit antennas and R=1 receive antenna. As expected, the degree of performance degradation depends upon the specific scheme and the Ec/Io ratio considered, although paradoxically, the correctly synchronised MIMO-aided system is capable of attaining its target bit error ratio performance at reduced SINR values. - Author(s): S. Chen ; A. Wolfgang ; Y. Shi ; L. Hanzo
- Source: IET Communications, Volume 1, Issue 4, p. 671 –678
- DOI: 10.1049/iet-com:20050170
- Type: Article
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A minimum bit error rate (MBER) decision feedback equaliser (DFE) designed for single-input multiple-output (SIMO) systems employing a quadrature phase shift keying (QPSK) modulation scheme is proposed. It is shown that this MBER design is superior over the standard minimum mean square error DFE in the SIMO scenario considered, in terms of the achievable system bit error rate. A sample-by-sample adaptive implementation of this MBER DFE is derived, which is referred to as the least bit error rate (LBER) algorithm. It is shown that for SIMO systems using a QPSK scheme, the LBER algorithm has a similar computational complexity as the simple least mean square (LMS) algorithm. Simulation results demonstrate that the proposed adaptive LBER-based DFE outperforms the adaptive LMS-based DFE, in both stationary and fading cases. - Author(s): L. Yi and Z. Hailin
- Source: IET Communications, Volume 1, Issue 4, p. 679 –683
- DOI: 10.1049/iet-com:20060292
- Type: Article
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The channel state information (CSI) at the transmitter can significantly improve the performance of multiple-antenna systems. However, providing full knowledge of CSI at the transmitter may not be affordable in many practical cases. Thus, exploiting the partial channel knowledge to improve system performance seems to be attractive. An interpolation based limited feedback precoding scheme (ILFP) for MIMO-OFDM systems is proposed. In this scheme, both the transmitter and the receiver store the codebook of precoding matrices constructed offline using two-variable joint vector quantisation. Considering the correlation between OFDM subcarriers, they are divided into subcarrier clusters. At the receiver, precoding is carried out on the clusters, and then the precoding information is conveyed to the transmitter by limited bits of feedback. At the transmitter, the precoding matrices for each subcarrier are obtained by interpolation according to the feedback. Simulation results show that the proposed scheme outperforms the existing schemes. - Author(s): H. Wang and G.-S. Poo
- Source: IET Communications, Volume 1, Issue 4, p. 684 –692
- DOI: 10.1049/iet-com:20060300
- Type: Article
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Load balancing in the provisioning of virtual private network (VPN) service in the hose model is studied. Single-path routing and tree routing for the hose model tend to aggregate bandwidth reservations on a small number of links, thus leading to congestion problems in service provider networks. If the link capacity is depleted as a result of improper routing, all future non-VPN traffic will be blocked. We propose a novel multi-objective multi-path (MOMP) routing linear program with the maximum fraction of traffic on a path (MFTP) constraint to solve the problem. The MOMP routing algorithm is able to reduce the bandwidth reservation on the most loaded link by as much as 50%, thus effectively alleviating the potential congestion problems in service provider network. The MFTP constraint provides a guarantee of the availability of multiple paths for each VPN endpoint pair. Further reduction of the bandwidth reservation can be achieved depending on the MFTP value. This is highly significant. - Author(s): S.C. Tan ; F.M. Abbou ; E.H. Tat
- Source: IET Communications, Volume 1, Issue 4, p. 693 –695
- DOI: 10.1049/iet-com:20060323
- Type: Article
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An ant-based contention resolution scheme for the slotted optical packet switched networks has been proposed, and the optimal number of fibre delay lines (FDLs) used in the switch under various traffic loads is investigated. The proposed algorithm can makes FDLs and output port assignment so as to improve the cell-loss rate under various traffic loads. It is found for traffic loads 0.9, 0.6, 0.3, the optimum value for FDL is 64 128 and 128. - Author(s): F. Benedetto ; G. Giunta ; A. Neri
- Source: IET Communications, Volume 1, Issue 4, p. 696 –704
- DOI: 10.1049/iet-com:20060331
- Type: Article
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Tracing watermarking has been recently proposed as a technique to provide a blind measure of the quality of service of the communication link, focusing on multimedia communication scenarios. 3G communication scenarios, where each customer transmits both voice and MPEG-4 video sequences in real time, have been considered. Typical video-phone call consists of close shots of speakers, framing their face in the foreground. For such particular application, a novel colour space (YST) is adopted to minimise the perceptual distortions on face coding introduced by watermarking. In the YST space, the luminance component (Y) is the same as in conventional YUV space, whereas the vectors S and T lie within the chrominance (UV) plane. The S (skin) component is a linear combination of U and V obtained as the ‘average’ chrominance estimated from an assorted set human faces to achieve a reasonable generalisation. The third component, T, is defined as orthogonal to the YS plane. The results show the benefits obtained in digital watermarking by the new representation against the conventional approach. In fact, the sensitivity of the YST representation outperforms the conventional one in terms of objective (mean square error, peak signal-to-noise ratio) and subjective (video-quality metrics) indicators. - Author(s): M. Inamori ; A.M. Bostamam ; Y. Sanada
- Source: IET Communications, Volume 1, Issue 4, p. 705 –710
- DOI: 10.1049/iet-com:20060358
- Type: Article
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The influence of timing jitter on quadrature charge sampling for a direct conversion receiver has been evaluated. In contrast to voltage sampling, the charge sampling mixer integrates the signal current instead of tracking the signal voltage. The charge sampling mixer has been applied to RF direct sampling in wireless receivers. The influence of timing jitter on charge sampling has been analysed in some literatures. However, in wireless receivers, quadrature sampling is required in order to demodulate I-phase and Q-phase signals. Different from charge sampling, timing jitter causes crosstalk between these signals. The influence of timing jitter on quadrature sampling is investigated. - Author(s): C.-Y. Ho ; Y.-C. Chan ; Y.-C. Chen
- Source: IET Communications, Volume 1, Issue 4, p. 711 –717
- DOI: 10.1049/iet-com:20060380
- Type: Article
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Queue management, bandwidth share and congestion control are very important to both the robustness and fairness of the Internet. A new TCP-friendly router-based active queue management scheme, called WARD, approximates the fair queueing policy. WARD is a simple packet dropping algorithm with a random mechanism and discriminates against the flows which submit more packets per second than is allowed by their fair share. By doing this, it not only protects transmission control protocol (TCP) connections from user datagram protocol (UDP) flows, but also solves the problem of competing bandwidth among different TCP versions, such as TCP Vegas and TCP Reno. Furthermore, it is stateless and easy to implement, so WARD controls unresponsive or misbehaving flows with a minimum overhead. In this article, we present a deterministic fluid model of TCP/WARD system, and explain the UDP throughput behaviour with WARD. Also, we prove that, provided the number of TCP flows is large, the UDP bandwidth share peaks at (2e)−1=0.184 when UDP input rate is slightly larger than link capacity and drops to zero as UDP input rate tends to infinity. - Author(s): G.A. Safdar and W.G. Scanlon
- Source: IET Communications, Volume 1, Issue 4, p. 718 –725
- DOI: 10.1049/iet-com:20050429
- Type: Article
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The performance of a new pointer-based medium-access control protocol that was designed to significantly improve the energy efficiency of user terminals in quality-of-service-enabled wireless local area networks was analysed. The new protocol, pointer-controlled slot allocation and resynchronisation protocol (PCSARe), is based on the hybrid coordination function-controlled channel access mode of the IEEE 802.11e standard. PCSARe reduces energy consumption by removing the need for power-saving stations to remain awake for channel listening. Discrete event network simulations were performed to compare the performance of PCSARe with the non-automatic power save delivery (APSD) and scheduled-APSD power-saving modes of IEEE 802.11e. The simulation results show a demonstrable improvement in energy efficiency without significant reduction in performance when using PCSARe. For a wireless network consisting of an access point and eight stations in power-saving mode, the energy saving was up to 39% when using PCSARe instead of IEEE 802.11e non-APSD. The results also show that PCSARe offers significantly reduced uplink access delay over IEEE 802.11e non-APSD, while modestly improving the uplink throughput. Furthermore, although both had the same energy consumption, PCSARe gave a 25% reduction in downlink access delay compared with IEEE 802.11e S-APSD. - Author(s): B.T. Ahmed
- Source: IET Communications, Volume 1, Issue 4, p. 726 –731
- DOI: 10.1049/iet-com:20060455
- Type: Article
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The multi-service (a combination of voice and data services) uplink capacity and the interference statistics (mean value and variance) of the sectors of a long-tunnel W-CDMA microcell are studied. A model of nine microcells in a long tunnel is used to analyse the uplink capacity and interference. The hybrid model of propagation is used in the analysis. The multi-service capacity and the interference statistics of the sector are studied for different sector ranges, antenna azimuth side lobe levels and power control standard deviation error. - Author(s): A.H. Wong ; M.J. Neve ; K.W. Sowerby
- Source: IET Communications, Volume 1, Issue 4, p. 732 –738
- DOI: 10.1049/iet-com:20050487
- Type: Article
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Effective antenna selection and deployment strategies are important for reducing co-channel interference in indoor wireless systems. Low-cost solutions are essential, and strategies that utilise simple (passive) antennas (such as directional patches) are advantageous from this perspective. However, performance is always an issue and the improvements achievable through clever antenna deployment (both placement and orientation) need to be quantified. An experimental investigation of indoor propagation comparing the performance of directional and omni-directional antennas is reported. In the case study of a voice-based indoor communication system employing DS-CDMA radio access technique with BPSK modulation, the outage probability for base stations fitted with directional antennas was observed to change in the −54% to +66% range relative to the omni-directional case. The effective change in the distribution of carrier-to-interference ratios by the use of directional antennas is well established in outdoor micro cellular deployment scenarios; however, the magnitude of the influence is quantified for an indoor environment in this case study. It is also shown that obstacles in the environment can amplify the effectiveness of the antenna deployment by acting as physical cell boundaries that restrict interference. External interference has been shown to cause a significant degradation to the performance of an indoor system when the carrier-to-external-interference ratio. This performance degradation can be minimised by appropriate deployment of directional antennas at the base stations, although the optimum antenna orientations depends on the strength of external interference. - Author(s): I. Berenguer ; A. Høst-Madsen ; X. Wang
- Source: IET Communications, Volume 1, Issue 4, p. 739 –750
- DOI: 10.1049/iet-com:20060510
- Type: Article
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Nonlinear precoding schemes for downlink time-division duplex–CDMA systems over multipath fading channels, are considered. First, the capacity results of a downlink CDMA system with either multiuser detection or precoding, were obtained and compared. It is seen that the two schemes exhibit similar capacity regions for both sum rate and maximum equal rate, which motivates the development of efficient nonlinear transmitter precoding techniques to reduce the receiver complexity at the mobile units without degrading the system performance. We then develop both bit-wise and chip-wise Tomlinson–Harashima (TH) multiuser precoding methods for downlink CDMA with multipath, to remove multi-user interference, inter-chip interference and inter-symbol interference. Efficient algorithms for multiuser power loading and ordering are also developed. Implementation of the proposed TH-precoding schemes in time-varying channels based on channel prediction is addressed as well. Simulations results are provided to demonstrate the effectiveness of the proposed techniques in suppressing interference in downlink CDMA. - Author(s): W.Q. Malik ; C.J. Stevens ; D.J. Edwards
- Source: IET Communications, Volume 1, Issue 4, p. 751 –759
- DOI: 10.1049/iet-com:20060551
- Type: Article
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A simple and efficient virtual-source ray-tracing technique for the simulation of indoor wideband radio and optical propagation channels is proposed. The parametric deterministic model considers the room geometry, transceiver locations, material properties and probe signal types. It is applied to the indoor ultrawideband channel in the FCC-allocated 3.1–10.6 GHz band, and a range of novel results are presented to illustrate several possible applications. The channel small-scale fading statistics and spatial variability are examined by synthesising a densely sampled aperture. Multiple-antenna array systems are simulated to evaluate multiple-input multiple-output performance. The multipath angular characteristics are analysed from the simulated azimuth-delay profile. The simulation results closely match previous channel measurement studies and statistical models, validating the proposed technique. It is shown that specular reflection is dominant, and power convergence is achieved with three reflections in a typical indoor environment. Thus, it is demonstrated that despite its simplicity, the model yields reliable and accurate results, and can therefore be a useful tool for indoor wireless network planning and performance prediction. - Author(s): X. Liu ; H. Wei ; L. Hanzo
- Source: IET Communications, Volume 1, Issue 4, p. 760 –764
- DOI: 10.1049/iet-com:20050549
- Type: Article
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The performance of large area synchronous (LAS) direct sequence code division multiple access (DS-CDMA) assisted ad hoc networks is investigated in the context of a single-hop infinite mesh of rectilinearly located ad hoc nodes. It is shown that LAS DS-CDMA exhibits a significantly better performance than the family of traditional spreading sequences used in a quasi-synchronous DS-CDMA scenario having a low number of resolvable multipath components and a sufficiently high number of RAKE receiver branches. The benefits of LAS codes in ad hoc networks are multifold: (i) Their performance is noise-limited, rather than interference-limited, provided that the multipath and multi-user interference arrives within their interference free window. (ii) Under the same conditions LAS codes are robust against the ‘near–far’ effects imposed by ad hoc networks operating without base-station-aided power control, without accurate synchronisation and without implementationally complex interference cancellers. - Author(s): L. Zhao ; J. Zhang ; H. Zhang
- Source: IET Communications, Volume 1, Issue 4, p. 765 –771
- DOI: 10.1049/iet-com:20060641
- Type: Article
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Directional distributed co-ordination function (D-DCF), a modified medium access control protocol of IEEE 802.11, is proposed to support hybrid antennas such as smart adaptive array antennas and normal omni-directional antennas, in one wireless local area network cell. Nodes equipped with smart antennas follow D-DCF and nodes equipped with normal antennas follow DCF. D-DCF based on a hybrid virtual carrier sense mechanism maintains compatibility with DCF. In D-DCF, before sending any data-frames, the sender and receiver node transmit a pilot sequence by means of an omni-directional request-to-send/clear-to-send handshake mechanism. Based on the pilot, the directional beam can be formed by the smart antenna. Then the node can transmit its data-frame in the directional mode. The other nodes save the transmission time between the sender and receiver in the omni-directional mode in their network allocation vectors. When the sender and receiver communicate in the directional mode, the other nodes can access the channel to send their data-frames. Hence, D-DCF supports space division multiplexing. Moreover, D-DCF fully supports time division duplex, namely both the forward and backward transmission in one access period. Simulation results show that D-DCF can support the hybrid antenna system effectively and provide much higher network throughput, lower delay, jitter and packet-loss-rate than DCF does. - Author(s): P. Yang and J.-H. Ge
- Source: IET Communications, Volume 1, Issue 4, p. 772 –775
- DOI: 10.1049/iet-com:20050489
- Type: Article
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A novel low-complexity scheme of Turbo Trellis-coded modulation (TCM) iterative equalisation and decoding is presented, which serially concatenates a soft-input–soft-output equaliser and symbol-by-symbol Turbo TCM (TTCM) decoder through an iterative process in order to realise iterative equalisation and decoding process. This scheme can not only improve the bandwidth efficiency, but also reduce the intersymbol interference. The equaliser with maximum a posteriori is replaced with linear one based on minimum mean-square error at the receiver so that the complexity of the system can be reduced greatly. Computer simulation results show that the novel low-complexity receiver on fading channels can achieve comparable performance with TTCM on Gaussian channels. - Author(s): Y. Zhou and G.-S. Poo
- Source: IET Communications, Volume 1, Issue 4, p. 776 –783
- DOI: 10.1049/iet-com:20060424
- Type: Article
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The multicast wavelength assignment problem in wavelength-routed wavelength-division multiplexing networks with limited wavelength conversions is addressed. A new multi-wavelength multicast wavelength assignment (MMWA) algorithm has been developed based on the multi-wavelength assignment strategy, by allowing multiple available wavelengths in a link to carry the multicast signal. This new multicast wavelength algorithm provides advantages for the network with limited wavelength conversions, by accommodating more multicast requests and providing good trade-off between wavelength cost and wavelength conversion cost. Simulation results show that the MMWA algorithm can satisfy more multicast requests in comparison with the previous single-wavelength assignment strategy. The improvement can be as high as 50–80%. This is highly significant. The MMWA algorithm also provides a good cost trade-off by making significant reduction of wavelength conversion cost (over 50%) while keeping the additional wavelength usage within a reasonable range (around 15%). - Author(s): B. Zhang ; Z. Zhao ; H.T. Mouftah
- Source: IET Communications, Volume 1, Issue 4, p. 784 –788
- DOI: 10.1049/iet-com:20060654
- Type: Article
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Scalability has been a crucial design concern for quality of service routing protocols to be deployed in high-speed communications networks. The issue of bandwidth-constrained widest-shortest path (WSP) routing, which selects the WSP connecting a pair of nodes subject to a bandwidth constraint is studied. The design objective is to enable fast route calculation in identifying such constrained paths. To achieve this goal, a polynomial optimal algorithm using bidirectional search is designed. The complexity of the designed algorithm is deduced to be O(|E|lg|V|), where |E| and |V| represent the number of links and nodes in the network, respectively. Simulation results demonstrate that the designed algorithm can significantly reduce the average-case computational overhead caused by the calculation of such constrained routes as compared with related work. - Author(s): X. Rui ; R. Jin ; J. Geng
- Source: IET Communications, Volume 1, Issue 4, p. 789 –794
- DOI: 10.1049/iet-com:20060642
- Type: Article
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The self-interference (SI), which is caused by imperfect channel estimation, and co-channel interference (CCI) are considered in multiple-input multiple-output systems employing maximal ratio combining under independent and identically distributed Rayleigh fading. The analysis is independent of any specified estimation scheme and the channel estimation errors are assumed to be Gaussian distributed. Closed-form expressions for cumulative distribution function of the output signal-to-interference plus noise ratio are derived for both equal-power and unequal-power CCI cases. On the basis of these expressions, the exact closed-form expressions for the symbol error rate are presented to investigate the impact of SI and CCI. The analytical results are compared with the simulation results and a good agreement is obtained. - Author(s): M. Huang ; X. Chen ; L. Xiao ; S. Zhou ; J. Wang
- Source: IET Communications, Volume 1, Issue 4, p. 795 –801
- DOI: 10.1049/iet-com:20070039
- Type: Article
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A low-complexity Kalman-filter-based channel estimation method for orthogonal frequency-division multiplexing systems is proposed. This method belongs to the pilot-symbol-aided parametric channel estimation method in which the channel responses are characterised as a collection of sparse propagation paths. Because of the slow variation of the signal subspace in the channel samples' correlation matrix, the estimation of channel parameters is translated into an unconstrained minimisation problem. Then, in order to solve this optimisation problem, a subspace tracking by Kalman filter is carried out, which is characterised in that the state equation and the measurement equation are constructed upon the constant signal subspace. Further, this Kalman-filter-based method is extended to the multi-antenna scenarios efficiently. Simulation results show that the proposal can effectively track the time variations in both the block fading channels and the Doppler frequency spread channels. - Author(s): Y.H. Ng ; H. Mohamad ; T.C. Chuah
- Source: IET Communications, Volume 1, Issue 4, p. 802 –809
- DOI: 10.1049/iet-com:20060529
- Type: Article
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In the downlink of a synchronous direct sequence code division multiple access (DS-CDMA) system utilising orthogonal codes, intersymbol interference (ISI) arises due to multi-path propagation, which destroys the code orthogonality and in turn, gives rise to multiple access interference (MAI). Therefore if the ISI can be mitigated through channel equalisation, the MAI can be effectively reduced. However, existing channel equalisers are plagued with different performance and complexity issues. A sub-band adaptive chip equalising (SACE) receiver is proposed as an effective solution for performance enhancement over time-dispersive DS-CDMA downlinks. The SACE receiver exploits the pre-whitening effect of the filter banks to reduce the eigenvalue spread of the input signal covariance matrix. Results based on the popular COST-207 channel models for bad urban and hilly terrain areas are presented with varying loaded conditions. It is observed that in highly dispersive channels, the proposed SACE receiver significantly outperforms the correlation receiver and the full-band equaliser while retaining the desirable attribute of graceful degradation in CDMA networks. - Author(s): S. Debnath ; S. Mahapatra ; R. Gangopadhyay
- Source: IET Communications, Volume 1, Issue 4, p. 810 –818
- DOI: 10.1049/iet-com:20060537
- Type: Article
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An analytical approach based on a reduced Markov chain (RMC) model of an optical packet switch with partially shared output buffer has been presented and a combined scheme for the contention resolution in optical packet switches has been proposed. The proposed scheme takes the advantage of output buffering, shared buffering and wavelength conversion to enhance the switch performance. The performance evaluation of the switch architecture based on RMC modelling has been validated through extensive simulation. Moreover, for a self-similar input traffic, the switch performance has been shown to achieve further improvement if a traffic shaping mechanism is incorporated at the input end of the switch architecture.
Chaos-based multi-user time division multiplexing communication system
Ant colony optimisation-based multiuser detection for direct-sequence CDMA systems with diversity reception
Location management for packet switched services in 3G partnership project networks
Performance analysis of asynchronous direct sequence code division multiple access for general chip waveforms over multi-path Rayleigh fading channels
Cross-layer cooperation for accurate admission control decisions in mobile ad hoc networks
Time-of-day Internet-access management by combining empirical data-based pricing with quota-based priority control
Performance of impulse radio direct sequence ultra-wideband system with variable-length spreading sequences
Low complexity blind estimation of residual carrier offset in orthogonal frequency division multiplexing-based wireless local area network systems
Unequal error protection for LZSS compressed data using Reed-Solomon codes
On economical timing-error detectors for QAM receivers
Performance bounds for uniformly interleaved serial concatenations with a general inner system
Iterative low-complexity multi-user detection for asynchronous multi-sequence signalling based bit-interleaved coded modulation code division multiple access systems
Code-aided quasi-maximum SINR algorithms for blind linear multiuser detection
Non-parametric maximum-likelihood channel estimator and detector for OFDM in presence of interference
Closed-form expressions for symbol error probability of orthogonal space–time block codes over Rician–Nakagami channels
Differentially coherent code acquisition in the MIMO-aided multi-carrier DS-CDMA downlink
Space–time decision feedback equalisation using a minimum bit error rate design for single-input multiple-output channels
Interpolation-based precoding with limited feedback for MIMO-OFDM systems
Load balancing in the provisioning of hose model virtual private networks with multi-path routing
Packet contention resolution in slotted optical packet switch using ant-colony based algorithm
QoS assessment of 3G video-phone calls by tracing watermarking exploiting the new colour space ‘YST’
Influence of timing jitter on quadrature charge sampling
WARD: A deterministic fluid model
Improved power-saving medium-access protocol for IEEE 802.11e QoS-enabled wireless networks
W-CDMA multi-service uplink capacity and interference statistics of a long-tunnel cigar-shaped microcells
Antenna selection and deployment strategies for indoor wireless communication systems
Multiuser TH-precoding for TDD–CDMA over multipath channels
Spatio-temporal ultrawideband indoor propagation modelling by reduced complexity geometric optics
Analytical bit error rate performance of DS-CDMA ad hoc networks using large area synchronous spreading sequences
Directional distributed co-ordination function – a medium access control protocol to simultaneously support both omni-directional and smart antennas in a same WLAN cell
Combination of turbo equalisation and Turbo Trellis-coded modulation with low complexity
Multi-wavelength multicast wavelength assignment algorithm for limited wavelength conversion in wavelength-division multiplexing networks
Fast bandwidth-constrained quality of service routing via bidirectional search
Symbol error rate analysis of multiple-input multiple-output maximal ratio combining systems with self-interference and co-channel interference
Kalman-filter-based channel estimation for orthogonal frequency-division multiplexing systems in time-varying channels
On sub-band adaptive chip equalisation for direct sequence code division multiple access downlink over dispersive channels
Analysis of an optical packet switch with partially shared buffer and wavelength conversion
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