Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 1, Issue 1, February 2007
Volumes & issues:
Volume 1, Issue 1
February 2007
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- Author(s): Y. Han and K.C. Teh
- Source: IET Communications, Volume 1, Issue 1, p. 1 –6
- DOI: 10.1049/iet-com:20060035
- Type: Article
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Based on the Fourier-Bessel series and exponential characteristic function approach, the paper presents analytical bit-error-rate expressions for synchronous fast frequency-hopped spread-spectrum multiple-access systems over Rician fading channels with M-ary frequency-shift-keying modulation. Linear-combining, product-combining and clipper receivers are studied. Numerical results show that both the clipper and product-combining receivers perform significantly better than the linear-combining receiver. The clipper receiver with an optimum threshold level slightly outperforms the product-combining receiver. However, the product-combining receiver is the preferred diversity-combining method because it is completely nonparametric. In addition, the optimum diversity levels for various diversity-combining receivers over Rayleigh fading channels are higher than that of the Rician fading channels. - Author(s): A. Kobravi ; M.R. Shikh-Bahaei ; S. Lambotharan
- Source: IET Communications, Volume 1, Issue 1, p. 7 –14
- DOI: 10.1049/iet-com:20050171
- Type: Article
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The performance of multi-user detectors in the presence of multiple frequency offsets under a Rayleigh fading channel environment is analysed, and techniques to estimate and remove multiple frequency offsets (FOs) for successive interference cancellation (SIC) and parallel interference cancellation (PIC) receivers are also proposed. The closed form expressions derived for bit error rate (BER) of SIC and PIC schemes in the presence of multiple FOs have been verified using extensive simulation results. The PIC is shown to be less sensitive to frequency offsets as compared to SIC. It is demonstrated through analytical and simulation results that the proposed frequency offset estimation and correction techniques provide approximately 8 dB gain in the BER performance over conventional SIC and PIC schemes in the presence of multiple frequency offsets. - Author(s): Y. Liu ; S. Yu ; X. Wang
- Source: IET Communications, Volume 1, Issue 1, p. 15 –18
- DOI: 10.1049/iet-com:20050685
- Type: Article
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Periodic broadcasting schemes can improve the efficiency of video-on-demand (VOD) services by reducing the bandwidth requirement to transmit popular videos. The harmonic broadcasting scheme has the best performance in reducing service bandwidth under a given access time, but it uses too many channels. However, a multiplexed harmonic broadcasting scheme that overcomes this drawback is now proposed. This scheme divides each video into equal-sized segments and then broadcasts segments periodically in a small number of sever channels with equal bandwidth. The idea of segment-to-channel mapping in the scheme is inspired by the time division multiplexing system. Each segment is divided equally into several subsegments; subsegments of different segments are multiplexed in a slot with the guarantee of being able to keep playing out continuously for every user. The proposed scheme outperforms the pagoda broadcasting and recursive frequency splitting schemes in reducing the viewers' maximum waiting time, and the scheme requires less client storage. - Author(s): J. Homer ; P.J. Kootsookos ; V. Selvaraju
- Source: IET Communications, Volume 1, Issue 1, p. 19 –26
- DOI: 10.1049/iet-com:20050650
- Type: Article
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In various adaptive array applications, the desired-user signal arrives from only a relatively small number of directions. The paper proposes an NLMS-based adaptive algorithm that incorporates a direction of arrival (DOA) detection criterion. The criterion stems from Akaike's information criterion and Donoho's thresholding principle. Within ‘low-dimensional’ DOA applications, the inclusion of the DOA detection criterion leads to a reduction in the number of NLMS adapted parameters. The result is significantly improved convergence and tracking speeds, as well as improved nulling of multi-user interference signals. Simulations demonstrate the favourable performance of the proposed NLMS adaptive-array system. - Author(s): Y. Hong and O.W.W. Yang
- Source: IET Communications, Volume 1, Issue 1, p. 27 –33
- DOI: 10.1049/iet-com:20060012
- Type: Article
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The paper proposes a self-tuning active queue management (AQM) controller for Internet protocol (IP) routers supporting transmission control protocol (TCP) traffic in the Internet. Classical control theory is applied in the design to meet the frequency-domain-specification gain margin. The user can assign a proper gain margin to achieve good AQM performance. Simple equations for obtaining the AQM controller are derived. The designed AQM controller self-tunes, only when changes in Internet traffic have drifted the traffic monitoring parameter outside its specified interval, otherwise the self-tuning AQM controller remains unchanged. The OPNET® simulations used by the authors in single and in multiple bottleneck links demonstrate that, with the use of a self-tuning AQM controller in the routers, this AQM control system adapts very well to great fluctuations in the TCP traffic, thus providing the network with good stability robustness. - Author(s): T.-L. Sheu and Y.-J. Wu
- Source: IET Communications, Volume 1, Issue 1, p. 34 –40
- DOI: 10.1049/iet-com:20050507
- Type: Article
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The paper presents a jamming-based MAC with dynamic priority adjustment (JMDPA) for multimedia services in wireless ad hoc networks. The proposed scheme differentiates multimedia traffic into classes with different priority levels. A mobile node is prioritised in frame transmissions by issuing a precalculated length of jamming noise: the one with the longest jamming length can win the frame transmission. The winner immediately broadcasts its current priority level (local priority) to update the global priorities of all the neighbouring nodes. The global priority is used as a contention baseline, which prevents any node with a local priority lower than the baseline from participating in the next contention. One of the innovative designs in the proposed scheme is right, in that the priority of a mobile node can be dynamically adjusted according to network conditions so that any possible starvation of low-priority traffic or any ineffective contention of high-priority traffic can be avoided. A multidimensional Markov model, together with the scalability analysis, is introduced to evaluate the performance of the proposed JMDPA. The analytical results provide very useful guidelines to tune the QoS parameters for supporting prioritised multimedia traffic in wireless ad hoc networks. - Author(s): Y.-J. Lee and M. Atiquzzaman
- Source: IET Communications, Volume 1, Issue 1, p. 41 –48
- DOI: 10.1049/iet-com:20050063
- Type: Article
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We have developed an exact model and algorithm for the delay-constrained minimum cost loop problem (DC-MCLP) of finding broadcast loops from a source node. While the traditional minimum cost loop problem (MCLP) deals with only the traffic capacity constraint served by a port of source node, the DC-MCLP deals with the mean network delay and traffic capacity constraints simultaneously. The DC-MCLP consists of finding a set of minimum cost loops to link end-user nodes to a source node satisfying the traffic requirements at end-nodes and the required mean delay of the network. In the DC-MCLP, the objective function is to minimise the total link cost. We have formulated the DC-MCLP and proposed an exact algorithm for its solution. The proposed algorithm is composed of two phases: in the first phase, it generates feasible paths to satisfy the traffic capacity constraint; in the second phase it finds the exact loop topology through matching and allocating optimal link capacity to satisfy the mean delay constraint. In addition, we have derived several properties including the memory and time complexity of the proposed algorithm. Performance evaluation shows that the proposed algorithm has good efficiency for networks with less than thirty nodes and light traffic. Our proposed algorithm can be applied to find the broadcast loops for real-time multimedia traffic. - Author(s): S. Papaharalabos ; P. Sweeney ; B.G. Evans
- Source: IET Communications, Volume 1, Issue 1, p. 49 –54
- DOI: 10.1049/iet-com:20060090
- Type: Article
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Novel soft-input soft-output (SISO) decoding algorithms suitable for turbo codes are proposed with good compromise between complexity and bit error rate (BER) performance. The algorithms are based on the application of the max/max* (i.e. Jacobian logarithm) operations at different levels when computing the decoder soft-output value. It is observed that some decoding schemes from the authors' previously published work fall into the family of methods described here. The effect is to provide a range of possibilities allowing system designers to make their own choices for turbo code BER performance against complexity. - Author(s): F.A. El-Moussa ; N. Linge ; M. Hope
- Source: IET Communications, Volume 1, Issue 1, p. 55 –63
- DOI: 10.1049/iet-com:20050441
- Type: Article
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Denial-of-service attacks represent a major threat to modern organisations who are increasingly dependent on the integrity of their computer networks. A new approach to combating such threats introduces active routers into the network architecture. These active routers offer the combined benefits of intrusion detection, firewall functionality and data encryption and work collaboratively to provide a distributed defence mechanism. The paper provides a detailed description of the design and operation of the algorithms used by the active routers and demonstrates how this approach is able to defeat a SYN and SMURF attack. Other approaches to network design, such as the introduction of a firewall and intrusion detection systems, can be used to protect networks, however, weaknesses remain. It is proposed that the adoption of an active router approach to protecting networks overcomes many of these weaknesses and therefore offers enhanced protection. - Author(s): R.J. Barton ; J. Chen ; K. Huang ; S. Perotta ; D. Wu
- Source: IET Communications, Volume 1, Issue 1, p. 64 –70
- DOI: 10.1049/iet-com:20050496
- Type: Article
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The properties and performance of a technique, called time reversal, for co-operative communication on power-constrained wireless sensor networks are studied. A brief discussion of the optimality properties of this approach is presented, and performance is studied experimentally via a simulated indoor environment containing multiple wireless sensors. Using numerical simulation, the behaviour of the peak power received at a target sensor as a function of the number of co-operating transmitting sensors as well as the level of transmitted signal distortion and timing synchronisation errors, is studied. The simulation results demonstrate that, subject to some rather stringent synchronisation requirements, time reversal is an effective generalisation of beamforming that provides an efficient basis for co-operative communication on broadband multipath channels. - Author(s): S. Vafi and T. Wysocki
- Source: IET Communications, Volume 1, Issue 1, p. 71 –78
- DOI: 10.1049/iet-com:20060007
- Type: Article
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A simple algorithm for the weight calculation of turbo codes with convolutional interleavers is presented. For codes with short interleaver lengths, the weight distributions are computed using conventionally proposed methods and then utilised together with the interleaver properties to determine the weight specifications for the code with a longer desired length. Based on the calculated weights, a new upper bound for the code is computed. It agrees with simulation results of the code performance in the error-floor region. - Author(s): M. Teimouri and N. Rezaee
- Source: IET Communications, Volume 1, Issue 1, p. 79 –85
- DOI: 10.1049/iet-com:20060030
- Type: Article
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The paper proposes an analytical method to solve the rate allocation problem in serial concatenated convolutional codes (SCCCs). The goal is to find the best rate allocation between the inner and the outer constituent convolutional codes of an SCCC for constant overall code rate, interleaver size and complexity. Simulation results are shown in the paper to demonstrate the optimum and superior design criteria. In addition, the ‘density evolution’ model is shown to verify the proposed rate allocation method, while indicating that a high rate inner code should not be used for SCCCs. Finally, it is also shown that the upper bounds on BER of ML decoded SCCCs do not provide good design criteria for allocating the rate in iteratively decoded SCCCs. - Author(s): G.D. Papadopoulos ; G.K. Karagiannidis ; F.N. Pavlidou
- Source: IET Communications, Volume 1, Issue 1, p. 86 –91
- DOI: 10.1049/iet-com:20060055
- Type: Article
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Analytical expressions concerning the capacity and bit error rate (BER) of multiple-input multiple-output systems with space-time block coding (STBC) are derived. Two fading environments are examined, log-normal and Rician channels. A tight closed-form upper bound is presented for the BER of systems operating in log-normal fading environments in addition to an upper bound for the capacity of this type of systems. The latter bound applies to systems that operate under Rician fading as well. The analytical results were validated against ample numerical simulations for three STBC schemes and three phase-shift-keying modulations. The proposed bounds proved to be a tractable way to evaluate the system performance when no closed-form expression for the probability density function or the moment generating function is known. - Author(s): J. Thompson and A. Smokvarski
- Source: IET Communications, Volume 1, Issue 1, p. 92 –100
- DOI: 10.1049/iet-com:20050388
- Type: Article
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The performance of diversity combining techniques with channel estimation for the case of unequal power branches is discussed. The performance of binary phase shift keying (BPSK), pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM) formats is investigated and their performance with nonideal channel estimation is explored. The case of combining multiple branches with unequal power levels is considered and optimal weighting factors for a log likelihood ratio test (LLRT) detector for the BPSK case are presented. These weights are shown to operate in a similar manner to those obtained by the linear minimum mean squared error (LMMSE) criterion and are compared with the well known maximal ratio combining (MRC) technique. The probability of error of this receiver is derived and simplifications for high signal-to-noise ratios are presented. Finally, numerical results are presented to compare the performance of the LLRT, LMMSE and MRC based receivers. - Author(s): T. Niyomsataya ; A. Miri ; M. Nevins
- Source: IET Communications, Volume 1, Issue 1, p. 101 –105
- DOI: 10.1049/iet-com:20060201
- Type: Article
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A closed-form upper bound is presented for the average pairwise error probabilities (PEP) of space–time codes for a keyhole channel. It is derived from the exact conditional PEP for given fading channel coefficients using a moment generating function-based approach. Simulation results are included for varying numbers of antennas that affirm that the proposed PEP serves as a tight bound for codes in a keyhole channel. - Author(s): Y. Li ; S. McLaughlin ; X. Wei ; D.G.M. Cruickshank
- Source: IET Communications, Volume 1, Issue 1, p. 106 –112
- DOI: 10.1049/iet-com:20050332
- Type: Article
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A novel iterative channel estimation approach is proposed for cyclic prefix–code division multiple access systems. Code-multiplexed pilots are used for channel estimation while maintaining bandwidth efficiency. The proposed method achieves a significant improvement when compared to the conventional correlation approach by reconstructing data signals for channel estimation. Simulation results demonstrate good estimation capability with an allocation of only 10% of the whole power to the pilot channel. In addition, an integrated channel estimator and parallel interference cancellation (PIC) detector are proposed. Data signals are reconstructed for channel estimation while the interference contributed by different data channels as well as the pilot channel are regenerated and subtracted from the received signal at the final stage. The channel estimation error reduces at each iteration and the PIC at the last stage enables further bit error rate performance improvement to be achieved for the system. The performance of the proposed scheme is studied through simulations and results verify its effectiveness. - Author(s): J.-Y. Lin ; J.-S. Jhou ; K.-T. Lee ; J.-H. Wen
- Source: IET Communications, Volume 1, Issue 1, p. 113 –121
- DOI: 10.1049/iet-com:20050686
- Type: Article
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A new family of two-dimensional (2-D) codes constructed by combining frequency-hop and time-spreading codes is presented. The proposed codes are designed to overcome the limitation imposed on the maximum permissible number of simultaneous users in optical code-division multiple-access (OCDMA) systems. To increase the data transmission rate, the 2-D codes employ a M-ary signalling scheme. The proposed family of codes has the favourable characteristics of a zero autocorrelation constraint and a cross-correlation constraint of one. The performance of the 2-D code is analysed in terms of the bit error rate (BER) and is compared with that of a conventional OCDMA system using optical orthogonal code (OOC). The numerical and simulation results reveal that the proposed system outperforms conventional OCDMA systems both in terms of the BER and the data transmission rate. In addition, the system capacity is sufficient to ensure reliable communication (BER≤10−9) in local area networks. - Author(s): L.G. Barbero and J.S. Thompson
- Source: IET Communications, Volume 1, Issue 1, p. 122 –130
- DOI: 10.1049/iet-com:20050414
- Type: Article
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The use of multiple antennas at both transmitter and receiver is a promising technique for significantly increasing the capacity and spectral efficiency of wireless communication systems. In particular, spatial multiplexing techniques provide a means of increasing the data rate of the system without having to increase the transmitter power or the bandwidth. In recent years, special attention has been paid to the sphere decoder (SD) to detect spatially multiplexed signals. It provides optimal maximum likelihood (ML) performance with reduced complexity, compared to the maximum likelihood detector (MLD). An analysis of the performance of the SD in the presence of spatially correlated multiple-input multiple-output (MIMO) channels is presented. Analytical and simulation results show that, compared to suboptimal linear and nonlinear MIMO detectors, the SD suffers a complexity increase when correlation exists between the antennas at the transmitter or the receiver. In addition, a novel low-complexity channel ordering technique is introduced to reduce the complexity of the SD. - Author(s): J.C. Olivier and W. Kleynhans
- Source: IET Communications, Volume 1, Issue 1, p. 131 –136
- DOI: 10.1049/iet-com:20050435
- Type: Article
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A novel cochannel single antenna interference cancellation (SAIC) receiver is proposed for synchronised Group Special Mobile (GSM) systems. The receiver uses a two-stage strategy, where in the first stage cochannel interference is cancelled by a widely linear filter, while inter-symbol interference due to the GSM frequency-selective Rayleigh-fading environment is removed by a second-stage equaliser. Analytical results for the optimal widely linear filter coefficients are derived. Simulation results show excellent performance with large gains over the conventional receiver under interference limited channel conditions. It is shown that the conventional maximum likelihood sequence estimator or maximum a posteriori probability receiver is optimal when cochannel interference it not the dominant impairment, and it is proposed that the SAIC algorithm is disabled when the estimated carrier-to-interference (C/I) ratio is above a certain threshold.
Performance study of linear and nonlinear diversity-combining techniques in synchronous FFH/MA communication systems over fading channels
Multi-user interference cancellation technology in the presence of multiple frequency offsets
Multiplexed harmonic broadcasting scheme for efficient video-on-demand services
Enhanced NLMS adaptive array via DOA detection
Self-tuning TCP traffic controller using gain margin specification
Jamming-based medium access control with dynamic priority adjustment in wireless ad-hoc networks
Exact topology discovery algorithm for the capacity and delay constrained loop network
SISO algorithms based on Max-Log-MAP and Log-MAP turbo decoding
Active router approach to defeating denial-of-service attacks in networks
Optimality properties and performance analysis of co-operative time-reversal communication in wireless sensor networks
Weight distribution of turbo codes with convolutional interleavers
Rate allocation for serial concatenated convolutional codes
Performance bounds of space-time block coding in Rician and log-normal fading channels
Bit error ratio performance of a receiver diversity scheme with channel estimation
Pairwise error probability of space–time codes for a keyhole channel
Channel estimation and interference cancellation in CP–CDMA systems
Construction and performance analysis of 2-D codes for M-ary OFFH–CDMA systems
Performance of the complex sphere decoder in spatially correlated MIMO channels
Single antenna interference cancellation for synchronised GSM networks using a widely linear receiver
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