Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 6, Issue 4, 6 March 2012
Volumes & issues:
Volume 6, Issue 4
6 March 2012
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- Author(s): S.-Y. Jung
- Source: IET Communications, Volume 6, Issue 4, p. 363 –369
- DOI: 10.1049/iet-com.2010.1046
- Type: Article
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p.
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A new modulation scheme termed as group waveform-coded biorthogonal pulse position modulation (GWC-BPPM) is proposed for an ultrawideband (UWB) impulse radio communication system. The group waveform-coded signal, generated using several orthogonal waveform codes to transmit data simultaneously, is converted to pulse position and polarity to improve data rate and obtain processing gain in reception. In addition, the authors also suggest greatly boosting the data rate of the proposed scheme by introducing the level cutting concept. By restricting the maximum level of the group waveform-coded signal, the authors can boost the data rate without any degradation in error performance. To guarantee the benefit and the validity of the proposed scheme, the authors focus on the achievable data rate as a performance measure and analyse it theoretically. Simulations show that the achievable data rate of the proposed systems can be increased by GWC-BPPM and can be boosted via level cutting compared with other schemes such as M-ary BPPM and MBOK. - Author(s): C. Tong ; J.W. Niu ; G.Z. Qu ; X. Long ; X.P. Gao
- Source: IET Communications, Volume 6, Issue 4, p. 370 –380
- DOI: 10.1049/iet-com.2010.0651
- Type: Article
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p.
370
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Recently, research on complex network theory and applications draws a lot of attention in both academy and industry. In mobile ad hoc networks (MANETs) area of research, a critical issue is to design the most effective topology for given problems. It is natural and significant to consider complex networks topology when optimising the MANET topology. Current works usually transform MANET or sensor network topologies into either small-world or scale-free. However, some fundamental problems remain unsolved. Specifically, what are the average shortest path length, degree distribution and clustering characteristics of MANETs? Do MANETs have small-world effect and scale-free property? In this work, the authors introduce complex networks theory into the context of MANET topology and study complex network properties of the MANETs to answer the above questions. The authors have theoretically analysed the degree distribution and clustering coefficient of MANETs and proposed approach to computing them. The degree distribution and clustering coefficient of MANETs are theoretically deduced from node space probability distribution on different mobility models (including but not limited to random waypoint model). Simulation results on average shortest path length, clustering coefficient and degree distribution show that in most cases MANETs do not have the small-world effect and scale-free property. - Author(s): T.-C. Chen
- Source: IET Communications, Volume 6, Issue 4, p. 381 –389
- DOI: 10.1049/iet-com.2010.0318
- Type: Article
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381
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In the problem of the parameter estimation of frequency-hopping (FH) signals, most of existing works can only provide the unauthorised detection of the FH signals or estimate the part of parameters of FH signals, therefore cannot provide sufficient information to demodulate signals for message deciphering applications in a non-cooperative communications. This study proposes a new method based on reassigned smoothed pseudo Wigner–Ville distribution (SPWVD) and maximum-likelihood estimation for joint signal parameter estimation of FH communications with M-ary frequency-shift-keyed (MFSK) orthogonal modulation. With the good time frequency concentration and restraining cross-term ability of reassigned SPWVD, this algorithm can efficiently estimate the parameters of FH signals which include hopping frequencies, hopping rate, hopping sequence and modulation type without making any assumption about the alphabet of hopping frequencies or the synchronisation. The algorithm has improved estimation accuracy, reduced estimation root-mean-squared error and obtained better performance than that of the approach based on conventional time–frequency distribution. The simulation results are presented to evaluate the performances of the proposed algorithm. The root-mean-squared error of hopping frequency estimation is <10−3 for signal-to-noise ratio (SNR) of >−2 dB. The percentage of correct modulation recognition goes to 90% when SNR >3 dB. - Author(s): A. Jurado-Navas ; J.M. Garrido-Balsells ; M. Castillo-Vázquez ; A. Puerta-Notario
- Source: IET Communications, Volume 6, Issue 4, p. 390 –397
- DOI: 10.1049/iet-com.2011.0650
- Type: Article
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p.
390
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In this study, we derive the analytical expression for the lower-bound performance of the light intensity fading induced by turbulence for one of the most favourable signalling techniques used in atmospheric optical communications: the variable weight multiple pulse-position modulation (vw-MPPM). This lower-bound performance is obtained when the additive white Gaussian noise (AWGN) is not present in the system, showing that it only depends on both the fixed-threshold detection and the intensity of the atmospheric turbulence. In this sense, the statistical models employed to characterise the irradiance fluctuations are the lognormal and the Gamma–Gamma atmospheric channels. These ones have been chosen as two of the most representative distribution models for the irradiance. In addition, the starting point to obtain the lower-bound performance of a communication system using vw-MPPM is to calculate the one for an on–off keying modulation technique. As we have derived in the manuscript, and for the ideal condition of absence of AWGN, when the transmitted bit is a binary ‘0’ (the laser is turned off), then no photodetector errors occur. Thus, the inclusion of the appropriate transmission probability of a binary ‘1’ let us obtain the desired lower-bound performance expression of a vw-MPPM modulation technique through atmospheric turbulence channels. Numerical results using Monte-Carlo simulation confirm the analytical expressions derived in this study. - Author(s): D. Adami ; C. Callegari ; S. Giordano ; M. Pagano
- Source: IET Communications, Volume 6, Issue 4, p. 398 –407
- DOI: 10.1049/iet-com.2010.0875
- Type: Article
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398
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The choice of the path computation algorithm is a key factor to design efficient traffic engineering strategies in multi-protocol label switching networks and different approaches have been proposed in the literature. The effectiveness of a path computation algorithm should be evaluated against its ability to optimise the utilisation of network resources as well as to satisfy both current and future label switched paths allocation requests. Although powerful and flexible simulation tools might be useful to assist a network manager in the selection of proper algorithms, state-of-the-art simulators and network planning tools do not currently offer a suitable support. This study deals with the design and performance evaluation of multi-constraints path computation algorithms. To this aim, ad hoc software modules have been developed and integrated within the MTENS simulator. New single-path and multi-path computation algorithms have been proposed and compared in terms of number of accepted requests, success probability, network resources utilisation and execution time. Finally, some guidelines and recommendations for the selection of path computation algorithms have also been provided. - Author(s): A.K.S. Al-Bayati
- Source: IET Communications, Volume 6, Issue 4, p. 408 –412
- DOI: 10.1049/iet-com.2011.0149
- Type: Article
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p.
408
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A new subspace-based blind method for channel estimation in nearly saturated downlink multicarrier code division multiple access systems is proposed. In this method, the authors exploit the subspace structure of the received signal to estimate the channel directly in the frequency domain irrespective of the length of the finite impulse response (FIR) channel, thus allowing operation in nearly saturated systems (number of users can be one less than process gain). The method is shown to outperform some earlier blind channel estimation methods, whereas at the same time avoiding the limitations in the number of users that these methods suffer from. - Author(s): X. Sun ; X. Wu ; M. Jiang ; C. Zhao
- Source: IET Communications, Volume 6, Issue 4, p. 413 –418
- DOI: 10.1049/iet-com.2010.0891
- Type: Article
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The authors study the optimisation of the rate-compatible (RC)-irregular-repeat-accumulate (IRA) codes for asymmetric Slepian–Wolf coding to deal with flexible correlated sources. By assuming two different additive white Gaussian noise channels, the authors formulate a non-uniform extrinsic information transfer method to optimise the degree distribution of RC-IRA codes. The parity check matrices of RC-IRA codes are constructed from a mother matrix by combining puncturing and check-splitting, which achieves a good trade-off between the lowest-rate codes and the highest-rate codes. Simulation results show that the optimised non-uniform error-correcting code performs very close to the Slepian–Wolf limit over the target compression rate range and outperforms the prior results. - Author(s): T. Wigren
- Source: IET Communications, Volume 6, Issue 4, p. 419 –427
- DOI: 10.1049/iet-com.2011.0410
- Type: Article
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The study develops algorithmic enhancements to a commercially operating self-learning fingerprinting algorithm, to fully exploit single-leg time measurements. Such timing advance (TA) and round trip time (RTT) measurements are available in all cellular systems. Their accuracies do not depend on the cell size, as do conventional signal strength measurements, which makes such time measurements particularly useful for positioning in large cells. The challenge is that the geographical regions associated with single-leg time measurements become curved and very wide laterally, while staying narrow in the radial direction, a fact which makes it difficult for the self-learning algorithm to compute accurate geographical descriptions of them. The study shows how to design enhanced algorithms that improve the accuracy and reduce the learning time of the fingerprinting positioning scheme. The performance gain is illustrated with simulations. It is also illustrated by simulation that the enhanced fingerprinting scheme can handle very poor base station geometries that would prevent the application of conventional trilatheration-based localisation technologies. This typically occurs along freeways in rural regions, where so called ‘string of pearls’ geometries are common. - Author(s): J. Wu ; L. Guo ; W. Hou
- Source: IET Communications, Volume 6, Issue 4, p. 428 –436
- DOI: 10.1049/iet-com.2011.0423
- Type: Article
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With the increasing of number of multimedia network applications, multi-cast services are becoming more and more popular. At the same time, the waveband switching technique is proposed to save ports and to reduce the cost of optical cross-connect. However, the existing multi-cast waveband grooming algorithms are mostly limited to single-domain optical networks. The size of optical backbones keeps enlarging, and the backbones are actually divided into multiple independent domains to provide the needed scalability and confidentiality. To solve these problems, the authors propose three heuristic algorithms: per-domain multi-cast grooming (PDMG), virtual topology multi-cast grooming (VTMG) and hierarchical multi-domain multi-cast grooming (HMMG). The main difference between these algorithms is that the inter-domain routing is performed in a different manner; in other words, the routings in PDMG, VTMG and HMMG are computed based on the domain-by-domain fixed routing table, the high layer in the aggregative virtual topology of multi-domains and the hierarchical integrated multi-cast auxiliary graph, respectively. For the intra-domain routing, the three algorithms employ the same method based on an intra-domain multi-cast integrated auxiliary graph. Simulation results show that compared with PDMG and VTMG, HMMG has the best performance in terms of the number of ports saved and the blocking probability. - Author(s): Y. Zhan ; J. Wu ; J. Lu
- Source: IET Communications, Volume 6, Issue 4, p. 437 –441
- DOI: 10.1049/iet-com.2010.1014
- Type: Article
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A new anti-interference algorithm based on correlation function to obtain the desired signal effectively from the interference environment at low signal-to-interference-plus-noise ratio (SINR) is proposed. At transmitter, the autocorrelation function of the original signal is transformed before transmission. At receiver, a mixing matrix of the desired signal and interference is calculated according to the correlation function of received signal to obtain the separation vector for interference elimination. The computer simulation and the field-programmable Gate Array (FPGA) hardware verification results show that the algorithm is not sensitive to the bandwidth of interference, and bit error rate (BER) performance degradation is only about 1 dB because of the separation residual error, as well as it is suitable for hardware realisation with low complexity. - Author(s): G. Indumathi and K. Murugesan
- Source: IET Communications, Volume 6, Issue 4, p. 442 –448
- DOI: 10.1049/iet-com.2011.0023
- Type: Article
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A cross-layer scheduling algorithm that combines packet scheduling and an efficient bandwidth allocation for orthogonal frequency division multiple access (OFDMA) systems with heterogeneous user's delay requirements are proposed. The proposed work employs channel fluctuation and queue states in their decision rules for packet scheduling, which determines the optimum subcarrier allocation policy to maximise the system throughput subject to individual user's delay constraints. The delay sensitive subcarrier allocation strategy has linear complexity with respect to the number of users and number of subcarriers. The cross-layer scheduling algorithm also use an adaptive modulation and coding (AMC) scheme, which adapt according to the channel condition and queue states in terms of signal-to-noise ratio (SNR) constraints to improve the bandwidth usage in an efficient manner. The simulation results show that substantial throughput gain and spectral efficiency improvement are obtained while satisfying the delay constraint when the delay sensitive jointly optimum rate and subcarrier allocation policy with AMC is adopted. - Author(s): R.G. Clegg ; S. Isam ; I. Kanaras ; I. Darwazeh
- Source: IET Communications, Volume 6, Issue 4, p. 449 –457
- DOI: 10.1049/iet-com.2011.0365
- Type: Article
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Spectral efficiency is a key design issue for all wireless communication systems. Orthogonal frequency division multiplexing (OFDM) is a very well-known technique for efficient data transmission over many carriers overlapped in frequency. Recently, several studies have appeared that describe spectrally efficient variations of multi-carrier systems where the condition of orthogonality is dropped. Proposed techniques suffer from two weaknesses: firstly, the complexity of generating the signal is increased. Secondly, the signal detection is computationally demanding. Known methods suffer either unusably high complexity or high error rates because of the inter-carrier interference. This study addresses both problems by proposing new transmitter and receiver architectures whose design is based on using the simplification that a rational spectrally efficient frequency division multiplexing (SEFDM) system can be treated as a set of overlapped and interleaving OFDM systems. The efficacy of the proposed designs is shown through detailed simulation of systems with different signal types and carrier dimensions. The decoder is heuristic but in practice produces very good results that are close to the theoretical best performance in a variety of settings. The system is able to produce efficiency gains of up to 20% with negligible impact on the required signal-to-noise ratio. - Author(s): M. Torabi and D. Haccoun
- Source: IET Communications, Volume 6, Issue 4, p. 458 –463
- DOI: 10.1049/iet-com.2010.1118
- Type: Article
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In this article, the impact of outdated channel information on the average bit error rate (BER) performance of the opportunistic relay selection in amplify-and-forward cooperative systems is analysed and evaluated over Rayleigh fading channels. Using the moment generating function (MGF)-based approach closed-form analytical expressions are derived for the average BER performance of M-ary modulations and the average signal-to-noise-ratio (SNR) gain obtained from opportunistic relaying. Numerical evaluation results obtained from the analytical expressions are provided to study and quantify the deteriorating effects of outdated channel information on the BER performance and on the achievable diversity and SNR gain obtained from relay selection. - Author(s): A.A. Tadaion ; M. Derakhtian ; S. Gazor
- Source: IET Communications, Volume 6, Issue 4, p. 464 –470
- DOI: 10.1049/iet-com.2010.0674
- Type: Article
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The authors assume a linear equidistance antenna array as the receiver for a fixed frame-length multiple-access system, which employs variable-gain receiver power and repetition encoding. They propose a robust maximum a posteriori probability (MAP) blind bit-rate detector (BBRD). This detector considers the rate detection (RD) as a multi-hypothesis test and maximises the likelihood functions (LFs) to find the true bit-rate, whereas the complex amplitude of the received signal, the noise variance and the direction of arrival are unknown parameters. First, assuming that the location parameter is known and the information sequence are independent and uniformly distributed random variables, the authors propose a hybrid likelihood ratio test (HLRT). The proposed HLRT requires to solve a set of non-linear equations that have no closed-form solution. Thus, an iterative numerical algorithm is proposed. In addition, a quasi-HLR detector which has a significantly lower computational complexity is also proposed. In the case of unknown location parameter, the authors develop two quasi-HLR methods. They use fast Fourier transform and search to estimate the unknown location. In Q-HLRT-Method-I, the non-linear equation similar to the one in known location parameter is iteratively solved. In Q-HLRT-Method-II, a low complexity solution is proposed. Simulation examples evaluate and compare the performances of the proposed BBRDs.
Group waveform-coded biorthogonal pulse position modulation with level cutting for ultra-wideband impulse radio communications
Complex networks properties analysis for mobile ad hoc networks
Joint signal parameter estimation of frequency-hopping communications
Closed-form expressions for the lower-bound performance of variable weight multiple pulse-position modulation optical links through turbulent atmospheric channels
Single-path and multi-path label switched path allocation algorithms with quality-of-service constraints: performance analysis and implementation in NS2
Subspace-based blind channel estimation in nearly saturated down link multicarrier code division multiple access systems
Optimised rate-compatible-irregular-repeat-accumulate code for asymmetric Slepian–Wolf coding
Fingerprinting localisation using round trip time and timing advance
Multi-cast waveband grooming algorithms in multi-domain optical networks
New anti-interference algorithm for wireless communications
Optimal error considerate cross-layer scheduler for heterogeneous users
A practical system for improved efficiency in frequency division multiplexed wireless networks
Impact of outdated channel information on the bit error rate performance for amplify-and-forward selective relaying systems
Hybrid likelihood ratio bit-rate detectors for variable-gain multiple-access systems in unknown noise variance
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