Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 3, Issue 2, February 2009
Volumes & issues:
Volume 3, Issue 2
February 2009
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- Author(s): X. Zhu ; G. Zhu ; T. Jiang
- Source: IET Communications, Volume 3, Issue 2, p. 161 –171
- DOI: 10.1049/iet-com:20080194
- Type: Article
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p.
161
–171
(11)
A theoretical analysis is presented to show that in orthogonal frequency division multiplexing systems, the peak-to-average power ratio (PAPR) can be reduced by performing a unitary matrix transformation on the input vector of N symbols. The authors also prove that this transformation does not degrade the bit error rate (BER) or power spectral density (PSD) performance. Based on this, the inverse discrete Fourier transform matrix is proposed as the unitary matrix to reduce the PAPR. The simulation results show that the proposed scheme can obtain significant PAPR reduction while maintaining good performance in the BER and the PSD. To further evaluate the performance of the proposed scheme, the authors compare it with some well known PAPR reduction techniques by simulations. It is demonstrated that the proposed scheme can offer better system performance and achieve a better compromise with regard to the PAPR reduction, BER, spectral efficiency and computational complexity. - Author(s): M.M. Ghandi ; B. Barmada ; E.V. Jones ; M. Ghanbari
- Source: IET Communications, Volume 3, Issue 2, p. 172 –184
- DOI: 10.1049/iet-com:20080053
- Type: Article
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p.
172
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(13)
For wireless video, the present paper demonstrates that combining adaptive source and channel coding can provide a robust service over a wide range of transmission channel conditions. Various feedback-controlled adaptive coding solutions are considered for orthogonal frequency-division multiplexing-based systems. At the receiver, the reliabilities of subchannels (SCHs) are estimated and decisions are fed back to the transmitter to adapt modulation modes and channel code-rates to provide reliable transmission and yet avoid over-protection. The resulting available transmission capacity (which can vary widely with channel conditions) can inform an online collaborating source coder which itself exploits the available feedback to reduce error propagation. To ensure further improvement for fading channels, an efficient low-delay retransmission arrangement is also considered in which only the contents of unreliable SCHs within an erroneous packet are retransmitted. Simulation results demonstrate that such collaborative adaptive source and channel coding can provide efficient use of a continuously varying wireless channel. - Author(s): H. Wu ; X. Dai ; H. Zhang
- Source: IET Communications, Volume 3, Issue 2, p. 185 –197
- DOI: 10.1049/iet-com:20080332
- Type: Article
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p.
185
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(13)
Timing offsets (TO) introduce misaligned interferences and phase errors, which degrade the performance of channel estimation. The authors propose a new semi-blind channel estimator that can cancel the TO effects on channel estimation and work well in the uplink of multi-carrier code-division multiple access systems in the presence of TO. The proposed channel estimator exploits the spreading sequence information instead of pilots to accomplish semi-blind estimation. Since the estimated channel coefficients are affected by the users' transmitted data, the effect of the users' data needs to be reduced. For this purpose, the authors also propose two smoothing algorithms, division smoothing and optimisation smoothing. In addition, to extend the new estimator to the system where the number of active users is too large, channel estimation over multiple symbols is discussed. The simulation results show that the proposed semi-blind estimator works better than a conventional estimator in the presence of TO, and its performance is very close to the conventional estimator in the absence of TO. Besides, the proposed estimator is compared with a sub-space estimator in simulation, and the results indicate that the new proposed estimator can achieve the same mean square error performance over the duration of a single symbol as the sub-space estimator over the duration of several symbols. - Author(s): C.-C. Sue and J.-Y. Du
- Source: IET Communications, Volume 3, Issue 2, p. 198 –208
- DOI: 10.1049/iet-com:20080029
- Type: Article
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p.
198
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(11)
The problem of achieving 100% dual-failure restorability utilising reconfigurable p-cycle mechanisms has been investigated via three different p-cycle mechanisms derived from the integer linear programming model; complete-repair (CRP), incremental-repair (IRP) and dynamic-repair (DRP). An enhanced 100% dual-failure restoration mechanism is proposed, designated as modified DRP with forcer filling concept (MDRP/wFF), in which network protection is achieved using only reconfigurable span-protecting p-cycles without the addition of path-segment-protecting p-cycles as in DRP. As a result, the overhead incurred in differentiating between the two p-cycles becomes non-existent upon network restoration. Furthermore, a FF concept is employed to reduce the amount of spare capacity required to restore the network. The performance of the MDRP/wFF scheme was benchmarked against that of the CRP, IRP and DRP mechanisms. The simulation results show that MDRP/wFF achieves a performance tradeoff among CRP, IRP and DRP in terms of its spare capacity requirements and average number of reconfigured spans during the reconfiguration process [designated as average reconfiguration overhead (ARO)]. The MDRP/wFF scheme was found to have a lower spare capacity requirement but incurs some additional ARO compared with DRP. - Author(s): Y. Chen ; L. Hu ; C. Yuen ; Y. Zhang ; Z. Zhang ; P. Rapajic
- Source: IET Communications, Volume 3, Issue 2, p. 209 –222
- DOI: 10.1049/iet-com:20080064
- Type: Article
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p.
209
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(14)
The diversity gains achievable in the generalised distributed antenna system with cooperative users (GDAS-CU) are considered. A GDAS-CU is comprised of M largely separated access points (APs) at one side of the link, and N geographically closed user terminals (UTs) at the other side. The UTs are collaborating together to enhance the system performance, where an idealised message sharing among the UTs is assumed. First, geometry-based network models are proposed to describe the topology of a GDAS-CU. The mean cross-correlation coefficients of signals received from non-collocated APs and UTs are calculated based on the network topology and the correlation models derived from the empirical data. The analysis is also extendable to more general scenarios where the APs are placed in a clustered form due to the constraints of street layout or building structure. Subsequently, a generalised signal attenuation model derived from several stochastic ray-tracing-based pathloss models is applied to describe the power-decaying pattern in urban built-up areas, where the GDAS-CU may be deployed. Armed with the cross-correlation and pathloss model preliminaries, an intrinsic measure of cooperative diversity obtainable from a GDAS-CU is then derived, which is the number of independent fading channels that can be averaged over to detect symbols. The proposed analytical framework would provide critical insight into the degree of possible performance improvement when combining multiple copies of the received signal in such systems. - Author(s): L. Song ; A. Hjørungnes ; M.R. Bhatnagar ; Q. Li
- Source: IET Communications, Volume 3, Issue 2, p. 223 –231
- DOI: 10.1049/iet-com:20080056
- Type: Article
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p.
223
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(9)
Joint transmitter and receiver design problem for frequency-selective, time-invariant fading channels are studied. The authors first propose a simple approximate maximum likelihood serial decision-feedback equaliser (A-ML-SDFE) through DFE, a Gaussian approximation, a pre-whitening filter and a matched filter. Secondly, assuming full channel knowledge available at the transmitter side, the authors perform pre-equalisation in a downlink scenario by moving the decision-feedback part of the A-ML-SDFE to the transmitter. The proposed A-ML-SDFE achieves much better performance than linear minimum mean square error (MMSE) and MMSE-DFE with a lower complexity. The pre-equaliser further improves the system performance at low signal-to-noise ratio with a reduced receiver complexity. - Author(s): T.-C. Lin ; T.-K. Truong ; W.-K. Su ; P.-Y. Shih ; G. Dubney
- Source: IET Communications, Volume 3, Issue 2, p. 232 –238
- DOI: 10.1049/iet-com:20080037
- Type: Article
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p.
232
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(7)
A new decoder is proposed to decode the (24, 12, 8) binary extended Golay code up to four errors. It consists of the conventional hard decoder for correcting up to three errors, the detection algorithm for four errors and the soft decoding for four errors. For a weight-4 error in a received 24-bit word, Method 1 or 2 is developed to determine all six possible error patterns. The emblematic probability value of each error pattern is then defined as the product of four individual bit-error probabilities corresponding to the locations of the four errors. The most likely one among these six error patterns is obtained by choosing the maximum of the emblematic probability values of all possible error patterns. Finally, simulation results of this decoder in additive white Gaussian noise show that at least 93% and 99% of weight-4 error patterns that occur are corrected if the two Eb/N0 ratios are greater than 2 and 5 dB, respectively. Consequently, the proposed method can achieve a better percentage of successful decoding for four errors at variable signal-to-noise ratios than Lu et al.'s algorithm in software. However, the speed of the method is slower than Lu et al.'s algorithm. - Author(s): F.S. Al-Kamali ; M.I. Dessouky ; B.M. Sallam ; F.E. Abd El-Samie
- Source: IET Communications, Volume 3, Issue 2, p. 239 –248
- DOI: 10.1049/iet-com:20080241
- Type: Article
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p.
239
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A hybrid receiver scheme for downlink code division multiple access (CDMA) systems over frequency selective channels is proposed. The proposed receiver combines a linear regularised zero forcing (RZF) equaliser and a parallel interference cancellation scheme with a tanh decision function (TPIC). It is called the RZF-TPIC receiver. The RAKE receiver is used to reduce the channel effects and obtain an initial estimate of the data. Multi-stages of TPIC are then employed to mitigate the multiple access interference (MAI). At the final stage, the RZF equaliser is used to provide a better estimate of the desired user's data. The effect of the decision function used for symbol estimation in the PIC stage is investigated. The performance of the proposed scheme is evaluated and compared with the traditional RAKE receiver by computer simulations. It is found that the proposed scheme offers significant gains, even with a large number of interfering users. - Author(s): A.M.P. de Lucena ; J.C.M. Mota ; C.C. Cavalcante
- Source: IET Communications, Volume 3, Issue 2, p. 249 –256
- DOI: 10.1049/iet-com:20080157
- Type: Article
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p.
249
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(8)
The authors evaluate and propose two approaches for the detection of two non-orthogonal m-QAM signals with spectral overlapping through an AWGN channel. Some previously reported works are revisited and alternative solutions in order to permit their application in practical communication systems are proposed. The subject method is proved to be relevant because it does not obey the Riesz basis condition for performing signal separation. The optimum maximum-likelihood receiver for this detection problem is also derived and the performance analysis is presented, including some analytical and Monte Carlo simulation results. - Author(s): F. Wang ; Z. Liu ; X. Song
- Source: IET Communications, Volume 3, Issue 2, p. 257 –267
- DOI: 10.1049/iet-com:20080355
- Type: Article
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p.
257
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(11)
In wireless communications, a sleep mode is commonly used to save power for mobile stations (MS). When there is no traffic to transmit, an MS periodically switches to sleep mode. Obviously, the performance of a power-saving mechanism depends on its sleep mode scheduling algorithm and the traffic characteristics of the user. In real systems, the power-saving mechanism of IEEE802.11 WLAN uses a constant sleep interval, and the IEEE802.16e WMAN adopts one with truncated exponentially extending sleep intervals denoted by PS-16, which contains constant sleep intervals as special cases. The two mechanisms are compared, resulting in the, finding that in the case of Poisson traffic, they have the same performance; whereas in the case of non-Poisson traffic PS-16 has better performance. For non-Poisson traffic, the performance of PS-16 lacks a closed form expression, which makes its design challenging. The authors propose to approximate the idle durations of an MS by hyper-exponentials, based on which an online sleep mode scheduling algorithm is developed. Numerical examples are provided to illustrate the efficiency of the proposed algorithm. - Author(s): F. Facchini ; R. Giuliano ; F. Mazzenga
- Source: IET Communications, Volume 3, Issue 2, p. 268 –278
- DOI: 10.1049/iet-com:20080452
- Type: Article
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p.
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Detect and avoid (DAA) procedures aim at improving ultra-wideband (UWB) coexistence with existing narrowband/wideband licenced/unlicenced victim terminals operating in the same band at the same time and area. The authors propose a DAA procedure that can be used to reduce the percentage of time the UWB interferes with victims operating in a time division duplexing (TDD) mode. The authors consider a system scenario where a TDD terminal has a primary role and UWB devices create a secondary network on a local area basis. A DAA procedure is implemented only in the UWB devices that adapt their transmissions in order to avoid or reduce interference on primary device(s) in the same area. The performance of the proposed DAA procedure is presented and discussed and its dependence on some key UWB transmission parameters, bit rate and the emitted power is evidenced. It is shown that the DAA timeout parameters can be tuned so as to arbitrarily reduce the average percentage of time the UWB interferes with the considered victim systems even well below the limits imposed by regulatory bodies. It is shown that interference reduction is obtained at the expense of reduced performance of the UWB transmission. The proper selection of DAA timeouts for a desired percentage of UWB interference and UWB link efficiency is discussed. - Author(s): A.A. Sobhi Afshar ; T. Eghlidos ; M.R. Aref
- Source: IET Communications, Volume 3, Issue 2, p. 279 –292
- DOI: 10.1049/iet-com:20080050
- Type: Article
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p.
279
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A secure channel coding (joint encryption-channel coding) scheme provides both data security and reliability in one combined process to achieve faster processing and/or more efficient implementation. The issue of using quasi-cyclic low-density parity-check (QC-LDPC) codes in a symmetric-key secure channel coding scheme is addressed. A set of this class of LDPC codes has recently been recommended by the NASA Goddard Space Flight Center for near-earth and deep-space communications. The proposed scheme provides an efficient error performance, an acceptable level of security and a low-complexity practicable implementation. The results indicate that the proposed scheme can efficiently employ large QC-LDPC codes to achieve a relatively smaller secret-key size to be exchanged by the sender and the receiver, and higher information rates in comparison with the previous symmetric-key McEliece-like schemes. Simulation results indicate that there is no trade-off between the error performance and the security level of the proposed scheme unlike that of the previous ones. These characteristics make the proposed scheme suitable for high-speed communications, such as satellite communication systems. - Author(s): R.E. Rezagah and A. Mohammadi
- Source: IET Communications, Volume 3, Issue 2, p. 293 –302
- DOI: 10.1049/iet-com:20080136
- Type: Article
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p.
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The authors employ a statistical method to characterise the wireless ad hoc network capacity problem. The channel parameters such as path loss and fading are considered in the analysis. Moreover, a simulation method based on the probability density function of signal-to-interference-plus-noise power-ratio is introduced. In both analysis and simulation, two receiving methods, matched filter (MF) and minimum-mean-square-error (MMSE) detector, are considered. After establishing the accuracy of the analytic approximation and comparing its results with simulation results, the scalability of a random network is studied. Moreover, the outage and ergodic capacities are determined for various network and channel parameters. It is shown that when MMSE detector is used in the network, the capacity is higher than when MF is used. When number of the nodes increases the total ergodic capacity raises, but per node capacity reduces when using both MF and MMSE detectors. It is shown that the total outage capacity reaches a maximum. This leads to the conclusion that an optimum value for the number of nodes in the network exists, which maximises the outage capacity. - Author(s): N.Y. Ermolova
- Source: IET Communications, Volume 3, Issue 2, p. 303 –308
- DOI: 10.1049/iet-com:20080189
- Type: Article
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p.
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The author obtains closed-form expressions for the averages of the Gaussian Q-function and product of two Gaussian Q-functions over the generalised η−μ and κ−μ distributions. These results can be useful in many practical applications when evaluating error rate performances of communication systems operating in radio channels modelled by the η−μ and κ−μ distributions. The formulas are obtained in terms of Appell's (F1(·) and Φ1(·)) and Lauricella's (FD3(·) and Φ1(3)(·)) hypergeometric functions. As examples of application, the average symbol error rates of general order rectangular quadrature amplitude modulation (QAM) in η−μ and κ−μ radio channels are evaluated. - Author(s): M. Jazayerifar ; J.A. Salehi ; B. Cabon
- Source: IET Communications, Volume 3, Issue 2, p. 309 –320
- DOI: 10.1049/iet-com:20080124
- Type: Article
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A binary differential impulse radio-ultra wide band (IR-UWB) communication scheme over a single-mode optical fibre is examined. For a receiver structure, the conventional electrical receiver as well as an optical receiver structure, which is similar to the optical receiver used for digital, optically phase-modulated differential phase shift keying, are considered. The optical receiver can alleviate the IR-UWB receiver implementation challenges and it is studied for the first time in the context of IR-UWB. Considering various important noises, for example, phase noise, laser intensity noise, thermal noise and shot noise, analytical expressions for the error probability of the aforementioned receivers are derived. The mathematical models for optical components including laser diode and single-mode fibre, along with the analytical expressions for the receiver's error probability, are used to evaluate the overall performance of an UWB communication system over a fibre transmission medium. Furthermore, the electrical receiver is compared with the optical receiver and it is shown that the performance of the optical receiver can be as good as that of the electrical receiver and even better. The impact of wireless channel fading, bias current of laser diode and the coherence time of laser diode on the UWB over fibre system performance is also examined. - Author(s): S. Zhu ; K.K. Leung ; A.G. Constantinides
- Source: IET Communications, Volume 3, Issue 2, p. 321 –330
- DOI: 10.1049/iet-com:20080058
- Type: Article
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p.
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The recently permitted unlicenced use of the regulated ultra-wideband (UWB) radio spectrum (regulated first by the US FCC in 2002 and subsequently by the standardisation bodies of EU and other major countries) provides wireless ad hoc networks a cheap and promising air-interface technology for their adopted wireless data links, thus offering the potential to greatly boost their applications. The impacts of such UWB data links, mainly the more likely adopted impulse-based UWB data links for low data rate applications, on the extensively developed cooperative wireless ad hoc networks are investigated. First, the authors investigate the diversity order of data transfer of each impulse-based UWB data link working in a corresponding fading channel, and give an approximate relationship between the diversity order and the channel model parameters (here the Saleh–Valenzuela model parameters); Secondly, the authors develop efficient cooperative and decentralised diversity schemes that can utilise the widely spread and independently distributed multiple paths of the fading UWB channels. Performance analysis and simulation studies show that proposed decentralised cooperative beamforming schemes can achieve full diversity and are more efficient than their decentralised cooperative routing counterparts.
Reducing the peak-to-average power ratio using unitary matrix transformation
Wireless video transmission using feedback-controlled adaptive H.264 source and channel coding
Semi-blind channel estimation for the uplink of multi-carrier code-division multiple access systems with timing offset
Capacity-efficient strategy for 100% dual-failure restorability in optical mesh networks utilising reconfigurable p-cycles and a forcer filling concept
Intrinsic measure of diversity gains in generalised distributed antenna systems with cooperative users
Approximate maximum likelihood serial decision-feedback equaliser and Tomlinson–Harashima pre-equalisation
Decoding of the (24, 12, 8) extended Golay code up to four errors
Regularised multi-stage parallel interference cancellation for downlink CDMA systems
Optimum detection of non-orthogonal QAM signals with spectral overlapping
Power-saving mechanisms for mobile devices in wireless communications
Ultra-wideband detect and avoid procedure for WiMAX victims
Efficient secure channel coding based on quasi-cyclic low-density parity-check codes
Capacity estimation of wireless ad hoc networks in fading channels
Useful integrals for performance evaluation of communication systems in generalised η−μ and κ−μ fading channels
Analytical study of binary differential impulse radio-ultra wide band over single-mode fibre systems using two receiver structures
Impacts of impulse-based ultra-wideband data links on cooperative wireless ad hoc networks
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