Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 3, Issue 4, April 2009
Volumes & issues:
Volume 3, Issue 4
April 2009
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- Author(s): H. Doğan
- Source: IET Communications, Volume 3, Issue 4, p. 501 –511
- DOI: 10.1049/iet-com.2008.0195
- Type: Article
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Transmit diversity-orthogonal frequency-division multiplexing (OFDM) systems have been proposed to mitigate the detrimental effects of channel fading. However, owing to the space and power limitations, the use of multiple transmit antennas is not practical in certain wireless devices, such as portable terminals and wireless sensors. Therefore cooperation among users at the physical layer has been proposed recently. Here, space-time block coded in amplify-and-forward (AF) relaying mode has been proposed as cooperative diversity for OFDM systems (CO-OFDM) in the presence of perfect channel-state information. Then, the channel estimation techniques for CO-OFDM systems in AF mode based on pilot symbols are investigated over frequency-selective channels. In particular, expectation-maximisation (EM) based maximum a posteriori (MAP) channel estimation is developed and compared with comp-type pilot-aided channel estimation (PACE) based the maximum likelihood (ML) estimator and the least minimum mean-square error (LMMSE) channel estimation techniques for CO-OFDM systems. To overcome the drawback owing to the receiver complexity, the Karhunen–Loeve expansion with the optimal truncation property is also considered. Simulation results that demonstrate the overall performance advantage of the EM-MAP based receiver over the PACE-ML and PACE-LMMSE based receivers are presented. - Author(s): C. Topal and C. Akinlar
- Source: IET Communications, Volume 3, Issue 4, p. 512 –519
- DOI: 10.1049/iet-com.2008.0364
- Type: Article
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Enabling peer-to-peer (P2P) communication for hosts behind network address translation (NAT) boxes is an important and difficult problem. Existing proposals, for example, UPnP, MIDCOM, TURN, STUN, STUNT, P2PNAT, NATBlaster among others, offer only partial, limited and non-deterministic solutions. A framework that offers a complete solution to the P2P communication problem is presented. The proposed framework is based on the use of IPv4+4 addresses and the standard IPv4 Loose Source Record Route (LSRR) option and requires no changes whatsoever to end-host protocol stacks and Internet routers. The only requirement is a simple upgrade of border routers with a new LSRR-based packet-forwarding algorithm for the P2P traffic. The implementation of a Linux-based border router that runs the proposed forwarding algorithm is detailed, and how P2P applications can benefit from this framework is described. - Author(s): O. Daoud and O. Alani
- Source: IET Communications, Volume 3, Issue 4, p. 520 –529
- DOI: 10.1049/iet-com.2008.0344
- Type: Article
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Peak-to-average power ratio (PAPR) is a major drawback in most multi-carrier communication techniques such as orthogonal frequency division multiplex system (OFDM). OFDM consists of lots of independent modulated subcarriers, as a result the amplitude of such a signal can have very large values. These large peaks increase the amount of intermodulation distortion resulting in an increase in the error rate. The PAPR of an OFDM signal can be reduced in several ways: selective mapping, Golay sequences, cyclic coding, clipping and filtering, and multiple signal representation techniques. The authors have improved the performance of the OFDM system by using low-density parity-check (LDPC) codes as an alternative to turbo coding in mitigating the PAPR problem which has been used in the pervious works of the authors. The authors present the design for the proposed (LDPC) code technique that achieves good error correction performance and is used to lower the PAPR in a multiple-input multiple-output OFDM system. The simulation results show that 6–60% reduction in PAPR over current values in the literature can be achieved depending on the system type. - Author(s): J.-S. Li ; H.-C. Kao ; J.-D. Ke
- Source: IET Communications, Volume 3, Issue 4, p. 530 –538
- DOI: 10.1049/iet-com.2008.0204
- Type: Article
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Energy consumption is a crucially important issue in battery-driven wireless sensor networks (WSNs). In most sensor networks, the sensors near the data collector (i.e. the sink) become drained more quickly than those elsewhere in the network since they are required to relay all of the data collected in the network to the sink. Therefore more balanced data paths to the sink should be established in order to extend the lifetime of the sensor network. Accordingly, a novel relay deployment scheme for WSNs based on the Voronoi diagram is proposed. The proposed scheme is applicable to both two-dimensional and three-dimensional network topologies and establishes effective routing paths that balance the traffic load within the sensor network and alleviate the burden on the sensors around the sink. Simulation results indicate that the number of relays deployed in the proposed scheme is similar to that deployed in the predetermined location scheme and is significantly less than that deployed in the minimum set cover scheme. Furthermore, the lifetime of the sensor network containing relay nodes deployed using the current scheme is longer than that achieved using either the predetermined location scheme or the minimum set cover scheme. - Author(s): Y. Chen ; Y. Xiong ; X. Shi ; J. Zhu ; B. Deng ; X. Li
- Source: IET Communications, Volume 3, Issue 4, p. 539 –548
- DOI: 10.1049/iet-com.2008.0187
- Type: Article
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Network coordinates (NC) system is an efficient mechanism for Internet distance prediction with scalable measurements. The intrinsical cause for the unsatisfactory accuracy of the simulation-based NC algorithms has been identified. Then Pharos, a fully decentralised and hierarchical scheme, is proposed to solve this problem. Pharos leverages multiple coordinate sets at different distance scales, with the right scale being chosen for prediction each time. We evaluate the performance of Pharos system with the King data set and latency data from PlanetLab, and compare it with the representative NC system, Vivaldi. The experimental results show that Pharos greatly outperforms Vivaldi in Internet distance prediction without adding any significant overhead. Our extensive evaluation results also demonstrate that Pharos can significantly improve the performance in distributed Internet applications, such as overlay multicast and server selection. - Author(s): K. Yu and Y.J. Guo
- Source: IET Communications, Volume 3, Issue 4, p. 549 –560
- DOI: 10.1049/iet-com.2007.0603
- Type: Article
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A hybrid anchor-free localisation scheme for multihop wireless sensor networks is presented. First, a relatively dense group of nodes is selected as a base, which are localised by using the multidimensional scaling method. Secondly, the robust quads (RQ) method is employed to localise other nodes, following which the robust triangle and radio range (RTRR) approach is used to perform the localisation task. The RQ and the RTRR methods are used alternately until no more nodes can be localised by the two approaches. Simulation results demonstrate that the proposed hybrid localisation algorithm performs well in terms of both accuracy and the success rate of localisation. To evaluate the accuracy of anchor-free localisation algorithms, the authors derive two different accuracy measures: the Cramer–Rao lower bound (CRLB) to benchmark the coordinate estimation errors and the approximate lower bound to benchmark the distance errors. Simulation results demonstrate that both the CRLB and the distance error lower bound provide references for the accuracy of the location algorithms. - Author(s): J.-C. Lin
- Source: IET Communications, Volume 3, Issue 4, p. 561 –570
- DOI: 10.1049/iet-com.2008.0089
- Type: Article
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A channel estimation (CE) technique that uses a postfixed pseudo-random sequence padded with zero samples is investigated to extend pseudo-random-postfix orthogonal-frequency-division-multiplexing (PRP-OFDM) communications onto mobile applications. The proposed technique takes advantage of pseudo-noise sequences periodically inserted after each OFDM block within the original guard interval (GI) in conventional zero-padded OFDM (ZP-OFDM) or within the original cyclic prefix (CP) in conventional CP-OFDM. This allows accurate estimation of the channel impulse response. In addition, the proposed technique takes advantage of the null samples padded after the PN sequences for reducing inter-symbol interference occurring with the CEs and with the overlap-add information detection in the conventional PRP-OFDM. The proposed technique successfully applies either (1) a least-squares (LS) CE with assistance from decision-directed data or (2) an approximate LS CE method onto PRP-OFDM-like communications for the purpose of improving CE performance on rapid time-varying channels. Computer simulations in conjunction with statistical analysis assess the performance evaluation of the proposed technique and show that it can achieve lower mean-square estimation errors and lower error probabilities in mobile environments. - Author(s): H. Khani and P. Azmi
- Source: IET Communications, Volume 3, Issue 4, p. 571 –584
- DOI: 10.1049/iet-com.2008.0159
- Type: Article
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A novel weighted high data rate single-user ultra-wideband transmitted-reference (UWB-TR) system is proposed and its performance in log-normal slow fading channels is investigated, which has not been addressed before. This system employs a novel signalling scheme, which provides a nearly inter-symbol interference (ISI) free-channel response at the receiver and eliminates the need for equalisation. It also enhances the reference pulse quality by employing optimum power allocation. The performance of the proposed system is compared with that of the differential transmitted-reference (DTR) system in IEEE 802.15.3a Channel Model 1 (CM1) both analytically and via simulations by taking into account noise, log-normal slow fading, inter-path/pulse interference (IPI) and ISI. Both analytical and simulation results show that our system significantly outperforms the DTR one. It is shown that the proposed method is robust against small changes in both weighting coefficients and integration interval, whereas the UWB-DTR scheme is too susceptible to such changes in the integration interval. - Author(s): L. Ghabeli and M.R. Aref
- Source: IET Communications, Volume 3, Issue 4, p. 585 –596
- DOI: 10.1049/iet-com.2008.0141
- Type: Article
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Partial decoding scheme is a scheme in which each relay decodes only part of the transmitted message. Obviously, the achievable rates proposed by the partial decoding scheme subsume the achievable rates proposed by the full decoding scheme. The other motivation of using partial decoding scheme is that there are some special classes of relay networks such as semi-deterministic and orthogonal relay networks such that their capacities are obtained via this scheme. The authors propose a comprehensive partial decoding scheme based on regular encoding/sliding window decoding analysis to propose a new achievable rate for two-level relay networks. In contrast with the previously proposed methods, here the authors consider all possible partial decoding states that can occur between the different parts of the messages of the source and the relays in a two-level relay network. In this way, the common and private parts of the message transmitted by the source are defined to be decoded by the appropriate relays. Moreover, in the proof, the authors take advantage of regular encoding/sliding window decoding scheme that has superiorities to regular encoding/backward decoding and irregular encoding/random partitioning, in having less delay and yielding higher rates, respectively. - Author(s): J. Park ; Y. Lee ; H. Park
- Source: IET Communications, Volume 3, Issue 4, p. 597 –602
- DOI: 10.1049/iet-com.2008.0249
- Type: Article
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This paper proposes a preamble structure for joint estimation of carrier frequency offset (CFO) and I/Q imbalance. Because existing methods cannot guarantee correct solutions within all range of CFOs, we derive two constraints of phase rotations applied to repetition patterns. By using the preamble based on the presented constraints, CFO is optimally estimated, and I/Q imbalance estimation is possible in all ranges of CFO with low complexity. Numerical results verify the importance and necessity of these constraints for joint estimation. - Author(s): B.T. Ahmed and M.C. Ramón
- Source: IET Communications, Volume 3, Issue 4, p. 603 –609
- DOI: 10.1049/iet-com.2008.0356
- Type: Article
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The wideband code division multiple access downlink interference statistics and the capacity of equally spaced tunnel cigar-shaped microcells, used to serve users travelling in trains or metros, are analysed. The hybrid propagation model, with two defined modes, is used in the analysis. Fast fading because of multipath interference is superimposed with the main value of the loss and the slow fading up to a certain distance beyond which it can be neglected. To calculate the interference statistics and the capacity, a scenario with ten cigar-shaped microcells has been considered. The downlink capacity is then derived for different sector radii, train lengths, break point distances and propagation parameters. It is found that increasing the sector range up to 1250 m increases the sector downlink capacity. It is noticed that the maximum downlink capacity can be obtained for a sector radius of 1250–1750 m. It is also found that the increment of the propagation parameter γ reduces the sector downlink capacity. It is also noticed that increasing the train length increases the downlink capacity. It is also found that the bend loss increases the downlink capacity and reduces the maximum sector range. - Author(s): C.-C. Teng ; J.P. Fonseka ; E.M. Dowling
- Source: IET Communications, Volume 3, Issue 4, p. 610 –619
- DOI: 10.1049/iet-com.2008.0091
- Type: Article
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Here, non-coherent detectors for quadrature-multiplexed continuous phase modulation (QM-CPM) signals are developed (Fonseka et al., 2008). QM-CPM signals are more spectrally efficient than CPM signals, and multiamplitude QM-CPM signals can be constructed that outperform QAM. The non-coherent detectors view a QM-CPM signal as having composite states that represent the information modulated both onto the in-phase and quadrature-phase carriers. Viterbi decoding is used to jointly detect the quadrature-multiplexed signal components. Optimal sequence-based quadrature-matched filter (QMF) detectors are presented for use with QM-CPM detection and a QM-MSK detector is developed in detail. Differential phase and envelope (DPE) detectors are also presented which require less computation and are able to outperform the QMF-type detectors when the unknown carrier phase varies (phase jitter, phase hits etc.) within the sequence length used in the sequence-based QMF detectors. In the absence of these phase fluctuation effects, as the sequence length used in the QMF detectors increases, the performance of the QMF detectors approaches the performance of optimal non-coherent detection. The DPE-type detectors perform within about 2.5 dB of optimal coherent detection. - Author(s): I. Hwang ; C. You ; Y. Kim ; V. Tarokh
- Source: IET Communications, Volume 3, Issue 4, p. 620 –629
- DOI: 10.1049/iet-com.2008.0456
- Type: Article
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A novel downlink transmission rate-control and feedback reduction strategy for closed-loop multiple-input multiple-output (MIMO) multiple-input multiple-output wireless systems is presented. Unlike conventional systems that use signal to interference plus noise ratio at the receiver as an indicator of channel quality, we propose using instantaneous MIMO capacity as an indicator for the downlink transmission rate-control. A set of instantaneous capacity thresholds is first chosen such that the expected weighted capacity loss because of thresholding effects are minimised. While computing the thresholds, we also consider the quality of service and weight function to meet different traffics and user needs. Then a set of codebooks can be constructed minimising the overall capacity loss with given quality of service constraint. Simulation results show that, with only four data rate-control bits, our algorithm gives only 12% capacity loss in 4×4 MIMO systems and almost twice better than the current IS-856 standard in single-input single-output systems. In case of 5-bit feedback scenario, the proposed algorithm outperforms conventional systems by minimising instantaneous capacity loss. - Author(s): J.S. Mandeep ; J.S. Ojo ; L.D. Emiliani
- Source: IET Communications, Volume 3, Issue 4, p. 630 –635
- DOI: 10.1049/iet-com.2008.0478
- Type: Article
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At frequencies above 10 GHz, cloud attenuation in equatorial climate is one of the components that need to be characterised for low-availability satellite links. In addition to annual and worst month cumulative cloud attenuation, the statistics of seasonal and diurnal variations are required for providing detailed insights into system design. The authors present the cloud occurrences observed during different months, seasons and cloud attenuation results obtained from Penang, Malaysia, for a period of 5 years. A comparison of the present results with the results obtained from the existing models is also presented. - Author(s): V. Amaradasa ; J. Schormans ; J. Pitts ; C.M. Leung
- Source: IET Communications, Volume 3, Issue 4, p. 636 –643
- DOI: 10.1049/iet-com.2008.0213
- Type: Article
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The provision of quality of service to different service types in broadband packet networks requires techniques for the evaluation of the probabilities of packet delays and loss. The authors analyse the multiplexing of independent and homogeneous Markovian ON–OFF traffic sources into a single buffer, extending earlier work. The resulting closed-form equation provides a virtually zero-complexity approach to the calculation of the buffer overflow probability via the burst-scale decay rate of the buffer state probabilities. Graphical results are provided, comparing our expression with the results from simulations and the ‘standard’ formula of Anick, Mitra and Sondhi. These show that our new formula provides excellent accuracy for medium to high loads, i.e. those load values at which queuing becomes important. This makes it ideal for quick calculations, with practical utility when dimensioning checks are required in many networking situations involving the accurate estimation of loss probabilities in e.g. buffer multiplexing VoIP traffic sources. - Author(s): R. Iqbal ; T.D. Abhayapala ; T.A. Lamahewa
- Source: IET Communications, Volume 3, Issue 4, p. 644 –654
- DOI: 10.1049/iet-com.2008.0054
- Type: Article
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Clarke's classical model of mobile-radio reception assumes isotropic-rich scattering around the mobile receiver antenna. The assumption of isotropic scattering is valid only in limited circumstances. Here, a generalised Clarke model is developed, which is applicable to mobile-radio reception in general scattering environments. The authors give expressions for the autocorrelation and power spectral density of the channel fading process and demonstrate the generality of the model by applying it to different non-isotropic scattering scenarios. Using the generalised model, the effect of mobile direction of travel and the non-isotropicity on the statistics of the channel fading process is analysed. It is also shown that if the mobile direction of travel is equiprobable in all directions, a non-isotropic scattering environment on average is as good as an isotropic scattering environment. - Author(s): M. Karimi ; M. Nasiri-Kenari ; F.S. Tabataba ; S.M. Aghajanzadeh
- Source: IET Communications, Volume 3, Issue 4, p. 655 –665
- DOI: 10.1049/iet-com.2008.0345
- Type: Article
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A multistage decoder for the internally convolutionally coded fibre-optic time-hopping code division multiple access system recently introduced is considered. In this system, the decoder consists of several stages. The first stage is implemented using one of the single-user decoders introduced. The following stages are maximum likelihood (ML) decoders each of which use the decisions made by the previous stage. The performance of the proposed decoder is evaluated by a Monte Carlo simulation. Numerical results show that a multistage decoder with only two stages greatly outperforms the single-stage decoder with negligible increase in complexity. The authors also derive the Chernoff bound for the ML decoder with known interference, which is the ultimate performance of the multistage decoder. - Author(s): X. Peng ; A.S. Madhukumar ; F. Chin ; T.T. Tjhung
- Source: IET Communications, Volume 3, Issue 4, p. 666 –676
- DOI: 10.1049/iet-com.2007.0536
- Type: Article
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A block-spreading code division multiple access (BS-CDMA) system is proposed for broadband uplink transmission, giving rise to a significantly improved multiuser performance without using complex multiuser detection techniques. This is because the code orthogonality is easily maintained when channel variation across the consecutive blocks, in a block-by-block high-speed transmission, is negligible. The proposed system uses frequency domain equalisation at the receiver to combat multipath interference efficiently over frequency selective fading channels. We propose despreading before equalisation, which reduces the frequency domain process to symbol-wise operation. A cell-specific scrambling code is employed to suppress other-cell interference for uplink transmission in a multicell system. Our analytical and simulation studies show that the proposed BS-CDMA system has superior multiuser performance over the conventional direct sequence CDMA and cyclic prefix CDMA systems for uplink transmission. - Author(s): K. Cui ; M.S. Leeson ; E.L. Hines
- Source: IET Communications, Volume 3, Issue 4, p. 677 –683
- DOI: 10.1049/iet-com.2008.0163
- Type: Article
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A novel class of optical signature codes based on combinatorial designs is proposed for optical spectral-amplitude code-division multiple-access (CDMA) systems. It is applicable to both synchronous and asynchronous incoherent optical CDMA and is compatible with both frequency-encoded and time-spreading schemes. Simplicity of construction, larger code cardinality and larger flexibility in cross-correlation (CC) control make the proposed code family an interesting candidate for future optical CDMA applications that require a large number of simultaneous users. It has been shown that the system performance can be significantly improved by using the proposed codes with ideal in-phase CC in preference to Hadamard codes.
Maximum a posteriori channel estimation for cooperative diversity orthogonal frequency-division multiplexing systems in amplify-and-forward mode
Enabling peer-to-peer communication for hosts in private address realms using IPv4 LSRR option and IPv4+4 addresses
Reducing the PAPR by utilisation of the LDPC code
Voronoi-based relay placement scheme for wireless sensor networks
Pharos: accurate and decentralised network coordinate system
Anchor-free localisation algorithm and performance analysis in wireless sensor networks
Channel estimation assisted by postfixed pseudo-noise sequences padded with zero samples for mobile orthogonal-frequency-division-multiplexing communications
Weighted high data rate ultra wideband transmitted-reference system in dense multipath fading channels
Comprehensive partial decoding approach for two-level relay networks
Preamble design for joint estimation of CFO and I/Q imbalance for direct conversion OFDM system
Downlink capacity and interference statistics of wideband code division multiple access microcells for trains in long tunnels
Non-coherent detectors for quadrature-multiplexed continuous phase modulation signals
Downlink transmission rate-control strategies for closed-loop multiple-input multiple-output systems
Statistics of annual and diurnal cloud attenuation over equatorial climate
Evaluating overflow probability for voice over internet protocol buffer dimensioning
Generalised Clarke model for mobile-radio reception
Multistage decoding for an internally coded fibre-optic time-hopping/optical code division multiple access communication system
Block spreading CDMA system: a simplified scheme using despreading before equalisation for broadband uplink transmission
Unipolar codes for optical spectral-amplitude code-division multiple-access systems based on combinatorial designs
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