Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 6, Issue 3, 14 February 2012
Volumes & issues:
Volume 6, Issue 3
14 February 2012
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- Author(s): H.-H. Chen ; C. Wang ; M. Peng
- Source: IET Communications, Volume 6, Issue 3, p. 243 –245
- DOI: 10.1049/iet-com.2012.0031
- Type: Article
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243
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- Author(s): C.-J. Wu ; D.W. Lin ; T.-H. Sang
- Source: IET Communications, Volume 6, Issue 3, p. 246 –256
- DOI: 10.1049/iet-com.2010.0981
- Type: Article
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Relays can potentially enhance the transmission performance of multi-input multi-output (MIMO) systems. A parallel single-antenna relay network has additional advantages in flexibility, diversity and cost, but also poses significant design problems because the absence of inter-antenna connections over different relays makes the underlying mathematical problems much more difficult to solve. In this study, the authors consider the design of parallel amplify-and-forward relay networks. More specifically, the authors consider the design of relay gains to maximise the system capacity. As no closed-form analytic solution can be found, the authors first develop an iterative algorithm to find a locally optimal solution. Since algorithmic optimisation provides little insight into the analytical properties of the solution, they also attempt analytical solutions for several asymptotic noise conditions. It turns out that the solutions involve some methods to select the optimal subsets of relays for signal forwarding. The authors analyse the resulting capacity outage diversity orders and confirm the analysis with simulation results. - Author(s): Y. Wang ; H. Dai ; T. Wang ; P. Zhang
- Source: IET Communications, Volume 6, Issue 3, p. 257 –263
- DOI: 10.1049/iet-com.2010.0983
- Type: Article
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257
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In distributed antenna systems (DAS), multi-user interference was shown to be asynchronous, which had not been paid much attention. In this study, the authors compare the performances of the DAS under the condition of asynchronous interference (AI) with four well-known multiple-input multiple-output (MIMO) algorithms namely zero-forcing (ZF), block diagonalisation (BD), signal-to-leakage-plus-noise ratio (SLNR) and dirty paper coding (DPC) algorithms. The simulation results clearly demonstrate significant performance degradations of these algorithms. To further improve the performance under the condition of AI, this study presents an improved BD algorithm and a significant improvement is shown through corresponding simulation results. - Author(s): L. Tian ; Y. Zhou ; Y. Zhang ; G. Sun ; J. Shi
- Source: IET Communications, Volume 6, Issue 3, p. 264 –271
- DOI: 10.1049/iet-com.2010.0985
- Type: Article
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This study focuses on the resource allocation of multicast services in distributed antenna systems (DAS). Firstly, the capacity limitation of conventional multicast transmission is analysed in DAS. Then a resource allocation algorithm is proposed for multicast services to improve the system throughput of DAS with quality of service (QoS) guarantees. A low-complexity suboptimal algorithm is also presented, which includes three steps: conservative allocation, greedy step and iterative enhancement. Simulation results show that the proposed algorithms significantly outperform conventional multicast transmission in throughput while guaranteeing the minimum data rates of all users as well. Moreover, the performance of the suboptimal algorithm is close to that of the optimal one and the throughput loss is negligible. Meanwhile, it is also shown that the proposed algorithms can exceed the upper bound of conventional multicast scheme when the user number is larger, which indicates the proposed algorithms can overcome the capacity limitation of conventional multicast transmission in DAS. - Author(s): W. Zhanji ; P. Mugen ; W. Wenbo
- Source: IET Communications, Volume 6, Issue 3, p. 272 –280
- DOI: 10.1049/iet-com.2010.0999
- Type: Article
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An improved high-spectral-efficiency coding-rotated modulation (CRM)-iterative demodulation/decoding (ID) scheme in the orthogonal frequency division multiplexing (OFDM) system is proposed. For the rotated QAM, it unveils the optimum rotation matrix depending on the modulation order, the code rate and the receiver scheme (ID or non-ID). The suboptimal solution of the rotation angle is proposed, and a novel two-dimensional time/frequency component interleaver is also put forward to make the best use of the modulation diversity, time diversity and frequency diversity. Besides, code-matched four-dimensional QAM rotation matrices and the corresponding time/frequency component interleaver are proposed to improve the error performance furthermore. The analysis of extrinsic information transfer chart (EXIT) chart is also given to explain the convergence characteristic. Simulation results have turned out that this new scheme can significantly outperform the conventional BICM scheme. - Author(s): J. Chang ; I.T. Lu ; Y.X. Li
- Source: IET Communications, Volume 6, Issue 3, p. 281 –288
- DOI: 10.1049/iet-com.2010.0960
- Type: Article
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281
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In multiple-input multiple-output–orthogonal frequency division multiplexing (MIMO–OFDM) communications, the channel state information (CSI) of the forward link at each subcarrier is needed for precoder design at the transmitter to achieve the maximal diversity and/or multiplexing gains. In frequency division duplex (FDD) systems, the CSI needs to be estimated at the receivers and fed back to the transmitters. Owing to the limited network resources, there will be CSI feedback errors due to quantisation, delay and clustering (where one CSI feedback is used to represent a cluster of adjacent subcarriers for feedback reduction). Consequently, the system performance degrades and the gains expected from using MIMO diminish. To mitigate this performance degradation, an adaptive codebook-based CSI prediction and interpolation scheme is proposed for multiuser MIMO–OFDM systems. In this scheme, geodesic CSI prediction is employed at the receiver to mitigate the feedback delay effect and geodesic CSI interpolation is performed at the transmitter to mitigate the clustering feedback effect. Since the performance gain assumed by the CSI prediction and interpolation is limited by the low-resolution CSI quantisation, an adaptive codebook scheme is proposed to be used to support the CSI prediction and interpolation. Simulation results show that the proposed scheme is effective in mitigating the performance loss due to quantisation, feedback delay and clustering feedback. - Author(s): Fan Huang ; Yafeng Wang ; Jian Geng ; Dacheng Yang
- Source: IET Communications, Volume 6, Issue 3, p. 289 –299
- DOI: 10.1049/iet-com.2010.0949
- Type: Article
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Recently, Coordinated Multi-Point (CoMP) transmission/Reception technology is introduced into the fourth-generation cellular mobile communication system. Time-division duplex (TDD) system is more suitable to apply CoMP when joint processing is needed because it can easily get the channel information through channel reciprocity. Actually, a crucial point to realise channel reciprocity is the antenna calibration, especially in the inter-base station (BS) case. Self-antenna calibration within the BS in the conventional system has been studied in previous works. In this paper, the authors investigate the impact of un-calibrated antennas of BSs and mobile stations (MSs) on the precoding matrix of two precoding techniques [block diagonal (BD) and zero forcing (ZF)] in the CoMP system. A theoretical model is set and analysed. The discussion of some properties gives a complete overview of the calibration problem in the CoMP system. In addition, the authors propose a practical scheme to solve inter-BS antenna calibration problem. System simulation results, which validate their analysis, are presented to show the necessity of antenna calibration. - Author(s): L. Liang ; G. Feng ; Y. Zhang
- Source: IET Communications, Volume 6, Issue 3, p. 300 –310
- DOI: 10.1049/iet-com.2010.0953
- Type: Article
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Deployment of relay nodes (RNs) in cellular orthogonal frequency division multiple access (OFDMA) systems provides an effective solution to increase high data rate coverage and improve cell throughput. However, a challenging issue is that additional interferences caused by RNs may substantially compromise the performance gain if no measure is taken. In this study, the authors address the problem of interference coordination in relay-aided cellular OFDMA systems, aiming at exploiting the benefits of RNs while minimising the negative effects of interferences introduced. The authors first analyse the possible interference scenarios in multi-cell systems. Based on the insights into their analysis, the authors propose resource allocation with interference coordination (RAIC) scheme for cellular OFDMA systems. RAIC selectively perform one of three resource allocation algorithms according to the offered traffic load in the system, to mitigate interferences and thus enhance system throughput. The authors conduct intensive simulation experiments based on the model with realistic broadband channel propagation conditions. Numerical results demonstrate that their proposed RAIC can effectively improve system throughput compared with the resource allocation schemes without appropriate interference coordination. - Author(s): J.H. Sarker and H.T. Mouftah
- Source: IET Communications, Volume 6, Issue 3, p. 311 –317
- DOI: 10.1049/iet-com.2010.0899
- Type: Article
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In an infrastructure-less wireless ad hoc or sensor network, communication may be achieved between mobile nodes without a central entity (base station) using a half-duplex Slotted ALOHA protocol. The probability of success and the throughput per mobile node can be reduced significantly, if the network is attacked by jamming signals. Mitigating the effect of jamming signals using multi-packet transmission (MPT) and/or multi-packet reception (MPR) capabilities of each mobile node is studied. The effect of the probability of success reduction due to jamming signals can be mitigated by using the MPT and the MPR capabilities of each mobile node. Similarly, reduced throughput can be increased using the same techniques. The maximum throughput per mobile node can be obtained by the proper adjustment of the transmitting probability of each mobile node and the receiving probability of each mobile node. A lower mitigation of the maximum throughput reduction can be obtained by using only the MPT, if the jamming signal rate is very low. On the other hand, only the MPR capability can provide a lower mitigation of the maximum throughput reduction. The effect of jamming signals on the maximum throughput can be mitigated successfully at all traffic load conditions, if the MPT and the MPR capabilities work together. - Author(s): Y. Rui ; H. Hu ; H. Yi ; H.-H. Chen
- Source: IET Communications, Volume 6, Issue 3, p. 318 –323
- DOI: 10.1049/iet-com.2010.0972
- Type: Article
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p.
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Employing user pairing schemes in uplink virtual multiple-input multiple-output (V-MIMO) systems can significantly improve system capacity owing to multi-user diversity. Most of the existing user pairing algorithms were developed under the assumption that a scheduler always possesses the perfect channel state information (CSI). In this paper, taking into account the effects of channel estimation error (CEE), the authors propose a robust user pairing algorithm based on a closed-form average sum rate under CEE. In addition, the authors further propose an adaptive user selection scheme as an effort to maximise the sum rates owing to the rate constraint under CEE. The gain of the proposed method is shown in simulation results.
Editorial: Evolution of air-link technologies for futuristic wireless communications
Design of distributed amplify-and-forward relay networks for multi-input multi-output transmission
Improved block diagonalisation algorithm under asynchronous interference condition
Resource allocation for multicast services in distributed antenna systems with quality of services guarantees
Improved coding-rotated-modulation orthogonal frequency division multiplexing system
Adaptive codebook-based channel prediction and interpolation for multiuser multiple-input multiple-output–orthogonal frequency division multiplexing systems
Antenna mismatch and calibration problem in coordinated multi-point transmission system
Resource allocation with interference coordination for relay-aided cellular orthogonal frequency division multiple access systems
Mitigating the effect of jamming signals in wireless ad hoc and sensor networks
Robust user pairing algorithm under channel estimation errors for uplink virtual multiple-input multiple-output systems
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- Author(s): J.-Y. Pan ; S.-C. Shiu ; W.-S. Lee ; S.-W. Huang
- Source: IET Communications, Volume 6, Issue 3, p. 324 –334
- DOI: 10.1049/iet-com.2010.0450
- Type: Article
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There are two fundamental bandwidth-request mechanisms specified in the IEEE 802.16 standard: contention-based random access and contention-free polling. For example, non-real-time polling and best-effort services mainly rely on the contention-based mechanism to submit bandwidth requests to the base station (BS). However, the performance degrades considerably when the number of requests is high and they collide with each other. To avoid collision, the standard supports a truncated binary exponential backoff resolution. Nevertheless this resolution is inefficient in dispersing the requests when the network traffic is overloaded. In order to improve the efficiency of the random-access mechanism in the standard, the authors propose a new mechanism that aids mobile stations (MSs) in sending bandwidth requests more efficiently and also avoiding peak traffic. By using the mechanism, MSs send bandwidth requests under low loads, thus avoiding collisions. - Author(s): C. Li ; D.A. Hutchins ; R.J. Green
- Source: IET Communications, Volume 6, Issue 3, p. 335 –343
- DOI: 10.1049/iet-com.2010.0916
- Type: Article
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The authors propose a model for estimating the response of an ultrasonic communication channel, where a specific type of capacitive transreceivers was used to give an effective bandwidth of over 1 MHz. Apart from the responses of transreceivers, the channel response at each location within the radiated field can be determined by attenuation response and special field response. The driving signal used to verify the model was a quadrature phase shift keying (QPSK) signal centred at 300 kHz, and with a signalling rate of 400 kbps. Simulations were firstly carried out to identify the variations in waveform as well as spectrum caused by predicted response at several coordinates. This is then compared with experimental results, and good agreements were found between the two. - Author(s): H. Attar ; L. Stankovic ; V. Stankovic
- Source: IET Communications, Volume 6, Issue 3, p. 344 –352
- DOI: 10.1049/iet-com.2011.0143
- Type: Article
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The authors propose two practical power- and bandwidth-efficient systems based on amplify-and-forward and decode-and-forward schemes to address the problem of information exchange via a relay. The key idea is to channel encode each source's message by using a high-performance non-binary turbo code based on partial unit memory codes to enhance the bit-error-rate performance, then reduce the energy consumption and increase spectrum efficiency by using network coding (NC) to combine individual nodes’ messages at the relay before forwarding to the destination. Two simple and low complexity physical layer NC schemes are proposed based on combinations of received source messages at the relay. The authors also present the theoretical limits and numerical analysis of the proposed schemes. Simulation results under additive white Gaussian noise confirm that the proposed schemes achieve significant bandwidth savings and fewer transmissions over the benchmark systems which do not resort to NC. Theoretical limits for capacity and signal-to-noise ratio behaviour for the proposed schemes are derived. This study also proposes a cooperative strategy that is useful when insufficient combined messages are received at a node to recover the desired source messages, thus enabling the system to retrieve all packets with significantly fewer retransmission request messages. - Author(s): H. Khodakarami and F. Lahouti
- Source: IET Communications, Volume 6, Issue 3, p. 353 –362
- DOI: 10.1049/iet-com.2011.0319
- Type: Article
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A secure link adaptation framework is proposed, which exploits the inherent fluctuations of wireless fading channels for high-performance communications and physical layer security in the presence of an eavesdropper. The authors use very sharp channel codes intended for reliability and demonstrate that they also provide security, when successfully incorporated in the link adaptation design framework and the security constraint is not very stringent. Two scenarios are considered in which the transmitter has access to the eavesdropper channel state information either instantaneously or statistically. The proposed secure link adaptation framework is formulated to maximise the spectral efficiency of the communication, whereas both reliability and security constraints are provisioned. Different designs are considered when the security constraint is quantified by instantaneous bit error rate (BER), average BER or leakage probability. For the problem with instantaneous BER constraint, an efficient analytical solution and a numerical solution are presented. A closed-form analytical solution is also provided for secure link adaptation with average BER constraint, whereas the problem with the leakage constraint is tackled numerically. Extensive results and detailed analysis are provided to draw insights on the effects of different design parameters on the performance.
Peak avoidance and collision control for contention-based bandwidth requests in WiMAX systems
Response of an ultrasonic communication channel in air
Cooperative network-coding system for wireless sensor networks
Link adaptation for physical layer security over wireless fading channels
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