Online ISSN
1751-8636
Print ISSN
1751-8628
IET Communications
Volume 4, Issue 15, 15 October 2010
Volumes & issues:
Volume 4, Issue 15
15 October 2010
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- Author(s): D.Y. Peng ; X.H. Niu ; X.H. Tang
- Source: IET Communications, Volume 4, Issue 15, p. 1775 –1786
- DOI: 10.1049/iet-com.2009.0783
- Type: Article
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Frequency hopping/time hopping (FH/TH) sequences have found wide applications in various modern FH/TH spread spectrum communications, namely ultra-wide bandwidth radio, multi-user radar, sonar systems, wireless sensor networks, and so on. The average Hamming correlation (AHC) is an important performance indicator of the FH/TH sequences. In order to evaluate the performance of the FH/TH sequences, it is important to find the tight theoretical bound on the AHC. The lower bound, which has not yet been previously reported, on the AHC for FH/TH sequences with respect to the size of the frequency slot set, the sequence length, the family size, the average Hamming autocorrelation and the average Hamming cross-correlation is established here. In addition, a new family of cubic and constant hopping sequences with large family size suitable for FH/TH code-division multiple-access systems is proposed. Further, the AHCs for the new cubic and constant hopping and some known cubic hopping sequences are derived analytically. It is shown that these cubic hopping sequences are optimal with respect to our new bound on the AHC. - Author(s): I. Krikidis
- Source: IET Communications, Volume 4, Issue 15, p. 1787 –1791
- DOI: 10.1049/iet-com.2009.0634
- Type: Article
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This study deals with opportunistic relay selection in cooperative networks with secrecy constraints, where an eavesdropper node tries to overhead the source message. Previously reported relay selection techniques are optimised for non-eavesdropper environments and cannot ensure security. Two new opportunistic relay selection techniques, which incorporate the quality of the relay-eavesdropper links and take into account secrecy rate issues, are investigated. The first scheme assumes an instantaneous knowledge of the eavesdropper channels and maximises the achievable secrecy rate. The second one assumes an average knowledge of the eavesdropper channels and is a suboptimal selection solution appropriate for practical applications. Both schemes are analysed in terms of secrecy outage probability and their enhancements against conventional opportunistic selection policies are validated via numerical and theoretical results. - Author(s): S. Salehkalaibar ; L. Ghabeli ; M.R. Aref
- Source: IET Communications, Volume 4, Issue 15, p. 1792 –1798
- DOI: 10.1049/iet-com.2010.0123
- Type: Article
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The authors introduce a generalisation of the multiple-access-relay-channel (MARC) called multiple-access-relay-network (MARN). The MARC model was first introduced by Kramer et al. and consists of many transmitters, one receiver and only one relay. In the MARN, there are many transmitters, many relays and one receiver. The authors obtained an achievable rate region for MARN by considering partial decode-and-forward (PDF) strategy at the relays. They showed that the region obtained using PDF strategy subsumes the region obtained by Kramer et al. for MARC. In the proposed coding scheme, the authors take advantage of PDF strategy based on regular encoding/backward decoding strategy. They also define semi-deterministic MARN, in which the output of the link between each transmitter and each relay is a deterministic function of the transmitter's input. The authors obtained an inner bound (using our achievable rate region) and also an outer bound on the capacity region of the semi-deterministic MARN and compared them. - Author(s): W.-H. Liao and C.-C. Chen
- Source: IET Communications, Volume 4, Issue 15, p. 1799 –1808
- DOI: 10.1049/iet-com.2010.0036
- Type: Article
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Wireless sensor networking (WSN) is an emerging technology that enables remote monitoring on a large scale. Data-centric storage is an effective and important technique in WSNs. Its function is to store sensed events according to their attribute values by mapping them to some nodes in order to avoid routing all the values outside the network and flooding the queries. There are many attributes with range values in an event, so the sensor will need to use multi-dimensional range queries to retrieve data. The authors propose a data storage and range query method for multi-dimensional attributes in WSNs. The main idea is to map multi-dimensional events to their corresponding range spaces and build an in-network distributed data structure to efficiently gather the data of multi-dimensional range queries. The performance evaluation shows that the proposed scheme can reduce message cost and hotspot problems to achieve load balancing even when a vast number of the events and sensor nodes are present in a sensor network. - Author(s): Y. Zhu and I.J. Fair
- Source: IET Communications, Volume 4, Issue 15, p. 1809 –1816
- DOI: 10.1049/iet-com.2009.0643
- Type: Article
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Multimode coding is a promising coding method owing to the simplicity of its code design and the attainment of high code rate. The authors present a multimode coding scheme for generating two-dimensional balanced t-conservative arrays for holographic storage. The multimode encoding process involves adding each unconstrained input array to a set of control arrays to form the selection set and selecting a pseudo-balanced t-conservative array from the selection set. By appropriately encoding the indices of the control arrays and using the remaining bits in the extra column or row appended to the selected pseudo-balanced t-conservative array to jointly balance the entire encoded array and to ensure that the extra column or row contains a sufficient number of transitions, the final output of the multimode encoder satisfies both the balanced and the t-conservative constraints. The decoding process is straightforward given the knowledge of the control array that was applied to the input array during the encoding process. - Author(s): J.-H. Lee and O.-S. Shin
- Source: IET Communications, Volume 4, Issue 15, p. 1817 –1826
- DOI: 10.1049/iet-com.2010.0056
- Type: Article
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The authors propose a full-duplex relay (FDR) based on a block diagonalisation (BD) method in multiple-input multiple-output (MIMO) relay channels. The BD method is employed to suppress the self-interference in MIMO FDR as well as to transmit multiple data streams to multiple users at the same time. The authors also derive the optimal power allocation strategy for MIMO FDR operation. Numerical results show that the use of the proposed FDR with BD can provide enhanced system performance compared with the FDR with zero-forcing beamforming. - Author(s): C. Kumar and R. Tripathi
- Source: IET Communications, Volume 4, Issue 15, p. 1827 –1837
- DOI: 10.1049/iet-com.2009.0839
- Type: Article
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In mobile networks, when the mobile terminal (MT) has an active call while crossing the boundary of two systems, it is required that the existing connection should not be lost. To meet this demand, the signalling protocol of mobility management must be designed for supporting location registration and call delivery for roaming users who move beyond their home network. The objective of this study is to provide a modified boundary location register (MBLR) signalling protocol for inter-system roaming. The idea of generating routing number in advance plays a key role for the proposal. The location registration and call delivery process of the new protocol are proposed which tries to reduce the signalling cost and latency. An analytical model is developed for comparative performance analysis of the boundary location register and MBLR protocol. However, this will result in increased processing requirements at the database server. Thus, trade-off between signalling, database access costs and processing overheads must be recognised. - Author(s): N. Mokari and K. Navaie
- Source: IET Communications, Volume 4, Issue 15, p. 1838 –1846
- DOI: 10.1049/iet-com.2009.0816
- Type: Article
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In this study, the authors propose a cross-layer resource allocation scheme for push to talk (PTT) service over orthogonal frequency division multiple access (OFDMA)-based networks. In our modelling, the authors consider two traffic types: streaming traffic, which requires a maximum guaranteed average delay and elastic traffic with flexible rate requirements. PTT traffic is also considered as a streaming traffic with more flexible delay requirements comparing to conventional streaming traffic. The authors consider queue state information as well as channel state information in a cross-layer framework to maximise the total transmission rate of the elastic users, while average delay constraint for streaming users, and maximum transmission power constraint are satisfied. An algorithm is then proposed based on dual decomposition method to obtain the subcarrier assignment and power allocation for each user. Using simulations, the authors then evaluate the impact of the streaming PTT traffic and other system parameters on the total rate of elastic users. - Author(s): J. Ham ; K. Kim ; M. Shin ; C. Lee
- Source: IET Communications, Volume 4, Issue 15, p. 1847 –1854
- DOI: 10.1049/iet-com.2010.0055
- Type: Article
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A quasi-orthogonal space–time block code (QO-STBC) has a rate one but a loss of diversity gain, compared with an orthogonal space–time block code such as Alamouti code. In this study, a code selection algorithm between QO-STBCs is proposed for a diversity gain improvement of a system based on a QO-STBC with four transmit antennas. The proposed algorithm improves diversity gain without a rate loss and provides better performance than the conventional closed-loop algorithm based on QO-STBC. Advantageously, the proposed algorithm can be applied to simple linear receivers, such as the zero-forcing receiver and minimum mean square error receiver, instead of the maximum likelihood receiver, which has a high computational complexity problem. The probability density function of two signal-to-interference and noise ratios (SINRs) is derived and by the derived pdf, an approximated bit error rate (BER) performance of the proposed system is also derived. The BER performance of the proposed system outperforms previous algorithms at least by about 0.5 dB SNR gain at BER 10−4. - Author(s): S. Peng ; X. Yang ; S. Shu ; X. Cao
- Source: IET Communications, Volume 4, Issue 15, p. 1855 –1864
- DOI: 10.1049/iet-com.2009.0787
- Type: Article
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Cognitive radio (CR) is a promising technology to alleviate current spectrum scarcity via enabling the secondary user (SU) to opportunistically access the unutilised spectrum band that has been licensed to the primary user (PU) for exclusive use. To identify the access opportunities, SU should reliably detect whether PU is present or not. Previous works on the problem of PU detection have suggested the approach of multi-SU cooperation in order to enhance detection reliability. In this study, the authors consider that PU maintains the same state (absence or presence) for at least M (M ≥ 2) slots and develop a new approach of exploiting M-slot temporal persistence for improving the accuracy of PU detection in terms of reducing the detection Bayesian cost. To achieve this goal, Bayesian energy detection (BED) scheme is firstly presented. Then based on BED scheme, the authors propose an improved scheme to exploit the M-slot temporal persistence. It is shown that, if M=2, exploitation of M-slot temporal persistence is certainly beneficial and can reduce as much as 1/3 of Bayesian cost. If M>2, more Bayesian cost reduction can also be obtained. - Author(s): M. Drieberg ; F.-C. Zheng ; R. Ahmad
- Source: IET Communications, Volume 4, Issue 15, p. 1865 –1875
- DOI: 10.1049/iet-com.2010.0069
- Type: Article
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Dense deployments of wireless local area networks (WLANs) are becoming a norm in many cities around the world. However, increased interference and traffic demands can severely limit the aggregate throughput achievable unless an effective channel assignment scheme is used. In this work, a simple and effective distributed channel assignment (DCA) scheme is proposed. It is shown that in order to maximise throughput, each access point (AP) simply chooses the channel with the minimum number of active neighbour nodes (i.e. nodes associated with neighbouring APs that have packets to send). However, application of such a scheme to practice depends critically on its ability to estimate the number of neighbour nodes in each channel, for which no practical estimator has been proposed before. In view of this, an extended Kalman filter (EKF) estimator and an estimate of the number of nodes by AP are proposed. These not only provide fast and accurate estimates but can also exploit channel switching information of neighbouring APs. Extensive packet level simulation results show that the proposed minimum neighbour and EKF estimator (MINEK) scheme is highly scalable and can provide significant throughput improvement over other channel assignment schemes. - Author(s): C. You ; I. Hwang ; I.-T. Hwang
- Source: IET Communications, Volume 4, Issue 15, p. 1876 –1888
- DOI: 10.1049/iet-com.2009.0632
- Type: Article
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The authors propose a joint dirty-paper coding (DPC) and beamforming scheme for use in multiuser multiple-input multiple-output (MIMO) systems. Unlike conventional maximum likelihood (ML)-based DPC schemes, this joint DPC and beamforming precoding scheme is intended as a suboptimal strategy in that it cancels only causal interference, thus offering a practical implementation option. In addition, a signal-to-interference plus noise ratio (SINR)-based ordering strategy that can be readily applied to conventional DPC schemes is also proposed as a way of improving the performance of the joint precoding scheme. The proposed schemes markedly improve classical spatial division multiple access (SDMA), and achieve the same data rates as spatial multiplexing (SM) for all users, but with significantly superior performance/diversity gain. When the number of active users per sector is much greater than the number of transmit antennas, the proposed schemes are able to achieve enough multiuser diversity to asymptotically approach the optimal DPC capacity. In addition, unlike BLAST, the receivers do not need to know each other's vector channels. Simulation results confirm that the proposed schemes provide significant gain over conventional zero-forcing SDMA in terms of average sector throughput for downlink multi-cell multiuser systems and symbol error rate as well. Finally, the proposed interference cancellation strategies at the transmitter can be expandable to MIMO systems with any number of multiple antennas. - Author(s): A. Khaleghi ; R. Chávez-Santiago ; I. Balasingham
- Source: IET Communications, Volume 4, Issue 15, p. 1889 –1897
- DOI: 10.1049/iet-com.2009.0692
- Type: Article
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Impulse radio (IR) ultra wideband (UWB) technology is assessed herein for wireless data communications with a capsule endoscope operating inside the digestive tract. The UWB channel is characterised for the frequency range of 1–5 GHz and line-of-sight (LOS) scenarios. Owing to the lack of a standardised mathematical model for in-body UWB signals, the channel characterisation is attained by using numerical simulations. Because of the lossy material properties of the human tissues, short delay spread of the in-body channel is observed. The design of a packet based IR-UWB transmitter is presented herein, considering the restrictions on power consumption, size, cost and complexity. A novel coherent receiver using a single-branch correlation scheme is proposed. The receiver system performance is optimised by adjusting the shape and the delay of the template pulse for providing maximum output of the correlator. Its bit-error-rate (BER) performance using bi-phase pulse amplitude modulation (BPAM) is evaluated. The effects of different templates on the system performance are also investigated. Fast synchronisation is achieved by using a bank of correlators; the number of correlator branches and the preamble length for successful synchronisation are estimated. This investigation reveals the feasibility of using IR-UWB for capsule endoscope fast data transmission.
Average Hamming correlation for the cubic polynomial hopping sequences
Opportunistic relay selection for cooperative networks with secrecy constraints
Achievable rate region for multiple-access-relay-networks
Data storage and range query mechanism for multi-dimensional attributes in wireless sensor networks
Multimode two-dimensional balanced conservative codes for holographic storage
Full-duplex relay based on block diagonalisation in multiple-input multiple-output relay systems
Modified boundary location register: an inter-system roaming signalling protocol
Cross-layer resource allocation for push to talk service over orthogonal frequency division multiple access-based networks with heterogeneous traffic
Performance analysis of code selection algorithm based on quasi-orthogonal space–time block code
Exploitation of temporal persistence for accuracy improvement in primary user detection
Minimum neighbour and extended Kalman filter estimator: a practical distributed channel assignment scheme for dense wireless local area networks
Precoded dirty-paper coding with signal-to-interference plus noise ratio-based ordering for multiuser multiple-input multiple-output communication
Ultra-wideband pulse-based data communications for medical implants
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