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Communications, IET

Issue 14 • Date September 24 2010

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Displaying Results 1 - 11 of 11
  • Centralised resource allocation policies for meshed high data rate wireless personal area networks

    Page(s): 1651 - 1664
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    Multi-media applications with demanding throughput requirements often raise issues of capacity limitations in wireless networks. High data rate (HDR) wireless personal area networks (WPANs) can operate in a mesh configuration to extend from the legacy single-hop communication to multiple hops. Although the range of WPANs is increased in a mesh configuration, there are capacity constraints because the superframe time is shared by multiple piconet clusters instead of being dedicated for a single piconet cluster just like in the legacy single-hop case. Furthermore, the distributed superframe sharing can cause fairness issues because there is no mechanism to determine the requirement of each mesh piconet coordinator (MPNC) and monitor a fair allocation to each MPNC. Here, the authors propose a centralised resource allocation approach and define three resource allocation policies for meshed HDR WPANs. The proposed approach is augmented by a traffic estimation strategy to predict a suitable fraction of superframe time for each cluster. Simulation results prove the effectiveness of the proposed resource allocation policies and the fairness index is shown to increase upto 42% with the proposed approach in some cases. View full abstract»

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  • Multicast and quality of service provisioning in parallel shared memory switches

    Page(s): 1665 - 1676
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (427 KB)  

    Growing demand for differentiated services and the proliferation of Internet multimedia applications requires not only faster switches/routers, but also the inclusion of guaranteed qualities of service (QoSs) and support for multicast traffic. Here, the authors introduce a parallel shared memory (PSM) architecture that addresses these demands by offering both QoS guarantees and support for multicast traffic. It is well known that PSM architectures represent an effective approach for distributing the high-memory bandwidth requirement found in output-queued (OQ) switches, while maintaining their desirable performance attributes. At the core of the PSM architecture is a memory management algorithm that determines, for each arriving packet, the memory unit in which it will be placed. The PSM architecture discussed should be considered with the context of fabric on a chip in mind, where an implementation is conceivable on a single chip, providing a plug-in emulated OQ switching solution. A description and detailed analysis of an efficient memory management algorithm that supports QoS and multicast traffic is given with a discussion of hardware implementation considerations that highlight the PSM architecture's scalability and performance attributes. View full abstract»

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  • Cooperative MIMO multiple-relay system with optimised beamforming and power allocation

    Page(s): 1677 - 1686
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (649 KB)  

    In this paper we investigate optimised power allocation over two-hop multiple-input multiple-output (MIMO) fixed multiple relays for a given power budget. Optimum beamforming weights under the total sum power constraint for all relays, as well as maximum per-relay power constraint, are found to maximise the received SNR at destination. Results show that optimising the allocation of power improves system performance, especially foe highly unbalanced links. The system with optimised power allocation can outperform a two-hop multiple relay system using uniform power allocation and distributed beamforming at the expense of increased computational complexity. We also study the threshold decode-and-forward fixed relay network with beamforming, which is more reliable than conventional decode-and-forward relaying. The impact of multiple antennas on the outage probability of cooperating fixed relays is considered. It is determined that increasing the number of relays and antennas at each relay increases capacity. The outage probability of threshold maximal-ratio combining and threshold selection combining for multiple-antenna multiple fixed relays is also derived. It is observed that the performance of the relay network with selection combining is close to that of the network with maximal-ratio combining, but the former is less complex and less expensive to implement. View full abstract»

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  • Evaluation of a new end-to-end quality of service algorithm in differentiated services networks

    Page(s): 1687 - 1695
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (425 KB)  

    A new end-point admission control algorithm is proposed. The proposed algorithm helps to manage the network traffic within a domain more efficiently in the next generation network where multiple classes of service are required by different applications. In the existing solutions, when a request for a new traffic is received by the network, according to the admission control mechanism the availability of resources for the requested service class is examined and the call is accepted if the resources are available. In the proposed algorithm, users' are allowed to temporarily use lower service classes in the routers along the path, whenever the requested service class is not available, given that the end-to-end service quality level is preserved unless a lower service quality is acceptable by the application. The probe-based end-point admission control mechanism proposed here, dynamically manages the available bandwidth. In this way more calls can be admitted and the utilisation of the network is increased. View full abstract»

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  • Energy-efficient quality-of-service-aware cooperation in wireless networks

    Page(s): 1696 - 1708
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (841 KB)  

    Conventional cooperative diversity techniques consider a three-node setup, which involves a pair of source-destination nodes and a signal relay node. It is noted that the existing cooperation schemes are performed in a session-based manner in which the role of each node being a source or relay remains unchanged during each session. The radio resource allocation and the associated performance analysis are not jointly performed. As a result, resource utilisation is less efficient. In this paper, an energy-efficient quality-of-service (QoS)-aware cooperative transmission strategy based on joint resource allocation is proposed. Two source nodes with distinct destinations and QoS requirements are simultaneously considered in resource allocation to optimise the energy efficiency. The QoS outage probability is derived analytically and the attainable energy efficiency is investigated for the proposed scheme. Numerical results show that significant performance gain can be achieved for both node pairs with the proposed cooperation scheme. View full abstract»

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  • ITARS: trust-aware recommender system using implicit trust networks

    Page(s): 1709 - 1721
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (683 KB)  

    Trust-aware recommender system (TARS) suggests the worthwhile information to the users on the basis of trust. Existing works of TARS suffers from the problem that they need extra user efforts to label the trust statements. The authors propose a novel model named iTARS to improve the existing TARS by using the implicit trust networks: instead of using the effort-consuming explicit trust, the easy available user similarity information is used to generate the implicit trusts for TARS. Further analysis shows that the implicit trust network has the small-world topology, which is independent of its dynamics. The rating prediction mechanism of iTARS is based on the small worldness of the implicit trust network: the authors set the maximum trust propagation distance of iTARS approximately equals the average path length of the trust network's corresponding random network. Experimental results show that with the same computational complexity, iTARS is able to improve the existing TARS works with higher rating prediction accuracy and slightly worse rating prediction coverage. View full abstract»

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  • Robust audio hashing based on discrete-wavelet-transform and non-negative matrix factorisation

    Page(s): 1722 - 1731
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (866 KB)  

    Robust audio hashing defines a feature vector that characterises the audio signal, independent of content preserving manipulations, such as MP3 compression, amplitude boosting/cutting, hiss reduction, and so on. It provides a tool for fast and reliable identification of content in audio communications. In this study, the authors propose a new audio hashing based on discrete wavelet transform and non-negative matrix factorisation (NMF). The desirable property of NMF for hashing algorithm is its non-negative constraints, which result in bases that capture local feature of the audio, thereby significantly reducing misclassification. In addition, to ensure perceptual robustness, NMF is performed on the coarse wavelet coefficients, which are a low-pass approximation of the audio and not easy to change by content preserving manipulations. Experimental results over a large database reveal that the proposed scheme is more robust and provides much stronger discrimination than the conventional energy spectrum-based hashing algorithm, and that the proposed scheme can be applied in broadcast monitoring, successfully. View full abstract»

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  • Dynamic multi-objective routing algorithm: a multi-objective routing algorithm for the simple hybrid routing protocol on wireless sensor networks

    Page(s): 1732 - 1741
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (430 KB)  

    This study describes a non-dominated algorithm which we call the dynamic multi-objective routing algorithm (DyMORA) developed to improve the simple hybrid routing protocol (SHRP) in choosing the best route towards the Sink node. The multi-objective approach presented allows simultaneous analysis of the four metrics used in the protocol and generates a Pareto-optimal solution. The performance of SHRP concerned to time convergence and reliability with and without DyMORA was analysed via simulation tool NS-2. The performance of SHRP with DyMORA proved to have closed performance to the original SHRP protocol and in many cases superior performance, despite the use of a more complex election algorithm. View full abstract»

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  • Iterative timing recovery via soft decision metrics of low-density parity-check decoding

    Page(s): 1742 - 1751
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (554 KB)  

    An efficient scheme for iterative timing recovery via soft decision metrics (SDMs) of low-density parity-check (LDPC) decoding is presented. This scheme employs new metrics from LDPC decoding to overcome the difficult problem of timing synchronisation at low signal-to-noise ratios. It also obtains accurate timing acquisition with a search window-aided Nelder-Mead simplex algorithm by maximising the sum of the absolute values of the SDMs. The whole scheme is implemented, and our algorithm is concatenated with the Mueller-Mu-ller algorithm, which performs timing tracking with LDPC decoding feedback. Our scheme has global convergence, moderate complexity and good performance. The simulation results indicate that the performance of the LDPC-coded binary phase shift keying system with rather large timing errors is within 0.1-dB of the ideal code performance at the cost of some computation and storage resources. View full abstract»

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  • Joint transmit/receive one-tap minimum mean square error frequency-domain equalisation for broadband multicode direct-sequence code division multiple access

    Page(s): 1752 - 1764
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    Multicode direct-sequence code division multiple access (DS-CDMA) can flexibly support multimedia services with various data rates simply by changing the code multiplexing order. The use of simple one-tap frequency-domain equalisation (FDE) at a receiver is known to improve the bit error rate (BER) performance of multicode DS-CDMA in a severe frequency-selective fading environment. However, the BER performance improvement is limited due to the presence of the residual inter-chip interference (ICI). The authors propose a joint transmit/receive minimum mean square error (MMSE) FDE, which carries out one-tap transmit FDE and one-tap receive FDE jointly based on the MMSE criterion. The authors theoretically derive a suboptimal set of transmit and receive FDE weights and investigate the BER performance improvement by computer simulation in a freqeuncy-selective Rayleigh fading channel. The proposed scheme improves the received signal-to-interference plus noise ratio after despreading, and consequently, the BER performance can be significantly improved compared to the conventioal receive MMSE-FDE by (a) making the variations in the equivalent channel gain shallower to reduce the residual ICI for large code multiplexing order U and (b) allocating the transmit power to the frequencies having good condition to improve the received signal-to-noise ratio for a small U. This is conformed by the computer simualtion. View full abstract»

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  • Hybrid-arq for layered space time MIMO systems with channel state information only at the receiver

    Page(s): 1765 - 1773
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (539 KB)  

    The authors investigate hybrid automatic repeat request (H-ARQ) schemes for spatially multiplexed multiple-input multiple-output (MIMO) systems with channel state information available only at the receiver. In particular, the authors compare the multiple H-ARQ scheme and the single H-ARQ scheme with repetition. The authors first propose a system model for symbol detection for the multiple H-ARQ processes, and then discuss joint and separate detection algorithms for both multiple H-ARQ and single H-ARQ. Simulation results show that with linear detection the single H-ARQ outperforms multiple H-ARQ in the high signal-to-noise ratio region. With the vertical Bell Labs space-time (V-BLAST) architecture, multiple H-ARQ always outperforms single H-ARQ. Additionally, joint detection always outperforms separate detection. View full abstract»

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IET Communications covers the theory and practice of systems, networks and applications involving line, mobile radio, satellite and optical technologies for telecommunications, and Internet and multimedia communications.

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