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Communications, IET

Issue 1 • Date January 2011

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Displaying Results 1 - 12 of 12
  • Performance of multiple-input and multipleoutput orthogonal frequency and code division multiplexing systems in fading channels

    Publication Year: 2011 , Page(s): 1 - 11
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (615 KB)  

    In broadband downlink transmission, orthogonal frequency-division multiplexing (OFDM) combined with code-division multiple access (CDMA) is a prospective technique for high-data rate transmission in future wireless communication systems. By adding spatial diversity, multiple-input and multiple-output orthogonal frequency and code division multiplexing (MIMO-OFCDM) offers superior performance relative to both traditional OFDM systems and single-input and single-output OFCDM (SISO-OFCDM) systems. In this study, the authors present an analytical study and investigation of a MIMO-OFCDM downlink system that hires orthogonal variable spreading factor codes to spread each transmitted symbol in both time and frequency domains. Different gain combining schemes are employed in the frequency domain to recover the data symbols of the desired code channels, and space-time block coding is used to achieve spatial diversity. The more general Ricean fading channel is used to model the MIMO channel. The OFCDM system employs Alamouti transmit diversity scheme with multiple receive antennas. For systems without multi-code interference (MCI), analytical bit-error rate results are obtained and compared with simulation results. The authors also investigate the effect of correlation in frequency domain, where we verify that minimum mean-square error frequency combining is more robust to MCI than equal-gain combining. View full abstract»

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  • Exact symbol and bit error probabilities of linearly modulated signals with maximum ratio combining diversity in frequency nonselective Rician and Rayleigh fading channels

    Publication Year: 2011 , Page(s): 12 - 26
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (890 KB)  

    The exact symbol and bit error probabilities of linearly modulated signals in frequency non-selective Rician fading channels with Lth diversity branches are derived, where coherent detection with maximum ratio combining (MRC) is used at the receiver. For performance evaluation, the multiplicative distortion is combined with the additive Gaussian noise and form an additive noise is formed. This method allows computing the exact symbol and bit error probabilities of M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM), M-ary amplitude modulation (M-AM) and M-ary amplitude modulation phase modulation (M-AMPM) for any arbitrary bit mappings. The results contain several versions of one simple integral. The error probabilities are also obtained for Rayleigh channel, which is a special case of Rice channel. Further, the results for Nakagami-m channel with the integer parameter are found. The results quite match with the previous ones while having simple forms. Also, for some unsolved cases, the exact error probabilities are presented. Simulations are carried out to verify the analytical evaluations. View full abstract»

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  • Transceiver design using linear precoding in a multiuser multiple-input multiple-output system with limited feedback

    Publication Year: 2011 , Page(s): 27 - 38
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (595 KB)  

    The authors investigate quantisation and feedback of channel state information in a multiuser (MU) multiple-input multiple-output (MIMO) system. Each user may receive multiple data streams. The authors design minimises the sum mean squared error (SMSE) while accounting for the imperfections in channel state information (CSI) at the transmitter. This study makes three contributions: first, the authors provide an end-to-end SMSE transceiver design that incorporates receiver combining, feedback policy and transmit precoder design with channel uncertainty. This enables the proposed transceiver to outperform the previously derived limited feedback MU linear transceivers. Second, the authors remove dimensionality constraints on the MIMO system, for the scenario with multiple data streams per user, using a combination of maximum expected signal combining and minimum MSE receiver. This makes each user's feedback independent of the others and the resulting feedback overhead scales linearly with the number of data streams instead of the number of receiving antennas. Finally, the authors analyse the SMSE of the proposed algorithm at high signal-to-noise ratio (SNR) and large number of transmit antennas. As an aside, the authors show analytically why the bit error rate, in the high SNR regime, increases if quantisation error is ignored. View full abstract»

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  • Implementation and performance of parallellised turbo decoders

    Publication Year: 2011 , Page(s): 39 - 50
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1071 KB)  

    In this study, the authors discuss the implementation of a low latency decoding algorithm for turbo codes and repeat accumulate codes and compare the implementation results in terms of maximum available clock speed, resource consumption, error correction performance and the data (information bit) rate. In order to decrease the latency a parallellised decoder structure is introduced for these mentioned codes and the results are obtained by implementing the decoders on a field programmable gate array. The memory collision problem is avoided by using collision-free interleavers. Through a proposed quantisation scheme and normalisation in forward/backward recursions, computational issues are handled for overcoming the overflow and underflow issues in a fixed point arithmetic. Also, the effect of different implementation styles are observed. View full abstract»

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  • Pricing, resource allocation and quality of service in multi-class networks with competitive market model

    Publication Year: 2011 , Page(s): 51 - 60
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (189 KB)  

    This study considers a multi-class network resource in a competitive market where each user endowed with an initial budget will purchase bandwidth from each class of the network resource to maximise its utility function. The authors use revenue as the utility function for the service provider, and enhance Kelly's utility function by including delay as the quality of service (QoS) parameter for users. A competitive equilibrium is reached when the total bandwidth is allocated, each user spends all its budget and the utility functions are independently and simultaneously maximised. The authors prove that such equilibriums always exist and, under fixed bandwidth supply for each class of service, the equilibrium is also unique. Furthermore, the authors discuss how to adjust the initial endowment of each user to meet his or her individual bandwidth constraint, either from constraint on the access network or the limitation of the user equipment. Under this bandwidth constraint condition, the proposed competitive equilibrium yields the price for each class of service, budget redistribution and bandwidth allocation among all users. The competitive market model presented provides a solution for pricing a multi-class network resource and allocating the resource that achieves both higher social utility and better individual satisfaction whereas maintaining the QoS of each class. View full abstract»

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  • Outage performance of orthogonal space-time block codes transmission in opportunistic decode-and-forward cooperative networks with incremental relaying

    Publication Year: 2011 , Page(s): 61 - 70
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (333 KB)  

    In this study, the authors propose an incremental opportunistic decode-and-forward (ODF) cooperation scheme employing orthogonal space-time block codes (OSTBC) under Rayleigh fading channels. Different from existing research, the authors use ODF and OSTBC together to maximise the diversity gain, while incremental relaying is implemented to improve transmission efficiency. Besides, a more practical system model is introduced where multiple geographically isolated nodes are equipped with multiple antennas and the large scale fading is taken into consideration. The exact expression of end-to-end outage probability is derived in the whole signal-to-noise ratio (SNR) region for arbitrary relay number, antenna configuration and incremental relaying trigger value. Through asymptotic analysis, the authors also obtain the closed-form expression of outage probability in high SNR region and derive the expression of diversity order. The results show that the proposed scheme outperforms traditional direct transmission and fixed ODF in arbitrary SNR region. Meanwhile, the outage probability and diversity order depend directly on the relay number, antenna configuration and incremental relaying trigger value. The analytical results can be utilised to facilitate network planning and optimisation. Simulation results are presented to verify the authors analysis. View full abstract»

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  • Quality-of-service performance bounds in wireless multi-hop relaying networks

    Publication Year: 2011 , Page(s): 71 - 78
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (407 KB)  

    The theoretical analysis on quality-of-service (QoS) performances is required to provide the guides for the developments of the next-generation wireless networks. As a good analysis tool, the probabilistic network calculus with moment generating functions (MGFs) recently can be used for delay and backlog performance measures in wireless networks. Different from the existed studies which mostly focused on the single-hop networks with single-user under a two state Markov channel model, this study develops an analytical framework for wireless multi-hop relaying networks under the finite-state Markov channel by using probabilistic network calculus with MGFs. By using the concatenation character of network calculus, the authors regard a two-hop wireless relaying channel as a single server equivalently, which consisting of two dynamic servers in series. When the single-user model is straightforwardly extended and applied in multi-user scenarios, the state space of service process is increased exponentially with the number of users, which is only applicable in case of very small user number. Then, in order to avoid the limitation of user number, the authors propose to reflect the multi-user effects by using the equivalent data rate of the modified service process, whose transition and stationary probabilities are kept unchanged with those in single-user scenarios. Next, delay and backlog bounds of multi-hop wireless relaying networks are derived with the proposed analytical framework. Simulation results show that analytical bounds match simulation results, whose accuracy depends on the required violation probability. The effectiveness of the relaying techniques in improving the performances is also demonstrated. View full abstract»

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  • Classifying network protocols: A 'two-way' flow approach

    Publication Year: 2011 , Page(s): 79 - 89
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (311 KB)  

    The identification and classification of network traffic and protocols is a vital step in many quality of service and security systems. Traffic classification strategies must evolve, alongside the protocols utilising the Internet, to overcome the use of ephemeral or masquerading port numbers and transport layer encryption. This research expands the concept of using machine learning on the initial statistics of flow of packets to determine its underlying protocol. Recognising the need for efficient training/retraining of a classifier and the requirement for fast classification, the authors investigate a new application of k-means clustering referred to as 'two-way' classification. The 'two-way' classification uniquely analyses a bidirectional flow as two unidirectional flows and is shown, through experiments on real network traffic, to improve classification accuracy by as much as 18% when measured against similar proposals. It achieves this accuracy while generating fewer clusters, that is, fewer comparisons are needed to classify a flow. A 'two-way' classification offers a new way to improve accuracy and efficiency of machine learning statistical classifiers while still maintaining the fast training times associated with the k-means. View full abstract»

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  • Adaptive bandwidth allocation model for multiple traffic classes in IEEE 802.16 worldwide interoperability for microwave access networks

    Publication Year: 2011 , Page(s): 90 - 98
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (614 KB)  

    This study presents an adaptive bandwidth allocation model for multiple classes in wireless broadband network, worldwide interoperability for microwave access (WiMAX) (IEEE 802.16). Data to and from Internet are all conveyed through WiMAX links to its final destination. In order to promise the quality of real-time traffic and allow more transmission opportunity for other traffic types, the proposed adaptive bandwidth allocation (ABA) algorithm would first reserve the unsolicited bandwidth for constant-bit-rate traffic (unsolicited grant services). Then, polling bandwidth is allocated for real-time traffic (rtPS) to meet their end-to-end delay constraints and for non-real-time traffic (nrtPS) to meet their minimum throughput requirements. One of the novelties presented by this study is right in that ABA does not greedily overtake too much bandwidth from the lowest-priority class, best effort (BE). Instead, it is very intelligent to only meet the delay constraint of rtPS and the minimum throughput requirement of nrtPS, while it endeavours to avoid any possible starvation of BE traffic. For the purpose of performance evaluation, a four-dimensional Markov chains is built to analyse the proposed ABA. The analytical results are validated by a simulation. Finally, from the comparison with a previous work, the authors observe the performance superiority of the ABA in satisfying the delay constraints (for rtPS), meeting the minimum throughput requirements (for nrtPS) and reducing the average packet drop ratio (for BE), when traffic environments are varied. View full abstract»

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  • Effective adaptive virtual queue: a stabilising active queue management algorithm for improving responsiveness and robustness

    Publication Year: 2011 , Page(s): 99 - 109
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (759 KB)  

    Adaptive virtual queue (AVQ) algorithm is an effective method aiming to achieve low loss, low delay and high-link utilisation at the link. However, it is difficult to guarantee fast response, strong robustness and good trade-off over a wide range of network dynamics. The authors propose a stabilising active queue management (AQM) algorithm - effective-AVQ, as an extension of AVQ, to improve the responsiveness and robustness of the transmission control protocol (TCP)/AQM system. Specifically, a proportional integral derivative (PID) neuron is introduced to tune the virtual link capacity dynamically. Also we derive the parameter self-tuning mechanism for the PID neuron from the Hebbian learning rule and gradient descent approach. The stability condition of the closed-loop system is presented based on the time-delay control theory. The performance of effective-AVQ is validated in the NS2 platform. Simulation results demonstrate that effective-AVQ outperforms AVQ in terms of steady-state and transient performance. It achieves fast response, expected link utilisation, low queue size and small delay jitter, being robust against dynamic network changes. View full abstract»

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  • Adaptive buffer control to minimise delay and guarantee service reliability

    Publication Year: 2011 , Page(s): 110 - 118
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (621 KB)  

    Delay-sensitive real-time applications require average latency to be reduced as far as possible, while maintaining the minimum necessary level of service quality. However, the interaction of these two performance metrics has not received much attention in the current standard air specification of CDMA2000 broadcast services. The authors analyse the performance of the forward error correction employed at the MAC layer of these broadcast services, with respect to the conditions of a fading wireless channel and the size of the error control block (ECB), which is a buffer in the form of a two-dimensional array. As a result, the authors establish the tradeoff between service reliability and delay, and show how it depends on the size of the ECB. The authors go on to propose a novel adaptive error-recovery scheme which dynamically adjusts the size of the ECB to suit the wireless environment of the mobile nodes, using either a moving-average or a weighted-average method. Reducing the service delay as far as possible necessarily compromises the reliability of the service, but the authors scheme still ensures the required minimum reliability. The authors have shown the effectiveness of their scheme through extensive simulations using a detailed threshold model, which accurately describes the statistics of the block error process in a fading channel. The authors also suggest a service implementation scenario to aid in the design. View full abstract»

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  • Lifetime enhancement routing algorithm for mobile ad hoc networks

    Publication Year: 2011 , Page(s): 119 - 125
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (255 KB)  

    In this study, the author investigates the problem of lifetime enhancement of mobile nodes in mobile ad hoc networks. Here, the author uses two metrics namely, residual battery capacity of the node and non-critical node to route the data packets from the source to the destination. The proposed model uses the non-critical node if all the nodes contain residual battery capacity above the threshold value. The proposed model has been simulated using Qualnet Simulator-4.5. The proposed model has compared against the existing algorithms such as minimum total transmission power routing, conditional max-min battery capacity routing and lifetime prediction routing. From the results, the author concludes that the proposed model has reached at the top position in terms of the number of survived nodes, energy saving and number of nodes with zero remaining energy. 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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