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Communications, IET

Issue 5 • Date March 25 2011

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Displaying Results 1 - 18 of 18
  • Power allocation for orthogonal frequency division multiplexing-based cognitive radio systems with and without integral bit rate consideration

    Page(s): 575 - 586
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (971 KB)  

    Cognitive radio (CR) has been recognised as one of the promising technologies to provide efficient utilisation of the limited wireless spectrum. The authors investigate the power allocation problem for orthogonal frequency division multiplexing (OFDM)-based CR systems that coexist with primary networks. Specifically, in two scenarios with and without integral bit rate constraint, the authors study the secondary users (SUs) power allocation under both individual transmit power constraints of their own and interference power constraints of all the primary users. When the bit rate of SUs can be continuous on each OFDM subchannel, an efficient power allocation algorithm that contains two level Lagrangian dual variable iterations is proposed to maximise the CR system sum-rate. Besides, when integral bit requirement exists, a heuristic power allocation and bit loading methodology which based on the iterative power rescaling operation is developed. Simulation results show that the algorithm proposed for the continuous rate case can achieve the same rate performance as the standard interior-point algorithm, but converges much faster. The proposed allocation scheme for the discrete rate case has the same bit rate performance as the greedy-based Max-Min scheme. View full abstract»

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  • Multimedia streaming using partially reliable concurrent multipath transfer for multihomed networks

    Page(s): 587 - 597
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (769 KB)  

    The authors propose a partially reliable-concurrent multipath transfer (PR-CMT) protocol for multimedia streaming. The novelty of PR-CMT is to combine techniques of CMT's concurrent multipath transfer, PR-SCTP's partially reliable transmission and prioritised stream transmission. Moving picture experts group (MPEG) frames are with varying priorities and lifetime. PR-CMT can transmit important frames before other frames but does not transmit lifetime expired frames. The combination of the aforementioned techniques, however, causes imprecise congestion window and receiver buffer blocking problems without suitable control. Consequently, the throughput and video quality degrade. PR-CMT adopts the concept of delay abandoning data to resolve the imprecise cwnd and the receiver buffer blocking problems. The simulation results show that PR-CMT can precisely infer cwnd. Most importantly, PR-CMT can prevent large gaps between two playable frames to have good video quality. View full abstract»

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  • Achieving higher uplink performance and capacity via non-overlapping window adaptive maximum noise fraction beamforming technique

    Page(s): 598 - 605
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (443 KB)  

    This study introduces a practical use of maximum noise fraction (MNF) in beamforming antennas that enhances users' uplink performance and capacity in cellular systems. The study introduces a non-overlapping window adaptive MNF technique. In addition, it mathematically analyses the proposed method. Moreover, the performance benefits created via MNF technique in uplink scenarios is also studied. A multi-carrier wideband code division multiple access (MC-WCDMA) system is used as a toy example to represent the benefits created by the proposed technique when it is used as a beamformer. The performance of the proposed technique for uplink MC-WCDMA is mathematically analysed. Simulations are conducted to study the performance and the capacity of the proposed method. The effect of the noise covariance matrix estimation that is vital for the operation of MNF systems on the performance is investigated. View full abstract»

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  • Blind signal detection algorithm for MIMO-OFDM systems over multipath channel using PARALIND model

    Page(s): 606 - 611
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (277 KB)  

    The authors consider the link of parallel profiles with linear dependencies (PARALIND) model with multiple-input multiple-output orthogonal frequency division multiplexing receiver. The authors derive a PARALIND-based blind receiver algorithm that has much close performance to non-blind minimum mean-squared error and it has better performance than constant modulus method. Neither the channel state information nor statistical characteristic is a necessity for the presented PARALIND algorithm, whereas the proposed algorithm distinctively supports small sample sizes. Numerical results verify its useful behaviour. View full abstract»

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  • Performance analysis on carrier scheduling schemes in the long-term evolution-advanced system with carrier aggregation

    Page(s): 612 - 619
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (633 KB)  

    Carrier aggregation (CA) is one of the promising techniques for the further advancements of the third-generation (3G) long-term evolution (LTE) system, referred to as LTE-Advanced. When CA is applied, a well-designed carrier scheduling (CS) scheme is essential to the LTE-Advanced system. Joint user scheduling (JUS) and separated random user scheduling (SRUS) are two straightforward CS schemes. JUS is optimal in performance but with very high complexity, whereas SRUS is contrary. Consequently, the authors propose a novel CS scheme, termed as `separated burst-level scheduling` (SBLS). In SBLS, the connected component carrier (CC) of one user can be changed in burst level, whereas in SRUS, it is fixed. Meanwhile, SBLS limits the users to receive from only one of the CCs simultaneously, which is the same as that in SRUS. In this way, SBLS is expected to achieve higher resource utilisation than SRUS but with acceptable complexity increase. There are two factors that are important to the performance of SBLS, namely the dispatching granularity and the dispatching policy. The authors` analysis is verified by system-level simulations. The simulation results also show that the resultant performance gain of SBLS over SRUS is notable and increasing dispatching granularity will quickly deteriorate the performance of SBLS. View full abstract»

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  • Robust on-demand routing mechanism for wireless multi-hop networks

    Page(s): 620 - 628
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (485 KB)  

    All traditional on-demand routing protocols for wireless networks perform well if routing is provided with few optimised fixed routes before transmissions, and each hop uses a fixed neighbour for forwarding a packet. This strategy, however, cannot be adopted effectively in practical dynamic environments with frequent transmission failures. By taking advantage of the broadcast nature of wireless media the authors propose a novel opportunistic routing scheme to overcome the drawbacks of wireless transmission called `network layer broadcast with confirmed opportunity routing` (NBC-OPP). NBC-OPP features a forwarding list built between source and destination upon the route request and route reply messages. Using the simulation of various network scenarios the authors have demonstrated the superior performance of this new method over traditional deterministic routing schemes for packet delivery, end-to-end delay and route control message load, especially for large node density, bad channel state and low traffic rate conditions. View full abstract»

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  • Spectral efficiency analysis of rate-adaptive user selection diversity in orthogonal space time block coding multiple-input multiple-output systems with antenna selection

    Page(s): 629 - 643
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1492 KB)  

    In this study, the performance of user selection diversity for rate-adaptive multiuser multiple-input multiple-output (MIMO) systems employing orthogonal space time block coding (OSTBC) is analysed and evaluated. An antenna selection scheme is used to overcome the drawback of channel hardening effects in multiuser MIMO systems. Closed-form expressions for the average spectral efficiency and outage probability of the system are derived. Using numerical evaluations the considered schemes are compared in terms of outage probability and spectral efficiency. The effects of antenna correlation at the receiver ends on the performance of the system are analysed and evaluated, indicating that spatial correlation may be beneficial for the spectral efficiency of the multiuser OSTBC MIMO systems employing user selection. View full abstract»

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  • Two-stage reinforcement-learning-based cognitive radio with exploration control

    Page(s): 644 - 651
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (407 KB)  

    This study presents a novel two-stage reinforcement-learning-based algorithm for distributed cognitive radio (CR) spectrum sharing. The traditional reinforcement-learning model is modified in order to be applied in a fully distributed CR scenario. CRs are able to discover the best available resources autonomously by utilising learning, which results in significantly improved performance, while reducing the need for spectrum sensing. Instead of sensing all available spectrum arbitrarily, the scheme is designed to share the spectrum based on an optimal spectrum sharing strategy, which is discovered by the CR agents from their trial-and-error interactions with the wireless communication environment. On the other hand, the inherent exploration against exploitation trade-off seen in reinforcement learning is also examined in the context of CR. A `warm-up` stage is proposed to effectively control the exploration phase of the learning process. A better system performance can be expected by carefully balancing the tradeoff between exploration and exploitation. The benefit of applying a warm-up stage is demonstrated. Comparisons of system performance using different warm-up strategies are also given to illustrate their impact on the spectrum sharing process. View full abstract»

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  • Ergodic and outage capacity of interference temperature-limited cognitive radio multi-input multi-output channel

    Page(s): 652 - 659
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (503 KB)  

    In this study, we consider a cognitive radio multi-input multi-output (CR-MIMO) system in which the cognitive radio (CR) users are allowed to access the spectrum of the licensed primary users, provided that interference power received at the primary receiver is less than a certain threshold. The authors investigate the effect of the MIMO diversity on such multi-constraint CR-MIMO systems. They consider peak interference power constraint at the primary receiver and peak transmit power constraint at the CR transmitter. In MIMO systems, the allowable transmit power is distributed over the transmit-antennas. The power allocation problem of such CR systems is studied under both sum power and interference constraints. The authors show that the equal power allocation does not improve the ergodic capacity but improves the outage capacity over the single-input single-output (SISO) system. Transmit antenna selection (TAS) which is a special case of power allocation is also investigated. The authors show that, under the peak interference and transmit power constraint, selecting a single transmit-antenna and allocating all the power to the selected best antenna achieves the same performance as the optimal power allocation (OPA). The authors evaluate ergodic capacity and outage capacity for both power allocation- and antenna selection-based schemes. The closed-form expressions of the outage probabilities are also derived. Results show that both OPA and TAS significantly improves the capacities over the SISO system. View full abstract»

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  • Hierarchical approach to interference mitigation in multi-cell downlink orthogonal frequency-division multiple-access networks with low feedback

    Page(s): 660 - 666
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (339 KB)  

    A low-complexity and low-feedback interference mitigation scheme is developed for multi-cell orthogonal frequency-division multiple-access (OFDMA) cellular systems. The problem is formulated as a weighted sum-rate maximisation problem for all users in the network. The centralised solution assuming full feedback of interfering base stations (BSs) from each mobile on each subchannel is prohibitively expensive in terms of computational complexity and feedback overhead. A hierarchical solution is proposed where the BSs solve only localised resource allocation problems, whereas a centralised controller arbitrates the conflicts of interest among different cells. Moreover, the mobiles apply simple threshold rules to reduce the feedback to the BSs. The simulation results show significant savings in the BS-mobile signalling as well as the signalling between the radio network controller (RNC) and the BSs, while maintaining comparable performance to the case of full feedback. View full abstract»

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  • Improving the internet protocol-based authentication process in a cooperative beyond third-generation network

    Page(s): 667 - 675
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (506 KB)  

    Under the beyond third-generation (B3G) vision, cellular operators (like Vodafone, T-mobile) construct a complementary environment - public wireless local area network (PWLAN) to compensate for the limited data access service to become cellular/PWLAN operators. In addition, PWLAN service coverage can be improved by bringing together various types of PWLAN operators, including PWLAN operators, cellular/PWLAN operators and PWLAN roaming brokers under PWLAN roaming agreements. To build a better PWLAN access service, the group formed by heterogeneous PWLAN roaming partners is markedly growing. In such a cooperative service, the user authentication process plays a foremost role for users and involves many back-and-forth authentication message transmissions among the PWLAN partners. Some factors causing the authentication delay are hard to be further improved, such as the authentication network condition since the networks are owned by many PWLAN partners and scattered in the Internet. If the Internet protocol (IP) lookup time for the authentication server can be shortened, the efficiency for the IP-based authentication process can be made. In this article, an improved mechanism for reducing the IP lookup latency prior to conveying authentication messages is presented. With theoretical analyses and simulation results, the proposed scheme can improve the authentication process in a cooperative B3G network. View full abstract»

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  • Game-theoretic approach for pricing strategy and network selection in heterogeneous wireless networks

    Page(s): 676 - 682
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (797 KB)  

    User selection for access network is considered to be one of the distinct features of heterogeneous wireless systems, in which users with multi-network interface terminals can freely select access network for better quality of service with lower expense. On the other hand, service providers (SPs) will have to face more intense competition for attracting more subscribers and increasing their profits, which can be achieved through either non-cooperative or cooperative strategies. In this study, the authors propose a unified quantification model for evaluating the access service of heterogeneous systems. The relation between competitive SPs and users is described by different game models, based on general assumptions and practical application scenarios. A novel network selection scheme for maximising user performance-cost ratio (PCR) is proposed. Numerical results demonstrate that all SPs can achieve Nash equilibrium price under non-cooperative game framework and coalition price for cooperative game case to maximise their absolute profits, and the maximal PCR criterion for user network selection scheme is analysed under different scenarios. View full abstract»

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  • Performance of multi-relay coded cooperative diversity in asynchronous code-division multiple-access over fading channels

    Page(s): 683 - 692
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (883 KB)  

    In this study, multi-relay decode-and forward (DAF) cooperative networks employing convolutional coding are studied for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems over frequency-selective slow fading channels. The authors show that the full benefits of coded cooperative diversity cannot be achieved if no multi-user interference suppression is employed at the cooperative end. The authors consider two scenarios; perfect and imperfect inter-user channels. In that, the bit-error-rate performance of the cooperative system is investigated for an uplink transmission where a decorrelator detector is used at both the relay and base station receivers. Both simulation and analytical results are presented to demonstrate the diversity gains of the convolutionally coded cooperative network. View full abstract»

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  • Non-synchronised time difference of arrival localisation scheme with time drift compensation capability

    Page(s): 693 - 699
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    Location finding is a major application for indoor wireless sensor networks. Some of these applications include, but not limited to, logistic tracking for goods, monitoring of patients in hospitals, security application and location aware advertising. In practice, there are many factors such as noise, non-line of sight (NLOS) influence, device crystal clock time drift and accurate synchronisation among sensor nodes that can affect the ranging accuracy. In this study, the authors first propose how non-synchronised sensor nodes can apply a time difference of arrival localisation technique to compute the position of the tags. Next, the authors discuss the impact of crystal clock time drift on localisation accuracy and propose a scheme to compensate them among the sensor nodes in order to reduce its influence on localisation errors. This allows low-cost devices to operate in the network with low crystal clock qualities. View full abstract»

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  • Topology-aware macro diversity handover technique for IEEE 802.16j multi-hop cellular networks

    Page(s): 700 - 708
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (558 KB)  

    Macro diversity handover (MDHO) is the process by which a mobile station (MS) maintains connection with two or more access stations called a diversity set. In this study, the authors propose a topology-aware MDHO technique for time division duplex (TDD)-orthogonal frequency division multiple access (OFDMA)-based interference-limited multi-hop cellular networks. The proposed MDHO receives all the data signals transmitted by the diversity set members of the MS. It ensures that the topology of the diversity set members is always fully exploited. The efficiency of the proposed MDHO is validated using a mathematical model and computer simulation. The performance evaluation is carried out for different relay station (RS) transmitted powers. Evaluation results show that the proposed MDHO significantly outperforms the conventional MDHO. Over the MDHO regions in which the diversity set members are multi-hop relay base station (MR-BS) and RS, the proposed MDHO offers a carrier to interference and noise ratio gain and a spectral efficiency gain of as much as 4.5 dB and 0.85 bps/Hz, respectively, compared to the conventional MDHO. View full abstract»

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  • Spectrally efficient sensing protocol in cognitive relay systems

    Page(s): 709 - 718
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (577 KB)  

    In this study, the authors consider a cognitive radio scenario and focus on the spectrum efficiency of sensing-transmission protocols for a secondary dual-hop relay system. A straightforward dedicated sensing protocol is first considered as a benchmark, where sensing is performed in dedicated sensing periods at both the source (S) and the relay (R) before their respective transmissions. This, however, leads to a substantial loss in spectrum efficiency for the secondary system. In view of the spectrum efficiency loss in the dedicated sensing protocol, the authors propose an alternative approach, namely simultaneous sensing protocol. In this protocol, sensing is only performed at S, during the period when R transmits to destination (D), by cancelling out the self-interference component that is known a priori. The authors derive the closed-form expression of the average probability of detection for the proposed simultaneous sensing protocol. Furthermore, by deriving the average collision time and average utilisation time for both the dedicated and simultaneous sensing protocols, the authors show that the simultaneous sensing protocol significantly improves the spectrum efficiency for the secondary system and also achieves a higher overall spectrum utilisation of the spectrum band, compared to the dedicated sensing protocol. View full abstract»

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  • Coset graphs for low-density parity check codes: performance on the binary erasure channel

    Page(s): 719 - 727
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1045 KB)  

    The authors show that a popular way of constructing quasi-cyclic low-density parity check (LDPC) codes is a special case of a construction which is common in graph theory and group theory. It is shown that a generalisation of this construction as coset graphs produces (dv, dc)-regular LDPC codes that have an advantage in terms of the minimum stopping set size compared to quasi-cyclic LDPC codes. A (dv, dc)-regular quasi-cyclic LDPC code cannot have minimum stopping set size larger than (dv+1)!. However, by using coset graphs, a (3, 5)-regular LDPC code with minimum stopping set size of 28 and a (3, 4)-regular LDPC code with minimum stopping set size larger than 32 have been obtained. In addition, the idea of coset graphs also provides a compact algebraic way of describing bipartite graph and the associated parity-check matrix of an LDPC code. Simulation results of iterative decoding of the coset graphs LDPC codes over the binary erasure channel show that some of the codes converge well and based on the truncated stopping set distributions of the codes, which are exhaustively and efficiently enumerated, the error-floor of the codes at low probability of erasure is estimated. View full abstract»

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  • Minimum mean squared error design of single-antenna two-way distributed relays based on full or partial channel state information

    Page(s): 728 - 735
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (403 KB)  

    A maximum mean squared error optimal relay beamformer is proposed here for two-way single-antenna distributed relaying systems. A constrained optimisation problem with respect to the relay beamforming vector is first formulated. It is then shown that the design problem of such a relay beamformer supporting both downlink and uplink transmissions simultaneously can be converted to convex optimisation when full channel state information (CSI) is available at the relays. By employing the Lagrangian multiplier method, a closed-form solution for the relaying vector is obtained. The proposed relay beamforming method is also extended to the situation where only the statistics of the CSI are available. A simulation study is conducted to confirm the merit of the proposed two-way relaying scheme. View full abstract»

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