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Communications, IET

Issue 6 • Date April 17 2014

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Displaying Results 1 - 24 of 24
  • Distributed allocation of subcarrier, power and bit-level in multicell orthogonal frequency-division multiple-access networks

    Page(s): 781 - 788
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (442 KB)  

    The downlink of multicell orthogonal frequency-division multiple-access (OFDMA) networks is studied, and the adaptive allocation of spectrum, power and rate is addressed. The authors consider networks with adaptive frequency reuse and discrete-level rates. Initially, the joint allocation problem is formulated as a centralised non-linear mixed-integer program (MIP), which is computationally intractable to solve optimally for practical problem sizes. Then, the capability of the receivers is exploited to estimate the subcarrier channel gains and the joint allocation problem is accordingly decomposed into subproblems, each of which is solved by a different base station with linear complexity. In the proposed iterative algorithm, the base stations perform rate and receiver allocation per subcarrier, with concurrent iterations. A filtering method is introduced to further decrease the algorithm complexity. Furthermore, for benchmarking purposes, the authors transform the original non-linear MIP to a linear MIP and find the optimal solution by means of standard branch-and-cut solvers. The merit of the proposed algorithm is demonstrated with numerical comparisons of its performance against the solutions of the linear MIP and the iterative waterfilling algorithm. View full abstract»

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  • Cognitive opportunistic relaying systems with mobile nodes: average outage rates and outage durations

    Page(s): 789 - 799
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (466 KB)  

    In the existing literature about cognitive radio opportunistic relaying (CR-OR) systems, the first-order statistics such as outage probability are investigated widely. However, for the second-order statistics, such as average outage duration (AOD) and average outage rate (AOR), there is not open works, still. To obtain a comprehensive cognition on the behaviour of mobile communication systems, this study focuses on the second-order statistical properties of CR-OR systems. There are two CR-OR schemes considered, in which the canonical amplify-and-forward (AF) and reactive decode-and-forward (RDF) are employed, respectively. Since the equivalent end-to-end signal-to-noise ratio (SNR) of AF CR-OR is complicated such that it is very difficult to obtain the closed-form solution to AOR of AF CR-OR schemes, the high SNR approximation in AF CR-OR schemes is employed. For the two schemes, first the closed-form solutions to AORs and AODs are obtained by using appropriate mathematical proof. Based on the derivations, the comparison analyses about AORs and AODs of the two schemes are provided. The comparison results show that, under high SNR approximation, the AF CR-OR scheme achieves the same AOR and AOD as RDF CR-OR. Finally, the impact of system parameters on AORs and AODs is provided. View full abstract»

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  • Investigation of the effect of an increased supervisory signal power in a high-loss loopback monitoring system

    Page(s): 800 - 804
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (345 KB)  

    We present experimental results for the effect of an increased supervisory signal power in a high-loss loopback supervisory system in an optically amplified wavelength division multiplexing (WDM) transmission line. The study focuses on the investigation of increasing the input power for the supervisory signal and the effect on the co-propagating WDM data signals using different channel spacing. This investigation is useful for determining the power limitation of the supervisory signal if extra power is needed to improve the monitoring. The study also shows the effect of spacing on the quality of the supervisory signal itself because of interaction with adjacent data signals. View full abstract»

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  • Extended low-density parity-check codes for feedback-based cooperative diversity schemes

    Page(s): 805 - 812
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (602 KB)  

    Cooperative diversity or user cooperation achieves the diversity gain without adding physical antennas to the users or mobile stations. The users work in a cooperative fashion by using their single antennas to create a virtual transmit diversity, called relay diversity or cooperative diversity. The diversity gain achieved by cooperative diversity can be further improved using error correction codes. Low-density parity-check (LDPC) codes are linear block codes with good error correction capabilities. The authors present a novel approach using extended LDPC codes to increase the diversity gain in cooperative diversity. The authors also compare the extended LDPC codes with the punctured LDPC codes in a cooperative diversity and show that there is a performance-complexity tradeoff between the punctured and the extended LDPC codes in the cooperative diversity. Furthermore, the authors will propose two feedback-based protocols for cooperative diversity and compare their throughput with non-feedback-based cooperative diversity using extended LDPC codes. View full abstract»

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  • Uplink scheduling solution for enhancing throughput and fairness in relayed long-term evolution networks

    Page(s): 813 - 825
    Save to Project icon | PDF file iconPDF (902 KB)  
    Freely Available from IEEE
  • Outage probability guaranteed relay selection in cooperative communications

    Page(s): 826 - 832
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (449 KB)  

    This study is focused on the multiple relay selection problem in cooperative communications. The objective is to select the minimum set of relays to minimise the spectrum cost while preserving the signal-to-noise ratio (SNR) requirement at the destination. A probabilistic constraint is adopted to characterise the SNR outage requirement, which turns out to be intractable in general. As a solution, a tractable bound is derived for the outage probability constraint, with which the multiple relay selection problem can be formulated as a mixed integer optimisation problem with the on-and-off power mode at the relays, which is NP-hard. By utilising the intersections of the proposed bound for different relays, the authors propose an outage probability guaranteed relay selection algorithm which can find the optimal solution with significantly reduced complexity. A heuristic algorithm is also proposed for comparison. Extensive simulation results are provided to show the effectiveness of the proposed schemes. View full abstract»

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  • Modified channel-independent weighted bit flipping decoding algorithm for low-density-parity-check codes

    Page(s): 833 - 840
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (562 KB)  

    In this study, a modified channel-independent weighted bit flipping (CIWBF) decoding algorithm is proposed for low-density-parity-check codes. This modification, based on the `additive offset term adjustment' in the reliability of the check sum, can also be applied to the reliability ratio weighted bit flipping algorithm. Simulation results show that the performance of the author's improved modified CIWBF algorithm is better than that of CIWBF algorithm about 0.45 dB at bit-error rate of 10-5 over an additive white Gaussian noise channel without much complexity increase. View full abstract»

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  • Efficient space-frequency block coded pilot-aided channel estimation method for multiple-input-multiple-output orthogonal frequency division multiplexing systems over mobile frequency-selective fading channels

    Page(s): 841 - 851
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (678 KB)  

    An iterative pilot-aided channel estimation technique for space-frequency block coded (SFBC) multiple-input multiple-output orthogonal frequency division multiplexing systems is proposed. Traditionally, when channel estimation techniques are utilised, the SFBC information signals are decoded one block at a time. In the proposed algorithm, multiple blocks of SFBC information signals are decoded simultaneously. The proposed channel estimation method can thus significantly reduce the amount of time required to decode information signals compared to similar channel estimation methods proposed in the literature. The proposed method is based on the maximum likelihood approach that offers linearity and simplicity of implementation. An expression for the pairwise error probability (PEP) is derived based on the estimated channel. The derived PEP is then used to determine the optimal power allocation for the pilot sequence. The performance of the proposed algorithm is demonstrated in high frequency selective channels, for different number of pilot symbols, using different modulation schemes. The algorithm is also tested under different levels of Doppler shift and for different number of transmit and receive antennas. The results show that the proposed scheme minimises the error margin between slow and high speed receivers compared to similar channel estimation methods in the literature. View full abstract»

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  • Improved opportunistic feedback with multiuser diversity for wireless systems with finite queue

    Page(s): 852 - 859
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (490 KB)  

    A contention-based opportunistic feedback protocol has been proposed in the literature, to achieve multiuser diversity for the downlink transmission of a multiuser wireless system, with the assumption that the incoming data for the active users are infinitely backlogged. However, this assumption is not valid if the authors consider the finite-length queuing effect in practical systems. By taking not only the channel states, but also the queuing states into account, the authors propose an improved opportunistic feedback protocol with multiuser diversity, and analyse its performance with adaptive modulation and coding. Additionally, instead of solving a system of equations directly, a simple iterative method is proposed to obtain the stationary distribution of the system, where the system behaviour is modelled by a two-dimensional finite-state Markov chain. Numerical results demonstrate that the authors proposed protocol is superior to the protocol in the literature in terms of the average throughput, the average spectral efficiency and the average packet delay, when considering the queuing dynamics. View full abstract»

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  • An effective approach to alleviating the challenges of transmission control protocol

    Page(s): 860 - 869
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    The transmission control protocol (TCP) has contributed to the tremendous success of the Internet but it also faces many challenges which are becoming more and more significant as the network grows. Although numerous congestion control algorithms have been proposed to improve the performance of TCP in heterogeneous networks, designing a congestion control algorithm that could achieve high utilisation, ensure fairness and maintain stability remains a great challenge. A novel congestion control algorithm named fair TCP (FTCP) has been proposed to mitigate these challenges. FTCP mitigates these challenges through the following strategies: First, increase the round trip time (RTT)-fairness by altering TCP's initial congestion control window (cwnd) and adjusting the cwnd's growth rate to make FTCP flows with different RTTs achieve the same throughput. Secondly, balance the transmission efficiency and TCP-friendliness by dynamically adjusting the aggressiveness of FTCP according to the congestion level of the link. Preliminary experimental evaluations verify that FTCP has obvious advantages in transmission efficiency, RTT-fairness and TCP-friendliness comparing to the state-of-the-art congestion control algorithms. View full abstract»

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  • Adaptive rate and power transmission in spectrum-sharing systems with statistical interference constraint

    Page(s): 870 - 877
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (530 KB)  

    The present study attempted to investigate the capacity gains in a spectrum-sharing system where the transmit power and rate of the secondary user (SU) are adapted based on the spectrum sensing information about activity of primary user (PU) and statistical channel fading gain between the SU transmitter (SUT) and PU receiver (PUR). It was assumed that the SU can use the spectrum band originally allocated to PU, based on the definition that when the PU is present in the spectrum band, the SU must consider the peak transmit power and statistical interference constraints. In addition, when the PU is absent at the spectrum band, the SU can only consider the peak transmit power constraint. The main advantage of using statistical interference constraint is that it does not require the instantaneous feedback channel between SUT and PUR. Furthermore, to maximise the achievable capacity of the SU, the average transmit power was first calculated. Then the adaptive rate and power policy were inspected for maximising the achievable capacity under said constraints and bit error rate requirements in multilevel quadrature amplitude modulation. Numerical and comparison results representing the efficiency of the proposed system are also provided. View full abstract»

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  • Packet error rate-based adaptive rate optimisation with selective-repeat automatic repeat request for convolutionally-coded M-ary quadrature amplitude modulation systems

    Page(s): 878 - 884
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (503 KB)  

    Link adaptation using adaptive modulation and coding (AMC) is a popular physical layer technique for efficient use of time-varying fading channels. Using a cross-layer approach, AMC and truncated automatic repeat request scheme at data link layer are jointly considered. For a convolutionally-coded M-ary quadrature amplitude modulation system under block fading channel condition, a variable rate transmission scheme that uses imperfect channel state information is derived. First, a closed-form expression for approximating packet error rate (PER) is found as a function of coded information rate. It is then shown that by solving an optimisation problem using this expression, optimum transmission rate can be determined in a way that maximises the spectral efficiency while satisfying an average PER constraint. Hence, the parameters in physical and medium access control layers are incorporated in the analysis. View full abstract»

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  • Optimal power allocation for asymmetric analogue network coding in cognitive radio

    Page(s): 885 - 892
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (433 KB)  

    In this study, the optimal power allocation (OPA) problem is studied for the two-way relay channel employing the analogue network coding protocol with the asymmetric traffic requirements in a cognitive radio network. The OPA scheme is proposed by maximising the sum-rate of the success delivery bit from the secondary user (SU) perspective subject to the sum-power constraint and the interference power threshold (IPT) constraints to the primary user (PU). In particular, for the purpose of accomplishing the power allocation more realistically, the interference to each other between the PU and the SU and the relay is taken into consideration and by solving the optimisation problem composed for each case, the closed form expressions of each node power are obtained. All the simulation results have demonstrated that the system with the proposed scheme outperforms the equal power allocation (EPA) scheme irrespective of the IPT. When the IPT constraint is introduced, the sum-rate of the success delivery bit of the SU communication converges to a certain level with the increasing total power. Meanwhile, the proposed strategy is superior to the conventional EPA scheme for any relay location, which is more remarkable when the relay is located on either end node regardless of the traffic symmetry or the asymmetry. View full abstract»

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  • Use of matroid theory to construct a class of good binary linear codes

    Page(s): 893 - 898
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (146 KB)  

    It is still an open challenge in coding theory how to design a systematic linear (n, k) - code C over GF(2) with maximal minimum distance d. In this study, based on matroid theory (MT), a limited class of good systematic binary linear codes (n, k, d) is constructed, where n = 2k-1 + · · · + 2k-δ and d = 2k-2 + · · · + 2k-δ-1 for k ≥ 4, 1 ≤ δ <; k. These codes are well known as special cases of codes constructed by Solomon and Stiffler (SS) back in 1960s. Furthermore, a new shortening method is presented. By shortening the optimal codes, we can design new kinds of good systematic binary linear codes with parameters n = 2k-1 + · · · + 2k-δ - 3u and d = 2k-2 + · · · + 2k-δ-1 - 2u for 2 ≤ u ≤ 4, 2 ≤ δ <; k. The advantage of MT over the original SS construction is that it has an advantage in yielding generator matrix on systematic form. In addition, the dual code C with relative high rate and optimal minimum distance can be obtained easily in this study. View full abstract»

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  • Performance analysis of V-BLAST reception under multiuser decode-and-forward cooperation

    Page(s): 899 - 904
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (261 KB)  

    The performance of a dual-hop system is studied and evaluated, where m single-antenna source nodes communicate with a destination equipped with nm antennas via m single-antenna relays. The decode-and-forward protocol is implemented at the relays whereas the classical ordered V-BLAST scheme is performed at the destination. The analysis involves spatially independent non-identically distributed Rayleigh channel fading channels, reflecting on distinct average received powers among the different source and/or relay nodes with the destination, suitable for practical applications. The identically distributed scenario is also included as a special case. Novel union closed-form system bound expressions are derived in terms of the outage probability and the average symbol error probability. These bounds correspond to the cases of both the perfect and the imperfect channel state information at the relay and the destination nodes. The numerical results, accompanied with the equivalent simulation ones, reveal the accuracy of the proposed approach. View full abstract»

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  • Low-complexity iterative channel estimation with lattice reduction-based detection for multiple-input multiple-output systems

    Page(s): 905 - 913
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (551 KB)  

    Iterative channel estimation and detection (ICED) can provide a better performance as the channel estimation can be improved through iterations. For a multiple-input multiple-output channel, owing to a large size of the signal alphabet, ICED becomes less practical unless a low-complexity detector such as a lattice reduction-based detector is employed. However, since the lattice basis reduction has to be carried out for each iteration, the resulting complexity can be still high. In this study, a computationally efficient technique was proposed to perform the lattice basis reduction within ICED over both static and slowly time-varying block-fading channels, where orthogonal defect of basis, as well as error probability are considered to decide whether or not basis reduction is needed for each iteration. View full abstract»

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  • Blind multiband spectrum sensing for cognitive radio systems with smart antennas

    Page(s): 914 - 920
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    Energy detection is a widely used method for spectrum sensing in cognitive radios because of its simplicity and accuracy. However, it is severely affected by noise uncertainty. To solve this problem, this study raises a blind multiband spectrum sensing method with smart antennas which is robust to noise uncertainty. The proposed method performs spectrum sensing simultaneously over the total frequency channels rather than a single channel each time. Owing to the fact that the noise eigenvectors of the sample covariance matrix are orthogonal to the direction matrix whereas the signal eigenvectors are not, the proposal utilises the Gerschgorin radii of the unitary transformed covariance matrix to distinguish the noise from the signal. Unlike the conventional sensing methods, the authors' approach does not need any prior knowledge of the noise power or the primary user signals, which makes it suitable for blind spectrum sensing. This study presents simulations in various conditions to validate the performance of the proposed scheme and shows that their proposal outperforms the other existing methods. View full abstract»

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  • Power allocation for orthogonal frequency division multiplexing-based cognitive radio networks with cooperative relays

    Page(s): 921 - 929
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    The power allocation problem in orthogonal frequency division multiplexing-based cognitive radio (CR) networks with cooperative relays has been investigated here, where both the interference to primary users (PUs) and the power budget of the CR network are considered. The authors try to maximise the overall throughput of the CR network within the given constraints. The coupling variables in the formulated problem make it hard to solve, so an iterative optimisation scheme to find out the optimal solution with a controllable complexity is developed. First, the original problem is decomposed into two subproblems that can be solved independently. A fast barrier method has been employed to work out the optimal solution to one of the subproblems with a complexity of O(L2N), where L and N are the number of PUs and subcarriers, respectively. Then, an iterative procedure is developed to solve the other subproblem. Numerical results show that the proposed method can significantly increase the throughput of the CR system, comparing with other representative ones. Furthermore, the proposed algorithm gives a general power optimisation framework for CR networks with cooperative relays. View full abstract»

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  • Probabilistic relay assignment strategy for cooperation networks with random relays

    Page(s): 930 - 937
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    A new approach in fairness is proposed by using a probabilistic relay assignment strategy for cooperative communication systems. In this approach, relays are allocated to sources based on a probabilistic relay assignment function, which is characterised by the outage probability. To examine the proposed relay assignment strategy, an exact expression for the outage probability of an opportunistic coded cooperation diversity system is derived. It is assumed that the relays in this system are distributed according to a two-dimensional homogeneous Poisson point process, and the transmission channels undergo Rayleigh fading as well as path loss. It is observed that the proposed strategy reduces the number of requests for using the relays and, thus, utilises the relays more efficiently. Furthermore, compared to the conventional opportunistic relay assignment strategy, the total power consumed by the relays decreases, while the quality of service requirements are still satisfied. View full abstract»

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  • Optimal diversity multiplexing tradeoff for opportunistic relaying coded cooperation protocols with quantised channel state information feedback

    Page(s): 938 - 946
    Save to Project icon | PDF file iconPDF (251 KB)  
    Freely Available from IEEE
  • Application of compressive sensing to limited feedback strategy in large-scale multiple-input single-output cellular networks

    Page(s): 947 - 955
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (562 KB)  

    A novel limited feedback strategy based on a compressive sensing technique is proposed for the downlink large-scale multiple-input single-output (MISO) system. The effectiveness of transmit beamformers relies on the feedback quality of channel state information (CSI). The instantaneous CSI is compressed and sent back to the base station (BS) by receivers. An efficient recovery algorithm is applied at the BS in the presence of measurement noise and feedback link noise. The proposed feedback strategy can provide the BS with much more precise CSI as compared with some conventional vector quantisation schemes. The proposed scheme also has lower-computational complexity. Furthermore, the authors derive a tight lower bound on the user sum rate, assuming that zero-forcing beamforming is applied at the BS, and that active users are semi-orthogonal to each other. Numerical results show that the proposed compressive sensing-based limited feedback scheme yields better performance gain than the conventional channel quantisation approaches. View full abstract»

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  • Performance analysis of asynchronous optical code division multiple access with spectral-amplitudecoding

    Page(s): 956 - 963
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    In this study, the performance of a spectral-amplitude-coding optical code division multiple access (SAC-OCDMA) system in the asynchronous regime is evaluated using a Gaussian approximation of the decision variable for codes with fixed cross-correlation used in SAC-OCDMA systems. The authors consider the effect of phase-induced intensity noise (PIIN), thermal noise and shot noise. Moreover, the validity of the Gaussian approximation is confirmed by a Kolmogorov-Smirnov fitness test. For sake of comparison, the bit error rate (BER) of the asynchronous SAC-OCDMA system is also plotted numerically in comparison with the BER of the synchronous SAC-OCDMA. They show that a SAC-OCDMA system without any time management for the users, that is, the asynchronous regime, has a better performance than the synchronous SAC-OCDMA when PIIN effect exists. View full abstract»

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  • Adaptive user selection of opportunistic multicast scheduling in wireless networks

    Page(s): 964 - 971
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (447 KB)  

    In this study, an adaptive user selection of opportunistic multicast scheduling system (OMS-AUS) scheme is proposed to improve the system throughput performance of opportunistic multicast scheduling system. Different from the previous literatures, the user selection ratio would no longer be a constant, but would vary as the number of users that have not received multicast bits changes, which can exploit the system transmission ability better. The objective is to obtain the optimal values of user selection fractions. (i) For the case without instantaneous channel state information (CSI), a channel gain distribution-based OMS-AUS is proposed. Firstly, a system throughput matrix (STM) is formulated to imitate the user grouping process. Secondly, the value of each element in STM is derived according to the channel gain distribution. Finally, by fully searching the elements in STM, the optimal solution is obtained. To reduce the computational complexity, a suboptimal heuristic searching scheme is also proposed. (ii) For the case with instantaneous CSI, an improved approach based on both the channel gain distribution and instantaneous CSIs is proposed. Simulation results show that both of the two proposed approaches can obtain better performance compared to the existing schemes. View full abstract»

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  • Coded cooperation: generalised outage analysis

    Page(s): 972 - 979
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (371 KB)  

    In this study, the authors derive the exact closed-form expression of the outage probability for coded cooperation using power-based approach. They consider a generalised system model with n relays (n > 1) over Nakagami-m fading channels. They also obtain the optimal number of relays for the given outage performance. Furthermore, they find analytically the critical cooperation ratio at which the total outage probability is minimum. View full abstract»

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