290 research outputs found

    Relay Selection for Bidirectional AF Relay Network with Outdated CSI

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    Most previous researches on bidirectional relay selection (RS) typically assume perfect channel state information (CSI). However, outdated CSI, caused by the the time-variation of channel, cannot be ignored in the practical system, and it will deteriorate the performance. In this paper, the effect of outdated CSI on the performance of bidirectional amplify-and-forward RS is investigated. The optimal single RS scheme in minimizing the symbol error rate (SER) is revised by incorporating the outdated channels. The analytical expressions of end-to-end signal to noise ratio (SNR) and symbol error rate (SER) are derived in a closed-form, along with the asymptotic SER expression in high SNR. All the analytical expressions are verified by the Monte-Carlo simulations. The analytical and the simulation results reveal that once CSI is outdated, the diversity order degrades to one from full diversity. Furthermore, a multiple RS scheme is proposed and verified that this scheme is a feasible solution to compensate the diversity loss caused by outdated CSI.Comment: accepted by IEEE Transactions on Vehicular Technolog

    Impact of outdated channel estimates on a distributed link-selection scheme for AF relaying networks

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    We investigate the impact of outdated channel estimates on the outage performance of a distributed link-selection scheme recently proposed for variable-gain amplify-and-forward relaying networks. In this scheme, either the direct link or the relaying link is preselected before each transmission, based on a distributed mechanism. We begin by showing that an exact analysis is rather intricate, yielding a multifold integral-form solution. Motivated by this, we then derive a simple closed-form lower bound, which, importantly, proves to be a very tight approximation to the exact outage probability. We also assess the system diversity order via asymptotic analysis42185188COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESnão te

    Adaptive Relay-Selection In Decode-And-Forward Cooperative Systems

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    In the past few years adaptive decode-and-forward cooperative diversity systems have been studied intensively in literature. Many schemes and protocols have been proposed to enhance the performance of the cooperative systems while trying to alleviate its drawbacks. One of the recent schemes that had been shown to give high improvements in performance is the best-relay selection scheme. In the best-relay selection scheme only one relaying nodes among the relays available in the system is selected to forward the source\u27s message to the destination. The best relay is selected as the relay node that can achieve the highest end-to-end signal-to-noise ratio (snr) at the destination node. Performance improvements have been reported as compared to regular fixed decode-and-forward relaying in which all relays are required to forward the source\u27s message to the destination in terms of spectral efficiency and diversity order. In this thesis, we use simulations to show the improvement in the outage performance of the best-relay selection scheme

    Performance Analysis of Best Relaying Protocol Selection with Interferences at Relays

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    In this paper, we investigate the performance of selecting the best protocol between amplify and forward (AF) and decode and forward (DF) in multiple relay networks with multiple interferences at relays. In the selection scheme, the best protocol between AF and DF is selected depending on the comparisons of signal-to-interference and noise ratio (SINR) for all source-relay links. All relays measure the received SINR to decide forwarding signal or not. When SINR is above a certain threshold then DF is used otherwise AF is used. Particularly, we develop an accurate mathematical model for best relaying protocol by considering the effect of interferences to our scheme. Firstly, we derive the asymptotic closed form expression for the symbol error rate (SER) for the system under study. Also we derive an upper and lower bound of symbol error rate and show how they were tight with exact SER. Furthermore an approximate expression for the outage probability is derived. Numerical results are finally presented to validate the theoretical analysis with a different number of relays

    Smart Relay Selection Scheme Based on Fuzzy Logic with Optimal Power Allocation and Adaptive Data Rate Assignment

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    In this paper fuzzy logic-based algorithm with improved process of relay selection is presented which not only allocate optimal power for transmission but also help in choosing adaptive data rate. This algorithm utilizes channel gain, cooperative gain and signal to noise ratio with two cases considered in this paper: In case-I nodes do not have their geographical location information while in case-II nodes are having their geographical location information. From Monte Carlo simulations, it can be observed that both cases improve the selection process along with data rate assignment and power allocation, but case-II is the most reliable with almost zero probability of error at the cost of computational complexity which is 10 times more than case-I
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