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1.
Half‐duplex amplify‐and‐forward (AF) transmissions may result in insufficient use of degrees of freedom if they always use the cooperative mode regardless of the fading states. In this paper, we investigate the conditions under which cooperation offers better performance and the corresponding optimal power allocation during cooperation. Specifically, we first derive an expression of ergodic capacity and its upper bound for an AF cooperative communication system with n relay nodes. Secondly, we propose a novel quasi‐optimal power allocation (QOPA) scheme to maximize the upper bound of the derived ergodic capacity. For the QOPA scheme, the cooperative mode is only adopted when the channel gain of source‐to‐destination is worse than that of relay‐to‐destination. Moreover, we analyze the performance of the system with QOPA scheme when the relay moves, which is based on the random direction model, in a single‐relay wireless network. For a multi‐relay AF network, we compare the ergodic capacity and symbol error rate, corresponding to the proposed QOPA and equal power allocation schemes, respectively. Extensive simulations were conducted to validate analytical results, showing that both ergodic capacity and symbol error rate of the system with QOPA scheme are better than those of the system with equal power allocation scheme in a multi‐relay AF network. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
2.
An Li Yizhu Xu Yuhao Wang Lihua Sun 《International Journal of Communication Systems》2015,28(10):1621-1627
This paper deals with the use of jamming transmission for secure amplify‐and‐forward‐based relay networks with total power constraints. An approach that the source and the relay use some of their available power to transmit jamming signals in order to create interference at the eavesdropper is investigated. Assume that the relay and destination have an a priori knowledge of the jamming signals. A power allocation policy that defines how the available power is distributed between the message signal and that of the jamming signal is presented. The results show that the proposed approach can increase the secrecy level and that a positive secrecy rate can be achieved even when the eavesdropper may be near the source. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
Hui Zhi Xiangdong Jia Longxiang Yang Haiyang Fu 《International Journal of Communication Systems》2014,27(3):403-421
In this paper, we investigate the statistical characteristics of the equivalent end‐to‐end signal‐to‐noise ratios (SNRs), the average symbol error ratios (SERs), and the optimal power allocation (OPA) for two‐way amplify‐and‐forward opportunistic relaying (TWOR‐AF) systems. First, with strict mathematic manipulation, we obtain the closed‐form solutions to the PDF, CDF, and moment generating function of the end‐to‐end SNRs. Then, based on the obtained statistical results, we present the total average SER of the Non‐OPA TWOR‐AF systems by using the appropriate approximation, in which only the greater segment of the two terminal SERs is considered. Finally, by aiming at minimizing the total average SER and using the SNRs balancing condition at both transceivers, we study the OPA problem subject to a total transmission power constraint. The comparison analysis shows that, for the Non‐OPA TWOR‐AF systems, we can only evaluate exactly the greater segment of the two SERs of the received signals at two transceivers by using the derivations. However, for the OPA TWOR‐AF systems, with our derivations we can evaluate exactly not only each segment of the two terminal SERs but also the sum SER (exact total SER). Moreover, the simulations show the OPA TWOR‐AF systems outperform the Non‐OPA TWOR‐AF systems. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
Chia‐Chang Hu Bo‐Hung Chen Yi‐Chi Kao 《International Journal of Communication Systems》2016,29(11):1777-1789
This paper focuses on the layered relay‐and‐antenna selection (LRAS) for achievable sum‐rate (ASR) maximization while considering the impacts of residual self‐interference due to channel estimation errors in multiple‐input multiple‐output two‐way amplify‐and‐forward relaying systems. Two LRAS algorithms, namely, the Gram–Schmidt and the adaptive discrete stochastic approximation selection techniques, are investigated based on the ASR maximization under an equal power allocation. To alleviate the complexity burden of the LRAS strategies, the optimal relay and the subset of transmit‐and‐receive antenna pairs are determined by a two‐stage selection mechanism. By taking two LRAS strategies and correlated channel uncertainties into account, the development of a two‐way multiple‐input multiple‐output multi‐amplify‐and‐forward‐relay system is able to provide improved robustness against the channel state information mismatch and the residual self‐interference. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
5.
Mohammad Abdizadeh Hadi Jamali‐Rad Bahman Abolhassani 《International Journal of Communication Systems》2014,27(12):3791-3804
We study the problem of optimizing the symbol error probability (SEP) performance of cluster‐based cooperative wireless sensor networks. Recent studies in literature show that an efficient relay selection protocol based on simple geographical information of the nodes to execute cooperative diversity can significantly improve the SEP performance at the destination of such networks. As well, similar line of research on optimal power allocation (for the source and relay nodes) can be found in literature. However, to achieve the best SEP performance at the destination of a cooperative wireless sensor network, joint optimization of power allocation and relay placement should be accomplished. To this aim, we reformulate the SEP of a multi‐hop cooperative communication in a general form and optimize transmitted power level and relay placement simultaneously. This analysis is developed for both amplify‐and‐forward and decode‐and‐forward relaying protocols. Simulation results demonstrate that the proposed joint optimization can effectively improve the SEP performance of the network. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
6.
Minghe Mao Ning Cao Yunfei Chen Haobing Chu 《International Journal of Communication Systems》2016,29(7):1293-1304
Because of the multiplication of fading gains and noise, the actual distributions of the received signals in multi‐hop amplify‐and‐forward relaying systems are no longer Gaussian. In this work, they are fitted with the t location‐scale distribution and the logistic distribution. Using these distributions, two novel noncoherent detectors are proposed based on the maximum likelihood method. Numerical results show that both new detectors outperform the conventional energy detector. The performance gain increases when the signal‐to‐noise ratio increases or when the hop number decreases. Importantly, the bit error rate of the conventional energy detector reaches an error floor while the bit error rates of the new detectors do not. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
7.
Ehsan Soleimani‐Nasab Sepideh Javadi 《International Journal of Communication Systems》2021,34(1):e4644
In this paper, we investigate the performance assessment of a bidirectional relaying system using energy harvesting techniques. We assume independent and nonidentically distributed (i.n.i.d.) Nakagami‐m fading channels where the amplify‐and‐forward relay is subject to co‐channel interference (CCI) due to transmissions of other transmitters. Two different scenarios, namely, scenario I and scenario II are evaluated. In scenario I, both end‐sources provide the required energy for the relay, whereas the relay also harvests energy from the co‐channel interferes. Then, in the first phase of cooperation, both end‐sources send the information to the relay, and after amplifying the received signal, relay transfers information to the appropriate destination in the second time‐slot. In the scenario II, both end‐sources harvest energy from the relay. After that, the information cooperative transmission is done similar to the first scenario. For both considered scenarios, tight closed‐form expressions of outage probability, symbol error probability, ergodic capacity, and throughput are obtained at arbitrary signal‐to‐noise‐ratios (SNRs). To get more insights, simplified high SNR results for both scenarios are also deduced where the diversity orders are obtained. Monte Carlo simulation results are presented to validate the correctness of our proposed analysis. Our results explicitly demonstrate that the first scenario has a better performance than the second one in the medium and high SNR region, whereas the second scenario outperforms the first one in the low SNR regime. 相似文献
8.
Cooperative communication based on relaying nodes has been considered as a promising technique to increase the physical layer security (PLS) performance in wireless communications. In this paper, an optimal power allocation (OPA) scheme based on Nelder‐Mead (NM) algorithm is proposed for improving the secrecy rate of amplify‐and‐forward (AF) cooperative relay networks employing cooperative jamming (CJ) scheme. The proposed hybrid jamming scheme allows the source and selected relay to transmit the jamming signal along with the information to confound the eavesdropper. The path selection probability of ant colony optimization (ACO) algorithm is used for selecting the relay for transmission. The performance based on secrecy rate is evaluated for “n” trusted relays distributed dispersedly between the source and destination. Gradient‐based optimization and three‐dimensional exhaustive search methods are used as benchmark schemes for comparison of the proposed power optimization algorithm. The secrecy performance is also compared with conventional AF scheme and CJ scheme without power optimization (EPA). The impact of single and multiple relays on secrecy performance is also evaluated. Numerical results reveal that, compared with the gradient method and exhaustive search algorithm, the proposed power allocation strategy achieves optimal performance. Also, the derived OPA results show a significantly higher secrecy rate than the EPA strategy for both CJ and AF schemes. 相似文献
9.
Two‐path or successive relaying, which aims to establish two relay links transmitting different information symbols in adjacent time slots, has recently emerged as an attractive wireless communication protocol to improve the spectral efficiency in half‐duplex cooperative systems. In this paper, we investigate power allocation and relay selection techniques for amplify‐and‐forward two‐path successive relaying networks. Our approach is based on the maximization of the received SNR subject to a total power budget consumed by the source and the relay assisting this specific transmission. Two scenarios including with and without direct link are considered here. We show that the main problem has a closed‐form solution and only requires a few amounts of feedback bits to be broadcasted. Numerical results reveal that the proposed approaches are more insensitive to the inter‐relay interference and robust to channel estimation errors; meanwhile, they perform better than the existing schemes. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
10.
The performance of wireless communication systems is improved over flat fading channel by using Alamouti coding scheme, which provides the quality of diversity gain. In this paper, performance analysis of symbol error rate (SER) and particle swarm optimization (PSO)–based power allocation (PA) for Alamouti amplify and forward (AF) relaying protocol using maximum ratio combining (MRC) technique is presented. Analytical expression of SER upper bound and SER approximation is derived for Alamouti AF relaying protocol with quadrature phase shift keying (QPSK) modulation over Rayleigh fading channel and Rician fading channel. In addition, PSO‐based optimum PA factor is calculated on the basis of the minimum SER of proposed method. PSO‐based optimum PA gives 0.5 dB of improved signal‐to‐noise ratio (SNR) compared with the equal power allocation (EPA). The theoretical approximate SER result is compared with the simulated SER. The proposed protocol provides full diversity gain and reduces SER compared with the existing AF and decode and forward (DF) relaying protocols over Rayleigh fading channel and Rician fading channel. 相似文献
11.
A kind of amplify‐and‐forward (AF) and decode‐and‐forward (DF) mixed relay communication system is proposed in this letter. The source broadcasts the signal to all the relays. Relays that can decode the signal adopt DF scheme to retransmit the signal, while the rest adopt AF scheme for retransmission. The destination employs maximum ratio combining technique to maximize the received signal‐to‐noise ratio. Another situation concerned in this letter is that when the relay cannot decode the source signal, it may retransmit the interference signal with AF scheme. Closed‐form expressions of outage probability are derived. Simulation results show that the analytical curves agree with the simulated ones very well, and the AF‐DF mixed relay system can improve the availability of the relays. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
12.
13.
Hassan A. Ahmed Ahmed Iyanda Sulyman Hossam S. Hassanein 《Wireless Communications and Mobile Computing》2013,13(8):734-744
This paper analyzes the bit error rate performance of orthogonal frequency‐division multiplexing systems in mobile multihop relaying channels. We considered the uplink scenario and quantified the effects of mobile channel impairments such as Doppler shift due to user mobility per hop, high power amplifier distortions when amplifying the transmitted/relayed orthogonal frequency‐division multiplexing symbol per hop, and the cumulative effects of these impairments on multihop relaying channels. It was shown that the resulting intercarrier interference due to the cumulative effects of the phase noise generated by these impairments per hop becomes very significant in a multihop relaying communication system and severely degrades the bit error rate performance of the system. Simulation results agree well with and validate the analysis. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
14.
Tan N. Nguyen Phuong T. Tran Miroslav Vozňák 《International Journal of Communication Systems》2018,31(13)
In this paper, we apply the power splitting–based energy‐harvesting protocol to enhance the transmission between a wireless access point and a mobile user via a helping relay. The mobile user exploits the energy supplied by the access point and forwarded by the relay to transmit its own data back to the access point, again with the helping of the relay. Here, the effect of various system parameters, including power‐splitting factor and the power‐to‐noise ratio on the system performance, is rigorously studied, with closed‐form expressions for the outage probability and system throughput as the results. Furthermore, we figure out the optimal power‐splitting ratio at which the information throughput from the user to the AP is maximized, subject to the constraint on the transmitting power at the access point. All above analytical results are also supported by Monte Carlo simulation. 相似文献
15.
Shao‐I Chu Wei‐Cheng Lin Hung‐Peng Lee Hsin‐Chiu Chang 《Wireless Communications and Mobile Computing》2013,13(16):1464-1481
This paper derives the asymptotic symbol error rate (SER) and outage probability of decode‐and‐forward (DF) cooperative communications over Rician fading channels. How to optimally allocate the total power is also addressed when the performance metric in terms of SER or outage probability is taken into consideration. Analysis reveals the insights that Rician factor has a great impact on the system performance as compared with the channel variance, and the relay–destination channel quality is of importance. In addition, the source–relay channel condition is irrelevant to the optimal power allocation design. Simulation and numerical evaluation substantiate the tightness of the asymptotic expressions in the high‐SNR regions and demonstrate the accuracy of our theoretical analysis. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
16.
Shashika Biyanwilage Upul Gunawardana Ranjith Liyanapathirana 《International Journal of Communication Systems》2015,28(10):1640-1656
In this paper, we study power allocation in OFDM cognitive radio (CR) relay networks. The objective of power allocation is to maximize the instantaneous capacity of the CR network. It is assumed that the available channel state information between the secondary and primary users is an outdated but correlated version of the actual instantaneous channel state information. Optimal power allocation schemes are developed for both decode‐and‐forward and amplify‐and‐forward relay assisted CR transmission, assuming that the primary users are subject to average interference constraints and the CR transmitters are subject to maximum transmit power constraint. In addition, suboptimal power allocation schemes with reduced complexity are also proposed. Performance of the proposed schemes is compared with uniform power allocation and numerical results confirm that the proposed power allocation schemes achieve significant capacity improvement in comparison to uniform power loading. Furthermore, the proposed suboptimal power allocation schemes can be used as less complex alternatives for optimal power allocation with some capacity degradation. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
17.
Mohammed W. Baidas Mohammed S. Bahbahani 《Wireless Communications and Mobile Computing》2016,16(5):500-518
In this paper, distributed single relay selection in cooperative wireless networks is modeled as a Chinese restaurant game (CRG). Specifically, the CRG is used to model strategic relay selection decisions of source nodes, taking into account negative network externality due to the potential sharing of relay nodes among source nodes. Two cases are studied as follows: (i) perfect relay transmit power (RTP) knowledge and (ii) imperfect RTP knowledge. Under the first case, a distributed relay selection algorithm is proposed and shown to converge to a Nash equilibrium grouping. Under the second case, a reinforcement learning algorithm is proposed and combined with the distributed relay selection algorithm to allow network nodes to select rate‐maximizing relays. Simulation results verify the efficiency of the proposed distributed relay selection algorithm when compared with other relay selection schemes and demonstrate that it yields a network sum‐rate that is comparable with that of centralized relay selection. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
18.
An artificial noise strategy is proposed for amplify‐and‐forward bi‐directional relay network where the eavesdropper can wiretap the relay channels in both hops. Artificial noise is used to confuse the eavesdropper and improve its secrecy. Specifically, the source and the relay are allowed to split their available transmit power into 2 parts: a useful information portion and a jamming portion to transmit a jamming signal. The mathematical model is established for 2‐way relay network with an eavesdropper. The secrecy rate achieved by using artificial jamming is derived from the above model. The optimal power allocation with individual power constraint is obtained via sequential quadratic programming to maximize the secrecy sum rate, and 2 special cases are investigated. Furthermore, the benchmark is provided for the purpose of performance comparison. Simulation results show that the proposed strategy can significantly improve the secrecy sum rate by using artificial noise to jam the eavesdropper. 相似文献
19.
In this paper, a fixed‐gain amplify‐and‐forward relaying under non‐ideal hardware is analyzed. The relaying system is impaired because of relay's power amplifier (PA) nonlinearity and in‐phase and quadrature‐phase (IQ) imbalance at a destination. Closed‐form expressions for outage probability as well as ergodic capacity approximation and its upper bound are derived. Also, the outage probability and the ergodic capacity asymptotic expressions in the high signal‐to‐noise ratio are deduced. For the first time, the joint influence of PA nonlinearity and IQ imbalance on the system in terms of outage probability, symbol error rate, and ergodic capacity is investigated. The results are compared with the respect to soft envelope limiter and traveling‐wave tube amplifier at the relay. Based on the analytical and the numerical results, important insights into the impact of IQ imbalance and nonlinearity of the aforementioned PA models on the system performance are gained as well as valuable information on the performance of practically deployed fixed‐gain amplify‐and‐forward relaying system. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
20.
Kamel Tourki Mohamed‐Slim Alouini Khalid A. Qaraqe Hong‐Chuan Yang 《Wireless Communications and Mobile Computing》2015,15(2):367-378
Opportunistic relaying in cooperative communication depends on careful relay selection. However, the traditional centralized method used for opportunistic amplify‐and‐forward protocols requires precise measurements of channel state information at the destination. In this paper, we adopt the max–min criterion as a relay selection framework for opportunistic amplify‐and‐forward cooperative communications, which was exhaustively used for the decode‐and‐forward protocol, and offer an accurate performance analysis based on exact statistics of the local signal‐to‐noise ratios of the best relay. Furthermore, we evaluate the asymptotical performance and deduce the diversity order of our proposed scheme. Finally, we validate our analysis by showing that performance simulation results coincide with our analytical results over Rayleigh fading channels, and we compare the max–min relay selection with their centralized channel state information‐based and partial relay selection counterparts. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献