多中继合作通信系统的功率分配研究

针对功率分配对于多中继系统的重要性,对混合转发多中继合作系统的功率分配进行了研究,提出了基于等效信噪比最大化的最优功率分配方案。仿真结果表明:合作伙伴的增加对于系统等效信噪比有积极的影响,但不是随着中继数目的增加无限地改善。在多中继混合转发合作系统中,最优的功率分配对于多中继合作系统的性能有很大的改善。     

Symbol error rate analysis and power allocation for hybrid cooperation in Rayleigh fading environment

In this paper, we investigate the symbol error rate (SER) performance and power allocation for hybrid cooperation (HC) system in a Rayleigh fading environment. Specifically, we derive closed‐form and approximate SER expressions for the HC system by using the moment generating function (MGF)‐based approach. However, the resultant SER expressions contain an MGF of the harmonic mean of two independent random variables, which is not tractable in SER analysis. Then, we present simple and tight bounds on the SER to show the asymptotic behavior of the HC system. It is shown that the HC system achieves full diversity order. On the basis of the tight SER bound, the power allocation is investigated. It is found that the optimal power allocation (OPA) of the HC system does not depend on the fading parameter of the source‐to‐destination channel and it only depends on the channel links related to the relay. With the increase of the ratio of mean channel power gains (i.e., the ratio of the relay‐to‐destination channel gain to the source‐to‐relay channel gain), more performance gain can be acquired by using the OPA scheme. Finally, the analytical results are validated through computer simulations. Copyright © 2012 John Wiley & Sons, Ltd.     

AF协作分集中的功率优化分配方案

在慢衰落信道中,协作分集是一种新的空间分集方式。为提高协作通信系统的性能,提出以最小化系统中断概率为目标的功率分配方案。综合考虑所有路径的信道噪声功率,运用注水原理,提出在接收端最大比合并下的最佳功率分配方案。该方案计算简单,且仅需已知各个中继节点的平均信道状态信息,无需在传输中实时更新,因而不增加系统的额外开销。仿真结果表明,该方案与等功率分配方案相比,能显著降低系统的中断概率。     

Optimal power allocation to minimize SER for multinode amplify-and-forward cooperative communication systems

An optimal power allocation （OPA） method with mean channel gains is proposed for a multinode amplify-and-forward cooperative communication system. By making use of M-PSK modulation, a closed-form symbol-error-rate （SER） formulation and corresponding upper bound are first derived. Subsequently the OPA method is utilized to minimize the SER. Comparison of the SER of the proposed OPA method with that of the equal power allocation （EPA） method, shows that the SER of both methods, which is approximately optimal performance, is almost the same when relays are near the source. OPA outperforms the EPA when the relays are near the middle between the source and destination or near the destination. The proposed OPA method depends only on the ratio of mean channel gains of the source-to-relay to those of the relay-to-destination. Extensive simulations are performed to validate the theoretical results.     

Joint precoding and power allocation for multiuser transmission in MIMO relay networks

This paper proposes a joint precoding and power allocation strategy to maximize the sum rate of multiuser multiple‐input multiple‐output (MIMO) relay networks. A two‐hop relay link working on amplify‐and‐forward (AF) mode is considered. Precoding and power allocation are designed jointly at the base station (BS). It is assumed that there are no direct links between the BS and users. Under individual power constraints at the BS and relay station, precoders designed based on zero forcing, minimum mean‐square error and maximum ratio transmission are derived, respectively. Optimal power allocation strategies for these precoders are given separately. To demonstrate the performance of the proposed strategies, we simulate the uncoded bit error rate performance of the underlined system. We also show the difference of the sum rate of the system with the optimal power allocation strategies and with average power transmission. The simulation results show the advantages of the proposed joint precoding and power allocation strategies as expected. Copyright © 2011 John Wiley & Sons, Ltd.     

混合中继转发机制下的资源分配

在基于放大转发( AF)和译码转发( DF)的混合中继转发机制模型下,为了使系统获得最大和速率,提出了相应的资源分配方案,在子载波对混合中继协议的判断选择和最优功率分配算法的基础上讨论了等效信道增益模型和非等效信道增益模型。在非等效信道增益模型中,为了降低计算复杂度提出了一种次优算法。在该机制模型下,系统自适应地选择AF或者DF转发,既克服了两种单一转发模式存在的弊端,又能获得更大的和速率,从而提高了资源利用率。仿真结果表明,当系统功率等因素变化时,该分配方案下的混合中继转发模型与传统的AF和DF模型相比系统和速率分别提高了60%和8%以上,充分说明了该系统的优越性。     

Low complexity bit allocation algorithm for OFDM systems

A bit allocation algorithm is presented for orthogonal frequency division multiplexing (OFDM) systems. The proposed algorithm is derived from the geometric progression of the additional transmission power required by the subcarriers and the arithmetic–geometric means inequality. Consequently, this algorithm has a simple procedure and low computational complexity. Copyright © 2008 John Wiley & Sons, Ltd.     

最小功耗的中继选择与功率分配的联合优化

研究采用放大转发协议的单向和双向中继网络中的中继选择与功率分配的联合优化策略。该策略以一定服务质量(QoS)要求为约束条件,以最小化中继网络中各节点的总功率为目标,建立优化问题。运用凸优化技术,得到了该优化问题的闭合解。仿真结果表明在满足相同的QoS要求下,该最优联合策略较传统的随机选择与等功率分配策略具有较低的功率消耗。     

Joint power allocation and relay selection for decode-and-forward cooperative relay in secure communication

In this paper, we investigate the cooperative strategy with total power constraint in decode-and-forward (DF) relaying scenario, in the presence of an eavesdropper. Due to the difference of channel for each source-relay link, not all relay nodes have constructive impacts on the achievable secrecy rate. Besides, the final achieved secrecy rate depends on both source-relay and relay-destination links in DF relaying scenario. Therefore, the principal question here is how to select cooperative strategy among relays with proper power allocation to maximize the secrecy rate. Three strategies are considered in this paper. First, we investigate the cooperative jamming (CJ) strategy, where one relay with achieved target transmission rate is selected as a conventional relay forwarding signal, and remaining relays generate artificial noise via CJ strategy to disrupt the eavesdropper. Two CJ schemes with closed-form solutions, optimal cooperative jamming (OCJ) and null space cooperative jamming (NSCJ), are proposed. With these solutions, the corresponding power allocation is formulated as a geometric programming (GP) problem and solved efficiently by convex programming technique. Then, to exploit the cooperative diversity, we investigate the cooperative relaying (CR) strategy. An iterative algorithm using semi-definite programming (SDP) and GP together with bisection search method is proposed to optimize the cooperative relaying weight and power allocated to the source and relays. Furthermore, to exploit the advantages of both CR and CJ, we propose an adaptive strategy to enhance the security. Simulation results demonstrate that the efficiency of the proposed cooperative strategies in terms of secrecy rate.     

Power allocation,relay selection and energy cooperation strategies in energy harvesting cooperative wireless networks

In this paper, optimal power allocation and relay selection strategies in energy harvesting cooperative wireless networks are studied. In particular, signal‐to‐noise ratio (SNR)‐maximizing based power allocation and relay selection without and with energy cooperation—via wireless energy transfer—are considered. Moreover, total relay power minimization subject to target end‐to‐end SNR is investigated. The different optimal strategies are formulated as optimization problems, which are non‐convex. Thus, intelligent transformations are applied to transform non‐convex problems into convex ones, and polynomial‐time solution procedures are proposed. Simulation results illustrate that power allocation strategies achieve higher end‐to‐end SNR than relay selection ones. Finally, energy cooperation is shown to be effective in improving end‐to‐end SNR, while total relay power minimization balances end‐to‐end SNR, transmit power consumption, and harvested energy. Copyright © 2016 John Wiley & Sons, Ltd.     

AF中继下行链路系统的能效资源分配方案

为最大化放大转发中继系统的下行链路总能效,结合系统的电路功率,提出了一种基于能效的中继选择和功率分配联合方案.为降低复杂度,采用分步式次优化方案,利用虚拟直传信道增益得到中继选择方法,并将中继系统转换为单跳系统;然后利用凸规划得到最优功率分配.此外,为适应不同的用户分布,提出联合小区呼吸机制的分配方案.仿真结果表明,所提次优联合方案逼近最优值,联合小区呼吸的方案可适应不同的用户分布并进一步提升能效.     

能量收集双向中继网络的中继选择和功率分配

结合能量收集技术,研究了放大转发双向中继网络的系统性能。基于双向中继系统中的两个端到端信噪比平衡准则,推导出了单中继选择情况下信源最优的功率分配方案和中继最优的能量收集比例。仿真结果证明所提方法能够实现最好的系统性能。通过比较发现,能量收集双向中继网络比传统双向中继网络能够实现更高的传输速率。     

Comparison of average symbol error rate and optimal power allocation for two‐way opportunistic relaying with amplify‐and‐forward protocol

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.     

放大转发OFDM协同中继系统多业务资源分配机制

提出了点到点多载波协同中继系统多业务资源分配框架,并给出了一种最优化自适应功率、载波和比特分配算法;为了降低算法复杂度,又提出了一种次优搜索算法,该算法依据信道特性,在满足业务QoS基础上使业务占用资源最小.仿真结果表明:提出的最优算法在保障多媒体业务QoS的基础上能够有效改善频谱效率,对比于传统算法有1～2bit/(s·Hz)的性能提升;而提出的次优搜索能够取得接近最优算法的性能(差别在0.6 bit/(s·Hz)左右),并且实现复杂度由指数级别降至线性.     

分布式双向中继选择算法及用户功率分配

针对放大转发的瑞利双向中继信道的节点选择问题,提出了基于部分信道信息的分布式双向中继选择算法。算法通过计算双向链路的接收信噪比,推导出满足目标接收信噪比的转发阈值,各中继节点根据该阈值决定是否参与转发,从而实现分布式选择。此外,考虑用户总功率受限的情况,在分布式中继选择基础上提出了优化功率分配策略,使双向信道的接收信噪比更加接近。仿真结果表明,分布式中继选择算法与最优多中继算法的系统传输速率相似,计算复杂度大大降低,尤其是在中继数目增大的情况下更加明显。优化功率分配策略能进一步提高系统能量效率,在相同性能下可节省7%左右的功率。     

Research on the low complexity adaptive power allocation algorithm in cooperative systems

Cooperative diversity is a new technology to improve bit error rate(BER)performance in wireless communications.A new power allocation algorithm to improve BER performance in cellular uplink has been proposed in this paper.Some existing power allocation schemes were proposed for the purpose of maximizing the channel capacity or minimizing the outage probability.Different from these schemes,the proposed algorithm aims at minimizing the BER of the systems under the constraint of total transmission power.Besides this characteristic,the proposed algorithm can realize a low complexity real-time power allocation according to the fluctuation of channels.Simulation results show that the proposed algorithm can decrease the BER performance of the systems effectively.     

Performance analysis of user fair-based relay adaptive power allocation in physical-layer network coding cooperation

Network Coding (NC) is an effective technology to enhance the cooperative system spectral efficiency. However, since it is network-oriented, the existing performance metric of single-user outage can not comprehensively evaluate its gain and the impact to the entire network, which affect the user fairness. This paper proposes two novel user fair-based adaptive relay power allocation algorithms in single-relay NC cooperative multiple access channels. Firstly, common outage probability is employed as the performance metric, and to minimize it, a specific condition is deduced. On this basis, the instantaneous channel information-based adaptive relay power allocation scheme and the channel statistic information-based one with lower complexity are designed respectively, which make users?? signals superimposed at accurately calculated proportion to maintain fairness. Simulation results show that compared with other existing schemes, the proposed schemes can best maintain user fairness, and effectively improve the common outage performance of the whole system, at the expense of small spectral efficiency.     

Low‐complexity energy efficient power allocation scheme for DAS with maximum power constraint

In this paper, a low‐complexity optimal power allocation (PA) scheme is developed to maximize energy efficiency (EE) in a distributed antenna system (DAS) under maximum power constraint and target bit error rate (BER) requirement. Composite Rayleigh fading, multiple receive antennas, and dynamic circuit power consumption are all considered in the system. Unlike conventional schemes, the presented scheme provides a closed‐form expression of PA. Firstly, the optimization problem is formulated according to the definition of EE. Using the Karush‐Kuhn‐Tucker conditions, a general form of the optimal PA, in which the number of active antennas and corresponding power allocation are required only, is then proposed. With this general form, an effective algorithm is presented to yield the closed‐form PA. The proposed scheme can be applied to the system with static circuit power consumption and/or without target BER constraint to obtain optimal PA. Simulation results corroborate the effectiveness of the developed scheme, and the scheme can achieve the same EE performance as the existing optimal schemes with lower complexity. Moreover, the distributed antenna system with multiple receive antennas has higher EE than that with single receive antenna.     

一种基于非正交信道的分布式中继选择及功率分配方法

针对非正交两跳多中继协作通信系统中的分布式中继选择问题,提出了一种基于非正交信道的中继选择准则,简化了系统的设计。分析了其误码率性能,给出了其解析表达式和以总功率为约束条件下的最优功率分配方案。仿真结果表明,最佳中继选择准则明显优于传统的中继选择准则,且在最优功率分配方案下,可以获得明显的分集增益,系统的误码率显著下降。     

基于中断概率的协作通信中继选择与功率分配算法

研究了功率受限情况下多中继协作通信网络的中继选择和功率优化问题。在AF网络中,提出了一种低复杂度中继选择与功率分配算法,其目标是在总功率一定的条件下使系统的中断概率最小。本算法对源节点和所有潜在中继节点进行功率分配,结合当前信噪比选择最优的中继集合,通过最速下降法求出使系统中断概率最低的功率分配因子。该算法不需要知道大量瞬时信道信息、不需要系统在等功率条件下进行中继选择,只需求得中继节点排列矩阵便可根据当前信噪比自适应获得最优中继节点集合。仿真结果表明,在相同条件下,该算法明显优于不同中继节点集合下几种算法的中断性能,并且与传统的SAF及AAF算法相比,有效降低了中断概率,提升了系统性能和功率效率。