QoS-guaranteed multi-relay selection and power allocation optimization in cooperative systems

This paper investigates the relay selection and power allocation problem in multi-user based cooperative networks, where intermediate relay nodes help source forward information to destination using decode-and-forward (DF) relaying protocol. Specifically, we propose a novel multi-relay nodes selection strategy taking both instantaneous channel state information (I-CSI) and residual energy into consideration, by which 'emergence' diversity gain can be achieved and the imbalance of resource utilization can be overcome. Besides, using Largangian dual-primal decomposition and subgradient projection approach, an optimal power allocation algorithm at source and cooperative relay nodes is presented with the constraints of each user's individual quality of service (QoS) requirements and system total transmit power. Theoretical analysis and simulation results demonstrate that the proposed scheme can significantly improve energy efficiency, while guaranteeing a good balance between achievable data rate and average network lifetime with relatively low implementation complexity.     

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。     

OFDM双向中继协作系统的资源分配策略

为了提高基于正交频分复用(OFDM)双向多中继协作通信系统的能量效率,降低发射总功率,提出了一种低能耗的无线资源优化分配方案.首先提出一种信道增益调和平均数排序算法完成子载波匹配与最优中继选择,然后从固定的比特速率出发,在保证一定误比特率的前提下,利用拉格朗日法和Fischer算法对各个子载波进行比特优化分配,进一步提升系统能效.仿真结果表明,相比于现有的策略,所提出的资源分配方案明显提升了系统的能量效率.     

Resource allocation scheme in two-way multi-relay OFDM system

A joint optimization scheme for power allocation and subcarrier pairing under high SNR in two-way multi-relay OFDM system was proposed.Unlike those schemes in which relays use subcarriers separately,all the relays were allowed to forward signal on each subcarrier pair for providing much space diversity.With the constraint of total system power,the proposed scheme firstly allocated each relay power with Cauchy inequality with the assuming that the total relay power was fixed.Then the dichotomy was used to calculate the power allocation between the source node and the relay node by maximizing the equivalent channel gain for different subcarrier pairs.Lastly,the power of different subcarrier pairs was allocated by convex programming,and the subcarriers were paired by Hungarian algorithm to obtain the maximum system capacity.There was no optimal power allocation method with low complexity because of the complexity of the power allocation algorithm in two-way multi-relay networks.This algorithm greatly reduces the complexity of power allocation and simulation results show that the proposed scheme outperforms the relay selection scheme and the relays use subcarriers separately scheme.     

能量收集双向中继网络的高能效联合中继选择和功率分配算法

为了实现双向中继系统在满足传输速率要求时的最小功率消耗,基于功率分割中继协议,在完美和非完美的信道估计两种不同的情况下,提出了能量收集双向中继网络的高能效联合中继选择和功率分配算法,得到了两个信源的最优功率分配和中继节点最优的能量收集比例.仿真结果表明,信道估计误差会增加系统的功率消耗;与传统双向中继比较发现,能量收集双向中继能够实现更少的系统功率消耗.     

认知无线传感器网络中基于GSC的协作传输机制

针对无线传感器网络中单个节点能量和发射功率均受限的特点,在发送端已知信道状态信息(CSI)的条件下提出了一种基于广义选择合并算法(GSC)的协作传输机制。根据GSC算法和节点的功率受限条件来决定具体参与协作传输的节点个数,并结合信道状态和节点的剩余能量来对节点进行调度。理论分析和仿真结果表明该机制能够有效地延长网络寿命。     

Joint power allocation and multi-relay selection scheme based on system outage probability

An amplify-and-forward （AF） based multi-relay network is studied. In order to minimize the system outage probability with a required transmission rate, a joint power allocation （PA） and multi-relay selection scheme is proposed under both total and individual power constraints （TIPC）. In the proposed scheme, the idea of ordering is adopted to avoid exhaustive search without losing much system performance. Besides the channel quantity, the ordering algorithm proposed in this article also takes relays＇ maximal output ability into consideration, which is usually ignored in traditional relay ordering algorithms. In addition, simple power reallocation method is provided to avoid repetitive PA operation during the process of searching all possible relay subsets. By Adopting the idea of ordering and using the proposed power reallocation method lead to remarkable decrease of the computation complexity, making the scheme easier and more feasible to implement in practical communication scenarios. Simulations show that the proposed multi-relay selection scheme provides similar performance compared to the optimal scheme with optimal PA and exhaustive search （OPAES） but with much lower complexity.     

AF双向中继网络中一种新的中继选择算法

通过高信噪比条件下AF双向中继网络总速率的近似表达,给出了链路增益乘积和系统总速率之间的关系式。基于此关系式提出一种最大化链路增益乘积中继选择算法(Maximum Relay Selection,MRS),在中继处引入门限,将链路质量超过门限的中继选出建立可靠候选集。在建立的可靠候选集中以两跳链路增益乘积最大化为标准,实现最佳中继选择。通过仿真将该中继选择算法与现有AF双向中继网络3种不同中继选择算法进行性能比较。仿真结果表明,该中继选择算法能在同时保证AF双向中继网络两跳链路质量的前提下,提高系统的总速率。     

双向中继信道的模拟网络编码最优功率分配

在双向信息非对称条件下,研究了基于模拟网络编码的双向中继信道中的最优功率分配问题。分别给出了中断概率最小化、和速率最大化意义下的最优功率分配闭式数学表达式,并证明了两种约束下最优功率分配问题的统一性。分析表明:现有的基于模拟网络编码的双向中继信道中的最优功率分配方法是本文提出方法在某些条件下的特例。计算机仿真分析证明了提出的最优功率分配方法在中断概率和和速率性能方面均优于平均功率分配方法。      

Distributed Relay Selection and Power Control for Multiuser Cooperative Communication Networks Using Stackelberg Game

The performance in cooperative communication depends on careful resource allocation such as relay selection and power control, but the traditional centralized resource allocation requires precise measurements of channel state information (CSI). In this paper, we propose a distributed game-theoretical framework over multiuser cooperative communication networks to achieve optimal relay selection and power allocation without knowledge of CSI. A two-level Stackelberg game is employed to jointly consider the benefits of the source node and the relay nodes in which the source node is modeled as a buyer and the relay nodes are modeled as sellers, respectively. The proposed approach not only helps the source find the relays at relatively better locations and "buy” an optimal amount of power from the relays, but also helps the competing relays maximize their own utilities by asking the optimal prices. The game is proved to converge to a unique optimal equilibrium. Moreover, the proposed resource allocation scheme with the distributed game can achieve comparable performance to that employing centralized schemes.     

一种基于混合智能算法的协作中继选择新方法

针对多用户多中继场景下协作通信系统的中继选择问题,提出了一种基于混合智能算法的协作中继选择新方法。不同于现有的为每个源节点分配一个中继节点的中继选择方法,新方法建立了为每个源节点分配一个或多个中继节点的优化模型,以最大化多用户多中继协作系统的最小接收信噪比为优化目标,采用结合了模拟退火与遗传算法的混合智能算法来搜寻中继选择问题的最优解。仿真结果表明,所提方法可显著提高目的端的接收信噪比,且算法具有较强的全局搜索和快速寻优能力。     

Performance Analysis and Enhancement for Opportunistic Analog Network Coding with Imperfect CSI

Imperfect channel state information (CSI) is among the main factors that affect system performance in wireless networks. In this paper, we investigate the impact of imperfect CSI on the performance of analog network coding (ANC) for a two-way relaying system based on opportunistic relay selection (ORS). An exact and generalized closed-form expression for system outage probability is presented in a Rayleigh flat-fading environment. To provide more insights, the closed-form asymptotic expression is then obtained. It is shown that the presence of channel estimation error causes outage probability maintain a fixed level even when a noiseless channel is adopted. Therefore, to mitigate the negative impact of imperfect CSI, we deduce the power allocation to minimize the system outage probability based on the knowledge of instantaneous channel information. Numerical results validate the accuracy of the derived expressions and highlight the effect of proposed power allocation algorithm compared with conventional uniform power allocation.     

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。     

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。     

Semi-blind amplify-and-forward in two-way relaying networks

This paper addresses the analysis of a two-way semi-blind amplify-and-forward (AF) relay network, in which the relay node requires partial instantaneous channel state information (CSI) to amplify the received signals. First, we derive the expression of end-to-end signal-to-noise ratio in dual-hop transmissions over independent and not necessarily identically distributed Rayleigh fading channels. Based on the opportunistic AF selection relaying, we define bounds of some metrics such as average sum-rate and outage probability. Furthermore, we provide exact and approximate expressions for the average symbol error rate. The obtained results show that the performance of the proposed system decreases slightly while the processing complexity is reduced significantly compared to those of CSI-assisted AF relay schemes. In order to prove the exactness of the proposed analysis, a selection of numerical results is provided.     

On the Design of Energy Efficient Transmission in Cooperative Networks with Bidirectional Asymmetric Traffic

Energy efficient transmission has become increasingly important in future green communications. We focus on cooperative networks with multiple Amplify-and-Forward relays deployed in this paper. A joint relay selection and power allocation transmission scheme applicable to both one-way and two-way relay networks is proposed for minimizing the weighted energy consumed per bit transmitted. Close-form analytical results of power allocation are first developed at each relay. Then the relay consuming the least energy or the direct transmission mode is chosen by the sources. Based on the proposed scheme, we characterize the energy consumption for training and power allocation information exchanging between nodes. Besides, the energy efficient cooperating regions are discussed in one-way and two-way relay networks. It is indicated that the shape of the region depends on both the path loss exponent and the asymmetry traffic in the one-way relay network while only lies on the path loss exponent in the two-way relay network. Simulation results demonstrate that the proposed scheme yields considerable reduced energy consumption compared to that of the best worse relay selection scheme when proper number of relays is deployed. It is also shown that the two-way relaying can achieve higher energy efficiency than the one-way relaying.     

单用户对双向中继系统中基于梯度下降的最大化和速率功率分配方案

针对单用户对双向中继系统中的功率分配问题,提出了一种基于梯度下降法的功率分配方案。该方案在总功率约束的条件下,以最大化和速率为目标函数,通过对中继波束成形矩阵和功率分配矩阵的反复迭代,求解出局部最优的功率分配和中继波束成形矩阵。仿真结果表明:提出方案的误码性能相比于等功率分配有明显提高,在误码率为10-2时,可获得2.5d B~3 d B的信噪比增益;同时,在中高信噪比下,相比于等功率分配,该方案可获得0.3(bit/s)/Hz~0.5(bit/s)/Hz的和速率增益。     

Power allocations in minimum-energy SER-constrained cooperative networks

In this paper, we propose minimum power allocation strategies for repetition-based amplify-and-forward (AF) relaying, given a required symbol error rate (SER) at the destination. We consider the scenario where one source and multiple relays cooperate to transmit messages to the destination. We derive the optimal power allocation strategy for two-hop AF cooperative network that minimizes the total relay power subject to the SER requirement at the destination. Two outstanding features of the proposed schemes are that the power coefficients have a simple solution and are independent of knowledge of instantaneous channel state information (CSI). We further extend the SER constraint minimum power allocation to the case of multibranch, multihop network and derive the closed-form solution for the power control coefficients. For the case of power-limited relays, we propose two iterative algorithms to find the power coefficients for the SER constraint minimum-energy cooperative networks. However, this power minimization strategy does not necessarily maximize the lifetime of battery-limited systems. Thus, we propose two other AF cooperative schemes which consider the residual battery energy, as well as the statistical CSI, for the purpose of lifetime maximization. Simulations show that the proposed minimum power allocation strategies could considerably save the total transmitted power compared to the equal transmit power scheme.     

混合蛙跳在网络编码协作系统资源分配中的应用

网络编码协作中继技术能合理分配IMT-Advanced的资源,从而提高系统性能,受到了广大学者的关注。针对基于网络编码的双向多中继协作系统,提出基于混合蛙跳的资源分配方案。以最小化系统传输功率为优化目标,在满足用户QoS下,推导每个节点的最优化功率,建立最优化资源分配模型,利用混合蛙跳算法解决系统资源分配问题。仿真结果表明,在满足单节点QoS下,所提出的基于混合蛙跳的资源分配方案能有效减小系统的总功率,提高了系统性能。     

A genetic algorithm based approach for energy efficient routing in two-tiered sensor networks

Higher power relay nodes can be used as cluster heads in two-tiered sensor networks to achieve improved network lifetime. The relay nodes may form a network among themselves to route data towards the base station. In this model, the lifetime of a network is determined mainly by the lifetimes of these relay nodes. An energy-aware communication strategy can greatly extend the lifetime of such networks. However, integer linear program (ILP) formulations for optimal, energy-aware routing quickly become computationally intractable and are not suitable for practical networks. In this paper, we have proposed an efficient solution, based on a genetic algorithm (GA), for scheduling the data gathering of relay nodes, which can significantly extend the lifetime of a relay node network. For smaller networks, where the global optimum can be determined, our GA based approach is always able to find the optimal solution. Furthermore, our algorithm can easily handle large networks, where it leads to significant improvements compared to traditional routing schemes.