Optimal power control for wireless cooperative relay networks: a cooperative game theoretic approach

Wireless nodes operating on batteries are always assumed to be selfish to consume their energy solely to maximize their own benefits. Thus, the two network objectives, that is, system efficiency and user fairness should be considered simultaneously. To this end, we propose two game theoretic mechanisms, that is, the signal‐to‐noise ratio (SNR) game and the data‐rate game to stimulate cooperation among selfish user nodes for cooperative relaying. Considering one node could trade its transmission power for its partner's relaying directly, the strategy of a node is defined as the amount of power that it is willing to contribute for relaying purpose. In the SNR game, selfish nodes are willing to achieve SNR increases at their receivers, while in the data‐rate game the nodes are willing to achieve data‐rate gains. We prove that each of the games has a unique Nash bargaining solution. Simulation results show that the Nash bargaining solution lead to fair and efficient resource allocation for both the cooperative partner nodes in the Pareto optimal sense, that is, both the nodes could experience better performance than they work independently and the degree of cooperation of a node only depends on how much contribution its partner can make to improve its own performance. Copyright © 2012 John Wiley & Sons, Ltd.     

Cooperative spectrum sharing of multiple primary users and multiple secondary users

This paper proposes a multiple-input multiple-output (MIMO) based cooperative dynamic spectrum access (DSA) framework that enables multiple primary users (PUs) and multiple secondary users (SUs) to cooperate in spectrum sharing. By exploiting MIMO in cooperative DSA, SUs can relay the primary traffic and send their own data at the same time, which greatly improves the performance of both PUs and SUs when compared to the non-MIMO time-division spectrum sharing schemes. Especially, we focus on the relay selection optimization problem among multiple PUs and multiple SUs. The network-wide cooperation and competition are formulated as a bargaining game, and an algorithm is developed to derive the optimal PU-SU relay assignment and resource allocation. Evaluation results show that both primary and secondary users achieve significant utility gains with the proposed framework, which gives all of them incentive for cooperation.     

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。     

PDA detector For DS-CDMA cooperative system

This paper considers the uplink of a cooperative Code-Division Multiple-Access (CDMA) sys-tem where parts of mobile nodes serve as source nodes while the others serve as relay nodes at any instant in time. When the non-orthogonal spreading codes are adopted, Multiple Access Interference (MAI) will exist at both the relay nodes and the base node, causing diversity gain to diminish. To mitigate MAI and exploit full advantages of cooperation, the Probabilistic Data Association (PDA) is developed at the relay nodes and the base node. Simulation results demonstrate that some performance gains can be obtained by the PDA de-tector over the Minimum Mean Square Error (MMSE) detector at high Signal-to-Noise Ratio (SNR) and conversely at low SNR.     

协作分集系统中基于注水算法的功率分配方案研究

为了提高协作分集系统的信道容量,该文在多中继节点协作背景下提出了基于注水算法的中继节点功率分配方案。首先,对空时矩阵的列序号提出了一种新的映射方案,该方案能够提升中继节点发射信号间的正交性。对于采用线性正交解码算法的GABBA码,列序号重新排布后能够降低误码率。然后,通过对接收信噪比与中继节点发射功率的分析,针对信道容量最大化问题提出了一种应用注水算法的两步求解方案。该文对瑞利平坦慢衰落信道下采用GABBA码的协作分集系统进行仿真,仿真结果表明,与中继节点发射功率均分方案相比,该文提出的功率分配方案能够提升系统抗误码性能,达到满分集增益NtNr。该文提出的方案在不同的仿真条件下对信道容量均有提升,并且信道容量与min{NtNr}log2M成正比。     

异步协同系统频选信道下基于线性预处理的DSTC结构设计

在协同中继系统中,应用分布式空时码(Distributed Space Time Coding, DSTC),可以在有效提高系统效率的同时获得全协同分集。但是,各中继节点的异步传输和节点间的多径衰落会破坏空时码字的结构,使之不能获得全分集。本文针对两中继的异步协同系统,提出了一种频率选择性信道下的基于线性预处理的DSTC传输结构。在此传输结构中,源节点对发送数据块进行预处理后发送给中继节点,中继节点对接收信号进行简单的共轭重排等处理,使得在目的节点形成DSTC的结构。其中,为抵抗异步传输和多径衰落引入的符号间干扰(Inter-symbol Interference, ISI),在源节点处和中继节点处均加入循环前缀(Cyclic Prefix, CP)。于是目的节点对接收到的信号进行DFT处理后,可以运用ML算法对数据信息进行检测。理论分析和仿真表明,当存在定时误差和节点间为频率选择性信道时,目的节点运用ML检测算法该传输结构可获得全空间分集和全多径分集。然后,本文考虑了信道各径延迟为整数倍符号周期的情况,并且证明了该传输结构的分集增益只与节点间信道的有效信道长度有关。      

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.     

Competitive Resource Sharing Based on Game Theory in Cooperative Relay Networks

This letter considers the problem of resource sharing among a relay and multiple user nodes in cooperative transmission networks. We formulate this problem as a sellers’ market competition and use a noncooperative game to jointly consider the benefits of the relay and the users. We also develop a distributed algorithm to search the Nash equilibrium, the solution of the game. The convergence of the proposed algorithm is analyzed. Simulation results demonstrate that the proposed game can stimulate cooperative diversity among the selfish user nodes and coordinate resource allocation among the user nodes effectively.     

Incentive Mechanism for Multiuser Cooperative Relaying in Wireless Ad Hoc Networks: A Resource-Exchange Based Approach

This paper studies the resource allocation (RA) and the relay selection (RS) problems in cooperative relaying (CR) based multiuser ad hoc networks, and a multiuser cooperative game is proposed to stimulate selfish user nodes to participate in the CR. The novelty of the game scheme lies in that it takes explicit count of that a wireless user can act as a data-source as well as a potential relay for other users. Consider a user has the selfish incentive to consume his/her spectrum resource solely to maximize his/her own data-rate and the selection cooperation (SC) rule which restricts relaying for a user to only one relay is explicitly imposed. To stimulate user nodes to share their energy and spectrum resource efficiently in the Pareto optimal sense, first, we formulate the RA problem for multiuser CR as a bargaining game. By solving the Nash bargaining solution of the game, Pareto optimal RA for cooperative partners can be achieved. Next, to implement the SC-rule imposed RS, a simple heuristic is proposed with the main method being to maintain the long-term priority fairness for cooperative partner selection for each selfish user. The proposed RS with RA (RS-RA) algorithm has a low computational complexity of $O(K^{2})$ , where $K$ is the number of users in a network. Simulation results demonstrate the system efficiency and fairness properties of the proposed bargaining game theoretic RS-RA scheme.     

Cooperative quadrature physical layer network coding in wireless relay networks

This paper proposes a cooperative quadrature physical layer network coding (CQPNC) scheme for a dual‐hop cooperative relay network, which consists of two source nodes, one relay node and one destination node. All nodes in the network have one antenna, and the two source nodes transmit their signals modulated with quadrature carriers. In this paper, a cooperative quadrature physical layer network coded decode‐and‐forward (DF) relay protocol (CQPNC‐DF) is proposed to transmit the composite information from the two source nodes via the relay node to the destination node simultaneously to reduce the number of time slots required for a transmission. The proposed CQPNC‐DF relay protocol is compared with time‐division multiple‐access amplify‐and‐forward (TDMA‐AF), TDMA‐DF, cooperative network coded DF (CNC‐DF) and cooperative analog network coded AF (CANC‐AF) relay protocols to demonstrate its effectiveness in terms of bit error rate (BER) and system throughput under different propagation conditions. The simulation results reveal that the proposed CQPNC‐DF relay protocol can significantly improve the network performance. Compared with two TDMA schemes and CNC‐DF, the proposal can provide up to 100% and 50% throughput gains, respectively. Moreover, no matter what the scene, the proposed scheme always has the lowest BER in the low SNR region. Copyright © 2013 John Wiley & Sons, Ltd.     

一种选择发送的协作网络编码及其性能分析

衰落环境中,自动重传技术是实现错误处理、完成数据传输的有效方法之一。本文提出了一种选择发送的协作网络编码（Cooperative Network Coding based on Selective Transmission,ST CNC）,该技术在数据重传过程中,将空时协同发送与网络编码技术相结合,可以有效减少重传次数,提高网络资源利用率。针对一发两收系统,单个中继节点辅助传输的情形,分析了ST CNC的中断性能和网络编码增益,结果表明:相对于传统的广播策略,选择发送的协作网络编码可以获得2阶分集增益;此外,在中低信噪比区域,ST CNC同时可以获得明显的网络编码增益。      

Shared relay assignment in cooperative communications for bandwidth maximization

Previous research mostly focused on mutually assigning one relay node for a source node to explore the transmission gains of cooperative communications. However, sharing a relay among multiple source nodes can improve the utilization of the relay node. This paper first defines the shared relay assignment for max–min bandwidth (SRA-MMB) problem and max–total bandwidth (SRA-MTB) problem, and formalizes them using integer programs. For the SRA-MMB problem, we propose a heuristic shared relay assignment algorithm (called RRA-MB) using binary search and rounding methods to maximize the minimum bandwidth of all the sources. The theoretical analysis proves that, in the worst case, the proposed algorithm can reach the approximate performance of \(2 + \varepsilon\), where \(\varepsilon\) is an arbitrarily small positive number. For the SRA-MTB problem, we propose a 2-approximation algorithm based on the rounding method to maximize the total bandwidth when each source has a relay usage time limit. Moreover, an optimal algorithm is designed to solve the special instance of SRA-MTB, in which all the source nodes have the same (i.e., uniform) limit on its relay usage time. Our simulations show that the proposed algorithms can achieve about 18 and 27 % improvements over the existing approaches in terms of minimum and total bandwidths respectively.     

A Unified Cross-Layer Framework for Resource Allocation in Cooperative Networks

Node cooperation is an emerging and powerful solution that can overcome the limitation of wireless systems as well as improve the capacity of the next generation wireless networks. By forming a virtual antenna array, node cooperation can achieve high antenna and diversity gains by using several partners to relay the transmitted signals. There has been a lot of work on improving the link performance in cooperative networks by using advanced signal processing or power allocation methods among a single source node and its relays. However, the resource allocation among multiple nodes has not received much attention yet. In this paper, we present a unified crosslayer framework for resource allocation in cooperative networks, which considers the physical and network layers jointly and can be applied for any cooperative transmission scheme. It is found that the fairness and energy constraint cannot be satisfied simultaneously if each node uses a fixed set of relays. To solve this problem, a multi-state cooperation methodology is proposed, where the energy is allocated among the nodes state-by-state via a geometric and network decomposition approach. Given the energy allocation, the duration of each state is then optimized so as to maximize the nodes utility. Numerical results will compare the performance of cooperative networks with and without resource allocation for cooperative beamforming and selection relaying. It is shown that without resource allocation, cooperation will result in a poor lifetime of the heavily-used nodes. In contrast, the proposed framework will not only guarantee fairness, but will also provide significant throughput and diversity gain over conventional cooperation schemes.     

非正交选择译码转发协同

为了提高两跳中继网络的传输速率和协同分集增益,该文提出一种非正交的选择译码转发策略传输数据。单节点协同时,协同节点仅在正确译码时采用和发送节点非正交的时序转发;在多节点协同时,采用一种节点选择算法选择译码正确且信道条件最佳的节点用于非正交转发。这种协同策略可获得和非正交放大转发相同的分集复用折衷性能,但其实现更简单,且在低信噪比时中断性能更好。     

Joint Optimization of Source Power Allocation and Relay Beamforming in Multiuser Cooperative Wireless Networks

Relay beamforming techniques have been shown to significantly enhance the sum capacity of a multiuser cooperative wireless network through the optimization of the relay weights, where concurrent communications of multiple source-destination pairs are achieved via spatial multiplexing. Further optimization of the transmit power allocation over the source nodes is expected to improve the network throughput as well. In this paper, we maximize the sum capacity of a multiuser cooperative wireless network through the joint optimization of power allocation among source nodes and relay beamforming weights across the relay nodes. We consider a two-hop cooperative wireless network, consisting of single-antenna nodes, in which multiple concurrent links are relayed by a number of cooperative nodes. When a large number of relay nodes are available, the channels of different source-destination pairs can be orthogonalized, yielding enhanced sum network capacity. Such cooperative advantage is particularly significant in high signal-to-noise ratio (SNR) regime, in which the capacity follows a logarithm law with the SNR, whereas exploiting spatial multiplexing of multiple links yields capacity increment linear to the number of users. However, the capacity performance is compromised when the input SNR is low and/or when the number of relay nodes is limited. Joint optimization of source power allocation and relay beamforming is important when the input SNR and/or the number of relay nodes are moderate or the wireless channels experience different channel variances. In these cases, joint optimization of source power and distributed beamforming weights achieves significant capacity increment over both source selection and equal source power spatial multiplexing schemes. With consideration of the needs to deliver data from each source node, we further examine the optimization of global sum capacity in the presence of individual capacity requirements by maximizing sum capacity of the network subject to a minimum capacity constraint over each individual user.     

Distributive High-Rate Space–Frequency Codes Achieving Full Cooperative and Multipath Diversities for Asynchronous Cooperative Communications

In user-cooperative communications, relay nodes are usually asynchronous. By realizing that the processing in the frequency domain is insensitive to the errors in the time domain, Mei and Shin recently applied the space-time-coded orthogonal frequency-division multiplexing (OFDM) technique to achieve full cooperative diversity for asynchronous cooperative communications, where orthogonal space-time block codes (particularly the Alamouti code) were used for relay nodes. In this paper, we consider asynchronous cooperative communications, and the channels from one node to another node are frequency-selective fading. We propose a high-rate space-frequency coding method and prove that it can achieve both cooperative and multipath diversities. Simulation results are shown to verify the performance of the constructed codes.     

一种联合中继节点选择的博弈功率控制算法

有效的资源分配在协同通信中占有举足轻重的地位,鉴于此,该文研究了其中的中继节点选择和功率控制问题,提出了一种联合中继节点选择的博弈功率控制算法。它的主要思想是从各节点信噪比的角度建立收益函数,并具体针对源节点和中继节点建立不同的代价函数。在认为每个节点都负责的前提下,通过调整各节点功率达到各自效用的最大化,并依据中继节点发送功率的策略空间,优化参与协同的中继节点集合。同时,该文还对纳什均衡的性能进行了数学分析。从仿真结果可以看出,所提算法在复杂度可接受的前提下,能使各节点间的功率得到合理有效的使用,确能改善系统性能。     

MIMO-AF协作中继网络中发送预编码器的优化

本文首先利用中继节点和目标节点在第一时隙中的接收信噪比之和最大准则,推导出优化问题并解得优化的预编码器矢量。然后又利用目标节点最大比合并后的接收信号信噪比最大准则,推导出性能更佳的预编码器优化问题,但由于表达式复杂不能得到闭式解。为此本文提出了两种次优解决方法,分别是梯度下降迭代法和近似求解法。仿真结果表明,提出的两种准则优化预编码器方法都能有效改进系统性能,且因后者更能直接反映接收端情况,效果更好。两种次优的解优化方法能够获得几乎相同的系统性能,但梯度下降法采用迭代运算,计算量比较大,而近似求解法在性能不损失的情况下大大降低了计算复杂度。      

Diversity–Multiplexing Tradeoff of Asynchronous Cooperative Diversity in Wireless Networks

Synchronization of relay nodes is an important and critical issue in exploiting cooperative diversity in wireless networks. In this paper, two asynchronous cooperative diversity schemes are proposed, namely, distributed delay diversity and asynchronous space-time coded cooperative diversity schemes. In terms of the overall diversity-multiplexing (DM) tradeoff function, we show that the proposed independent coding based distributed delay diversity and asynchronous space-time coded cooperative diversity schemes achieve the same performance as the synchronous space-time coded approach which requires an accurate symbol-level timing synchronization to ensure signals arriving at the destination from different relay nodes are perfectly synchronized. This demonstrates diversity order is maintained even at the presence of asynchronism between relay node. Moreover, when all relay nodes succeed in decoding the source information, the asynchronous space-time coded approach is capable of achieving better DM tradeoff than synchronous schemes and performs equivalently to transmitting information through a parallel fading channel as far as the DM tradeoff is concerned. Our results suggest the benefits of fully exploiting the space-time degrees of freedom in multiple antenna systems by employing asynchronous space-time codes even in a frequency-flat-fading channel. In addition, it is shown asynchronous space-time coded systems are able to achieve higher mutual information than synchronous space-time coded systems for any finite signal-to-noise ratio (SNR) when properly selected baseband waveforms are employed.     

改进蛙跳算法的多中继协作系统最优功率分配

协作通信与直接通信相比能够显著地提高系统性能,功率分配是协作通信中的一个关键问题。为了获得合理的协作中继通信系统功率分配方案,提出一种基于改进蛙跳算法的多中继节点功率分配方法。首先对功率分配问题进行分析,将其转换为一个非线性优化问题,然后将青蛙表示为源节点,中继节点的功率,以平均信噪比作为青蛙的食物,并通过青蛙的信息交流和协作找到最优的功率分配方案,最后采用仿真对比实验对本文算法性能进行测试。仿真结果表明,相对于其它功率分配方法,改进蛙跳算法有效地提高了系统的信道容量,降低了中断概率,以较低的复杂度提高了系统的性能。