Transmission scheme and performance analysis for decode-and-forward MIMO two-way relay systems

In decode-and-forward (DF) MIMO two-way relay systems, the transmission schemes are designed and the closed-form expressions for the outage probability and average symbol error rate (ASER) of the twoway relay system are derived based on two different scenarios of channel state information (CSI). For perfect CSI, the maximum-ratio-transmission and combining (MRT-MRC) technique is applied to design the beamforming and combining vectors. Without perfect CSI, the transmission scheme with limited feedback is designed, and the analytical results are verified through two kinds of codebooks, i.e., random vector quantization and Grassmann. The simulation results show that, the proposed transmission schemes for the two-way relay system can outperform other transmission schemes in the performance of outage probability and ASER, and the accuracy of the derived closed-form expressions is also verified by the numerical simulations.     

ICRN功率分配与中继选择联合优化

针对工业认知无线电网络中出现的无线干扰和冲突严重,特别是工业现场的金属环境和移动特性造成多径与阴影衰落,从而使得传输可靠性难以保证的问题,引入感知信道概率及信道可用度概念,提出一种联合优化中继选择与功率分配的算法。该算法给出3种认知中继选择方案,分别是信道增益最大准则、最近准则及调和平均准则,并在源节点和所选中继节点之间进行最优功率分配,以最小化网络中断概率。仿真结果表明,与平均功率分配算法相比,所提算法能更好地降低系统中断概率,提高传输可靠性。     

Cross-layer resource allocation in wireless multi-hop networks with outdated channel state information

The cross-layer resource allocation problem in wireless multi-hop networks （WMHNs） has been ex-tensively studied in the past few years. Most of these studies assume that every node has the perfect channel state information （CSI） of other nodes. In practical settings, however, the networks are generally dynamic and CSI usually becomes outdated when it is used, due to the time-variant channel and feedback delay. To deal with this issue, we study the cross-layer resource allocation problem in dynamic WMHNs with outdated CSI under channel conditions where there is correlation between the outdated CSI and current CSI. Two major contributions are made in this work： （1） a closed-form expression of conditional average capacity is derived under the signal-to-interference-plus-noise ratio （SINR） model; （2） a joint optimization problem of congestion control, power control, and channel allocation in the context of outdated CSI is formulated and solved in both centralized and distributed manners. Simulation results show that the network utility can be improved significantly using our proposed algorithm.     

改进的解码转发多跳中继系统及最优功率分配

多跳信道的中断性能较差,且节点接收设备上的多跳分集信道较为复杂。为此,基于解码转发多跳信道和多跳分集信道,提出一种改进的解码转发多跳中继系统,解决上述2种信道性能和复杂度的矛盾。推导中断概率的计算公式,以最小化系统中断概率为目标,利用拉格朗日乘子优化各节点的功率分配。仿真结果表明,改进系统能获得比传统多跳中继系统更低的中断概率,最优功率分配方案下系统的中断性能优于均匀功率分配方案,并且性能优势随跳数增加更为明显。     

Optimization of resource allocation for underlay device-to-device communications in cellular networks

Underlay device-to-device (D2D) communication in cellular networks has been considered as a promising technique that can improve the spectral efficiency of cellular systems and meet the growing demand for wireless local services. In underlay D2D, it is of primary importance to manage the mutual interference between cellular links and D2D links through effective resource allocation. While most of previous works on D2D resource allocation are developed based on the knowledge of the channel state information (CSI) on the interference channels as well as the desired channels, it is hard to obtain full CSI in practice. Accordingly, we consider D2D resource allocation schemes based on distance between nodes. In particular, we formulate two optimization problems for D2D resource allocation using the outage probability computed based on the distance information as cost functions. One is a linear sum assignment problem (LSAP) and the other is a linear bottleneck assignment problem (LBAP). By applying the graph theory, we provide efficient algorithms for solving the optimization problems. Numerical results are provided to show the effectiveness of the proposed optimization as compared to previously proposed distance-based resource allocation algorithms.     

能量收集无线网络中面向统计服务质量的最优功率分配

针对能量收集无线网络中的服务质量（QoS）保障问题,提出了面向统计QoS的最优功率分配方案,从而最大化时延QoS约束下的有效容量。首先,构建能量收集无线网络的有效容量最大化问题。其次,利用凸优化理论求解出最优功率分配方案以及该方案下的最大有效容量,并得出了两种特例下的最优功率分配方案,即：当QoS需求非常松弛时,最优化功率分配方案收敛于注水策略;当QoS需求非常严格时,最优化功率分配方案收敛于信道反转策略。然后,求解了所提最优功率分配方案得到的信道中断概率。最后,通过仿真实验,检验了该最优功率分配方案的性能。实验结果表明,与现有策略相比,所提方案能够获得更大的有效容量。     

基于误码率与中断概率约束的femtocell网络分布式功率控制

家庭基站(femtocell)网络可有效改善无线通信业务的室内覆盖性能,提高信道容量.然而,复杂的动态通信环境导致信道的不确定性,影响用户服务质量.基于此,研究双层femtocell网络在快衰落信道环境下基于误码率约束的功率控制问题;考虑信号传输的中断概率,以及服务质量指标–误码率等方面的要求,构造在此约束下的优化问题;最大化双层femtocell网络的净收益,使得网络系统的通信性能最优;通过对概率约束进行数学处理,将其转化为确定性形式,并提出分布式鲁棒优化算法对等价的确定性优化问题进行求解,从而获得最优功率分配策略.最后,通过仿真验证了所提出算法的收敛性和有效性.     

基于合作博弈的认知卫星网络信道分配与上行功率控制算法

随着通信业务需求的不断增长,频谱资源的有限性使得卫星通信网络和地面网络都面临着严重的频谱危机。认知无线电技术的出现,使得卫星网络与地面网络共用频率资源以提升网络效用成为可能。文中对认知接入分配给地面网络作为主用户的同一频谱资源的认知卫星网络的功率控制和信道分配问题进行了研究。根据卫星网络和地面网络的特性构建了合理的系统模型,并利用中断概率门限表征了信道估计误差对系统容量的影响。为了保护主基站的通信性能,在考虑信道估计误差、信道资源约束、认知卫星用户最大发射功率和微波基站干扰约束的条件下,根据议价博弈理论设计了优化函数。其次,根据凸优化理论推导了最优发射功率和信道分配的闭式解,并在此基础上设计了一种对偶迭代算法来求解该优化问题。最后,根据卫星网络的特性设置了合理的网络参数,并根据参数利用Matlab仿真平台对提出的算法进行了仿真实验。仿真结果表明:所提方法在不同到达速率的条件下均具备良好的收敛性;信道估计误差会降低网络的总容量;所提方法在波束数多于15个时,相比比例公平性算法容量提升超过50 bps/Hz,相比最大容量法公平性能提升超过一倍,因此,相较于这两种方法,该方法能在系统容量和用户间公平性之间获得较好的折中。     

Optimization of a robust collaborative-relay beamforming design for simultaneous wireless information and power transfer

We investigate a collaborative-relay beamforming design for simultaneous wireless information and power transfer. A non-robust beamforming design that assumes availability of perfect channel state information (CSI) in the relay nodes is addressed. In practical scenarios, CSI errors are usually inevitable; therefore, a robust collaborative-relay beamforming design is proposed. By applying the bisection method and the semidefinite relaxation (SDR) technique, the non-convex optimization problems of both non-robust and robust beamforming designs can be solved. Moreover, the solution returned by the SDR technique may not always be rank-one; thus, an iterative sub-gradient method is presented to acquire the rank-one solution. Simulation results show that under an imperfect CSI case, the proposed robust beamforming design can obtain a better performance than the non-robust one.     

Robust capacity maximization transceiver design for MIMO OFDM systems多天线正交频分复用系统中鲁棒性容量最大化的收发机设计

In this paper, we investigated capacity maximization problem for Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing systems with imperfect channel state information (CSI). To the best of our knowledge, the considered problem is still an open problem. However, the transceiver designs for MIMO OFDM systems have been extensively studied. It seems nobody gives closed-form solutions for resource allocation for MIMO OFDM systems with statistical channel estimation errors up to date. In our work, based on practical channel estimation algorithm, the channel estimation errors are first derived and then the robust resource allocation problem has been formulated. The structure of the optimal robust precoder is first derived, based on which the optimization problem will be simplified significantly. Furthermore, based on the Lagrangian dual method, a robust power allocation algorithm is proposed. The proposed power allocation can be considered as a variant of water-filling solution named cluster water-filling solution. Finally, simulation results show that our proposed robust design outperforms the non-robust design in terms of channel capacity.     

OFDMA系统的一种资源分配方法

针对OFDMA下行链路发送端只能获得部分信道信息的情况,提出了一种基于部分信道信息的资源分配算法.该算法通过建立部分信道信息模型,考虑传输的中断概率,保证分配的数据速率、子载波等资源与真实的信道条件匹配.仿真结果表明,该方法实现了较好的多用户分集增益和实际吞吐量性能.     

Two-path中继系统中基于最小化中断概率的功率分配方法

为了降低two-path中继系统的通信中断概率,针对DF协议中继,推导了two-path中继系统在存在中继间干扰情况下的中断概率闭式解,并在总功率受限的情况下,提出了一种最小化中断概率的最优功率分配算法。仿真验证结果表明该算法能够有效地降低系统的中断概率,提高系统的性能。     

一种双信道协作中继的认知网络功率分配算法

针对认知无线网络主、次用户的互相干扰对网络中断性能以及系统传输效率的影响进行了研究,采用一种双信道协作中继的传输方案来减少干扰,并提出一种基于中断概率的最优功率分配方案来改善中断性能和传输效率。在该传输方案中,主、次系统通过对接收的主信号和复合信号进行处理,采用连续的干扰解码和消除得到去干扰信号。该功率分配方案在保障主系统中断性能的前提下,提出次系统中断概率的优化方程,通过关联功率分配因子来实现最大化次系统吞吐量。实验结果表明,该算法在改善中断性能和系统吞吐量方面具有较好的效果。     

Joint relay selection and power control for robust cooperative multicast in mmWave WPANs

We propose an optimization algorithm for joint relay selection and source and relay power allocation under mixed line-of-sight (LoS) and non-LoS path scenarios for both power saving and robustness enhancement of cooperative multicast in millimeter-wave wireless personal area networks. Our aims are to reduce power consumption and enhance the robustness of cooperative multicasts in millimeter-wave wireless personal area networks. First, we describe a novel beam training protocol that is capable of overhearing and information feedback to filter relay candidates with non-LoS links and avoid selecting relays for transceivers with LoS paths. Second, the joint relay selection and power allocation issue is formulated as an optimization problem with the objective of minimizing the maximum combined power consumption of the source and relay under maximum tolerable outage probabilities and transmit powers. By introducing relaxation and Lagrange multiplier methods, a closed-form expression for the joint relay selection and power allocation is obtained. Finally, simulation results indicate significant improvements in terms of both outage probability and power consumption over the conventional combined transmit power minimization algorithm.     

空时分组编码在多入多出系统中的容量分析

研究瑞利衰落信道下正交空时分组编码的信道容量,针对收端已知信道状态信息(CSI)以及收发两端均知CSI的2种情况,给出相应的容量分析及计算公式的推导。在收端已知CSI情况下,采用泰勒级数展开方法,给出一种信道容量的近似表达式,该式可有效简化原有精确公式的计算,获得与真实值非常相似的结果。在收发两端均知CSI情况下,提出一种基于最陡下降算法的简单计算方法,用于求解最优中断门限值,该方法可避免原有求解方法的大量搜索和计算。仿真结果表明,所给出的信道容量精确表达式以及近似表达式均与相应的计算机仿真结果一致,从而验证了所推公式的有效性。     

基于QoE的LTE多业务资源分配算法

高效地利用无线频谱资源和保证用户体验质量是未来无线网络的主要目标。基于此，提出一种基于QoE的LTE多业务资源分配算法。在考虑信道信息、QoS要求及公平性的基础上，引入QoE来计算的用户优先级。特别的，引入最小QoE约束来保证RT用户QoE要求；提出一种次优资源块（Resource Block，RB）分配算法来解决复杂的资源分配优化问题，该算法主要分为两步：保证RT用户最小QoE要求；最大化系统加权和速率。仿真结果表明，相较现有的RT/NRT资源分配算法，该算法在用户分组丢失率、平均QoE和小区频谱效率方面性能都有所提升。     

A simple amplify-and-forward opportunistic relaying based on outdated channel state information

Opportunistic relay selection(ORS)is a promising approach for cooperative communications owing to its low complexity by activating only the best relay.However,in mobile scenarios,the channel state information(CSI)estimated in relay selection may be different from the actual CSI employed in data transmission due to relatively fast varying channels,i.e.,CSI is outdated,which may lead to incorrect relay selection,and hence system performance deteriorates.To address the problem,this paper designs a relay selection strategy with instaneous and statistical CSIs in amplify-and-forward(AF)cooperative networks whose instantaneous CSIs of two hops employed in relay selection are both outdated.Based on high signal-to-noise ratio(SNR)analysis,we propose a distinctive relay selection strategy which can be described as selecting the relay with the asymptotic optimum average symbol error probability(SEP)and outage probability at high SNR.The corresponding asymptotic outage probability and SEP performance analysis are also provided.Finally,simulation results not only validate our theoretical analysis,but also show that in asymmetrical outdated CSI scenarios,the proposed strategy achieves better performance than existing relay selection strategies at medium and high SNR values.     

鲁棒的双向多中继物理层安全传输方案

针对双向多中继系统物理层安全传输无法获取窃听者的精确信道状态信息（CSI）的问题,提出鲁棒的多中继协作波束形成和人工噪声联合物理层安全传输方案,以最大化系统总功率约束下信道状态"最差情况"时的安全总速率。在该方案中,待求解的问题是一个复杂的非凸优化问题。采用交替迭代和连续凸近似（SCA）方法,对波束形成向量、人工噪声协方差矩阵和源节点发射功率进行交替优化迭代,得到了问题的优化解。仿真实验验证了所提方案的有效性,并表明该方案具有更优的安全性能。     

中继OFDMA系统容量公平资源分配算法研究

针对OFMDA解码-转发中继系统的资源分配问题,提出了一种以系统总功率和用户间的数据速率比例公平为约束条件,以最大化系统总速率为目标的资源分配算法。该资源分配问题为非线性最优化问题,联合求解所有变量复杂度很高,通过次优化的方法降低计算复杂度。算法包括：子载波分配和功率分配。子载波分配是以功率平均分配为前提,对基站-中继站和中继站-用户链路的子载波按照信道条件进行配对,并根据比例公平约束将配对的子载波分配给相应的用户。功率分配是对每个用户利用Lagrange方法调整每个子载波的功率,进一步提高系统的数据速率。算法仿真分析表明,该算法既能同时满足多用户不同数据速率的要求,又能提高系统的数据速率。     

异构网络中基于鸽群优化算法的D2D资源分配机制

针对异构蜂窝网络中D2D(device-to-device)通信用户复用蜂窝用户上行信道产生的频谱资源分配优化问题,提出一种基于改进离散鸽群算法(PIO)的D2D通信资源分配机制.通过设置信干噪比(SINR)门限值保证用户的通信服务质量(QoS),使用基于改进地图-指南针算子和认知因子的离散鸽群算法(IMCBPIO)为D2D用户进行资源分配,并采用基于接收SINR的闭环功率控制算法动态调整用户的发送功率,以减少用户与基站以及用户与用户之间存在的干扰.仿真结果表明,所提出方案能够有效抑制异构网络中由于引入D2D用户后导致的干扰,降低通信用户的中断概率,大大提高频谱利用率和系统吞吐量.