多中继协作通信系统容量分析及中继选择协作分集策略

本文针对多中继辅助通信系统,将系统建模为一个两跳通信链路,并进行了系统容量分析。针对两种特殊情况:用户端接收噪声方差远小于中继端接收噪声方差和中继端接收噪声方差远小于用户端接收噪声方差的情况,本文具体给出了系统传输容量上限与协作中继个数之间的关系。基于容量的分析,本文设计了两种中继选择策略。在第一种情况下,根据中继与用户间的信道特征值对多路数据流分别选取不同的中继子信道进行传输;在第二种情况下,选择一个信道条件最好的中继完成多路数据流的并行传输。仿真分析表明,不同的信道环境需要选择不同的中继选择策略。      

基于NOMA的D2D辅助中继系统性能分析与优化

本文针对两阶段NOMA(Non-Orthogonal Multiple Access)-D2D((Device-to-Device)辅助中继场景提出了一种功率优化算法，推导分析了各用户的中断概率。构建了以最大化系统各态历经容量为目标的优化问题，由于一、二两阶段通信用户的差异性，重点优化了对提升系统容量起决定作用的第一阶段功率分配因子，分析证明了原优化问题存在极值点，并利用凸函数性质获得了优化的功率分配因子，并且进一步推导分析了各个用户的中断概率。仿真结果表明，理论推导的中断概率值与仿真结果完全一致，证明了推导的正确性，本文提出的功率优化算法能显著提高系统容量，且降低了中断概率。例如当SNR为35dB时，本文算法可以提高约17.6%的系统容量，而作为辅助中继用户的中断概率大约降低了81.3%。      

Cooperative power allocation with partial channel information in multi‐cell multi‐user dual‐hop MIMO relay systems

This paper considers cooperative power allocation with the use of partial channel state information (CSI) in a multi‐user dual‐hop relay system with multiple antennas. The end‐to‐end capacity can be improved by dynamically allocating the transmit power of the base station and relay according to co‐channel interference caused by the adjacent relays. The proposed scheme allocates the transmit power in association with the eigenvalues and angle difference between the eigenvectors of transmit correlation matrices of the desired and interference channel. It is shown by means of upper‐bound analysis that the end‐to‐end capacity of the proposed scheme can be maximized in highly correlated channel environments when the principal eigenvectors of transmit correlation matrices of the desired and interference channel are orthogonal to each other. It is also shown that the proposed scheme is robust to the channel estimation error. Finally, the performance of the proposed scheme is verified by the computer simulation. Copyright © 2010 John Wiley & Sons, Ltd.     

Diversity achieving full-duplex DF relaying with joint relay-antenna selection under Nakagami-m fading environment

One of the main imperfections degrading the performance of full-duplex (FD) relaying systems is the outage floor. In this work, a power scaling method is proposed, which overcomes this effect even when there does not exist a direct channel between source and destination nodes. The system is composed of $K$ decode-and-forward (DF) FD relays over the Nakagami-m fading environment. To promote system performance, joint antenna and relay selection methods are employed in the FD relaying systems. Each FD relay is equipped with multiple antennas for receiving and the other for transmitting the information. The transmitting and receiving antennas are chosen based on the instantaneous channel variations, and one relay is selected to improve the signal-to-interference and noise ratio (SINR) of the FD relaying system. The performance of the proposed design is investigated. Moreover, the closed-form equations of the ergodic capacity and outage probability are attained. The analytical results are confirmed by different simulations. Results indicate that the proposed design achieves an additional spatial diversity gain because of using the antenna selection at the relay nodes. Moreover, by power scaling (PS) method, the system performance is effectively improved compared to the conventional FD relaying structures.     

ADS‐B aided robust relay selection for cooperative communications in aircraft approach

The ground‐to‐air communications in the aircraft approach stage suffer from multipath fading. We propose to combat this problem using cooperative communication technique. The relay selection problem is formulated to minimize the spectrum cost while preserving the signal‐to‐noise‐ratio (SNR) outage requirement of the approaching aircraft. By leveraging the position and velocity information in the automatic dependent surveillance‐broadcast messages, the average channel gains can be derived with uncertainty sets based on the Ricean channel model. Because the outage probability of the received SNR is intractable, we transform the outage constraint into a simple but efficient reliability requirement. The formulated problem is a mixed integer nonlinear optimization problem, with robustness in the worst‐case average SNR. A robust greedy relay selection algorithm is proposed as a solution, whereby a Kalman filter based trace prediction algorithm is adopted to determine the order of relays. Simulation results are given to show the effectiveness of the proposed scheme.Copyright © 2014 John Wiley & Sons, Ltd.     

认知中继网络中认知用户基于频谱感知机会中继的中断性能分析

认知无线电中继网络中,认知用户需要成功感知到其所在簇内的主用户频谱空穴后才能成为认知中继节点,且各认知中继节点发射功率受到各自主用户干扰温度限制(ITC)。该文对认知中继节点采用分布式空时编码和解码转发协议时认知用户的中断性能进行了分析;给出了认知用户在干扰温度限制下中断概率的上下界,得出中断概率的上下界在不同干扰温度限下与认知用户归一化数据速率、中继数量和其对主用户检测概率的关系。给出了源节点和频谱感知中继节点在相同干扰温度限下的数值仿真,并对仿真结果进行了分析。     

Distributed power allocation strategies for parallel relay networks

We consider a source-destination pair assisted by parallel regenerative decode-and-forward relays operating in orthogonal channels. We investigate distributed power allocation strategies for this system with limited channel state information at the source and the relay nodes. We first propose a distributed decision mechanism for each relay to individually make its decision on whether to forward the source data. The decision mechanism calls for each relay that is able to decode the information from the source to compare its relay-to-destination channel gain with a given threshold. We identify the optimum distributed power allocation strategy that minimizes the total transmit power while providing a target signal-to-noise ratio at the destination with a target outage probability. The strategy dictates the optimum choices for the source power as well as the threshold value at the relays. Next, we consider two simpler distributed power allocation strategies, namely the passive source model where the source power and the relay threshold are fixed, and the single relay model where only one relay is allowed to forward the source data. These models are motivated by limitations on the available channel state information as well as ease of implementation as compared to the optimum distributed strategy. Simulation results are presented to demonstrate the performance of the proposed distributed power allocation schemes. Specifically, we observe significant power savings with proposed methods as compared to random relay selection.     

Secure Energy Harvesting Communications with Relay Selection over Nakagami-m Fading Channels

In this paper, an energy harvesting relay network over Nakagami-m fading is investigated. In the considered system, the power beacon can provide wireless energy for the source and relays which deploy time-switching-based radio frequency energy harvesting technique. Two relay selection schemes, namely partial relay selection and optimal relay selection, are proposed in order to enhance the system performance. In the former, the source only has the channel state information of the first hop, while in the latter it has the full knowledge of the channel state information. The eavesdropper is able to wiretap to the signal transmitted from the source and the relays. The exact closed-form expressions of secrecy outage probability are derived. The results show that optimal relay selection performs better than partial relay selection. With increasing number of relays, the considered system shows better performance. In addition, the energy harvesting duration has a significant effect on the secrecy outage probability.     

Outage-based design of robust Tomlinson–Harashima transceivers for the MISO downlink with QoS requirements

We consider a broadcast channel in which the base station is equipped with multiple antennas and each user has a single antenna, and we study the design of transceivers based on Tomlinson–Harashima precoders with probabilistic quality of service (QoS) requirements for each user, in scenarios with uncertain channel state information (CSI) at the transmitter. Each user's QoS requirement is specified as a constraint on the maximum allowed outage probability of the receiver's mean square error (MSE) with respect to a specified target MSE, and we demonstrate that these outage constraints are associated with constraints on the outage of the received signal-to-interference-plus-noise-ratio (SINR). We consider four different stochastic models for the channel uncertainty, and we design the downlink transceiver so as to minimize the total transmitted power subject to the satisfaction of the probabilistic QoS constraints. We present three conservative approaches to solving the resulting chance constrained optimization problems. These approaches are based on efficiently solvable deterministic convex design formulations that guarantee the satisfaction of the probabilistic QoS constraints. We also demonstrate how to apply these approaches in order to obtain computationally efficient solutions to some related design problems. Our simulations indicate that the proposed methods can significantly expand the range of QoS requirements that can be satisfied in the presence of uncertainty in the CSI.     

Comparison of Tightly Power-Constrained Performances for Opportunistic Amplify-and-Forward Relaying with Partial or Full Channel Information

In this letter, we present exact statistical expressions for opportunistic amplify-and-forward (AF) relaying under a tight power constraint, where a best relaying node is selected based on partial channel information (PCI) or full channel information (FCI), respectively. Based on the statistical analysis, we compare PCI with FCI strategy in terms of outage and average capacity. Numerical investigation shows that, as the number of candidate relays increases, the performances with FCI are continuously improved while those improvements with PCI are bounded. However, for the small number of the relays at a low SNR region, PCI and FCI achieve very similar performances. The numerical results also show that the relaxed power constraint that ignores the noise power at the relay leads to significant deviations from the tight constraint, which is the more reasonable one, especially in computing the outage with FCI.     

PHY-layer Fairness in Amplify and Forward Cooperative Diversity Systems

We deal with the concept of physical-layer fairness in amplify and forward cooperative diversity systems, which reflects the need for equally allocating the consumed power among the relays. To this end, we propose a method which utilizes knowledge on both the instantaneous and average channel conditions in order to encompass this concept, by attributing a weight coefficient to each relay depending on its average channel state and then selecting the relay with the best instantaneous "weighted" channel conditions. We also provide a performance analysis of the proposed scheme that includes an analytical expression for the outage probability, together with a closed form one in the high signal-to-noise-ratio (SNR) regime. Through the latter expression, the average symbol error probability (ASEP) for high SNRs is also derived. Numerical results demonstrate that, for small number of available relays or for high SNRs, the performance of the proposed scheme resembles that of the "best relay selection" scheme, in terms of outage probability and ASEP, despite maintaining the average power consumptions equal.     

全双工协作多播业务在NOMA系统中的应用和性能

研究了多播业务在协作非正交多址接入（non-orthogonal multiple access,NOMA）系统中的应用及其性能。在一个单播和多播混合业务的场景中,多播用户组中选择某个信道状态最好的用户作为中继进行解码转发单播用户的信号,并在中继用户支持全双工的模式下,分析和推导了单播用户的中断概率和平均可达速率的闭式表达式。蒙特卡洛仿真结果和理论推导高度一致,表明提出的协作多播应用可以极大改善单播用户的中断性能,且多播用户的容量性能在中继发射功率不是很高的情况下不会受到影响。     

Security versus reliability analysis for multi-eavesdropper cooperation wireless networks with best relay

Physical-layer security could be used to effectively combat eavesdroppers and the transmission reliability of the main link could be improved.A wireless relay network with multiple both decode and forward eavesdroppers and relays were considered,in the presence of the link from source to destination.A best relay selection scheme based on multieavesdropper’s cooperation was proposed,and the outage probability and the intercept probability was deduced under both schemes without relay and with best relay.Then,the security and reliability influenced by different relay selection schemes were analyzed.The simulation results show that the achievable channel capacity at the destination node and the system outage probability are directly affected by different relay selection scheme.Lower system outage probability can be achieved by the proposed scheme,and the system outage probability and intercept probability are both decreased with the increase of the number of relays.The intercept probability increases with the increase of the number of eavesdroppers,which,however,can be reduced by increasing the number of relays to ensure the main link’s reliable transmission.     

可重构智能表面辅助的非正交多址接入网络鲁棒能量效率资源分配算法

为提高非正交多址接入(NOMA)网络的鲁棒性和系统能效(EE),考虑了不完美信道状态信息,该文提出一种可重构智能表面(RIS)辅助的NOMA网络鲁棒能效最大资源分配算法。考虑用户信干噪比(SINR)中断概率约束、基站的最大发射功率约束以及连续相移约束,建立了一个非线性的能效最大化资源分配模型。用Dinkelbach方法将分式形式的目标函数转换为线性的参数相减的形式,利用S-procedure方法将含有信道不确定性的SINR中断概率约束转换成确定性形式,利用交替优化算法将多变量耦合的非凸优化问题分解成多个凸优化子问题,最后用CVX对分解出的子问题进行求解。仿真结果表明,在EE方面,所提算法比无可重构智能表面(RIS)算法提高了7.4%。在SINR中断概率方面,所提算法比非鲁棒算法降低了85.5%。     

Opportunistic Decode-and-Forward Relaying with Interferences at Relays

In this paper, a decode-and-forward cooperative interference-limited multiple relay network is considered. An efficient relay selection strategy and its performance analysis are proposed, where only the relay nodes are affected by multiple interferences. In the proposed relay selection scheme, the selected relay is not always used, depending on the power of interferences and the channel state information of all links, while the direct path between source and destination is always used. For analytical tractability the distribution of interference-limited channel is approximated as an exponential distribution with high accuracy. Analysis of cooperative networks with interference-limited relays can be performed using the approximate exponential distribution by the same methods which have been used without interferences. We derive the bit error probability and outage probability of the proposed opportunistic max-min relay selection (OMRS) scheme in independent non-identically distributed Rayleigh fading channels. Numerical results present the superiority of OMRS over the conventional relay selection scheme which always uses the selected relay path. The exactness of the approximate analysis for interference-limited relays is also shown in numerical results.     

多跳协同中继网络下物理层安全传输方案

针对多跳中继传输系统的信息安全传输问题,提出了一种基于全双工模式下多节点协作干扰(FD-MCJ)的物理层安全传输方案。该方案利用通信网络中的中继节点发送干扰信号恶化窃听节点的接收性能,同时中继节点根据信道状态信息(Channel State Information, CSI)自适应的选择两种情况下的安全传输方案。本文首先利用泊松点过程对窃听节点位置进行安全建模;然后,根据CSI可用程度,给出不同的安全传输具体方案,在考虑系统的跳数、天线间自干扰以及发射功率和干扰功率等因素下,推导FD-MCJ方案下系统保密中断概率的闭式解;最后,数值分析和蒙特卡洛仿真表明,理论推导的正确性以及多跳中继系统中采用全双工多节点协作干扰方案能够有效提升系统安全性能。      

OFDM固定中继系统中单中继多源用户资源分配方案

通过基站的反馈信息,一个固定中继节点可以用一个OFDM符号同时帮助多个源用户转发信息,这样可以有效地利用带宽。因此,为了进一步提高系统容量,降低中断概率,先在中继节点间进行子载波调整,然后以获取信道容量最大为原则,提出了源用户和中继节点间子载波配对和功率分配的联合优化算法。仿真结果表明,相对于随机中继子载波选择算法以及平均功率分配算法,所提算法的中继系统容量有较大提升,同时中断概率有较为明显的下降。     

Power Allocation with Max–Min and Min–Max Fairness for Cognitive Radio Networks with Imperfect CSI

This paper consider the power allocation strategies in the cognitive radio (CR) system in the presence of channel estimation errors. As the user has different channel condition in CR systems, different amount of power resource is required to meets the QoS request. In order to guarantee the fairness of each CR user, ensure the interference from the primary user and other CR users meet the QoS requirement of the CR user and limit the interference that is caused by CR users on primary user within the range into the level that primary user can tolerate, we proposed some new power allocation schemes. The targets are to minimize the maximum power allocated to CR users, to maximize the minimum signal-to-interference-plus-noise ratio (SINR) among all CR users and to minimize the maximum outage probability over all CR users. The first power allocation scheme can be formulated using Geometric Programming (GP). Since GP problem is equivalent to the convex optimization problem, we can obtain the optimal solutions for the first scheme. The latter two power allocation schemes are not GP problems. We propose iterative algorithms to solve them. Simulation results show that proposed schemes can efficiently guarantee the fairness of CR users under the QoS constraint of the primary user and CR users.     

A coalitional game‐based relay load balancing and power allocation scheme in decode‐and‐forward cellular relay networks

In this paper, a game theoretic relay load balancing and power allocation scheme is proposed for downlink transmission in a decode‐and‐forward orthogonal frequency division multiple access‐based cellular relay network. A system with a base station communicating with multiple users via multiple relays is considered. The relays have limited power, which must be divided among the users they support. In traditional scheme, each relay simply divides its transmit power equally among all its users. Moreover, each user selects the relay with the highest channel gain. In this work, we do not apply the traditional relay scheme. It is because the users are distributed randomly, and by applying the traditional relay selection scheme, it may happen that some relays have more users connected to them than other relays, which results in having unbalanced load among the relays. In order to avoid performance degradation, achieve relay load balancing, and maximize the total data rate of the network, a game theoretic approach is proposed, which efficiently assigns the users to relays. The power of each relay is wisely distributed among users by the efficient power allocation scheme. Simulation results indicate that the proposed game‐based scheme can considerably improve the average sum‐spectral efficiency. Moreover, it shows that by applying the game, users who can connect to uncongested relays join them as opposed to connecting to congested relays. Copyright © 2015 John Wiley & Sons, Ltd.     

D2D辅助的协作中继NOMA系统中TSRS策略及其中断性能分析

该文研究了D2D辅助的协作中继NOMA（DC-NOMA）网络,在中继用户（RU）转发信息的第二时隙,利用RU到蜂窝中心用户（CCU）的D2D通信链路传输新的信号。为了提高传输可靠性,设计了新的信号检测策略,通过完全利用边缘信息消除了用户间的干扰。基于新的信号检测策略,提出了一种两阶段中继选择策略（TSRS）。在满足蜂窝边缘用户（CEU）可靠接收的中继集合中,选择使CCU成功解码概率最大的中继。为了评估所提出的DC-NOMA方案,推导了每个用户的确切中断概率且通过仿真得到验证。仿真结果表明,在高信噪比区域,该文所提出的基于新的信号检测策略的DC-NOMA在TSRS方案下的中断性能优于部分中继选择方案（PRSS）和传统的DC-NOMA。特别地,增大中继数量可有效提高DC-NOMA系统的中断性能。