非理想信道状态信息的认知无线网络下行功率分配和波束赋形方法

针对非理想信道状态信息(CSI)条件下工作于underlay模式的认知无线网络(CRN)多用户下行功率分配和波束赋形研究中普遍存在的问题,包括忽略主网络(PN)对认知用户(SU)的干扰、传统的凸优化SDR方法对约束条件的近似要求以及实现算法复杂、实用性受限等,首先建立CRN模型,增添PN对SU的干扰项,而后在非理想CSI的最差条件下形成优化问题。再通过Lagrange对偶对问题的约束条件进行变换,并基于变换后的问题形式,利用上行和下行的对偶特性,引入虚拟功率,将优化问题转换为上行功率分配和波束赋形问题,进一步得到简便、快速和实用的迭代算法。数值仿真显示,算法收敛很快。并且发现非理想CSI引起的误差不仅对下行功率影响明显而且还改变优化问题的可行解区域;PN基站(PBS)的发送功率的变化对可行解区域有显著的影响。     

On Achievable Data Rates and Optimal Power Allocation in Fading Channels with Imperfect Channel State Information

Achievable rates of wireless communication systems with pilot-based channel estimation are investigated for the case of time-selective fading. Novel analytical expressions for the maximum achievable rates of such systems are derived in terms of the system signal-to-noise ratio (SNR), fading rate and estimation scheme deployed. The frame size is optimized jointly based on the SNR and the fading rate. The maximum rate achieving coding scheme is suggested and shown to be a modified version of the classical water-filling algorithm that accounts for imperfect channel state information (CSI) at the transmitter. The impact of the estimation scheme and the angular spread of the received signal on the quality of estimation and achievable rates is evaluated. A number of numerical simulations are provided to illustrate the dependence of the optimal block length and achievable rates on SNR, fading rate, estimation scheme and angular spread of the channel.

基于过时信道状态信息的放大转发中继选择协议性能分析(英文)

The impact of outdated Channel State Information(CSI) on the performance of relay selections,including the partial relay selection and the best relay selection,is studied,with respect to Amplify-and-Forward(AF) mode cooperative systems.The proposed method is analysed by deriving the asymptotic closedform expressions for some figures of merit such as the outage probability and the Symbol Error Probability(SEP).Moreover,the validity of the proposed theoretical analysis is proven via simulations.Numerical results prove that the performance of the proposed scheme is impacted considerably by various parameters such as the number of candidate relays and the end-to-end Signal-to-Noise Ratio(SNR).In the presence of cooperative networks with outdated CSI feedback,a performance improvement of more than 3 dB in terms of either outage probability or SEP can be observed by utilizing the Source-to-Destination(S D) link rather than the method of simply increasing the number of relays.     

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。      

Subchannel Allocation and Power Control for Uplink Femtocell Radio Networks with Imperfect Channel State Information

Wireless Personal Communications - Femtocell technology is emerging as a key solution for mobile operators for its advantage in coverage and capacity enhancement along with its cost effectiveness....     

Power Allocation Schemes for Amplify-and-Forward MIMO-OFDM Relay Links

We consider a two-hop MIMO-OFDM communication scheme with a source, an amplify-and-forward relay, and a destination. We examine the possibilities of power allocation (PA) over the subchannels in frequency and space domains to maximize the instantaneous rate of this link if channel state information at the transmitter (CSIT) is available. We consider two approaches: (i) separate optimization of the source or the relay PA with individual per node transmit power constraints and (ii) joint optimization of the source and the relay PA with joint transmit power constraint. We provide the optimal PA at the source (or the relay) with a node transmit power constraint that maximizes the instantaneous rate for a given relay (or source) PA. Furthermore, we show that repeating this separate optimization of the source and the relay PA alternately converges and improves the achievable rate of the considered link. Since the joint optimization of the source and the relay PA is analytically not tractable we use a high SNR approximation of the SNR at the destination. This approximation leads to rates which are quite tight to the optimum.     

无线并行放大转发中继传输中基于信噪比的功率分配研究

在无线通信网中,高效的功率分配可显著降低资源消耗、获得更好的服务质量、并减少网络内干扰.本文以无线并行中继协作通信系统为背景,在目的节点目标信噪比的约束条件下,对如何最小化中继链路中各通信节点的发射功率进行了研究.文章首先建立了无线中继协作通信系统模型,推导出了无线中继协作通信系统中信噪比的表达式.接着,文章将功率分配...     

Optimal Power Allocation with Limited Feedback of Channel State Information in Multi-User MIMO Systems

In this paper,an expression for the user’s achievable data rate in the multi-user multiple-input multiple-output(MU-MIMO)system with limited feedback(LF)of channel state information(CSI)is derived.The energy efficiency(EE)is optimized through power allocation under quality of service(QoS)constraints.Based on mathematical equivalence and Lagrange multiplier approach,an energy-efficient unequal power allocation(EEUPA)with LF of CSI scheme is proposed.The simulation results show that as the number of transmitting antennas increases,the EE also increases which is promising for the next generation wireless communication networks.Moreover,it can be seen that the QoS requirement has an effect on the EE of the system.Ultimately,the proposed EEUPA with LF of CSI algorithm performs better than the existing energy-efficient equal power allocation(EEEPA)with LF of CSI schemes.     

Optimal Transmission with Imperfect Channel State Information at the Transmit Antenna Array

We study the optimal transmission strategy of a multiple-inputsingle-output wireless communication link. The receiver has perfectchannel state information while the transmitter hasonly long-term channel state information in terms of the channelcovariance matrix. It was recently shown that the optimal eigenvectors of the transmitcovariance matrix correspond with the eigenvalues of the channelcovariance matrix. However, the optimal eigenvalues are difficult tocompute. We study the properties of these optimal capacity achieving eigenvalues, and present a necessary and sufficient condition for theoptimal eigenvalues of the transmit covariance matrix. Furthermore, we develop a necessary and sufficient condition forachieving capacity when transmitting in all directions. We compare thecapacity gain of an optimal diversity system with a system which works with beamforming, and we derive an upperbound. We answer the main questions regarding the system design using the developed results. Additionally, we show inwhich way the multiplexing gain can be computed in case the channel covariancematrix is given. We compute the maximum number of required paralleldata streams, and we define a multiplexing function inorder to obtain a measure for the available multiplexinggain. Furthermore, we show that the capacity gain is small considering theadditional complexity at the receiver. We illustrate allresults by numerical simulations.     

多中继放大转发协作通信中的功率分配和中继位置联合优化

文章研究了多中继放大转发协作分集系统中的功率分配和中继位置联合优化问题。利用信道的统计状态信息,在总功率一定的条件下,以最大化系统的信道容量为目标,推导了多中继和选择中继两种模型下基于高信噪比近似的联合优化算法的闭式解。理论分析和仿真验证表明,提出的算法大大提高了传统的等功率分配方案下系统的性能。     

具有功率分配因子的不可信中继系统的中断性能和遍历保密容量

基于不存在直接链路的具有不可信中继的三节点系统,本文在协作干扰模型中引入功率分配因子,对两种放大转发因子下系统的中断概率和遍历保密容量进行了计算及对比分析。首先,系统采用平均放大因子,推导出其保密中断概率;然后,在引入同样功率分配因子的基础上,系统改用自适应瞬时放大因子,得出保密中断概率的下界;为了对比,本文接着给出了系统两种情况下的遍历保密容量;最后,仿真验证了中断概率和遍历保密容量计算的准确性,数值仿真表明引入功率分配因子可减小系统的中断概率和提高系统的遍历保密容量,瞬时放大因子下系统性能较平均放大因子下更好。      

非理想信道状态信息对频谱共享认知中继网络性能的影响

在频谱共享认知中继网络中,非理想信道状态信息可能导致次级用户的干扰超过主用户所能容忍的最大干扰值,从而影响到主用户的正常通信。为了衡量次级用户的传输对主用户性能的影响,该文提出了干扰概率这一性能指标。在非理想的信道状态信息条件下,推导了次级用户采用机会中继与选择协作协议时的干扰概率闭式解析式。理论分析表明,从干扰概率角度看,选择协作协议优于机会中继协议,但二者的极限干扰概率相同。此外,在非理想信道状态信息条件下,无论是采用机会中继还是选择协作协议,增加中继数量都会对主用户造成更大的干扰。最后,仿真结果验证了理论分析的正确性。     

非精确信道状态信息下MIMO系统中的干扰删除

复杂的多天线环境中,未知的干扰和噪声无处不在,这些因素不但引起了多输入多输出(MIMO)系统信号检测的偏差,还加大了获取精确信道状态信息(CSI)的难度。因此,为了删除MIMO系统中的未知干扰,该文建立了非精确CSI下的系统模型,模型中的非线性函数表示MIMO系统中的干扰。基于非参数理论提出了针对这种干扰的干扰删除方法。与以往方法不同的是,模型中的干扰是完全未知的。进一步地,从理论上证明了干扰删除的有效性,即证明了估计函数的收敛性。仿真结果表明,所提出的方法能有效地删除系统中的干扰。     

窃听环境下AF中继选择与功率分配的研究

传统的最佳中继选择方案仅参考了合法用户的信道状态信息,在实际的通信系统中由于存在窃听用户而无法保证信息的可靠传输。现有的最佳中继选择方案将窃听用户的信道状态信息纳入考虑后,系统的安全性能得到了一定改善,但是依然采用的是等功率分配。针对放大转发协议,本文在现有最佳中继选择方案的基础上,以降低系统安全中断概率为目标,在系统总功率受限的前提下,根据源节点和中继节点以及中继节点和目的节点间的信道参数引出功率分配因子,对源节点和中继节点间的功率进行适当分配。通过仿真对比,可以发现功率分配能够降低系统的安全中断概率,从而改善系统的安全性能。      

Distributed SNR-Based Power Allocation in Wireless Parallel Amplify-and-Forward Relay Transmissions Using Cournot Game

In wireless communications, power allocation plays a paramount role in sustainable network lifetime prolongation with quality-of-service and network interference reduction. This paper investigates a distributed power allocation problem in wireless parallel amplify-and-forward (AF) relay transmissions. Particularly, the objective is set to minimize the total transmit power while guaranteeing the signal-to-noise ratio (SNR) requirement at the destination node. The distributed SNR-based power allocation problem is formulated and modeled as a Cournot game. Moreover, a distributed SNR-based power allocation algorithm is proposed to solve the Cournot game. The proposed distributed SNR-based power allocation algorithm is proved to converge to a unique equilibrium. To evaluate the distributed method, a centralized optimal SNR-based power allocation algorithm is also proposed. Numerical results show that the proposed distributed SNR-based power allocation algorithm can achieve comparable performance to the centralized optimal SNR-based power allocation algorithm.     

基于非理想信道状态信息的鲁棒安全发送方法

针对协方差信道状态信息(Channel State Information, CSI)不理想导致的通信系统安全性能恶化问题,该文提出一种鲁棒的人工噪声辅助的物理层安全发送方法。该方法基于非理想的协方差信道信息,对发送者的波束成形向量及人工噪声协方差进行联合优化设计,从而最大化系统的最差情况安全速率(Worst-Case Secrecy Rate, WCSR)。该功率受限的安全速率最大化问题是非凸的,采用半定松弛(SemiDefinite Relaxation, SDR)技术和Lagrange对偶理论将其转化为一系列的半定规划(SemiDefinite Program, SDP)问题进行求解。仿真结果表明,与现有方案相比,所提方法的安全性能有了明显的提升。     

Impact of Imperfect Channel State Information on the Physical Layer Security in D2D Wireless Networks Using Untrusted Relays

In this paper, we investigate the impact of channel estimation errors on the physical layer security of an overlaying device-to-device (D2D) wireless network with an amplify-and-forward untrusted relay. An untrusted relay assists D2D communication while may capture the confidential data. Under the practical assumption of imperfect channel state information (ICSI) for the relay-to-receiver D2D link, we take into account optimal power allocation (OPA) problem to maximize the achievable secrecy rate of two different scenarios which are without jamming and with friendly jamming. Based on these OPA solutions, we study the secrecy performance of the two scenarios by driving closed-form expressions for the ergodic secrecy rate (ESR) in Rayleigh fading channel. We also calculate the high signal-to-noise ratio (SNR) slope and high SNR power offset of the optimized scenarios by finding the asymptotic ESR. Numerical results confirm the accuracy of our proposed theoretical analysis. The results also demonstrate that our proposed OPAs enhance the ESR performance compared with other power allocation techniques. Moreover, they show the effect of ICSI on the ESR such that as channel estimation error grows, the ESR performance reduction is occurred.

     

基于功率分配能量采集的全双工放大转发中继系统

针对三节点放大转发中继系统,研究了基于功率分配能量采集的全双工中继传输方案。在中继配置大规模天线的情况下,提出了三种天线选择方法,并通过合理的假设分别推导了三种天线选择方法的速率的近似闭合表达式,并设计了天线选择模式切换方案。基于三种不同的天线选择方法,该文分析了基于功率分配采集协议中的最优功率分配因子以及不同方案的算法复杂度。最后,通过蒙特卡洛仿真证明了闭合表达式的准确性,并基于发射功率和信道增益分析了三种方案的优缺点。其中在大发射功率的情况下,方案一的性能最优;在小发射功率的情况下,方案二的性能最优;在中等发射功率的情况下,折中的方案三的性能最优。      

非理想状态信息下SC-FDMA上行链路的信道调度

信道依赖调度(CDS)通过在信道里使用多用户分集和频率选择性来增加蜂窝系统的数据吞吐量,主要研究非理想信道状态信息(CSI)对CDS的影响。具体来说,当CSI有反馈延时,分析具有未编码自适应调制及CDS的上行链路单载波频分多址(SC-FDMA)系统的数据吞吐量。频域资源分配采用集中式和分布式的子载波映射方案。通过仿真可以看到在应用CDS时,集中式的子载波映射产生最高的总数据吞吐量,然而,当信道迅速变化时,集中式映射对CSI的质量以及信道容量增益的迅速减少非常灵敏。对于高机动性的用户来说,具有静态轮询调度方案的分布式映射更加合适。