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%。      

一种基于粒子群算法的DC-NOMA系统遍历容量优化方案

为提升设备到设备（Device-to-Device,D2D）辅助的协作非正交多址接入（Non-orthogonal Multiple Access,NOMA）中继系统的性能,以最大化系统遍历容量为目标建立优化模型,利用粒子群优化（Particle Swarm Optimization,PSO）算法设计最优功率分配策略,求出每个用户的最佳功率分配因子,从而得到系统遍历容量的最优值。仿真结果表明,所提出的基于PSO的功率分配方案不仅能提高系统容量,还可以降低用户的中断概率。     

基于网络编码的双向多中继系统中断概率分析

网络编码在双向多中继系统中已经得到了广泛地研究,并有效地提高了双向多中继系统的吞吐量。首先本文导出了在译码转发方式时,独立正交信道和多接入信道下基于网络编码的双向多中继系统平均中断概率表达式。Monte Carlo仿真和理论分析非常吻合,验证了理论分析的正确性。之后分析了系统平均中断性能在不同信噪比和不同中继节点个数等多种情形下与功率分配因子的关系,揭示了功率分配因子与系统总功率和中继节点数量之间的内在关系。仿真结果表明,双向多中继系统采用网络编码进行传输时,在独立正交信道下和多接入信道下的功率分配因子取值在区间 内能够获得最优的系统中断概率性能,并且多接入信道下的系统中断性能要好于独立正交信道。      

多中继AF协作系统功率分配研究

功率分配是协作通信中一个重要的研究方向,文章分析了放大转发（AF）协作方式下,基于正交信道的多协作中继系统模型,在此基础上推导了系统中断概率。并以最小化系统中断概率为目标,给出系统功率分配约束表达式,进一步分析了功率分配与中继节点位置的关系,计算求得单中继和两中继情况系统最优功率分配系数。系统仿真表明最优功率分配相对常规的等功率分配,系统性能明显提升。     

一种协作网络编码方案的功率优化分配方法

该文针对传统双路无线中继系统中的源和中继采用等功率发送,导致系统资源利用率低的问题,提出一种译码转发-空时协作网络编码方案的功率优化分配方法。该方法以最小化两源用户中断概率中的较大者为目标,并利用中断概率的高阶近似解,通过迭代计算获得最优功率分配因子。所提功率优化分配方法计算复杂度低且仅需信道的平均增益信息。仿真结果表明,与平均功率分配方法相比,所提功率优化分配方法使系统的中断概率和误码率性能均得到有效提升。     

基于非正交多址接入的移动边缘计算安全节能联合资源分配

为提高基于非正交多址接入(NOMA)的移动边缘计算(MEC)系统中计算任务部分卸载时的安全性,该文在存在窃听者情况下研究MEC网络的物理层安全,采用保密中断概率来衡量计算卸载的保密性能,考虑发射功率约束、本地任务计算约束和保密中断概率约束,同时引入能耗权重因子以平衡传输能耗和计算能耗,最终实现系统能耗加权和最小。在满足两个用户优先级情况下,为降低系统开销,提出一种联合任务卸载和资源分配机制,通过基于二分搜索的迭代优化算法寻求问题变换后的最优解,并获得最优的任务卸载和功率分配。仿真结果表明,所提算法可有效降低系统能耗。     

双向协作系统的中继选择和功率分配策略

针对瑞利衰落信道下双向多中继协作通信系统,为了降低中断概率,提出了一种基于最小化中断概率的中继选择策略和功率分配方案。首先联合考虑两条链路的中继节点处信噪比和信道增益实现双链路中继选择,然后推导出一种新的最优中继下双向放大转发协作中断概率的近似表达式上界,并利用凸优化求解得到使中断概率最小的最优功率分配解。仿真结果表明,与现有策略相比,提出的策略能够明显降低系统中断概率和误码率,显著提高系统性能。     

非再生中继网络的功率优化分配

为了降低非再生中继网络的中断概率,研究了基于中断概率最小化的功率分配问题.首先分析了两跳中继传输方式和协同分集传输方式中断概率近似表达式,然后以中断概率最小化作为优化目标,在总功率一定的条件下,建立了非再生中继系统中基于中断概率最小化的功率分配优化模型,通过Lagrange乘数法获得了源节点和中继的最优功率分配.仿真实验表明,与在源节点和中继中采用平均功率分配策略相比,采用基于中断概率最小化的最优功率分配策略,在降低中断概率的同时,也增加了系统的容量.     

非对称信道下协作通信系统中断概率的研究

首先建立了非对称信道下协作系统的数学模型,考虑了源节点到目的节点的直通链路,利用特征函数法推导出协作系统的平均中断概率公式,通过仿真验证了该中断概率公式的精确性,理论和仿真都表明协作系统的中断概率和中继节点的个数、位置分布以及协作系统的功率分配因子有着密切关系,并且考虑源到目的节点的直通链路相对于不考虑直通链路的情况具有更高的性能增益;然后又在此公式基础卜就协作系统中继节点的位置分布对最优功率分配因子的影响进行了仿真分析,并指出协作系统的最优功率分配因子受制于中继节点的位置分布情况.     

基于信道相关性的物理层安全性能分析

针对物理层安全研究中主窃信道具有相关性的场景,研究了主窃信道间的相关性对系统安全性能产生的影响,推导得到了遍历保密容量及中断概率的精确计算式,以及主窃信道的信道状态差异较大和较小这2种场景下的渐近计算式,并通过仿真验证了理论分析的正确性.研究结果表明,信道相关性会造成遍历保密容量的损失,但信道相关性强并不一定表明通信中...     

Asymptotic performance analysis of untrusted relay system with full-duplex jamming destination

The cooperative relay technique in the field of physical layer security is widely concerned by the academic community,due to the advantages of increasing the network capacity and expanding the network coverage.However,cooperative relays may play as untrusted nodes in some certain circumstances.Based on this,to enhance the secrecy performance of untrusted relay systems,a novel full-duplex destination jamming (FDJ) scheme was proposed in the Rayleigh fading channel.In order to maximize the system’s secrecy capacity,a switchable split-optimal antenna selection (OAS) scheme was proposed for a multiple-antenna destination,the power allocation optimization scheme between the source and destination was designed,and the corresponding closed-form expressions of secrecy performance were given.In the large-scale antennas analysis,the closed-form expressions of the ergodic achievable secrecy rate and the optimal power allocation factor of instantaneous secrecy capacity for the FDJ-OAS scheme were derived.Furthermore,based on different asymptotic cases,the asymptotic analyses of secrecy outage probability for the FDJ-OAS scheme were significantly analyzed.Simulation results show that the analytical curves match well with the Monte-Carlo simulation results.It is concluded that the diversity order of the FDJ-OAS scheme is proportional to the number of antennas and antenna diversity can be achieved,which reveals the advantages of the proposed FDJ-OAS scheme.     

Performance analysis of two-way relay cooperation underlay cognitive radio networks based on WIPT

The two-way relay cooperation for underlay cognitive radio networks based on WIPT was presented,where secondary system adopted the two-way relay cooperative transmission.First,the relay adopted a power splitting protocol to harvest energy and to decode information transmitted by secondary users,then the relay forwarded information to two secondary users by using the harvested energy.Subsequently the exact expression of the outage probability,the ergodic capacity and energy efficiency of the secondary user system were derived.Finally,numerical simulation discusses the impact on the system performance with regard to secondary transmission power.The results reveal that the two-way relay cooperation effectively reduces the outage probability of data transmission.The capacity and energy efficiency of the system reaches optimal level when the power allocation coefficient is 0.5.     

Secure communication via an energy-harvesting untrusted relay in the presence of an eavesdropper

This article studies a secure communication of a simultaneous wireless information and power transfer system in which an energy-constrained untrusted relay, which harvests energy from the wireless signals, helps the communication between the source and destination and is able to decode the source’s confidential signal. Additionally, the source’s confidential signal is also overheard by a passive eavesdropper. To create positive secrecy capacity, a destination-assisted jamming signal that is completely cancelled at the destination is adopted. Moreover, the jamming signal is also exploited as an additional energy source. To evaluate the secrecy performance, analytical expressions for the secrecy outage probability (SOP) and the average secrecy capacity are derived. Moreover, a high-power approximation for the SOP is presented. The accuracy of the analytical results is verified by Monte Carlo simulations. Numerical results provide valuable insights into the effect of various system parameters, such as the energy-harvesting efficiency, secrecy rate threshold, power-splitting ratio, transmit powers, and locations of the relay and eavesdropper, on the secrecy performance.     

Secure Communication Over Fading Channels

The fading broadcast channel with confidential messages (BCC) is investigated, where a source node has common information for two receivers (receivers 1 and 2), and has confidential information intended only for receiver 1. The confidential information needs to be kept as secret as possible from receiver 2. The broadcast channel from the source node to receivers 1 and 2 is corrupted by multiplicative fading gain coefficients in addition to additive Gaussian noise terms. The channel state information (CSI) is assumed to be known at both the transmitter and the receivers. The parallel BCC with independent subchannels is first studied, which serves as an information-theoretic model for the fading BCC. The secrecy capacity region of the parallel BCC is established, which gives the secrecy capacity region of the parallel BCC with degraded subchannels. The secrecy capacity region is then established for the parallel Gaussian BCC, and the optimal source power allocations that achieve the boundary of the secrecy capacity region are derived. In particular, the secrecy capacity region is established for the basic Gaussian BCC. The secrecy capacity results are then applied to study the fading BCC. The ergodic performance is first studied. The ergodic secrecy capacity region and the optimal power allocations that achieve the boundary of this region are derived. The outage performance is then studied, where a long-term power constraint is assumed. The power allocation is derived that minimizes the outage probability where either the target rate of the common message or the target rate of the confidential message is not achieved. The power allocation is also derived that minimizes the outage probability where the target rate of the confidential message is not achieved subject to the constraint that the target rate of the common message must be achieved for all channel states.     

Secure communication in untrusted relay selection networks with wireless energy harvesting

In this paper, we consider the secrecy performance of an energy-harvesting relaying system with Kth best partial relay selection where the communication of a multi-antenna source-destination pair is assisted via single-antenna untrusted relays. To protect confidential source messages from untrusted relays, transmit beamforming and destination jamming signals are used. The relays are energy-constrained nodes that use the power-splitting policy to harvest energy through the wireless signals from both the source and destination. For performance evaluation, closed-form expressions of the secrecy outage probability and average secrecy capacity (ASC) are derived for Nakagami-m fading channels. The analytical results are confirmed via Monte Carlo simulations. Numerical results provide valuable insights into the effect of various system parameters, such as relay location, number of relays, and power splitting ratio, on the secrecy performance. Specifically, the maximum ASC is achieved when the relay is located between the source and destination.

     

Ergodic capacity and outage probability optimization for secondary user in cognitive radio networks under interference outage constraint

This paper considers a cognitive radio network where a secondary user (SU) coexists with a primary user (PU). The interference outage constraint is applied to protect the primary transmission. The power allocation problem to jointly maximize the ergodic capacity and minimize the outage probability of the SU, subject to the average transmit power constraint and the interference outage constraint, is studied. Suppose that the perfect knowledge of the instantaneous channel state information (CSI) of the interference link between the SU transmitter and the PU receiver is available at the SU, the optimal power allocation strategy is then proposed. Additionally, to manage more practical situations, we further assume only the interference link channel distribution is known and derive the corresponding optimal power allocation strategy. Extensive simulation results are given to verify the effectiveness of the proposed strategies. It is shown that the proposed strategies achieve high ergodic capacity and low outage probability simultaneously, whereas optimizing the ergodic capacity (or outage probability) only leads to much higher outage probability (or lower ergodic capacity). It is also shown that the SU performance is not degraded due to partial knowledge of the interference link CSI if tight transmit power constraint is applied.     

射频能量采集非可信中继网络中物理层安全传输

射频能量采集技术为能量受限无线通信系统提供了一种有效的能量供给方式.假设能量受限中继节点具有射频能量采集能力,本文设计了中继非可信情况下的物理层安全传输方案,配置多天线的源节点采用发送天线选择策略来增强中继节点的能量采集性能,目的节点发送人工干扰来抑制非可信中继对保密信息的窃听.在瑞利块衰落信道条件下研究了所提方案的物理层安全性能,推导了系统安全中断概率、连接中断概率和安全吞吐量的闭式表达式.计算机仿真验证了理论推导的正确性,揭示了各系统参数对物理层安全性能的影响关系.     

Opportunistic Selection for Decode-and-Forward Cooperative Networks with Secure Probabilistic Constraints

This work presents theoretical analysis on security performance for relay selections based on either statistical or instantaneous channel state information (CSI) of the eavesdropper (CSI-E) channels in a decode-and-forward relaying network. By considering security constraints, we have derived exact expressions for the average secrecy rate and the secrecy outage probability. Moreover, analytical expressions of the false secrecy probability are derived for the suboptimal relay selection based on statistical CSI-E, which are used as the constrained functions of new selection metrics. Furthermore, our work achieves a better tradeoff between the outage probability and the false secrecy probability. The accuracy of our performance analysis is verified by simulation results.     

Service outage based power and rate allocation for parallel fading channels

The service outage based allocation problem explores variable-rate transmission schemes and combines the concepts of ergodic capacity and outage capacity for fading channels. A service outage occurs when the transmission rate is below a given basic rate r/sub o/. The allocation problem is to maximize the expected rate subject to the average power constraint and the constraint that the outage probability is less than /spl epsi/. A general class of probabilistic power allocation schemes is considered for an M-parallel fading channel model. The optimum power allocation scheme is derived and shown to be deterministic except at channel states of a boundary set. The resulting service outage achievable rate ranges from 1-/spl epsi/ of the outage capacity up to the ergodic capacity with increasing average power. Two near-optimum schemes are also derived by exploiting the fact that the outage probability is usually small. The second near-optimum scheme significantly reduces the computational complexity of the optimum solution; moreover, it has a simple structure for the implementation of transmission of mixed real-time and non-real-time services.     

Evaluating secrecy performance of cooperative NOMA networks under existence of relay link and direct link

The secrecy performance of a nonorthogonal multiple access (NOMA) system is examined in this study by employment of a dual‐hop decode‐and‐forward (DF) relay under existence of eavesdropper. Due to the fact that the relay is trusted or untrusted device and thus eavesdropper may wiretap information from the base station or the relay. In this regard, three scenarios related to trusted and untrusted relays are proposed, with different assumptions on the information overhearing ability of the eavesdropper; ie, the first scenario is that an eavesdropper overhears signal from the relay while the BS is overheard by eavesdropper in the second scenarios. More specifically, we derive closed‐form expressions for the secure probability metrics when the direct and relay links experience independent Rayleigh fading. There metrics include strictly positive secrecy capacity (SPSC) and the secure outage probability (SOP). Furthermore, secure performance of traditional orthogonal multiple access (OMA) is also provided as further comparison with NOMA counterpart. We analyze the influence of main coefficients such as the target rates and the transmit SNR factors on the secrecy performance. Our results specify that for reasonable selection of such parameters, secrecy performance can be enhanced remarkably. Numerical results are delivered to corroborate the derived results.