基于OSS-RS系统的中继选择和功率分配策略

为了提高系统的可达速率和,降低系统的中断概率,本文提出了一种联合机会源选择(OSS)和中继选择(RS)的OSS-RS系统。在最大化可达速率和的基础上,提出了最大化瞬时信噪比(Maximize the instantaneoussignal-to-noise ratio,MISNR)的中继选择策略。在等功率分配条件下,提出了基于AF的OSS-RS系统的最大化信道增益的调和平均值(Maximize Harmonic Average,MHA)的中继选择策略。进一步,在最大化瞬时信噪比的基础上提出了一种最优功率分配方案。理论分析和仿真结果均表明,本文提出的中继选择和功率分配策略提高了系统的可达速率和,降低了系统的中断概率,改善了系统的性能。     

基于中继放大转发的多天线基站下行传输性能分析

研究基站具有多根天线、中继与用户具有单天线的中继放大转发多用户系统,利用正交空时分组编码和机会主义调度策略同时获得空间分集和多用户分集.针对自适应增益和固定增益转发策略,首先导出独立不同分布瑞利衰落下系统中断概率和误码率的闭合表达式;随后根据高信噪比下系统的渐近性能确定系统的分集阶数,分析空间分集和多用户分集对系统性能的联合影响,并与单跳多天线基站下行传输系统进行性能比较;最后利用计算机仿真验证理论分析结果的正确性.     

过时信道状态信息下的机会式中继选择系统的安全性能分析

在 Nakagami m衰落信道下,目的端和窃听者采用最大比合并策略,本文研究了在机会式自适应解码转发中继选择安全协作系统中的安全性能。由于实际信道中的反馈延迟,最优的合法中继选择基于合法信道反馈的过时信道状态信息。为了评价机会式中继选择在改善安全性能上的表现,分别推导了准确的正安全容量概率和准确的安全中断概率闭合表达式。此外,针对两种不同情况, 推导了形式简单的渐近表达式,并明确给出安全分集阶数和安全阵列增益。理论分析和数值仿真表明,增加中继个数和目的节点的天线数能够改善安全中断概率的性能表现,且在信道状态信息过时的条件下,系统的安全分集阶数与中继数无关。      

不可信无线中继网络中基于用户选择的安全通信研究

该文研究在不可信解码转发无线中继网络中,基于用户选择的安全通信策略与性能分析.根据直接链路与中继链路的信道增益,本文提出三种不同的选择准则以提升系统的安全性;文章推导了三种选择准则下安全截断概率的闭式解析表达式及渐近表达式.根据渐近表达式和数值仿真结果可知,次优准则可以达到与最优准则几乎相同的系统安全性能.同时部分选择准则也能达到全分集增益性能.     

多中继与多用户选择的中继系统安全性能分析

为了考察使用多中继选择与多用户选择的放大转发（AF）中继系统的物理层安全性能,推导了其在瑞利衰落信道上和联合发送天线选择/接收最大比合并天线分集下的非零安全容量概率和安全中断概率的精确表达式以及在高信噪比下的渐近安全中断概率解析表达式。AF中继系统的非零安全容量概率和安全中断概率的数值计算和仿真结果相吻合,验证了以上理论分析的正确性;分析结果表明,其安全分集增益为源节点发射天线数、最优中继节点接收天线数、中继节点数的三者乘积与最优中继节点发射天线数、最优用户接收天线数、用户数三者乘积之间的最小值,且与窃听信道无关。     

MIMO多中继辅助通信中的优化调度

针对中继辅助通信系统,讨论了多中继并行传输下的优化设计问题,提出了一种简化的线性优化方案,并从多用户分集的角度,在等待服务用户中选择中继协作分集增益较大的用户对其进行服务.这种方案巧妙地减少了由于多中继并行传输所造成的用户间干扰,保持了多中继并行传输引入的空间分集所带来的性能优势,达到了提高系统总吞吐量的目的.     

多用户MIMO网络的OFDM放大转发双向中继策略

在多用户MIMO通信网络中,该文提出一种新的放大转发双向中继策略,在第1时隙的多址传输中采用OFDMA,在第2时隙的广播传输中采用OFDM/SDMA,通过利用频率分集和空间分集提高了系统性能。针对双向中继传输的特点,采用两种方法在每个子载波上设计了中继波束形成矩阵,即信漏噪比(SLNR)准则和块对角化迫零(BDZF)准则。利用割集理论推导了该双向中继网络的容量域上界。仿真结论表明,所提出的双向中继策略在系统和速率性能上优于其他3种中继策略,并能逼近所推导的容量域上界。     

基于分布式中继选择的自适应协作传输方案

协作分集通过使网络用户共享彼此天线以形成虚拟多天线阵列,可以显著提高网络容量,然而针对网络拓扑的动态变化与无线传输的时变特性,仅靠协作分集并不能十分有效地解决这些问题,必须结合考虑相应的自适应传输策略.本文提出动态网络环境中协作中继的最佳选择准则,在此基础上给出最佳协作中继的分布式选择协议.根据协作中继与源节点间的无线信道质量,进一步提出一种自适应协作传输方案,以有效抵抗多用户网络环境中的无线衰落.此外,对自适应协作传输方案的误码性能,在瑞利衰落信道下进行相应的理论分析,得到了系统误比特率的解析表达式,据此给出数值仿真实验以进行性能比较.结果表明:相对于传统协作分集而言,本文提出的自适应协作传输方案获得了进一步的性能增益,误比特率显著下降.     

多用户SIMO-OFDM系统中的协作分集性能分析

协作分集使得在多用户环境下,具有单天线的多个终端可以共享彼此的天线,以形成一个虚拟的天线阵列结构,实现空域分集。首先介绍了多用户SIMO—OFDM系统中的两种协作方式,放大前传和译码前传。然后针对源结点和目的结点之间是否存在路径损耗,提出了一种基于信道状态信息的选择中继协作方式,并对系统性能进行了理论和仿真分析。仿真结果表明,这种基于信道状态信息的选择中继协作方式可以获得较好的系统性能。     

多用户协作和中继的性能分析与比较

以蜂窝网的下行线路为例,描述了不采用协作、多用户协作、基于最优用户选择的多用户协作、多中继协作和基于最优中继选择的多中继协作等五种模式的具体场景和时隙分配示意图,给出了五种模式下的基站和目的用户之间的互信息和一帧内所消耗的总能量。对五种模式下中断概率进行了数值仿真。理论分析和仿真结果表明,多用户协作能获得较大的分集增益,而多中继协作的能量效率较高。信噪比受限条件下,无论多用户协作还是多中继协作,采用协作选择技术后,能量效率更高。     

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.     

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.     

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.

     

Optimal Power Allocation in an Amplify-and-Forward Untrusted Relay Network with Imperfect Channel State Information

The characteristics of the wireless medium create difficulty to shield the data transmission from unauthorized recipients. In this paper, power optimization in an amplify-and-forward untrusted relay network is presented, using cooperative jamming transmission to prevent the untrusted relay from intercepting the confidential signals. Considering imperfect channel estimation error at the destination, an optimal power allocation (OPA) is designed to maximize the achievable secrecy rate for the network. Simplified OPA is derived for high signal-to-noise ratio regime with imperfect CSI and the ergodic secrecy rate is also analyzed to evaluate the achievable average secrecy rate for different scenarios as a common performance metric. The numerical results show that when the error of CSI is considered, the proposed OPA generates limited and acceptable degradation on the secrecy rate.     

基于携能通信的非信任双向中继网络安全传输方案

针对非信任双向中继网络的能量受限和信息安全问题,该文提出一种基于无线携能通信(SWIPT)与人工噪声辅助的物理层安全传输方案。该方案中的非信任中继采用功率分割(PS)策略辅助合法用户进行保密通信,而全双工干扰机在进行能量采集的同时发送人工噪声以确保系统安全。以最大化系统保密性能为目标,优化了中继的PS因子,推导了保密和速率的解析式及高信噪比条件下最佳PS因子的闭式解。特别针对非理想信道状态信息的情况,分析了信道估计误差对系统保密性能的影响。仿真结果验证了理论推导的正确性,并证明了所提的基于PS策略的干扰机协同传输方案相比采用时间切换(TS)策略或目的节点协同干扰的方案具有更优的保密性能。     

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.

     

基于AF策略的高斯正交不信任中继信道的最优资源分配

本文研究了高斯正交中继窃听信道,中继节点同时作为窃听者的情况,源节点同中继节点和目的节点在信道1上传输信号,中继节点同目的节点在信道2上传输信号,信道1和信道2在频率上是正交的。通过分析,在总的信道资源受限的情况下,通过优化功率及信道带宽获得最大的安全速率。本文给出了在高斯正交信道下,当只考虑功率或带宽时,存在唯一的功率或带宽使得安全速率达到最大,并且通过仿真结果说明了采用最优资源分配可得到比等资源分配更大的安全速率。     

Secrecy analysis of a cooperative NOMA network using an EH untrusted relay

In this paper, a down-link non-orthogonal multiple access (NOMA) system with imperfect successive interference cancellation (SIC) using Energy-Harvesting untrusted relays is investigated. These relaying nodes use in this study use a power-switching architecture to harvest energy from the sources signals and apply an amplify-and-forward protocol to forward the signals. In addition, transmit jamming or artificial noise, is generated by a source node to improve the security of the system and protect confidential source information from untrusted relays. Likewise, three relaying selection strategies are employed to examine the secrecy performance of the proposed system. In order to evaluate the performance evaluation of the proposed system, closed-form expressions of the Secrecy Outage Probability (SOP) are studied over Rayleigh fading channels and a Monte Carlo simulation is used to confirm the analytical results. Furthermore, we study the effects of various parameters, such as power allocation factors, relay node selection, the number of relays, energy harvesting efficiency and the location of relay nodes on the secure outage performances for two users of NOMA system and conventional orthogonal multiple access (OMA). These results show that NOMA offers the better security performance with multiple users.     

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.