基于协作非正交多址的无人机辅助卫星通信系统中断性能分析

针对无人机(UAV)辅助的卫星通信系统下行链路,该文研究了基于多天线波束成形和协作非正交多址(NOMA)技术相结合的多用户传输系统。首先,在UAV采用多天线和NOMA技术服务多个用户的情况下,基于用户平均信干噪比最大化准则,提出一种利用角度信息的波束成形方案。其次,在卫星-UAV链路服从相关阴影莱斯分布,而UAV-地面用户链路服从Nakagami-m分布的条件下,推导出系统的中断概率闭合表达式。然后,为了进一步分析系统性能,还推导了高信噪比条件下系统的中断概率近似表达式。最后,计算机仿真验证了理论分析的正确性和所提方案的优越性。     

基于混合光电传输的无人机中继通信系统性能分析

针对基于光电混合架构的无人机中继通信系统下行链路多用户传输场景,提出了一种基于统计信道状态信息的波束成形方案,并进一步分析了系统的中断概率。在该混合架构中,基站—无人机链路和无人机—用户链路采用自由空间光技术和射频传输完成通信过程。在已知RF链路统计信道状态信息的情况下,首先提出了一种波束成形方案以抑制用户间干扰,实现所有用户同时通信,提升了系统的频谱效率。然后,在自由空间光链路和射频链路分别服从Gamma-Gamma分布和Nakagami-m分布的条件下,推导出了系统中断概率的闭合表达式。进一步,得到了高信噪比条件下中断概率的渐进表达式,获得了系统的分集度。最后,仿真结果验证了理论分析的正确性以及所提方案的优越性。     

协同通信中双向多中继网络的中断概率分析

针对频率非选择性瑞利衰落信道条件下,研究了双向多中继协同通信系统的中断概率性能.首先基于模型的信号传输过程分析了系统的信道容量.然后根据单条链路接收信噪比的累积分布函数,推导了系统中断概率的闭合上界表达式;根据接收端采取最大比合并时的接收信噪比最大,计算了信噪比最大时的概率密度函数,推导了系统中断概率的闭合下界表达式.最后,结合具体的数值仿真对不同参数下的系统中断概率分别进行了详细的分析比较.仿真实验验证了理论推导的结果,并且还表明了双向多中继模型的中断概率优于双向单中继模型.     

Underlay协同频谱共享系统中基于SDF-DZFB的物理层安全传输

协同中继传输不仅能改善认知用户的传输可靠性,而且也能增强认知用户物理层安全性。针对Underlay模式下多中继协同频谱共享认知无线网络,本文设计了基于选择译码转发和分布式迫零波束成形（SDF-DZFB）的物理层安全传输方案,其中,假设存在单个被动窃听节点窃听中继节点的发送信号,在认知用户发送端同时考虑峰值干扰温度约束和最大发射功率约束,中继和认知用户目的端都受到主用户干扰。在此情况下,分析了认知用户发送端分别到目的端（称为主链路）和到窃听节点（称为窃听链路）的等效信干噪比的统计特性,进而推导出系统安全中断概率性能的闭式表达式。为了揭示所提物理层安全传输方案的安全分集度性能,本文进一步分析了高信噪比条件下安全中断概率的渐近表达式。计算机仿真验证了本文的理论分析结果。      

同频干扰环境下双向AF中继性能分析及参数优化

双向中继（two-way relaying, TWR）作为提高中继网络频谱效率的一种有效手段,近年来受到广泛关注。本文研究同频干扰环境下三时隙TWR策略的中断概率性能,中继采用放大转发（amplify-and-forward, AF）策略。首先,理论推导了策略中断概率下界的闭合表达式和高信噪比下的渐进表达式。仿真表明,理论结果能够匹配策略的实际中断概率性能。根据理论结果,以最小化中断概率为目标对中继节点功率分配和中继位置参数进行优化。提出三种优化问题,即（1）给定中继位置,中继功率分配优化问题,（2）给定中继功率分配方案,中继位置优化问题,（3）联合优化中继功率分配和中继位置。仿真结果表明,联合优化能够实现最优的中断概率性能。      

非理想硬件条件下协作NOMA系统安全中断性能研究

实际收发设备的非理想硬件(RHI,Residual Hardware Impairment)特性会对协作非正交多址接入(NOMA,Non?Orthogonal Multiple Access)系统性能产生重要影响.因此,本文提出了基于RHI的下行链路单窃听多中继协作NOMA系统模型,推导了联合考虑合法链路和窃听链路使目标信噪比最大化(M?LaE?SNR,Maximized SNR for Legiti-mate and Eavesdropping link)中继传输方案下的安全中断概率闭合表达式和渐近表达式.分析和仿真结果表明,所提M?LaE?SNR方案相比其他方案可有效提高用户的安全中断性能,且中继数越多所提方案性能优势越明显;同时RHI使得系统安全传输性能降低,且RHI对性能的影响程度主要与主链路信噪比以及协作中继个数有关;且不同节点处的RHI对系统安全性能造成的影响程度不同.研究结果还证明了用户的安全分集阶数等于中继数量K.     

双向多中继协同通信系统的性能分析

针对频率非选择性瑞利衰落信道,研究了双向多中继协同通信模型的系统性能。首先,基于模型的信号传输过程分析了系统的信道容量;然后,根据接收信噪比的累积分布函数推导了系统中断概率的闭合上界表达式;进一步在MPSK调制方式下,通过计算在高信噪比条件下的矩母函数,推导了平均误码率的闭合表达式。仿真结果验证了理论推导的正确性,并且表明双向多中继模型的中断概率和平均误码率两项性能指标都优于双向单中继模型。     

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。      

不对称放大转发双向中继功率分配及中继位置选择

该文研究基于放大转发中继的不对称双向中继系统容量问题。首先,在瑞利衰落信道环境下,从双向通信的角度,通过理论分析得出其中断概率精确表达式和渐进表达式。理论分析发现节点发射功率和源节点目标速率共同决定系统中断概率,并且在大多数业务下系统中断性能仅取决于单向链路,而与另一链路无关。基于此,以优化系统中断性能为目标,提出一种基于业务知识的节点功率分配算法和中继位置选择算法。数值仿真实验结果表明,通过功率分配和中继位置选择可以显著提高不对称放大转发双向中继系统的中断性能。     

功率约束下的星地协作网络中断概率分析

针对星地协作网络,考虑中继节点转发卫星节点信号时会受发射功率和干扰功率约束,提出了一种基于中继节点与目的节点间链路最大信噪比准则来选择中继节点的放大转发部分中继选择策略。在卫星链路遭受阴影莱斯衰落和地面链路遭受瑞利衰落情况下,推导出系统中断概率下界的闭合表达式。仿真结果表明了理论分析的正确性,并展示了不同阴影莱斯信道参数、不同中继数目、不同功率约束对中断概率的影响。     

Performance analysis of beamforming in two-hop AF relay networks with antenna correlation and interference

This paper investigates the performance of a two-hop amplify-and-forward (AF) relay network with antenna correlation and co-channel interference (CCI) over Rayleigh fading channels. In this network, the relay has multiple antennas while both the source and destination are equipped with a single antenna. By assuming that the statistical channel state information (SCSI) is available at the relay, the maximal output signal-to-interference-plus-noise ratio (SINR) is first obtained. Then, with the help of the specialized functions, the analytical expressions for the outage probability (OP), Ergodic capacity and average symbol error rates (ASERs) of the considered AF relay network are all derived. Moreover, the asymptotic analysis at high signal-to-noise ratio (SNR) is also presented to reveal the diversity order and array gain of the relay system. Finally, computer simulations are given to confirm the validity of the theoretical analysis and indicate the effects of antenna correlation and interference on the system performance.     

Performance analysis of AF OFDM system using multiple relay in presence of nonlinear‐PA over inid Nakagami‐m fading

In this paper, performance of an orthogonal frequency division multiplexing–based variable‐gain amplify and forward cooperative system using multiple relay with relay selection is analyzed over independent but not necessarily identically distributed frequency selective Nakagami‐m fading channels. For the analysis, nonlinear power amplifier is considered at the relay, and selection combining is adopted at destination node. Closed‐form expressions of the outage probability for various threshold signal‐to‐noise ratio (SNR) values and average symbol error rate for M‐ary quadrature amplitude modulation techniques are derived for the considered system. Further, the outage probability analysis is performed in high SNR regime to obtain the diversity order. Furthermore, impact of different fading parameters, multiple relay, and nonlinear power amplifier is highlighted on the outage probability and asymptotic outage probability for various threshold SNRs and on the average symbol error rate for various quadrature amplitude modulation constellations. The derived analytical expressions are generalized for various fading environments while considering the integer‐valued fading parameters. Finally, all the analytical results are verified through the Monte Carlo simulations for various SNR levels and system configurations.     

Performance Analysis of Maximum SNR Scheduling with an Infrastructure Relay Link

We consider infrastructure-based amplify-and-forward (AF) relaying for extending downlink and uplink coverage areas of a cellular base station. The base station serves multiple mobile users via a multi-hop backhaul relay link by sharing out access link channel resources with maximum signal-to-noise ratio (SNR) scheduling. We analyze the performance of the system by deriving closed-form expressions for outage probability, outage capacity, ergodic capacity, average end-to-end SNR and amount of fading (AoF). These measures show that maximum SNR scheduling of multiple users in a cellular relay link offers significant diversity, capacity and SNR improvement over single-user transmission and round robin scheduling. We also relate performance of the relay link to that of a distributed antenna system (DAS), and show that the noisy wireless backhaul relay link induces tolerable performance deterioration compared to deploying a cable-connected distributed antenna.     

Beamforming in Dual-Hop AF Relaying with Imperfect CSI and Co-channel Interference

This letter studies the joint effects of imperfect channel state information (CSI) and co-channel interference (CCI) on a dual-hop variable gain amplify-and-forward (AF) relay network with beamforming. The source and destination are both equipped with multiple antenna, while the relay has a single antenna. Specifically, the analytical expressions for the outage probability and average symbol error rate of the considered AF relaying are derived. Moreover, the asymptotic analysis at high SNR is also presented to reveal the diversity order and array gain of the relay system. Finally, computer simulations are given to confirm the validity of the proposed theoretical analysis and quantify the combined influence of imperfect CSI and CCI on the system performance.     

Application of best relay selection approach to cooperative DF IDMA systems over Rayleigh/Weibull fading channels

This paper analyzes the performance of cooperative decode‐and‐forward (DF) interleave‐division multiple‐access (IDMA) networks with best relay selection over Rayleigh/Weibull fading environments. In the analysis, approximate outage probability (OP) and bit error probability (BEP) expressions are derived for the considered system. Further, a 2‐hop DF IDMA system is also designed to compare with cooperative one. We propose OP and BEP expression for 2‐hop DF IDMA systems. Numerical results are obtained by changing the number of relays and the value of fading parameter in the proposed expressions. Also, simulations are provided to corroborate the exactness of the derived approximate OP and BEP expressions.     

Performance analysis of cooperative multi‐carrier relay‐based UAV networks over generalized fading channels

The outage probability in a network of cooperative unmanned airborne vehicles (UAVs) over generalized fading channels is studied analytically using finite mixture with expectation maximization technique. A relay‐based topology with one ground control unit (GCU) is considered, where the cooperative UAVs can communicate with the GCU directly or through relay. The application the UAV is assigned for specifies the minimum required transmission rate the UAV should achieve. The outage probability of the system is defined as the probability that either the transmission rate over any of the links drops below a predefined minimum threshold for that link or the Relay‐GCU link is not able to transmit the aggregate data from all relayed UAVs and the minimum rate required by the relay UAV itself. Throughout the paper, expressions for the outage probability and the average achievable bit rate of a cooperative multi‐carrier system are derived over generalized fading channels. Finite mixture with expectation maximization algorithm is utilized to derive a simple approximate expression for the probability density function (pdf) of the achievable bit rate assuming adaptive M‐ary quadrature amplitude modulation (M‐QAM). This pdf is used to derive closed‐form expressions for the outage probability and the average bit rate. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance Analysis of OSTBC Transmission in Amplify-and-Forward Cooperative Relay Networks

A performance analysis is presented for amplify-and-forward (AF) cooperative relay networks employing transmit antenna diversity with orthogonal space-time block codes (OSTBCs), where multiple antennas are equipped at the transmitter. We develop a symbol-error-rate (SER) and outage performance analysis for OSTBC transmissions with and without cooperative diversity over flat Rayleigh fading channels. We first derive exact probability density functions (pdf's) and cumulative distribution functions (cdf's) for the system SNR without direct transmission with an arbitrary number of transmit antennas and then present the exact closed-form SER and outage probability expressions. Next, we derive the moment-generating function (MGF) for the overall system SNR with direct transmission and present the exact SER and outage probability with joint transmit antenna diversity and cooperative diversity. The theoretical analysis is validated by simulations, which indicate an exact match between them. The results also show how the transmit antenna diversity and the cooperative diversity affect the overall system performance.      

Joint Relay and Antenna Selection in MIMO PLNC Inter-vehicular Communication Systems over Cascaded Fading Channels

We investigate the joint relay and antenna selection performance in a multiple input multiple output (MIMO) Vehicle-to-Vehicle (V2V) communication system employing physical layer network coding (PLNC) with amplify-and-forward (AF) scheme at the relay antenna. Analytic results are derived under the cascaded Nakagami-m fading channel model assumption, which covers cascaded Rayleigh and conventional cellular channel models as well. We evaluate the performance of the system in terms of joint outage probability of sources and derive closed-form expressions for lower and upper bounds while an exact expression is found as a single integral form. Besides, the asymptotic diversity order is analyzed and quantified as a function of number of relays and antennas installed on the source and relay vehicles, and channel parameters. Finally, we verify the analytic derivations by computer simulations. Our results show that the outage probability performance decreases with the increasing cascading degrees of the channels but joint relay and antenna selection enhances the performance of the system superbly with the increasing number of relays and antennas. Also it is shown throughout all the simulation results, the lower bound for the joint outage probability seems to consistently be well tight for large SNR. Therefore it can be used for practical design of inter-vehicular communication systems which contain multiple relays and antennas.     

非理想SIC下全双工NOMA系统的安全性能分析

针对存在多个非共谋窃听者,研究了一种基于全双工中继和两阶段中继选择（TSRS）的非正交多址接入（NOMA）物理层安全通信方案。每个通信过程包含一个传输时隙,系统在每个时隙开始由TSRS策略选择最优中继,所选中继在从源节点接收NOMA叠加信号的同时,向两个目的节点转发上一时隙的再编码叠加信号,两个目的节点采用串行干扰消除（SIC）技术从中继叠加信号中解码获取各自的期望信号。推导了非理想SIC下系统安全中断概率的近似表达式,进行了蒙特卡洛（Monte-Carlo）仿真验证,同时分析了各仿真参数（SIC残余干扰系数、目标安全速率、中继规模等）与系统安全中断概率的关系。理论分析与模拟仿真的结果表明,全双工技术与TSRS的结合方案能有效提升系统的安全中断性能。将该方案应用于实际通信系统设计时,选择合适传输信噪比（SNR）、提高串行干扰消除能力或适当增加中继数量均可实现更好的保密性能。      

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.