基于机会中继和最大比合并下的协作通信系统

分析了机会中继和最大比合并下的协作通信系统性能.首次给出了Nakagami衰落信道下的符号错误率和中断概率的精确闭式结果.通过对中断概率的近似结果分析发现对于任意一条源节点-中继-目的节点链路,分集增益均由源节点-中继链路和中继-目的节点链路中的深衰落链路决定.     

基于过时信道状态信息的机会协作性能研究

机会中继是协作通信系统中提高频谱效率和节省功率消耗的常用方法.在通信过程中,信道估计时刻和实际中继传输信息时刻存在一定的延时,其产生的过时信道状态信息（Outdated CSI）会严重地影响协作通信系统的性能.分别从考虑直传链路和不考虑直传链路两方面,分析了过时信道状态信息对机会协作分集系统中断概率的影响.仿真结果表明,系统性能随着相关系数ρ的减小而变差,并且随着中继节点数目的增加而提高.     

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。     

硬件损伤下能量采集双向中继网络系统中断性能分析

在硬件损伤条件下分析了能量采集双向中继网络的系统中断性能,该网络的终端节点对直达链路信号和中继链路信号分别进行选择合并（Selection Combining, SC）和最大比合并（Maximum Ratio Combining,MRC）。首先,推导了该网络在SC方案下的系统中断概率,并在此基础上得到了由硬件损伤而引起的两种效应,即中继协作效应和系统协作效应。然后,推导了该网络在MRC方案下的系统中断概率。最后,通过仿真分析了硬件损伤及系统参数对系统中断性能的影响,并比较了该网络在SC方案和MRC方案下的系统中断性能。仿真结果表明:在硬件损伤条件下,MRC方案仅引起系统协作效应;相比于MRC方案,SC方案对硬件损伤更加敏感;当数据传输速率低于系统协作门限时,采用MRC能够实现更好的系统中断性能。      

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.     

DF协同通信网络两种机会中继选择策略研究

本文针对DF协同通信网络,对两种机会中继选择策略的系统中继概率和复杂度进行了分析,其一是分布式机会中继,通过引入定时器,由各个中继节点根据本地信道状态信息竞争选出最佳中继,其二是集中式机会中继,由目的节点选择候选中继集合中瞬时信噪比最大的节点作为最佳中继。仿真结果表明,集中式机会中继的中断概率性能在高sNR时略优于分布式机会中继策略,但其复杂度和系统开销较高。     

全光自由空间光通信中继协作方案的研究

提出了一种结合副载波强度调制直接探测技术和全光放大转发中继的自由空间光通信(FSO)系统的基本结构,考虑背景噪声和放大自发辐射噪声对系统性能的影响,建立了Gamma-Gamma湍流模型下的全光通信系统模型。提出了两种中继协作方案,即全活跃中继方案与选择中继方案,基于相应的方案给出功率分配方式,仿真对比了中继辅助传输链路与直传链路的中断概率,以及在不同信道参数及中继数下采用这两种方案的系统中断概率。结果表明,中继传输能够明显改善链路的性能,选择中继方案优于全活跃中继方案。     

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.     

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。      

同信道干扰下的中继网络性能分析

分析了两跳中继网络在同信道干扰下的中断概率。在中继网络中,源节点广播信号至所有的中继节点,此时同信道干扰在中继节点或者目的节点处被引入。中继节点采用解码转发策略转发源节点的信号,而目的节点采用最大比合并技术接收来自中继节点的信号。最终推导了各种干扰情形下系统中断概率的闭合表达式。仿真结果表明,解析曲线和蒙特卡洛仿真曲线非常吻合,而同信道干扰在某些场合会对系统性能造成较大影响。分析结果对中继网络的系统设计和参数设置都有一定的参考意义。     

A cooperative phase steering scheme in multi-relay node environments

We propose a decode-and-forward (DF) based cooperative phase steering scheme and analyze its outage probability. The cooperative phase steering scheme is to make the received signals from multiple relay nodes co-phased at a destination node by pre-adjusting the phase differences.With a reasonable amount of feedback information from a destination node, the cooperative phase steering scheme circumvents the drawbacks of conventional cooperative diversity techniques such as maximal ratio combining (MRC) reception, maximal ratio transmission (MRT), and opportunistic relay selection schemes. Our analytical and simulation results show that the cooperative phase steering scheme outperforms the opportunistic relay selection scheme and approaches the MRT scheme known as a theoretically optimal cooperative diversity technique. It is also shown that cooperative phase steering has sufficient robustness to phase incoherence.     

Outage performance of two-hop multi-antenna co-operative relaying in rayleigh fading channel

Performance of co-operative relaying employing infrastructure based fixed relays having multiple antennas has been investigated. A closed-form expression of outage probability for such a system has been derived when the relay performs selection combining and the destination performs MRC combining of signals. The effect of relay placement on the system performance has also been studied.     

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.     

Multi-antenna Decode and Forward Relay Selection over Nakagami-m Fading Channels

This paper analyzes the performance of opportunistic relay under aggregate power constraint in Decode-and-Forward (DF) relay networks over independent, non-identical, Nakagami-m fading channels, assuming multiple antennas are available at the relay node. According to whether instantaneous Signal-to-Noise Ratio (SNR) or average SNR can be exploited for relay selection, two opportunistic relay schemes, opportunistic multi-antenna relay selection (OMRS) and average best relay selection (ABRS) are proposed. The closed form expressions of outage probability and error performance for binary phase shift keying (BPSK) modulation of OMRS and ABRS are determined using the moment generating function (MGF) of the total signal-to-noise ratio (SNR) at the destination. Simulations are provided to verify the correctness of theoretical analysis. It is observed that OMRS is outage-optimal among multi-antenna relay selection schemes and approaches the Beamforming (BF) scheme known as theoretical outage-optimal very closely. Compared with previous single-antenna Opportunistic Relaying (OR) scheme, OMRS brings remarkable performance improvement obtained from maximum ratio combining (MRC) and beamforming, which proves that multiple antennas at the relays could provide more array gain and diversity order. It also shows that the performance of ABRS in asymmetric channels is close to OMRS in the low and median SNR range.     

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.     

Performance of MRC combining multi-antenna cooperative relay network

Performance of cooperative relaying employing infrastructure based fixed relays having multiple antennas has been investigated. Employing MGF based approach, closed form expression for outage probability and bit error rate performance of BPSK signal have been derived, when relay and destination are assumed to perform MRC combining of the signals. The effect of relay placement on the system performance has also been studied under different path loss conditions.     

Performance of Transmit Antenna Selection and Maximal-Ratio Combining in Dual Hop Amplify-and-Forward Relay Network over Nakagami-m Fading Channels

In this paper, we study end-to-end performance of transmit antenna selection (TAS) and maximal ratio combining (MRC) in dual hop amplify-and-forward relay network in flat and asymmetric Nakagami-m fading channels. In the network, source and destination communicate by the help of single relay and source-destination link is not available. Source and destination are equipped with multiple antennas, and relay is equipped with single antenna. TAS and MRC are used for transmission at the source and reception at the destination, respectively. The relay simply amplifies and forwards the signal sent by the source to the destination by using channel state information (CSI) based gain or fixed gain. By considering relay location, for CSI based and fixed relay gains, we derive closed-form cumulative distribution function, moments and moment generating function of end-to-end signal-to-noise ratio, and closed-form symbol error probability expression. Moreover, asymptotical outage probability and symbol error probability expressions are also derived for both CSI based and fixed gains to obtain diversity order of the network. Analytical results are validated by the Monte Carlo simulations. Results show that diversity order is minimum of products of fading parameter and number of antennas at the end in each hop. In addition, for optimum performance the relay must be closer to the source when the diversity order of the first hop is smaller than or equal to that of the second hop.