一种超宽带模拟合并转发协作通信系统

针对频率选择性衰弱信道下协作通信系统信道估计复杂的问题,提出了一种模拟合并放大转发超宽带(UWB)协作通信方案.该方案在源节点处对发送符号进行实数分布式空时编码并附加传输参考,在中继节点处利用传输参考对多径分量进行模拟合并,从而构建了一种改进型非正交放大转发协作通信系统.仿真结果证明,相对于无协作通信系统,模拟合并转发...     

基于协作干扰的全双工中继系统混合安全传输协议

针对全双工中继系统的安全问题,提出一种基于协作干扰的物理层安全混合传输协议.系统根据自身信道状态信息,自适应地选择基于中继节点与信源节点轮流发送干扰(RSCJ)协议或基于中继节点与目的节点轮流发送干扰(RDCJ)协议中安全容量相对较高的协议进行信息的传输.在全双工节点自干扰因素被抑制的条件下,给出了系统的传输协议选择策略,并理论推导了采用RSCJ或RDCJ传输协议下系统的安全中断概率表达式.仿真结果表明,利用所提的混合安全传输协议可以显著提高全双工中继系统的安全中断性能,与传统未利用协作干扰的传输机制相比,具有明显的安全性能优势.     

基于能量有效性的协作节点配置问题研究

无线通信的能耗主要由功放能耗和电路能耗两部分组成。在大距离传输中,通信能耗由功放能耗主导,电路能耗往往被忽略不计。而在以短距离传输为主的传感器网络中,电路能耗成为不可忽略的一部分,甚至有可能超过功放能耗成为通信能耗的主导。本文就如何通过节点间协作降低网络的通信能耗展开研究,拟解决协作通信中的协作节点配置问题。本文将信源-协作节点间距离纳入协作通信系统模型,提出一种针对调制参数、协作中继数、信源-协作簇距离对协作通信能耗进行联合优化的策略,并在无线传感器网络环境下对该模型的能耗进行了仿真。仿真结果表明,在传输距离一定的情况下,通过协作节点的数量、调制参数和信源-协作簇距离的联合优化配置,可以更有效地提高协作传输的节能效果。      

一种在宽带无线网络环境下的协作分集方法

协作通信可以使单天线的移动终端共享它们的天线而产生虚拟多发射天线阵列以获得发射分集。提出了一种在频率选择性衰落信道条件下的协作分集方法,信宿不仅利用转接节点转发的信号而且还利用了信源直接传来的信号来进行解码。通过计算机仿真,比较了考虑信源到信宿的直接传输的协作方法和未考虑信源到信宿的直接传输的协作方法的误比特率性能。结果表明,考虑信源到信宿的直接传输可提高系统的协作分集增益。     

基于认知无线电系统的协作中继分布式功率分配算法

协作通信与直接通信相比能够显著地提高系统性能。协作通信中的一个关键问题是管理中继节点及有效地进行功率分配。尤其对于频谱共享的认知无线电(Cognitive Radio,CR)系统,协作方案的设计不仅要最大限度地提高认知网络协作的功率效率,而且需要最小化对主系统的干扰。该文针对认知无线电系统的协作通信问题,在多个中继节点与源节点协同通信的场景下,提出了一种基于放大转发(Amplify and Forward,AF)模式下的功率分配及联合优化算法,在保证主系统传输性能不受影响的前提下,提高认知系统的传输速率。仿真结果表明该文提出的自适应协作传输方案,和直接传输及等功率传输方案相比获得了进一步的性能增益,中断概率显著下降。     

多跳协同中继网络下物理层安全传输方案

针对多跳中继传输系统的信息安全传输问题,提出了一种基于全双工模式下多节点协作干扰(FD-MCJ)的物理层安全传输方案。该方案利用通信网络中的中继节点发送干扰信号恶化窃听节点的接收性能,同时中继节点根据信道状态信息(Channel State Information, CSI)自适应的选择两种情况下的安全传输方案。本文首先利用泊松点过程对窃听节点位置进行安全建模;然后,根据CSI可用程度,给出不同的安全传输具体方案,在考虑系统的跳数、天线间自干扰以及发射功率和干扰功率等因素下,推导FD-MCJ方案下系统保密中断概率的闭式解;最后,数值分析和蒙特卡洛仿真表明,理论推导的正确性以及多跳中继系统中采用全双工多节点协作干扰方案能够有效提升系统安全性能。      

基于混合信号的放大转发中继系统的物理层安全传输

中继系统可以增强物理层安全算法的系统性能,这种系统一般包含两阶段的通信过程:从信源到中继节点,在从中继节点到目的节点.通常来说,第一阶段的信息传输缺乏保护,如果窃听者距离信源节点比较近的话,系统性能就无法保证了.该文提出了一种基于混合信号的三阶段的传输方法确保整个传输过程中的保密性能,这样,当窃听者接近信源节点的时候,仍可以保证系统的安全性能.这种方法的优化解是一个复杂的非凸优化问题,该文中建议了一种低复杂度的次优解来解决其中的优化问题.理论分析以及方针结果证明,该方法可以有效确保系统的全过程的安全性能.     

基于空时码的协作节点功率分配策略

为了优化协作通信系统的性能,文中提出了一种基于空时编码、以最大化系统互信息量为目标的各节点最优功率分配算法。通过采用凸优化的算法,功率在源节点和中继节点间得到了合理的分配。采用了更接近实际衰落环境的Nakagami模型。理论分析和仿真表明,所提算法能显著提高系统性能和功率效率,因而可以有效地用于协作通信中。     

智能窃听下协作NOMA网络的性能分析

针对下行双用户NOMA (Non-Orthogonal Multiple Access)系统模型中存在智能窃听者,该窃听者可以自适应地选择被动窃听或主动干扰工作模式,在不精确了解其干扰水平的情况下,部分NOMA用户很有可能遭遇传输质量下降乃至保密中断,这将对信息安全传输构成严重威胁。另外,由于信道衰落,用户的位置对系统整体性能有很大影响,难以保证距离源节点较远用户的传输质量。为解决上述问题,本文提出了一种新型的两阶段用户协作方案。第一阶段,远用户采用全双工(full-duplex,FD)干扰智能窃听者,第二阶段,近用户可作为一个中继协助源节点转发远用户信号信息,并在接收端采用串行干扰消除（Successive Interference Cancellation, SIC）技术进行解码。使用户间达成合作,提高通信链路安全性和用户服务质量。考虑到系统中不同用户的信息接收速率与通信需求不同之间的相关性,分别推导了遍历安全容量和遍历容量的解析表达式,同时分析了功率分配因子和用户间协作发射功率等因素对性能的影响,并通过Monte-Carlo仿真验证了其正确性。      

全双工窃听者主动干扰的协作NOMA网络性能分析

研究了瑞利衰落信道下协作非正交多址系统的安全性能。通信过程由一个时隙构成,源节点向中继广播叠加信号,全双工中继使用串行干扰消除技术解码信号协助用户通信。假设存在潜在全双工主动窃听者,窃听者能够从中继处截获信息并同时向用户发送人工噪声进行干扰。基于上述假设,在高信噪比条件下,推导了安全中断概率的近似表达式,分析了各节点传输信噪比与功率分配因子对系统中断概率的影响,分析结果与蒙特卡洛仿真结果吻合。     

一种基于源端网络编码和交替传输的中继协作方案

针对源节点通过两个中继向目的节点发送数据的无线通信系统,为了减小传统中继协作方案的复用损失,提出了一种将源端网络编码和交替传输有效结合起来的新方案,称为交替源端网络编码(SSNC)。该方案在源端每三个时隙对发送数据进行一次网络编码,并且两个中继在相邻的时隙中交替的发送和接收数据,每个时隙中,一个中继接收源端数据的同时另一个中继转发上一个时隙其接收到的数据给目的端。通过对该方案的中断概率和分集复用折中性能的推导和分析,发现该方案相对于传统的重复编码和分布式空时码方案在获得相同分集阶数的情况下有更高的传输效率,在实际的通信系统中可以兼顾性能和效率。仿真结果证实了我们的结论。      

A Non-Orthogonal Selection Cooperation Protocol with Interference in Multi-Source Cooperative Networks

This work proposes a non-orthogonal selection cooperation scheme with interference for multi-source and single destination cooperative networks. In our model, the source nodes can cooperate for one another, i.e., each source node plays the dual role of a source and a relay, thus there is no need for relays. In addition, the source nodes can be continuously transmitted and without dedicated timeslots for cooperative transmissions, which can save system resources and improve spectral efficiency. However, by this way, it will introduce interference with the non-orthogonal transmission mechanism. To overcome this problem, we use general reception scheme in source nodes and successive interference cancellation technology in the destination node, which can reduce the effect of interference effectively. For interference-limited networks, we also derive the theoretical upper bound and lower bound of outage probability of our method. Through the outage probability analysis and comparison, the results show that the spectral efficiency is improved while the system still keeps acceptable transmission reliability.

     

Decode-and-Forward Cooperative Diversity with Power Allocation in Wireless Networks

We study power allocation for the decode-and-forward cooperative diversity protocol in a wireless network under the assumption that only mean channel gains are available at the transmitters. In a Rayleigh fading channel with uniformly distributed node locations, we aim to find the power allocation that minimizes the outage probability under a short-term power constraint, wherein the total power for all nodes is less than a prescribed value during each two-stage transmission. Due to the computational and implementation complexity of the optimal solution, we derived a simple near-optimal solution. In this near-optimal scheme, a fixed fraction of the total power is allocated to the source node in stage I. In stage II, the remaining power is split equally among a set of selected nodes if the selected set is not empty, and otherwise is allocated to the source node. A node is selected if it can decode the message from the source and its mean channel gain to the destination is above a threshold. In this scheme, each node only needs to know its own mean channel gain to the destination and the number of selected nodes. Simulation results show that the proposed scheme achieves an outage probability close to that for the optimal scheme obtained by numerical search, and achieves significant performance gain over other schemes in the literature     

Relaying methods with high coding rate for wireless communications

A cooperative wireless relaying communication system usually consists of a source node, a destination node and one or more relay nodes. In this work Amplify-and-Forward/Decode-and-Forward relaying techniques are discussed in order to improve the performance of a wireless relaying communication system under the case of high code rate. As a performance metric, the outage probability of the proposed Amplify- and-Forward/Decode-and-Forward relaying structure is compared with and without coding issue. Results from the proposed modeling and simulations illustrate that our Amplify-and-Forward/Decode-and-Forward relaying method with high code rating enables robust cooperative wireless communication.     

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.     

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。     

一种选择发送的协作网络编码及其性能分析

衰落环境中,自动重传技术是实现错误处理、完成数据传输的有效方法之一。本文提出了一种选择发送的协作网络编码（Cooperative Network Coding based on Selective Transmission,ST CNC）,该技术在数据重传过程中,将空时协同发送与网络编码技术相结合,可以有效减少重传次数,提高网络资源利用率。针对一发两收系统,单个中继节点辅助传输的情形,分析了ST CNC的中断性能和网络编码增益,结果表明:相对于传统的广播策略,选择发送的协作网络编码可以获得2阶分集增益;此外,在中低信噪比区域,ST CNC同时可以获得明显的网络编码增益。      

非正交选择译码转发协同

为了提高两跳中继网络的传输速率和协同分集增益,该文提出一种非正交的选择译码转发策略传输数据。单节点协同时,协同节点仅在正确译码时采用和发送节点非正交的时序转发;在多节点协同时,采用一种节点选择算法选择译码正确且信道条件最佳的节点用于非正交转发。这种协同策略可获得和非正交放大转发相同的分集复用折衷性能,但其实现更简单,且在低信噪比时中断性能更好。     

On the performance of two‐user full‐duplex network‐coded cooperation

In this paper, we propose two schemes based on a full‐duplex network‐coded cooperative communication (FD‐NCC) strategy, namely, full‐duplex dynamic network coding (FD‐DNC) and full‐duplex generalized dynamic network coding (FD‐GDNC). The use of full‐duplex communication aims at improving the spectrum efficiency of a two‐user network where the users cooperatively transmit their independent information to a common destination. In the proposed FD‐NCC schemes, the self‐interference imposed by full‐duplexing is modeled as a fading channel, whose harmful effect can be partially mitigated by interference cancellation techniques. Nevertheless, our results show that, even in the presence of self‐interference, the proposed FD‐NCC schemes can outperform (in terms of outage probability) the equivalent half‐duplex network‐coded cooperative (HD‐NCC) schemes, as well as traditional cooperation techniques. Moreover, the ?‐outage capacity, that is, the maximum information rate achieved by the users given a target outage probability, is evaluated. Finally, we examine the use of multiple antennas at the destination node, which increases the advantage of the FD‐NCC (in terms of the diversity‐multiplexing trade‐off and ?‐outage capacity).     

Space-time cooperative diversity scheme using full feedback

This article proposes a new space-time cooperative diversity scheme called full feedback-based cooperative diversity scheme (FFBCD). In contrast to the conventional adaptive space-time cooperative diversity schemes that utilize the feedback from only the destination node, the new scheme utilizes the feedback from both the destination node and the cooperation node. With the feedback from the destination node, the occasional successful reception of the destination node in the information distribution stage can be detected, thus avoiding unnecessary retransmissions in the information delivery stage. The feedback from the cooperation node indicates the receiving state of the cooperation node in the information distribution stage, and the source node and the cooperation node will not perform cooperative retransmission during the information delivery stage unless the cooperation node is received successfully in the information distribution stage. In this way the new scheme can reduce the number of transmission attempt and improve the channel utilization. The expressions of the average number of transmission attempt are given. Numerical approximations and simulation results both show that the new scheme performs better than the non-cooperative scheme and the conventional adaptive space-time cooperative diversity scheme.