频率选择性衰落信道DS-CDMA无人机中继通信系统航迹规划

无人机中继通信是实现远距离无线通信的一种重要技术手段，无人机的飞行航迹对无人机中继通信系统的链路传输可靠性存在显著的影响，在频率选择性衰落信道环境下研究了基于直序列码分多址（DS-CDMA）的无人机中继通信系统的航迹优化的问题。首先，给出了基于DS-CDMA的译码转发无人机中继通信系统的模型，并理论分析给出无人机中继通信系统的链路中断概率及平均误码率计算公式，以此为基础，基于链路中断概率最小化准则提出了中继无人机的航迹规划方法，最后通过仿真验证了所提出方法的正确性与有效性。研究表明：最大比值合并DS-CDMA无人机中继通信系统可充分获取频率选择性衰落信道提供的分集增益，显著改善链路传输的可靠性。     

非对称衰落信道下无人机中继传输方案及性能分析

 无人机(UAV)作为中继传输平台受到了国内外研究人员的广泛关注。本文研究了非对称衰落信道下的无人机中继传输系统,提出了输出信噪比最大化准则下的波束形成(BF)优化方案,并推导出系统中断概率、遍历容量和平均误符号率等无线通信系统主要性能指标的理论表达式。通过计算机仿真验证了本文提出的中继传输方案及性能分析的正确性,并定量分析了天线数量、信道参数以及功率分配对系统性能的影响,为无人机中继传输系统的设计及性能评估提供了参考和依据。     

基于无人机下行链路的OFDM信道估计研究

该文将正交频分复用技术(OFDM)传输系统应用于无人机下行数据链路中,基于无人机通信信道的组成、冲激响应模型,构建了无人机链路中的OFDM通信系统.针对无人机信道快时变和高动态等特点.提出一种改进的OFDM信道估计算法,给出了在无人机飞行状态下误码率性能的仿真结果.实验结果表明该OFDM信道估计算法可以满足未来无人机下行数据链路系统要求.     

一种全速率协作通信系统传输方案

针对协作通信带来链路传输效率降低的问题,在译码转发中继方案的基础上,提出一种新的全速率协作通信传输方案。首先给出全速率协作通信系统的接收信号模型,并利用矩函数方法理论推导给出全速率协作通信系统最大似然接收机的链路成对差错概率及链路分集增益,理论分析表明：全速率协作通信传输方案可获得1符号/时隙的传输效率,且最大似然接收机可获取4重分集增益。计算机仿真结果证明理论分析的正确性。     

一种基于多无人机的中继节点布置问题建模与优化方法

针对战场环境下急需在无法通信的节点间构建有效通信链路的情形,使用多无人机作为中继节点,建立了中继节点布置(RNP)问题模型。模型以中继链路有效和无人机安全为约束,以中继布置点位置及相应的无人机为输出,不但考虑了使用的中继无人机数量,还考虑了构建中继链路花费的时间。考虑到该问题是难以求解的混合整数多目标优化问题,同时在紧急应用情形下,要求求解算法快速有效,建立了一种多项式时间中继节点布置算法(PTRPA)。仿真实验验证了所提模型确实能够在更短的时间内完成有效中继链路构建;通过Monte-Carlo方法对比和分析不同因素对PTRPA算法、随机抽样算法、遗传算法求解该问题的结果性能和时间性能的影响,验证了PTRPA算法不但能够给出接近最优的解,且快速有效,满足战场决策需求。     

块空时分组编码SC—FDMA虚拟MIMO迭代均衡接收机

以块空时分组编码的SC—FDMA虚拟MIMO系统为研究对象,理论推导给出块空时分组编码的SC—FDMA虚拟MIMO系统接收信号模型及虚拟MIMO接收机迭代均衡算法：仿真结果表明：迭代均衡接收机可显著提高块空时分组编码的sc—FDMA虚拟MIMO系统的链路可靠性。     

多天线结构对无人机MIMO信道容量的影响

为进一步提高无人机(UAV)遥测链路传输容量,分析了无人机多输入多输出(UAV-MIMO)天线间隔、阵列等结构参数对信道容量的影响。建立了无人机MIMO基于散射体三维几何分布的单跳同心椭圆(GBSBCERS)信道模型,结合机载MIMO天线布局方案,给出了无人机MIMO信道矩阵及遍历容量的表达式。数值仿真表明,受无人机远距离通信的影响,信道容量与天线间隔呈正比变化;且相比于线阵布局,圆阵布局虽然受到无人机姿态变化的影响,但仍具有较高的信道容量。通过分析多天线结构对无人机MIMO信道容量的影响,对设计实现高速无人机数据链具有实际意义。     

CCSDS遥控通信操作规程应用

由于遥控通信的重要性,为了在有噪声的链路空间中可靠地传输遥控数据,CCSDS(空间数据系统咨询委员会)提供了遥控COP-1(通信操作规程)建议书。该探作规程使用遥控空间链路协议,规定了空间任务中地—空或空—空通信链路间应用数据的自动重传操作规程,保证了用户业务数据的正确传输。此外,还介绍了CCSDS标准建议书中的遥控通信操作规程的概念、业务类型,并对其中使用的内部规程接口、业务数据传输操作规程以及滑动窗口的应用进行了详细说明。     

基于网络编码的空间DTN中CGR改进算法

随着空间通信技术的发展,卫星节点的增多,以及容延迟容中断通信需求的不断提高,空间DTN (DelayTolerant Network,容延迟网络)环境中各通信节点间的路由技术日益重要,相继出现了多种适用于DTN的路由技术.基于空间DTN的结构与特点,对CGR(Contact Graph Routing,接触图路由)算法以及基于编码的路由算法进行了分析比较,然后针对空间DTN中CGR算法的缺点和不足,研究提出了基于NC(Network Coding,网络编码)的空间DTN中的CGR改进算法(NC-CGR),并通过仿真实验平台对算法性能进行了分析评估.仿真结果表明,相比于CGR算法,NC-CGR算法在链路传输时延、传输包裹数目、中继缓存大小、链路丢包率等不同条件下的适应性方面均表现出较大优势,更适用于具有复杂拓扑、带宽受限、高动态特性的空间DTN环境.     

深空通信中继文件传输协议设计

深空通信极远的传输距离导致链路误码率高,使文件的可靠传输需要较多的重传次数,而其传播时延长的特点,进一步加大了文件传输时延。研究以CCSDS(空间数据系统咨询委员会)文件传输协议的存储-转发机制,提出一种R-CFDP(中继型CFDP协议),设计了3种中继"存储-转发"策略,并数学建模推导了R-CFDP协议的文件传输时延理论计算式。仿真证明R-CFDP协议相对于CFDP(CCSDS文件传输协议)协议在传输时延方面具有优势。     

Proactive optimization of transmission power and 3D trajectory in UAV-assisted relay systems with mobile ground users

In this paper, an Unmanned Aerial Vehicle (UAV)-assisted relay communication system is studied, where a UAV is served as a flying relay to maintain a communication link between a mobile source node and a remote destination node. Specifically, an average outage probability minimization problem is formulated firstly, with the constraints on the transmission power of the source node, the maximum energy consumption budget, the transmission power, the speed and acceleration of the flying UAV relay. Next, the closed-form of outage probability is derived, under the hybrid line-of-sight and non-line-of-sight probability channel model. To deal with the formulated nonconvex optimization, a long-term proactive optimization mechanism is developed. In particular, firstly, an approximation for line-of-sight probability and a reformulation of the primal problem are given, respectively. Then, the reformulated problem is transformed into two subproblems: one is the transmission power optimization with given UAV’s trajectory and the other is the trajectory optimization with given transmission power allocation. Next, two subproblems are tackled via tailoring primal–dual subgradient method and successive convex approximation, respectively. Furthermore, a proactive optimization algorithm is proposed to jointly optimize the transmission power allocation and the three-dimensional trajectory. Finally, simulation results demonstrate the performance of the proposed algorithm under various parameter configurations.     

Energy-efficiency maximization for fixed-wing UAV-enabled relay network with circular trajectory

With the development of Unmanned Aerial Vehicles (UAVs), the applications of UAVs have been extensively explored. In the field of wireless communications, the relay nodes are often used to extend network coverage. However, traditional fixed ground relays cannot be flexibly deployed due to their low heights and fixed locations. Hence, deploying UAV as relay node is a promising solution and has become a research hotspot. In this paper, we consider an UAV-enabled relaying network in which a fixed-wing UAV is deployed between the Base Station (BS) and Ground Users (GUs). We study the energy-efficiency gap between the link “BS-UAV-GUs” and the link “BS-GUs”, and jointly optimize UAV relay transmission power and flight radius to achieve the highest energy-efficiency. Firstly, the UAV/BS-GUs channels models and the UAV energy consumption model are built. Secondly, the optimization objective function is formulated to maximize the energy-efficiency gap. Then, the solution of the optimization problem is divided into a two-step iteration process, in which the UAV relay transmission power and flight radius are adjusted to maximize the energy-efficiency gap. Finally, the experimental results under different simulation scenarios (such as cities, forests, deserts, oceans, etc.) are shown to illustrate the effectiveness of the proposed algorithm. The results show that the proposed algorithm can always find the optimal UAV relay transmission power and flight radius settings, and achieve the largest energy-efficiency gap. The convergency speed of the proposed algorithm is fast, and can obtain the optimal solution within only a few iterations.     

Ergodic sum rate for uplink NOMA transmission in satellite-aerial-ground integrated networks

The application of Non-Orthogonal Multiple Access (NOMA) technology into satellite-aerial-ground integrated networks can meet the requirements of ultra-high rate and massive connectivity for the Sixth-Generation (6G) communication systems. We consider an uplink NOMA scenario for such a satellite-aerial-ground integrated network where multiple users communicate with satellite under the help of an Unmanned Aerial Vehicle (UAV) as an aerial relay equipped with a phased array. Supposing that buffer-aided decode-and-forward protocol is adopted at the UAV relay, we first formulate an optimization problem to maximize Ergodic Sum Rate (ESR) of the considered system subject to individual power constraint and quality-of-service constraint of each user. Then, with known imperfect channel state information of each user, we propose a joint power allocation and robust Beam Forming (BF) iterative algorithm to maximize ESR for the user-to-UAV link. Besides, to take the advantages of Free-Space Optical (FSO) and millimeter Wave (mmWave) communications, we present a switch-based hybrid FSO/mmWave scheme and a robust BF algorithm for the UAV-to-satellite link to achieve higher rate. Moreover, a closed-form ESR expression is derived. Finally, the effectiveness and correctness of the proposed solutions are verified by numerical simulations, and the performance evaluation results show that the proposed solutions not only achieve performance enhancement and robustness, but also outperform the orthogonal multiple access significantly.     

无人机编队支撑网络的协同通信中继策略

针对无人机编队支撑网络优化选择中继成员进而提高编队协同通信能力问题，基于端到端技术（Device-to-Device，D2D），提出了一种同时考虑无人机编队成员的邻近域及编队成员间的社会性依存关系来优化选择中继成员的中继策略，旨在既能保证无人机编队的基本通信能力，又能同时优化提高编队的吞吐量，从而进一步提升编队支撑网络的整体性能。研究结果表明，所提的无人机编队支撑网络中继成员优化选择策略在系统吞吐量方面较已有方法具有明显优势。     

Optimization of beamforming and path planning for UAV-assisted wireless relay networks

Recently, unmanned aerial vehicles （UAVs） acting as relay platforms have attracted considerable attention due to the advantages of extending coverage and improving connectivity for long-range communications. Specifically, in the scenario where the access point （AP） is mobile, a UAV needs to find an efficient path to guarantee the connectivity of the relay link. Motivated by this fact, this paper proposes an optimal design for beamforming （BF） and UAV path planning. First of all, we study a dual-hop amplify-and-forward （AF） wireless relay network, in which a UAV is used as relay between a mobile AP and a fixed base station （BS）. In the network, both of the AP and the BS are equipped with multiple antennas, whereas the UAV has a single antenna. Then, we obtain the output signal~to-noise ratio （SNR） of the dual-hop relay network. Based on the criterion of maximizing the output SNR, we develop an optimal design to obtain the solution of the optimal BF weight vector and the UAV heading angle. Next, we derive the closed-form outage probability （OP） expression to investigate the performance of the dual-hop relay network conveniently. Finally, computer simulations show that the proposed approach can obtain nearly optimal flying path and OP performance, indicating the effectiveness of the proposed algorithm. Furthermore, we find that increasing the antenna number at the BS or the maximal heading angle can significantly improve the performance of the considered relay network.     

无人机自组网络多媒体数据传输路由算法研究

针对无人机自组网络多媒体数据传输中链路不稳定问题,提出了一种无人机自组网络多媒体数据传输路由算法。该算法在GPSR路由算法基础上,结合无人机多媒体通信的特点,充分考虑了位置、速度、运动方向这三个因素对选择下一跳节点的影响,从而达到同时兼顾三者和提高链路性能的目的。提出的算法具有开销小、可靠性高等优点,有效提高了分组交付率以及降低了平均端到端延迟,从而提高了无人机自组网络多媒体数据传输的性能。     

Mobility control of unmanned aerial vehicle as communication relay in airborne multi-user systems

In this paper, a model-based adaptive mobility control method for an Unmanned Aerial Vehicle(UAV) acting as a communication relay is presented, which is intended to improve the network performance in airborne multi-user systems. The mobility control problem is addressed by jointly considering unknown Radio Frequency(RF) channel parameters, unknown multi-user mobility, and non-available Angle of Arrival(AoA) information of the received signal. A Kalman filter and a least-square-based estimation algorithm are used to predict the future user positions and estimate the RF channel parameters between the users and the UAV, respectively. Two different relay application cases are considered: end-to-end and multi-user communications. A line search algorithm is proposed for the former, with its stability given and proven, whereas a simplified gradient-based algorithm is proposed for the latter to provide a target relay position at each decision time step, decreasing the two-dimensional search to a one-dimensional search. Simulation results show that the proposed mobility control algorithms can drive the UAV to reach or track the optimal relay position movement, as well as improving network performance. The proposed method reflects the properties of using different metrics as objective network performance functions.     

飞行器进近中的自适应协同传输与节点选择

针对单中继非再生放大转发(AF)的进近飞行器协同传输网络,在给出系统模型后,推导并分析了系统的输出信噪比(SNR)表达式,得到了中继节点参与协同传输的条件,提出了一种自适应的协同传输方案.目的节点判断是否采用中继传输并将结果发送到中继节点,中继节点根据接收到的信息调整传输模式.在此基础上,针对多节点正交性协同传输会显著...