对无人机自组织网络中的协作机制进行了研究,提出一种基于动态中继选择的无人机自组网协作时分信道接入协议.该协议在传输中继数据包时引入了双队列协作机制,在网络层数据包缓存队列之外引入了独立的媒体接入控制(Media access control,MAC)层中继数据包缓存队列,并且能够实现默认中继节点与辅助中继节点的动态选择,以满足大流量负载及网络拓扑快速变化的要求.仿真结果表明,通过中继节点动态选择机制,在网络业务流量负载较大、网络拓扑快速变化的情况下,所提出的协作时分信道接入协议可获得比传统时分多址(Time division multiple access,TDMA)协议与机会协作中继时分多址(Opportunistic cooperative relay time division multiple access,OCR-TDMA)协议更高的中继数据包投递率及更低的端到端时延.

The Low-Earth Orbit(LEO) satellite communication system has the advantages of good global coverage, mobility, and scalability.It has played a significant role in providing global Internet services and disaster emergency response.However, owing to the limited storage and computing resources of satellites, traditional routing algorithms are unsuitable for LEO communication networks.Therefore, combined with Software-Defined Network(SDN) architecture, this study proposes a high-performance and Quality of Service(QoS) guaranteed inter-satellite routing algorithm for LEO satellites.We define the survival time of the Inter-Satellite Link(ISL) according to the remaining link duration and obtain the stability degree of each ISL to alleviate the problem of service path reconstruction caused by link switching. Based on the traffic status of the ISLs obtained by Geostationary-Earth Orbit(GEO) satellites, we define the link load matrix to provide the ISL load degree function, and use the Label Switching Path(LSP) set to obtain the load degree of each path to avoid node congestion and realize network load balancing.Finally, we define a weighting factor matrix for different required business service types and reduce the influence of the bottleneck node on the routing algorithm by adjusting the factor and guaranteeing the QoS requirements of multiple users.The simulation results show that under different QoS requirements, the algorithm has obvious advantages in terms of business delay, system throughput, and network load balancing, and the low algorithm complexity significantly reduces the limited on-board storage and computing resources.

In passive radio frequency identification (RFID) systems, the capture effect may occur that the reader is possible to successfully decode the strongest signal when multiple tags reply simultaneously.In this situation, the weaker signals will be covered resulting in a tag hidden problem which greatly affects the system performance.To solve the problem, a bit-detecting M-ary tree (BMT) protocol was proposed.First, a bit-detecting tag number estimation method was proposed to estimate the number of tags and group them with a few slots.Next, an M-ary tree protocol was developed to eliminate all the idle slots and identify tags quickly.At the same time, a hash muting strategy was given to mute the identified tags and label the hidden ones with small communication cost.Both theoretic analysis and simulation results demonstrate that BMT can effectively reduce the identification delay by at least 15%.

In order to solve the problem of frequent link disconnections caused by high-speed movement of nodes in Flying Ad-hoc Networks(FANETs),a multicast routing protocol that supports link lifetime prediction and autonomous routing repair is proposed for highly dynamic FANETs.The protocol can predict the lifetime of residual links between neighboring nodes according to the changes of the distance between the nodes.Based on the prediction result,the number of routing hops and the residual energy,the link quality is evaluated comprehensively.On this basis,the best relay node is selected to ensure the reliability of the established route.Then the established route is dynamically maintained by using local route repair and global route refreshing,so the frequent link disconnections caused by high-speed movement of nodes can be relieved,improving the delivery rate of data.The experimental results show that the proposed protocol is superior to the classical multicast routing protocol ODMRP in terms of data delivery rate,network throughput and routing overhead in various scenarios.

针对传统无人机航迹规划算法应用在突发威胁场景下存在搜索点冗余、路径规划实时性较差等问题,提出了一种基于多因素Dubins路径的无人机动态航迹规划算法.该算法首先根据无人机自身性能约束及突发威胁区域的位置,并且考虑无人机的起始和最终位置,利用传统的Dubins路径找到有效的路径扩展点.然后结合启发式搜索思想建立基于路径长度和威胁的路径扩展点评估函数.最后通过路径评估函数计算,比较路径点的代价值,选取每一步的路径扩展点,规划出较优路径.仿真结果表明,在突发威胁场景下利用该算法进行航迹规划时路径长度较短、路径扩展点较少,并且符合无人机实际飞行过程中航向角变化,可有效保障无人机的安全性和航迹规划的实时性.

To address the problems of high latency and low channel utilization in underwater acoustic sensor networks,this paper proposes a new multi-link transmission Medium Access Control(MAC) protocol.In this protocol,nodes exchange the delay information and transmission plans through the RTS/CTS handshake protocol to implement multi-link data transmission.When the sink node receives data from multiple nodes,the sink node plans the sending order of nodes according to the delay between nodes and the size of the received data frames,avoiding the energy loss and the low channel utilization rate caused by transmission conflicts.At the same time,in order to obtain the maximum network throughput,the theoretical expression of the optimal backoff window value is given.Simulation results show that compared with the RC-FAMA,S-FAMA protocols,this protocol can improve the throughput of underwater acoustic sensor networks and reduce transmission conflicts,thus prolonging the lifetime of underwater nodes.

Orthogonal circular orbit constellation combines the advantages of polar orbit constellation and equatorial orbit constellation to achieve continuous global coverage,improving the coverage performance of pure polar orbit constellation at low and middle latitudes to some extent.However,the traditional design method of orthogonal circular orbit constellation is to divide the coverage of polar orbit constellation and equatorial orbit constellation by latitude lines,which is too rough to fully utilize geometric properties of two constellations.To solve this problem,according to the motion features and coverage features of the polar orbit constellation satellites,this paper analyzes the features of the coverage gaps generated in the areas that do not meet the continuous coverage requirements,and integrates the characteristics of the equatorial orbit constellation satellites to propose a design method of orthogonal circular orbit constellation based on geometric analysis.By using the analytical method,the parameters of the half-width angle for minimum ground coverage of the equatorial satellite is determined.The typical constellation scheme is given to compare with the traditional design method of orthogonal circular orbit constellation,and the effectiveness of the proposed method is demonstrated by the STK simulations.

As one of the key technologies of UAV swarm, the collaborative algorithms are of great significance in collision avoidance, formation controlling and so on. However, due to the high risk of real-world UAV swarm testing, the performance of the collaborative algorithms is hardly verified in reality. In this work, we developed an experimental testbed, named “CK-YAN”, for UAV swarm collaborative algorithms. CK-YAN is composed of two main parts, the UAV control system and the ground control system. In the UAV control system, a self-built network module with Flask framework is developed to enable the collaborative communications among UAVs. In the ground control system, the Dronekit and MAVProxy are implemented to reduce the flying risk and controlling difficulty of UAVs. We also developed a visualization module to reflect the 3D virtual scene of the testing UAVs in real time. The experimental results demonstrate the high stability of CK-YAN and verify the performance of the collaborative algorithm.

Radio frequency identification (RFID) has been widely used in various areas, such as logistics, healthcare, manufacture and so on. However, tag collision problem greatly affects the performance of RFID systems by reducing bandwidth utilization and increasing identification delay etc. In this paper, we propose a dynamic query tree anti-collision (DQTA) protocol, which dynamically adjusts the number of subgroups of each collision slot. Based on the number of consecutive colliding bits in tag response k, DQTA splits colliding tags into 2^k subgroups. Dividing colliding tags into more appropriate subgroups, the number of collision slots and transmitted message bits are effectively reduced. Comparing with the most related state-of-art works, the proposed DQTA protocol can identify tags with less time and fewer transmitting message bits.

针对现有的频谱感知存在信号稀疏度估计所需压缩观测值不能满足信号稀疏度变化时实时跟踪的问题,研究一种基于稀疏系数信息估计的自适应宽带频谱压缩感知方法,在流信号进行稀疏度未知的压缩时,先采集由先验信息得到的观测值数目.在采集到的观测值数目上自适应调整,得到信号稀疏度估计所需的观测值数目,并精确估计信号的稀疏度.仿真结果表明,SCI-CSS算法对流信号频谱能够保持良好的收敛性和较快的跟踪速度,且能有效地确定使信号稀疏度估计所需压缩观测值数目并随信号稀疏度自适应调整,实现对信号稀疏度变化的实时跟踪.

For the power-limited orthogonal frequency division multiple access(OFDMA) cognitive networks,a low-complexity resource allocation algorithm is proposed,including subcarrier allocation and power allocation.In the subcarrier allocation,the algorithm assigns the subcarriers with the worst channel quality to the users at a higher priority.Then,the remaining subcarriers are sorted in descending order according to the variance of channel quality and assigned to the users.Thus,the remaining subcarriers will not be allocated to the users with the worst channel quality.In the power allocation,the judgment of the anti-interference threshold of the primary user is introduced into the traditional linear water-filling algorithm.This algorithm can maximize the throughput of secondary users and improve the anti-interference ability of the primary user simultaneously.The simulation results show that,compared with the existing algorithms,the proposed algorithm can effectively improve the channel quality for the subcarriers allocated to users.The throughput of secondary users is very close to the theoretical upper bound.The proposed algorithm has an acceptable fairness for primary users and low computational complexity.

Using directional antennas is a valid method to improve bandwidth utilization in wireless Mesh networks.However,this brings new Medium Access Control(MAC) problems,such as deafness and new hidden terminals.To solve these problems,a novel time-division MAC protocol based on link scheduling for directional wireless Mesh networks is proposed.It uses an effective algorithm for concurrent transmissions to maximize network capacity and provide per-link fairness.In the protocol,time is divided into continuous frames of constant length and each frame consists of a scheduling subframe and a transmission one.Nodes perform channel sensing during the scheduling subframe and transmit packets in parallel during the transmission subframe.Simulation results show that compared with the typical Basic DMAC scheme,the proposed MAC protocol achieves significant improvement in network throughput and provides better per-link fairness.

Aeronautical Ad Hoc Network(AANET) allows nodes to communicate though single hop or multi-hip way,and it does not need to rely on the ground control center.It provides flexible network architecture for aeronautical communication.Aiming at this characteristic,this paper proposes an Evolutionary Self-organizing Time Division Multiple Access(ESTDMA) protocol for AANET.It aims to optimize the slot utilization of the existing STDMA protocol while preserving the advantages of it.By introducing a contention-based secondary slot allocation strategy,ESTDMA enables nodes to contend to utilize the free and collision slots in the frame.Meanwhile,an analytical model is developed to obtain the optimal contention probability for the nodes to contend for the slots.The accuracy of analytical model is validated through the comparison of the simulation results and the analytical results.Also,the simulation results in EXata network show that the proposed protocol can effectively improve the slot utilization of the STDMA protocol,thus improving the performance dramatically.

In this paper,we study the available bandwidth estimation in multi-hop ad hoc networks,pointing out limitations of the existing available bandwidth estimations:estimation based on active approaches may interfere final results;Estimation based on passive approaches is usually used for monitoring of single point,and it is difficult to know the end-to-end performance.According to the above limitations,we present a new algorithm to evaluate the available bandwidth based on the available period in 802.11 DCF protocol,which is the improvement of current passive approaches.Firstly,we define the maximum of the available bandwidth in a link;Then,we calculate probability of the desynchrony in available period between transmitter and receiver to get the preliminary estimate;Lastly,we discuss the transmitting failures because of hidden nodes in two cases to amend the preliminary estimate.The simulation results verify the effectiveness and accuracy of the new algorithm.

Neighbor discovery is the difficult issues of the MAC protocol design which is based on the directional antennas in wireless Ad hoc networks.After analyzing the conflict problem during neighbor discovery in the directional transmission condition,we put forward a directional neighbor discovery mechanism based on the model of optimization.This mechanism adopts Markov chain to model the random back-off state when beam aligns and the request frame is in transmit,and then obtains the probability expressions of steady state,and finally combines the geometric calculation method to obtain the expression of probability of beam alignment,and according to the probability expression analyzes the joint optimized parameters.The numerical simulation and analysis of result show that this mechanism can effectively improve the efficiency of neighbor discovery in directional transmission condition compared with the existing typical directional time division access neighbor discovery mechanism.

In large scale mobile IP networks,the registration request from the mobile nodes collides at the agent node,and results large handoff delay.To solve this problem,a one-dimensional Markov chain model is proposed,which takes the mobile nodes needing to register into consideration.On the basis of the model,the relationship between the total time for all the mobile nodes finishing their registration and the value of their contention window is derived.Mobile nodes can adjust the value of their contention window to avoid collisions,thus achieve better registration time performance.Afterwards,the mobile IP protocol is implemented in GloMoSim.The effectiveness of the model in optimizing the value of the contention window is validated by comparing the simulation results with the theoretical results.

针对大范围地空通信信道无法采用传统信道模型确切描述的问题,根据空基平台高度,利用Markov过程对改进和修正后的Rice信道模型和Loo信道模型进行相互转换来尽可能精确地描述地空衰落信道.对每个模型都将其分为经历轻度遮蔽和严重遮蔽2种状态,根据特定地区环境,利用Markov过程对2种不同环境状态进行切换.去掉多径来波入射角在[0,2π)上均匀分布的理想化假设,采用2个相关的实高斯随机过程构成Rice过程的方法,完成对Rice信道模型和Loo信道模型的改进和修正,推导得到了改进和修正后两模型的多普勒功率谱和幅相概率密度函数表达式.仿真结果表明:改进和修正后模型的多普勒功率谱曲线呈非对称形状,模型的自由度和适应性得到扩展和提升,可以描述不同信道情形对信号传输的不同影响,能较好地反映实际情况.

The distributed coordination function(DCF)of wireless local area networks(WLANs)is an essential part of teaching communication networks. This paper designs a teaching session of modeling the saturation through-put of the DCF protocol by Markov chain in WLANs. By analyzing the limitations of the model,we effectively in-spire the students of innovation thinking. This paper can serve as a significant guide in the teaching of the DCF pro-tocol in WLANs.

详细分析了传统的TCP拥塞控制算法在无线多跳网络环境下面临的问题,指出无线多跳环境下的MAC层信道竞争以及TCP拥塞窗口的过激增长机制是影响TCP性能的主要原因,提出一种新的TCP跨层拥塞控制机制TCP-CR.该机制中节点通过MAC层维护的链表信息,将冲突概率定时向源节点的传输层进行反馈,源节点根据获取的反馈信息做出拥塞窗口调整.仿真结果证明,该机制中源节点能有效根据当前MAC层网络状况做出及时动态调整,从而提高TCP的吞吐量.

针对基于半马尔科夫平滑移动模型(SMS)的无线Ad Hoc网络节点相对运动速率概率分布展开研究,指出了现有基于SMS模型的节点相对运动速率概率分布分析方法存在的局限性:(1)现有分析方法得到的加速阶段节点速率概率分布与仿真结果相比偏差较大,在节点速率较小的情况下,偏差更为严重;(2)随着最小运动速率的增加,现有分析方法得出的相对速率概率分布与仿真结果相比偏差增大.针对上述局限性,本文首先通过分析得到了节点运动速率的概率分布函数,然后在此基础上提出了分析节点相对运动速率概率分布的新方法.仿真结果证明了本文提出的节点相对速率分析方法的有效性.