利用复杂信道空变性获得冲突避免的水声网络多址接入机理

It is the harsh underwater environment that causes the complex space varied features of underwater acoustic channel. Utilizing the complex space varied features of underwater acoustic channel, time reversal could lead to adaptive time and space focusing. Our previous study has confirmed that it is the time and space focusing ability of time reversal that could greatly weaken the broadcast feature of underwater acoustic channel. Thus, we present a hypothesis that time reversal may play a significant role in isolating signal interference between adjacent links and then in completing collision avoidance and covert transmission for underwater acoustic networks. To accelerate the development of the ocean underwater acoustic networking, considering the limited energy supply of each node, facing the problem of achiving collision avoidance utilizing the complex space varied features of underwater acoustic channel, we plan to study the energy efficient medium access control mechanism for distributed multi-hop underwater acoustic networks based on time reversal, (1) analyze the complex space varied features of underwater acoustic channel and the time and space focusing ability of time reversal, (2) establish a probe sense based collision avoidance model based on proactive time reversal, (3) study the random multiple access control mechanism based on proactive time reversal probe reservation, the probe updating strategy based on optimized frame size, and the strategy to minimize energy consumption when the proactive time reversal medium access control mechanism is adopted, thus aiming at resolving the transmission collisions and induce packet retransmissions which cause low channel utilization, long access delay and great energy consumption for bandwidth and energy both constrained underwater acoustic networks. Finally, the proposed methods and algorithm are verified by simulations and experiments. The establishment of project is significant for the enhancement of underwater acoustic networking, information acquiring and maritime monitor networks establishment.

恶劣海洋环境造成水声信道复杂的空变性。时间反转（TR）利用复杂信道空变性可实现接收信号空时聚焦。申请者前期研究证实TR空时聚焦性可有效削弱水声信道广播特性，因此提出：利用复杂信道空变性，TR在水声网络中可发挥隔离链路间信号干扰进而获得冲突避免与隐蔽传输的重要作用。应水声网络技术发展的迫切需要，结合结点能量受限，本项目研究复杂空变信道下基于TR的水声网络多址接入机理，（1）分析水声信道复杂空变特性与水声网络TR空时聚焦性；（2）建立基于主动TR探针侦听的冲突避免模型；（3）突破基于探针预约的随机多址接入、基于最佳帧长的探针更新、低能耗主动TR多址接入等关键技术，解决复杂恶劣海洋环境下带宽能耗双受限的水声网络存在的数据包传输碰撞及其带来的重传，导致信道利用率低、时延长与能耗大的问题；（4）开展水池/湖上实验，验证并完善所提理论方法。为增强水下组网与信息感知能力、建立海洋监测网提供有力支持。

恶劣海洋环境造成水声信道复杂的空变性。时间反转（TR）利用复杂信道空变性可实现接收信号空时聚焦。主动TR利用复杂水声多径传播造成的网络中不同链路间信道响应的空间弱相关性，获得信号在接收位置的空时聚焦，发挥了有效隔离分布式多跳环境下相邻链路间信号干扰的关键作用，显著提高水声网络链路的空分复用度。应水声网络技术发展的迫切需要，结合结点能量受限，本项目在分析水声信道复杂空变特性与水声网络TR空时聚焦性的基础上，研究复杂空变信道下基于TR的水声网络多址接入机理，验证了主动时反多址接入在水声网络中的可行性与优越性。通过本项目的研究，建立了基于主动TR探针侦听的冲突避免模型，提出了面向链路间干扰抑制的水声网络时反多址接入方法，进一步提升了网络空间复用度，这对带宽有限的水声网络具有重要的价值和意义；在此基础上，本项目基于湖试实验结果，研究了信道时变性对时反多址接入的影响，并提出了基于时变周期的探针更新方法；针对结点能耗受限，本项目提出了按需休眠机制和基于按需休眠的水声网络时反多址接入机制，提出了基于功率控制的时反多址方法，有效延长水声网络寿命；为了构建逼真的水声网络仿真环境，构建了基于BELLHOP+MATLAB+OPNET的水声网络联合仿真模型，为复杂海洋环境下水声网络建模奠定基础。时反多址接入技术是继CDMA之后的一种新的提高网络空间复用度的接入方法。该方法适用于信道具有空变性的网络中，而水声网络是典型的具有空变信道的网络，这为时反多址接入在水声网络中的成功应用奠定了基础。本项目变水声环境劣势为优势，提出的基于主动时反冲突避免的多址接入机制，为复杂恶劣海洋信道下带宽与能耗双受限的分布式多跳水声网络，减小数据包传输碰撞与重传，提高信道利用率并降低时延与能耗提供了新的途径，同时也为水下网络化低截获传输提供了新的技术途径。其研究成果可应用在水下物联网、空天地海一体化、大范围海域监测、海洋灾情监测与预报等领域。