基于渗流方法的新型反截获抗干扰通信技术研究

Owing to the openness of the free space and the non-perfect directionality of the transmitting antenna, wireless communications systems are inherently quite vulnerable to unauthorized receivers (a.k.a. interceptors). On the other hand, the achievable channel capacity is often limited by deliberate or non-deliberate interferences which are ubiquitous in today's extremely crowed radio propagation environment. Therefore, the robustness to jammer and interception must be taken into consideration in the design of wireless communications systems. Against this background, in the current proposal we highlight a novel Physical Layer Anti-Jamming and Anti-Interception (PL-AJI) technique. The basic idea is to process the source message by a rateless channel coder and then multiplex the coded data onto a number of percolating channels. With the data packets which arrive along many different routes in the network, the destination node may perform an "assembling" operation and thereby restore the original information-bearing message in a reliable way. As percolation-based transmission is adopted, the coded packets are randomly distributed over a large number of percolation channels, which makes it rather difficult for the interceptors to collect sufficient data for accurate decoding. Furthermore, the cascading rateless codes are capable of working at a SNR level close to the lower bound predicted by Shannon's Information Theory, in which case the noise-induced random errror will hash the input of the second-layer decoder and hence provide a strong protection against interception and jammer.

无线环境的开放性和发送天线的各向发散性使通信信号很容易被截获,从而传输信息被非法获取；同时，无线传播环境复杂，干扰信号使信道容量下降、有用信号阻塞，信号的有效接收变得十分困难。因此，通信系统应具备反截获和抗干扰能力。本项目提出一种基于物理层的新型反截获抗干扰通信技术，其基本思想是将源数据经过无比率信道编码后通过渗流方式分路，由网络中的多个路由并行转发，目的节点将各路转发来的数据进行"组装"并解码恢复源数据。数据经过渗流传送，由于信息随机分布在多个节点中，信息的分散性使截获者难以获得能够正常译码的完整信号。而且，无比率预编码和各节点的网络编码是随机的，截获者无法掌握信源预编码和物理层编码信息，因而使信息传输具有很强的反截获能力。同时采用级联结构的无比率编码工作在Shannon限附近，信道引入的随机差错在第二级解码器会带来信道散列性，对数据形成很强的保护，从而获得优异的反截获和抗干扰性能。

本项目研究了分布式信道环境下反截获和抗干扰技术，主要包括基于渗流方法的物理层反截获抗干扰方法研究，分布式系统信道容量和安全容量计算，反截获抗干扰的渗流技术及其编码和解码技术研究，取得的研究成果包括：（1）基于小世界模型建立了基于渗流的无线网络物理层安全模型。在此基础上，基于多载波调制提出一种频域稀疏信号设计方法，研究了频谱资源受限条件下的低检测概率信号设计及检测方法，提出一种LDPC编码软扩频系统。（2）在衰落非相干信道中研究了采用空时编码保证信息的安全传输问题，提出基于非相干安全容量的多天线无线通信空时编码理论与方法。研究了MIMO窃听信道中提升通信系统的安全容量的信噪一体化设计方法及安全容量计算方法。（3）在MIMO窃听信道中，提出一种随机复数域编码设计方法。在此基础上，分别采用加扰的LDPC码与LT码作为安全编码方案，建立了通信系统中断概率模型。最后，基于频域稀疏信号提出了一种具有低实现复杂度的IRA-LDPC陪集安全编码方案。本项目发表论文15篇，其中SCI收录4篇；申请发明专利6项。