Secure Communication Research Based On The Physical-layer Network Coding

Software Defined Radio(SDR) is a kind of wireless communication technology, which uses software to achieve the traditional "pure hardware circuit" wireless communication. The system communication functions and the signal processing functions are implemented by the software. As a reconfigurable radio signal scheme, GNU Radio provides users a convenient and efficient way to build the communication system and verify the theoretical research results. Physical-layer Network Coding(PNC) is a hot research topic in the field of wireless communication, which applies the network coding idea in wireless communication system. Channel Quantization Physical-layer Network Coding(CQ-PNC) is a new physical network coding algorithm. Base on the channels between terminal node and relay node in the two-way relay channel, the algorithm first estimates two channel coefficients. Then according to the relationship of two channel coefficients, the CQ-PNC algorithm encodes the signals to several different forms, thereby reducing the encoding/decoding error and improving the system performance.In this paper, the USRP hardware platform and the GNU Radio are understood insightfully. The design and working principles of software Radio communication system are deeply explored. As the core of the system design algorithm, this paper makes a research on the development and analysis of Physical-layer Network Coding(PNC). And it analyses the transmission mechanism and the security of the PNC. Especially, the Channel Quantization Physical-layer Network Coding(CQ-PNC) which is used in this article is made in-depth theoretical study. The study of single antenna relay algorithm includes the Channel Quantization, PNC mapping and decoding algorithm in end-nodes.This paper uses the Universal Software Radio Peripheral(USRP) to build a three-node secure relay communication system involving the eavesdrop node under Linux operating system. Using the Physical-layer Network Coding in Frequency domain as the prototype, modifying the CQ-PNC as the system core coding scheme and adopting the OFDM as the modulation, the communication system is realized in 2.4G frequency band by the software in GNU Radio with the N210 motherboard and XCVR2450 daughterboard. To simplify the system design, the system assumes that the channel meets the demand of reciprocity. The test result shows that the system complies with the design purpose. This paper compares the CQPNC algorithm and ML algorithm in relay node, CQ-PNC has 2-8d B SER performance degradation with ML which is consistent with the conclusion of simulation theory. But the time complexity reduces one order of magnitude under the small difference of performance. Meanwhile, this paper analyses the BER performance of the end nodes A and B, and discuss the information capture of the eavesdropper from the end nodes. In addition, we analyze one case of the eavesdropper, and the performance results imply that the eavesdropper is unable to detect the message from the end nodes.