Research and implement of spectrum watermark embedding and extracting method based on spread spectrum

To effectively identify the radio system, this paper presents a spectrum watermark embedding and extracting method based on the spread spectrum. The spectrum watermark identifying the radio equipment is modulated by the spread spectrum code with high code rate and long code length at the transmitting terminal, and is periodically embedded in the communication signals based on the additive rule. The received intermediate frequency communication signal is divided into N segments at the receiving terminal. The spectrum watermark can be obtained by the fusion decision based on the demodulation of these segmented signals. The experiment system testing the proposed method is built based on the USRP platform. Theory analysis and experiment results show that the proposed method can effectively extract the spectrum watermark with no harmful inference to normal demodulation of the communication signal, and there is no need to demodulate the communication signal. The proposed method can effectively reduce the complexity of spectrum watermark extraction which provides a technique support for effectively identifying and ascertaining the radio system.