Research On Watermarking Scheme For FSK Signal In Wireless Channel

In recent years,as the physical layer security technology has continued to attract researchers' attention,and attention has been paid to the physical layer watermarking of information hiding.Secret transmission technology has always been a hot topic,but until now the carrier signals in most of the research are multimedia digital signals,namely digital watermarking technology.This article focuses on the radio frequency signals and studies the secret information transmission technology in the radio frequency signals,which is called the physical layer watermarking.FSK(Frequency Shift Keying)modulation signals have the advantages of simple implementation method,demodulation without restoring local carrier,asynchronous transmission,anti-noise and strong anti-fading performance.It has a wide range of applications in the transmission of medium and low speed data transmission,especially fading channels.Therefore,it is of great significance to study the watermark transmission algorithm based on the FSK signal.This paper mainly studies the transmission scheme of watermark signals under wireless channel.The content of this scheme includes embedding the watermark signals to FSK modulation signals at the transmitters,letting the modulated signals pass separately through Additive White Gaussian Noise channel and Flat Rayleigh fading channel,extracting the watermark signals and demodulating the original FSK signals at the receivers.In this paper,a watermark embedding model is proposed by using a FSK/PSK(Phase Shift Keying)new hybrid modulation method,to realize the phase superposition of the FSK carrier signals and the watermark signals.The algorithms of the watermark embedding and extraction for FSK signals are proposed.And it makes a theoretical and quantitative analysis of imperceptibility and reliability which are two indicators of system performance.Imperceptibility is measured by the bit-error-rate(BER)of the carrier signals,and reliability is measured by the BER of the watermark bits.Then,the BER formulas are deduced.The theoretical analysis shows that watermark signals make little effect on the BER performance of the original FSK receivers,when embedded to the FSK signals with the orthogonal frequencies;the reliability of the watermark system is good when the error rate of the watermark signal transmission is small.In this paper,a very low watermark strength is set to guarantee the imperceptibility of this system.Therefore,channel coding is added to this watermark system to reduce the bit error rate(BER)of watermark signal transmission.Secret information is encoded respectively by LDPC(Low-Density Parity-Check)and BCH(Bose Chaudhuri Hocquenghem)codes before embedded to watermark signal embedding system,and it needs to be decoded after extracted from the system.Finally,a complete watermarking communication system before or after channel coding based on FSK signals is established on the software platform MATLAB.And the practice is consistent with the expectation.To summarize,in practical applications,we should consider the impact of system performance on the basis of the actual scenario requirements,reasonably configure related parameters,and optimize coding performance.