Security transmission with modulator structure hopping in cooperative system with untrusted relay

Researches show that the MSK (Minimum-shift Keying) modulation has the variety characteristic of modulator structure; moreover its modulator structure has the certain waveform encryption function for the input messages. In this paper, referring to the idea of frequency hopping communication, we apply the variety of MSK modulator structure to enhance the physical layer security of the cooperative transmission with untrusted relay. A cooperative transmission scheme with MSK modulation is proposed for the three nodes AF (Amplify-andForward) cooperative system with untrusted relay, where the MSK modulator structure can be changed according to a secret between the source and the destination. Through theoretical analysis and experimental simulation, we show that the BER (bit error rate) as high as about 50% makes demodulating practically infeasible for the untrusted relay in the proposed cooperative scheme, thus securing the communication between the source and destination. Furthermore, this security transmission scheme is independent on the channel variations of the wireless environment, and is very suitable for the wireless networks where the channel remains static for most of the network lifetime.