Secure Transmission for Buffer-Aided Relay Networks with Delay Constraints

Cooperative Relaying plays an important role in the Internet of Things (IoT). However, due to the broadcast nature of wireless channel and the computing limitation of the IoT devices, the security of the cooperative transmission is threatened by the eavesdropper. This paper considers the transmission security in the buffer-aided relay cooperative networks with delay constraints, where there exists an eavesdropper attempt to overhear the data transmitted in the wireless channels. Apart from the security problem caused by eavesdropper, the cooperative transmission with the help of buffer may also lead to the increase of delay, while some wireless services have the demand of maximum transmission delay. In this paper, we propose a secure cooperative transmission protocol with the optimization of transmit delay. In the first transmission phase, multicast scheme is applied to make sure that multiple relays can obtain total data in a lower delay. The rateless code is introduced into our proposed scheme to keep multicast transmission reliable and decrease the transmit delay. Moreover, the relay selection strategy is combined in the second phase to improve the security and further decrease the transmit delay. Through adjusting the system parameter which is the number of relays that can obtain total data in the first phase, the delay constraints can be assure in some way. Closed-form expression of transmission delay and interception probability are obtained and the influences of the parameter on the two performances are analyzed. The simulation results show that the proposed scheme can achieve high transmission security and a low transmission delay.