Improving the secrecy rate of wireless SIMO systems via two-step transmission

The issue of physical layer security of the wireless single-input multiple-output (SIMO) system is addressed in this paper. We proposed a two-step transmission approach to improve the secrecy rate with perfect knowledge of channel state information. In the first step, the destination which has multiple antennas generates a random message and transmits it to the source which has a single antenna. The message is transmitted in a system of multiple-input single-output (MISO) in this step, and it is encoded under the secrecy capacity of the MISO system and thus can be securely transmitted to the source without leaking to the eavesdropper. In the second step, the message of the source is encrypted to a new message by using the received random message in the first step. The new message is then transmitted to the destination under the capacity of the SIMO system without considering the security. The secrecy of the source's message is guaranteed by the first random message, thus it is unknown for the eavesdropper. The information-theoretic security of the two-step transmission approach is proven in this paper, and the optimal power allocation is also proposed by solving an equation. The performance of the two-step transmission approach is analyzed in theory and evaluated by numerical simulations, and the results show that the proposed approach outperforms the traditional approach when the transmit power is great.