Secure Joint Transmitter-Receiver Spatial Media-Based Modulation

Joint transmitter-receiver spatial modulation (JSM) is a promising multiple-input multiple-output communication technique that achieves transmit diversity, receive diversity, and multiplexing gain simultaneously. However, the conventional JSM scheme has security risks due to the broadcast nature of the wireless channels. In addition, the spectral efficiency of JSM is not satisfactory since the antenna elements are not fully utilized and a single modulated symbol is transmitted only. In this paper, we propose a secure joint transmitter-receiver spatial media-based modulation (JSMBM) to improve the security and spectral efficiency. Specifically, multiple radio frequency (RF) mirrors are placed close by the transmitting antennas and the transmit index bits can be mapped to the mirror activation patterns. As a result, the spectral efficiency scales linearly with the number of RF mirrors, instead of logarithmical scaling with the number of transmitting antennas. Moreover, the proposed JSMBM scheme enables the transmission of multiple modulated symbols such that the spectral efficiency is further enhanced. In order to protect the proposed JSMBM scheme against passive eavesdropping, we use friendly jamming and probabilistic shaping in a collaborative manner to improve the secrecy performance. The mechanism of probabilistic shaping is to adjust the probability of transmitting each symbol such that the favorable symbols are transmitted with higher probability. We propose a simplified iterative conjugate gradient algorithm to optimize the input probability mass function, which maximizes the secrecy rate. Simulation results validate the proposed algorithm and show that the proposed secure JSMBM scheme achieves higher secrecy rate than the benchmark schemes, especially when the eavesdropper has more receive antennas than the legitimate receiver.