2020 Volume 9 Issue 6 Pages 207-212
As a physical layer security technique, directional modulation (DM) using an array antenna was proposed. By the method, modulated signal can be correctly reconstructed in only the pre-specified direction from the array. On the other hand, Space Selective Modulation (SSM) was proposed. SSM shares the similar principle to DM. Using the technique, modulated signal is correctly reconstructed in only the specified space, not the specified direction by utilizing fading characteristics. The originally proposed SSM uses three or four transmitting antennas. However, the transmissible probability is not 100%. Because a modulated signal is formed by summing up phase-controlled channel coefficients in SSM, symbols of the all constellation points may not be formed depending on the channel conditions. It brings about a decrease in the secrecy capacity of the secure information transmission. In this paper, we consider solving the problem by increasing the number of antennas. We quantitatively evaluated the secrecy capacity by computer simulations. The results confirm the improvement of the total performance in the secrecy capacity of SSM.
