Combined Constellation Rotation With Weighted FRFT for Secure Transmission in Polarization Modulation Based Dual-Polarized Satellite Communications

In this paper, a novel transmission scheme based on constellation rotation and weighted fractional Fourier transform (WFRFT) is proposed to enhance the physical-layer security in polarization modulation (PM)-based dual-polarized satellite communications. Typically, by appropriately selecting the WFRFT order, the distribution of the signals processed by WFRFT can be close to Gaussian, which makes them difficult to be detected by eavesdroppers. However, once the signals are captured, it is possible for eavesdroppers to recover the information through the WFRFT order scanning method. To overcome this problem, in the proposed scheme, the constellation points are randomly rotated before the WFRFT operation, making it almost impossible to crack the WFRFT order. In this manner, the constellations are distorted, which is difficult for the eavesdropper to demodulate the signals accurately. Furthermore, a robust nonzero secrecy capacity is guaranteed. In addition, the impairment to the PM from the polarization-dependent loss effect is discussed, and a zero-forcing prefilter is applied at the receiver side to mitigate this adverse effect. Finally, the security performance of the proposed scheme is evaluated in terms of the average secrecy capacity and symbol error rate by numerical simulations in dual-polarized satellite communications.