In this paper, we propose a novel resource allocation criterion based on physical layer security, which means choosing the proper subcarrier to ensure the device to device (D2D) security capacity maximum based on guaranteeing the cellular users basic capacity. We analyze the relationship between D2D security capacity and D2D power. We also prove that the strategies based on the D2D secrecy rate maximum and cellular sum rate maximum are the same when the transmit SNR of BS is high enough. Through the numerical calculation and simulation analysis, we show that the resource allocation criterion proposed in this paper is valid and rational.

In mobile satellite communication based on OFDM technology, the system performance can’t be optimal if the cyclic prefix (CP) length and subcarrier interval of LTE specification are transplanted into mobile satellite communication directly. In this paper, we analyze the impact of inter symbol interference (ISI) and inter carrier interference (ICI) which are caused by multipath delay spread and Doppler frequency shift separately on system capacity, and derive the optimal CP length and subcarrier interval for GEO, MEO and LEO mobile satellite communication by numeric calculation. Finally, the simulation results show that the OFDM parameters of LTE specification can be used in GEO mobile satellite communications, but cannot in MEO and LEO.