An orthogonal subspace based signal design framework for satellite-terrestrial cognitive coexistence

To address the spectrum scarcity caused by the development of broadband services, cognitive radio is recognized as one of the most effective methods. Herein, in the perspective of cognitive radio, we study anti-interference techniques for the coexistence of satellite and terrestrial systems with the terrestrial downlink as primary and the satellite reverse link as secondary. First, a design framework based on the orthogonal subspace theory for anti-interference signals is proposed in this paper. With the extraction of the subspace gathering the interference characteristics, the satellite anti-interference signal is designed to be orthogonal to the terrestrial interference signal in the orthogonal complementary subspace. Then non-contiguous OFDMA (NC-OFDMA) and eigen-based CDMA (ECDMA) are unified in the proposed framework and their distinctions are analyzed. Finally, the performances of NC-OFDMA and ECDMA under different interference scenarios and the spectral efficiency are evaluated respectively by simulations, providing references for system engineering design.