Rearch Into The Key Problems Of Signal Transmission In OTHR

Over-the-horizon radar(OTHR) works at the high frequency band of 3-30 MHz. It can detect the over-distance targets which are over the horizon. With the development of the multiple-input-multiple-output(MIMO) technology, the concept of OTHR based on MIMO was born, which is referred to as MIMO-OTHR. Due to the introduction of MIMO, OTHR can transmit multiple independent signals at the transmitter. So, OTHR can obtain the spatial diversity gain, which greatly enhance the performance of target detection and localization for OTHR. In addtion, MIMO-OTHR makes the non-causal adaptive processing for the deversity transmission signals at the receiver, which make OTHR achieve the non-causal transmit adaptive beamforming. Futhermore, MIMO-OTHR brings the spatial direction into the radar managment, and balances the the relations of radar sensitivity and coverage area, which effectively improve the overall performance of OTHR.This thesis makes a more in-depth reseach into the adaptive beamforming technology in MIMO-OTHR and the frequency management system in OTHR. The main contents of this thesis are as follows:1. The loading factor is not easy to solve in the loading sample matrix inversion(LSMI)algorithm for MIMO-OTHR. For the problem, we proposed an LSMI algorithm based on the golden section method to solve the loading factor. The loading factor can be dynamically adjusted according to the array output data in the algorithm. Simulations show that compared with the traditional algorithms, the proposed algorithm can maintain the robustness and better performance in the case of small sample data.2. For how to improve the detection performance of MIMO-OTHR in the presence of clutter, we proposed an iterative algorithm based on the joint optimization of receiving filters and transmitted waveforms. After analysis, the proposed algorithm has a good convergence.In addtion, the transmission channels of the echo signal and clutter are maintained using priori information, which results in certain estimation errors. The estimation errors cause the performance degration of the beamformer. For the problem, we develop the joint optimization of the receving filters and transmitted waveforms in the worst case. Simulations show that the proposed algorithms can improve the detection performance for MIMO-OTHR radar with a good robustness.3. For the problem that users are crowded at the high frequency band, an intelligent spectrum handoff method is put forward to select the working frequency for OTHR. On thebasis of the traditional queuing theory, we propose an intelligent spectrum handoff scheme.The proposed method solves the problem that the second user in the handoff queue will have the priority over the arriving primary user when the system channel and the handoff queue are not idle at the same time. Simulations show that the proposed method can achieve the normal legitimate communication among the primary users and second users, and improve the utilization of the spectrum resources.