Research on the Gain Control algorithms of Long Baseline Positioning System based on High Performance FPGA

The protection, exploitation and utilization of ocean resources cannot be separated from effective underwater acoustic equipment. Long baseline underwater acoustic positioning system (LBL) plays a very important role in underwater acoustic engineering. LBL system is composed of transponder array placed on the seabed. The relative position of carrier relative to transponder is determined by receiving transponder array signal by ship-borne interrogator or receiver, and then the absolute position of carrier is determined according to the absolute geographical position of transponder array known. The positioning accuracy of LBL system depends heavily on the accuracy of time delay estimation, and the accuracy of time delay estimation depends on the quality of received underwater acoustic signal. In order to ensure that the received analog signal is sent to AD converter with high fidelity and full scale, FPGA is used to control programmable gain controller VCA810 in real time, and then gain control of analog signal under the condition of dynamic variation of working distance is realized. A high performance FPGA is used to detect the desired signal, estimate the average amplitude of the desired signal, and calculate the gain control voltage for controlling VCA810 based on the target signal amplitude, thus achieving the high fidelity and full range gain control requirements. Modelsim simulation and lake test verify the effectiveness of the gain control scheme proposed in this paper.