Design And Implementation Of LEO Satellite Channel Emulator

LEO (Low Earth Orbit) satellite communication system has become a main development direction of satellite communication system because of its low running track, small transmission delay and low terminal cost. In the development process of LEO satellite mobile communication system, in order to verify the reliability of the system, we must understand the influence of LEO satellite channel on the system signal, because the signal of LEO satellite mobile communication system will be affected by the Doppler effect, shadowing, multipath effect and noise factors. In the past, people mostly adopts the method of field test, test for real satellite link, but this method is expensive and vulnerable to external factors. So this paper designs a LEO satellite channel emulator based on DSP, which can simulate the transmission characteristics of LEO satellite channel in real time in laboratory condition. It provides a test method for the development of LEO satellite communication system and has important practical significance.The main work of this paper include the following contents:(1) Through the analysis and comparison of several commonly used satellite channel model, LMS model is selected as the theoretical model of the LEO satellite channel emulator.(2) According to the LMS model, the block diagram of the LEO satellite channel simulator is proposed. And the digital down converter system is simulated by the Simulink, the simulation results verify the performance of decimation filter in DDC (digital down converter) system, which provides parameter validation in the actual development of DDC.(3) A scheme of LEO satellite channel emulator combined DDC chip and DSP is put forward, the hardware design is completed combined with the intermediate frequency processing card and DSP card SEED-DEC6713, and introduces the specific circuit modules and between modules.(4) The optimal filter rate is obtained by the AD6620filter design software Fltrdsn, complete the initialization by the single chip microcomputer AT89LV51, and then introduces the design of interface program and signal processing program between TMS320C6713and AD6620.(5) A system test platform is built, the signal generator provides analog IF (Intermediate frequency) test signal to the system, and then observe and analysis the test results through the CCS (Code Composer Studio) software, the test results show that the channel emulator can simulate channel fading and Doppler frequency shift effect, which gets the expected design goals.