Research On Polarization Diversity And Combining Based On FPGA

Polarization Diversity and Maximum Ratio Combining (MRC) is used to restrain the sharp signal fading in the telemetry systems, in which the object is in flight at a high speed and rotating and in low elevation.Firstly, the combining theory and technology are researched, and the performances of the different combining method are analyzed. The essential theory of Analog Phase Lock Loop (APLL) and Digital Phase Lock Loop (DPLL) are introduced. And then the stability and the stable error response of the DPLL are analyzed. There is an obvious Doppler shift frequency offset in the received signal with flight at a high speed, in the dissertation the uniform sampling second-order DPLL is used to remove the frequency bias for its excellent high-pass characteristic of the error transfer function. And the theory of Automatic Gain Control is also researched.In the traditional polarization diversity and combining scheme, differential mode loop and common mode loop is combined to lock in the phase and frequency of the diversity signals and remove the carrier frequency bias and Doppler shift. Because of the structure of the traditional polarization diversity and combining scheme is too complex, after researching the polarization diversity and diversity combining technology, a new structure of receiver is proposed. In this structure the uniform sampling second-order DPLL is used to remove the frequency bias after frequency discrimination. And then the scheme is analyzed and demonstrated. The performance of the differential mode loop, the characteristic of MRC combining and the high-pass characteristic of the error transfer function of the uniform sampling second-order DPLL are simulated in the Matlab, the simulation results are given. The hardware design based on FPGA is proposed, including the designs of A/D block, D/A block and the polarization diversity and combining block based on FPGA. The simulation in QuartusII for the blocks with FPGA is proposed at last.Compare with the traditional polarization diversity and combining receiver, the stability of the scheme proposed in this paper is better, the parameter of it is reprogrammable, and upgrading of the system is also easily. Then the diversity...