Research And Design Of Anti-multipath Interference Telemetry Receiving System Based On FPGA

In the process of wireless channel transmission, telemetry signal will be affected by scattering, reflection and refraction, which leads to signals sending through multiple paths to a receiver, thus producing multipath interference. Multipath interference makes the base-band PCM signal waveform distorted seriously in time domain, also sudden failure rate increased greatly, which means synchronization signal frequently missing. In the frequency domain, the multipath interference performs denting in the PCM/FM spectrum. When the code rate is low(less than 500 Kbps), the waveform in time domain is narrower, the waveform in frequency domain is wider, by increasing the power to improve the decline of system; When the code rate is high(more than 1Mbps), serious signal inter-symbol interference and frequent selectively fading will appear, while increasing the system power to improve the decline of system can not work any more.Traditional anti-multipath interference technology need to know the channel transfer function, and transfer function is not change over time. However, the actual telemetry channel is time-varying, whose characteristics are unpredictable. Therefore, this thesis puts forward the anti-multipath interference technology based on blind equalization algorithm. Blind equalization is in the case of not knowing the channel characteristics,using algorithms to adjust the equalizer weights makes the equalizer output sequence to the input sequence. This thesis adopts PCM/FM code modulation, as required in the project: code rate above 2 Mbps, maximum bandwidth of the signal lower than 8 MHz,signal-to-noise ratio under 20 dB, and bit error rate less than3101??. The anti-multipath interference of telemetry receiving system is designed and implemented based on FPGA.The main work is as follows:1. According to the requirements of project designing, FM modulation PCM NRZ-L is designed for production and the code rate is 2 Mbps. The signal sampling rate is 56 MHz. modulated carrier frequency is 70 MHz, and the roll-off factor of the sending signal shaping filter is 0.6.2. The characteristics of wireless channel in telemetry system are analyzed and two-path model is adopted to simulate the multipath channel, and making a simulation model of the PCM/FM telemetry system.3. According to the project design requirements, the system design scheme is explained in detail. Each unit is given a detailed algorithm description and simulation in the MATLAB. The design of digital filter in digital down conversion unit and algorithm in the channel equalization unit are mainly described. The digital filter in digital down conversion unit with the method of CIC filter cascaded ISOP compensating filter, while channel equalization unit use the improved constant modulus algorithm, both have very good balancing effect for the amplitude and phase of the signal.4. Introduce the software radio platform to realize the anti-multipath interference telemetry receiving system. Give a specific structure of the system implementation based on FPGA. And through the simulation of various modules in Modelsim, verify the correctness and reliability practicability of the project.