Research On The Technique Of Digital Adaptive Heterodyne Filters

Mankind will enter the information society in the 21st century. This requires high-quality information service to adapt the fast development. The modern communication system must guarantee the availability and the reliability of signal's transmission in order to meet the demands of big capacity, multi-service, long distance and anti-interference. That means it should suppress the interference of communication system.It's impossible to avoid all interference in the communication system. Especially the narrowband interference, which generates much higher power density than the wideband interference does, has a great influence on the quality of the communication, even it can hinder the normal communication. Therefore finding a more efficient method to decrease the narrowband interference becomes one key problem for a good communication system.Many kinds of filters are presented in this paper, e.g. Adaptive Transversal Filter,Direct two-order IIR Filter, Lattice IIR Filter, High-Order IIR Filter and Adaptive Sampling Filter. Because these filters have some limitations and defects, the adaptive filter of other structure is discussed in the paper.Digital adaptive heterodyne filter adopts the heterodyne-modulation conception, which makes the filter work in low frequency and lessens the complexity of design. After discussing this kind of filter in this paper in detail, the grads algorithm in time domain and frequency domain is set up when the change of frequency is slow, so it means the algorithm only process the narrowband interference what it changes slowly. According to the characteristic of digital adaptive heterodyne filter and the conception of interference counteraction, the paper presents a new structure to enable the filter track the interference signal precisely and control the width and depth of notch. Through simulation, it is demonstrated that the new structure can suppress one or more interference signals and the filtering operation has little influence on signal spectrum.The system-controlled IIR filter and FFT were realized using FPGA in this paper, and modified pipeline structure is adopted to greatly raise the running speed in the system-controlled IIR filter. In the same time, it is used that the algorithm of N-point complex to compute 2N-point real data block in the radix-2 FFT. It is different to the normal method in the adoption of pipeline single dual RAM for each stage.The research and implementation of this kind of filter widen the idea of filterdesigning and offer a good idea for the research of other high-speed adaptive signal processing.