Research And Hardware Implementation Of Key Technology Of Digital Processing In Wideband HF Communication

Software radio has the advantages of flexibility and openness, and it plays an important role in the design of wideband HF communication.This paper mainly deals with the key techniques of Digital Down Conversion and the implementation of field-programmable gate array (FPGA). Firstly, the basic theories of Digital Down Conversion ,including signal sampling, orthogonal transformation, decimation and interpolation, are analysed. Secondly, multirate cascade digital filters and related theories are presented. Finally, the design and FPGA implementation of some main components in the Digital Down Conversion are implemented, such as numerically controlled oscillator (NCO), cascade integrator-comb (CIC) filter, half-band filter and finite impulse response (FIR) filter.In the design of NCO, some improved measures are proposed with the an analysis of two different methods which are based on look up table (LUT) and CORDIC algorithms.And a high-precision numerically controlled oscillator implemented with the FPGA is achieved. The decimating digital filter of Digital Down Conversion is designed as the cascade of a CIC filter and three half-band filters. At last, a high order low pass FIR filter is used to suppress the noise out-of-band. Due to the limitation of the number of multipliers in FPGA chip, the adoption of fixed-coefficient multipliers with the Canonic Signed Digit (CSD) code has largely reduced the resources used in FPGA implementation.