Research Of Digital Down-converting Technology Based On Software-defined Radio

With software programming, the software-defined radio (SDR) based on hardware platform can realize various the digital signal process (DSP) algorithms, and it has some advantages of flexibility in design and processing. Digital down-converting (DDC) is one of the key technologies of the SDR.Wide band and high bit-rate digital signal can be transformed to narrow band and low bit-rate digital signal by DDC technology. It decreases the cost of computation of the DSP followed and the digital signals can be processed in real-time.The realization of DDC algorithm was studied from the perspective of software.DDC system commonly needs to complete mixing, filtering, extracting and compensation operations. Therefore, the orthogonal digital mixing technology, the multi-level extraction filtering and the second-order polynomial interpolation (ISOP) compensation technology are studied in this paper. Moreover, the direct digital synthesis (DDS) technology is used in the numerical control oscillator (NCO), and we focus on the method to eliminate stray by random sequence. For multi-level extraction filtering, we make use of cascaded integrator-comb (CIC) and half-band (HB) filter which are two highly efficient filters. With the ISOP technology, we compensate CIC-band attenuation to achieve the intended results.Ultimately, the overall functions are achieved by MATLAB simulation tools, and the wide band and high bit-rate digital signal is successful converted into the narrow band and low bit-rate digital signal with the DDC technology.