The Research Of Digital Down Conversion Technology Based On Software Radio

The key conception of Software Radio is to construct a hardware platform,which has characteristics of commonality,standardization and modularization,implement different function by software,and make A/D converter and D/A converter as close to antenna as possible in order to develop a new kind of flexible and exoteric wireless communication system.Due to the poor processing speed of A/D converter and DSPs,the receiver of Software Radio now often adopt the project based on Digital Down Conversion(DDC) technology added so as to decrease the sampling rate of RF signal and IF signal to meet the real-time signal processing requirement of DSPs.The technology based on DDC has become a very important part of software radio receiver nowadays,which is a kind of critical technology of software radio receiver.In this dissertation,DDC is focused on,which is a critical part of software radio receiver.Firstly,the module of analog-to-digital is researched,which is the input of DDC.The theory of sampling in Software Radio is presented,and the passband sampling theory is emphasized,which helps to decreasing the sampling rate.The expression of signal in frequency domain is derived,which is put window fuction on.The influence of window function on digital spectrum analysis is analyzed.Secondly,the multi-rate signal processing theory and digital channelization technology are discussed,and the polyphase mathematic modules of decimation and analysis filter banks are established.The spectrum characteristic of CIC filter is also analyzed.Thirdly,the theory derivation of NCO design based on DDS is presented in detail.The factors are educed by rigorous math formula,by which the performance of NCO is affected,and the simulation figures of some critical performance in matlab are also presented.At last,the realization scheme of all the modules of DDC in TMS320C6713 is presented innovatively.The software of DSP is designed by assembly language and the simulation is made in CCS,by which the original design is proved correct.The scheme of DDC with all-TMS320C6713 which is a high-performance processor produced by TI proposed in this dissertation is an innovation in DDC,which provides helpful theory discussion and corresponding software design for the realization of DDC with all-DSP.