Research And Analysis On The Digital Down Down Converter Modules Of The Software Radio

Software Radio carry out each kind of function by software on the hardware platform composed of general PLD or digital signal processor. Software radio is one of the hotspots in mobil communication research. The key conception of Software Radio is to construct a hardware platform, which has characteristics of commonality, standardization and modularization then implement different function by software; In order to digitize the analog signal as early as possible,it required to make A/D converter as close to RF antenna as possible. However, limited by the current device development level, it is difficult to realize RF signal digitalization. Thus ,the prevalent choice is to make analog IF signal digitalized, convert IF signal to baseband by using digital down converter, then accomplish digital signal processing in baseband,thus the technology of Digital Down Convert has become one of the important technologies in the Software Radio. The DDC in Software Radio system can reduce the rate of data flow, and send this low-speed data to the DSP devices which can process this data fluently. DDC as a bridge between the ADC and the DSP devices, its performance will have a direct impact on the stability of Software Radio system.The realization measures of the DDC in Software Radio system on FPGA has been researched in the paper. The analysis and optimization to the arithmetic involved in the main module have been completed,also. The VHDL program design and time simulation and verification have been completed too.The results showed that the design and structure is correct, and realized the project of improving operation efficiency and saving the hardware resources,made important theoretical bases and abundant practice preparation.In this thesis, the current status of the DDC technology research at home and abroad was analyzed. The theoretical bases of the DDC technology has been described, then introduce two realization architectures and corresponding features of the DDC system. Through the comparing of three representative hardware realization functions of the DDC system, obtain the advantage of using FPGA to complete the design of DDC. In the paper an in-depth study was made in the implement of the NCO, Mixer, CIC filter, HB filter in the digital down-converter moudle and multi-rate conversion filter group moudle of the DDC system, and the mathematical model simulation, optimization was completed in MATLAB for these modules. Based on look-up table(LUT) and Coordinate Rotation Digital Computer(CORDIC) algorithm,a method for implementing a numerically controlled oscillator(NCO) is described in the paper, detailed analysis is made on the influence of the design parameter to corresponding performance; The NCO based on the CORDIC algorithm is proved to be superior to the other one after contrasting the result of simulation and synthesis; In the design of multi-rate conversion filter group moudle,the distribute arithmetic(DA) is adopted to design the half-band (HD) filter and optimization is made to it, greatly improved operation efficiency and saved the hardware resources.