The Research And Realization Of Digital Down Conversion Technologies In Software Radio

Software Radio carry out each kind of function undertaken by software on the hardware platform composed of general PLD or digital signal processor. Software radio is one of the hotspots in mobile communication research. The ideal Software Radio is to make the digitization process as far as possible approaches the antenna. That is, analog-to-digital conversion is done in radio frequency. Due to the poor processing speed of A/D/A conversion and DSP processor, Software radio often adopts inter-specific schemes of digital intermediate frequency(IF). By using specific DDC&DUC or PDC (Programmable down Converter), the radio frequency signal is converted to intermediate frequency (IF) signal. Then the processing of digitized signal is undertaken in IF. It will be much flexible in the application that changing the sample frequency of radio frequency analogy signal. The analysis indicates that the specific DDC chip has many virtues, such as having great decimation ratio and steady performance. But it too expensive, less flexible and can't exhibit the advantage of software radio.In this dissertation, signal processing of DDC is investigated. Based on the theory of DDC signal processing and the analysis and design on the key module, the technology of design DDC using PLD is focused on. The paper mainly includes some follows:This thesis analysis signal sample theory in DDC, multi-speed signal processing theory as well as digital signal orthogonal theory based on the basic structure of DDC, technology characteristic and actuality of domestic and foreign. So the PLD complete or partially replace the specific ASIC chip to develop the flexibility of DDC.In this paper, we deeply study the key techniques including digital mixing, design of optimum NCO and high-efficiency digital filter used for decimation based on the basic principle of DDC. We put forward two scheme of DDC in the thesis.Focus on the scheme of DDC and adapt to the demand of DDC in the actual digital communication system based on the software radio, we accomplish the simulation and hardware testing of each function module and analyse the testing result.The DDC based on the FPGA can show adequately the great flexible and broad adaptability of software radio. The DDC system in the paper has definite generality.