Research On RF Direct Sampling Structure Based On Parallel Sampling

With the rapid development of FPGA, DSP and other hardware platforms, digital signal processing speed is also constantly increased, digital processing technology is widely used,the digitizing of analog signal becomes critical. Along with the rise and development of software radio technologies, it becomes the focus of attention on that how to achieve efficient implementation of RF front-end analog signal digitization. Under the premise of sampling frequency and accuracy of existing ADC hardware can be achieved,how to sample a GHz analog bandwidth wide band signal as a digitized signal becomes a difficulty. To meet the demands of software defined radio for broadband signal processing, force RF front-end architecture developing to achieve the goal of higher input bandwidth, which makes a high demand of ADC's sampling rate and accuracy.A multi-chip parallel sampling ADC structure, make up the traditional way's shortcomings of sampling, which the high sampling rate can only correspond to less than 12 bit sampling bits. It can achieve not only sufficiently high enough sampling rate, but also to obtain a sufficiently high sampling accuracy, which makes the RF front-end architecture be closer to the ideal RF direct sampling structure. This paper compares the three sampling structures of the software defined radio front-end,and analyzed the advantages and necessity of using an RF direct sampling structure of the RF front-end, and put forward the direct sampling system that using the parallel sampling structure which based on HFB to replace the multi-stage mixer superheterodyne structure. Deduced perfect reconstruction condition and power complementary relationship,and completed the designing of a two-channel power complementary hybrid filter bank, designed a direct sampling simulation system which based on the HFB structure. The main contents include following:Firstly, the analysis of the development background of the current RF front-end sampling structures of the software defined radio platforms,and a simple comparison of the advantages and disadvantages of the three sampling structures and theories,presented the advantages and difficulties of the RF direct sampling structure. A brief overview of the key technology of digital signal processing including of multi-rate sampling, ADC and filter banks to learn about their basic principles. And then, the analysis and comparison of three parallel sampling ADC architectures, focusing on the theory of HFB ADC systems and deriving the perfect reconstruction condition of signals. And derived the expression of the optimized transfer function coefficients,it combined the advantages of genetic algorithm,Using genetic algorithms toolbox to optimize the coefficients. Obtained analog filter set with tight power complementary relationship. Secondly, deduced the IFFT algorithm, obtained the algorithm that to design and optimize the synthesis filters bank. Put forward the optimization of system delay parameter and the parameter of filters order based on the genetic algorithm. It designed hybrid filter bank which meeting the power complementary relationship, compared and analyzed the error performance of different types of HFB structures. Finally, completed the design of the RF direct sampling system based on the modulation and demodulation of BPSK signals, in which using a two-channel power complementary HFB parallel sampling structure.Analyzing of the BPSK demodulation bit error rat curves with different signal noises rats,verify the effectiveness of the HFB structure in RF direct sampling system which is the replacement of multi-stage mixing structure.