Truncation Optimization Of FPGA Real-time Algorithm For Solar Radio Observation

Establishing solar radio observation system for long-term observation of solar radio signals is one of the important ways to study the solar activity.The digital receiver is a key part of the observation system,and the digital signal processing is realized in Field Programmable Gate Array(FPGA).At present,the processing speed and the resources of FPGA have been improved,but the digital signal processing in FPGA takes up too many resources.The application of high-precision Analog-to-Digital Converter(ADC)increases the amount of data to be processed by FPGA.Therefore,to complete the digital signal processing of a large amount of data under the limited FPGA resources,it is necessary to carry out truncation to realize the effective use of resources.Based on the 1.25 GSPS solar radio digital receiver developed by Laboratory for ElectromAgnetic Detection,Institute of Space Science Shandong University,this thesis researches on the FPGA data truncation,and proposes an optimal truncation selection method that is suitable for the FPGA data truncation in the digital receiver.Firstly,the simulation of the digital signal processing by FPGA in the digital receiver in MATLAB,combined with the principle of digital signal processing,the truncation effect of the operation results such as windowing,Fast Fourier Transform(FFT)is obtained.Then,the truncated data is compared with the data reserved full precision significant bits,and the relative error value is calculated.According to the relative error value and the occupation of FPGA resources,the optimal scheme for direct truncation in FPGA is determined.Finally,on the basis of the optimal scheme of direct truncation,the absolute value method,truncation plus method,rounding method and approximate truncation method are used to optimize truncation.And the optimal solution for the FPGA data truncation in the digital receiver is selected according to the optimization effect and the FPGA resource occupation.The optimal truncation selection method is applied to the 1.25 GSPS solar radio digital receiver,and the optimal truncation scheme is obtained.The approximate truncation method is used to process the data in the windowing and FFT output parts,and the former significant bits are reserved as[27:14],and the latter data bits are reserved after truncation as[20:5].In the butterfly operation of the FFT,according to the FFT operation principle,the data should be processed by the direct truncation method after each complex number multiplication,and the effective data bits are reserved as[39:15],which means the amplification effect of the rotation factor is offset.And the truncation is selected as[25:11 after each addition or subtraction.After the truncation,the Look-Up-Table(LUT),Look-Up-Table RAM(LUTRAM)and Flip Flop(FF)are reduced by 7.25%,14.64%,8.12%respectively,and the resources of the Digital Signal Processor(DSP)dedicated to computing have been reduced by 24.94%.The overall relative error of the observation system is less than 2.5×10-4,which satisfies the observation requirements of solar radio,and successfully realizes the real-time observation of solar radio signals at 35-40 GHz.At the same time,the research method has been applied in the 1-50 MHz low-frequency radio observation system,which realizes real-time observation of signals in the 1-50 MHz frequency band.