Implementation of digital down converter in GPU

Amit Upadhyay, Yawatkar Shakun Rajan
Department of Avionics, Indian Institute of Space Science and Technology, Thiruvananthpuram
Indian Institute of Space Science and Technology, 2012


   title={Implementation of digital down converter in GPU},

   author={Upadhyay, A. and Shakun Rajan, Y.},




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Giant Metrewave Radio Telescope is undergoing an upgradation. GMRT is mainly used for pulsar, continuum and spectral line observations. Spectral Line observations require more resolution which can be achieved by narrowband mode. Thus to utilize the GMRT correlator resources efficiently and to speed up the further signal processing, Digital Down Converter is of great use. Digital Down Conversion down-converts the desired band to baseband resulting into the increased resolution of signal. The limited FFT size can be utilized to get more resolution of signal. Graphic Processing Unit (GPU) decreases the time of various operations in DDC significantly. Hence, the DDC design is done in GPU The project work includes the design of DDC block in GPU using a programming tool Compute Unified Device Architecture C (CUDA-C). All the sub blocks of DDC were designed and combined to form DDC. The block was tested for the CW signal and also the channel noise signal; it showed the desired down-conversion of the band to baseband. DDC block also increases resolution of the signal. It decimates the output and spreads it over all the channels. It reduces the data rate in the GMRT correlator program to a great extent. The timing analysis of the DDC block was done with and without using shared memory of the GPU. Using shared memory is beneficial as far as the convolution time is considered. When the same code for DDC was run on CPU, it was observed that GPU gives about 250 times enhancement in the time consumed. The design of the DDC block was integrated with the existing GMRT Correlator program. It was placed just before the FFT block. Local GMRT software "TAX" was used to visualize the outputs obtained from the program. The desired down converted band was observed with the increased resolution. The GMRT Correlator program along with the DDC block has been further modified as per the requirements of Phase Correction and MAC block of the GMRT Correlator design. It enabled us for the sky testing of the GMRT Correlator program with the DDC feature. The sky test results were obtained and verified successfully.
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