A real-time software backend for the GMRT
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The new era of software signal processing has a large impact on radio astronomy instrumentation. Our design and implementation of a 32 antennae, 33 MHz, dual polarization, fully real-time software backend for the GMRT, using only off-the-shelf components, is an example of this. We have built a correlator and a beamformer, using PCI-based ADC cards and a Linux cluster of 48 nodes with dual gigabit inter-node connectivity for real-time data transfer requirements. The highly optimized compute pipeline uses cache efficient, multi-threaded parallel code, with the aid of vectorized processing. This backend allows flexibility in final time and frequency resolutions, and the ability to implement algorithms for radio frequency interference rejection. Our approach has allowed relatively rapid development of a fairly sophisticated and flexible backend receiver system for the GMRT, which will greatly enhance the productivity of the telescope. In this paper we describe some of the first lights using this software processing pipeline. We believe this is the first instance of such a real-time observatory backend for an intermediate sized array like the GMRT.
KeywordsRadio interferometer Correlator Beamformer COTS High performance computing Parallel processing RFI
We would like to thank many of the staff members from NCRA who have helped at various stages of implementing the GSB as an observatory backend. We acknowledge Santaji Katore and Nilesh Raskar for their contribution towards building a Graphical User Interface for the GSB. We are grateful to Subhashis Roy for help in analyzing and debugging the performance of the GSB, working on several test data sets, and also for providing the high dynamic range image of the J1609+266 field. We thank Sharwari Kulkarni for her contribution in implementing the narrow-band module for the GSB, to support the high spectral resolution observing mode. We specially thank the computer group at the GMRT (Mangesh Umbarje and Sumit Mirajkar) for extensive help at various stages of assembling and testing the GSB cluster and network. We thank Rajaram Nityananda and Jayaram Chengalur for their useful comments during the design phase. We also thank Dipankar Bhattacharya for useful discussions during implementation of the coherent dedispersion pipeline of the GSB. We acknowledge Adam Deller for helping in the comparative study of the results from the GSB with the DiFX. Finally, we thank B. Ajithkumar and his group at the GMRT, for building the new 32 MHz baseband system that feeds the analog signals to the GSB. The GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.
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