Implementing and Characterizing Real-Time Broadband RFI Excision System for the GMRT Wideband Backend

Abstract

ABSTRACTThe Giant Metrewave Radio Telescope (GMRT) is being upgraded to increase the receiver sensitivity. This makes the receiver more susceptible to man-made Radio Frequency Interference (RFI). To improve the receiver performance in the presence of RFI, real-time RFI excision (filtering) is incorporated in the GMRT wideband backend (GWB). The RFI filtering system is implemented on FPGA (Field Programmable Gate Array) and CPU (Central Processing Unit)–GPU (Graphics Processing Unit) platforms to detect and remove broadband and narrowband RFI, respectively. The RFI is detected using a threshold-based technique where the threshold is computed using Median Absolute Deviation (MAD) estimator. The filtering is carried out by replacing the RFI samples by either noise samples or constant value or threshold. This paper describes the status of the real-time broadband RFI excision system in the wideband receiver chain of the upgraded GMRT. The methodology for carrying out various tests to demonstrate the performance of broadband RFI excision at the system level and on the radio astronomical imaging experiments is also described.