Programmable Real-Time Cancellation ofGLONASSInterference with the Green Bank Telescope

Abstract

A programmable, real-time, digital signal processing (DSP), least-mean-squares (LMS) interference canceler was developed and demonstrated as a successful method of excising the GLONASS satellite L-band downlink signals from the 100 m Green Bank Telescope (GBT). This canceler has the potential for aiding the observation of redshifted OH lines near 1600 MHz in the presence of GLONASS signals. Our canceler approach is similar to experiments reported by Barnbaum and Bradley, Baan et al., and Kesteven et al. for mitigating ground-based radio frequency interference (RFI), but we add the new features of a tracking dish antenna to follow the satellite for improved cancellation performance, complex adaptive filter coefficients that reduce the required filter length, and a programmable delay line for bulk time delay correction. An analysis of LMS tracking performance for moving satellites is presented, and effective use of a reference antenna distantly located from the telescope is demonstrated. As is expected from the known properties of LMS cancelers, larger filter orders are shown to yield more reliable cancellation and are less sensitive to data time misalignment. GLONASS interference seen by the GBT was suppressed below the noise floor without corrupting a signal that simulated an astronomical source, even with rapid orbital transits and long integration times.