Alternative Adaptive Filter Structures for Improved Radio Frequency Interference Cancellation in Radio Astronomy

Abstract

In radio astronomy, reference signals from auxiliary antennae, receiving only the radio frequency interference (RFI), can be modified to model the RFI environment at the astronomy receivers. The RFI can then be cancelled from the astronomy signal paths. However, astronomers typically only require signal statistics. If the RFI statistics are changing slowly, the cancellation can be applied to the signal correlations at a much lower rate than required for standard adaptive filters. In this paper we describe five canceller setups; pre-and postcorrelation cancellers that use one or two reference signals in different ways. The theoretical residual RFI and added noise levels are examined, and demonstrated using microwave television RFI at the Australia Telescope Compact Array. The RFI is attenuated to below the system noise, a reduction of at least 20 dB. While dualreference cancellers add more reference noise than single-reference cancellers, this noise is zero-mean and only adds to the system noise, decreasing the sensitivity. The residual RFI that remains in the output of singlereference cancellers (but not dual-reference cancellers) sets a non-zero noise floor that does not act like random system noise and may limit the achievable sensitivity. Thus dual-reference cancellers often result in superior cancellation. Dual-reference pre-correlation cancellers require a double-canceller setup to be useful and to give equivalent results to dual-reference post-correlation cancellers.

VAST: An ASKAP Survey for Variables and Slow Transients

“…2. Adaptive cancellation techniques such as those described in Mitchell, Robertson, & Sault (2005), Briggs & Kocz (2005), and Kesteven et al (2010). These require a separate reference antenna or beam on the sky to sample the RFI.…”

“… Post-detection flagging based on the recognition of data that are affected by interference. This has been the traditional approach in radio interferometry and is appropriate for moderately strong interference, but it does come with a loss of sensitivity. Adaptive cancellation techniques such as those described in Mitchell, Robertson, & Sault (2005), Briggs & Kocz (2005), and Kesteven et al (2010). These require a separate reference antenna or beam on the sky to sample the RFI.…”

Statistically Stable Estimates of Variance in Radio-Astronomy Observations as Tools for Radio-Frequency Interference Mitigation

“…Radio observatory computers are themselves often the sources of RFI. Many authors demonstrated the effectiveness of different RFI mit-igation methods (Ellingson & Hampson 2003;Baan, Fridman & Millenaar 2004;Fisher et al 2005;Mitchell, Robertson & Sault 2005;Poulsen, Jeffs & Warnick 2005;Zhang et al 2005;Kesteven 2007) in observations with single dishes and radio interferometers. Adaptive noise cancellation (ANC) with reference antenna was described in (Barnbaum & Bradley 1998).…”