Multi-tier interference-cancelling array processing for the ASKAP radio telescope

The ASKAP radio telescope in Australia is the first synthesis imaging array to use phased-array feeds (PAFs). These permit wider fields of view and new modalities for radio-frequency interference (RFI) mitigation. Previous work on imaging-array RFI cancellation has assumed that processing bandwidths are very narrow, and correlator integration times are short. However, these assumptions do not necessarily reflect real-world instrument limitations. This paper explores adaptive array cancellation algorithm effectiveness on ASKAP for realistic bandwidths and integration times. With ASKAP's beamforming PAFs on each dish, followed by a central correlation processor across beamformed signals from all dishes, one may consider algorithms that span multiple levels in the hierarchical signal processing chain. We compare performance for several subspace-projection-based algorithms applied to different tiers of this extended architecture. Simulation results demonstrate that it is most effective to cancel at the PAF beamformers.