A Scalable Hybrid FPGA/GPU FX Correlator
  Radio astronomical imaging arrays comprising large numbers of antennas, O(10^2-10^3) have posed a signal processing challenge because of the required O(N^2) cross correlation of signals from each antenna and requisite signal routing. This motivated the implementation of a Packetized Correlator architecture that applies Field Programmable Gate Arrays (FPGAs) to the O(N) "F-stage" transforming time domain to frequency domain data, and Graphics Processing Units (GPUs) to the O(N^2) "X-stage" performing an outer product among spectra for each antenna. The design is readily scalable to at least O(10^3) antennas. Fringes, visibility amplitudes and sky image results obtained during field testing are presented. 
J. Kocz, L.J. Greenhill, B.R. Barsdell, G. Bernardi, A. Jameson, M.A.   Clark, J. Craig, D. Price, G.B. Taylor, F. Schinzel,...
astro-ph.IM