RFI Mitigation at Westerbork:RFI Mitigation at Westerbork:algorithms, test observations, algorithms, test observations, system implementationsystem implementation

Willem Baan, Willem Baan,

Peter Fridman Peter Fridman

& Rob Millenaar& Rob Millenaar

Implementing Implementing Mitigation Hardware in Mitigation Hardware in the WSRT systemthe WSRT system

• 3 locations in data flow of 3 locations in data flow of systemsystem• different algorithms at different algorithms at different stagesdifferent stages• stapling of methods stapling of methods • AI decision-making AI decision-making subsystem for control subsystem for control

Our first DSP system

WSRT RFIMSWSRT RFIMS• Main goal RFIMS is to recover (full) sensitivity Main goal RFIMS is to recover (full) sensitivity

of WSRT across all observing bands with hostile of WSRT across all observing bands with hostile RFI environmentRFI environment

• Three year implementation planThree year implementation plan• System scalability and upgradeabilitySystem scalability and upgradeability• RFIMS pre-processing 14 x 2 x 20 MHz FPGA RFIMS pre-processing 14 x 2 x 20 MHz FPGA

hardwarehardware• Possible implementation of 10msec sampling Possible implementation of 10msec sampling

at WSRT correlator for on-line processingat WSRT correlator for on-line processing• Envisioned implementation on other telescopesEnvisioned implementation on other telescopes

WSRT RFI Mitigation System WSRT RFI Mitigation System Real-time pre-detection and pre-Real-time pre-detection and pre-correlation baseband processingcorrelation baseband processing

a) 12bit ADCa) 12bit ADC

b) Altera Stratix b) Altera Stratix FPGA FPGA

c) 14bit DAC c) 14bit DAC

d) VME controld) VME control

e) 40Msamples/sece) 40Msamples/sec

14 RTs & 2pol 14 RTs & 2pol

& 20 MHz & 20 MHz

RFIMS

Processor Board Layout

A fancy processor

RFI time-frequency domains

Thresholding in Time Domain

Thresholding in Frequency DomainReference power spectrum Median Filtering of spectrum

Adaptive Filtering with WSRTAdaptive Filtering with WSRT

2004Adaptive Filtering - ProposedAdaptive Filtering - Proposed

Adaptive Filtering - UltimateAdaptive Filtering - Ultimate

Dual Channel FPGA Layout

FPGA layout with Reference antennas

T-f thresholding

First trial of 14 RT system

20 MHz 5X band cleaned

All other 7 bands at same frequency

10 hr synthesis of DA240

Auto Corr Amp

5X5X b0 & b1

RT 5X, 6X, 7X, 9XRT 5X, 6X, 7X, 9X

Cross Corr Amp

5X6X b0 & b1

Cross Corr Func

5X6X b0 & b1

RFIMS 4X & 5X

DA240 field

Short Term Plans

• Persuade astronomers to use the system• Use RFIMS with new 14 RT LFFE system in LOFAR

band 110- 180 MHz • Implement adjacent RT for reference antenna• Introduce separate Refants• Apply ANC for pulsar operations (PuMa I & II)• Implement HOS for blanking

• Evaluate efficiency and impact on the imaging and spectrum data

1. Single dishes and connected radio interferometer

2. Evaluate algortihms for RFI environments

3. Implement in ALL new RTs ( multi-bit ADC (>14)), short averaging intervals, higher order statistics, auxiliary reference channels).

4. Number crunching aspects

5. Dedicated devices ?

Conclusions