[Pafgbt] PAF beamformer size and cost

[Rick Fisher]

Brian,

Is your assumed beamformer architecture voltage sums or post-correlation? 
In other words, are the beams formed by summing complex weighted voltages 
from the array elements or by combining cross products of all of the 
elements?  John's reference at http://arxiv.org/abs/0912.0380v1 shows a 
voltage-sum beamformer.  The post-correlaion bamformer may use fewer 
processing resources, but it precludes further coherent signal processing 
of each beam.

Very roughly, the science requirements for a beamformer fall into two 
camps, which may be operational definitions of first science and 
cadallac/dream machine: 1. spectral line surveys with bandwidths in the 
3-100 MHz range and very modest time resolution and 2. pulsar and fast 
transient source surveys with bandwidths on the order of 500+ MHz and <=50 
microsecond time resolution.  The 2001 science case says pulsar work 
requires bandwidths of 200+ MHz, but the bar has gone higher in the 
meantime.  One can always think of something to do with a wide bandwidth, 
low time resolution beamformer, but it would be a stretch.  The GBT 
sensitivity isn't high enough to see HI at redshifts below, say, 1350 MHz 
in a very wide-area survey.  Hence, building a beamformer with wide 
bandwith but low time resolution may not be the optimum use of resources. 
Also, the 2001 science cases assumes 7 formed beams, but the minimum now 
would be, maybe, 19 and growing as the competition heats up.

Counter-thoughts?

Rick

On Wed, 3 Feb 2010, Brian Jeffs wrote:

> Rick,
>
> We have a rough architecture and cost estimate for a 40 channel 
> correlator/beamformer capable of 40 channels (19 dual pol antennas plus 
> reference or RFI auxiliary) over 250 MHz BW.  We worked this out with CASOER 
> head Dan Werthimer and his crack correlator/beamformer developer Jason 
> Manley.  It will require 20 ROACH boards, 20 iADC boards, 1 20-port 10 Gbit 
> ethernet switch, and some lesser associated parts.
>
> Our recent ROACH order was $2750 each, iADC: $1300 each, enclosures: $750 
> each, XiLinx chip: free or $3000,  ethernet switch: $12000.
>
> You can use your existing data acquisition array of PCs as the stream-to-disk 
> farm, but will need to buy 10 Gbit cards and hardware RAID controllers.
>
> The total (which will be a bit low) assuming no free XiLinx parts and not 
> including  is:  $168,000.
>
> Of course this does not include development manpower costs.
>
> Brian
>
>
> On Feb 3, 2010, at 3:05 PM, Rick Fisher wrote:
>
>> This is an incomplete question, but maybe we can beat it into something
>> answerable:  Do we know enough about existing applications on CASPER
>> hardware to make a conservative estimate of what it would cost to build a
>> PAF beamformer with a given set of specs?  I'm looking for at least two
>> estimates.  What is a realistic set of specs for the first science PAF
>> beamformer, and what would the dream machine that would make a big
>> scientific impact cost?  You're welcome to define the specs that go with
>> either of these two questions or I'll start defining them by thinking "out
>> loud".  The first science beamformer will guide the initial system design,
>> and the dream machine will help get a handle on longer range expectations.
>> 
>> Cheers,
>> Rick
>> 
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