Differences
This shows you the differences between two versions of the page.
|
projects:meerkat:first_thoughts [2016/05/20 15:19] wucknitz |
projects:meerkat:first_thoughts [2016/11/24 10:46] (current) wucknitz |
||
|---|---|---|---|
| Line 15: | Line 15: | ||
| * The (Feng?) voltage buffer keeps 2.5 sec of data. Upgrade to 4 sec or so may be possible, but if 10 or more are needed, it is better to buffer in our cluster. | * The (Feng?) voltage buffer keeps 2.5 sec of data. Upgrade to 4 sec or so may be possible, but if 10 or more are needed, it is better to buffer in our cluster. | ||
| * VLBI output will not be available within the next two years, probably only later than that. | * VLBI output will not be available within the next two years, probably only later than that. | ||
| - | * The standard beamformer (Scarab board) will produce 4 beams or maybe more. | + | * The standard beamformer (SKARAB boards) will produce 4 beams or maybe more. |
| * SETI will use similar approach as we are thinking of: Tap Feng output and beamform from that. | * SETI will use similar approach as we are thinking of: Tap Feng output and beamform from that. | ||
| * We will need 64 links of 40Gbps each. Some data can be sent back to the switch (e.g. beamformed products). | * We will need 64 links of 40Gbps each. Some data can be sent back to the switch (e.g. beamformed products). | ||
| Line 23: | Line 23: | ||
| * Is pretty straight-forward: Take Feng output, correct for atmospheric phase terms, then shift to residual offsets with phase factors. For >= 4k channels this should be fine, at least in S band. For L band and UHF we have to check this critically. | * Is pretty straight-forward: Take Feng output, correct for atmospheric phase terms, then shift to residual offsets with phase factors. For >= 4k channels this should be fine, at least in S band. For L band and UHF we have to check this critically. | ||
| * Decimation in the beamformers, then transpose by sending back to switch (from band per node to beam per node). | * Decimation in the beamformers, then transpose by sending back to switch (from band per node to beam per node). | ||
| - | * Need ca. 4k channels, time resolution 50 microsec. With 8 bit per sample and only Stokes I this corresponds to 80 MB/sec (640 Mb/sec). For 400 beams that is 32 GB/sec. When spread over 64 nodes or links, this is 0.5 GB/sec or 4 Gb/sec. This should be compared to the ~ 25 Gbps x 64 for the Feng data. | + | * Need ca. 4k channels, time resolution 50 microsec. With 8 bit per sample and only Stokes I this corresponds to 80 MB/sec (640 Mb/sec). For 400 beams that is 32 GB/sec. When spread over 64 nodes or links, this is 0.5 GB/sec or 4 Gb/sec. This should be compared to the ~ 25 Gbps x 64 for the Feng data. This should still fit in the big switch so that we can use it for additional transpose operations (from beamformer to pulsar search). |
| * 4k channels have a time resolution of 4.7 microsec. We need 50, so the decimation factor is about 11. Input data are complex with two polarisations, output is real with only one Stokes I (factor of 4). In total the decimation factor is 43. We have 400 beams, which is a factor of 6.25 more than antennas. 6.25/43=0.145, the estimated ratio of data rates is 4/25=0.16, so this is consistent. | * 4k channels have a time resolution of 4.7 microsec. We need 50, so the decimation factor is about 11. Input data are complex with two polarisations, output is real with only one Stokes I (factor of 4). In total the decimation factor is 43. We have 400 beams, which is a factor of 6.25 more than antennas. 6.25/43=0.145, the estimated ratio of data rates is 4/25=0.16, so this is consistent. | ||
| * **Second half of band is more difficult:** Need own Feng and maybe correlator and determination of phase solutions (dispersive and non-dispersive delay?). Expand their hardware or do own Feng in GPUs? Second half should go into same switch. | * **Second half of band is more difficult:** Need own Feng and maybe correlator and determination of phase solutions (dispersive and non-dispersive delay?). Expand their hardware or do own Feng in GPUs? Second half should go into same switch. | ||
