streaming 50MS/s

[Alann]

hello ..

I am using RFSA to acquire complex IQ data at 50MS/s. How can I stream this data at 100 MB/s (as one sample is 2 bytes so this makes 100MB/s) to 1 TB RAID?

[TCPlomp]

Sorry, but you can't.

The 100 MB/s of ethernet is 100 megabit per second so basically 12 megabyte per second.

Even with Gigabit (120 megabit per second) you would have issues continually streaming data, I advise you to  look at some faster connection than ethernet. (SATA for instance).

Ton

[S_Hong]

Hi Alann,

If you are returning a complex waveform at 50 MS/s, you are effectively returning 4 bytes of data per sample (2 bytes for I and 2 bytes for Q). This means that you will need to stream data at around 200 MB/s. Depending on what kind of RFSA hardware you are using, the maximum throughput will vary. For a NI-5661, since this uses the PXI bus, the theoretical bandwidth is limited to 133 MB/s, whereas a NI-5663 is based off of the PXI Express architecture which can theoretically reach 1GB/s (since the NI-5622 digitizer on the NI-5633 is a x4 Express card where each lane has a bandwidth of 250MB/s). Therefore, the only way you can achieve this bandwidth is to use our NI-5663. That being said, you still need to be able to write data to a HD fast enough to keep up with these rates. In most systems, the HD will be the bottleneck and therefore, to stream at these rates, you will definitely need to use a RAID array. Please take a look at the following links for more info.

Perform RF Streaming Successfully

http://zone.ni.com/devzone/cda/tut/p/id/7209#toc0 

Introduction to Streaming

http://zone.ni.com/devzone/cda/tut/p/id/6355

I hope this helps. Please let me know if you have any questions

[Alann]

I am using 5661 and a 1TB RAID. What i understood by your reply was that I cant stream 200 MB/s because max bandwidth is 133 MB/s.

So is there any way in which i can write 1 byte for I and 1 for Q?? In this way the bandwidth required for data transfer will reduce to 100 MB/s ? 

[S_Hong]

Hi Alann,

That is correct, the bus limitations on the 5661 will not allow you to stream at 200 MB/s.

As for reducing your IQ data to 1 byte each, you may be able to do this by pulling out the NI-Scope session from your RFSA session and changing the Binary Sample Width property (found under Acquisition) using the niScope property node as this will reduce the samples to 1 byte. To get the NI-Scope session handle from the RFSA instrument handle, you will need to use the niRFSA Get NI-Scope Session.vi which is not found in the LabVIEW RFSA palette, but rather in the niRFSA.llb in your C:\Program Files\National Instruments\LabVIEW X.X\instr.lib\niRFSA directory. (Replace X.X with your version of LabVIEW).

Note that even after making these changes, you may not reach exactly 100 MS/s as streaming is a very system dependent specification, but at least you will be closer to your target than before. Please let me know if you have any other questions.

Message Edited by S_Hong on 04-06-2009 05:03 PM

Message Edited by S_Hong on 04-06-2009 05:04 PM

[Alann]

Thanks a lot for your prompt reply..

 

I didn’t know about the property. When I had 2 bytes for I and 2 bytes for Q, the binary sample width was 32. Now if I want one byte for each, then binary sample width should be set to 16. When I try doing this the program returns an error. How can I make this work and compatible with other settings?

I am using the ref code to check this property (which is available of the website).