topic Re: signal generation using the data from matlab script node in Signal Generators

signal generation using the data from matlab script node

pjj — Fri, 04 Jan 2008 09:46:29 GMT

Hello everyone.

I'm using the data from matlab script node to generate signal. The data will change each time in a loop according the matlab script, I'm wondering whether the RF hardware (signal generator module) will experience a time break in transmitting between the data changing?

Thanks for your help:-)

Re: signal generation using the data from matlab script node

Raajit_Lall — Mon, 07 Jan 2008 16:49:18 GMT

Hi,

The waveform generator actually has onboard memory, which is pretty much going to act like a buffer. So depending on the size of the "data chunks" that you are writing to the onboard memory, you should see no delay. This is a fairly commom application used for streaming purposes, where you would write data to the onboard memory and as soon as the generator is done with writing the previous waveform it will continue with the waveform/s written on the onboard memory.

You did mention that you are using RF hardware? Are you using the 5671? Could you please give me a little more details on what kind of hardware you are using, what programming environment you are using and whether you are using our RFSG driver.

It would also help to know how much data you are writing and how fast/often you are writing it.

Thank you,

Re: signal generation using the data from matlab script node

pjj — Tue, 08 Jan 2008 02:57:50 GMT

Hello Raajit L

Thanks for your kind reply. The upconverter is 5610, and the arbitrary waveform generator is 5441. The programming environment is Labview 8.2.

At the transmitter, I'm using data from matlab script, which is in a loop, to generate waveform, and the data updates every 1 second.

But at the receiver the constellation is out of order. So I put a module of "Clear Arbitrary Memory" in the loop. The result is that the constellation of receiver seems much better now, but there is error in transmitter namely:

Error 1074126847 occurred at niFgen Clear Arbitrary Memory.vi. Drive Status:(Hex OxBFFA2001) The operation cannot be completed because the device is not configurable while it is generating a signal.

I don't know how to figure it out.

Best regards!

Re: signal generation using the data from matlab script node

Raajit_Lall — Wed, 09 Jan 2008 17:26:51 GMT

Hi,

What is the VI that you are using to write to the onboard memory again? You should just be able to use a NIFgen Write Waveform to write to the memory again. What you could do is just monitor when the memory is free and only when write the memory. There is an example called Fgen Arb Waveform Streaming.vi. Here the memory is being checked before writing new data to the onboard memory.

I think that might also be the reason why your constellation was not correct, because the data that was there onboard was getting erased, but I am just speculating here. Please take a look at the example and see if that helps out any. Also make sure that you are not changing any session parameters on the fly, which is probably what is causing the error that you are seeing.

Regards,

Message Edited by Raajit L on 01-09-2008 11:26 AM

Re: signal generation using the data from matlab script node

pjj — Thu, 10 Jan 2008 02:24:24 GMT

Hi Raajit L:

Thanks a lot. I'll digest the example and get some insight from it. If I have further questions, can I contact with you by Email? Could you share your email address?

Best Regards!

Re: signal generation using the data from matlab script node

Raajit_Lall — Thu, 10 Jan 2008 17:14:27 GMT

Hi,

The best method to get in touch with me would be to post back on this forum or make a new thread for new questions. Our support is a paid service where as the forums are free :). We monitor the forums regularly and usually I will post back or someone else from my team will post back, if I am out of the office.

Let me know how the example works out for you and you can post back with any further questions.

Thank you and have a great day.

Regards,

Re: signal generation using the data from matlab script node

pjj — Mon, 14 Jan 2008 05:48:52 GMT

Hello Raajit L:

I'm not so sure whether "waveform streaming" you mentioned is suitable in my application. I'll elaborate my application here:

1.The data source for waveform is from Matlab script node, which generates data almost every 1second (which is not a constant time slot, because it also depends on other blocks).

2.The output data from Matlab is then fed into "niFgen create waveform", (this RF labview program is done by other people, so I'm not very familiar with it).

I have a few questions:

1. If the "niFgen create waveform" creates multiple waveforms in the onboard memory (since the output data from Matlab is updating)?

If so, can I clear the former waveforms and only generate the current waveform? The former waveforms are outdated and not needed.

2. I tried the following case: abort generation -- configure waveform -- clear memory -- create waveform

However it'll cause uncontinously generation, I don't want any delay or idle time.

3. If streaming is applicable, how to realize it to fit for my application?

Thanks very much

Best Regards

Re: signal generation using the data from matlab script node

pjj — Mon, 14 Jan 2008 11:36:51 GMT

Hello Raajit L

I have some further questions about waveform streaming:

1. How to define the onboard memory allocated to the waveform?

The parameters sets are: symbol rate: 8M/s, center frequency:2.38GHz, the data from matlab script is 1920 complex data. Does the memory size have some relationship with these parameters?

2. Is initial data necessary to be set?

3. What's role of the trigger?

Wish you would kindly help me with these questions.

Best Regards:-)

Re: signal generation using the data from matlab script node

Raajit_Lall — Tue, 15 Jan 2008 16:37:36 GMT

Here are the answers to your questions. You probably do not need to use the entire streaming example. I just recommended that to show you how to write to onboard memory. The niFgen Allocate Waveform is the VI that is allocating the memory up front. This is the amount of memory that will be reserved for your waveform. This depends on how much memory you as the user want to use and also on how much onboard memory your card has. We sell different generators with different memory options.

Only when you call your niFgen Initiate Generation function the waveform generation will begin. As the waveform generates, onboard memory space becomes free.

You can monitor available memory (like in the example) as the waveform is generating.

Calling the niFgen Write Waveform will write a new block of waveform data to the onboard memory.

The initial data is not required to be set.

The reason I recommended the streaming example is because if you close out and start the program every time that will induce a software lag into your program. You will be closing and starting new sessions on the board every time. Also, monitoring the memory is important, if you perform a write function before the waveform from the board has been output that will cause problems.

Triggering is used as an event to output a waveform on your device. More information on this can be found in the NIFGEN help. Start >> Programs >> National Instruments >> NI Fgen >> Documentation >> NI Signal Generators Help >> Search for streaming.

Regards,

Message Edited by Raajit L on 01-15-2008 10:37 AM

Re: signal generation using the data from matlab script node

Raajit_Lall — Tue, 15 Jan 2008 16:46:01 GMT

It would also help if you could post a little more information on how you have everything set up and maybe a screenshot of your code, so that I can get a better understanding of how your program is set up.

Regards,

Re: signal generation using the data from matlab script node

pjj — Thu, 17 Jan 2008 12:27:39 GMT

Hello Raajit L:

In streaming mode, I'm still not sure what size of memory to allocate to the waveform. I tried several amount of memory, each time I get an error like "memory full" even for a very large memory. Is there any relationship between the memory needed and the complex data symbols used for generating waveform?

I have one more question about the block of "niFgen Create Waveform (poly)".

In the help, it's said that that "signal generator must not be in the Generating state when you call any instance of this polymorphic VI". But I find that the waveform handle (output) of this VI is increasing with the loop, for example: 10001,10002...and so on. Does it mean the dynamic waveform is being generated according to the varying data from matlab srcipt, or just being created in the memory without being generated ? If the former case, then it's the right waveform for my application and I should look into other potential problem.

Attached is the vi for reference.

Thanks a lot for your kind help:-)

Best Regards!

Re: signal generation using the data from matlab script node

Raajit_Lall — Mon, 21 Jan 2008 05:57:11 GMT

Hi,

Thank you for the VI, it is easier to see what you are trying to achieve now. The waveform handle does change according to every new waveform that you are generating. Could you tell me what kind of board you are using as your function generator? Each board has onboard memory and as long as there is enough memory onboard you should not be getting a memory full error. The PXI 5421 for example comes with 8MB, 32MB or 512 MB options. Could you give me the error code for the memory full error that you are getting. It might be related to LabVIEW memory and not the FGEN memory.

The Create Waveform VI should be called before the FGEN is in writing state because the waveforms are written to the memory. You could also use the niFgen Set Waveform Next Write Position VI to write the waveform to a particular position on the onboard memory. Although, as you can see in the streaming VI that I posted before you could also wait for the memory to be empty and then write the next waveform. This depends on how you want to utilize the memory.

Regards,

Re: signal generation using the data from matlab script node

pjj — Mon, 21 Jan 2008 07:43:32 GMT

Hello Raajit L:

Thanks very much. The board I'm using is 5441 and the onboard memory is 256M.

After modification like you mentioned, the error is 1074118519 occurred at niFgen Initiate Generation:

Drive Status:(Hex OxBFFA4089)

The data being written to the streaming waveform cannot keep up with the output. Decrease the sample rate or write data to the streaming waveform more frequently.

(I allocate the memory size to the waveform is 67108864, I guess it's 64M)

Enclosed is the modified VI for your reference.

Best Regards!

Jingjing

Re: signal generation using the data from matlab script node

pjj — Mon, 21 Jan 2008 08:20:20 GMT

Hello Raajit L:

I get from "niFgen Query Arb Waveform Capabilities.vi" that the maximum waveform size is 67108864, so I allocate 64M to the waveform. Am I right?

I guess the error I just mentioned in the last thread will be memory full, if the case structure of query for the space available is deleted.

Best Regards!

Jingjing

Re: signal generation using the data from matlab script node

Ryan_V[DE] — Mon, 21 Jan 2008 19:48:24 GMT

Hello Jingjing,

After reading this thread, I have a question about your overall application. How is it that you are trying to output your data? Are you looking for real-time performance (e.g. you create IQ data in Matlab at least as fast as you generate (output) it)? Or are you interested in aperiodically generating a waveform (you want your generator to output a "packet," then cease generating until you download a new "packet")? Or do you want some kind of repetitive generation (you repeatedly output one waveform until you create a new one in matlab, then when the initial waveform completes, you begin repeatedly generating the new one). Let's call these options A, B, and C:

A: real-time, continuous (what we would call streaming) output
B: aperiodic waveform generation
C: repetitive waveform generation, with aperiodic updates

Under which of these would you classify your application? A few comments for each scenario:

A: This will require high performance to calculate data in real time and potentially large buffers requiring lots of memory. What is your IQ rate? Are you sure that your matlab computation can run fast enough on your machine?
B: This should be very simple, requiring only that you wait for generation to complete, clear the waveform, then begin generating again.
C: This can be done in Arbitrary Sequence mode, which basically controls how multiple waveforms can be generated in succesion . More information on this technique can be found here.

Please let us know your desired behavior, and that will help us to get you going in the right direction. I'm also intrigued by this application. Any details you have on the application as a whole would be very much appreciated. Thanks!

Regards,

Message Edited by Ryan V[DE] on 01-21-2008 01:48 PM

Re: signal generation using the data from matlab script node

Ryan_V[DE] — Mon, 21 Jan 2008 20:11:56 GMT

Hi Jingjing,

One more thing... I noticed you were sharing the 10 MHz reference of the two upconverters (and thus AWGs). I wanted to point out that though you will be phase locked and your clocks will not drift over time, the phase noise will be uncorrelated.

Ryan

Re: signal generation using the data from matlab script node

pjj — Tue, 22 Jan 2008 03:13:59 GMT

Hello Ryan

Thank you for your kind support:-)
I cannot explicitly attribute it to one of the three scenarios. The overall application seems like a

mixture of A and B.

Just like you've mentioned, the matlab computation cannot run fast enough. One reason of time

consuming is matrixes manipulation in the script, and another important reason is that the input of

matlab depends on higher level(Tcp in my application). Thus matlab script computes in a loop of nearly

1 second according to the data from Tcp link. (New data from Tcp will trigger a new cycle of the

loop.)

It's expected that before new data arrives from output of matlab, the waveform continously keeps

generating using the current data. As soon as new data is created, the waveform should be update to

overwrite the original one.

It seems more like the option B. But I've already tested: abort generation-> clear memory-> create waveform. The result is no explicit waveform can be seen from spectrum analyser, since the duration of each waveform is small(about 1second). At the receiver, only noise is captured.

If the application can be attributed to option B, then how can I solve the above problem due to abort generation and clear memory?

Thanks^_^

Best Regards!
Jingjing

Re: signal generation using the data from matlab script node

Ryan_V[DE] — Tue, 22 Jan 2008 05:33:30 GMT

Hello Jingjing,

Are you sure this would not fall under option C? It sounds like it to me. In this scenario, you would always have something on the output of the generator. You would also generate contiguous waveforms, updating with a new waveform only after the prior waveform has been completely generated. The basic method is that you set up a sequence of two waveforms, with a burst software trigger to advance to the next waveform. You first download waveform #1, then begin generating. When you have new data, you then download waveform # 2, and send a software trigger. Upon completion of the current iteration of waveform #1, the AWG will begin generating waveform #2. Again, when you have new data, you overwrite waveform #1 and send a software trigger, etc., etc. Effectively, you are "hopping" back and forth between the two waveforms, guaranteeing continuous output. Does that sound like it would work? Thanks!

Re: signal generation using the data from matlab script node

pjj — Wed, 23 Jan 2008 02:58:12 GMT

Hello Ryan:

Thanks for your suggestion:-) I've gained your point. But one question is that for "niFgen Create Advanced Arb Sequence.vi", I don't know to fill "loop counts array ". But the duration of each waveform is not configurable since it depends on the time duration between the data arrival from higher application(Tcp). Can this problem be solved?

Best Regards!

Jingjing

Re: signal generation using the data from matlab script node

pjj — Wed, 23 Jan 2008 03:34:16 GMT

Hello Ryan:

One more question: I got from the help that "The signal generator must not be in the Generating state when you call this VI".

So I guess when downloading a new waveform, this vi cannot work and change the waveform on the fly.

Best Regards!

Jingjing