GLONASS Generation thru 5671

[stLeung]

Hi,

Recently I encountered some problems when using 5671 to transmit GPS signal.Here are my question:

1.I downloaded the GNSS3.0 Toolkit from NI website and run niGPS Streaming From File (5671).vi to generate GPS signal. The 5671 transmitted GPS signal correctly. But when I tried to run niGPS Streaming From File.vi or niGPS Direct Streaming Generation.vi by selecting the same GPS binary file,the error occured,it says "attribute ID is not reconized."I am not quite clear about this problem.Any clue will be appreciated.

2.After reading the readme file of the GNSS3.0 Toolkit,I noticed that this toolkit support the generation of GLONASS.Therefore I generated a GLONASS binary file and would like to transmit GLONASS signal thru 5671,but I noticed the frequency of GLONASS,1.602GHz, is different to the one of GPS,which is 1.57542GHz.My question is:

Do I only need to modify the frequency on the niGPS Streaming From File (5671).vi to transmit GLONASS signal?or need more?

3.Furthermore,is it possible to transmit GPS and GLONASS signal simultaneously?

Thanks in advance.

[Hardik.Asawa]

Hi stLeung,

First of all, I would like to point out that GNSS toolkit doesn't fully support PXI-5671. You can check the same in readme file of toolkit (also in screenshot attached). Now PXI-5671, though not supported, will still work with toolkit as it uses same niRFSG drivers. PXI-5671 consist of PXI-5441 & PXI-5610. PXI-5441 doesn't support streaming & most likely that was the reason why you were getting the error. The examples in folder niGPS Streaming from File (5671) are optimized for 5671 & hence you were able to use it. Can you give some more detail about the error (error code, source string etc) , that will help us understand exactly what is going wrong.

The centre frequencies which you are observing are as expected. GPS is generated at 1.57542GHz frequency whereas GLONASS signals are generated near 1.602 GHz.

Using 5671 it won't be possible to generate both GPS & GLONASS, as instantaneous bandwidth of PXI-5671 is 20MHz, whereas you need around 30MHz bandwidth for both of them to lie within a band.

Hope this help.

Regards,

Hardik Asawa

AE Specialist

[stLeung]

Hi Hardik,

Thank you so much for your quick response.

I still have a little confusion on my second question.Do you mean that I can change the frequency from 1.57542G into 1.602G and select a GLONASS binary file in order to generate GLONASS signal on niGPS Streaming from File (5671).vi.Please kindly see from pic1 to pic2 and give me some point whether it is right or not.

When I ran the niGPS Streaming From File.vi to transmit GPS signal thru 5671,I got such error,see attachment pic3.

On the other hand,we have a set of 5673(bandwith of which is up to 100 MHz) in our lab and I want to use it to transmit both GPS and GLONASS signal at the same time.So I am wondering whether it is possible to do so depending on your preivous sayings," bandwidth of PXI-5671 is 20MHz, whereas you need around 30MHz bandwidth for both of them to lie within a band".If possible,could you give me some clue about how to do it.

Any point above unclear,please point out,I will explain it further.

Thanks in advance.

Leung

[Hardik.Asawa]

Hi Leung,

Why do you want to generate both GPS & GLONASS at same frequency? The protocols are already defined & frequencies are fixed. Even if in software you change the frequency, receivers won't be able to comprehend the signal correctly. 

Regarding the error you are getting, the error code which you are getting is most likely occuring because of 5441 which doesn't support streaming. If you have access to PXIe-5673 then you may want to try running the same example using it, most likely you won't get this error as PXIe-5673 support streaming.

Now answering to your third question regarding generation of both GPS & GLONASS simultaneously, theoritically you can do it using PXIe-5673. I don't think toolkit directly support generation of both the signal simultaneously. But using proper signal processing you can implement this. You can add the IQ data corresponding to GPS and GLONASS after doing appropriate resampling and frequency shifting, & then using niRFSG drivers you can generate both the signal together, but this process is easier said then done. 

Regards,

Hardik Asawa

[KittF]

stLeung

There are 4 modes that are supported.

1. GPS only
2. GLONASSS only
3. GPS+GLONASS using 2 generators
4. GPS+GLONASS using 1 generator.

http://zone.ni.com/reference/en-XX/help/372446D-01/nigpshelp/gnss_simulation_modes/

In order for 4 to work, both signals must fall in the same instantaneous bandwide of the generator, which is not the case for the 5671 but is the case for the 5673.

I think Hardik misunderstood you.  You want to generate GPS+GLONASS at the same time not the same frequency.  

Do you understand what Hardik means about streaming?  This is the ability to have the CPU continuously create and send IQ data down to the generator on-the-fly, why the generator takes the data and generates the corresponding RF.  The 5671 is an early RF generator and does not have this ability.  Instead you have to save to file and then generate from file.  The 5673 does have streaming.  We generally recommend 5672 and 5673 for GPS (note the 5673 is the widest bandwide for GLONASS+GPS).

So, if you try and use examples that are not tuned for 5671 (i.e. they have 5671 in their name), you may likely get errors.  

[Hardik.Asawa]

Thanks Nemo.

I guess I overlooked certain things. Thanks for correcting me. 

[stLeung]

Cool.

I do appreciate your help.What Nemo pointed out is what I have been looking for.At first,I study the case that using 5671 to generate GPS or GLONASS signal separately and work so well,then I would like to generate both signal at the same time using ONLY one 5671,but I failed to accomplish this case.Thank you Nemo again for your answer.

I am a newbie to GNSS area,so maybe this is the reason I mislead Hardik.I am so sorry for that.

I found the example generates GPS+GLONASS constellation using a single RFSG by writing to a TDMS file and streaming from it. A new question came to my mind.Is it possible to generates GPS+GLONASS using a single 5673 by direct steaming(No any kind of file needed)?

Thanks for your patience

Leung

[KittF]

I am pretty sure the answer is yes, but I haven't done that yet. The streaming is supported as this is really just the same as streaming GPS only. The difference is thst the CPU must do more calculations on the fly to create and merge both GPS and GLONASS satellite data concurrently. I'm not 100 percent certain your CPU can keep up.

By writing to disk first, your CPU can take its time to create data. Then later it can play from disk with no computation needed during RF generation.

[LV_COder]

Hi,

Can you please help me to find the out the example "niGNSS Streaming from TDMS file.vi" use for GPS+GLONASS Single RFSG mode. 

I have installed the toolkit but did not able to find the example mentioned.

Thanks