Re: [Discuss-gnuradio] Enable/Disable TX ports in B210 in 2x2 setup

Hi Marcus,

I am still trying to implement the idea of multiplying with vector source to toggle 0/1 before outputting to the USRP. This thing does work, but some error occurs in some packets:

gr::log :INFO: packet_headerparser_b0 - Detected an invalid packet at item 4416

gr::log :INFO: header_payload_demux0 - Parser returned #f

I am using the OFDM_tx /rx example blocks (just replacing with USRPs). The packet length is 960 bytes just before sending to the USRP. Therefore I am multiplying this signal with a vector source of (960 1’s and 960 0’s) so that it exactly takes this amount of time to pass/drop the packet on each USRP i/p port. Though I can receive packet at receiver but in almost 50% of the packets has the above mentioned error.

I am also trying to test the same scenario without using USRPs (Virtual sink/source). And here I found something interesting. The transmission & reception of packets works perfectly up to 20 sec but after that it starts throwing error for 4 sec. This happens every 30 sec. (Here I have used a sample rate of 64K, and varying this varies the time of error).

I am really having tough time to figure this out. If you could kindly help me on this:

Is the above error caused for some time synchronization issue?
Am I multiplying with correct vector (960 1s and 960 0’s)? If I multiple with only 1 & 0 it throws the same error ( what I think packet is not received correctly in this manner).
In your previous reply you said “I'd probably have a couple of vector sources of alternating 1s and 0s, interpolate them up to the desired sample rate X the switching interval, and multiply the stream going into the USRP by that stream of 1s and 0s”. What did you mean by interpolating up to desired sample rate?

Thanks,

Ayaz

Hi Marcus/Muller,

I was trying a simple flow graph to implement what you said earlier :

“
If it were *my* problem, I'd probably have a couple of vector sources of alternating 1s and 0s, interpolate them up to the desired sample rate
X the switching interval, and multiply the stream going into the USRP by that stream of 1s and 0s.

“

To make things simpler, I am trying:

Vector source (0,1) multiplying with a sine wave. As an out put I want 1 period of sine wave (say 1kHz frequency) and the next period to be zero. I believe I need to set the sample rate and match this period with the vector source.

Can you just help be in deducing this please. Having hard time to sort this out ☹

Thanks

Ayaz

From: Müller, Marcus (CEL)
Sent: Wednesday, July 18, 2018 6:34 AM
To: address@hidden; address@hidden; address@hidden
Subject: Re: [Discuss-gnuradio] Enable/Disable TX ports in B210 in 2x2 setup

The Selector block comes from the "deprecated" category, and that for good reason: Don't use it, it causes a huge teardown/setup effort behind the scenes, and not all is guaranteed to work.

Follow Marcus' advice with the 0/1 multiplication and offset tuning.

Best regards,

the other Marcus

On Tue, 2018-07-17 at 23:06 +0000, Ayaz Mahmud wrote:

Hey Marcus,

I think the Selector block works well with my setup.

But I need a solution with which I can do a dynamic change in the input/output index. Can you let me know how is this possible

Ayaz

From: Ayaz Mahmud
Sent: Tuesday, July 17, 2018 4:39 PM
To: Marcus D. Leech; "Müller, Marcus (CEL)"; address@hidden
Subject: Re: [Discuss-gnuradio] Enable/Disable TX ports in B210 in 2x2 setup

Hi Marcus,

The situation still is same.

By browsing the archive I found some switching of blocks with SELECTOR. Is there any example that will be helpful on how this block actually functions ?

Thanks

Ayaz

From: Marcus D. Leech
Sent: Monday, July 16, 2018 1:26 PM
To: Ayaz Mahmud; "Müller, Marcus (CEL)"; address@hidden
Subject: Re: [Discuss-gnuradio] Enable/Disable TX ports in B210 in 2x2 setup

On 07/16/2018 02:05 PM, Ayaz Mahmud wrote:

Hi Marcus,

The issue is even I put the vector source toggling with 1 and 0s it transmit a signal. So I need something that will not transmit at all and switch between these 2 radio chains.

Thanks,

Ayaz

You're probably seeing the residual LO leakage during periods of "no transmit".

You can try using offset-tuning to move the leakage out-of-band:

Use:

uhd.tune_request(frequency,offset)

In the UHD sink for the "frequency" field.

From: Marcus D. Leech
Sent: Saturday, July 14, 2018 8:15 PM
To: Ayaz Mahmud; "Müller, Marcus (CEL)"; address@hidden
Subject: Re: [Discuss-gnuradio] Enable/Disable TX ports in B210 in 2x2 setup

On 07/14/2018 06:40 PM, Ayaz Mahmud wrote:

Hi Muller / Marcus,

I got the testing right now, but unfortunately it doesn’t work while I put it in my original file.

Here is the attached .grc where I have used vector source as input and multiply a period with 1 and then with zeros on one radio channel and opposite on the other.

Can you please have a look, and check if I am doing anything wrong ?

Ayaz

You're asking us to debug a very complex signal flow.

Why don't you try something a *lot* simpler to get the TX-flow-switching-logic correct first, and then work up from there.

From:	Ayaz Mahmud
Subject:	Re: [Discuss-gnuradio] Enable/Disable TX ports in B210 in 2x2 setup
Date:	Fri, 10 Aug 2018 03:31:39 +0000