SISO TDD OFDM on NI USRP-RIO example in LabVIEW Comms does not work with two devices

[hangcao]

Hi,

Currently, I am doing the SISO OFDM TDD Example with two USRP-RIO 2953R. The example reference is the link:https://decibel.ni.com/content/docs/DOC-40747

First , I can do streaming within one USRP-RIO with loop back selection in the example, and the video streaming works fine.

But when it comes to two USRP-RIO streaming, one is base station and the other is UE, there is no right constellation result. 

I was wondering whether I fail to configure the parameters in the front panel, can anyone help me review it ? Thanks a lot.

Here is the hardware configuration.

Here is the controls of Base station:

Here is the configuration of UE

I am also confused about some other configuration in the link:https://decibel.ni.com/content/docs/DOC-40747

There are several hardware configration in the link, but I can only get the demo work with the first configuration as shown below, other topology didn't work at all.

Thanks for any advice and comments.

[Wired_]

Hi!

Neither did it work with me!

I was trying instead to send some known sequences which I added at phy end in the base station while working with two devices.

Issues:-

1. No PSS locking. Consequence:- Mobile Station never starts to work.

As a result we just see BS receiving it's own signal as self interference!

And MS receiving the BS signal after few attenutation and delay.

Even if PSS gets locked I dont see how to avoid BS from receiving self transmitted data. Since its a TDD system at times it can happpen that self-ntefernce and data from MS gets added, if not perfect time sync at both sides.

I tried using sending forced data from BS overwriting PSS lock. BS self-data was dominating in receiving chain!

To make it work we need to:-

1. Find if there are issue with PSS.

2. Find ways to cancel self data stream( one way I did was to read data from DMA FIFO only when I am not transmitting, but even then may be due to some delay in chain, it received parts of data.)

Of all the most beautiful solution which I think would be good would be using RF Switch available with RF0 ports. Hence 2nd point will not be an issue. It would be faster and efficient.

Is anyone familiar with methods to use switch to route antenna between receiver and transmitter chain?

Regards

[Marwanjk]

Hi hangcao,
Finally you were able to making work with two devices? I was trying but don't find a way to make it work.
regards

[hangcao]

Marwanjk, It is a pity that I have not get it worked with two devices. I also found it does not work with two RF channels in one USRP-RIO. I am trying to figure it out.

[Marwanjk]

hangcao, You used an external generator for the ref 10MHz clock? or a internal?

[hangcao]

Internal clk. At first, I think this might be the reason of the problem,  I connected the REF CLK out to another REF CLK in with cable, it still did not work.

[Marwanjk]

I used the same process with the same results. I'm going to try change the ref clock in the fpga program.

[tcap]

Hello All,

I just wanted to let you know that we are currently investigating this isse.

Regards,

[dfaur]

Hello Thomas,

We were also trying to run the demo using two NI USRP-2952R platforms and we encountered the same problems as the ones described previously by the other users. Is there any progress regarding your investigation?

Also, I noticed the FPGA is compiled such that the OFDM signal is sent/received  only on channel RF0 of the DUC/DDC. I recompiled the transceiver_top.gvi after changing the FIFO reference Tx Stream 1 into tx_samples_00. After this I ran the host VI but I got a new error. I assume other modifications have to be made but at present I do not know what is required exactly.

Has this project ever functioned in no-loopback mode for anyone? I also noticed that it has been taken down from the decibel.ni.com website, or I can't find it anymore.

Best regards,

Alexandru

[muffin.vi]

dfaur,

We did some investigation into the example, and unfortunately, it was never as complete as it was supposed to be. The non-loopback functionality did not work because it was only partially implemented. The example was pulled from the website because it is now being shipped with LV Communications. The next release of LV Communications will have an updated example that does not claim multi-user support.