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Synchronization of multiple USRPs and Stability of transmit power (NI-USRP-2920)

Hi. I have some questions.

 

1. I configured 1 - 2 - 1 relay link (1 source - 2 relay - 1 destination). Each USRP has its own host PC (1 USRP is connected 1 PC).

I want to set my destination to receive packets from two relays synchronously (by symbol level, if possible).

I can use external 10MHz reference signal and external 1 PPS signal. Then, can I make my destination USRP to operate as my intention ?

 

I think it can be done by starting 2 USRPs at the perfectly same time. Is there any way to turn on 2 USRPs connected on 2 independent hosts synchronously ?

 

2. I want to know the stability of transmit power of 2920. Actually, I estimated EbNo of transmitted signal by transmitting known QPSK symbols and
calculating this formula 
EbNo=10*log10((mean(abs(samples).^2)/(mean(abs(samples-mean(samples)).^2))-1)/2)      // { P(signal+noise) / P(noise) } - 1

P(signal+noise) can be estimated by mean square of received samples and P(noise) can be estimated by calculate the variance of received samples.

(Before calculate, I rotated symbols to locate same constellation point since I transmitted known symbols. I checked this method by MATLAB and it operates well)

 

However, when using USRP, the estimated value varies upto 8~9dB. I changed the number of samples from a few hundreds to hundreds of thousand, it also fluctuates.

Besides, BER of system is well fitted by instantaneous value of EbNo. So, I concluded that the transmission power changes.

However, 8~9dB is to large scale to power variation. I would like to know the stability of transmit power of NI-USRP-2920.

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It would be helpful if someone of the staff could answer these questions.

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Hi DIris,

 

I'm doing a project on bidirectional relay (1 tx-1relay-1 rx)..I'm newbie in labview and USRP. Really need your help to guide and share your project with me. Right now i'm just doing the exercise that is provided by NI USRP.

 

TQ

 

Regards,

 

Mardiah

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Hi...

 

Right now i'm doing relay using 1-1-1(1transmitter, 1 relay and 1 receiver). I try to use the existing VI exercise provided in this forum (6x6 mimo USRP) to do this project. The idea is by using one transmitter (usrp_tx_mimo), one relay (consist of one receiver(usrp_rx_mimo) connected to one transmitter (usrp_tx_mimo)) and finally one receiver (usrp_rx_mimo). 

The problem is at the relay part.  FYI, i have put the QAM DEMOD block diagram at the receiver so that the output (bit) can be the input the to the transmitter.  But, how and which part to connect between the output (bit) at the receiver and transmitter. Are there any block diagram to insert or delete?

 

Hope someone can help me to solve this problem asap. Your feedback is really appreciate.

 

Thank you.

 

 

Regards,

Mardiah

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