How to calculate SNR and BER using USRP 2920 with LFTX and LFRX daugher boards.

[josephkirmani]

I have few questions regarding SNR and BER measurement:

I am using two USRP 2920 with daughter boards LFTX and LFRX. One is completely Tx and anothe one is completely Rx. I have following few questions:

Q1: How to control/change Energy per bit (Eb) in LabView? Since for calculating BER you have to increase SNR, and for increasing SNR you have to increase Eb. So can anybody guide me how to increase Eb in LabView?

Q2: Can any body tell me about the noise floor of the above mentioned daughter boards?

Q3: How to set the transmit power of the USRP in LabView? What is the maximum power the above mentioned daughter boards can provide and How should I adjust the "Gain" parameter to transmit the signal with the maximun power?

Thanks

JK 

[josephkirmani]

I have found the answer of the Q3 which is given below. Can some body confirm me that it is right?

The gain of the LFTX board is 0. What ever the value of the Tx gain I am tryng to set the coerced gain always remain 0. On the otherhand LFRX has a gain range from 0 TO 6.5dB. If i set gain between 0 to 6.5dB the coerced gain also shows the same value. But if I increase Rx gain higher than 6.5dB the coerced gain remains at 6.5dB.

So conclusion the gain which is supported by LFTX is 0 dB and gain for LFRX is 0 to 6.5dB.

It is my finding but can any body confim that it is right for LFTX and LFRX daughter boards.

Thanks

JK 

[James-B]

Hi JK,

The energy per bit calculation, as I understand it, is the ratio of the signal power to the bit rate. This means that to increase it, you have to either increase the overall power you are transmitting or decrease the user bit rate. In LabVIEW, you would do this by increasing the gain or by decreasing the IQ rate.

I'm not sure of the noise floor on those boards, but I did have a question. The USRP 2920 is sold in a particular configuration. Did you take it apart and put in the LFTX and LFRX boards? Or is it an Ettus board with these daughterboards attached?

[josephkirmani]

Thans for your reply. 

Also can you confirm me the answer of Q3.

Also you are talking about gain and IQ rate. Do I need to change these two on Tx side or Rx side. Since I tried increasing the gain of Tx but its coerced gain always remain at 0 dB. But on Rx side I am abLe to icncrease the gain between 0 to 6.5 dB.

I bought USRP 2920 but since these boards work on 50MHz to 2.2GHz. But I need daughter board from 0 to few MHz so I found that LFTX and LFRX are compatible with USRP 2920. So I bought them separately from my local NI distributor.

Thanks 

JK

[James-B]

I was talking about on the TX side because as I understand it, you want to increase the energy of transmitted bits.

As for the specific stats of the daughterboards, it might be best to either contact Ettus directly or hope that one of them jumps onto this forum. I've really only worked on the NI side of things so I can help out if you have further LabVIEW and NI-USRP questions.

[josephkirmani]

As far as gain is concerned as you told me that I have to increase it on Tx side. But when I tried to increase it the coerced gain always remains at 0. So what does thos means. Does t means that LFTX daughter board does not support gain higher than 0?

Also currently I am using Carrier freq 500k and I/Q rate 200k. Also when I try to reduce I/Q rate beyond 200k the coerced gain does not decrease beyond 195k. So what does this means. Why it is not decreasing?

[sanareh]

Can i please know about the noise floor for the lftx and lfrx daughterboard ?