[srslte-users] TX Power and Signal Power received at UE

[Rúben Queirós]

Good afternoon,

After some testing done with VNA's to figure it out if the problem was 
the antennas or something else related to the configuration, i realised 
both the antennas and the SDR frontend had some issues that could be 
fixed.

First of all, the antenna wasn't completely adapted to the frequencies 
used. That was fixed with the replacement of the antennas that were 
tested and showed a return loss of less than -10dB.

However, the SDR had also an issue. I was expecting that the SDRs would 
transmit atleast at 0dBm, and when i measured the TX Power that came out 
from the SDR when using srsENB i read on the VNA an average number of 
-40dBm which is quite lower than what it was advertised.

Is there any configuration in enb.conf or any similar file that could be 
limiting the TX gain or TX power that is coming out of the SDR? Im using 
the max gain possible.

Sorry for the spam, but i didn't get an answer last time!
Rúben Queirós

Em 26.05.2020 16:55, Rúben Queirós escreveu:
> Good Afternoon,
> 
> First of all thank you for developing srsLTE. I'm currently
> researching to my MSc degree and i'm using srsLTE to evaluate the
> performance of different SDR hardwares namely, BladeRFx40, BladeRF
> micro 2.0 and USRP B210 The antennas used are TriBand from Nuand. For
> the UE i'm using a commercial Samsung J7 that connects sucessfully to
> the srseNB and srsEPC.
> 
> I've been using the software for a couple months already and i'm
> running out of options so i'm writing you this e-mail hoping that you
> can help me with my problem.
> 
> Im transmitting in Band 3, 7 and 20, Central frequencies, switching
> between NRBs ( from 15 up to 50 sucessfully ) and according to some
> LTE Throughput Calculators, the results are way lower than the
> expected at Low range ( 1 Meter between the eNB station and UE ).
> After logging the Signal Power Received at the UE, i realised the
> signal power is way weaker than it should be.
> 
> Assuming the information in
> https://www.pasternack.com/t-calculator-friis.aspx is correct, and
> considering no antenna gains in RX or TX, i should be expecting
> 
> 
> Tx Power   1m ( range)	  2600 MHz	 1800 MHz	 800 MHz
> 8dBm	   Blade Micro	-32,75 dBm	-29,55 dBm	-22,51 dBm
> 6dBm	   Blade x40	-34,75 dBm	-31,55 dBm	-24,51 dBm
> 10dBm	   USRP B210	-30,75 dBm	-27,55 dBm	-20,51 dBm
> 
> However the values im getting are between -70 to -95 dBm. This tests
> were done with LOS between the eNB and the UE and i've noticed the
> software always sets the TX Gain of the RF hardware to the max, yet it
> is still a weak signal.
> I will attach an example of an enb.conf used in one of this tests. If
> it is not enough to detect the problem, i also attach the other logs i
> capture for the same test performed.
> 
> Thank you in advance!
> Ruben Queirós