[srslte-users] RSRP/SINR issues with pdsch_ue

Ismael Gomez ismael.gomez at softwareradiosystems.com
Wed May 10 11:55:05 UTC 2017


Hi Sina,

On Tue, 9 May 2017 at 21:38 Sina Khanifar <sina at rsrf.com> wrote:

> Similar to the recent thread around issues with the cell_measurement
> thread, I'm seeing problems with the pdsch_ue example script. I've tried
> changing the RSRP and SINR calculations to make them better match real UE
> measurements. For example, I am currently using:
>
>
rsrp = 12*log10(rsrp/rf_gain_offset) where rf_gain_offset is set via an arg
> to 2e9
> sinr = 20*log10(sinr/noise/5)
>
> I've experimented with various values here, but continue to have issues.
> In particular:
>
> * The RSRP gain offset appears to vary both with frequency and the carrier
> signal's bandwidth. srs-lte shows higher rsrp at higher frequencies, and
> higher rsrp at higher bandwidths.
>

That's because the frequency response of the RF frontend is not flat
throughout all the frequencies. That's why we use the RSSI on-chip sensor
to compute the rf_gain_offset automatically. Have you tried that?


> * The SINR in the default code is never negative, whereas it is often
> negative as measured by test UEs. It also generally doesn't match up to the
> UE measurements, hence my 20*log10(sinr/noise/5) adjustment. This
> alternative equation is still not very accurate, but at least generates
> some negative values.
>

The way SINR is computed is vendor-specific so it's difficult to compare
across devices. You can try looking at RSRQ and compare that value. RSRQ is
a standarized equivalent metric of the SINR.


>
> Any thoughts on what might be causing these two issues?
>
> Thanks.
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