Hi Harald,
Just a fun fact: afaik current commercial multi-purpose (2G/3G/4G) base stations use generic SDRs to accomplish support for all technologies in a compact package. Of course those SDRs are in a completely different league in terms of accuracy, calibration and price :).
Cheers, Domi
2019. jan. 13. dátummal, 10:30 időpontban Harald Welte laforge@gnumonks.org írta:
Hi Gullik,
On Sat, Jan 12, 2019 at 08:22:05PM +0100, Gullik Webjorn wrote: Below is a measurement on my "most distant" BTS, BTS 1. From what I see, downlink is 35 dB
What do you mean by "downlink is 35dB"?
below uplink, which of course is natural when the MS can produce 30 dBm, and the BTS which
in this case uses a bareback Limesdr min, can only produce 10 dBm.
If you are using a general-purpose SDR hardware you cannot expect that any of the signal levels written anywhere actually meany anything at all. There is no absolute levels reported by SDR hardware anywhere, and there is no calibration of either transmit nor receiver. This means:
- there's no general calibration curve for the chip/board
- there's no per-unit individual calibration curve for the unit you have
This is *very* different from a real GSM base station. Without designing a calibration procedure for the above, as well as some mechanism to apply it in production, I don't think one can expect any of the readings to state anything realistic, nor expect any power control loops to operate.
Please don't get me wrong, general-purpose SDRs such as USRPs or LimeSDR are great tools for experiments in the lab. But that's what they are - at least for the time being. There is a *big* difference between a real-world base station and a GP-SDR board.
the bsc parameter ms max power is set to 15 for both bts 0 and bts 1. However, it seems MS output power is *much* stronger.
The 16dBm is probably the closest one can get to the 15 dBm you requested:
L1 MS Power: 16 dBm, Timing Advance: 0How do you establish this fact? Did you attach a RF power meter to the MS output and masure the output power?
--
- Harald Welte laforge@gnumonks.org http://laforge.gnumonks.org/
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