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 <[email protected]> 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: 0 > > How do you establish this fact? Did you attach a RF power meter to the > MS output and masure the output power? > > -- > - Harald Welte <[email protected]> http://laforge.gnumonks.org/ > ============================================================================ > "Privacy in residential applications is a desirable marketing option." > (ETSI EN 300 175-7 Ch. A6)
