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Re: [Openbts-discuss] How to set RxGain in GPRS branch?
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From: oxccoxcc o. <oxc...@ya...> - 2013-06-26 08:43:06
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As i understand, L1 layer is the same in GSM and GPRS. When i use openbts-master branch, bursts quality is some better because of MS power control messages is implemented. About "wavy process": signal quality can be very different with same bursts RSSI. Downlink signal quality looks good. I checked it with osmocom-bb sniffer and airpobe. Uhfortunatelly airprobe didn`t support uplink sniffing and i didn`t have a phone with filter reworked to try it with osmocom-bb uplink sniffer. Receive gain adjustment is implemented in grps branch, as is see. But it is not enough to downgrade uplink signal to 80-90 dB. Yes, the problem can be related to ADC or amplifier, but i didn`t check it and don`t know how it can be done, yet. I tried to connect USRP with own DC power supply and change usb cable, nothing good. Now i try to change gr-uhd and USRP image version. May be it needs to connect usrp with sinus signal generator and check the output PCM. 25.06.2013, 18:46, "Gullik Webjörn" <gul...@co...>: > Sorry if my answer was a little hasty. Given my experience, the gain in > the link is essential to > good operation, and getting within the linear range of the ADC's. > Possibly the same is true > for the downlink, i.e. not overloading the phone. > > When you first wrote this I had a look at the various posts, and I could > see as Alexander says, that > power control is not implemented (yet). > > This could explain the "wavy process", i.e. alternating between loop > regulated power for some signalling, > and then no power control when source is GPRS. > > Anyway, if you are running wireshark, and getting 60-70% throught, it > should be possible to determine > if it is the pings ( to phone) or replies (to BTS) that are lost, to > clarify if it is up or down link related. > > Do you mean there is something within GPRS that prevents integration > with voice/SMS, or do you > mean it "may not be so easy to do"? > > Should not the layer 1, be independent of what we are running un top, > (excluding control plane just > to ensure L1 reliability such as power control algo) ? > > From my view, and I am a newbe at this, it seems like there should be a > common power control > since operating conditions for a phone would be same for > voice/SMS/Packet/IP. > > If I understand correctly the L1 is exactly the same, it is only with > EDGE it changes (modulation etc). > Or, are there other considerationes? > > Another Q: Are there no gain adjustments in the GPRS code? (since it is > not integrated) > > Gullik > On 06/25/2013 02:50 PM, oxccoxcc oxccoxcc wrote: > >> I didn`t find anything helpful in other grps or osmocom-pcu threads. >> As i inderstand, Alexander says about MS power control loop setting, that transmits in GPRS on other channel than in GSM. It can`t be unioned with GSM MS power control algorithm. >> RxGain using is identical in both master and gprs branches, as i see. But in GPRS the phone is using full transmit power. >> I tried to set small wifi antenna instead of vert900, set RxGain to 1, and go away from usrp. After that RSSI of bursts became -70 - -80. May be bursts quality became some better, but still not normal. >> For example, when i make ping, 60-70% of packets are lost. And most of tcp sessions are broken, as i see in wireshark. >> >> 25.06.2013, 16:10, "Gullik Webjörn" <gul...@co...>: >>> Hah, I'm getting better in "guessing", in fact a lot of this >>> is documented in the pcu / gprs threads.... >>> >>> It seems to me that the power algorithm maybe should be >>> located somewhere where ALL modes of communication >>> converge, i.e. before multiplexer / demultiplexing. >>> >>> Gullik >>> >>> On 06/25/2013 08:42 AM, Alexander Chemeris wrote: >>>> GPRS has it's own power control, independent of the CS (circuit >>>> switched aka voice/sms) service. Ivan could comment more, but IIRC >>>> power control is not implemented in the current code yet. So you >>>> mobile could easily transmit with too much or too small power. >>>> >>>> Patches to implement power control control are welcome. :) >>>> >>>> On Tue, Jun 25, 2013 at 1:30 AM, Gullik Webjörn >>>> <gul...@co...> wrote: >>>>> Hmm, can you see the MS tx power in chans command? >>>>> >>>>> I had to experiment quite some before i got the phones to adjust down, >>>>> but at >>>>> that time I was more ignorant :-) >>>>> >>>>> What happens if you move the phones away? When I was trying to >>>>> understand my problems >>>>> I would call the "echo service" from different places. For your case >>>>> that would be a "packet" >>>>> connection? Where in the stack does GPRS interface itself? >>>>> >>>>> Gullik >>>>> On 06/24/2013 05:10 PM, oxccoxcc oxccoxcc wrote: >>>>>> I tried to set GSM.MS.Power.Max to 1 and GSM.MS.Power.Min to 1. But RSSI value is still high (about -25 for WBX, -15 for SBX). >>>>>> Tried to change WBX daughterboard to SBX. Receive burst quality is also bad and not all of them can be resolved. It looks like a wavy process. >>>>>> At some time bursts have an ideal quality. At another time they are broken. Periodically they are broken partially, for eaxample: (10100...11100110010100--------------...--) >>>>>> I also tried to change ARFCN, but it didn`t help. Before i checked this arfcn with uhd_fft. >>>>>> One thing, that looks some strange is a timing value=2.00391. This value is constantly at all sessions for PDTCH channel and 2 symbols offset is looks too high for phone, that places near USRP. >>>>>> >>>>>> 24.06.2013, 17:00, "Gullik Webjörn" <gul...@co...>: >>>>>>> Maybe a moot point, but I think it is not a B100 problem if >>>>>>> exactness is the issue, but rather a WBX issue. >>>>>>> >>>>>>> The same thing should happen on another USRP equipped with WBX, >>>>>>> if RxGain is left at +47 dB. >>>>>>> >>>>>>> Regards, >>>>>>> >>>>>>> Gullik >>>>>>> >>>>>>> On 06/24/2013 12:59 PM, oxccoxcc oxccoxcc wrote: >>>>>>>> According to USRP B100 RxGain problem, i set GSM.Radio.RxGain to 7dB. After that not RACH bursts have an RSSI value about -80 - -87 and normal quality. >>>>>>>> But when i starting GPRS and connect to web page, receive bursts RSSI grow to -10 - -15. And, because of that, receive bursts have a bad quality and most of them can`t be resolved. >>>>>>>> >>>>>>>> ------------------------------------------------------------------------------ >>>>>>>> This SF.net email is sponsored by Windows: >>>>>>>> >>>>>>>> Build for Windows Store. >>>>>>>> >>>>>>>> http://p.sf.net/sfu/windows-dev2dev >>>>>>>> _______________________________________________ >>>>>>>> Openbts-discuss mailing list >>>>>>>> Ope...@li... >>>>>>>> https://lists.sourceforge.net/lists/listinfo/openbts-discuss >>>>> ------------------------------------------------------------------------------ >>>>> This SF.net email is sponsored by Windows: >>>>> >>>>> Build for Windows Store. >>>>> >>>>> http://p.sf.net/sfu/windows-dev2dev >>>>> _______________________________________________ >>>>> Openbts-discuss mailing list >>>>> Ope...@li... >>>>> https://lists.sourceforge.net/lists/listinfo/openbts-discuss |
