FreeCalypso > hg > freecalypso-reveng
comparison pirelli/rssi @ 279:a7707c174510
pirelli/{rssi,txcal}: results of the Pirelli to CMU200 experiment
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Sat, 16 Feb 2019 18:30:11 +0000 |
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| 278:42575bc59702 | 279:a7707c174510 |
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| 1 I have been wondering for a long time now how the RSSI bars displayed in end | |
| 2 user phone UIs correspond to actual Rx signal levels; Pirelli's RSSI icon on | |
| 3 the left side of the home screen can go up to 6 bars, but it was not clear at | |
| 4 all what these bars actually correspond to. I just did an experiment to shed | |
| 5 some light on this issue: I took a decased Pirelli motherboard and connected it | |
| 6 to our CMU200 instrument via the RF test port which Pirelli's mobo has like | |
| 7 most phones. Pirelli's RF test port is of the Murata SWD/SWF type, same as | |
| 8 Openmoko GTA0x and Motorola C139, and we have a test probe for these ports with | |
| 9 precisely known insertion loss numbers, thus combined with the properly | |
| 10 calibrated CMU200 instrument and our "main" SMA cable for which we also have | |
| 11 precisely known insertion loss numbers (it is the setup we use to calibrate our | |
| 12 FCDEV3B modem boards), it is a very trustworthy setup. I varied the downlink | |
| 13 signal level put out by the CMU200 and observed the bars displayed by Pirelli's | |
| 14 fw on the home screen, and this is what I got: | |
| 15 | |
| 16 transition from 5 to 6 bars at -75 dBm | |
| 17 transition from 6 to 5 bars at -80 dBm | |
| 18 | |
| 19 transition from 4 to 5 bars at -85 dBm | |
| 20 transition from 5 to 4 bars at -90 dBm | |
| 21 | |
| 22 transition from 3 to 4 bars at -92 dBm | |
| 23 transition from 4 to 3 bars at -97 dBm | |
| 24 | |
| 25 transition from 2 to 3 bars at -97 dBm | |
| 26 transition from 3 to 2 bars at -102 dBm | |
| 27 | |
| 28 transition from 1 to 2 bars at -104 dBm | |
| 29 transition from 2 to 1 bars at -105 dBm | |
| 30 | |
| 31 at -110 dBm it is marginal: sometimes 1 bar, sometimes 0 bars, sometimes no srvc | |
| 32 | |
| 33 Looking at TI's reference firmware which Pirelli's fw must be based on, the Rx | |
| 34 signal strength is passed from L1 to the G23M PS in the form of RxLev numbers | |
| 35 that go into GSM 05.08 measurement reports (the standard [0,63] range with 0 | |
| 36 corresponding to -110 dBm), ALR does no transformation, and RR passes these | |
| 37 RxLev numbers to the Rx driver in the Condat drivers layer, which then converts | |
| 38 them to the "bars" numbers for the UI. Pirelli's fw most likely retains this | |
| 39 architecture, and their modified version of the Rx driver appears to have the | |
| 40 following thresholds or somewhere around there: | |
| 41 | |
| 42 RxLev >= 35: 6 bars | |
| 43 RxLev >= 25: 5 bars | |
| 44 RxLev >= 15: 4 bars | |
| 45 RxLev >= 10: 3 bars | |
| 46 RxLev >= 5 or maybe 6: 2 bars | |
| 47 RxLev abysmally low: 1 bar | |
| 48 | |
| 49 The 5 dB hysteresis seen in my CMU200 experiment is probably caused by the | |
| 50 RSSI_MIN_DIFFERENCE logic seen in rr_csf.c in our TCS3-sourced version. |