Bug #3814
openMS Power Control Problem with Osmo-BSC and nanoBTS
0%
Description
Greetings,
I seem to be having a problem with MS power control on an OsmoBSC/nanoBTS setup using the following software versions:
OsmoBSC: 1.4.0 (binary package: "Latest")
OsmoMSC: 1.3.1 (binary package: "Latest")
OsmoHLR: 1.0.0 (binary package: "Latest")
OsmoMGW: 1.5.0 (binary package: "Latest")
OsmoSTP: 1.0.0 (binary package: "Latest")
OsmoSIPConnector: 1.2.0.2-e911-dirty (compiled from source to add workaround for OsmoMSC issue #3650 / OsmoSIPConnector issue #3724)
This is a single-BTS system. The BTS in question is a nanoBTS 165BU.
This is a small test system with the BTS and all MSes contained within the same isolated room. In addition to other interference-avoidance measures, I want to configure the system to limit the MS transmit power to the lowest possible value.
The Osmo-BSC documentation suggests that this can be achieved by limiting the MS transmit power to 0 dBm with the following command (in BTS configuration mode on the BSC) :
ms max power 0
When I issue this command, start a test call, then issue the "show lchan" command on the OsmoBSC vty, I get the following output:
BTS 0, TRX 0, Timeslot 1, Lchan 0: Type TCH_F
Connection: 1, State: ESTABLISHED
BS Power: 3 dBm, MS Power: 0 dBm
Channel Mode / Codec: SPEECH_V1
No Subscriber
Bound IP: 10.x.x.x Port 4004 RTP_TYPE2=0 CONN_ID=2
Conn. IP: 10.x.x.x Port 4258 RTP_TYPE=3 SPEECH_MODE=0x00
Measurement Report:
Flags:
MS Timing Offset: 2
L1 MS Power: 33 dBm, Timing Advance: 0
RXL-FULL-dl: -48 dBm, RXL-SUB-dl: -48 dBm RXQ-FULL-dl: 0, RXQ-SUB-dl: 0
RXL-FULL-ul: -54 dBm, RXL-SUB-ul: -54 dBm RXQ-FULL-ul: 0, RXQ-SUB-ul: 0
The following line looks normal; it seems to represent the configuration I gave OsmoBSC:
BS Power: 3 dBm, MS Power: 0 dBm
On the other hand, the following line confuses me. It seems to be the very opposite of the MS transmit power limit I requested (and also, I believe, is more power than the MS, a Nokia 5190, is capable of transmitting) :
L1 MS Power: 33 dBm, Timing Advance: 0
I have tried a number of variations of the "ms max power X" command, which have given the following results:
ms max power 1
BS Power: 3 dBm, MS Power: 2 dBm
L1 MS Power: 4294967274 dBm, Timing Advance: 8
ms max power 2
BS Power: 3 dBm, MS Power: 2 dBm
L1 MS Power: 4294967274 dBm, Timing Advance: 8
ms max power 3
BS Power: 3 dBm, MS Power: 4 dBm
L1 MS Power: 4294967274 dBm, Timing Advance: 8
ms max power 4
BS Power: 3 dBm, MS Power: 4 dBm
L1 MS Power: 4294967274 dBm, Timing Advance: 8
ms max power 10
BS Power: 3 dBm, MS Power: 10 dBm
L1 MS Power: 4294967274 dBm, Timing Advance: 8
ms max power 15
BS Power: 3 dBm, MS Power: 16 dBm
L1 MS Power: 2 dBm, Timing Advance: 8
ms max power 20
BS Power: 3 dBm, MS Power: 20 dBm
L1 MS Power: 10 dBm, Timing Advance: 8
I am puzzled by these results.
If I am interpreting this correctly, the "BS Power / MS Power" line represents the values that are being commanded by the BSC, and the "Measurement Report: L1 MS Power" line is the transmit power being reported to the BTS/BSC from the MS.
If this is the case, the "BS Power / MS Power" results seem to make sense, but the L1 MS Power results seem to be either incorrect or nonsensical, depending on the value given to the "ms max power" directive.
Also, I do not understand why the timing advance would be anything other than 0, since the MS for all of these tests was only about 3 meters away from the BTS.
There were no audio quality problems during these tests. Two-way audio was being passed between the MS and the SIP PBX and it sounded every bit as good as a GSM call on a production network would.
Please let me know if you have any ideas about this or if there is anything I should try or any additional information I can provide which may be of assistance.
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