Cellular Network Infrastructure » Radio Access Network » OsmoBSC

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.