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Bug #4467

closed

bad voice quality in current osmo-bts-trx master

Added by laforge almost 2 years ago. Updated 2 months ago.

Status:
Closed
Priority:
Normal
Assignee:
-
Category:
osmo-bts-trx
Target version:
-
Start date:
03/20/2020
Due date:
% Done:

50%

Spec Reference:

Description

As has been confirmed by pespin and myself, voice quality is very problematic in current osmo-trx + osmo-bts-master. It works within 1m of the SDR (USRP B2xx in this case), but as soon as the MS are moved further away, considerable audible codec artefacts are observed.

  • the radio link should not be that bad in the first plcae. RxLev UL/DL are reported better than -70dBm
  • even if there are problems on the radio link, we would expect the bad frames to be dropped and the ECU to smooth over the drop-outs. WE would expect interrupted voice, or periods of quiet, but not beepy chirpy crazy codec artefacts.

What's strange is the bad RxQual in uplink, typically between 4..7.

BTS 0, TRX 0, Timeslot 1, Lchan 0: Type TCH_F
  Connection: 1, State: ESTABLISHED
  BS Power: 3 dBm, MS Power: 16 dBm
  Channel Mode / Codec: SPEECH_V1
  No Subscriber
  Bound IP: 127.0.0.1 Port 16412 RTP_TYPE2=0 CONN_ID=0
  Conn. IP: 192.168.103.248 Port 4180 RTP_TYPE=3 SPEECH_MODE=0x00
  Measurement Report:
    Flags:  
    MS Timing Offset: 0
    L1 MS Power: 0 dBm, Timing Advance: 0
    RXL-FULL-dl:  -71 dBm, RXL-SUB-dl:  -72 dBm RXQ-FULL-dl: 0, RXQ-SUB-dl: 0
    RXL-FULL-ul:  -72 dBm, RXL-SUB-ul:  -72 dBm RXQ-FULL-ul: 5, RXQ-SUB-ul: 4
BTS 0, TRX 0, Timeslot 2, Lchan 0: Type TCH_F
  Connection: 1, State: ESTABLISHED
  BS Power: 3 dBm, MS Power: 16 dBm
  Channel Mode / Codec: SPEECH_V1
  Subscriber:
    IMSI: 901700000025130
    TMSI: 0x2100bc7e
    Use count: 1
  Bound IP: 127.0.0.1 Port 16414 RTP_TYPE2=0 CONN_ID=0
  Conn. IP: 192.168.103.248 Port 4188 RTP_TYPE=3 SPEECH_MODE=0x00
  Measurement Report:
    Flags: DLinval 
    RXL-FULL-ul:  -74 dBm, RXL-SUB-ul:  -75 dBm RXQ-FULL-ul: 7, RXQ-SUB-ul: 7

So my working theory is that there's something broken in our decoder/receiver that causes lots of BER (and hence bad RxQual), and then there's a second bug which causes the ECU not to work as expected.


Related issues

Related to OsmoBTS - Bug #4466: " N(S) sequence error" when operating osmo-bts-trxRejectedsysmocom03/20/2020

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Related to OsmoBTS - Bug #4465: Incorrect number of SUB measurements detectedResolveddexter03/20/2020

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Related to libosmo-abis - Bug #4464: "osmo_rtp_socket_poll(): ERROR!" messages during normal osmo-bts usageIn Progresslaforge03/20/2020

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Related to OsmoTRX - Bug #4468: "RSSI offset" default of 0 is not usefulFeedbackHoernchen03/21/2020

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