Change in osmo-bts[master]: TA loop: Take into account UL SACCH 'Actual Timing advance' field

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pespin gerrit-no-reply at
Thu Sep 9 17:31:54 UTC 2021

Hello Jenkins Builder, laforge, fixeria, dexter, 

I'd like you to reexamine a change. Please visit

to look at the new patch set (#2).

Change subject: TA loop: Take into account UL SACCH 'Actual Timing advance' field

TA loop: Take into account UL SACCH 'Actual Timing advance' field

First step improving and reworking TA loop:
Move trigger of the loop to similar place done by BS/MS Power Control
Loop, that is, upon receivial of UL SACCH block, which contains
information about the TA used to transmit the block encode in L1SACCH
Header. Hence, from computed received TOA and TA used when transmitting
from the MS, we can infer the desired TA to be used by the MS, which
will send back to it later during DL SACCH block.

The values taken are actually the ones calculated for the previous SACCH
block and stored in lchan->meas.ms_toa256. That's because L1SACCH
contains the TA used for the previous reporting period, similarly to
what's specified for MS Power Control loop (TS 45.008 sec 4.2):
The MS shall confirm the power control level that it is currently employing
in the SACCH L1 header on each uplink  channel. The indicated value shall
be the power control level actually used by the mobile for the last burst
of the  previous SACCH period.
(The reader may observe that currently this is not properly done for MS
Power Control loop when calling lchan_ms_pwr_ctrl(): this is a bug.)

This new method also permits changing TA quicker, since we have more
confidence that the TA we request is aligned with the one used to
transmit, and we don't simply increment/decrement based on the value we
request to transmit.

Related: SYS#5371
Change-Id: I2d0f128c8dcac93ee382283a1c91fca76623b8fc
M include/osmo-bts/ta_control.h
M src/common/l1sap.c
M src/common/measurement.c
M src/common/ta_control.c
M tests/ta_control/ta_control_test.c
5 files changed, 74 insertions(+), 28 deletions(-)

  git pull ssh:// refs/changes/86/25386/2
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Gerrit-Project: osmo-bts
Gerrit-Branch: master
Gerrit-Change-Id: I2d0f128c8dcac93ee382283a1c91fca76623b8fc
Gerrit-Change-Number: 25386
Gerrit-PatchSet: 2
Gerrit-Owner: pespin <pespin at>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: dexter <pmaier at>
Gerrit-Reviewer: fixeria <vyanitskiy at>
Gerrit-Reviewer: laforge <laforge at>
Gerrit-MessageType: newpatchset
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