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author | Vadim Yanitskiy <vyanitskiy@sysmocom.de> | 2021-11-12 22:44:12 +0300 |
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committer | Vadim Yanitskiy <vyanitskiy@sysmocom.de> | 2021-11-12 22:52:02 +0300 |
commit | a507875ae75d67842975ece95e349ab643c86d94 (patch) | |
tree | 2389cf18b92b77e12eac6c4780a336e175f8badd /doc | |
parent | 9a310f818fe945e5d1c682f7d6a71fac384c88d1 (diff) |
doc/manuals: add documentation for Temporary ACCH Overpower
Change-Id: Ie995dac6c7083a2b0b4d582f71f55b3736381edb
Related: SYS#5319
Diffstat (limited to 'doc')
-rw-r--r-- | doc/manuals/chapters/power_control.adoc | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/doc/manuals/chapters/power_control.adoc b/doc/manuals/chapters/power_control.adoc index f94dd2edb..dee0470c8 100644 --- a/doc/manuals/chapters/power_control.adoc +++ b/doc/manuals/chapters/power_control.adoc @@ -565,3 +565,61 @@ Got message: b'GET_REPLY 3652121201381481804 bts.0.c0-power-reduction 4 <2>' ---- <1> Remote address of the host running osmo-bsc (localhost in this example) <2> Maximum BCCH carrier power reduction currently applied + +=== Temporary ACCH overpower + +Temporary overpower (TOP) is a power control technique that allows to improve +SACCH/FACCH performance in case of bad C/I. The key idea of TOP is to +increment the BS transmit power by 2..4 dB only for FACCH/SACCH bursts, while +keeping all voice bursts at the lower (normal) level as determined by the +downlink power control loop. This allows to reduce call drop rate and +increase capacity in deployments with tight frequency reuse. + +NOTE: It's not possible to increase the current BS power beyond the maximum +transmit power level supported by the PHY. Thus if the BTS is already +transmitting at full power, the overpower logic cannot increase it even +further. This is also why TOP must be employed *together with BS power +control*, either static or dynamic. + +The main area of use for TOP is traffic channels employing the AMR (Adaptive +Multi Rate) codec, which is more robust to interference than the associated +signalling channels. While AMR provides sufficient speech quality even at +very low C/I levels, the associated signalling channels may be suffering from +channel coding errors. This imbalance can be compensated by employing TOP, +which can be efficiently combined with the ACCH repetition technique. + +This feature requires no support on the mobile station side and can be used +with UEs implementing the most recent 3GPP relese features, as well as legacy +UEs. However, it needs to be implemented in the BTS. Given that TOP itself +is not specified in 3GPP specifications, osmo-bsc uses Osmocom specific +A-bis/RSL IEs in order to activate it. Therefore, only the recent osmo-bts +versions may be instructed to activate this feature. Make sure that feature +#023 "FACCH/SACCH Temporary overpower" is present in the feature vector. +This can be checked by issuing `show bts` command in OsmoBSC's VTY interface. + +TOP is disabled by default. Below is a configuration example enabling it: + +---- +network + bts 0 + overpower dl-acch 2 <1> + overpower rxqual 4 <2> +---- +<1> Overpower of maximum 2 dB for both SACCH and FACCH. +<2> Enable TOP only if RxQual is worse than 4 (BER >= 1.6%). + +It's also possible to enable TOP only for FACCH or SACCH selectively, or +or keep it enabled permanently regardless of the reported RxQual: + +---- +OsmoBSC(config-net-bts)# overpower ? + dl-acch Enable overpower for both SACCH and FACCH + dl-sacch Enable overpower for SACCH only + dl-facch Enable overpower for FACCH only + +OsmoBSC(config-net-bts)# overpower rxqual 0? + 0 BER >= 0% (always on) +---- + +These parameters are indicated to the BTS during a logical channel activation +or modifications procedures, so they can be changed at run-time. |