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diff --git a/doc/manuals/chapters/power_control.adoc b/doc/manuals/chapters/power_control.adoc index 4c1a275b8..bb87c850c 100644 --- a/doc/manuals/chapters/power_control.adoc +++ b/doc/manuals/chapters/power_control.adoc @@ -327,3 +327,84 @@ network // TODO: Document other power control parameters: // OsmoBSC(config-net-bts)# ms max power <0-40> // OsmoBSC(config-net-bts-trx)# max_power_red <0-100> + +=== BCCH carrier power reduction operation + +According to 3GPP TS 45.008, section 7.1, the BCCH carrier (sometimes called C0) of +a BTS shall maintain continuous Downlink transmission at full power in order to +stay "visible" to the mobile stations. Because of that, early versions of this 3GPP +document prohibited BS power reduction on C0. However, a new feature was introduced +in version 13.0.0 (2015-11) - "BCCH carrier power reduction operation". + +This is a special mode of operation, in which the variation of RF power level for +some timeslots is relaxed for the purpose of energy saving. In other words, the +output power on some timeslots, except the timeslot(s) carrying BCCH/CCCH, can be +lower than the full power. In this case the maximum allowed difference is 6 dB. + +Of course, energy saving comes at a price and has impacts to the network KPI. In +particular, it does negatively affect cell reselection performance and does increase +handover failure and call drop rates. This is why BCCH carrier power reduction +operation mode is not enabled by default. More information on potential impact +and the simulation results can be found in 3GPP TR 45.926. + +==== Supported BTS models + +At the time of writing this manual, the only BTS model that can be instructed to +enter or leave the BCCH power reduction mode is osmo-bts-trx. Support for other +BTS vendors/models may be added in the future. + +TIP: If you're using OsmoBTS, make sure that it reports feature #021 "BCCH carrier +power reduction mode" in the feature vector. This can be checked by issuing +`show bts` command in OsmoBSC's VTY interface. + +==== Managing BCCH carrier power reduction + +The BCCH carrier power reduction can be controlled via the CTRL and VTY interfaces. +There is currently no logic in OsmoBSC for automatic activation and deactivation +of this mode, so it's up to the network operator (or an external monitoring suite) +when and depending on which factors to toggle it. Setting a value greater than +zero enables the BCCH power reduction mode; setting zero disables it completely. + +.Example: Activating BCCH carrier power reduction via the VTY +---- +OsmoBSC> enable +OsmoBSC# bts 0 <1> c0-power-reduction ? + <0-6> Power reduction value (in dB, even numbers only) +OsmoBSC# bts 0 <1> c0-power-reduction 4 <2> +---- +<1> BTS number for which to activate BCCH carrier power reduction +<2> Maximum BCCH carrier power reduction (in 2 dB steps, 4 dB in this example) + +.Example: Activating BCCH carrier power reduction via the CTRL +---- +$ osmo_ctrl.py \ + --host 127.0.0.1 <1> -p 4249 \ + --set "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 (in 2 dB steps, 4 dB in this example) + +Once activated, it's possible to introspect the current maximum reduction value: + +.Example: Checking BCCH carrier power reduction state via the VTY +---- +OsmoBSC> enable +OsmoBSC# show bts 0 <1> +BTS 0 is of osmo-bts type in band DCS1800, has CI 0 LAC 1, BSIC 63 (NCC=7, BCC=7) and 2 TRX + Description: (null) + ARFCNs: 751 753 + BCCH carrier power reduction (maximum): 4 dB <2> + ... +---- +<1> BTS number for which to show BCCH carrier power reduction state +<2> Maximum BCCH carrier power reduction currently applied + +.Example: Checking BCCH carrier power reduction state via the CTRL +---- +$ osmo_ctrl.py \ + --host 127.0.0.1 <1> -p 4249 \ + --get "bts.0.c0-power-reduction" +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 |