Energy saving is important for operators' operational efficiency. Energy consumption is a significant operational cost factor, for example in developing markets, up to 30% of OPEX is spent on energy. For one operator group, almost 80% of base stations in Africa and India use diesel as the primary or as a backup power source. Furthermore, base stations account up to 80% of the total CO2 emissions in a mobile operator network. Many operators have a target to cut CO2 emissions as part of their environmental objectives. With increasing voice usage, data usage (e.g. introduction of smart phones, MTC devices, etc.) and more dense networks, the thirst for energy consumption is expected to increase further, hence, motivating the need for low energy base station technology. Increasing the energy efficiency of base stations or reducing the energy consumption of base stations will also facilitate the possibility for operators to power all types of base stations with alternative fuels and rely less on fossil fuels either from diesel generators or from the electricity grid.

The present document provides a study into BTS energy saving solutions. The present document analyses and evaluates different solutions to determine the benefits provided compared to the legacy BTS energy consumption. In the scope of this study there are following solutions:

• Reduction of Power on the BCCH carrier (potentially enabling dynamic adjustment of BCCH power)
• Reduction of power on DL common control channels
• Reduction of power on DL channels in dedicated mode, DTM and packet transfer mode
• Deactivation of cells (e.g. Cell Power Down and Cell DTX like concepts as discussed in RAN [4])
• Deactivation of other RATs in areas with multi-RAT deployments, for example, where the mobile station could assist the network to suspend/minimize specific in-use RATs at specific times of day
• And any other radio interface impacted power reduction solutions

The solutions will also consider the following aspects:

• Impacts on the time for legacy and new mobile stations to gain access to service from the BTS
• Impacts on legacy and new mobile stations to keep the ongoing service (without increasing drop rate)
• Impacts on legacy and new mobile stations implementation and power consumption, e.g. due to reduction in DL power, cell (re-)selection performance, handover performance, etc.
• Impacts on UL/DL coverage balance, especially to CS voice

Solutions will be considered for both BTS energy saving non-supporting and supporting mobile stations (i.e. solutions that are non-backwards compatible towards legacy mobile stations will be out of the scope of this study). The contents of the present document when stable will determine the modifications to existing GERAN specifications.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.