1. Field of the Invention
The present invention relates to energy saving in a mobile communications network. For example, the invention can be applied to LTE (long term evolution) and LTE-advanced systems.
2. Description of Related Art
There are different methods of potentially offering energy savings to a network operator, which include centrally controlled network optimizations, self-optimizing network methods and eNB based optimizations.
The centrally controlled network optimizations comprise e.g. sector, site, or even sub-network switch-off at least for some frequency bands during low traffic periods. The self-optimizing network methods include antenna tilting and alternating site switch-off, etc. And the eNB based optimizations comprise optimization of baseband processing resources in low traffic situations, optimization of power amplifier efficiency, local adjustment of transmit bandwidth, local adjustment of time of transmission e.g. through MBMS (multimedia broadcast/multicast service) subframe configurations, and local reduction of number of active transmit antenna ports.
A direct and efficient method for enhancing power amplifier efficiency includes providing DTX (discontinuous transmission) phases already on a Layer 1 (L1) of an LTE air interface.
DTX phases (so-called “blank subframes”) through MBMS configurations as used in an LTE Release 10 network may, however, impact LTE Release 8 UEs (user equipments), even that the UEs may not be connected to a cell of the network (using blank subframes). This is because measurements e.g. for handover or for RRC (radio resource control) connection establishment will indicate a lower RSRP (received signal reference power) than is the case, and cause the UEs to start measuring for handover candidates at a premature time in terms of handover. This may cause increased UE power consumption, call-drops in the worst case, and visibly lower network reliability.
Higher level optimizations such as switching off cells completely have also been proposed, but such proposals suffer from the cell's ability to ‘wake up’ in case there is traffic in the vicinity of the cell center, or in the cell coverage area.
The present invention aims at providing eNB energy savings while allowing backward compatibility in terms of Release 8 UE measurements for mobility, and providing possibility to Release 10 UEs for some data transmission in subframes.
This is achieved by the apparatus and method as defined in the appended claims. The invention may also be implemented as a computer program product.