Friday, 19 October 2018

Energy Savings

Mobile network operators are increasingly aiming at decreasing power consumption in telecom networks to lower their OPEX and reduce greenhouse emissions with network energy saving solutions for long term sustainable development. With the expected deployment of large numbers of mobile network radio equipment, in the form of Home NB/eNBs, OPEX reduction becomes even more crucial.

Energy consumption is a significant part of an operator’s OPEX. OPEX reduction can be accomplished by designing network elements with lower power consumption and temporarily shutting down unused capacity when not needed. Power amplifiers consume a significant portion of the total energy consumption in a wireless network.

When a cell is switched off, there may be a need for the neighboring cells to pick up the load. However switching off a cell should not cause coverage holes or create undue load on the surrounding cells. A switched off cell is not considered a cell outage or a fault condition. All traffic on that cell is expected to be moved to the underlying umbrella cells before any switch off occurs.

When a NE is "switched off" for energy savings purposes, no alarms should be raised to the OAM manager for a condition that is a consequence of a "switched off" NE. The operator should have the capability to prevent the network from automatically compensating based on the cell that is in energy savings mode in order to prevent unnecessary disruption in the network.

OAM of mobile networks can contribute to energy saving by allowing the operator to set policies to minimize consumption of energy, while maintaining coverage, capacity and quality of service. The permitted impact on coverage, capacity and quality of service is determined by an operator’s policy.

3GPP Rel-11 has defined two energy saving states for a cell with respect to energy saving namely: notEnergySaving state and energySaving state.Based on the above energy saving states, a full energy saving solution includes two elementary procedures: energy saving activation (change from notEnergySaving to energySaving state) and energy saving deactivation (change from energySaving to notEnergySaving state).

When a cell is in an energy saving state it may need neighboring cells to pick up the load. However, a cell in energySaving state cannot cause coverage holes or create undue load on the surrounding cells. All traffic on that cell is expected to be drained to other overlaid/umbrella cells before any cell moves to energySaving state.

A cell in energySaving state is not considered a cell outage or a fault condition. No alarms should be raised for any condition that is a consequence of a network element moving into energySaving state.
Criteria for the energySaving state is defined in 3GPP namely: degree of energy saving effect, controllability from the network, and service availability.

The various Energy Savings Management (ESM) concepts can apply to different RATs, for example UMTS and LTE. However, 3GPP has specified that some of these ESM concepts may be limited to specific RATs and network elements, and specific solutions may be required for them.

In Rel-11, three general architectures that are candidates to offer energy savings functionalities are described, namely: distributed, network management centralized, and element management centralized. Energy savings management use cases such as the cell overlay use case and the capacity limited network use case, are described in detail. Requirements for element management centralized energy savings and distributed energy saving are specified. Coordination between energy saving and cell outage is addressed.

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