LTE Advanced: 3GPP Solution for IMT-Advanced

10.5 SON Features in 3GPP Release 11

3GPP Release 11 work started with following SON features:

• Mobility Robustness Optimization (MRO) enhancements. MRO was included in Release 10 for intra-LTE cases. Release 11 enhances the functionality to inter-RAT cases.
• Ping-pong and short-stay minimization in intra-RAT and inter-RAT cases. The target is to minimize unnecessary mobility events and the related signalling and UE power consumption.
• Optimal RAT selection based on QoS requirements and each RAT QoS capability.
• Enhancements to automatic neighbour relations to inter-RAT cases.
• Coordination between MRO and other traffic control mechanism, like mobility load balancing.
• Studying methods to verify the status of the cell's radio resources.

After the evaluation phase, at RAN3 #75 (February, 2012), the Release 11 Work Item was limited to the topic identified as the most relevant, that is those addressing failure scenarios and inter-RAT ping-pong.

Failure scenarios:

• Failure while moving out of LTE coverage: connection fails in LTE, UE reconnects at 2G or 3G. The handover at LTE has not been triggered in time.
• Failure when entering LTE coverage: a handover is triggered toward LTE from 2G or 3G, but the LTE connection fails either during handover, or soon after and the UE reconnects to the original RAT. The handover to LTE has been triggered too early.
• In intra-LTE HetNet deployment: a handover to a pico cell is triggered too early or to a wrong target; the existing Release 9/10 mechanisms ...