There are three ways of optimizing handovers in LTE:

a) Via the modification of the parameters a3offset and hysteresisa3

b) By changing the parameter timetotriggereventa3

c) Via the modification of the parameter filtercoefficient for event a3.

These set of blogs will dealt with parameter setting for Periodic Reporting of Event A3 only. The intention is to deal with each of the cases mentioned above, one at a time. Hence, this blog will concentrate in case a).

Definitions:

Event A3 is defined as a triggering event when a neighbour cell becomes an offset better than the serving cell. The UE creates a measurement report, populates the triggering details and sends the message to the serving cell. The parameters that define the trigger include:

a3offset: This parameter can be found in 3GPP 36.331. It configures the RRC IE a3-Offset included in the IE reportConfigEUTRA in the MeasurementConfiguration IE. The value sent over the RRC interface is twice the value configured, that is, the UE has to divide the received value by 2.The role of the offset in Event A3 is to make the serving cell look better than its current measurement in comparison to the neighbor.

Hysteresisa3: The role of the hysteresis in Event A3 is to make the measured neighbor look worse than measured to ensure it is really stronger before the UE decides to send a measurement report to initiate a handover.

timetoTriggera3: The role of ttt in Event A3 is to avoid a ping-pong effect.

CellIndividualoffsetEutran: This parameter is applied individually to each neighbor cell with load management purposes. The higher the value allocated to a neighbor cell, the “more attractive” it will be. This parameter can only be used if the neighbor list is broadcast in SIB4 or in an RRC connection reconfiguration.

Ping pong is the effect caused by the MS to widely switch links with either BS when the MS is exactly between the two BSs.

These links will be helpful

http://www.ijfcc.org/vol4/391-W203.pdf

http://tishreen.edu.sy/sites/default/files/Tishreen_Magazine/16_20.pdf

http://lteuniversity.com/get_trained/expert_opinion1/b/lauroortigoza/archive/2012/02/22/handover-parameters-part-1-of-3.aspx

This is a useful document https://tetcos.com/pdf/v13.2/v13.2.35-Time-to-Trigger.pdf which explains (i) handover offset or margin (ii) time to trigger (TTT) and (iii) handover interruption time Tuning the handover offset and TTT correctly would reduce the ping-pong handover rate