LTE中A3和A6事件的有什么区别？A6出现与那些场景？
A3事件是邻区服务质量比服务小区服务好时，引发同频切换；
A6事件是邻区服务质量好于辅小区服务质量，eNodeB自动挑选更好的SCC小区，来提供优质Scell，引发的切换。
这两个事件区分的话，应该怎样理解。 A6事件会出现与那些场景呢？
要了解A3，A6事件，首先得要了解LTE中载波聚合（可以到网上搜寻）首先连接3个概念：PCELL,SCELL,和serving cell
Primary Cell: the cell, operating on the primary frequency, in which the UE either performs the initial connection establishment procedure or initiates the connection re-establishment procedure, or the cell indicated as the primary cell in the handover procedure.
Secondary Cell: a cell, operating on a secondary frequency, which may be configured once an RRC connection is established and which may be used to provide additional radio resources.
Serving Cell: For a UE in RRC_CONNECTED not configured with CA there is only one serving cell comprising of the primary cell. For a UE in RRC_CONNECTED configured with CA the term 'serving cells' is used to denote the set of one or more cells comprising of the primary cell and all secondary cells.
如果没有载波聚合，那么只有一个Pcell,一个Serving cell（也就是Pcell)，无Scell
如果存在载波聚合，那么有一个Pcell，多个Scell，这样就有多个Serving cell。虽然有多个Scell，但可能有的Scell信号比较差，没有使用，这样Serving cell就存在一个集合（Pcell+较好的Scell)
我们再看A3 A6的概念：
Event A3 (Neighbour becomes offset better than PCell)
Event A6 (Neighbour becomes offset better than SCell)
那么就很显然了，A3主要是针对Pcell的，可以用于同频，异频的切换测量
A6用于载波聚合中，这里需要注意，A6中的Scell与Pcell必须是同频的（The neighbour(s) is on the same frequency as the SCell），用于多个Scell间的测量，看谁能进入Serving Cell小区列表。