RAT小区，异RAT小区是什么意思？

即是開啟3G & 2G的neighbor關係, 可以讓3G,2G彼此handover or cell reselection , 稱為IRAT .
Inter-Radio Access Technology Cell Change (IRATCC) handles the Cell Change and Cell Reselection of a UE in connected state to and from a GSM/GPRS system. The IRATCC handles the Cell Change and Cell Reselection when the UE is connected to a Packet-Switched service.
Once the evaluation carried by the Inter-Rat Handover Evaluation algorithm has lead to a proposed GSM/GPRS cell, Inter-RAT Cell Change Execution is enabled if the UE is connected to a Packet-Switched service, and the Inter-RAT Cell Change execution part starts. The result of the execution part is one of the following:
• The UE, in CELL_DCH state, changes cell and continues connected to a Packet-Switched service in the new GSM/GPRS cell.
• The UE, in CELL_FACH state, reselects cell and the UE contacts the new GSM/GPRS system.
• The UE remains in the WCDMA RAN connected to a Packed-Switched service, due to Inter-RAT Cell Change failure.