US Patent 9210619 Signalling mechanisms for wireless device handover

A serving base station transmits, in response to making a handover decision for a wireless device, a first message to a target base station. The serving base station receives from the target base station a second message comprising configuration parameters of a plurality of cells. The configuration parameters comprise a cell group index for a secondary cell identifying a cell group. The serving base station transmits a third message to the wireless device. The third message comprises configuration parameters and is configured to cause the wireless device to start a synchronization process with the target base station.