Signalling mechanisms for wireless device handover

1. A method comprising:

a) transmitting, by a serving base station to a target base station, at least one first message in response to making a handover decision by said serving base station for a wireless device;

b) receiving, by said serving base station from said target base station, at least one second message comprising a plurality of parameters of a plurality of cells for said wireless device, said plurality of parameters comprising:

i) configuration parameters of a primary cell and at least one secondary cell; and

ii) a cell group index for a secondary cell in said at least one secondary cell, said cell group index identifying one of a plurality of cell groups, said plurality of cell groups comprising:

(1) a primary cell group comprising a first subset of said plurality of cells, said first subset comprising said primary cell; and

(2) a secondary cell group comprising a second subset of said at least one secondary cell; and

c) transmitting, by said serving base station to said wireless device, a third message:

i) comprising said plurality of parameters; and

ii) configured to cause said wireless device to start a synchronization process with said target base station.

2. The method of claim 1 , wherein said at least one first message comprises at least one parameter indicating whether said wireless device supports configuration of a first plurality of cell groups.

3. The method of claim 2 , wherein said at least one parameter further indicates whether said wireless device supports configuration of said plurality of cell groups for each of one or more band combinations supported by said wireless device.

4. The method of claim 1 , wherein said third message is configured to further cause in said wireless device configuration of a time alignment timer for each of said plurality of cell groups.

5. The method of claim 1 , wherein said third message comprises a media access control dedicated information element comprising a sequence of at least one first information element, each of said at least one first information element comprising: a first cell group index of a first secondary cell group and a first time alignment timer value for said first secondary cell group.

6. The method of claim 1 , further comprising:

encrypting said third message; and

protecting said third message by an integrity header.

7. The method of claim 1 , wherein said third message:

further comprises configuration information for physical channels for said wireless device; and

is configured to cause said wireless device to set up or modify at least one radio bearer.

8. The method of claim 1 , wherein said third message is configured to further cause said wireless device to configure at least one of: a physical layer parameter; a MAC layer parameter; and an RLC layer parameter.

9. The method of claim 1 , wherein said plurality of cells of said target base station are in more than one frequency band.

10. The method of claim 1 , wherein said wireless device supports configuration of a first plurality of cell groups.

11. A serving base station comprising:

a) one or more communication interfaces;

b) one or more processors; and

c) memory storing instructions that, when executed, cause said serving base station to:

i) transmit at least one first message to a target base station in response to making a handover decision by said serving base station for a wireless device;

ii) receive, at least one second message from said target base station, said at least one second message comprising a plurality of parameters of a plurality of cells for said wireless device, said plurality of parameters comprising:

(1) configuration parameters of a primary cell and at least one secondary cell; and

(2) a cell group index for a secondary cell in said at least one secondary cell, said cell group index identifying one of a plurality of cell groups, said plurality of cell groups comprising:

a primary cell group comprising a first subset of said plurality of cells, said first subset comprising said primary cell; and

a secondary cell group comprising a second subset of said at least one secondary cell; and

iii) transmit to said wireless device, a third message:

(1) comprising said plurality of parameters; and

(2) configured to cause said wireless device to start a synchronization process with said target base station.

12. The serving base station of claim 11 , wherein said third message:

further comprises configuration information for physical channels for said wireless device; and

is configured to cause said wireless device to set up or modify at least one radio bearer.

13. The serving base station of claim 11 , wherein said third message is configured to cause said wireless device to configure at least one of: a physical layer parameter; a MAC layer parameter; and an RLC layer parameter.

14. The serving base station of claim 11 , wherein said plurality of cells of said target base station are in more than one frequency band.

15. The serving base station of claim 11 , wherein said wireless device supports configuration of a first plurality of cell groups.