Wireless device handover signalling

1. A method comprising:

transmitting, by a first base station to a second base station and after making a handover decision for a wireless device, a first message comprising at least one parameter indicating the wireless device supports configuration of a plurality of cell groups;

receiving from the second base station at least one second message comprising first configuration parameters of a plurality of cells grouped into a first plurality of cell groups comprising a first cell group and a second cell group, wherein:

uplink transmission timing in the first cell group is derived employing a first cell in the first cell group; and

uplink transmission timing in the second cell group is derived employing a second cell in the second cell group; and

transmitting, to the wireless device, a third message comprising the first configuration parameters.

2. The method of claim 1 , wherein the third message is configured to cause the wireless device to start a synchronization process with a cell of the second base station.

3. The method of claim 1 , wherein the at least one parameter further indicates whether the wireless device supports configuration of the plurality of cell groups for each of one or more band combinations supported by the wireless device.

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

5. The method of claim 1 , wherein the third message comprises a media access control dedicated information element (IE) comprising a sequence of at least one first IE, an IE in the at least one first IE comprising: a first cell group index and a first time alignment timer value.

6. The method of claim 1 , further comprising:

encrypting the third message; and

protecting the third message employing an integrity header.

7. The method of claim 1 , wherein the third message further comprises:

configuration parameters of physical channels for the wireless device; and

configuration parameters of at least one radio bearer.

8. The method of claim 1 , wherein the third message further comprises configuration parameters of at least one of: a physical layer parameter; a MAC layer parameter; and an RLC layer parameter.

9. A first base station comprising:

one or more processors; and

memory storing instructions that, when executed, cause the first base station to:

transmit, to a second base station and after making a handover decision for a wireless device, a first message comprising at least one parameter indicating the wireless device supports configuration of a plurality of cell groups;

receive from the second base station at least one second message comprising first configuration parameters of a plurality of cells grouped into a first plurality of cell groups comprising a first cell group and a second cell group, wherein:

uplink transmission timing in the first cell group is derived employing a first cell in the first cell group; and

uplink transmission timing in the second cell group is derived employing a second cell in the second cell group; and

transmit, to the wireless device, a third message comprising the first configuration parameters.

10. The first base station of claim 9 , wherein the third message is configured to cause the wireless device to start a synchronization process with a cell of the second base station.

11. The first base station of claim 9 , wherein the at least one parameter further indicates whether the wireless device supports configuration of the plurality of cell groups for each of one or more band combinations supported by the wireless device.

12. The first base station of claim 9 , wherein the third message is configured to further cause configuration of a time alignment timer for each of the first plurality of cell groups.

13. The first base station of claim 9 , wherein the third message comprises a media access control dedicated information element (IE) comprising a sequence of at least one first IE, an IE in the at least one first IE comprising: a first cell group index and a first time alignment timer value.

14. The first base station of claim 9 , wherein the instructions, when executed, further cause the first base station to:

encrypt the third message; and

protect the third message employing an integrity header.

15. The first base station of claim 9 , wherein the third message further comprises:

configuration parameters of physical channels for the wireless device; and

configuration parameters of at least one radio bearer.

16. The first base station of claim 9 , wherein the third message further comprises configuration parameters of at least one of: a physical layer parameter; a MAC layer parameter; and an RLC layer parameter.

17. A method for use in a wireless network, the method comprising:

transmitting, by a first base station to a second base station and after making a handover decision for a wireless device, a first message comprising at least one parameter indicating the wireless device supports configuration of a plurality of cell groups;

receiving, by the first base station from the second base station, at least one second message comprising first configuration parameters of a plurality of cells grouped into a first plurality of cell groups comprising a first cell group and a second cell group, wherein:

uplink transmission timing in the first cell group is derived employing a first cell in the first cell group; and

uplink transmission timing in the second cell group is derived employing a second cell in the second cell group; and

receiving, by the wireless device from the first base station, a third message comprising the first configuration parameters.

18. The method of claim 17 , wherein the third message is configured to cause the wireless device to start a synchronization process with a cell of the second base station.

19. The method of claim 17 , wherein the at least one parameter further indicates whether the wireless device supports configuration of the plurality of cell groups for each of one or more band combinations supported by the wireless device.

20. The method of claim 17 , wherein the third message is configured to further cause configuration of a time alignment timer for each of the first plurality of cell groups.