Handover random access

1. A method comprising:

transmitting, by a wireless device and to a first base station associated with a first cell, a first message comprising a measurement report based on one or more second cells;

receiving, by the wireless device and from the first base station, a second message comprising a command for a handover from the first cell to a second cell of the one or more second cells, wherein the second message comprises one or more parameters indicating a type of a random access procedure for the handover, and wherein the type of the random access procedure comprises a two-step random access procedure or a four-step random access procedure; and

transmitting, by the wireless device and to a second base station associated with the second cell, a random access preamble employing the type of the random access procedure indicated in the second message.

2. The method of claim 1 , further comprising transmitting, by the wireless device, one or more transport blocks overlapping in time with the random access preamble.

3. The method of claim 2 , wherein the one or more transport blocks comprise one or more of:

a handover complete message;

uplink data;

a buffer status report; or

an identifier of the wireless device.

4. The method of claim 1 , wherein the one or more parameters of the second message comprise, for the random access procedure, one or more of:

a preamble identifier; or

random access resource information.

5. The method of claim 1 , wherein the second message further comprises:

timing advance information for transmission of one or more of the random access preamble or one or more transport blocks.

6. The method of claim 5 , further comprising:

receiving, from the one or more second cells, a plurality of third messages comprising one or more of:

an indication of a power associated with a cell;

an indication of a quality associated with a cell; or

an indication of a cell priority.

7. The method of claim 1 , further comprising transmitting, by the wireless device and in a first step of a four-step random access procedure, a second random access preamble.

8. The method of claim 1 , wherein the second message comprises a preamble identifier, and wherein the method further comprises:

determining, based on the preamble identifier, radio resources associated with the random access procedure.

9. The method of claim 1 , wherein the second message comprises:

random access channel configuration information for a two-step random access procedure; and

radio resource configuration parameters for the two-step random access procedure.

10. A method comprising:

receiving, by a first base station associated with a first cell and from a wireless device, a first message comprising a measurement report based on one or more second cells;

determining, based on the measurement report, to handover the wireless device from the first cell to a second cell of the one or more second cells;

transmitting, by the first base station and to a third device, a second message comprising an indication for the handover;

receiving, by the first base station and from the third device, a third message indicating a type of a random access procedure for the handover, wherein the type of the random access procedure comprises a two-step random access procedure or a four-step random access procedure; and

transmitting, by the first base station and to the wireless device, a fourth message comprising:

one or more parameters indicating the type of the random access procedure for the handover; and

a command to proceed with the handover.

11. The method of claim 10 , wherein:

the third device comprises a second base station associated with the second cell; and

the second message comprises a handover request.

12. The method of claim 10 , wherein:

the third device comprises a core network device; and

the second message indicates that the handover is requested.

13. The method of claim 12 , further comprising:

transmitting, by the core network device, to a second base station, and based on the second message, a fifth message comprising a handover request; and

receiving, by the core network device and from the second base station, a sixth message indicating the type of the random access procedure for the handover and comprising an acknowledgement of the handover request.

14. The method of claim 10 , wherein the one or more parameters of the fourth message comprise, for the random access procedure, one or more of:

a preamble identifier; or

random access resource information.

15. The method of claim 10 , wherein the fourth message further comprises timing advance information for transmission, by the wireless device, of one or more of a random access preamble or one or more transport blocks.

16. The method of claim 15 , wherein the timing advance information comprises one or more of:

an indication of a zero timing advance; or

a value for a timing advance, wherein the value is estimated by the first base station or the third device.

17. A method comprising:

receiving, by a network device and from a first base station associated with a first cell, a first message comprising an indication for a handover of a wireless device from the first cell to a second cell of one or more second cells;

determining, by the network device and based on the first message, to proceed with the handover; and

transmitting, by the network device and to the first base station, a second message comprising:

an acknowledgement for the handover; and

one or more parameters indicating a type of a random access procedure for the handover, wherein the type of the random access procedure comprises a two-step random access procedure or a four-step random access procedure.

18. The method of claim 17 , wherein:

the network device comprises a second base station that is associated with the second cell; and

the second message comprises a handover request.

19. The method of claim 17 , wherein:

the network device comprises a core network device; and

the second message comprises an indication that the handover is required.

20. The method of claim 19 , further comprising:

transmitting, by the core network device, to a second base station, and based on the first message, a third message comprising a handover request; and

receiving, by the core network device and from the second base station, a fourth message indicating the type of the random access procedure for the handover and comprising an acknowledgement of a request for a handover request.