Method and apparatus for cell reselection

1. A method performed by a wireless transmit receive unit (WTRU), the method comprising:

performing measurements on cells neighboring a source cell;

transmitting information obtained from the measurements to the source cell;

receiving a message via the source cell indicating that the WTRU is to communicate via a target cell that is not the source cell; and

in response to the received message:

resetting a medium access control;

ceasing using an enhanced radio network terminal identifier (E-RNTI) associated with the source cell;

transmitting a random access preamble via the target cell;

receiving, from a radio network controller via the target cell, an E-RNTI associated with the target cell; and

communicating via the target cell using the received E-RNTI.

2. The method of claim 1 , wherein the WTRU receives resource allocation information via the target cell.

3. The method of claim 2 , wherein the target cell communicates over an enhanced dedicated channel in accordance with the resource allocation information.

4. The method of claim 1 , further comprising initiating a timer in response to the received message.

5. The method of claim 1 , wherein the received message is a handover message.

6. The method of claim 1 , wherein the received message includes a cell identity of the target cell.

7. The method of claim 1 , wherein the resetting of the medium access control includes flushing a hybrid automatic retransmission request buffer in the WTRU.

8. The method of claim 1 , wherein the resetting of the medium access control includes resetting a transmission sequence number in the WTRU.

9. A wireless transmit receive unit (WTRU) comprising:

a receiver configured to receive signals via cells neighboring a source cell;

a processor, responsive to the receiver, configured to perform measurements on the received signals; and

a transmitter, responsive to the processor, configured to transmit information obtained from the cell measurements via the source cell;

wherein the receiver is further configured to receive a message via the source cell indicating that the WTRU is to communication via a target cell that is not the source cell; and

wherein the processor, in response to the received message, is further configured to:

reset a medium access control;

cease using an enhanced radio network temporary identifier (E-RNTI) associated with the source cell;

cause the transmitter to transmit a random access preamble via the target cell;

cause the receiver to receive, from a radio network controller via the target cell, an E-RNTI associated with the target cell; and

cause the WTRU to communicate via the target cell using the received E-RNTI.

10. The WTRU of claim 9 , wherein the WTRU receives resource allocation information via the target cell.

11. The WTRU of claim 10 , wherein the WTRU communicates via the target cell over an enhanced dedicated channel in accordance with the resource allocation information.

12. The WTRU of claim 9 , wherein the processor is further configured to initiate a timer in response to the received message.

13. The WTRU of claim 9 , wherein the received message is a handover message.

14. The WTRU of claim 9 , wherein the received message includes a cell identity of the target cell.

15. The WTRU of claim 9 , wherein the processor is further configured to flush a hybrid automatic retransmission request buffer in the WTRU when the processor resets the medium access control.

16. The WTRU of claim 15 , wherein the processor is further configured to reset a transmission sequence number in the WTRU when the processor resets the medium access control.

17. In a network configured to communicate with at least one wireless transmit receive unit (WTRU), a method comprising:

receiving, via a source cell, a message sent from the WTRU containing information from measurements made by the WTRU of signals obtained via a neighboring cell;

transmitting, via the source cell, a handover message indicating that the WTRU is to change to a target cell that is not the source cell, the message including i) a cell identity of the target cell, ii) a command to cease using an enhanced radio network terminal identifier (E-RNTI) associated with the source cell, and iii) a command to reset medium access control resources in the WTRU;

receiving, via the target cell, a random access preamble from the WTRU;

transmitting, via the target cell, resource allocation information and a message including an E-RNTI for use by the WTRU when transmitting via the target cell, wherein the E-RNTI is from a radio network controller; and

wherein the target cell, after receiving the random access preamble and in accordance with the resource allocation information, establishes an enhanced dedicated channel between the WTRU and the target cell, and

wherein resources allocated to the WTRU in the source cell are released after the handover message is transmitted via the source cell.

18. A network configured to communicate with at least one wireless transmit receive unit (WTRU), the network comprising:

a receiver serving a source cell and configured to receive a message sent from the WTRU containing information from measurements made by the WTRU of signals via a neighboring cell;

a transmitter serving the source cell and configured to send a handover message indicating that the WTRU is to change to a target cell that is not the source cell, the message indicating i) a cell identity of the target cell, ii) a command to cease using an enhanced radio network terminal identifier (E-RNTI) associated with the source cell, and iii) a command to reset medium access control resources in the WTRU;

a receiver serving the target cell and configured receive to a random access preamble from the WTRU;

a transmitter serving the target cell and configured to send resource allocation information and a message including an enhanced radio network temporary identifier (E-RNTI) for use by the WTRU when transmitting via the target cell, wherein the E-RNTI is from a radio network controller; and

wherein the transmitter and receiver serving the target cell, after receiving the random access preamble and in accordance with the resource allocation information, establishes an enhanced dedicated channel between the WTRU and the target cell, and

wherein the source cell is configured to release resources allocated to the WTRU in the source cell after the handover message is transmitted via the source cell.