Method and apparatus for cell reselection

Abstract

A method and wireless transmit receive unit (WTRU) are disclosed that is configured to perform cell reselection to another cell when the WTRU is in a CELL_FACH state using an Enhanced-Dedicated Channel (E-DCH). The cell reselection is based on internal measurements by the WTRU. Alternatively, the cell reselection can be WTRU based on the WTRU measurements reported to the network.

What is claimed is: 
     
         1 . A method performed by a wireless transmit/receive unit (WTRU), the method comprising:
 communicating with a source cell;   performing measurements on a plurality of neighboring cells;   transmitting, via the source cell, information from the measurements;   receiving, via the source cell, a message indicating that the WTRU is to communicate via a target cell, the target cell being one of the plurality of neighboring cells; and   after receiving the message:
 ceasing using an enhanced radio network terminal identifier (E-RNTI) associated with the source cell; 
 resetting a medium access control; 
 receiving, via the source 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 , further comprising receiving resource allocation information via the target cell. 
     
     
         3 . The method of  claim 2 , wherein the communicating via the target cell includes communicating 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 an identification 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 . The method of  claim 1 , further comprising:
 transmitting, in response to the received message, a random access preamble via the target cell.   
     
     
         10 . The method of  claim 1 , wherein the received E-RNTI is assigned to the WTRU by a radio network controller. 
     
     
         11 . A wireless transmit/receive unit (WTRU) comprising:
 a transmitter;   a receiver; and   a processor to:   perform measurements by the receiver on signals received from a plurality of neighboring cells;   cause the transmitter to transmit, via a source cell, information from the measurements;   process a message received by the receiver via the source cell, the message indicating that the WTRU is to communicate via a target cell, the target cell being one of the plurality of neighboring cells; and
 after processing the message, reset a medium access control, cease using an E-RNTI associated with the source cell, and cause the WTRU to communicate, via the target cell, using an enhanced radio network temporary identifier (E-RNTI) associated with the target cell and received by the receiver via the source cell. 
   
     
     
         12 . The WTRU of  claim 11 , wherein the processor processes resource allocation information received by the receiver via the target cell. 
     
     
         13 . The WTRU of  claim 12 , wherein the WTRU communicates, via the target cell, over an enhanced dedicated channel in accordance with the resource allocation information. 
     
     
         14 . The WTRU of  claim 11 , wherein the processor initiates a timer in response to the message received by the receiver. 
     
     
         15 . The WTRU of  claim 11 , wherein the message received by the receiver is a handover message. 
     
     
         16 . The WTRU of  claim 11 , wherein the message received by the receiver includes an identification of the target cell. 
     
     
         17 . The WTRU of  claim 11 , wherein the resetting of the medium access control by the processor includes the processor flushing a hybrid automatic retransmission request buffer in the WTRU. 
     
     
         18 . The WTRU of  claim 17 , wherein resetting of the medium access control by the processor includes the processor resetting a transmission sequence number in the WTRU. 
     
     
         19 . The WTRU of  claim 11 , wherein the received E-RNTI is assigned to the WTRU by a radio network controller. 
     
     
         20 . The WTRU of  claim 11 , wherein the processor, in response to the message received by the receiver, causes the transmitter to transmit a random access preamble via the target cell.