Method and apparatus for cell update while in an enhanced cell_fach state

A method for performing cell reselection from a source cell to a target cell, the method comprising:

• detecting a cell update triggering event while receiving a high speed downlink packet access (HSDPA) transmission;
• initiating a cell update procedure upon detecting the cell update triggering event;
• clearing a radio network temporary identity (RNTI) received in the source cell;
• reading system information in the target cell;
• and
• based on the system information, resetting a high speed downlink shared channel (HS-DSCH) medium access control (MAC) entity configured for the source cell, and enabling HS-DSCH reception in the target cell.

A wireless transmit/receive unit (WTRU) configured to perform cell reselection from a source cell to a target cell, the WTRU comprising:

• a transceiver configured to transmit and receive signals;
• a controller configured to:
• detect a cell update triggering event while receiving a high speed downlink packet access (HSDPA) transmission via the transceiver;
• initiating a cell update procedure upon detecting the cell update triggering event;
• clearing a radio network temporary identity (RNTI) received in the source cell;
• reading system information received in the target cell via the transceiver;
• and
• based on the system information, reset a high speed downlink shared channel (HS-DSCH) medium access control (MAC) entity configured for the source cell, and enabling HS-DSCH reception in the target cell.