Method And Apparatus For Performing An Enhanced Random Access Channel Procedure In A Cell_Fach State

Abstract

A method and apparatus for performing an enhanced random access procedure in a Cell_FACH state are disclosed. A wireless transmit/receive unit (WTRU) transmits a random access channel (RACH) preamble for random access. If a positive acknowledgement (ACK) is received in response to the RACH preamble, the WTRU enters a contention resolution phase and transmits a message via an enhanced dedicated channel (E-DCH). If contention resolution fails, the RACH preamble is retransmitted. A contention back-off timer may be used for retransmission. A physical random access channel (PRACH) code may be reselected. The RACH preamble may be retransmitted using a reserved PRACH resource so that E-DCH resource is allocated to the collided WTRUs. Data transmitted during the contention resolution phase may remain in a hybrid automatic repeat request (HARQ) buffer. The MAC-i/is entity may be reset. All data sent during the contention resolution phase may be stored in a temporary buffer.

What is claimed is: 
     
         1 . A method comprising:
 entering a contention resolution phase; and   on a condition that contention resolution fails because no E-DCH absolute grant channel (E-AGCH) with a WTRU's E-DCH radio network temporary identity (E-RNTI) is received within a period of time resetting a medium access control (MAC)-i/is entity.   
     
     
         2 . The method of  claim 1 , further comprising:
 initiating an enhanced dedicated channel (E-DCH) transmission on an assigned E-DCH resource;   transmitting data using the assigned E-DCH resource; and   releasing the assigned E-DCH resource on the condition that contention resolution fails because no E-AGCH with a WTRU's E-RNTI is received within the period of time.   
     
     
         3 . The method of  claim 2 , further comprising requesting access to the assigned E-DCH resource. 
     
     
         4 . The method of  claim 2 , wherein when the contention resolution fails the E-DCH transmission is stopped. 
     
     
         5 . The method of  claim 1 , wherein when the contention resolution fails E-DCH reception is stopped. 
     
     
         6 . The method of  claim 1 , further comprising:
 setting a back-off timer if the contention resolution fails; and   starting a random access procedure after expiration of the back-off timer.   
     
     
         7 . The method of  claim 1 , wherein a MAC-STATUS-Ind primitive indicates the contention resolution failure, indicating a transmission was unsuccessful due to collision. 
     
     
         8 . The method of  claim 1 , wherein a RACH preamble is transmitted using a reserved physical random access channel (PRACH) resource if the contention resolution fails. 
     
     
         9 . The method of  claim 1 , wherein when the contention resolution fails a hybrid automatic repeat request (HARQ) buffer is flushed. 
     
     
         10 . The method of  claim 1 , wherein a physical layer controls transmission of radio resource control (RRC) messages after the contention resolution fails. 
     
     
         11 . The method of  claim 1 , wherein when the contention resolution fails, indicating contention resolution failure to a higher layer. 
     
     
         12 . A wireless transmit/receive unit (WTRU) comprising:
 a processor configured to:
 enter a contention resolution phase; and 
 if contention resolution fails because no E-DCH absolute grant channel (E-AGCH) with a WTRU's E-DCH radio network temporary identifier (E-RNTI) is received within a period of time, reset an MAC-i/is entity. 
   
     
     
         13 . The WTRU of  claim 12 , wherein the processor is further configured to:
 initiate an enhanced dedicated channel (E-DCH) transmission on an assigned E-DCH resource;   enter the contention resolution phase upon transmission of data using the assigned E-DCH resource; and   release the assigned E-DCH resource if contention resolution fails because no E-AGCH with a WTRU's E-RNTI is received within the period of time.   
     
     
         14 . The WTRU of  claim 13 , further comprising a physical layer entity configured to request access to the assigned E-DCH resource. 
     
     
         15 . The WTRU of  claim 13 , wherein en the contention resolution fails, the WTRU is configured to stop the E-DCH transmission. 
     
     
         16 . The WTRU of  claim 12 , wherein when the contention resolution fails, the WTRU is configured to stop E-DCH reception. 
     
     
         17 . The WTRU of  claim 12 , wherein the processor is further configured to set a back-off timer if the contention resolution fails, and start a random access procedure after expiration of the back-off timer. 
     
     
         18 . The WTRU of  claim 12 , wherein the processor is further configured to initiate a physical random access channel (PRACH) code selection if a maximum number of consecutive contention resolution failures occur. 
     
     
         19 . The WTRU of  claim 12 , wherein the processor is further configured to transmit a RACH preamble using a reserved physical random access channel (PRACH) resource if the contention resolution fails. 
     
     
         20 . The WTRU of  claim 12 , wherein a MAC-STATUS-Ind primitive indicates the contention resolution failure, indicating a transmission was unsuccessful due to collision, 
     
     
         21 . The WTRU of  claim 12 , wherein when the contention resolution fails, the WTRU is configured to flush a hybrid automatic repeat request (HARQ) buffer. 
     
     
         22 . The WTRU of  claim 12 , wherein when the contention resolution fails, the WTRU is configured to indicate contention resolution failure to a higher layer.