METHOD AND APPARATUS FOR PERFORMING AN ENHANCED RANDOM ACCESS CHANNEL PROCEDURE IN A CELL_FACH STATE

• US 20090186624A1
• Filed: 12/30/2008
• Published: 07/23/2009
• Est. Priority Date: 01/04/2008
• Status: Active Grant

• Current Assignee: InterDigital Patent Holdings, Inc. (InterDigital, Inc.)
• Original Assignee: InterDigital Patent Holdings, Inc. (InterDigital, Inc.)
• Inventors: Marinier, Paul, Pani, Diana, Cave, Christopher R., DiGirolamo, Rocco, Pelletier, Benoit
• Granted Patent: US 8,428,014 B2
• Time in Patent Office: Days
• US Class Current: 455/450
• CPC Class Codes: H04L 1/1812 Hybrid protocols; Hybrid automatic repeat request [HARQ]
• CPC Class Codes: H04L 1/1887 Scheduling and prioritising arrangements
• CPC Class Codes: H04W 28/26 Resource reservation
• CPC Class Codes: H04W 72/04 Wireless resource allocation
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 74/0841 with collision treatment
• CPC Class Codes: H04W 74/0866 using a dedicated channel for access

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.

Claims

1. A method for performing an enhanced random access procedure in a Cell_FACH state, the method comprising:

transmitting a random access channel (RACH) preamble;

obtaining an enhanced dedicated channel (E-DCH) resource index in response to the RACH preamble;

entering a contention resolution phase and transmitting a message using an assigned E-DCH resource; and

if contention resolution fails, releasing the E-DCH resource and resetting an MAC-i/is entity.

2. The method of claim 1 wherein a contention resolution failure is detected if the contention resolution is not indicated until a contention resolution timer expires.

3. The method of claim 1 further comprising:

setting a back-off timer if contention resolution fails; and

starting a new enhanced random access procedure after expiration of the back-off timer.

4. The method of claim 3 wherein the back-off timer is same as a legacy RACH back-off timer that is set when a negative acknowledgement is received in response to the RACH preamble.

5. The method of claim 3 further comprising:

reselecting a physical random access channel (PRACH) code after the back-off timer expires; and

retransmitting the RACH preamble using the reselected PRACH code.

6. The method of claim 1 further comprising:

initiating a physical random access channel (PRACH) code selection if a maximum number of consecutive contention resolution failures occur; and

reinitiating an enhanced random access procedure.

7. The method of claim 1 wherein a signature used for transmission of the RACH preamble that resulted in contention resolution failure is removed from a list of available signatures if the contention resolution fails.

8. The method of claim 1 wherein the RACH preamble is retransmitted 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 at least one of following actions is performed:

stopping E-DCH transmission, stopping E-DCH reception, and flushing a hybrid automatic repeat request (HARQ) buffer.

10. The method of claim 1 wherein all data sent to a hybrid automatic repeat request (HARQ) process during the contention resolution phase is stored in a temporary buffer.

11. The method of claim 1 further comprising:

sending a transmission failure indication to a radio link control (RLC) entity if the contention resolution fails; and

triggering retransmission of the message at the RLC entity.

12. The method of claim 11 wherein the contention resolution failure indication is provided implicitly by a transmission success indication after obtaining the E-DCH resource index, followed by a transmission failure indication after the contention resolution failure.

13. The method of claim 11 wherein a transmission success indication is not sent to the RLC entity until the contention resolution succeeds.

14. The method of claim 1 wherein a physical layer controls retransmission of radio resource control (RRC) messages after the contention resolution failure.

15. A wireless transmit/receive unit (WTRU) configured to perform an enhanced random access procedure in a Cell_FACH state, the WTRU comprising:

a physical layer configured to transmit a random access channel (RACH) preamble; and

a medium access control (MAC) entity configured to obtain an enhanced dedicated channel (E-DCH) resource index in response to the RACH preamble, enter a contention resolution phase upon transmission of a message using an assigned E-DCH resource, and if contention resolution fails, release the E-DCH resource and reset an MAC-i/is entity.

16. The WTRU of claim 15 wherein a contention resolution failure is detected if the contention resolution is not indicated until a contention resolution timer expires.

17. The WTRU of claim 15 wherein the MAC entity is configured to set a back-off timer if the contention resolution fails, and start a new enhanced random access procedure after expiration of the back-off timer.

18. The WTRU of claim 17 wherein a physical random access channel (PRACH) code is reselected after the back-off timer expires, and the RACH preamble is retransmitted using the reselected PRACH code.

19. The WTRU of claim 15 wherein the MAC entity is configured to initiate a physical random access channel (PRACH) code selection if a maximum number of consecutive contention resolution failures occur.

20. The WTRU of claim 15 wherein the MAC entity removes a signature used for transmission of the RACH preamble that resulted in contention resolution failure from a list of available signatures if the contention resolution fails.

21. The WTRU of claim 15 wherein the MAC entity is configured to retransmit the RACH preamble using a reserved physical random access channel (PRACH) resource if the contention resolution fails.

22. The WTRU of claim 15 wherein all data sent to a hybrid automatic repeat request (HARQ) process during the contention resolution phase is stored in a temporary buffer.

23. The WTRU of claim 15 further comprising a radio link control (RLC) entity configured to receive a contention resolution failure indication from the MAC entity if the contention resolution fails and retransmit the message.

24. The WTRU of claim 23 wherein the MAC entity is configured to send a transmission success indication to the RLC entity after obtaining the E-DCH resource, and the RLC entity recognized that transmission of the message fails when the transmission failure indication is received.

25. The WTRU of claim 23 wherein the MAC entity is configured to send a transmission success indication to the RLC entity only after the contention resolution succeeds.

26. The WTRU of claim 15 wherein the physical layer is configured to control retransmission of radio resource control (RRC) messages after the contention resolution failure.