Method and apparatus for accessing a random access channel by selectively using dedicated or contention-based preambles during handover

• US 8,649,353 B2
• Filed: 02/25/2009
• Issued: 02/11/2014
• Est. Priority Date: 03/04/2008
• Status: Active Grant

• Current Assignee: InterDigital Patent Holdings, Inc. (InterDigital, Inc.)
• Original Assignee: InterDigital Patent Holdings, Inc. (InterDigital, Inc.)
• Inventors: Zhang, Guodong, Wang, Jin
• Primary Examiner(s): Wong, Warner
• Application Number:
  US12/392,235
• Publication Number:
  US 20090285180A1
• Time in Patent Office: 1,812 Days
• Field of Search: 370/329, 370/331, 370/431, 370/252, 370/310.2, 370/328, 370/338, 370/395.4, 370464-465, 455/436
• US Class Current: 370/331
• CPC Class Codes: H04W 36/0005 Control or signalling for completing the hand-off
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 74/004 in the uplink, i.e. towards network
• CPC Class Codes: H04W 74/0833 Random access procedures, e.g. with 4-step access
• CPC Class Codes: H04W 74/0866 using a dedicated channel for access
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A method and apparatus for accessing a random access channel (RACH) during handover are disclosed. A handover procedure is initiated and a maximum handover interruption timer is activated. A dedicated preamble is transmitted in an attempt to access the RACH on a condition that the dedicated preamble is reserved in a current random access opportunity and the maximum handover interruption timer has not expired. A contention-based preamble is transmitted in an attempt to access the RACH on a condition that a dedicated preamble is not reserved in a current random access opportunity. If the maximum handover interruption timer has expired, a contention-based preamble is transmitted in an attempt to access the RACH.

Claims

1. A method implemented in a wireless transmit/receive unit (WTRU) for random access during handover, the method comprising:

initiating a handover procedure;

receiving preamble configuration information including an indication of a dedicated preamble and a dedicated preamble period, wherein the dedicated preamble is used for random access in a cell during available random access channel (RACH) opportunities of the dedicated preamble period;

receiving a dedicated preamble reservation, wherein the dedicated preamble reservation indicates a subset of the available RACH opportunities of the dedicated preamble period during which the dedicated preamble is reserved for the WTRU; and

transmitting the dedicated preamble during a RACH opportunity selected from the subset of the available RACH opportunities of the dedicated preamble period based on the dedicated preamble reservation.

2. The method of claim 1 further comprising:

determining that a maximum handover interruption timer has expired; and

transmitting a contention-based preamble.

5. The method of claim 1, further comprising:

activating a maximum handover interruption timer in the WTRU; and

transmitting the dedicated preamble on a condition that the maximum handover interruption timer has not expired.

6. The method of claim 5, wherein the dedicated preamble period ends when the maximum handover interruption timer has expired.

7. The method of claim 1, wherein the available RACH opportunities of the dedicated preamble period is an integer M number of RACH opportunities and the subset of the available RACH opportunities of the dedicated preamble period is an integer N number of RACH opportunities, wherein N is less than M.

8. The method of claim 1, further comprising:

a second WTRU receiving a different dedicated preamble reservation, wherein the different dedicated preamble reservation indicates a different subset of RACH opportunities of the dedicated preamble period;

the second WTRU transmitting the dedicated preamble during a RACH opportunity selected from the different subset of RACH opportunities of the dedicated preamble period based on the different dedicated preamble reservation.

9. The method of claim 1, wherein the preamble configuration information is common to all WTRUs of a cell, and wherein the dedicated preamble reservation is only for a single WTRU of the cell.

3. A wireless transmit/receive unit (WTRU), the WTRU comprising:

a processor configured to initiate a handover procedure;

a receiver configured to receive preamble configuration information including an indication of a dedicated preamble and a dedicated preamble period, wherein the dedicated preamble is used for random access in a cell during available random access channel (RACH) opportunities of the dedicated preamble period, and to receive a dedicated preamble reservation, wherein the dedicated preamble reservation indicates a subset of the available RACH opportunities of the dedicated preamble period during which the dedicated preamble is reserved for the WTRU; and

a transmitter configured to transmit the dedicated preamble during a RACH opportunity selected from of the subset of the available RACH opportunities of the dedicated preamble period based on the dedicated preamble reservation.

4. The WTRU of claim 3 wherein the transmitter is configured to transmit a contention-based preamble on a condition that a maximum handover interruption timer has expired.

10. The WTRU of claim 3, further comprising:

a maximum handover interruption timer; and

the transmitter further configured to transmit the dedicated preamble on a condition that the maximum handover interruption timer has not expired.

11. The WTRU of claim 10, wherein the dedicated preamble period ends when the maximum handover interruption timer has expired.

12. The WTRU of claim 3, wherein the available RACH opportunities of the dedicated preamble period is an integer M number of RACH opportunities and the subset of the available RACH opportunities of the dedicated preamble period is an integer N number of RACH opportunities, wherein N is less than M.

13. The WTRU of claim 3, wherein the preamble configuration information is common to all WTRUs of a cell, and wherein the dedicated preamble reservation is only for a single WTRU of the cell.

14. A method for managing random access of wireless transmit/receive units (WTRUs) in a cell, the method comprising:

transmitting preamble configuration information including an indication of a dedicated preamble and a dedicated preamble period, wherein the dedicated preamble is used for random access channel (RACH) access in the cell during available random access channel (RACH) opportunities of the dedicated preamble period; and

transmitting a first dedicated preamble reservation to a first WTRU, wherein the first dedicated preamble reservation indicates a first subset of the available RACH opportunities of the dedicated preamble period during which the dedicated preamble is reserved for the first WTRU.

15. The method of claim 14, further comprising receiving the dedicated preamble from the first WTRU during a RACH opportunity selected from the first subset of the available RACH opportunities of the dedicated preamble period.

16. The method of claim 14, further comprising transmitting a second dedicated preamble reservation to a second WTRU, wherein the second dedicated preamble reservation indicates a second subset of the available RACH opportunities of the dedicated preamble period different than the first subset during which the dedicated preamble is reserved for the second WTRU.

17. The method of claim 16, further comprising receiving the dedicated preamble from the second WTRU during a RACH opportunity of selected from the second subset of the available RACH opportunities of the dedicated preamble period.

18. The method of claim 14, wherein the available RACH opportunities of the dedicated preamble period is an integer M number of RACH opportunities and the subset of the available RACH opportunities of the dedicated preamble period is an integer N number of RACH opportunities, wherein N is less than M.

19. The method of claim 14, wherein the preamble configuration information is common to all WTRUs of a cell, and wherein the first dedicated preamble reservation is only for the first WTRU.

20. The method of claim 16, wherein the preamble configuration information is common to all WTRUs of a cell, and wherein the second dedicated preamble reservation is only for the second WTRU.

21. A method implemented in a wireless transmit/receive unit (WTRU) for random access during handover, the method comprising:

receiving a handover command, the handover command having dedicated preamble configuration information including an indication of a dedicated preamble and an indication of random access channel (RACH) opportunities during which the dedicated preamble is reserved for the WTRU;

initiating a timer in response to the handover command;

transmitting, on a condition that the timer has not expired, the indicated dedicated preamble during a RACH opportunity selected from the indicated RACH opportunities for the dedicated preamble; and

transmitting, subsequent to expiration of the timer and on a condition that RACH access using the dedicated preamble was not successful, a contention based preamble during a RACH opportunity selected from RACH opportunities for the contention based preamble.

22. The method of claim 21, wherein the transmitting the indicated dedicated preamble further includes transmitting the indicated dedicated preamble interleaved over the time domain with at least one other WTRU.

23. The method of claim 21, wherein the indicated dedicated preamble is not reserved for the WTRU in every frame.

24. A wireless transmit/receive unit (WTRU), the WTRU comprising:

a receiver configured to receive a handover command, the handover command having dedicated preamble configuration information including an indication of a dedicated preamble and an indication of random access channel (RACH) opportunities during which the dedicated preamble is reserved for the WTRU;

a timer configured to initiate in response to the handover command; and

a transmitter configured to;

transmit, on a condition that the timer has not expired, the indicated dedicated preamble during a RACH opportunity selected from the indicated RACH opportunities for the dedicated preamble; and

transmit, subsequent to expiration of the timer and on a condition that RACH access using the dedicated preamble was not successful, a contention based preamble during a RACH opportunity selected from RACH opportunities for the contention based preamble.

25. The WTRU of claim 24, wherein the transmitter is further configured to transmit, on a condition that the timer has not expired, the indicated dedicated preamble interleaved over the time domain with at least one other WTRU.

26. The WTRU of claim 24, wherein the indicated dedicated preamble is not reserved for the WTRU in every frame.