Method and apparatus for accessing a random access channel by selectively using dedicated or contention-based preambles
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.
1. A wireless transmit/receive unit (WTRU) comprising:
a transmitter; and
a processor configured to:
receive, via the transmitter, configuration information comprising an indication of non-contention-based random access channel (RACH) resources;
determine a time period, wherein the WTRU is allowed to attempt RACH access using the non-contention-based RACH resources indicated in the configuration information during the time period;
attempt a first RACH access during the time period, wherein the first RACH access is attempted using the non-contention-based RACH resources based on the first RACH access being attempted during the time period;
determine that the time period has ended; and
attempt a second RACH access after the time period has ended, wherein the second RACH access is attempted using contention-based RACH resources based on the second RACH access being attempted after the time period has ended.
2. The WTRU of claim 1 , wherein the processor configured to attempt the first RACH access is further configured to:
transmit, via the transmitter, one or more dedicated non-contention-based RACH preambles in accordance with the received configuration information.
3. The WTRU of claim 2 , wherein the processor being configured to transmit one or more dedicated non-contention-based RACH preambles in accordance with the received configuration information is configured to:
transmit, via the transmitter, the one or more dedicated non-contention-based RACH preambles in a subset of available RACH opportunities.
4. The WTRU of claim 2 , wherein the indication of the non-contention-based RACH resources comprised in the configuration information comprises an indication of the one or more dedicated non-contention-based RACH preambles.
5. The WTRU of claim 4 , wherein the indication of the non-contention-based RACH resources comprised in the configuration information comprises an indication of a subset of available RACH opportunities for attempting RACH access using the one or more dedicated non-contention-based RACH preambles.
6. The WTRU of claim 1 , wherein the processor configured to attempt the second RACH access is further configured to:
transmit, via the transmitter, a contention-based RACH preamble.
7. The WTRU of claim 1 , wherein the processor is configured to receive the configuration information from an evolved Node B (eNB).
8. The WTRU of claim 1 , wherein the processor configured to attempt the first RACH access is further configured to:
transmit, via the transmitter, a dedicated non-contention-based RACH preamble in a subset N out of M available random access opportunities.
9. The WTRU of claim 1 , wherein the processor is configured to attempt the first RACH access and the second RACH access during a handover procedure for handover to a target cell.
10. The WTRU of claim 1 , wherein the processor is configured to:
use the contention-based RACH resources if the second RACH access is successful; and
continue using the contention-based RACH resources until a third RACH access attempt is initiated using the non-contention-based RACH resources.
11. A method comprising:
receiving configuration information comprising an indication of non-contention-based random access channel (RACH) resources;
determine a time period, wherein a wireless transmit/receive unit (WTRU) is allowed to attempt RACH access using the non-contention-based RACH resources indicated in the configuration information during the time period;
attempting a first RACH access during the time period, wherein the first RACH access is attempted using the non-contention-based RACH resources based on the first RACH access being attempted during the time period;
determining that the time period has ended; and
attempting a second RACH access after the time period has ended, wherein the second RACH access is attempted using contention-based RACH resources based on the second RACH access being attempted after the time period has ended.
12. The method of claim 11 , wherein attempting the first RACH access comprises:
transmitting one or more dedicated non-contention-based RACH preambles in accordance with the received configuration information.
13. The method of claim 12 , wherein transmitting one or more dedicated non-contention-based RACH preambles in accordance with the received configuration information comprises:
transmitting the one or more dedicated non-contention-based RACH preambles in a subset of available RACH opportunities.
14. The method of claim 12 , wherein the indication of the non-contention-based RACH resources comprised in the configuration information comprises an indication of the one or more dedicated non-contention-based RACH preambles.
15. The method of claim 14 , wherein the indication of the non-contention-based RACH resources comprised in the configuration information comprises an indication of a subset of available RACH opportunities for attempting RACH access using the one or more dedicated non-contention-based RACH preambles.
16. The method of claim 11 , wherein attempting the second RACH access comprises:
transmitting a contention-based RACH preamble.
17. The method of claim 11 , wherein the configuration information is received from an evolved Node B (eNB).
18. The method of claim 11 , wherein attempting the first RACH access comprises:
transmitting a dedicated non-contention-based RACH preamble in a subset N out of M available random access opportunities.
19. The method of claim 11 , wherein the first RACH access and the second RACH access are attempted during a handover procedure for handover to a target cell.
20. The method of claim 11 , further comprising:
using the contention-based RACH resources if the second RACH access was successful; and continue using the contention-based RACH resources until a third RACH access attempt is initiated using the non-contention-based RACH resources.