Method and apparatus for accessing an uplink random access channel in a singular carrier frequency division multiple access system
A method and apparatus for accessing a contention-based uplink random access channel (RACH) in a single carrier frequency division multiple access (SC-FDMA) system are disclosed. A wireless transmit/receive unit (WTRU) randomly selects a RACH subchannel and a signature among a plurality of available RACH subchannels and signatures. The WTRU transmits a preamble using the selected signature via the selected RACH subchannel at a predetermined or computed transmission power. A base station monitors the RACH to detect the preamble and sends an acquisition indicator (AI) to the WTRU when a signature is detected on the RACH. When receiving a positive acknowledgement, the WTRU sends a message part to the base station. If receiving a negative acknowledgement or no response, the WTRU retransmits the preamble.
1. A wireless transmit/receive unit (WTRU) comprising:
a processor and a transmitter configured to:
transmit a random access preamble, using single carrier frequency division multiple access (SC-FDMA), based on obtained control information;
monitor for a received response to the random access preamble, which includes a timing advance, a power command and a resource allocation; and
transmit a random access message using the SC-FDMA, having a timing derived at least from the timing advance, a transmission power level derived at least from the power command and utilizing resources derived from at least the resource allocation.
2. The WTRU of claim 1 wherein the resource allocation indicates one or more resource blocks to transmit the random access message.
3. The WTRU of claim 1 wherein the one or more resource blocks indicate a plurality of subcarriers to transmit the random access message.
4. The WTRU of claim 3 wherein the indicated subcarriers are consecutive subcarriers or distributed subcarriers.
5. The WTRU of claim 1 wherein the random access preamble is derived from a sequence, the sequence being indicated by the received response.
6. The WTRU of claim 1 wherein the transmitter is configured to transmit the random access preamble including pilot signals.
7. The WTRU of claim 1 wherein the transmitter is configured to transmit the random access preamble having a duration which is variable.
8. The WTRU of claim 1 wherein the transmitter is configured to transmit a subsequent random access preamble at an increased power level relative to a previously transmitted random access preamble.
9. The WTRU of claim 1 , configured to:
perform a cell search; and
obtain the control information thereafter.
10. A method implemented by a wireless transmit/receive unit (WTRU), the method comprising:
transmitting a random access preamble, using single carrier frequency division multiple access (SC-FDMA), based on obtained control information;
monitoring for a received response to the random access preamble, which includes a timing advance, a power command and a resource allocation; and
transmitting a random access message, using the SC-FDMA, having a timing derived at least from the timing advance, a transmission power level derived at least from the power command and utilizing resources derived from at least the resource allocation.
11. The method of claim 10 further comprising
indicating, via the resource allocation, one or more resource blocks to transmit the random access message.
12. The method of claim 11 further comprising:
indicating, via the one or more resource blocks, a plurality of consecutive or distributed subcarriers to transmit the random access message.
13. The method of claim 10 , further comprising deriving the random access preamble from at least a sequence indicated by the received response.
14. The method of claim 10 , further comprising including pilot signals in the random access message.
15. The method of claim 10 , further comprising setting a duration of the random access preamble, wherein the transmitting of the random access preamble includes transmitting the random access preamble of the set duration.
16. The method of claim 10 , further comprising:
performing a cell search; and
obtaining the control information thereafter.