Method and apparatus for accessing an uplink random access channel in a single 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:
perform a cell search;
obtain control information in response to the cell search;
establish a preamble transmission power level used to transmit a random access preamble over a Random Access Channel (RACH);
transmit the random access preamble using single carrier frequency division multiple access (SC-FDMA) in accordance with the obtained control information over the RACH on a set of consecutive resource blocks carrying the RACH;
monitor for a received response to the random access preamble, which includes at least a resource allocation; and
transmit a random access message including an identifier of the WTRU using the SC-FDMA utilizing resources derived from at least the resource allocation.
2. The WTRU of claim 1 , wherein:
the processor, which is configured to monitor for the resource allocation, further monitors for a timing advance; and
the transmitter is configured to transmit the random access message with a timing derived from the timing advance.
3. The WTRU of claim 1 , wherein:
the processor, which is configured to monitor for the resource allocation, further monitors for a power command; and
the transmitter is configured to transmit the random access message with a transmission power level derived from the power command.
4. A method implemented by a wireless transmit/receive unit (WTRU), the method comprising:
performing a cell search;
obtaining control information in response to the cell search;
establishing a preamble transmission power level used to transmit a random access preamble over a Random Access Channel (RACH);
transmitting the random access preamble, using single carrier frequency division multiple access (SC-FDMA) in accordance with the obtained control information over the RACH on a set of consecutive resource blocks carrying the RACH;
monitoring for a received response to the random access preamble, which includes at least a resource allocation; and
transmitting a random access message including an identifier of the WTRU, using the SC-FDMA utilizing resources derived from at least the resource allocation.
5. The method of claim 4 , wherein:
the monitoring for the received response includes monitoring for a timing advance in the received response; and
the transmitting of the random access message includes transmitting the random access message with a timing derived from the timing advance.
6. The method of claim 4 , wherein:
the monitoring for the received response includes monitoring for a power command in the received response; and
the transmitting of the random access message includes transmitting the random access message with a transmission power level derived from the power command.