Method and apparatus for obtaining uplink timing alignment on a secondary cell

A method performed by an evolved Node B (eNodeB), the method comprising:

• transmitting, on a primary cell (PCell), a physical downlink control channel (PDCCH) order to a wireless transmit receive unit (WTRU), wherein the PDCCH order includes a carrier indicator field indicating a secondary cell (SCell) to transmit a physical random access channel (PRACH) transmission and the PDCCH order is transmitted using a downlink control information (DCI) format 1A;
• receiving the PRACH transmission from the WTRU on the indicated SCell, wherein on a condition that the PRACH transmission coincides with a scheduled sounding reference signal (SRS) transmission of the WTRU, receiving the PRACH transmission alone or in combination with the SRS transmission;
• and
• transmitting, in response to the PRACH transmission received on the secondary cell, on the PCell, a random access response (RAR), wherein the RAR includes a timing advance to adjust a timing of the WTRU for the SCell.

A method for uplink timing alignment in a wireless transmit/receive unit (WTRU), the method comprising:

• receiving on a primary cell (PCell), a physical downlink control channel (PDCCH) order;
• wherein the PDCCH order includes a carrier indicator field indicating a secondary cell (SCell) to transmit a physical random access channel (PRACH) transmission and the PDCCH order is received using a downlink control information (DCI) format 1A;
• in response to receiving the PDCCH order:
• on a condition that the PRACH transmission coincides with a scheduled sounding reference signal (SRS) transmission, determining whether to drop the scheduled SRS transmission;
• and
• on a condition a determination is made to drop the scheduled SRS transmission, transmitting the PRACH transmission without the SRS transmission;
• on a condition a determination is made to transmit the scheduled SRS transmission, transmitting the PRACH transmission with the SRS transmission;
• in response to transmitting the PRACH transmission, monitoring the PCell for a random access response (RAR);
• and
• in response to detecting a RAR associated with the PRACH transmission, adjusting a timing for the SCell in accordance with a timing advance included in the detected RAR.

A wireless transmit/receive unit (WTRU) comprising:

• a receiver configured to receive, on a primary cell (PCell), a physical downlink control channel (PDCCH) order;
• wherein the PDCCH order includes a carrier indicator field indicating a secondary cell (SCell) to transmit a physical random access channel (PRACH) transmission and the PDCCH order is received using a downlink control information (DCI) format 1A;
• circuitry, in response to the received PDCCH order, configured to, on a condition that the PRACH transmission coincides with a scheduled sounding reference signal (SRS) transmission, determine whether to drop the scheduled SRS transmission;
• and
• a transmitter configured to, on a condition a determination is made to drop the scheduled SRS transmission, transmit the PRACH transmission without the SRS transmission;
• the transmitter further configured to, on a condition a determination is made to transmit the scheduled SRS transmission, transmit the PRACH transmission with the SRS transmission;
• the receiver and the circuitry configured to, in response to the transmitted PRACH transmission, monitor the PCell for a random access response (RAR);
• and
• the circuitry, in response to detecting a RAR associated with the PRACH transmission, configured to adjust a timing for the SCell in accordance with a timing advance included in the detected RAR.