METHOD AND APPARATUS FOR PHYSICAL RANDOM ACCESS CHANNEL (PRACH) TRANSMISSION

1 . A user equipment (UE) used for wireless communication, the UE comprising:

a transceiver; and

a processor, wherein the transceiver and the processor are configured to:

transmit at least one preamble, wherein the at least one preamble is associated with L1 reference signal (RS) resources;

determine an RS resource from L1 RS resources such that:

on a condition that L1 equals 1 , the RS resource is a single L1 RS resource, and

on a condition that L1 is greater than 1 and no two of the L1 RS resources are quasi co-located (QCL) with each other, the RS resource is determined by default; and

in response to transmitting the at least one preamble, monitor and receive a first physical downlink control channel (PDCCH) in a time window, wherein the first PDCCH is QCL with the RS resource.

2 . The UE of claim 1 , wherein the transceiver and the processor are further configured to:

receive a signaling including a radio resource control (RRC) message; and

configure the RS resource based on the signaling.

3 . The UE of claim 1 , wherein the transceiver and the processor are further configured to:

monitor a second PDCCH in a CORESET,

wherein the second PDCCH in the CORESET is QCL with the RS resource.

4 . The UE of claim 1 , wherein the transceiver and the processor are further configured to:

transmit a preamble group comprising one or more preambles; and

in response to transmitting the preamble group, receive, before the at least one preamble, a wireless signal

indicating that a random access procedure is successful, wherein the RS resource is associated with the preamble group.

5 . The UE of any one of claim 1 , wherein the transceiver and the processor are further configured to:

receive a third PDCCH before the at least one preamble is sent, wherein the third PDCCH is scrambled by a cell radio network temporary identifier (C-RNTI); and

determine the RS resource based on the third PDCCH.

6 . The UE of claim 1 , wherein the RS resource is determined by default comprises:

the RS resource does not change with the L1 RS resources.

7 . The UE of claim 1 , wherein a triggering event of the at least one preamble is a first event, and wherein the first event is any candidate event in a first candidate event set, and wherein the first candidate event set comprises initial access.

8 . A base station used for wireless communication, the base station comprising:

a transceiver; and

a processor, wherein the transceiver and the processor are configured to:

receive at least one preamble associated with L1 reference signal (RS) resources; and

in response to receiving the at least one preamble, transmit a first physical downlink control channel (PDCCH);

quasi co-located (QCL) with a RS resource,

wherein on a condition that L1 equals 1, the RS resource is a single L1 RS resource, and

wherein on a condition that L1 is greater than 1 and no two of the L1 RS resources are QCL with each other, the RS resource is determined by default.

9 . A method used in user equipment (UE) for wireless communication, the method comprising:

transmitting at least one preamble, wherein the at least one preamble is associated with L1 reference signal (RS) resources;

determining an RS resource from L1 RS resources such that:

on a condition that L1 equals 1 , the RS resource is a single L1 RS resource, and

on a condition that L1 is greater than 1 and no two of the L1 RS resources are quasi co-located (QCL) with each other, the RS resource is determined by default; and

in response to transmitting the at least one preamble, monitoring and receiving a physical downlink control channel (PDCCH) in a time window, wherein the PDCCH is QCL with the RS resource.

10 . (canceled)