Method and device for performing random access process in unlicensed band
Provided are a method for performing a random access process in an unlicensed band, and a device using the same. The device receives a random access preamble (RAP) order instructing the transmission of a RAP. The device performs a clear channel assessment (CCA) in an unlicensed cell during an RAP window so as to transmit the RAP when the device succeeds in CCA.
1. A method for performing a random access process in an unlicensed band, the method comprising:
receiving, by a wireless device, a random access preamble (RAP) order for instructing a transmission of an RAP;
performing, by the wireless device, clear channel assessment (CCA) during an RAP window in an unlicensed cell;
if the CCA is successful, transmitting, by the wireless device, the RAP;
receiving, by the wireless device, a random access response (RAR) as a response to the RAP, the RAR comprising a timing advance command (TAC);
adjusting, by the wireless device, uplink time alignment in the unlicensed cell based on the TAC and a time point at which the RAP is transmitted,
wherein the adjusting the uplink time alignment in the unlicensed cell includes:
determining an offset based on the time point at which the RAP is transmitted and a reference time point; and
adjusting the uplink time alignment based on the TAC and the offset, and
wherein the reference time point is a pre-defined value.
2. The method of claim 1 , wherein the RAP order includes information regarding the RAP window and a resource used for the transmission of the RAP.
3. The method of claim 2 , wherein the RAP order further includes cell information indicating the unlicensed cell in which the RAP is transmitted.
4. The method of claim 1 , wherein the RAR is received in the unlicensed cell.
5. The method of claim 1 , wherein the RAR includes information regarding a parameter required to perform the CCA for UL transmission in the unlicensed cell.
6. The method of claim 1 , further comprising:
if the CCA is failed by performing the CCA during the RAP window in the unlicensed cell, performing the CCA for transmitting the RAP during a next RAP window.
7. The method of claim 6 , wherein an RAP transmit power is set identically in the RAP window and the next RAP window.
8. A device for performing a random access process in an unlicensed band, the device comprising:
a transceiver configured to transmit and receive a radio signal; and
a processor operatively coupled to the transceiver and configured to:
instruct the transceiver to receive a random access preamble (RAP) order for instructing a transmission of an RAP;
instruct the transceiver to perform clear channel assessment (CCA) during an RAP window in an unlicensed cell;
instruct the transceiver to transmit the RAP if the CCA is successful;
instruct the transceiver to receive a random access response (RAR) as a response to the RAP, the RAR comprising a timing advance command (TAC);
adjust an uplink time alignment in the unlicensed cell based on the TAC and a time point at which the RAP is transmitted;
adjust the uplink time alignment in the unlicensed cell by:
determining an offset based on the time point at which the RAP is transmitted and a reference time point; and
adjusting the uplink time alignment based on the TAC and the offset, and
wherein the reference time point is a pre-defined value.
9. The device of claim 8 , wherein the RAP order includes information regarding the RAP window and a resource used in transmission of the RAP.
10. The device of claim 9 , wherein the RAP order further includes cell information indicating the unlicensed cell in which the RAP is transmitted.