Method and apparatus for channel access in unlicensed band in wireless communication system
Disclosed are: a communication technique for merging, with IoT technology, a 5G communication system for supporting a data transmission rate higher than that of a 4G system; and a system therefor. The present disclosure can be applied to intelligent services (for example, smart home, smart building, smart city, smart car or connected car, healthcare, digital education, retail, security, and safety-related services, and the like) on the basis of 5G communication technology and an IoT-related technology. The present invention relates to a method and an apparatus for channel access in a wireless communication system operating in an unlicensed band. More particularly, disclosed are a method by which a node for transmitting a signal through an unlicensed band determines a channel occupation state of the unlicensed band, and a method for transmitting the signal to the unlicensed band according to the determined channel occupation state of the unlicensed band.
1. A method performed by a base station in a wireless communication system using an unlicensed band, the method comprising:
transmitting, to a terminal, downlink data on the unlicensed band;
receiving, from the terminal, hybrid automatic repeat request-acknowledgement (HARQ-ACK) information, wherein the HARQ-ACK information is for code block groups (CBGs) of the downlink data in response to a transmission of the downlink data being associated with the CBGs;
identifying a size of a contention window for a channel access based on a ratio of acknowledgement (ACK) and negative acknowledgement (NACK) in the HARQ-ACK information for the CBGs of the downlink data in a reference duration and a predetermined threshold value; and
performing a channel sensing based on the identified size of the contention window,
wherein a number of bits included in the HARQ-ACK information corresponds to a number of CBGs configured to the terminal, in case that the transmission of the downlink data is associated with the CBGs, and
wherein, in case that a number of CBGs of the downlink data is smaller than the number of CBGs configured to the terminal, the HARQ-ACK information includes at least a first number of bits indicating NACK value, the first number of bits being a difference between the number of CBGs configured to the terminal and the number of CBGs of the downlink data.
2. The method of claim 1 , wherein the size of the contention window is initialized as a minimum value corresponding to a channel access priority class, in case that the transmission of the downlink data is associated with the CBGs and the ratio of the ACK of the HARQ-ACK information for the CBGs is greater than or equal to the threshold value.
3. The method of claim 2 , wherein the size of the contention window increases to a next higher value of the size of the contention window corresponding to the channel access priority class, in case that the transmission of the downlink data is associated with the CBGs and the ratio of the ACK of the HARQ-ACK information for the CBGs is smaller than the threshold value.
4. The method of claim 1 , wherein, in case that the transmission of the downlink data is associated with a transport block and the HARQ-ACK information includes at least one ACK, the size of the contention window is initialized as a minimum value corresponding to a channel access priority class.
5. The method of claim 4 , wherein, in case that the transmission of the downlink data is associated with the transport block and none of ACK is included in the HARQ-ACK information, the size of the contention window increases to a next higher value of the size of contention window corresponding to the channel access priority class.
6. The method of claim 1 , wherein the ratio of the ACK and the NACK in the HARQ-ACK information for the CBGs is obtained based on HARQ-ACK information corresponding to one or more transmitted CBGs by disregarding HARQ-ACK information corresponding to CBGs which are not transmitted.
7. A method performed by a terminal of a wireless communication system using an unlicensed band, the method comprising:
receiving, from a base station, downlink data on the unlicensed band;
obtaining hybrid automatic repeat request-acknowledgement (HARQ-ACK) information, wherein the HARQ-ACK information is for code block groups (CBGs) of the downlink data in response to a transmission of the downlink data being associated with the CBGs; and
transmitting, to the base station, the HARQ-ACK information,
wherein a size of a contention window for a channel access depends on a ratio of acknowledgement (ACK) and negative acknowledgement (NACK) in the HARQ-ACK information for the CBGs of the downlink data in a reference duration and a predetermined threshold value,
wherein a number of bits included in the HARQ-ACK information corresponds to a number of CBGs configured to the terminal, in case that the transmission of the downlink data is associated with the CBGs, and
wherein, in case that a number of CBGs of the downlink data is smaller than the number of CBGs configured to the terminal, the HARQ-ACK information includes at least a first number of bits indicating NACK value, the first number of bits being a difference between the number of CBGs configured to the terminal and the number of CBGs of the downlink data.
8. A base station in a wireless communication system using an unlicensed band, the base station comprising:
a transceiver; and
a controller coupled with the transceiver, and configured to:
transmit, to a terminal, downlink data on the unlicensed band,
receive, from the terminal, hybrid automatic repeat request-acknowledgement (HARQ-ACK) information, wherein the HARQ-ACK information is for code block groups (CBGs) of the downlink data in response to a transmission of the downlink data being associated with the CBGs,
identify a size of a contention window for a channel access based on a ratio of acknowledgement (ACK) and negative acknowledgement (NACK) in the HARQ-ACK information for the CBGs of the downlink data in a reference duration and a predetermined threshold value, and
perform a channel sensing based on the identified size of the contention window,
wherein a number of bits included in the HARQ-ACK information corresponds to a number of CBGs configured to the terminal, in case that the transmission of the downlink data is associated with the CBGs, and
wherein, in case that a number of CBGs of the downlink data is smaller than the number of CBGs configured to the terminal, the HARQ-ACK information includes at least a first number of bits indicating NACK value, the first number of bits being a difference between the number of CBGs configured to the terminal and the number of CBGs of the downlink data.
9. The base station of claim 8 , wherein the size of the contention window is initialized as a minimum value corresponding to a channel access priority class, in case that the transmission of the downlink data is associated with the CBGs and the ratio of ACK of the HARQ-ACK information for the CBGs is greater than or equal to the threshold value.
10. The base station of claim 9 , wherein the size of the contention window increases to a next higher value of the size of the contention window corresponding to the channel access priority class, in case that the transmission of the downlink data is associated with the CBGs and the ratio of the ACK of the HARQ-ACK information for the CBGs is smaller than the threshold value.
11. The base station of claim 8 , wherein, in case that the transmission of the downlink data is associated with a transport block and the HARQ-ACK information includes at least one ACK, the size of the contention window is initialized as a minimum value corresponding to a channel access priority class.
12. The base station of claim 11 , wherein, in case that the transmission of the downlink data is associated with a transport block and none of ACK is included in the HARQ-ACK information, the size of the contention window increases to a next higher value of the size of contention window corresponding to the channel access priority class.
13. The base station of claim 8 , wherein the ratio of the ACK and the NACK in the HARQ-ACK information for the CBGs is obtained based on HARQ-ACK information corresponding to one or more transmitted CBGs by disregarding HARQ-ACK information corresponding to CBGs which are not transmitted.
14. A terminal in a wireless communication system using an unlicensed band, the terminal comprising:
a transceiver; and
a controller coupled with the transceiver, and configured to:
receive, from a base station, downlink data on the unlicensed band,
obtain hybrid automatic repeat request-acknowledgement (HARQ-ACK) information, wherein the HARQ-ACK information is for code block groups (CBGs) of the downlink data in response to a transmission of the downlink data being associated with the CBGs, and
transmit, to the base station, the HARQ-ACK information,
wherein a size of a contention window for a channel access depends on a ratio of acknowledgement (ACK) and negative acknowledgement (NACK) in the HARQ-ACK information for the CBGs of the downlink data in a reference duration and a predetermined threshold value,
wherein a number of bits included in the HARQ-ACK information corresponds to a number of CBGs configured to the terminal, in case that the transmission of the downlink data is associated with the CBGs, and
wherein, in case that a number of CBGs of the downlink data is smaller than the number of CBGs configured to the terminal, the HARQ-ACK information includes at least a first number of bits indicating NACK value, the first number of bits being a difference between the number of CBGs configured to the terminal and the number of CBGs of the downlink data.