Method, apparatus, and system for transmitting control channel in unlicensed band

1. A base station of a wireless communication system, the base station comprising:

a communication module; and

a processor,

wherein the processor is configured to:

transmit a radio frame divided into a plurality of subframes by using the communication module, wherein a duration of each of the plurality of subframes is 1 ms,

transmit a radio resource control (RRC) signaling which indicates that a user equipment is required to set up for receiving a partial subframe having a duration shorter than the duration of each of the plurality of subframes in an unlicensed serving cell, and

when the base station transmits a control channel for scheduling data transmitted on the partial subframe in the unlicensed serving cell, start to transmit the control channel at an Orthogonal Frequency Division Multiplexing (OFDM) symbol position at which half of the duration of each of the plurality of subframes elapses from a boundary of one of the plurality of subframes,

wherein the OFDM symbol position at which half of the duration of each of the plurality of subframes elapses from the boundary of one of the plurality of subframes is one of a plurality of OFDM symbol positions for transmitting a reference signal.

2. The base station of claim 1 , wherein the processor is configured to start to transmit the partial subframe at an OFDM symbol position other than the boundary of each of the plurality of subframes.

3. The base station of claim 2 , wherein the control channel schedules only data transmitted later than the control channel.

4. The base station of claim 3 , wherein the processor is configured to transmit at least one of the plurality of subframes in consecutive to the partial subframe.

5. The base station of claim 1 , wherein the reference signal is a signal for estimating a channel state of a cell in which the partial subframe is transmitted.

6. The base station of claim 1 , wherein the processor is configured to transmit a signal for occupying a radio resource before starting to transmit the control channel.

7. The base station of claim 6 , wherein the signal for occupying the radio resource indicates that the transmission of the base station starts.

8. A user equipment of a wireless communication system, the user equipment comprising:

a communication module; and

a processor,

wherein the processor is configured to:

receive a radio frame divided into a plurality of subframes by using the communication module, wherein a duration of each of the plurality of subframes is 1 ms, and

when the user equipment receives a radio resource control (RRC) signaling which indicates that the user equipment is required to set up for receiving a partial subframe in an unlicensed serving cell, monitor, in the unlicensed serving cell, both a control channel starting at a boundary of one of the plurality of subframes and a control channel starting at Orthogonal Frequency Division Multiplexing (OFDM) symbol position at which half of the duration of each of the plurality of subframes elapses from the boundary of one of the plurality of subframes,

wherein the OFDM symbol position at which half of the duration of each of the plurality of subframes elapses from the boundary of one of the plurality of subframes is one of a plurality of OFDM symbol positions for receiving a reference signal, and

wherein the partial subframe has a duration shorter than the duration of each of the plurality of subframes.

9. The user equipment of claim 8 , wherein the processor is configured to start to receive the partial subframe at an OFDM symbol position other than the boundary of each of the plurality of subframes.

10. The user equipment of claim 9 , wherein the control channel schedules only data transmitted later than the control channel.

11. The user equipment of claim 10 , wherein the processor is configured to receive at least one of the plurality of subframes in consecutive to the partial subframe.

12. The user equipment of claim 8 , wherein the reference signal is a signal for estimating a channel state of a cell in which the partial subframe is transmitted.

13. The user equipment of claim 8 , wherein when the user equipment receives the partial subframe, the processor is configured to ignore a signal received prior to the control channel.

14. The user equipment of claim 8 , wherein the control channel schedules data transmitted from a cell other than a cell in which the control channel is transmitted.

15. A method of operating a user equipment of a wireless communication system, the method comprising:

receiving a radio frame divided into a plurality of subframes, wherein a duration of each of the plurality of subframes is 1 ms,

wherein the receiving of the radio frame comprises

when the user equipment receives a radio resource control (RRC) signaling which indicates that the user equipment is required to set up for receiving a partial subframe in an unlicensed serving cell, monitoring, in the unlicensed serving cell, both a control channel starting at a boundary of one of the plurality of subframes and a control channel starting at Orthogonal Frequency Division Multiplexing (OFDM) symbol position at which half of the duration of each of the plurality of subframes elapses from the boundary of one of the plurality of subframes,

wherein the OFDM symbol position at which half of the duration of each of the plurality of subframes elapses from the boundary of one of the plurality of subframes is one of a plurality of OFDM symbol positions for receiving a reference signal, wherein the partial subframe has a duration shorter than the duration of each of the plurality of subframes.