Media access control for license-assisted access

1. A base station, comprising:

a memory comprising a computer program code; and

a processor configured to execute the computer program code to cause the base station to:

perform transmissions on a first communication channel and a second communication channel, wherein the transmissions on the first communication channel are synchronized by a plurality of first subframes, and the transmissions on the second communication channel are synchronized by a plurality of second subframes;

generate a time shift between the plurality of first subframes and the plurality of second subframes;

transmit a request-to-send message over the first communication channel, the request-to-send message indicating that the base station has data to be transmitted to user equipment (UE) over the second communication channel;

receive an indication from the UE that the second communication channel is available for use by the base station; and

in response to receiving the indication, transmit, at a beginning of a next available second subframe after the indication is received, the data to the UE over the second communication channel.

2. The base station of claim 1 , wherein in receiving the indication from the UE that the second communication channel is available for use by the base station, the processor is further configured to execute the computer program code to cause the base station to:

receive a clear-to-send-to-self message over the second communication channel.

3. The base station of claim 1 , wherein in receiving the indication from the UE that the second communication channel is available for use by the base station, the processor is further configured to execute the computer program code to cause the base station to:

receive an OK-to-send message from the UE over the first communication channel.

4. The base station of claim 1 , wherein the processor is further configured to execute the computer program code to cause the base station to:

after the data is transmitted, receive an acknowledgement message from the UE over the first communication channel.

5. The base station of claim 1 , wherein the processor is further configured to execute the computer program code to cause the base station to:

before transmitting the data to the UE over the second communication channel, perform a listen-before-talk (LBT) operation to determine whether the second communication channel is free of communications.

6. The base station of claim 1 , wherein the first communication channel comprises licensed radio resources, and the second communication channel comprises unlicensed radio resources.

7. The base station of claim 6 , wherein the first communication channel comprises a synchronous communication channel, and the second communication channel comprises an asynchronous communication channel.

8. The base station of claim 7 , wherein the first communication channel uses a media access control (MAC) protocol in which transmission resources are scheduled, and the second communication channel uses a MAC protocol that uses a distributed control function.

9. The base station of claim 1 , wherein in transmitting the request-to-send message, the processor is further configured to execute the computer program code to cause the base station to:

transmit the request-to-send message via a control channel on the first communication channel.

10. The base station of claim 1 , wherein the first communication channel uses a Long-Term Evolution (LTE) standard.

11. The base station of claim 1 , wherein the second communication channel uses a Wireless Local Area Network (WLAN) standard.

12. The base station of claim 1 , wherein the base station is an eNodeB (eNB) comprising:

a primary cell (PCell) that communicates using the first communication channel, and

a secondary cell (SCell) that communicates using the second communication channel.

13. The base station of claim 1 , further comprising:

a radio transceiver coupled to the processor.

14. A method performed by a base station, comprising:

performing transmissions on a first communication channel and a second communication channel, wherein the transmissions on the first communication channel are synchronized by a plurality of first subframes, and the transmissions on the second communication channel are synchronized by a plurality of second subframes;

generating a time shift between the plurality of first subframes and the plurality of second subframes;

transmitting a request-to-send message over the first communication channel, the request-to-send message indicating that the base station has data to be transmitted to user equipment (UE) over the second communication channel;

receiving an indication from the UE that the second communication channel is available for use by the base station; and

in response to receiving the indication, transmitting, at a beginning of a next available second subframe after the indication is received, the data to the UE over the second communication channel.

15. The method of claim 14 , wherein receiving the indication from the UE that the second communication channel is available for use by the base station comprises:

receiving a clear-to-send-to-self message over the second communication channel.

16. The method of claim 14 , wherein receiving the indication from the UE that the second communication channel is available for use by the base station comprises:

receiving an OK-to-send message from the UE over the first communication channel.

17. The method of claim 14 , further comprising:

before transmitting the data to the UE over the second communication channel, performing a listen-before-talk (LBT) operation to determine whether the second communication channel is free of communications.

18. The method of claim 14 , wherein the first communication channel comprises licensed radio resources, and the second communication channel comprises unlicensed radio resources.

19. The method of claim 14 , wherein the base station is an eNodeB (eNB) comprising:

a primary cell (PCell) that communicates using the first communication channel, and

a secondary cell (SCell) that communicates using the second communication channel.

20. A non-transitory computer-readable medium comprising a computer program code that, when executed by a processor coupled to a base station, causes the base station to perform operations comprising:

performing transmissions on a first communication channel and a second communication channel, wherein the transmissions on the first communication channel are synchronized by a plurality of first subframes, and the transmissions on the second communication channel are synchronized by a plurality of second subframes;

generating a time shift between the plurality of first subframes and the plurality of second subframes;

transmitting a request-to-send message over the first communication channel, the request-to-send message indicating that the base station has data to be transmitted to user equipment (UE) over the second communication channel;

receiving an indication from the UE that the second communication channel is available for use by the base station; and

in response to receiving the indication, transmitting, at a beginning of a next available second subframe after the indication is received, the data to the UE over the second communication channel.