Listen-before-talk operation in an unlicensed downlink and licensed uplink deployment
Methods, systems, and devices for wireless communications are described. In systems supporting unlicensed downlink and licensed uplink communications, transmitter-based and/or receiver-based listen-before-talk may be implemented. In a transmitter-based scheme, a base station performs listen-before-talk on a downlink unlicensed band to monitor for signals from other base stations. In a first receiver-based scheme, a user equipment may send a clear to send signal on the licensed uplink channel or unlicensed downlink channel to assist a listen-before-talk operation at a serving base station. In a second receiver-based scheme, the user equipment monitors for downlink preamble transmissions from base stations other than a serving base station and reports detected preambles to the serving base station. The base station may schedule the user equipment based on the reported preambles. In some cases, the serving base station may signal other base stations to back off and reduce interference on the unlicensed downlink spectrum.
1. A method for gaining access to a channel of a shared spectrum implemented by a user equipment (UE), comprising:
receiving, from a first base station on an unlicensed downlink carrier, a request to send (RTS) signal for a downlink transmission;
detecting a signal on the unlicensed downlink carrier, wherein the detected signal comprises a preamble of a channel reservation (CR) signal from a second base station;
reporting, to the first base station on a licensed uplink carrier, a preamble detection report indicating the preamble of the detected signal; and
receiving, from the first base station on the unlicensed downlink carrier, the downlink transmission according to scheduling based at least in part on the preamble detection report.
2. The method of claim 1 , further comprising:
monitoring the unlicensed downlink carrier based at least in part on the receiving the RTS signal, wherein the detecting is based at least in part on the monitoring.
3. The method of claim 1 , further comprising:
detecting a network allocation vector (NAV) associated with the detected signal; and
reporting the NAV with the detected signal.
4. The method of claim 1 , wherein the reporting indicates a signal strength associated with the detected signal, a signal duration associated with the detected signal, or a combination thereof.
5. The method of claim 1 , wherein receiving the downlink transmission according to the scheduling based at least in part on the preamble detection report comprises:
receiving the downlink transmission according to the scheduling further based at least in part on the received RTS signal.
6. The method of claim 1 , further comprising:
detecting a reduction in a magnitude of interference from the second base station, wherein the downlink transmission is received according to the scheduling further based at least in part on the reduction in the magnitude of the interference.
7. A user equipment (UE), comprising:
a memory; and
a processor, coupled with the memory, the processor configured to:
receive, from a first base station on an unlicensed downlink carrier, a request to send (RTS) signal for a downlink transmission;
detect a signal on the unlicensed downlink carrier, wherein the detected signal comprises a preamble of a channel reservation (CR) signal from a second base station;
report, to the first base station on a licensed uplink carrier, a preamble detection report indicating the preamble of the detected signal; and
receive, from the first base station on the unlicensed downlink carrier, the downlink transmission according to scheduling based at least in part on the preamble detection report.
8. The UE of claim 7 , wherein the processor is further configured to:
monitor the unlicensed downlink carrier based at least in part on the receiving the RTS signal, wherein the detecting is based at least in part on the monitoring.
9. The UE of claim 7 , wherein the processor is further configured to:
detect a network allocation vector (NAV) associated with the detected signal; and
report the NAV with the detected signal.
10. The UE of claim 7 , wherein the reporting indicates a signal strength associated with the detected signal, a signal duration associated with the detected signal, or a combination thereof.
11. The UE of claim 7 , wherein the processor configured to receive the downlink transmission according to the scheduling based at least in part on the preamble detection report is further configured to:
receive the downlink transmission according to the scheduling further based at least in part on the received RTS signal.
12. The UE of claim 7 , wherein the processor is further configured to:
detect a reduction in a magnitude of interference from the second base station, wherein the downlink transmission is received according to the scheduling further based at least in part on the reduction in the magnitude of the interference.
13. An apparatus for gaining access to a channel of a shared spectrum, comprising:
means for receiving, from a first base station on an unlicensed downlink carrier, a request to send (RTS) signal for a downlink transmission;
means for detecting a signal on the unlicensed downlink carrier, wherein the detected signal comprises a preamble of a channel reservation (CR) signal from a second base station;
means for reporting, to the first base station on a licensed uplink carrier, a preamble detection report indicating the preamble of the detected signal; and
means for receiving, from the first base station on the unlicensed downlink carrier, the downlink transmission according to scheduling based at least in part on the preamble detection report.
14. The apparatus of claim 13 , further comprising:
means for monitoring the unlicensed downlink carrier based at least in part on the receiving the RTS signal, wherein the detecting is based at least in part on the monitoring.
15. The apparatus of claim 13 , further comprising:
means for detecting a network allocation vector (NAV) associated with the detected signal; and
means for reporting the NAV with the detected signal.
16. The apparatus of claim 13 , wherein the reporting indicates a signal strength associated with the detected signal, a signal duration associated with the detected signal, or a combination thereof.
17. The apparatus of claim 13 , wherein the means for receiving the downlink transmission according to the scheduling based at least in part on the preamble detection report comprise:
means for receiving the downlink transmission according to the scheduling further based at least in part on the received RTS signal.
18. The apparatus of claim 13 , further comprising:
means for detecting a reduction in a magnitude of interference from the second base station, wherein the downlink transmission is received according to the scheduling further based at least in part on the reduction in the magnitude of the interference.