Distributed joint access for unlicensed sidelink

1. A method of sidelink wireless communication at a first transmitting device, comprising:

listening to a sidelink channel comprising unlicensed spectrum;

initializing a back-off timer when the sidelink channel is idle;

upon expiration of the back-off timer, if the sidelink channel remains idle, transmitting an initial joint access synchronization signal to synchronize access to the sidelink channel by sidelink devices including the first transmitting device through distributed handshake signaling, wherein the initial joint access synchronization signal comprises an initial duration of time that the sidelink channel is accessible to the sidelink devices;

after transmitting the initial joint access synchronization signal, transmitting a request signal indicating a first requested duration of time for the first transmitting device to utilize the sidelink channel to transmit a sidelink signal;

receiving a confirmation signal indicating availability of the sidelink channel for the first requested duration of time; and

transmitting the sidelink signal over the sidelink channel;

wherein transmitting the initial joint access synchronization signal occurs prior to any of the sidelink devices requesting access to the sidelink channel to communicate sidelink traffic since the initializing of the back-off timer.

2. The method of claim 1 , further comprising:

transmitting one or more additional joint access synchronization signals at periodic intervals after the initial joint access synchronization signal, wherein the one or more additional joint access synchronization signals each comprise a respective remaining duration of time that the sidelink channel is accessible to the sidelink devices.

3. The method of claim 2 , wherein transmitting the one or more additional joint access synchronization signals further comprises:

calculating the remaining duration of time for a current joint access synchronization signal of the one or more additional joint access synchronization signals based on the initial duration of time of the initial joint access synchronization signal and an amount of lapsed time since transmitting the initial joint access synchronization signal.

4. The method of claim 2 , wherein transmitting the one or more additional joint access synchronization signals at periodic intervals further comprises:

transmitting the one or more additional joint access synchronization signals at periodic intervals corresponding to a number of slots.

5. The method of claim 4 , wherein transmitting the one or more additional joint access synchronization signals at periodic intervals corresponding to a number of slots further comprises:

transmitting an additional joint access synchronization signal of the one or more additional joint access synchronization signals each slot.

6. The method of claim 1 , further comprising:

receiving an additional request signal at the first transmitting device, the additional request signal indicating an additional requested duration of time overlapping the first

requested duration of time for an additional transmitting device of the one or more sidelink devices to utilize the sidelink channel to transmit an additional sidelink signal.

7. The method of claim 1 , further comprising:

freezing the back-off timer when the sidelink channel becomes busy.

8. The method of claim 1 , further comprising:

canceling the back-off timer upon receiving a received initial joint access synchronization signal during a back-off time set by the back-off timer.

9. An apparatus for sidelink wireless communication, the apparatus comprising:

a processor;

a transceiver communicatively coupled to the processor; and

a memory communicatively coupled to the processor, wherein the processor is configured to:

listen to a sidelink channel comprising unlicensed spectrum;

initialize a back-off timer when the sidelink channel is idle;

upon expiration of the back-off timer, if the sidelink channel remains idle, transmit an initial joint access synchronization signal via the transceiver to synchronize access to the sidelink channel by sidelink devices including the apparatus through distributed handshake signaling, wherein the initial joint access synchronization signal comprises an initial duration of time that the sidelink channel is accessible to the sidelink devices;

after transmitting the initial joint access synchronization signal, transmit a request signal indicating a first requested duration of time for the apparatus to utilize the sidelink channel to transmit a sidelink signal via the transceiver;

receive a confirmation signal indicating availability of the sidelink channel for the first requested duration of time via the transceiver; and

transmit the sidelink signal over the sidelink channel via the transceiver;

wherein the initial joint access synchronization signal is transmitted prior to any of the sidelink devices requesting access to the sidelink channel to communicate sidelink traffic since initialization of the back-off timer.

10. The apparatus of claim 9 , wherein the processor is further configured to:

transmit one or more additional joint access synchronization signals at periodic intervals after the initial joint access synchronization signal, wherein the one or more additional joint access synchronization signals each comprise a respective remaining duration of time that the sidelink channel is accessible to the sidelink devices.

11. The apparatus of claim 10 , wherein the processor is further configured to:

calculate the remaining duration of time for a current joint access synchronization signal of the one or more additional joint access synchronization signals based on the initial duration of time of the initial joint access synchronization signal and an amount of lapsed time since transmitting the initial joint access synchronization signal.

12. The apparatus of claim 10 , wherein the processor is further configured to:

transmit the one or more additional joint access synchronization signals at periodic intervals corresponding to a number of slots.

13. The apparatus of claim 9 , wherein the processor is further configured to:

freeze the back-off timer when the sidelink channel becomes busy; and

cancel the back-off timer upon receiving a received initial joint access synchronization signal during a back-off time set by the back-off timer.

14. An apparatus for sidelink wireless communication, the apparatus comprising:

means for listening to a sidelink channel comprising unlicensed spectrum;

means for initializing a back-off timer when the sidelink channel is idle; and

upon expiration of the back-off timer, if the sidelink channel remains idle, means for transmitting an initial joint access synchronization signal to synchronize access to the sidelink channel by sidelink devices including the apparatus through distributed handshake signaling, wherein the initial joint access synchronization signal comprises an initial duration of time that the sidelink channel is accessible to the sidelink devices;

after transmitting the initial joint access synchronization signal, means for transmitting a request signal indicating a first requested duration of time for the apparatus to utilize the sidelink channel to transmit a sidelink signal;

means for receiving a confirmation signal indicating availability of the sidelink channel for the first requested duration of time; and

means for transmitting the sidelink signal over the sidelink channel;

wherein transmitting the initial joint access synchronization signal occurs prior to any of the sidelink devices requesting access to the sidelink channel to communicate sidelink traffic since the initializing of the back-off timer.

15. The apparatus of claim 14 , further comprising:

means for transmitting one or more additional joint access synchronization signals at periodic intervals after the initial joint access synchronization signal, wherein the one or more additional joint access synchronization signals each comprise a respective remaining duration of time that the sidelink channel is accessible to the sidelink devices.

16. The apparatus of claim 15 , wherein the means for transmitting the one or more additional joint access synchronization signals further comprises:

means for calculating the remaining duration of time for a current joint access synchronization signal of the one or more additional joint access synchronization signals based on the initial duration of time of the initial joint access synchronization signal and an amount of lapsed time since transmitting the initial joint access synchronization signal.

17. The apparatus of claim 15 , wherein the means for transmitting the one or more additional joint access synchronization signals at periodic intervals further comprises:

means for transmitting the one or more additional joint access synchronization signals at periodic intervals corresponding to a number of slots.

18. The apparatus of claim 14 , further comprising:

means for freezing the back-off timer when the sidelink channel becomes busy; and

means for canceling the back-off timer upon receiving a received initial joint access synchronization signal during a back-off time set by the back-off timer.

19. A non-transitory computer-readable medium storing computer executable code, which when executed by a processor, causes an apparatus for sidelink wireless communication to:

listen to a sidelink channel comprising unlicensed spectrum;

initialize a back-off timer when the sidelink channel is idle; and

upon expiration of the back-off timer, if the sidelink channel remains idle, transmit an initial joint access synchronization signal to synchronize access to the sidelink channel by sidelink devices including the apparatus through distributed handshake signaling, wherein the initial joint access synchronization signal comprises an initial duration of time that the sidelink channel is accessible to the sidelink devices;

after transmitting the initial joint access synchronization signal, transmit a request signal indicating a first requested duration of time for the apparatus to utilize the sidelink channel to transmit a sidelink signal;

receive a confirmation signal indicating availability of the sidelink channel for the first requested duration of time; and

transmit the sidelink signal from the transmitting device over the sidelink channel;

wherein transmitting the initial joint access synchronization signal occurs prior to any of the sidelink devices requesting access to the sidelink channel to communicate sidelink traffic since the initializing of the back-off timer.

20. The non-transitory computer-readable medium of claim 19 , further comprising computer executable code, which when executed by the processor, causes the apparatus to:

transmit one or more additional joint access synchronization signals at periodic intervals after the initial joint access synchronization signal, wherein the one or more additional joint access synchronization signals each comprise a respective remaining duration of time that the sidelink channel is accessible to the sidelink devices.

21. The non-transitory computer-readable medium of claim 20 , further comprising computer executable code, which when executed by the processor, causes the apparatus to:

transmit the one or more additional joint access synchronization signals at periodic intervals corresponding to a number of slots.

22. The non-transitory computer-readable medium of claim 19 , further comprising computer executable code, which when executed by the processor, causes the apparatus to:

freeze the back-off timer when the sidelink channel becomes busy; and

cancel the back-off timer upon receiving a received initial joint access synchronization signal during a back-off time set by the back-off timer.