Channel access mechanism for random access channel in unlicensed spectrum

1. A method for wireless communications occurring in an unlicensed spectrum for accessing a network, the method comprising:

transmitting in a random access procedure, by an apparatus, a first message in a random access channel (RACH) resource using a contention window size (CWS), the first message including a random access preamble;

maintaining in the random access procedure, by the apparatus, the CWS for a listen-before-talk (LBT) category 4 (CAT 4) contention procedure or type 1 UL channel access procedure for an uplink (UL) transmission subsequent to the first message, the UL transmission to be based on receipt of a second message to be received from a base station during a specified message reception time window; and

transmitting, by the apparatus, the UL transmission using the CWS.

2. The method of claim 1 , further comprising:

receiving, by the apparatus, the second message from the base station in the specified message reception time window that includes a UL grant for the UL transmission and an indication that the apparatus is to use the LBT CAT 4 contention procedure for a subsequent UL transmission;

in response to information received in the second message, setting, by the apparatus, the CWS for the LBT CAT 4 contention procedure for the subsequent UL transmission of a third message that includes an identification indication for identifying the apparatus; and

transmitting, by the apparatus, the third message.

3. The method of claim 1 ,

wherein the CWS used for the first message is used for all channel access priority classes for a subsequent UL transmission.

4. A method for wireless communications occurring in an unlicensed spectrum for accessing a network comprising:

transmitting, by an apparatus, a first message in a random access channel (RACH) resource, the first message including a random access preamble and using a category 4 (CAT 4) contention procedure having a contention window size (CWS);

receiving, by the apparatus, a second message from a base station that includes an indication that a type of listen-before-talk (LBT) contention procedure to be used for a subsequent uplink (UL) transmission is CAT 4;

maintaining, by the apparatus based on the second message, the CWS for a first UL transmission of the subsequent UL transmission; and

transmitting, by the apparatus, the first UL transmission using the CWS.

5. The method of claim 4 ,

wherein the second message is a random access response (RAR) responding to the first message.

6. The method of claim 5 , wherein the RAR includes a UL grant for the first UL transmission.

7. An apparatus comprising:

one or more processors; and

a non-transitory computer readable storage medium storing programming for execution by the one or more processors, the programming including instructions to cause the apparatus to:

transmit in a random access procedure a first message in a random access channel (RACH) resource using a contention window size (CWS), the first message including a random access preamble;

maintain in the random access procedure the CWS for a listen-before-talk (LBT) category 4 (CAT 4) contention procedure or type 1 UL channel access procedure for an uplink (UL) transmission subsequent to the first message, the UL transmission to be based on receipt of a second message to be received from a base station during a specified message reception time window; and

transmit the UL transmission using the CWS.

8. The apparatus of claim 7 , the programming further including instructions to:

receive the second message from the base station in the specified message reception time window that includes a UL grant for the UL transmission and an indication that the apparatus is to use the LBT CAT 4 contention procedure for a subsequent UL transmission;

in response to information received in the second message, set the CWS for the LBT CAT 4 contention procedure for the subsequent UL transmission of a third message that includes an identification indication for identifying the apparatus; and

transmit the third message.

9. The apparatus of claim 7 ,

wherein the CWS used for the first message is used for all channel access priority classes for a subsequent UL transmission.

10. An apparatus comprising:

one or more processors; and

a non-transitory computer readable storage medium storing programming for execution by the one or more processors, the programming including instructions to cause the apparatus to:

transmit a first message in a random access channel (RACH) resource, the first message including a random access preamble and using a category 4 (CAT 4) contention procedure having a contention window size (CWS);

receive a second message from a base station that includes an indication that a type of listen-before-talk (LBT) contention procedure to be used for a subsequent uplink (UL) transmission is CAT 4;

maintain, based on the second message, the CWS for a first UL transmission of the subsequent UL transmission; and

transmit the first UL transmission using the CWS.

11. The apparatus of claim 10 ,

wherein the second message is a random access response (RAR) responding to the first message.

12. The apparatus of claim 11 , wherein the RAR includes a UL grant for the first UL transmission.

13. A non-transitory computer-readable storage medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform operations comprising:

transmitting in a random access procedure a first message in a random access channel (RACH) resource using a contention window size (CWS), the first message including a random access preamble;

maintaining in the random access procedure the CWS for a listen-before-talk (LBT) category 4 (CAT 4) contention procedure or type 1 UL channel access procedure for an uplink (UL) transmission subsequent to the first message, the UL transmission to be based on receipt of a second message to be received from a base station during a specified message reception time window, wherein the CWS is a CWS used for the first message; and

transmitting the UL transmission using the CWS.

14. The non-transitory computer-readable storage medium of claim 13 , the operations further comprising:

receiving the second message from the base station in the specified message reception time window that includes a UL grant for the UL transmission and an indication that the apparatus is to use the LBT CAT 4 contention procedure for a subsequent UL transmission;

in response to information received in the second message, setting the CWS for the LBT CAT 4 contention procedure for the subsequent UL transmission of a third message that includes an identification indication for identifying the apparatus; and

transmitting the third message.

15. The non-transitory computer-readable storage medium of claim 13 , wherein the CWS used for the first message is used for all channel access priority classes for a subsequent UL transmission.

16. A non-transitory computer-readable storage medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform operations comprising:

transmitting a first message in a random access channel (RACH) resource, the first message including a random access preamble and using a category 4 (CAT 4) contention procedure having a contention window size (CWS);

receiving a second message from a base station that includes an indication that a type of listen-before-talk (LBT) contention procedure to be used for a subsequent uplink (UL) transmission is CAT 4;

maintaining the CWS for a first UL transmission of the subsequent UL transmission based on the second message; and

transmit the first UL transmission using the CWS.

17. The non-transitory computer-readable storage medium of claim 16 , wherein the second message is a random access response (RAR) responding to the first message.

18. The non-transitory computer-readable storage medium of claim 17 , wherein the RAR includes a UL grant for the first UL transmission.