Techniques for large round trip times in random access channel procedures
Methods, systems, and devices for wireless communications are described. A first wireless device may receive, from a second wireless device, a first message of a random access channel procedure. The first message may include a preamble having a cyclic prefix and a set of sequences. The first wireless device may transmit a second message of the random access channel procedure indicating a first timing parameter for subsequent communications between the devices. The first wireless device may transmit a third message to the second wireless device that indicates a second timing parameter. In some cases, the second wireless device may receive control signaling from the first wireless device indicating a timing offset for the first message of the random access channel procedure. The second wireless device may transmit the first message using the timing offset in response to receiving the control signaling.
1. A first wireless device for wireless communications, comprising:
a processor; and
memory coupled to the processor, the processor and memory configured to:
receive a first message of a random access channel procedure from a second wireless device, the first message comprising a preamble having a cyclic prefix and a set of sequences;
transmit a second message of the random access channel procedure to the second wireless device, the second message indicating a first timing parameter for at least a portion of subsequent communications between the first wireless device and the second wireless device, the first timing parameter based at least in part on the preamble of the first message; and
transmit a third message to the second wireless device indicating a second timing parameter.
2. The first wireless device of claim 1 , wherein the first timing parameter corresponds to a first symbol associated with a first sequence of the set of sequences and the second timing parameter corresponds to a second symbol associated with a second sequence of the set of sequences.
3. The first wireless device of claim 1 , wherein, to transmit the third message, the processor and memory are configured to:
retransmit the second message of the random access channel procedure indicating the second timing parameter based at least in part on failing to receive a response to the second message.
4. The first wireless device of claim 3 , wherein the processor and memory are further configured to:
retransmit the second message of the random access channel procedure indicating a third timing parameter based at least in part on failing to receive a response to the third message.
5. The first wireless device of claim 1 , wherein, to transmit the third message, the processor and memory are configured to:
transmit, to the second wireless device, a grant for a retransmission of a response to the second message based at least in part on failing to receive the response to the second message, the grant indicating the second timing parameter.
6. The first wireless device of claim 5 , wherein the processor and memory are further configured to:
transmit a second grant for a second retransmission of the response to the second message based at least in part on failing to receive the response to the third message, the second grant indicating a third timing parameter.
7. The first wireless device of claim 1 , wherein the processor and memory are further configured to:
receive a response to the second message using the second timing parameter, wherein transmitting the third message indicating the second timing parameter is based at least in part on receiving the response to the second message using the second timing parameter.
8. The first wireless device of claim 7 , wherein the third message comprises a last message of the random access channel procedure.
9. The first wireless device of claim 7 , wherein, to receive the response to the second message, the processor and memory are configured to:
attempt to receive the response using the first timing parameter; and
receive the response using the second timing parameter based at least in part on failing to receive the response using the first timing parameter.
10. The first wireless device of claim 7 , wherein, to receive the response to the second message, the processor and memory are configured to:
receive the response using the second timing parameter based at least in part on one or more reference signals of the response.
11. The first wireless device of claim 1 , wherein the processor and memory are further configured to:
communicate one or more messages of the random access channel procedure via dedicated resources based at least in part on the second wireless device being a threshold distance from the first wireless device.
12. A method for wireless communications at a first wireless device, comprising:
receiving a first message of a random access channel procedure from a second wireless device, the first message comprising a preamble having a cyclic prefix and a set of sequences;
transmitting a second message of the random access channel procedure to the second wireless device, the second message indicating a first timing parameter for at least a portion of subsequent communications between the first wireless device and the second wireless device, the first timing parameter based at least in part on the preamble of the first message; and
transmitting a third message to the second wireless device indicating a second timing parameter.
13. The method of claim 12 , wherein the first timing parameter corresponds to a first symbol associated with a first sequence of the set of sequences and the second timing parameter corresponds to a second symbol associated with a second sequence of the set of sequences.
14. The method of claim 12 , wherein transmitting the third message comprises:
retransmitting the second message of the random access channel procedure indicating the second timing parameter based at least in part on failing to receive a response to the second message.
15. The method of claim 14 , further comprising:
retransmitting the second message of the random access channel procedure indicating a third timing parameter based at least in part on failing to receive a response to the third message.
16. The method of claim 12 , wherein transmitting the third message comprises:
transmitting, to the second wireless device, a grant for a retransmission of a response to the second message based at least in part on failing to receive the response to the second message, the grant indicating the second timing parameter.
17. The method of claim 16 , further comprising:
transmitting a second grant for a second retransmission of the response to the second message based at least in part on failing to receive the response to the third message, the second grant indicating a third timing parameter.
18. The method of claim 12 , further comprising:
receiving a response to the second message using the second timing parameter, wherein transmitting the third message indicating the second timing parameter is based at least in part on receiving the response to the second message using the second timing parameter.
19. The method of claim 18 , wherein the third message comprises a last message of the random access channel procedure.
20. The method of claim 18 , wherein receiving the response to the second message comprises:
attempting to receive the response using the first timing parameter; and
receiving the response using the second timing parameter based at least in part on failing to receive the response using the first timing parameter.
21. The method of claim 18 , wherein receiving the response to the second message comprises:
receiving the response using the second timing parameter based at least in part on one or more reference signals of the response.
22. The method of claim 12 , further comprising:
communicating one or more messages of the random access channel procedure via dedicated resources based at least in part on the second wireless device being a threshold distance from the first wireless device.
23. A non-transitory computer-readable medium storing code for wireless communication at a first wireless device, the code comprising instructions executable by one or more processors to:
receive a first message of a random access channel procedure from a second wireless device, the first message comprising a preamble having a cyclic prefix and a set of sequences;
transmit a second message of the random access channel procedure to the second wireless device, the second message indicating a first timing parameter for at least a portion of subsequent communications between the first wireless device and the second wireless device, the first timing parameter based at least in part on the preamble of the first message; and
transmit a third message to the second wireless device indicating a second timing parameter.
24. The non-transitory computer-readable medium of claim 23 , wherein the first timing parameter corresponds to a first symbol associated with a first sequence of the set of sequences and the second timing parameter corresponds to a second symbol associated with a second sequence of the set of sequences.
25. The non-transitory computer-readable medium of claim 23 , wherein the instructions to transmit the third message are executable by the one or more processors to:
retransmit the second message of the random access channel procedure indicating the second timing parameter based at least in part on failing to receive a response to the second message.
26. The non-transitory computer-readable medium of claim 25 , wherein the instructions are further executable by the one or more processors to:
retransmit the second message of the random access channel procedure indicating a third timing parameter based at least in part on failing to receive a response to the third message.
27. A first wireless device for wireless communication, comprising:
means for receiving a first message of a random access channel procedure from a second wireless device, the first message comprising a preamble having a cyclic prefix and a set of sequences;
means for transmitting a second message of the random access channel procedure to the second wireless device, the second message indicating a first timing parameter for at least a portion of subsequent communications between the first wireless device and the second wireless device, the first timing parameter based at least in part on the preamble of the first message; and
means for transmitting a third message to the second wireless device indicating a second timing parameter.
28. The first wireless device of claim 27 , wherein the first timing parameter corresponds to a first symbol associated with a first sequence of the set of sequences and the second timing parameter corresponds to a second symbol associated with a second sequence of the set of sequences.
29. The first wireless device of claim 27 , wherein the means for transmitting the third message comprise:
retransmitting the second message of the random access channel procedure indicating the second timing parameter based at least in part on failing to receive a response to the second message.
30. The first wireless device of claim 29 , further comprising:
means for retransmitting the second message of the random access channel procedure indicating a third timing parameter based at least in part on failing to receive a response to the third message.