Reference signal transmission techniques for random access messages
Methods, systems, and devices for wireless communications are described for a two-step random access channel (RACH) procedure in which uplink random access preamble and message transmission occasions may span multiple transmission slots. Reference signal resources for transmitting a reference signal with a first random access message of the two-step RACH procedure may include at least one symbol in each of the multiple transmission slots. The reference signal resources, reference signal sequence, or both, may be identified based on a particular uplink random access message transmission occasion, random access preamble transmission occasion, random access preamble sequence configuration, or any combinations thereof.
1. A method for wireless communication at a user equipment (UE), comprising:
receiving system information from a base station, the system information including an indication of two or more available uplink shared channel transmission occasions for a random access message transmission from the UE;
selecting a first uplink shared channel transmission occasion of the two or more available uplink shared channel transmission occasions for transmission of a first random access message, wherein the first uplink shared channel transmission occasion spans at least two transmission slots;
determining, based at least in part on the system information and the first uplink shared channel transmission occasion, reference signal resources within the first uplink shared channel transmission occasion for transmitting a reference signal with the first random access message, wherein the reference signal resources are associated with the first uplink shared channel transmission occasion and include at least one symbol in each of the at least two transmission slots;
formatting the first random access message based at least in part on the selected first uplink shared channel transmission occasion and the determined reference signal resources, the first random access message including the reference signal and uplink shared channel data; and
transmitting the first random access message to the base station.
2. The method of claim 1 , further comprising:
determining a random access preamble for transmission with the first random access message; and
determining a reference signal sequence for the reference signal based at least in part on the random access preamble.
3. The method of claim 2 , wherein the reference signal is a demodulation reference signal, and wherein the reference signal resources in each of the two or more transmission slots are front-loaded in each of the at least two transmission slots, are distributed in each of the at least two transmission slots, or combinations thereof.
4. The method of claim 1 , wherein the formatting further comprises:
applying a cover code to the reference signal that is associated with the UE.
5. The method of claim 4 , wherein the formatting further comprises:
determining the cover code based at least in part on a codebook indicated by the system information, and wherein the cover code spans all of the reference signal resources in each of the at least two transmission slots.
6. The method of claim 4 , wherein the formatting further comprises:
determining separate cover codes associated with each of the at least two transmission slots based at least in part on different codebooks associated with each of the at least two transmission slots.
7. The method of claim 6 , wherein the different codebooks are each associated with different subsets of the two or more available uplink shared channel transmission occasions.
8. The method of claim 4 , wherein the cover code is applied separately or jointly across frequency domain resources associated with the two or more available uplink shared channel transmission occasions.
9. The method of claim 1 , wherein the UE is in a radio resource control (RRC) connected state and the system information is received via RRC signaling.