Method and apparatus for supporting two-step random access channel usage in a wireless communication system
Methods and apparatuses related to a two-step RACH procedure are provided. Channel conditions can be estimated based on a UE PRACH transmission rather than the subsequent PUSCH transmission in the first part of the two-step RACH. A variable length gap can be provided between the PRACH preamble transmission and the PUSCH transmission. Other solutions are also provided.
1. A method for channel estimation by a radio access network (RAN) infrastructure node, the method comprising:
receiving, as part of a two-step random access channel (RACH) access procedure, a combination of a message 1 plus a message 3 from a UE; and
estimating channel conditions using characteristics of the message 1 ;
wherein the message 1 includes a physical RACH (PRACH) preamble in a PRACH slot within a first time range spanning a first frequency range, the PRACH preamble selected from a set of PRACH preambles;
wherein the message 3 is a physical uplink shared channel (PUSCH) message in one or more PUSCH slots within a second time range spanning a second frequency, the PUSCH message including a demodulation reference signal (DMRS) symbol pattern selected from a set of DMRS symbol patterns;
wherein one or more of the first frequency range, the first time range, the second time range and the second frequency range are signaled in a parameter set; and
wherein the parameter set includes one or more of PRACH preamble sequences, PRACH formats, power offset, a receive target power of the PRACH preamble and a power ramp step for PRACH preambles.
2. The method according to claim 1 , wherein no two members of the set of DMRS symbol patterns are associated with the same member of the set of PRACH preambles.
3. The method of claim 1 , further comprising:
upon detecting a DMRS collision, estimating the channel conditions using only characteristics of the message 1 ; or
upon absence of detecting a DMRS collision, estimating the channel conditions using the DMRS symbol pattern of the message 3 , either alone or in combination with the characteristics of the message 1 .
4. The method according to claim 1 , wherein receiving includes receiving a downlink quality indicator within one or more of message 1 and message 3 , and the method further comprises adapting subsequent transmissions based on the downlink quality indicator.
5. The method according to claim 1 , the method further comprising:
specifying and transmitting, to a UE, a configuration parameter set for use by the UE in performing the two-step RACH procedure, the configuration parameter set including a parameter specifying a receive target power for a PRACH preamble transmitted in a message 1 of the two-step RACH procedure.