Indicating beam correspondence using a RACH procedure
Apparatuses, methods, and systems are disclosed for UL beam/panel selection indication. One apparatus includes a transceiver comprising a plurality of UE panels associated with one or more beams, the transceiver receiving a plurality of SSBs on at least two UE panels. The apparatus includes a processor that determines a corresponding set of UE panels from the SSBs and sends, via the transceiver, an indication of the corresponding set of UE panels from the apparatus to a RAN node using a random-access procedure.
1 . A base station for wireless communication, comprising:
at least one memory; and
at least one processor coupled with the at least one memory and configure to cause the base station to:
transmit a plurality of synchronization signal blocks (SSBs) on at least two beams;
transmit a configuration for a physical random-access channel (PRACH) preamble transmission;
receive, during a random-access procedure, a plurality of PRACH preambles on a plurality of uplink (UL) beams, wherein each PRACH preamble of the plurality of PRACH preambles corresponds to a different root sequence and a respective UL beam;
associate the plurality of PRACH preambles with a user equipment (UE); and
determine, from the plurality of PRACH preambles, a corresponding set of UL beams associated with the UE, wherein the corresponding set of UL beams are based on the SSBs.
2 . The base station of claim 1 , wherein each PRACH preamble of the set of PRACH preambles comprises a sequence generated using different parameters corresponding to beam identities.
3 . The base station of claim 1 , wherein the at least one processor is configured to cause the base station to transmit a configuration parameter indicating M root sequences for generating a plurality of PRACH preambles, each root sequence associated with a UE transmit beam index.
4 . The base station of claim 1 , wherein the at least one processor is configured to cause the base station to transmit a Radio Resource Control (RRC) random-access configuration table from a radio access network (RAN) node, wherein the configuration comprises the RRC random-access configuration table, and wherein the RRC random-access configuration table correlates a beam identity to one or more of: a PRACH configuration index, a subframe number, a slot number, or a combination thereof.
5 . The base station of claim 1 , wherein to receive the plurality of PRACH preambles, the at least one processor is configured to cause the base station to receive L PRACH preambles in a message 1 (Msg1), wherein the L PRACH preambles correspond to L UL beams, and wherein the corresponding set of UL beams is implicitly indicated based on a preamble identity.
6 . The base station of claim 5 , wherein the at least one processor is configured to cause the base station to transmit a message 2 (Msg2) that indicates P detected preambles each associated with a UE transmit beam to be used for a following UL transmission, where P and L are positive integers with P≤L, and wherein the Msg2 comprises a random-access response message of the random-access procedure.
7 . The base station of claim 5 , wherein the at least one processor is configured to cause the base station to configure the UE with a number of candidate beams, wherein L≤min(N, M), where N represents a number of best beams based on the plurality of SSBs, and where M represents the number of candidate beams.
8 . The base station of claim 1 , wherein to receive the plurality of PRACH preambles, the at least one processor is configured to cause the base station to receive L PRACH preambles in a message-A (MsgA), wherein the L PRACH preambles correspond to L UL beams, and wherein the MsgA is accompanied by a physical uplink shared channel (PUSCH) transmission.
9 . The base station of claim 8 , wherein the corresponding set of UL beams is implicitly indicated based on a preamble identity or a demodulation reference signal (DMRS) sequence of the MsgA PUSCH transmission, or explicitly indicated using a payload of the MsgA PUSCH transmission.
10 . The base station of claim 8 , wherein the at least one processor is configured to cause the base station to transmit a second indication from a radio access network (RAN) node in a message-B (MsgB) for P detected preambles each associated with a UE transmit beam to be used for a following UL transmission, where P≤L, and wherein the MsgB comprises a random-access response message of the random-access procedure.
11 . The base station of claim 8 , wherein the at least one processor is configured to cause the base station to configure the UE with a number of candidate beams, wherein L≤min(N, M), where N represents a number of best beams based on the plurality of SSBs, and where M represents the number of candidate beams.
12 . The base station of claim 1 , wherein the at least one processor is configured to cause the base station to transmit a configuration parameter indicating M random-access configuration indices each associated with a UE transmit beam index, where Mis a positive integer.
13 . A method performed by a base station, the method comprising:
transmitting a plurality of synchronization signal blocks (SSBs) on at least two beams;
transmitting a configuration for a physical random-access channel (PRACH) preamble transmission;
receiving, during a random-access procedure, a plurality of PRACH preambles on a plurality of uplink (UL) beams, wherein each PRACH preamble of the plurality of PRACH preambles corresponds to a different root sequence and a respective UL beam;
associating the plurality of PRACH preambles with a user equipment (UE); and
determining, from the plurality of PRACH preambles, a corresponding set of UL beams associated with the UE, wherein the corresponding set of UL beams are based on the SSBs.
14 . The method of claim 13 , wherein each PRACH preamble of the set of PRACH preambles comprises a sequence generated using different parameters corresponding to beam identities.
15 . The method of claim 13 , further comprising transmitting a configuration parameter indicating M root sequences for generating a plurality of PRACH preambles, each root sequence associated with a UE transmit beam index.
16 . The method of claim 13 , wherein receiving the plurality of PRACH preambles, further comprises receiving L PRACH preambles in a message 1 (Msg1), wherein the L PRACH preambles correspond to L UL beams, and wherein the corresponding set of UL beams is implicitly indicated based on a preamble identity.
17 . The method of claim 16 , further comprising transmitting a message 2 (Msg2) that indicates P detected preambles each associated with a UE transmit beam to be used for a following UL transmission, where P and L are positive integers with P≤L, and wherein the Msg2 comprises a random-access response message of the random-access procedure.
18 . The method of claim 13 , wherein receiving the plurality of PRACH preambles further comprises receiving L PRACH preambles in a message-A (MsgA), wherein the L PRACH preambles correspond to L UL beams, and wherein the MsgA is accompanied by a physical uplink shared channel (PUSCH) transmission.
19 . The method of claim 18 , wherein the corresponding set of UL beams is implicitly indicated based on a preamble identity or a demodulation reference signal (DMRS) sequence of the MsgA PUSCH transmission, or explicitly indicated using a payload of the MsgA PUSCH transmission.
20 . The method of claim 18 , further comprising transmitting a second indication from a radio access network (RAN) node in a message-B (MsgB) for P detected preambles each associated with a UE transmit beam to be used for a following UL transmission, where P≤L, and wherein the MsgB comprises a random-access response message of the random-access procedure.