BEAM SELECTION FOR UPLINK AND DOWNLINK BASED MOBILITY
Aspects of the present disclosure provide methods and apparatus for beam selection in uplink-based and downlink-based mobility scenarios, for example, for new radio (NR) systems which can improve handover reliability, reduce handover frequency, and improve power efficiency. Certain aspects provide a method for wireless communications by a user equipment (UE). The method generally includes transmitting an uplink reference signal with an indication of a preferred downlink beam and receiving a downlink transmission based, at least in part, on the uplink reference signal.
1 . A method for wireless communication by a user equipment (UE), comprising:
transmitting an uplink reference signal with an indication of a preferred downlink beam; and
receiving a downlink transmission based, at least in part, on the uplink reference signal.
2 . The method of claim 1 , further comprising including an ID of the UE in the uplink reference signal.
3 . The method of claim 1 , further comprising:
selecting the preferred beam during a connection establishment procedure, wherein
transmitting the uplink reference signal comprises transmitting the uplink reference signal during the connection establishment procedure.
4 . The method of claim 3 , further comprising:
receiving one or more measurement reference signals (MRSs) transmitted using different beams; and
selecting the preferred beam based on the one or more MRSs.
5 . The method of claim 4 , wherein:
receiving the one or more MRSs comprises receiving the one or more MRSs from a plurality of base stations (BSs); and
selecting the preferred beam comprises the preferred beam based on.
6 . The method of claim 1 , wherein:
the preferred beam is selected after a connection establishment procedure; and
the uplink reference signal is transmitted while the UE is in a connected state.
7 . The method of claim 6 , further comprising:
during the connection establishment procedure, transmitting another uplink reference signal without an indication of a preferred beam.
8 . The method of claim 6 , wherein:
the uplink reference signal does not include an ID of the UE.
9 . The method of claim 1 , further comprising:
receiving a handover command based on the uplink reference signal.
10 . A method for wireless communication by a base station (BS), comprising:
receiving, from a user equipment (UE), an uplink reference signal with an indication of a preferred downlink beam; and
transmitting a downlink transmission to the UE based, at least in part, on the uplink reference signal.
11 . The method of claim 10 , wherein the uplink reference signal includes an ID of the UE.
12 . The method of claim 10 , further comprising:
performing a connection establishment procedure with the UE, wherein
receiving the uplink reference signal comprises receiving the preferred beam during the connection establishment procedure.
13 . The method of claim 12 , further comprising:
transmitting one or more measurement reference signals (MRSs) using different beams, and wherein the preferred beam is based on the one or more MRSs.
14 . The method of claim 10 , further comprising:
performing a connection establishment procedure with the UE, wherein
receiving the uplink reference signal comprises receiving the uplink reference signal after the connection establishment procedure while the UE is in a connected state.
15 . The method of claim 14 , further comprising:
during the connection establishment procedure, receiving another uplink reference signal without an indication of a preferred beam.
16 . The method of claim 14 , wherein:
the uplink reference signal does not include an ID of the UE.
17 . The method of claim 10 , further comprising:
transmitting a handover command based on the uplink reference signal.
18 . The method of claim 10 , wherein transmitting the handover command based on the uplink reference signal comprises transmitting the handover command based on at least one of the indication of the preferred beam or measurement of the uplink reference signal.
19 . An apparatus for wireless communication by a user equipment (UE), comprising:
at least one processor configured to:
transmit an uplink reference signal with an indication of a preferred downlink beam; and
receive a downlink transmission based, at least in part, on the uplink reference signal; and
a memory coupled with the at least one processor.
20 . The apparatus of claim 19 , wherein the at least one processor is configured to:
select the preferred beam during a connection establishment procedure; and
transmit the uplink reference signal during the connection establishment procedure.
21 . The apparatus of claim 20 , wherein the at least one processor is configured to:
receive one or more measurement reference signals (MRSs) transmitted using different beams, and
select the preferred beam based on the one or more MRSs.
22 . The apparatus of claim 20 , wherein the at least one processor is configured to:
select the preferred beam after a connection establishment procedure; and
transmit the uplink reference signal while the UE is in a connected state.
23 . The apparatus of claim 22 , wherein the at least one processor is further configured to:
during the connection establishment procedure, transmit another uplink reference signal without an indication of a preferred beam.
24 . The apparatus of claim 20 , wherein the at least one processor is further configured to:
receive a handover command based on the uplink reference signal.
25 . An apparatus for wireless communication by a base station (BS), comprising:
at least one processor configured to:
receive, from a user equipment (UE), an uplink reference signal with an indication of a preferred downlink beam; and
transmit a downlink transmission to the UE based, at least in part, on the uplink reference signal; and
a memory coupled with the at least one processor.
26 . The apparatus of claim 25 , wherein the at least one processor is configured to:
perform a connection establishment procedure with the UE; and
receive the uplink reference signal during the connection establishment procedure.
27 . The apparatus of claim 26 , wherein:
the at least one processor is further configured to transmit one or more measurement reference signals (MRSs) using different beams, and
the preferred beam is selected based on the one or more MRSs.
28 . The apparatus of claim 25 , wherein the at least one processor is configured to:
perform a connection establishment procedure with the UE; and
receive the uplink reference signal while the UE is in a connected state.
29 . The apparatus of claim 25 , wherein the at least one processor is configured to:
transmit a handover command based on the uplink reference signal.
30 . The apparatus of claim 25 , wherein the at least one processor is configured to transmit the handover command based on at least one of the indication of the preferred beam or measurement of the uplink reference signal.