Random access procedure in next generation wireless networks
Some of the present implementations provide a method for a user equipment (UE) for performing a random access (RA) procedure. The method transmits, to a base station, an RA preamble. The method then receives, from the base station, an RA response (RAR) associated with the RA preamble, the RAR containing a media access control (MAC) payload. The MAC payload identifies a set of one or more uplink (UL) grants for the UE. The method selects a UL grant from the set of one or more UL grants identified by the MAC payload for transmitting an Msg3 to the base station.
1. A method for a user equipment (UE) for performing a random access (RA) procedure, the method comprising:
transmitting, to a base station, an RA preamble;
receiving, from the base station, an RA response (RAR) associated with the RA preamble, the RAR containing a media access control (MAC) payload that identifies a set of one or more uplink (UL) grants for the UE;
selecting, a UL grant from the set of one or more UL grants identified by the MAC payload for transmitting a scheduled UL transmission (Msg3) to the base station; and
before selecting the UL grant, determining that a listen-before-talk (LBT) procedure performed on the UL grant is successful.
2. The method of claim 1 , wherein the MAC payload comprises a field for indicating whether more than one UL grant is included in the MAC payload.
3. The method of claim 1 , wherein when the set of uplink grants comprises a first UL grant and a second UL grant, the first UL grant is associated with a current bandwidth part (BWP) and the second UL grant is associated with another BWP identified by a field in the MAC payload.
4. The method of claim 1 , wherein when the set of uplink grants comprises a first UL grant and a second UL grant, the MAC payload comprises a first field identifying a first bandwidth part (BWP) associated with the first UL grant and a second field identifying a second BWP associated with the second UL grant.
5. The method of claim 1 further comprising determining that the RA procedure has failed after receiving, at a MAC layer of the UE, a consecutive number of LBT failure indicators.
6. The method of claim 5 , wherein an LBT failure indicator comprises a power ramping suspend indicator sent from a physical layer of the UE.
7. The method of claim 5 further comprising receiving, through broadcasting system information, a parameter that indicates a value for the consecutive number of LBT failure indicators.
8. The method of claim 5 further comprising, after determining that the RA procedure has failed, at least one of:
performing an LBT channel reselection procedure;
barring an unlicensed cell on which the RA procedure is performed before performing a cell reselection procedure;
barring all unlicensed cells before performing a cell reselection procedure; and
transitioning to an RRC Idle state.
9. A user equipment (UE) comprising:
one or more non-transitory computer-readable media having computer-executable instructions for performing a random access (RA) procedure; and
at least one processor coupled to the one or more non-transitory computer-readable media, and configured to execute the computer-executable instructions to:
transmit, to a base station, an RA preamble;
receive, from the base station, an RA response (RAR) associated with the RA preamble, the RAR containing a media access control (MAC) payload that identifies a set of one or more uplink (UL) grants for the UE;
select a UL grant from the set of one or more UL grants identified by the MAC payload for transmitting a scheduled UL transmission (Msg3) to the base station; and
before selecting the UL grant, determine that a listen-before-talk (LBT) procedure performed on the UL grant is successful.
10. The UE of claim 9 , wherein the MAC payload comprises a field for indicating whether more than one UL grant is included in the MAC payload.