Method and apparatus for performing contention based random access in a carrier frequency
A method and user equipment are provided, in which an indication that a cell in a carrier frequency supports a 2-step random access procedure is received. A physical random access channel preamble is transmitted on a first time-frequency resource. A physical uplink channel carrying data is transmitted, where the physical uplink channel carrying the data is associated with the transmitted physical random access channel preamble. In response to the transmitted physical random access channel preamble and the transmitted physical uplink channel carrying the data, a user equipment specific channel is received within a random access response window The data includes a user equipment identity.
1 . A method performed by a user equipment (UE), the method comprising:
receiving an indication that a cell in a carrier frequency supports a 2-step random access procedure;
transmitting a random access channel (RACH) preamble of the 2-step random access procedure to initiate the 2-step random access procedure;
transmitting, based at least in part on a resource associated with the RACH preamble, data comprising a cell-radio network temporary identifier (C-RNTI) associated with the UE; and
receiving, in response to the RACH preamble and the data, a downlink control information (DCI) addressed by the C-RNTI associated with the UE, wherein the DCI is received within a random access response (RAR) window, wherein the DCI is associated with a RAR message of the 2-step random access procedure.
2 . The method of claim 1 , wherein the DCI is associated with a UE specific physical downlink control channel (PDCCH), and wherein the UE specific PDCCH comprises cyclic redundancy check (CRC) bits scrambled by the C-RNTI.
3 . The method of claim 1 , wherein the RACH preamble is transmitted on a first time-frequency resource, wherein the data is transmitted on a second time-frequency resource, and wherein the method further comprises determining the second time-frequency resource based at least in part on the RACH preamble.
4 . The method of claim 1 , further comprising transmitting a demodulation reference signal (DMRS) associated with the data, wherein a DMRS sequence of the DMRS is determined based at least in part on the RACH preamble.
5 . The method of claim 1 , wherein one or more bits corresponding to the data are scrambled by a scrambling sequence, wherein the scrambling sequence is based at least in part on a preamble index of the RACH preamble, and wherein the preamble index is based at least in part on an order of the RACH preamble in a plurality of RACH preambles associated with a time-frequency resource, and wherein the RACH preamble is transmitted on the time-frequency resource.
6 . The method of claim 1 , wherein a demodulation reference signal (DMRS) symbol associated with the data corresponds to an earliest symbol in a time-frequency resource associated with the RACH preamble, and wherein the earliest symbol in the time-frequency resource has a longer cyclic prefix than one or more data symbols of the data.
7 . The method of claim 1 , further comprising:
receiving an indication that the cell in the carrier frequency supports a 4-step random access procedure; and
selecting between the 2-step random access procedure and the 4-step random access procedure, wherein the RACH preamble and the data are transmitted based at least in part on the 2-step random access procedure being selected.
8 . The method of claim 7 , further comprising receiving information of a reference signal received power (RSRP) threshold value, wherein selecting between the 2-step random access procedure and the 4-step random access procedure is based at least in part on an RSRP measurement, wherein the 2-step random access procedure is selected if the RSRP measurement is greater than the RSRP threshold value, and wherein the 4-step random access procedure is selected if the RSRP measurement is equal to or less than the RSRP threshold value.
9 . The method of claim 1 , wherein the RACH preamble is randomly selected from at least one preamble associated with the 2-step random access procedure.
10 . The method of claim 1 , wherein the DCI comprises information associated with an uplink timing advance value.
11 . The method of claim 1 , wherein the DCI comprises information associated with an uplink grant.
12 . A user equipment (UE) for wireless communication, comprising:
at least one memory; and
at least one processor coupled with the at least one memory and operable to cause the UE to:
receive an indication that a cell in a carrier frequency supports a 2-step random access procedure;
transmit a random access channel (RACH) preamble of the 2-step random access procedure to initiate the 2-step random access procedure;
transmit, based at least in part on a resource associated with the RACH preamble, data comprising a cell-radio network temporary identifier (C-RNTI) associated with the UE; and
receive, in response to the RACH preamble and the data, a downlink control information (DCI) addressed by the C-RNTI associated with the UE, wherein the DCI is received within a random access response (RAR) window, wherein the DCI is associated with a RAR message of the 2-step random access procedure.
13 . The UE of claim 12 , wherein the RACH preamble is transmitted on a first time-frequency resource, wherein the data is transmitted on a second time-frequency resource, and wherein the at least one processor is further configured to cause the UE to determine the second time-frequency resource based at least in part on the RACH preamble.
14 . The UE of claim 12 , wherein one or more bits corresponding to the data are scrambled by a scrambling sequence, wherein the scrambling sequence is based at least in part on a preamble index of the RACH preamble, wherein the preamble index is based at least in part on an order of the RACH preamble in a plurality of RACH preambles associated with a time-frequency resource, wherein the RACH preamble is transmitted on the time-frequency resource, and wherein the scrambling sequence is further based at least in part on a cell identity and the preamble index of the RACH preamble.
15 . The UE of claim 12 , wherein the at least one processor is further operable to cause the UE to:
receive an indication that the cell in the carrier frequency supports a 4-step random access procedure; and
select between the 2-step random access procedure and the 4-step random access procedure, wherein the RACH preamble and the data are transmitted based at least in part on the 2-step random access procedure being selected.
16 . The UE of claim 15 , wherein the at least one processor is further operable to cause the UE to receive information of a reference signal received power (RSRP) threshold value, wherein selecting between the 2-step random access procedure and the 4-step random access procedure is based at least in part on an RSRP measurement, wherein the 2-step random access procedure is selected if the RSRP measurement is greater than the RSRP threshold value, and wherein the 4-step random access procedure is selected if the RSRP measurement is equal to or less than the RSRP threshold value.
17 . The UE of claim 15 , wherein the RACH preamble is transmitted on a time-frequency resource, and wherein a plurality of RACH preambles associated with the time-frequency resource comprises two mutually exclusive subsets of RACH preambles that are separately associated with one of the 2-step random access procedure or the 4-step random access procedure.
18 . A base station for wireless communication, comprising:
at least one memory; and
at least one processor coupled with the at least one memory and operable to cause the base station to:
transmit an indication that the base station supports a 2-step random access procedure, wherein the base station is associated with a carrier frequency;
receive a random access channel (RACH) preamble of the 2-step random access procedure, wherein the RACH preamble initiates the 2-step random access procedure;
receive, based at least in part on a resource associated with the RACH preamble, data comprising a cell-radio network temporary identifier (C-RNTI) associated with a user equipment (UE); and
transmit, in response to the RACH preamble and the data, a downlink control information (DCI) addressed by the C-RNTI associated with the UE, wherein the DCI is transmitted within a random access response (RAR) window, wherein the DCI is associated with a RAR message of the 2-step random access procedure.
19 . The base station of claim 18 , wherein the at least one processor is further operable to cause the base station to:
determine, based at least in part on the RACH preamble, the C-RNTI; and
scramble one or more cyclic redundancy check (CRC) bits appended to the RAR message using the C-RNTI.
20 . A method performed by a base station, the method comprising:
transmitting an indication that the base station supports a 2-step random access procedure, wherein the base station is associated with a carrier frequency;
receiving a random access channel (RACH) preamble of the 2-step random access procedure, wherein the RACH preamble initiates the 2-step random access procedure;
receiving, based at least in part on a resource associated with the RACH preamble, data comprising a cell-radio network temporary identifier (C-RNTI) associated with a user equipment (UE); and
transmitting, in response to the RACH preamble and the data, a downlink control information (DCI) addressed by the C-RNTI associated with the UE, wherein the DCI is transmitted within a random access response (RAR) window, wherein the DCI is associated with a RAR message of the 2-step random access procedure.