# US 11,445,549 B2 · Two-step random access channel (RACH) procedure to four-step RACH procedure fallback > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,445,549 B2 - Document ID: US11445549B2 - Status: Granted - Kind: B2 - Application number: 16/597,672 - Filed: 2019-10-09 - Published: 2020-04-16 - Granted: 2022-09-13 - Earliest claimed: 2018-10-10 - Assignees: QUALCOMM Incorporated - Applicants: QUALCOMM Incorporated - Inventors: Srinivas Yerramalli; Xiaoxia Zhang; Jing Sun; Seyed Ali Akbar Fakoorian; Ozcan Ozturk; Tao Luo - Web page: https://patentgrep.com/patent/US11445549B2 ## CPC - H04W 24/10: Scheduling measurement reports {; Arrangements for measurement reports} - H04L 5/0044: {Allocation of payload; Allocation of data channels, e.g. PDSCH or PUSCH} - H04W 24/02: Arrangements for optimising operational condition - H04W 24/08: Testing, {supervising or monitoring} using real traffic - H04W 48/12: using downlink control channel - H04W 52/34: TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading - H04W 52/362: {Aspects of the step size} - H04W 52/50: at the moment of starting communication in a multiple access environment - H04W 74/006: {in the downlink, i.e. towards the terminal} - H04W 74/0833: Random access procedures, e.g. with 4-step access - H04W 74/0836: with 2-step access - H04L 5/0053: {Allocation of signalling, i.e. of overhead other than pilot signals} - H04W 74/0838: using contention-free random access [CFRA] - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Certain aspects of the present disclosure provide techniques for random-access channel (RACH) communication. For example, certain aspects provide a method for falling back from a 2-step RACH procedure to a 4-step RACH procedure. ## Claims ### Claim 1 A method for wireless communications by a user equipment (UE), comprising: receiving remaining minimum system information (RMSI) configuring the UE with one or more parameters to support selecting between a two-step random access channel (RACH) procedure and a four-step RACH procedure, wherein the one or more parameters include at least a first reference signal receive power (RSRP) threshold for the two-step RACH procedure and a second RSRP threshold for the four-step RACH procedure different from the first RSRP threshold; initiating, based on the first RSRP threshold, the two-step random access channel (RACH) procedure including sending a first message to a base station, the first message comprising at least a preamble portion, including a RACH preamble, and a payload portion, including a payload, wherein sending the first message includes applying a power offset to the payload portion of the first message; receiving a random access response (RAR) message from the base station, wherein the RAR message indicates successful reception, by the base station, of both the RACH preamble and the payload when the response message is of a first format; and transitioning to the four-step RACH procedure before successful completion of the two-step RACH procedure when the RAR message is of a second format. ### Claim 2 (depends on 1) The method of claim 1, wherein the RAR message that triggers the transition to the four-step RACH procedure has a random access preamble identifier (RAPID) field that indicates the base station, at least, successfully detected the RACH preamble of the first message. ### Claim 3 (depends on 2) The method of claim 2, wherein: the UE begins the four-step RACH procedure by sending a message with an indication of an identifier (ID) of the UE. ### Claim 4 (depends on 1) The method of claim 1, wherein the RAR message is broadcast to a plurality of UEs with a same random access radio network temporary identity (RA-RNTI). ### Claim 5 (depends on 1) The method of claim 1, wherein the RAR message is sent as a unicast message to the UE. ### Claim 6 (depends on 1) The method of claim 1, wherein: the UE is configured with separate transmit power control parameters for the two-step and four-step RACH procedures; and the power control parameters comprise at least a preamble received target power and a power ramping step size. ### Claim 7 (depends on 1) The method of claim 1, wherein the UE initiates the four-step RACH procedure with a transmit power level dependent on a current transmit power level of the two-step RACH procedure prior to the transition. ### Claim 8 (depends on 7) The method of claim 7, wherein the UE initiates the four-step RACH procedure with a transmit power level with additional power ramping relative to the current transmit power level of the two-step RACH procedure prior to the transition. ### Claim 9 (depends on 1) The method of claim 1, wherein the UE is configured to select between the two-step RACH procedure and the four-step RACH procedure based on a measurement of channel loading or occupancy. ### Claim 10 (depends on 1) The method of claim 1, wherein the UE applies an additional power offset to the payload portion of the first message when re-transmitted in the four-step RACH procedure. ### Claim 11 (depends on 1) The method of claim 1, wherein subcarrier spacings (SCSs) for a preamble portion of the first message and the payload portion of the first message are configured separately. ### Claim 12 (depends on 1) The method of claim 1, wherein: the UE uses a same subcarrier spacing (SCS) for the preamble portion and the payload portion of the first message of the two-step RACH procedure; and the SCS for the preamble portion and the payload portion of the first message of the two-step RACH procedure is indicated separately from an SCS used by the UE for message transmission for the four-step RACH procedure. ### Claim 13 (depends on 1) The method of claim 1, further comprising receiving signaling indicating that the UE is to include both the payload and the RACH preamble in the first message only when sending the first message of the two-step RACH procedure for contention free random access (CFRA). ### Claim 14 A method for wireless communications by a network entity, comprising: transmitting remaining minimum system information (RMSI) configuring a user equipment (UE) with one or more parameters to support transitioning from a two-step random access channel (RACH) procedure to a four-step RACH procedure, wherein the one or more parameters include at least a first reference signal receive power (RSRP) threshold for the two-step RACH procedure and a second RSRP threshold for the four-step RACH procedure different from the first RSRP threshold; receiving, based on the first RSRP threshold, a first message from a user equipment (UE) as part of a two-step RACH procedure, the first message comprising at least a random access channel (RACH) preamble; and sending a random access response (RAR) message to the UE, wherein a first format of the RAR message indicates successful reception of both the RACH preamble and a payload included in a payload portion of the first message and a second format of the RAR message signals the UE to transition to a four-step RACH procedure before successful completion of the two-step RACH procedure, wherein a power offset is applied to the payload portion of the first message. ### Claim 15 (depends on 14) The method of claim 14, wherein: the RAR message of the second format that triggers the transition has a random access preamble identifier (RAPID) field that indicates the network entity at least successfully detected the RACH preamble of the first message. ### Claim 16 (depends on 15) The method of claim 15, wherein: the network entity begins the four-step RACH procedure by detecting a message that has an indication of an identifier (ID) of the UE. ### Claim 17 (depends on 14) The method of claim 14, wherein the RAR message of the second format that triggers the transition is broadcast to a plurality of UEs with a same random access radio network temporary identity (RA-RNTI). ### Claim 18 (depends on 14) The method of claim 14, wherein the RAR message of the second format that triggers the transition is sent as a unicast message to the UE. ### Claim 19 (depends on 14) The method of claim 14, wherein the network entity is configured to perform soft-combining of the payload portion of the first message of the two-step RACH procedure to help decode at least a portion of a message the four-step RACH procedure. ### Claim 20 An apparatus for wireless communications by a user equipment (UE), comprising: means for receiving remaining minimum system information (RMSI) configuring the UE with one or more parameters to support transitioning from a two-step random access channel (RACH) procedure to a four-step RACH procedure, wherein the one or more parameters include at least a first reference signal receive power (RSRP) threshold for the two-step RACH procedure and a second RSRP threshold for the four-step RACH procedure different from the first RSRP threshold; means for initiating, based on the first RSRP threshold, a two-step random access channel (RACH) procedure including sending a first message to a base station, the first message comprising at least a preamble portion, including a RACH preamble, and a payload portion, including a payload, wherein the means for initiating comprise means for applying a power offset to the payload portion of the first message of the two-step RACH procedure; means for receiving a random access response (RAR) message from the base station, wherein the RAR message indicates successful reception, by the base station, of both the RACH preamble and the payload when the response message is of a first format; and means for transitioning to a four-step RACH procedure before successful completion of the two-step RACH procedure when the RAR message is of a second format. ### Claim 21 An apparatus for wireless communications by a network entity, comprising: means for transmitting remaining minimum system information (RMSI) configuring a user equipment (UE) with one or more parameters to support selecting between a two-step random access channel (RACH) procedure and a four-step RACH procedure, wherein the one or more parameters include at least a first reference signal receive power (RSRP) threshold for the two-step RACH procedure and a second RSRP threshold for the four-step RACH procedure different from the first RSRP threshold; means for receiving, based on the first RSRP threshold, a first message from a user equipment (UE) as part of a two-step RACH procedure, the first message comprising at least a random access channel (RACH) preamble; and means for sending a random access response (RAR) message to the UE, wherein a first format of the RAR message indicates successful reception of both the RACH preamble and a payload included in a payload portion of the first message and a second format of the RAR message signals the UE to transition to a four-step RACH procedure before successful completion of the two-step RACH procedure, wherein a power offset is applied to the payload portion of the first message. ### Claim 22 A non-transitory computer readable medium for wireless communication, comprising: instructions that, when executed by at least one processor, cause the at least one processor to: receive remaining minimum system information (RMSI) configuring a UE with one or more parameters to support selecting between a two-step random access channel (RACH) procedure and a four-step RACH procedure, wherein the one or more parameters include at least a first reference signal receive power (RSRP) threshold for the two-step RACH procedure and a second RSRP threshold for the four-step RACH procedure different from the first RSRP threshold; initiate, based on the first RSRP threshold, a two-step random access channel (RACH) procedure including sending a first message to a base station, the first message comprising at least a preamble portion, including a RACH preamble, and a payload portion, including a payload, wherein sending the first message includes applying a power offset to the payload portion of the first message; receive a random access response (RAR) message from the base station, wherein the RAR message indicates successful reception, by the base station, of both the RACH preamble and the payload when the response message is of a first format; and transition to a four-step RACH procedure before successful completion of the two-step RACH procedure when the RAR message is of a second format. ### Claim 23 A non-transitory computer readable medium for wireless communication, comprising: instructions that, when executed by at least one processor, cause the at least one processor to: transmit remaining minimum system information (RMSI) configuring a user equipment (UE) with one or more parameters to support selecting between a two-step random access channel (RACH) procedure and a four-step RACH procedure, wherein the one or more parameters include at least a first reference signal receive power (RSRP) threshold for the two-step RACH procedure and a second RSRP threshold for the four-step RACH procedure different from the first RSRP threshold; receive, based on the first RSRP threshold, a first message from a user equipment (UE) as part of a two-step RACH procedure, the first message comprising at least a random access channel (RACH) preamble; and send a random access response (RAR) message to the UE, wherein a first format of the RAR message indicates successful reception of both the RACH preamble and a payload included in a payload portion of the first message and a second format of the RAR message signals the UE to transition to a four-step RACH procedure before successful completion of the two-step RACH procedure, wherein a power offset is applied to the payload portion of the first message.