CONFIGURABLE MODE FOR RESPONSE TO RANDOM ACCESS MESSAGE

Certain aspects of the present disclosure provide techniques for a configurable mode for a response to random access message. A method that may be performed by a user equipment (UE) includes receiving an indication from a base station (BS) that the BS operates according to a first mode in which the BS unicasts a RACH response during a two-step RACH procedure or a second mode in which the BS multicasts the RACH response. The RACH response includes a PDCCH and PDSCH. The UE sends a RACH message to the BS comprising a preamble and payload. The UE monitors and decodes the PDCCH of the RACH response based on the indicated first mode or second mode. The UE decodes the PDSCH of the RACH response and sends feedback to the BS based on the indicated first mode or second mode.

BACKGROUND

Field of the Disclosure

Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for a configurable mode for a response to random access message.

Description of Related Art

SUMMARY

Certain aspects provide a method for wireless communication by a base station (BS). The method generally includes determining to operate according to a first mode in which the BS unicasts a downlink random access channel (RACH) response message during a two-step RACH procedure or a second mode in which the BS multicasts the downlink RACH response message during the two-step RACH procedure, the downlink RACH response message transmission including a physical downlink control channel (PDCCH) transmission and a physical downlink shared channel (PDSCH) transmission. The method generally includes providing an indication to at least one user equipment (UE) of the determined first mode or second mode.

Certain aspects provide a method for wireless communication by a user equipment (UE). The method generally includes receiving an indication from a BS that the BS operates according to a first mode in which the BS unicasts a downlink RACH response message during a two-step RACH procedure or a second mode in which the BS multicasts the downlink RACH response message during the two-step RACH procedure, the downlink RACH response message transmission including a PDCCH transmission and a PDSCH transmission. The method generally includes sending an uplink RACH message to the BS comprising a RACH preamble and a RACH payload. The method generally includes monitoring and decoding the PDCCH transmission of the downlink RACH response message transmission from the BS based on the indicated first mode or second mode. The method generally includes decoding the PDSCH transmission of the downlink RACH response message transmission and sending a hybrid automatic repeat request (HARQ) feedback to the BS based on the indicated first mode or second mode.

Aspects of the present disclosure provide means for, apparatus, processors, and computer-readable mediums for performing the methods described herein.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums for a configurable mode for a response to random access message. In a two-step random access channel (RACH) procedure, user equipment (UE) send a base station (BS) a RACH message (e.g., referred to as MSG A) that includes a RACH preamble and a RACH payload. The BS responds with a RACH response message (MSG B) transmission that includes a physical downlink control channel (PDCCH) transmission and a physical downlink shared channel (PDSCH) transmission. Unicasting the RACH response message may allow the BS to send the UE a large payload. However, multicasting the RACH response message can reduce complexity for blind decoding and allow the RACH response message to carry multiple small payloads for multiple UEs.

Aspects of the present disclosure provide for a configurable mode for the RACH response message. For example, the BS can determine to use the unicast mode or multicast mode for sending the RACH response message based on various parameters, such as system loading, cell coverage, and/or resource availability. The BS can indicate the mode to the UE, so the UE can monitor/decode the RACH response message depending on the indicated mode. In addition, the content of the RACH response message may be based on whether the RACH preamble and/or RACH payload were received, as well as based on the radio resource control (RRC) state of the UE.

The techniques described herein may be used for various wireless networks and radio technologies. While aspects may be described herein using terminology commonly associated with 3G, 4G, and/or new radio (e.g., 5G NR) wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems.

FIG. 1illustrates an example wireless communication network100in which aspects of the present disclosure may be performed. For example, the wireless communication network100may be an NR system (e.g., a 5G NR network). As shown inFIG. 1, the wireless communication network100may be in communication with a core network132. The core network132may in communication with one or more base station (BSs)110110a-z(each also individually referred to herein as BS110or collectively as BSs110) and/or user equipment (UE)120a-y(each also individually referred to herein as UE120or collectively as UEs120) in the wireless communication network100via one or more interfaces.

According to certain aspects, the BSs110and UEs120may be configured for a two-step RACH with a configurable mode for the RACH response message. As shown inFIG. 1, the BS110aincludes a RACH manager112. The RACH manager112may be configured for a two-step RACH with a configurable mode for the RACH response message, in accordance with aspects of the present disclosure. As shown inFIG. 1, the UE120aincludes a RACH manager122. The RACH manager122may be configured for a two-step RACH with a configurable mode for the RACH response message, in accordance with aspects of the present disclosure.

Wireless communication network100may also include relay stations (e.g., relay station110r), also referred to as relays or the like, that receive a transmission of data and/or other information from an upstream station (e.g., a BS110aor a UE120r) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE120or a BS110), or that relays transmissions between UEs120, to facilitate communication between devices.

A network controller130may couple to a set of BSs110and provide coordination and control for these BSs110. The network controller130may communicate with the BSs110via a backhaul. The BSs110may also communicate with one another (e.g., directly or indirectly) via wireless or wireline backhaul.

FIG. 2illustrates example components of BS110aand UE120a(e.g., in the wireless communication network100ofFIG. 1), which may be used to implement aspects of the present disclosure.

At the BS110a, a transmit processor220may receive data from a data source212and control information from a controller/processor240. The control information may be for the physical broadcast channel (PBCH), physical control format indicator channel (PCFICH), physical hybrid ARQ indicator channel (PHICH), PDCCH, group common PDCCH (GC PDCCH), etc. The data may be for the PDSCH, etc. The processor220may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor220may also generate reference symbols, such as for the primary synchronization signal (PSS), secondary synchronization signal (SSS), and channel state information reference signal (CSI-RS). A transmit (TX) multiple-input multiple-output (MIMO) processor230may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs)232a-232t. Each modulator232may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators232a-232tmay be transmitted via the antennas234a-234t, respectively.

The memories242and282may store data and program codes for BS110aand UE120a, respectively. A scheduler244may schedule UEs for data transmission on the downlink and/or uplink.

The controller/processor280and/or other processors and modules at the UE120amay perform or direct the execution of processes for the techniques described herein. For example, as shown inFIG. 2, the controller/processor240of the BS110ahas a RACH manager241that may be configured for a configurable RACH response message for a two-step RACH procedure, according to aspects described herein. As shown inFIG. 2, the controller/processor280of the UE120ahas a RACH manager241that may be configured for a configurable RACH response message for a two-step RACH procedure, according to aspects described herein. Although shown at the Controller/Processor, other components of the UE120aand BS110amay be used performing the operations described herein.

FIG. 3is a diagram showing an example of a frame format300for NR. The transmission timeline for each of the downlink and uplink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 ms) and may be partitioned into 10 subframes, each of 1 ms, with indices of 0 through 9. Each subframe may include a variable number of slots (e.g., 1, 2, 4, 8, 16, . . . slots) depending on the SCS. Each slot may include a variable number of symbol periods (e.g., 7, 12, or 14 symbols) depending on the SCS. The symbol periods in each slot may be assigned indices. A mini-slot, which may be referred to as a sub-slot structure, refers to a transmit time interval having a duration less than a slot (e.g., 2, 3, or 4 symbols). Each symbol in a slot may indicate a link direction (e.g., DL, UL, or flexible) for data transmission and the link direction for each subframe may be dynamically switched. The link directions may be based on the slot format. Each slot may include DL/UL data as well as DL/UL control information.

In NR, a synchronization signal block (SSB) is transmitted. In certain aspects, SSBs may be transmitted in a burst where each SSB in the burst corresponds to a different beam direction for UE-side beam management (e.g., including beam selection and/or beam refinement). The SSB includes a PSS, a SSS, and a two symbol PBCH. The SSB can be transmitted in a fixed slot location, such as the symbols 0-3 as shown inFIG. 3. The PSS and SSS may be used by UEs for cell search and acquisition. The PSS may provide half-frame timing, the SS may provide the CP length and frame timing. The PSS and SSS may provide the cell identity. The PBCH carries some basic system information, such as downlink system bandwidth, timing information within radio frame, SS burst set periodicity, system frame number, etc. The SSBs may be organized into SS bursts to support beam sweeping. Further system information such as, remaining minimum system information (RMSI), system information blocks (SIBs), other system information (OSI) can be transmitted on a physical downlink shared channel (PDSCH) in certain subframes. The SSB can be transmitted up to sixty-four times, for example, with up to sixty-four different beam directions for mmWave. The multiple transmissions of the SSB are referred to as a SS burst set. SSBs in an SS burst set may be transmitted in the same frequency region, while SSBs in different SS bursts sets can be transmitted at different frequency regions.

A random access channel (RACH) refers to a wireless channel (medium) that may be shared by multiple UEs, and may be used by the UEs to (randomly) access the network for communications. For example, the RACH may be used for call setup and to access the network for data transmissions. In some cases, RACH may be used for initial access to a network when the UE switches from a RRC connected idle mode to active mode, or when handing over in RRC connected mode. Moreover, RACH may be used for downlink (DL) and/or uplink (UL) data arrival when the UE is in RRC idle or RRC inactive modes, and when reestablishing a connection with the network.

FIG. 4is a timing (or “call-flow”) diagram400illustrating an example four-step RACH procedure. A first message (MSG1) may be sent from the UE120ato BS110aon the physical random access channel (PRACH), at402. In the four-step RACH procedure, the MSG1 may only include a RACH preamble. BS110amay respond with a random access response (RAR) message (MSG2) which may include the identifier (ID) of the RACH preamble, a timing advance (TA), an uplink grant, a cell radio network temporary identifier (C-RNTI), and/or a back off indicator, at404. MSG2 may include a PDCCH communication including control information for a following communication on the PDSCH, as illustrated. In response to the MSG2, the UE120atransmits MSG3 to the BS110aon the PUSCH, at406. The MSG3 may include one or more of a RRC connection request, a tracking area update (TAU) request, a system information request, a positioning fix or positioning signal request, or a scheduling request. The BS110athen responds with the MSG4which may include a contention resolution message, at408.

In some cases, to speed up access, a two-step RACH procedure may be supported. As the name implies, the two-step RACH procedure may effectively “collapse” the four messages of the four-step RACH procedure into two messages. There are several benefits to a two-step RACH procedure, such as speed of access and the ability to send a relatively small amount of data without the overhead of a full four-step RACH procedure to establish a connection (when the four-step RACH messages may be larger than the payload). The two-step RACH procedure can operate in any RRC state and any supported cell size. Networks that use two-step RACH procedures can typically support contention-based random access (CBRA) transmission of messages (e.g., MSG A) within a finite range of payload sizes and with a finite number of modulation coding scheme (MCS) levels.

FIG. 5is a timing diagram500illustrating an example two-step RACH procedure, in accordance with certain aspects of the present disclosure. In the two-step RACH procedure, a first message (MSG A) may be sent from the UE120ato BS110a, at502. The MSG A may include some or all the information from both the MSG1 and MSG3 from the four-step RACH procedure (effectively combining MSG1 and MSG3). For example, MSG A may include MSG1 and MSG3 multiplexed together such as using one of time-division multiplexing (TDM) or frequency-division multiplexing (FDM). The MSG A may include a RACH preamble for random access and a payload. The MSG A payload, for example, may include the UE-ID and other signaling information (e.g., buffer status report (BSR) or scheduling request (SR)). BS110amay respond with a RAR message (MSG B) which may effectively combine the MSG2 and MSG4 of the four-step RACH procedure described above, at504. For example, MSG B may include the ID of the RACH preamble (RAPID), a timing advance (TA), a back off indicator, a contention resolution message, UL/DL grant, and/or transmit power control (TPC) commands.

FIG. 6is a timing diagram illustrating a more detailed example of the two-step RACH procedure, in accordance with certain aspects of the present disclosure. As shown inFIG. 6, the UE120amay receive and decode information from the BS, such as a SSB, system information block (SIB), and/or RS prior to the RACH procedure, which may be used by the UE120ato perform the RACH procedure with the BS110a. As shown inFIG. 6, in the two-step RACH procedure, the MSG A may include a both a preamble (e.g., PRACH) and a payload (e.g., DMRS and PUSCH). The BS attempts to decode the process/decode the SMG A preamble and payload and then sends the MSG B (e.g., based on the MSG A processing). As shown inFIG. 6, the MSG B may include both the PDCCH and PDSCH.

FIG. 7Aillustrates the channel structure for an example MSG A transmission occasion that may be validated, in accordance with certain aspects of the present disclosure. As shown inFIG. 7A, the MSG A transmission occasion generally includes a MSG A preamble occasion (for transmitting a preamble signal) and a MSG A payload occasion for transmitting a PUSCH. As illustrated inFIG. 7A, the MSG A preamble transmission may involve (1) selection of a preamble sequence; and (2) selection of a preamble occasion in time/frequency domain (for transmitting the selected preamble sequence). The MSG A payload transmission may involve: (1) construction of the random access message payload (DMRS/PUSCH); and (2) selection of one or multiple PUSCH resource units (PRUs) in time/frequency domain to transmit this message (payload). As illustrated inFIG. 7B, the UE monitors SSB transmissions which are sent (e.g., sent repeatedly by the BS using different TX beams) and are associated with a finite set of time/frequency resources defining RACH occasions (ROs) and PRUs. The RACH preamble occasion (RO) may be the time and frequency resource assigned for preamble transmission.

Upon detecting an SSB, the UE may select an RO and one or more PRUs associated with that SSB for a MSG A transmission. The finite set of ROs and PRUs may help reduce monitoring overhead (blind decodes) by a base station.

In certain systems (e.g., 5G NR), up to 64 preamble sequences are configured on each RO. Multiple four-step and/or multiple two-step RACH UEs can share the same RO, and randomly select their preamble sequences from a common pool. In some examples, the network configures separate ROs for the two-step and four-step RACH UEs, or the network configures separate pools but a shared RO for the two-step and four-step RACH UEs.

As mentioned above, the MSG B could be unicast or multicast. In some cases, unicast MSG B may be desirable/supportable, while in other cases multicasting the MSG B may be desirable/supportable. Unicasting the MSG B may allow the BS to send the UE a large payload, while multicasting the MSG B can reduce complexity for blind decoding and allow the RACH response message to carry multiple small payloads for multiple UEs.

Example Configurable Mode for Response to Random Access Message

Aspects of the present disclosure provide a configurable mode of a random access channel (RACH) response message (e.g., MSG B) transmission and construction. In some examples, the network can configure the mode (e.g., unicast or multicast) based on various parameters, such as system loading (e.g., how many user equipment (UEs) will perform the two-step RACH procedure at the same time), cell coverage, and resource availability (e.g., how much time/frequency resources and RACH sequences are available). For example, if the system loading is high and/or if a physical downlink control charm& (PDCCH) payload will be large, then the unicast mode may be used, whereas if the system loading is low and/or the PDCCH payload is small then the multicast mode may be used.

The configured mode can be indicated to a UE. Indicating the mode may allow to determine a search space to monitor/decode the RACH response message. In addition, the UE can know the multiple access signature based on the indicated mode. In some examples, content of the RACE response message may depend on the radio resource control (RRC) state of the UE and/or based on processing of the RACH message (e.g., MSG A).

According to certain aspects, in the unicast mode for the RACH response message, the PDCCH of the RACH response message carries a downlink assignment for the physical downlink shared channel (PDSCH) of the RACH response message targeting a single two-step UE. The PDCCH of the RACH response message is transmitted in a UE-specific search space (USS). In some examples, the cyclic redundancy check (CRC) of PDCCH of the unicast RACH response message is masked by a UE-specific multiple access signature (e.g., denoted by msgB-RNTI_1). Thus, based on indicating the unicast mode, the UE knows to monitor/decode the PDCCH, whose CRC is masked by the multiple access signature, of the RACH response message in the USS.

According to certain aspects, the multiple access signature depends on the outcome of the RACH message (e.g., MSG A) processing and on the RRC state of the UE. For example, if the UE is in an RRC idle or RRC inactive state and the BS detects the RACH message, then the multiple access signature (e.g., msgB_RNTI_1) can be calculated, such as by a weighted combination of the resource index used for the RACH message transmission, including RO index, preamble index and UL carrier index. In an example, the multiple access signature can be calculated as follows:

where rf_id is modular operation of radio frame index (rf_id=(radio frame index) mod 2+1), PRACH_preamble_id is the index of preamble sequence on the selected RO (0≤PRACH_preamble_id<64), s_id is the index of the first OFDM symbol of the specified PRACH (0≤s_id<14), t_id is the index of the first slot symbol of the specified PRACH in a system frame (0≤t_id<80), f_id is the index of the specified PRACH in the frequency domain(0≤f_id<8), ul_carrier_id is the UL carrier used for RACH message (e.g., MSG A) transmission (0=normal carrier, 1=SUL carrier), C_1≥1 and C_2≥0 are constants. Otherwise, if the BS does not detect the RACH message, the BS does not need to transmit a RACH response message.

In another example, if the UE is in an RRC connected state and the BS detects the RACH message payload, then the multiple access signature (C-RNTI) of UE can be used (e.g., used as the msgB_RNTI_1). Otherwise, if only the BS only detects the RACH preamble, then same formula above for the RRC_IDLE or RRC_INACTIVE UE can be reused.

To mitigate potential collision between C-RNTI and other multiple access signature (e.g., msgB_RNTI_1) values, a 1-bit flag for C-RNTI can be carried by the downlink control information (DCI) of the PDCCH of the RACH response message. The 1-bit flag may indicate whether the multiple access signature is a C-RNTI or a msgB_RNTI_1.

According to certain aspects, in the unicast mode for the RACH response message, the PDSCH of the RACH response message carries the response information for a single UE. According to certain aspects, contents of the unicast RACH response message depends on the outcome of the RACH message (e.g., MSG A) processing and on the RRC state of the UE.FIG. 8is a table800showing example contents of the unicast RACH response message PDCCH and PDSCH depending on the RRC state and whether the BS successfully decoded the RACH payload and preamble from the UE.

According to certain aspects, in the multicast mode for the RACH response message, the PDCCH of the RACH response message is transmitted in a common search space (CSS). The PDCCH of the RACH response message carries the DL assignment of a MSG B PDSCH targeting a group of two-step RACH UEs. In some examples, the CRC of the PDCCH of the RACH response message is masked by a group-specific multiple access signature (e.g., denoted by msgB-RNTI). The PDCCH of the RACH response message may be differentiated from msg2 PDCCH, if two-step RACH and four-step RACH are sharing the same ROs. For example, the PDCCH of the RACH response message for the two-step and four-step RACH can be differentiated based on different control resource set (CORESET), different search space configurations for msgB PDCCH and msg2 PDCCH, different quasi co-location (QCL) relations, different demodulation reference signal (DMRS) resource configuration, and/or different values for the multiple access signature (e.g., different msgB-RNTI_2 and random access radio network temporary identifier (RA-RNTI)).

According to certain aspects, for the multicast RACH response message, the PDSCH of the RACH response message carries an aggregation of the response information for each UE in the group. According to certain aspects, contents of the multicast RACH response message depends on the outcome of the RACH message (e.g., MSG A) processing and on the RRC state of the UE.FIG. 9is a table900showing example contents of the multicast RACH response message PDCCH and PDSCH depending on the RRC state and whether the BS successfully decoded the RACH payload and preamble from the UE.

FIGS. 10 and 11are flow diagrams illustrating example operations1000and1100, respectively, for wireless communication, in accordance with certain aspects of the present disclosure. The operations1000and1100may be performed, for example, by a BS (e.g., such as the BS110ain the wireless communication network100). Operations1000and1100may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor240ofFIG. 2). Further, the transmission and reception of signals by the BS in operations1000and1100may be enabled, for example, by one or more antennas (e.g., antennas234ofFIG. 2). In certain aspects, the transmission and/or reception of signals by the BS may be implemented via a bus interface of one or more processors (e.g., controller/processor240) obtaining and/or outputting signals.

Operations1000may begin, at1002, by receiving a RACH message from a UE. The RACH message includes a RACH preamble transmission and a PUSCH transmission.

At1004, the BS sends a RACH response message to the UE. The RACH response message includes a PDCCH transmission and a PDSCH transmission. Sending the RACH message to the UE includes, at1006, scrambling a CRC associated with the PDCCH transmission of the RACH response message masked by a UE-specific or group-specific multiple access signature and, at1008, sending the PDSCH to the UE based on the PDCCH.

The operations1100may begin, at1102, by determining to operate according to a first mode in which the BS unicasts a downlink RACH response message (e.g., MSG B) transmission during a two-step RACH procedure or a second mode in which the BS multicasts the downlink RACH response message transmission during the two-step RACH procedure. The downlink RACH response message including a PDCCH transmission and a PDSCH transmission.

At1204, the BS provides an indication to at least one UE of the determined first mode or second mode.

In a first aspect, the determination is based on at least one of: system loading, cell coverage, or resource availability.

In a second aspect, alone or in combination with the first aspect, the indication is broadcast in system information or transmitted via RRC signaling to the at least one UE before the two-step RACH procedure is performed.

In a third aspect, alone or in combination with one or more of the first aspect and second aspects, the BS further performs the two-step RACH procedure with the at least one UE in accordance with the indicated first mode or second mode.

In a fourth aspect, alone or in combination with one or more of the first through third aspects, performing the RACH procedure with the at least one UE includes determining whether the BS successfully decoded a RACH preamble and a RACH payload in an uplink RACH message from the UE; and determining a RRC state of the UE.

In a fifth aspect, alone or in combination with one or more of the first through fourth aspects, determining whether the BS received the RACH preamble from the UE comprises determining whether the BS successfully decoded the RACH preamble during an assigned RACH preamble occasion (RO); determining whether the BS received the RACH payload comprises determining whether the BS successfully decoded the RACH payload during an assigned RACH payload occasion; and determining the RRC state of the UE is based at least on an indication from the UE in the uplink RACH message.

In a sixth aspect, alone or in combination with one or more of the first through fifth aspects, content of the downlink RACH response message is based on determined first mode or second mode, the RRC state of the UE, and whether the BS successfully decoded the RACH preamble and RACH payload from the UE.

In a seventh aspect, alone or in combination with one or more of the first through sixth aspects, performing the RACH procedure with the at least one UE comprises: DTX (discontinuous transmission) or sending the downlink RACH response message with a BI when the BS did not successfully decode the RACH preamble.

In an eighth aspect, alone or in combination with one or more of the first through seventh aspects, the PDSCH transmission of the RACH response message transmission carries at least a TAC and a fallback RAR when the BS successfully decoded the RACH preamble without successfully decoding the RACH payload.

In a ninth aspect, alone or in combination with one or more of the first through eighth aspects, the PDCCH transmission of the RACH response message transmission carries at least a downlink assignment for the PDSCH transmission of the RACH response message transmission when the BS successfully decoded the RACH preamble without successfully decoding the RACH payload.

In a tenth aspect, alone or in combination with one or more of the first through ninth aspects, the PDCCH transmission of the RACH response message transmission further carries a PUCCH resource configuration for HARQ procedures of the PDSCH transmission of the RACH response message transmission.

In an eleventh aspect, alone or in combination with one or more of the first through tenth aspects, the PDSCH transmission of the RACH response message transmission carries at least a TAC when the BS successfully decoded the RACH payload and the UE is in an RRC connected state.

In a twelfth aspect, alone or in combination with one or more of the first through eleventh aspects, the PDSCH transmission of the RACH response message transmission further carries at least one of: an RRC message or an uplink grant for new data.

In a thirteenth aspect, alone or in combination with one or more of the first through twelfth aspects, the PDSCH transmission of the RACH response message transmission carries at least a successful RAR and a TAC when the BS successfully decoded the RACH payload and the UE is in an RRC inactive or RRC idle state.

In a fourteenth aspect, alone or in combination with one or more of the first through thirteenth aspects, the PDSCH transmission of the RACH response message transmission further carries at least one of: an RRC message, an uplink grant for new data, or a PUCCH resource configuration for a HARQ procedure of the PDSCH transmission of the RACH response message transmission.

In a fifteenth aspect, alone or in combination with one or more of the first through fourteenth aspects, performing the RACH procedure with the at least one UE comprises unicasting the PDCCH transmission of RACH response message transmission, in a USS configured for PDCCH, carrying a downlink assignment for the PDSCH transmission of the RACH response message transmission when the BS operates according to the first mode, wherein the PDSCH transmission carries the response information for a single UE.

In a sixteenth aspect, alone or in combination with one or more of the first through fifteenth aspects, a CRC associated with the PDCCH transmission of the RACH response message transmission is masked by a UE-specific multiple access signature; the signature is calculated based on resources used for the at least one of: the RACH preamble or RACH payload when the BS successfully decoded the RACH payload and the UE is in the RRC inactive or RRC idle state; and the multiple access signature is a unique identifier (e.g. C-RNTI) assigned for the UE in RRC connected state when the BS successfully decoded the RACH payload; and the multiple access signature for RRC connected UE can use the same formula as RRC inactive or RRC idle UE when the BS decoded the RACH preamble without successfully decoding the RACH payload.

In a seventeenth aspect, alone or in combination with one or more of the first through sixteenth aspects, a flag in DCI of the PDCCH transmission of the RACH response message transmission indicates whether the signature is calculated for UE in RRC inactive or idle state, or is the unique identifier assigned for the UE in RRC connected state.

In an eighteenth aspect, alone or in combination with one or more of the first through seventeenth aspects, the PDCCH transmission of the RACH response message transmission further indicates a configuration for the PUCCH resources for HARQ feedback to the PDSCH transmission of the RACH response message transmission.

In a nineteenth aspect, alone or in combination with one or more of the first through eighteenth aspects, performing the RACH procedure with the at least one UE comprises transmitting a PDCCH transmission of the RACH response message transmission, in a CSS configured for group common PDCCH, carrying a downlink assignment for the PDSCH transmission of the RACH response message transmission when the BS operates according to the second mode.

In a twentieth aspect, alone or in combination with one or more of the first through nineteenth aspects, a CRC associated with the PDCCH is masked by a group-specific multiple access signature that is different than a signature associated with PDCCH used for the first mode.

In a twenty-first aspect, alone or in combination with one or more of the first through twentieth aspects, the PDCCH transmission of the RACH response message transmission for a two-step RACH procedure uses at least one of: a different CORESET, a different search space configuration, a different QCL relation, a different DMRS resource configuration, or a different multiple access signature than a PDCCH transmission of the RACH response message (message2) transmission by the BS for a four-step RACH procedure.

In a twenty-second aspect, alone or in combination with one or more of the first through twenty-first aspects, the PDCCH transmission of the RACH response message transmission further carries an indication of PUCCH resources for HARQ feedback to the PDSCH transmission of the RACH response message transmission when the BS successfully decoded the RACH payload and the UE is in the RRC connected state.

In a twenty-third aspect, alone or in combination with one or more of the first through twenty-second aspects, the PDSCH transmission of the RACH response message transmission further carries an indication of physical uplink control channel (PUCCH) resources for HARQ feedback when the BS successfully decoded the RACH payload and the UE is in the RRC inactive or RRC idle state.

FIGS. 12 and 13are flow diagrams illustrating example operations1200and1300, respectively, for wireless communication, in accordance with certain aspects of the present disclosure. The operations1200and1300may be performed, for example, by a UE (e.g., such as a UE120ain the wireless communication network100). The operations1200and1300may be complimentary operations by the UE to the operations1000and1100, respectively, performed by the BS. Operations1200and1300may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor280ofFIG. 2). Further, the transmission and reception of signals by the UE in operations1200and1300may be enabled, for example, by one or more antennas (e.g., antennas252ofFIG. 2). In certain aspects, the transmission and/or reception of signals by the UE may be implemented via a bus interface of one or more processors (e.g., controller/processor280) obtaining and/or outputting signals.

Operations1200may begin, at1202, by sending a RACH message to a BS. The RACH message includes a RACH preamble transmission and a PUSCH transmission.

At1204, the UE receives a RACH response message from the BS. The RACH message from the BS includes a PDCCH transmission and a PDSCH transmission.

Receiving the RACH response message from the BS includes, at1206, descrambling a CRC associated with the PDCCH transmission of the RACH response message masked by a UE-specific or group-specific multiple access signature and, at1208, monitoring the PDSCH based on the PDCCH.

Operations1300may begin, at1302, by receiving an indication from a BS that the BS operates according to a first mode in which the BS unicasts a downlink RACH response message during a two-step RACH procedure or a second mode in which the BS multicasts the downlink RACH response message during the two-step RACH procedure, the downlink RACH response message transmission including a PDCCH transmission and a PDSCH transmission.

At1304, the UE sends an uplink RACH message transmission to the BS comprising a RACH preamble and a RACH payload.

At1306, the UE monitors and decodes the PDCCH transmission of the downlink RACH response message from the BS based on the indicated first mode or second mode.

At1308, the UE decodes the PDSCH transmission of the downlink RACH response message transmission and sends a HARQ feedback to the BS based on the indicated first mode or second mode.

In a first aspect, the indication is broadcast in system information or transmitted via RRC signaling from the BS before the two-step RACH procedure is performed.

In a second aspect, alone or in combination with the first aspect, the RACH preamble is transmitted during an assigned RO; and the RACH payload is transmitted during an assigned RACH payload occasion.

In a third aspect, alone or in combination with one or more of the first aspect and second aspects, the UE further provides an indication of a RRC state of the UE in the uplink RACH message transmission.

In a fourth aspect, alone or in combination with one or more of the first through third aspects, the PDSCH transmission of the RACH response message transmission carries at least a TAC and a fallback RAR.

In a fifth aspect, alone or in combination with one or more of the first through fourth aspects, the PDCCH transmission of the RACH response message transmission carries at least a downlink assignment for the PDSCH transmission of the RACH response message transmission.

In a sixth aspect, alone or in combination with one or more of the first through fifth aspects, the PDCCH transmission of the RACH response message transmission further carries a PUCCH resource configuration for HARQ procedures of the PDSCH transmission of the RACH response message transmission.

In a seventh aspect, alone or in combination with one or more of the first through sixth aspects, the PDSCH transmission of the RACH response message transmission carries at least a TAC when the UE is in an RRC connected state.

In an eighth aspect, alone or in combination with one or more of the first through seventh aspects, the PDSCH transmission of the RACH response message transmission further carries at least one of: an RRC message or an uplink grant for new data.

In a ninth aspect, alone or in combination with one or more of the first through eighth aspects, the PDSCH transmission of the RACH response message transmission carries at least a successful RAR and a TAC when the UE is in an RRC inactive or RRC idle state.

In a tenth aspect, alone or in combination with one or more of the first through ninth aspects, the PDSCH transmission of the RACH response message transmission further carries at least one of: an RRC message, an uplink grant for new data, or a PUCCH resource configuration for a HARQ procedures of the PDSCH transmission of the RACH response message transmission.

In an eleventh aspect, alone or in combination with one or more of the first through tenth aspects, monitoring the PDCCH transmission of the downlink RACH response message transmission comprises monitoring a unicast PDCCH transmission of the RACH response message transmission, in a USS configured for PDCCH, carrying a downlink assignment for the PDSCH transmission of the RACH response message transmission when the BS operates according to the first mode, wherein the PDSCH transmission carries the response information for a single UE.

In a twelfth aspect, alone or in combination with one or more of the first through eleventh aspects, the UE descrambles a CRC associated with the PDCCH transmission of the RACH response message transmission masked by a UE-specific multiple access signature, wherein the signature is calculated based on resources used for the at least one of: the RACH preamble or RACH payload; or the multiple access signature is a unique identifier (e.g. C-RNTI) assigned for the UE in RRC connected state.

In a thirteenth aspect, alone or in combination with one or more of the first through twelfth aspects, a flag in downlink control information of the PDCCH transmission of the RACH response message transmission indicates whether the signature is calculated for UE in RRC inactive or idle state, or is the unique identifier assigned for the UE in RRC connected state.

In a fourteenth aspect, alone or in combination with one or more of the first through thirteenth aspects, the PDCCH transmission of the RACH response message transmission further indicates a configuration for the PUCCH resources for HARQ feedback to the PDSCH transmission of the RACH response message transmission.

In a fifteenth aspect, alone or in combination with one or more of the first through fourteenth aspects, monitoring the PDCCH transmission of the downlink RACH response message transmission comprises transmitting a PDCCH transmission of the RACH response message transmission, in a CSS configured for group common PDCCH, carrying a downlink assignment for the PDSCH transmission of the RACH response message transmission when the BS operates according to the second mode.

In a sixteenth aspect, alone or in combination with one or more of the first through fifteenth aspects, the UE descrambles a CRC associated with the PDCCH masked by a group-specific multiple access signature that is different than a signature associated with PDCCH used for the first mode.

In a seventeenth aspect, alone or in combination with one or more of the first through sixteenth aspects, the UE monitors the PDCCH transmission of the RACH response message transmission for a two-step RACH procedure based on at least one of: a different CORESET, a different search space configuration, a different QCL relation, a different DMRS resource configuration, or a different multiple access signature than a PDCCH transmission of the RACH response message (message2) transmission by the BS for a four-step RACH procedure.

In an eighteenth aspect, alone or in combination with one or more of the first through seventeenth aspects, the PDCCH transmission of the RACH response message transmission further carries an indication of PUCCH resources for HARQ feedback to the PDSCH transmission of the RACH response message transmission when the UE is in the RRC connected state.

In a nineteenth aspect, alone or in combination with one or more of the first through eighteenth aspects, the PDSCH transmission of the RACH response message transmission further carries an indication of PUCCH resources for HARQ feedback when the UE is in the RRC inactive or RRC idle state.

FIG. 14illustrates a communications device1400that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated inFIG. 10and/orFIG. 11. The communications device1400includes a processing system1402coupled to a transceiver1408. The transceiver1408is configured to transmit and receive signals for the communications device1400via an antenna1410, such as the various signals as described herein. The processing system1402may be configured to perform processing functions for the communications device1400, including processing signals received and/or to be transmitted by the communications device1400.

The processing system1402includes a processor1404coupled to a computer-readable medium/memory1412via a bus1406. In certain aspects, the computer-readable medium/memory1412is configured to store instructions (e.g., computer-executable code) that when executed by the processor1404, cause the processor1404to perform the operations illustrated inFIG. 10and/orFIG. 11, or other operations for performing the various techniques discussed herein for a configurable mode for a response to random access message. In certain aspects, computer-readable medium/memory1412stores code1414for receiving; code1416for sending; code1418for scrambling; code1420for determining; and/or code1422for providing, in accordance with aspects of the present disclosure. In certain aspects, the processor1404has circuitry configured to implement the code stored in the computer-readable medium/memory1412. The processor1404includes circuitry1424for receiving; circuitry1426for sending; circuitry1428for scrambling; circuitry1430for determining; and/or circuitry1432for providing, in accordance with aspects of the present disclosure.

FIG. 15illustrates a communications device1500that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated inFIG. 12and/orFIG. 13. The communications device1500includes a processing system1502coupled to a transceiver1508. The transceiver1508is configured to transmit and receive signals for the communications device1500via an antenna1510, such as the various signals as described herein. The processing system1502may be configured to perform processing functions for the communications device1500, including processing signals received and/or to be transmitted by the communications device1500.

The processing system1502includes a processor1504coupled to a computer-readable medium/memory1512via a bus1506. In certain aspects, the computer-readable medium/memory1512is configured to store instructions (e.g., computer-executable code) that when executed by the processor1504, cause the processor1504to perform the operations illustrated inFIG. 12and/orFIG. 13, or other operations for performing the various techniques discussed herein for a configurable mode for a response to random access message. In certain aspects, computer-readable medium/memory1512stores code1514for receiving; code1516for sending; code1518for descrambling; code1520for monitoring; and/or code1522for decoding, in accordance with aspects of the present disclosure. In certain aspects, the processor1504has circuitry configured to implement the code stored in the computer-readable medium/memory1512. The processor1504includes circuitry1524for receiving; circuitry1526for sending; circuitry1528for descrambling; code1530for monitoring; and/or code1532for decoding, in accordance with aspects of the present disclosure.

The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. For clarity, while aspects may be described herein using terminology commonly associated with 3G, 4G, and/or 5G wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems.