Method and apparatus for supporting a process for step 2 random access

Abstract

A communication method and system are provided for converging a 5th-Generation (5G) communication system supporting higher data rates beyond a 4th-Generation (4G) system with an Internet of Things (IoT) technology. The communication method and system can be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method for performing a random access (RA) procedure by a terminal configured with at least one serving cell is provided. The method includes measuring a downlink reference signal received power (DL RSRP) of a serving cell on which an RA procedure is initiated, determining whether the DL RSRP of the serving cell is greater than a threshold, and performing a 2-step RA procedure based on the DL RSRP of the serving cell being greater than the threshold.

Description

[0001] This application is a divisional application of a patent application with an application date of September 23, 2019 and application number 201980062113.5. Technical Field

[0002] The present disclosure relates to systems and methods for supporting multiple message A (MsgA) sizes and uplink (UL) coverage for a 2-step random access procedure. Background Art

[0003] In order to meet the increased demand for wireless data services since the deployment of the fourth generation (4G) communication system, efforts have been made to develop an improved fifth generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a "super 4G network" or a "post-long term evolution (LTE) system". The 5G wireless communication system is considered to be implemented not only in a lower frequency band but also in a higher frequency millimeter wave (mmWave) band (e.g., 10 gigahertz (GHz) to 100 GHz band) to achieve higher data rates. In order to mitigate the propagation loss of radio waves and increase the transmission distance, beamforming, massive multiple-input multiple-output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antenna technology are considered in the design of the 5G wireless communication system. Furthermore, in the 5G communication system, development of system network improvements is being conducted based on advanced small cells, cloud radio access networks (RAN), ultra-dense networks, device-to-device (D2D) communications, wireless backhaul, mobile networks, cooperative communications, coordinated multipoint (CoMP), receiving-end interference cancellation, etc. In the 5G system, frequency and quadrature amplitude modulation (FQAM) which is a combination of hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) and sliding window superposition coding (SWSC) are also being developed as advanced coded modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) are also being developed as advanced access technologies.

[0004] Likewise, the Internet, which is a human-centered connected network in which humans generate and consume information, is now evolving into the Internet of Things (IoT), in which distributed entities (such as things) exchange and process information without human intervention. The Internet of Everything (IoE) has also emerged, which is the combination of IoT technology and big data processing technology through connection with cloud servers. As IoT implementation requires technical elements such as "sensing technology", "wired / wireless communication and network infrastructure", "service interface technology", and "security technology", sensor networks, machine-to-machine (M2M) communication, machine type communication, etc. have been studied recently. This IoT environment can provide smart Internet technology services that create new value for human life by collecting and analyzing data generated between connected things. In this case, IoT can be applied to various fields including smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, healthcare, smart appliances, and advanced medical services through the convergence and combination between existing information technology (IT) and various industrial applications.

[0005] In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, MTC, and M2M communications can be implemented through beamforming, MIMO, and array antennas. Cloud RAN as an application of the above-mentioned big data processing technology can also be considered an example of the fusion of 5G technology and IoT technology.

[0006] In recent years, several broadband wireless technologies have been developed to meet the growing number of broadband subscribers and to provide more and better applications and services such as these. The second generation (2G) wireless communication system has been developed to provide voice services while ensuring the mobility of users. The third generation (3G) wireless communication system supports not only voice services but also data services. The 4G wireless communication system has been developed to provide high-speed data services. However, the 4G wireless communication system currently suffers from a lack of resources to meet the growing demand for high-speed data services. Therefore, the 5G wireless communication system is being developed to meet the growing demand for various services with different requirements (e.g., high-speed data services), supporting ultra-reliability and low-latency applications.

[0007] Furthermore, 5G wireless communication systems are expected to address different use cases with very different requirements in terms of data rate, latency, reliability, mobility, etc. However, it is expected that the design of the air interface of the 5G wireless communication system will be flexible enough to serve user equipment (UE) with quite different capabilities, depending on the use case and market segment that the UE serves for the end customer. Example use cases that the 5G wireless communication system is expected to address include enhanced mobile broadband (eMBB), massive machine type communication (m-MTC), ultra-reliable low latency communication (URLL), etc. eMBB requirements, such as data rates of tens of gigabits per second (Gbps), low latency, high mobility, etc., address the market segment that represents the wireless broadband users in the relevant fields who need Internet connectivity anytime and anywhere. m-MTC requirements, such as extremely high connection density, infrequent data transmission, extremely long battery life, low mobility address the market segment that represents the connectivity of billions of devices envisioned by IoT / IoE. URLL requirements, such as extremely low latency, extremely high reliability, and variable mobility, address the market segment that represents the vehicle-to-vehicle / vehicle-to-infrastructure communication that represents industrial automation applications and is foreseen as one of the enabling factors for autonomous vehicles.

[0008] In 5G (also known as NR or New Radio) wireless communication systems, the Random Access procedure is used to achieve uplink (UL) time synchronization. The RA procedure is used during initial access, handover, Radio Resource Control (RRC) connection re-establishment procedure, scheduling request transmission, Secondary Cell Group (SCG) addition / modification, beam failure recovery, and data or control information transmission in the UL by an unsynchronized UE in the RRC CONNECTED state. During the RA procedure (which consists of 4 steps), the UE first transmits a RA preamble (also known as Message 1 (Msg1)) and then waits for a RA Response (RAR) or Message 2 (Msg2) in the RAR window corresponding to its RA preamble transmission. The Next Generation Node B (gNB) transmits the RAR on the Physical Downlink Shared Channel (PDSCH) addressed to the RA-Radio Network Temporary Identifier (RA-RNTI). The RA-RNTI identifies the time-frequency resource (also known as Physical RA Channel (PRACH) opportunity or PRACH Transmit (TX) opportunity or RA Channel (RACH) opportunity) where the RA preamble is detected by the gNB. The maximum size of the RAR window is one radio frame, i.e., 10ms. The RA-RNTI is calculated as follows: ,in:

[0009] s_id is the index of the first orthogonal frequency division multiplexing (OFDM) symbol of the PRACH opportunity for which the UE has sent Msg1 (ie, RA preamble); 0≤s_id<14,

[0010] t_id is the index of the first time slot of the PRACH opportunity (0≤t_id<80),

[0011] f_id is the frequency domain index of the PRACH opportunity in this time slot (0 ≤ f_id < 8), and

[0012] ul_carrier_id is the UL carrier used for Msg1 transmission (0 for Normal UL (NUL) carrier, 1 for Supplementary UL (SUL) carrier.

[0013] Several RARs for various RA preambles detected by the gNB may be multiplexed by the gNB in ​​the same RAR Medium Access Control (MAC) Protocol Data Unit (PDU). If the RAR includes the RA preamble identifier (RAPID) of the RA preamble transmitted by the UE, the RAR in the MAC PDU corresponds to the RA preamble transmission of the UE. If the RAR corresponding to its RA preamble transmission is not received during the RAR window, and the UE has not transmitted the RA preamble for a configurable number of times (configured by the gNB in ​​the RACH configuration), the UE retransmits the RA preamble.

[0014] The RA procedure is considered successful if the RAR corresponding to its RA preamble transmission is received and the UE has sent a dedicated RA preamble. If the UE has sent a non-dedicated (i.e., contention-based) RA preamble, then upon successful reception of the RAR, the UE sends a message 3 (Msg3) in the UL grant received in the RAR. Msg3 includes messages such as RRC connection request, RRC connection reestablishment request, RRC handover confirmation, scheduling request, system information (SI) request, etc. It also includes the UE identity (i.e., cell-radio network temporary identifier (C-RNTI) or system architecture evolution (SAE)-temporary mobile subscriber identity (S-TMSI) or a random number). After sending Msg3, the UE starts a contention resolution timer. While the contention resolution timer is running, if the UE receives a physical downlink control channel (PDCCH) addressed to the C-RNTI included in Msg3, contention resolution is considered successful, the contention resolution timer is stopped, and the RA procedure is completed. While the contention resolution timer is running, if the UE receives a contention resolution MAC control element (CE) including the UE's contention resolution identifier (the first X bits of the common control channel (CCCH) service data unit (SDU) sent in Msg3), the contention resolution is considered successful, the contention resolution timer is stopped, and the contention resolution process is completed. If the contention resolution timer expires and the UE has not sent the RA preamble for a configurable number of times, the UE retransmits the RA preamble.

[0015] In 5G wireless communication systems, a 2-step contention-free RA (CFRA) procedure is also supported. The CFRA procedure is used for scenarios such as handovers that require low latency, timing advance establishment of secondary cells (Scells), etc. The evolved Node B (eNB) allocates a contention-free RA preamble to the UE in dedicated signaling. The UE sends the allocated contention-free RA preamble. The ENB sends the RAR on the PDSCH addressed to the RA-RNTI. The RAR conveys the RA preamble identifier and timing alignment information. The RAR may also include a UL grant. Similar to the contention-based RA (CBRA) procedure, the RAR is sent in the RAR window. The CFRA procedure terminates after receiving the RAR.

[0016] To reduce the latency of the 4-step CBRA procedure, a 2-step CBRA procedure is being studied. In the first step of the 2-step CBRA procedure, the UE sends an RA preamble on the PRACH and a payload on the physical uplink shared channel (PUSCH). The RA preamble and payload transmission is also referred to as message A (MsgA). In the second step, after the MsgA transmission, the UE monitors the response from the network within the configured window. The response is also referred to as message B (MsgB). The UE performs contention resolution using the contention resolution information in MsgB. If contention resolution is successful, the RA procedure is considered to have been successfully completed. Instead of the contention resolution information corresponding to the transmitted MsgA, MsgB may include a backoff indication corresponding to the RA preamble sent in MsgA. If a backoff indication is received, the UE sends Msg3 as in the 4-step CBRA procedure and performs contention resolution using message 4 (Msg4). If contention resolution is successful, the RA procedure is considered to have been successfully completed. If contention resolution fails at fallback (i.e., when sending Msg3), the UE retransmits MsgA. If the configured window in which the UE monitors the network response expires after sending MsgA, and the UE does not receive MsgB including contention resolution information or fallback indication as described above, the UE retransmits MsgA. If the RA procedure is not successfully completed even after sending a configurable number of MsgA, the UE falls back to the 4-step RACH procedure, i.e., the UE only sends the PRACH preamble.

[0017] In the 2-step RA process, depending on the RRC state of the UE (i.e., idle, inactive, or connected) or the event that triggers the RA process (such as a scheduling request, a PDCCH command, a beam failure recovery, etc.), one or more types of information such as RRC messages, buffer status reports, power headroom reports, UL data, UE ID, etc. may be included in the MsgA payload. As a result, the size of the MsgA payload may be variable. A resource pool including a set of PUSCH resources (time / frequency resources) is configured, where the MsgA payload may be sent by selecting a PUSCH resource (also called a PUSCH opportunity) from the resource pool. In order to support the variable size of the MsgA payload, the PUSCH resource needs to be configured large enough to accommodate the maximum size of the MsgA payload. However, this will result in a waste of resources for MsgA payloads of smaller sizes. Therefore, a method is needed to efficiently support MsgA payloads of variable sizes.

[0018] Similar to 2-step CBRA, in 2-step CFRA procedure, in addition to the preamble, the payload may also be sent in MsgA. RA preamble and / or PUSCH resources are allocated exclusively to the UE for 2-step CFRA procedure.

[0019] The above information is provided as background information only to assist in understanding the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above may be applied as prior art with respect to the present disclosure. Summary of the invention

[0020] Technical issues

[0021] Various aspects of the present disclosure are intended to solve at least the above-mentioned problems and / or disadvantages and provide at least the following advantages. Therefore, one aspect of the present disclosure is to provide a communication method and system for integrating a fifth generation (5G) communication system to support a higher data rate than a fourth generation (4G) system.

[0022] Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the presented embodiments.

[0023] In a 2-step random access (RA) procedure, depending on the RRC state of the UE (i.e., idle, inactive, or connected) or the event that triggers the RA procedure (such as a scheduling request, a physical downlink control channel (PDCCH) command, beam failure recovery, etc.), a message A (MsgA) payload may include one or more types of information, such as a radio resource control (RRC) message, a buffer status report, a power headroom report, an uplink (UL) data, a user equipment (UE) identifier (ID), etc. As a result, the size of the MsgA payload may be variable. A resource pool including a set of physical uplink shared channel (PUSCH) resources (time / frequency resources) is configured, wherein the MsgA payload may be transmitted by selecting a PUSCH resource (also referred to as a PUSCH opportunity) from the resource pool. In order to support the variable size of the MsgA payload, the PUSCH resource needs to be configured large enough to accommodate the maximum size of the MsgA payload. However, this will result in a waste of resources for a smaller size of the MsgA payload. Therefore, a method is needed to efficiently support a variable size of the MsgA payload.

[0024] Unlike the 4-step RACH procedure, the MsgA of the 2-step RA procedure includes information bits. In the 4-step RACH procedure, these information bits are sent using Message 3 (Msg3), where Hybrid Automatic Repeat Request (HARQ) or Transmission Time Interval (TTI) bundling is used for Msg3 transmission. HARQ or TTI bundling ensures that Msg3 can be reliably sent by UEs close to the gNB and UEs far from the gNB (i.e., at the cell edge). In the case of MsgA, mechanisms are required so that MsgA can be reliably sent by UEs close to and far from the gNB.

[0025] There may be ambiguity in determining whether the network response sent by the gNB is for a 2-step or 4-step RA. For example, UE1 sends Msg1 for a 4-step RA. UE2 sends MsgA for a 2-step RA. For the network response, the UE monitors the PDCCH addressed to the RA-Radio Network Temporary Identifier (RA-RNTI), where the RA-RNTI is determined as follows: The s_id, t_id, f_id and ul_carrier_id corresponding to the MsgA opportunity of the 2-step RA and the Msg1 opportunity of the 4-step RA may be the same. Therefore, a method is needed to avoid this ambiguity.

[0026] Problem Solution

[0027] According to one aspect of the present disclosure, a method for performing an RA procedure by a terminal configured with at least one serving cell is provided. The method includes measuring a downlink reference signal received power (DL RSRP) of a serving cell on which the RA procedure is initiated, determining whether the DL RSRP of the serving cell is greater than a threshold, and performing a 2-step RA procedure based on the DL RSRP of the serving cell being greater than the threshold.

[0028] According to another aspect of the present disclosure, a terminal configured with at least one serving cell in a wireless communication system is provided. The terminal includes a transceiver and a processor coupled to the transceiver. The processor is configured to measure the downlink reference signal received power of the serving cell on which the RA process is initiated, determine whether the DL RSRP of the serving cell is greater than a threshold, and perform a 2-step random access (RA) process based on the DL RSRP of the serving cell being greater than the threshold.

[0029] Advantageous Effects of the Invention

[0030] Based on the features of the present disclosure, MsgA payloads of variable sizes can be efficiently supported. MsgA can also be reliably sent by UEs close to and far from the gNB. The features of the present disclosure also eliminate ambiguity in determining whether the network response sent by the gNB is for a 2-step or 4-step RA.

[0031] Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent from the following description in conjunction with the accompanying drawings, in which:

[0033] FIG1 illustrates a MsgA physical (PHY) protocol data unit (PDU) transmitted in a message A (MsgA) opportunity (or MsgA resource) for a 2-step random access (RA) according to an embodiment of the present disclosure;

[0034] FIG2 illustrates another MsgA PHY PDU transmitted in a MsgA physical uplink shared channel (PUSCH) opportunity (or MsgA PUSCH resource) according to an embodiment of the present disclosure;

[0035] FIG3 illustrates a process performed by a UE to support variable-sized information to be sent in Msg1 according to an embodiment of the present disclosure;

[0036] 4 is a diagram in which a next generation Node B (gNB) may signal up to two MsgA PUSCH resource pools according to an embodiment of the present disclosure;

[0037] FIG5 is a flowchart illustrating UE operations for performing a RA process according to an embodiment of the present disclosure;

[0038] FIG6 illustrates a process performed by a UE to support reliable transmission of MsgA according to an embodiment of the present disclosure;

[0039] FIG7 is a diagram of another embodiment of the disclosure in which a gNB may signal up to two MsgA PUSCH resource pools according to an embodiment of the disclosure;

[0040] FIG8 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure;

[0041] FIG9 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure;

[0042] FIG10 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure;

[0043] FIG11 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure;

[0044] FIG12 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure;

[0045] FIG13 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure;

[0046] FIG14 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure;

[0047] 15a and 15b illustrate a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure;

[0048] 16a and 16b are flow charts illustrating UE operations for performing a RA procedure according to an alternative embodiment of the present disclosure;

[0049] FIG. 17 is a block diagram of a terminal according to an embodiment of the present disclosure; and

[0050] FIG. 18 is a block diagram of a base station according to an embodiment of the present disclosure.

[0051] Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. DETAILED DESCRIPTION

[0052] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of the various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details that aid in understanding, but these are considered to be exemplary only. Therefore, it will be appreciated by those of ordinary skill in the art that various changes and modifications may be made to the various embodiments described herein without departing from the scope and spirit of the present disclosure. In addition, for the sake of clarity and conciseness, descriptions of well-known functions and configurations may be omitted.

[0053] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Therefore, it will be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustrative purposes only and not for limiting the present disclosure as defined by the appended claims and their equivalents.

[0054] It should be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

[0055] The term "substantially" means that the characteristic, parameter or value described need not be achieved precisely, but rather deviations or variations including, for example, tolerances, measurement errors, measurement precision limitations and other factors known to those skilled in the art, may occur in amounts that do not eliminate the effect that the characteristic is intended to provide.

[0056] It is known to those skilled in the art that the blocks of a flowchart (or sequence diagram) and the combination of flowcharts can be represented and executed by computer program instructions. These computer program instructions can be loaded onto a processor of a general-purpose computer, a special-purpose computer, or a programmable data processing device. When the loaded program instructions are executed by the processor, they create means for performing the functions described in the flowchart. Because computer program instructions can be stored in a computer-readable memory available in a special-purpose computer or a programmable data processing device, an article of manufacture that performs the functions described in the flowchart can also be created. Because computer program instructions can be loaded onto a computer or a programmable data processing device, when executed as a process, they can perform the operations of the functions described in the flowchart.

[0057] The blocks of the flow chart may correspond to a module, segment or code containing one or more executable instructions that implement one or more logical functions, or may correspond to a portion thereof. In some cases, the functions described by the blocks may be performed in an order different from the order listed. For example, two blocks listed in order may be performed simultaneously or in reverse order.

[0058] In this specification, the words "unit", "module", etc. may refer to software components or hardware components, for example, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) capable of performing a function or operation. However, "unit", etc. are not limited to hardware or software. Units, etc. may be configured to reside in an addressable storage medium or drive one or more processors. Units, etc. may also refer to software components, object-oriented software components, class components, task components, processes, functions, attributes, procedures, subroutines, program code segments, drivers, firmware, microcodes, circuits, data, databases, data structures, tables, arrays, or variables. The functions provided by components and units may be a combination of smaller components and units, and may be combined with other components and units to form larger components and units. Components and units may be configured to drive one or more processors in a device or a secure multimedia card.

[0059] Before the detailed description, terms or definitions necessary for understanding the present disclosure are described. However, these terms should be interpreted in a non-limiting manner.

[0060] A “base station (BS)” is an entity that communicates with a user equipment (UE) and may be referred to as a BS, base transceiver station (BTS), Node B (NB), evolved NB (eNB), access point (AP), fifth generation (5G) NB (5GNB), or next generation NB (gNB).

[0061] A “UE” is an entity communicating with a BS and may be referred to as a UE, a device, a mobile station (MS), a mobile equipment (ME), or a terminal.

[0062] In the present disclosure, a 2-step random access (RA) procedure including message A (MsgA) and message B (MsgB) refers to the following procedure: In the first step of the 2-step contention-based RA (CBRA) procedure, the UE transmits an RA preamble on a physical RA channel (PRACH) and transmits a payload on a physical uplink shared channel (PUSCH). The RA preamble and payload transmission are also referred to as MsgA. In the second step, after the MsgA transmission, the UE monitors a response from the network within a configured window. The response is also referred to as MsgB. The UE performs contention resolution using the contention resolution information in MsgB. If the contention resolution is successful, the RA procedure is considered to be successfully completed. Instead of the contention resolution information corresponding to the transmitted MsgA, MsgB may include a backoff indication corresponding to the RA preamble transmitted in MsgA. If the backoff indication is received, the UE transmits Msg3 as in the 4-step CBRA procedure and performs contention resolution using message 4 (Msg4). If the contention resolution is successful, the RA procedure is considered to be successfully completed. If contention resolution fails upon fallback, the UE retransmits MsgA. If the configured window in which the UE monitors the network response after sending MsgA expires, and the UE does not receive MsgB including contention resolution information or fallback indication as described above, the UE retransmits MsgA. If the RA procedure is not successfully completed even after sending MsgA a configurable number of times, the UE falls back to the 4-step Random Access Channel (RACH) procedure, i.e., the UE only sends the PRACH preamble. In the 2-step RA procedure, one or more types of information such as radio resource control (RRC) message, buffer status report, power headroom report, uplink (UL) data, UE identifier (ID) (e.g., cell-radio network temporary identifier (C-RNTI), system architecture evolution (SAE)-temporary mobile subscriber identity (S-TMSI), recovery ID, etc.) may be included in the MsgA payload, depending on the RRC state of the UE (i.e., idle, inactive, or connected) or the event that triggers the RA procedure (such as scheduling request, physical downlink control channel (PDCCH) command, beam failure recovery, etc.).

[0063] The information in the MsgA payload may include one or more of the following: a connection request message, a connection recovery request message, a system information (SI) request message, a buffer status indication, beam information (e.g., one or more downlink (DL) transmit (TX) beam IDs or synchronization signal block (SSB) IDs), a beam failure recovery indication / information, a data indicator, a cell / BS / transmit reception point (TRP) transition indication, a connection reestablishment message, a reconfiguration complete or handover complete message, etc. Note that any other information is not excluded. In the case where the MsgA includes a dedicated RACH preamble, the UE ID (i.e., C-RNTI) may be skipped (i.e., not included) in the MsgA payload. In this case, the gNB may identify the UE based on the dedicated preamble and send a PDCCH addressed to the C-RNTI in the response. In the present disclosure, the 4-step RA procedure refers to the conventional RA procedure including Msg1 to Msg4 as described in the TS 38.321 and 36.321 specifications.

[0064] 1. How to handle Msg1 of variable size

[0065] FIG. 1 illustrates a MsgA physical (PHY) protocol data unit (PDU) transmitted in an MsgA opportunity (or MsgA resource) for 2-step RA according to an embodiment of the present disclosure.

[0066] Referring to Figure 1, the MsgA PHY PDU consists of a cyclic prefix (CP), a PRACH preamble sequence, a medium access control (MAC) PDU, a cyclic redundancy check (CRC), and a guard time (GT). MsgA is another name for Msg1 of a 2-step RACH.

[0067] FIG2 illustrates another MsgA PHY PDU transmitted in a MsgA PUSCH opportunity (or MsgA PUSCH resource) according to an embodiment of the present disclosure.

[0068] In this case, only the payload part of MsgA is transmitted in the MsgA PUSCH opportunity (or MsgA PUSCH resource). The RA preamble part of MsgA is transmitted separately in the PRACH opportunity.

[0069] Referring to Figure 2, the MsgA PHY PDU used to transmit the payload part of MsgA consists of CP, MAC PDU, CRC and GT. MsgA PUSCH opportunity (or MsgA PUSCH resource) is the time / frequency opportunity for transmitting the MsgA payload. MsgAPUSCH opportunity (or MsgA PUSCH resource) includes one or more physical resource blocks (PRBs) in the frequency domain and one or more orthogonal frequency division multiplexing (OFDM) symbols / slots in the time domain.

[0070] In an embodiment, the MAC PDU in the MsgA PHY PDU may include one or more of the following: common control channel (CCCH) service data unit (SDU), dedicated control channel (DCCH) SDU, dedicated traffic channel (DTCH) SDU, buffer status report (BSR) MAC control element (CE), power headroom report (PHR) MAC CE, SSB information, C-RNTI MAC CE, or padding.

[0071] In another embodiment, MsgA may include a UE ID (e.g., a random ID, S-TMSI, C-RNTI, recovery ID, etc.) together with the preamble in the first step. The UE ID may be included in the MAC PDU of MsgA. The UE ID, such as C-RNTI, may be carried in a MAC CE, where the MAC CE is included in the MAC PDU. Other UE IDs (such as a random ID, S-TMSI, C-RNTI, recovery ID, etc.) may be carried in a CCCH SDU. The UE ID may be one of the following: a random ID, S-TMSI, C-RNTI, recovery ID, international mobile subscriber identity (IMSI), idle mode ID, inactive mode ID, etc. The UE ID may be different in different scenarios where the UE performs the RA process. When the UE performs RA after power-on (before attaching to the network), the UE ID is a random ID. When the UE performs RA in an idle state after attaching to the network, the UE ID is an S-TMSI. If the UE has an assigned C-RNTI (e.g., in a connected state), the UE ID is a C-RNTI. In the case where the UE is in an inactive state, the UE ID is the recovery ID. In addition to the UE ID, some additional control information may be sent in MsgA. The control information may be included in the MAC PDU of MsgA. The control information may include one or more of the following: connection request indication, connection recovery request indication, SI request indication, buffer status indication, beam information (e.g., one or more DL TX beam IDs or SSB IDs), beam failure recovery indication / information, data indicator, cell / BS / TRP transition indication, connection reestablishment indication, reconfiguration complete or handover complete message, etc. Note that any other control information is not excluded. In the case where MsgA includes a dedicated RACH preamble, the UE ID (i.e., C-RNTI) may be skipped (i.e., not included) in Msg1. In this case, the gNB may identify the UE based on the dedicated preamble and send a PDCCH addressed to the C-RNTI in response to MsgA.

[0072] According to an embodiment of the present disclosure, in order to support variable-sized information to be sent in the MsgA payload, multiple MsgA PUSCH resource pools (or RACH configurations) for the 2-step RA process may be configured. The MsgA PUSCH opportunities (or PUSCH resources) in each of these multiple resource pools support different MsgA sizes (or the size of the MAC PDU size or information carried in MsgA). The MsgA PUSCH resource pool is signaled by the gNB in ​​SI and / or dedicated RRC signaling.

[0073] FIG. 3 illustrates a process performed by a UE to support variable-sized information to be sent in Msg1 according to an embodiment of the present disclosure.

[0074] 3 , at operation 310 , the UE receives a plurality of MsgA PUSCH resource pools / configurations for a 2-step RA procedure. For MsgA payload transmission, at operation 320 , the UE selects a resource pool from the plurality of resource pools. The size of the MsgA payload (or the size of the MAC PDU or the size of the information carried in MsgA) that can be transmitted in the MsgAPUSCH opportunity (or PUSCH resource) of the selected resource pool is greater than or equal to the size of the MsgA payload (or the size of the MAC PDU or the size of the information carried in MsgA) that the UE intends to transmit. Each MsgA PUSCH opportunity (or PUSCH resource) in the selected resource pool is mapped to one or more SSBs. At operation 330 , the UE selects a MsgA PUSCH opportunity (or PUSCH resource) from the selected resource pool corresponding to a suitable SSB. If the SS block reference signal received power (RSRP) is greater than a threshold, where the threshold is signaled by the gNB, the SS block is suitable. If there is no suitable SSB, the UE may select an MsgA PUSCH opportunity (or PUSCH resource) from the selected resource pool corresponding to any SSB. If there are multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, the UE may randomly select one MsgA PUSCH opportunity from the multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, or the UE may select the earliest MsgA PUSCH opportunity from the multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB. Then, in operation 340, the UE sends an MsgA payload (i.e., MsgA MAC PDU) in the selected MsgA PUSCH opportunity (or PUSCH resource). In an embodiment of the process, the multiple MsgA PUSCH resource pools refer to multiple MsgA PUSCH resource pools configured in the active UL bandwidth part (BWP) of the selected UL carrier. Note that both normal UL (NUL) and supplementary UL (SUL) carriers can be configured in the cell. For RA on a serving cell configured with both NUL and SUL carriers, the UE selects one of these carriers based on the DL RSRP of the cell. If the RSRP of the DL path loss reference (ie, SSB) is less than the configured threshold, the UE selects SUL; otherwise, it selects NUL.

[0075] In embodiments where the RACH preamble is also sent in MsgA, a list of RACH preambles that can be used may be signaled by the gNB. Each RACH preamble in the list is mapped to one or more SSBs. The UE selects the RACH preamble corresponding to a suitable SSB (a SSB is suitable if the SS block RSRP is greater than a threshold, where the threshold is signaled by the gNB). If there is no suitable SSB, the UE may select a RACH preamble corresponding to any SSB. If there are multiple RACH preambles corresponding to the selected SSB, the UE may randomly select one from the multiple RACH preambles corresponding to the selected SSB. In one embodiment, each MsgA PUSCH resource pool may be associated with a different set of preambles so that the gNB can identify the MsgA PUSCH resources used by the UE and decode the MsgA payload accordingly. In this case, the UE selects the preamble corresponding to the selected SSB from the preambles associated with the selected MsgAPUSCH resource pool. In an embodiment, two groups (Group A and Group B) of RA preambles may be signaled. The UE selects a group of preambles based on the MsgA payload size, or based on the MsgA payload size and path loss (if groups are configured, and if the MsgA payload size (UL data available for transmission plus MAC header and, if needed, MAC CE) is greater than SizeGroupA and the path loss is less than a threshold, or if the RA procedure is initiated for the CCCH logical channel and the CCCH SDU size plus the MAC subheader is greater than SizeGroupA, then preamble group B is selected. Otherwise group A is selected. SizeGroupA is configured by the gNB). In this case, the UE selects the preamble corresponding to the selected SSB from the preambles associated with the selected preamble group.

[0076] So far, MsgA transmission in the 2-step RA process,

[0077] - The UE selects the UL carrier (NUL or SUL) when the RA procedure is started.

[0078] - The UE selects the SSB for each MsgA transmission during the RA procedure.

[0079] - As described above, the UE selects a PUSCH resource pool from the PUSCH resource pools of the active UL BWP. This step may be performed only once during the RA procedure.

[0080] -The UE selects a PUSCH opportunity corresponding to the selected SSB from the selected PUSCH resource pool.

[0081] -The UE selects a preamble corresponding to the selected SSB from the preambles of the selected PUSCH resource pool. Alternatively, the UE selects a preamble group, and then the UE selects a preamble corresponding to the selected SSB from the preambles of the selected preamble group.

[0082] -UE selects the PRACH opportunity corresponding to the selected SSB. The PRACH opportunities of 2-step RA are mapped to SSBs as in 4-step RA. If there are multiple RACH opportunities corresponding to the selected SSB, the UE may randomly select one RACH opportunity from the multiple RACH opportunities corresponding to the selected SSB, or the UE may select the earliest RACH opportunity from the multiple RACH opportunities corresponding to the selected SSB.

[0083] -The UE then sends the selected preamble at the selected PRACH opportunity. The UE sends the MsgA payload at the selected PUSCH opportunity.

[0084] 4 is a diagram in which a gNB may signal up to two MsgA PUSCH resource pools (e.g., resource pool A and resource pool B) according to an embodiment of the present disclosure.

[0085] 4 , at operation 410 , the UE receives one or more MsgA PUSCH resource pools / configurations for 2-step RA. Resource pool A should be signaled, but resource pool B may be selectively signaled. At operation 420 , the UE determines whether resource pool B has been signaled. In addition, at operation 430 , the UE determines whether the MsgA payload size (or the size of the MAC PDU size or the size of the information carried in MsgA) is greater than a threshold, i.e., MsgASizeThreshold. If resource pool B is signaled and if the MsgA payload size (or the size of the MAC PDU size or the size of the information carried in Msg1) is greater than a threshold, i.e., MsgASizeThreshold, then at operation 440 , the UE selects MsgA PUSCH resources (or PUSCH opportunities) from resource pool B. Otherwise, at operation 450 , the UE selects MsgA PUSCH resources from resource pool A. MsgASizeThreshold is signaled by the gNB. Each MsgA PUSCH opportunity (or PUSCH resource) in the selected resource pool is mapped to one or more SSBs. The UE selects a MsgA PUSCH opportunity (or PUSCH resource) from the selected resource pool corresponding to a suitable SSB (the SSB is suitable if the SS block RSRP is greater than a threshold, where the threshold is signaled by the gNB). If there is no suitable SSB, the UE may select a MsgA PUSCH opportunity (or PUSCH resource) from the selected resource pool corresponding to any SSB. If there are multiple MsgAPUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, the UE may randomly select one MsgA PUSCH opportunity from the multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, or the UE may select the earliest MsgA PUSCH opportunity from the multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB. Then, at operation 460, the UE transmits the MsgA payload (or MAC PDU) in the selected MsgA PUSCH opportunity (or PUSCH resource). In an embodiment of this process, the MsgA PUSCH resource pool refers to the MsgA PUSCH resource pool configured in the active UL BWP of the selected UL carrier. Note that both NUL and SUL carriers can be configured in a cell. For RA on a serving cell configured with both NUL and SUL carriers, the UE selects one of these carriers based on the DL RSRP of the cell. If the RSRP of the DL path loss reference (i.e., SSB) is less than the configured threshold, the UE selects SUL; otherwise, NUL is selected.

[0086] FIG5 is a flowchart illustrating a UE operation for performing a RA procedure according to an embodiment of the present disclosure.

[0087] 5 , when the RA procedure is initiated at operation 510 , at operation 520 , the UE determines whether the MsgA payload size (or the MAC PDU size or the size of information carried in MsgA) for 2-step RA is larger than the MsgA payload size (or the MAC PDU size or the size of information carried in MsgA) that can be sent in the MsgA PUSCH resources of the PUSCH resource pool for 2-step RA (or any MsgA PUSCH resource pool if multiple PUSCH resource pools are configured). As shown in FIG. 5 , if the MsgA payload size (or the MAC PDU size or the size of information carried in MsgA payload) for 2-step RA is larger than the MsgA payload size (or the MAC PDU size or the size of information carried in MsgA payload) that can be sent in the MsgA PUSCH resources of the PUSCH resource pool for 2-step RA (or any Msg1 resource pool if multiple PUSCH resource pools are configured), then at operation 530 , the UE performs a 4-step RA procedure. Otherwise, at operation 540, the UE performs a 2-step RA procedure.

[0088] 2. Methods for dealing with the reliability of MsgA

[0089] Unlike the 4-step RACH procedure, the MsgA of the 2-step RA procedure includes information bits. In the 4-step RACH procedure, these information bits are sent using Msg3, where Hybrid Automatic Repeat Request (HARQ) or Transmission Time Interval (TTI) bundling is used for Msg3 transmission. HARQ or TTI bundling ensures that Msg3 can be reliably sent by UEs close to or far away from the gNB (i.e., at the cell edge). In the case of MsgA, mechanisms are required so that MsgA can be reliably sent by UEs close to and far away from the gNB.

[0090] According to an embodiment of the present disclosure, in order to support reliable transmission of MsgA by UEs close to and far from the gNB, multiple MsgA PUSCH resource pools for a 2-step RA procedure may be configured. The MsgA PUSCH opportunities (or PUSCH resources) in each of these multiple resource pools support a different number of repetitions of MsgA information (except CP and GT). The number of repetitions in each resource pool is indicated in the resource pool configuration. The MsgA PUSCH resource pools are signaled by the gNB in ​​system information and / or dedicated RRC signaling. The gNB also indicates the DL RSRP range for which a particular resource pool may be selected. In an embodiment of the procedure, multiple MsgA PUSCH resource pools refer to multiple MsgA PUSCH resource pools configured in the active UL BWP of the selected UL carrier. Note that both NUL and SUL carriers may be configured in a cell. For RA on a serving cell configured with both NUL and SUL carriers, the UE selects one of these carriers based on the DL RSRP of the cell.

[0091] FIG6 illustrates a process performed by a UE to support reliable transmission of MsgA according to an embodiment of the present disclosure.

[0092] 6, at operation 610, the UE receives multiple MsgA PUSCH resource pools / configurations for a 2-step RA procedure. For MsgA payload transmission, at operation 620, the UE selects a resource pool from the multiple resource pools, where the DL RSRP measured by the UE is within the range of the DL RSRP of the selected resource pool. The range of DL RSRP for each resource pool that can be used is signaled by the gNB. For example, three resource pools are configured. When DL RSRP <= threshold 1, resource pool 1 is used. When threshold 1 < DL RSRP <= threshold 2, resource pool 2 is used. When threshold 2 < DL RSRP, resource pool 3 is used. Thresholds 1 and 2 are signaled by the gNB. In an embodiment, the UE performs the selection of the resource pool at the beginning of the RA procedure for the first MsgA transmission, and then uses the same resource pool for all RA transmissions during the RA procedure. In another embodiment, the UE performs the selection of the resource pool before each MsgA transmission or RA attempt during the RA procedure. In an embodiment, the DL RSRP for resource pool selection is the RSRP derived from the SSB measurement of the cell on which MsgA is transmitted. In another embodiment, the DL RSRP for resource pool selection is the RSRP of the DL path loss reference. The DL path loss reference may be a synchronization signal, i.e., an SSB. The DL path loss reference may be an SSB selected for selecting PRACH resources (preamble, PRACH opportunity) and PUSCH resources for MsgA transmission. In an embodiment, the DL RSRP for resource pool selection is the synchronization signal RSRP (SS-RSRP) of the best SSB (i.e., the highest RSRP value among the SS-RSRP values ​​of all SSBs). In another embodiment, the DL RSRP for resource pool selection is the DL RSRP of the cell on which MsgA is transmitted. It is obtained as follows: The maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and the threshold (absThreshSS-Consolidation) are signaled by the gNB. The UE obtains them from SI or RRC signaling. If the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs (or beams) is below the threshold, the RSRP value of the cell is the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs. Otherwise, the RSRP of the cell is the linear average of the SS-RSRPs of up to a maximum number (nrofSS-ResourcesToAverage) of the highest SS-RSRP values ​​above the threshold.

[0093] Each MsgA PUSCH opportunity (or PUSCH resource) in the selected resource pool is mapped to one or more SSBs. At operation 630, the UE selects a MsgA PUSCH opportunity (or PUSCH resource) from the selected resource pool corresponding to a suitable SSB. If the SS block RSRP is greater than a threshold, the SS block is suitable, where the threshold is signaled by the gNB. If there is no suitable SSB, the UE may select a MsgA PUSCH opportunity (or PUSCH resource) from the selected resource pool corresponding to any SSB. If there are multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, the UE may randomly select one MsgA PUSCH opportunity from the multiple MsgAPUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, or the UE may select the earliest MsgA PUSCH opportunity from the multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB. Then, at operation 640, the UE sends MsgA in the selected MsgA PUSCH opportunity (or PUSCH resource). In an embodiment of the process, the multiple MsgA PUSCH resource pools refer to the multiple MsgA PUSCH resource pools configured in the active UL BWP of the selected UL carrier. Note that both NUL and SUL carriers can be configured in a cell. For RA on a serving cell configured with both NUL and SUL carriers, the UE selects one of these carriers based on the DL RSRP of the cell.

[0094] In embodiments where the RACH preamble is also sent in MsgA, a list of RACH preambles that can be used may be signaled by the gNB. Each RACH preamble in the list is mapped to one or more SSBs. The UE selects a RACH preamble corresponding to a suitable SSB (the SSB is suitable if the SSB block RSRP is greater than a threshold, where the threshold is signaled by the gNB). If there is no suitable SSB, the UE may select a RACH preamble corresponding to any SSB. If there are multiple RACH preambles corresponding to the selected SSB, the UE may randomly select one from the multiple RACH preambles corresponding to the selected SSB. In embodiments, each MsgA PUSCH resource pool may be associated with a different set of preambles so that the gNB can identify the MsgAPUSCH resources used by the UE and decode the MsgA payload accordingly. In this case, the UE selects the preamble corresponding to the selected SSB from the preambles associated with the selected MsgA PUSCH resource pool. In embodiments, two sets of RA preambles may be signaled. The UE selects a group of preambles based on the MsgA payload size, or based on the MsgA payload size and path loss (if groups are configured, and if the MsgA payload size (UL data available for transmission plus MAC header and, if required, MAC header) is greater than SizeGroupA and the path loss is less than a threshold, or if the RA procedure is initiated for a CCCH logical channel and the CCCH SDU size plus MAC subheader is greater than SizeGroupA, then preamble group B is selected. Otherwise group A is selected. SizeGroupA is configured by the gNB). In this case, the UE selects the preamble corresponding to the selected SSB from the preambles associated with the selected preamble group. So far, MsgA transmission in a 2-step RA procedure,

[0095] - The UE selects the UL carrier (NUL or SUL) when the RA procedure is started.

[0096] - The UE selects the SSB for each MsgA transmission during the RA procedure.

[0097] - As described above, the UE selects a PUSCH resource pool from the PUSCH resource pools of the active UL BWP. This step may be performed only once during the RA procedure.

[0098] -The UE selects a PUSCH opportunity corresponding to the selected SSB from the selected PUSCH resource pool.

[0099] -The UE selects a preamble corresponding to the selected SSB from the preambles of the selected PUSCH resource pool. Alternatively, the UE selects a preamble group, and then the UE selects a preamble corresponding to the selected SSB from the preambles of the selected preamble group.

[0100] - The UE selects the PRACH opportunity corresponding to the selected SSB. The PRACH opportunities for 2-step RA are mapped to SSBs as in 4-step RA.

[0101] -The UE then sends the selected preamble at the selected PRACH opportunity. The UE sends the MsgA payload at the selected PUSCH opportunity.

[0102] 7 is a diagram of another disclosed embodiment in which a gNB may signal up to two MsgA PUSCH resource pools (e.g., resource pool A and resource pool B) according to an embodiment of the present disclosure.

[0103] 7 , at operation 710 , the UE receives one or more MsgA PUSCH resource pools / configurations for 2-step RA. Resource pool A should be signaled, but resource pool B may be selectively signaled. At operation 720 , the UE determines whether resource pool B has been signaled. In addition, at operation 730 , the UE determines whether the DL RSRP of the cell (on which the UE will send MsgA) is less than Threshold. If resource pool B is signaled, and if the DL RSRP of the cell (on which the UE will send MsgA) is less than Threshold, then at operation 740 , the UE selects MsgA PUSCH resources from resource pool B. Otherwise, at operation 750 , the UE selects MsgA PUSCH resources from resource pool A. Threshold is signaled by the gNB. Each MsgA PUSCH opportunity (or PUSCH resource) in the selected resource pool is mapped to one or more SSBs. In an embodiment, the DL RSRP for resource pool selection is the RSRP derived from the SSB measurement of the cell on which MsgA is transmitted. In another embodiment, the DL RSRP for resource pool selection is the RSRP of the DL path loss reference. The DL path loss reference may be a synchronization signal, i.e., an SSB. The DL path loss reference may be the SSB selected for selecting the PRACH resources (preamble, PRACH opportunity) and PUSCH resources for MsgA transmission. In an embodiment, the DL RSRP for resource pool selection is the SS-RSRP value of the best SSB (i.e., the highest RSRP value among the SS-RSRP values ​​of all SSBs). In another embodiment, the DL RSRP for resource pool selection is the DL RSRP of the cell on which Msg1 is transmitted. It is obtained as follows: The maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and the threshold (absThreshSS-Consolidation) are signaled by the gNB. The UE obtains them from SI or RRC signaling. If the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs (or beams) is below the threshold, the RSRP value of the cell is the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs. Otherwise, the RSRP of the cell is the linear average of the SS-RSRP of up to a maximum number (nrofSS-ResourcesToAverage) of the highest SS-RSRP values ​​above the threshold. The UE selects a MsgA PUSCH opportunity (or PUSCH resource) from the selected resource pool corresponding to a suitable SSB (an SSB is suitable if its block RSRP is greater than a threshold, where the threshold is signaled by the gNB).If there is no suitable SSB, the UE may select a MsgA PUSCH opportunity (or resource) from the selected resource pool corresponding to any SSB. If there are multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, the UE may randomly select one MsgA PUSCH opportunity from the multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, or the UE may select the earliest MsgA PUSCH opportunity from the multiple MsgAPUSCH opportunities (or PUSCH resources) corresponding to the selected SSB. Then, at operation 760, the UE sends the MsgA payload (or MAC PDU) in the selected MsgAPUSCH opportunity (or PUSCH resource). In an embodiment of the process, the MsgAPUSCH resource pool refers to the MsgA PUSCH resource pool configured in the active UL BWP of the selected UL carrier. Note that both NUL and SUL carriers can be configured in a cell. For RA on a serving cell configured with both NUL and SUL carriers, the UE selects one of these carriers based on the DL RSRP of the cell.

[0104] FIG8 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure.

[0105] This procedure is applied when both 2-step and 4-step RA are supported in the cell initiating RA and the UE supports both 2-step and 4-step RA procedures. In a system supporting BWP: In RRC IDLE / INACTIVE state, the UE performs the RRC procedure on the initial DLBWP and the initial UL BWP of the camping cell. In the case where the camping cell is configured with both NUL and SUL, the UE selects the UL carrier based on the DL RSRP of the camping cell (for example, if the RSRP of the DL path loss reference (i.e., SSB) is less than the configured threshold, the UE selects SUL; otherwise NUL), and the initial UL BWP of the RA procedure is the initial UL BWP of the selected UL carrier. In the case where the camping cell is only configured with NUL, the UE selects NUL, and the initial UL BWP for the RA procedure is the initial UL BWP of NUL. Therefore, when both 2-step and 4-step RA are supported in the initial UL BWP of the selected UL carrier (i.e., the SI received from the camping cell includes 2-step and 4-step RA configurations), the UE in RRC IDLE / INACTIVE applies this procedure. In the RRC CONNECTED state, the UE performs the RA procedure on the active DL BWP and active UL BWP of the serving cell on which RA is initiated. In the case that the serving cell on which RA is initiated has both NUL and SUL configured, the active UL BWP for the RA procedure is the active UL BWP of the selected UL carrier. The UL carrier to be used (NUL or SUL) may be indicated by the gNB, and if not indicated, the UE selects the UL carrier based on the DL RSRP of the serving cell on which RA is initiated (e.g., if the RSRP of the DL path loss reference (i.e., SSB) is less than a configured threshold, the UE selects SUL; otherwise NUL). In the case that the serving cell on which RA is initiated has only NUL configured, the UE selects NUL. Therefore, a UE in RRC CONNECTED applies this procedure when the active UL BWP for the selected UL carrier supports 2-step and 4-step RA (i.e., the dedicated RRC signaling received from the gNB includes both 2-step and 4-step RA configurations).

[0106] The gNB signals the DL RSRP threshold for selecting the 2 / 4-step RA procedure. In an embodiment, the DL RSRP threshold may be configured separately for the NUL carrier and the SUL carrier, and the UE uses the DL RSRP threshold corresponding to the UL carrier selected for RA. In another embodiment, the DL RSRP threshold may be included in the RA configuration, where the RA configuration is signaled per UL BWP, and the UE uses the DL RSRP threshold included in the RA configuration corresponding to the active UL BWP (note that in RRCIDLE / INACTIVE, the initial UL BWP is the active UL BWP). In another embodiment, the DL RSRP threshold may be cell-specific, i.e., common for all BWPs, but may be configured separately for NUL and SUL. In another embodiment, the DL RSRP threshold is common for all BWPs and UL carriers of a cell.

[0107] In an embodiment of the present disclosure, the UE measures the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In an embodiment, the DL RSRP is the RSRP derived from the SSB measurement of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In another embodiment, the DL RSRP is the RSRP of the DL path loss reference. The DL path loss reference may be a synchronization signal, i.e., an SSB. The DL path loss reference may be an SSB selected for selecting PRACH resources (preamble, PRACH opportunity). In another embodiment, the DL RSRP is the SS-RSRP of the best SSB (i.e., the highest RSRP value among the SS-RSRP values ​​of all SSBs). In another embodiment, the DL RSRP is the DL RSRP of the cell on which RA is started, and it is obtained as follows: the maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and the threshold (absThreshSS-Consolidation) are signaled by the gNB. The UE obtains them from SI or RRC signaling. If the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs (or beams) is below the threshold, the DL RSRP value of the cell is the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs. Otherwise, the DL RSRP of the cell is the linear average of the SS-RSRP of the highest SS-RSRP values ​​up to the maximum number (nrofSS-ResourcesToAverage) above the threshold. In an embodiment, the DL RSRP of the cell may be the channel state information RSRP (CSI-RSRP).

[0108] If the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is less than or equal to the DL RSRP threshold, the UE performs the 4-step RA procedure. In an embodiment of the present disclosure, if the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is greater than the DL RSRP threshold, the UE performs the 2-step RA procedure. The DL RSRP threshold is signaled by the gNB (as described above). Referring to FIG. 8, when the RA procedure is initiated at operation 810, the UE checks at operation 820 whether the DL RSRP of the serving cell (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) is less than or equal to the DL RSRP threshold. If so, at operation 830, the UE performs the 4-step RA procedure. Otherwise (ie, the DL RSRP of the serving cell is greater than the DL RSRP threshold), at operation 840, the UE performs a 2-step RA procedure.

[0109] In an alternative embodiment of the present disclosure, if the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is greater than the DL RSRP threshold, the UE may perform a 4-step or 2-step RA procedure. In this case, the selection of a 4-step or 2-step RA procedure may depend on the implementation of the UE. Alternatively, in this case, the UE may randomly select a 4-step or 2-step RA procedure. Alternatively, the gNB may signal a distribution factor. The UE randomly selects a number within a specified range, and if the selected number is greater than the distribution factor, the UE selects a 2-step RA procedure, otherwise the UE selects a 4-step RA procedure.

[0110] In an alternative embodiment of the present disclosure, the selection of the 2 / 4-step RA procedure may be based on DL reference signal received quality (RSRQ) instead of DL RSRP.

[0111] In an embodiment of the present disclosure, if the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is less than the DL RSRP threshold, the UE performs the 4-step RA procedure. In an embodiment of the present disclosure, if the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is greater than or equal to the DL RSRP threshold, the UE performs the 2-step RA procedure. The DL RSRP threshold is signaled by the gNB (as described above). In an alternative embodiment of the present disclosure, if the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is greater than or equal to the DL RSRP threshold, the UE may perform the 4-step or 2-step RA procedure. In this case, the selection of the 4-step or 2-step RA procedure may depend on the implementation of the UE. Alternatively, in this case, the UE may randomly select either the 4-step or 2-step RA procedure. Alternatively, the gNB may signal a distribution factor. The UE randomly selects a number within a specified range, and if the selected number is greater than the distribution factor, the UE selects the 2-step RA procedure, otherwise the UE selects the 4-step RA procedure.

[0112] FIG. 9 shows a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure.

[0113] This procedure is applied when both 2-step and 4-step RA are supported in the cell initiating RA and the UE supports both 2-step and 4-step RA procedures. In a system supporting BWP: In RRC IDLE / INACTIVE state, the UE performs the RRC procedure on the initial DLBWP and the initial UL BWP of the camping cell. In the case where the camping cell is configured with both NUL and SUL, the UE selects the UL carrier based on the DL RSRP of the camping cell (for example, if the RSRP of the DL path loss reference (i.e., SSB) is less than the configured threshold, the UE selects SUL; otherwise NUL), and the initial UL BWP of the RA procedure is the initial UL BWP of the selected UL carrier. In the case where the camping cell is only configured with NUL, the UE selects NUL, and the initial UL BWP for the RA procedure is the initial UL BWP of NUL. Therefore, when both 2-step and 4-step RA are supported in the initial UL BWP of the selected UL carrier (i.e., the SI received from the camping cell includes 2-step and 4-step RA configurations), the UE in RRC IDLE / INACTIVE applies this procedure. In the RRC CONNECTED state, the UE performs the RA procedure on the active DL BWP and active UL BWP of the serving cell on which RA is initiated. In the case that the serving cell on which RA is initiated has both NUL and SUL configured, the active UL BWP for the RA procedure is the active UL BWP of the selected UL carrier. The UL carrier to be used (NUL or SUL) may be indicated by the gNB, and if not indicated, the UE selects the UL carrier based on the DL RSRP of the serving cell on which RA is initiated (e.g., if the RSRP of the DL path loss reference (i.e., SSB) is less than a configured threshold, the UE selects SUL; otherwise NUL). In the case that the serving cell on which RA is initiated has only NUL configured, the UE selects NUL. Therefore, a UE in RRC CONNECTED applies this procedure when the active UL BWP for the selected UL carrier supports both 2-step and 4-step RA (i.e., the dedicated RRC signaling received from the gNB includes both 2-step and 4-step RA configurations).

[0114] The gNB signals the DL RSRP threshold for selecting the 2 / 4-step RA procedure. In an embodiment, the DL RSRP threshold may be configured separately for the NUL carrier and the SUL carrier, and the UE uses the DL RSRP threshold corresponding to the UL carrier selected for RA. In another embodiment, the DL RSRP threshold may be included in the RA configuration, where the RA configuration is signaled per UL BWP, and the UE uses the DL RSRP threshold included in the RA configuration corresponding to the active UL BWP (note that in RRC IDLE / INACTIVE, the initial UL BWP is the active UL BWP). In another embodiment, the DL RSRP threshold may be cell-specific, i.e., common for all BWPs, but may be configured separately for NUL and SUL. In another embodiment, the DL RSRP threshold is common for all BWPs and UL carriers of a cell.

[0115] In an embodiment of the present disclosure, the UE measures the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In an embodiment, the DL RSRP is the RSRP derived from the SSB measurement of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In another embodiment, the DL RSRP is the RSRP of the DL path loss reference. The DL path loss reference may be a synchronization signal, i.e., an SSB. The DL path loss reference may be an SSB selected for selecting PRACH resources (preamble, PRACH opportunity) and PUSCH resources for MsgA transmission. In another embodiment, the DL RSRP is the SS-RSRP of the best SSB (i.e., the highest RSRP value among the SS-RSRP values ​​of all SSBs). In another embodiment, the DL RSRP is the DL RSRP of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA), and it is obtained as follows: the maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and the threshold (absThreshSS-Consolidation) are signaled by the gNB. The UE obtains them from SI or RRC signaling. If the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs (or beams) is below the threshold, the DL RSRP of the cell is the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs. Otherwise, the DL RSRP of the cell is the linear average of the SS-RSRP of the highest SS-RSRP values ​​up to the maximum number (nrofSS-ResourcesToAverage) above the threshold. In an embodiment, the DL RSRP of the cell may be the CSI-RSRP.

[0116] In the process shown in FIG. 9 of the present disclosure, the UE may perform selection between 2-step and 4-step based on the DL RSRP of the cell initiating RA before each RA attempt of the RA process instead of at the start of the RA process.

[0117] 9 , at the time of RA (re)transmission, at operation 920 , the UE determines whether the DL RSRP of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) is less than or equal to a threshold. If the DL RSRP of the serving cell (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) is less than or equal to the threshold, at operation 930 , the UE selects RA resources (preamble / RA opportunity) from the resources configured for 4-step RA. Otherwise (i.e., the DL RSRP of the serving cell on which RA is initiated is greater than the threshold), at operation 940 , the UE selects RA resources (preamble / MsgA PUSCH opportunity / RA opportunity) from the resources configured for 2-step RA. This is beneficial because channel conditions may change during the RA process.

[0118] FIG. 10 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure.

[0119] This procedure is applied when both 2-step and 4-step RA are supported in the cell initiating RA and the UE supports both 2-step and 4-step RA procedures. In a system supporting BWP: In RRC IDLE / INACTIVE state, the UE performs the RRC procedure on the initial DLBWP and the initial UL BWP of the camping cell. In the case where the camping cell is configured with both NUL and SUL, the UE selects the UL carrier based on the DL RSRP of the camping cell (for example, if the RSRP of the DL path loss reference (i.e., SSB) is less than the configured threshold, the UE selects SUL; otherwise NUL), and the initial UL BWP of the RA procedure is the initial UL BWP of the selected UL carrier. In the case where the camping cell is only configured with NUL, the UE selects NUL, and the initial UL BWP for the RA procedure is the initial ULBWP of NUL. Therefore, when both 2-step and 4-step RA are supported in the initial UL BWP of the selected UL carrier (i.e., the SI received from the camping cell includes 2-step and 4-step RA configurations), the UE in RRC IDLE / INACTIVE applies this procedure. In the RRC CONNECTED state, the UE performs the RRC procedure on the active DL BWP and active UL BWP of the serving cell on which RA is initiated. In the case that the serving cell on which RA is initiated is configured with both NUL and SUL, then the active UL BWP for the RA procedure is the active UL BWP of the selected UL carrier. The UL carrier to be used (NUL or SUL) may be indicated by the gNB, and if not indicated, the UE selects the UL carrier based on the DL RSRP of the serving cell on which RA is initiated (e.g., if the RSRP of the DL path loss reference (i.e., SSB) is less than a configured threshold, then the UE selects SUL; otherwise NUL). In the case that the serving cell on which RA is initiated is configured with only NUL, then the UE selects NUL. Therefore, a UE in RRC CONNECTED applies this procedure when the active UL BWP for the selected UL carrier supports both 2-step and 4-step RA (i.e., the dedicated RRC signaling received from the gNB includes both 2-step and 4-step RA configurations).

[0120] The gNB signals the DL RSRP threshold for selecting the 2 / 4-step RA procedure. In an embodiment, the DL RSRP threshold may be configured separately for the NUL carrier and the SUL carrier, and the UE uses the DL RSRP threshold corresponding to the UL carrier selected for RA. In another embodiment, the DL RSRP threshold may be included in the RA configuration, where the RA configuration is signaled per UL BWP, and the UE uses the DL RSRP threshold included in the RA configuration corresponding to the active UL BWP (note that in RRC IDLE / INACTIVE, the initial UL BWP is the active UL BWP). In another embodiment, the DL RSRP threshold may be cell-specific, i.e., common for all BWPs, but may be configured separately for NUL and SUL. In another embodiment, the DL RSRP threshold is common for all BWPs and UL carriers of a cell.

[0121] In an embodiment of the present disclosure, the UE measures the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In an embodiment, the DL RSRP is the RSRP derived from the SSB measurement of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In another embodiment, the DL RSRP is the RSRP of the DL path loss reference. The DL path loss reference may be a synchronization signal, i.e., an SSB. The DL path loss reference may be an SSB selected for selecting PRACH resources (preamble, PRACH opportunity) and PUSCH resources for MsgA transmission. In another embodiment, the DL RSRP is the SS-RSRP of the best SSB (i.e., the highest RSRP value among the SS-RSRP values ​​of all SSBs). In another embodiment, the DL RSRP is the DL RSRP of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA), and it is obtained as follows: the maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and the threshold (absThreshSS-Consolidation) are signaled by the gNB. The UE obtains them from SI or RRC signaling. If the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs (or beams) is below the threshold, the DL RSRP of the cell is the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs. Otherwise, the DL RSRP of the cell is the linear average of the SS-RSRP of the highest SS-RSRP values ​​up to the maximum number (nrofSS-ResourcesToAverage) above the threshold. In an embodiment, the DL RSRP of the cell may be the CSI-RSRP.

[0122] In another embodiment of the present disclosure, if the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is less than or equal to a threshold value, and TTI bundling of Msg3 transmission is supported, the UE performs the 4-step RA procedure as shown in FIG10. The threshold value is signaled by the gNB (as described above).

[0123] 10 , when the RA procedure is initiated at operation 1010, the UE checks at operation 1020 whether the DL RSRP of the cell on which the RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) is less than or equal to a threshold. In addition, at operation 1030, the UE determines whether TTI bundling for Msg3 transmission is supported. If yes, that is, the DL RSRP of the serving cell on which the RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) is less than or equal to the threshold, and TTI bundling for Msg3 transmission is supported, then at operation 1040, the UE performs the 4-step RA procedure. Otherwise (i.e., the DL RSRP of the serving cell on which the RA is initiated is greater than the threshold), at operation 1050, the UE performs the 2-step RA procedure. In an alternative embodiment, the UE may perform the selection between 2-step and 4-step based on the DL RSRP of the cell before each RA attempt of the RA procedure, rather than at the start of the RA procedure. This is beneficial because channel conditions may change during the RA process.

[0124] In another embodiment of the present disclosure, if the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is less than a threshold value and supports TTI bundling for Msg3 transmission, the UE performs a 4-step RA procedure. The threshold value is signaled by the gNB (as described above). When initiating the RA procedure, the UE checks whether the DL RSRP of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) is less than the threshold value. In addition, the UE determines whether TTI bundling for Msg3 transmission is supported. If yes, that is, the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) is less than the threshold value and supports TTI bundling for Msg3 transmission, the UE performs a 4-step RA procedure. Otherwise (i.e., the DL RSRP of the serving cell on which RA is initiated is greater than or equal to the threshold), the UE performs a 2-step RA. In an alternative embodiment, the UE may perform this selection between 2-step and 4-step based on the DL RSRP of the cell before each RA attempt of the RA procedure, rather than at the start of the RA procedure.

[0125] FIG. 11 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure.

[0126] In an embodiment of the present disclosure, the UE measures the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In an embodiment, the DL RSRP is the RSRP derived from the SSB measurement of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In another embodiment, the DL RSRP is the RSRP of the DL path loss reference. The DL path loss reference may be a synchronization signal, i.e., an SSB. The DL path loss reference may be an SSB selected for selecting PRACH resources (preamble, PRACH opportunity) and PUSCH resources for MsgA transmission. In another embodiment, the DL RSRP is the SS-RSRP of the best SSB (i.e., the highest RSRP value among the SS-RSRP values ​​of all SSBs). In another embodiment, the DL RSRP is the DL RSRP of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA), and it is obtained as follows: the maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and the threshold (absThreshSS-Consolidation) are signaled by the gNB. The UE obtains them from SI or RRC signaling. If the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs (or beams) is below the threshold, the DL RSRP value of the cell is the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs. Otherwise, the DL RSRP of the cell is the linear average of the SS-RSRP of the highest SS-RSRP values ​​up to the maximum number (nrofSS-ResourcesToAverage) above the threshold. In an embodiment, the DL RSRP of the cell may be the CSI-RSRP.

[0127] 11 , at operation 1110 , the UE receives a plurality of MsgA resource pools (or MsgA PUSCH resource pools) / configurations for a 2-step RA procedure. A range of DL RSRPs that can be used for each MsgA resource pool (or MsgA PUSCH resource pool) is signaled by the gNB. The MsgA payload size that can be sent in the MsgA PUSCH opportunity (or PUSCH resource) of the resource pool is also indicated by the gNB. For MsgA payload transmission, at operation 1120 , the UE selects a resource pool from the plurality of resource pools. The DL RSRP (i.e., the RSRP of the RS used as a DL path loss reference) of the serving cell on which RA is initiated (i.e., the cell on which the UE will send MsgA for 2-step RA) measured by the UE is within the range of the DL RSRP of the selected resource pool. In addition, the size of the MsgA payload (or the size of the MAC PDU or the size of the information carried in MsgA) that can be sent in the MsgA PUSCH resource of the selected resource pool is greater than or equal to the size of the MsgA payload (or the size of the MAC PDU or the size of the information carried in MsgA) that the UE intends to send. For example, four resource pools are configured. When DL RSRP <= threshold 1 and the MsgA payload size <= X, resource pool 1 is used. When DL RSRP > threshold 1 and the MsgA payload size <= X, resource pool 2 is used. When DL RSRP <= threshold 1 and the MsgA payload size > X, resource pool 3 is used. When DL RSRP > threshold 1 and the MsgA payload size > X, resource pool 4 is used. Each Msg1 PUSCH opportunity (or PUSCH resource) in the selected resource pool is mapped to one or more SSBs. At operation 1130, the UE selects an MsgAPUSCH opportunity (or PUSCH resource) from the selected resource pool corresponding to the appropriate SSB. If the SS block RSRP is greater than a threshold, the SSB is suitable, where the threshold is signaled by the gNB. If there is no suitable SSB, the UE may select a MsgA PUSCH opportunity (or PUSCH resource) from the selected resource pool corresponding to any SSB. If there are multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, the UE may randomly select one MsgA PUSCH opportunity from the multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB, or the UE may select the earliest MsgAPUSCH opportunity from the multiple MsgA PUSCH opportunities (or PUSCH resources) corresponding to the selected SSB. The UE then sends the MsgA payload in the selected MsgA PUSCH opportunity (or PUSCH resource).

[0128] FIG. 12 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure.

[0129] This procedure is applied when both 2-step and 4-step RA are supported in the cell initiating RA and the UE supports both 2-step and 4-step RA procedures. In a system supporting BWP: In RRC IDLE / INACTIVE state, the UE performs the RRC procedure on the initial DLBWP and the initial UL BWP of the camping cell. In the case where the camping cell is configured with both NUL and SUL, the UE selects the UL carrier based on the DL RSRP of the camping cell (for example, if the RSRP of the DL path loss reference (i.e., SSB) is less than the configured threshold, the UE selects SUL; otherwise NUL), and the initial UL BWP of the RA procedure is the initial UL BWP of the selected UL carrier. In the case where the camping cell is only configured with NUL, the UE selects NUL, and the initial UL BWP for the RA procedure is the initial UL BWP of NUL. Therefore, when 2-step and 4-step RA are supported for NUL and SUL respectively in the initial UL BWP of the selected UL carrier (i.e., the SI received from the camping cell includes both 2-step and 4-step RA configurations), the UE in RRC IDLE / INACTIVE applies this procedure. In RRC CONNECTED state, the UE performs the RA procedure on the active DL BWP and active UL BWP of the serving cell on which RA is initiated. In the case that the serving cell on which RA is initiated has both NUL and SUL configured, the active UL BWP for the RA procedure is the active UL BWP of the selected UL carrier. The UL carrier to be used (NUL or SUL) may be indicated by the gNB, and if not indicated, the UE selects the UL carrier based on the DL RSRP of the serving cell on which RA is initiated (e.g., if the RSRP of the DL path loss reference (i.e., SSB) is less than a configured threshold, the UE selects SUL; otherwise NUL). In the case that the serving cell on which RA is initiated has only NUL configured, the UE selects NUL. Therefore, a UE in RRC CONNECTED applies this procedure when the active UL BWP for the selected UL carrier supports 2-step and 4-step RA (i.e., the dedicated RRC signaling received from the gNB includes 2-step and 4-step RA configuration).

[0130] The gNB signals the DL RSRP threshold for selecting the 2 / 4-step RA procedure. In an embodiment, the DL RSRP threshold may be configured separately for the NUL carrier and the SUL carrier, and the UE uses the DL RSRP threshold corresponding to the UL carrier selected for RA. In another embodiment, the DL RSRP threshold may be included in the RA configuration, where the RA configuration is signaled per UL BWP, and the UE uses the DL RSRP threshold included in the RA configuration corresponding to the active UL BWP (note that in RRC IDLE / INACTIVE, the initial UL BWP is the active UL BWP). In another embodiment, the DL RSRP threshold may be cell-specific, i.e., common for all BWPs, but may be configured separately for NUL and SUL. In another embodiment, the DL RSRP threshold is common for all BWPs and UL carriers of a cell.

[0131] In an embodiment of the present disclosure, the UE measures the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In an embodiment, the DL RSRP is the RSRP derived from the SSB measurement of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In another embodiment, the DL RSRP is the RSRP of the DL path loss reference. The DL path loss reference may be a synchronization signal, i.e., an SSB. The DL path loss reference may be an SSB selected for selecting PRACH resources (preamble, PRACH opportunity) and PUSCH resources for MsgA transmission. In another embodiment, the DL RSRP is the SS-RSRP of the best SSB (i.e., the highest RSRP value among the SS-RSRP values ​​of all SSBs). In another embodiment, the DL RSRP is the DL RSRP of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA), and it is obtained as follows: the maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and the threshold (absThreshSS-Consolidation) are signaled by the gNB. The UE obtains them from SI or RRC signaling. If the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs (or beams) is below the threshold, the DL RSRP of the cell is the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs. Otherwise, the DL RSRP of the cell is the linear average of the SS-RSRP of the highest SS-RSRP values ​​up to the maximum number (nrofSS-ResourcesToAverage) above the threshold. In an embodiment, the DL RSRP of the cell may be the CSI-RSRP.

[0132] 12 , when the RA procedure is initiated at operation 1210, the UE determines at operation 1220 whether the DL RSRP of the cell on which the RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is less than or equal to a threshold and / or whether the MsgA payload size for 2-step RA (or the MAC PDU size or information size carried in MsgA) is greater than the MsgA payload size (or the MAC PDU size or information size carried in MsgA) that can be transmitted in the MsgA PUSCH resources for 2-step RA. If the DL RSRP of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is less than or equal to the threshold, or if the MsgA payload size (or the MAC PDU size or information size carried in MsgA) for 2-step RA is larger than the MsgA payload size (or the MAC PDU size or information size carried in MsgA) that can be sent in the MsgA PUSCH resource for 2-step RA, then at operation 1230, the UE performs a 4-step RA procedure as shown in FIG12. Otherwise, at operation 1240, the UE performs a 2-step RA procedure. The threshold is signaled by the gNB (as described above).

[0133] FIG. 13 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure.

[0134] This procedure is applied when both 2-step and 4-step RA are supported in the cell initiating RA and the UE supports both 2-step and 4-step RA procedures. In a system supporting BWP: In RRC IDLE / INACTIVE state, the UE performs the RRC procedure on the initial DLBWP and the initial UL BWP of the camping cell. In the case where the camping cell is configured with both NUL and SUL, the UE selects the UL carrier based on the DL RSRP of the camping cell (for example, if the RSRP of the DL path loss reference (i.e., SSB) is less than the configured threshold, the UE selects SUL; otherwise NUL), and the initial UL BWP of the RA procedure is the initial UL BWP of the selected UL carrier. In the case where the camping cell is only configured with NUL, the UE selects NUL, and the initial UL BWP for the RA procedure is the initial UL BWP of NUL. Therefore, when both 2-step and 4-step RA are supported in the initial UL BWP of the selected UL carrier (i.e., the SI received from the camping cell includes both 2-step and 4-step RA configurations), the UE in RRC IDLE / INACTIVE applies this procedure. In the RRC CONNECTED state, the UE performs the RA procedure on the active DL BWP and active UL BWP of the serving cell on which RA is initiated. In the case that the serving cell on which RA is initiated has both NUL and SUL configured, the active UL BWP for the RA procedure is the active UL BWP of the selected UL carrier. The UL carrier to be used (NUL or SUL) may be indicated by the gNB, and if not indicated, the UE selects the UL carrier based on the DL RSRP of the serving cell on which RA is initiated (e.g., if the RSRP of the DL path loss reference (i.e., SSB) is less than a configured threshold, the UE selects SUL; otherwise NUL). In the case that the serving cell on which RA is initiated has only NUL configured, the UE selects NUL. Therefore, a UE in RRC CONNECTED applies this procedure when the active UL BWP for the selected UL carrier supports both 2-step and 4-step RA (i.e., the dedicated RRC signaling received from the gNB includes both 2-step and 4-step RA configurations).

[0135] The gNB signals the DL RSRP threshold for selecting the 2 / 4-step RA procedure. In an embodiment, the DL RSRP threshold may be configured separately for the NUL carrier and the SUL carrier, and the UE uses the DL RSRP threshold corresponding to the UL carrier selected for RA. In another embodiment, the DL RSRP threshold may be included in the RA configuration, where the RA configuration is signaled per UL BWP, and the UE uses the DL RSRP threshold included in the RA configuration corresponding to the active UL BWP (note that in RRC IDLE / INACTIVE, the initial UL BWP is the active UL BWP). In another embodiment, the DL RSRP threshold may be cell-specific, i.e., common for all BWPs, but may be configured separately for NUL and SUL. In another embodiment, the DL RSRP threshold is common for all BWPs and UL carriers of a cell.

[0136] In an embodiment of the present disclosure, the UE measures the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In an embodiment, the DL RSRP is the RSRP derived from the SSB measurement of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In another embodiment, the DL RSRP is the RSRP of the DL path loss reference. The DL path loss reference may be a synchronization signal, i.e., an SSB. The DL path loss reference may be an SSB selected for selecting PRACH resources (preamble, PRACH opportunity) and PUSCH resources for MsgA transmission. In another embodiment, the DL RSRP is the SS-RSRP of the best SSB (i.e., the highest RSRP value among the SS-RSRP values ​​of all SSBs). In another embodiment, the DL RSRP is the DL RSRP of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA), and it is obtained as follows: the maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and the threshold (absThreshSS-Consolidation) are signaled by the gNB. The UE obtains them from SI or RRC signaling. If the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs (or beams) is below the threshold, the DL RSRP of the cell is the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs. Otherwise, the DL RSRP of the cell is the linear average of the SS-RSRP of the highest SS-RSRP values ​​up to the maximum number (nrofSS-ResourcesToAverage) above the threshold. In an embodiment, the DL RSRP of the cell may be the CSI-RSRP.

[0137] 13 , when the RA procedure is initiated at operation 1310, at operation 1320, the UE determines whether the DL RSRP of the cell on which the RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is within the range of DL RSRP of any resource pool for 2-step RA and / or whether the MsgA payload size for 2-step RA (or the size of the MAC PDU size or information carried in MsgA) is greater than the MsgA payload size that can be transmitted in the MsgA PUSCH resources for 2-step RA. If the DL RSRP of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is not within the range of DL RSRP of any resource pool for 2-step RA, or if the MsgA payload size for 2-step RA (or the MAC PDU size or information size carried in MsgA) is larger than the MsgA payload size (or the MAC PDU size or information size carried in MsgA) that can be sent in the MsgAPUSCH resources for 2-step RA, then at operation 1330, the UE performs a 4-step RA procedure as shown in FIG13. Otherwise, at operation 1340, the UE performs a 2-step RA procedure.

[0138] FIG. 14 illustrates a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure.

[0139] 14 , at operation 1410, when the RA procedure is initiated, the UE determines at operation 1420 whether the RA procedure is initiated for CCCH transmission and whether the CCCH is CCCH 2. If the RA procedure is initiated for CCCH 2 transmission, the UE performs a 4-step RA procedure at operation 1430. Otherwise, for example, if the CCCH is CCCH1, the UE performs a 2-step RA at operation 1440, as shown in FIG. 14 .

[0140] 15a and 15b illustrate a process performed by a UE to support reliable transmission of MsgA according to another embodiment of the present disclosure.

[0141] This procedure is applied when both 2-step and 4-step RA are supported in the cell initiating RA and the UE supports both 2-step and 4-step RA procedures. In a system supporting BWP: In RRC IDLE / INACTIVE state, the UE performs the RRC procedure on the initial DLBWP and the initial UL BWP of the camping cell. In the case where the camping cell is configured with both NUL and SUL, the UE selects the UL carrier based on the DL RSRP of the camping cell (for example, if the RSRP of the DL path loss reference (i.e., SSB) is less than the configured threshold, the UE selects SUL; otherwise NUL), and the initial UL BWP of the RA procedure is the initial UL BWP of the selected UL carrier. In the case where the camping cell is only configured with NUL, the UE selects NUL, and the initial UL BWP for the RA procedure is the initial UL BWP of NUL. Therefore, when both 2-step and 4-step RA are supported in the initial UL BWP of the selected UL carrier (i.e., the SI received from the camping cell includes both 2-step and 4-step RA configurations), the UE in RRC IDLE / INACTIVE applies this procedure. In the RRC CONNECTED state, the UE performs the RA procedure on the active DL BWP and active UL BWP of the serving cell on which RA is initiated. In the case that the serving cell on which RA is initiated has both NUL and SUL configured, the active UL BWP for the RA procedure is the active UL BWP of the selected UL carrier. The UL carrier to be used (NUL or SUL) may be indicated by the gNB, and if not indicated, the UE selects the UL carrier based on the DL RSRP of the serving cell on which RA is initiated (e.g., if the RSRP of the DL path loss reference (i.e., SSB) is less than a configured threshold, the UE selects SUL; otherwise NUL). In the case that the serving cell on which RA is initiated has only NUL configured, the UE selects NUL. Therefore, a UE in RRC CONNECTED applies this procedure when the active UL BWP for the selected UL carrier supports both 2-step and 4-step RA (i.e., the dedicated RRC signaling received from the gNB includes both 2-step and 4-step RA configurations).

[0142] The gNB signals the DL RSRP threshold for selecting the 2 / 4-step RA procedure. In an embodiment, the DL RSRP threshold may be configured separately for the NUL carrier and the SUL carrier, and the UE uses the DL RSRP threshold corresponding to the UL carrier selected for RA. In another embodiment, the DL RSRP threshold may be included in the RA configuration, where the RA configuration is signaled per UL BWP, and the UE uses the DL RSRP threshold included in the RA configuration corresponding to the active UL BWP (note that in RRC IDLE / INACTIVE, the initial UL BWP is the active UL BWP). In another embodiment, the DL RSRP threshold may be cell-specific, i.e., common for all BWPs, but may be configured separately for NUL and SUL. In another embodiment, the DL RSRP threshold is common for all BWPs and UL carriers of a cell.

[0143] In an embodiment of the present disclosure, the UE measures the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In an embodiment, the DL RSRP is the RSRP derived from the SSB measurement of the cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA). In another embodiment, the DL RSRP is the RSRP of the DL path loss reference. The DL path loss reference may be a synchronization signal, i.e., an SSB. The DL path loss reference may be an SSB selected for selecting PRACH resources (preamble, PRACH opportunity). In another embodiment, the DL RSRP is the SS-RSRP of the best SSB (i.e., the highest RSRP value among the SS-RSRP values ​​of all SSBs). In another embodiment, the DL RSRP is the DL RSRP of the cell on which RA is started, and it is obtained as follows: the maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and the threshold (absThreshSS-Consolidation) are signaled by the gNB. The UE obtains them from SI or RRC signaling. If the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs (or beams) is below the threshold, the DL RSRP of the cell is the highest SS-RSRP value among the SS-RSRP values ​​of all SSBs. Otherwise, the DL RSRP of the cell is the linear average of the SS-RSRP of the highest SS-RSRP values ​​up to the maximum number (nrofSS-ResourcesToAverage) above the threshold. In an embodiment, the DL RSRP of the cell may be the CSI-RSRP.

[0144] 15A , when starting the RA procedure at operation 1510 , the UE checks at operation 1520 whether the DL RSRP of the serving cell (ie, the cell on which the UE will transmit Msg1 for 4-step RA and MsgA for 2-step RA) is greater than the DL RSRP threshold.

[0145] In an embodiment of the present disclosure, if at operation 1520, the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is less than or equal to the DL RSRP threshold, the UE performs the following operations:

[0146] At operation 1530, the UE determines whether contention-free RA (CFRA) resources associated with the SSB and / or CSI reference signal (CSI-RS) are signaled by the gNB. If the determination at operation 1530 is yes, at operation 1540, the UE determines whether at least one SSB / CSI-RS having an SS-RSRP / CSI-RSRP higher than rsrp-ThresholdSSB / rsrp-ThresholdCSIRS among the associated SSB / CSI-RS is available. If the determination at operation 1540 is yes, the UE performs CFRA, i.e., at operation 1550, Msg1 is sent using CFRA resources. If the UE fails to receive a RAR corresponding to the Msg1 it sent in the RAR window and the maximum number of RA attempts has not been reached, the UE performs operation 1530.

[0147] If it is determined to be negative at operation 1530 or operation 1540, the UE performs 4-step CBRA, i.e., sends Msg1 using CBRA resources at operation 1560. If the UE fails to receive the RAR corresponding to the Msg1 sent by it in the RAR window, or the contention resolution timer expires, and the maximum number of RA attempts has not been reached, the UE performs operation 1530.

[0148] In an embodiment of the present disclosure, if at operation 1520, the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is greater than the DL RSRP threshold, the UE performs the following operations:

[0149] 15b, at operation 1570, the UE determines whether CFRA resources associated with the SSB and / or CSI-RS are signaled by the gNB. If it is determined to be yes at operation 1570, at operation 1580, the UE determines whether at least one SSB / CSI-RS having an SS-RSRP / CSI-RSRP higher than rsrp-ThresholdSSB / rsrp-ThresholdCSIRS among the associated SSB / CSI-RS is available. If it is determined to be yes at operation 1580, the UE performs CFRA, that is, at operation 1590, Msg1 is sent using CFRA resources. If the UE fails to receive a RAR corresponding to the Msg1 it sent in the RAR window and the maximum number of RA attempts has not been reached, the UE performs operation 1570.

[0150] If it is determined to be no at operation 1570 or operation 1580, the UE performs 2-step CBRA, i.e., sends MsgA using CBRA resources at operation 1600. If the UE fails to receive MsgB corresponding to the MsgA sent by it in the MsgB window, or if a backoff indication is received in MsgB, the contention resolution timer expires when Msg3 is sent; and the maximum number of RA attempts has not been reached, the UE performs operation 1570.

[0151] If the maximum number of MsgA transmissions is configured, if the UE fails to receive MsgB corresponding to the MsgA it sent in the MsgB window, or if a backoff indication is received in MsgB, and the contention resolution timer expires when sending Msg3, the UE will perform operation 1530.

[0152] 16a and 16b are flow charts illustrating UE operations for performing a RA procedure according to alternative embodiments of the present disclosure.

[0153] 16A , when starting the RA procedure at operation 1610 , the UE checks at operation 1620 whether the DL RSRP of the serving cell (ie, the cell on which the UE will transmit Msg1 for 4-step RA and MsgA for 2-step RA) is greater than the DL RSRP threshold.

[0154] In an embodiment of the present disclosure, if at operation 1620, the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) measured by the UE is less than or equal to the DL RSRP threshold, the UE performs the following operations:

[0155] At operation 1630, the UE determines whether CFRA resources associated with the SSB and / or CSI-RS are signaled by the gNB. If the determination at operation 1630 is yes, at operation 1640, the UE determines whether at least one SSB / CSI-RS having an SS-RSRP / CSI-RSRP higher than rsrp-ThresholdSSB / rsrp-ThresholdCSIRS among the associated SSB / CSI-RS is available. If the determination at operation 1640 is yes, the UE performs CFRA, i.e., at operation 1650, Msg1 is sent using CFRA resources. If the UE fails to receive a RAR corresponding to the Msg1 it sent in the RAR window and the maximum number of RA attempts has not been reached, the UE performs operation 1630.

[0156] If the determination at operation 1630 or operation 1640 is no, the UE performs 4-step CBRA, i.e., at operation 1660, Msg1 is sent using CBRA resources. If the UE fails to receive the RAR corresponding to the Msg1 sent by it in the RAR window, or the contention resolution timer expires and the maximum number of RA attempts has not been reached, the UE performs operation 1630.

[0157] In an embodiment of the present disclosure, if at operation 1620, the DL RSRP of the serving cell on which RA is initiated (i.e., the cell on which the UE will send Msg1 for 4-step RA and MsgA for 2-step RA) is greater than the DL RSRP threshold, the UE performs the following operations:

[0158] Referring to FIG. 16b, at operation 1670, the UE determines whether the CFRA resources associated with the SSB and / or CSI-RS are signaled by the gNB. If it is determined to be yes at operation 1670, at operation 1680, the UE determines whether at least one SSB / CSI-RS having an SS-RSRP / CSI-RSRP higher than rsrp-ThresholdSSB / rsrp-ThresholdCSIRS among the associated SSB / CSI-RS is available. If it is determined to be yes at operation 1680, the UE performs CFRA, that is, at operation 1690, if the CFRA resources are for legacy CFRA, Msg1 is sent using the CFRA resources, or if the CFRA resources are for 2-step CFRA, MsgA is sent using the CFRA resources. If the UE fails to receive the RAR / MsgB corresponding to the Msg1 / MsgA sent by it within the response window, and the maximum number of RA attempts has not been reached, the UE performs operation 1670.

[0159] If it is determined to be no at operation 1670 or operation 1680, the UE performs 2-step CBRA, i.e., sends MsgA at operation 1700. If the UE fails to receive MsgB corresponding to the MsgA sent by it in the MsgB window, or if a backoff indication is received in Msgb, the contention resolution timer expires when Msg3 is sent; and the maximum number of RA attempts has not been reached, the UE performs operation 1670.

[0160] If the maximum number of MsgA transmissions is configured, if the UE fails to receive MsgB corresponding to the MsgA it sent in the MsgB window, or if a backoff indication is received in MsgB, and the contention resolution timer expires when sending Msg3, the UE will perform operation 1630.

[0161] 3. Methods for handling RA-RNTI ambiguity between 2-step and 4-step RA procedures

[0162] There may be ambiguity in determining whether the network response sent by the gNB is for a 2-step or 4-step RA. For example, UE1 sends Msg1 for a 4-step RA. UE2 sends MsgA for a 2-step RA. For the network response (i.e., Msg2 for a 4-step RA procedure, MsgB for a 2-step RA procedure), the UE monitors the PDCCH addressed to the RA-RNTI, where the RA-RNTI is determined as follows: The s_id, t_id, f_id and ul_carrier_id corresponding to the MsgA opportunity of the 2-step RA and the Msg1 opportunity of the 4-step RA may be the same. Therefore, a method is needed to avoid this ambiguity.

[0163] In an embodiment, an additional parameter "RACH_Type" is added in the RA-RNTI calculation. The RA-RNTI is derived as follows:

[0164] ,

[0165] Among them, the RACH type of the traditional RACH process = 0; the RACH type of the new 2-step RACH process = 1,

[0166] s_id is the index of the first OFDM symbol of the specified PRACH or Msg1 opportunity (0≤ s_id<14). The MsgA opportunity can be a PRACH opportunity or a PUSCH opportunity.

[0167] t_id is the index of the first time slot of the specified PRACH or Msg1 opportunity (0≤ t_id< 80). The MsgA opportunity can be a PRACH opportunity or a PUSCH opportunity.

[0168] f_id is the index of the PRACH or MsgA opportunity specified in the time slot in the frequency domain. The MsgA opportunity can be a PRACH opportunity or a PUSCH opportunity, and

[0169] ul_carrier_id is the UL carrier used for Msg1 transmission (0 for NUL, 1 for SUL).

[0170] For the conventional RA procedure, for the RA response (RAR), the UE monitors the address to For the new 2-step RA procedure, for MsgB, the UE monitors the PDCCH addressed to PDCCH.

[0171] In another embodiment, separate control resource sets (CORESETs) or search spaces are signaled for the new 2-step RA procedure and the legacy 4-step RA procedure. For the legacy RA procedure, for RAR, the UE monitors the PDCCH in the RAR CORESET / search space (say X, X is the ID of the search space, a list of search spaces is configured, where each search space has a unique ID). For the new 2-step RA procedure, for MsgB, the UE monitors the PDCCH in the MsgB CORESET / search space (say Y, Y is the ID of the search space, a list of search spaces is configured, where each search space has a unique ID). The RAR CORESET / search space for legacy RA and the MsgB CORESET / search space for the new 2-step RA are signaled by the gNB. In an embodiment, the configuration of the MsgB CORESET / search space for the new 2-step RA is optionally signaled by the gNB. For example, if the RACH opportunities for 2-step and legacy RA procedures are shared, the gNB may not signal this. If the MsgB CORESET / search space is not signaled, then for MsgB the UE monitors the PDCCH in the RAR CORESET / search space.

[0172] In another embodiment, a fixed RNTI value is used instead of RA-RNTI to address the PDCCH for MsgB of the new 2-step RA. If the UE selects the Msg1 resource from the resource pool or RACH configuration used for the traditional RA procedure, in other words, for the traditional RA procedure, for RAR, the UE monitors the PDCCH addressed to If the UE selects MsgA resources from the resource pool or RACH configuration for the new 2-step RA procedure, in other words, for the 2-step RA procedure, for MsgB, the UE monitors the PDCCH addressed to RA-RNTI = fixed RNTI value. The fixed RNTI value may be reserved and predefined in the specification.

[0173] In another embodiment, in the BWP where the RACH or MsgA opportunities for the new 2-step RA are configured, the RACH or Msg1 opportunities for the legacy RA procedure are not configured. For example, the RACH or Msg1 opportunities for the legacy RA procedure are configured by the gNB in ​​BWP X, and then the RACH or MsgA opportunities for the new 2-step RA procedure are configured by the gNB in ​​BWP Y, where Y is not equal to X. The DL BWP used to receive the network response (Msg2 / MsgB) has the same BWP ID as the UL BWP ID in which Msg1 / MsgB is sent. Therefore, this approach will ensure that the DL BWPs used for Msg2 for the legacy RA procedure and MsgB for the new 2-step RA procedure are different.

[0174] In another embodiment, the gNB may configure non-overlapping (i.e., t_id, f_id, and s_id of the PRACH occasions of the new 2-step RA and the PRACH occasions of the legacy RA are all different) RACH opportunities for the new 2-step RA and the legacy RA procedures. This will ensure that the RA-RNTI determined for the new 2-step RA and the legacy RA procedures will be different.

[0175] In another embodiment, an additional parameter "RA Preamble ID (RAPID)" is added to the RA-RNTI calculation. The RA-RNTI is derived as follows:

[0176] ,

[0177] Where RAPID = RAPID of the RACH preamble sent in MsgA,

[0178] s_id is the index of the first OFDM symbol of the specified PRACH or Msg1 opportunity (0≤ s_id<14),

[0179] t_id is the index of the first time slot of the specified PRACH or Msg1 opportunity (0≤ t_id< 80),

[0180] f_id is the index of the PRACH specified in this time slot in the frequency domain, and

[0181] ul_carrier_id is the UL carrier used for Msg1 transmission (0 for NUL, 1 for SUL).

[0182] If the UE selects the Msg1 resource from the resource pool or RACH configuration used for the conventional RA procedure, i.e., for RAR, the UE monitors the If the UE selects the MsgA resource from the resource pool or RACH configuration for the new 2-step RA procedure, in other words, for the 2-step RA procedure, i.e., for MsgB, the UE monitors the PDCCH addressed to This will ensure that the RA-RNTI determined for the new 2-step RA and legacy RA procedures will be different.

[0183] In another embodiment, an additional parameter "f_id offset" is added to the RNTI calculation. The RA-RNTI is derived as follows:

[0184] ,

[0185] Where RAPID = RAPID of the RACH preamble sent in MsgA,

[0186] s_id is the index of the first OFDM symbol of the specified PRACH or Msg1 opportunity (0≤ s_id<14),

[0187] t_id is the index of the first time slot of the specified PRACH or Msg1 opportunity (0≤t_id<80),

[0188] f_id is the index of the PRACH specified in the time slot in the frequency domain.

[0189] ul_carrier_id is the UL carrier used for Msg1 transmission (0 for NUL, 1 for SUL), and

[0190] f_id offset is signaled by the gNB for new 2-step RA. If not signaled, f_id offset is zero.

[0191] If the UE selects the Msg1 resource from the resource pool or RACH configuration used for the conventional RA procedure, i.e., for RAR, the UE monitors the If the UE selects MsgA resources from the resource pool or RACH configuration for the new 2-step RA procedure, in other words, for the 2-step RA procedure, i.e., for MsgB, the UE monitors the PDCCH addressed to This will ensure that the RA-RNTI determined for the new 2-step RA and legacy RA procedures will be different.

[0192] In another embodiment, the gNB signals a parameter "f_id start offset". The frequency-division multiplexed PRACH opportunities for 2-step RA are sequentially numbered starting from 'f_id start offset'. If 'f_id start offset' is not signaled, the frequency-division multiplexed PRACH opportunities for 2-step RA are sequentially numbered starting from 0.

[0193] In another embodiment, in the RA-RNTI calculation for the new 2-step RA, ul_carrier_id may be set to 2 (if NUL is used for MsgA transmission) and 3 (if SUL is used for MsgA transmission). If the UE selects the Msg1 resource from the resource pool or RACH configuration used for the legacy RA procedure, i.e., for RAR, the UE monitors the PDCCH.

[0194] s_id is the index of the first OFDM symbol of the specified PRACH or Msg1 opportunity (0≤ s_id<14),

[0195] t_id is the index of the first time slot of the specified PRACH or Msg1 opportunity (0≤t_id<80),

[0196] f_id is the index of the PRACH specified in this time slot in the frequency domain, and

[0197] ul_carrier_id is the UL carrier used for Msg1 transmission (0 for NUL, 1 for SUL).

[0198] If the UE selects MsgA resources from the resource pool or RACH configuration for the new 2-step RA procedure, i.e., for MsgB, the UE monitors the PDCCH, where:

[0199] s_id is the index of the first OFDM symbol of the specified PRACH or Msg1 opportunity (0≤ s_id<14),

[0200] t_id is the index of the first time slot of the specified PRACH or Msg1 opportunity (0≤t_id<80),

[0201] f_id is the index of the PRACH specified in this time slot in the frequency domain, and

[0202] ul_carrier_id is the UL carrier used for MsgA transmission (2 for NUL, 3 for SUL).

[0203] Note that in the RA-RNTI calculation, additional parameter(s) indicating the frame index or BWP index may also be included.

[0204] FIG. 17 is a block diagram of a terminal according to an embodiment of the present disclosure.

[0205] Referring to Figure 17, the terminal includes a transceiver 1710, a controller 1720, and a memory 1730. The controller 1720 may refer to a circuit, an ASIC, or at least one processor. The transceiver 1710, the controller 1720, and the memory 1730 are configured to perform the operations of the UE shown in the figure (e.g., Figures 1 to 16B) or otherwise described above. Although the transceiver 1710, the controller 1720, and the memory 1730 are shown as separate entities, they can be implemented as a single entity like a single chip. The transceiver 1710, the controller 1720, and the memory 1730 may also be electrically connected or coupled to each other.

[0206] The transceiver 1710 may transmit and receive signals to and from other network entities (eg, base stations).

[0207] The controller 1720 may control the UE to perform a function according to one of the above embodiments. For example, the controller 1720 is configured to measure the DL RSRP of the cell (the cell on which the terminal will send Msg1). The controller 1720 may be configured to identify the DL RSRP of the cell based on the SSB measurement or the channel CSI-RS measurement of the serving cell. The controller 1720 may be configured to perform measurement of the DL RSRP of the cell at the start of the RA process or before each RA attempt of the RA process. The controller 1720 is configured to determine whether the DL RSRP of the cell is greater than a threshold. The controller 1720 is configured to perform a 2-step RA process on the cell if the DL RSRP of the cell is greater than the threshold, or to perform a 4-step RA process on the cell if the DL RSRP of the cell is less than or equal to the threshold. The controller 1720 may be configured to perform a 2-step RA process by controlling the transceiver 1710 to send MsgA including an RA preamble and a MAC PDU to a base station controlling a cell, and controlling the transceiver 1710 to receive MsgB corresponding to MsgA from the base station. The controller 1720 may be configured to control the transceiver 1710 to receive information about a threshold from the base station. The controller 1720 may be configured to determine whether the cell supports the 2-step RA process. The 2-step RA process can only be performed if the cell supports the 2-step RA process. The controller 1720 may be configured to control the transceiver 1710 to receive one or more resource pools for the 2-step RA process from the base station, and select a timing for sending MsgA in the 2-step RA process from the one or more resource pools. The controller 1720 may be configured to determine whether the size of MsgA to be sent in the 2-step RA process is greater than the size of MsgA that can be sent in the 2-step RA process. If the size of MsgA to be transmitted in the 2-step RA procedure is less than or equal to the size of MsgA that can be transmitted in the 2-step RA procedure, the 2-step RA procedure may be performed.

[0208] In an embodiment, the operation of the terminal can be implemented using a memory 1730 storing corresponding program codes. Specifically, the terminal can be equipped with a memory 1730 to store program codes that implement the desired operation. In order to perform the desired operation, the controller 1720 can read and execute the program code stored in the memory 1730 by using a processor or a central processing unit (CPU).

[0209] FIG. 18 is a block diagram of a base station according to an embodiment of the present disclosure.

[0210] 18, the base station includes a transceiver 1810, a controller 1820, and a memory 1830. The controller 1820 may refer to a circuit, an ASIC, or at least one processor. The transceiver 1810, the controller 1820, and the memory 1830 are configured to perform the operations of the network (e.g., gNB) as described above. Although the transceiver 1810, the controller 1820, and the memory 1830 are shown as separate entities, they may be implemented as a single entity like a single chip. The transceiver 1810, the controller 1820, and the memory 1830 may also be electrically connected or coupled to each other.

[0211] The transceiver 1810 may send signals to other network entities (e.g., terminals) and receive signals from other network entities (e.g., terminals). The controller 1820 may control the base station to perform the functions according to one of the above embodiments. For example, the controller 1820 may be configured to control the transceiver 1810 to receive MsgA including an RA preamble and a MAC PDU from the terminal, and to send MsgB corresponding to MsgA to the terminal. The controller 1820 may be configured to control the transceiver 1810 to send information about a threshold for determining whether to perform a 2-step RA process or a 4-step RA process to the terminal. The controller 1820 may be configured to control the transceiver 1810 to send one or more resource pools for a 2-step RA process to the terminal. The controller 1820 may be configured to control the transceiver 1810 to send information about the maximum number of beams (or SSBs) (nrofSS-ResourcesToAverage) and a threshold (absThreshSS-Consolidation). In an embodiment, the operation of the base station may be implemented using a memory 1830 storing corresponding program codes. Specifically, the base station may be equipped with a memory 1830 to store program codes for implementing desired operations. In order to perform desired operations, the controller 1820 may read and execute the program codes stored in the memory 1830 by using a processor or a CPU.

[0212] While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.

Claims

1. A method performed by a terminal in a wireless communication system, the method comprising: receiving a radio resource control RRC message including dedicated random access channel RACH configuration information from a base station; Identifying, through dedicated configuration information, whether a contention-free random access CFRA resource associated with a synchronization signal block SSB is configured for a 2-step random access RA type, and identifying whether at least one SSB among the SSBs having a reference signal received power RSRP higher than a threshold is available; In a case where it is identified through dedicated configuration information that a CFRA resource associated with an SSB is configured as a 2-step RA type and at least one SSB having an RSRP higher than a threshold value among the SSBs is available, selecting an SSB among the at least one SSB; selecting a PUSCH opportunity from among the physical uplink shared channel PUSCH opportunities configured by the dedicated RACH configuration information based on the selected SSB; and A CFRA procedure of a 2-step RA type is performed based on the selected PUSCH opportunity.

2. The method according to claim 1, further comprising: receiving, from a base station, information about an RSRP threshold for selecting between an RA procedure of a 2-step RA type and an RA procedure of a 4-step RA type; as well as Based on the RSRP for the downlink being above the RSRP threshold, a RA procedure of 2-step RA type is selected.

3. The method according to claim 2, further comprising: In the case where the CFRA resources associated with the SSB are not configured for the 2-step RA type through dedicated configuration information, a contention-based random access CBRA procedure of the 2-step RA type is performed based on the selected SSB.

4. The method according to claim 1, wherein: The process for performing a 2-step RA type CFRA includes: Send a message MSG A to the base station using the physical random access channel PRACH opportunity corresponding to the selected SSB and the selected PUSCH opportunity, Among them, MSG A includes a random access preamble code and a media access control MAC protocol data unit PDU corresponding to the selected SSB.

5. The method according to claim 4, further comprising: receiving from the base station a MSG B for MSG A based on a radio network temporary identifier RNTI, Among them, RNTI is identified as: RNTI = 1 + s_id + 14 × t_id + 14 × 80 × f_id + 14 × 80 × 8 × ul_carrier_id + 14 × 80 × 8 × 2, Among them, s_id is the index of the first orthogonal frequency division multiplexing OFDM symbol of the PRACH opportunity, t_id is the index of the first time slot of the PRACH opportunity, f_id is the index of the PRACH opportunity in the frequency domain, and ul_carrier_id is the uplink carrier used for transmission of MSG A.

6. A method performed by a base station in a wireless communication system, the method comprising: Sending a radio resource control RRC message including dedicated random access channel RACH configuration information to the terminal; In case that a contention-free random access CFRA resource associated with a synchronization signal block SSB is configured for a 2-step random access RA type through dedicated RACH configuration information, performing a 2-step RA type CFRA procedure with the terminal, Among them, the 2-step RA type CFRA process is performed based on the SSB with a reference signal received power RSRP higher than the threshold among the SSBs and the PUSCH opportunity corresponding to the SSB among the physical uplink shared channel PUSCH opportunities configured by dedicated RACH configuration information.

7. The method according to claim 6, further comprising: transmitting, to the terminal, information about an RSRP threshold for selecting between an RA procedure of a 2-step RA type and an RA procedure of a 4-step RA type; as well as Among them, the RA process of the 2-step RA type is selected based on the RSRP for the downlink being higher than the RSRP threshold.

8. The method according to claim 7, further comprising: In a case where a CFRA resource associated with an SSB is not configured for the 2-step RA type through dedicated configuration information, a contention-based random access CBRA procedure of the 2-step RA type is performed based on the SSB.

9. The method according to claim 6, wherein: The process of performing a CFRA of the 2-step RA type with a terminal includes: Based on the physical random access channel PRACH timing and PUSCH timing corresponding to the SSB, a message MSG A is received from the terminal, Among them, MSG A includes the random access preamble code and the media access control MAC protocol data unit PDU corresponding to the SSB.

10. The method according to claim 9, further comprising: Sending MSG B for MSG A based on the radio network temporary identifier RNTI to the terminal, Among them, RNTI is identified as: RNTI = 1 + s_id + 14 × t_id + 14 × 80 × f_id + 14 × 80 × 8 × ul_carrier_id + 14 × 80 × 8 × 2, Among them, s_id is the index of the first orthogonal frequency division multiplexing OFDM symbol of the PRACH opportunity, t_id is the index of the first time slot of the PRACH opportunity, f_id is the index of the PRACH opportunity in the frequency domain, and ul_carrier_id is the uplink carrier used for transmission of MSG A.

11. A terminal in a wireless communication system, the terminal comprising: Transceiver; as well as The controller is configured as: Controlling the transceiver to receive a radio resource control RRC message including dedicated random access channel RACH configuration information from a base station; Identifying, through dedicated configuration information, whether a contention-free random access CFRA resource associated with a synchronization signal block SSB is configured for a 2-step random access RA type, and identifying whether at least one SSB among the SSBs having a reference signal received power RSRP higher than a threshold is available; In a case where it is identified through dedicated configuration information that a CFRA resource associated with an SSB is configured as a 2-step RA type and at least one SSB having an RSRP higher than a threshold value among the SSBs is available, selecting an SSB among the at least one SSB; selecting a PUSCH opportunity from among the physical uplink shared channel PUSCH opportunities configured by the dedicated RACH configuration information based on the selected SSB; and A CFRA procedure of a 2-step RA type is performed based on the selected PUSCH opportunity.

12. The terminal according to claim 11, wherein: The controller is also configured to: controlling the transceiver to receive information about an RSRP threshold for selecting between an RA procedure of a 2-step RA type and an RA procedure of a 4-step RA type from a base station; and Based on the RSRP for the downlink being above the RSRP threshold, a RA procedure of 2-step RA type is selected.

13. The terminal according to claim 12, wherein: The controller is also configured to: In the case where the CFRA resources associated with the SSB are not configured for the 2-step RA type through dedicated configuration information, a contention-based random access CBRA procedure of the 2-step RA type is performed based on the selected SSB.

14. The terminal according to claim 11, in, The controller is further configured to control the transceiver to send a message MSG A to the base station using a physical random access channel PRACH opportunity corresponding to the selected SSB and the selected PUSCH opportunity, Among them, MSG A includes a random access preamble code and a media access control MAC protocol data unit PDU corresponding to the selected SSB.

15. The terminal according to claim 14, in, The controller is further configured to control the transceiver to receive, from the base station, a MSG B for MSG A based on a radio network temporary identifier RNTI, Among them, RNTI is identified as: RNTI = 1 + s_id + 14 × t_id + 14 × 80 × f_id + 14 × 80 × 8 × ul_carrier_id + 14 × 80 × 8 × 2, Among them, s_id is the index of the first orthogonal frequency division multiplexing OFDM symbol of the PRACH opportunity, t_id is the index of the first time slot of the PRACH opportunity, f_id is the index of the PRACH opportunity in the frequency domain, and ul_carrier_id is the uplink carrier used for transmission of MSG A.

16. A base station in a wireless communication system, the base station comprising: Transceiver; as well as The controller is configured as: Controlling the transceiver to send a radio resource control RRC message including dedicated random access channel RACH configuration information to the terminal; In case that a contention-free random access CFRA resource associated with a synchronization signal block SSB is configured for a 2-step random access RA type through dedicated RACH configuration information, performing a 2-step RA type CFRA procedure with the terminal, Among them, the 2-step RA type CFRA process is performed based on the SSB with a reference signal received power RSRP higher than the threshold among the SSBs and the PUSCH opportunity corresponding to the SSB among the physical uplink shared channel PUSCH opportunities configured by dedicated RACH configuration information.

17. The base station according to claim 16, in, The controller is further configured to control the transceiver to transmit, to the terminal, information about an RSRP threshold for selecting between an RA procedure of a 2-step RA type and an RA procedure of a 4-step RA type; and Among them, the RA process of the 2-step RA type is selected based on the RSRP for the downlink being higher than the RSRP threshold.

18. The base station according to claim 17, in, In the case where the CFRA resources associated with the SSB are not configured for the 2-step RA type through dedicated configuration information, the controller is further configured to perform a contention-based random access CBRA procedure of the 2-step RA type based on the selected SSB.

19. The base station according to claim 16, wherein: Perform a CFRA procedure with a 2-step RA type of terminal include: The controller is further configured to control the transceiver to receive a message MSG A from the terminal based on a physical random access channel PRACH opportunity and a PUSCH opportunity corresponding to the SSB, Among them, MSG A includes the random access preamble code and the media access control MAC protocol data unit PDU corresponding to the SSB.

20. The base station according to claim 19, in, The controller is further configured to control the transceiver to send MSG B for MSG A based on a radio network temporary identifier RNTI to the terminal, Among them, RNTI is identified as: RNTI = 1 + s_id + 14 × t_id + 14 × 80 × f_id + 14 × 80 × 8 × ul_carrier_id + 14 × 80 × 8 × 2, Among them, s_id is the index of the first orthogonal frequency division multiplexing OFDM symbol of the PRACH opportunity, t_id is the index of the first time slot of the PRACH opportunity, f_id is the index of the PRACH opportunity in the frequency domain, and ul_carrier_id is the uplink carrier used for transmission of MSG A.

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