Method and apparatus for random access procedure in a wireless communication system

Abstract

A communication method and system for integrating a fifth generation (5G) communication system supporting a higher data rate than a fourth generation (4G) system with Internet of Things (IoT) technology is provided. The communication method and system can be applied to smart services based on 5G communication technology and IoT-related technologies, such as smart homes, smart buildings, smart cities, smart cars, connected cars, healthcare, digital education, smart retail, safety and security services. A method for performing a random access procedure in a wireless communication system is provided.

Description

Technical Field

[0001] The present disclosure relates to an apparatus and method for performing a random access procedure in a wireless communication system. Background Art

[0002] In order to meet the increased demand for wireless data traffic since the deployment of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also called 'super 4G networks' or 'post-LTE systems'. 5G communication systems are considered to be implemented in higher frequency (millimeter wave) bands (e.g., 60GHz bands) in order to achieve higher data rates. In order to reduce 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 discussed in 5G communication systems. In addition, in 5G communication systems, system network improvements are being developed based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communications, wireless backhaul, mobile networks, collaborative communications, coordinated multi-point (CoMP), receiving-end interference elimination, etc. In 5G systems, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) have been developed as advanced coded modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0003] The Internet, as a human-centered connected network in which humans generate and consume information, is now developing towards the Internet of Things (IoT), in which distributed entities (such as things) exchange and process information without human intervention. The Internet of Everything (IoE), which combines IoT technology and big data processing technology through connection with cloud servers, has emerged. Since the realization of IoT 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 (MTC), etc. have been studied recently. Such an IoT environment can provide intelligent Internet technology services that create new value for human life by collecting and analyzing data generated between connected things. Through the integration and combination between existing information technology (IT) and various industrial applications, 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.

[0004] In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine type communications (MTC), and machine-to-machine (M2M) communications can be implemented through beamforming, MIMO, and array antennas. Cloud radio access networks (RANs) as an application of the above-mentioned big data processing technologies can also be considered as an example of the fusion between 5G technologies and IoT technologies.

[0005] The above information is presented as background information only to assist in understanding the present disclosure. No determination has been made, and no assertion has been made, as to whether any of the above might be applicable as prior art to the present disclosure. Summary of the invention

[0006] Technical issues

[0007] In the case of 2-step CBRA, the preambles in some PRACH opportunities are not mapped to any valid PUSCH opportunity. In the case where the UE selects a PRACH opportunity where there is no valid PUSCH opportunity, the UE only sends the PRACH preamble during MsgA transmission. This is not an effective method because in this case, RA cannot be completed in two steps. If the network receives the sent preamble, it will send a fallback RAR. The UE then performs a fallback operation, i.e., sends Msg3 in the UL grant received in the fallback RAR and performs contention resolution using Msg4. Additionally, the UE monitors the response to MsgA in a response window that starts at the first PDCCH opportunity that is at least one symbol away from the end of the PUSCH opportunity in which the MsgA payload is sent. In the case where the UE has not yet sent the MsgA payload, the start of the response window for receiving MsgB cannot be unknown according to the current process. So some improvements are needed.

[0008] Technical Solution

[0009] Various aspects of the present disclosure at least address 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 converging a fifth generation (5G) communication system that supports a higher data rate than a fourth generation (4G) system.

[0010] 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.

[0011] According to aspects of the present disclosure, a method for a 2-step random access procedure performed by a terminal in a wireless communication system is provided. The method includes: sending a message A (MsgA) for the 2-step random access procedure; starting a window at a symbol of a physical downlink control channel (PDCCH) for receiving a message B (MsgB), wherein the symbol is identified based on whether a physical uplink shared channel (PUSCH) is sent together with a physical random access channel (PRACH) in MsgA; and detecting downlink control information on the PDCCH of MsgB during the window.

[0012] According to another aspect of the present disclosure, a terminal for a 2-step random access procedure in a wireless communication system is provided. The terminal includes a transceiver and at least one processor, the processor being configured to send a message A (MsgA) for a 2-step random access procedure via the transceiver, start a window at a symbol of a physical downlink control channel (PDCCH) for receiving a message B (MsgB), wherein the symbol is identified based on whether a physical uplink shared channel (PUSCH) is sent together with a physical random access channel (PRACH) in MsgA, and detect downlink control information on the PDCCH of MsgB during the window.

[0013] Advantageous Effects of the Invention

[0014] Aspects of the present disclosure provide methods so that a UE can avoid selecting a PRACH opportunity that is not mapped to a valid PUSCH opportunity. This reduces latency because falling back to a 4-step RA can be avoided. Additionally, embodiments in the present disclosure provide methods for determining a response window for receiving a MsgB in case an MsgA payload is not sent during a 2-step RA procedure based on the reason for not sending the MsgA payload. This ensures that the network and the UE are synchronized with respect to the response window, and the UE can avoid missing a MsgB sent by the gNB.

[0015] 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

[0016] 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:

[0017] Figure 1A and Figure 1B A 2-step random access procedure including contention-based random access (CBRA) and contention-free random access (CFRA) according to an embodiment of the present disclosure is shown;

[0018] Figure 2Preamble selection in case of invalid PUSCH opportunity according to an embodiment of the present disclosure is shown;

[0019] Figure 3 PRACH timing selection in case of invalid PUSCH timing according to an embodiment of the present disclosure is shown;

[0020] Figure 4 is a block diagram of a terminal according to an embodiment of the present disclosure; and

[0021] Figure 5 is a block diagram of a base station according to an embodiment of the present disclosure.

[0022] Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. DETAILED DESCRIPTION

[0023] 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 to assist in understanding, but these specific details are to be regarded as 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, descriptions of well-known functions and structures may be omitted for clarity and conciseness.

[0024] 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 is 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 is not intended to limit the present disclosure as defined by the appended claims and their equivalents.

[0025] 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.

[0026] The term "substantially" means that the characteristic, parameter or value described need not be achieved precisely, but deviations or changes 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.

[0027] Those skilled in the art know that the combination of the blocks and flow charts of the flow chart (or sequence diagram) can be represented and executed by computer program instructions. These computer program instructions can be loaded on 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 a device for performing the functions described in the flow chart. Because the computer program instructions can be stored in a computer-readable memory available in a special-purpose computer or a programmable data processing device, it is also possible to create an article that performs the functions described in the flow chart. Because the computer program instructions can be loaded on a computer or a programmable data processing device, when executed as a process, they can perform the operations of the functions described in the flow chart.

[0028] The blocks of the flow chart may correspond to a module, a fragment or a 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.

[0029] In this specification, the words "unit", "module", etc. may refer to software components or hardware components, such as field programmable gate arrays (FPGAs) or application specific integrated circuits (ASICs) that can perform functions or operations. However, "units", 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 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 combinations 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 devices or one or more processors in a secure multimedia card.

[0030] 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.

[0031] 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).

[0032] 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.

[0033] In recent years, several broadband wireless technologies have been developed to meet the growing number of broadband users and provide more and better applications and services. The second generation of wireless communication systems has been developed to provide voice services while ensuring the mobility of users. The third generation of wireless communication systems supports not only voice services but also data services. In recent years, the fourth generation of wireless communication systems has been developed to provide high-speed data services. However, at present, the fourth generation of wireless communication systems lacks the resources to meet the growing demand for high-speed data services. Therefore, the fifth generation of wireless communication systems (also called next generation radio or NR) is being developed to meet the growing demand for high-speed data services and support ultra-reliability and low-latency applications.

[0034] The fifth generation wireless communication system supports not only lower frequency bands but also higher frequency (millimeter wave) bands, such as the 10 GHz to 100 GHz band, in order 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 technologies are being considered in the design of the fifth generation wireless communication system. In addition, the fifth generation wireless communication system is expected to address different use cases with completely different requirements in terms of data rate, latency, reliability, mobility, etc. However, it is expected that the design of the air interface of the fifth generation wireless communication system will be flexible enough to serve UEs with completely different capabilities, which depends on the use cases and market segments that the UE provides services to end customers. Example use cases that the fifth generation 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 Gbps, low latency, high mobility, etc., are aimed at the market segment representing traditional wireless broadband users who need to maintain Internet connection anytime, anywhere. m-MTC requirements, such as very high connection density, infrequent data transfers, very long battery life, low mobility addresses, etc., for the market segments representing the Internet of Things (IoT) / Internet of Everything (IoE) where billions of devices are envisioned to be connected. URLL requirements, such as very low latency, very high reliability, and variable mobility, for the market segments representing industrial automation applications, vehicle-to-vehicle / vehicle-to-infrastructure communications, which are envisioned as one of the enablers of autonomous vehicles.

[0035] In the fifth generation wireless communication system operating in the higher frequency (millimeter wave) band, the UE and the gNB communicate with each other using beamforming. Beamforming technology is used to mitigate propagation path loss and increase the propagation distance of higher frequency band communications. Beamforming uses high-gain antennas to enhance transmission and reception performance. Beamforming can be classified into transmit (TX) beamforming performed at the transmitting end and receive (RX) beamforming performed at the receiving end. Generally, TX beamforming increases directivity by allowing the area reached by propagation to be densely located in a specific direction using multiple antennas. In this case, the aggregation of multiple antennas can be referred to as an antenna array, and each antenna included in the array can be referred to as an array element. The antenna array can be configured in various forms, such as a linear array, a planar array, and the like. The use of TX beamforming leads to an increase in signal directivity, thereby increasing the propagation distance. Additionally, since the signal is hardly transmitted in directions other than the directional direction, the signal interference acting on the other receiving end is significantly reduced. The receiving end can perform beamforming on the RX signal by using an RX antenna array. RX beamforming increases the strength of the RX signal sent in a specific direction by allowing propagation to be concentrated in a specific direction, and excludes signals transmitted in directions other than the specific direction in the RX signal, thereby providing the effect of blocking interference signals. By using beamforming technology, the transmitter can generate multiple transmit beam patterns in different directions. Each of these transmit beam patterns can also be referred to as a transmit (TX) beam. Wireless communication systems operating at high frequencies use multiple narrow TX beams to transmit signals in a cell because each narrow TX beam provides coverage for a portion of the cell. The narrower the TX beam, the higher the antenna gain, and therefore the greater the propagation distance of the signal sent using beamforming. The receiver can also generate multiple receive (RX) beam patterns in different directions. Each of these receive patterns can also be referred to as a receive (RX) beam.

[0036] The fifth generation wireless communication system supports independent operation mode as well as dual connection (DC). In DC, multiple Rx / Tx UEs can be configured to utilize resources provided by two different nodes (or NBs) connected via a non-ideal backhaul. One node acts as a master node (MN) and the other acts as a secondary node (SN). MN and SN are connected via a network interface, and at least MN is connected to the core network. NR also supports multi-RAT dual connection (MR-DC) operation, whereby the UE in RRC_CONNECTED is configured to utilize radio resources provided by two different schedulers, which are located in two different nodes connected via a non-ideal backhaul and providing E-UTRA (ie, if the node is an ng-eNB) or NR access (ie, if the node is a gNB). In NR, for a UE in RRC_CONNECTED that is not configured with CA / DC, there is only one serving cell including a primary cell. For a UE in RRC_CONNECTED that is configured with CA / DC, the term 'serving cell' is used to refer to a cell set including (multiple) special cells and all secondary cells. In NR, the term Master Cell Group (MCG) refers to a set of service cells associated with a master node, including PCell and optionally one or more SCells. In NR, the term Secondary Cell Group (SCG) refers to a set of service cells associated with a secondary node, including PSCell and optionally one or more SCells. In NR, PCell (primary cell) refers to a service cell operating on the primary frequency in MCG, where the UE either performs an initial connection establishment procedure or initiates a connection reestablishment procedure. In NR, for UEs configured with CA, Scell ​​is a cell that provides additional radio resources on top of a special cell. Primary SCG cell (PSCell) refers to a service cell in the SCG where the UE performs random access when performing a synchronization reconfiguration procedure. For dual connectivity operation, the term SpCell (i.e., special cell) refers to the PCell of the MCG or the PSCell of the SCG, otherwise the term special cell refers to the PCell.

[0037] In the fifth generation wireless communication system, the Node B (gNB) or base station in a cell broadcasts synchronization signals and PBCH blocks (SSBs) consisting of primary and secondary synchronization signals (PSS, SSS) and system information. The system information includes common parameters required for communication in the cell. In the fifth generation wireless communication system (also known as next generation radio or NR), the system information (SI) is divided into MIB and multiple SIBs, where:

[0038] -MIB is always transmitted on PBCH with a period of 80ms and repeated within 80ms, and it includes the parameters required to obtain SIB1 from the cell.

[0039] -SIB1 is transmitted on DL-SCH with a periodicity of 160ms and variable transmission repetition. The default transmission repetition period of SIB1 is 20ms, but the actual transmission repetition period depends on the network implementation. SIB1 includes information about the availability and scheduling of other SIBs (e.g., mapping of SIBs to SI messages, periodicity, SI window size), as well as an indication of whether one or more SIBs are provided only on demand, and in this case, the configuration required for the UE to perform the SI request. SIB1 is a cell-specific SIB;

[0040] - The SystemInformation (SI) message carries SIBs other than SIB1, which are transmitted on the DL-SCH. Only SIBs with the same periodicity can be mapped to the same SI message.

[0041] In the fifth generation wireless communication system, the physical downlink control channel (PDCCH) is used to schedule DL transmission on PDSCH and UL transmission on PUSCH, wherein the downlink control information (DCI) on PDCCH includes: downlink allocation, including at least modulation and coding format, resource allocation and hybrid ARQ information related to DL-SCH; uplink scheduling grant, including at least modulation and coding format, resource allocation and hybrid ARQ information related to UL-SCH. In addition to scheduling, PDCCH can be used to: activate and deactivate configured PUSCH transmission with configured grant; activate and deactivate PDSCH semi-persistent transmission; notify one or more UEs of the time slot format; notify one or more UEs of (multiple) PRBs and (multiple) OFDM symbols, where the UE can assume that there is no transmission for the UE; transmission of TPC commands for PUCCH and PUSCH; transmission of one or more TPC commands for SRS transmission of one or more UEs; switching the active bandwidth part of the UE; initiating a random access process. The UE monitors the set of PDCCH candidates in the configured monitoring opportunities in one or more configured control resource sets (CORESET) configured according to the corresponding search space configuration. A CORESET consists of a set of PRBs with a duration of 1 to 3 OFDM symbols. Resource elements Resource element groups (REGs) and control channel elements (CCEs) are defined in a CORESET, and each CCE consists of a set of REGs. The control channel is formed by the aggregation of CCEs. Different code rates for the control channel are achieved by aggregating different numbers of CCEs. Interleaved and non-interleaved CCE to REG mapping are supported in a CORESET. Polarization coding is used for PDCCH. Each resource element group carrying PDCCH carries its own DMRS. QPSK modulation is used for PDCCH.

[0042] In the fifth generation wireless communication system, a list of search space configurations is signaled by the gNB for each configured BWP, where each search configuration is uniquely identified by an identifier. The gNB explicitly signals the identifier of the search space configuration to be used for a specific purpose such as paging reception, SI reception, random access response reception. In NR, the search space configuration includes parameters Monitoring-periodicity-PDCCH-slot, Monitoring-offset-PDCCH-slot, Monitoring-symbols-PDCCH-within-slot and duration. The UE uses the parameters PDCCH monitoring period (Monitoring-periodicity-PDCCH-slot), PDCCH monitoring offset (Monitoring-offset-PDCCH-slot) and PDCCH monitoring mode (Monitoring-symbols-PDCCH-within-slot) to determine the (multiple) PDCCH monitoring opportunities within the timeslot. The PDCCH monitoring opportunities exist in timeslots 'x' to x+duration, where the timeslot numbered 'x' in the radio frame numbered 'y' satisfies the following equation:

[0043] (y*(number of slots in a radio frame)+x-Monitoring-offset-PDCCH-slot)mod(Monitoring-periodicity-PDCCH-slot)=0

[0044] The starting symbol of the PDCCH monitoring opportunity in each slot with a PDCCH monitoring opportunity is given by Monitoring-symbols-PDCCH-within-slot. The length of the PDCCH monitoring opportunity (in symbols) is given in the coreset associated with the search space. The search space configuration includes an identifier of the coreset configuration associated with it. The gNB signals a list of coreset configurations for each configured BWP, where each coreset configuration is uniquely identified by an identifier. Note that the duration of each radio frame is 10ms. A radio frame is identified by a radio frame number or a system frame number. Each radio frame consists of several slots, where the number of slots and the slot duration in a radio frame depends on the subcarrier spacing. The number of slots and the slot duration in a radio frame depends on the radio frames for each supported SCS predefined in the NR. Each coreset configuration is associated with a list of TCI (Transmission Configuration Indicator) states. A DL RSID (SSB or CSI-RS) is configured for each TCI state. The list of TCI states corresponding to the coreset configuration is signaled by the gNB via RRC signaling. One of the TCI states in the list of TCI states is activated and indicated to the UE by the gNB. The TCI state indicates the DL TX beam used by the gNB to transmit PDCCH in the PDCCH monitoring occasions in the search space (the DL TX beam is QCL (quasi co-located) with the SSB / CSI-RS of the TCI state).

[0045] Bandwidth Adaptation (BA) is supported in the fifth generation wireless communication system. With BA, the receiving and transmitting bandwidth of the UE does not need to be as large as the bandwidth of the cell and can be adjusted: the width can be commanded to change (for example, shrink during low activity periods to save power); the position can be moved in the frequency domain (for example, to increase scheduling flexibility); and the subcarrier spacing can be commanded to change (for example, to allow different services). A subset of the total cell bandwidth of a cell is called a bandwidth part (BWP). BA is implemented by configuring an RRC-connected UE with (multiple) BWPs and telling the UE which (which) configured BWPs are currently the active BWPs. When BA is configured, the UE only needs to monitor the PDCCH on one active BWP (that is, the UE does not need to monitor the PDCCH on the entire DL frequency of the serving cell). In the RRC connected state, for each configured serving cell (that is, PCell or SCell), the UE is configured with one or more DL BWPs and UL BWPs. For an activated serving cell, there is always an active UL BWP and DL BWP at any point in time. BWP switching of a serving cell is used to activate an inactive BWP and deactivate an active BWP at one time. BWP switching is controlled by the PDCCH indicating a downlink allocation or uplink grant, by the bwp-InactivityTimer, by RRC signaling or by the MAC entity itself when initiating a random access procedure. When adding a SpCell or activating an SCell, the DL BWP and UL BWP indicated by firstActiveDownlinkBWP-Id and firstActiveUplinkBWP-Id, respectively, are active without receiving a PDCCH indicating a downlink allocation or uplink grant. The active BWP of the serving cell is indicated by RRC or PDCCH. For unpaired spectrum, the DL BWP is paired with the UL BWP, and BWP switching is common to both UL and DL. When the BWP inactivity timer expires, the UE switches to the active DL BWP, to the default DL BWP or the initial DL BWP (if the default DL BWP is not configured).

[0046] In 5G wireless communication systems, random access (RA) is supported. Random access (RA) is used to achieve uplink (UL) time synchronization. RA is used during initial access, handover, radio resource control (RRC) connection reestablishment process, scheduling request transmission, secondary cell group (SCG) addition / modification, beam failure recovery, and non-synchronized UE in RRC CONNECTED state during UL data or control information transmission. Several types of random access procedures are supported.

[0047] Contention-based random access (CBRA)

[0048] This is also known as 4-step CBRA. In this type of random access, the UE first sends a random access preamble (also known as Msg1) and then waits for a random access response (RAR) in the RAR window. The RAR is also known as Msg2. The next generation Node B (gNB) sends the RAR on the physical downlink shared channel (PDSCH). The PDCCH that schedules the PDSCH carrying the RAR is addressed to the RA-Radio Network Temporary Identifier (RA-RNTI). The RA-RNTI identifies the time-frequency resource (also known as the physical RA channel (PRACH) opportunity or PRACH transmit (TX) opportunity or RA channel (RACH) opportunity) in which the RA preamble is detected by the gNB. RA-RNTI is calculated as follows: RA-RNTI = 1 + s_id + 14 * t_id + 14 * 80 * f_id + 14 * 80 * 8 * ul_carrier_id, where s_id is the index of the first orthogonal frequency division multiplexing (OFDM) symbol of the PRACH opportunity where the UE sends Msg1 (i.e., RA preamble); 0 ≤ s_id < 14; t_id is the index of the first time slot of the PRACH opportunity (0 ≤ t_id < 80); f_id is the index of the PRACH opportunity in the frequency domain within the time slot (0 ≤ f_id < 8), and ul_carrier_id is the UL carrier used for Msg1 transmission (0 for normal UL (NUL) carrier and 1 for supplementary UL (SUL) carrier). The gNB can multiplex several RARs for various random access preambles detected by the gNB into the same RAR media access control (MAC) protocol data unit (PDU). If the RAR includes the RA preamble identifier (RAPID) of the RA preamble sent by the UE, then the RAR in the MAC PDU corresponds to the RA preamble transmission of the UE. If no RAR corresponding to its RA preamble transmission is received during the RAR window, and the UE has not sent the RA preamble for a configurable (configured by the gNB in ​​the RACH configuration) number of times, then the UE returns to the first step, i.e. selecting a random access resource (preamble / RACH opportunity) and sending the RA preamble. A fallback may be applied before returning to the first step.

[0049] If a RAR corresponding to the UE's RA preamble transmission is received, 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, SI request, etc. It may include a UE identity (i.e., a cell radio network temporary identifier (C-RNTI) or a 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 identity (the first X bits of the common control channel (CCCH) service data unit (SDU) sent in Msg3), contention resolution is considered successful, the contention resolution timer is stopped and the RA procedure is completed. If the contention resolution timer expires and the UE has not sent a RA preamble for a configurable number of times, the UE returns to the first step (i.e., selecting random access resources (preamble / RACH opportunity)) and sends a RA preamble. Before returning to the first step, a backoff may be applied.

[0050] Contention-Free Random Access (CFRA)

[0051] This is also known as legacy CFRA or 4-step CFRA. 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 dedicated random access preamble to the UE. The UE sends a dedicated RA preamble. The ENB sends a 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 an UL grant. The RAR is transmitted in the RAR window, similar to the contention-based RA (CBRA) procedure. The CFRA is considered to be successfully completed after receiving the RAR sent by the UE including the RA preamble identifier (RAPID) of the RA preamble. In the case where RA is initiated for beam failure recovery, the CFRA is considered to be successfully completed if a PDCCH addressed to the C-RNTI is received in the search space for beam failure recovery. If the RAR window expires and the RA is not successfully completed, and the UE has not sent the RA preamble for a configurable number of times (configured by the gNB in ​​the RACH configuration), the UE retransmits the RA preamble.

[0052] For certain events, such as handover and beam failure recovery, if (multiple) dedicated preambles are assigned to the UE, then during the first step of random access, i.e., during random access resource selection for Msg1 transmission, the UE determines whether to send a dedicated preamble or a non-dedicated preamble. Dedicated preambles are usually provided for a subset of SSB / CSI-RS. If there is no SSB / CSI-RS with a DLRSRP above a threshold among the SSB / CSI-RS for which contention-free random access resources (i.e., dedicated preambles / RO) are provided by the gNB, the UE selects a non-dedicated preamble. Otherwise, the UE selects a dedicated preamble. Therefore, during the RA procedure, one random access attempt can be CFRA and another random access attempt can be CBRA.

[0053] Figure 1A and 1B A 2-step random access procedure according to an embodiment of the present disclosure is shown, including contention-based random access (CBRA) and contention-free random access (CFRA).

[0054] 2-step Contention-Based Random Access (2-step CBRA)

[0055] refer to Figure 1A In a first step, UE 100 transmits a random access preamble on PRACH and a payload (i.e., MAC PDU) on PUSCH (120). The random access preamble and payload transmission is also referred to as message A (MsgA). In a second step, after the MsgA transmission, the UE monitors for a response from the network (i.e., gNB 110) within a configured window (130). The response is also referred to as message B (MsgB).

[0056] If the CCCH SDU is transmitted in the MsgA payload, the UE performs contention resolution using the contention resolution information in MsgB. If the contention resolution identifier received in MsgB matches the first 48 bits of the CCCH SDU sent in MsgA, contention resolution is successful. If the C-RNTI is transmitted in the MsgA payload, contention resolution is successful if the UE receives a PDCCH addressed to the C-RNTI. If contention resolution is successful, the random access procedure is considered to have been successfully completed. Instead of the contention resolution information corresponding to the transmitted MsgA, MsgB may include fallback information corresponding to the random access preamble sent in MsgA. If fallback information is received, the UE sends Msg3 and performs contention resolution using Msg4, as in the CBRA process. If contention resolution is successful, the random access procedure is considered to have been successfully completed. If contention resolution fails at fallback (i.e., when Msg3 is sent), the UE retransmits MsgA. If the configured window for the UE to monitor the network response after sending MsgA expires, and the UE does not receive MsgB including the contention resolution information or fallback information as above, the UE retransmits MsgA. If the random access procedure is not successfully completed even after sending MsgA for a configurable number of times, the UE falls back to the 4-step RACH procedure, i.e., the UE only sends the PRACH preamble.

[0057] The MsgA payload may include one or more of a common control channel (CCCH) service data unit (SDU), a dedicated control channel (DCCH) SDU, a dedicated traffic channel (DTCH) SDU, a buffer status report (BSR) MAC control element (CE), a power headroom report (PHR) MAC CE, SSB information, a C-RNTI MAC CE, or padding. MsgA may include a UE ID (e.g., a random ID, S-TMSI, C-RNTI, recovery ID, etc.) and the preamble in the first step. The UE ID may be included in the MAC PDU of MsgA. A UE ID such as a 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 a random ID, S-TMSI, C-RNTI, recovery ID, IMSI, idle mode ID, inactive mode ID, etc. The UE ID may be different in different scenarios where the UE performs a RA process. When the UE performs RA after power-on (before the UE attaches to the network), the UEID is a random ID. When the UE performs RA in the IDLE state after the UE attaches to the network, the UE ID is the S-TMSI. If the UE has an assigned C-RNTI (for example, in a connected state), the UE ID is the C-RNTI. In the case where the UE is in the INACTIVE state, the UE ID is a 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 a connection request indication, a connection recovery request indication, an SI request indication, a buffer status indication, beam information (for example, one or more DL TX beam IDs or SSB IDs), a beam failure recovery indication / information, a data indicator, a cell / BS / TRP switching indication, a connection reconstruction indication, a reconfiguration completion or switching completion message, and the like. One or more.

[0058] The UE determines the preamble / PRACH opportunity and its association with the SS / PBCH block as follows:

[0059] For 2-step CBRA with common PRACH opportunities with 4-step CBRA, the number N of SS / PBCH blocks associated with one PRACH opportunity is provided to the UE by ssb-perRACH-OccasionAndCB-PreamblesPerSSB, and the number R of contention-based preambles per SS / PBCH block per valid PRACH opportunity is provided by msgA-CB-PreamblesPerSSB. The R contention-based preambles per SS / PBCH block per valid PRACH opportunity for 2-step CBRA start after the preamble for 4-step CBRA.

[0060] For 2-step CBRA with separate PRACH opportunities with 4-step CBRA, the number of SS / PBCH blocks associated with one PRACH opportunity, N, and the number of contention-based preambles per SS / PBCH block per valid PRACH opportunity, R, are provided to the UE by ssb-perRACH-OccasionAndCB-PreamblesPerSSB-msgA, when provided; otherwise, they are provided by ssb-perRACH-OccasionAndCB-PreamblesPerSSB.

[0061] For 2-step CBRA with single PRACH opportunity with 4-step CBRA, if N<1, one SS / PBCH block is mapped to 1 / N consecutive valid PRACH opportunities, and the R contention-based preambles with consecutive indices associated with the SS / PBCH block of each valid PRACH opportunity start from zero. If N≥1, the R contention-based preambles with consecutive indices associated with the SS / PBCH block n (0≤n≤N-1) of each valid PRACH opportunity start from preamble index Start, where It is provided by msgA-totalNumberOfRA-Preambles and is an integer multiple of N.

[0062] For 2-step CBRA with common PRACH opportunities with 4-step CBRA, if N<1, one SS / PBCH block is mapped to 1 / N consecutive valid PRACH opportunities, and the R contention-based preambles with consecutive indices associated with the SS / PBCH block of each valid PRACH opportunity start from 'last preamble index of 4-step CBRA+1'. If N≥1, the R contention-based preambles with consecutive indices associated with the SS / PBCH block n (0≤n≤N-1) of each valid PRACH opportunity start from preamble index 'last preamble index of 4-step CBRA+1'+ Start, where It is provided by msgA-totalNumberOfRA-Preambles and is an integer multiple of N.

[0063] The PRACH opportunity is indicated by the parameter prach-ConfigIndex. The SS / PBCH block index provided by ssb-PositionsInBurst in SIB1 or ServingCellConfigCommon is mapped to the valid PRACH opportunity in the following order:

[0064] - First, within a single PRACH opportunity, in ascending order of preamble index

[0065] - Second, for frequency reused PRACH opportunities, in ascending order of frequency resource index

[0066] - Third, for time-multiplexed PRACH opportunities within a PRACH time slot, in ascending order of time resource index

[0067] - Fourth, for PRACH time slots, in ascending order of index

[0068] The association period for mapping SS / PBCH blocks to PRACH opportunities starting from frame 0 is a period such that SS / PBCH blocks are mapped to PRACH opportunities at least once during the association period, where the UE obtains the value of ssb-PositionsInBurst from SIB1 or ServingCellConfigCommon The association pattern period includes one or more association periods and is determined such that the pattern between the PRACH opportunities and the SS / PBCH blocks is repeated at most every 160 milliseconds.

[0069] 2-step Contention-Free Random Access (2-step CFRA)

[0070] refer to Figure 1B, in which case the gNB 110 allocates to the UE 100 (multiple) dedicated random access preambles and (multiple) PUSCH resources for MsgA transmission (140). The (multiple) ROs to be used for preamble transmission may also be indicated. In a first step, the UE 100 sends a random access preamble on the PRACH using contention-free random access resources (i.e., dedicated preamble / PUSCH resources / RO) and sends a payload on the PUSCH (150). In a second step, after the MsgA transmission, the UE monitors for a response from the network (i.e., gNB) within a configured window (160). If the UE receives a PDCCH addressed to the C-RNTI, the random access procedure is considered to have been successfully completed. If the UE receives backoff information corresponding to the preamble it sent, the random access procedure is considered to have been successfully completed.

[0071] For certain events, such as handover and beam failure recovery, if dedicated preamble(s) and PUSCH resources(s) are allocated to the UE, then during the first step of random access, i.e., during random access resource selection for MsgA transmission, the UE determines whether to send a dedicated preamble or a non-dedicated preamble. Dedicated preambles are typically provided for a subset of SSB / CSI-RS. If there is no SSB / CSI-RS with DL RSRP above a threshold among the SSB / CSI-RS for which contention-free random access resources (i.e., dedicated preamble / RO / PUSCH resources) are provided by the gNB, the UE selects a non-dedicated preamble. Otherwise, the UE selects a dedicated preamble. Therefore, during the RA procedure, one random access attempt can be a 2-step CFRA, while the other random access attempts can be a 2-step CBRA.

[0072] When initiating a random access procedure, the UE first selects a carrier (SUL or NUL). If the carrier to be used for the random access procedure is explicitly signaled by the gNB, the UE selects the signaled carrier to perform the random access procedure. If the carrier to be used for the random access procedure is not explicitly signaled by the gNB, and if the serving cell for the random access procedure is configured with a supplementary uplink, and if the RSRP referenced by the downlink path loss is less than rsrp-ThresholdSSB-SUL, the UE selects the SUL carrier to perform the random access procedure. Otherwise, the UE selects the NUL carrier to perform the random access procedure. Once the UL carrier is selected, the UE determines the UL BWP and DL BWP for the random access procedure, as specified in Section 5.15 of TS38.321. The UE then determines whether to perform a 2-step or 4-step RACH for the random access procedure.

[0073] - If the random access procedure is initiated by a PDCCH order and if the ra-PreambleIndex explicitly provided by the PDCCH is not 0b000000, the UE selects 4-step RACH.

[0074] - Otherwise, if the gNB signals 2-step contention-free random access resources for this random access procedure, the UE selects 2-step RACH.

[0075] - Otherwise, if the gNB signals 4-step contention-free random access resources for this random access procedure, the UE selects 4-step RACH.

[0076] - Otherwise, if the UL BWP selected for this random access procedure is only configured with 2-step RACH resources, the UE selects 2-step RACH.

[0077] - Otherwise, if the UL BWP selected for this random access procedure is only configured with 4-step RACH resources, the UE selects 4-step RACH.

[0078] - Otherwise if the UL BWP selected for this random access procedure is configured with both 2-step and 4-step RACH resources,

[0079] - If the downlink path loss referenced RSRP is below the configured threshold, the UE selects 4-step RACH. Otherwise, the UE selects 2-step RACH.

[0080] For 2-step CBRA, the UE determines the time and frequency resources for PUSCH opportunities in the active UL BWP from the msgA-PUSCH-config for the active UL BWP. If the active UL BWP is not the initial UL BWP and no msgA-PUSCH-config is provided for the active UL BWP, the UE uses the msgA-PUSCH-config provided for the initial active UL BWP. The PRACH opportunities / preambles are mapped to PUSCH opportunities (configured by msgA-PUSCH-config) as follows:

[0081] The consecutively numbered preamble index N starting from the valid PRACH opportunity in the PRACH slot preamble

[0082] - First, within a single PRACH opportunity, in ascending order of preamble index

[0083] - Second, for frequency reused PRACH opportunities, in ascending order of frequency resource index

[0084] - Third, for time-multiplexed PRACH opportunities within a PRACH time slot, in ascending order of time resource index

[0085] Mapped to valid PUSCH timing

[0086] -First, for frequency reused PUSCH opportunities, according to the frequency resource index f id In ascending order

[0087] - Second, in the PUSCH occasion in increasing order of DMRS index, where DMRS index DMRS id First, in increasing order of DMRS port index, then in increasing order of DMRS sequence index [4, TS 38.211]

[0088] Third, for the PUSCH timing of time multiplexing within the PUSCH time slot, according to the time resource index t id In ascending order

[0089] Fourth, for the PUSCH time slot corresponding to the PRACH time slot, in ascending order of index

[0090] Among them, N preamble =ceil(T preamble / T PUSCH) , T preamble is the total number of preambles in valid PRACH opportunities per association pattern period, and T PUSCH is the total number of valid sets of PUSCH opportunities per associated pattern period multiplied by the number of DMRS indices per valid PUSCH opportunity. A PUSCH opportunity is valid if it does not overlap in time and frequency with any PRACH opportunity associated with 4-step RA or 2-step RA. Additionally, if the UE is provided with tdd-UL-DL-ConfigurationCommon (signalled by the gNB), the PUSCH opportunity is valid if

[0091] -PUSCH opportunity is within a UL symbol, or

[0092] - A PUSCH opportunity does not precede an SS / PBCH block in a PUSCH slot and is at least N after the last downlink symbol gap symbols and at least N after the last SS / PBCH block symbol. gap symbols, where for the 1.25KHz / 5KHz preamble SCS, N gap Is 0, for 15 / 30 / 60 / 120KHz preamble SCS, N gap Serves 2.

[0093] Based on the above mapping rules, the preambles in some PRACH opportunities may not be mapped to any valid PUSCH opportunity. In the case where the UE selects a PRACH opportunity where there is no valid PUSCH opportunity, the UE sends the PRACH preamble only during MsgA transmission. This is not an effective method because in this case, RA cannot be completed in two steps. If the network receives the sent preamble, the network will send a fallback RAR. The UE then performs a fallback operation, i.e., sends Msg3 in the UL grant received in the fallback RAR, and performs contention resolution using Msg4. Additionally, the UE monitors the response to MsgA in a response window that starts at the first PDCCH opportunity, which is at least one symbol away from the end of the PUSCH opportunity in which the MsgA payload is sent. In the absence of a valid PUSCH opportunity, according to the current process, the start of the response window for receiving MsgB cannot be unknown. So some enhancements are needed.

[0094] The 2-step random access method according to an embodiment of the present disclosure will be explained below.

[0095] Step 0: During the initialization of the random access procedure, the UE first selects a carrier (SUL or NUL). If the carrier to be used for the random access procedure is explicitly signaled by the gNB, the UE selects the signaled carrier to perform the random access procedure. If the carrier to be used for the random access procedure is not explicitly signaled; and if the serving cell for the random access procedure is configured with supplementary uplink, and if the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL: The UE selects the SUL carrier to perform the random access procedure. Otherwise, the UE selects the NUL carrier to perform the random access procedure.

[0096] After selecting the UL carrier, the UE determines the UL BWP and DL BWP for the random access procedure as specified below:

[0097] For the selected carrier of the serving cell:

[0098] 1> if no PRACH opportunity is configured for the active UL BWP; or

[0099] 1> If the random access procedure is initiated by a PDCCH order and the ra-PreambleIndex explicitly provided by the PDCCH is not 0b000000, and no 4-step PRACH opportunity is configured for the active UL BWP (or if the random access procedure is initiated by a PDCCH order and the ra-PreambleIndex explicitly provided by the PDCCH is not 0b000000, and no 4-step PRACH opportunity is configured for the active UL BWP, and 2-step PRACH opportunity is configured for the active UL BWP):

[0100] 2> Switch the active UL BWP to the BWP indicated by initialUplinkBWP;

[0101] 2> If the serving cell is SpCell:

[0102] 3> Switch the active DL BWP to the BWP indicated by initialDownlinkBWP.

[0103] 1> Otherwise:

[0104] 2> If the serving cell is SpCell:

[0105] 3> If the active DL BWP does not have the same bwp-Id as the active UL BWP:

[0106] 4> Switch the active DL BWP to a DL BWP with the same bwp-Id as the active UL BWP.

[0107] The UE then determines whether to perform a 2-step or 4-step RACH for the random access procedure.

[0108] If the random access procedure is initiated by a PDCCH order, and if the ra-PreambleIndex explicitly provided by the PDCCH is not 0b000000; or

[0109] If the random access procedure is initiated for an SI request and RRC has explicitly provided random access resources for the SI request; or

[0110] if the random access procedure is initiated for beam failure recovery and if RRC has explicitly provided contention-free random access resources for beam failure recovery request for 4-step random access for the BWP selected for the random access procedure; or

[0111] If the random access procedure is initiated for reconfiguration with synchronization and if contention-free random access resources for 4-step random access have been explicitly provided in the rach-ConfigDedicated for the BWP selected for the random access:

[0112] -UE selects 4-step RA.

[0113] Otherwise, if the BWP selected for the random access procedure is configured with both 2-step and 4-step random access resources and the RSRP of the downlink path loss reference is higher than RSRP_THRESHOLD_RA_TYPE_SELECTION; or

[0114] If the BWP selected for the random access procedure is configured with only 2-step random access resources (i.e., no 4-step RACH resources are configured); or

[0115] If the random access procedure is initiated for reconfiguration with synchronization and if contention-free random access resources for 2-step random access have been explicitly provided in the rach-ConfigDedicated for the BWP selected for the random access:

[0116] -UE selects 2-step RA.

[0117] Otherwise: UE selects 4-step RA

[0118] For 4-step RACH, the UL carrier used for the random access procedure is explicitly signaled by the gNB during handover or reconfiguration with synchronization. If the gNB wants the UE to select NUL for 4-step RACH, the gNB provides the 4-step contention-free random access resources for NUL in the reconfiguration message. If the gNB wants the UE to select SUL for 4-step RACH, the gNB provides the 4-step contention-free random access resources for SUL in the reconfiguration message. The UL carrier used for the 2-step random access procedure may also be explicitly signaled by the gNB during handover or reconfiguration with synchronization. If the gNB wants the UE to select NUL for 2-step RACH, the gNB provides the 2-step contention-free random access resources for NUL in the reconfiguration message. If the gNB wants the UE to select SUL for 2-step RACH, it provides the 2-step contention-free random access resources for SUL in the reconfiguration message.

[0119] If during handover or reconfiguration with synchronization, the gNB signals 2-step contention-free random access resources for SUL, the UE selects SUL and the selected RACH type is 2-step RACH. If during handover or reconfiguration with synchronization, the gNB signals 2-step contention-free random access resources for NUL, the UE selects NUL and the selected RACH type is 2-step RACH. If during handover or reconfiguration with synchronization, the gNB signals 4-step contention-free random access resources for SUL, the UE selects SUL and the selected RACH type is 4-step RACH. If during handover or reconfiguration with synchronization, the gNB signals 4-step contention-free random access resources for NUL, the UE selects NUL and the selected RACH type is 4-step RACH.

[0120] Based on the above criteria, the UE has selected the 2-step RA procedure. The UE initializes the preamble transmission counter (PREAMBLE_TRANSMISSION_COUNTER) to zero.

[0121] Step 1A: If contention-free random access resources are provided by the gNB and at least one of the SSB / CSI-RS for which contention-free random access resources are provided has an SS-RSRP / CSI-RSRP above the threshold, the UE sends MsgA, i.e., random access preamble (also called MsgA preamble), on PRACH occasion using the allocated contention-free random access resources, and sends MAC PDU (also called MsgA payload) on PUSCH occasion.

[0122] - In this case, the UE selects an SSB / CSI-RS with an SS-RSRP / CSI-RSRP above a threshold among the SSB / CSI-RS for which contention-free random access resources are provided. The UE selects a random access preamble (ra-PreambleIndex) corresponding to the selected SSB / CSI-RS allocated by the gNB. The UE selects the next available PRACH opportunity corresponding to the selected SSB / CSI-RS. The UE selects a PUSCH opportunity corresponding to the selected PRACH opportunity and preamble. (Note that there may be several PUSCH opportunities / resources corresponding to the PRACH slot of the selected PRACH opportunity. The gNB may indicate in dedicated signaling for a given SSB / CSI-RS which PUSCH opportunity / resource will be used).

[0123] Step 1B: Otherwise (i.e., if the gNB does not provide contention-free random access resources, or if there is no available SSB / CSI-RS with SS-RSRP / CSI-RSRP above the threshold among the SSB / CSI-RS for which contention-free random access resources are provided), the UE sends MsgA, i.e., PRACH preamble (also called MsgA preamble), on a PRACH occasion using contention-based random access resources, and sends MAC PDU (also called MsgA payload) on a PUSCH occasion.

[0124] SSB Selection: In this case, the UE selects an SSB having an SS-RSRP higher than a threshold value among the transmitted SSBs. If no SSB having an SS-RSRP higher than a threshold value is available, the UE selects any SSB.

[0125] Preamble Group Selection : The UE selects the random access preamble group as follows:

[0126] 1> If MsgA has not been sent:

[0127] 2> If random access preamble group B for 2-step RA is configured:

[0128] 3> If the potential MsgA payload size (UL data available for transmission plus MAC header, and, if required, MAC CE) is larger than the transport block size of the MsgA payload associated with preamble group A, and the nominal required PUSCH power of MsgA is less than PCMAX (of the serving cell performing the random access procedure); alternatively, if the potential MsgA payload size (UL data available for transmission plus MAC header, and, if required, MAC CE) is larger than ra-MsgASizeGroupA, and the path loss is less than PCMAX-MsgA-preambleReceivedTargetPower-msgA-Delta Preamble-messageAPowerOffsetGroupB (of the serving cell performing the random access procedure), or

[0129] 3> If the random access procedure is initiated for the CCCH logical channel and the CCCH SDU size plus the MAC subheader is greater than the transport block size of the MsgA payload associated with preamble group A (or if the random access procedure is initiated for the CCCH logical channel and the CCCH SDU size plus the MAC subheader is equal to the transport block size of the MsgA payload associated with preamble group B):

[0130] 4> Select random access preamble group B.

[0131] 3> Otherwise:

[0132] 4> Select random access preamble group A.

[0133] 2> Otherwise:

[0134] 3> Select random access preamble group A.

[0135] 1> Otherwise, if MsgA has been sent using contention-free random access resources and has not been sent using contention-based random access resources:

[0136] 2> If Random Access Preamble Group B for 2-step RA is configured and if the payload size of MsgA (including MAC header and all MAC CEs) is larger than the transport block size of the MsgA payload size associated with Preamble Group A (or if a Random Access procedure is initiated for a CCCH logical channel and the CCCH SDU size plus the MAC sub-header):

[0137] 3> Select random access preamble group B.

[0138] 2> Otherwise:

[0139] 3> Select random access preamble group A.

[0140] 1> Otherwise (i.e., use contention-based random access resources to retransmit MsgA):

[0141] 2> Select the same random access preamble group as that used for the random access preamble transmission attempt corresponding to the first transmission of MsgA using contention-based random access resources.

[0142] Preamble selection: In the current design, the UE randomly selects a random access preamble from the random access preambles associated with the selected SSB and the selected random access preamble group with equal probability.

[0143] Figure 2 Preamble selection in case of invalid PUSCH opportunity according to an embodiment of the present disclosure is shown.

[0144] refer to Figure 2 , if some of the preambles in certain PRACH opportunities (i.e., RO) are not associated with PUSCH resource elements (i.e., PUSCH opportunity + DMRS resources or PUSCH opportunity), it is recommended that the UE may avoid these preambles during preamble selection. Figure 2As shown, there are two ROs in the PRACH slot. They are mapped to SSB1 and SSB2 respectively. Each RO has 8 preambles. There are two PUSCH slots, each with 2 PUSCH opportunities (i.e. (multiple) POs). One of the POs in the second PUSCH slot is invalid. A PUSCH opportunity is valid if it does not overlap in time and frequency with any PRACH opportunity associated with a 4-step random access procedure or a 2-step random access procedure. Additionally, if the UE is provided with tdd-UL-DL-ConfigurationCommon, if the PUSCH opportunity is within a UL symbol, or it is not before a SS / PBCH block in the PUSCH slot, and is at least N after the last downlink symbol. gap symbols and at least N after the last SS / PBCH block symbol. gap symbol, the PUSCH opportunity is valid, where for the 1.25 and 5KHz preamble SCS, N gap is 0, and for 15 / 30 / 60 / 120KHz preamble SCS, N gap Yes 2. Each PO has 4 DMRS resources. In this case, if the UE has selected SSB 2 for PRACH transmission, the UE will randomly select from preambles 0 to 7 according to the current design. However, preambles 4 to 7 are not mapped to valid PUSCH resource units (PRUs). Therefore, it is recommended that the UE can randomly select from preambles 0 to 3 instead of 4 to 7.

[0145] According to the proposed disclosed embodiment, among the random access preambles associated with the selected SSB and the selected random access preamble group, when selecting a random access preamble, the UE excludes preambles that are not mapped to a valid PUSCH opportunity. The UE randomly selects a random access preamble from the remaining random access preambles associated with the selected SSB and the selected random access preamble group with equal probability.

[0146] According to the proposed disclosed embodiment, among the random access preambles associated with the selected SSB and the selected random access preamble group, for the PRACH opportunity selected for PRACH transmission, when selecting the random access preamble, the UE excludes the preambles that are not mapped to the valid PUSCH opportunity. The UE randomly selects the random access preamble from the remaining random access preambles associated with the selected SSB and the selected random access preamble group with equal probability.

[0147] In the case where all random access preambles associated with the selected SSB and the selected random access preamble group are not mapped to a valid PUSCH opportunity, the UE randomly selects a random access preamble from the random access preambles associated with the selected SSB and the selected random access preamble group with equal probability. In this case, when selecting a random access preamble, the UE does not exclude a preamble that is not mapped to a valid PUSCH opportunity.

[0148] PRACH timing selection: In the current design, the UE selects the next available PRACH opportunity corresponding to the selected SSB / CSI-RS. The UE determines the next available PRACH opportunity from the PRACH opportunities corresponding to the selected SSB (the MAC entity will randomly select a PRACH opportunity with equal probability among the consecutive PRACH opportunities corresponding to the selected SSB; when determining the next available PRACH opportunity corresponding to the selected SSB, the MAC entity may take into account the possible occurrence of measurement gaps).

[0149] According to an embodiment of the present disclosure, when determining the next available PRACH opportunity corresponding to the selected SSB, the UE first excludes PRACH opportunities that are not mapped to valid PUSCH opportunities. Then, the UE selects the next available PRACH opportunity from the remaining PRACH opportunities corresponding to the selected SSB (the MAC entity will randomly select a PRACH opportunity with equal probability among the consecutive PRACH opportunities corresponding to the selected SSB; when determining the next available PRACH opportunity corresponding to the selected SSB, the MAC entity may consider the possible occurrence of a measurement gap). The PRACH opportunity can be selected before the preamble selection.

[0150] Figure 3 PRACH opportunity selection in case of invalid PUSCH opportunity according to an embodiment of the present disclosure is shown.

[0151] refer to Figure 3 , there are two FDM ROs in the PRACH slot mapped to SSB1. Each RO has 8 preambles. There are two PUSCH slots, each with 2 POs. One of the PUSCH slots is invalid. A PUSCH opportunity is valid if it does not overlap in time and frequency with any PRACH opportunity associated with a 4-step random access procedure or a 2-step random access procedure. Additionally, if a tdd-UL-DL-ConfigurationCommon is provided to the UE, it is present if it is within a UL symbol, or the UE is not before an SS / PBCH block in a PUSCH slot and at least N after the last downlink symbol. gapsymbols and at least N after the last SS / PBCH block symbol. gap The PUSCH opportunity is valid for the 1.25 and 5 kHz preamble SCS. gap Is 0, for 15 / 30 / 60 / 120KHz preamble SCS, N gap Yes 2. In this case, if the UE has selected SSB 1 for PRACH transmission, the UE will randomly select from RO1 and RO2. However, since the preamble in RO2 is not mapped to a valid PRU, the UE can skip RO2 in RO selection.

[0152] PUSCH timing selection: The UE selects a PUSCH opportunity corresponding to the selected PRACH opportunity and preamble. If the PUSCH opportunity is not available, the UE may send only the PRACH preamble. Alternatively, if the PUSCH opportunity is not available, the UE may perform step 1 again.

[0153] Step 2: The UE then starts msgB-ResponseWindow and monitors the PDCCH of the random access response (ie, msgB) in the msgB-ResponseWindow. To determine the start of the msgB-ResponseWindow, the UE first determines whether the MsgA payload is transmitted during the MsgA transmission.

[0154] If only the PRACH preamble is transmitted during MsgA transmission (ie, the MsgA payload is not transmitted), the UE further determines whether the UE does not transmit the MsgA payload because a valid PUSCH opportunity for MsgA payload transmission is unavailable.

[0155] If the UE does not send the MsgA payload because a valid PUSCH opportunity for MsgA payload transmission is not available:

[0156] Option 1: The MsgB reception window starts at the first PDCCH opportunity at least one symbol from the end of the RO in which the random access preamble (also called MsgA preamble) is transmitted. The PDCCH opportunity for MsgB reception is signaled by the RAR search space parameters.

[0157] Option 2: The MsgB reception window starts at the first PDCCH opportunity at least one symbol from the start of the first PUSCH slot corresponding to the RACH slot in which the random access preamble (also called MsgA preamble) is transmitted. The PDCCH opportunity for MsgB reception is signaled by the RAR search space parameters.

[0158] Option 3: The MsgB reception window starts at the first PDCCH opportunity at least one symbol from the end of the last valid PO corresponding to the RACH slot in which the random access preamble (also called MsgA preamble) was sent. The PDCCH opportunity for MsgB reception is signaled by the RAR search space parameters.

[0159] Option 4: The MsgB reception window starts at the first PDCCH opportunity at least one symbol from the end of the predefined valid PO (first or last or any other) corresponding to the RACH slot in which the random access preamble (also called MsgA preamble) is sent. The PDCCH opportunity for MsgB reception is signaled by the RAR search space parameters.

[0160] If the UE does not send the MsgA payload due to a Listen Before Talk (LBT) failure in the PUSCH opportunity selected for MsgA payload transmission (in this case, the PUSCH opportunity is selected for MsgA payload transmission in step 1, i.e., the UE does not send the MsgA payload even though a valid PUSCH opportunity is available. In the case of unlicensed spectrum, before transmitting in a PUSCH opportunity, the UE performs a channel access procedure (also called LBT) to determine whether the channel is available. If LBT fails, i.e., the channel is not available, the UE does not transmit):

[0161] - The MsgB reception window starts at the first PDCCH opportunity that is at least one symbol away from the end of the PUSCH opportunity selected for MsgA payload transmission. The PDCCH opportunity for MsgB reception is signaled by the RAR search space parameters.

[0162] Otherwise, if both PRACH preamble and MsgA payload are transmitted during MsgA transmission:

[0163] - The MsgB reception window starts at the first PDCCH opportunity at least one symbol from the end of PUSCH transmission. The PDCCH opportunity for MsgB reception is signaled by the RAR search space parameters.

[0164] When the msgB-ResponseWindow is running, the UE monitors the PDCCH of the SpCell identified by the MsgB-RNTI for random access response. If only the PRACH preamble is sent during the MsgA transmission (i.e., the MsgA payload is not sent on the PUSCH opportunity), the UE monitors the PDCCH addressed to the MsgB-RNTI to receive the fallback information from the gNB.

[0165] If both the PRACH preamble and the MsgA payload are transmitted during MsgA transmission, the UE monitors the PDCCH addressed to the MsgB-RNTI to receive backoff information or success information from the gNB. In this case, if the C-RNTI MAC CE is included in the MsgA: When the msgB-ResponseWindow is running, the UE additionally monitors the PDCCH of the SpCell identified by the C-RNTI for random access response.

[0166] MSGB-RNTI=1+s_id+14×t_id+14×80×f_id+14×80×8×ul_carrier_id+14×80×8×2

[0167] Where s_id is the index of the first OFDM symbol of the PRACH opportunity (0≤s_id<14), t_id is the index of the first time slot of the PRACH opportunity in the system frame (0≤t_id<80), f_id is the index of the PRACH opportunity in the frequency domain (0≤f_id<8), and ul_carrier_id is the UL carrier used for random access preamble transmission (0 for NUL carrier and 1 for SUL carrier).

[0168] Step 3: When msgB-ResponseWindow runs:

[0169] - If C-RNTI is included in MsgA, the UE receives a PDCCH addressed to C-RNTI and the random access procedure is initiated for BFR: RAR reception is successful. The RA procedure is successfully completed. According to an embodiment of the present disclosure, this operation is performed only when both the PRACH preamble and the MsgA payload are transmitted during MsgA transmission. Go to step 8.

[0170] -Otherwise, if the C-RNTI is included in the MsgA and the time alignment timer (TAT) associated with the primary timing advance group (PTAG) is running, and the UE receives a PDCCH addressed to the C-RNTI and the PDCCH contains a UL grant for a new transmission: RAR reception is successful. The RA procedure is completed successfully. The UE releases the 2-step CFRA resources ((multiple) random access preambles, RACH opportunities, PUSCH resources) configured (if any) for this random access procedure. The release here means that the UE will not use these resources for subsequent random access procedures. According to an embodiment of the present disclosure, this operation is performed only when both the PRACH preamble and the MsgA payload are transmitted during the MsgA transmission. Go to step 8. In this case, the release operation may not be performed because for the case where the PTAG is running and the RA is initiated for an event other than beam failure recovery (BFR), contention-free resources may not be configured.

[0171] - Otherwise, if the C-RNTI is included in MsgA, the TAT timer associated with the PTAG is not running, and the UE receives a PDCCH addressed to the C-RNTI and the DL transport block (TB) scheduled by this PDCCH includes an absolute timing advance command MACCE: RAR reception successful. The RA procedure is completed successfully. The UE releases the 2-step CFRA resources ((multiple) random access preambles, RACH opportunities, PUSCH resources) configured (if any) for this random access procedure. This operation is performed only if both the PRACH preamble and the MsgA payload are transmitted during MsgA transmission. Go to step 8. The release here means that the UE will not use these resources for subsequent random access procedures.

[0172] - Otherwise, if the UE receives a PDCCH addressed to the MsgB-RNTI and the decoded TB includes the fallbackRAR MAC subPDU corresponding to the preamble it sent: RAR reception is successful.

[0173] -If the sent random access preamble is a contention-free random access preamble: The RA procedure is completed successfully. The UE releases the 2-step CFRA resources ((multiple) random access preambles, RACH opportunities, PUSCH resources) configured (if any) for this random access procedure. Process the received TA command of SpCell. Transmit the MsgA MAC PDU as Msg3 in the UL grant received by fallbackRAR. Go to step 8. The release here means that the UE will not use these resources for subsequent random access procedures.

[0174] -otherwise

[0175] Process the received TA command of SpCell. Transmit the MsgA MAC PDU as Msg3 in the UL grant received by fallbackRAR

[0176] Start the contention resolution timer

[0177] Go to step 5

[0178] - Otherwise, if the UE receives a PDCCH addressed to MsgB-RNTI and the decoded TB includes a successRAR MAC sub-PDU corresponding to the UE's contention resolution identifier (i.e., the received contention resolution identifier matches the first 48 bits of the CCCH SDU sent in MsgA): RAR reception is successful. The RA procedure is completed successfully. Go to step 8. Note that this is the case when the CCCH SDU is included in MsgA, i.e., the UE is idle / inactive or performing RRC connection reestablishment. For these cases, no contention-free resources are configured and therefore no release is required. In an alternative embodiment, the UE releases the 2-step CFRA resources ((multiple) random access preambles, RACH opportunities, PUSCH resources) configured (if any) for this random access procedure. The release here means that the UE will not use these resources for subsequent random access procedures.

[0179] Step 4: If the RAR window (i.e. msgB-ResponseWindow) expires:

[0180] -Increase PREAMBLE_TRANSMISSION_COUNTER by 1.

[0181] - If msgATransMax is configured, and if PREAMBLE_TRANSMISSION_COUNTERmsgATransMax+1:

[0182] - Switch to 4-step RA. Go to step 7.

[0183] -otherwise:

[0184] -Go to step 1

[0185] Step 5: While the contention resolution timer is running:

[0186] -If the random access procedure is initiated for beam failure recovery and the UE receives a PDCCH transmission addressed to the C-RNTI; or if the random access procedure is initiated by a PDCCH command and the UE receives a PDCCH transmission addressed to the C-RNTI; or if the random access procedure is initiated by the MAC sublayer itself or by the RRC sublayer and the UE receives a PDCCH transmission addressed to the C-RNTI and contains an UL grant for a new transmission, then contention resolution is successful; the RA procedure is completed successfully. Release the 2-step CFRA resources, i.e., the preamble / RO / PUSCH resources configured for this RA procedure (if any). Go to step 8. The release here means that the UE will not use these resources for subsequent random access procedures.

[0187] Step 6: If the contention resolution timer expires:

[0188] -Increase PREAMBLE_TRANSMISSION_COUNTER by 1.

[0189] - If msgATransMax is configured and PREAMBLE_TRANSMISSION_COUNTER = msgATransMax+1:

[0190] - Switch to 4-step RA. Go to step 7.

[0191] -otherwise:

[0192] -Go to step 1

[0193] Step 7: Perform 4-step RA.

[0194] Step 8. Stop

[0195] The 2-step CFRA resource signaling according to an embodiment of the present disclosure is explained below.

[0196] PUSCH resource signaling: According to an embodiment of the present disclosure, the PUSCH resource configuration for 2-step CFRA is configured separately from the PUSCH resource configuration for 2-step CBRA.

[0197] - For PUSCH resource configuration for 2-step CBRA, msgA-PUSCH-ResourceList is included in the common configuration of the BWP. This is a list of MsgA-PUSCH-Resource. The MsgA-PUSCH-Resource IE includes PUSCH parameters to determine PUSCH timing. If 2-step RA is supported in a BWP and msgA-PUSCH-ResourceList is not included in the common configuration of this BWP, the msgA-PUSCH-ResourceList from the initial BWP is used.

[0198] - For 2-step CFRA configuration, msgA-PUSCH-Resource-CFRA is included in the RACH-ConfigDedicated IE of the RRC reconfiguration message. msgA-PUSCH-Resource-CFRA applies to the BWP indicated by the parameter First Active Uplink BWP. msgA-PUSCH-Resource-CFRA includes PUSCH parameters to determine the PUSCH opportunities. The MCS / PRB number for each PUSCH opportunity is part of msgA-PUSCH-Resource-CFRA

[0199] -MsgA-PUSCH-Resource / MsgA-PUSCH-Resource-CFRA parameters:

[0200] frequencyStartMsgAPUSCH: The UE determines the first RB of the first PUSCH opportunity in the UL BWP from the frequencyStartMsgAPUSCH which provides the offset relative to the first RB of the UL BWP, the offset being expressed in number of RBs of the UL BWP.

[0201] nrofPRBsperMsgAPO: A PUSCH opportunity includes a number of RBs provided by nrofPRBsperMsgAPO.

[0202] guardBandMsgAPUSCH: Consecutive PUSCH opportunities in the frequency domain of UL BWP are separated by multiple RBs provided by guardBandMsgAPUSCH.

[0203] nrMsgAPO-FDM: Multiple PUSCH opportunities in the frequency domain of UL BWP are provided by nrMsgAPO-FDM.

[0204] msgAPUSCH-timeDomainOffset: The UE determines the first time slot of the first PUSCH opportunity in the UL BWP from msgAPUSCH-timeDomainOffset, which provides an offset relative to the start of each PRACH time slot, expressed in the number of time slots in the UL BWP.

[0205] guardPeriodMsgAPUSCH: Consecutive PUSCH opportunities within each slot are separated by guardPeriodMsgAPUSCH symbols and have the same duration.

[0206] nrofMsgAPOperSlot: The number of time-domain PUSCH opportunities in each time slot N t Provided by nrofMsgAPOperSlot,

[0207] nrofSlotsMsgAPUSCH: includes a number of consecutive time slots of PUSCH opportunities provided by nrofSlotsMsgAPUSCH.

[0208] startSymbolAndLengthMsgAPO: The starting symbol and length of the PUSCH opportunity in the PUSCH slot are given by startSymbolAndLengthMsgAPO

[0209] msgA-DMRS-Configuration: Through msgA-DMRS-Configuration, the UE is provided with the DMRS configuration for PUSCH transmission in PUSCH opportunities in the active UL BWP.

[0210] msgA-MCS: The MCS of data information in PUSCH transmission for PUSCH opportunities is provided to the UE through msgA-MCS.

[0211] - For 2-step CFRA, if GNB does not signal msgA-PUSCH-Resource-CFRA:

[0212] -UE uses MsgA-PUSCH-Resource from msgA-PUSCH-ResourceList configured for 2-step CBRA. In case msgA-PUSCH-ResourceList includes both Group A and Group PUSCH resources:

[0213] The UE may use the PUSCH resource configuration corresponding to Group A from the configuration for 2-step CBRA; or

[0214] The UE may use the PUSCH resource configuration corresponding to Group B from the configuration for 2-step CBRA; or

[0215] Indicate in a 2-step CFRA configuration the PUSCH resource configuration (Group A or Group B) to be used in the configuration for 2-step CBRA; or

[0216] The UE may select the PUSCH resource configuration corresponding to group A or group B based on the MsgA MAC PDU size.

[0217] For example, if the potential MsgA payload size (UL data available for transmission plus MAC header and, if needed, MAC CE) is larger than the Group A MsgA size, and the path loss is less than PCMAX-preambleReceivedTargetPower-msgA-DeltaPreamble-messagePowerOffsetGroupB (of the serving cell performing the random access procedure): select Group B. Otherwise, select Group A

[0218] According to an embodiment of the present disclosure, for 2-step CFRA, in RACH-ConfigDedicated, the RA preamble index is signaled for one or more SSB / CSI-RS. rach-ConfigGeneric2step (providing an RO different from that of 2-step CBRA) can also be signaled in RACH-ConfigDedicated. In the case where the RO of 2-step CFRA is shared with 4-step and indicates which of the 4-step ROs are shared with 2-step CFRA, msgA-SSB-sharedRO-MaskIndex can also be signaled (in RACH-ConfigDedicated, note that msgA-SSB-sharedRO-MaskIndex is configured separately for 2-step CBRA and 2-step CFRA). For SSB, there can be several ROs, and msgA-SSB-sharedRO-MaskIndex is used to represent a subset of these ROs.

[0219]

Table 1

[0220]

[0221]

[0222] PRACH opportunity / preamble mapped to PUSCH opportunity:

[0223] The PRACH opportunities / preambles used for 2-step contention-free random access resources can be mapped to PUSCH opportunities as follows:

[0224] The UE determines the set of all 2-step contention-free preambles used by the gNB. Note that the ra-PreambleIndex(s) assigned to the UE for SSB / CSI-RS belongs to this set. The UE may determine the set of 2-step contention-free preambles as follows:

[0225] If the RO of the 2-step CFRA is the same as the RO of the 2-step CBRA, and these ROs are shared with the 4-step CBRA:

[0226] Step 1: The UE first determines X, the total number of random access preambles used for random access. X is given by the parameter totalNumberOfRA-Preambles. The parameter totalNumberOfRA-Preambles is signaled by the gNB in ​​the 4-step RACH configuration (i.e. in the RACH-ConfigCommon IE). If totalNumberOfRA-Preambles is signaled, preambles from preamble index 0 to preamble index X-1 are used for random access. If the gNB does not signal totalNumberOfRA-Preambles, all 64 preambles are used for random access.

[0227] Step 2: The UE then determines the contention-based random access preamble for 4-step RA.

[0228] For 4-step CBRA, the number N of SS / PBCH blocks associated with one PRACH opportunity and the number R of contention-based preambles per SS / PBCH block per valid PRACH opportunity are provided to the UE by ssb-perRACH-OccasionAndCB-PreamblesPerSSB. The parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB is signaled by the gNB in ​​the 4-step RACH configuration (i.e. in the RACH-ConfigCommon IE). If N<1, one SS / PBCH block is mapped to 1 / N consecutive valid PRACH opportunities and the R contention-based preambles with consecutive indices associated with the SS / PBCH block of each valid PRACH opportunity start from zero. If N≥1, the R contention-based preambles with consecutive indices associated with SS / PBCH block n (0≤n≤N-1) of each valid PRACH opportunity start from preamble index Start, where Provided by totalNumberOfRA-Preambles and is an integer multiple of N.

[0229] Step 3: The UE then determines the contention-based random access preamble for 2-step RA.

[0230] For 2-step CBRA with common PRACH opportunities with 4-step CBRA, the number N1 of SS / PBCH blocks associated with one PRACH opportunity is provided to the UE through ssb-perRACH-OccasionAndCB-PreamblesPerSSB, and the number R1 of contention-based preambles per SS / PBCH block per valid PRACH opportunity is provided to the UE through msgA-CB-PreamblesPerSSB. The R1 contention-based preambles per SS / PBCH block per valid PRACH opportunity for 2-step CBRA starts after the preamble for 4-step CBRA. If N1<1, one SS / PBCH block is mapped to 1 / N1 consecutive valid PRACH opportunities, and the R1 contention-based preambles of 2-step CBRA associated with the SS / PBCH block of each valid PRACH opportunity with consecutive indices start from "R". If N1>=1, for 2-step CBRA, R1 contention-based preambles with consecutive indices associated with SS / PBCH block n (0≤n≤N1-1) of each valid PRACH opportunity are indexed from preamble index Start, where Provided by totalNumberOfRA-Preambles and is an integer multiple of N.

[0231] The set of all 2-step contention-free preambles used by the gNB includes the random access preamble used for random access while excluding the contention-based random access preamble used for 4-step RA and the contention-based random access preamble used for 2-step RA. For example, assume that the random access preambles used for random access are 0 to 63 as determined in step 1. The contention-based random access preambles used for 4-step RA are 0 to 7 and 31 to 38 as determined in step 2. The contention-based random access preambles used for 2-step RA are 8 to 15 and 39 to 45 as determined in step 3. So all 2-step contention-free preambles used by the gNB are: 16 to 30 and 46 to 63.

[0232] If the RO of the 2-step CFRA is the same as the RO of the 2-step CBRA, and these ROs are shared with the 4-step CBRA (alternative):

[0233] Step 1: The UE first determines X, the total number of random access preambles used for random access. X is given by the parameter totalNumberOfRA-Preambles. The parameter totalNumberOfRA-Preambles is signaled by the gNB in ​​the 4-step RACH configuration (i.e. in the RACH-ConfigCommon IE). If totalNumberOfRA-Preambles is signaled, preambles from preamble index 0 to preamble index X-1 are used for random access. If the gNB does not signal totalNumberOfRA-Preambles, all 64 preambles are used for random access.

[0234] Step 2: The UE then determines the contention-based random access preamble for 4-step RA.

[0235] For 4-step CBRA, the number N of SS / PBCH blocks associated with one PRACH opportunity and the number R of contention-based preambles per SS / PBCH block per valid PRACH opportunity are provided to the UE via ssb-perRACH-OccasionAndCB-PreamblesPerSSB. The parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB is signaled by the gNB in ​​the 4-step RACH configuration (i.e. in the RACH-ConfigCommon IE). If N<1, one SS / PBCH block is mapped to 1 / N consecutive valid PRACH opportunities and the R contention-based preambles with consecutive indices associated with the SS / PBCH block of each valid PRACH opportunity start from zero. If N≥1, the R contention-based preambles with consecutive indices associated with SS / PBCH block n (0≤n≤N-1) of each valid PRACH opportunity start from preamble index Start, where Provided by totalNumberOfRA-Preambles and is an integer multiple of N.

[0236] Step 3: The UE then determines the contention-based random access preamble for 2-step RA.

[0237] For 2-step CBRA with common PRACH opportunities with 4-step CBRA, the number N1 of SS / PBCH blocks associated with one PRACH opportunity is provided to the UE through ssb-perRACH-OccasionAndCB-PreamblesPerSSB, and the number R1 of contention-based preambles per SS / PBCH block per valid PRACH opportunity is provided to the UE through msgA-CB-PreamblesPerSSB. The R1 contention-based preambles per SS / PBCH block per valid PRACH opportunity for 2-step CBRA starts after the preamble for 4-step CBRA. If N1<1, one SS / PBCH block is mapped to 1 / N1 consecutive valid PRACH opportunities, and the R1 contention-based preambles associated with the SS / PBCH block of each valid PRACH opportunity start from 'R'. If N1>=1, then R1 contention-based preambles with consecutive indices associated with SS / PBCH block n (0≤n≤N1-1) of each valid PRACH opportunity are indexed from preamble index Start, where Provided by totalNumberOfRA-Preambles and is an integer multiple of N.

[0238] Step 4: The UE then determines the contention-free random access preamble for 2-step RA.

[0239] For 2-step CBRA with PRACH opportunities common to 4-step CBRA, the number N1 of SS / PBCH blocks associated with one PRACH opportunity is provided to the UE via ssb-perRACH-OccasionAndCB-PreamblesPerSSB, and the number R1 of contention-based preambles per SS / PBCH block per valid PRACH opportunity is provided to the UE via msgA-CB-PreamblesPerSSB, and the number R2 of contention-free preambles per SS / PBCH block per valid PRACH opportunity is provided to the UE via msgA-CF-PreamblesPerSSB. If N1<1, one SS / PBCH block is mapped to 1 / N1 consecutive valid PRACH opportunities, and R2 contention-free preambles with consecutive indices associated with the SS / PBCH block of each valid PRACH opportunity start from 'R+R1'. If N1>=1, then R2 contention-based preambles with consecutive indices associated with SS / PBCH block n (0≤n≤N1-1) of each valid PRACH opportunity are indexed from preamble index 'R+R1'+ Start, where Provided by totalNumberOfRA-Preambles and is an integer multiple of N.

[0240] If the RO of the 2-step CFRA is the same as the RO of the 2-step CBRA, and these ROs are not shared with the 4-step CBRA.

[0241] Step 1: The UE first determines the total number X of random access preambles used for 2-step random access. X is given by the parameter msgA-totalNumberOfRA-Preambles. The parameter msgA-totalNumberOfRA-Preambles is signaled by the gNB in ​​the 2-step RACH configuration (i.e. in the RACH-ConfigCommonTwoStepRA IE). If msgA-totalNumberOfRA-Preambles is signaled, preambles from preamble index 0 to preamble index X-1 are used for 2-step random access. If the gNB does not signal msgA-totalNumberOfRA-Preambles, all 64 preambles are used for 2-step random access.

[0242] Step 2: The UE then determines the contention-based random access preamble for 2-step RA.

[0243] For 2-step CBRA, the number N of SS / PBCH blocks associated with one PRACH opportunity and the number R of contention-based preambles per SS / PBCH block per valid PRACH opportunity are provided to the UE via msgA-ssb-perRACH-OccasionAndCB-PreamblesPerSSB. The parameter msgA-ssb-perRACH-OccasionAndCB-PreamblesPerSSB is signaled by the gNB in ​​the 4-step RACH configuration (i.e. in RACH-ConfigCommonTwoStepRAIE). If N<1, one SS / PBCH block is mapped to 1 / N consecutive valid PRACH opportunities and the R contention-based preambles with consecutive indices associated with the SS / PBCH block of each valid PRACH opportunity start from zero. If N≥1, the R contention-based preambles with consecutive indices associated with SS / PBCH block n (0≤n≤N-1) of each valid PRACH opportunity start from preamble index Start, where It is provided by msgA-totalNumberOfRA-Preambles and is an integer multiple of N.

[0244] The set of all 2-step contention-free preambles used by the gNB includes the random access preamble used for 2-step random access while excluding the contention-based random access preamble used for 2-step RA. For example, assume that the random access preambles used for 2-step random access are 0 to 63 as determined in step 1. The contention-based random access preambles used for 2-step RA are 0 to 7 and 31 to 38 as determined in step 2. So all 2-step contention-free preambles used by the gNB are: 8 to 30 and 39 to 63.

[0245] If the RO of the 2-step CFRA is the same as the RO of the 2-step CBRA, and these ROs are not shared with the 4-step CBRA (alternative):

[0246] Step 1: The UE first determines the total number X of random access preambles used for 2-step random access. X is given by the parameter msgA-totalNumberOfRA-Preambles. The parameter msgA-totalNumberOfRA-Preambles is signaled by the gNB in ​​the 2-step RACH configuration (i.e. in the RACH-ConfigCommonTwoStepRA IE). If msgA-totalNumberOfRA-Preambles is signaled, preambles from preamble index 0 to preamble index X-1 are used for 2-step random access. If the gNB does not signal msgA-totalNumberOfRA-Preambles, all 64 preambles are used for 2-step random access.

[0247] Step 2: The UE then determines the contention-based random access preamble for 2-step RA.

[0248] For 2-step CBRA, the number N of SS / PBCH blocks associated with one PRACH opportunity and the number R of contention-based preambles per SS / PBCH block per valid PRACH opportunity are provided to the UE via msgA-ssb-perRACH-OccasionAndCB-PreamblesPerSSB. The parameter msgA-ssb-perRACH-OccasionAndCB-PreamblesPerSSB is signaled by the gNB in ​​the 4-step RACH configuration (i.e. in RACH-ConfigCommonTwoStepRAIE). If N<1, one SS / PBCH block is mapped to 1 / N consecutive valid PRACH opportunities and the R contention-based preambles with consecutive indices associated with the SS / PBCH block of each valid PRACH opportunity start from zero. If N≥1, the R contention-based preambles with consecutive indices associated with SS / PBCH block n (0≤n≤N-1) of each valid PRACH opportunity start from preamble index Start, where It is provided by msgA-totalNumberOfRA-Preambles and is an integer multiple of N.

[0249] Step 3: The UE then determines the contention-free random access preamble for 2-step RA.

[0250] The number N of SS / PBCH blocks associated with one PRACH opportunity and the number R of contention-based preambles per SS / PBCH block per PRACH opportunity are provided to the UE via msgA-ssb-perRACH-OccasionAndCB-PreamblesPerSSB, and the number R1 of contention-free preambles per SS / PBCH block per valid PRACH opportunity are provided to the UE via msgA-CF-PreamblesPerSSB. If N<1, one SS / PBCH block is mapped to 1 / N consecutive valid PRACH opportunities, and the R1 contention-free preambles with consecutive indices associated with the SS / PBCH block of each valid PRACH opportunity start from 'R'. If N>=1, the R1 contention-based preambles with consecutive indices associated with SS / PBCH block n (0≤n≤N-1) of each valid PRACH opportunity start from the preamble index Start, where It is provided by msgA-totalNumberOfRA-Preambles and is an integer multiple of N.

[0251] If the RO of the 2-step CFRA is different from the RO of the 2-step CBRA (i.e., configured separately for the 2-step CFRA):

[0252] In this case, all preambles (i.e., 0 to 63) are 2-step contention-free random access preambles. Alternatively, the network can signal X, the total number of random access preambles used for 2-step contention-free random access. X is signaled in the RACHConfig Dedicated IE. If X is signaled, preambles from preamble index 0 to preamble index X-1 are used for 2-step contention-free random access.

[0253] According to an embodiment of the present disclosure, the gNB may signal a starting preamble index and a number of preamble indices for indicating a 2-step contention-free random access preamble. In an alternative embodiment for indicating a 2-step contention-free random access preamble, a list of one or more entries may be signaled, wherein each entry in the list indicates a starting preamble index and a number of preamble indices.

[0254] The PRACH opportunities / preambles used for 2-step contention-free random access resources are mapped to PUSCH opportunities as follows:

[0255] The consecutive number N of indices of valid PRACH opportunities in a PRACH slot preamble Contention-free preamble

[0256] -First, in a single PRACH opportunity, according to the preamble index f id In ascending order

[0257] Second, for frequency reused PRACH opportunities, follow the ascending order of frequency resource indexes.

[0258] Third, for the time-multiplexed PRACH opportunities within the PRACH time slot, in ascending order of the time resource index

[0259] Mapping to valid PUSCH timing

[0260] -First, for frequency reused PUSCH opportunities, according to the frequency resource index f id In ascending order

[0261] - Second, in the PUSCH occasion, the DMRS index is determined in the increasing order of the DMRS index, where the DMRS index is first determined in the increasing order of the DMRS port index and then in the increasing order of the DMRS sequence index. id

[0262] - Third, for the PUSCH opportunities that are time-multiplexed within the PUSCH time slot, according to the time resource index t idIn ascending order

[0263] - Fourth, in ascending order of the index of the PUSCH time slot corresponding to the PRACH time slot

[0264] Among them, N preamble =ceil(T preamble / T PUSCH) , T preamble is the total number of contention-free preambles in the valid PRACH opportunities in each association pattern period, and T PUSCH is the total number of active sets of PUSCH opportunities per association pattern period multiplied by the number of DMRS indices per active PUSCH opportunity.

[0265] PUSCH timing selection for 2-step CFRA based on SSB:

[0266] The UE first selects an SSB, where the selected SSB is the SSB whose SS-RSRP is above a configured threshold (which is signaled by the gNB).

[0267] The UE selects the preamble corresponding to the selected SSB (indicated by ra-PreambleIndex).

[0268] Then, as specified in TS 38.321, the UE selects a RO corresponding to the selected SSB (note that the ROs are mapped to the previously defined SSBs, and the UE selects one of the ROs mapped to the selected SSB).

[0269] Then, the UE selects a PUSCH opportunity corresponding to the PRACH slot of the selected RO from the PUSCH opportunities. The UE selects a PUSCH opportunity corresponding to the selected RO and preamble.

[0270] Then, the UE sends the selected preamble and MsgA MACPDU at the selected PRACH opportunity and PUSCH opportunity respectively.

[0271] PUSCH timing selection based on 2-step CFRA of CSI-RS;

[0272] The UE first selects a CSI-RS, where the selected CSI-RS is a CSI-RS whose CSI-RSRP is higher than a configured threshold (the threshold is signaled by the gNB).

[0273] The UE selects the preamble corresponding to the selected CSI-RS (indicated by ra-PreambleIndex).

[0274] The UE then selects the RO (indicated by ra-OccasionList) corresponding to the selected CSI-RS (note that the ROs are mapped to the previously defined SSBs, and the UE selects one of the ROs mapped to the selected SSBs).

[0275] Then, the UE selects a PUSCH opportunity corresponding to the PRACH slot of the selected RO from the PUSCH opportunities. The UE selects a PUSCH opportunity corresponding to the selected RO and preamble.

[0276] Then, the UE sends the selected preamble and MsgA MACPDU at the selected PRACH opportunity and PUSCH opportunity respectively.

[0277] Figure 4 is a block diagram of a terminal (eg, UE) according to an embodiment of the present disclosure.

[0278] refer to Figure 4 , the terminal includes a transceiver 410, a controller 420 and a memory 430. The controller 420 may refer to a circuit, an ASIC or at least one processor. The transceiver 410, the controller 420 and the memory 430 are configured to perform at least one operation including a combination of non-conflicting steps shown in at least one figure or described above. Although the transceiver 410, the controller 420 and the memory 430 are shown as separate entities, they may be implemented as a single entity, such as a single chip. Alternatively, the transceiver 410, the controller 420 and the memory 430 may be electrically connected or coupled to each other.

[0279] The transceiver 410 may transmit and receive signals to and from other network entities (eg, a base station).

[0280] The controller 420 may control the UE to perform a function according to at least one of the above operations.

[0281] The operation of the terminal can be implemented using a memory 430 storing corresponding program codes. The terminal can be equipped with a memory 430 to store program codes for implementing desired operations. In order to perform desired operations, the controller 420 can read and execute the program codes stored in the memory 430 by using a processor or a central processing unit (CPU).

[0282] Figure 5 is a block diagram of a base station (e.g., gNB) according to an embodiment of the present disclosure.

[0283] refer to Figure 5, a base station (BS) includes a transceiver 510, a controller 520, and a memory 530. The controller 520 may refer to a circuit, an ASIC, or at least one processor. The transceiver 510, the controller 520, and the memory 530 are configured to perform at least one operation including a combination of non-conflicting steps shown in at least one of the figures or described above. Although the transceiver 510, the controller 520, and the memory 530 are shown as separate entities, they may be implemented as a single entity, such as a single chip. Alternatively, the transceiver 510, the controller 520, and the memory 530 may be electrically connected or coupled to each other.

[0284] The transceiver 510 may transmit and receive signals to and from other network entities (eg, terminals).

[0285] The controller 520 may control the BS to perform a function according to the foregoing at least one operation.

[0286] The operation of the BS may be implemented using a memory 530 storing corresponding program codes. The BS may be equipped with a memory 530 to store program codes that implement desired operations. In order to perform desired operations, the controller 520 may read and execute program codes stored in the memory 530 by using a processor or CPU.

[0287] 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: Sending message A MsgA for the 2-step random access procedure; In response to only physical random access channel PRACH transmission in the MsgA without physical uplink shared channel PUSCH transmission, monitoring physical downlink control channel PDCCH of message B MsgB during the window period; and Receiving downlink control information on the PDCCH of the MsgB; The starting point of the window for monitoring the PDCCH is determined based on whether the PRACH is associated with a valid PUSCH opportunity.

2. The method according to claim 1, wherein: In response to only the PRACH being transmitted without the PUSCH being transmitted in the MsgA, when the PRACH is associated with the valid PUSCH opportunity, the window starts at a start symbol of the earliest resource of the PDCCH after a last symbol of the valid PUSCH opportunity.

3. The method according to claim 1, wherein: In response to only the PRACH being transmitted without the PUSCH being transmitted in the MsgA, the window starts at a start symbol of the earliest resource of the PDCCH after a last symbol of a PRACH opportunity of the PRACH when the PRACH is not associated with the valid PUSCH opportunity.

4. The method according to claim 1, further comprising: A control message including information about a search space of a random access procedure is received.

5. The method according to claim 4, wherein: Downlink control information on the PDCCH is detected in the search space based on the information.

6. A terminal in a wireless communication system, the terminal comprising: Transceiver; and At least one processor configured to: sending, via the transceiver, a message A MsgA for a 2-step random access procedure, In response to only physical random access channel PRACH transmission in the MsgA without physical uplink shared channel PUSCH transmission, monitoring physical downlink control channel PDCCH of message B MsgB during the window period; and Receiving downlink control information on the PDCCH of the MsgB via the transceiver; The starting point of the window for monitoring the PDCCH is determined based on whether the PRACH is associated with a valid PUSCH opportunity.

7. The terminal according to claim 6, wherein: In response to only the PRACH being transmitted without the PUSCH being transmitted in the MsgA, when the PRACH is associated with the valid PUSCH opportunity, the window starts at a start symbol of the earliest resource of the PDCCH after a last symbol of the valid PUSCH opportunity.

8. The terminal according to claim 6, wherein: In response to only the PRACH being transmitted without the PUSCH being transmitted in the MsgA, the window starts at a start symbol of the earliest resource of the PDCCH after a last symbol of a PRACH opportunity of the PRACH when the PRACH is not associated with the valid PUSCH opportunity.

9. The terminal according to claim 6, wherein: The at least one processor is further configured to: A control message is received via the transceiver, the control message including information about a search space of a random access procedure.

10. The terminal according to claim 9, wherein: Downlink control information on the PDCCH is detected in a search space based on the information.

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