Patent Description:
In the <NUM> system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

An example is known from <NPL>.

In case of <NUM> step CBRA, preambles in certain PRACH occasions are not mapped to any valid PUSCH occasion. In case UE select a PRACH occasion for which there is no valid PUSCH occasion, UE only transmits PRACH preamble during the MsgA transmission. This is not an efficient approach, as in this case RA cannot be completed in <NUM> step. If the network receives the transmitted preamble, it will transmit fallback RAR. UE then perform fallback operation i.e. transmit Msg3 in UL grant received in fallback RAR and perform contention resolution using Msg4. Additionally, the UE monitors a response for MsgA in a response window which starts at first PDCCH occasion that is at least one symbol away from the end of PUSCH occasion in which MsgA payload is transmitted. In case UE has not transmitted MsgA payload, starting of response window for receiving MsgB cannot be unknown as per the current procedure. So some enhancement is needed.

Accordingly, an aspect of the disclosure is to provide a communication method and system for converging a fifth generation (<NUM>) communication system for supporting higher data rates beyond a fourth generation (<NUM>) system.

In accordance with an aspect of the disclosure, a method performed by a terminal of a <NUM>-step random access procedure in a wireless communication system is provided. The method includes transmitting a message A (MsgA) for the <NUM>-step random access procedure, starting a window at a symbol for receiving a physical downlink control channel (PDCCH) of a message B (MsgB), wherein the symbol is identified based on whether a physical uplink shared channel (PUSCH) is transmitted in the MsgA with a physical random access channel (PRACH), and detecting downlink control information on the PDCCH of the MsgB during the window.

In accordance with another aspect of the disclosure, a terminal of a <NUM>-step random access procedure in a wireless communication system is provided. The terminal includes a transceiver, and at least one processor configured to transmit, via the transceiver, a message A (MsgA) for the <NUM>-step random access procedure, start a window at a symbol for receiving a physical downlink control channel (PDCCH) of a message B (MsgB), wherein the symbol is identified based on whether a physical uplink shared channel (PUSCH) is transmitted in the MsgA with a physical random access channel (PRACH), and detect downlink control information on the PDCCH of the MsgB during the window.

Aspects of the present disclosure provide methods so that UE can avoid selection of PRACH occasions which are not mapped to valid PUSCH occasions. This reduces the latency as fallback to <NUM> step RA can be avoided. Additionally, embodiments in this disclosure provides methods to determine response window for receiving MsgB, in case MsgA payload is not transmitted during the <NUM> step RA procedure depending on the reason for not transmitting MsgA payload. This ensures that network and UE are synchronized with respect to response window and UE can avoid missing the MsgB transmitted by gNB.

It is known to those skilled in the art that blocks of a flowchart (or sequence diagram) and a combination of flowcharts may be represented and executed by computer program instructions. These computer program instructions may be loaded on a processor of a general purpose computer, special purpose computer, or programmable data processing equipment. When the loaded program instructions are executed by the processor, they create a means for carrying out functions described in the flowchart. Because the computer program instructions may be stored in a computer readable memory that is usable in a specialized computer or a programmable data processing equipment, it is also possible to create articles of manufacture that carry out functions described in the flowchart. Because the computer program instructions may be loaded on a computer or a programmable data processing equipment, when executed as processes, they may carry out operations of functions described in the flowchart.

A block of a flowchart may correspond to a module, a segment, or a code containing one or more executable instructions implementing one or more logical functions, or may correspond to a part thereof. In some cases, functions described by blocks may be executed in an order different from the listed order. For example, two blocks listed in sequence may be executed at the same time or executed in reverse order.

In this description, the words "unit", "module" or the like may refer to a software component or hardware component, such as, for example, a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC) capable of carrying out a function or an operation. However, a "unit", or the like, is not limited to hardware or software. A unit, or the like, may be configured so as to reside in an addressable storage medium or to drive one or more processors. Units, or the like, may refer to software components, object-oriented software components, class components, task components, processes, functions, attributes, procedures, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays or variables. A function provided by a component and unit may be a combination of smaller components and units, and may be combined with others to compose larger components and units. Components and units may be configured to drive a device or one or more processors in a secure multimedia card.

Prior to the detailed description, terms or definitions necessary to understand the disclosure are described. However, these terms should be construed in a non-limiting way.

The "base station (BS)" is an entity communicating with a user equipment (UE) and may be referred to as BS, base transceiver station (BTS), node B (NB), evolved NB (eNB), access point (AP), fifth generation (<NUM>) NB (5gNB), or next generation NB (gNB).

The "UE" is an entity communicating with a BS and may be referred to as UE, device, mobile station (MS), mobile equipment (ME), or terminal.

In the recent years several broadband wireless technologies have been developed to meet the growing number of broadband subscribers and to provide more and better applications and services. The second generation wireless communication system has been developed to provide voice services while ensuring the mobility of users. Third generation wireless communication system supports not only the voice service but also data service. In recent years, the fourth wireless communication system has been developed to provide high-speed data service. However, currently, the fourth generation wireless communication system suffers from lack of resources to meet the growing demand for high speed data services. So fifth generation wireless communication system (also referred as next generation radio or NR) is being developed to meet the growing demand for high speed data services, support ultra-reliability and low latency applications.

The fifth generation wireless communication system supports not only lower frequency bands but also in higher frequency (mmWave) bands, e.g., <NUM> to <NUM> bands, so as to accomplish higher data rates. To mitigate propagation loss of the radio waves and increase the transmission distance, the beamforming, massive Multiple-Input Multiple-Output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are being considered in the design of fifth generation wireless communication system. In addition, the fifth generation wireless communication system is expected to address different use cases having quite 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 would be flexible enough to serve the UEs having quite different capabilities depending on the use case and market segment the UE cater service to the end customer. Example use cases that the fifth generation wireless communication system wireless system is expected to address includes enhanced Mobile Broadband (eMBB), massive Machine Type Communication (m-MTC), ultra-reliable low latency communication (URLL) etc. The eMBB requirements, such as tens of Gbps data rate, low latency, high mobility, etc., address the market segment representing the conventional wireless broadband subscribers needing internet connectivity everywhere, all the time and on the go. The m-MTC requirements like very high connection density, infrequent data transmission, very long battery life, low mobility address so on and so forth address the market segment representing the Internet of Things (IoT)/Internet of Everything (IoE) envisioning connectivity of billions of devices. The URLL requirements like very low latency, very high reliability and variable mobility so on and so forth address the market segment representing the Industrial automation application, vehicle-to-vehicle/vehicle-to-infrastructure communication foreseen as one of the enabler for autonomous cars.

In the fifth generation wireless communication system operating in higher frequency (mmWave) bands, UE and gNB communicates with each other using Beamforming. Beamforming techniques are used to mitigate the propagation path losses and to increase the propagation distance for communication at higher frequency band. Beamforming enhances the transmission and reception performance using a high-gain antenna. Beamforming can be classified into Transmission (TX) beamforming performed in a transmitting end and reception (RX) beamforming performed in a receiving end. In general, the TX beamforming increases directivity by allowing an area in which propagation reaches to be densely located in a specific direction by using a plurality of antennas. In this situation, aggregation of the plurality of 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, etc. The use of the TX beamforming results in the increase in the directivity of a signal, thereby increasing a propagation distance. Further, since the signal is almost not transmitted in a direction other than a directivity direction, a signal interference acting on another receiving end is significantly decreased. The receiving end can perform beamforming on a RX signal by using a RX antenna array. The RX beamforming increases the RX signal strength transmitted in a specific direction by allowing propagation to be concentrated in a specific direction, and excludes a signal transmitted in a direction other than the specific direction from the RX signal, thereby providing an effect of blocking an interference signal. By using beamforming technique, a transmitter can make plurality of transmit beam patterns of different directions. Each of these transmit beam patterns can be also referred as transmit (TX) beam. Wireless communication system operating at high frequency uses plurality of narrow TX beams to transmit signals in the cell as each narrow TX beam provides coverage to a part of cell. The narrower the TX beam, higher the antenna gain and hence the larger the propagation distance of signal transmitted using beamforming. A receiver can also make plurality of receive (RX) beam patterns of different directions. Each of these receive patterns can be also referred as receive (RX) beam.

The fifth generation wireless communication system, supports standalone mode of operation as well dual connectivity (DC). In DC a multiple Rx/Tx UE may be configured to utilize resources provided by two different nodes (or NBs) connected via non-ideal backhaul. One node acts as the Master Node (MN) and the other as the Secondary Node (SN). The MN and SN are connected via a network interface and at least the MN is connected to the core network. NR also supports Multi-RAT Dual Connectivity (MR-DC) operation whereby a UE in RRC_CONNECTED is configured to utilize radio resources provided by two distinct schedulers, located in two different nodes connected via a non-ideal backhaul and providing either E-UTRA (i.e. if the node is an ng-eNB) or NR access (i.e. if the node is a gNB). In NR for a UE in RRC_CONNECTED not configured with CA/DC there is only one serving cell comprising of the primary cell. For a UE in RRC_CONNECTED configured with CA/ DC the term 'serving cells' is used to denote the set of cells comprising of the Special Cell(s) and all secondary cells. In NR the term Master Cell Group (MCG) refers to a group of serving cells associated with the Master Node, comprising of the PCell and optionally one or more SCells. In NR the term Secondary Cell Group (SCG) refers to a group of serving cells associated with the Secondary Node, comprising of the PSCell and optionally one or more SCells. In NR PCell (primary cell) refers to a serving cell in MCG, operating on the primary frequency, in which the UE either performs the initial connection establishment procedure or initiates the connection re-establishment procedure. In NR for a UE configured with CA, Scell is a cell providing additional radio resources on top of Special Cell. Primary SCG Cell (PSCell) refers to a serving cell in SCG in which the UE performs random access when performing the Reconfiguration with Sync 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.

In the fifth generation wireless communication system, node B (gNB) or base station in cell broadcast Synchronization Signal and PBCH block (SSB) consists of primary and secondary synchronization signals (PSS, SSS) and system information. The system information includes common parameters needed to communicate in cell. In the fifth generation wireless communication system (also referred as next generation radio or NR), System Information (SI) is divided into the MIB and a number of SIBs where:.

In the fifth generation wireless communication system, Physical Downlink Control Channel (PDCCH) is used to schedule DL transmissions on PDSCH and UL transmissions on PUSCH, where the Downlink Control Information (DCI) on PDCCH includes: Downlink assignments containing at least modulation and coding format, resource allocation, and hybrid-ARQ information related to DL-SCH; Uplink scheduling grants containing 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 for: Activation and deactivation of configured PUSCH transmission with configured grant; Activation and deactivation of PDSCH semi-persistent transmission; Notifying one or more UEs of the slot format; Notifying one or more UEs of the PRB(s) and OFDM symbol(s) where the UE may assume no transmission is intended for the UE; Transmission of TPC commands for PUCCH and PUSCH; Transmission of one or more TPC commands for SRS transmissions by one or more UEs; Switching a UE's active bandwidth part; Initiating a random access procedure. A UE monitors a set of PDCCH candidates in the configured monitoring occasions in one or more configured COntrol REsource SETs (CORESETs) according to the corresponding search space configurations. A CORESET consists of a set of PRBs with a time duration of <NUM> to <NUM> OFDM symbols. The resource units Resource Element Groups (REGs) and Control Channel Elements (CCEs) are defined within a CORESET with each CCE consisting a set of REGs. Control channels are formed by aggregation of CCE. Different code rates for the control channels are realized by aggregating different number of CCE. Interleaved and non-interleaved CCE-to-REG mapping are supported in a CORESET. Polar coding is used for PDCCH. Each resource element group carrying PDCCH carries its own DMRS. QPSK modulation is used for PDCCH.

In the fifth generation wireless communication system, a list of search space configurations are signaled by gNB for each configured BWP wherein each search configuration is uniquely identified by an identifier. An identifier of a search space configuration to be used for specific purpose such as paging reception, SI reception, random access response reception is explicitly signaled by gNB. In NR search space configuration comprises of parameters Monitoring-periodicity-PDCCH-slot, Monitoring-offset-PDCCH-slot, Monitoring-symbols-PDCCH-within-slot and duration. A UE determines PDCCH monitoring occasion (s) within a slot using the parameters PDCCH monitoring periodicity (Monitoring-periodicity-PDCCH-slot), the PDCCH monitoring offset (Monitoring-offset-PDCCH-slot), and the PDCCH monitoring pattern (Monitoring-symbols-PDCCH-within-slot). PDCCH monitoring occasions are there in slots 'x' to x+duration where the slot with number 'x' in a radio frame with number 'y' satisfies the equation below:
<MAT>.

The starting symbol of a PDCCH monitoring occasion in each slot having PDCCH monitoring occasion is given by Monitoring-symbols-PDCCH-within-slot. The length (in symbols) of a PDCCH monitoring occasion is given in the corset associated with the search space. Search space configuration includes the identifier of coreset configuration associated with it. A list of coreset configurations are signaled by gNB for each configured BWP wherein each coreset configuration is uniquely identified by an identifier. Note that each radio frame is of <NUM> duration. Radio frame is identified by a radio frame number or system frame number. Each radio frame comprises of several slots wherein the number of slots in a radio frame and duration of slots depends on sub carrier spacing. The number of slots in a radio frame and duration of slots depends radio frame for each supported SCS is pre-defined in NR. Each coreset configuration is associated with a list of TCI (Transmission configuration indicator) states. One DL RS ID (SSB or CSI-RS) is configured per TCI state. The list of TCI states corresponding to a coreset configuration is signaled by gNB via RRC signaling. One of the TCI state in TCI state list is activated and indicated to UE by gNB. TCI state indicates the DL TX beam (DL TX beam is QCLed with SSB/CSI-RS of TCI state) used by gNB for transmission of PDCCH in the PDCCH monitoring occasions of a search space.

Bandwidth adaptation (BA) is supported in the fifth generation wireless communication system. With BA, the receive and transmit bandwidth of a UE need not be as large as the bandwidth of the cell and can be adjusted: the width can be ordered to change (e.g. to shrink during period of low activity to save power); the location can move in the frequency domain (e.g. to increase scheduling flexibility); and the subcarrier spacing can be ordered to change (e.g. to allow different services). A subset of the total cell bandwidth of a cell is referred to as a Bandwidth Part (BWP). BA is achieved by configuring RRC connected UE with BWP(s) and telling the UE which of the configured BWPs is currently the active one. When BA is configured, the UE only has to monitor PDCCH on the one active BWP (i.e., the UE does not have to monitor PDCCH on the entire DL frequency of the serving cell. ) In RRC connected state, the UE is configured with one or more DL and UL BWPs, for each configured Serving Cell (i.e. PCell or SCell). For an activated Serving Cell, there is always one active UL and DL BWP at any point in time. The BWP switching for a Serving Cell is used to activate an inactive BWP and deactivate an active BWP at a time. The BWP switching is controlled by the PDCCH indicating a downlink assignment or an uplink grant, by the bwp-InactivityTimer, by RRC signaling, or by the MAC entity itself upon initiation of Random Access procedure. Upon addition of SpCell or activation of an SCell, the DL BWP and UL BWP indicated by firstActiveDownlinkBWP-Id and firstActiveU-plinkBWP-Id respectively is active without receiving PDCCH indicating a downlink assignment or an uplink grant. The active BWP for a Serving Cell is indicated by either RRC or PDCCH. For unpaired spectrum, a DL BWP is paired with a UL BWP, and BWP switching is common for both UL and DL. Upon expiry of BWP inactivity timer UE switch to the active DL BWP to the default DL BWP or initial DL BWP (if default DL BWP is not configured).

In the <NUM> wireless communication system, 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 re-establishment procedure, scheduling request transmission, secondary cell group (SCG) addition/modification, beam failure recovery and data or control information transmission in UL by non-synchronized UE in RRC CONNECTED state. Several types of random access procedure is supported.

This is also referred as <NUM> step CBRA. In this type of random access, UE first transmits Random Access preamble (also referred as Msg1) and then waits for Random access response (RAR) in the RAR window. RAR is also referred as Msg2. Next generation node B (gNB) transmits the RAR on physical downlink shared channel (PDSCH). PDCCH scheduling the PDSCH carrying RAR is addressed to RA-radio network temporary identifier (RA-RNTI). RA-RNTI identifies the time-frequency resource (also referred as physical RA channel (PRACH) occasion or PRACH transmission (TX) occasion or RA channel (RACH) occasion) in which RA preamble was detected by gNB. The RA-RNTI is calculated as follows: RA-RNTI= <NUM> + s_id + <NUM>*t_id + <NUM>*<NUM>*f_id + <NUM>*<NUM>*<NUM>*ul_carrier_id, where s_id is the index of the first orthogonal frequency division multiplexing (OFDM) symbol of the PRACH occasion where UE has transmitted Msg1, i.e. RA preamble; <NUM>≤s_id<<NUM>; t_id is the index of the first slot of the PRACH occasion (<NUM>≤t_id< <NUM>); f_id is the index of the PRACH occasion within the slot in the frequency domain (<NUM>≤f_id< <NUM>), and ul_carrier_id is the UL carrier used for Msg1 transmission (<NUM> for normal UL (NUL) carrier and <NUM> for supplementary UL (SUL) carrier. Several RARs for various Random access preambles detected by gNB can be multiplexed in the same RAR media access control (MAC) protocol data unit (PDU) by gNB. An RAR in MAC PDU corresponds to UE's RA preamble transmission if the RAR includes an RA preamble identifier (RAPID) of RA preamble transmitted by the UE. If the RAR corresponding to its RA preamble transmission is not received during the RAR window and UE has not yet transmitted the RA preamble for a configurable (configured by gNB in RACH configuration) number of times, the UE goes back to first step i.e. select random access resource (preamble/RACH occasion) and transmits the RA preamble. A backoff may be applied before going back to first step.

If the RAR corresponding to the UE's RA preamble transmission is received, the UE transmits message <NUM> (Msg3) in UL grant received in RAR. Msg3 includes message such as RRC connection request, RRC connection re-establishment request, RRC handover confirm, scheduling request, SI request etc. It may include the UE identity (i.e. cell-radio network temporary identifier (C-RNTI) or system architecture evolution (SAE)-temporary mobile subscriber identity (S-TMSI) or a random number). After transmitting the 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 C-RNTI included in Msg3, contention resolution is considered successful, contention resolution timer is stopped and RA procedure is completed. While the contention resolution timer is running, if the UE receives contention resolution MAC control element (CE) including the UE's contention resolution identity (first X bits of common control channel (CCCH) service data unit (SDU) transmitted in Msg3), contention resolution is considered successful, contention resolution timer is stopped and RA procedure is completed. If the contention resolution timer expires and the UE has not yet transmitted the RA preamble for a configurable number of times, the UE goes back to the first step (i.e. select random access resource (preamble/RACH occasion)) and transmits the RA preamble. A backoff may be applied before going back to the first step.

This is also referred as legacy CFRA or <NUM> step CFRA. CFRA procedure is used for scenarios such as handover where low latency is required, timing advance establishment for secondary cell (Scell), etc. Evolved node B (eNB) assigns to UE dedicated Random access preamble. UE transmits the dedicated RA preamble. ENB transmits the RAR on PDSCH addressed to RA-RNTI. RAR conveys RA preamble identifier and timing alignment information. RAR may also include UL grant. RAR is transmitted in RAR window similar to contention based RA (CBRA) procedure. CFRA is considered successfully completed after receiving the RAR including RA preamble identifier (RAPID) of RA preamble transmitted by the UE. In case RA is initiated for beam failure recovery, CFRA is considered successfully completed if PDCCH addressed to C-RNTI is received in search space for beam failure recovery. If the RAR window expires and RA is not successfully completed and UE has not yet transmitted the RA preamble for a configurable (configured by gNB in RACH configuration) number of times, the UE retransmits the RA preamble.

For certain events such has handover and beam failure recovery if dedicated preamble(s) are assigned to UE, during first step of random access i.e. during random access resource selection for Msg1 transmission UE determines whether to transmit dedicated preamble or non dedicated preamble. Dedicated preambles is typically provided for a subset of SSBs/CSI-RSs. If there is no SSB/CSI-RS having DL RSRP above a threshold amongst the SSBs/CSI-RSs for which contention free random access resources (i.e. dedicated preambles/ROs) are provided by gNB, UE select non dedicated preamble. Otherwise UE select dedicated preamble. So during the RA procedure, one random access attempt can be CFRA while other random access attempt can be CBRA.

<FIG> illustrate <NUM> step random access procedure including a contention-based random access (CBRA) and a contention-free random access (CFRA) according to an embodiment of the disclosure.

Referring to <FIG>, in the first step, a UE <NUM> transmits random access preamble on PRACH and a payload (i.e. MAC PDU) on PUSCH (<NUM>). The random access preamble and payload transmission is also referred as message A (MsgA). In the second step, after MsgA transmission, the UE monitors for a response from the network (i.e., gNB <NUM>) within a configured window (<NUM>). The response is also referred as message B (MsgB).

If CCCH SDU was transmitted in MsgA payload, UE performs contention resolution using the contention resolution information in MsgB. The contention resolution is successful if the contention resolution identity received in MsgB matches first <NUM> bits of CCCH SDU transmitted in MsgA. If C-RNTI was transmitted in MsgA payload, the contention resolution is successful if UE receives PDCCH addressed to C-RNTI. If contention resolution is successful, random access procedure is considered successfully completed. Instead of contention resolution information corresponding to the transmitted MsgA, MsgB may include a fallback information corresponding to the random access preamble transmitted in MsgA. If the fallback information is received, UE transmits Msg3 and performs contention resolution using Msg4 as in CBRA procedure. If contention resolution is successful, random access procedure is considered successfully completed. If contention resolution fails upon fallback (i.e. upon transmitting Msg3), UE retransmits MsgA. If the configured window in which the UE monitor network response after transmitting MsgA expires and the UE has not received MsgB including contention resolution information or fallback information as explained above, the UE retransmits MsgA. If the random access procedure is not successfully completed even after transmitting the msgA configurable number of times, UE fallbacks to <NUM> step RACH procedure i.e. UE only transmits the PRACH preamble.

MsgA payload may include one or more of common control channel (CCCH) service data unit (SDU), dedicated control channel (DCCH) SDU, dedicated traffic channel (DTCH) SDU, buffer status report (BSR) MAC control element (CE), power headroom report (PHR) MAC CE, SSB information, C-RNTI MAC CE, or padding. MsgA may include UE ID (e.g. random ID, S-TMSI, C-RNTI, resume ID, etc.) along with preamble in first step. The UE ID may be included in the MAC PDU of the MsgA. A UE ID such as C-RNTI may be carried in a MAC CE, wherein the MAC CE is included in the MAC PDU. Other UE IDs (such as random ID, S-TMSI, C-RNTI, resume ID, etc.) may be carried in CCCH SDU. The UE ID can be one of random ID, S-TMSI, C-RNTI, resume ID, IMSI, idle mode ID, inactive mode ID, etc. The UE ID can be different in different scenarios in which UE performs the RA procedure. When the UE performs RA after power on (before the UE is attached to the network), then the UE ID is the random ID. When the UE performs RA in IDLE state after the UE is attached to the network, the UE ID is S-TMSI. If the UE has an assigned C-RNTI (e.g. in connected state), the UE ID is C-RNTI. In case the UE is in INACTIVE state, the UE ID is resume ID. In addition to the UE ID, some additional control information can be sent in MsgA. The control information may be included in the MAC PDU of the MsgA. The control information may include one or more of connection request indication, connection resume request indication, SI request indication, buffer status indication, beam information (e.g. one or more DL TX beam ID(s) or SSB ID(s)), beam failure recovery indication/information, data indicator, cell/BS/TRP switching indication, connection re-establishment indication, reconfiguration complete or handover complete message, etc..

The UE determines the preambles/PRACH occasions and their association with SS/ PBCH blocks as follows:.

For <NUM> step CBRA with common PRACH occasions with <NUM> step CBRA, a UE is provided a number N of SS/PBCH blocks associated with one PRACH occasion by ssb-perRACH-OccasionAndCB-PreamblesPerSSB and a number R of contention-based preambles per SS/PBCH block per valid PRACH occasion by msgA-CB-PreamblesPerSSB. The R contention based preambles per SS/PBCH block per valid PRACH occasion for <NUM> step CBRA start after the ones for <NUM> step CBRA.

For <NUM> step CBRA, with separate PRACH occasions with <NUM> step CBRA, the UE is provided a number N of SS/PBCH blocks associated with one PRACH occasion and a number R of contention-based preambles per SS/PBCH block per valid PRACH occasion by ssb-perRACH-OccasionAndCB-PreamblesPerSSB-msgA when provided; otherwise, by ssb-perRACH-OccasionAndCB-PreamblesPerSSB.

For <NUM> step CBRA, with separate PRACH occasions with <NUM> step CBRA, if N<<NUM>, one SS/PBCH block is mapped to <NUM>/N consecutive valid PRACH occasions and R contention based preambles with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from zero. If N≥<NUM>, R contention based preambles with consecutive indexes associated with SS/PBCH block n, <NUM>≤n≤ N-<NUM>, per valid PRACH occasion start from preamble index <MAT> where <MAT> is provided by msgA-totalNumberOfRA-Preambles, and is an integer multiple of N.

For <NUM> step CBRA, with common PRACH occasions with <NUM> step CBRA, if N<<NUM>,one SS/PBCH block is mapped to <NUM>/N consecutive valid PRACH occasions and R contention-based preambles with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from 'last preamble index for <NUM> step CBRA +<NUM>'. If N≥<NUM>, R contention based preambles with consecutive indexes associated with SS/ PBCH block n, <NUM>≤n≤ N-<NUM>, per valid PRACH occasion start from preamble index 'last preamble index for <NUM> step <MAT> where <MAT> is provided by msgA-totalNumberOfRA-Preambles, and is an integer multiple of N.

PRACH occasions are indicated by parameter prach-ConfigIndex. SS/PBCH block indexes provided by ssb-PositionsInBurst in SIB1 or in ServingCellConfigCommon are mapped to valid PRACH occasions in the following order:.

An association period, starting from frame <NUM>, for mapping SS/PBCH blocks to PRACH occasions is the period such that <MAT> SS/PBCH blocks are mapped at least once to the PRACH occasions within the association period, where a UE obtains <MAT> from the value of ssb-PositionsInBurst in SIB1 or in ServingCellConfigCommon. An association pattern period includes one or more association periods and is determined so that a pattern between PRACH occasions and SS/PBCH blocks repeats at most every <NUM> msec.

Referring to <FIG>, in this case the gNB <NUM> assigns to the UE <NUM> dedicated Random access preamble (s) and PUSCH resource(s) for MsgA transmission (<NUM>). RO(s) to be used for preamble transmission may also be indicated. In the first step, the UE <NUM> transmits random access preamble on PRACH and a payload on PUSCH using the contention free random access resources (i.e. dedicated preamble/PUSCH resource/ RO) (<NUM>). In the second step, after MsgA transmission, the UE monitors for a response from the network (i.e. gNB) within a configured window (<NUM>). If the UE receives PDCCH addressed to C-RNTI, random access procedure is considered successfully completed. If UE receives fallback information corresponding to its transmitted preamble, random access procedure is considered successfully completed.

For certain events such has handover and beam failure recovery if dedicated preamble(s) and PUSCH resource(s) are assigned to UE, during first step of random access i.e. during random access resource selection for MsgA transmission UE determines whether to transmit dedicated preamble or non dedicated preamble. Dedicated preambles is typically provided for a subset of SSBs/CSI-RSs. If there is no SSB/ CSI-RS having DL RSRP above a threshold amongst the SSBs/CSI-RSs for which contention free random access resources (i.e. dedicated preambles/ROs/PUSCH resources) are provided by gNB, UE select non dedicated preamble. Otherwise UE select dedicated preamble. So during the RA procedure, one random access attempt can be <NUM> step CFRA while other random access attempt can be <NUM> step CBRA.

Upon initiation of random access procedure, the UE first selects the carrier (SUL or NUL). If the carrier to use for the Random Access procedure is explicitly signaled by the gNB, the UE selects the signaled carrier for performing Random Access procedure. If the carrier to use for the Random Access procedure is not explicitly signaled by gNB, and if the Serving Cell for the Random Access procedure is configured with supplementary uplink, and if the RSRP of the downlink pathloss reference is less than rsrp-ThresholdSSB-SUL, then the UE selects the SUL carrier for performing Random Access procedure. Otherwise, the UE selects the NUL carrier for performing Random Access procedure. Upon selecting the UL carrier, the UE determines the UL and DL BWP for random access procedure as specified in section <NUM> of TS <NUM>. The UE then determines whether to perform <NUM> step or <NUM> step RACH for this random access procedure.

For <NUM> step CBRA, the UE determines time resources and frequency resources for PUSCH occasions in an active UL BWP from msgA-PUSCH-config for the active UL BWP. If the active UL BWP is not the initial UL BWP and msgA-PUSCH-config is not provided for the active UL BWP, the UE uses the msgA-PUSCH-config provided for the initial active UL BWP. The PRACH occasions/preambles are mapped to PUSCH occasions (configured by msgA-PUSCH-config) as follows:.

A consecutive number of preamble indexes Npreamble from valid PRACH occasions in a PRACH slot.

Based on the above mapping rule it is possible that preambles in certain PRACH occasions are not mapped to any valid PUSCH occasion. In case the UE selects a PRACH occasion for which there is no valid PUSCH occasion, the UE only transmits PRACH preamble during the MsgA transmission. This is not an efficient approach, as in this case RA cannot be completed in <NUM> step. If the network receives the transmitted preamble, the network will transmit fallback RAR. The UE then perform fallback operation i.e. transmit Msg3 in UL grant received in fallback RAR and perform contention resolution using Msg4. Additionally, the UE monitors response for MsgA in a response window which starts at first PDCCH occasion that is at least one symbol away from the end of PUSCH occasion in which MsgA payload is transmitted. In the absence of valid PUSCH occasion, starting of response window for receiving MsgB cannot be unknown as per the current procedure. So some enhancement is needed.

A method of <NUM> step random access according to an embodiment of the disclosure will be explained below.

Step <NUM>: During the random access procedure initialisation, UE first selects the carrier (SUL or NUL). If the carrier to use for the Random Access procedure is explicitly signaled by gNB, UE select the signaled carrier for performing the Random Access procedure. If the carrier to use 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 pathloss reference is less than rsrp-ThresholdSSB-SUL: UE select the SUL carrier for performing Random Access procedure. Otherwise, UE select the NUL carrier for performing Random Access procedure.

Upon selecting the UL carrier, UE determines the UL and DL BWP for random access procedure as specified below:.

For the selected carrier of this Serving Cell:.

The UE then determines whether to perform <NUM> step or <NUM> step RACH for this random access procedure.

If this random access procedure is initiated by PDCCH order and if the ra-PreambleIndex explicitly provided by PDCCH is not 0b000000; or.

A UL carrier for random access procedure is explicitly signaled by gNB during handover or reconfiguration with sync for <NUM> step RACH. If the gNB wants UE to select NUL for <NUM> step RACH, the gNB provides <NUM> step contention free random access resources for NUL in reconfiguration message. If the gNB wants the UE to select SUL for <NUM> step RACH, the gNB provides <NUM> step contention free random access resources for SUL in reconfiguration message. A UL carrier for <NUM> step random access procedure may also be explicitly signaled by gNB during handover or reconfiguration with sync. If the gNB wants the UE to select NUL for <NUM> step RACH, the gNB provides <NUM> step contention free random access resources for NUL in reconfiguration message. If gNB wants UE to select SUL for <NUM> step RACH, it provides <NUM> step contention free random access resources for SUL in reconfiguration message.

If <NUM> step contention free random access resources for SUL is signaled by gNB during handover or reconfiguration with sync, the UE selects SUL and RACH type selected is <NUM> step RACH. If <NUM> step contention free random access resources for NUL is signaled by the gNB during handover or reconfiguration with sync, the UE selects NUL and RACH type selected is <NUM> step RACH. If <NUM> step contention free random access resources for SUL is signaled by the gNB during handover or reconfiguration with sync, the UE selects SUL and RACH type selected is <NUM> step RACH. If <NUM> step contention free random access resources for NUL is signaled by the gNB during handover or reconfiguration with sync, the UE selects NUL and RACH type selected is <NUM> step RACH.

Based on the above criteria, the UE has selected <NUM> step RA procedure. The UE initializes the preamble transmission counter (PREAMBLE_TRANSMISSION_COUNTER) to zero.

Step 1A: If contention Free Random Access Resources are provided by the gNB and there is at least one SSB/CSI-RS having SS-RSRP/CSI-RSRP above a threshold amongst the SSBs/CSI-RSs for which contention free random access resources are provided, the UE transmits MsgA i.e. Random Access Preamble (also referred as MsgA preamble) in PRACH occasion and MAC PDU (also referred as MsgA payload) in PUSCH occasion using the assigned contention free random access resources.

Step 1B: Otherwise (i.e., if contention Free Random Access Resources are not provided by gNB or if there is no available SSB/CSI-RS having SS-RSRP/CSI-RSRP above a threshold amongst the SSBs/CSI-RSs for which contention free random access resources are provided), UE transmits MsgA i.e. PRACH Preamble (also referred as MsgA preamble) in PRACH occasion and MAC PDU (also referred as MsgA payload) in PUSCH occasion using the contention based random access resources.

SSB selection: In this case UE selects an SSB having SS-RSRP above a threshold amongst the transmitted SSBs. If no SSB having SS-RSRP above a threshold is available, UE select any SSB.

Preamble Selection: In the current design, the UE selects a Random Access Preamble randomly with equal probability from the Random Access Preambles associated with the selected SSB and the selected Random Access Preambles group.

<FIG> illustrates preamble selection in case of invalid PUSCH occasion according to an embodiment of the disclosure.

Referring to <FIG>, if some of the preambles in certain PRACH occasions (i.e., ROs) are not associated with PUSCH resource unit (i.e. PUSCH occasion+DMRS resource or PUSCH occasion), it is proposed that UE can avoid those during the preamble selection. As shown in <FIG>, there are two ROs in a PRACH slot. These are mapped to SSB1 and SSB2 respectively. Each RO has <NUM> preambles. There are two PUSCH slots each having <NUM> PUSCH occasions (i.e. PO(s)). One of the POs in <NUM>nd PUSCH slot is not valid. A PUSCH occasion is valid if it does not overlap in time and frequency with any PRACH occasion associated with either a <NUM> step random access procedure or a <NUM> step random access procedure. Additionally, if a UE is provided tdd-UL-DL-ConfigurationCommon, a PUSCH occasion is valid if it is within UL symbols, or it does not precede a SS/PBCH block in the PUSCH slot and starts at least Ngap symbols after a last downlink symbol and at least Ngap symbols after a last SS/PBCH block symbol, where Ngap is zero for preamble SCS of <NUM> and <NUM>, is <NUM> for preamble SCS of <NUM>/<NUM>/<NUM>/<NUM>. Each PO has <NUM> DMRS resources. In this case, if the UE has selected SSB <NUM> for PRACH transmission, as per current design the UE will randomly select from preambles <NUM> to <NUM>. However preambles <NUM> to <NUM> are not mapped to valid PUSCH resource unit (PRU). So it is proposed that the UE can randomly select from preambles <NUM> to <NUM> instead of <NUM> to <NUM>.

According to an embodiment of the proposed disclosure, amongst the Random Access Preambles associated with the selected SSB and the selected Random Access Preambles group, the UE excludes the preambles not mapped to valid PUSCH occasions when selecting the random access preamble. The UE selects the Random Access Preamble randomly with equal probability from the remaining Random Access Preambles associated with the selected SSB and the selected Random Access Preambles group.

According to an embodiment of the proposed disclosure, amongst the Random Access Preambles associated with the selected SSB and the selected Random Access Preambles group, for the PRACH occasion selected for PRACH transmission, the UE excludes the preambles not mapped to valid PUSCH occasions when selecting the random access preamble. UE select Random Access Preamble randomly with equal probability from the remaining Random Access Preambles associated with the selected SSB and the selected Random Access Preambles group.

In case all the Random Access Preambles associated with the selected SSB and the selected Random Access Preambles group are not mapped to valid PUSCH occasions, the UE selects a Random Access Preamble randomly with equal probability from the Random Access Preambles associated with the selected SSB and the selected Random Access Preambles group. In this case, the UE does not exclude the preambles not mapped to valid PUSCH occasions when selecting the random access preamble.

PRACH occasion selection: In the current design, the UE selects the next available PRACH occasion corresponding to selected SSB/CSI-RS. The UE determines the next available PRACH occasion from the PRACH occasions corresponding to the selected SSB (the MAC entity shall select a PRACH occasion randomly with equal probability amongst the consecutive PRACH occasions corresponding to the selected SSB; the MAC entity may take into account the possible occurrence of measurement gaps when determining the next available PRACH occasion corresponding to the selected SSB).

According to an embodiment of the disclosure, the UE first excludes the PRACH occasions not mapped to valid PUSCH occasions when determining the next available PRACH occasion corresponding to the selected SSB. The UE then selects next available PRACH occasion from the remaining PRACH occasions corresponding to the selected SSB (the MAC entity shall select a PRACH occasion randomly with equal probability amongst the consecutive PRACH occasions corresponding to the selected SSB; the MAC entity may take into account the possible occurrence of measurement gaps when determining the next available PRACH occasion corresponding to the selected SSB). The PRACH occasion can be selected before preamble selection.

<FIG> illustrates PRACH occasion selection in case of invalid PUSCH occasion according to an embodiment of the disclosure.

Referring to <FIG>, there are two FDMed ROs in a PRACH slot mapped to SSB1. Each RO has <NUM> preambles. There are two PUSCH slots each having <NUM> POs. One of the PUSCH slot is not valid. A PUSCH occasion is valid if it does not overlap in time and frequency with any PRACH occasion associated with either a <NUM> step random access procedure or a <NUM> step random access procedure. Additionally, if a UE is provided tdd-UL-DL-ConfigurationCommon, a PUSCH occasion is valid if it is within UL symbols, or the UE does not precede a SS/PBCH block in the PUSCH slot and starts at least Ngap symbols after a last downlink symbol and at least Ngap symbols after a last SS/ PBCH block symbol, where Ngap is zero for preamble SCS of <NUM> and <NUM>, is <NUM> for preamble SCS of <NUM>/<NUM>/<NUM>/<NUM>. In this case, if the UE has selected SSB <NUM> for PRACH transmission, UE will randomly select from RO1 and RO2. However, since preambles in RO2 is not mapped to valid PRUs, he UE can skip RO2 in RO selection.

PUSCH occasion selection: The UE selects the PUSCH occasion corresponding to selected PRACH occasion and preamble. If the PUSCH occasion is not available, the UE may only transmit PRACH preamble. Alternately, If PUSCH occasion is not available, the UE may perform step <NUM> again.

Step <NUM>: The UE then starts msgB-ResponseWindow and monitor the PDCCH for random access response (i.e. MsgB) in msgB-ResponseWindow. In order to determine the start of msgB-ResponseWindow, the UE first determines whether the MsgA payload was transmitted or not during the MsgA transmission.

If only the PRACH preamble is transmitted (i.e., the MsgA payload is not transmitted) during the MsgA transmission, the UE further determines whether UE has not transmitted MsgA payload due to unavailability of valid PUSCH occasion for MsgA payload transmission or not.

If the UE has not transmitted MsgA payload due to unavailability of valid PUSCH occasion for MsgA payload transmission:.

If the UE has not transmitted MsgA payload due to Listen before Talk (LBT) failure in PUSCH occasion selected for MsgA payload transmission (in this case PUSCH occasion is selected for MsgA payload transmission in step <NUM>, i.e. the UE has not transmitted MsgA payload even though valid PUSCH occasion was available. In case of unlicensed spectrum, before transmitting in PUSCH occasion, UE performs channel access procedure (also refereed as LBT) to determine whether the channel is available or not. If LBT fails i.e. channel is not available, UE does not transmit):.

Else if both PRACH preamble and MsgA payload is transmitted during the MsgA transmission:.

The UE monitors the PDCCH of the SpCell for a random access response identified by MsgB-RNTI while the msgB-ResponseWindow is running. If only PRACH preamble is transmitted (i.e. MsgA payload is not transmitted in PUSCH occasion) during the MsgA transmission, UE monitors PDCCH addressed to MsgB-RNTI for receiving fallback information from gNB.

If both PRACH preamble and MsgA payload is transmitted during the MsgA transmission, the UE monitors the PDCCH addressed to MsgB-RNTI for receiving fallback information or success information from gNB. In this case, if C-RNTI MAC CE was included in the MsgA: the UE additionally monitors the PDCCH of the SpCell for random access response identified by the C-RNTI while the msgB-ResponseWindow is running. <MAT>
where s_id is the index of the first OFDM symbol of the PRACH occasion (<NUM>≤s_id<<NUM>), t_id is the index of the first slot of the PRACH occasion in a system frame (<NUM>≤t_id<<NUM>), f_id is the index of the PRACH occasion in the frequency domain (<NUM>≤f_id<<NUM>), and ul_carrier_id is the UL carrier used for Random Access Preamble transmission (<NUM> for NUL carrier, and <NUM> for SUL carrier).

Step <NUM>: While msgB-ResponseWindow is running:.

Step <NUM>: If RAR window (i.e. msgB-ResponseWindow ) expires:.

Step <NUM>: While contention resolution timer is running:.

Step <NUM>: If contention resolution timer expires:.

<NUM> step CFRA resource signaling according to an embodiment of the disclosure is explained below.

PUSCH Resource Signalling: According to an embodiment of the disclosure, PUSCH resource configuration for <NUM> step CFRA is separately configured from PUSCH resource configuration for <NUM> step CBRA.

The UE can use PUSCH Resource configuration corresponding to group A from configuration for <NUM> step CBRA; or.

if the potential MsgA payload size (UL data available for transmission plus MAC header and, where required, MAC CEs) is greater than group A MsgA size and the pathloss is less than PCMAX (of the Serving Cell performing the Random Access Procedure) - preambleReceivedTargetPower - msgA-DeltaPreamble - message-PowerOffsetGroupB: select group B. Otherwise, select the group A.

According to an embodiment of the disclosure, for <NUM> step CFRA, in RACH-ConfigDedicated, the RA preamble index is signalled for one or more SSBs/CSI-RSs. rach-ConfigGeneric2step (to provide ROs which are different from <NUM> step CBRA) can also be signalled in RACH-ConfigDedicated. msgA-SSB-sharedRO-MaskIndex can also be signaled (in RACH-ConfigDedicated, note that msgA-SSB-sharedRO-MaskIndex is configured separately for <NUM> step CBRA and <NUM> step CFRA) in case ROs for <NUM> step CFRA are shared with <NUM> step and indicated which of the <NUM> step ROs are shared with <NUM> step CFRA. For an SSB, there can be several ROs and msgA-SSB-sharedRO-MaskIndex is used to indicated a subset of these ROs.

The PRACH occasions/preambles for <NUM> step contention free random access resources may be mapped to PUSCH occasions as follows:.

The UE determines a set of all the <NUM> step contention free preambles used by gNB. Note that ra-PreambleIndex(s) assigned to UE for SSBs/CSI-RSs belongs to this set. UE can determine the set of <NUM> step contention free preambles as follows:.

If ROs for <NUM> step CFRA are same as ROs for <NUM> step CBRA and these ROs are shared with <NUM> step CBRA:.

For <NUM> step CBRA, the UE is provided a number N of SS/PBCH blocks associated with one PRACH occasion and a number R of contention based preambles per SS/ PBCH block per valid PRACH occasion by ssb-perRACH-OccasionAndCB-PreamblesPerSSB. The parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB is signaled by gNB in <NUM> step RACH configuration (i.e. in RACH-ConfigCommon IE). If N<<NUM>, one SS/PBCH block is mapped to <NUM>/N consecutive valid PRACH occasions and Rcontention based preambles with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from zero. If N≥<NUM>, R contention based preambles with consecutive indexes associated with SS/PBCH block n, <NUM>≤n≤ N- <NUM> per valid PRACH occasion start from preamble index <MAT> is provided by totalNumberOfRA-Preambles, and is an integer multiple of N.

Step <NUM>: The UE then determines the contention based random access preambles used for <NUM> step RA.

For <NUM> step CBRA with common PRACH occasions with <NUM> step CBRA, a UE is provided a number N1 of SS/PBCH blocks associated with one PRACH occasion by ssb-perRACH-OccasionAndCB-PreamblesPerSSB and a number R1 of contention based preambles per SS/PBCH block per valid PRACH occasion by msgA-CB-PreamblesPerSSB. The R1 contention based preambles per SS/PBCH block per valid PRACH occasion for <NUM> step CBRA start after the ones for <NUM> step CBRA. If N1<<NUM>, one SS/PBCH block is mapped to <NUM>/N1 consecutive valid PRACH occasions and R1 contention based preambles for <NUM> step CBRA with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from 'R'. If N1>=<NUM>, for <NUM> step CBRA R1 contention based preambles with consecutive indexes associated with SS/ PBCH block n, <NUM>≤n≤N1-<NUM>, per valid PRACH occasion start from preamble index 'R'+ <MAT> where <MAT> is provided by totalNumberOfRA-Preambles, and is an integer multiple of N.

The set of all the <NUM> step contention free preambles used by the gNB consists of random access preambles used for random access excluding the contention based random access preambles used for <NUM> step RA and the contention based random access preambles used for <NUM> step RA. For example, assume as determined in step <NUM>, random access preambles used for random access are <NUM> to <NUM>. As determined in step <NUM>, contention based random access preambles used for <NUM> step RA are <NUM> to <NUM> and <NUM> to <NUM>. As determined in step <NUM>, contention based random access preambles used for <NUM> step RA are <NUM> to <NUM> and <NUM> to <NUM>. So all the <NUM> step contention free preambles used by gNB are: <NUM> to <NUM> and <NUM> to <NUM>.

If ROs for <NUM> step CFRA are same as ROs for <NUM> step CBRA and these ROs are shared with <NUM> step CBRA (Alternate):.

For <NUM> step CBRA, the UE is provided a number N of SS/PBCH blocks associated with one PRACH occasion and a number R of contention based preambles per SS/ PBCH block per valid PRACH occasion by ssb-perRACH-OccasionAndCB-PreamblesPerSSB. The parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB is signaled by gNB in <NUM> step RACH configuration (i.e. in RACH-ConfigCommon IE). If N<<NUM>, one SS/PBCH block is mapped to <NUM>/N consecutive valid PRACH occasions and R contention based preambles with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from zero. If N≥<NUM>, R contention based preambles with consecutive indexes associated with SS/PBCH block n, <NUM>≤n≤ N-<NUM>, per valid PRACH occasion start from preamble index <MAT> where <MAT> is provided by totalNumberOfRA-Preambles, and is an integer multiple of N.

For <NUM> step CBRA with common PRACH occasions with <NUM> step CBRA, a UE is provided a number N1 of SS/PBCH blocks associated with one PRACH occasion by ssb-perRACH-OccasionAndCB-PreamblesPerSSB and a number R1 of contention based preambles per SS/PBCH block per valid PRACH occasion by msgA-CB-PreamblesPerSSB. The R1 contention based preambles per SS/PBCH block per valid PRACH occasion for <NUM> step CBRA start after the ones for <NUM> step CBRA. If N1<<NUM>, one SS/PBCH block is mapped to <NUM>/N1 consecutive valid PRACH occasions and R1 contention based preambles with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from 'R'. If N1>=<NUM>, R1 contention based preambles with consecutive indexes associated with SS/PBCH block n, <NUM>≤n≤N1-<NUM>, per valid PRACH occasion start from preamble index <MAT> where <MAT> is provided by totalNumberOfRA-Preambles, and is an integer multiple of N.

Step <NUM>: The UE then determine the contention free random access preambles used for <NUM> step RA.

For <NUM> step CBRA with common PRACH occasions with <NUM> step CBRA, a UE is provided a number N1 of SS/PBCH blocks associated with one PRACH occasion by ssb-perRACH-OccasionAndCB-PreamblesPerSSB and a number R1 of contention based preambles per SS/PBCH block per valid PRACH occasion by msgA-CB-PreamblesPerSSB and a number R2 of contention free preambles per SS/PBCH block per valid PRACH occasion by msgA-CF-PreamblesPerSSB. If N1<<NUM>, one SS/ PBCH block is mapped to <NUM>/N1 consecutive valid PRACH occasions and R2 contention free preambles with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from 'R+R1'. If N1>=<NUM>, R2 contention based preambles with consecutive indexes associated with SS/PBCH block n, <NUM>≤n≤N1-<NUM>, per valid PRACH occasion start from preamble index <MAT> where <MAT> is provided by totalNumberOfRA-Preambles, and is an integer multiple of N.

If ROs for <NUM> step CFRA are same as ROs for <NUM> step CBRA and these ROs are not shared with <NUM> step CBRA.

Step <NUM>: The UE first determine X, the total number of Random Access preambles used for <NUM> step random access. X is given by parameter msgA-totalNumberOfRA-Preambles. The parameter msgA-totalNumberOfRA-Preambles is signaled by gNB in <NUM> step RACH configuration (i.e., in RACH-ConfigCommonTwoStepRA IE). If msgA-totalNumberOfRA-Preambles is signaled, preambles from preamble index <NUM> to preamble index X-<NUM> are used for <NUM> step random access. If msgA-totalNumberOfRA-Preambles is not signaled by gNB, all <NUM> preambles are used for <NUM> step random access.

Step <NUM>: The UE then determine the contention based random access preambles used for <NUM> step RA.

For <NUM> step CBRA, the UE is provided a number N of SS/PBCH blocks associated with one PRACH occasion and a number R of contention based preambles per SS/ PBCH block per valid PRACH occasion by msgA- ssb-perRACH-OccasionAndCB-PreamblesPerSSB. The parameter msgA- ssb-perRACH-OccasionAndCB-PreamblesPerSSB is signaled by gNB in <NUM> step RACH configuration (i.e. in RACH-ConfigCommonTwoStepRA IE). If N<<NUM>, one SS/PBCH block is mapped to <NUM>/N consecutive valid PRACH occasions and R contention based preambles with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from zero. If N≥<NUM>, R contention based preambles with consecutive indexes associated with SS/PBCH block n, <NUM>≤n≤N - <NUM>, per valid PRACH occasion start from preamble index <MAT> where <MAT> is provided by msgA-totalNumberOfRA-Preambles, and is an integer multiple of N.

The set of all the <NUM> step contention free preambles used by the gNB consists of random access preambles used for <NUM> step random access excluding the contention based random access preambles used for <NUM> step RA. For example, assume that as determined in step <NUM>, random access preambles used for <NUM> step random access are <NUM> to <NUM>. As determined in step <NUM>, contention based random access preambles used for <NUM> step RA are <NUM> to <NUM> and <NUM> to <NUM>. So all the <NUM> step contention free preambles used by gNB are: <NUM> to <NUM> and <NUM> to <NUM>.

If ROs for <NUM> step CFRA are same as ROs for <NUM> step CBRA and these ROs are not shared with <NUM> step CBRA (Alternate):.

For <NUM> step CBRA, the UE is provided a number N of SS/PBCH blocks associated with one PRACH occasion and a number R of contention based preambles per SS/ PBCH block per valid PRACH occasion by msgA- ssb-perRACH-OccasionAndCB-PreamblesPerSSB. The parameter msgA- ssb-perRACH-OccasionAndCB-PreamblesPerSSB is signaled by gNB in <NUM> step RACH configuration (i.e. in RACH-ConfigCommonTwoStepRA IE). If N<<NUM>, one SS/PBCH block is mapped to <NUM>/N consecutive valid PRACH occasions and R contention based preambles with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from zero. If N≥<NUM>, R contention based preambles with consecutive indexes associated with SS/PBCH block n, <NUM>≤n≤N-<NUM>, per valid PRACH occasion start from preamble index <MAT> where <MAT> is provided by msgA-totalNumberOfRA-Preambles, and is an integer multiple of N.

Step <NUM>: The UE then determines the contention free random access preambles used for <NUM> step RA.

The UE is provided a number N of SS/PBCH blocks associated with one PRACH occasion and a number R of contention based preambles per SS/PBCH block per valid PRACH occasion by msgA-ssb-perRACH-OccasionAndCB-PreamblesPerSSB and a number R1 of contention free preambles per SS/PBCH block per valid PRACH occasion by msgA-CF-PreamblesPerSSB. If N<<NUM>, one SS/PBCH block is mapped to <NUM>/N consecutive valid PRACH occasions and R1 contention free preambles with consecutive indexes associated with the SS/PBCH block per valid PRACH occasion start from 'R'. If N>=<NUM>, R1 contention based preambles with consecutive indexes associated with SS/PBCH block n, <NUM>≤n≤ N- <NUM>, per valid PRACH occasion start from preamble index <MAT> where <MAT> is provided by msgA-total-NumberOfRA-Preambles, and is an integer multiple of N.

If ROs for <NUM> step CFRA are not same as ROs for <NUM> step CBRA (i.e. separately configured for <NUM> step CFRA):
In this case, all preambles (i.e., <NUM> to <NUM>) are <NUM> step contention free random access preambles. Alternately, network can signal X i.e. the total number of Random Access preambles used for <NUM> step contention free random access. X is signaled in RACH config dedicated IE. If X is signaled, preambles from preamble index <NUM> to preamble index X-<NUM> are used for <NUM> step contention free random access.

According to an embodiment of the disclosure, the gNB can signal starting preamble index and number of preamble indexes for indicating <NUM> step contention free random access preambles. In an alternate embodiment for indicating <NUM> step contention free random access preambles, a list of one or more entries can be signaled wherein each entry in the list indicates starting preamble index and number of preamble indexes.

The PRACH occasions/preambles for <NUM> step contention free random access resources are mapped to PUSCH occasions as follows:
A consecutive number of Npreamble contention free preamble indexes from valid PRACH occasions in a PRACH slot.

where Npreamble = ceil(Tpreamble/TPUSCH),Tpreamble is a total number of contention free preambles in valid PRACH occasions per association pattern period, and TPUSCH is a total number of valid sets of PUSCH occasions per association pattern period multiplied by the number of DMRS indexes per valid PUSCH occasion.

The UE first selects an SSB, where the selected SSB is the one for which SS-RSRP is above a configured threshold (the threshold is signalled by the gNB).

The UE selects a preamble (indicated by ra-PreambleIndex) corresponding to selected SSB.

The UE then selects an RO corresponding to selected SSB as specified in TS <NUM> (note that ROs are mapped to SSBs as defined earlier and UE select one of ROs mapped to selected SSB).

The UE then selects a PUSCH occasion from PUSCH occasions corresponding to PRACH slot of selected RO. The UE selects the PUSCH occasion corresponding to selected RO and preamble.

The UE then transmits the selected preamble and MsgA MAC PDU in selected PRACH occasion and PUSCH occasion, respectively.

The UE first selects CSI-RS, where the selected CSI-RS is the one for which CSI-RSRP is above a configured threshold (threshold is signaled by gNB).

The UE selects a preamble (indicated by ra-PreambleIndex) corresponding to selected CSI-RS.

The UE then selects an RO (indicated by ra-OccasionList) corresponding to selected CSI-RS (note that ROs are mapped to SSBs as defined earlier and UE select one of ROs mapped to selected SSB).

The UE then selects a PUSCH occasion from PUSCH occasions corresponding to PRACH slot of selected RO. The UE selects the PUSCH occasion corresponding to the selected RO and preamble.

The UE then transmits the selected preamble and MsgA MAC PDU in selected PRACH occasion and PUSCH occasion respectively.

<FIG> is a block diagram of a terminal, (e.g., a UE) according to an embodiment of the disclosure.

Referring to <FIG>, the terminal includes a transceiver <NUM>, a controller <NUM> and a memory <NUM>. The controller <NUM> may refer to circuitry, an ASIC, or at least one processor. The transceiver <NUM>, the controller <NUM>, and the memory <NUM> are configured to perform at least one operation including a combination of steps, which are not in conflict, illustrated in at least one of the drawings or described above. Although the transceiver <NUM>, the controller <NUM>, and the memory <NUM> are shown as separate entities, they may be realized as a single entity, such as a single chip. Alternatively, the transceiver <NUM>, the controller <NUM>, and the memory <NUM> may be electrically connected to or coupled with each other.

The transceiver <NUM> may transmit and receive signals to and from other network entities, e.g., a base station.

The controller <NUM> may control the UE to perform functions according at least one operation described above.

The operations of the terminal may be implemented using the memory <NUM> storing corresponding program codes. The terminal may be equipped with the memory <NUM> to store program codes implementing desired operations. To perform the desired operations, the controller <NUM> may read and execute the program codes stored in the memory <NUM> by using a processor or a central processing unit (CPU).

<FIG> is a block diagram of a base station (e.g., a gNB) according to an embodiment of the disclosure.

Referring to <FIG>, the base station (BS) includes a transceiver <NUM>, a controller <NUM> and a memory <NUM>. The controller <NUM> may refer to a circuitry, an ASIC, or at least one processor. The transceiver <NUM>, the controller <NUM>, and the memory <NUM> are configured to perform at least one operation including a combination of steps, which are not in conflict, illustrated in at least one of the drawings or described above. Although the transceiver <NUM>, the controller <NUM>, and the memory <NUM> are shown as separate entities, they may be realized as a single entity like a single chip. Alternatively, the transceiver <NUM>, the controller <NUM>, and the memory <NUM> may be electrically connected to or coupled with each other.

The transceiver <NUM> may transmit and receive signals to and from other network entities, e.g., a terminal.

The controller <NUM> may control the BS to perform functions according to at least one operation described above.

Claim 1:
A method for a terminal (<NUM>) for a wireless communication system, the method comprising:
transmitting a message A, MsgA, for a <NUM>-step random access procedure; characterized by in response to a transmission of only a physical random access channel, PRACH, in the MsgA, without a physical uplink shared channel, PUSCH, monitoring a physical downlink control channel, PDCCH, for a message B, MsgB, during a window; and
receiving downlink control information on the PDCCH for the MsgB,
wherein a starting point of the window for monitoring the PDCCH depends on whether the PRACH is associated with a valid PUSCH occasion.