Systems and methods for latency reduction for 2-step random access channel (RACH) HARQs (HYBRID AUTOMATIC REPEAT REQUEST)

Abstract

Wireless communication systems and methods related to timing arrangements and transmission gap configurations of 2-step RACH procedures are provided to improve system latency and reliability of Random Access Channel (RACH) HARQ processes. A UE transmits a first message containing a random access preamble and a payload, and then monitors for a second message that is a response to the first message during a Random Access Response (RAR) window. In response to a determination that the UE has not received the second message from the BS or that a backoff indicator has been received within the RAR window, the UE retransmits the preamble and payload of the first message after the RAR window has elapsed. In response to a determination that the second message received within the RAR window returns a fallback RAR or a success RAR, the UE determines whether to retransmit the payload of the first message based on the fallback RAR or to transmit an acknowledgment message based on the success RAR.

Description

Technology Field

[0001] The patented technology discussed below relates to wireless communication systems, and more specifically, to reducing latency in the retransmission method of 2-step random access channel (RACH) HARQ (hybrid automatic repeat request) that can be utilized in 5th generation (5G) NR (new radio) networks. Background Technology

[0002] Wireless communication systems are widely deployed to provide various types of communication content, such as voice, video, packet data, messaging, and broadcast. These systems can support communication with multiple users by sharing available system resources (e.g., time, frequency, and power). A wireless multiple-access communication system may include multiple base stations (BS) that each simultaneously support communications for multiple communication devices, which may be otherwise known as user equipment (UE).

[0003] In a wireless system, BSs can broadcast synchronization signals, such as PSS (Primary Synchronization Signal), SSS (Secondary Synchronization Signal), ESS (Extended Synchronization Signal), BRS (Beam Reference Signal), and system information, through multiple directional beams. Furthermore, BSs can transmit other reference signals, such as CSI-RS (Channel State Information Reference Signal), through the beams to enable UEs to measure channels between the BS and corresponding UEs. A UE can perform initial cell acquisition by listening to the broadcast signals and perform signal measurements based on the synchronization signals, BRS, and / or other signals. Based on the received signals, the UE can determine the received signal strengths and select a cell and a beam within the selected cell to perform an access procedure.

[0004] To perform the access procedure, the UE initiates the Random Access Channel (RACH) procedure by transmitting a Random Access Preamble using the same subarray and beam direction as the selected beam, and can monitor for Random Access Responses (RAR) within the RAR window. When the BS detects the Random Access Preamble, the BS transmits the RAR to the UE in the same beam direction as where the Random Access Preamble was received. The RAR may contain a transmission opportunity for the UE to transmit the next Random Access message. Due to beam correspondence, user mobility, rotation, and / or signal blockage, beam characteristics may change over time or differ between the uplink and downlink at the UE or BS. Consequently, the UE may fail to receive the RAR. When failing to receive the RAR within the RAR window, the UE may have the option to retry the RACH procedure after the RAR window has expired. However, the UE may need to wait a significant amount of time whenever retransmission is implemented (e.g., at least until the RAR window expires + additional back-off time). Therefore, retransmission can cause significant system latency.

[0005] Therefore, it is necessary to improve latency performance in the RACH procedure in wireless communication systems.

[0006] The following summarizes some aspects of the present disclosure to provide a basic understanding of the technology discussed. This summary is not a comprehensive overview of all features considered in the present disclosure, nor is it intended to identify key or important elements of all aspects of the present disclosure or to limit the scope of any or all aspects of the present disclosure. The sole purpose of this summary is to present some concepts of one or more aspects of the present disclosure in a summary form as an introduction to the more detailed description to be provided later.

[0007] For example, in an aspect of the present disclosure, a wireless communication method includes the step of a user device (UE) receiving system information from a base station (BS) to initiate a random access channel (RACH) procedure. The method further includes the step of the UE transmitting a first message to the BS, the first payload comprising a random access preamble and a connection request, and the step of the UE monitoring for a second message from the BS that is a response to the first message during a random access response (RAR) window. The method further includes the step of the UE retransmitting the first message to the BS in response to a determination, based on monitoring, that the UE has not received the second message from the BS within the RAR window. The method further includes the step of the UE determining, based on the type of the second payload decoded from the second message, whether to retransmit the first payload to the BS or to transmit an acknowledgment message to the BS in response to a determination that the UE has received the second message from the BS within the RAR window.

[0008] In another aspect of the present disclosure, a wireless communication method comprises the step of a BS broadcasting system information to a UE to initiate a random access channel procedure. The method further comprises the step of the BS receiving from the UE a first message comprising a random access preamble and a first payload of a connection request, and the step of the BS determining whether at least a portion of the first message is decodingable. The method further comprises the step of suppressing the transmission of any message to the UE within a random access response (RAR) window in response to a failure to decode the first message. The method further comprises the step of the BS transmitting to the UE a RAR message comprising a second payload determined based on the type of the portion of the first message in response to a success in decoding at least a portion of the first message.

[0009] In another aspect of the present disclosure, a UE of a wireless communication receives system information for initiating a Random Access Channel (RACH) procedure and transmits a first message comprising a Random Access preamble and a first payload of a connection request, monitors for a second message that is a response to the first message during a Random Access Response (RAR) window, and includes a transceiver configured to retransmit the first message in response to a determination that the UE has not received the second message from the BS within the RAR window based on the monitoring. The UE further includes a processor configured to determine, based on the type of the second payload decoded from the second message, whether to retransmit the first payload to the BS or to transmit an acknowledgment message to the BS in response to a determination that the UE has received the second message from the BS within the RAR window.

[0010] In another aspect of the present disclosure, a BS of a wireless communication comprises a transceiver configured to receive a first message comprising a random access preamble and a first payload of a connection request, for broadcasting system information to initiate a random access channel procedure. The BS further comprises a processor configured to determine whether at least a portion of the first message is decodingable and to suppress the transmission of any message to a UE within a random access response (RAR) window in response to a failure to decode the first message. The transceiver is further configured to transmit a RAR message comprising a second payload determined based on the type of the portion of the first message in response to a successful decoding of at least a portion of the first message.

[0011] Other aspects, features, and aspects of the present invention will become apparent to those skilled in the art when reviewing the subsequent description of specific exemplary aspects of the present invention in connection with the accompanying drawings. While features of the present invention may be discussed with respect to the specific aspects and drawings below, all aspects of the present invention may include one or more of the advantageous features discussed herein. In other words, while one or more aspects may be discussed as having specific advantageous features, one or more of such features may also be used according to the various aspects of the present invention discussed herein. In a similar manner, exemplary aspects may be discussed below as device, system, or method aspects, but it should be understood that these exemplary aspects may be implemented in various devices, systems, and methods. Brief explanation of the drawing

[0012] FIG. 1 illustrates a wireless communication network according to some aspects of the present disclosure.

[0013] FIG. 2 illustrates a random access method in a wireless communication network illustrated in FIG. 1 according to aspects of the present disclosure.

[0014] FIGS. 3a through 3c illustrate various transmission scenarios of a 2-step RACH method between a UE and a BS that can be implemented in a wireless communication network illustrated in FIGS. 1 and 2 according to some aspects of the present disclosure.

[0015] FIG. 4 is a block diagram of a user device (UE) according to some aspects of the present disclosure.

[0016] FIG. 5 is a block diagram of an exemplary base station (BS) according to some aspects of the present disclosure.

[0017] FIGS. 6a-6c illustrate retransmission timeline designs in different scenarios of a 2-step RACH procedure between a UE and a BS according to some aspects of the present disclosure.

[0018] FIGS. 7a-7b illustrate a logic flow performed by a UE corresponding to retransmission timeline designs in different scenarios of the 2-step RACH procedure illustrated in FIGS. 6a-6b, according to some aspects of the present disclosure.

[0019] FIG. 8 illustrates a logic flow performed by BS corresponding to retransmission timeline designs in different scenarios of the 2-step RACH procedure illustrated in FIG. 6a-6b, according to some aspects of the present disclosure.

[0020] FIG. 9 illustrates a logical flow for configuring a random access response (RAR) window length in a 2-step RACH procedure according to some aspects of the present disclosure.

[0021] FIG. 10 illustrates a logical flow that constitutes the starting point of a Random Access Response (RAR) window in a 2-step RACH procedure according to some aspects of the present disclosure. Specific details for implementing the invention

[0022] The detailed description below, in connection with the attached drawings, is intended to describe various configurations and is not intended to represent only the configurations in which the concepts described herein can be implemented. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be obvious to those skilled in the art that these concepts can be implemented without these specific details. In some cases, to avoid obscuring these concepts, well-known structures and components are depicted in block diagram form.

[0023] The present disclosure relates to wireless communication systems, also generally referred to as wireless communication networks. In various aspects, techniques and devices may be used for wireless communication networks such as CDMA (code division multiple access) networks, TDMA (time division multiple access) networks, FDMA (frequency division multiple access) networks, OFDMA (orthogonal FDMA) networks, SC-FDMA (single-carrier FDMA) networks, LTE networks, GSM (Global System for Mobile Communications) networks, 5th generation (5G) or NR (new radio) networks, as well as other communication networks. As described herein, the terms “networks” and “systems” may be used interchangeably.

[0024] OFDMA networks can implement radio technologies such as E-UTRA (evolved UTRA), IEEE (Institute of Electrical and Electronics Engineers) 802.11, IEEE 802.16, IEEE 802.20, and flash-OFDM. UTRA, E-UTRA, and GSM are part of the Universal Mobile Telecommunication System (UMTS). In particular, LTE (long term evolution) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS, and LTE are described in literature provided by an organization named “3GPP (3rd Generation Partnership Project),” and cdma2000 is described in literature from an organization named “3GPP2 (3rd Generation Partnership Project 2).” These various radio technologies and standards are known or are under development. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration among groups of telecommunications commissions aimed at defining globally applicable 3rd generation (3G) mobile phone specifications. 3GPP LTE (long term evolution) is a 3GPP project aimed at improving UMTS mobile phone standards. 3GPP can define specifications for next-generation mobile networks, mobile systems, and mobile devices. The present disclosure relates to advancements in radio technologies from LTE, 4G, 5G, NR, and beyond that utilizing shared access to the radio spectrum between networks using a set of new and different radio access technologies or radio air interfaces.

[0025] In particular, 5G networks consider various deployments, various spectra, and various services and devices that can be implemented using OFDM-based integrated air interfaces. To achieve these goals, additional enhancements to LTE and LTE-A are considered in addition to the deployment of new radio technologies for 5G NR networks. 5G NR is (1) ultra-high density (e.g., ~1M nodes / km 2 (1) providing coverage for massive IoT (Internet of things) with deep coverage having ultra-low complexity (e.g., ~10s bits / sec), ultra-low energy (e.g., ~10+ years battery life), and the ability to reach demanding locations; (2) providing strong security to protect sensitive personal, financial, or confidential information, ultra-high reliability (e.g., ~99.9999% reliability), ultra-low latency (e.g., ~1 ms), and mission-critical control for users with or without mobility; and (3) extremely high capacity (e.g., ~10 Tbps / km 2 It can be scaled to provide enhanced mobile broadband including extreme data rates (e.g., multi-Gbps rates, 100+ Mbps user-experienced rates), and deep awareness with advanced discoveries and optimizations.

[0026] 5G NR has a common flexible framework for efficiently multiplexing services and features using dynamic, low-latency TDD (time division duplex) / FDD (frequency division duplex) designs; and can be implemented using optimized OFDM-based waveforms with scalable numerology and transmit time intervals (TTI) featuring advanced radio technologies, such as massive multiple input multiple output (MIMO), robust millimeter wave (mmWave) transmits, advanced channel coding, and device-centric mobility. The scalability of 5G NR numerology allows for the efficient handling of operating various services across various spectrums and deployments by utilizing the scaling of subcarrier spacing. For example, in various outdoor and macro coverage deployments of FDD / TDD implementations below 3 GHz, the subcarrier spacing can occur at 15 kHz across bandwidths (BW), such as 5, 10, or 20 MHz. For various other outdoor and small cell coverage deployments of TDD above 3 GHz, the subcarrier spacing can be 30 kHz over an 80 / 100 MHz BW. For various other indoor broadband implementations using TDD over the unlicensed portion of the 5 GHz band, the subcarrier spacing can be 60 kHz over a 160 MHz BW. Finally, for various deployments transmitting using mmWave components with TDD at 28 GHz, the subcarrier spacing can be 120 kHz over a 500 MHz BW.

[0027] Scalable numerology in 5G NR facilitates scalable TTI for various latency and Quality of Service (QoS) requirements. For example, shorter TTIs can be used for low-latency and high reliability, while longer TTIs can be used for higher spectrum efficiency. Efficient multiplexing of long and short TTIs allows transmits to be initiated on symbol boundaries. 5G NR also considers a self-contained, integrated subframe design containing uplink / downlink scheduling information, data, and acknowledgments within the same subframe. Self-contained, integrated subframes support communications in adaptive uplink / downlink on unlicensed or contention-based shared spectrum that can be flexibly configured at the cellular level to dynamically switch between uplink and downlink to meet current traffic needs.

[0028] Various other aspects and characteristics of the present disclosure are further described below. It should be apparent that the teachings of this application may be embodied in a wide variety of forms, and that any specific structure, function, or both disclosed herein are merely representative and not limiting. Based on the teachings of this application, those skilled in the art should recognize that an aspect disclosed herein may be embodied independently of any other aspect, and that two or more of these aspects may be combined in various ways. For example, an apparatus may be embodied or a method may be practiced using any number of aspects described herein. Additionally, such an apparatus may be embodied or such a method may be practiced in addition to one or more of the aspects described herein, or by using other structures, functions, or structures and functions. For example, a method may be embodied as a system, device, part of an apparatus, and / or as instructions stored on a computer-readable medium for execution on a processor or computer. Furthermore, an aspect may include at least one element of a claim.

[0029] In a wireless system, when a UE wishes to access a network, the UE may attach to a BS or attempt to synchronize with the BS. To synchronize with the network, a RACH procedure is used. For example, typically, a 4-step RACH procedure is used for the UE to establish a synchronized connection with the BS. Specifically, in the System Information Block (SIB2), a BS, such as a next-generation Node B (gNB), periodically broadcasts several parameters, such as the root sequence ID, RACH configuration index, power offset, and initial power. In a contention-based RACH procedure, the UE randomly selects a preamble from 54 orthogonal ZC (zadoff-chu) sequences generated by a root sequence cyclic shift, and this preamble is transmitted through a random access subframe of the frequency resource block (RB) and time as Msg 1, which implicitly defines the RA-RNTI (RA-radio network temporary identifier). Upon success of Msg 1, the gNB responds with a Msg 2 Random Access Response (RAR) containing a temporary C-RNTI (cell-RNTI), a TA (timing advance), and an uplink resource grant. In Msg 3, the UE decodes the RB allocation from Msg 2 and transmits a radio resource control (RRC) connection request containing a randomly selected initial device identity. Multiple UEs may select the same preamble, the RA-RNTI of Msg 1, and the corresponding C-RNTI of Msg 2, and transmit their own Msg 3 over the uplink resources, which are detected as collisions by the gNB. In Msg 4, the gNB transmits an RRC connection setup along with an echo of the initial identity transmitted by the device in Msg 3 and a permanent C-RNTI.The RACH procedure is considered successful if the identities match; otherwise, the device retries the procedure after a back-off interval. A successful UE is ready to transmit uplink data.

[0030] To reduce the access latency of a 4-step RACH access procedure, a 2-step RACH procedure may be used in which the UE combines Msg 1 and Msg 3 into a single initial message and the BS responds in turn with a combined message of the usual Msg 2 and Msg 4. According to aspects of the present disclosure, a 2-step RACH procedure as further described in connection with FIG. 3a-3c may include a timeline mechanism for implementing a hybrid automatic repeat request (HARQ) to avoid excessive latency when the UE retransmits.

[0031] In light of the need to reduce overall latency in a 2-step RACH procedure, the aspects described herein provide timeline designs for retransmission schemes in a 2-step RACH procedure with improved system latency. Specifically, as further described in connection with FIGS. 6a-10, various timing parameters are adopted to align the transmission and / or retransmission of messages in a 2-step RACH procedure. Through defined timeline arrangements, the overall latency of the 2-step RACH procedure is improved.

[0032] FIG. 1 illustrates a wireless communication network (100) according to some aspects of the present disclosure. The network (100) may be a 5G network. The network (100) includes a plurality of base stations (BS) (105) (individually labeled as 105a, 105b, 105c, 105d, 105e, and 105f) and other network entities. A BS (105) may be a station communicating with UEs (115) and may also be referred to as an eNB (evolved node B), next-generation eNB (gNB), access point, etc. Each BS (105) may provide communication coverage for a specific geographic area. In 3GPP, the term “cell” may refer to this specific geographic coverage area of ​​a BS (105) and / or a BS subsystem serving the coverage area, depending on the context in which the term is used.

[0033] A BS (105) can provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell and / or other types of cells. A macro cell generally covers a relatively large geographical area (e.g., a radius of several kilometers) and can allow unrestricted access by UEs that have subscribed to services from a network provider. A small cell, such as a pico cell, generally covers a relatively smaller geographical area and can allow unrestricted access by UEs that have subscribed to services from a network provider. A small cell, such as a femto cell, generally also covers a relatively small geographical area (e.g., a home) and, in addition to unrestricted access, can also provide restricted access by UEs that have an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, etc.). A BS for a macro cell may be referred to as a macro BS. A BS for a small cell may be referred to as a small cell BS, pico BS, femto BS, or home BS. In the example illustrated in FIG. 1, the BSs (105d and 105e) may be conventional macro BSs, whereas the BSs (105a-105c) may be macro BSs enabled as 3D (three dimension), FD (full dimension), or large-scale MIMO. The BSs (105a to 105c) may utilize the higher-dimensional MIMO capabilities of the BSs to utilize 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. BS (105f) may be a small cell BS that may be a home node or a portable access point. A BS (105) may support one or more cells (e.g., two, three, four, etc.).

[0034] The network (100) may support synchronous or asynchronous operation. In the case of synchronous operation, the BSs may have similar frame timings, and transmissions from different BSs may be roughly aligned in time. In the case of asynchronous operation, the BSs may have different frame timings, and transmissions from different BSs may not be aligned in time.

[0035] UEs (115) are scattered throughout the wireless network (100), and each UE (115) may be fixed or mobile. A UE (115) may also be referred to as a terminal, mobile station, subscriber unit, station, etc. A UE (115) may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, etc. In one aspect, a UE (115) may be a device including a Universal Integrated Circuit Card (UICC). In another aspect, a UE may be a device not including a UICC. In some aspects, UEs (115) not including UICCs may also be referred to as IoT devices or Internet of Everything (IoE) devices. UEs (115a-115d) are examples of mobile smartphone-type devices accessing the network (100). The UE (115) may also be a machine specially configured for connected communication, including machine type communication (MTC), enhanced MTC (eMTC), narrowband IoT (NB-IoT), etc. UEs (115e-115k) are examples of various machines configured for communication that access the network (100). The UE (115) may be able to communicate with any type of BS, whether macro BS, small cell, etc. In FIG. 1, lightning bolts (e.g., communication links) indicate wireless transmissions between the UE (115) and a serving BS (105), which is a BS designated to serve the UE (115) via a downlink and / or uplink, or desired transmissions between BSs, and backhaul transmissions between BSs.

[0036] In operation, BSs (105a-105c) can serve UEs (115a-115b) using 3D beamforming and cooperative space techniques, such as CoMP (coordinated multipoint) or multi-connectivity. A macro BS (105d) can perform backhaul communications with small cells, BS (105f), as well as with BSs (105a-105c). A macro BS (105d) can also transmit multicast services to be subscribed to and received by UEs (115c and 115d). Such multicast services may include mobile television or stream video, or other services for providing community information, such as weather emergency advisories or warnings, such as Amber warnings or Gray warnings.

[0037] The BSs (105) can also communicate with the core network. The core network may provide user authentication, access authorization, tracking, IP (Internet Protocol) connectivity, and other access, routing, or mobility functions. At least some of the BSs (105) (e.g., gNB or an example of an ANC (access node controller)) may interface with the core network via backhaul links (e.g., NG-C, NG-U, etc.) and perform radio configuration and scheduling for communication with UEs (115). In various examples, the BSs (105) may communicate with each other directly or indirectly (e.g., via the core network) via backhaul links (e.g., X1, X2, etc.) which may be wired or wireless communication links.

[0038] The network (100) can also support mission-critical communications using highly reliable and redundant links to mission-critical devices, such as a UE (115e) which may be a drone. Redundant communication links with the UE (115e) may include links from macro BSs (105d and 105e) as well as links from small cell BSs (105f). Other machine-type devices, such as UE (115f) (e.g., thermometer), UE (115g) (smart meter), and UE (115h) (wearable device), can communicate through the network (100) in multi-hop configurations by communicating directly with BSs, such as small cell BS (105f) and macro BS (105e), or with other user devices that relay their information to the network, such as UE (115f) communicating temperature measurement information to the smart meter, i.e., UE (115g) (the information is subsequently reported to the network via the small cell BS (105f)). The network (100) can also provide additional network efficiency through dynamic low-latency TDD / FDD communications, such as in V2V (vehicle-to-vehicle).

[0039] In some implementations, the network (100) utilizes OFDM-based waveforms for communications. An OFDM-based system can divide the system BW into a number (K) of orthogonal subcarriers, which are also generally referred to as subcarriers, tones, bins, etc. Each subcarrier can be modulated with data. In some cases, the subcarrier spacing between adjacent subcarriers can be fixed, and the total number of subcarriers (K) can depend on the system BW. The system BW can also be partitioned into subbands. In other cases, the subcarrier spacing and / or duration of the TTIs can be scalable.

[0040] BSs (105) can allocate or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RBs)) for downlink (DL) and uplink (UL) transmissions in the network (100). DL refers to the transmission direction from the BS (105) to the UE (115), while UL refers to the transmission direction from the UE (115) to the BS (105). Communication may take the form of radio frames. A radio frame may be divided into multiple subframes or slots, e.g., about 10 subframes or slots. Each slot may be further divided into mini-slots. In FDD mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes the UL subframe in the UL frequency band and the DL subframe in the DL frequency band. In TDD mode, UL and DL transmissions occur in different time periods using the same frequency bands. For example, a subset of subframes of radio frames (e.g., DL subframes) may be used for DL ​​transmissions, and another subset of subframes of radio frames (e.g., UL subframes) may be used for UL transmissions.

[0041] DL subframes and UL subframes may be further divided into several zones. For example, each DL or UL subframe may have pre-defined zones for transmitting reference signals, control information, and data. Reference signals are predetermined signals that facilitate communication between BSs (105) and UEs (115). For example, the reference signals may have a specific pilot pattern or structure, where the pilot tones may span an operating BW or frequency band, and, for example, each is positioned at a pre-defined time and a pre-defined frequency. For example, the BS (105) may transmit cell-specific reference signals (CRS) and / or channel state information-reference signals (CSI-RS) to enable the UE (115) to estimate the DL channel. Similarly, the UE (115) may transmit sounding reference signals (SRS) to enable the BS (105) to estimate the UL channel. Control information may include resource allocations and protocol controls. Data may include protocol data and / or operation data. Some aspects, BSs (105) and UEs (115) may communicate using self-contained subframes. A self-contained subframe may include a portion for DL ​​communication and a portion for UL communication. A self-contained subframe may be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL ​​communication than for UL communication. A UL-centric subframe may include a longer duration for UL communication than for DL ​​communication.

[0042] In some aspects, the network (100) may be an NR network deployed across the licensed spectrum. BSs (105) may transmit synchronization signals (e.g., including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS)) in the network (100) to facilitate synchronization. BSs (105) may broadcast system information associated with the network (100) (e.g., including a master information block (MIB), residual system information (RMSI), and other system information (OSI)) to facilitate initial network access. In some cases, BSs (105) may broadcast the PSS, SSS, and / or MIB in the form of synchronization-signal-blocks (SSBs) over a physical broadcast channel (PBCH), and broadcast the RMSI and / or OSI over a physical downlink shared channel (PDSCH).

[0043] In some aspects, a UE (115) attempting to access the network (100) may perform an initial cell search by detecting a PSS from the BS (105). The PSS may enable synchronization of period timing and may display a physical layer identity value. Subsequently, the UE (115) may receive an SSS. The SSS may enable radio frame synchronization and may provide a cell identity value that can be combined with the physical layer identity value to identify the cell. The PSS and SSS may be located in the center of the carrier or at any suitable frequencies within the carrier.

[0044] After receiving the PSS and SSS, the UE (115) may receive the MIB. The MIB may contain system information for initial network access and scheduling information for the RMSI and / or OSI. After decoding the MIB, the UE (115) may receive the RMSI and / or OSI. The RMSI and / or OSI may contain RRC (radio resource control) information related to random access channel (RACH) procedures, paging, control resource set (CORESET) for monitoring the physical downlink control channel (PDCCH), physical uplink control channel (PUCCH), physical uplink shared channel (PUSCH), power control, and SRS.

[0045] After obtaining the MIB, RMSI and / or OSI, the UE (115) may perform a random access procedure to establish a connection with the BS (105). In some examples, the random access procedure may be a 4-step random access procedure. For instance, the UE (115) may transmit a random access preamble, and the BS (105) may respond with a random access response. The random access response (RAR) may include a detected random access preamble identifier (ID) corresponding to the random access preamble, timing advance (TA) information, a UL grant, a temporary cell-radio network temporary identifier (C-RNTI), and / or a backoff indicator. Upon receiving the random access response, the UE (115) may transmit a connection request to the BS (105), and the BS (105) may respond with a connection response. The connection response may indicate contention resolution. In some examples, the random access preamble, RAR, connection request, and connection response may be referred to as message 1 (Msg 1), message 2 (Msg 2), message 3 (Msg 3), and message 4 (Msg 4), respectively. In some examples, the random access procedure may be a two-step random access procedure, wherein the UE (115) may transmit the random access preamble and connection request in a single transmission, and the BS (105) may respond by transmitting the random access response and connection response in a single transmission.

[0046] After establishing the connection, the UE (115) and the BS (105) can enter a normal operation stage, where operation data can be exchanged. For example, the BS (105) can schedule the UE (115) for UL and / or DL ​​communications. The BS (105) can transmit UL and / or DL ​​scheduling grants to the UE (115) via PDCCH. The BS (105) can transmit DL communication signals to the UE (115) via PDSCH according to the DL scheduling grants. The UE (115) can transmit UL communication signals to the BS (105) via PUSCH and / or PUCCH according to the UL scheduling grants.

[0047] In some cases, the BS (105) may communicate data with the UE (115) using a hybrid automatic request (HARQ) to improve communication reliability. The BS (105) may schedule the UE (115) for PDSCH communication by sending a DL grant from the PDSCH. The BS (105) may send a DL data packet to the UE (115) according to the schedule of the PDSCH. The DL data packet may be sent in the form of a transport block (TB). If the UE (115) successfully receives the DL data packet, the UE (115) may send a HARQ ACK to the BS (105). Conversely, if the UE (115) does not successfully receive the DL transmission, the UE (115) may send a HARQ NACK to the BS (105). When the BS (105) receives a HARQ NACK from the UE (115), it may retransmit a DL data packet to the UE (115). The retransmission may contain a coded version of the DL data identical to the initial transmission. Alternatively, the retransmission may contain a coded version of the DL data different from the initial transmission. The UE (115) may apply soft-combining to combine the encoded data received from the initial transmission and the retransmission for decoding. The BS (105) and the UE (115) may also apply HARQ for UL communications using mechanisms substantially similar to DL HARQ.

[0048] In some aspects, the network (100) may operate through a system BW or a component carrier BW. The network (100) may partition the system BW into multiple BWPs (e.g., parts). The BS (105) may dynamically assign a UE (115) to operate through a specific BWP (e.g., a specific part of the system BW). The assigned BWP may be referred to as an active BWP. The UE (115) may monitor the active BWP for signaling information from the BS (105). The BS (105) may schedule the UE (115) for UL or DL ​​communications in the active BWP. In some aspects, the BS (105) may assign a pair of BWPs within the component carrier to the UE (115) for UL and DL communications. For example, a pair of BWPs may include one BWP for UL communications and one BWP for DL ​​communications. The BS (105) may further configure the UE (115) with one or more CORESETs in the BWP. A CORESET may include a set of frequency resources spanning multiple symbols over time. The BS (105) may configure the UE (115) with one or more search spaces for PDCCH monitoring based on the CORESETs. The UE (115) may perform blind decoding in the search spaces to search for DL ​​control information (e.g., UL and / or DL ​​scheduling grants) from the BS. In one example, the BS (105) may configure the UE (115) with BWPs, CORESETs, and / or PDCCH search spaces through RRC configurations.

[0049] In some aspects, the network (100) may operate across a shared frequency band or an unlicensed frequency band, for example, at approximately 3.5 gigahertz (GHz), sub-6 GHz, or higher frequencies in the mmWave band. The network (100) may partition the frequency band into multiple channels, each of which occupies approximately 20 megahertz (MHz). BSs (105) and UEs (115) may be operated by multiple network operating entities that share resources of a shared communication medium and may use an LBT procedure to acquire a channel occupancy time (COT) in the shared medium for communications. The COT may be discontinuous in time and may refer to an amount of time during which a wireless node can transmit frames when it wins contention for the wireless medium. Each COT may include multiple transmission slots. The COT may also be referred to as a transmission opportunity (TXOP). The BS (105) or UE (115) may perform LBT in the frequency band before transmitting in the frequency band. LBT may be based on energy detection or signal detection. For energy detection, the BS (105) or UE (115) may determine that the channel is busy or occupied when the signal energy measured from the channel is greater than a specific signal energy threshold. For signal detection, the BS (105) or UE (115) may determine that the channel is busy or occupied when a specific pre-signal (e.g., a preamble signal sequence) is detected in the channel.

[0050] In addition, BS (105) may configure the UE (115) to have narrowband operation capabilities (e.g., transmission and / or reception limited to a BW of 20 MHz or less) to perform BWP hopping for channel monitoring and communications. Mechanisms for performing BWP hopping are described in more detail herein.

[0051] FIG. 2 illustrates a random access method in a wireless communication network (200) according to aspects of the present disclosure. The network (200) corresponds to a part of the network (100). FIG. 2 illustrates one BS (204) and one UE (202) for the sake of brevity, but it will be recognized that aspects of the present disclosure can be scaled to more UEs (202) and / or BSs (204). The BS (204) corresponds to one of the BSs (104). The UE (202) corresponds to one of the UEs (102). The UE (202) and the BS (204) can communicate with each other at any suitable frequencies.

[0052] In FIG. 2, the BS (204) transmits synchronization signals, BRSs, and system information through multiple directional beams (211) in multiple directions as illustrated by the dashed ellipse (220). To access the network (200), the UE (202) listens for the synchronization signals and / or BRSs and selects a beam to perform a random access procedure. For example, the UE (202) may receive beams (211a, 211b, and 211c) and selects beam (211b) for random access. The UE (202) transmits a random access preamble through beam (221) in the direction of beam (211b) and monitors for a RAR from the BS (204). When the random access preamble is detected, the BS (204) transmits a RAR through beam (211b) in the same direction as the random access preamble was received. The BS (204) uses the entire subframe to transmit the RAR through the beam (211b). This can be an inefficient resource when large bandwidth is available. Furthermore, by the time the BS (204) transmits the RAR, the UE (202) may have moved to a different location away from the beam (211b), as indicated by the dotted arrows. Consequently, the UE (202) may fail to receive the RAR from the beam (211b). An additional cause of RAR failure may be beam similarity. Although the UE (202) may retry another random access attempt after waiting for a certain period of time (e.g., a backoff period), the retry adds additional latency. Therefore, transmitting a single random access preamble across a single beam direction for each random access attempt may not be robust enough to successfully complete the RACH procedure.

[0053] FIGS. 3a-3c illustrate various transmission scenarios of a 2-step RACH method between a UE (202) and a BS (204) that can be implemented in a wireless communication network illustrated in FIG. 1-2 according to some aspects of the present disclosure.

[0054] The diagram (300a) in FIG. 3a illustrates a 2-step RACH procedure that reduces access delay in the control plane compared to a conventional 4-step RACH. After a system information block (e.g., SIB2) and RRC signaling are transmitted from the BS (204) to the UE (202) at 315 and the UE (202) decodes the system information and RRC signaling at 320, the UE (202) transmits Msg A at 340, which returns standard 4-step LTE RACH Msg 1 and Msg 3, including a random access preamble for random access messages (connection request, device ID, buffer status report, etc.) and the following payload. Subsequently, the UE (202) monitors for Msg B from the BS (204) at 345, while the BS (204) processes and decodes Msg A at 350. In 355, Msg B is transmitted from the BS (204), and Msg B corresponds to Msg 2 and Msg 4 of a standard 4-step LTE RACH, such as RAR, TA (timing advance), and finally, connection completion via an RRC response message. Thus, the 2-step RACH can set up a connection between the UE (202) and the BS (204) so ​​that the UE (202) can begin transmitting uplink data with reduced access delay, such as with 2 message exchanges compared to traditional 4 message exchanges.

[0055] The diagram (300b) in FIG. 3b illustrates a scenario for retransmission when the BS (204) fails to receive the Msg A preamble or payload. For example, due to channel collision, channel fading, or interference, the transmission of Msg A (340) may fail. The BS (204) may monitor for Msg A at 375 but receives nothing. Or the BS (204) may receive a corrupted Msg A but fails to decode the preamble or payload from the corrupted version. In this case, the BS (204) may not respond to the UE (202) with Msg B. The UE (202) may monitor for Msg B (345) for a period of time and attempt to retransmit Msg A at 380. Because the waiting time for the UE (202) to monitor Msg B (345) or the retransmission method is not specified by the 2-step RACH, additional latency (310) may occur in the retransmission process.

[0056] The diagram (300c) in FIG. 3b illustrates a different scenario for retransmission when the UE (202) fails to receive Msg B from the BS (204). For example, even if the BS (204) successfully receives and decodes Msg A at 350 and then transmits Msg B to the UE (202) in response to Msg A at 355, the transmission of Msg B at 355 may fail due to channel damage, receiver malfunction at the UE (202), etc. In this case, the UE (202) may monitor for Msg B for a certain period of time (345) but fails to receive any of it, or receives only a corrupted version of Msg B that cannot be decoded. When the UE (202) fails to receive or decode the RAR response from Msg B in response to the transmitted Msg A, similar to the scenario in diagram (300b), the UE (202) may attempt to retransmit Msg A at 380, and subsequently, the BS (204) may attempt to retransmit Msg B at 385. Since the retransmission timeline of Msg A or Msg B is not defined in the 2-step RACH, additional latency (310) may occur if the UE (202) waits indefinitely for retransmission.

[0057] In light of the need to reduce overall latency in a 2-step RACH procedure, the aspects described herein provide timeline designs for retransmission schemes in a 2-step RACH procedure with improved system latency. Specifically, as further described in connection with FIGS. 6a-10, Msg A or Msg B may be retransmitted according to a specific scenario of decoding failure in the UE (202) or BS (204), and various timing parameters are adopted to align the transmission or retransmission of Msg A and Msg B in the 2-step RACH procedure. When defined timeline arrangements are used during retransmission, the overall latency of the 2-step RACH procedure is improved.

[0058] FIG. 4 is a block diagram of an exemplary UE (400) according to some aspects of the present disclosure. The UE (400) may be, for example, the UE (115) previously discussed in FIG. 1 or the UE (202) shown in other drawings. As illustrated, the UE (400) may include a processor (402), memory (404), a BWP hopping module (408), a communication interface (409), a transceiver (410) including a modem subsystem (412) and a radio frequency (RF) unit (414), and one or more antennas (416). These elements may communicate with each other indirectly or directly, for example, through one or more buses.

[0059] The processor (402) may include a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a controller, a field programmable gate array (FPGA) device, other hardware devices, a firmware device, or any combination thereof configured to perform the operations described herein. Additionally, the processor (402) may be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration.

[0060] Memory (404) may include cache memory (e.g., cache memory of the processor (402), random access memory (RAM), magnetoresistive RAM (MRAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, solid-state memory devices, hard disk drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In one embodiment, memory (404) includes a non-transient computer-readable medium. Memory (404) may store or write instructions (406). The instructions (406) may include instructions that, when executed by the processor (402), cause the processor (402) to perform the operations described herein with reference to the UEs (115) in relation to aspects of the disclosure, e.g., FIGS. 3a-3c and FIGS. 6a-10. The instructions (406) may also be referred to as program code. The program code may be intended to cause the wireless communication device to perform these operations by, for example, causing one or more processors (e.g., processor (402)) to control or command the wireless communication device to perform these operations. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement(s). For example, the terms “instructions” and “code” may refer to one or more programs, routines, sub-routines, functions, procedures, etc. "Instructions" and "code" may include a single computer-readable instruction or many computer-readable instructions.

[0061] The 2-step RACH module (408) can communicate with the communication interface (409) to receive messages from another device or send messages to another device. Each of the 2-step RACH module (408) and the communication interface (409) may be implemented through hardware, software, or a combination thereof. For example, each of the 2-step RACH module (408) and the communication interface (409) may be implemented as instructions (406) stored in a processor, circuit, and / or memory (404) and executed by the processor (402). In some examples, the 2-step RACH module (408) and the communication interface (409) may be integrated within a modem subsystem (412). For example, the 2-step RACH module (408) and the communication interface (409) may be implemented by a combination of software components (e.g., executed by a DSP or general processor) and hardware components (e.g., logic gates and circuits) within the modem subsystem (412). In some examples, the UE may include one of the 2-step RACH module (408) and the communication interface (409). In other examples, the UE may include both the 2-step RACH module (408) and the communication interface (409).

[0062] The 2-step RACH module (408) and the communication interface (409) may be used for various aspects of the present disclosure, e.g., aspects of FIG. 2-3 and FIG. 6-17. The 2-step RACH module (408) is configured to receive BS (e.g., 204) system information for initiating a RACH procedure. The 2-step RACH module (408) is further configured to transmit Msg A to the BS, which includes a payload containing a connection request and a random access preamble. The 2-step RACH module (408) is further configured to monitor for Msg B from the BS, which is a response to Msg A, during a random access response (RAR) window. The 2-step RACH module (408) is further configured to retransmit Msg A if Msg B is not received from the BS within the RAR window. Alternatively, the 2-step RACH module (408) is further configured to determine whether to resend a connection request in Msg 3 or send an acknowledgment message as a fallback to the standard 4-step RACH, based on the type of payload decoded from the received Msg B when Msg B is received from BS within the RAR window.

[0063] The communication interface (409) is configured to work in cooperation with the 2-step RACH module (408) to receive system information, Msg B and / or other DL scheduling grants from the BS and / or communicate with the BS according to the UL and / or DL ​​scheduling grants. The communication interface (409) is further configured to transmit Msg A and / or other UL data to the BS.

[0064] As described, the transceiver (410) may include a modem subsystem (412) and an RF unit (414). The transceiver (410) may be configured to communicate bidirectionally with other devices, such as BSs (105). The modem subsystem (412) may be configured to modulate and / or encode data from a memory (404), a 2-step RACH module (408), and / or a communication interface (409) according to a modulation and coding scheme (MCS), such as a low-density parity check (LDPC) coding scheme, a turbo coding scheme, a convolution coding scheme, a digital beamforming scheme, etc. The RF unit (414) may be configured to process (e.g., perform analog-to-digital conversion or digital-to-analog conversion, etc.) transmissions originating from other sources such as the UE (115) or BS (105) or modulated / encoded data (e.g., PUCCH, PUSCH, channel reports, ACK / NACKs) from the modem subsystem (412) (for outbound transmissions). The RF unit (414) may be additionally configured to perform analog beamforming along with digital beamforming. Although shown as being integrated together in the transceiver (410), the modem subsystem (412) and the RF unit (414) may be separate devices coupled together in the UE (115) to enable the UE (115) to communicate with other devices.

[0065] The RF unit (414) may provide modulated and / or processed data, such as data packets (or, more generally, data messages that may include one or more data packets and other information), to the antenna (416) for transmission to one or more other devices. The antennas (416) may additionally receive data messages transmitted from other devices. The antennas (416) may provide the received data messages for processing and / or demodulation in the transceiver (410). The transceiver (410) may provide the demodulated and decoded data (e.g., DL data blocks, PDSCH, PUSCH, BWP hopping configurations and / or commands) to the 2-step RACH module (408) and / or communication interface (409) for processing. The antennas (416) may include multiple antennas of similar or different designs to maintain multiple transmission links. The RF unit (414) can configure antennas (416).

[0066] In one aspect, the UE (400) may include a plurality of transceivers (410) that implement different RATs (e.g., NR and LTE). In one aspect, the UE (400) may include a single transceiver (410) that implements a plurality of RATs (e.g., NR and LTE). In one aspect, the transceiver (410) may include various components, wherein different combinations of components may implement different RATs.

[0067] FIG. 5 is a block diagram of an exemplary BS (500) according to some aspects of the present disclosure. The BS (500) may be, for example, the BS (105) described above in FIG. 1 and the BS (204) described in other drawings. As illustrated, the BS (500) may include a processor (502), a memory (504), a 2-step RACH module (508), a communication interface (509), a transceiver (510) including a modem subsystem (512) and an RF unit (514), and one or more antennas (516). These elements may communicate with each other indirectly or directly, for example, through one or more buses.

[0068] The processor (502) may have various features as a specific-type processor. For example, it may include a CPU, DSP, ASIC, controller, FPGA device, other hardware device, firmware device, or any combination thereof configured to perform the operations described herein. Additionally, the processor (502) may be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration.

[0069] Memory (504) may include cache memory (e.g., cache memory of the processor (502)), RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, solid-state memory device, one or more hard disk drives, memristor-based arrays, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some aspects, memory (504) may include a non-transient computer-readable medium. Memory (504) may store instructions (506). Instructions (506) may include instructions that, when executed by the processor (502), cause the processor (502) to perform the operations described herein, such as aspects of FIG. 2-3, FIG. 6-16, and FIG. 18. The commands (506) may also be referred to as code that can be broadly interpreted to include any type of computer-readable command(s), as previously discussed in relation to FIG. 4.

[0070] The 2-step RACH module (408) can communicate with the communication interface (409) to receive messages from another device or send messages to another device. Each of the 2-step RACH module (508) and the communication interface (509) may be implemented through hardware, software, or a combination thereof. For example, each of the 2-step RACH module (508) and the communication interface (509) may be implemented as instructions (506) stored in a processor, circuit, and / or memory (504) and executed by the processor (502). In some examples, the 2-step RACH module (508) and the communication interface (509) may be integrated within a modem subsystem (512). For example, the 2-step RACH module (508) and the communication interface (509) may be implemented by a combination of software components (e.g., executed by a DSP or general processor) and hardware components (e.g., logic gates and circuits) within the modem subsystem (512). In some examples, the UE may include one of the 2-step RACH module (508) and the communication interface (509). In other examples, the UE may include both the 2-step RACH module (508) and the communication interface (509).

[0071] The 2-step RACH module (508) and the communication interface (509) may be used for various aspects of the present disclosure, such as the aspects of FIG. 3a-3c and FIG. 6a-10. The 2-step RACH module (508) is configured to broadcast system information to initiate a random access channel procedure. The 2-step RACH module (508) is further configured to receive Msg A, which includes a payload containing a connection request and a random access preamble, at the BS. The 2-step RACH module (508) is further configured to determine whether at least a portion of Msg A is decodingable. In response to a failure to decode Msg A, the 2-step RACH module (508) is further configured to suppress the transmission of any message to the UE (202) within the RAR window. In response to the successful decoding of at least a portion of the first message, the 2-step RACH module (508) is further configured to transmit a RAR message containing a payload determined based on the type of the portion of Msg A that was successfully decoded.

[0072] The communication interface (509) is configured to work in cooperation with the 2-step RACH module (508) to broadcast system information or transmit Msg B to the UE. The communication interface (509) is further configured to receive Msg A and / or other UL data from the UE.

[0073] As described, the transceiver (510) may include a modem subsystem (512) and an RF unit (514). The transceiver (510) may be configured to communicate bidirectionally with other devices, such as UEs (115 and / or 400) and / or other core network elements. The modem subsystem (512) may be configured to modulate and / or encode data according to an MCS, such as an LDPC coding scheme, a turbo coding scheme, a convolution coding scheme, a digital beamforming scheme, etc. The RF unit (514) may be configured to process (e.g., perform analog-to-digital conversion or digital-to-analog conversion, etc.) transmissions sent from other sources, such as UEs (115 and 400), or modulated / encoded data (e.g., BWP hopping configurations and commands, PDCCH, PDSCH) from the modem subsystem (512) (for outbound transmissions). The RF unit (514) may be additionally configured to perform analog beamforming along with digital beamforming. Although shown as being integrated together in the transceiver (510), the modem subsystem (512) and / or the RF unit (514) may be separate devices coupled together in the BS (105) to enable the BS (105) to communicate with other devices.

[0074] The RF unit (514) may provide the antennas (516) with modulated and / or processed data, such as data packets (or, more generally, data messages that may include one or more data packets and other information), for transmission to one or more other devices. This may include, for example, the transmission of information to complete attachment to a network and communication with a camped UE (115 or 400) according to aspects of the present disclosure. The antennas (516) may further receive data messages transmitted from other devices and provide the received data messages for processing and / or demodulation in the transceiver (510). The transceiver (510) may provide the demodulated and decoded data (e.g., channel reports, PUSCH, PUCCH, HARQ ACK / NACKs) to the 2-step RACH module (508) and / or communication interface (509) for processing. The antennas (516) may include multiple antennas of similar or different designs to maintain multiple transmission links.

[0075] In one aspect, the BS (500) may include a plurality of transceivers (510) that implement different RATs (e.g., NR and LTE). In one aspect, the BS (500) may include a single transceiver (510) that implements a plurality of RATs (e.g., NR and LTE). In one aspect, the transceiver (510) may include various components, wherein different combinations of components may implement different RATs.

[0076] FIGS. 6a-6c illustrate retransmission timeline designs in different scenarios of a 2-step RACH procedure between a UE and a BS according to some aspects of the present disclosure. In FIGS. 6a-6c, the schemes (600a-c) may be utilized by a BS, such as the BSs (105) of FIG. 1, the BS (204) of FIG. 2, and / or the BS (500) of FIG. 5, and a UE, such as the UEs (115) of FIG. 1, the UE (202) of FIG. 2, and / or the UE (400) of FIG. 4, in a network such as a network (100) operating over a shared frequency band or an unlicensed frequency band. The UE (202) may be a low-cost UE device operating over a narrow band of about 20 MHz or less. Additionally, in FIGS. 6a-6c, the horizontal axes represent time in some integer units.

[0077] Diagram (600a) illustrates a scenario in which a 2-step RACH procedure between a UE (202) and a BS (204) successfully establishes a connection. The BS (204) may broadcast downlink channels or signals (605) to multiple UEs within communication range. For example, downlink channels or signals (605) may include a block of system information containing a root sequence identifier, a circular shift, an RA subframe, uplink grants, etc. Upon completion of receiving downlink data (605), the UE (202) may wait for a time gap of T0 after the last downlink data symbol and before transmitting Msg A (collectively also referred to as 610, 610a-b) to the BS (204).

[0078] In some aspects, the time gap (T0) facilitates the transition from downlink transmission to uplink transmission and may have a lower bound value. The lower bound of T0 may be predetermined based on various factors, the various factors include, but are not limited to, the duplexing mode between the BS (202) and the UE (204) (e.g., time domain duplex or frequency domain duplex), the tuning time for the numerology or BWP (bandwidth part) transition between the first uplink data symbol and the last downlink data symbol of Msg A (610), the preparation time required by the UE (202) in preparing the Msg A payload (610b), and the processing time required for the downlink channel transmitting downlink channel information (610) from the BS (204) to the UE (202).

[0079] In some aspects, after a time gap (T0), the UE (202) transmits a Msg A preamble (610a) and a Msg A payload (610b) to the BS (204). For example, the Msg A payload (610b) may include an RRC connection request with the BS (204) (e.g., RA-RNTI, uplink data, initial device identity, etc.). To transmit Msg A, the UE (202) transmits the Msg A preamble (610a) and the Msg A payload (610b) during a time gap (T0). g It can wait for ), which facilitates BS (204) detecting the start of the Msg A payload (610b). Time interval (T g) is greater than a lower limit value that can be predetermined by various factors, the various factors include, but are not limited to, the physical random access channel (PRACH) format of Msg A (610), time-domain resource allocation for Msg A (610), time slot format, tuning time for numerology transition between Msg A preamble (610a) and Msg A payload (610b), LBT (listen-before-talk) mechanism between BS (204) and UE (202), channel occupancy time between BS (204) and UE (202), frequency band for the RACH procedure, and PUSCH (physical uplink shared channel) mapping type for Msg A (610).

[0080] In some aspects, timing parameters (T0 and T g ) can be pre-stored in lookup tables. For example, T0 and T g The parameter values ​​of can be empirically determined according to various combinations of the factors described above and stored in a lookup table. The UE (202) can obtain the corresponding timing parameters (T0 and T) from a pre-defined lookup table based on the system factors. g Can retrieve ).

[0081] Upon completion of the transmission of Msg A (610), the UE (202) may start a timer for the RAR window to monitor for Msg B from the BS (204). The starting point (615a) of the RAR window (615) is aligned with the first PDCCH symbol of the PDCCH search space of Msg B. The determination of the starting point (615a) of the RAR window (615) is further discussed in relation to FIG. 10. The UE (202) runs a timer for the RAR window length to the end of the RAR window (615b). The length of the RAR window may be provided to the UE (202) by the BS (204), which is further explained in relation to FIG. 9.

[0082] During the RAR window (615), the BS (204) can receive and decode Msg A (610) and prepare Msg B (including Msg B PDCCH (620a) and Msg B payload (620b), collectively referred to as 620) while the UE (202) can monitor for Msg B. If the BS (204) successfully decodes and retrieves information from the Msg A payload (610b), the BS (205) may include a RAR response indicated by "Successful RAR" (620b) in the payload of Msg B (620). Subsequently, the BS (204) transmits Msg B (620) to the UE (202).

[0083] When receiving Msg B (620), the UE (202) can decode Msg B (620). If a successful RAR (620b) is decoded from the payload of Msg B (620), the UE (202) sends an acknowledgment message (625) to the BS (204) to notify that an RRC connection has been established. The UE (202) may wait for a time gap (T1) after the last data symbol of the PDSCH of Msg B (620) and before sending the acknowledgment message (625). For example, the time gap (T1) provides processing time for the UE (202) to decode the received Msg B (620) and TA-based uplink timing adjustment for the UE (202). The time gap (T1) is also determined such that the acknowledgment message (625) is transmitted along with the RAR window (615) but is also greater than the lower limit. The lower limit for T1 may be predetermined based on various factors, which include, but are not limited to, PDSCH processing time, time slot format (whether TDD is used), whether the acknowledgment message (625) is piggybacked to PUSCH.

[0084] In some aspects, time gaps (T0 and T gSimilar to ), T1 can be retrieved from a pre-stored lookup table listing empirically determined values ​​for T1 corresponding to various combinations of factors. In some aspects, the time gap (T1) can be dynamically determined according to the RAR window (615) so that sufficient time remains for an acknowledgment message (625) before the end of the RAR window (615b).

[0085] Diagram (600b) illustrates a scenario in which the 2-step RACH procedure between UE (202) and BS (204) falls back to the normal 4-step RACH procedure due to a failure to decode the Msg A payload (610b). Similar to diagram (600a), BS (204) broadcasts downlink channels or signals (605) to multiple UEs within communication range, and then UE (202) transmits Msg A (610) to BS (204). UE (202) may start a timer for the RAR window to monitor for Msg B from BS (204).

[0086] Unlike in diagram (600a), in diagram (600b), if the BS (204) fails to decode the Msg A payload (610b), for example, if the received Msg A (610) is corrupted due to channel fading or collision and only the Msg A preamble (610a) can be detected from the received message, the BS (204) cannot respond with a connection setup when the connection request from the Msg A payload (610b) is missed. In this case, the BS (204) may include a fallback indication indicated by "fallback RAR" (620c) in the payload of Msg B (620) and transmit Msg B (620) to the UE (202) to indicate that the RRC connection setup was unsuccessful and the 2-step RACH will fall back in a 4-step manner.

[0087] When receiving Msg B (620) from BS (204), UE (202) decodes the received Msg B (620). If a fallback RAR (620c) is decoded from the payload of Msg B (620), UE (202) transmits Msg 3 (630) via PUSCH to notify BS (204) that the RACH procedure will fall back to 4-step RACH. In some aspects, Msg 3 (630) may be a retransmitted version of the Msg A payload (610b) that was not successfully decoded by BS (204). In some aspects, Msg 3 (630) may differ from the Msg A payload (610b), for example, to initiate a new RRC connection request. When Msg 3 (630) has a different length from Msg A payload (610b), the UE (202) may add padding bits or truncate Msg 3 to ensure that the transmission of Msg 3 can be completed to the end of the RAR window (615b).

[0088] The UE (202) may wait for a time gap (T2) after the last data symbol of Msg B (620) and before retransmitting the Msg A payload (610b). For example, the time gap (T2) provides processing time for the UE (202) to decode the received Msg B (620) and TA-based uplink timing adjustment for the UE (202). The time gap (T2) is also determined to be sufficient time remaining in the RAR window (615) to transmit Msg 3 (630), but also greater than a lower limit. The lower limit for T1 may be predetermined based on various factors, which include, but are not limited to, PDSCH processing time, time slot format, PUSCH preparation time, etc.

[0089] In some aspects, time gaps (T0 and T gSimilar to ), T2 can be retrieved from a pre-stored lookup table listing empirically determined values ​​for T2 corresponding to various combinations of factors. In some aspects, the time gap (T2) can be dynamically determined according to the RAR window (615) so that sufficient time remains for Msg 3 (630) before the end of the RAR window (615b). In some aspects, the time gap (T2) can be shorter than the time gap (T1) because Msg 3 (630) may require more transmission time than the acknowledgment message (625).

[0090] Diagram (600c) illustrates a scenario in which a 2-step RACH procedure between UE (202) and BS (204) requests a complete retransmission of Msg A when BS (204) fails to decode or receive Msg A at all. Similar to diagrams (600a-b), BS (204) broadcasts downlink channels or signals (605) to multiple UEs within communication range, and then UE (202) transmits Msg A (610) to BS (204). UE (202) may start a timer for the RAR window to monitor for Msg B from BS (204).

[0091] Unlike in diagrams (600a-b), in FIG. 600c, the BS (204) may not receive any message from the UE (202) due to channel corruption, or it may receive a corrupted Msg A (610) that cannot be decoded. If the BS (204) fails to detect either the Msg A preamble (610a) or the Msg A payload (610b) due to a decoding failure in 613 during the RAR window (615), the BS (204) may not operate during the RAR window (615) and does not transmit anything. Meanwhile, the UE (202) may monitor during the RAR window (615) but may not receive anything from the BS (204).

[0092] In this case, when the UE (202) does not receive Msg B (620) from the BS (204) during the RAR window (615), the UE (202) may request the retransmission of Msg A (610). After backoff and MAC protocol processing at 623, the UE (202) may retransmit Msg A, which includes a Msg A preamble (635a) and a Msg A payload (635b). In some aspects, the Msg A preamble (635a) and the Msg A payload (635b) may be identical to the Msg A preamble (610a) and the Msg A payload (610b), respectively. In some aspects, the UE (202) may reselect a PUSCH opportunity in the time or frequency domain, or the Msg A preamble (635a), or a demodulation reference signal source for retransmission. In some aspects, the UE (202) may reconstruct the Msg A payload (635b) with different content, a different modulation and coding scheme (MCS), a different transport block size (TBS), etc., from the Msg A payload (610b) for the retransmitted Msg A. In some aspects, the retransmitted Msg A preamble (635a) or Msg A payload (635b) may be configured with power ramping or transmitter beam switching.

[0093] As illustrated in FIGS. 6a through 6c, the UE (202) does not always send a HARQ feedback signal for Msg B, such as an acknowledgment message or a non-acknowledgment message, to the BS (204) to notify whether the RRC connection has been successfully established. As illustrated in diagram (600b), if the UE (202) successfully decodes the fallback RAR (620b) from Msg B (620), the UE (202) does not send an "ACK" or "NACK" to the BS (204). As illustrated in diagram (600c), if the UE (202) does not receive the successful RAR (620b) or the fallback RAR (620c), the UE (202) does not send either an "ACK" or a "NACK" to the BS (204).

[0094] As illustrated in diagram (600a), the UE (202) sends an "ACK" to the BS (204) only when the UE (202) can decode the success RAR (620b) from the Msg B (620). Before the UE (202) sends the acknowledgment message (625), the UE (202) may apply a "timing advance" to adjust the timing offset for the uplink. For example, the timing advance command may be included in the success RAR (620b) as a MAC (medium access control) control element.

[0095] In some aspects, the acknowledgment message (625) may be transmitted via uplink control information (UCI) or uplink reference signals piggybacked to PUCCH, PUSCH. In some aspects, the UE (202) may configure a resource allocation indicator for the acknowledgment message (625) with an index of a sub-protocol data unit (PDU) corresponding to the payload (620b), a MAC sub-header, and a MAC control element. Alternatively, the UE (202) may configure a resource allocation indicator for the acknowledgment message (625) with a resource mapping pattern of a CCE on the PDCCH or a subfield of downlink control information (DCI). Alternatively, the UE (202) may configure a resource allocation indicator for the acknowledgment message (625) with a joint indicator by Msg B PDCCH and Msg B PDSCH. Alternatively, the UE (202) can configure a resource allocation indicator for the acknowledgment message (625) through the RRC and preamble resource index.

[0096] FIGS. 7a-7b illustrates a logic flow performed by BS corresponding to retransmission timeline designs in different scenarios of the 2-step RACH procedure illustrated in FIGS. 6a-6c according to some aspects of the present disclosure. The steps of method (700) may be performed by a computing device of a wireless communication device (e.g., a processor, a processing circuit, and / or other suitable components) or by other suitable means for performing the steps. For example, a wireless communication device such as UE (115), UE (202), or UE (400) may utilize one or more components, such as a processor (402), memory (404), 2-step RACH module (408), communication interface (409), transceiver (410), modem (412), and one or more antennas (416) to perform the steps of method (700). Method (700) may be used in conjunction with the diagrams (600a-c) previously described in relation to FIGS. 6a-6c. As illustrated, Method (700) comprises a number of enumerated steps, but aspects of Method (700) include additional steps before, after, and between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

[0097] In step (702), the UE (202) receives system information or RRC signaling to configure a RACH procedure, for example, from a BS (204). For example, the system information or RRC signaling may be transmitted through a downlink channel or signaling (605) illustrated in FIGS. 6a-6c.

[0098] In step (704), the UE (202) waits for a time gap after the last downlink symbol from the BS (e.g., the last symbol of system information, control, or reference signal) and before transmitting the first message to the BS. For example, as shown in FIG. 6a, the UE (202) waits for a time period of T0 before transmitting the Msg A preamble (610a). In some embodiments, the value of T0 may be predetermined based on various factors, the various factors include, but are not limited to, the duplexing mode between BS (202) and UE (204) (e.g., time domain duplex or frequency domain duplex), the tuning time for the numerology or BWP (bandwidth part) transition between the last symbol and the first uplink symbol random access preamble of the first message of Msg A (610), the preparation time required by the UE (202) in preparing the Msg A payload (610b), the processing latency for the MAC (medium access control) protocol, the processing time required for the downlink channel transmitting downlink channel information (610) from BS (204) to UE (202).

[0099] In step (706), the UE (204) initiates the uplink transmission of a first message to the BS, e.g., Msg A (610) of FIG. 6a. Specifically, in step (708), the UE (202) [transmits] the transmission of the Msg A preamble (e.g., 610a in FIG. 6a) and the transmission of the Msg A payload (e.g., 610b in FIG. 6a). g Waits for the time gap of (shown in FIG. 6a). In some embodiments, T gThe value of is greater than a lower limit value that can be predetermined by various factors, the various factors include, but are not limited to, the preamble format of the PRACH format, the time-domain resource allocation for the Msg A preamble (610a), the slot format used in the TDD (time division duplexing) mode, the tuning time for the numerology transition between the PUSCH that returns the Msg A preamble (610a) and the Msg A payload (610b), the LBT mechanism between the BS (204) and the UE (202) when the RACH procedure is operating on a shared or unlicensed frequency spectrum, the channel occupancy time for the UE (202) when the RACH procedure is operating on a shared or unlicensed frequency spectrum, the frequency band for the RACH procedure, and the PUSCH mapping type for the Msg A payload (610b).

[0100] In step (710), the UE (202) starts a timer for the Msg B RAR window (e.g., 615 in FIG. 6a). For example, the starting point of the Msg B RAR window is determined by the method (1000) of FIG. 10.

[0101] In step (712), the UE (202) monitors for a second message that is a response to a first message during the RAR window. For example, the UE (202) can search for Msg B (e.g., 620 in FIG. 6a) in the Msg B PDCCH search space in response to Msg A during the RAR window.

[0102] In step (714), the UE (202) determines whether a second message (e.g., Msg B (620)) is received. If Msg B is not received, the method (700) proceeds to step (716), where the UE (202) determines whether the RAR window has expired. If the RAR window has not yet expired, the method (700) proceeds to step (712), where the UE (202) continues monitoring for Msg B.

[0103] If the RAR window expires in step (716), the UE (202) stops the timer for the Msg B RAR window in step (718). In step (720), the UE (202) waits for a backoff time for uplink timing adjustment, and then in step (722), the UE (202) retransmits the first message. For example, the UE (202) may retransmit Msg A (e.g., see 635a-b in FIG. 6c). In some embodiments, the UE (202) may reconstruct the message payload for the retransmitted Msg A. Returning to step (714), if the UE (202) determines that the second message (e.g., Msg B (620)) has been received, the method (700) proceeds to step (724) in which the UE (202) processes and decodes Msg B. In step (726), the UE (202) determines whether a portion of Msg B can be decoded and which portion of Msg B can be decoded. If the preamble of Msg B cannot be decoded at all, the method (700) proceeds to step (718). For example, if in step (726) the payload from Msg B is not decoded and only the backoff indicator (BI) is decoded, in step (720), the UE (202) performs backoff based on the processing latency of the MAC protocol and the backoff indicator decoded from Msg B after the RAR window has elapsed. Subsequently, the UE (202) retransmits Msg A in step 722.

[0104] In some embodiments, the UE (202) reselects a PUSCH resource or random access preamble resource in the code, space, time, or frequency domain for retransmission of Msg A in step (722).

[0105] In some embodiments, the UE (202) reconstructs the payload for Msg A that has been retransmitted with content different from the Msg A payload (610b) and applies power ramping for the retransmission of Msg A.

[0106] If at least a portion of Msg B (e.g., Msg B preamble (620a) or payload (620b)) is decoded, the method (700) proceeds to step (728), at step (728), the UE (202) determines what type of Msg B payload can be decoded from Msg B, e.g., whether it is a successful RAR (620b) or a fallback RAR (620c). If the decoded Msg B payload indicates that the Msg A payload has been successfully decoded in the BS (204), e.g., that the successful RAR (620b) has been decoded, the method (700) proceeds to step (730), at step (730), the UE (202) waits for a time gap (T1) (e.g., illustrated in FIG. 6a) after the last symbol of Msg B and before any uplink transmission. For example, the time gap (T1) provides the processing time for the UE (202) to decode the received Msg B (620) and the TA-based uplink timing adjustment for the UE (202). The time gap (T1) is also determined such that the acknowledgment message (625) is transmitted with the RAR window (615) but is also greater than the lower limit. The lower limit for T1 may be determined based on various factors, which include, but are not limited to, PDSCH processing time, time slot format (whether TDD is used), MAC protocol processing latency, and whether the acknowledgment message (625) is piggybacked to PUSCH.

[0107] In some embodiments, after decoding the success RAR in step (728), the UE (202) decodes the resource allocation configured by the network to prepare an acknowledgment message by the UE in response to the success RAR.

[0108] In step (732), the UE (202) transmits an acknowledgment message (e.g., 625 in FIG. 6a) indicating the successful completion of the random access procedure before the RAR window expires. For example, the acknowledgment message may be transmitted via UCI or uplink reference signals piggybacked to PUCCH, PUSCH.

[0109] In some embodiments, the UE (202) applies a timing advance command to adjust the timing offset for the uplink from the UE to the BS before transmitting an acknowledgment message. The timing advance command is included in the random access response from the Msg B payload.

[0110] Returning to step (728), if the UE (202) determines that the type of payload decoded from Msg B, i.e., the failure of decoding the Msg A payload in BS, e.g., the fallback RAR (620c), is decoded, the method (700) proceeds to step (731), where the UE (202) waits for a time gap (T2) after the last symbol of Msg B and before any uplink transmission (e.g., illustrated in FIG. 6a). For example, the value of T2 is determined such that there is sufficient time remaining in the RAR window (615) for transmitting Msg 3 (630), which may be predetermined based on various factors, which include, but are not limited to, PDSCH processing time, MAC protocol processing latency, time slot format of TDD, PUSCH preparation time, etc. In step (733), the UE (202) retransmits the Msg A payload of Msg 3 (e.g., 630 in FIG. 6b) via PUSCH based on the uplink grant included in the fallback RAR.

[0111] FIG. 8 illustrates a logic flow performed by a BS corresponding to retransmission timeline designs in different scenarios of the 2-step RACH procedure illustrated in FIG. 6a-6c according to some aspects of the present disclosure. The steps of the method (800) may be performed by a computing device of a wireless communication device (e.g., a processor, a processing circuit, and / or other suitable components) or by other suitable means for performing the steps. For example, a wireless communication device such as a BS (105), a BS (204), or a BS (500) may utilize one or more components, such as a processor (502), a memory (504), a 2-step RACH module (508), a communication interface (509), a transceiver (510), a modem (512), and one or more antennas (516) to perform the steps of the method (800). Method (800) may be used in conjunction with the diagrams (600a-c) previously described in relation to FIGS. 6a-6c. As illustrated, method (800) comprises a number of enumerated steps, but aspects of method (800) include additional steps before, after, and between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

[0112] In step (802), the BS (204) transmits system information and RRC signaling downlinks to multiple UE(s). For example, the system information and RRC signaling may be communicated through the downlink channel or signals (605) shown in FIG. 6a.

[0113] In step (804), BS (204) receives an uplink transmission of the first message. For example, BS (204) receives Msg A (e.g., 610 in FIG. 6a) from UE (202).

[0114] In step (806), BS (204) decodes the received first message. For example, BS (204) processes and decodes Msg A during the RAR window (615) as shown in FIG. 6a.

[0115] In step (808), BS (204) determines whether the first message can be decoded. If the first message cannot be decoded, the method (800) proceeds to step (810), and in step (810), BS (204) suppresses the transmission of any downlink during the RAR window. For example, if in step (808) the Msg A preamble is not decoded from Msg A, BS (204) transmits a backoff indicator to the UE (202).

[0116] In step (812), BS (204) monitors for the retransmission of Msg A after the RAR window has expired. In step (814), BS (204) receives the retransmitted first message. For example, the retransmitted message (e.g., 635a-b in FIG. 6c) may have the same Msg A payload (610b) or may have a reconfigured payload (e.g., a new connection request).

[0117] Returning to step (808), if BS (204) determines that at least part of the first message can be decoded, for example, that the Msg A payload (e.g., 610b in FIG. 6a) can be decoded, the method (800) proceeds to step (818), where BS (204) decodes the Msg A payload to obtain the unique identifier of the UE (202) and prepares a second message having a payload to indicate successful decoding. For example, BS (204) prepares Msg B having a payload of success RAR (e.g., 620b in FIG. 6a) to indicate successful connection. BS (204) further prepares Msg B having PDCCH and PDSCH and configures scheduling information for PSDCH for Msg B. In another example, BS (204) further prepares Msg B by scrambling the cyclic redundancy check of PDCCH by C-RNTI (cell-radio-network-tempary-identifier) ​​or group RNT and mapping the payload of Msg B to PDSCH. The Msg B payload includes at least a backoff indicator (BI).

[0118] In some embodiments, BS (204) detects the Msg A preamble from Msg A to obtain the timing advance of the UE (202), and then prepares Msg B which includes a timing advance command, a unique identifier of the UE (202), and resource allocation for the UE in Msg B.

[0119] In step (820), BS (204) transmits Msg B, which has a second message, e.g., a success RAR (620b), to the UE. In step (822), BS (204) receives an acknowledgment message (e.g., 625 in FIG. 6a) from the UE indicating the successful completion of the random access procedure.

[0120] Returning to step (808), if BS (204) determines that only the preamble of the first message (e.g., the Msg A preamble (610a) in FIG. 6b) can be decoded, the method (800) proceeds to step (819), at which step (819), BS (204) prepares a second message having a payload to indicate a decoding failure. For example, BS (204) prepares Msg B having a payload of a fallback RAR (e.g., 620c in FIG. 6b) to indicate a decoding failure of the Msg A payload, thus requiring a fallback to 4-step RACH.

[0121] In some embodiments, BS (204) includes in Msg B an uplink grant for UE (202) to retransmit Msg A payload, an index of a random access preamble sequence (RAPID), and a timing advance command.

[0122] In step (821), BS (204) transmits Msg B having a second message, e.g., Msg B fallback RAR (e.g., 620b in FIG. 6b). In step (823), BS (204) receives a third message notifying that the UE will fall back to 4-step RACH. For example, the Msg A payload may be retransmitted to BS (204) in the form of Msg 3 of 4-step RACH. In this way, BS (204) is notified that 4-step RACH is being implemented upon receiving Msg 3.

[0123] FIG. 9 illustrates a logical flow that constitutes the Random Access Response (RAR) window length in a 2-step RACH procedure according to some aspects of the present disclosure. The steps of method (900) may be executed by a computing device of a wireless communication device (e.g., a processor, a processing circuit, and / or other suitable components) or by other suitable means for performing the steps. For example, a wireless communication device such as BS (105), BS (204), or BS (500) may utilize one or more components, such as a processor (502), memory (504), a 2-step RACH module (508), a communication interface (509), a transceiver (510), a modem (512), and one or more antennas (516) to execute the steps of method (800). Method (900) may be used in conjunction with the diagrams (600a-c) previously described in relation to FIG. 6a-6c. As illustrated, the method (900) includes a number of enumerated steps, but aspects of the method (900) include additional steps before, after, and between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

[0124] In step (902), BS (204) obtains the length of the Msg B RAR window, which can be predetermined by the network. In some embodiments, the RAR window length may be determined based on factors such as (but not limited to) Msg A priority, density for Msg A preamble / payload resource allocation, SSB (synchronization-signal-block) to occasion association periodicity, UE capability, etc. For example, the RAR window length may be inversely proportional to the Msg A priority level, for example, a shorter window length may be allocated to Msg A having a higher priority. As another example, the RAR window length may be increased when resource allocation for Msg A decreases.

[0125] In step (904), the BS (204) determines whether a UE is in an RRC connection state. If the UE (202) is not RRC connected, for example, in an idle state, the BS (204) may transmit the RAR window length to the UE in system information broadcasts in step (906). If the UE (202) is RRC connected in step (904), the BS (204) transmits the RAR window length to the UE (202) via RRC signaling in step (908). In step (910), the UE (202) may dynamically update the RAR window length from the BS (204) via RRC signaling.

[0126] FIG. 10 illustrates a logical flow that constitutes the starting point of a Random Access Response (RAR) window in a 2-step RACH procedure according to some aspects of the present disclosure. The steps of the method (1000) may be executed by a computing device of a wireless communication device (e.g., a processor, a processing circuit, and / or other suitable components) or by other suitable means for performing the steps. For example, a wireless communication device such as a UE (115), UE (202), or UE (400) may utilize one or more components, such as a processor (402), memory (404), a 2-step RACH module (408), a communication interface (409), a transceiver (410), a modem (412), and one or more antennas (416), to execute the steps of the method (1000). The method (1000) may be used in conjunction with the diagrams (600a-c) previously described in relation to FIG. 6a-6c. As illustrated, the method (1000) includes a number of enumerated steps, but aspects of the method (700) include additional steps before, after, and between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

[0127] In step (1002), the UE (202) completes the PUSCH opportunity. In step (1004), the UE (202) determines whether the UE is in an RRC connection state, for example, whether the UE is connected to the BS. If the UE (202) is not in an RRC connection, for example, in an idle state, the method (1000) proceeds to step (1006), and in step (1006), the UE (202) starts a timer for the RAR window at the first PDCCH symbol of the fastest CSS (common search space) for Msg B PDCCH. In this case, the UE (202) searches for the first PDCCH symbol of Msg B within the CSS configured by system information.

[0128] If not, and the UE (202) is RRC connected, the UE (202) further determines in step (1008) whether the random access is contention-based (CBRA) or contention-free (CFRA). Depending on the CBRA method in step (1008), the UE (202) starts a timer for the Msg B RAR window in step (1010) at the first PDCCH symbol of the fastest CSS or USS (UE-specific search space) for Msg B PDCCH. In this case, the UE (202) searches for the first PDCCH symbol of Msg B within the CSS configured by system information or within the USS configured by RRC signaling.

[0129] If not, according to the CFBA method in step (1008), the method proceeds to step (1012), and in step (1012), the UE (202) starts a timer for the Msg B RAR window at the first PDCCH symbol of the fastest USS for Msg B PDCCH. In this case, the search space for Msg B PDCCH is only USS.

[0130] Information and signals may be represented using any of various other technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented as voltages, currents, electromagnetic waves, magnetic fields or magnetic particles, optical fields or optical particles, or any combination thereof.

[0131] The various exemplary blocks and modules described in connection with the disclosure herein may be implemented or performed by general-purpose processors, DSPs, ASICs, FPGAs or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but alternatively, the processor may be any conventional processor, controller, microcontroller, or state machine. Additionally, the processor may be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration).

[0132] The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, these functions may be stored as one or more instructions or code on a computer-readable medium or transmitted therethrough. Other examples and implementations are within the scope of this disclosure and the appended claims. For example, due to the nature of the software, the functions described above may be implemented using software executed by a processor, hardware, firmware, hardwiring, or any combination thereof. Features implementing the functions may also be physically located in various positions, including distributed so that parts of the functions are implemented in different physical locations. Additionally, as used herein, including in the claims, “or” as used in a list of items (e.g., a list of items followed by phrases such as “at least one of” or “one or more of”) indicates a comprehensive list such that, for example, a list of [at least one of A, B, or C] means A or B or C or AB or AC or BC or ABC (i.e., A, B, and C).

[0133] As will now be recognized by those skilled in the art and depending on the specific application at hand, many variations, substitutions, and modifications may be made to and with respect to the materials, apparatuses, configurations, and devices of the present disclosure without departing from the spirit and scope of the present disclosure. In this regard, the scope of the present disclosure should not be limited to the specific aspects illustrated and described herein, as such aspects are merely examples of the present disclosure, but rather should be fully equivalent to the scope of the claims appended below and their functional equivalents.

Claims

Claim 1 A wireless communication method comprises: a user device (UE) receiving system information from a base station (BS) for initiating a random access channel (RACH) procedure; the UE transmitting a first message to the BS, the first payload comprising a random access preamble and a connection request; and the UE monitoring a second message from the BS in response to the first message during a random access response (RAR) window; the UE retransmitting the first message to the BS in response to a determination that, based on the monitoring, no second message is received by the UE from the BS within the RAR window; and the UE retransmitting the first payload to the BS in response to a determination that the second message is received by the UE from the BS within the RAR window and that a second payload decoded from the second message indicates a fallback response. A wireless communication method comprising the step of the UE transmitting an acknowledgment message to the BS in response to the UE receiving the second message from the BS within the RAR window and determining that the second payload indicates a success response. Claim 2 The wireless communication method of claim 1, wherein the method further comprises the step of the UE waiting for a time gap after receiving the last data symbol of the system information from the BS and before transmitting the first message to the BS, wherein the time gap is determined by at least one of: a duplexing mode between the BS and the UE; a tuning time for switching the numerology or BWP (bandwidth part) between the last data symbol and the first data symbol of the first message; a preparation time for the first payload; or a processing time for a downlink channel transmitting the system information from the BS to the UE. Claim 3 A wireless communication method according to claim 1, wherein the method further comprises the step of the UE waiting for a time gap between the transmission of the random access preamble and the transmission of the first payload, wherein the time gap is determined by at least one of: a physical random access channel (PRACH) format; a time-domain resource allocation; a time slot format; a tuning time for a numerology transition between the random access preamble and the first payload; a listen-before-talk (LBT) mechanism between the BS and the UE; a channel occupancy time between the BS and the UE; a frequency band for the RACH procedure; or a physical uplink shared channel (PUSCH) mapping type for the first message. Claim 4 A wireless communication method according to claim 1, wherein the UE determines: the UE determines to retransmit the connection request to the BS in response to the determination that the second message from the BS is received by the UE within the RAR window but no payload is decoded from the second message; and the method further comprises the step of: after the RAR window has elapsed, the UE retransmits the first message to the BS. Claim 5 A wireless communication method according to claim 4, further comprising the step of the UE reselecting a PUSCH opportunity (occasion) used for the random access preamble in the time or frequency domain for the first message being retransmitted, or the random access preamble. Claim 6 A wireless communication method according to claim 4, further comprising the step of reconstructing the payload for the first message being retransmitted into content different from the first payload. Claim 7 A wireless communication method according to claim 1, wherein the UE determines: further comprises determining that the second message is received by the UE from the BS within the RAR window, and the method further comprises: decoding the second payload from the second message; and in response to determining that the decoded second payload indicates that the first payload was successfully decoded at the BS, the UE transmits an acknowledgment message indicating a connection setup in response to the connection request within the RAR window to the BS. Claim 8 A wireless communication method according to claim 7, wherein the method further comprises the step of waiting for a time gap after the last data symbol of the second message and before transmitting the acknowledgment message, wherein the time gap is determined by at least one of: a PDSCH (physical downlink shared channel) processing time; a time slot format; or whether the acknowledgment message is piggybacked on the PUSCH. Claim 9 A wireless communication method according to claim 7, further comprising the step of the UE applying a timing advance offset to adjust the timing offset for the uplink from the UE to the BS before transmitting the acknowledgment message. Claim 10 In claim 7, the above acknowledgment is: a PUCCH (physical uplink control channel); UCI (uplink control information) piggybacked on the PUCCH; or a wireless communication method transmitted via an uplink reference signal. Claim 11 delete Claim 12 delete Claim 13 delete Claim 14 delete Claim 15 delete Claim 16 delete Claim 17 delete Claim 18 delete Claim 19 delete Claim 20 delete Claim 21 A wireless communication method comprising: a step in which a base station (BS) broadcasts system information to a user equipment (UE) to initiate a random access channel procedure; a step in which the BS receives from the UE a first message including a random access preamble and a first payload of a connection request; a step in which the BS determines whether at least a portion of the first message is decodingable; a step in which the BS suppresses the transmission of any message to the UE within a random access response (RAR) window in response to a failure to decode the first message; and a step in which the BS transmits to the UE a second message including a second payload indicating a fallback response or a success response determined based on the type of the portion of the first message in response to a successful decoding of at least the portion of the first message. Claim 22 A wireless communication method according to claim 21, wherein the first message is received after a certain time gap following the last data symbol of the system information, and the time gap is determined by at least one of: a duplexing mode between the BS and the UE; a tuning time for a numerology or BWP (bandwidth part) switching between the last data symbol and the first data symbol of the first message; a preparation time for the first payload; or a processing time for a downlink channel transmitting the system information from the BS to the UE. Claim 23 A wireless communication method according to claim 21, wherein the transmission of the random access preamble and the transmission of the first payload are separated by a certain time gap, and the time gap is determined by at least one of: a physical random access channel (PRACH) format; a time-domain resource allocation; a time slot format; a tuning time for numerology transition between the random access preamble and the first payload; a listen-before-talk (LBT) mechanism between the BS and the UE; a channel occupancy time between the BS and the UE; a frequency band for the RACH procedure; or a physical uplink shared channel (PUSCH) mapping type for the first message. Claim 24 A wireless communication method according to claim 21, further comprising the step of the BS receiving a retransmission of the first message from the UE after the RAR window has elapsed in response to a decoding failure of the first message. Claim 25 A wireless communication method according to claim 24, wherein a PUSCH opportunity or the random access preamble is reselected in the time or frequency domain for the first message being retransmitted. Claim 26 A wireless communication method according to claim 24, wherein the payload is reconfigured with content different from the first payload for the first message being retransmitted. Claim 27 A wireless communication method according to claim 21, further comprising: a step of decoding the first payload from the first message; a step in which the BS prepares and transmits the second message, which includes the second payload indicating successful decoding, in response to a determination that the first payload has been successfully decoded; and a step in which the BS receives from the UE an acknowledgment message indicating a connection setup in response to the connection request within the RAR window. Claim 28 A wireless communication method according to claim 27, wherein the acknowledgment message is received after a certain time gap following the last data symbol of the second message, and the time gap is lower bounded by a value determined by at least one of: a PDSCH (physical downlink shared channel) processing time; a time slot format; and whether the acknowledgment message is piggybacked on PUSCH. Claim 29 A wireless communication method according to claim 27, wherein a timing advance offset is applied to adjust the timing offset for the uplink from the UE to the BS before the acknowledgment message is transmitted. Claim 30 In claim 27, the above acknowledgment message is received through at least one of: a PUCCH (physical uplink control channel); UCI (uplink control information) piggybacked on the PUCCH; and an uplink reference signal, in a wireless communication method. Claim 31 delete Claim 32 delete Claim 33 delete Claim 34 delete Claim 35 delete Claim 36 delete Claim 37 delete Claim 38 delete Claim 39 delete Claim 40 delete Claim 41 User Equipment (UE) of wireless communication comprises: a transceiver; and a processor, wherein the transceiver: receives system information for initiating a Random Access Channel (RACH) procedure; transmits a first message comprising a Random Access preamble and a first payload of a connection request; monitors for a second message that is a response to the first message during a Random Access Response (RAR) window; and is configured to retransmit the first message in response to a determination that, based on the monitoring, no second message is received by the UE from the BS within the RAR window; and the processor: retransmits the first payload to the BS in response to a determination that the second message is received by the UE from the BS within the RAR window and that a second payload decoded from the second message indicates a fallback response; A user device (UE) configured to send an acknowledgment message to the BS in response to the second message received by the UE from the BS within the RAR window and the determination that the second payload indicates a success response. Claim 42 delete Claim 43 delete Claim 44 delete Claim 45 delete Claim 46 delete Claim 47 delete Claim 48 delete Claim 49 delete Claim 50 delete Claim 51 delete Claim 52 In claim 41, the processor is further configured to: determine that the second message from the BS is received by the UE within the RAR window; decode the second payload from the second message; and retransmit the first payload including the connection request using PUSCH within the RAR window in response to determining that the decoded second payload indicates a failure to decode the first payload at the BS. Claim 53 In claim 52, the processor is additionally configured to wait for a time gap after the last data symbol of the second message and before retransmitting the first payload, said time gap is determined by at least one of: PDSCH processing time; time slot format; or PUSCH preparation time, user equipment (UE). Claim 54 delete Claim 55 In claim 41, the processor is further configured to obtain an indication of the length of the RAR window from RRC signaling when the UE is connected to the BS and RRC (radio resource control), and the length of the RAR window overrides previously obtained length information of the RAR window, user equipment (UE). Claim 56 In claim 41, the length of the RAR window is determined based on at least one of: the priority level of the first message; the density of resource allocation for the first message; or the synchronization-signal-block (SSB) to occasion association periodicity, user equipment (UE). Claim 57 delete Claim 58 delete Claim 59 delete Claim 60 delete Claim 61 A base station (BS) for wireless communication comprising: a transceiver; and a processor, wherein the transceiver is configured to: broadcast system information for initiating a random access channel procedure; and receive a first message comprising a first payload of a random access preamble and a connection request; and the processor is configured to: determine whether at least a portion of the first message is decodingable; and suppress the transmission of any message to a UE within a random access response (RAR) window in response to a failure to decode the first message; and the transceiver is further configured to transmit a second message comprising a second payload indicating a fallback response or a success response determined based on the type of the portion of the first message in response to a successful decoding of at least the portion of the first message. Claim 62 delete Claim 63 delete Claim 64 delete Claim 65 delete Claim 66 delete Claim 67 delete Claim 68 delete Claim 69 delete Claim 70 delete Claim 71 delete Claim 72 delete Claim 73 delete Claim 74 delete Claim 75 delete Claim 76 delete Claim 77 In claim 61, the first PDCCH symbol of the second message is a base station (BS) that is searched using a common search space when the UE is RRC disabled at the start of the RAR window. Claim 78 In claim 61, the first PDCCH symbol of the second message is a base station (BS) that is searched using a common search space (CSS) or a UE-specific search space (USS) when the UE connects to the BS through a CBRA (contention based random access) procedure, or using the UE-specific search space (USS) when the UE connects to the BS through a CFRA (contention free random access) procedure. Claim 79 In claim 61, the RAR window is a base station (BS) that starts at a starting point aligned with the first PDCCH symbol of the PDCCH search space of the second message. Claim 80 In claim 61, the starting point of the RAR window is aligned with the first PDCCH symbol of the fastest CSS or USS for the PDCCH of the second message under CBRA, and the starting point of the RAR window is aligned with the first PDCCH symbol of the fastest USS for the PDCCH of the second message under CFRA, a base station (BS). Claim 81 A non-transient storage medium storing processor-executable instructions for user equipment of wireless communication, wherein the processor-executable instructions comprise: receiving system information for initiating a Random Access Channel (RACH) procedure; transmitting a first message comprising a random access preamble and a first payload of a connection request; monitoring for a second message that is a response to the first message during a Random Access Response (RAR) window; retransmitting the first message in response to a determination that, based on the monitoring, no second message is received within the RAR window; and retransmitting the first payload to the BS in response to a determination that, within the RAR window, the second message is received by the UE from the BS and that a second payload decoded from the second message indicates a fallback response; A non-transient storage medium comprising instructions executable by a processor to send an acknowledgment message to the BS in response to the second message from the BS being received by the UE within the RAR window and the second payload determining that it indicates a success response. Claim 82 delete Claim 83 delete Claim 84 delete Claim 85 delete Claim 86 delete Claim 87 delete Claim 88 delete Claim 89 delete Claim 90 delete Claim 91 delete Claim 92 delete Claim 93 delete Claim 94 delete Claim 95 delete Claim 96 delete Claim 97 In claim 81, the above commands further comprise: commands for searching for a first PDCCH symbol of the second message using a common search space when the medium is RRC disabled at the start of the RAR window, a non-transient storage medium. Claim 98 A non-transient storage medium according to claim 81, wherein the instructions further comprise instructions for searching for a first PDCCH symbol of the second message using a common search space (CSS) or a media-specific search space (USS) when the medium is connected via a contention-based random access (CBRA) procedure, or using only the USS when the medium is connected via a contention-free random access (CFRA) procedure. Claim 99 In claim 81, the commands further include commands for starting a timer for the RAR window after the PUSCH opportunity of the first message, and the starting point of the RAR window is aligned with the first PDCCH symbol of the PDCCH search space of the second message, a non-transient storage medium. Claim 100 A non-transient storage medium, wherein, in claim 81, the instructions further include instructions for starting a timer for the RAR window after the PUSCH opportunity of the first message, the starting point of the RAR window is aligned with the first PDCCH symbol of the earliest CSS or USS for the PDCCH of the second message under CBRA, and the starting point of the RAR window is aligned with the first PDCCH symbol of the earliest USS for the PDCCH of the second message under CFRA. 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