HARQ process for RACH response messages in two-stage rach

Abstract

Some aspects of the present disclosure provide techniques for a hybrid automatic repeat request (HARQ) procedure of a random access channel (RACH) response message in a two-step RACH procedure. A method, which may be performed by a user equipment (UE), includes transmitting a RACH message to a base station (BS) during a two-step RACH procedure. The RACH message includes a RACH preamble and a RACH payload. The UE monitors a random access response (RAR) message from the BS during a RACH window. The UE transmits, to the BS, a retransmission of the RACH message, an acknowledgement (ACK) of the RACH response message, a negative acknowledgement (NACK) of the RACH response message, or does not transmit, based on whether the RACH response message carrying a successful RAR or a fallback RAR is received from the BS or not during the RAR window.

Description

[0001] This application is a divisional application of the invention patent application with application number "202080056576.3" filed on August 13, 2020 and invention name "HARQ process for RACH response message in two-step RACH".

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of and priority to International Patent Cooperation Treaty Application No. PCT / CN2019 / 101168, filed on August 16, 2019, which is hereby assigned to the assignee of this application and is hereby expressly incorporated by reference in its entirety as if fully set forth below and for all applicable purposes. Technical Field

[0004] Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for a hybrid automatic repeat request (HARQ) process for a random access channel (RACH) response message in a two-step RACH process. Background Art

[0005] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcast, etc. These wireless communication systems may employ multiple access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple access systems include 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, Advanced LTE (LTE-A) systems, Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, and Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems, to name a few.

[0006] These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate at the city, country, region, and even global level. New radio (e.g., 5GNR) is an example of an emerging telecommunication standard. NR is an enhancement set of the LTE mobile standard released by 3GPP. NR is designed to better support mobile broadband Internet access by improving spectrum efficiency, reducing costs, improving services, utilizing new spectrum, and better integrating with other open standards using OFDMA with cyclic prefix (CP) on downlink (DL) and uplink (UL). To this end, NR supports beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

[0007] However, as the demand for mobile broadband access continues to increase, there is a need for further improvements to NR and LTE technologies. Preferably, these improvements should be applicable to other multi-access technologies and telecommunication standards that employ these technologies. Summary of the invention

[0008] The systems, methods, and devices of the present disclosure each have several aspects, no single aspect being solely responsible for its desirable attributes. Without limiting the scope of the present disclosure as expressed by the appended claims, some features will now be briefly discussed. After considering this discussion, and particularly after reading the section entitled "Detailed Description of the Invention," it will be understood how the features of the present disclosure provide advantages including an improved random access procedure.

[0009] Some aspects provide a method for wireless communication by a user equipment (UE). The method generally includes sending a RACH message to a base station (BS) during a two-step random access channel (RACH) process. The RACH message includes a RACH preamble and a RACH payload. The method generally includes: monitoring a RACH response message from a BS during a random access response (RAR) window. The method generally includes: based on whether a RACH response message carrying a successful RAR or a fallback RAR is received from the BS during the RAR window or no RACH response message is received, a retransmission of the RACH message, an acknowledgment (ACK) of the RACH response message, a negative acknowledgment (NACK) of the RACH response message, or no transmission is sent to the BS.

[0010] Some aspects provide a method for wireless communication by a BS. The method generally includes: during a two-step RACH process, sending a RACH response message to a UE in a RAR window. The RACH response message includes a successful RAR or a fallback RAR. The method generally includes: based on the RACH response message, receiving a retransmission of the RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or receiving nothing from the UE.

[0011] Some aspects provide an apparatus for wireless communication. The apparatus generally includes at least one processor and a memory coupled to the at least one processor. The memory includes code that can be executed by at least one processor to enable the apparatus to send a RACH message to a BS during a two-step RACH process. The RACH message includes a RACH preamble and a RACH payload. The memory includes code that can be executed by at least one processor to enable the apparatus to monitor a RACH response message from the BS during a RAR window. The memory includes code that can be executed by at least one processor to enable the apparatus to perform the following operations: based on whether a RACH response message carrying a successful RAR or a fallback RAR is received from the BS during the RAR window or no RACH response message is received, a retransmission of the RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or no transmission is sent to the BS.

[0012] Some aspects provide an apparatus for wireless communication. The apparatus generally includes at least one processor and a memory coupled to the at least one processor. The memory includes code executable by the at least one processor to enable the apparatus to send a RACH response message to a UE in a RAR window during a two-step RACH process. The RACH response message includes a successful RAR or a fallback RAR. The memory includes code executable by the at least one processor to enable the apparatus to perform the following operations: based on the RACH response message, receive a retransmission of the RACH message from the UE, an ACK for the RACH response message, a NACK for the RACH response message, or receive nothing.

[0013] Some aspects provide an apparatus for wireless communication. The apparatus generally includes a component for sending a RACH message to a BS during a two-step RACH process. The RACH message includes a RACH preamble and a RACH payload. The apparatus generally includes: a component for monitoring a RACH response message from the BS during a RAR window. The apparatus generally includes a component for the following operations: based on whether a RACH response message carrying a successful RAR or a fallback RAR is received from the BS during the RAR window or no RACH response message is received, a retransmission of the RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or no transmission is sent to the BS.

[0014] Some aspects provide an apparatus for wireless communication. The apparatus generally includes: a component for sending a RACH response message to a UE in a RAR window during a two-step RACH process. The RACH response message includes a successful RAR or a fallback RAR. The apparatus generally includes: a component for receiving a retransmission of a RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or receiving nothing from the UE based on the RACH response message.

[0015] Some aspects provide a computer-readable medium having computer executable code for wireless communication stored thereon. The computer-readable medium generally includes code for sending a RACH message to a BS during a two-step RACH process. The RACH message includes a RACH preamble and a RACH payload. The computer-readable medium generally includes code for monitoring a RACH response message from a BS during a RAR window. The computer-readable medium generally includes code for the following operations: based on whether a RACH response message carrying a successful RAR or a fallback RAR is received from the BS during the RAR window or no RACH response message is received, a retransmission of a RACH message, an ACK for a RACH response message, a NACK for a RACH response message, or no transmission is sent to the BS.

[0016] Some aspects provide a computer-readable medium having computer executable code stored thereon for wireless communication. The computer-readable medium generally includes code for sending a RACH response message to a UE in a RAR window during a two-step RACH procedure. The RACH response message includes a successful RAR or a fallback RAR. The computer-readable medium generally includes code for the following operations: receiving a retransmission of a RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or receiving nothing from the UE based on the RACH response message.

[0017] To achieve the foregoing and related purposes, one or more aspects include features fully described below and particularly pointed out in the claims. The following description and the accompanying drawings set forth in detail some illustrative features of one or more aspects. However, these features are only indicative of some of the various ways in which the principles of the various aspects can be employed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to be able to understand in detail the manner in which the above-mentioned features of the present disclosure are achieved, a more particular description briefly outlined above may be obtained by reference to various aspects, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only some typical aspects of the present disclosure and are therefore not to be considered limiting of its scope, as the description may admit of other equally effective aspects.

[0019] Figure 1 is a block diagram conceptually illustrating an example telecommunications system in accordance with some aspects of the present disclosure.

[0020] Figure 2 is a block diagram conceptually illustrating a design of an example base station (BS) and user equipment (UE) according to some aspects of the present disclosure.

[0021] Figure 3 is an example frame format for some wireless communication systems (e.g., New Radio (NR)) according to some aspects of the present disclosure.

[0022] Figure 4 is a timing diagram illustrating an example four-step random access channel (RACH) procedure in accordance with some aspects of the present disclosure.

[0023] Figure 5 is a timing diagram illustrating an example two-step RACH procedure in accordance with some aspects of the present disclosure.

[0024] Figure 6 is a timing diagram illustrating an example two-step RACH procedure in accordance with some aspects of the present disclosure.

[0025] Fig. 7A A channel structure for MSG A is shown according to some aspects of the present disclosure.

[0026] Figure 7B Transmission opportunities for MSG A are shown according to some aspects of the present disclosure.

[0027] Figure 8 is a table illustrating MSG A content for unicast mode according to some aspects of the present disclosure.

[0028] Fig. 9 is a table illustrating MSG A content for multicast mode according to some aspects of the present disclosure.

[0029] Fig.10 is a timing diagram illustrating an example hybrid automatic repeat request (HARQ) process for a RACH response message with a successful random access response (RAR) in an example two-step RACH process in accordance with some aspects of the present disclosure.

[0030] Fig.11 is a timing diagram illustrating an example HARQ process for a RACH response message with fallback RAR in an example two-step RACH process, in accordance with some aspects of the present disclosure.

[0031] Fig.12 is a flow diagram illustrating example operations for wireless communications by a UE in accordance with some aspects of the present disclosure.

[0032] Fig.13 is a flow diagram illustrating example operations for wireless communications by a BS in accordance with some aspects of the present disclosure.

[0033] Fig.14 is a call flow diagram illustrating example operations for a HARQ process in a two-step process in accordance with some aspects of the present disclosure.

[0034] Fig.15 A communication device according to aspects of the present disclosure is shown that may include various components configured to perform operations of the techniques disclosed herein.

[0035] Fig.16 A communication device according to aspects of the present disclosure is shown that may include various components configured to perform operations of the techniques disclosed herein.

[0036] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that components disclosed in one aspect may be beneficially utilized on other aspects without specific recitation. DETAILED DESCRIPTION

[0037] Various aspects of the present disclosure provide apparatus, methods, processing systems, and computer-readable media for a hybrid automatic repeat request (HARQ) process for a RACH response message in a two-step random access channel (RACH) process. In the two-step RACH process, a user equipment (UE) sends a RACH message (e.g., referred to as MSG A) including a RACH preamble and a RACH payload to a base station (BS). The BS can respond with a RACH response message (e.g., referred to as MSG B), which includes a physical downlink control channel (PDCCH) transmission and a physical downlink shared channel (PDSCH) transmission.

[0038] Aspects of the present disclosure provide a HARQ process for a RACH response message in a two-step RACH process. For example, the UE can provide HARQ feedback based on whether a RACH response message is received and if the RACH response message is received, whether the RACH response message includes a fallback random access response (RAR) or a successful RAR, or not send HARQ feedback, or send a RACH message retransmission.

[0039] The following description provides an example of a configurable mode for responding to a random access message in a communication system, and does not limit the scope, applicability or examples set forth in the claims. Without departing from the scope of the present disclosure, the functions and arrangements of the elements discussed may be changed. Various examples may omit, replace or add various processes or components as appropriate. For example, the method described may be performed in an order different from the order described, and various steps may be added, omitted or combined. In addition, the features described with respect to some examples may be combined in some other examples. For example, any number of aspects set forth herein may be used to implement a device or practice method. In addition, the scope of the present disclosure is intended to cover such a device or method that is practiced using other structures, functions, or structures and functions other than or different from the various aspects of the present disclosure set forth herein. It should be understood that any aspect of the present disclosure disclosed herein may be embodied by one or more elements of the claims. The word "exemplary" is used herein to mean "used as an example, instance or illustration". Any aspect described as "exemplary" herein is not necessarily to be interpreted as being preferred or advantageous over other aspects.

[0040] Generally, any number of wireless networks can be deployed in a given geographic area. Each wireless network can support a specific radio access technology (RAT) and can operate on one or more frequencies. RAT can also be referred to as radio technology, air interface, etc. Frequency can also be referred to as carrier, subcarrier, frequency channel, frequency modulation (tone), subband, etc. Each frequency can support a single RAT in a given geographic area to avoid interference between wireless networks of different RATs. In some cases, 5G NR RAT networks can be deployed.

[0041] The technology described herein can be used for various wireless networks and radio technologies. Although this article may use terms commonly associated with 3G, 4G and / or new radio (e.g., 5GNR) wireless technologies to describe various aspects, various aspects of the present disclosure can be applied to communication systems based on other generations.

[0042] NR access can support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth, millimeter wave mmW, massive machine type communication MTC (mMTC) targeting non-backward compatible MTC technology, and / or mission-critical services targeting ultra-reliable low-latency communication (URLLC). These services may include latency and reliability requirements. These services may also have different transmission time intervals (TTIs) to meet various quality of service (QoS) requirements. In addition, these services can coexist in the same subframe.

[0043] The electromagnetic spectrum is typically subdivided into various categories, bands, channels, etc. based on frequency / wavelength. In 5GNR, two initial operating bands have been identified as frequency range designations FR1 (410 MHz-7.125 GHz) and FR2 (24.25 GHz-52.6 GHz). Frequencies between FR1 and FR2 are typically referred to as mid-band frequencies. Although a portion of FR1 is greater than 6 GHz, FR1 is often referred to (interchangeably) as the "below 6 GHz" band in various documents and articles. Similar naming issues sometimes arise regarding FR2, although unlike the extremely high frequency (EHF) band (30 GHz-300 GHz), which is identified as the "millimeter wave" band by the International Telecommunication Union (ITU), FR2 is often referred to (interchangeably) as the "millimeter wave" band in literature and articles.

[0044] In view of the above, unless otherwise specifically stated, it should be understood that the term "below 6 GHz" and the like (if used herein) can broadly represent frequencies that can be less than 6 GHz, can be within FR1, or can include mid-band frequencies. In addition, unless otherwise specifically stated, it should be understood that the term "millimeter wave" and the like (if used herein) can broadly represent frequencies that can include mid-band frequencies, can be within FR2, or can be within the EHF band.

[0045] NR supports beamforming and can dynamically configure the beam direction. MIMO transmission with precoding can also be supported. MIMO configuration in DL can support up to 8 transmit antennas, where multi-layer DL transmission has up to 8 streams and up to 2 streams per UE. Multi-layer transmission with up to 2 streams per UE can be supported. Aggregation of multiple cells with up to 8 serving cells can be supported.

[0046] Figure 1 An example wireless communication network 100 is shown in which aspects of the present disclosure may be performed. For example, the wireless communication network 100 may be a NR system (e.g., a 5G NR network). Figure 1 As shown, the wireless communication network 100 may communicate with a core network 132. The core network 132 may communicate with one or more base stations (BSs) 110 110a-z (each also individually referred to herein as BS 110 or collectively referred to herein as BS 110) and / or user equipments (UEs) 120a-y (each also individually referred to herein as UE 120 or collectively referred to herein as UE 120) in the wireless communication network 100 via one or more interfaces.

[0047] BS 110 may provide communication coverage for a particular geographic area (sometimes referred to as a "cell"), which may be fixed or may move depending on the location of mobile BS 110. In some examples, BS 110 may interconnect with each other and / or one or more other BSs or network nodes (not shown) in wireless communication network 100 through various types of backhaul interfaces (e.g., direct physical connections, wireless connections, virtual networks, etc.) using any suitable transport network. Figure 1 In the example shown, BSs 110a, 110b, and 110c may be macro BSs for macro cells 102a, 102b, and 102c, respectively. BS 110x may be a pico BS for pico cell 102x. BSs 110y and 110z may be femto BSs for femto cells 102y and 102z, respectively. The BS may support one or more cells. BS 110 communicates with UE 120. UE 120 may be dispersed throughout wireless communication network 100, and each UE 120 may be fixed or mobile.

[0048] According to some aspects, BS 110 and UE 120 may be configured as a HARQ process for RACH response messages in a two-step RACH process. Figure 1 As shown, BS 110a includes a RACH manager 112. According to aspects of the present disclosure, RACH manager 112 may be configured to: during the two-step RACH process, send a RACH response message to the UE in the RAR window, the RACH response message including a successful RAR or a fallback RAR; and receive a retransmission of the RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or nothing from the UE based on the RACH response message. Figure 1 As shown, UE 120a includes a RACH manager 122. The RACH manager 122 may be configured to: send a RACH message to the BS during a two-step RACH procedure, the RACH message including a RACH preamble and a RACH payload; monitor a RACH response message from the BS during a RAR window; and send a retransmission of the RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or a DTX to the RACH response message to the BS based on whether a RACH response message carrying a successful RAR or a fallback RAR is received from the BS during the RAR window or no RACH response message is received.

[0049] The wireless communication network 100 may also include a relay station (e.g., relay station 110r), also referred to as a relay, etc., which receives transmissions of data and / or other information from an upstream station (e.g., BS110a or UE 120r) and sends transmissions of the data and / or other information to a downstream station (e.g., UE 120 or BS110), or relays transmissions between UEs 120 to facilitate communication between devices.

[0050] The network controller 130 may be coupled to a set of BSs 110 and provide coordination and control for these BSs 110. The network controller 130 may communicate with the BSs 110 via a backhaul. In various aspects, the network controller 130 may communicate with a core network 132 (e.g., a 5G core network (5GC)), which provides various network functions such as access and mobility management, session management, user plane functions, policy control functions, authentication service functions, unified data management, application functions, network exposure functions, network repository functions, network slice selection functions, etc.

[0051] Figure 2 1 shows a BS 110a and a UE 120a (eg, in Figure 1 Example components of the wireless communication network 100).

[0052] At BS 110a, a transmit processor 220 may receive data from a data source 212 and control information from a controller / processor 240. The control information may be for a physical broadcast channel (PBCH), a physical control format indicator channel (PCFICH), a physical hybrid ARQ indicator channel (PHICH), a PDCCH, a group common PDCCH (GC PDCCH), etc. The data may be for a PDSCH, etc. The processor 220 may process (e.g., encode and symbol map) the data and the control information to obtain data symbols and control symbols, respectively. The transmit processor 220 may also generate reference symbols, such as for a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a channel state information reference signal (CSI-RS). A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on ​​data symbols, control symbols, and / or reference symbols, where applicable, and may provide an output symbol stream to a modulator (MOD) in a transceiver 232a-232t. Each modulator can process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator can further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. The downlink signals from the modulators in transceivers 232a-232t can be transmitted via antennas 234a-234t, respectively.

[0053] At UE 120a, antennas 252a-252r may receive downlink signals from BS110a and may provide received signals to demodulators (DEMODs) in transceivers 254a-254r, respectively. Each demodulator may adjust (e.g., filter, amplify, downconvert, and digitize) respective received signals to obtain input samples. Each demodulator may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all demodulators in transceivers 254a-254r, perform MIMO detection on the received symbols where applicable, and provide detected symbols. A receive processor 258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide the decoded data for UE 120a to a data sink 260, and provide the decoded control information to a controller / processor 280.

[0054] On the uplink, at the UE 120a, a transmit processor 264 may receive and process data from a data source 262 (e.g., for a physical uplink shared channel (PUSCH)) and control information from a controller / processor 280 (e.g., for a physical uplink control channel (PUCCH)). The transmit processor 264 may also generate reference symbols for reference signals (e.g., for a sounding reference signal (SRS)). The symbols from the transmit processor 264 may be precoded by the TX MIMO processor 266 where applicable, further processed by modulators in the transceivers 254a-254r (e.g., for SC-FDM, etc.), and transmitted to the BS 110a. At BS 110a, the uplink signal from UE 120a may be received by antenna 234, processed by demodulators in transceivers 232a-232t, detected by MIMO detector 236 (if applicable), and further processed by receive processor 238 to obtain decoded data and control information sent by UE 120a. Receive processor 238 may provide the decoded data to data receiver 239 and the decoded control information to controller / processor 240.

[0055] Memories 242 and 282 may store data and program codes for BS 110a and UE 120a, respectively.A scheduler 244 may schedule UEs for data transmission on the downlink and / or uplink.

[0056] The antenna 252, processors 266, 258, 264 and / or controller / processor 280 of the UE 120a and / or the antenna 234, processors 220, 230, 238 and / or controller / processor 240 of the BS 110a may be used to perform the various techniques and methods described herein. Figure 2 As shown in FIG. 1 , according to various aspects described herein, the controller / processor 240 of the BS 110a has a RACH manager 241, which can be configured as a HARQ process for a RACH response message in a two-step RACH process. Figure 2 As shown in FIG. 1 , according to various aspects described herein, the controller / processor 280 of the UE 120a has a RACH manager 241, which can be configured as a HARQ process for a RACH response message in a two-step RACH process. Although shown at the controller / processor, other components of the UE 120a and the BS 110a can be used to perform the operations described herein.

[0057] NR can utilize orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP) on uplink and downlink. NR can support half-duplex operation using time division duplex (TDD). OFDM and single carrier frequency division multiplexing (SC-FDM) divide the system bandwidth into multiple orthogonal subcarriers, which are also commonly referred to as tone, bin, etc. Each subcarrier can be modulated with data. Modulation symbols can be sent in the frequency domain using OFDM, and modulation symbols can be sent in the time domain using SC-FDM. The spacing between adjacent subcarriers can be fixed, and the total number of subcarriers can depend on the system bandwidth. The minimum resource allocation, called a resource block (RB), can be 12 consecutive subcarriers. The system bandwidth can also be divided into subbands. For example, a subband can cover multiple RBs. NR can support a basic subcarrier spacing (SCS) of 15KHz, and other SCSs (e.g., 30kHz, 60kHz, 120kHz, 240kHz, etc.) can be defined with respect to the basic SCS.

[0058] Figure 3300 is a diagram showing an example of a frame format for NR. The transmission timeline of each of the downlink and uplink can be divided into units of radio frames. Each radio frame can have a predetermined duration (e.g., 10ms) and can be divided into 10 subframes with indices from 0 to 9, each subframe 1ms. Depending on the SCS, each subframe can include a variable number of slots (e.g., 1, 2, 4, 8, 16, ... slots). Depending on the SCS, each slot can include a variable number of symbol periods (e.g., 7, 12 or 14 symbols). The symbol period in each slot can be assigned an index. A microslot, which can be referred to as a subslot structure, refers to a transmission time interval having a duration less than a slot (e.g., 2, 3 or 4 symbols). Each symbol in a slot can indicate a link direction (e.g., DL, UL or flexible) for data transmission, and the link direction of each subframe can be dynamically switched. The link direction can be based on the slot format. Each slot can include DL / UL data and DL / UL control information.

[0059] In NR, synchronization signal blocks (SSBs) are transmitted. In some aspects, SSBs may be transmitted in bursts, where each SSB in the burst corresponds to a different beam direction for UE-side beam management (e.g., including beam selection and / or beam refinement). SSBs include PSS, SSS, and two-symbol PBCH. SSBs can be transmitted in fixed time slot locations (e.g., Figure 3 0-3) shown in . PSS and SSS can be used by UE for cell search and acquisition. PSS can provide half-frame timing, and SS can provide CP length and frame timing. PSS and SSS can provide cell identification. PBCH carries some basic system information, such as downlink system bandwidth, timing information within radio frames, SS burst set periodicity, system frame number, etc. SSB can be organized into SS bursts to support beam scanning. Additional system information, such as remaining minimum system information (RMSI), system information block (SIB), and other system information (OSI) can be sent on the physical downlink shared channel (PDSCH) in some subframes. For example, for mmWave, SSB can be sent up to 64 times using up to 64 different beam directions. Multiple transmissions of SSB are called SS burst sets. SSBs in an SS burst set can be sent in the same frequency region, and SSBs in different SS burst sets can be sent at different frequency regions.

[0060] As described above, various aspects of the present disclosure relate to a hybrid automatic repeat request (HARQ) process for a two-step random access channel (RACH) process. RACH refers to a wireless channel (medium) that can be shared by multiple UEs and can be used by UEs to (randomly) access a network for communication. For example, RACH can be used for call establishment and access to a network for data transmission. In some cases, RACH can be used for initial access to a network when a UE switches from RRC connected idle mode to active mode, or when switching in RRC connected mode. In addition, RACH can be used for downlink (DL) and / or uplink (UL) data arrival when the UE is in RRC idle mode or RRC inactive mode, and when reestablishing a connection with the network.

[0061] Figure 4 4 is a timing (or "call flow") diagram 400 illustrating an example four-step RACH procedure. At 402, a first message (MSG1) may be sent from UE 120a to BS 110a on a physical random access channel (PRACH). In a four-step RACH procedure, MSG1 may include only a RACH preamble. At 404, BS 110a may respond with a random access response (RAR) message (MSG2), which may include an identifier (ID) of the RACH preamble, a timing advance (TA), an uplink grant, a cell radio network temporary identifier (C-RNTI), and / or a backoff indicator. MSG2 may include a PDCCH communication including control information for subsequent communications on the PDSCH, as shown. In response to MSG2, at 406, UE 120a sends MSG3 to BS 110a on the PUSCH. MSG3 may include one or more of an RRC connection request, a tracking area update (TAU) request, a system information request, a positioning fix or positioning signal request, or a scheduling request.Then, at 408, BS 110a responds with MSG 4, which may include a contention resolution message.

[0062] In some cases, in order to speed up access, a two-step RACH procedure may be supported. As the name implies, the two-step RACH procedure can effectively "fold" the four messages of the four-step RACH procedure into two messages. The two-step RACH procedure has several benefits, such as access speed and the ability to send a relatively small amount of data to establish a connection without the overhead of a full four-step RACH procedure (when the four-step RACH message would be larger than the payload). The two-step RACH procedure can operate in any RRC state and any supported cell size. Networks using the two-step RACH procedure are typically able to support contention-based random access (CBRA) transmission of messages (e.g., MSG A) within a limited range of payload sizes and with a limited number of modulation and coding scheme (MCS) levels.

[0063] Figure 5 5 is a timing diagram 500 illustrating an example two-step RACH process according to some aspects of the present disclosure. In the two-step RACH process, at 502, a first message (MSG A) may be sent from UE 120a to BS110a. MSG A may include some or all information from both MSG1 and MSG3 of the four-step RACH process (effectively combining MSG1 and MSG3). For example, MSG A may include MSG1 and MSG3 multiplexed together, such as using one of time division multiplexing (TDM) or frequency division multiplexing (FDM). MSG A may include a RACH preamble and a payload for random access. The MSG A payload may include, for example, a UE-ID and other signaling information (e.g., a buffer status report (BSR) or a scheduling request (SR)). At 504, BS110a may respond with a RAR message (MSG B), which may effectively combine MSG2 and MSG4 of the above-described four-step RACH process. For example, the MSGB may include an ID of a RACH preamble (RAPID), a timing advance (TA), a backoff indicator, a contention resolution message, a UL / DL grant, and / or a transmit power control (TPC) command.

[0064] Figure 6 is a timing diagram illustrating a more detailed example of a two-step RACH procedure according to some aspects of the present disclosure. Figure 6 As shown in , the UE may receive information from the BS prior to the RACH procedure, such as SSB, system information block (SIB) and / or reference signal (RS), which may be used by UE 120a to perform the RACH procedure with BS 110a. Figure 6As shown in , in a two-step RACH process, MSG A may include both a preamble (e.g., PRACH) and a payload (e.g., DMRS and PUSCH). BS 110a attempts to decode the process / decodes the MSG A preamble and payload, and then sends MSG B (e.g., based on MSG A processing). Figure 5 As shown, MSG B may include both PDCCH and PDSCH.

[0065] Fig. 7A FIG. 4 shows a channel structure of an example MSG A transmission opportunity that can be verified according to some aspects of the present disclosure. Fig. 7A As shown in FIG. 1 , the MSG A transmission opportunity generally includes a MSG A preamble opportunity (for sending a preamble signal) and a MSG A payload opportunity for sending a PUSCH. Fig. 7A As shown, MSG A preamble transmission may involve selecting a preamble sequence; and selecting a preamble timing in the time domain / frequency domain (e.g., for sending the selected preamble sequence). MSG A payload transmission may involve: constructing a random access message payload (DMRS / PUSCH); and selecting one or more PUSCH resource units (PRUs) in the time domain / frequency domain to send the message (e.g., payload). Figure 7B As shown, the UE monitors SSB transmissions that are transmitted (e.g., repeatedly transmitted by the gNB using different TX beams) and are associated with a limited set of time / frequency resources that define RACH opportunities (ROs) and PRUs. Upon detecting an SSB, the UE may select the RO and one or more PRUs associated with the SSB for MSG A transmission. The limited set of ROs and PRUs may help reduce the monitoring overhead (blind decoding) of BS 110a.

[0066] In some systems (e.g., 5G NR), up to 64 preamble sequences are configured on each RO. Multiple four-step and / or multiple two-step RACH UEs can share the same RO and randomly select their preamble sequences from a common pool. In some examples, the network configures separate ROs for two-step and four-step RACH UEs, or the network configures separate pools for two-step and four-step RACH UEs but shares the RO.

[0067] The two-step RACH can support both contention-based random access (CBRA) and contention-free random access (CFRA). In some examples, in the CBRA two-step RACH procedure, a contention resolution identifier (ID) is sent in the payload of MSG A. In some examples, in the CFRA two-step RACH procedure, a medium access control (MAC) control element (CE) or small data can be sent in the payload of MSG A.

[0068] In some examples, the content of MSG B depends on the RRC state of the UE and the MSG A processing results. Figure 8 and Fig. 9 is a table showing example contents of RACH response messages (e.g., PDCCH and PDSCH) for unicast and multicast, respectively, depending on the RRC state and whether the BS successfully decodes the RACH payload and preamble from the UE. As shown, if the BS is able to successfully decode the MSG A payload, the BS sends a SuccessRAR in the MSG B PDSCH. For a UE in an RRC connected state, the SuccessRAR includes at least a timing advance command (TAC). For a UE in an RRC idle / inactive state, the SuccessRAR includes at least a TAC, a contention resolution ID, and a C-RNTI. If the BS cannot decode the MSG A payload, but is able to detect the MSG A preamble, the BS sends a FallbackRAR in the MSG B PDSCH. The FallbackRAR includes at least a RAR grant for retransmitting the PUSCH, a temporary cell radio network temporary identifier (TC-RNTI), and a TAC.

[0069] All that is required is a HARQ process for the RACH response message in the two-step RACH process.

[0070] Example HARQ procedure for RACH response message in two-step RACH

[0071] Aspects of the present disclosure provide for a two-step RACH procedure (e.g., such as described above with reference to Figure 5-9 A hybrid automatic repeat request (HARQ) process for a random access channel (RACH) response message (e.g., MSG B) in a two-step RACH process described in the specification. The HARQ process can improve the reliability of the two-step RACH process while accommodating various user equipment (UE) radio resource control (RRC) states, various results of RACH message (e.g., MSG A) processing, flexibility of acknowledgement (ACK) / negative ACK (NACK) or discontinuous transmission (DTX) indication (e.g., which can help support asynchronous uplink communication, handover, best effort delivery of small data, and / or power saving), and both contention-based random access (CBRA) and contention-free random access (CFRA) two-step processes.

[0072] Example HARQ feedback for SuccessRAR:

[0073] As discussed above, when a base station (BS) such as Figure 1When the BS 110 shown in FIG. 1 successfully decodes the RACH message payload, the BS sends a RACH response message (e.g., MSG B) with a SuccessRAR in a physical downlink shared channel (PDSCH) having content that may depend on the RRC state of the UE. In some examples, for an RRC connected UE in CBRA or CFRA mode, the SuccessRAR includes at least a timing advance command (TAC). In some examples, for an RRC idle / inactive UE in CBRA mode, the SuccessRAR includes at least a TAC, a contention resolution identifier (ID), and a common radio network temporary identifier (C-RNTI).

[0074] If the UE successfully decodes a SuccessRAR within the random access response (RAR) window, the UE adjusts the timing offset for uplink transmission by executing the TAC carried in the SuccessRAR. In some examples, the granularity of the TAC is based on a parameter set of a configured physical uplink control channel (PUCCH) / physical uplink shared channel (PUSCH) for the active uplink bandwidth part (BWP).

[0075] According to some aspects, when the UE successfully decodes the SuccessRAR in the RACH response message within the RAR window, the UE sends an ACK in the uplink control information (UCI). If the UE has PUCCH resources, the UE sends UCI on the PUCCH. In some examples, the PUCCH resources are provided in the RACH response message. In some examples, the PUCCH resources are pre-configured in the system information (SI), radio resource control (RRC) signaling, or downlink control information (DCI). In some examples, the PUCCH resources are selected by the UE. For example, the UE can select the PUCCH resources based on the UE's multi-access signature (signature) (e.g., MSG A preamble ID). In some examples, if the UE has new uplink data to send, but does not have a valid uplink grant for the new data, the UE can multiplex a scheduling request (SR) with an ACK in the UCI to request an uplink grant for the new data. In some examples, UCI (e.g., ACK) can be sent on the PUSCH. For example, UCI may be sent on the PUSCH when the UE does not have valid PUCCH resources but does have a valid uplink grant for new data transmission.

[0076] According to some aspects, when the UE does not successfully decode the SuccessRAR in the RACH response message within the RAR window, the UE may send a NACK. If the UE has valid PUCCH resources, the UE may send a NACK on the PUCCH. In some examples, the PUCCH resources are pre-configured in the SI, RRC signaling, or DCI. In some examples, the PUCCH resources are selected by the UE. For example, the UE may select the PUCCH resources based on the UE's multi-access signature (e.g., MSG A preamble ID). On the other hand, if the UE does not have valid PUCCH resources, the UE will not send HARQ feedback (e.g., no NACK or ACK), which may be referred to as discontinuous transmission (DTX).

[0077] According to some aspects, the UE can further determine whether to provide HARQ feedback for the RACH response message based on an indication from the BS. For example, the BS can provide a HARQ feedback request indicator to the UE indicating whether HARQ feedback is requested / allowed. The BS can provide an indication to the UE in a PUCCH resource configuration (e.g., as described above, which can be pre-configured and / or provided in the RACH response message). In some examples, the indication can be provided via an additional field in the ACK / NACK transmission indicator. For example, the PUCCH resource configuration for HARQ of MSG B PDSCH can include a first field having a PUCCH resource set indicator (e.g., FieldA, which can be 3 or 4 bits) and a second field having a HARQ feedback request indicator (e.g., FieldB, which can be 1 or 2 bits).

[0078] In an illustrative example of a 1-bit ACK / NACK transmission indicator in a PUCCH resource configuration: a value of "0" may indicate that if the UE cannot decode MSG B PDSCH, a NACK may be sent regardless of whether the UE has a valid timing advance (TA); and a value of "1" may indicate that if the UE cannot decode MSG B PDSCH, a NACK may not be sent regardless of whether the UE has a valid TA. In an illustrative example of a 2-bit ACK / NACK transmission indicator in a PUCCH resource configuration: a value of "00" may indicate that if the UE cannot decode MSG B PDSCH, a NACK may be sent regardless of whether the UE has a valid TA; a value of "01" may indicate that if the UE has a valid TA but cannot decode MSG B PDSCH, a NACK may be sent; if the UE does not have a valid TA, a NACK may not be sent; a value of "10" may indicate that no ACK or NACK is sent; and a value of "11" may indicate that if the UE cannot decode MSG B PDSCH, a NACK is not sent regardless of whether the UE has a valid TA.

[0079] Fig.10 is a timing diagram illustrating an example HARQ process for a RACH response message with SuccessRAR in an example two-step RACH process according to some aspects of the present disclosure. Fig.10 As shown in , at 1002, the UE sends a MSG A preamble and a MSG A payload (e.g., PUCCH and PUSCH for MSG 1 of a two-step RACH procedure). The RAR window 1004 may start at the end of the transmission of the MSG A payload. If the BS successfully decodes the MSG A preamble and the MSG A payload, at 1006, the BS sends a MSG B PDCCH and a MSG B PDSCH with SuccessRAR (e.g., MSG2 for a two-step RACH procedure). If the UE decodes MSG B with SuccessRAR during the RAR window 1004 at 1008, the UE sends an ACK (which may include an SR) at 1008. If the UE does not decode SuccessRAR during the RAR window, at 1010, the UE sends a NACK or DTX. As discussed above, sending HARQ feedback for the RACH response message may also be based on an indication from the BS, such as a HARQ feedback request indicator that may be included in a field in the PUCCH resource configuration.

[0080] Example HARQ feedback for FallbackRAR:

[0081] As discussed above, when the UE sends a MSG A preamble and a MSG A payload (e.g., PUCCH and PUSCH for MSG 1 of a two-step RACH procedure), if the BS is able to detect the RACH preamble but cannot decode the RACH payload, the BS sends a FallbackRAR in the RACH response message PDSCH. As described above, for UEs in CBRA mode and any RRC state, the FallbackRAR includes at least the TAC, the uplink grant for PUSCH (e.g., MSG A payload) retransmission, the TC-RNTI, and the RAPID. For UEs in CFRA mode, the FallbackRAR includes at least the TAC, the uplink grant for PUSCH retransmission, and the RAPID.

[0082] When the UE successfully decodes the FallbackRAR in the RACH response message within the RAR window, the UE may adjust the uplink timing based on the TAC. According to some aspects, the UE may not send an ACK for the RACH response message (e.g., unlike the SuccessRAR case). Instead, the UE retransmits the PUSCH (of MSG A) on the uplink resources granted in the FallbackRAR.

[0083] When the UE does not successfully decode the FallbackRAR in the RACH response message within the RAR window (e.g., does not decode the RACH response message), the UE may determine whether to send HARQ feedback for the RACH response message. In some examples, when the UE does not successfully decode the FallbackRAR in the RAR window, the UE sends a NACK in the UCI. As discussed above, if the UE has PUCCH resources, the UE sends a NACK on the PUCCH, where the PUCCH resources may be provided in the RACH response, pre-configured in the SI, RRC signaling, or DCI, or selected by the UE (e.g., based on the UE's multi-access signature). On the other hand, if the UE does not have valid PUCCH resources, the UE will not send a NACK (e.g., the UE will perform DTX).

[0084] As discussed above, the UE can further determine whether to provide HARQ feedback for the RACH response message based on an indication from the BS, such as a HARQ feedback request indicator.

[0085] Fig.11 is a timing diagram illustrating an example HARQ process for a RACH response message with fallback RAR in an example two-step RACH process according to some aspects of the present disclosure. Fig.11As shown in , at 1102, the UE transmits the MSG A preamble and the MSG A payload (e.g., the PUCCH and PUSCH of MSG 1 for the two-step RACH procedure). The RAR window 1104 may start at the end of the MSG A payload transmission. If the BS successfully decodes the MSG A preamble and does not successfully decode the MSG A payload, at 1106, the BS transmits the MSG B PDCCH and MSG B PDSCH with FallbackRAR (e.g., MSG 2 for the two-step RACH procedure). If the UE decodes MSG B with FallbackRAR during the RAR window 1104 at 1108, the UE transmits a retransmission of the MSG A PUSCH at 1108. If the UE does not decode SuccessRAR during the RAR window, at 1110, the UE transmits a NACK or DTX. As discussed above, sending HARQ feedback for the RACH response message may also be based on an indication from the BS, such as a HARQ feedback request indicator that may be included in a field in the PUCCH resource configuration.

[0086] Example MSG B retransmission:

[0087] According to some aspects, if the BS receives an ACK for SuccessRAR, the network (e.g., BS) will consider the two-step RACH process to be completed for the corresponding UE. In this case, there is no more RACH response message retransmission for the UE. If the BS receives a MSG APUSCH retransmission from the UE on the granted resources (e.g., the granted resources indicated in FallbackRAR) and there is no SR from the UE, the network can consider the two-step RACH process to be completed for the corresponding UE, and in this case, there is no more RACH response message retransmission for the UE.

[0088] According to some aspects, if the BS receives a NACK for the RACH response message (e.g., in the UCI), the BS will retransmit the RACH response message RAR (e.g., with SucessRAR or FallbackRAR) to the corresponding UE (or multiple) within a predefined time interval. As mentioned above, the UE can select the PUCCH resource based on the UE's multi-access signature (e.g., MSG A preamble ID). In this case, the BS can detect the identity of the sender (e.g., detect which UE did not decode the MSG B PDSCH) based on at least the PUCCH resource configuration.

[0089] According to some aspects, if the BS does not receive HARQ feedback (e.g., ACK or NACK) for the RACH response message PDSCH, such as in the case of DTX by the UE, the BS retransmits the RACH response message SuccessRAR / FallbackRAR. For example, the BS may retransmit after a predefined timer for ACK / NACK monitoring expires. In some examples, if the counter of MSG B retransmissions is equal to or less than the maximum number of retransmissions configured by the network, the retransmission is performed. If the counter of MSG B retransmissions exceeds the maximum number of retransmissions configured by the NW or if the timing advance counter expires, the BS aborts the retransmission.

[0090] Fig.12 1 is a flow diagram illustrating example operations 1200 for wireless communications according to some aspects of the present disclosure. Operations 1200 may be performed, for example, by a UE (e.g., such as UE 120a in wireless communication network 100). Operations 1200 may be implemented as a processor on one or more processors (e.g., Figure 2 In addition, the UE may transmit and receive signals in operation 1200, for example, through one or more antennas (e.g., Figure 2 In some aspects, the UE's transmission and / or reception of signals may be implemented via a bus interface of one or more processors (eg, controller / processor 280) that obtain and / or output signals.

[0091] Operations 1200 may begin at 1205 by sending a RACH message to a BS during a two-step RACH procedure, the RACH message including a RACH preamble and a RACH payload.

[0092] At 1210, the UE monitors a RACH response message from the BS during the RAR window.

[0093] At 1215, the UE sends a retransmission of the RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or a DTX for the RACH response message to the BS based on whether the RACH response message carrying a successful RAR or a fallback RAR is received from the BS during the RAR window or no RACH response message is received.

[0094] In a first aspect, the UE is in a CFRA mode or a CBRA mode; and the UE is in an RRC idle state, an RRC inactive state, or an RRC connected state.

[0095] In a second aspect, alone or in combination with the first aspect, the RACH preamble comprises a PRACH carrying a RACH sequence; the RACH payload comprises a DMRS and a PUSCH, the PUSCH carrying: a MAC control element (MAC CE) or small data when the UE is in CFRA mode; and a contention resolution ID when the UE is in CBRA mode.

[0096] In a third aspect, alone or in combination with one or more of the first and second aspects, the RACH response message includes a PDCCH; the RACH response message includes a PDSCH carrying a successful RAR or a fallback RAR, the successful RAR or the fallback RAR includes at least a TAC; and the method further includes: adjusting a timing offset for uplink transmission based on the TAC.

[0097] In a fourth aspect, alone or in combination with one or more of the first to third aspects, the granularity of the TAC is based on a parameter set configured for a data or control channel in an active uplink BWP.

[0098] In a fifth aspect, alone or in combination with one or more of the first to fourth aspects, when the UE is in RRC idle or inactive state and in CBRA mode, the successful RAR further includes a contention resolution ID and a UE ID.

[0099] In a sixth aspect, alone or in combination with one or more of the first to fifth aspects, the fallback RAR further includes a RAR grant and a RAPID for retransmission.

[0100] In a seventh aspect, alone or in combination with one or more of the first to sixth aspects, when the UE is in CBRA mode, the fallback RAR further includes a TC-RNTI.

[0101] In an eighth aspect, alone or in combination with one or more of the first to seventh aspects, an ACK or a retransmission is sent within a RAR window.

[0102] In a ninth aspect, alone or in combination with one or more of the first to eighth aspects, the NACK or DTX is after the RAR window.

[0103] In a tenth aspect, alone or in combination with one or more of the first to ninth aspects, the sending step includes: sending ACK in the UCI when the UE receives a RACH response message carrying a successful RAR during the RAR window.

[0104] In an eleventh aspect, alone or in combination with one or more of the first to tenth aspects, ACK is sent on a pre-configured PUCCH resource.

[0105] In a twelfth aspect, alone or in combination with one or more of the first to eleventh aspects, PUCCH resources are pre-configured via SI, RRC or DCI.

[0106] In a thirteenth aspect, alone or in combination with one or more of the first to twelfth aspects, when the UE has new uplink data to send and does not have a valid uplink grant for the new data, ACK is multiplexed with the SR in the UCI and sent.

[0107] In a fourteenth aspect, alone or in combination with one or more of the first to thirteenth aspects, when the UE has no valid configured PUCCH resources and has a valid uplink grant for new data transmission on PUSCH, ACK is multiplexed on PUSCH.

[0108] In a fifteenth aspect, alone or in combination with one or more of the first to fourteenth aspects, the sending includes: when the UE receives a RACH response message carrying a fallback RAR during a RAR window, a PUSCH retransmitting the RACH message.

[0109] In a sixteenth aspect, alone or in combination with one or more of the first to fifteenth aspects, the PUSCH is retransmitted on resources granted in the fallback RAR.

[0110] In a seventeenth aspect, alone or in combination with one or more of the first to sixteenth aspects, sending includes: sending a NACK when the UE does not successfully decode the RACH response message during the RAR window and the UE has valid PUCCH resources.

[0111] In an eighteenth aspect, alone or in combination with one or more of the first to seventeenth aspects, the method further includes: selecting PUCCH resources based on the UE's multiple access signature.

[0112] In a nineteenth aspect, alone or in combination with one or more of the first to eighteenth aspects, not transmitting includes performing DTX when the UE does not successfully decode the RACH response message during the RAR window and the UE does not have valid PUCCH resources.

[0113] In a twentieth aspect, alone or in combination with one or more of the first to nineteenth aspects, sending ACK or NACK or performing DTX is based at least in part on an indication from a BS indicating whether HARQ feedback is requested.

[0114] In a twenty-first aspect, alone or in combination with one or more of the first to twentieth aspects, the indication is provided via 1 or 2 bits using a PUCCH resource configuration.

[0115] In a twenty-second aspect, alone or in combination with one or more of the first to twenty-first aspects, a 1-bit indication indicates whether to provide HARQ feedback; and a 2-bit indication indicates whether to provide HARQ feedback based on whether the UE has a valid TA.

[0116] In a twenty-third aspect, alone or in combination with one or more of the first to twenty-second aspects, the method further includes: in response to sending the NACK, receiving a retransmitted RACH response message from the BS.

[0117] In a twenty-fourth aspect, alone or in combination with one or more of the first to twenty-third aspects, the method further includes: receiving a retransmitted RACH response message from the BS after a duration in which the UE does not send an ACK, a NACK, or a retransmission to the BS.

[0118] Fig.13 1 is a flow chart illustrating example operations 1300 for wireless communication according to some aspects of the present disclosure. Operations 1300 may be performed, for example, by a BS (e.g., such as BS 110a in wireless communication network 100). Operations 1300 may be complementary operations to operations 1300 performed by the BS for a UE. Operations 1300 may be implemented as a processor on one or more processors (e.g., Figure 2 In addition, the communication may be performed, for example, via one or more antennas (e.g., Figure 2 The BS may transmit and receive signals in operation 1300 using antenna 234. In some aspects, the BS may transmit and / or receive signals via a bus interface of one or more processors (e.g., controller / processor 240) that obtain and / or output signals.

[0119] Operations 1300 may begin at 1305 by sending a RACH response message to a UE in a RAR window during a two-step RACH procedure, the RACH response message including a successful RAR or a fallback RAR.

[0120] At 1310, the BS receives a retransmission of the RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or nothing from the UE based on the RACH response message.

[0121] In a first aspect, the method further includes: determining that the UE is in a CFRA mode or a CBRA mode; and determining that the UE is in an RRC idle state, an RRC inactive state, or an RRC connected state.

[0122] In a second aspect, alone or in combination with the first aspect, the method further comprises monitoring a RACH message, the RACH message comprising a RACH preamble and a RACH payload, the RACH preamble comprising a PRACH carrying a RACH sequence, and the RACH payload comprising a DMRS and a PUSCH, the PUSCH carrying: a MAC control element (MAC CE) or small data when the UE is in CFRA mode; and a contention resolution ID when the UE is in CBRA mode.

[0123] In a third aspect, alone or in combination with one or more of the first and second aspects, the RACH response message includes a PDCCH; the RACH response message includes a PDSCH carrying a successful RAR or a fallback RAR, and the successful RAR or the fallback RAR includes at least a TAC.

[0124] In a fourth aspect, alone or in combination with one or more of the first to third aspects, the granularity of the TAC is based on a parameter set configured for a data or control channel in an active uplink BWP.

[0125] In a fifth aspect, alone or in combination with one or more of the first to fourth aspects, when the UE is in RRC idle or RRC inactive state and in CBRA mode, the successful RAR further includes a contention resolution ID and a UE ID.

[0126] In a sixth aspect, alone or in combination with one or more of the first to fifth aspects, the fallback RAR further includes a RAR grant and a RAPID for retransmission.

[0127] In a seventh aspect, alone or in combination with one or more of the first to sixth aspects, when the UE is in CBRA mode, the fallback RAR further includes a TC-RNTI.

[0128] In an eighth aspect, alone or in combination with one or more of the first to seventh aspects, the ACK or retransmission is received within the RAR window.

[0129] In a ninth aspect, alone or in combination with one or more of the first to eighth aspects, the NACK or DTX is after the RAR window.

[0130] In a tenth aspect, alone or in combination with one or more of the first to ninth aspects, an ACK is received in the UCI in response to a successful RAR.

[0131] In an eleventh aspect, alone or in combination with one or more of the first to tenth aspects, an ACK is received on a pre-configured PUCCH resource.

[0132] In a twelfth aspect, alone or in combination with one or more of the first to eleventh aspects, the method further includes: pre-configuring PUCCH resources via SI, RRC signaling or DCI.

[0133] In a thirteenth aspect, alone or in combination with one or more of the first to twelfth aspects, ACK is multiplexed with SR in UCI.

[0134] In a fourteenth aspect, alone or in combination with one or more of the first to thirteenth aspects, ACK is multiplexed on a PUSCH.

[0135] In a fifteenth aspect, alone or in combination with one or more of the first to fourteenth aspects, receiving includes receiving a retransmission of a PUSCH in response to a RACH message falling back on RAR.

[0136] In a sixteenth aspect, alone or in combination with one or more of the first to fifteenth aspects, retransmissions of the PUSCH are received on resources granted in the fallback RAR.

[0137] In a seventeenth aspect, alone or in combination with one or more of the first to sixteenth aspects, the method further comprises: providing an indication to the UE indicating whether HARQ feedback is requested for the RACH response message.

[0138] In an eighteenth aspect, alone or in combination with one or more of the first to seventeenth aspects, the indication is provided via 1 or 2 bits using a PUCCH resource configuration.

[0139] In a nineteenth aspect, alone or in combination with one or more of the first to eighteenth aspects, a 1-bit indication indicates whether to provide HARQ feedback; and a 2-bit indication indicates whether to provide HARQ feedback based on whether the UE has a valid TA.

[0140] In a twentieth aspect, alone or in combination with one or more of the first to nineteenth aspects, the method further comprises: in response to receiving a NACK, retransmitting a RACH response message to the UE.

[0141] In a twenty-first aspect, alone or in combination with one or more of the first to twentieth aspects, the method further comprises: in response to a duration for which the UE does not send an ACK, a NACK, or a retransmission to the BS after sending the RACH response message, retransmitting the RACH response message.

[0142] Fig.141400 is a call flow diagram illustrating example operations for a HARQ process in a two-step process 1400 according to some aspects of the present disclosure. As shown at 1402, UE 120a sends MSG A (e.g., PUCCH and PUSCH) to BS 110a. If BS 110a successfully decodes MSG A (e.g., preamble and PUSCH) at 1404a, BS 110a sends MSG B (e.g., PDCCH and PDSCH) to UE 120a and includes SuccessRAR (e.g., in PDSCH) at 1406a. Alternatively, if BS 110a does successfully decode MSG A at 1404b (e.g., does not successfully decode PUSCH), BS 110a sends MSG B (e.g., PDCCH and PDSCH) to UE 120a and includes FallbackRAR (e.g., in PDSCH) at 140ba. If UE 120a successfully decodes MSG B at 1408c, UE 120a sends an ACK at 1410a (in the case of SuccessRAR) or sends a retransmission of MSG A PUSCH at 1410b (in the case of FallbackRAR). Once BS 110a receives the ACK or the MSG A PUSCH retransmission, the two-step RACH process is considered complete at 1412. Alternatively, if MSG B is not successfully decoded at 1408d, UE 120a sends a NACK (if there are available HARQ resources) or a DTX (if there are no resources for HARQ feedback) at 1414. When BS 110a receives the NACK or the DTX, BS 110a retransmits MSG B to UE 120a at 1416. As discussed above, the sending of HARQ feedback (eg, ACK or NACK) may be further based on whether UE 120a is configured / indicated by the HARQ feedback indicator in the PUCCH resource configuration to provide HARQ feedback.

[0143] Fig.15 The invention shows that it may include operations configured to perform the techniques disclosed herein (such as Fig.12 1500 includes various components (e.g., corresponding to means-plus-function components) of the communication device 1500 and the operations shown in FIG. 1502 . The communication device 1500 includes a processing system 1502 coupled to a transceiver 1508. The transceiver 1508 is configured to send and receive signals for the communication device 1500, such as various signals as described herein, via an antenna 1510. The processing system 1502 can be configured to perform processing functions for the communication device 1500, including processing signals received and / or to be transmitted by the communication device 1500.

[0144] The processing system 1502 includes a processor 1504 coupled to a computer readable medium / memory 1512 via a bus 1506. In some aspects, the computer readable medium / memory 1512 is configured to store instructions (e.g., computer executable code) that, when executed by the processor 1504, cause the processor 1504 to perform Fig.12 , or other operations for performing the various techniques discussed herein for the HARQ process of a RACH response message in a two-step RACH process. In some aspects, according to various aspects of the present disclosure, the computer-readable medium / memory 1512 stores code 1514 for sending a RACH message during a two-step RACH process; code 1516 for monitoring a RACH response during a RAR window; and code 1518 for sending a retransmission, an ACK or NAK for a RACH response, or not sending (DTX) based on whether a RACH response with a fallback RAR, a successful RAR, or no RACH response is received during the RAR window. In some aspects, the processor 1504 has circuitry configured to implement the code stored in the computer-readable medium / memory 1512. Processor 1504 includes circuitry 1520 for sending a RACH message during a two-step RACH procedure; circuitry 1522 for monitoring a RACH response during a RAR window; and circuitry 1524 for sending a retransmission, an ACK or NAK for a RACH response, or not sending (DTX) based on whether a RACH response with a fallback RAR, a successful RAR, or no RACH response is received during the RAR window in accordance with aspects of the present disclosure.

[0145] Fig.16 The invention shows that it may include operations configured to perform the techniques disclosed herein (such as Fig.13 1600 includes various components (e.g., corresponding to means-plus-function components) of the communication device 1600 and the operations shown in FIG. 1600 . The communication device 1600 includes a processing system 1602 coupled to a transceiver 1608. The transceiver 1608 is configured to send and receive signals for the communication device 1600, such as various signals described herein, via an antenna 1610. The processing system 1602 may be configured to perform processing functions of the communication device 1600, including processing signals received and / or to be transmitted by the communication device 1600.

[0146] The processing system 1602 includes a processor 1604 coupled to a computer readable medium / memory 1612 via a bus 1606. In some aspects, the computer readable medium / memory 1612 is configured to store instructions (e.g., computer executable code) that, when executed by the processor 1604, cause the processor 1604 to perform Fig.13, or other operations for performing the various techniques discussed herein for the HARQ process of a RACH response message in a two-step RACH process. In some aspects, the computer-readable medium / memory 1612 stores, according to various aspects of the present disclosure: code 1614 for sending a RACH response message to a UE in a RAR window during a two-step RACH process, the RACH response message including a successful RAR or a fallback RAR; and code 1616 for receiving a retransmission of a RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or receiving nothing from the UE based on the RACH response message. In some aspects, the processor 1604 has circuitry configured to implement the code stored in the computer-readable medium / memory 1612. According to aspects of the present disclosure, processor 1604 includes: circuit 1618, which is used to send a RACH response message to the UE in the RAR window during the two-step RACH process, the RACH response message including a successful RAR or a fallback RAR; and circuit 1620, which receives a retransmission of the RACH message, an ACK for the RACH response message, a NACK for the RACH response message, or nothing from the UE based on the RACH response message.

[0147] The techniques described herein can be used for various wireless communication technologies, such as NR (e.g., 5GNR), 3GPP Long Term Evolution (LTE), Advanced LTE (LTE-A), Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SCFDMA), Time Division Synchronous Code Division Multiple Access (TD-SCDMA), and other networks. The terms "network" and "system" are often used interchangeably. A CDMA network can implement radio technologies such as Universal Terrestrial Radio Access (UTRA), CDMA2000, etc. Cdma2000 covers IS-2000, IS-95, and IS-856 standards. A TDMA network can implement radio technologies such as Global System for Mobile Communications (GSM). OFDMA networks may implement radio technologies such as NR (e.g., 5G RA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (WiFi), IEEE 802.16 (WiMAX), IEEE802.20, Flash-OFDMA, etc. LTE and LTE-A are versions of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and GSM are described in documents from an organization named "3rd Generation Partnership Project" (3GPP). cdma2000 and UMB are described in documents from an organization named "3rd Generation Partnership Project 2" (3GPP2). NR is an emerging wireless communication technology under development.

[0148] In 3GPP, the term "cell" can refer to the coverage area of ​​a Node B (NB) and / or a NB subsystem serving the coverage area, depending on the context in which the term is used. In NR systems, the terms "cell" and BS, next generation NodeB (gNB or gNodeB), access point (AP), distributed unit (DU), carrier or transmit receive point (TRP) can be used interchangeably. The BS can provide communication coverage for macro cells, pico cells, femto cells and / or other types of cells. A macro cell can cover a relatively large geographic area (e.g., a radius of several thousand meters) and can allow unrestricted access by UEs with service subscriptions. A pico cell can cover a relatively small geographic area and can allow unrestricted access by UEs with service subscriptions. A femto cell can cover a relatively small geographic area (e.g., a home) and can allow restricted access by UEs associated with a femto cell (e.g., UEs in a closed subscriber group (CSG), UEs of users in a home, etc.). A BS for a macro cell can be referred to as a macro BS. A BS for a pico cell can be referred to as a pico BS. A BS for a femto cell may be called a femto BS or a home BS.

[0149] UE may also be referred to as a mobile station, terminal, access terminal, subscriber unit, station, customer premises equipment (CPE), cellular phone, smart phone, personal digital assistant (PDA), wireless modem, wireless communication device, handheld device, laptop computer, cordless phone, wireless local loop (WLL) station, tablet computer, camera, gaming device, netbook, smartbook, ultrabook, appliance, medical device or medical apparatus, biometric sensor / device, wearable device such as smart watch, smart clothing, smart glasses, smart wristband, smart jewelry (e.g., smart ring, smart bracelet, etc.), entertainment device (e.g., music device, video device, satellite radio, etc.), vehicle component or sensor, smart meter / sensor, industrial manufacturing device, global positioning system device, or any other suitable device configured to communicate via wireless or wired medium. Some UEs may be considered as machine type communication (MTC) devices or evolved MTC (eMTC) devices. MTC and eMTC UEs include, for example, robots, drones, remote devices, sensors, meters, monitors, location tags, etc. that can communicate with a BS, another device (e.g., a remote device), or some other entity. A wireless node can provide, for example, connectivity to a network (e.g., a wide area network such as the Internet or a cellular network) or to a network (e.g., a wide area network such as the Internet or a cellular network) via a wired or wireless communication link. Some UEs may be considered Internet of Things (IoT) devices, which may be narrowband IoT (NB-IoT) devices.

[0150] In some examples, access to the air interface can be scheduled. The scheduling entity (e.g., BS) allocates resources for communication between some or all devices and apparatuses within its service area or cell. The scheduling entity may be responsible for scheduling, allocating, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communications, the subordinate entity utilizes resources allocated by the scheduling entity. The base station is not the only entity that can be used as a scheduling entity. In some examples, the UE may be used as a scheduling entity and may schedule resources for one or more subordinate entities (e.g., one or more other UEs), and other UEs may utilize the resources scheduled by the UE for wireless communication. In some examples, the UE may be used as a scheduling entity in a peer-to-peer (P2P) network and / or a mesh network. In the mesh network example, in addition to communicating with the scheduling entity, the UEs may also communicate directly with each other.

[0151] In some examples, two or more slave entities (e.g., UEs) can communicate with each other using sidelink signals. Real-world applications of such sidelink communications may include public safety, proximity services, UE-to-network relay, vehicle-to-vehicle (V2V) communications, Internet of Everything (IoE) communications, IoT communications, mission-critical grids, and / or various other suitable applications. In general, a sidelink signal may refer to a signal that is transmitted from one slave entity (e.g., UE 1) to another slave entity (e.g., UE2) without relaying the communication through a scheduling entity (e.g., UE or BS), even though the scheduling entity may be used for scheduling and / or control purposes. In some examples, a licensed spectrum may be used to transmit sidelink signals (unlike wireless local area networks that typically use unlicensed spectrum).

[0152] The method disclosed herein includes one or more steps or actions for implementing the method. Without departing from the scope of the claims, the method steps and / or actions can be interchangeable with each other. In other words, unless a specific order of steps or actions is specified, the order and / or use of specific steps and / or actions can be modified without departing from the scope of the claims.

[0153] As used herein, a phrase referring to "at least one" of a listed item refers to any combination of those items, including single members. As an example, "at least one of a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination with multiples of the same elements (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc or any other order of a, b, and c).

[0154] As used herein, the term "determine" encompasses a wide variety of actions. For example, "determine" may include calculating, computing, processing, deriving, investigating, searching (e.g., searching in a table, a database, or another data structure), ascertaining, etc. In addition, "determine" may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), etc. In addition, "determine" may include parsing, selecting, choosing, establishing, etc.

[0155] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be clear to those skilled in the art, and the general principles defined herein can be applied to other aspects. Therefore, the claims are not intended to be limited to the various aspects shown herein, but to the full scope consistent with the language of the claims, wherein, unless otherwise specified, references to elements in the singular form are not intended to mean "one and only one", but "one or more". Unless otherwise specifically stated, the term "some" refers to one or more. All structural and functional equivalents of elements throughout the various aspects described in this disclosure that are known or will be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be covered by the claims. In addition, nothing disclosed herein is intended to be dedicated to the public, regardless of whether such disclosure is explicitly recorded in the claims. Unless the claim element is explicitly recorded using the phrase "device for...", or in the case of a method claim, the claim element is recorded using the phrase "step for...", otherwise the claim element should not be interpreted according to the provisions of 35 U.S.C. §112 (f).

[0156] The various operations of the above method can be performed by any suitable device capable of performing the corresponding functions. These devices may include various hardware and / or software components and / or modules, including but not limited to circuits, application specific integrated circuits (ASICs) or processors. Generally, where there are operations shown in the accompanying drawings, those operations may have corresponding paired function-defining device components with similar numbers.

[0157] The various illustrative logical blocks, modules, and circuits described in conjunction with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLD), 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 in an alternative, the processor may be any commercially available processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, a combination of one or more microprocessors with a DSP core, or any other such configuration.

[0158] If the example hardware configuration is implemented in hardware, the example hardware configuration may include a processing system in a wireless node. The processing system may be implemented using a bus architecture. Depending on the specific application and overall design constraints of the processing system, the bus may include any number of interconnecting buses and bridges. The bus may link together various circuits including a processor, a machine-readable medium, and a bus interface. The bus interface may be used to connect a network adapter, etc., to the processing system via the bus. The network adapter may be used to implement the signal processing functions of the PHY layer. In the user terminal 120 (see Figure 1 ), a user interface (e.g., keyboard, display, mouse, joystick, etc.) may also be connected to the bus. The bus may also link various other circuits, such as timing sources, peripherals, voltage regulators, power management circuits, etc., which are well known in the art and will not be described further. The processor may be implemented with one or more general and / or special purpose processors. Examples include microprocessors, microcontrollers, DSP processors, and other circuits capable of executing software. Those skilled in the art will recognize how to best implement the described functionality of the processing system depending on the specific application and the overall design constraints imposed on the entire system.

[0159] If the function is implemented in software, the function can be stored on or transmitted through a computer-readable medium as one or more instructions or codes. Whether it is referred to as software, firmware, middleware, microcode, hardware description language or other terms, software should be broadly interpreted as meaning instructions, data or any combination thereof. Computer-readable media include both computer storage media and communication media, and communication media include any media that facilitates the transmission of computer programs from one place to another. The processor can be responsible for managing the bus and general processing, including executing software modules stored on a machine-readable storage medium. The computer-readable storage medium can be coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. In an alternative, the storage medium can be integrated into the processor. As an example, the machine-readable medium can include a transmission line, a carrier modulated by data, and / or a computer-readable storage medium with instructions stored thereon separated from the wireless node, all of which can be accessed by the processor through a bus interface. Alternatively or additionally, the machine-readable medium or any part thereof can be integrated into the processor, such as a cache and / or a general register file can be used in this case. As an example, examples of machine-readable storage media may include RAM (random access memory), flash memory, ROM (read only memory), PROM (programmable read only memory), EPROM (erasable programmable read only memory), EEPROM (electrically erasable programmable read only memory), registers, magnetic disks, optical disks, hard drives, or any other suitable storage media, or any combination thereof. The machine-readable medium may be embodied in a computer program product.

[0160] A software module may include a single instruction or many instructions, and may be distributed over several different code segments, between different programs, and over multiple storage media. A computer-readable medium may include multiple software modules. A software module includes instructions that cause a processing system to perform various functions when executed by a device such as a processor. A software module may include a sending module and a receiving module. Each software module may reside in a single storage device or may be distributed over multiple storage devices. For example, when a triggering event occurs, a software module may be loaded from a hard drive into a RAM. During the execution of a software module, a processor may load some of the instructions into a cache to increase access speed. One or more cache lines may then be loaded into a general register file for execution by the processor. When referring to the functions of the following software modules, it will be understood that such functions are implemented by the processor when executing instructions from the software module.

[0161] In addition, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared (IR), radio and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio and microwave are included in the definition of medium. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray Disks, where magnetic disks typically reproduce data magnetically, and optical disks reproduce data optically with lasers. Thus, in some aspects, computer-readable media may include non-transitory computer-readable media (e.g., tangible media). Additionally, for other aspects, computer-readable media may include transitory computer-readable media (e.g., signals). Combinations of the above should also be included within the scope of computer-readable media.

[0162] Thus, some aspects may include a computer program product for performing the operations presented herein. For example, such a computer program product may include a computer-readable medium having instructions stored (and / or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein, for example, for performing the operations described herein and Fig.12 and / or Fig.13 The operations shown in the instructions.

[0163] In addition, it should be appreciated that the modules and / or other appropriate devices for performing the methods and techniques described herein can be downloaded and / or otherwise obtained by a user terminal and / or base station where applicable. For example, such a device can be coupled to a server to facilitate the transmission of a device for performing the methods described herein. Alternatively, the various methods described herein can be provided via a storage device (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or a floppy disk, etc.), so that the user terminal and / or base station can obtain the various methods when the storage device is coupled or provided to the device. In addition, any other suitable technology for providing the methods and techniques described herein to a device can be used.

[0164] It is to be understood that the claims are not limited to the precise configuration and components described above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.

Claims

1. A method for wireless communication by a user equipment (UE), the method comprising: transmitting a random access channel (RACH) message during a two-step RACH procedure, the RACH message comprising a RACH preamble and a RACH payload; monitoring a RACH response message during a random access response (RAR) window; receiving a physical downlink control channel (PDCCH) of the RACH response message, wherein the PDCCH of the RACH response message includes a field indicating whether hybrid automatic repeat request (HARQ) feedback is requested for a physical downlink shared channel (PDSCH) of the RACH response message; and one of: If the UE successfully decodes the PDSCH of the RACH response message during the RAR window: If during the RAR window, the PDSCH of the RACH response message carries a successful RAR, and a field in the PDCCH of the RACH response message indicates that HARQ feedback is requested for the PDSCH of the RACH response message, sending an acknowledgment ACK for the RACH response message; or transmitting a retransmission of the RACH payload of the RACH message on a physical uplink shared channel (PUSCH) if the PDSCH of the RACH response message carries a fallback RAR; and If the UE fails to successfully decode the PDSCH of the RACH response message during the RAR window: If a field in the PDCCH of the RACH response message indicates that the PDSCH for the RACH response message requests HARQ feedback, sending a negative acknowledgement (NACK) for the RACH response message; or If a field in the PDCCH of the RACH response message indicates that HARQ feedback is not requested for the PDSCH of the RACH response message, discontinuous transmission (DTX) is performed.

2. The method according to claim 1, wherein: The ACK is sent on a physical uplink control channel (PUCCH) resource.

3. The method according to claim 2, wherein: The PUCCH resource is provided in the RACH response message.

4. The method according to claim 2, wherein: The PUCCH resources are preconfigured via system information (SI), radio resource control (RRC) signaling or downlink control information (DCI).

5. The method of claim 2, further comprising selecting the PUCCH resource based on a multiple access signature of the UE.

6. The method according to claim 1, wherein: The PUSCH is on resources granted in the RACH response message carrying the fallback RAR.

7. The method according to claim 1, wherein: If the UE does not have valid resources for providing HARQ feedback, DTX is further performed.

8. The method according to claim 1, wherein: The NACK is sent if the UE has valid resources for providing HARQ feedback.

9. The method according to claim 1, wherein: The ACK is multiplexed with a scheduling request (SR) in uplink control information (UCI) when the UE has new uplink data to send and does not have a valid uplink grant for the new uplink data.

10. The method according to claim 1, further comprising receiving a retransmitted RACH response message in response to sending the NACK or the DTX, wherein: The retransmitted RACH response message includes a Radio Network Temporary Identifier (RNTI).

11. The method according to claim 1, wherein: The ACK is multiplexed on the PUSCH when the UE does not have validly configured physical uplink control channel (PUCCH) resources and has a valid uplink grant for new data transmission on the PUSCH.

12. The method of claim 1, wherein: The RACH response message includes at least a timing advance command (TAC); and The method also includes adjusting a timing offset of an uplink transmission based on the TAC.

13. The method according to claim 12, wherein: The granularity of the TAC is based on the parameter set configured for the data channel or control channel in the active uplink bandwidth part (BWP).

14. The method according to claim 1, wherein: When the UE is in a radio resource control (RRC) idle or inactive state and in a contention based random access (CBRA) mode, the RACH response message further includes a contention resolution identifier (ID) and a UE ID.

15. The method according to claim 1, wherein: The RACH response message with fallback RAR also includes a RACH preamble identifier (RAPID).

16. The method according to claim 1, wherein: When the UE is in contention based random access (CBRA) mode, the RACH response message with fallback RAR also includes a temporary cell radio network temporary identifier (TC-RNTI).

17. The method according to claim 1, wherein: A field indicating whether HARQ feedback is requested for the PDSCH of the RACH response message is provided via 1 bit or 2 bits in the PDCCH of the RACH response message in a physical uplink control channel (PUCCH) resource configuration further including a PUCCH resource set indicator field.

18. The method of claim 17, wherein: The field is 1 bit and indicates whether the UE provides NACK feedback regardless of whether the UE has a valid timing advance (TA), or whether the UE does not provide NACK feedback regardless of whether the UE has a valid TA; or The field is 2 bits and indicates whether NACK feedback is provided regardless of whether the UE has a valid TA, whether NACK feedback is provided only when the UE has a valid TA, whether HARQ feedback is not provided regardless of whether the UE has a valid TA, or whether NACK feedback is not provided regardless of whether the UE has a valid TA.

19. The method of claim 1, wherein: The UE is in contention-free random access (CFRA) mode or contention-based random access (CBRA) mode; and The UE is in a radio resource control (RRC) idle, inactive or connected state.

20. The method of claim 1, wherein: The RACH preamble includes a physical random access channel (PRACH) carrying a RACH sequence; The RACH payload includes a demodulation reference signal (DMRS) and a physical uplink shared channel (PUSCH), carrying: Medium Access Control (MAC) control elements or small data when the UE is in Contention Free Random Access (CFRA) mode; and Contention Resolution Identifier (ID) when the UE is in Contention Based Random Access (CBRA) mode.

21. An apparatus for wireless communication, the apparatus comprising: at least one processor; as well as a memory coupled to the at least one processor, the memory comprising code executable by the at least one processor to individually or collectively cause the apparatus to: transmitting a random access channel (RACH) message during a two-step RACH procedure, the RACH message comprising a RACH preamble and a RACH payload; monitoring a RACH response message during a random access response (RAR) window; receiving a physical downlink control channel (PDCCH) of the RACH response message, wherein the PDCCH of the RACH response message includes a field indicating whether hybrid automatic repeat request (HARQ) feedback is requested for a physical downlink shared channel (PDSCH) of the RACH response message; If the apparatus successfully decodes the PDSCH of the RACH response message during the RAR window: If the RACH response message carries a successful RAR, and a field in the PDCCH of the RACH response message indicates that the PDSCH requests HARQ feedback for the RACH response message, sending an acknowledgement (ACK) for the RACH response message; and transmitting a retransmission of the RACH payload of the RACH message on a physical uplink shared channel (PUSCH) if the RACH response message carries the fallback RAR during the RAR window; and If the apparatus successfully decodes the PDSCH of the RACH response message during the RAR window: If a field in the PDCCH of the RACH response message indicates that the PDSCH requests HARQ feedback for the RACH response message, sending a negative acknowledgement (NACK) for the RACH response message; and If a field in the PDCCH of the RACH response message indicates that HARQ feedback is not requested for the PDSCH of the RACH response message, discontinuous transmission (DTX) is performed.

22. A non-transitory computer-readable medium having stored thereon computer-executable code for wireless communication by a user equipment (UE), the computer-executable code comprising: code for transmitting a random access channel (RACH) message during a two-step RACH procedure, the RACH message comprising a RACH preamble and a RACH payload; Code for monitoring a RACH response message during a random access response (RAR) window; code for receiving a physical downlink control channel (PDCCH) of the RACH response message, wherein the PDCCH of the RACH response message includes a field indicating whether hybrid automatic repeat request (HARQ) feedback is requested for a physical downlink shared channel (PDSCH) of the RACH response message; code for sending an acknowledgment (ACK) of the RACH response message if the UE successfully decodes the PDSCH of the RACH response message carrying a successful RAR during the RAR window and a field in the PDCCH of the RACH response message indicates that HARQ feedback is requested for the PDSCH of the RACH response message; code for sending a negative acknowledgement (NACK) for the RACH response message if the UE does not successfully decode the PDSCH of the RACH response message during the RAR window and a field in the PDCCH of the RACH response message indicates that HARQ feedback is not requested for the PDSCH of the RACH response message; code for performing discontinuous transmission (DTX) if the UE does not successfully decode the PDSCH of the RACH response message during the RAR window and a field in the PDCCH of the RACH response message indicates that HARQ feedback is not requested for the PDSCH of the RACH response message; and Code for sending a retransmission of the RACH payload of the RACH message on a physical uplink shared channel (PUSCH) if the UE successfully decodes the PDSCH of the RACH response message carrying a fallback RAR during the RAR window.

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