Random access procedure

Abstract

Some of the techniques and apparatuses described herein provide an indication of the result of decoding a two-step random access channel (RACH) message and an action to be performed by a user equipment (UE). For example, some of the techniques and apparatuses described herein may use a UE contention resolution identity approach to provide the indication, where the UE's contention resolution identity may be provided in a random access response. Some of the techniques and apparatuses described herein may use a fallback indicator indicating the result of decoding and / or the action to be performed. Some of the techniques and apparatuses described herein may use a random access response (RAR) subheader that selectively omits a random access preamble identifier based at least in part on the result of decoding and / or the action to be performed.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to Patent Cooperation Treaty (PCT) Patent Application No. PCT / CN2019 / 082238, filed on April 11, 2019, and PCT Patent Application No. PCT / CN2019 / 085126, filed on April 30, 2019. The titles of these two applications are "INDICATION FOR TWO - STEP RACH FALLBACK TO FOUR - STEP RACH" and both are hereby incorporated by reference in their entireties.

[0003] Background

[0004] Field

[0005] Aspects of the present disclosure generally relate to wireless communication and techniques and devices for indication of fallback from two - step random access channel (RACH) to four - step RACH. Background Art

[0006] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasting. A typical wireless communication system may employ a multiple access technology capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple access technologies include 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, time - division synchronous code division multiple access (TD - SCDMA) systems, and long - term evolution (LTE). LTE / Advanced LTE is an enhanced set of the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by the 3rd Generation Partnership Project (3GPP).

[0007] A wireless communication network may include several base stations (BSs) capable of supporting communication of several user equipments (UEs). The UEs may communicate with the BSs via a downlink and an uplink. The downlink (or forward link) refers to the communication link from the BS to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the BS. As will be described in more detail herein, the BS may be referred to as a B - node, gNB, access point (AP), radio head, transmission reception point (TRP), 5G BS, 5G B - node, etc.

[0008] The above multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless communication devices to communicate at the urban, national, regional, and even global levels. 5G (which may also be referred to as New Radio (NR)) is an enhanced set of the LTE mobile standard promulgated by the Third Generation Partnership Project (3GPP). 5G is designed to better support mobile broadband Internet access by improving spectral efficiency, reducing costs, improving services, leveraging new spectrums, and better integrating with other open standards that use OFDM with cyclic prefix (CP) (CP-OFDM) on the downlink (DL), CP-OFDM and / or SC-FDM (e.g., also referred to as Discrete Fourier Transform Spread OFDM (DFT-s-OFDM)) on the uplink (UL), and support beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation. However, as the demand for mobile broadband access continues to grow, there is a need for further improvement in LTE and 5G technologies. Preferably, these improvements should be applicable to other multiple access technologies and the telecommunication standards that employ these technologies.

[0009] Overview

[0010] A UE can perform a random access procedure (e.g., a random access channel (RACH) procedure, a physical RACH (PRACH) procedure, etc.) to access the network via a BS. In some cases, the UE can perform a four-step RACH procedure, which involves a first uplink random access message (e.g., message 1 or Msg1) for providing a preamble of the UE, a second downlink random access response to the first uplink random access message (e.g., message 2 or Msg2), a third uplink random access message with a payload (e.g., message 3 or Msg3), and a fourth downlink random access message (e.g., message 4 or Msg4). In some cases, the UE can perform a two-step RACH procedure, where message 1 and message 3 are combined into a single uplink message (message A or MsgA) and message 2 and message 4 are combined into a single downlink message (e.g., message B or MsgB). In some cases, the BS can successfully receive the preamble of the RACH message and may fail to receive the payload of the RACH message (e.g., message A). In this case, the UE can fallback to a four-step RACH approach or can reattempt the random access. In other cases, the BS can successfully receive the payload and the preamble. In this case, the RACH procedure can continue without interruption. A messaging system that can be used by the BS to signal the result of decoding the RACH message (e.g., the preamble and the payload are successfully received, the preamble is successfully received and the payload is not successfully received, the preamble and the payload are not successfully received, etc.) and the actions to be performed by the UE (e.g., fallback to a four-step RACH procedure, reattempt a two-step RACH procedure or a four-step RACH procedure, retransmit the payload of the RACH message, etc.) can be useful.

[0011] Some of the techniques and apparatuses described herein provide an indication of the result of decoding a two-step RACH message and an action to be performed by a UE. For example, some of the techniques and apparatuses described herein may use a UE contention resolution identity approach to provide the indication, where the UE's contention resolution identity may be provided in a random access response. Some of the techniques and apparatuses described herein may use a fallback indicator that indicates the result of decoding and / or the action to be performed. Some of the techniques and apparatuses described herein may use a random access response (RAR) sub-header that selectively omits a random access preamble identifier based at least in part on the result of decoding and / or the action to be performed. In this way, the BS may signal to the UE the result of decoding and / or the action to be performed. The UE may perform the action based on the indication (e.g., fallback to a four-step RACH procedure, retry RACH, etc.). Thereby, the granularity of the action to be signaled in conjunction with the two-step RACH procedure may be improved, thereby improving network performance and the reliability of the two-step RACH procedure. In addition, the techniques and apparatuses described herein provide a messaging structure for indicating RACH results to a plurality of UEs in a media access control (MAC) message to the plurality of UEs, e.g., using contention resolution information or other information associated with the plurality of UEs. For example, if a first UE receives a MAC message having contention resolution information for a second UE, the first UE may perform an action based at least in part on the information in the MAC message. If a second UE receives a MAC message having contention resolution information for the second UE, the second UE may determine that the second UE's RACH message has been successfully received. These MAC messages may be used to provide an indication of the result of decoding and / or an action to a plurality of UEs (e.g., four UEs, eight UEs, etc.). Relative to per-UE indication of whether the RACH procedure was successful, combining such feedback to a plurality of UEs in association with an indication of the action to be performed may improve the utilization of network resources and reduce the use of UE computing resources.

[0012] In this way, the amount of monitoring of scheduling information to be performed by the UE is reduced, thereby saving the UE's computing resources and power. In addition, the communication and computing resource usage of the UE is reduced by providing contention resolution information in the random access response as compared to providing contention resolution information separately from the random access response. In addition, the decoding complexity and decoding error probability of the indication are reduced by providing contention resolution information in the random access response as compared to providing contention resolution information separately from the random access response.

[0013] In one aspect of the present disclosure, a method, a user equipment (UE), a base station, an apparatus, and a computer program product are provided.

[0014] In some aspects, a wireless communication method performed by a UE may include: attempting random access by transmitting a random access message associated with a two-step random access procedure; receiving an indication indicating that the preamble of the random access message and the payload of the random access message have been successfully received or that the payload has not been successfully received; and selectively performing one of the following operations: completing the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or reattempting random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received.

[0015] In some aspects, the UE may include a memory and one or more processors operatively coupled to the memory. The memory and the one or more processors may be configured to: attempt random access by transmitting a random access message associated with a two-step random access procedure; receive an indication indicating that the preamble of the random access message and the payload of the random access message have been successfully received or that the payload has not been successfully received; and selectively perform one of the following operations: completing the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or reattempting random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received.

[0016] In some aspects, the device may include: means for attempting random access by transmitting a random access message associated with a two-step random access procedure; means for receiving an indication indicating that the preamble of the random access message and the payload of the random access message have been successfully received or that the payload has not been successfully received; and means for selectively performing one of the following operations: completing the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or reattempting random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received.

[0017] In some aspects, a computer program product may include a non-transitory computer-readable medium storing one or more instructions. The one or more instructions, when executed by one or more processors of a UE, may cause the one or more processors to: attempt random access by transmitting a random access message associated with a two-step random access procedure; receive an indication indicating that a preamble of the random access message and a payload of the random access message have been successfully received or that the payload has not been successfully received; and selectively perform the following operations: complete the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or re-attempt random access or perform a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received.

[0018] In some aspects, a wireless communication method performed by a base station may include: receiving, from a UE attempting random access, a random access message associated with a two-step random access procedure; transmitting an indication indicating that a preamble of the random access message and a payload of the random access message have been successfully received or that the payload has not been successfully received; and selectively perform the following operations: complete the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or receive messaging associated with the UE re-attempting random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received.

[0019] In some aspects, the base station may include a memory and one or more processors operatively coupled to the memory. The memory and the one or more processors may be configured to: receive, from a UE attempting random access, a random access message associated with a two-step random access procedure; transmit an indication indicating that a preamble of the random access message and a payload of the random access message have been successfully received or that the payload has not been successfully received; and selectively perform the following operations: complete the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or receive messaging associated with the UE re-attempting random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received.

[0020] In some aspects, the apparatus may include means for receiving, from a UE attempting random access, a random access message associated with a two-step random access procedure; means for transmitting an indication that a preamble of the random access message and a payload of the random access message have been successfully received or that the payload has not been successfully received; and means for selectively performing: completing the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or receiving messaging associated with the UE reattempting random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received.

[0021] In some aspects, a computer program product may include a non-transitory computer-readable medium storing one or more instructions. The one or more instructions, when executed by one or more processors of a base station, may cause the one or more processors to: receive, from a UE attempting random access, a random access message associated with a two-step random access procedure; transmit an indication that a preamble of the random access message and a payload of the random access message have been successfully received or that the payload has not been successfully received; and select: completing the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or receiving messaging associated with the UE reattempting random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received.

[0022] Aspects generally include methods, apparatus, systems, computer program products, non-transitory computer-readable media, user equipment, base stations, wireless communication devices, and processing systems substantially as described herein with reference to the figures and as illustrated in the figures.

[0023] The foregoing has outlined rather broadly the features and technical advantages of examples in accordance with the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter. The disclosed concepts and specific examples may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the present disclosure. Such equivalent constructions do not depart from the scope of the appended claims. The characteristics of the concepts disclosed herein, both as to their organization and operation methods, as well as the associated advantages, will be better understood when considered in conjunction with the following description taken in connection with the accompanying figures. Each of the figures is provided for the purpose of illustration and description and is not intended to define a limitation of the claims. Brief Description of the Drawings

[0025] Figure 1 is a diagram illustrating an example of a wireless communication network.

[0026] Figure 2 It is a diagram illustrating an example where a base station and a UE are in communication in a wireless communication network.

[0027] Figure 3 It is a diagram illustrating an example of an indication for a two-step random access backoff procedure.

[0028] Figure 4 It is a diagram illustrating an example of a media access control message passing structure for an indication as described in conjunction with Figure 3 description.

[0029] Figure 5 It is a diagram illustrating an example of a media access control message passing structure for multiple UEs.

[0030] Figure 6 It is a diagram illustrating an example of a media access control message passing structure for an indication as described in conjunction with Figure 3 description.

[0031] Figure 7 It is a diagram illustrating an example of a media access control message passing structure for multiple UEs.

[0032] Figure 8 It is a diagram illustrating an example of a media access control message passing structure for an indication as described in conjunction with Figure 3 description.

[0033] Figure 9 It is a diagram illustrating an example of a media access control message passing structure for multiple UEs.

[0034] Figure 10 It is a flowchart of a wireless communication method.

[0035] Figure 11 It is a conceptual data flow diagram illustrating the data flow between different modules / devices / components in an example device.

[0036] Figure 12 It is a diagram illustrating an example of the hardware implementation of equipment employing a processing system.

[0037] Figure 13 It is a flowchart of a wireless communication method.

[0038] Figure 14 It is a conceptual data flow diagram illustrating the data flow between different modules / devices / components in an example device.

[0039] Figure 15 It is a diagram illustrating an example of the hardware implementation of a device employing a processing system.

[0040] Figure 16It is a diagram illustrating an example of a media access control message transfer structure for an idle mode or inactive mode UE associated with a successful random access message.

[0041] Figure 17A And 17B It is a diagram illustrating an example of a media access control message transfer structure for a UE associated with a random access message whose payload has not been successfully received and an example of a media access control sub-header for a UE for which any part of the random access message from it has not been successfully received.

[0042] Figure 18 It is a diagram illustrating an example of a media access control message transfer structure for a connected mode UE associated with a random access message whose payload has been successfully received.

[0043] Figure 19 It is a diagram illustrating an example of a media access control message payload for a connected mode UE associated with a successful random access message.

[0044] Figure 20 It is a diagram illustrating an example of a media access control message transfer structure for multiple UEs.

[0045] Detailed Description

[0046] The following detailed description set forth in conjunction with the accompanying drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form to avoid obscuring such concepts.

[0047] Certain aspects of a telecommunications system will now be presented with reference to various devices and methods. These devices and methods will be described in the following detailed description and illustrated in the drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as "elements"). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0048] As an example, an element, or any portion of an element, or any combination of elements can be implemented with a "processing system" that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functions described throughout this disclosure. One or more processors in the processing system can execute software. Software should be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to in software, firmware, middleware, microcode, hardware description language, or otherwise.

[0049] Accordingly, in one or more example embodiments, the described functionality can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions can be stored or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media can be any available media that can be accessed by a computer. By way of example and not limitation, such computer-readable media can include random access memory (RAM), read only memory (ROM), electrically erasable programmable ROM (EEPROM), compact disc ROM (CD-ROM) or other optical disc storage, magnetic disk storage or other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other media that can be used to store computer-executable code in the form of instructions or data structures that can be accessed by a computer.

[0050] It should be noted that while aspects may be described herein using terms typically associated with 3G and / or 4G wireless technologies, aspects of the present disclosure can be applied in communication systems based on other generations, such as 5G and later communication systems.

[0051] Figure 1FIG. 0 is a diagram illustrating a wireless network 100 in which aspects of the present disclosure may be practiced. The wireless network 100 may be an LTE network or some other wireless network, such as a 5G network. The wireless network 100 may include several BSs 110 (shown as BS110a, BS 110b, BS 110c, and BS 110d) and other network entities. A BS is an entity that communicates with user equipment (UE) and may also be referred to as a base station, 5G BS, Node B, gNB, 5G NB, access point, transmission reception point (TRP), etc. Each BS may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” may refer to the coverage area of a BS and / or the BS subsystem serving that coverage area, depending on the context in which the term is used.

[0052] A BS may provide communication coverage for a macro cell, a pico cell, a femto cell, and / or another type of cell. A macro cell may cover a relatively large geographic area (e.g., with a radius of several kilometers) and may allow unrestricted access by UEs having a service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs having a service subscription. A femto cell may cover a relatively small geographic area (e.g., a residence) and may allow restricted access by UEs associated with the femto cell (e.g., UEs in a closed subscriber group (CSG)). A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS. In the example shown in Figure 1 FIG. 5, BS 110a may be a macro BS for macro cell 102a, BS 110b may be a pico BS for pico cell 102b, and BS 110c may be a femto BS for femto cell 102c. A BS may support one or more (e.g., three) cells. The terms “eNB,” “base station,” “5G BS,” “gNB,” “TRP,” “AP,” “Node B,” “5G NB,” and “cell” may be used interchangeably herein.

[0053] In some examples, a cell may not have to be stationary, and the geographic area of a cell may move according to the location of a mobile BS. In some examples, BSs may be interconnected with each other and / or with one or more other BSs or network nodes (not shown) in the wireless network 100 via various types of backhaul interfaces, such as direct physical connections, virtual networks, and / or the like using any suitable transport network.

[0054] The wireless network 100 may also include a relay station. A relay station is an entity that can receive a transmission of data from an upstream station (e.g., a BS or a UE) and send the transmission of the data to a downstream station (e.g., a UE or a BS). A relay station can also be a UE that can relay transmissions for other UEs. In Figure 1 the example shown in

[0055] the relay station 110d may communicate with the macro BS 110a and the UE 120d to facilitate communication between the BS 110a and the UE 120d. A relay station may also be referred to as a relay BS, a relay base station, a relay, etc.

[0056] The network controller 130 may be coupled to the set of BSs and may provide coordination and control of these BSs. The network controller 130 may communicate with each BS via a backhaul. These BSs may also communicate with each other directly or indirectly, e.g., via a wireless or wired backhaul.

[0057] The UEs 120 (e.g., 120a, 120b, 120c) may be dispersed throughout the wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as an access terminal, a terminal, a mobile station, a subscriber unit, a station, etc. A UE may be a cellular phone (e.g., a smart phone), a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet, a camera, a gaming device, a netbook, a smartbook, a superbook, a medical device or equipment, a biometric sensor / device, a wearable device (a smart watch, smart clothing, smart glasses, a smart wristband, smart jewelry (e.g., a smart ring, a smart bracelet)), an entertainment device (e.g., a music or video device, or a satellite radio), a vehicle component or sensor, a smart meter / sensor, an industrial manufacturing equipment, a global positioning system device, or any other suitable device configured to communicate via a wireless or wired medium.

[0058] Some UEs may be considered as Machine Type Communication (MTC) UEs, or evolved or enhanced Machine Type Communication (eMTC) UEs. MTC UEs and eMTC UEs include, for example, robots, drones, remote devices, sensors, meters, monitors, location tags, etc., which may communicate with a base station, another device (e.g., a remote device), or some other entity. A wireless node may provide connectivity to a network (e.g., a wide area network such as the Internet or a cellular network) or provide connectivity to the network, for example, via a wired or wireless communication link. Some UEs may be considered as Internet of Things (IoT) devices, and / or may be implemented as NarrowBand IoT (NB-IoT) devices. Some UEs may be considered as Customer Premises Equipment (CPE). The UE 120 may be included inside a housing that houses components of the UE 120, such as a processor component, a memory component, and so on.

[0059] Generally, any number of wireless networks may be deployed in a given geographical area. Each wireless network may support a specific RAT and may operate on one or more frequencies. The RAT may also be referred to as a radio technology, an air interface, etc. The frequency may also be referred to as a carrier, a frequency channel, etc. Each frequency may support a single RAT in a given geographical area to avoid interference between wireless networks of different RATs. In some cases, a 5G RAT network may be deployed.

[0060] In some examples, access to the air interface may be scheduled, where a scheduling entity (e.g., a base station) allocates resources for communication among some or all of the devices and equipment within the service area or cell of the scheduling entity. Within this disclosure, as discussed further below, the scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. That is, for the scheduled communication, the subordinate entities utilize the resources allocated by the scheduling entity. In some cases, a UE may access the air interface by performing a random access procedure (such as a Physical Random Access (PRACH) procedure, etc.). For example, the random access procedure may include a two-step random access procedure or a four-step random access procedure. "RACH procedure" may be used interchangeably with "random access procedure" herein.

[0061] A base station is not the only entity that can act as a scheduling entity. That is, in some examples, a UE can act as a scheduling entity, thus scheduling resources for one or more subordinate entities (e.g., one or more other UEs). In these examples, the UE is acting as a scheduling entity, and the other UEs utilize the resources scheduled by the UE for wireless communication. A UE may act as a scheduling entity in a peer-to-peer (P2P) network and / or in a mesh network. In the mesh network example, the UEs may optionally communicate directly with each other in addition to communicating with the scheduling entity.

[0062] Thus, in a wireless communication network having scheduled access to time-frequency resources and having a cellular configuration, a P2P configuration, and a mesh configuration, a scheduling entity and one or more subordinate entities may utilize the scheduled resources to communicate.

[0063] As indicated above, Figure 1 is provided merely as an example. Other examples may be different from the example regarding Figure 1 described.

[0064] Figure 2 illustrates a block diagram 200 of the design of a base station 110 and a UE 120 that can be one of the base stations and one of the UEs in Figure 1 respectively. The base station 110 may be equipped with T antennas 234a to 234t, while the UE 120 may be equipped with R antennas 252a to 252r, where generally T≥1 and R≥1.

[0065] At the base station 110, a transmit processor 220 may receive data for one or more UEs from a data source 212, may select one or more modulation and coding schemes (MCSs) for a UE at least in part based on a channel quality indicator (CQI) received from each UE, process (e.g., encode and modulate) the data for the UE at least in part based on the MCS selected for each UE, and provide data symbols for all UEs. The transmit processor 220 may also process system information (e.g., for semi-static resource partitioning information (SRPI), etc.) and control information (e.g., CQI requests, grants, upper layer signaling, etc.), and provide overhead symbols and control symbols. The transmit processor 220 may also generate reference symbols for reference signals (e.g., cell-specific reference signals) and synchronization signals (e.g., a primary synchronization signal (PSS) and a secondary synchronization signal (SSS)). A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on the data symbols, control symbols, overhead symbols, and / or reference symbols when applicable, and may provide T output symbol streams to T modulators (MOD) 232a to 232t. Each modulator 232 may process its respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 232 may further process (e.g., convert to analog, amplify, filter, and up-convert) the output sample stream to obtain a downlink signal. The T downlink signals from the modulators 232a to 232t may be transmitted via the T antennas 234a to 234t, respectively. According to various aspects described in more detail below, position coding may be utilized to generate synchronization signals to convey additional information.

[0066] At the UE 120, antennas 252a through 252r may receive downlink signals from the base station 110 and / or other base stations and may provide the received signals to demodulators (DEMOD) 254a through 254r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, down-convert, and digitize) the received signal to obtain input samples. Each demodulator 254 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. The MIMO detector 256 may obtain the received symbols from all R demodulators 254a through 254r, perform MIMO detection on the received symbols when applicable, and provide detected symbols. The receive (RX) processor 258 may process (e.g., demodulate and decode) the detected symbols, provide the decoded data for the UE 120 to the data sink 260, and provide the decoded control information and system information to the controller / processor 280. The channel processor may determine the reference signal received power (RSRP), received signal strength indicator (RSSI), reference signal received quality (RSRQ), channel quality indicator (CQI), etc.

[0067] On the uplink, at the UE 120, the transmit processor 264 may receive and process data from the data source 262 and control information from the controller / processor 280 (e.g., for reports including RSRP, RSSI, RSRQ, CQI, etc.). The transmit processor 264 may also generate reference symbols for one or more reference signals. The symbols from the transmit processor 264 may be precoded by the TX MIMO processor 266 when applicable, further processed by modulators 254a through 254r (e.g., for DFT-s-OFDM, CP-OFDM, etc.), and transmitted to the base station 110. At the base station 110, the uplink signals from the UE 120 and other UEs may be received by the antenna 234, processed by the demodulator 232, detected by the MIMO detector 236 when applicable, and further processed by the receive processor 238 to obtain the decoded data and control information transmitted by the UE 120. The receive processor 238 may provide the decoded data to the data sink 239 and provide the decoded control information to the controller / processor 240. The base station 110 may include a communication unit 244 and communicate with the network controller 130 via the communication unit 244. The network controller 130 may include a communication unit 294, a controller / processor 290, and a memory 292.

[0068] The controller / processor 240 of the base station 110, the controller / processor 280 of the UE 120, and / or Figure 2Any other component(s) of may perform one or more techniques associated with an indication for a two-step RACH fallback to a four-step RACH, as described in more detail elsewhere herein. For example, the controller / processor 240 of the base station 110, the controller / processor 280 of the UE 120, and / or Figure 2 Any other component(s) of may execute or direct, for example Figure 10 Method 1000 of Figure 13 Method 1300 of, and / or operations of other processes as described herein. The memories 242 and 282 may store data and program codes for use by the BS 110 and the UE 120, respectively. The scheduler 246 may schedule the UE for data transmission on the downlink and / or uplink.

[0069] As indicated above, Figure 2 is provided merely as an example. Other examples may be different from the example described with respect to Figure 2

[0070] Figure 3 is a diagram illustrating example 300 of an indication for a two-step random access fallback procedure. As shown, example 300 includes the UE 120 and the BS 110.

[0071] As in Figure 3 and as indicated by reference numeral 310, the UE 120 may transmit a RACH message (Msg) A to the BS 110. For example, the UE 120 may transmit the RACH message A as part of a random access procedure, an initial access procedure, etc. The RACH message A may be associated with a two-step RACH procedure. As further shown, the RACH message A may include a preamble and a payload. The preamble may be encoded at least in part based on a random access radio network temporary identifier and / or may identify the UE 120. The payload may include a physical uplink shared channel (PUSCH) and may include contention information for the UE 120. The BS 110 may perform contention resolution based at least in part on the RACH message A, as described in more detail below.

[0072] ​As indicated by reference numeral 320, the BS 110 may attempt to receive a RACH message A. For example, the BS 110 may attempt to receive a preamble and a payload. Successfully receiving, decoding, and processing the preamble may be referred to herein as successfully receiving the preamble, and successfully receiving, decoding, and processing the payload may be referred to herein as successfully receiving the payload. The BS 110 may be more likely to successfully receive the preamble than the payload because the preamble is shorter and simpler to decode. Thus, three results of decoding may be expected: a first case, referred to as case A, in which the preamble and the payload are detected and successfully received by the BS 110; a second case, referred to as case B, in which the preamble is successfully received but the payload is not successfully received; and a third case, referred to as case C, in which neither the preamble nor the payload is successfully received. For case C, a MAC subheader including a backoff indicator may be used to indicate the result in a RACH message B. The techniques and devices described herein provide signaling for distinguishing between case A and case B and indicating whether the UE should reattempt the RACH procedure, fallback to a four-step RACH procedure, or continue random access due to the preamble and payload being successfully received.

[0073] As indicated by reference numeral 330, the BS 110 may provide an indication as to whether the preamble and the payload have been successfully received (e.g., case A) or the payload has not been successfully received (e.g., case B). The indication may indicate (e.g., implicitly or explicitly) whether the UE 120 is to complete a two-step random access procedure, reattempt the random access procedure, or fallback to a four-step RACH procedure. The specific structure of the indication is described in more detail in Figure 3-9 more detail. In some aspects, the indication may be provided in a random access response (RAR) (such as a RACH message B) or provided in association with the random access response, as described in more detail in Figure 3-9 more detail. In some aspects, the indication may be provided in a RACH message 2 (e.g., a RACH message 2 associated with a four-step RACH procedure), as also described in more detail in Figure 3-9 more detail.

[0074] As indicated by reference numeral 340, the UE 120 may selectively re-attempt the RACH procedure or fallback to a four-step RACH procedure (e.g., when the indication is associated with Scenario B), or may complete the RACH procedure (e.g., when the indication is associated with Scenario A). As used herein, re-attempting the RACH procedure may refer to selecting another RACH preamble and transmitting another RACH message (e.g., RACH message A associated with a two-step RACH procedure or RACH message 1 associated with a four-step RACH procedure). When the UE 120 uses a two-step RACH procedure to re-attempt random access, the UE 120 may retransmit the payload in RACH message A. When the UE 120 falls back to a four-step RACH procedure, the UE 120 may retransmit the payload in RACH message 3. In some aspects, the UE 120 may re-attempt random access at least in part based on determining that the indication indicates that the payload has not been successfully received and / or that the contention of the UE 120 with another UE has been resolved in favor of the other UE 120. When the UE 120 falls back to a four-step RACH procedure, the UE 120 may use RACH message 3 of the four-step RACH procedure to transmit the payload, thereby providing a second attempt to transmit the payload without retransmitting the preamble. When the UE 120 completes the RACH procedure, the UE 120 may receive radio resource control (RRC) information, may configure the RRC connection at least in part based on the indication, and so on.

[0075] As indicated above, Figure 3 is provided as an example. Other examples may be different from the example regarding Figure 3 described.

[0076] Figure 4 is an illustration of an example 400 of a media access control message passing structure for an indication as described in connection with Figure 3 The indication described in connection with example 400 may be included in a RAR from the BS 110 to the UE 120. As shown, example 400 shows a MAC payload 410 and a corresponding MAC sub-header 420. The indication may be provided using a UE contention resolution identity indicated by reference numeral 430. For example, the UE contention resolution identity may identify the UE whose payload has been successfully received by the BS 110. For example, the contention resolution identity may identify the UE identifier corresponding to the UE 120. The length of the RAR may be indicated by a value L indicated by reference numeral 440 in the MAC sub-header 420.

[0077] If the BS 110 successfully receives the preamble and payload from the UE 120, the BS 110 may use the structure shown in Example 400 to transmit an indication as the RACH message B. If the preamble is successfully received and the payload is not successfully received, the BS 110 may transmit a RACH message 2 (e.g., a RACH message 2 associated with a four-step RACH procedure), which may be multiplexed in a MAC packet data unit (PDU) with a RACH message B for a UE whose both payload and preamble have been successfully received. Additionally or alternatively, the BS 110 may transmit a RACH message B without a UE contention resolution identity, which may indicate to the receiving UE 120 that the corresponding payload has not been successfully received, or that the receiving UE 120 has not been selected in the contention resolution phase of the BS 110.

[0078] If the UE 120 receives a RACH message B with a UE contention resolution identity that matches the UE 120, the UE 120 may determine that the two-step RACH procedure is successful. If the UE 120 receives a RACH message B and the RACH message B does not include UE contention resolution information or the UE contention resolution information does not identify the UE 120, the UE 120 may use the two-step RACH procedure to reattempt random access (e.g., by retransmitting the RACH message A at a subsequent RACH opportunity) or use the four-step RACH procedure to reattempt random access (e.g., by transmitting a preamble associated with the UE 120 at a subsequent RACH opportunity). If the UE 120 receives a RACH message 2, the UE 120 may use the timing advance command, uplink grant, and temporary cell radio network temporary identifier (TC-RNTI) of the RACH message 2 to retransmit the payload of the RACH message A using a RACH message 3 of the four-step RACH procedure. In other words, the UE 120 may fallback to the four-step RACH procedure when the UE 120 receives an indication of a RACH message 2 as the four-step RACH procedure.

[0079] In some aspects, when the payload and preamble are successfully received, if the payload includes contention resolution information in the RACH message A (e.g., in a common control channel (CCCH) service data unit (SDU)), the BS 110 may provide information identifying a timing advance command, uplink grant, cell radio network temporary identifier (C-RNTI), or UE contention resolution identity in the RACH message B. Additionally, the BS 110 may use the MAC subheader shown in Reference Numeral 420.

[0080] In some aspects, when the payload is not successfully received, UE 120 may receive a RACH message B in the format indicated by reference numeral 410, but the contention resolution identity of the RACH message B will not match UE 120. In this case, UE 120 may ignore the RACH message B and may use a two-step RACH procedure or a four-step RACH procedure to re-attempt random access.

[0081] In some aspects, if UE 120 receives a RACH message 2 or a RACH message B without a UE contention resolution identity field (identifying UE 120), UE 120 may use the timing advance (TA) command, uplink grant, and TC-RNTI of the RACH message 2 or RACH message B to retransmit the payload of the RACH message A, and thereby fallback to the remaining steps of the four-step RACH procedure.

[0082] An example of how the messaging structure described in connection with example 400 may be used in combination with multiple UEs is described below with reference to the accompanying Figure 5 description.

[0083] As indicated above, Figure 4 is provided as an example. Other examples may be different from those described with respect to Figure 4 what is described.

[0084] Figure 5 FIG. is an illustration of example 500 that illustrates a media access control messaging structure for multiple UEs. Example 500 includes a random access response that includes a set of MAC sub-packet data units (sub-PDUs) for a set of UEs that attempted random access with respect to BS 110. BS 110 may provide an indication to the set of UEs as to whether the preamble and / or payload of each UE has been successfully received. For Figure 5 purposes, it is assumed that on the same RACH occasion, UE1 and UE2 use a first preamble index and UE3 and UE4 use a second preamble index, and it is assumed that UE1, UE2, UE3, and UE4 perform a two-step RACH procedure. It is further assumed that BS 110 successfully receives the preambles of all four UEs and that BS 110 only successfully receives the payload of UE1.

[0085] In this scenario, the BS 110 may provide a first MAC sub-header (shown by reference numeral 510) for UE1 and UE2, which first MAC sub-header indicates the length of the corresponding RACH message B (using the variable L shown in the MAC sub-header). The corresponding RACH message B shown by reference numeral 520 may include the UE contention resolution identity of UE1 (not shown), since the payload of UE1 has been successfully received and the payload of UE2 has not been successfully received, thereby resulting in the BS 110 resolving the contention in favor of UE1. Additionally, the BS 110 may provide a second MAC sub-header shown by reference numeral 530 for UE3 and UE4. As shown, the second MAC sub-header may indicate the length of the corresponding RACH message B or RACH message 2 (using the variable L). As shown by reference numeral 540, the BS 110 may provide the RACH message 2 in combination with the MAC sub-header 530 identifying the length of the corresponding RACH message 2 (or may provide a RACH message B without a UE contention resolution identity, which RACH message B is not shown), thereby indicating that the payloads of UE3 and UE4 have not been received. Thereby, UE3 and UE4 may fallback to a four-step RACH procedure to retransmit the payload of the RACH message A.

[0086] As indicated above, Figure 5 is provided as an example. Other examples may be different from the example regarding Figure 5 described.

[0087] Figure 6 is an illustration showing an example 600 of a media access control messaging structure for indication as described in conjunction with Figure 3 described. Example 600 shows the MAC payload of the RACH message B. In this MAC payload, the indication bit shown by reference numeral 610 is used as an indicator (e.g., by toggling the value of F). In this scenario, if the BS 110 receives the preamble and payload of UE 120, the BS 110 may set F to a first value (e.g., 0) in the RACH message B. If the BS 110 does not successfully receive the payload, the BS 110 may set F to a second value (e.g., 1).

[0088] If the UE 120 receives a RACH message B with a fallback indicator having a first value, the UE 120 may check the value of the contention resolution MAC control element (CE). If the contention resolution identity matches the UE 120, the UE 120 may complete the two-step RACH procedure. If the contention resolution identity does not match the UE 120, the UE 120 may use the two-step RACH procedure or the four-step RACH procedure to reattempt the RACH procedure. If the UE 120 receives a RACH message B with a fallback indicator having a second value, the UE 120 may use the TA command, uplink grant, and C-RNTI of the RACH message B to retransmit the payload of the RACH message A (e.g., by falling back to the four-step RACH procedure).

[0089] In a case where the payload and preamble are successfully received, the payload may include contention resolution information in the RACH message A (e.g., in the CCCH SDU), and the RACH message B may identify the TA command, uplink grant, C-RNTI, and a MAC subheader having a RAPID and a UE contention resolution MAC CE identifying the UE 120 from which the payload and preamble have been successfully received.

[0090] In a case where the payload is not successfully received, the RACH message B may be transmitted by the BS 110 together with a MAC subheader including a RAPID. If the indication bit is set to a first value, the UE 120 may ignore the RACH message B and may use the two-step or four-step RACH procedure to reattempt transmission. If the indication bit is set to a second value, the UE 120 may use the TA command, uplink grant, and C-RNTI identified by the RACH message B to retransmit the payload of the RACH message A to perform a fallback to the four-step RACH procedure.

[0091] Examples of how the messaging structure described in connection with Example 600 may be used in combination with multiple UEs are described below with reference to the accompanying Figure 7 description.

[0092] As indicated above, Figure 6 is provided as an example. Other examples may be different from the example described with respect to Figure 6 the example.

[0093] Figure 7FIG. 700 is a diagram illustrating an example 700 of a media access control message transfer structure for multiple UEs. Example 700 includes a random access response that includes a set of MAC sub-packet data units (sub-PDUs) for a set of UEs that attempt random access with respect to BS 110. BS 110 may provide an indication to the set of UEs as to whether the preamble and / or payload of each UE has been successfully received. For purposes of Figure 7 the example, it is assumed that on the same RACH occasion, UE1 and UE2 use a first preamble index and UE3 and UE4 use a second preamble index, and it is assumed that UE1, UE2, UE3, and UE4 perform a two-step RACH procedure. It is further assumed that BS 110 successfully receives the preambles of all four UEs and BS 110 only successfully receives the payload of UE1.

[0094] As indicated by reference numeral 710 in Figure 7 FIG. 700, BS 110 may provide UE contention resolution information identifying UE1 based at least in part on successfully decoding the payload of UE1. Additionally, as indicated by reference numeral 720, the MAC subheaders associated with UE1 and UE2 may identify the RAPID of UE1 and UE2 (e.g., RAPID1), and as indicated by reference numeral 730, the random access response associated with UE1 and UE2 may include an indication bit set to a first value (e.g., F = 0), which may indicate that UE1 and UE2 will not perform a fallback to a four-step RACH procedure. Thus, UE1 may determine that the two-step RACH procedure was successful (e.g., at least in part based on the UE contention resolution identity MAC CE identifying UE1 and the indication bit being set to the first value), and UE2 may determine that UE2 will reattempt the RACH procedure (e.g., at least in part based on the UE contention resolution identity MAC CE not identifying UE2 and the indication bit being set to the first value).

[0095] As indicated by reference numeral 740, the MAC subheaders associated with UE3 and UE4 may identify the RAPID of UE3 and UE4 (e.g., RAPID2). As indicated by reference numeral 750, the random access response associated with UE3 and UE4 may include an indication bit set to a second value (e.g., F = 1), which may indicate that UE3 and UE4 will fallback to a four-step RACH procedure.

[0096] As indicated above, Figure 7 is provided as an example. Other examples may differ from the example described with respect to Figure 7 FIG. 700.

[0097] Figure 8 FIG. 700 is a diagram illustrating an example as described in connection with Figure 3Diagram of an example 800 of the described indicator media access control messaging structure. In example 800, if the preamble and payload of UE 120 are successfully received, the MAC subheader without RAPID can be used for RACH message B. If the payload is not successfully received, the MAC subheader with RAPID can be used for RACH message B. UE 120 can determine whether BS 110 has successfully received the payload at least in part based on whether the MAC subheader associated with the UE 120 includes the RAPID associated with the UE 120 and at least in part based on whether the contention resolution MAC CE of UE 120 is included in RACH message B. For example, if the contention resolution MAC CE of UE 120 matches the UE identifier of UE 120 and if the MAC subheader does not include RAPID, UE 120 can determine that the two-step RACH procedure has been successful. If the MAC subheader identifies the RAPID associated with UE 120, UE 120 can identify the RAPID and can use the TA command, uplink grant, and C-RNTI of RACH message B to retransmit the payload to fallback to the four-step RACH. In some aspects, each MAC CE and each corresponding MAC subheader are provided in sequence along with each random access response. For example, if the MAC CE of UE1 is the first MAC CE and the MAC CE of UE2 is the second MAC CE, the random access response of UE1 can use the first sub-PDU and the random access response of UE2 can use the second sub-PDU.

[0098] Reference numeral 810 illustrates a first MAC subheader with a backoff indicator (BI) and without RAPID. The values T and F in the MAC subheader can indicate whether the first MAC subheader will include a backoff indicator, RAPID, or a set of reserved bits. Here, T can be associated with a first value and F can be associated with a first value, indicating that the first MAC subheader will include a backoff indicator and not include RAPID.

[0099] Reference numeral 820 illustrates a second MAC subheader with RAPID, which can be used to indicate that UE 120 will retransmit the payload. In the second MAC subheader, T can be associated with a second value, indicating that the second MAC subheader will include RAPID.

[0100] Reference numeral 830 illustrates a third MAC subheader with one or more reserved bits and without RAPID, which can be used in combination with the contention resolution MAC CE to indicate that the payload has been successfully received. Here, the value T can be set to the first value and the value F can be set to the second value, which can indicate that the third MAC subheader will include one or more reserved bits and not include RAPID or a backoff indicator.

[0101] An example of how the messaging structure described in conjunction with Example 800 can be used in combination with multiple UEs is described below with reference to the accompanying Figure 9 description.

[0102] As indicated above, Figure 8 is provided as an example. Other examples may be different from those Figure 8 described.

[0103] Figure 9 FIG. 900 is a diagram illustrating an example of a media access control messaging structure for multiple UEs.

[0104] Example 900 includes a random access response that includes a set of MAC sub-packet data units (sub-PDUs) for a set of UEs that attempt random access with respect to BS 110. BS 110 may provide an indication to the set of UEs as to whether the preamble and / or payload of each UE has been successfully received. For Figure 9 purposes, it is assumed that on the same RACH occasion, UE1 and UE2 use a first preamble index and UE3 and UE4 use a second preamble index, and it is assumed that UE1, UE2, UE3, and UE4 perform a two-step RACH procedure. It is further assumed that BS 110 successfully receives the preambles of all four UEs and BS110 only successfully receives the payload of UE1.

[0105] As shown by reference numeral 910 in Figure 9 , as part of the random access response, BS 110 may provide UE contention resolution information identifying UE1 based at least in part on successfully decoding the payload of UE1. As shown by reference numeral 920, the MAC sub-header associated with UE1 and UE2 may not include a RAPID, thereby indicating that BS 110 has successfully received the payload associated with UE1 or UE2. Thus, UE1 may complete the two-step RACH procedure. UE2 may not receive the random access response because the random access response does not include the RAPID of UE2. As shown by reference numeral 930, the MAC sub-headers associated with UE3 and UE4 may include the RAPIDs associated with UE3 and UE4, whereby UE3 and UE4 may accordingly fallback to a four-step RACH procedure.

[0106] In some aspects, the procedures described in connection with Examples 400 and 500, 600 and 700, and 800 and 900 can be performed in combination. For example, consider the combination of Examples 400 / 500 and 800 / 900. In this case, if the preamble and payload in RACH message A are successfully received, the BS can transmit RACH message B including UE contention resolution information, as described in more detail in connection with Examples 400 and 500. In addition, RACH message B can include a MAC subheader that does not have a RAPID, has an F value indicating that the backoff indicator is not included in the MAC subheader, and an L value indicating the length of RACH message B. In some aspects, Examples 400 / 500, 600 / 700, and 800 / 900 can all be combined, or any pair of Examples 400 / 500, 600 / 700, and 800 / 900 can be combined.

[0107] As indicated above, Figure 9 is provided as an example. Other examples may be different from the examples Figure 9 described herein.

[0108] Figure 10 is a flowchart of a wireless communication method 1000. The method can be performed by a UE (e.g., Figure 1 UE 120, device 1102 / 1102', etc.).

[0109] At 1010, the UE (e.g., using controller / processor 280, transmit processor 264, TX MIMO processor 266, MOD 254, antenna 252, etc.) can attempt random access by transmitting a random access message associated with a two-step random access procedure. For example, the random access message can include RACH message A. The random access message can include a preamble and a payload.

[0110] At 1020, the UE (e.g., using antenna 252, DEMOD 254, MIMO detector 256, receive processor 258, controller / processor 280, etc.) can receive an indication regarding the random access message. For example, the indication can indicate that the preamble of the random access message and the payload of the random access message have been successfully received or that the payload has not been successfully received.

[0111] At 1030, the UE (e.g., using controller / processor 280, transmit processor 264, TX MIMO processor 266, MOD 254, antenna 252, etc.) can complete the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received. For example, the UE can establish an RRC connection with the base station, can camp on a cell provided by the base station, etc.

[0112] At 1040, the user equipment (e.g., using the controller / processor 280, transmission processor 264, TX MIMO processor 266, MOD 254, antenna 252, etc.) can re - attempt random access or perform a fallback to a four - step random access procedure at least in part based on determining that the indication indicates that the payload was not successfully received. For example, the UE can use a two - step random access procedure or a four - step random access procedure to re - attempt random access. In this case, the UE can re - transmit the preamble and the payload according to the two - step random access procedure or the four - step random access procedure. In some aspects, the UE can perform a fallback to a four - step random access procedure. For example, the UE can re - transmit the payload of the random access message as the RACH message 3 of the four - step RACH procedure. As used herein, re - attempting random access can refer to transmitting the preamble and / or payload after the preamble and / or payload of a random access message have been transmitted by the user equipment (e.g., on the same RACH occasion or on a different RACH occasion).

[0113] In a first aspect, the indication includes a random access response associated with a two - step random access procedure, and the payload of the random access response includes contention resolution information identifying the specific UE from which the payload of the random access message has been successfully received. In a second aspect, either alone or in combination with the first aspect, the method further includes re - attempting random access at least in part based on determining that the contention resolution information within the random access response does not identify the UE configured to re - attempt the random access procedure. In a third aspect, either alone or in combination with the first and / or second aspects, the media access control (MAC) sub - header of the random access response indicates the length of the random access response. In a fourth aspect, either alone or in combination with one or more of the first to third aspects, the random access response indicates that the payload of the random access message was not successfully received at least in part based on the absence of contention resolution information identifying the UE in the random access response.

[0114] In a fifth aspect, either alone or in combination with one or more of the first to fourth aspects, the MAC sub-header of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC sub-header. In a sixth aspect, either alone or in combination with one or more of the first to fifth aspects, the indication includes a random access response associated with a two-step random access procedure, and contention resolution for the UE is at least partially based on a control channel addressed to the UE using the UE's C-RNTI. In a seventh aspect, either alone or in combination with one or more of the first to sixth aspects, the payload of the random access response does not include the C-RNTI. In an eighth aspect, either alone or in combination with one or more of the first to seventh aspects, the random access response includes an uplink grant. In a ninth aspect, either alone or in combination with one or more of the first to eighth aspects, the random access response does not include an uplink grant. In a tenth aspect, either alone or in combination with one or more of the first to ninth aspects, the indication includes a random access response associated with a two-step random access procedure, and the random access response identifies the UE's C-RNTI. In an eleventh aspect, either alone or in combination with one or more of the first to tenth aspects, the MAC sub-header of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for a connected-mode UE. In a twelfth aspect, either alone or in combination with one or more of the first to eleventh aspects, the random access response includes an uplink grant. In a thirteenth aspect, either alone or in combination with one or more of the first to twelfth aspects, the random access response does not include an uplink grant. In a fourteenth aspect, either alone or in combination with one or more of the first to thirteenth aspects, the UE is in an idle mode or an inactive mode when attempting random access. In a fifteenth aspect, either alone or in combination with one or more of the first to fourteenth aspects, the indication is associated with a MAC sub-header that includes a backoff indicator and a set of bits indicating that the MAC sub-header includes the backoff indicator.

[0115] In a sixteenth aspect, either alone or in combination with one or more of the first to fifteenth aspects, the indication includes a second message of a four-step random access procedure. In a seventeenth aspect, either alone or in combination with one or more of the first to sixteenth aspects, the second message indicates that the payload has not been successfully received. In an eighteenth aspect, either alone or in combination with one or more of the first to seventeenth aspects, the method further includes performing a fallback to the four-step random access procedure at least partially based on receiving the second message.

[0116] In a nineteenth aspect, either alone or in combination with one or more of the first to eighteenth aspects, the indication comprises an indication bit in the MAC payload of the random access response message. In a twentieth aspect, either alone or in combination with one or more of the first to nineteenth aspects, the indication bit indicates whether to perform a fallback to a four-step random access procedure. In a twenty-first aspect, either alone or in combination with one or more of the first to twentieth aspects, at least partially based on the indication bit indicating not to perform a fallback to a four-step random access procedure, the UE is configured to complete a two-step random access procedure by identifying the UE at least partially based on the contention resolution information of the random access response message. In a twenty-second aspect, either alone or in combination with one or more of the first to twenty-first aspects, at least partially based on the indication bit indicating not to perform a fallback to a four-step random access procedure, the UE is configured to reattempt random access at least partially based on the contention resolution information of the random access response message not identifying the UE.

[0117] In a twenty-third aspect, either alone or in combination with one or more of the first to twenty-second aspects, at least partially based on the preamble and the payload being successfully received, the MAC sub-header of the indication does not include a preamble identifier. In a twenty-fourth aspect, either alone or in combination with one or more of the first to twenty-third aspects, the MAC sub-header does not include a preamble identifier, and the contention resolution MAC control element of the indication identifies a specific UE whose payload and preamble have been successfully received, wherein each contention resolution MAC control element including the contention resolution MAC control element and each corresponding MAC sub-header including the MAC sub-header are provided in sequence together with each corresponding random access response. In a twenty-fifth aspect, either alone or in combination with one or more of the first to twenty-fourth aspects, the MAC sub-header includes a first bit indicating whether a backoff indicator or a preamble identifier is included in the MAC sub-header and a second bit indicating whether the field of the MAC sub-header is for the backoff indicator or for one or more reserved bits. In a twenty-sixth aspect, either alone or in combination with one or more of the first to twenty-fifth aspects, the media access control (MAC) sub-header of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for an idle-mode UE or a non-active-mode UE.

[0118] In a twenty-seventh aspect, alone or in combination with one or more of the first to twenty-sixth aspects, at least partially based on successful reception of a preamble and a payload, the indication includes a random access response associated with a two-step random access procedure, the random access response including contention resolution information in the payload of the random access response, wherein the indication includes a MAC sub-header without a preamble identifier. In a twenty-eighth aspect, alone or in combination with one or more of the first to twenty-seventh aspects, the MAC sub-header indicates the length of the random access response and whether the MAC sub-header is to include a backoff indicator.

[0119] Although Figure 10 example blocks of a wireless communication method are shown, in some aspects, the method may include more blocks, fewer blocks, different blocks, or differently arranged blocks than those shown in Figure 10 . Additionally or alternatively, Figure 10 two or more blocks shown in

[0120] Figure 11 may be performed in parallel.

[0121] Conceptual data flow diagram 1100 illustrates data flow between different modules / devices / components in example device 1102. Device 1102 may be a UE. In some aspects, device 1102 includes a receiving module 1104 and / or a transmitting module 1106.

[0122] The device may include additional modules that perform each block of the algorithms in Figure 10 the foregoing method 1000 etc. Figure 10Each block in the foregoing method 1000 etc. may be performed by a module, and the device may include one or more of those modules. Each module may be one or more hardware components specifically configured to implement the process / algorithm, implemented by a processor configured to execute the process / algorithm, stored in a computer-readable medium for implementation by a processor, or some combination thereof.

[0123] Figure 11 The number and arrangement of the modules shown therein are provided as an example. In practice, there may be more modules, fewer modules, different modules, or differently arranged modules compared to those shown in Figure 11 In addition, Figure 11 two or more of the modules shown therein may be implemented within a single module, or Figure 11 a single module shown therein may be implemented as multiple distributed modules. Additionally or alternatively, Figure 11 a set of modules (e.g., one or more modules) shown therein may perform one or more functions described as being performed by Figure 11 another set of modules shown in

[0124] Figure 12 FIG. 1200 is a diagram illustrating an example of a hardware implementation of a device 1102' employing a processing system 1202. The device 1102' may be a UE.

[0125] The processing system 1202 may be implemented to have a bus architecture generally represented by a bus 1204. Depending on the specific application and overall design constraints of the processing system 1202, the bus 1204 may include any number of interconnecting buses and bridges. The bus 1204 links together various circuits including one or more processors and / or hardware modules (represented by processors 1206, modules 1104, 1106, and computer-readable medium / memory 1208). The bus 1204 may also link various other circuits such as a timing source, peripherals, voltage regulators, and power management circuits, which are well known in the art and will not be described further herein.

[0126] The processing system 1202 may be coupled to a transceiver 1210. The transceiver 1210 is coupled to one or more antennas 1212. The transceiver 1210 provides means for communicating with various other devices over a transmission medium. The transceiver 1210 receives signals from the one or more antennas 1212, extracts information from the received signals, and provides the extracted information to the processing system 1202, specifically to the receiving module 1104. Additionally, the transceiver 1210 receives information from the processing system 1202, specifically from the transmission module 1106, and generates signals to be applied to the one or more antennas 1212 based at least in part on the received information. The processing system 1202 includes a processor 1206 coupled to a computer-readable medium / memory 1208. The processor 1206 is responsible for general processing, including the execution of software stored on the computer-readable medium / memory 1208. The software, when executed by the processor 1206, causes the processing system 1202 to perform the various functions described herein for any particular device. The computer-readable medium / memory 1208 may also be used to store data manipulated by the processor 1206 when executing the software. The processing system further includes at least one of modules 1104 and 1106. The modules may be software modules running in the processor 1206, software modules resident / stored in the computer-readable medium / memory 1208, one or more hardware modules coupled to the processor 1206, or some combination thereof. The processing system 1202 may be a component of the UE 120 and may include the memory 282 and / or at least one of the following: a TX MIMO processor 266, an RX processor 258, and / or a controller / processor 280.

[0127] In some aspects, the apparatus 1102 / 1102' for wireless communication includes: means for attempting random access by transmitting a random access message associated with a two-step random access procedure; means for receiving an indication that the preamble of the random access message and the payload of the random access message have been successfully received or that the payload has not been successfully received; and / or means for selectively performing the following operations: completing the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or reattempting random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received. The foregoing means may be one or more of the foregoing modules in the processing system 1202 of the apparatus 1102 and / or the apparatus 1102' configured to perform the functions recited by the foregoing means. As described elsewhere herein, the processing system 1202 may include a TX MIMO processor 266, an RX processor 258, and / or a controller / processor 280. In one configuration, the foregoing means may be the TX MIMO processor 266, the RX processor 258, and / or the controller / processor 280 configured to perform the functions and / or operations described herein.

[0128] Figure 12 is provided as an example. Other examples may be different from the example described in connection with Figure 12 what is described.

[0129] Figure 13 is a flowchart of a wireless communication method 1300. The method may be performed by a base station (e.g., Figure 1 BS 110, apparatus 1402 / 1402', etc.) of.

[0130] At 1310, a base station (e.g., using antenna 234, DEMOD 232, MIMO detector 236, receive processor 238, controller / processor 240, etc.) may receive a random access message associated with a two-step random access procedure from a user equipment (UE) attempting random access. For example, the random access message may include a RACH message A. The random access message may include a preamble and a payload.

[0131] At 1320, the base station (e.g., using controller / processor 240, transmit processor 220, TX MIMO processor 230, MOD 232, antenna 234, etc.) may transmit an indication regarding the random access message. For example, the indication may indicate that the preamble of the random access message and the payload of the random access message have been successfully received or that the payload has not been successfully received.

[0132] At 1330, the base station (e.g., using controller / processor 240, transmit processor 220, TX MIMO processor 230, MOD 232, antenna 234, etc.) can complete the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received. For example, the base station can establish an RRC connection with the base station, can camp on the cell provided by the base station, and so on.

[0133] At 1340, the base station (e.g., using antenna 234, DEMOD 232, MIMO detector 236, receive processor 238, controller / processor 240, etc.) can receive messaging associated with the UE re-trying random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received. For example, the UE can use the two-step random access procedure or the four-step random access procedure to re-try random access. In this case, the UE can re-transmit the preamble and the payload according to the two-step random access procedure or the four-step random access procedure. In some aspects, the UE can perform a fallback to the four-step random access procedure. For example, the UE can re-transmit the payload of the random access message as the RACH message 3 of the four-step RACH procedure. The base station can receive the above messaging.

[0134] In a first aspect, the indication includes a random access response associated with a two-step random access procedure, wherein the payload of the random access response includes contention resolution information identifying a particular UE whose random access message payload has been successfully received. In a second aspect, either alone or in combination with the first aspect, the MAC sub-header of the random access response indicates the length of the random access response. In a third aspect, either alone or in combination with the first and / or second aspects, the random access response indicates that the payload has not been successfully received at least in part based on the absence of contention resolution information identifying the UE in the random access response. In a fourth aspect, either alone or in combination with one or more of the first to third aspects, the MAC sub-header of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC sub-header. In a fifth aspect, either alone or in combination with one or more of the first to fourth aspects, the indication includes a random access response associated with a two-step random access procedure, and contention resolution for the UE is at least in part based on a control channel addressed to the UE using the UE's C-RNTI. In a fifth aspect, either alone or in combination with one or more of the first to fourth aspects, the payload of the random access response does not include the C-RNTI. In a sixth aspect, either alone or in combination with one or more of the first to fifth aspects, the random access response includes a uplink grant. In a seventh aspect, either alone or in combination with one or more of the first to sixth aspects, the random access response does not include a uplink grant. In an eighth aspect, either alone or in combination with one or more of the first to seventh aspects, the indication includes a random access response associated with a two-step random access procedure, and the random access response identifies the UE's C-RNTI. In a ninth aspect, either alone or in combination with one or more of the first to eighth aspects, the MAC sub-header of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for a connected-mode UE. In a tenth aspect, either alone or in combination with one or more of the first to ninth aspects, the random access response includes a uplink grant. In an eleventh aspect, either alone or in combination with one or more of the first to tenth aspects, the random access response does not include a uplink grant. In a twelfth aspect, either alone or in combination with one or more of the first to eleventh aspects, the UE is in an idle mode or an inactive mode when attempting random access. In a thirteenth aspect, either alone or in combination with one or more of the first to twelfth aspects, the indication is associated with a MAC sub-header that includes a backoff indicator and a set of bits indicating that the MAC sub-header includes the backoff indicator.

[0135] In a fourteenth aspect, either alone or in combination with one or more of the first to thirteenth aspects, the indication includes a second message of a four-step random access procedure, where the second message indicates that the payload has not been successfully received.

[0136] In a fifteenth aspect, either alone or in combination with one or more of the first to fourteenth aspects, the indication includes an indication bit in the MAC payload of a random access response message. In a sixteenth aspect, either alone or in combination with one or more of the first to fifteenth aspects, the indication bit indicates whether to perform a fallback to a four-step random access procedure. In a seventeenth aspect, either alone or in combination with one or more of the first to sixteenth aspects, at least partially based on the indication bit indicating not to perform a fallback to a four-step random access procedure, the base station is configured to complete a two-step random access procedure by at least partially identifying the UE based on the contention resolution information of the random access response message. In an eighteenth aspect, either alone or in combination with one or more of the first to seventeenth aspects, at least partially based on the indication bit indicating not to perform a fallback to a four-step random access procedure, the base station is configured to receive messaging associated with a reattempted random access based on the contention resolution information of the random access response message not identifying the UE.

[0137] In a nineteenth aspect, either alone or in combination with one or more of the first to eighteenth aspects, at least partially based on the preamble and payload being successfully received, the MAC subheader of the indication does not include a preamble identifier. In a twentieth aspect, either alone or in combination with one or more of the first to nineteenth aspects, at least partially based on the preamble and payload of a specific UE being successfully received, the MAC subheader does not include a preamble identifier and the contention resolution MAC control element of the indication identifies the specific UE. In a twenty-first aspect, either alone or in combination with one or more of the first to twentieth aspects, each contention resolution MAC control element including the contention resolution MAC control element and each corresponding MAC subheader including the MAC subheader are provided in sequence along with each corresponding random access response.

[0138] In a twenty-second aspect, either alone or in combination with one or more of the first to twenty-first aspects, the MAC subheader includes a first bit indicating whether a backoff indicator or a preamble identifier is included in the MAC subheader and a second bit indicating whether the field of the MAC subheader is for the backoff indicator or for one or more reserved bits.

[0139] In a twenty-third aspect, alone or in combination with one or more of the first to twenty-second aspects, at least partially based on successful reception of a preamble and a payload, the indication includes a random access response associated with a two-step random access procedure, the random access response including contention resolution information in a payload of the random access response, wherein the indication includes a MAC subheader without a preamble identifier. In a twenty-fourth aspect, alone or in combination with one or more of the first to twenty-third aspects, the MAC subheader indicates a length of the random access response and whether the MAC subheader is to include a backoff indicator.

[0140] In a twenty-fifth aspect, alone or in combination with one or more of the first to twenty-fourth aspects, the indication relates to a plurality of UEs including the UE. In a twenty-sixth aspect, alone or in combination with one or more of the first to twenty-fifth aspects, the UE is a first UE, and the indication indicates whether corresponding payloads or corresponding preambles of the first UE and a second UE have been received. In a twenty-seventh aspect, alone or in combination with one or more of the first to twenty-sixth aspects, a media access control (MAC) subheader of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for an idle-mode UE or an inactive-mode UE.

[0141] Although Figure 13 example blocks of a wireless communication method are shown, in some aspects, the method may include more blocks, fewer blocks, different blocks, or differently arranged blocks than those shown in Figure 13 . Additionally or alternatively, Figure 13 two or more blocks shown in

[0142] Figure 14 may be performed in parallel.

[0143] The receiving module 1404 can receive a signal 1408 from a UE 1450 (e.g., UE 120, etc.). The signal 1408 can include a random access message, such as RACH message A, RACH message 3, etc. In some aspects, the transmitting module 1404 can receive a random access message associated with a two-step random access procedure, complete the two-step RACH procedure, retry random access, or perform a fallback to a four-step random access procedure, as described elsewhere herein. The transmitting module 1406 can transmit a signal 1410 to the UE 1450. The signal 1410 can include a random access response, such as RACH message B or RACH message 2, which includes an indication of the result of decoding RACH message A, as described in more detail elsewhere herein. In some aspects, the transmitting module 1406 can transmit an indication that the preamble of the random access message and the payload of the random access message have been successfully received or that the payload has not been successfully received.

[0144] The device can include additional modules that execute each block of the algorithms in the foregoing method 1300, etc. Figure 13 and so on. Figure 13 Each block of the foregoing method 1300, etc. can be performed by a module, and the device can include one or more of those modules. The modules can be one or more hardware components specifically configured to implement the process / algorithm, implemented by a processor configured to execute the process / algorithm, stored in a computer-readable medium for implementation by a processor, or some combination thereof.

[0145] Figure 14 The number and arrangement of the modules shown in are provided as an example. In practice, there can be more modules, fewer modules, different modules, or differently arranged modules compared to those shown in. Additionally, Figure 14 and so on. Figure 14 Two or more of the modules shown in can be implemented within a single module, or Figure 14 and so on. Figure 14 a single module shown in can be implemented as multiple distributed modules. Additionally or alternatively, Figure 14 and so on.

[0146] Figure 15 FIG. 1500 is a diagram illustrating an example of a hardware implementation of a device 1402' that employs a processing system 1502. The device 1402' can be a UE.

[0147] Processing system 1502 may be implemented to have a bus architecture generally represented by bus 1504. Depending on the specific application and overall design constraints of processing system 1502, bus 1504 may include any number of interconnecting buses and bridges. Bus 1504 links together various circuits including one or more processors and / or hardware modules (represented by processor 1506, modules 1404, 1406, and computer-readable medium / memory 1508). Bus 1504 may also link various other circuits such as a timing source, peripherals, voltage regulators, and power management circuits, which are well known in the art and thus will not be described further.

[0148] Processing system 1502 may be coupled to transceiver 1510. Transceiver 1510 is coupled to one or more antennas 1512. Transceiver 1510 provides means for communicating with various other devices via a transmission medium. Transceiver 1510 receives signals from one or more antennas 1512, extracts information from the received signals, and provides the extracted information to processing system 1502 (specifically, receiving module 1404). Additionally, transceiver 1510 receives information from processing system 1502 (specifically, transmission module 1406) and generates signals to be applied to the one or more antennas 1512 based at least in part on the received information. Processing system 1502 includes processor 1506 coupled to computer-readable medium / memory 1508. Processor 1506 is responsible for general processing, including execution of software stored on computer-readable medium / memory 1508. The software, when executed by processor 1506, causes processing system 1502 to perform the various functions described herein for any particular device. Computer-readable medium / memory 1508 may also be used to store data manipulated by processor 1506 when executing the software. The processing system further includes at least one of modules 1404 and 1406. The modules may be software modules running in processor 1506, software modules resident / stored in computer-readable medium / memory 1508, one or more hardware modules coupled to processor 1506, or some combination thereof. Processing system 1502 may be a component of eNB 110 and may include memory 242 and / or at least one of the following: TX MIMO processor 230, RX processor 238, and / or controller / processor 240.

[0149] In some aspects, a device 1402 / 1402’ for wireless communication includes: means for receiving, from a user equipment (UE) attempting random access, a random access message associated with a two-step random access procedure; means for transmitting an indication that a preamble of the random access message and a payload of the random access message have been successfully received or that the payload has not been successfully received; and means for selectively performing one of the following operations: completing the two-step random access procedure at least in part based on determining that the indication indicates that the preamble of the random access message and the payload of the random access message have been successfully received, or receiving messaging associated with the UE reattempting random access or performing a fallback to a four-step random access procedure at least in part based on determining that the indication indicates that the payload has not been successfully received. The foregoing means may be one or more of the foregoing modules in a processing system 1502 of device 1402 and / or device 1402' configured to perform the functions recited by the foregoing means. As described elsewhere herein, the processing system 1502 may include a TX MIMO processor 230, a receive processor 238, and / or a controller / processor 240. In one configuration, the foregoing means may be the TX MIMO processor 230, the receive processor 238, and / or the controller / processor 240 configured to perform the functions and / or operations recited herein.

[0150] Figure 15 is provided as an example. Other examples may be different from the example(s) described in conjunction with Figure 15 the example(s) described.

[0151] Figure 16FIG. 1600 is a diagram illustrating an example 1600 of a media access control message transfer structure for an idle mode or inactive mode UE associated with a successful random access message. In other words, the MAC message transfer structure shown in example 1600 can be used for a UE 120 that is in the idle mode or inactive mode and whose random access message payload and preamble have been successfully received. The payload of the indicator (e.g., random access response) of this MAC message transfer structure is shown by reference numeral 1610. For example, the payload can be part of the random access response and can identify contention resolution information for UE 120. In this case, uplink grant and C-RNTI can be used for subsequent data. As shown by reference numeral 1620, the indicator can be associated with a MAC sub-header. For example, the MAC sub-header can include a set of bits (shown as F1 and F2). The value of this set of bits can indicate information about the MAC sub-header and / or the payload. As an example, in example 1600, the value of this set of bits can indicate that there is no BI field in the MAC sub-header and can indicate that there is contention resolution information in the random access response. In this case, the message B random access response can include a timing advance command, uplink grant, C-RNTI, and contention resolution information of the successful random access message.

[0152] Figure 16 is provided as an example. Other examples may be different from the example described in conjunction with Figure 16 the example.

[0153] Figure 17A and 17B FIG. 1700 is a diagram illustrating an example 1700 of a media access control message transfer structure for a UE associated with a random access message whose payload has not been successfully received but whose preamble has been successfully received, and an example of a media access control sub-header for a UE whose random access message has not been successfully received in any part. Example 1700 includes a MAC sub-header 1710 and a MAC payload 1720 (shown in Figure 17A ), and / or a MAC sub-header 1730 (shown in Figure 17B ). For example, the MAC sub-header 1710 and the MAC payload 1720 can include the RACH message 2 of the four-step RACH process. The UE that receives the MAC sub-header 1710 and the MAC payload 1720 can determine that the payload of the random access message transmitted by the UE has not been successfully received.

[0154] As shown, the MAC sub-header 1730 may include a set of bits (e.g., F1 and F2). In this case, the value of the set of bits may indicate that the MAC sub-header 1730 includes a BI field. The BI field may be used by a UE whose preamble and payload have not been successfully received. For example, the UE may determine that the RACH procedure is unsuccessful based at least in part on determining that the contention resolution information and preamble identifier of the UE are not identified by a set of random access responses, and may accordingly read the MAC sub-header with BI information only to determine the BI value for subsequent random access messages for the UE.

[0155] Example 1700 applies to connected-mode UEs, idle-mode UEs, and inactive-mode UEs.

[0156] Figure 17A and 17B are provided as examples. Other examples may be different from the examples described in connection with Figure 17A and 17B which are described.

[0157] Figure 18 FIG. is a diagram of Example 1800 that illustrates a media access control messaging structure for a connected-mode UE associated with a random access message whose payload has been successfully received. As shown, Example 1800 includes a MAC sub-header 1810 and a MAC payload 1820. In this case, contention resolution may be performed using a physical downlink control channel (PDCCH) that is addressed using the C-RNTI identified by the random access message transmitted by the UE. For example, in some cases (referred to herein as Option 1), if the RACH message A includes a C-RNTI MAC-CE, contention resolution may be performed using the PDCCH addressed to the C-RNTI of the successfully received RACH message A, and message B may be directed to the UE associated with that C-RNTI. Otherwise, the RACH message B may be addressed to the RA-RNTI and may contain information about multiple UEs. Contention resolution may be based on a contention resolution ID included in the RACH message B, which may match the UE ID identified in the RACH message A.

[0158] In other cases (referred to herein as Option 2), the RACH message B may contain information about multiple UEs and may be addressed to the RA-RNTI. In this case, the C-RNTI may be included in the random access response as contention resolution information for RRC_CONNECTED (RRC connected) UEs. Example 1800 pertains to Option 1.

[0159] As shown, the MAC sub-header 1810 may include a set of bits (e.g., F1 and F2). In this case, the set of bits may be set to indicate the value of the random access response for a connected mode UE. In some aspects, the set of bits may indicate that the random access response is to include contention resolution information, as described in more detail below in conjunction with Figure 19 In some aspects, the set of bits may indicate whether the random access response is to include a BI field or other reserved bits. In some aspects, the set of bits may indicate whether the random access response is for a connected mode UE or an idle mode or inactive mode UE.

[0160] As shown, the MAC payload 1820 includes an uplink grant. The uplink grant may be optional, as described elsewhere herein. As further shown, the MAC payload 1820 may not include contention resolution information. For example, when using Option 1, the MAC payload 1820 may not need to include contention resolution information. In this case, the uplink grant may be used for subsequent data transmission. Additionally, the MAC sub-header 1810 may not identify the preamble identifier, since contention resolution is handled using the PDCCH addressed to the C-RNTI.

[0161] Figure 18 is provided as an example. Other examples may be different from the example described in conjunction with Figure 18 as described.

[0162] Figure 19 is a diagram illustrating Example 1900 of a media access control message payload for a connected mode UE associated with a successful random access message. Example 1910 illustrates a first example in which the MAC payload includes an uplink grant and does not include contention resolution information. Example 1920 illustrates a second example in which the MAC payload does not include an uplink grant and does not include contention resolution information. Example 1930 illustrates a third example in which the MAC payload includes an uplink grant and contention resolution information. Example 1940 illustrates a fourth example in which the MAC payload includes contention resolution information and does not include an uplink grant. In Examples 1930 and 1940, the contention resolution information is included in the random access response in the form of a C-RNTI, since the UE may use the RA-RNTI to receive the random access response sent from the BS 110.

[0163] Figure 19 is provided as an example. Other examples may be different from the example described in conjunction with Figure 19 as described.

[0164] Figure 20FIG. 2000 is a diagram illustrating an example of a media access control message transfer structure for multiple UEs. The random access responses for multiple UEs can be multiplexed, as illustrated in example 2000. For example, as indicated by reference numeral 2010, a first MAC payload using RACH message format 2 can indicate that the random access payloads of one or more corresponding UEs have not been successfully received. As indicated by reference numeral 2020, the MAC sub-header can include a set of bits (e.g., F1 and F2) indicating whether the MAC sub-header is for an idle mode UE or a connected mode UE. The corresponding MAC payload indicated by reference numeral 2030 can include a RACH message B identifying one or more UEs for which the corresponding random access responses have been successfully received. In addition, as indicated by reference numeral 2040, the MAC sub-header of MAC sub-PDU1 can include a set of bits (e.g., F1 and F2) indicating whether the MAC sub-header includes a backoff indicator. The MAC sub-header can be used to provide backoff information for UEs whose preambles and payloads have not been successfully received.

[0165] Figure 20 is provided by way of example. Other examples may be different from the example Figure 20 described in connection with

[0166] It should be understood that the specific order or hierarchy of the blocks in the disclosed process / flowchart is an illustration of an example approach. Based on design preferences, it should be understood that the specific order or hierarchy of the blocks in these process / flowcharts can be rearranged. In addition, some blocks may be combined or omitted. The appended method claims present the elements of the various blocks in exemplary order and are not meant to be limited to the specific order or hierarchy presented.

[0167] The foregoing 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 readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein the recitation of a singular element is not intended to mean "one and only one" unless specifically stated otherwise, but rather "one or more." The phrase "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or superior to other aspects. Unless specifically stated otherwise, the term "some" refers to one or more. Combinations such as "at least one of A, B, or C," "at least one of A, B, and C," and "any combination of A, B, C, or the like" include any combination of A, B, and / or C and may include multiple As, multiple Bs, or multiple Cs. Specifically, combinations such as "at least one of A, B, or C," "at least one of A, B, and C," and "any combination of A, B, C, or the like" can be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combination can include one or more members of A, B, or C. Elements of the various aspects described throughout this disclosure that are presently known or later come to be known to those of ordinary skill in the art as structural and functional equivalents are expressly incorporated herein by reference and are intended to be covered by the claims. Furthermore, nothing disclosed herein is intended to be dedicated to the public, whether or not such disclosure is explicitly recited in the claims. No claim element is to be construed as a means-plus-function unless the element is expressly recited using the phrase "means for" followed by a function.

Claims

1. A wireless communication method performed by a user equipment (UE), comprising: attempting random access by transmitting a random access message associated with a two-step random access procedure, wherein the random access message includes a preamble and a payload in a single uplink message, and wherein the payload includes contention resolution information; receiving a random access response, the random access response including a media access control (MAC) sub-header and a MAC control element (MAC CE), the MAC sub-header including a set of reserved bits, the MAC CE including a contention resolution identity associated with the contention resolution information of the payload of the random access message, wherein the random access response is associated with the two-step random access procedure and multiplexed with a random access channel message 2 associated with a four-step random access procedure for other UEs, and wherein the contention resolution identity, in combination with the set of reserved bits, indicates that the preamble of the random access message and the payload of the random access message have been successfully received; and completing the two-step random access procedure at least in part based on the contention resolution identity and the set of reserved bits indicating that the preamble of the random access message and the payload of the random access message have been successfully received.

2. The method according to claim 1, wherein the contention resolution identity identifies a particular UE from which the payload of the random access message has been successfully received.

3. The method according to claim 2, wherein the MAC sub-header of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC sub-header.

4. The method according to claim 1, wherein the random access response is addressed to a cell radio network temporary identifier (C-RNTI) of the UE.

5. The method according to claim 4, wherein the payload of the random access response does not include the C-RNTI.

6. The method according to claim 4, wherein the random access response does not include an uplink grant.

7. The method according to claim 1, wherein the random access response identifies a cell radio network temporary identifier (C-RNTI) of the UE.

8. The method according to claim 7, wherein the random access response does not include an uplink grant.

9. The method according to claim 7, wherein the MAC sub-header of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for an idle mode UE or a non-active mode UE.

10. The method according to claim 1, wherein the UE is in an idle mode or a non-active mode when attempting the random access.

11. The method according to claim 1, wherein the UE is in a connected mode when attempting the random access.

12. The method according to claim 1, wherein at least in part based on the preamble and the payload of the random access message being successfully received, the MAC sub-header of the random access response does not include a preamble identifier.

13. The method according to claim 12, wherein the MAC CE of the random access response identifies a specific UE whose payload and preamble have been successfully received.

14. The method according to claim 12, wherein the MAC sub-header includes a first bit indicating whether a backoff indicator or the preamble identifier is included in the MAC sub-header and a second bit indicating whether the field of the MAC sub-header is for the backoff indicator or for the set of reserved bits.

15. A wireless communication method performed by a node, comprising: receiving, from a user equipment (UE) attempting random access, a random access message associated with a two-step random access procedure, wherein the random access message includes a preamble and a payload in a single uplink message, and wherein the payload includes contention resolution information; transmitting a random access response, the random access response including a media access control (MAC) sub-header and a MAC control element (MAC CE), the MAC sub-header including a set of reserved bits, the MAC CE including a contention resolution identity associated with the contention resolution information of the payload of the random access message, wherein the random access response is associated with the two-step random access procedure and can be multiplexed with a random access channel message 2 associated with a four-step random access procedure for other UEs, and wherein the contention resolution identity, in combination with the set of reserved bits, indicates that the preamble of the random access message and the payload of the random access message have been successfully received; and completing the two-step random access procedure at least in part based on the contention resolution identity and the set of reserved bits indicating that the preamble of the random access message and the payload of the random access message have been successfully received.

16. The method according to claim 15, wherein the payload of the random access response includes contention resolution information identifying a specific UE whose payload of the random access message has been successfully received.

17. The method according to claim 16, wherein the MAC sub-header of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC sub-header.

18. The method according to claim 15, wherein the random access response is addressed to a cell radio network temporary identifier (C-RNTI) of the UE.

19. The method according to claim 18, wherein the MAC sub-header of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for an idle mode UE or a non-active mode UE.

20. A user equipment (UE) for wireless communication, comprising: a memory; and one or more processors coupled to the memory, the memory and the one or more processors being configured to: Attempting random access by transmitting a random access message associated with a two-step random access procedure, wherein the random access message includes a preamble and a payload in a single uplink message, and wherein the payload includes contention resolution information; Receiving a random access response that includes a media access control (MAC) sub-header and a MAC control element (MAC CE), the MAC sub-header including a set of reserved bits, the MAC CE including a contention resolution identity associated with the contention resolution information of the payload of the random access message, wherein the random access response is associated with the two-step random access procedure and can be multiplexed with a random access channel message 2 associated with a four-step random access procedure for other UEs, and wherein the contention resolution identity, in combination with the set of reserved bits, indicates that the preamble of the random access message and the payload of the random access message have been successfully received; And Completing the two-step random access procedure at least in part based on the contention resolution identity and the set of reserved bits indicating that the preamble of the random access message and the payload of the random access message have been successfully received.

21. The UE according to claim 20, wherein the payload of the random access response includes contention resolution information identifying a particular UE from which the payload of the random access message has been successfully received.

22. The UE according to claim 21, wherein the MAC sub-header of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC sub-header.

23. The UE according to claim 20, wherein the random access response is addressed to a cell radio network temporary identifier (C-RNTI) of the UE.

24. The UE according to claim 23, wherein the payload of the random access response does not include the C-RNTI.

25. The UE according to claim 23, wherein the random access response does not include an uplink grant.

26. The UE according to claim 20, wherein the random access response identifies a cell radio network temporary identifier (C-RNTI) of the UE.

27. The UE according to claim 26, wherein the random access response does not include an uplink grant.

28. The UE according to claim 26, wherein the MAC sub-header of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for an idle mode UE or a non-active mode UE.

29. The UE according to claim 20, wherein the UE is in an idle mode or a non-active mode when attempting the random access.

30. The UE according to claim 20, wherein the UE is in a connected mode when attempting the random access.

31. The UE according to claim 20, wherein at least in part based on the preamble and the payload of the random access message being successfully received, the MAC sub-header of the random access response does not include a preamble identifier.

32. The UE according to claim 31, wherein the MAC CE of the random access response identifies a specific UE whose payload and preamble have been successfully received.

33. The UE according to claim 31, wherein the MAC sub-header includes a first bit indicating whether a backoff indicator or the preamble identifier is included in the MAC sub-header, and a second bit indicating whether the field of the MAC sub-header is for the backoff indicator or for the set of reserved bits.

34. A node for wireless communication, comprising: a memory; and one or more processors coupled to the memory, the memory and the one or more processors being configured to: receive, from a user equipment (UE) attempting random access, a random access message associated with a two-step random access procedure, wherein the random access message includes a preamble and a payload in a single uplink message, and wherein the payload includes contention resolution information; transmit a random access response, the random access response including a media access control (MAC) sub-header and a MAC control element (MAC CE), the MAC sub-header including a set of reserved bits, the MAC CE including a contention resolution identity associated with the contention resolution information of the payload of the random access message, wherein the random access response is associated with the two-step random access procedure and can be multiplexed with a random access channel message 2 associated with a four-step random access procedure for other UEs, and wherein the contention resolution identity, in combination with the set of reserved bits, indicates that the preamble of the random access message and the payload of the random access message have been successfully received; and complete the two-step random access procedure at least in part based on the contention resolution identity and the set of reserved bits indicating that the preamble of the random access message and the payload of the random access message have been successfully received.

35. The node according to claim 34, wherein the payload of the random access response includes contention resolution information identifying a specific UE whose payload of the random access message has been successfully received.

36. The node according to claim 35, wherein the MAC sub-header of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC sub-header.

37. The node according to claim 34, wherein the random access response is addressed to a cell radio network temporary identifier (C-RNTI) of the UE.

38. The node according to claim 37, wherein the MAC sub-header of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for an idle mode UE or an inactive mode UE.

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