Random access procedure

Abstract

Some techniques and devices described herein provide an indication of a 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 techniques and devices described herein may provide the indication using a UE contention resolution identity-based approach, where the UE's contention resolution identity may be provided in a random access response. Some techniques and devices described herein may use a fallback indicator indicating a result of decoding and / or an action to be performed. Some techniques and devices 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 a result of the decoding and / or an action to be performed.

Description

[0001] This application is a divisional application of the patent application with an international application date of April 8, 2020, an international application number of PCT / CN2020 / 083627, a Chinese national application date of April 8, 2020, an application number of 202080025180.2, and an invention name of “Random Access Procedure”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] 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, both of which are entitled “INDICATION FOR TWO-STEP RACH FALLBACK TO FOUR-STEP RACH” and are both expressly incorporated herein by reference.

[0004] background

[0005] field

[0006] Aspects of the present disclosure generally relate to wireless communications and techniques and devices for indicating fallback to a four-step random access channel (RACH) for a two-step RACH. Background Art

[0007] Wireless communication systems are widely deployed to provide a variety of telecommunication services, such as telephony, video, data, messaging, and broadcasting. Typical wireless communication systems may employ multiple access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple access 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 / LTE-Advanced is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by the Third Generation Partnership Project (3GPP).

[0008] A wireless communication network may include several base stations (BSs) capable of supporting communications for several user equipment (UEs). The UEs may communicate with the BSs via downlinks and uplinks. The downlink (or forward link) refers to the communication link from the BS to the UE, while the uplink (or reverse link) refers to the communication link from the UE to the BS. As will be described in more detail herein, a BS may be referred to as a Node B, gNB, access point (AP), radio head, transmit / receive point (TRP), 5G BS, 5G Node B, and so on.

[0009] 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 city, country, region, and even global levels. 5G (which may also be referred to as New Radio (NR)) is an enhancement set to the LTE mobile standard promulgated by the Third Generation Partnership Project (3GPP). 5G is designed to better support mobile broadband Internet access by improving spectrum efficiency, reducing costs, improving services, utilizing new spectrum, and using OFDM (CP-OFDM) with a cyclic prefix (CP) on the downlink (DL), using CP-OFDM and / or SC-FDM (e.g., also known as discrete Fourier transform spread OFDM (DFT-s-OFDM) on the uplink (UL), and supporting 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 improvements to LTE and 5G technology. Preferably, these improvements should be applicable to other multiple access technologies and the telecommunication standards that employ these technologies.

[0010] Overview

[0011] A UE may perform a random access procedure (e.g., a random access channel (RACH) procedure, a physical RACH (PRACH) procedure, etc.) to access a network via a base station (BS). In some cases, the UE may perform a four-step RACH procedure, which involves a first uplink random access message (e.g., Message 1 or Msg1) providing a preamble for the UE, a second downlink random access response (e.g., Message 2 or Msg2) to the first uplink random access message, 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 may perform a two-step RACH procedure, in which Messages 1 and 3 are combined into a single uplink message (Message A or MsgA) and Messages 2 and 4 are combined into a single downlink message (e.g., Message B or MsgB). In some cases, the BS may successfully receive the preamble of the RACH message but may fail to receive the payload of the RACH message (e.g., Message A). In this case, the UE may fall back to the four-step RACH approach or may retry the random access. In other cases, the BS may successfully receive the payload and preamble. In this case, the RACH procedure may continue uninterrupted. It may be useful to provide a messaging system that the BS can use to signal the result of decoding the RACH message (e.g., preamble and payload successfully received, preamble successfully received and payload not successfully received, preamble and payload not successfully received, etc.) and the action to be performed by the UE (e.g., fall back to the four-step RACH procedure, retry the two-step RACH procedure or the four-step RACH procedure, retransmit the payload of the RACH message, etc.).

[0012] Some techniques and devices described herein provide an indication of the result of decoding a two-step RACH message and the action to be performed by the UE. For example, some techniques and devices described herein may provide this indication using a method based on a UE contention resolution identity, where the UE contention resolution identity may be provided in a random access response. Some techniques and devices described herein may use a fallback indicator that indicates the result of decoding and / or the action to be performed. Some techniques and devices 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. In this way, the BS may signal the result of decoding and / or the action to be performed to the UE. The UE may perform the action (e.g., fall back to a four-step RACH procedure, retry RACH, etc.) based on the indication. As a result, the granularity of the actions to be signaled in conjunction with the two-step RACH procedure may be improved, thereby improving network performance and increasing the reliability of the two-step RACH procedure. In addition, the techniques and devices described herein provide a messaging structure for indicating RACH results to multiple UEs in a media access control (MAC) message to the multiple UEs, for example using contention resolution information or other information associated with the multiple UEs. For example, if a first UE receives a MAC message with contention resolution information for a second UE, the first UE can perform an action based at least in part on the information in the MAC message. If a second UE receives a MAC message with contention resolution information for the second UE, the second UE can determine that the RACH message for the second UE was successfully received. These MAC messages can be used to provide indications of decoding results and / or actions to multiple UEs (e.g., four UEs, eight UEs, etc.). Relative to a UE-by-UE indication of whether the RACH procedure was successful, such feedback combined to multiple UEs in association with an indication of actions to be performed can improve utilization of network resources and reduce use of UE computing resources.

[0013] In this way, the amount of scheduling information to be monitored by the UE is reduced, thereby saving computational resources and power of the UE. Furthermore, by providing the contention resolution information in the random access response, the UE's communication and computational resource usage is reduced, compared to providing the contention resolution information separately from the random access response. Furthermore, by providing the contention resolution information in the random access response, the indicated decoding complexity and decoding error probability are reduced, compared to providing the contention resolution information separately from the random access response.

[0014] In one aspect of the present disclosure, a method, a user equipment (UE), a base station, a device, and a computer program product are provided.

[0015] 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 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 performing the following operations: completing the two-step random access procedure based at least in part 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 retrying random access or performing a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload has not been successfully received.

[0016] 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 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: completing the two-step random access procedure based at least in part 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 retrying random access or performing a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload has not been successfully received.

[0017] In some aspects, the apparatus 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 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 the following operations: completing the two-step random access procedure based at least in part 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 based at least in part on determining that the indication indicates that the payload has not been successfully received.

[0018] In some aspects, a computer program product may include a non-transitory computer-readable medium storing one or more instructions that, 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 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: completing the two-step random access procedure based at least in part 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 retrying random access or performing a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload has not been successfully received.

[0019] In some aspects, a wireless communication method performed by a base station may include: receiving a random access message associated with a two-step random access procedure from a UE attempting random access; 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 performing the following operations: completing the two-step random access procedure based at least in part 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 a message transmission associated with the UE retrying random access or performing a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload has not been successfully received.

[0020] 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 a random access message associated with a two-step random access procedure from a UE attempting random access; 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: completing the two-step random access procedure based at least in part 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 retrying random access or performing a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload has not been successfully received.

[0021] In some aspects, the apparatus may include means for receiving a random access message associated with a two-step random access procedure from a UE attempting random access; 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 the following operations: completing the two-step random access procedure based at least in part 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 a message delivery associated with the UE reattempting random access or performing a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload has not been successfully received.

[0022] In some aspects, a computer program product may include a non-transitory computer-readable medium storing one or more instructions that, when executed by one or more processors of a base station, may cause the one or more processors to: receive a random access message associated with a two-step random access procedure from a UE attempting random access; 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 select to: complete the two-step random access procedure based at least in part on a determination 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 to receive messaging associated with the UE retrying random access or performing a fallback to a four-step random access procedure based at least in part on a determination that the indication indicates that the payload has not been successfully received.

[0023] 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 and as illustrated in the accompanying figures.

[0024] The foregoing has broadly outlined the features and technical advantages of examples according to the present disclosure in an effort to make the following detailed description better understood. Additional features and advantages will be described hereinafter. The concepts and specific examples disclosed can be readily used as a basis for modifying or designing other structures for implementing 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 in terms of their organization and method of operation, as well as the associated advantages, will be better understood by considering the following description in conjunction with the accompanying drawings. Each of the figures is provided for illustration and description purposes and is not intended to define limitations on the claims. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0028] Figure 4 Is the explanation used for combining Figure 3 A diagram of an example of a media access control messaging structure is described.

[0029] Figure 5 is a diagram illustrating an example of a medium access control messaging structure for multiple UEs.

[0030] Figure 6 Is the explanation used for combining Figure 3 A diagram of an example of a media access control messaging structure is described.

[0031] Figure 7 is a diagram illustrating an example of a medium access control messaging structure for multiple UEs.

[0032] Figure 8 Is the explanation used for combining Figure 3 A diagram of an example of a media access control messaging structure is described.

[0033] Figure 9 is a diagram illustrating an example of a medium access control messaging structure for multiple UEs.

[0034] Figure 10 is a flow chart of a wireless communication method.

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

[0036] Figure 12 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system.

[0037] Figure 13 is a flow chart of a wireless communication method.

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

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

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

[0041] Figure 17A and 17B is a diagram illustrating an example of a medium access control messaging structure for a UE associated with a random access message whose payload was not successfully received and an example of a medium access control subheader for a UE from which any portion of a random access message was not successfully received.

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

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

[0044] Figure 20 is a diagram illustrating an example of a medium access control messaging structure for multiple UEs. Detailed description

[0045] The detailed description set forth below in conjunction with the accompanying drawings is intended as a description of various configurations and is not intended to represent configurations in which the concepts described herein may be practiced. This detailed description includes specific details to provide a thorough understanding of the 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.

[0046] Several aspects of telecommunication systems will now be presented with reference to various devices and methods. These devices and methods are described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively, "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 on the specific application and the design constraints imposed on the overall system.

[0047] As an example, an element, or any part of an element, or any combination of elements can be implemented with a "processing system" comprising 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, gating logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionalities described throughout this disclosure. One or more processors in a processing system can execute software. Software should be broadly interpreted as meaning instructions, instruction sets, codes, code segments, program codes, programs, subroutines, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether described in software, firmware, middleware, microcode, hardware description languages, or other terms.

[0048] Accordingly, in one or more example embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, these functions may be stored or encoded as one or more instructions or codes on a computer-readable medium. Computer-readable media include computer storage media. Storage media can be any available medium that can be accessed by a computer. By way of example and not limitation, such computer-readable media may 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 device, a combination of the above-mentioned types of computer-readable media, or any other medium that can be used to store computer-executable code in the form of instructions or data structures that can be accessed by a computer.

[0049] It should be noted that although various aspects may be described herein using terminology generally associated with 3G and / or 4G wireless technologies, various aspects of the present disclosure may be applied in communication systems based on other generations, such as 5G and beyond.

[0050] Figure 11 is a diagram illustrating a wireless network 100 in which various 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 base stations 110 (shown as BS110a, BS110b, BS110c, and BS110d) and other network entities. A base station is an entity that communicates with user equipment (UE) and may also be referred to as a base station, 5G base station, node B, gNB, 5G NB, access point, transmit reception point (TRP), etc. Each base station may provide communication coverage for a specific geographic area. In 3GPP, the term "cell" may refer to the coverage area of ​​a base station and / or the base station subsystem serving that coverage area, depending on the context in which the term is used.

[0051] 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., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscriptions. 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 Figure 1 In the example shown in FIG, 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.

[0052] In some examples, the cells may not necessarily be stationary, and the geographic area of ​​the cells may move depending on the location of the mobile BS. In some examples, the BSs may be interconnected to each other and / or to one or more other BSs or network nodes (not shown) in 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.

[0053] The wireless network 100 may also include a relay station. A relay station is an entity that can receive transmissions of data from an upstream station (e.g., a BS or a UE) and send transmissions of the data to a downstream station (e.g., a UE or a BS). A relay station may also be a UE that can relay transmissions for other UEs. Figure 1 In the example shown in , a relay station 110d may communicate with a macro BS 110a and a 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, or the like.

[0054] The wireless network 100 may be a heterogeneous network including different types of BSs (e.g., macro BSs, pico BSs, femto BSs, relay BSs, etc.). These different types of BSs may have different transmit power levels, different coverage areas, and different impacts on interference in the wireless network 100. For example, a macro BS may have a high transmit power level (e.g., 5 to 40 watts), while a pico BS, a femto BS, and a relay BS may have a lower transmit power level (e.g., 0.1 to 2 watts).

[0055] The network controller 130 may be coupled to a 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, for example, via a wireless or wired backhaul.

[0056] 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, terminal, mobile station, subscriber unit, station, etc. A UE may be a cellular phone (e.g., a smartphone), 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, an ultrabook, a medical device or equipment, a biometric sensor / device, a wearable device (e.g., 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), an in-vehicle component or sensor, a smart meter / sensor, industrial manufacturing equipment, a global positioning system device, or any other suitable device configured to communicate via a wireless or wired medium.

[0057] Some UEs may be considered 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 can communicate with a base station, another device (e.g., a remote device), or some other entity. A wireless node may provide connectivity to or to a network (e.g., a wide area network (such as the Internet) or a cellular network), for example, via a wired or wireless communication link. Some UEs may be considered Internet of Things (IoT) devices and / or may be implemented as NB-IoT (narrowband Internet of Things) devices. Some UEs may be considered customer premises equipment (CPE). UE 120 may be included inside a housing that houses components of UE 120, such as a processor component, a memory component, and the like.

[0058] Generally speaking, any number of wireless networks can be deployed in a given geographic area. Each wireless network can support a specific RAT and can operate on one or more frequencies. RAT can also be referred to as radio technology, air interface, etc. Frequency can also be referred to as carrier, frequency channel, etc. Each frequency can support a single RAT in a given geographic area to avoid interference between wireless networks of different RATs. In some cases, 5G RAT networks can be deployed.

[0059] In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a base station) allocates resources for communication among some or all devices and equipment within a service area or cell of the scheduling entity. Within the present disclosure, as discussed further below, a scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communications, the subordinate entities utilize the resources allocated by the scheduling entity. In some cases, the UE may access the air interface by executing a random access procedure, such as a physical random access (PRACH) procedure. 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.

[0060] 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, thereby 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 other UEs utilize the resources scheduled by the UE for wireless communication. A UE can act as a scheduling entity in a peer-to-peer (P2P) network and / or in a mesh network. In the mesh network example, UEs can optionally communicate directly with each other in addition to communicating with the scheduling entity.

[0061] 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 communicate using the scheduled resources.

[0062] As indicated above, Figure 1 These are provided as examples only. Other examples may differ from those regarding Figure 1 Examples described.

[0063] Figure 2 Shows that it can be Figure 1 Block diagram 200 shows a design of base station 110 and UE 120 for one of the base stations and one of the UEs in a wireless communication network. Base station 110 may be equipped with T antennas 234a through 234t, and UE 120 may be equipped with R antennas 252a through 252r, where in general T≥1 and R≥1.

[0064] At base station 110, transmit processor 220 may receive data for one or more UEs from data source 212, select one or more modulation and coding schemes (MCS) for each UE based at least in part on a channel quality indicator (CQI) received from the UE, process (e.g., encode and modulate) the data for each UE based at least in part on the MCS selected for the UE, and provide data symbols for all UEs. Transmit processor 220 may also process system information (e.g., for semi-static resource partitioning information (SRPI) and control information (e.g., CQI requests, grants, upper layer signaling, etc.) and provide overhead symbols and control symbols. Transmit processor 220 may also generate reference symbols for reference signals (e.g., cell-specific reference signals) and synchronization signals (e.g., primary synchronization signal (PSS) and secondary synchronization signal (SSS)). A transmit (TX) multiple-input, multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on ​​data symbols, control symbols, overhead symbols, and / or reference symbols, as applicable, and may provide T output symbol streams to T modulators (MODs) 232a through 232t. Each modulator 232 may process a 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 frequency upconvert) the output sample stream to obtain a downlink signal. The T downlink signals from modulators 232a through 232t may be transmitted via T antennas 234a through 234t, respectively. According to various aspects described in greater detail below, position coding may be utilized to generate synchronization signals to convey additional information.

[0065] At UE 120, antennas 252a through 252r may receive downlink signals from base station 110 and / or other base stations and may provide received signals to demodulators (DEMODs) 254a through 254r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, 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. A MIMO detector 256 may obtain received symbols from all R demodulators 254a through 254r, perform MIMO detection on the received symbols where applicable, and provide detected symbols. A receive (RX) processor 258 may process (e.g., demodulate and decode) the detected symbols, provide decoded data for UE 120 to a data sink 260, and provide decoded control information and system information to a controller / processor 280. The channel processor may determine reference signal received power (RSRP), received signal strength indicator (RSSI), reference signal received quality (RSRQ), channel quality indicator (CQI), and the like.

[0066] On the uplink, at UE 120, a transmit processor 264 may receive and process data from a data source 262 and control information (e.g., for reports including RSRP, RSSI, RSRQ, CQI, etc.) from a controller / processor 280. 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 a TX MIMO processor 266, if 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, uplink signals from UE 120 and other UEs may be received by antennas 234, processed by demodulators 232, detected by MIMO detector 236, if applicable, and further processed by a receive processor 238 to obtain decoded data and control information sent by UE 120. Receive processor 238 may provide decoded data to data sink 239 and decoded control information to controller / processor 240. Base station 110 may include communication unit 244 and communicate with network controller 130 via communication unit 244. Network controller 130 may include communication unit 294, controller / processor 290, and memory 292.

[0067] 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 the base station 110 may perform one or more techniques associated with indicating a fallback to four-step RACH for two-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) may perform or direct e.g. Figure 10 Method 1000, Figure 13 The operations of method 1300, and / or other processes as described herein. Memories 242 and 282 may store data and program codes for use by BS 110 and UE 120, respectively. Scheduler 246 may schedule UEs for data transmission on the downlink and / or uplink.

[0068] As indicated above, Figure 2 These are provided as examples only. Other examples may differ from those regarding Figure 2 Examples described.

[0069] Figure 3 is a diagram illustrating an example 300 of an indication for a two-step random access fallback procedure. As shown, example 300 includes UE 120 and BS 110.

[0070] As in Figure 3 3 and indicated by reference numeral 310, UE 120 may transmit a RACH message (Msg) A to BS 110. For example, UE 120 may transmit RACH message A as part of a random access procedure, an initial access procedure, etc. RACH message A may be associated with a two-step RACH procedure. As further shown, RACH message A may include a preamble and a payload. The preamble may be encoded based at least in part on a random access radio network temporary identifier and / or may identify UE 120. The payload may include a physical uplink shared channel (PUSCH) and may include contention information for UE 120. BS 110 may perform contention resolution based at least in part on RACH message A, as described in more detail below.

[0071] As indicated by reference numeral 320, BS 110 may attempt to receive RACH message A. For example, BS 110 may attempt to receive a preamble and a payload. Successfully receiving, decoding, and processing a preamble may be referred to herein as successfully receiving the preamble, and successfully receiving, decoding, and processing a payload may be referred to herein as successfully receiving the payload. BS 110 may be more likely to successfully receive the preamble than the payload because the preamble is shorter and simpler to decode than the payload. Thus, three outcomes of the decoding may be expected: a first scenario, referred to as scenario A, in which the preamble and payload are detected and successfully received by BS 110; a second scenario, referred to as scenario B, in which the preamble is successfully received but the payload is not; and a third scenario, referred to as scenario C, in which neither the preamble nor the payload is successfully received. For scenario C, a MAC subheader including a backoff indicator may be used to indicate this outcome in 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 retry the RACH procedure, fall back to the four-step RACH procedure, or continue with random access since the preamble and payload were successfully received.

[0072] As shown by reference numeral 330, BS 110 may provide an indication of whether the preamble and payload have been successfully received (e.g., scenario A) or whether the payload has not been successfully received (e.g., scenario B). The indication may indicate (e.g., implicitly or explicitly) whether UE 120 will complete the two-step random access procedure, retry the random access procedure, or fall back to the four-step RACH procedure. The specific structure of the indication may be combined with the Figure 3-9 In some aspects, the indication may be provided in or associated with a random access response (RAR) (such as RACH message B), such as in conjunction with Figure 3-9 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 provided in conjunction with Figure 3-9 Described in more detail.

[0073] As indicated by reference numeral 340, UE 120 may selectively retry the RACH procedure or fall back to the 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, retrying a 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 UE 120 retries random access using the two-step RACH procedure, UE 120 may retransmit the payload in RACH message A. When UE 120 falls back to the four-step RACH procedure, UE 120 may retransmit the payload in RACH message 3. In some aspects, the UE 120 may retry random access based at least in part on determining that the indication indicates that the payload was not successfully received and / or that contention between the UE 120 and another UE has been resolved in favor of the other UE 120. When the UE 120 falls back to the four-step RACH procedure, the UE 120 may transmit the payload using RACH message 3 of the four-step RACH procedure, 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 an RRC connection based at least in part on the indication, and so on.

[0074] As indicated above, Figure 3 are provided as examples. Other examples may differ from those described in Figure 3 Examples described.

[0075] Figure 4 Is the explanation used for combining Figure 3 4 is a diagram of an example 400 of a medium access control messaging structure for an indication as described. The indication described in conjunction with example 400 may be included in a RAR from BS 110 to UE 120. As shown, example 400 illustrates a MAC payload 410 and a corresponding MAC subheader 420. The indication may be provided using a UE contention resolution identity, shown by reference numeral 430. For example, the UE contention resolution identity may identify a UE whose payload has been successfully received by BS 110. For example, the contention resolution identity may identify a UE identifier of corresponding UE 120. The length of the RAR may be indicated by a value L, shown by reference numeral 440, in MAC subheader 420.

[0076] If BS 110 successfully receives the preamble and payload of UE 120, BS 110 may transmit an indication as RACH message B using the structure shown in example 400. If the preamble is successfully received and the payload is not successfully received, BS 110 may transmit RACH message 2 (e.g., RACH message 2 associated with a four-step RACH procedure), which may be multiplexed in a MAC packet data unit (PDU) with RACH message B for a UE for which both the payload and preamble were successfully received. Additionally or alternatively, BS 110 may transmit RACH message B without a UE contention resolution identity, which may indicate to the receiving UE 120 that the corresponding payload was not successfully received or that the receiving UE 120 was not selected during the contention resolution phase of BS 110.

[0077] If UE 120 receives RACH message B with a UE contention resolution identity that matches UE 120, UE 120 may determine that the two-step RACH procedure is successful. If UE 120 receives RACH message B and RACH message B does not include UE contention resolution information or the UE contention resolution information does not identify UE 120, UE 120 may retry random access using a two-step RACH procedure (e.g., by retransmitting RACH message A on a subsequent RACH opportunity) or retry random access using a four-step RACH procedure (e.g., by transmitting a preamble associated with UE 120 on a subsequent RACH opportunity). If UE 120 receives RACH message 2, UE 120 may retransmit the payload of RACH message A using RACH message 3 of the four-step RACH procedure using the timing advance command, uplink grant, and temporary cell radio network temporary identifier (TC-RNTI) of RACH message 2. In other words, UE 120 may fall back to the four-step RACH procedure when UE 120 receives an indication of RACH message 2 being a four-step RACH procedure.

[0078] In some aspects, when the payload and preamble are successfully received, if the payload includes contention resolution information (e.g., in a common control channel (CCCH) service data unit (SDU)) in RACH message A, BS 110 may provide information identifying a timing advance command, an uplink grant, a cell radio network temporary identifier (C-RNTI), or a UE contention resolution identity in RACH message B. Furthermore, BS 110 may use a MAC subheader, shown as reference numeral 420.

[0079] In some aspects, when the payload is not successfully received, the UE 120 may receive a RACH message B in the format shown by reference numeral 410, but the contention resolution identity of the RACH message B will not match the UE 120. In this case, the UE 120 may ignore the RACH message B and may retry random access using a two-step RACH procedure or a four-step RACH procedure.

[0080] In some aspects, if UE 120 receives RACH message 2 or RACH message B without a UE contention resolution identity field (identifying UE 120), UE 120 may retransmit the payload of RACH message A using the timing advance (TA) command, uplink grant, and TC-RNTI of RACH message 2 or RACH message B and thereby fall back to the remaining steps of the four-step RACH procedure.

[0081] For an example of how the messaging structure described in conjunction with example 400 may be used in conjunction with multiple UEs, see below with reference to the accompanying Figure 5 Description.

[0082] As indicated above, Figure 4 are provided as examples. Other examples may differ from those described in Figure 4 Examples described.

[0083] Figure 5 1 is a diagram illustrating an example 500 of 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 group of UEs attempting random access relative to BS 110. BS 110 may provide an indication for the group of UEs indicating whether a preamble and / or payload for each UE has been successfully received. Figure 5 For the purpose of FIG, it is assumed that, on the same RACH opportunity, UE1 and UE2 use a first preamble index and UE3 and UE4 use a second preamble index, and 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 successfully receives only the payload of UE1.

[0084] In this scenario, BS 110 may provide UE1 and UE2 with a first MAC subheader (shown by reference numeral 510) indicating the length of the corresponding RACH message B (using the variable L shown in the MAC subheader). The corresponding RACH message B, shown by reference numeral 520, may include the UE contention resolution identity (not shown) of UE1 because UE1's payload was successfully received and UE2's payload was not, thereby causing BS 110 to resolve contention in favor of UE1. Furthermore, BS 110 may provide UE3 and UE4 with a second MAC subheader, shown by reference numeral 530. As shown, the second MAC subheader may indicate the length of the corresponding RACH message B or RACH message 2 (using the variable L). As shown by reference numeral 540, BS 110 may provide RACH message 2 in conjunction with MAC subheader 530 identifying the length of the corresponding RACH message 2 (or may provide RACH message B without the UE contention resolution identity, which is not shown), thereby indicating that the payloads of UE3 and UE4 were not received. Thus, UE3 and UE4 may fall back to the four-step RACH procedure to retransmit the payload of RACH message A.

[0085] As indicated above, Figure 5 are provided as examples. Other examples may differ from those described in Figure 5 Examples described.

[0086] Figure 6 Is the explanation used for combining Figure 3 6 shows an example 600 of a medium access control messaging structure for a RACH message B. Example 600 illustrates a MAC payload of a RACH message B. In the MAC payload, an indication bit, indicated by reference numeral 610, is used as an indicator (e.g., by toggling the value of F). In this scenario, if BS 110 receives the preamble and payload of UE 120, BS 110 may set F to a first value (e.g., 0) in RACH message B. If BS 110 does not successfully receive the payload, BS 110 may set F to a second value (e.g., 1).

[0087] If UE 120 receives RACH message B with a fallback indicator having a first value, UE 120 may check the value of the contention resolution MAC control element (CE). If the contention resolution identity matches UE 120, UE 120 may complete the two-step RACH procedure. If the contention resolution identity does not match UE 120, UE 120 may retry the RACH procedure using a two-step RACH procedure or a four-step RACH procedure. If UE 120 receives RACH message B with a fallback indicator having a second value, UE 120 may retransmit the payload of RACH message A using the TA command, uplink grant, and C-RNTI of RACH message B (e.g., by falling back to the four-step RACH procedure).

[0088] In the event that the payload and preamble are successfully received, the payload may include contention resolution information in RACH message A (e.g., in a CCCH SDU), and RACH message B may identify the TA command, uplink grant, C-RNTI, and a MAC subheader with a RAPID and a UE contention resolution MAC CE identifying the UE 120 from which the payload and preamble were successfully received.

[0089] In the event that the payload is not successfully received, RACH message B may be transmitted by BS 110 along with a MAC subheader including a RAPID. If the indication bit is set to a first value, UE 120 may ignore RACH message B and retry transmission using a two-step or four-step RACH procedure. If the indication bit is set to a second value, UE 120 may retransmit the payload of RACH message A using the TA command, uplink grant, and C-RNTI identified by RACH message B to perform a fallback to a four-step RACH procedure.

[0090] For an example of how the messaging structure described in conjunction with example 600 may be used in conjunction with multiple UEs, see below with reference to the accompanying Figure 7 Description.

[0091] As indicated above, Figure 6 are provided as examples. Other examples may differ from those described in Figure 6 Examples described.

[0092] Figure 77 is a diagram illustrating an example 700 of a media access control messaging 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 group of UEs attempting random access relative to BS 110. BS 110 may provide an indication for the group of UEs indicating whether a preamble and / or payload for each UE has been successfully received. Figure 7 For the purpose of FIG, it is assumed that, on the same RACH opportunity, UE1 and UE2 use a first preamble index and UE3 and UE4 use a second preamble index, and 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 successfully receives only the payload of UE1.

[0093] As in Figure 7 , BS 110 may provide UE contention resolution information identifying UE 1 based at least in part on successfully decoding the payload of UE 1. In addition, as shown by reference numeral 720, the MAC subheaders associated with UE 1 and UE 2 may identify the RAPIDs of UE 1 and UE 2 (e.g., RAPID 1), and as shown by reference numeral 730, the random access responses associated with UE 1 and UE 2 may include an indication bit set to a first value (e.g., F=0), which may indicate that UE 1 and UE 2 will not perform a fallback to a four-step RACH procedure. Thus, UE 1 may determine that the two-step RACH procedure was successful (e.g., based at least in part on the UE contention resolution identity MAC CE identifying UE 1 and the indication bit being set to the first value), and UE 2 may determine that UE 2 will retry the RACH procedure (e.g., based at least in part on the UE contention resolution identity MAC CE not identifying UE 2 and the indication bit being set to the first value).

[0094] As shown by reference numeral 740, the MAC subheader associated with UE3 and UE4 may identify the RAPID (e.g., RAPID2) of UE3 and UE4. As shown 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 fall back to the four-step RACH procedure.

[0095] As indicated above, Figure 7 are provided as examples. Other examples may differ from those described in Figure 7 Examples described.

[0096] Figure 8 Is the explanation used for combining Figure 3FIG8 is a diagram of an example 800 of a medium access control messaging structure for an indication. In example 800, if the preamble and payload of UE 120 are successfully received, a MAC subheader that does not include a RAPID may be used for RACH message B. If the payload is not successfully received, a MAC subheader that includes a RAPID may be used for RACH message B. UE 120 may determine whether BS 110 successfully received the payload based at least in part on whether a MAC subheader associated with UE 120 includes a RAPID associated with UE 120 and based at least in part on whether a contention resolution MAC CE for UE 120 is included in RACH message B. For example, if the contention resolution MAC CE for UE 120 matches the UE identifier of UE 120 and if the MAC subheader does not include a RAPID, UE 120 may determine that the two-step RACH procedure was successful. If the MAC subheader identifies a RAPID associated with UE 120, UE 120 may identify the RAPID and may retransmit the payload using the TA command, uplink grant, and C-RNTI of RACH message B to fall back to 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 may use the first sub-PDU and the random access response of UE2 may use the second sub-PDU.

[0097] Reference numeral 810 illustrates a first MAC subheader with a backoff indicator (BI) and without a RAPID. The values ​​T and F in the MAC subheader may indicate whether the first MAC subheader will include a backoff indicator, a RAPID, or a set of reserved bits. Here, T may be associated with a first value and F may be associated with a first value, indicating that the first MAC subheader will include a backoff indicator and not a RAPID.

[0098] Reference numeral 820 illustrates a second MAC subheader with a RAPID, which may be used to indicate that the payload is to be retransmitted by the UE 120. In the second MAC subheader, T may be associated with a second value, indicating that the second MAC subheader is to include a RAPID.

[0099] Reference numeral 830 illustrates a third MAC subheader having one or more reserved bits and no RAPID, which may be used in conjunction with a contention resolution MAC CE to indicate that the payload has been successfully received. Here, the value T may be set to a first value and F may be set to a second value, which may indicate that the third MAC subheader is to include one or more reserved bits and not include a RAPID or backoff indicator.

[0100] For an example of how the messaging structure described in conjunction with example 800 may be used in conjunction with multiple UEs, see the accompanying Figure 9 Description.

[0101] As indicated above, Figure 8 are provided as examples. Other examples may differ from those described in Figure 8 Examples described.

[0102] Figure 9 is a diagram illustrating an example 900 of a medium access control messaging structure for multiple UEs.

[0103] Example 900 includes a random access response that includes a set of MAC sub-packet data units (sub-PDUs) for a set of UEs attempting random access relative to BS 110. BS 110 may provide an indication for the set of UEs indicating whether a preamble and / or payload for each UE has been successfully received. Figure 9 For the purpose of FIG, it is assumed that, on the same RACH opportunity, UE1 and UE2 use a first preamble index and UE3 and UE4 use a second preamble index, and 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 successfully receives only the payload of UE1.

[0104] As in Figure 9 As shown by reference numeral 910, 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 subheaders associated with UE1 and UE2 may not include a RAPID, thereby indicating that BS 110 successfully received the payload associated with UE1 or UE2. Therefore, UE1 may complete the two-step RACH procedure. UE2 may not receive the random access response because the random access response does not include UE2's RAPID. As shown by reference numeral 930, the MAC subheaders associated with UE3 and UE4 may include the RAPID associated with UE3 and UE4, whereby UE3 and UE4 may fall back to the four-step RACH procedure accordingly.

[0105] In some aspects, the procedures described in conjunction with Examples 400 and 500, 600 and 700, and 800 and 900 may be performed in combination. For example, consider a combination of Examples 400 / 500 and 800 / 900. In this scenario, if the preamble and payload in RACH message A are successfully received, the BS may transmit RACH message B including UE contention resolution information, as described in more detail in conjunction with Examples 400 and 500. Furthermore, RACH message B may include a MAC subheader that does not include a RAPID, an F value indicating that a 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 may all be combined, or any pair of Examples 400 / 500, 600 / 700, and 800 / 900 may be combined.

[0106] As indicated above, Figure 9 are provided as examples. Other examples may differ from those described in Figure 9 Examples described.

[0107] Figure 10 1 is a flow chart of a wireless communication method 1000. The method may be performed by a UE (eg, Figure 1 UE 120, device 1102 / 1102', etc.) to execute.

[0108] At 1010, the UE (e.g., using the controller / processor 280, the transmit processor 264, the TX MIMO processor 266, the MOD 254, the antenna 252, etc.) may attempt random access by transmitting a random access message associated with a two-step random access procedure. For example, the random access message may include a RACH message A. The random access message may include a preamble and a payload.

[0109] At 1020, the UE (e.g., using antenna 252, DEMOD 254, MIMO detector 256, receive processor 258, controller / processor 280, etc.) may receive an indication regarding a random access message. For example, the indication may indicate that a preamble of the random access message and a payload of the random access message were successfully received or that the payload was not successfully received.

[0110] At 1030, the UE (e.g., using the controller / processor 280, the transmit processor 264, the TX MIMO processor 266, the MOD 254, the antenna 252, etc.) may complete a two-step random access procedure based at least in part 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 may establish an RRC connection with the base station, may camp on a cell provided by the base station, etc.

[0111] At 1040, the user equipment (e.g., using the controller / processor 280, the transmit processor 264, the TX MIMO processor 266, the MOD 254, the antenna 252, etc.) may retry random access or perform a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload was not successfully received. For example, the UE may retry random access using a two-step random access procedure or a four-step random access procedure. In this case, the UE may retransmit the preamble and payload according to the two-step random access procedure or the four-step random access procedure. In some aspects, the UE may perform a fallback to a four-step random access procedure. For example, the UE may retransmit the payload of the random access message as RACH message 3 of a four-step RACH procedure. As used herein, retrying random access may refer to transmitting the preamble and / or payload of the random access message after the preamble and / or payload have already been transmitted by the user equipment (e.g., on the same RACH opportunity or on a different RACH opportunity).

[0112] In a first aspect, the indication comprises a random access response associated with a two-step random access procedure, and the payload of the random access response comprises contention resolution information identifying a specific UE from which the payload of the random access message has been successfully received. In a second aspect, alone or in combination with the first aspect, the method further comprises retrying random access based at least in part on determining that the contention resolution information within the random access response does not identify the UE, the UE being configured to retry the random access procedure. In a third aspect, alone or in combination with the first aspect and / or the second aspect, a media access control (MAC) subheader of the random access response indicates a length of the random access response. In a fourth aspect, 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 based at least in part on a lack of contention resolution information identifying the UE in the random access response.

[0113] In a fifth aspect, alone or in combination with one or more of the first to fourth aspects, the MAC subheader of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC subheader. In a sixth aspect, 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 based at least in part on a control channel addressed to the UE using the C-RNTI of the UE. In a seventh aspect, 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, 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, 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, alone or in combination with one or more of the first to ninth aspects, the indication comprises a random access response associated with a two-step random access procedure, and the random access response identifies the C-RNTI of the UE. In an eleventh aspect, alone or in combination with one or more of the first to tenth aspects, the MAC subheader of the random access response comprises a set of bits indicating that the random access response is associated with contention resolution for a connected mode UE. In a twelfth aspect, alone or in combination with one or more of the first to eleventh aspects, the random access response comprises an uplink grant. In a thirteenth aspect, 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, alone or in combination with one or more of the first to thirteenth aspects, the UE is in idle mode or inactive mode when attempting random access. In a fifteenth aspect, alone or in combination with one or more of the first to fourteenth aspects, the indication is associated with a MAC subheader, the MAC subheader comprising a backoff indicator and a set of bits indicating that the MAC subheader comprises the backoff indicator.

[0114] In a sixteenth aspect, alone or in combination with one or more of aspects 1 to 15, the indication comprises a second message of a four-step random access procedure. In a seventeenth aspect, alone or in combination with one or more of aspects 1 to 16, the second message indicates that the payload was not successfully received. In an eighteenth aspect, alone or in combination with one or more of aspects 1 to 17, the method further comprises performing a fallback to a four-step random access procedure based at least in part on receiving the second message.

[0115] In a nineteenth aspect, alone or in combination with one or more of the first to eighteenth aspects, the indication comprises an indication bit in a MAC payload of a random access response message. In a twentieth aspect, alone or in combination with one or more of the first to nineteenth aspects, the indication bit indicates whether a fallback to a four-step random access procedure is to be performed. In a twenty-first aspect, alone or in combination with one or more of the first to twentieth aspects, based at least in part on the indication bit indicating that a fallback to a four-step random access procedure is not to be performed, the UE is configured to complete a two-step random access procedure based at least in part on contention resolution information of the random access response message identifying the UE. In a twenty-second aspect, alone or in combination with one or more of the first to twenty-first aspects, based at least in part on the indication bit indicating that a fallback to a four-step random access procedure is not to be performed, the UE is configured to retry random access based at least in part on the contention resolution information of the random access response message not identifying the UE.

[0116] In a twenty-third aspect, either alone or in combination with one or more of the first to twenty-second aspects, based at least in part on the preamble and payload being successfully received, the indicated MAC subheader 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 subheader does not include a preamble identifier, and the indicated contention resolution MAC control element 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 subheader including the MAC subheader are provided in sequence along 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 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 a field of the MAC subheader is used for the backoff indicator or for one or more reserved bits. In a twenty-sixth aspect, alone or in combination with one or more of the first to twenty-fifth aspects, a medium 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.

[0117] In a twenty-seventh aspect, alone or in combination with one or more of aspects 1 to 26, based at least in part on a preamble and a payload being successfully received, the indication comprises 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 comprises a MAC subheader without a preamble identifier. In a twenty-eighth aspect, alone or in combination with one or more of aspects 1 to 27, the MAC subheader indicates a length of the random access response and whether the MAC subheader is to include a backoff indicator.

[0118] although Figure 10 An example block diagram of a wireless communication method is shown, but in some aspects the method may include Figure 10 More boxes, fewer boxes, different boxes, or differently arranged boxes than those shown in FIG. Additionally or alternatively, Figure 10 Two or more blocks shown in FIG. 1 may be executed in parallel.

[0119] Figure 11 1100 is a conceptual data flow diagram illustrating the data flow between different modules / means / components in an example device 1102. The device 1102 may be a UE. In some aspects, the device 1102 includes a receiving module 1104 and / or a transmitting module 1106.

[0120] The receiving module 1104 may receive a signal 1108 from a base station 1150 (e.g., BS 110, etc.). The signal 1108 may include a random access response, such as RACH Message B or RACH Message 2, including an indication of the results of decoding RACH Message A, as described in greater detail elsewhere herein. In some aspects, the receiving module 1104 may receive an indication indicating that the preamble of the random access message and the payload of the random access message were successfully received, or that the payload was not successfully received. The transmitting module 1106 may transmit a signal 1110 to the base station 1150. The signal 1110 may include a random access message, such as RACH Message A, RACH Message 3, etc. In some aspects, the transmitting module 1106 may transmit a random access message associated with a two-step random access procedure, completing the two-step RACH procedure, retrying random access, or performing a fallback to a four-step random access procedure, as described elsewhere herein.

[0121] The apparatus may include executing Figure 10 The aforementioned method 1000 and the like are additional modules for each block of the algorithm. Figure 10Each block in the aforementioned 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.

[0122] Figure 11 The number and arrangement of modules shown in FIG are provided as examples. In practice, there may be Figure 11 More modules, fewer modules, different modules, or differently arranged modules than those shown in FIG. Figure 11 Two or more modules shown in FIG may be implemented in a single module, or Figure 11 The single module shown in can be implemented as multiple distributed modules. Additionally or alternatively, Figure 11 The module collection (e.g., one or more modules) shown in FIG can perform the operations described as being performed by Figure 11 Another module shown in FIG. 1 performs one or more functions.

[0123] Figure 12 is a diagram 1200 illustrating an example of a hardware implementation for a device 1102' employing a processing system 1202. The device 1102' may be a UE.

[0124] The processing system 1202 can be implemented with a bus architecture generally represented by 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 processor 1206, modules 1104, 1106, and computer-readable media / memory 1208). The bus 1204 may also link various other circuits, such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art and, therefore, will not be described further.

[0125] Processing system 1202 may be coupled to a transceiver 1210. Transceiver 1210 is coupled to one or more antennas 1212. Transceiver 1210 provides a means for communicating with various other devices over a transmission medium. Transceiver 1210 receives signals from one or more antennas 1212, extracts information from the received signals, and provides the extracted information to processing system 1202 (specifically, receive module 1104). Additionally, transceiver 1210 receives information from processing system 1202 (specifically, transmit module 1106) and generates signals to be applied to one or more antennas 1212 based at least in part on the received information. Processing system 1202 includes a processor 1206 coupled to a computer-readable medium / memory 1208. Processor 1206 is responsible for general processing, including the execution of software stored on computer-readable medium / memory 1208. When executed by processor 1206, the software enables 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 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 residing / 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: the TX MIMO processor 266, the RX processor 258, and / or the controller / processor 280.

[0126] In some aspects, an 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 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 / or means for selectively performing the following operations: completing the two-step random access procedure based at least in part 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 retrying random access or performing a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload has not been successfully received. The aforementioned means may be one or more of the aforementioned modules in the processing system 1202 of the apparatus 1102 and / or the apparatus 1102' configured to perform the functions recited by the aforementioned means. As described elsewhere herein, the processing system 1202 may include the TX MIMO processor 266, the RX processor 258, and / or the controller / processor 280. In one configuration, the aforementioned 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 recited herein.

[0127] Figure 12 are provided as examples. Other examples may differ from those incorporating Figure 12 Examples described.

[0128] Figure 13 1300 is a flow chart of a wireless communication method. The method may be performed by a base station (e.g., Figure 1 BS110, device 1402 / 1402', etc.) to execute.

[0129] 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.

[0130] At 1320, the base station (e.g., using the controller / processor 240, the transmit processor 220, the TX MIMO processor 230, the MOD 232, the 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 were successfully received or that the payload was not successfully received.

[0131] At 1330, the base station (e.g., using the controller / processor 240, the transmit processor 220, the TX MIMO processor 230, the MOD 232, the antenna 234, etc.) may complete a two-step random access procedure based at least in part 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 may establish an RRC connection with the base station, may camp on a cell provided by the base station, etc.

[0132] At 1340, the base station (e.g., using antenna 234, DEMOD 232, MIMO detector 236, receive processor 238, controller / processor 240, etc.) may receive messaging associated with the UE retrying random access or performing a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload was not successfully received. For example, the UE may retry random access using a two-step random access procedure or a four-step random access procedure. In this case, the UE may retransmit the preamble and payload according to the two-step random access procedure or the four-step random access procedure. In some aspects, the UE may perform a fallback to a four-step random access procedure. For example, the UE may retransmit the payload of the random access message as RACH message 3 of a four-step RACH procedure. The base station may receive the messaging described above.

[0133] In a first aspect, the indication comprises a random access response associated with a two-step random access procedure, wherein the payload of the random access response comprises contention resolution information identifying a specific UE whose random access message payload has been successfully received. In a second aspect, alone or in combination with the first aspect, a MAC subheader of the random access response indicates a length of the random access response. In a third aspect, alone or in combination with the first and / or second aspects, the random access response indicates that the payload was not successfully received based at least in part on a lack of contention resolution information identifying the UE in the random access response. In a fourth aspect, alone or in combination with one or more of the first to third aspects, the MAC subheader of the random access response comprises a set of bits indicating whether a backoff indicator is included in the MAC subheader. In a fifth aspect, alone or in combination with one or more of the first to fourth aspects, the indication comprises a random access response associated with a two-step random access procedure, and contention resolution for the UE is based at least in part on a control channel addressed to the UE using the UE's C-RNTI. In a fifth aspect, 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, alone or in combination with one or more of the first to fifth aspects, the random access response includes an uplink grant. In a seventh aspect, alone or in combination with one or more of the first to sixth aspects, the random access response does not include an uplink grant. In an eighth aspect, 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 C-RNTI of the UE. In a ninth aspect, alone or in combination with one or more of the first to eighth aspects, the MAC subheader of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for connected mode UEs. In a tenth aspect, alone or in combination with one or more of the first to ninth aspects, the random access response includes an uplink grant. In an eleventh aspect, alone or in combination with one or more of the first to tenth aspects, the random access response does not include an uplink grant. In a twelfth aspect, alone or in combination with one or more of the first to eleventh aspects, the UE is in idle mode or inactive mode when attempting random access. In a thirteenth aspect, alone or in combination with one or more of the first to twelfth aspects, the indication is associated with a MAC subheader, the MAC subheader including a backoff indicator and a set of bits indicating that the MAC subheader includes the backoff indicator.

[0134] In a fourteenth aspect, alone or in combination with one or more of the first to thirteenth aspects, the indication comprises a second message of a four-step random access procedure, wherein the second message indicates that the payload was not successfully received.

[0135] In a fifteenth aspect, alone or in combination with one or more of the first to fourteenth aspects, the indication comprises an indication bit in a MAC payload of a random access response message. In a sixteenth aspect, alone or in combination with one or more of the first to fifteenth aspects, the indication bit indicates whether a fallback to a four-step random access procedure is to be performed. In a seventeenth aspect, alone or in combination with one or more of the first to sixteenth aspects, based at least in part on the indication bit indicating that a fallback to a four-step random access procedure is not to be performed, the base station is configured to complete a two-step random access procedure based at least in part on contention resolution information of a random access response message identifying the UE. In an eighteenth aspect, alone or in combination with one or more of the first to seventeenth aspects, based at least in part on the indication bit indicating that a fallback to a four-step random access procedure is not to be performed, the base station is configured to receive messaging associated with a retry of random access based at least in part on the contention resolution information of a random access response message not identifying the UE.

[0136] In a nineteenth aspect, alone or in combination with one or more of the first to eighteenth aspects, based at least in part on the successful reception of a preamble and payload, the indicated MAC subheader does not include a preamble identifier. In a twentieth aspect, alone or in combination with one or more of the first to nineteenth aspects, based at least in part on the successful reception of a preamble and payload for a particular UE, the MAC subheader does not include a preamble identifier and the indicated contention resolution MAC control element identifies the particular UE. In a twenty-first aspect, 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.

[0137] In aspect 22, alone or in combination with one or more of aspects 1 to 21, 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 a field of the MAC subheader is used for the backoff indicator or for one or more reserved bits.

[0138] In a twenty-third aspect, alone or in combination with one or more of aspects 1 to 22, based at least in part on the successful reception of a preamble and a payload, the indication comprises 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 comprises a MAC subheader without a preamble identifier. In a twenty-fourth aspect, alone or in combination with one or more of aspects 1 to 23, the MAC subheader indicates a length of the random access response and whether the MAC subheader is to include a backoff indicator.

[0139] In a twenty-fifth aspect, alone or in combination with one or more of aspects 1 to 24, 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 aspects 1 to 25, the UE is a first UE, and the indication indicates whether a corresponding payload or a corresponding preamble of the first UE and a second UE has been received. In a twenty-seventh aspect, alone or in combination with one or more of aspects 1 to 26, a medium 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.

[0140] although Figure 13 An example block diagram of a wireless communication method is shown, but in some aspects the method may include Figure 13 More boxes, fewer boxes, different boxes, or differently arranged boxes than those shown in FIG. Additionally or alternatively, Figure 13 Two or more blocks shown in FIG. 1 may be executed in parallel.

[0141] Figure 14 1400 is a conceptual data flow diagram illustrating the flow of data between different modules / means / components in an example device 1402. The device 1402 may be a base station. In some aspects, the device 1402 includes a receiving module 1404 and / or a transmitting module 1406.

[0142] Receiving module 1404 may receive signal 1408 from UE 1450 (e.g., UE 120, etc.). Signal 1408 may include a random access message, such as RACH Message A, RACH Message 3, etc. In some aspects, transmitting module 1404 may 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. Transmitting module 1406 may transmit signal 1410 to UE 1450. Signal 1410 may include a random access response, such as RACH Message B or RACH Message 2, including an indication of the results of decoding RACH Message A, as described in greater detail elsewhere herein. In some aspects, transmitting module 1406 may transmit an indication indicating that the preamble of the random access message and the payload of the random access message were successfully received, or that the payload was not successfully received.

[0143] The apparatus may include executing Figure 13 The aforementioned method 1300 and the like are additional modules for each box of the algorithm. Figure 13 Each block in the aforementioned method 1300, 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.

[0144] Figure 14 The number and arrangement of modules shown in FIG are provided as examples. In practice, there may be Figure 14 More modules, fewer modules, different modules, or differently arranged modules than those shown in FIG. Figure 14 Two or more modules shown in FIG may be implemented in a single module, or Figure 14 The single module shown in can be implemented as multiple distributed modules. Additionally or alternatively, Figure 14 The module collection (e.g., one or more modules) shown in FIG can perform the operations described as being performed by Figure 14 Another module shown in FIG. 1 performs one or more functions.

[0145] Figure 15 is a diagram 1500 illustrating an example of a hardware implementation for a device 1402' employing a processing system 1502. The device 1402' may be a UE.

[0146] The processing system 1502 can be implemented with a bus architecture generally represented by bus 1504. Depending on the specific application and overall design constraints of the processing system 1502, the bus 1504 can include any number of interconnecting buses and bridges. The 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 media / memory 1508). The bus 1504 can also link various other circuits, such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art and, therefore, will not be described further.

[0147] Processing system 1502 may be coupled to a transceiver 1510. Transceiver 1510 is coupled to one or more antennas 1512. Transceiver 1510 provides a 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). In addition, transceiver 1510 receives information from processing system 1502 (specifically, transmitting 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 a processor 1506 coupled to a computer-readable medium / memory 1508. Processor 1506 is responsible for general processing, including the execution of software stored on computer-readable medium / memory 1508. When executed by processor 1506, the software enables processing system 1502 to perform the various functions described herein for any particular device. The computer-readable medium / memory 1508 may also be used to store data manipulated by the processor 1506 when executing software. The processing system further includes at least one of the modules 1404 and 1406. The modules may be software modules running in the processor 1506, software modules residing / stored in the computer-readable medium / memory 1508, one or more hardware modules coupled to the processor 1506, or some combination thereof. The processing system 1502 may be a component of the eNB 110 and may include the memory 242 and / or at least one of the following: the TX MIMO processor 230, the RX processor 238, and / or the controller / processor 240.

[0148] In some aspects, a device 1402 / 1402' for wireless communication includes: means for receiving a random access message associated with a two-step random access procedure from a user equipment (UE) attempting random access; 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 the following operations: completing the two-step random access procedure based at least in part 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 retrying random access or performing a fallback to a four-step random access procedure based at least in part on determining that the indication indicates that the payload has not been successfully received. The aforementioned means may be one or more of the aforementioned modules in the processing system 1502 of the device 1402 and / or device 1402' configured to perform the functions recited by the aforementioned means. As described elsewhere herein, the processing system 1502 may include the TX MIMO processor 230, the receive processor 238, and / or the controller / processor 240. In one configuration, the aforementioned 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.

[0149] Figure 15 are provided as examples. Other examples may differ from those incorporating Figure 15 Examples described.

[0150] Figure 161 is a diagram illustrating an example 1600 of a media access control messaging structure for an idle mode or inactive mode UE associated with a successful random access message. In other words, the MAC messaging structure shown in example 1600 can be used for a UE 120 that is in idle mode or inactive mode and whose random access message payload and preamble are successfully received. The payload of an indicator (e.g., a random access response) of the MAC messaging 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 the UE 120. In this case, the 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 subheader. For example, the MAC subheader can include a set of bits (shown as F1 and F2). The value of the set of bits can indicate information about the MAC subheader and / or payload. As an example, in example 1600, the value of the set of bits may indicate that the BI field is not present in the MAC subheader and may indicate that contention resolution information is present in the random access response. In this case, the Message B random access response may include a timing advance command, an uplink grant, a C-RNTI, and contention resolution information for a successful random access message.

[0151] Figure 16 are provided as examples. Other examples may differ from those incorporating Figure 16 Examples described.

[0152] Figure 17A and 17B is a diagram illustrating an example 1700 of a medium access control messaging structure for a UE associated with a random access message whose payload was not successfully received and whose preamble was successfully received, and an example of a medium access control subheader for a UE whose random access message was not successfully received. Example 1700 includes a MAC subheader 1710 and a MAC payload 1720 (in Figure 17A ) and / or MAC subheader 1730 (shown in Figure 17B For example, the MAC subheader 1710 and the MAC payload 1720 may include RACH message 2 of the four-step RACH procedure. A UE that receives the MAC subheader 1710 and the MAC payload 1720 may determine that the payload of the random access message transmitted by the UE was not successfully received.

[0153] As shown, the MAC subheader 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 subheader 1730 includes a BI field. The BI field may be used by a UE whose preamble and payload were not successfully received. For example, the UE may determine that the RACH procedure was unsuccessful based at least in part on determining that the UE's contention resolution information and preamble identifier were not identified by a set of random access responses, and may accordingly read the MAC subheader with the BI information only to determine the BI value for a subsequent random access message for the UE.

[0154] Example 1700 is applicable to connected mode UEs, idle mode UEs, and inactive mode UEs.

[0155] Figure 17A and 17B are provided as examples. Other examples may vary and combine Figure 17A and 17B Examples described.

[0156] Figure 18 1 is a diagram illustrating an example 1800 of a medium 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 subheader 1810 and a MAC payload 1820. In this scenario, contention resolution may be performed using a physical downlink control channel (PDCCH) addressed using the C-RNTI identified by the random access message transmitted by the UE. For example, in some scenarios (referred to herein as Option 1), if RACH message A includes a C-RNTI MAC-CE, contention resolution may be performed using a 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, RACH message B may be addressed to the RA-RNTI and may include information about multiple UEs. Contention resolution may be based on a contention resolution ID included in RACH message B, which may match the UE ID identified in RACH message A.

[0157] In another scenario (referred to herein as Option 2), RACH message B may contain information about multiple UEs and may be addressed to the RA-RNTI. In this scenario, the C-RNTI may be included in the random access response as contention resolution information for RRC_CONNECTED UEs. Example 1800 relates to Option 1.

[0158] As shown, the MAC subheader 1810 may include a set of bits (e.g., F1 and F2). In this case, the set of bits may be set to a value indicating that the random access response is 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, such as the following 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.

[0159] As shown, MAC payload 1820 includes an uplink grant. This uplink grant may be optional, as described elsewhere herein. As further shown, MAC payload 1820 may not include contention resolution information. For example, when Option 1 is used, MAC payload 1820 may not need to include contention resolution information. In this case, the uplink grant may be used for subsequent data transmission. Furthermore, MAC subheader 1810 may not identify a preamble identifier, as contention resolution is handled using the PDCCH addressed to the C-RNTI.

[0160] Figure 18 are provided as examples. Other examples may differ from those incorporating Figure 18 Examples described.

[0161] Figure 19 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, contention resolution information is included in the random access response in the form of a C-RNTI because the UE can use the RA-RNTI to receive the random access response sent from BS 110.

[0162] Figure 19 are provided as examples. Other examples may differ from those incorporating Figure 19 Examples described.

[0163] Figure 202000 is a diagram illustrating an example of a media access control messaging structure for multiple UEs. Random access responses for multiple UEs may be multiplexed, as illustrated in example 2000. For example, as shown by reference numeral 2010, a first MAC payload using the RACH message 2 format may indicate that the random access payload of one or more corresponding UEs was not successfully received. As shown by reference numeral 2020, the MAC subheader may include a set of bits (e.g., F1 and F2) indicating whether the MAC subheader is for an idle mode UE or a connected mode UE. The corresponding MAC payload shown by reference numeral 2030 may include a RACH message B identifying one or more UEs for which the corresponding random access response has been successfully received. In addition, as shown by reference numeral 2040, the MAC subheader of the MAC sub-PDU1 may include a set of bits (e.g., F1 and F2) indicating whether the MAC subheader includes a backoff indicator. The MAC subheader may be used to provide backoff information for UEs whose preamble and payload were not successfully received.

[0164] Figure 20 are provided as examples. Other examples may differ from those incorporating Figure 20 Examples described.

[0165] It should be understood that the specific order or hierarchy of the blocks in the disclosed process / flowcharts is illustrative of example approaches. 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 can be combined or omitted. The accompanying method claims present the elements of the various blocks in an example order and are not meant to be limited to the specific order or hierarchy presented.

[0166] The preceding 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 universal principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but rather should be granted the full scope consistent with the language of the claims, wherein references to the singular form of an element are not intended to mean "one and only one," but rather "one or more," unless otherwise stated. The term "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 superior to or superior to other aspects. Unless otherwise specifically stated, 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 "A, B, C, or any combination thereof" include any combination of A, B, and / or C, and may include multiple A, multiple B, or multiple C. Specifically, combinations such as "at least one of A, B, or C," "at least one of A, B, and C," and "A, B, C, or any combination thereof" may 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 may include one or more members of A, B, or C. All structural and functional equivalents to the various aspects described throughout this disclosure that are now or hereafter known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. In addition, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is expressly recited in the claims. No claim element should be construed as means-plus-function unless the element is expressly recited using the phrase "means-for-" or "means-for-" ("means-for").

Claims

1. A method of wireless communication performed by a user equipment (UE), comprising: attempting random access by transmitting a random access message associated with a two-step random access procedure, the random access message comprising a preamble and a payload in a single uplink message, and the payload comprising contention resolution information; receiving a random access response comprising a medium access control (MAC) subheader including a set of reserved bits and a MAC control element (MAC CE), the MAC subheader including a contention resolution identity associated with the contention resolution information of the payload of the random access message, wherein the contention resolution identity, in combination with the set of reserved bits, provides an indication of whether the preamble and the payload of the random access message are successfully received; If both the preamble and the payload of the random access message are successfully received, completing the two-step random access procedure; as well as If the preamble and the payload of the random access message are not both successfully received, a four-step random access procedure is performed.

2. The method of claim 1 , wherein the random access response is associated with the two-step random access procedure, and wherein the contention resolution identity identifies a specific UE from which the payload of the random access message was successfully received.

3. The method of claim 2, wherein the MAC subheader of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC subheader. The method of claim 1 , wherein the random access response identifies an uplink grant.

5. The method of claim 1, wherein the random access response is associated with the two-step random access procedure, and wherein the random access response is addressed to a cell radio network temporary identifier (C-RNTI) of the UE. The method of claim 5 , wherein a payload of the random access response does not include the C-RNTI.

7. The method of claim 5, wherein the random access response does not include an uplink grant.

8. The method of claim 1, wherein the random access response is associated with the two-step random access procedure, and wherein the random access response identifies a cell radio network temporary identifier (C-RNTI) of the UE.

9. The method of claim 8, wherein the random access response does not include an uplink grant.

10. The method of claim 8, wherein the MAC subheader of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for idle mode UEs or inactive mode UEs.

11. The method of claim 1, wherein the UE is in an idle mode or an inactive activity mode when attempting the random access.

12. The method of claim 1, wherein the UE is in a connected mode when attempting the random access.

13. The method of claim 1, wherein if both the preamble and the payload of the random access message are successfully received, the MAC subheader of the random access response does not include a preamble identifier.

14. The method of claim 13, wherein the MAC CE of the random access response identifies a specific UE at which both the preamble and the payload were successfully received.

15. The method of claim 13, wherein the MAC subheader comprises a first bit and a second bit, the first bit indicating whether a backoff indicator or the preamble identifier is included in the MAC subheader, the second bit indicating whether a field of the MAC subheader is used for the backoff indicator or for the set of reserved bits.

16. A method for performing wireless communication by a base station, comprising: receiving, from a user equipment (UE) attempting random access, a random access message associated with a two-step random access procedure, the random access message comprising a preamble and a payload in a single uplink message, and the payload comprising contention resolution information; transmitting a random access response comprising a medium access control (MAC) subheader including a set of reserved bits and a MAC control element (MAC CE), the MAC subheader including a contention resolution identity associated with the contention resolution information of the payload of the random access message, wherein the contention resolution identity, in combination with the set of reserved bits, provides an indication of whether the preamble and the payload of the random access message are successfully received; If both the preamble and the payload of the random access message are successfully received, completing the two-step random access procedure; as well as If the preamble and the payload of the random access message are not both successfully received, a four-step random access procedure is performed.

17. The method of claim 16, wherein the random access response is associated with the two-step random access procedure, wherein the contention resolution identity identifies a specific UE for which the payload of the random access message was successfully received.

18. The method of claim 17, wherein the MAC subheader of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC subheader.

19. The method of claim 16, wherein the random access response identifies an uplink grant.

20. The method of claim 16, wherein the random access response is associated with the two-step random access procedure, and wherein the random access response is addressed to a cell radio network temporary identifier (C-RNTI) of the UE.

21. The method of claim 20, wherein the MAC subheader of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for idle mode UEs or inactive mode UEs.

22. A user equipment (UE) for wireless communication, comprising: one or more memories; as well as One or more processors coupled to the one or more memories, the one or more processors being configured, individually or in any combination, to: attempting random access by transmitting a random access message associated with a two-step random access procedure, the random access message comprising a preamble and a payload in a single uplink message, and the payload comprising contention resolution information; receiving a random access response comprising a medium access control (MAC) subheader including a set of reserved bits and a MAC control element (MAC CE), the MAC subheader including a contention resolution identity associated with the contention resolution information of the payload of the random access message, wherein the contention resolution identity, in combination with the set of reserved bits, provides an indication of whether the preamble and the payload of the random access message are successfully received; If both the preamble and the payload of the random access message are successfully received, completing the two-step random access procedure; as well as If the preamble and the payload of the random access message are not both successfully received, a four-step random access procedure is performed.

23. The UE of claim 22, wherein the random access response is associated with the two-step random access procedure, and wherein the contention resolution identity identifies a specific UE from which the payload of the random access message was successfully received.

24. The UE of claim 22, wherein the random access response is associated with the two-step random access procedure, and wherein the random access response is addressed to a Cell Radio Network Temporary Identifier (C-RNTI) of the UE.

25. The UE of claim 22, wherein the random access response is associated with the two-step random access procedure, and wherein the random access response identifies a cell radio network temporary identifier (C-RNTI) of the UE.

26. The UE of claim 22, wherein if both the preamble and the payload of the random access message are successfully received, the MAC subheader of the random access response does not include a preamble identifier.

27. The UE of claim 22, wherein the random access response identifies an uplink grant.

28. A base station for wireless communication, comprising: one or more memories; as well as One or more processors coupled to the one or more memories, the one or more processors being configured, individually or in any combination, to: receiving, from a user equipment (UE) attempting random access, a random access message associated with a two-step random access procedure, the random access message comprising a preamble and a payload in a single uplink message, and the payload comprising contention resolution information; transmitting a random access response comprising a medium access control (MAC) subheader including a set of reserved bits and a MAC control element (MAC CE), the MAC subheader including a contention resolution identity associated with the contention resolution information of the payload of the random access message, wherein the contention resolution identity, in combination with the set of reserved bits, provides an indication of whether the preamble and the payload of the random access message are successfully received; If both the preamble and the payload of the random access message are successfully received, completing the two-step random access procedure; as well as If the preamble and the payload of the random access message are not both successfully received, a four-step random access procedure is performed.

29. The base station of claim 28, wherein the random access response is associated with the two-step random access procedure, wherein the contention resolution identity identifies a specific UE for which the payload of the random access message was successfully received.

30. The base station of claim 28, wherein the random access response identifies an uplink grant.

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