CN113647191A

CN113647191A - Random access procedure

Info

Publication number: CN113647191A
Application number: CN202080025180.2A
Authority: CN
Inventors: 郑瑞明; L·何; 魏超; 雷静; 张晓霞; O·奥兹图科; G·B·霍恩
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 2019-04-11
Filing date: 2020-04-08
Publication date: 2021-11-12
Also published as: WO2020206651A1; WO2020206768A1; SG11202109913QA

Abstract

Some techniques and devices described herein provide for 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 contention resolution identity of the UE may be provided in a random access response. Some of the techniques and apparatus described herein may use a fallback indicator indicating a result of the decoding and/or an 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 the decoding and/or the action to be performed.

Description

Random access procedure

Cross Reference to Related Applications

This application claims priority from Patent Cooperation Treaty (PCT) patent application No. PCT/CN2019/082238, filed on 11/4/2019, and PCT patent application No. PCT/CN2019/085126, filed on 30/4/2019, entitled "INDICATION FOR TWO-STEP RACH FALLBACK TO FOUR-STEP RACH (INDICATION of a TWO-STEP RACH FALLBACK TO a FOUR-STEP RACH)" and both of which are expressly incorporated herein by reference.

Background

FIELD

Aspects of the present disclosure generally relate to wireless communications and techniques and apparatus for indication of a two-step Random Access Channel (RACH) fallback to a four-step RACH.

Background

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasting. Typical wireless communication systems may employ multiple-access techniques capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple-access techniques 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 an enhanced set of Universal Mobile Telecommunications System (UMTS) mobile standards promulgated by the third generation partnership project (3 GPP).

A wireless communication network may include a number of Base Stations (BSs) capable of supporting communication for a number of User Equipments (UEs). The UE may communicate with the BS via a downlink and an uplink. The downlink (or forward link) refers to the communication link from the BS to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the BS. As will be described in greater detail herein, a BS may be referred to as a node B, a gNB, an Access Point (AP), a radio head, a Transmission Reception Point (TRP), a 5G BS, a 5G B node, and so on.

The above multiple access techniques have been adopted in various telecommunications standards to provide a common protocol that enables different wireless communication devices to communicate on a city, country, region, and even global level. 5G, which may also be referred to as New Radio (NR), is an enhanced set of LTE mobile standards promulgated by the third generation partnership project (3 GPP). 5G is designed to better support mobile broadband internet access by improving spectral efficiency, reducing costs, improving services, utilizing new spectrum, and better integrating with the use of OFDM with Cyclic Prefix (CP) (CP-OFDM) on the Downlink (DL), CP-OFDM and/or SC-FDM (e.g., also known as discrete fourier transform spread OFDM (DFT-s-OFDM)) on the Uplink (UL), and other open standards that support beamforming, Multiple Input Multiple Output (MIMO) antenna technology, and carrier aggregation. However, as the demand for mobile broadband access continues to grow, there is a need for further improvements in LTE and 5G technologies. Preferably, these improvements should be applicable to other multiple access techniques and telecommunications standards employing these techniques.

SUMMARY

The UE may perform a random access procedure (e.g., a Random Access Channel (RACH) procedure, a physical RACH (prach) procedure, etc.) to access the network via the BS. In some cases, the UE may perform a four-step RACH procedure involving a first uplink random access message (e.g., message 1 or Msg1) for providing a preamble of the UE, a second downlink random access response to the first uplink random access message (e.g., message 2 or Msg2), a third uplink random access message with a payload (e.g., message 3 or Msg3), and a fourth downlink random access message (e.g., message 4 or Msg 4). In some cases, the UE may perform a two-step RACH procedure in which message 1 and message 3 are combined into a single uplink message (message a or MsgA) and message 2 and message 4 are combined into a single downlink message (e.g., message B or MsgB). In some cases, the BS may successfully receive the preamble of the RACH message and may fail to receive the payload of the RACH message (e.g., message a). In this case, the UE may fall back to the four-step RACH approach or may reattempt the random access. In other cases, the BS may successfully receive the payload and the preamble. In this case, the RACH procedure may continue uninterrupted. It may be useful to provide a messaging system by which the BS can signal the results of decoding the RACH message (e.g., preamble and payload successfully received, preamble successfully received and payload unsuccessfully received, preamble and payload unsuccessfully received, etc.) and actions to be performed by the UE (e.g., fallback to a four-step RACH procedure, reattempting a two-step RACH procedure or a four-step RACH procedure, retransmitting the payload of the RACH message, etc.).

Some of the techniques and apparatus 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 the indication using a UE contention resolution identity based approach, where the contention resolution identity of the UE may be provided in a random access response. Some of the techniques and apparatus described herein may use a fallback indicator indicating a result of the decoding and/or an 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 the decoding and/or the action to be performed. In this way, the BS may signal to the UE the result of the decoding and/or the action to be performed. The UE may perform the action (e.g., fallback to a four-step RACH procedure, reattempt the RACH, etc.) according to the indication. Thereby, the granularity of actions to be signaled in connection with the two-step RACH procedure may be improved, thereby increasing the network performance and increasing the reliability of the two-step RACH procedure. Further, the techniques and devices described herein provide a messaging structure for indicating RACH results to a plurality of UEs in a Medium Access Control (MAC) message to the plurality of UEs, e.g., using contention resolution information or other information associated with the plurality of UEs. For example, if a first UE receives a MAC message with contention resolution information for a second UE, the first UE may perform an action based at least in part on information in the MAC message. The second UE may determine that the RACH message of the second UE was successfully received if the second UE receives the MAC message with contention resolution information for the second UE. These MAC messages may be used to provide indications of decoding results and/or actions for multiple UEs (e.g., four UEs, eight UEs, etc.). Such feedback, combined to multiple UEs in association with an indication of an action to be performed, may improve utilization of network resources and reduce usage of UE computing resources relative to a UE-by-UE indication of whether a RACH procedure was successful.

In this way, the amount of monitoring scheduling information to be performed by the UE is reduced, thereby saving computational resources and power for the UE. Furthermore, by providing contention resolution information in the random access response, the communication and computational resource usage of the UE is reduced relative to providing the contention resolution information separately from the random access response. Furthermore, by providing contention resolution information in the random access response, the indicated decoding complexity and decoding error probability is reduced relative to providing contention resolution information separately from the random access response.

In an aspect of the disclosure, a method, a User Equipment (UE), a base station, an apparatus, and a computer program product are provided.

In some aspects, a method of wireless communication performed by a UE may comprise: attempting random access by transmitting a random access message associated with the two-step random access procedure; receiving a preamble indicating the random access message and an indication that a payload of the random access message has been successfully received or that the payload has not been successfully received; and selectively performing the following: completing 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, 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.

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: attempting random access by transmitting a random access message associated with the two-step random access procedure; receiving a preamble indicating the random access message and an indication that a payload of the random access message has been successfully received or that the payload has not been successfully received; and selectively performing the following: completing 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, 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.

In some aspects, the apparatus may comprise: means for attempting random access by transmitting a random access message associated with a two-step random access procedure; means for receiving a preamble indicating the random access message and an indication that a payload of the random access message has been successfully received or that the payload has not been successfully received; and means for selectively performing the following: completing 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, 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.

In some aspects, a computer program product may include a non-transitory computer-readable medium storing one or more instructions. The one or more instructions, when executed by the one or more processors of the UE, may cause the one or more processors to: attempting random access by transmitting a random access message associated with the two-step random access procedure; receiving a preamble indicating the random access message and an indication that a payload of the random access message has been successfully received or that the payload has not been successfully received; and selectively performing the following: completing 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, 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.

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

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: receiving a random access message associated with a two-step random access procedure from a UE attempting random access; transmitting a preamble indicating the random access message and an indication that the payload of the random access message has been successfully received or that the payload has not been successfully received; and selectively performing the following: completing a two-step random access procedure based at least in part on determining that the indication indicates that a preamble of the random access message and a payload of the random access message have been successfully received, or receiving messaging associated with a UE re-attempting random access or performing 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.

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 a preamble indicating the random access message and an indication that a payload of the random access message has been successfully received or that a payload has not been successfully received; and means for selectively performing the following: completing a two-step random access procedure based at least in part on determining that the indication indicates that a preamble of the random access message and a payload of the random access message have been successfully received, or receiving messaging associated with a UE re-attempting random access or performing 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.

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

Aspects generally include methods, devices, 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 by the accompanying figures.

The foregoing has outlined rather broadly the features and technical advantages of an example in accordance with the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter. The conception and specific examples disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Such equivalent constructions do not depart from the scope of the appended claims. The features of the concepts disclosed herein, both as to their organization and method of operation, together with associated advantages, will be better understood from the following description when considered in connection with the accompanying figures. Each of the figures is provided for the purpose of illustration and description, and not for the purpose of defining the limits of the claims.

Brief Description of Drawings

Fig. 1 is a diagram illustrating an example of a wireless communication network.

Fig. 2 is a diagram illustrating an example of a base station in communication with a UE in a wireless communication network.

Fig. 3 is a diagram illustrating an example of an indication for a two-step random access backoff procedure.

Fig. 4 is a diagram illustrating an example of a media access control messaging structure for the indication as described in connection with fig. 3.

Fig. 5 is a diagram illustrating an example of a media access control messaging structure for multiple UEs.

Fig. 6 is a diagram illustrating an example of a media access control messaging structure for the indication as described in connection with fig. 3.

Fig. 7 is a diagram illustrating an example of a media access control messaging structure for multiple UEs.

Fig. 8 is a diagram illustrating an example of a media access control messaging structure for the indication as described in connection with fig. 3.

Fig. 9 is a diagram illustrating an example of a media access control messaging structure for multiple UEs.

Fig. 10 is a flow chart of a method of wireless communication.

Fig. 11 is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an example apparatus.

Fig. 12 is a diagram illustrating an example of a hardware implementation of an apparatus employing a processing system.

Fig. 13 is a flow chart of a method of wireless communication.

Fig. 14 is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an example apparatus.

Fig. 15 is a diagram illustrating an example of a hardware implementation of a device employing a processing system.

Fig. 16 is a diagram illustrating an example of a media access control messaging structure for an idle mode or inactive mode UE associated with a successful random access message.

Fig. 17A and 17B are diagrams 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 no portion of the random access message was successfully received.

Fig. 18 is a diagram illustrating an example of a media access control messaging structure for a connected mode UE associated with a random access message whose payload has been successfully received.

Fig. 19 is a diagram illustrating an example of a media access control message payload for a connected mode UE associated with a successful random access message.

Fig. 20 is a diagram illustrating an example of a media access control messaging structure for multiple UEs.

Detailed Description

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the configurations in which the concepts described herein may be practiced. The detailed description includes specific details to provide a thorough understanding of the various concepts. It will be apparent, however, to one 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 in order to avoid obscuring such concepts.

Several aspects of a telecommunications system will now be presented with reference to various apparatus and methods. These apparatus and methods are described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, procedures, algorithms, and so forth (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 upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a "processing system" that includes one or more processors. Examples of processors include microprocessors, microcontrollers, Digital Signal Processors (DSPs), Field Programmable Gate Arrays (FPGAs), Programmable Logic Devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionalities described throughout this disclosure. One or more processors in the processing system may execute software. Software should be construed broadly to mean instructions, instruction sets, code segments, program code, programs, subprograms, software modules, applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to in software, firmware, middleware, microcode, hardware description language, or other terminology.

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, the functions may be stored or encoded as one or more instructions or code on a computer-readable medium. Computer readable media includes computer storage media. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise Random Access Memory (RAM), Read Only Memory (ROM), Electrically Erasable Programmable ROM (EEPROM), compact disk ROM (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, combinations of the above types of computer-readable media, or any other medium which can be used to store computer-executable code in the form of instructions or data structures that can be accessed by a computer.

It should be noted that although aspects may be described herein using terms commonly associated with 3G and/or 4G wireless technologies, aspects of the present disclosure may be applied in other generation-based communication systems, such as 5G and beyond.

Fig. 1 is a diagram illustrating a wireless network 100 in which aspects of the present disclosure may be practiced. The wireless network 100 may be an LTE network or some other wireless network, such as a 5G network. Wireless network 100 may include several BSs 110 (shown as BS 110a, BS 110b, BS 110c, and BS 110d) and other network entities. A BS is an entity that communicates with User Equipment (UE) and may also be referred to as a base station, a 5G BS, a node B, a gNB, a 5G NB, an access point, a Transmit Receive Point (TRP), and so on. Each BS may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to a coverage area of a BS and/or a BS subsystem serving that coverage area, depending on the context in which the term is used.

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. Picocells may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscriptions. A femtocell may cover a relatively small geographic area (e.g., a residence) and may allow restricted access by UEs associated with the femtocell (e.g., UEs in a Closed Subscriber Group (CSG)). The BS for the macro cell may be referred to as a macro BS. A BS for a picocell may be referred to as a pico BS. The BS for the femtocell may be referred to as a femto BS or a home BS. In the example shown in fig. 1, 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 102 c. 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.

In some examples, the cell may not necessarily be stationary, and the geographic area of the cell may move according to 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 the wireless network 100 by various types of backhaul interfaces, such as direct physical connections, virtual networks, and/or the like using any suitable transport network.

Wireless network 100 may also include relay stations. A relay station is an entity that can receive a transmission of data from an upstream station (e.g., a BS or a UE) and send the transmission of the data to a downstream station (e.g., the UE or the BS). The relay station may also be a UE that can relay transmissions for other UEs. In the example shown in fig. 1, relay 110d may communicate with macro BS 110a and UE120 d to facilitate communication between BS 110a and UE120 d. The relay station may also be referred to as a relay BS, a relay base station, a relay, etc.

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 effects on interference in 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).

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

UEs 120 (e.g., 120a, 120b, 120c) may be dispersed throughout wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as an access 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, 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 (a smartwatch, a smartgarment, smartglasses, a smartwristband, smartjewelry (e.g., a smartring, a smartband)), an entertainment device (e.g., a music or video device, or a satellite radio), a vehicle-mounted component or sensor, a smartmeter/sensor, industrial manufacturing equipment, a global positioning system device, or any other suitable device configured to communicate via a wireless or wired medium.

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, a robot, a drone, a remote device, a sensor, a meter, a monitor, a location tag, etc., which may communicate with a base station, another device (e.g., a remote device), or some other entity. A wireless node may provide connectivity for or to a network, e.g., a wide area network such as the internet or a cellular network, e.g., 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 Premise Equipment (CPE). UE120 may be included within a housing that houses components of UE120, such as a processor component, a memory component, and so forth.

In general, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a particular RAT and may operate on one or more frequencies. A RAT may also be referred to as a radio technology, air interface, etc. A frequency may also be referred to as a carrier, a frequency channel, etc. Each frequency may support a single RAT in a given geographic area to avoid interference between wireless networks of different RATs. In some cases, a 5GRAT network may be deployed.

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

The base station is not the only entity that can be used as a scheduling entity. That is, in some examples, a UE may function as a scheduling entity, 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 resources scheduled by the UE for wireless communications. The UE may be used as a scheduling entity in a peer-to-peer (P2P) network and/or in a mesh network. In the mesh network example, the UEs may optionally communicate directly with each other in addition to communicating with the scheduling entity.

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

As indicated above, fig. 1 is provided merely as an example. Other examples may differ from the example described with respect to fig. 1.

Fig. 2 shows a block diagram 200 of a design of base station 110 and UE120, which may be one of the base stations and one of the UEs in fig. 1. The base station 110 may be equipped with T antennas 234a through 234T, while the UE120 may be equipped with R antennas 252a through 252R, where T ≧ 1 and R ≧ 1 in general.

At base station 110, a transmit processor 220 may receive data from a data source 212 for one or more UEs, may select one or more Modulation and Coding Schemes (MCSs) 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), etc.) 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 the data symbols, the control symbols, the overhead symbols, and/or the reference symbols, if 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 upconvert) the output sample stream to obtain a downlink signal. T downlink signals from modulators 232a through 232T may be transmitted via T antennas 234a through 234T, respectively. According to various aspects described in more detail below, a synchronization signal may be generated utilizing position coding to convey additional information.

At UE120, 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) a 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 if applicable, and provide detected symbols. A Receive (RX) processor 258 may process (e.g., demodulate and decode) the detected symbols, provide decoded data for UE120 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.

On the uplink, at UE120, a transmit processor 264 may receive and process data from a data source 262 and control information from a controller/processor 280 (e.g., for reports including RSRP, RSSI, RSRQ, CQI, etc.). Transmit processor 264 may also generate reference symbols for one or more reference signals. The symbols from 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 base station 110. At base station 110, the uplink signals from UE120 and other UEs may be received by antennas 234, processed by demodulators 232, detected by a 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 a data sink 239 and decoded control information to controller/processor 240. The base station 110 may include a communication unit 244 and communicate with the network controller 130 via the communication unit 244. Network controller 130 may include a communication unit 294, a controller/processor 290, and a memory 292.

The controller/processor 240 of the base station 110, the controller/processor 280 of the UE120, and/or any other component(s) of fig. 2 may perform one or more techniques associated with the indication of the two-step RACH to the four-step RACH, as described in more detail elsewhere herein. For example, controller/processor 240 of base station 110, controller/processor 280 of UE120, and/or any other component(s) of fig. 2 may perform or direct operations of, for example, method 1000 of fig. 10, method 1300 of fig. 13, and/or other processes as described herein. Memories 242 and 282 may store data and program codes for BS 110 and UE120, respectively. A scheduler 246 may schedule UEs for data transmission on the downlink and/or uplink.

As indicated above, fig. 2 is provided merely as an example. Other examples may differ from the example described with respect to fig. 2.

Fig. 3 is a diagram illustrating an example 300 of an indication for a two-step random access backoff procedure. As shown, example 300 includes UE120 and BS 110.

As shown in fig. 3 and by reference numeral 310, UE120 may transmit RACH message (Msg) a to BS 110. For example, UE120 may transmit RACH message a as part of a random access procedure, an initial access procedure, and/or the like. 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 encode and/or may identify the UE120 based at least in part on a random access radio network temporary identifier. The payload may include a Physical Uplink Shared Channel (PUSCH) and may include contention information for the UE 120. BS 110 may perform contention resolution based at least in part on RACH message a, as described in more detail below.

As shown 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 the preamble may be referred to herein as successfully receiving the preamble, and successfully receiving, decoding, and processing the payload may be referred to herein as successfully receiving the payload. 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 results of decoding can 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 successfully received; and a third scenario, referred to as scenario C, in which neither the preamble nor the payload is successfully received. For case C, the result may be indicated in RACH message B using a MAC subheader including a backoff indicator. The techniques and devices described herein provide signaling to distinguish between case a and case B and indicate whether the UE should reattempt the RACH procedure, fall back to a four-step RACH procedure, or continue random access because the preamble and payload are successfully received.

As shown by reference numeral 330, BS 110 may provide an indication of whether the preamble and payload have been successfully received (e.g., case a) or whether the payload has not been successfully received (e.g., case B). The indication may indicate (e.g., implicitly or explicitly) whether the UE120 is to complete the two-step random access procedure, reattempt the random access procedure, or fall back to the four-step RACH procedure. The specific structure of this indication is described in more detail in connection with fig. 3-9. In some aspects, the indication may be provided in or in association with a Random Access Response (RAR), such as RACH message B, as described in more detail in connection with fig. 3-9. In some aspects, the indication may be provided in RACH message 2 (e.g., RACH message 2 associated with a four-step RACH procedure), as also described in more detail in conjunction with fig. 3-9.

As illustrated by reference numeral 340, the UE120 can selectively reattempt the RACH procedure or fall back to a four-step RACH procedure as a function of the indication (e.g., when the indication is associated with case B), or can complete the RACH procedure (e.g., when the indication is associated with case a). As used herein, reattempting the RACH procedure may refer to selecting another RACH preamble and transmitting another RACH message (e.g., RACH message a associated with a two-step RACH procedure or RACH message 1 associated with a four-step RACH procedure). When UE120 re-attempts random access using the two-step RACH procedure, UE120 may retransmit the payload in RACH message a. When UE120 falls back to the four-step RACH procedure, UE120 may retransmit the payload in RACH message 3. In some aspects, the UE120 may reattempt random access based at least in part on determining that the indication indicates that the payload was not successfully received and/or that contention of the UE120 with another UE has been resolved in favor of the other UE 120. When UE120 falls back to the four-step RACH procedure, UE120 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 UE120 completes the RACH procedure, UE120 may receive Radio Resource Control (RRC) information, may configure an RRC connection based at least in part on the indication, and so on.

As indicated above, fig. 3 is provided as an example. Other examples may differ from the example described with respect to fig. 3.

Fig. 4 is a diagram illustrating an example 400 for a media access control messaging structure for indications as described in connection with fig. 3. The indication described in connection with example 400 may be included in a RAR from BS 110 to UE 120. As shown, example 400 shows 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 the corresponding UE 120. The length of the RAR may be indicated by a value L shown by reference numeral 440 in the MAC subheader 420.

If BS 110 successfully receives the preamble and payload of UE120, 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 RACH message 2 may be multiplexed in a MAC Packet Data Unit (PDU) with RACH message B for UEs whose payloads and preambles have both been successfully received. Additionally or alternatively, BS 110 may transmit RACH message B without a UE contention resolution identity, which may indicate to receiving UE120 that the corresponding payload was not successfully received, or that receiving UE120 was not selected during the contention resolution phase of BS 110.

If UE120 receives RACH message B with a UE contention resolution identity matching that UE120, UE120 may determine that the two-step RACH procedure is successful. If UE120 receives RACH message B and either RACH message B does not include UE contention resolution information or UE contention resolution information does not identify UE120, UE120 may reattempt random access using a two-step RACH procedure (e.g., by retransmitting RACH message a on a subsequent RACH occasion) or a four-step RACH procedure (e.g., by transmitting a preamble associated with UE120 on a subsequent RACH occasion). If the UE120 receives RACH message 2, the UE120 can retransmit the payload of RACH message A using RACH message 3 of the four-step RACH procedure using the timing advance command, the uplink grant, and the temporary cell radio network temporary identifier (TC-RNTI) of RACH message 2. In other words, the UE120 may fall back to the four-step RACH procedure when the UE120 receives an indication of RACH message 2 as the four-step RACH procedure.

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. Further, BS 110 may use a MAC subheader as shown at reference numeral 420.

In some aspects, when the payload is not successfully received, UE120 may receive RACH message B of the format shown by reference numeral 410, but the contention resolution identity of RACH message B will not match UE 120. In this case, the UE120 may ignore RACH message B and may reattempt random access using the two-step RACH procedure or the four-step RACH procedure.

In some aspects, if the UE120 receives RACH message 2 or RACH message B without a UE contention resolution identity field (identifying the UE 120), the UE120 may retransmit the payload of RACH message a using a Timing Advance (TA) command, an uplink grant, and a TC-RNTI of RACH message 2 or RACH message B and thus fall back to the remaining steps of the four-step RACH procedure.

An example of how the messaging structure described in connection with example 400 may be used in connection with multiple UEs is described below with reference to accompanying fig. 5.

As indicated above, fig. 4 is provided as an example. Other examples may differ from the example described with respect to fig. 4.

Fig. 5 is a diagram illustrating an example 500 of a media access control messaging structure for multiple UEs. Example 500 includes a random access response including a set of MAC sub-packet data units (sub-PDUs) for a set of UEs attempting random access with respect to BS 110. BS 110 may provide an indication to the group of UEs indicating whether the preamble and/or payload of each UE has been successfully received. For the purposes of fig. 5, assume that on the same RACH occasion, UE1 and UE2 use a first preamble index and UE3 and UE4 use a second preamble index, and assume that UE1, UE2, UE3, and UE4 perform a two-step RACH procedure. Further assume that BS 110 successfully receives preambles for all four UEs and that BS 110 successfully receives only the payload of UE 1.

In this case, BS 110 may provide UE1 and UE2 with a first MAC subheader (indicated by reference numeral 510) indicating the length of the corresponding RACH message B (using variable L shown in the MAC subheader). The corresponding RACH message B, shown by reference numeral 520, may include a UE contention resolution identity (not shown) for UE1 because the payload of UE1 was successfully received and the payload of UE2 was not successfully received, thereby causing BS 110 to resolve contention in favor of UE 1. Further, 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 variable L). As shown by reference numeral 540, BS 110 may provide RACH message 2 (or may provide RACH message B without a UE contention resolution identity, which is not shown) in conjunction with MAC subheader 530 identifying the length of the corresponding RACH message 2, thereby indicating that the payloads of UE3 and UE4 are not received. As such, UE3 and UE4 may fall back to the four-step RACH procedure to retransmit the payload of RACH message a.

As indicated above, fig. 5 is provided as an example. Other examples may differ from the example described with respect to fig. 5.

Fig. 6 is a diagram illustrating an example 600 for a media access control messaging structure for indications as described in connection with fig. 3. Example 600 illustrates a MAC payload of RACH message B. In the MAC payload, an indication bit shown by reference numeral 610 is used as an indicator (e.g., by switching the value of F). In this case, if BS 110 receives the preamble and payload of UE120, BS 110 may set F to a first value (e.g., 0) in RACH message B. If BS 110 did not successfully receive the payload, BS 110 may set F to a second value (e.g., 1).

If UE120 receives RACH message B with a backoff indicator of a first value, UE120 may check the value of a contention resolution MAC Control Element (CE). If the contention resolution identity matches the UE120, the UE120 may complete the two-step RACH procedure. If the contention resolution identity does not match the UE120, the UE120 may reattempt the RACH procedure using either the two-step RACH procedure or the four-step RACH procedure. If the UE120 receives the RACH message B with the fallback indicator of the second value, the UE120 may retransmit the payload of RACH message A (e.g., by fallback to a four-step RACH procedure) using the TA command, the uplink grant, and the C-RNTI of RACH message B.

In the case where the payload and preamble are successfully received, the payload may include contention resolution information (e.g., in a CCCH SDU) in RACH message a, and RACH message B may identify a TA command, an uplink grant, a C-RNTI, and a MAC subheader with a RAPID and a UE contention resolution MAC CE identifying the UE120 from which the payload and preamble have been successfully received.

In the case where the payload is not successfully received, RACH message B may be transmitted by BS 110 with a MAC subheader including RAPID. If the indicator bit is set to the first value, the UE120 may ignore RACH message B and may reattempt transmission using a two-step or four-step RACH procedure. If the indicator bit is set to the second value, the UE120 may retransmit the payload of RACH message A using the TA command, the uplink grant, and the C-RNTI identified by RACH message B to perform fallback to the four-step RACH procedure.

An example of how the messaging structure described in connection with example 600 may be used in connection with multiple UEs is described below with reference to accompanying fig. 7.

As indicated above, fig. 6 is provided as an example. Other examples may differ from the example described with respect to fig. 6.

Fig. 7 is a diagram illustrating an example 700 of a media access control messaging structure for multiple UEs. Example 700 includes a random access response including a set of MAC sub-packet data units (sub-PDUs) for a set of UEs attempting random access with respect to BS 110. BS 110 may provide an indication to the group of UEs indicating whether the preamble and/or payload of each UE has been successfully received. For the purposes of fig. 7, assume that on the same RACH occasion, UE1 and UE2 use a first preamble index and UE3 and UE4 use a second preamble index, and assume that UE1, UE2, UE3, and UE4 perform a two-step RACH procedure. Further assume that BS 110 successfully receives preambles for all four UEs and that BS 110 successfully receives only the payload of UE 1.

As illustrated by reference numeral 710 in fig. 7, BS 110 may provide UE contention resolution information identifying UE1 based at least in part on successfully decoding a payload of UE 1. Further, as shown by reference numeral 720, the MAC subheader associated with the UE1 and UE2 may identify the RAPID (e.g., RAPID1) of the UE1 and UE2, and as shown by reference numeral 730, the random access response associated with the UE1 and UE2 may include an indication bit set to a first value (e.g., F ═ 0), which may indicate that the UE1 and UE2 will not perform fallback to the four-step RACH procedure. Thus, the UE1 may determine that the two-step RACH procedure was successful (e.g., the UE1 is identified based at least in part on the UE contention resolution identity MAC CE and the indication bit is set to the first value), and the UE2 may determine that the UE2 is to reattempt the RACH procedure (e.g., the UE2 is not identified based at least in part on the UE contention resolution identity MAC CE and the indication bit is set to the first value).

As shown by reference numeral 740, the MAC subheaders associated with UE3 and UE4 may identify RAPID (e.g., RAPID2) of UE3 and UE 4. As shown by reference numeral 750, the random access responses associated with the UE3 and the UE4 may include an indication bit set to a second value (e.g., F ═ 1), which may indicate that the UE3 and the UE4 are to fall back to the four-step RACH procedure.

As indicated above, fig. 7 is provided as an example. Other examples may differ from the example described with respect to fig. 7.

Fig. 8 is a diagram illustrating an example 800 for a media access control messaging structure for indications as described in connection with fig. 3. In example 800, if the preamble and payload of UE120 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 including RAPID may be used for RACH message B. UE120 may determine whether BS 110 successfully received the payload based at least in part on whether a MAC subheader associated with the UE120 includes a RAPID associated with the UE120 and based at least in part on whether a contention resolution MAC CE for the UE120 is included in RACH message B. For example, if the contention resolution MAC CE of the UE120 matches the UE identifier of the UE120 and if the MAC subheader does not include a RAPID, the UE120 may determine that the two-step RACH procedure has been successful. If the MAC subheader identifies a RAPID associated with the UE120, the UE120 can identify the RAPID and can retransmit the payload back to the four-step RACH using the TA command, the uplink grant, and the C-RNTI of RACH message B. 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 a first MAC CE and the MAC CE of UE2 is a 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.

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 is to 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 the first value, indicating that the first MAC subheader is to include a backoff indicator and does not include a RAPID.

Reference numeral 820 illustrates a second MAC subheader with RAPID that may be used to indicate that the UE120 is to retransmit the payload. In the second MAC subheader, T may be associated with a second value, indicating that the second MAC subheader is to include a RAPID.

Reference numeral 830 illustrates a third MAC subheader with 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 does not include a RAPID or backoff indicator.

An example of how the messaging structure described in connection with example 800 may be used in connection with multiple UEs is described below with reference to accompanying fig. 9.

As indicated above, fig. 8 is provided as an example. Other examples may differ from the example described with respect to fig. 8.

Fig. 9 is a diagram illustrating an example 900 of a media access control messaging structure for multiple UEs.

Example 900 includes a random access response including a set of MAC sub-packet data units (sub-PDUs) for a set of UEs attempting random access with respect to BS 110. BS 110 may provide an indication to the group of UEs indicating whether the preamble and/or payload of each UE has been successfully received. For the purposes of fig. 9, assume that on the same RACH occasion, UE1 and UE2 use a first preamble index and UE3 and UE4 use a second preamble index, and assume that UE1, UE2, UE3, and UE4 perform a two-step RACH procedure. Further assume that BS 110 successfully receives preambles for all four UEs and that BS 110 successfully receives only the payload of UE 1.

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 illustrated by reference numeral 910 in fig. 9. As shown by reference numeral 920, the MAC subheaders associated with UE1 and UE2 may not include RAPID, indicating that BS 110 successfully received the payload associated with UE1 or UE 2. Thus, the UE1 may complete a two-step RACH procedure. The UE2 may not receive the random access response because the random access response does not include the RAPID of the UE 2. As shown by reference numeral 930, the MAC subheaders associated with UE3 and UE4 may include RAPID associated with UE3 and UE4, whereby UE3 and UE4 may fall back to the four-step RACH procedure accordingly.

In some aspects, the procedures described in connection with examples 400 and 500, 600 and 700, and 800 and 900 may be performed in combination. For example, consider the combination of examples 400/500 and 800/900. In this case, if the preamble and payload in RACH message a are successfully received, the BS may transmit RACH message B including UE contention resolution information, as described in more detail in connection with examples 400 and 500. Further, the RACH message B may include a MAC subheader having no RAPID, an F value indicating that a backoff indicator is not included in the MAC subheader, and an L value indicating the length of the 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.

As indicated above, fig. 9 is provided as an example. Other examples may differ from the example described with respect to fig. 9.

Fig. 10 is a flow chart of a method 1000 of wireless communication. The method may be performed by a UE (e.g., UE120, device 1102/1102', etc. of fig. 1).

At 1010, the UE (e.g., using controller/processor 280, transmit processor 264, TX MIMO processor 266, MOD 254, 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 RACH message a. The random access message may include a preamble and a payload.

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

At 1030, the UE (e.g., using controller/processor 280, transmit processor 264, TX MIMO processor 266, MOD 254, antenna 252, etc.) may complete 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. For example, the UE may establish an RRC connection with the base station, may camp on a cell provided by the base station, and so on.

At 1040, the user equipment (e.g., using controller/processor 280, transmit processor 264, TX MIMO processor 266, MOD 254, antenna 252, etc.) can reattempt random access or perform 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 re-attempt 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 the payload according to a two-step random access procedure or a four-step random access procedure. In some aspects, the UE may perform 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, reattempting random access may refer to transmitting a preamble and/or payload of a random access message after the preamble and/or payload has been transmitted by a user equipment (e.g., on the same RACH occasion or on a different RACH occasion).

In a first aspect, the indication comprises a random access response associated with a two-step random access procedure, and a payload of the random access response comprises contention resolution information identifying a particular UE from which a payload of a random access message has been successfully received. In a second aspect, alone or in combination with the first aspect, the method further comprises reattempting the random access based at least in part on determining that the UE is not identified by the contention resolution information within the random access response, the UE configured to reattempt the random access procedure. In a third aspect, alone or in combination with the first and/or 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.

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 comprises 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 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 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 comprises 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 connected mode UEs. 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 an idle mode or an 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 comprising a backoff indicator and a set of bits indicating that the MAC subheader comprises the backoff indicator.

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

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

In a twenty-third aspect, alone or in combination with one or more of the first to twenty-second aspects, the indicated MAC subheader does not include a preamble identifier based at least in part on the preamble and the payload being successfully received. In a twenty-fourth aspect, the MAC subheader does not include a preamble identifier, and the indicated contention resolution MAC control element identifies the particular 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 order along with each corresponding random access response, alone or in combination with one or more of the first to twenty-third aspects. In a twenty-fifth aspect, the MAC subheader comprises 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 for the backoff indicator or for one or more reserved bits, alone or in combination with one or more of the first to twenty-fourth aspects. In a twenty-sixth aspect, alone or in combination with one or more of the first to twenty-fifth aspects, a Media Access Control (MAC) subheader of the random access response includes a set of bits indicating that the random access response is associated with contention resolution for idle mode UEs or inactive mode UEs.

In a twenty-seventh aspect, alone or in combination with one or more of the first to twenty-sixth aspects, the indication comprises a random access response associated with a two-step random access procedure, the random access response comprising contention resolution information in a payload of the random access response, wherein the indication comprises a MAC subheader without a preamble identifier, is successfully received based at least in part on the preamble and the payload. In a twenty-eighth aspect, the MAC subheader indicates a length of the random access response and whether the MAC subheader is to include a backoff indicator, alone or in combination with one or more of the first to twenty-seventh aspects.

Although fig. 10 illustrates example blocks of a wireless communication method, in some aspects, the method may include more blocks, fewer blocks, different blocks, or differently arranged blocks than those illustrated in fig. 10. Additionally or alternatively, two or more of the blocks shown in fig. 10 may be performed in parallel.

Fig. 11 is a conceptual data flow diagram 1100 illustrating the data flow between different modules/means/components in an example apparatus 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.

The receiving module 1104 may receive a signal 1108 from a base station 1150 (e.g., BS 110, etc.). Signal 1108 may include a random access response, such as RACH message B or RACH message 2, including an indication of the result of decoding RACH message a, as described in more detail elsewhere herein. In some aspects, the receiving module 1104 may receive a preamble indicating the random access message and an indication that a payload of the random access message has been successfully received or that the payload has not been successfully received. The transmission module 1106 can transmit a signal 1110 to a base station 1150. Signal 1110 may comprise a random access message such as RACH message A, RACH message 3, or the like. In some aspects, the transmission module 1106 may transmit a random access message associated with a two-step random access procedure, complete a two-step RACH procedure, reattempt random access, or perform fallback to a four-step random access procedure, as described elsewhere herein.

The apparatus may include additional modules that perform each block of the algorithm in the aforementioned method 1000 of fig. 10, and so on. Each block in the aforementioned method 1000 and the like of fig. 10 may be performed by a module, and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to implement the processes/algorithms, implemented by a processor configured to execute the processes/algorithms, stored in a computer-readable medium for implementation by a processor, or some combination thereof.

The number and arrangement of modules shown in fig. 11 are provided as examples. In practice, there may be more modules, fewer modules, different modules, or differently arranged modules than those shown in fig. 11. Further, two or more of the modules shown in fig. 11 may be implemented within a single module, or a single module shown in fig. 11 may be implemented as a plurality of distributed modules. Additionally or alternatively, a set of modules (e.g., one or more modules) shown in fig. 11 may perform one or more functions described as being performed by another set of modules shown in fig. 11.

Fig. 12 is a diagram 1200 illustrating an example of a hardware implementation of a device 1102' employing a processing system 1202. The device 1102' may be a UE.

The processing system 1202 may be implemented with a bus architecture, represented generally by the bus 1204. The bus 1204 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 1202 and the overall design constraints. The bus 1204 links together various circuits including one or more processors and/or hardware modules, represented by the processor 1206, the

modules

1104, 1106, and the computer-readable medium/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 any further.

The processing system 1202 may be coupled to a transceiver 1210. The transceiver 1210 is coupled to one or more antennas 1212. The transceiver 1210 provides a means for communicating with various other apparatus over a transmission medium. The transceiver 1210 receives a signal from the one or more antennas 1212, extracts information from the received signal, and provides the extracted information to the processing system 1202 (and in particular the receive module 1104). Additionally, the transceiver 1210 receives information from the processing system 1202 (and in particular the transmission module 1106) and generates a signal to be applied to the one or more antennas 1212 based at least in part on the received information. The processing system 1202 includes a processor 1206 coupled to a computer-readable medium/memory 1208. The processor 1206 is responsible for general processing, including the execution of software stored on the computer-readable medium/memory 1208. The software, when executed by the processor 1206, causes the processing system 1202 to perform the various functions described herein for any particular apparatus. The computer-readable medium/memory 1208 may also be used for storing data that is 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, resident/stored in the computer readable medium/memory 1208, one or more hardware modules coupled to the processor 1206, or some combination thereof. Processing system 1202 may be a component of UE120 and may include memory 282 and/or at least one of: a TX MIMO processor 266, an RX processor 258, and/or a controller/processor 280.

In some aspects, the apparatus 1102/1102' for wireless communication includes: means for attempting random access by transmitting a random access message associated with a two-step random access procedure; means for receiving a preamble indicating the random access message and an indication that a payload of the random access message has been successfully received or that the payload has not been successfully received; and/or means for selectively performing the following: completing 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, 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. The aforementioned means may be one or more of the aforementioned modules of the device 1102 and/or the processing system 1202 of the device 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.

Fig. 12 is provided as an example. Other examples may differ from the example described in connection with fig. 12.

Fig. 13 is a flow chart of a method 1300 of wireless communication. The method may be performed by a base station (e.g., BS 110, device 1402/1402', etc. of fig. 1).

At 1310, the base station (e.g., using antennas 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 RACH message a. The random access message may include a preamble and a payload.

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

At 1330, the base station (e.g., using controller/processor 240, transmit processor 220, TX MIMO processor 230, MOD 232, antenna 234, etc.) may complete 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. For example, the base station may establish an RRC connection with the base station, may camp on a cell provided by the base station, and so on.

At 1340, the base station (e.g., using antennas 234, DEMOD 232, MIMO detector 236, receive processor 238, controller/processor 240, etc.) may receive messaging associated with the UE re-attempting random access or performing fallback to 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 re-attempt 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 the payload according to a two-step random access procedure or a four-step random access procedure. In some aspects, the UE may perform 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.

In a first aspect, the indication comprises a random access response associated with a two-step random access procedure, wherein a payload of the random access response comprises contention resolution information identifying a particular UE whose payload of a random access message has been successfully received. In a second aspect, alone or in combination with the first aspect, the 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 C-RNTI of the UE. 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 comprises 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 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 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 comprises 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 comprises 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 an idle mode or an inactive mode when attempting random access. In a thirteenth aspect, the indication is associated with a MAC subheader that includes a backoff indicator and a set of bits indicating that the MAC subheader includes the backoff indicator, alone or in combination with one or more of the first to twelfth aspects.

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.

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 the random access response message. In a sixteenth aspect, the indication bit indicates whether to perform a fallback to four-step random access procedure, alone or in combination with one or more of the first to fifteenth aspects. In a seventeenth aspect, alone or in combination with one or more of the first to sixteenth aspects, the base station is configured to indicate not to perform fallback to a four-step random access procedure based at least in part on the indication bit, the base station is configured to identify the UE to complete the two-step random access procedure based at least in part on contention resolution information of a random access response message. In an eighteenth aspect, alone or in combination with one or more of the first to seventeenth aspects, the base station is configured to indicate not to perform fallback to a four-step random access procedure based at least in part on the indication bit, the UE not being identified to receive messaging associated with reattempting random access based at least in part on contention resolution information of a random access response message.

In a nineteenth aspect, alone or in combination with one or more of the first through eighteenth aspects, the MAC subheader of the indication does not include a preamble identifier based at least in part on the preamble and the payload being successfully received. In a twentieth aspect, alone or in combination with one or more of the first through nineteenth aspects, the MAC subheader does not include a preamble identifier and the indicated contention resolution MAC control element identifies the particular UE based at least in part on the preamble and payload of the particular UE being successfully received. In a twenty-first aspect, 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 with each corresponding random access response, either alone or in combination with one or more of the first to twentieth aspects.

In a twenty-second aspect, 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 for the backoff indicator or for one or more reserved bits, either alone or in combination with one or more of the first to twenty-first aspects.

In a twenty-third aspect, alone or in combination with one or more of the first to twenty-second aspects, the indication comprises a random access response associated with a two-step random access procedure, the random access response comprising contention resolution information in a payload of the random access response, wherein the indication comprises a MAC subheader without a preamble identifier, based at least in part on the preamble and the payload being successfully received. In a twenty-fourth aspect, the MAC subheader indicates a length of the random access response and whether the MAC subheader is to include a backoff indicator, alone or in combination with one or more of the first to twenty-third aspects.

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

Although fig. 13 illustrates example blocks of a wireless communication method, in some aspects, the method may include more blocks, fewer blocks, different blocks, or differently arranged blocks than those illustrated in fig. 13. Additionally or alternatively, two or more of the blocks shown in fig. 13 may be performed in parallel.

Fig. 14 is a conceptual data flow diagram 1400 illustrating the data flow between different modules/means/components in an example apparatus 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.

The receiving module 1404 may receive a signal 1408 from a UE 1450 (e.g., UE120, etc.). Signal 1408 may include a random access message, such as RACH message A, RACH message 3, or the like. In some aspects, the transmission module 1404 may receive a random access message associated with a two-step random access procedure, complete a two-step RACH procedure, reattempt random access, or perform fallback to a four-step random access procedure, as described elsewhere herein. The transmission module 1406 may transmit the signal 1410 to the UE 1450. Signal 1410 may include a random access response, such as RACH message B or RACH message 2, that includes an indication of the result of decoding RACH message a, as described in more detail elsewhere herein. In some aspects, the transmission module 1406 may transmit a preamble indicating the random access message and an indication that the payload of the random access message has been successfully received or that the payload has not been successfully received.

The apparatus may include additional modules that perform each block of the algorithm in the aforementioned method 1300 and so on of fig. 13. Each block in the aforementioned method 1300, etc., of fig. 13 may be performed by a module, and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to implement the processes/algorithms, implemented by a processor configured to execute the processes/algorithms, stored in a computer-readable medium for implementation by a processor, or some combination thereof.

The number and arrangement of modules shown in fig. 14 are provided as examples. In practice, there may be more modules, fewer modules, different modules, or differently arranged modules than those shown in fig. 14. Further, two or more of the modules shown in fig. 14 may be implemented within a single module, or a single module shown in fig. 14 may be implemented as a plurality of distributed modules. Additionally or alternatively, a set of modules (e.g., one or more modules) shown in fig. 14 may perform one or more functions described as being performed by another set of modules shown in fig. 14.

Fig. 15 is a diagram 1500 illustrating an example of a hardware implementation of a device 1402' employing a processing system 1502. The device 1402' may be a UE.

The processing system 1502 may be implemented with a bus architecture, represented generally by the bus 1504. The bus 1504 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 1502 and the overall design constraints. The bus 1504 links together various circuits including one or more processors and/or hardware modules, represented by the processor 1506, the

modules

1404, 1406, and the computer-readable medium/memory 1508. The bus 1504 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 any further.

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

In some aspects, the apparatus 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 a preamble indicating the random access message and an indication that the payload of the random access message has been successfully received or that the payload has not been successfully received; and means for selectively performing the following: completing a two-step random access procedure based at least in part on determining that the indication indicates that a preamble of the random access message and a payload of the random access message have been successfully received, or receiving messaging associated with a UE re-attempting random access or performing 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 of the device 1402 and/or the processing system 1502 of the 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.

Fig. 15 is provided as an example. Other examples may differ from the example described in connection with fig. 15.

Fig. 16 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 may be used for UEs 120 that are in idle mode or inactive mode and whose payload and preamble of random access message are successfully received. The payload of an indicator (e.g., random access response) of the MAC messaging structure is shown by reference numeral 1610. For example, the payload may be part of a random access response and may identify contention resolution information for the UE 120. In this case, the uplink grant and the C-RNTI may be used for subsequent data. As indicated by reference numeral 1620, the indicator may be associated with a MAC subheader. For example, the MAC subheader may include a set of bits (shown as F1 and F2). The value of the set of bits may indicate information about the MAC subheader and/or payload. As one example, in example 1600, the value of the set of bits may indicate that a 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 the timing advance command, the uplink grant, the C-RNTI, and the contention resolution information of the successful random access message.

Fig. 16 is provided as an example. Other examples may differ from the example described in connection with fig. 16.

Fig. 17A and 17B are diagrams illustrating an example 1700 of a media access control messaging structure for a UE associated with a random access message whose payload has not been successfully received and whose preamble has been successfully received, and an example of a media access control subheader for a UE whose any portion of the random access message has not been successfully received. The example 1700 includes a MAC subheader 1710 and a MAC payload 1720 (shown in fig. 17A) and/or a MAC subheader 1730 (shown in fig. 17B). For example, the MAC subheader 1710 and the MAC payload 1720 may comprise the RACH message 2 of a four-step RACH procedure. A UE receiving the MAC subheader 1710 and the MAC payload 1720 may determine that the payload of a random access message transmitted by the UE was not successfully received.

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

The example 1700 is applicable to connected mode UEs, idle mode UEs, and inactive mode UEs.

Fig. 17A and 17B are provided as examples. Other examples may differ from the example described in connection with fig. 17A and 17B.

Fig. 18 is a diagram illustrating an example 1800 of a media access control messaging structure for a connected mode UE associated with a random access message whose payload has been successfully received. As shown, example 1800 includes MAC subheader 1810 and MAC payload 1820. In this case, 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 cases (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 RA-RNTI and may contain 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.

In other cases (referred to herein as option 2), RACH message B may contain information about multiple UEs and may be addressed to RA-RNTI. In this case, the C-RNTI may be included in the random access response as contention resolution information for the RRC _ CONNECTED (RRC CONNECTED) UE. Example 1800 relates to option 1.

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, as described in more detail below in connection with fig. 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.

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

Fig. 18 is provided as an example. Other examples may differ from the example described in connection with fig. 18.

Fig. 19 is a diagram illustrating an 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 a 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 a MAC payload includes an uplink grant and contention resolution information. Example 1940 illustrates a fourth example in which the MAC payload includes contention resolution information and does not include an uplink grant. In examples 1930 and 1940, the contention resolution information is included in the random access response in the form of the C-RNTI because the UE may use the RA-RNTI to receive the random access response transmitted from BS 110.

Fig. 19 is provided as an example. Other examples may differ from the example described in connection with fig. 19.

Fig. 20 is a diagram illustrating an example 2000 of a media access control messaging structure for multiple UEs. The random access responses for the multiple UEs may be multiplexed, as illustrated in example 2000. For example, as shown by reference numeral 2010, using a first MAC payload in RACH message 2 format may indicate that random access payloads of one or more corresponding UEs were 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 idle mode UEs or connected mode UEs. The corresponding MAC payload, shown by reference numeral 2030, may include a RACH message B identifying one or more UEs for which corresponding random access responses have been successfully received. Further, as shown by reference numeral 2040, the MAC subheader of the MAC subpdu 1 may include a set of bits (e.g., F1 and F2) that indicate whether the MAC subheader includes a backoff indicator. The MAC subheader may be used to provide backoff information for UEs whose preambles and payloads were not successfully received.

Fig. 20 is provided as an example. Other examples may differ from the example described in connection with fig. 20.

It should be understood that the specific order or hierarchy of blocks in the processes/flow diagrams disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes/flow diagrams can be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects. The term "some" or "an" refers to one or more, unless specifically stated otherwise. Combinations such as "A, B or at least one of C", "A, B and at least one of C", and "A, B, C or any combination thereof" include any combination of A, B and/or C, and may include a plurality of a, a plurality of B, or a plurality of C. In particular, 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, A and B, A and C, B and C only, or a and B and C, wherein any such combination may contain one or more members of A, B or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element should be construed as a means-plus-function unless the element is specifically recited in a device turned using the phrase .

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 the two-step random access procedure;

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

selectively performing the following:

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 the 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.

2. The method of claim 1, wherein the indication comprises a random access response associated with the two-step random access procedure, and wherein a payload of the random access response comprises contention resolution information identifying a particular UE from which a payload of a random access message has been successfully received.

3. The method of claim 2, further comprising reattempting the random access based at least in part on determining that the contention resolution information within the random access response does not identify the UE.

4. The method of claim 2, wherein the random access response indicates that the payload of the random access message was not successfully received based at least in part on an absence of contention resolution information identifying the UE in the random access response.

5. The method of claim 2, wherein a Media Access Control (MAC) subheader of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC subheader.

6. The method of claim 1, wherein the indication comprises a random access response 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.

7. The method of claim 6, wherein a payload of the random access response does not include the C-RNTI.

8. The method of claim 6, wherein the random access response does not include an uplink grant.

9. The method of claim 1, wherein the indication comprises a random access response 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.

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

11. The method of claim 9, wherein a Media Access Control (MAC) subheader of the random access response comprises a set of bits indicating that the random access response is associated with contention resolution for idle mode UEs or inactive mode UEs.

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

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

14. The method of claim 1, wherein the indication comprises a second message of the four-step random access procedure.

15. The method of claim 14, wherein the second message indicates that the payload was not successfully received.

16. The method of claim 14, further comprising performing the fallback to the four-step random access procedure based at least in part on receiving the second message.

17. The method of claim 1, wherein the indicated Medium Access Control (MAC) subheader does not include a preamble identifier based at least in part on the preamble and the payload being successfully received.

18. The method of claim 17, wherein the indicated contention resolution MAC control element identifies a particular UE whose payload and preamble have been successfully received.

19. The method of claim 17, wherein the MAC subheader includes a first bit indicating whether a backoff indicator or the preamble identifier is included in the MAC subheader and a second bit indicating whether a field of the MAC subheader is for the backoff indicator or for one or more reserved bits.

20. The method of claim 1, wherein the indication comprises a random access response associated with the two-step random access procedure based at least in part on the preamble and the payload being successfully received, the random access response comprising contention resolution information in a payload of the random access response, wherein the indication comprises a Medium Access Control (MAC) subheader without a preamble identifier.

21. A method of wireless communication performed by a base station, comprising:

receiving a random access message associated with a two-step random access procedure from a User Equipment (UE) attempting random access;

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

selectively performing the following:

Receiving messaging associated with the UE re-attempting the random access or performing fallback to a four-step random access procedure based at least in part on determining that the payload was not successfully received.

22. The method of claim 21, wherein the indication comprises a random access response associated with the two-step random access procedure, wherein a payload of the random access response comprises contention resolution information identifying a particular UE whose payload of a random access message has been successfully received.

23. The method of claim 22, wherein a Media Access Control (MAC) subheader of the random access response includes a set of bits indicating whether a backoff indicator is included in the MAC subheader.

24. The method of claim 21, wherein the indication comprises a random access response 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 method of claim 24, wherein a Media Access Control (MAC) subheader of the random access response comprises a set of bits indicating that the random access response is associated with contention resolution for idle mode UEs or inactive mode UEs.

26. The method of claim 21, wherein the indication comprises a random access response associated with the two-step random access procedure based at least in part on the preamble and the payload being successfully received, the random access response comprising contention resolution information in a payload of the random access response, wherein the indication comprises a Medium Access Control (MAC) subheader without a preamble identifier.

27. A User Equipment (UE) for wireless communication, comprising:

a memory; and

one or more processors coupled to the memory, the memory and the one or more processors configured to:

selectively performing the following:

28. The UE of claim 27, wherein the indication comprises a random access response associated with the two-step random access procedure, and wherein a payload of the random access response comprises contention resolution information identifying a particular UE from which a payload of a random access message has been successfully received.

29. A base station for wireless communication, comprising:

a memory; and

selectively performing the following:

30. The base station of claim 29, wherein the indication comprises a random access response associated with the two-step random access procedure, wherein a payload of the random access response comprises contention resolution information identifying a particular UE whose payload of a random access message has been successfully received.