Message 1CFO Compensation Method Based on RAPID Discontinuity

Abstract

To resolve mismatched RAPIDs caused by uplink Doppler shifts in HST deployments, an aspect is provided that enables a UE to apply CFO compensation. The UE obtains one or more RARs, each including a RAPID, where each of the RARs responds to a random access message including a preamble. The UE determines that in each of a threshold number of the one or more RARs, the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message. The UE then offsets a carrier frequency for each of one or more subsequent random access messages in response to the determination. As a result, mismatched RAPIDs caused by uplink Doppler shifts may be avoided, which may improve the RACH success rate.

Description

Technical Field

[0001]

[0001] The present invention generally relates to a communication system, and more particularly to a wireless communication system between a user equipment (UE) and a base station.

Background Art

[0002]

[0002] Wireless communication systems have been widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasting. A typical wireless communication system may employ a multiple access technology capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

[0003]

[0003] These multi-connectivity techniques are adopted in various telecommunications standards to provide a common protocol that enables various wireless devices to communicate on an urban, national, regional, and even global scale. An exemplary telecommunications standard is 5G New Radio (NR). 5G NR is part of the evolution of continuous mobile broadband, promulgated by the Third Generation Partnership Project (3GPP®) to meet new requirements related to latency, reliability, security, scalability (e.g., by the Internet of Things (IoT)), and other requirements. 5G NR includes services related to enhanced mobile broadband (eMBB), massive machine type communication (mMTC), and ultra-reliable low latency communication (URLLC). Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE®) standard. In 5G NR technology, further improvements are needed. These improvements may also be applicable to other multi-connectivity techniques and the telecommunications standards that employ these techniques.

Summary of the Invention

[0004]

[0004] Hereinafter, to provide a basic understanding of one or more aspects, a simplified summary of such aspects is presented. This summary is not an extensive overview of all contemplated aspects, nor does it identify the main or critical elements of all aspects, nor does it delimit the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as an introduction to the more detailed description that follows.

[0005]

[0005] In one aspect of the present disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus can be a UE. The UE acquires one or more random access responses (RARs). Each of the one or more RARs includes a random access preamble identifier (RAPID), and each of the one or more RARs responds to a random access message including a preamble. The UE determines that, in each of the one or more RARs of a threshold number, the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message. In response to the determination, the UE offsets the carrier frequency for each of one or more subsequent random access messages.

[0006]

[0006] To achieve the above object and related objects, one or more aspects have the features that are fully described below and particularly pointed out in the claims. The following description and the accompanying drawings detail some exemplary features of one or more aspects. However, these features are only some of the various ways in which the principles of the various aspects can be employed, and this description is intended to cover all such aspects and their equivalents.

Brief Description of the Drawings

[0007]

Figure 1

[0007] A diagram showing an example of a wireless communication system and an access network.

Figure 2A

[0008] A diagram showing an example of a first frame according to various aspects of the present disclosure.

Figure 2B

[0009] A diagram showing an example of a DL channel in a subframe according to various aspects of the present disclosure.

Figure 2C

[0010] A diagram showing an example of a second frame according to various aspects of the present disclosure.

Figure 2D

[0011] A diagram showing an example of a UL channel in a subframe according to various aspects of the present disclosure.

Figure 3

[0012] A diagram showing an example of a base station and a user equipment (UE) in an access network.

Figure 4

[0013] A diagram showing an example of high-speed train equipment.

Figure 5

[0014] A diagram showing an example of a UE that compensates for uplink Doppler shift when executing a random access channel (RACH) procedure with a base station.

Figure 6

[0015] A diagram showing an example of a UE that transmits a RACH preamble on the condition of an uplink Doppler shift in either the positive or negative frequency direction.

Figure 7

[0016] A diagram showing an example of a UE that offsets the carrier frequency for different RACH preambles to compensate for uplink Doppler shift.

Figure 8

[0017] A diagram showing the call flow between a UE and a base station.

Figure 9

[0018] A flowchart of a method for wireless communication.

Figure 10

[0019] A diagram showing an example of a hardware implementation form for an exemplary device.

Mode for Carrying Out the Invention

[0008]

[0020] The mode for carrying out the invention described below with reference to the accompanying drawings describes various configurations, and does not represent only the configurations in which the concepts described in this specification can be implemented. The mode for carrying out the invention includes specific details for providing a complete understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts can be implemented without these specific details. In some cases, well-known structures and components are shown in the form of block diagrams in order to avoid obscuring such concepts.

[0009]

[0021] In a 4-step contention-based RACH procedure, four messages can be provided between the UE and the base station. For example, during the initial attach procedure, the UE sends a preamble to the base station (e.g., message 1), receives a Random Access Response (RAR) from the base station (e.g., message 2), sends an RRC connection request message or other payload to the base station (e.g., message 3), and may receive an RRC connection setup message or other transmission that depends on contention resolution from the base station (e.g., message 4). This 4-step RACH procedure can be simplified to a 2-step RACH procedure in which the UE sends a preamble and a payload in the first message. For example, message A ("msgA") of the 2-step RACH procedure may correspond to messages 1 and 3 of the 4-step RACH procedure, and message B ("msgB") may correspond to messages 2 and 4 of the 4-step RACH procedure. Thus, in the 2-step RACH procedure, the UE may send a preamble and a subsequent payload to the base station during msgA transmission, and the base station may send an RAR and an RRC response message to the UE during msgB transmission.

[0010]

[0022] The UE may select a preamble for message 1 or msgA from a set of randomly generated access preambles generated by the UE. The set of random access preambles may be a function of various configured RACH parameters including physical random access channel (PRACH) preamble formats. The preamble format may then be associated with the PRACH preamble subcarrier spacing. After the UE selects a preamble from the set of generated preambles, the UE may transmit the preamble to the base station in the configured time and frequency resources. The time and frequency resources may be a function of various configured RACH parameters. For example, the slot or symbol in which the preamble is transmitted may depend on the PRACH configuration index, and the subcarrier in which the preamble is transmitted may depend on the PRACH preamble subcarrier spacing.

[0011]

[0023] After the UE transmits the selected preamble in the PRACH subcarrier (in Message 1 or msgA) to the base station, the base station can decode the message and identify the preamble transmitted by the UE. For example, the base station can receive and demodulate the data in the PRACH subcarrier and determine the selected preamble sequence of the UE based on the subcarrier on which the PRACH data was received. In response to identifying the preamble, the base station can construct a RAR including a Random Access Preamble Identifier (RAPID). The base station can construct the RAPID using an identifier associated with the decoded preamble sequence (e.g., the preamble sequence determined to be transmitted by the UE). The base station can then transmit the RAR to the UE in Message 2 or msgB.

[0012]

[0024] When the UE receives and decodes the RAR, the UE can determine whether the RAPID in the RAR is the same as the identifier associated with the selected preamble sequence of the UE. If the RAPID matches the preamble, the UE can determine that the preamble was received correctly or that the RACH procedure was executed correctly, and the UE can communicate with the base station accordingly. Otherwise, if the RAPID does not match the preamble (e.g., the RAPID is a mismatched RAPID), the UE can determine that the RACH procedure has failed, and the UE can restart the RACH procedure from Message 1 or msgA.

[0013]

[0025] One scenario where discontinuous RAPID can be observed is in high-speed train (HST) deployments. HSTs have recently been developed as a fast, convenient, environmentally friendly, and flexible means of transportation. As an increasing number of passengers carrying UEs tend to move on HSTs, new challenges have arisen in providing reliable communication services to meet the growing communication demand. For example, typical HSTs may move at speeds exceeding 200 kilometers per hour (km / h), or even exceeding 350 km / h, resulting in frequent and fast handovers, large Doppler spreads, and other effects. In an attempt to overcome these challenges, millimeter wave (mmW) and massive multiple-input multiple-output (MIMO) technologies, as well as multi-point cooperation (CoMP) and mobile relay station architectures, have been considered for HST deployments.

[0014]

[0026] However, despite such techniques, conventional HST deployment may still be insufficient to cover all possible scenarios that can occur in an HST, including the above-mentioned RAPID of the inconsistency. For example, a UE located within or on the HST (referred to herein as an HST UE) often camps on a non-HST cell (e.g., a cell served by a base station located outside or away from the HST). Since these non-HST cells were originally designed to support UEs located outside or away from the HST (referred to herein as non-HST UEs), the base stations serving these non-HST cells may configure both the HST UE and the non-HST UE in a similar manner using a similar RACH configuration. For example, a base station in a non-HST cell may provide a RACH configuration that indicates PRACH preamble format 0 to both the HST UE and the non-HST UE and employs an unlimited set of preamble sequences. As a result, an HST UE camping on a non-HST cell tends to experience frequent RACH failures due to the inconsistency between the RAPID in the RAR and the UE's selected preamble. These RAPID inconsistencies are typically due to the relatively small PRACH preamble sub-carrier spacing (e.g., Δf RA = 1.25 kHz) associated with such preamble formats and the relatively large uplink Doppler shift that an HST UE may experience when transmitting message 1 or msgA. Therefore, in order to improve the RACH success rate of the HST UE, it is useful to compensate for this uplink Doppler shift.

[0015]

[0027] Aspects of the present disclosure enable a UE to compensate for uplink Doppler shifts when transmitting a RACH preamble (e.g., in an HST). In one example, the UE may monitor the number N of consecutive RACH attempts (e.g., the RACH attempts from the first to the Nth) for inconsistent RAPIDs. For example, the UE may obtain N consecutive RARs, where each RAR responds to a transmitted preamble, and the UE may determine whether any of the RARs contains a RAPID that does not match the identifier of the corresponding preamble sequence transmitted by the UE. If the UE determines that these RACH attempts have failed due to inconsistent RAPIDs a threshold number K of times in response to the aforementioned Doppler shift effect, the UE may compensate for this offset in subsequent RACH attempts. For example, if the UE determines that K out of N consecutive RARs contain RAPIDs that do not match the identifier of the corresponding preamble sequence due to a positive or negative Doppler shift, the UE may offset the carrier frequency of a subsequent Message 1 or msgA (e.g., in RACH attempts N+1 and later) positively or negatively to compensate for this Doppler shift. For example, if the UE transmits a preamble in RACH attempts 1 to N on a carrier frequency of 3.8 GHz, the UE may transmit a preamble in a subsequent RACH attempt N+1 with a carrier frequency offset of 600 Hz (3.8000006 GHz) or -600 Hz (3.7999994 GHz). The UE may offset (shift) the carrier frequency (positively or negatively) and transmit subsequent RACH preambles in a similar manner until the UE successfully decodes the preamble transmitted by the base station and receives a RAR with a RAPID that matches the preamble transmitted by the UE. As a result, the RACH success rate may be increased for HST UEs.

[0016]

[0028] Here, some aspects of a telecommunications system are presented with reference to various devices and methods. These devices and methods are described in the context of implementing the following invention and are shown in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as "elements"). These elements can be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system.

[0017]

[0029] By way of example, an element, or any part of an element, or any combination of elements may be implemented as a "processing system" including one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, system on a chip (SoC), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gate logic, discrete hardware circuits, and other suitable hardware configured to perform the various functions described throughout this disclosure. One or more processors in the processing system may execute software. Software is broadly construed to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executable files, execution threads, procedures, functions, etc., regardless of the name given to it, such as software, firmware, middleware, microcode, hardware description language, etc.

[0018]

[0030] Accordingly, in one or more exemplary embodiments, the functions described can be implemented in hardware, software, or any combination thereof. When implemented in software, the functions can be stored on or encoded as one or more instructions or code on a computer-readable medium. The computer-readable medium includes computer storage media. The storage media can be any available media that can be accessed by a computer. By way of example and not limitation, such computer-readable media can comprise random access memory (RAM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM (registered trademark)), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the types of computer-readable media noted above, or any other media that can be used to store computer-executable code in the form of instructions or data structures and that can be accessed by a computer.

[0019]

[0031] FIG. 1 is a diagram illustrating an example of a wireless communication system and an access network 100. The wireless communication system (also referred to as a wireless wide area network (WWAN)) includes a base station 102, a user equipment (UE) 104, an evolved packet core (EPC) 160, and another core network 190 (e.g., a 5G core (5GC)). The base station 102 can include macro cells (high-power cellular base stations) and / or small cells (low-power cellular base stations). The macro cells include the base stations. The small cells include femto cells, pico cells, and micro cells.

[0020]

[0032] (Collectively referred to as the evolved Universal Mobile Telecommunications System (UMTS) terrestrial radio access network (E-UTRAN),) The base station 102 configured for 4G Long Term Evolution (LTE) can interface with the EPC 160 via a first backhaul link 132 (e.g., the S1 interface). The base station 102 configured for 5G New Radio (NR) (collectively referred to as the Next Generation RAN (NG-RAN)) can interface with the core network 190 via a second backhaul link 184. In addition to other functions, the base station 102 can perform one or more of the following functions: namely, transfer of user data, radio channel encryption and decryption, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load distribution, delivery for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and device tracing, radio access network information management (RIM), paging, positioning, and delivery of warning messages. The base stations 102 may communicate directly or indirectly with each other (e.g., via the EPC 160 or the core network 190) over a third backhaul link 134 (e.g., the X2 interface). The first backhaul link 132, the second backhaul link 184, and the third backhaul link 134 may be wired or wireless.

[0021]

[0033] Base station 102 can wirelessly communicate with UE 104. Each of base stations 102 can provide communication coverage to its respective geographic coverage area 110. There can be overlapping geographic coverage areas 110. For example, small cell 102’ can have a coverage area 110’ that overlaps with the coverage area 110 of one or more macro base stations 102. A network including both small cells and macro cells can be known as a heterogeneous network. The heterogeneous network can also include a home evolved Node B (eNB) (HeNB) that can provide services to a limited group known as a closed subscriber group (CSG). The communication link 120 between base station 102 and UE 104 can include an uplink (UL) transmission (also called a reverse link) from UE 104 to base station 102 and / or a downlink (DL) transmission (also called a forward link) from base station 102 to UE 104. The communication link 120 can use multiple-input multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and / or transmit diversity. The communication link can be through one or more carriers. Base station 102 / UE 104 may use a spectrum with a bandwidth of up to Y megahertz (MHz) (e.g., 5, 10, 15, 20, 100, 400 MHz, etc.) per carrier allocated in carrier aggregation up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. The allocation of carriers may be asymmetric for DL and UL (e.g., more or fewer carriers may be allocated to DL than UL). The component carriers may include a primary component carrier and one or more secondary component carriers. The primary component carrier may sometimes be called a primary cell (PCell), and the secondary component carrier may sometimes be called a secondary cell (SCell).

[0022]

[0034] Some UEs 104 may communicate with each other using device-to-device (D2D) communication links 158. The D2D communication links 158 may use the DL / UL WWAN spectrum. The D2D communication links 158 may use one or more sidelink channels such as the Physical Sidelink Broadcast Channel (PSBCH), Physical Sidelink Discovery Channel (PSDCH), Physical Sidelink Shared Channel (PSSCH), and Physical Sidelink Control Channel (PSCCH). The D2D communication may be through various wireless D2D communication systems such as, for example, WiMedia, Bluetooth®, ZigBee®, Wi-Fi®, based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, LTE, or NR.

[0023]

[0035] The wireless communication system may further include a Wi-Fi access point (AP) 150 communicating with a Wi-Fi station (STA) 152 via a communication link 154, for example, in the 5 gigahertz (GHz) unlicensed frequency spectrum. When communicating in the unlicensed frequency spectrum, the STA 152 / AP 150 may perform a Clear Channel Assessment (CCA) prior to communicating to determine whether the channel is available.

[0024]

[0036] The small cell 102' can operate within an authorized and / or unlicensed frequency spectrum. When operating in the unlicensed frequency spectrum, the small cell 102' may adopt NR and use the same unlicensed frequency spectrum (such as 5 GHz, etc.) used by the Wi-Fi AP 150. The small cell 102' adopting NR in the unlicensed frequency spectrum may enhance the coverage of the access network and / or increase the capacity of the access network.

[0025]

[0037] The electromagnetic spectrum is often re-divided into various classes, bands, channels, etc. based on frequency / wavelength. In 5G NR, two initial operating bands have been identified as frequency range designations FR1 (410 MHz to 7.125 GHz) and FR2 (24.25 GHz to 52.6 GHz). The frequencies between FR1 and FR2 are often referred to as mid-band frequencies. A portion of FR1 is greater than 6 GHz, but FR1 is often (interchangeably) referred to as the "sub-6 GHz" band in various documents and papers. Similar naming issues sometimes occur with respect to FR2, which, although different from the extremely high frequency (EHF) band (30 GHz to 300 GHz) identified by the International Telecommunication Union (ITU) as the "millimeter wave" band, is often (interchangeably) referred to as the "millimeter wave" band in documents and papers.

[0026]

[0038] With the above aspects in mind, unless otherwise specified, terms such as "sub-6 GHz" should be understood to broadly represent frequencies that can be less than 6 GHz, within FR1, or can include mid-band frequencies when used in this specification. Further, unless otherwise specified, terms such as "millimeter wave" should be understood to broadly represent frequencies that can include mid-band frequencies, be within FR2, or be within the EHF band when used in this specification.

[0027]

[0039] Base station 102 includes an eNB, a g Node B (gNB), or another type of base station, whether it is a small cell 102’ or a large cell (e.g., a macro base station), and / or may be referred to as such. Some base stations, such as gNB 180, can operate in the conventional sub-6 GHz spectrum, in the millimeter wave frequency, and / or in the near millimeter wave frequency in communication with UE 104. When gNB 180 operates at millimeter wave or near millimeter wave frequencies, gNB 180 may be referred to as a millimeter wave base station. The millimeter wave base station 180 may utilize beamforming 182 with UE 104 to compensate for path loss and short range. The base station 180 and UE 104 may each include a plurality of antennas, such as antenna elements, antenna panels, and / or antenna arrays, to enable beamforming.

[0028]

[0040] Base station 180 may transmit a beamformed signal to UE 104 in one or more transmission directions 182’. UE 104 may receive a beamformed signal from base station 180 in one or more reception directions 182’’. UE 104 can also transmit a beamformed signal to base station 180 in one or more transmission directions. Base station 180 can receive a beamformed signal from UE 104 in one or more reception directions. Base station 180 / UE 104 can perform beam training to determine the best reception and transmission directions for each of base station 180 / UE 104. The transmission direction and reception direction for base station 180 may or may not be the same. The transmission and reception directions for UE 104 may or may not be the same.

[0029]

[0041] The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, an MBMS Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may communicate with a Home Subscriber Server (HSS) 174. The MME 162 is a control node that processes signaling between the UE 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet Protocol (IP) packets are transferred through the Serving Gateway 166, and the Serving Gateway 166 itself is connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation and other functions. The PDN Gateway 172 and the BM-SC 170 are connected to an IP service 176. The IP service 176 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a PS streaming service, and / or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and distribution. The BM-SC 170 may act as an entry point for content provider MBMS transmissions, be used to permit and initiate MBMS bearer services within a Public Land Mobile Network (PLMN), and be used to schedule MBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMS traffic to base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area that broadcasts a specific service, and may be responsible for session management (start / stop) and collecting charging information related to eMBMS.

[0030]

[0042] The core network 190 may include an access and mobility management function (AMF) 192, other AMFs 193, a session management function (SMF) 194, and a user plane function (UPF) 195. The AMF 192 may communicate with an integrated data management (UDM) 196. The AMF 192 is a control node that processes signaling between the UE 104 and the core network 190. Generally, the AMF 192 provides service quality (QoS) flow and session management. All user IP packets are transferred via the UPF 195. The UPF 195 provides UE IP address allocation and other functions. The UPF 195 is connected to an IP service 197. The IP service 197 may include the Internet, an intranet, IMS, a packet switch (PS) streaming service, and / or other IP services.

[0031]

[0043] The base station includes a gNB, Node B, eNB, access point, base transceiver station, radio base station, radio transceiver, transceiver function, basic service set (BSS), extended service set (ESS), transmission and reception point (TRP), or some other suitable term, and / or may be referred to as such. The base station 102 provides an access point for the UE 104 to the EPC 160 or the core network 190. Examples of the UE 104 include mobile phones, smartphones, session initiation protocol (SIP) phones, laptops, personal digital assistants (PDAs), satellite radios, global positioning systems, multimedia devices, video devices, digital audio players (e.g., MP3 players), cameras, game consoles, tablets, smart devices, wearable devices, vehicles, electricity meters, gas pumps, large or small kitchen appliances, healthcare devices, implants, sensors / actuators, displays, or any other similar functional device. Some of the UE 104 may be referred to as IoT devices (e.g., parking meters, gas pumps, toasters, vehicles, heart monitors, etc.). The UE 104 may also be called a station, mobile station, subscriber station, mobile unit, subscriber unit, wireless unit, remote unit, mobile device, wireless device, wireless communication device, remote device, mobile subscriber station, access terminal, mobile terminal, wireless terminal, remote terminal, handset, user agent, mobile client, client, or some other appropriate term.

[0032]

[0044] Although the present disclosure may focus on 5G NR, the concepts and various aspects described herein may be applicable to other similar fields, such as LTE, Long Term Evolution - Advanced (LTE - A), Code Division Multiple Access (CDMA), Global System for Mobile Communications (GSM®), or other wireless / wireless access technologies.

[0033]

[0045] Referring back to FIG. 1, in some aspects, UE 104 may include a carrier frequency offset (CFO) compensation component 198 configured to obtain one or more RARs, where each of the one or more RARs includes a RAPID and each of the one or more RARs responds to a random access message that includes a preamble. The CFO compensation component 198 is also configured to determine, in each of one or more RARs of a threshold number, that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message. In response to the determination, the CFO compensation component 198 is further configured to offset (shift) the carrier frequency for each of one or more subsequent random access messages.

[0034]

[0046] FIG. 2A is a diagram 200 showing an example of a first subframe within a 5G NR frame structure. FIG. 2B is a diagram 230 showing an example of a DL channel within a 5G NR subframe. FIG. 2C is a diagram 250 showing an example of a second subframe within a 5G NR frame structure. FIG. 2D is a diagram 280 showing an example of a UL channel within a 5G NR subframe. The 5G NR frame structure can be frequency division duplexing (FDD) where a subframe within a set of subcarriers (carrier system bandwidth) is dedicated to either DL or UL for a particular set of subcarriers, or time division duplexing (TDD) where a subframe within a set of subcarriers (carrier system bandwidth) is dedicated to both DL and UL. In the examples given by FIGS. 2A and 2C, the 5G NR frame structure is assumed to be TDD, where subframe 4 is configured with slot format 28 (mostly DL), where D is DL, U is UL, and F is flexible for use between DL / UL, and subframe 3 is configured with slot format 34 (mostly UL). Although subframes 3 and 4 are shown with slot formats 34 and 28 respectively, any particular subframe can be configured with any of the various available slot formats 0 - 61. Slot formats 0 and 1 are all DL and UL respectively. The other slot formats 2 - 61 include a mixture of DL, UL, and flexible symbols. The UE is configured with a slot format through the received slot format indicator (SFI) (dynamically through DL control information (DCI) or semi-statically / statically through radio resource control (RRC) signaling). Note that the following description also applies to a 5G NR frame structure that is TDD.

[0035]

[0047] Other wireless communication technologies may have different frame structures and / or different channels. For example, a 10 millisecond (ms) frame may be divided into 10 equal-sized subframes (1 ms). Each subframe may include one or more time slots. The subframe may also include minislots, which may include 7, 4, or 2 symbols. Each slot may include 7 or 14 symbols depending on the slot configuration. In the case of slot configuration 0, each slot may include 14 symbols, and in the case of slot configuration 1, each slot may include 7 symbols. The symbols on the DL may be cyclic prefix (CP) orthogonal frequency-division multiplexing (OFDM) (CP-OFDM) symbols. The symbols on the UL may be (in the case of high throughput scenarios) CP-OFDM symbols, or (in the case of power-limited scenarios, limited to single-stream transmission) discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (also called single carrier frequency division multiple access (SC-FDMA) symbols). The number of slots in a subframe is based on the slot configuration and numerology. In the case of slot configuration 0, different numerologies μ0 to 4 enable 1, 2, 4, 8, and 16 slots per subframe, respectively. In the case of slot configuration 1, different numerologies 0 to 2 enable 2, 4, and 8 slots per subframe, respectively. Thus, in the case of slot configuration 0 and numerology μ, there are 14 symbols / slot and 2 μ slots / subframe. The subcarrier spacing and symbol length / duration are functions of the numerology. The subcarrier spacing is 2 μ*It can be equal to 15 kilohertz (kHz), where μ is a numerology from 0 to 4. Thus, numerology μ = 0 has a subcarrier spacing of 15 kHz, and numerology μ = 4 has a subcarrier spacing of 240 kHz. The symbol length / duration is inversely related to the subcarrier spacing. FIGS. 2A - 2D provide an example of slot configuration 0 with 14 symbols per slot and numerology μ = 2 with 4 slots per subframe. The slot duration is 0.25 ms, the subcarrier spacing is 60 kHz, and the symbol duration is approximately 16.67 μs. Within a set of frames, there can be one or more different bandwidth parts (BWPs) (see FIG. 2B) that are frequency-division multiplexed. Each BWP can have a specific numerology.

[0036]

[0048] A resource grid can be used to represent the frame structure. Each time slot includes a resource block (RB) (also called a physical RB (PRB)) that extends 12 consecutive subcarriers. The resource grid is divided into a plurality of resource elements (REs). The number of bits carried by each RE depends on the modulation scheme.

[0037]

[0049] As shown in FIG. 2A, some of the REs carry a reference (pilot) signal (RS) for the UE. The RS can include a demodulation RS (DM-RS) (shown as R x for one particular configuration, where 100x is the port number, although other DM-RS configurations are possible) and a channel state information reference signal (CSI-RS) for channel estimation at the UE. The RS can also include a beam measurement RS (BRS), a beam refinement RS (BRRS), and a phase tracking RS (PT-RS).

[0038]

[0050] Figure 2B shows an example of various DL channels within a subframe of a frame. The Physical Downlink Control Channel (PDCCH) carries DCI within one or more Control Channel Elements (CCEs), where each CCE contains nine Resource Element Groups (REGs), and each REG contains four consecutive Resource Elements (REs) within an OFDM symbol. The PDCCH within one Bandwidth Part (BWP) may be referred to as a Control Resource Set (CORESET). Additional BWPs may be located at higher and / or lower frequencies across the channel bandwidth. The Primary Synchronization Signal (PSS) may be within symbol 2 of a particular subframe of a frame. The PSS is used by the UE104 to determine subframe / symbol timing and physical layer identification information. The Secondary Synchronization Signal (SSS) may be within symbol 4 of a particular subframe of a frame. The SSS is used by the UE to determine the physical layer cell identification information group number and radio frame timing. Based on the physical layer identification information and the physical layer cell identification information group number, the UE can determine the Physical Cell Identifier (PCI). Based on the PCI, the UE can determine the position of the aforementioned DM-RS. The Physical Broadcast Channel (PBCH) that carries the Master Information Block (MIB) may be logically grouped using the PSS and SSS to form a Synchronization Signal (SS) / PBCH Block (also called an SS Block (SSB)). The MIB provides the number of Resource Blocks (RBs) in the system bandwidth and the System Frame Number (SFN). The Physical Downlink Shared Channel (PDSCH) carries user data, broadcast system information not transmitted through the PBCH such as System Information Blocks (SIBs), and paging messages.

[0039]

[0051] As shown in Figure 2C, some of the REs carry DM-RS for channel estimation at the base station (shown as R for one particular configuration, although other DM-RS configurations are possible). The UE may transmit DM-RS for the physical uplink control channel (PUCCH) and DM-RS for the physical uplink shared channel (PUSCH). The PUSCH DM-RS may be transmitted in the first one or two symbols of the PUSCH. The PUCCH DM-RS may be transmitted in different configurations depending on whether a short PUCCH or a long PUCCH is being transmitted and depending on the particular PUCCH format used. The UE may transmit a sounding reference signal (SRS). The SRS may be transmitted in the last symbol of the subframe. The SRS may have a comb structure and the UE may transmit the SRS on one of the combs. The SRS may be used by the base station for channel quality estimation to enable frequency-dependent scheduling on the UL.

[0040]

[0052] Figure 2D shows an example of the various UL channels within a subframe of a frame. The PUCCH may be located as shown in one configuration. The PUCCH carries uplink control information (UCI) such as scheduling requests, channel quality indicator (CQI), precoding matrix indicator (PMI), rank indicator (RI), and hybrid automatic repeat request (HARQ) acknowledgement (ACK) / negative acknowledgement (NACK) feedback. The PUSCH carries data and may be further used to carry a buffer status report (BSR), a power headroom report (PHR), and / or UCI.

[0041]

[0053] FIG. 3 is a block diagram of base station 310 communicating with UE 350 within an access network. In the DL, IP packets from EPC 160 can be provided to controller / processor 375. Controller / processor 375 implements layer 3 and layer 2 functions. Layer 3 includes the radio resource control (RRC) layer, and layer 2 includes the service data adaptation protocol (SDAP) layer, the packet data convergence protocol (PDCP) layer, the radio link control (RLC) layer, and the media access control (MAC) layer. Controller / processor 375 is related to RRC layer functions such as broadcasting of system information (e.g., MIB, SIB), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), mobility between radio access technologies (RATs), measurement configuration for UE measurement reports, as well as PDCP layer functions related to header compression / decompression, security (encryption, decryption, integrity protection, integrity verification), and handover support functions, and RLC layer functions related to transfer of upper layer packet data units (PDUs), error correction via ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), resegmentation of RLC data PDUs, and reordering of RLC data PDUs, and MAC layer functions related to mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction via HARQ, priority handling, and logical channel prioritization.

[0042]

[0054] The transmitting (TX) processor 316 and the receiving (RX) processor 370 implement layer 1 functions associated with various signal processing functions. Layer 1, which includes the physical (PHY) layer, may include error detection on the transport channel, forward error correction (FEC) coding / decoding of the transport channel, interleaving, rate matching, mapping onto the physical channel, modulation / demodulation of the physical channel, and MIMO antenna processing. The TX processor 316 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), M-phase shift keying (M-PSK), multi-level quadrature amplitude modulation (M-QAM)). The coded and modulated symbols may then be split into parallel streams. Each stream is then mapped to OFDM subcarriers to generate a physical channel carrying a time-domain OFDM symbol stream, multiplexed with a reference signal (e.g., a pilot) in the time domain and / or frequency domain, and then may be combined with each other using an inverse fast Fourier transform (IFFT). The OFDM stream is spatially precoded to generate a plurality of spatial streams. Channel estimates from the channel estimator 374 may be used to determine the coding and modulation schemes and for spatial processing. The channel estimates may be derived from reference signals transmitted by the UE 350 and / or channel state feedback. Each spatial stream may then be supplied to a different antenna 320 via a separate transmitter 318TX. Each transmitter 318TX can modulate an RF carrier having its respective spatial stream for transmission.

[0043]

[0055] In UE350, each receiver 354RX receives signals via its respective antenna 352. Each receiver 354RX recovers the information modulated on the RF carrier and supplies that information to the receive (RX) processor 356. The TX processor 368 and the RX processor 356 implement layer 1 functions related to various signal processing functions. The RX processor 356 may perform spatial processing on the information to recover the spatial streams directed to UE350. If multiple spatial streams are directed to UE350, they may be combined by the RX processor 356 into a single OFDM symbol stream. The RX processor 356 then uses a fast Fourier transform (FFT) to transform the OFDM symbol stream from the time domain to the frequency domain. The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier and the reference signals are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station 310. These soft decisions may be based on the channel estimates calculated by the channel estimator 358. The soft decisions are then decoded and deinterleaved to recover the data and control signals originally transmitted by the base station 310 on the physical channel. The data and control signals are then provided to the controller / processor 359 that implements layer 3 and layer 2 functions.

[0044]

[0056] The controller / processor 359 can be associated with a memory 360 that stores program code and data. The memory 360 may be referred to as a computer-readable medium. In the UL, the controller / processor 359 provides demultiplexing in reverse between the transport channel and the logical channel, packet reassembly, decoding, header decompression, and control signal processing to recover IP packets from the EPC160. The controller / processor 359 is also responsible for error detection using the ACK and / or NACK protocols to support HARQ operations.

[0045]

[0057] Similar to the functions described for DL transmission by base station 310, the controller / processor 359 includes RRC layer functions associated with system information (e.g., MIB, SIB) collection, RRC connection, and measurement reporting, PDCP layer functions associated with header compression / decompression and security (encryption, decryption, integrity protection, integrity verification), RLC layer functions associated with transfer of upper layer PDUs, error correction via ARQ, concatenation, segmentation, and reassembly of RLC SDUs, resegmentation of RLC data PDUs, and reordering of RLC data PDUs, and MAC layer functions associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction via HARQ, priority handling, and logical channel prioritization.

[0046]

[0058] Channel estimates derived by channel estimator 358 from reference signals or feedback transmitted by base station 310 may be used by TX processor 368 to select an appropriate coding and modulation scheme and to facilitate spatial processing. The spatial streams generated by TX processor 368 may be supplied to different antennas 352 via separate transmitters 354TX. Each transmitter 354TX can modulate an RF carrier with its respective spatial stream for transmission.

[0047]

[0059] UL transmission is processed at base station 310 in a manner similar to that described for the receiver function at UE 350. Each receiver 318RX receives signals via its respective antenna 320 of the receiver. Each receiver 318RX recovers the information modulated on the RF carrier and provides that information to RX processor 370.

[0048]

[0060] The controller / processor 375 may be associated with a memory 376 that stores program code and data. The memory 376 may be referred to as a computer-readable medium. In the UL, the controller / processor 375 provides demultiplexing between the transport channel and the logical channel, packet reassembly, decoding, header decompression, and control signal processing to recover IP packets from the UE 350. The IP packets from the controller / processor 375 may be provided to the EPC 160. The controller / processor 375 is also responsible for error detection using the ACK and / or NACK protocol to support HARQ operations.

[0049]

[0061] At least one of the TX processor 368, the RX processor 356, and the controller / processor 359 may be configured to perform aspects related to the CFO compensation component 198 of FIG. 1.

[0050]

[0062] In a 4-step contention-based RACH procedure, four messages may be provided between the UE and the base station. For example, during an initial attach procedure, the UE sends a preamble to the base station (e.g., message 1), receives a RAR from the base station (e.g., message 2), sends an RRC connection request message or other payload to the base station (e.g., message 3), and may receive a contention-resolved RRC connection setup message or other transmission from the base station (e.g., message 4). This 4-step RACH procedure may be simplified to a 2-step RACH procedure in which the UE sends a preamble and a subsequent payload in the first message. For example, message A ("msgA") of the 2-step RACH procedure may correspond to messages 1 and 3 of the 4-step RACH procedure, and message B ("msgB") may correspond to messages 2 and 4 of the 4-step RACH procedure. Thus, in the 2-step RACH procedure, the UE may send a preamble and a subsequent payload to the base station during msgA transmission, and the base station may send a RAR and an RRC response message to the UE during msgB transmission.

[0051]

[0063] The UE may select a preamble for Message 1 or msgA from a set of random access preambles (x u,v (n)) generated by the UE. The set of random access preambles may be a function of various configured RACH parameters. For example, the random access preamble may depend at least on a preamble sequence number (u) obtained from a logical root sequence index, a length (L RA ) related to a physical random access channel (PRACH) preamble format, and a cyclic shift (C v ) of the logical root sequence. The preamble format, in turn, is as shown in the example of Table 1 below, the PRACH preamble subcarrier spacing (Δf RA ), the preamble length (N u ), the preamble cyclic prefix length

[0052]

Number

[0053] , and may be associated with the support of a restricted set of preamble sequences. Further, in the case of an unrestricted set of preamble sequences, the cyclic shift (C v ) may be a function of a cyclic shift parameter (N CS ), and in the case of a restricted set of preamble sequences, the cyclic shift may be a function of N CS and a Doppler shift parameter (d u ).

[0054]

Table 1

[0055]

[0064] After the UE selects a preamble from the set of generated preambles, the UE may transmit the preamble to the base station within the configured time and frequency resources. The time and frequency resources may be a function of various configured RACH parameters. For example, the slot or symbol in which the preamble is transmitted may depend on the PRACH configuration index, and the subcarrier in which the preamble is transmitted may depend on the length (L RA ) and the PRACH preamble subcarrier spacing (Δf RA ). The subcarriers may be spread across the frequency domain according to the frequency domain representation (y u,v (n)) of the set of generated preamble sequences, and the frequency domain representation is a function of the cyclic shift (C v ). Thus, each preamble sequence in the set may be configured in the frequency domain across different combinations of PRACH subcarriers based on their respective cyclic shifts, where each PRACH subcarrier is spaced apart in frequency according to the PRACH preamble subcarrier spacing. As a result, adjacent PRACH subcarriers (separated by Δf RA only) may be configured for different preamble sequences, and the UE may transmit the selected preamble in the corresponding PRACH subcarriers of that preamble sequence.

[0056]

[0065] After the UE transmits the selected preamble in the PRACH subcarrier (in Message 1 or msgA) to the base station, the base station can decode the message and identify the preamble transmitted by the UE. For example, the base station can receive and demodulate the data in the PRACH subcarrier and determine the selected preamble sequence of the UE based on the subcarrier on which the PRACH data was received. In response to identifying the preamble, the base station can construct a RAR including a Random Access Preamble Identifier (RAPID). The base station can construct the RAPID using an identifier associated with the decoded preamble sequence (e.g., the preamble sequence determined to be transmitted by the UE). Then, the base station can transmit the RAR to the UE in Message 2 or msgB.

[0057]

[0066] When the UE receives and decodes the RAR, the UE can determine whether the RAPID in the RAR is the same as the identifier associated with the selected preamble sequence of the UE. If the RAPID matches the preamble, the UE can determine that the preamble was received correctly or that the RACH procedure was executed successfully, and the UE can communicate with the base station accordingly. Otherwise, if the RAPID does not match the preamble (e.g., the RAPID is a mismatched RAPID), the UE can determine that the RACH procedure has failed, and the UE can restart the RACH procedure from Message 1 or msgA.

[0058]

[0067] One scenario where RAPID handovers can be observed is in HST deployments. The HST has recently been developed as a fast, convenient, environmentally friendly, and flexible means of transportation. As an increasing number of passengers carrying UEs tend to move on the HST, new challenges arise in providing reliable communication services to meet the growing communication demand. For example, a typical HST may move at speeds exceeding 200 kilometers per hour (km / h), or even exceeding 350 km / h, resulting in frequent and high-speed handovers, large Doppler spreads, and other effects. In an attempt to overcome these challenges, mmW and massive MIMO technologies, as well as CoMP and mobile relay station architectures, have been considered for HST deployments.

[0059]

[0068] However, despite such techniques, conventional HST deployment may still be insufficient to cover all possible scenarios that can occur in an HST, including the above-mentioned RAPID of the inconsistency. For example, a UE located within or on the HST (referred to herein as an HST UE) often camps on a non-HST cell (e.g., a cell served by a base station located outside or away from the HST). Since these non-HST cells were originally designed to support UEs located outside or away from the HST (referred to herein as non-HST UEs), the base stations serving these non-HST cells may configure the HST UE and the non-HST UE in the same manner using a similar RACH configuration. For example, a base station within a non-HST cell may provide a RACH configuration that indicates preamble format 0 of the PRACH (see Table 1 above) to both the HST UE and the non-HST UE and employs an unlimited set of preamble sequences. As a result, an HST UE camping on a non-HST cell tends to experience frequent RACH failures due to the inconsistency between the RAPID in the RAR and the selected preamble of the UE. These RAPID inconsistencies are typically due to the relatively small PRACH preamble sub-carrier spacing (e.g., Δf RA = 1.25 kHz) associated with such preamble formats and the relatively large uplink Doppler shift that an HST UE may experience when transmitting message 1 or msgA.

[0060]

[0069] Here, the uplink Doppler shift refers to the frequency shift of a radio signal received by a base station with respect to the movement of a transmitting UE. For example, when a fixed base station receives a RACH message from an HST UE within an HST moving at 200 km / h via a carrier frequency of 3.5 GHz, the RACH message may experience a Doppler shift or frequency offset that varies between ±600 Hz. Further, when a fixed base station receives a RACH message from an HST UE within an HST moving at 350 km / h via a carrier frequency of 3.8 GHz, the RACH message may experience a Doppler shift or frequency offset that varies between ±1230 Hz. Such Doppler shifts can be relatively large compared to the small preamble sub-carrier spacing typically associated with a common preamble format for HST UEs and non-HST UEs. For example, when Δf RA = 1.25 kHz, the base station may receive Message 1 or msgA from an HST UE moving on an HST at 350 km / h with a frequency offset of approximately one PRACH sub-carrier. In some cases, the frequency offset can be even larger and can typically be up to two PRACH sub-carriers at most. As a result of this frequency offset applied to the received signal, the base station may misidentify the transmitted preamble as a different preamble, and as a result, the base station may identify a different RAPID, leading to a final RACH failure. This misidentification can occur from either a positive Doppler shift (e.g., when the preamble is received at a higher frequency than it was transmitted) or a negative Doppler shift (e.g., when the preamble is received at a lower frequency than it was transmitted). Therefore, it is useful to compensate for these carrier frequency offsets in order to improve the RACH success rate of HST UEs.

[0061]

[0070] For example, FIG. 4 shows an example 400 of HST deployment in which a UE on the HST (HST UE 402) can communicate with a base station 404 in a non-HST cell. The base station 404 can also communicate with a UE outside the HST (non-HST UE 406). During the RACH procedure, the HST UE 402 can transmit a RACH message 408 (e.g., message 1 or msgA) containing a preamble at a given frequency A to the base station 404. However, due to the high speed of the HST UE relative to the base station, a Doppler shift 410 or frequency offset may be applied, such that the RACH message is received by the base station at a different frequency B. As a result of this frequency offset, the base station 404 may identify an inaccurate preamble and, accordingly, transmit a RAR 412 (e.g., message 2 or msgB) containing an inaccurate RAPID to the HST UE. As a result of the mismatch between the preamble of the RACH message 408 and the RAPID of the RAR 412, the RACH procedure may fail and the process may be inefficiently repeated for subsequent RACH attempts.

[0062]

[0071] To solve this problem, aspects of the present disclosure enable a UE to compensate for uplink Doppler shifts when transmitting a RACH preamble (e.g., in an HST). In one example, the UE may monitor the number N of consecutive RACH attempts (e.g., the RACH attempts from the 1st to the Nth) for inconsistent RAPIDs. For example, the UE may obtain N consecutive RARs, where each RAR responds to the transmitted preamble, and the UE may determine whether any of the RARs contains a RAPID that does not match the identifier of the corresponding preamble sequence transmitted by the UE. If the UE determines that these RACH attempts have failed due to inconsistent RAPIDs a threshold number K of times in response to the aforementioned Doppler shift effect, the UE may compensate for this frequency offset in subsequent RACH attempts. For example, if the UE determines that K out of N consecutive RARs contain RAPIDs that do not match the identifier of the corresponding preamble sequence due to a positive or negative Doppler shift, the UE may offset the carrier frequency of a subsequent Message 1 or msgA (e.g., after RACH attempt N + 1) positively or negatively to compensate for this Doppler shift. For example, if the UE transmits a preamble in RACH attempts 1 to N on a carrier frequency of 3.8 GHz, the UE may transmit a preamble in subsequent RACH attempt N + 1 with a carrier frequency offset of 600 Hz (3.8000006 GHz) or -600 Hz (3.7999994 GHz). The UE may similarly transmit subsequent RACH preambles with various (positive or negative) carrier frequency offsets until the UE successfully decodes the preamble transmitted by the base station and receives a RAR with a RAPID that matches the preamble transmitted by the UE. As a result, the RACH success rate can be increased for HST UEs.

[0063]

[0072] FIG. 5 shows an example 500 of a UE 502 that compensates for uplink Doppler shift when performing a RACH procedure with a base station 504. The UE 502 may correspond to the HST UE 402 of FIG. 4, and the base station 504 may correspond to the base station 404 of FIG. 4. First, the UE 502 may monitor up to N consecutive RACH attempts. In each RACH attempt 506, the UE transmits a RACH message 508 (e.g., message 1 or msgA) to the base station 504 and receives a RAR 510 (e.g., message 2 or msgB) from the base station. Each RACH message 508 may include a preamble selected by the UE 502, and each RAR 510 may include a RAPID configured by the base station 504. The number N may be a configurable value that is a function of the maximum number of preamble transmissions configured for the UE. The maximum number of preamble transmissions may be configured by the base station via a parameter preambleTransMax that it may signal to the UE in an RRC message. For example, the base station may configure N = minimum(preambleTransMax, 10).

[0064]

[0073] For each RACH attempt 506 in which the UE 502 receives a RAPID in the RAR 510, the UE checks whether the RAPID matches the preamble in the corresponding RACH message 508. If the UE 502 determines that a threshold number 512 of RACH attempts 506 (e.g., K RACH attempts within N consecutive RACH attempts) have failed due to inconsistent RAPIDs (e.g., the RAPID does not match the preamble in each of the K attempts), the UE may determine whether each of these failed attempts is due to an uplink Doppler shift or offset at the carrier frequency 514 for each RACH message 508. The threshold number K can include any combination of consecutive or non - consecutive RACH attempts within N consecutive RACH attempts. For example, when N = 10 and K = 5, the threshold number of RACH attempts can include the first 5 different RACH attempts, the 3rd to 7th RACH attempts, the 6th to 10th RACH attempts, the 1st, 3rd, 5th, 7th, 9th RACH attempts, the 2nd, 4th, 6th, 8th, 10th RACH attempts, the 3rd, 4th, 7th, 9th, 10th RACH attempts, or any other combination of K different RACH attempts within N consecutive RACH attempts.

[0065]

[0074] The UE may also determine how many of these K RACH attempts (if any) include a positive Doppler shift (represented by the number K1) and how many of these K RACH attempts (if any) include a negative Doppler shift (represented by the number K2), where K = K1 + K2. For example, FIG. 6 shows an example 600 of a UE 602 transmitting a RACH preamble to a base station 604, where the RACH preambles carried in the PRACH 606 each undergo an uplink Doppler shift in the positive (K1) or negative (K2) direction. The UE 602 may correspond to the HST UEs 402 and 502 of FIGS. 4 and 5, and the base station 604 may correspond to the base stations 404, 504 of FIGS. 4 and 5. In this example, when the UE 602 transmits a RACH preamble for RACH attempt 1 in PRACH1, PRACH1 may undergo a positive Doppler shift such that the base station 604 receives PRACH1 at a higher frequency than it is transmitted. As a result, the base station may misidentify PRACH1 as containing a different preamble and accordingly construct an inaccurate RAPID. Thus, PRACH1 may be included in the sum of K1. Similarly, when the UE 602 transmits a RACH preamble for RACH attempt 2 in PRACH2, PRACH2 may undergo a negative Doppler shift such that the base station 604 receives PRACH2 at a lower frequency than it is transmitted. As a result, the base station may similarly misidentify PRACH2 as containing a different preamble and accordingly construct an inaccurate RAPID. Thus, PRACH2 may be included in the sum of K2. The UE may continue to transmit RACH preambles in the PRACH for other RACH attempts, where each PRACH may undergo either a positive or negative Doppler shift.

[0066]

[0075] In one example, the UE determines whether a RAPID inconsistency is caused by the uplink Doppler shift effect and the direction (positive or negative) of the Doppler shift based on the expected RAPID at the base station. For example, the UE may apply the following equation to determine the presence and direction of the Doppler shift or carrier frequency offset (CFO).

[0067]

[0076]

[0068]

Equation

[0069]

[0077] Here, RAPID0 represents the RAPID of root u with cyclic shift C v = 0.

[0070]

[0078]

[0071]

Equation

[0072]

[0079] Here, v UE represents the cyclic shift index of RAPID UE .

[0073]

[0080]

[0074]

Equation

[0075]

[0081] Here,

[0076]

Equation

[0077] represents the shift with respect to RAPID0 when CFO > 0 (positive Doppler shift).

[0078]

[0082]

[0079]

Number

[0080]

[0083] Here,

[0081]

Number

[0082] represents the shift for RAPID0 in the case of CFO < 0 (negative Doppler shift).

[0083]

[0084]

[0084]

Number

[0085]

[0085]

[0086] Here, g represents the mapping to RAPID.

[0086]

[0087] delay d D in the case of, the RAPID expected at the receiver is

[0088]

[0087]

Number

[0088]

[0089]

[0090] and here,

[0089]

Number

[0090] or

[0091]

Number

[0092] represents the total shift with respect to RAPID0. Further,

[0091]

[0093]

Number

[0094]

[0092]

[0093] Here, RAPID pos and RAPID neg each represent the receivable RAPID for positive and negative frequency offsets when 0 ≦ d D ≦ N CS - 1.

[0095]

[0094] When determining the predicted RAPID (RAPID pos and RAPID neg ) and the actual RAPID received from the base station (RAPID gNB ) in the RAR, the UE may apply the following decision rules to determine whether the RAPID inconsistency is due to the CFO, and if so, to determine the direction of the CFO.

[0096]

[0095]

[0097]

Number

[0098] In Equation 8, "Not Doppler" represents the determination that the inconsistent RAPID was not due to the Doppler effect (no frequency offset), "Positive Doppler" represents the determination that the inconsistent RAPID was due to a positive frequency offset (e.g., PRACH1 in FIG. 6), "Negative Doppler" represents the determination that the inconsistent RAPID was due to a negative frequency offset (e.g., PRACH2 in FIG. 6), and "Ambiguity" represents the determination that the inconsistent RAPID could be due to either a positive or negative frequency offset.

[0099]

[0097] In another example, the UE may determine whether the RAPID inconsistency was caused by the uplink Doppler shift effect and the direction (positive or negative) of the Doppler shift based on the expected RAPID at the base station and the timing advance received in the RAR from the base station. For example, the UE may apply the following equation to determine the presence and direction of the Doppler shift or CFO.

[0100]

[0098]

[0101]

Number

[0102]

[0099] Here, RAPID0 represents the RAPID of root u with cyclic shift C v = 0.

[0103]

[0100]

[0104]

Number

[0105]

[0101] Here, v UE represents the cyclic shift index of RAPID UE .

[0106]

[0102]

[0107]

Number

[0108]

[0103] Here,

[0109]

Number

[0110] represents the shift for RAPID0 when CFO > 0 (positive Doppler shift).

[0111]

[0104]

[0112]

Number

[0113]

[0105] That is, here,

[0114]

Number

[0115] represents the shift for RAPID0 when CFO < 0 (negative Doppler shift).

[0116]

[0106]

[0117]

Number

[0118]

[0107] Here, v gNB represents the cyclic shift index of RAPID gNB

[0119]

[0108] ​

[0120]

Number

[0121]

[0109] Here, T NW represents the timing advance reported by the network in seconds, and T RA represents the RACH sampling period.

[0122]

[0110]

[0123]

Number

[0124]

[0111]

[0112] Here, Equation 15 defines the lower bound LB and upper bound UB related to the cyclic shift for the expected RAPID, and ε represents the error margin for covering the error in T NW .

[0125]

[0113]

[0126]

Number

[0127]

[0114] Here, I D represents the possible received cyclic shift for the expected RAPID.

[0128]

[0115] When determining the cyclic shift for the expected RAPID (I D ), the UE may apply the following decision rules to determine whether the RAPID inconsistency is due to the CFO and, if so, the direction of the CFO.

[0129]

[0116]

[0130]

Number

[0131]

[0117] In Equation 17, “Not Doppler” represents the determination that the inconsistent RAPID was not due to the Doppler effect (no frequency offset), “Positive Doppler” represents the determination that the inconsistent RAPID was due to a positive frequency offset (e.g., PRACH1 in FIG. 6), “Negative Doppler” represents the determination that the inconsistent RAPID was due to a negative frequency offset (e.g., PRACH2 in FIG. 6), and “Ambiguity” represents the determination that the inconsistent RAPID could be due to either a positive or negative frequency offset.

[0132]

[0118] The above two examples show specific parameters and equations that the UE can apply to determine the CFO and direction. However, the UE can apply other parameters or equations to make that determination. Therefore, the above examples are only intended to be illustrative in nature, and the determination of the CFO and direction is not limited to the parameters and equations shown in these examples.

[0133]

[0119] For example, as explained in the above example, the UE can determine the presence and direction of the Doppler shift based on the Doppler shift parameter d u (see, e.g., Equations 3, 4, 11, and 12). Usually, the maximum uplink CFO observed in HST can be twice the maximum Doppler shift (e.g., for a 350 km / h HST, 2 × 1230 Hz = 2460 Hz, or assuming Δf RA = 1.25 kHz, approximately two PRACH subcarriers). Therefore, d u is either d (1) u or d (2) ucan be represented as any one of them, and each can represent the cyclic shift position of the false alarm peak due to a frequency offset of approximately the same magnitude as one or two PRACH sub-carriers. For example, the cyclic shift d on sequence u (1) u can result from a frequency offset of approximately the same magnitude as one PRACH sub-carrier, and the cyclic shift d on sequence u (2) u can result from a frequency offset of approximately the same magnitude as two PRACH sub-carriers. Therefore, in the above equations 3, 4, 11, and 12, d u can be replaced with either (at most for one PRACH sub-carrier offset) d (1) u or (at most for two PRACH sub-carrier offsets) d (2) u where d (1) u is the smallest positive integer or the largest negative integer that satisfies u * d (1) u mod L RA = + / - 1, and where d (2) u is the smallest positive integer or the largest negative integer that satisfies u * d (2) u mod L RA = + / - 2.

[0134] Referring again to FIG. 5, in response to the UE 502 determining, for example, a positive Doppler, negative Doppler, or ambiguity in the above Equation 8 or Equation 17, if the RACH attempts of the threshold number 512 (K out of N times) are each determined to have failed due to the uplink Doppler shift, the UE may compensate for the Doppler shift in subsequent RACH attempts 516 by offsetting the carrier frequency 514 for each subsequent RACH message 518 (starting from the N+1-th RACH attempt). For example, the UE may apply an offset 520 to the carrier frequency 514 for the subsequent RACH message 518 during the RACH attempt N+1 by transmitting a preamble in the subsequent RACH message at the offset carrier frequency. For example, if the UE transmits RACH attempts 1 to N at a frequency of 3.8 GHz, the UE may apply an offset of 600 Hz or -600 Hz to the RACH attempt N+1 by transmitting a preamble during that RACH attempt at the offset carrier frequency (e.g., 3.8000006 GHz or 3.7999994 GHz, respectively). The UE may apply different offsets (or the same offset) in each subsequent RACH attempt (e.g., N+2, etc.), and the UE may continue to apply the offset to the subsequent RACH message accordingly until the UE receives a subsequent RAPID 522 that matches the transmitted preamble.

[0135]

[0121] For example, FIG. 7 shows an example 700 of a UE 702 that offsets the carrier frequency for different RACH preambles following the determination of K out-of-match RAPIDs during N initial RACH attempts. UE 702 may correspond to the HST UEs 402, 502, and 602 of FIGS. 4 - 6. The UE may offset the carrier frequency for each RACH preamble by transmitting each preamble in PRACH 704 with a different (positive or negative) frequency offset, for example, to compensate for the Doppler shift effect. For example, UE 702 may transmit the RACH preamble for RACH attempt N + 1 in PRACH N + 1 according to a first carrier frequency offset in either the positive or negative direction. For example, if a previous PRACH (in RACH attempt N or a previous attempt) received a positive Doppler shift, the UE may transmit PRACH N + 1 at a lower frequency (negative frequency offset) in an attempt to compensate for the positive Doppler shift, but if the previous PRACH received a negative Doppler shift, the UE may transmit PRACH N + 1 at a higher frequency (positive frequency offset) in an attempt to compensate for the negative Doppler shift. If the value of the first carrier frequency offset is insufficient to compensate for the Doppler shift, the base station may still incorrectly identify PRACH N + 1 as containing a different preamble and accordingly construct an inaccurate RAPID. Thus, the UE may attempt to apply more compensation (a different offset) in the next RACH attempt. For example, UE 702 may transmit the RACH preamble for RACH attempt N + 2 according to a second carrier frequency offset in either the positive or negative direction, where the second carrier frequency offset is different from the first carrier frequency offset. For example, the UE may transmit PRACH N + 2 at a lower frequency than PRACH N + 1 to increase the compensation for a positive Doppler shift or at a higher frequency than PRACH N + 1 to increase the compensation for a negative Doppler shift. Alternatively, the second carrier frequency offset may be the same as the first carrier frequency offset.The UE may continue to offset the PRACH for subsequent RACH attempts until the Doppler shift is sufficiently compensated and the base station 704 correctly identifies the preamble in the PRACH. As a result, the base station may be able to construct the correct RAPID, thereby potentially increasing the likelihood of RACH success.

[0136]

[0122] Referring again to FIG. 5, in one example, the value of each offset 520 may be limited to a range that can be configured based on the preamble subcarrier spacing Δf RA of the base station. For example, the base station may configure the following ranges for CFO compensation.

[0137]

[0123]

[0138]

Number

[0139]

[0124] Or,

[0125]

[0140]

Number

[0141]

[0126] Here, the first range (18) represents an example of a negative range that the UE may apply in response to determining a negative (or ambiguous) frequency offset in Equation 8 or 17, and the second range (19) represents an example of a positive range that the UE may apply in response to determining a positive (or ambiguous) frequency offset in Equation 8 or 17, where RA_SCS is the preamble subcarrier spacing Δf RA refers to. Further, the value of L is such that the frequency offset causing RAPID mismatch is as large as one PRACH subcarrier (in which case the UE is d in the above equations 3, 4, 11, or 12 (1) ucan be applied), or whether it is as large as two PRACH sub - carriers (in which case, the UE uses d in the above equations 3, 4, 11, or 12 (2) u and can depend on it. For example, if the frequency offset is one PRACH sub - carrier, L = 0, and if the frequency offset is two PRACH sub - carriers, L = 1.

[0142]

[0127] In addition, in another example, the aforementioned range (e.g., the negative range (18) or the positive range (19)) can be further optimized by the maximum uplink carrier frequency offset. In the above - exemplified ranges (18) and (19), the lower and upper limits can be - 2.5*RA_SCS and 2.5RA_SCS respectively when L = 1 (i.e., -(1.5+[L = 1])*RA_SCS and (1.5+[L = 1])*RA_SCS). However, these ranges can be optimized (narrowed) to account for the maximum uplink CFO observable in HST deployment. For example, as described above, the maximum uplink CFO observed in HST is twice the maximum Doppler shift (e.g., for a 350 km / h HST, 2×1230 Hz = 2460 Hz, or assuming Δf RA = 1.25 kHz, approximately two PRACH sub - carriers). Since 2460 Hz < 2.5 kHz = 2*(Δf RA = 1.25 kHz), the UE can apply a positive CFO compensation of up to 2*RA_SCS for L = 1 (two PRACH sub - carriers) instead of 2.5*RA_SCS as in the previous - exemplified range (19). Similarly, the UE can apply a negative CFO compensation up to - 2*RA_SCS for L = 1 instead of - 2.5*RA_SCS as in the previous - exemplified range (18). Therefore, the aforementioned ranges (18) and (19) can be modified by replacing (1.5 + L)*RA_SCS with 2*RA_SCS, narrowing the range and enabling a more optimal offset determination.

[0143]

[0128] The UE may determine the value of each offset 520 to be applied for each subsequent RACH attempt 516 (within the boundaries of the above range) based on one or more configured or pre-configured tables or other data structures. For example, the base station may configure the UE to apply the offsets identified in Table 2 below for positive frequency offsets or in Table 3 below for negative frequency offsets.

[0144]

Table 2

[0145]

Table 3

[0146]

[0129] Here, M represents the configurable CFO compensation step per RACH attempt (e.g., M = 200 Hz or some other configured or pre-configured value), O represents the configurable starting frequency for CFO compensation (e.g.,

[0147]

Equation

[0148] or some other function), and X represents the maximum number of RACH attempts for which CFO compensation can be applied. The value of X may depend on the values of O and M. For example, X may be

[0149]

Equation

[0150] or equal to some other value.

[0151]

[0130] The above Table 2 and Table 3 each refer to an exemplary configuration where the UE applies different positive offsets or different negative offsets for subsequent RACH attempts, but the configuration is not limited as such. For example, different values or functions for M, O, and X, or parameters different from M, O, or X, may be applied to the RACH attempts in either table. In another example, Table 2 and Table 3 can be combined into a single table showing alternating positive and negative offsets (or some other combination of positive and negative offsets) across the RACH attempts, and the UE can accordingly apply positive or negative offsets for different ones of the subsequent RACH attempts. In a further example, multiple RACH attempts can be associated with the same offset instead of different offsets as in the case of Table 2 and Table 3. For example, RACH attempts N + 1 and N + 2 can both be associated with offset O*M instead of offsets O*M and (O + 1)*M respectively. The UE can apply the same offset to multiple RACH attempts, for example, when M is a large value (e.g., M = 600 Hz).

[0152]

[0131] Further referring to FIG. 5, in another example, if the consecutive number (Y) of RAPID mismatches is due to frequency offsets in the same direction (e.g., all positive Doppler shifts or all negative Doppler shifts), the UE may apply CFO compensation. If the UE determines that the consecutive number Y of RAPID mismatches is due to all positive CFOs, the UE may apply a negative frequency offset to each subsequent RACH attempt 516 as shown in Table 2 above. Alternatively, if the UE determines that the consecutive number Y of RAPID mismatches is due to all negative CFOs, the UE may apply a positive frequency offset to each subsequent RACH attempt 516 as shown in Table 3 above. The value of Y can be configurable by the base station or pre-configured for the UE (e.g., Y = 3 or some other value). Consecutive RAPID mismatches may include the last (K-th) RAPID mismatch identified by the UE in RAPID attempts 1 to N times.

[0153]

[0132] For example, assuming K = 5 and Y = 3, the UE determines the RAPID mismatch due to the CFO in RACH attempts 1 to 5 with the following directions, i.e., negative (K2 = 2) for the 1st and 2nd RACH attempts and positive (K1 = 3) for the 3rd, 4th, and 5th RACH attempts. In such a case, three consecutive RACH attempts (including the last or K-th RACH attempt) are associated with the positive Doppler shift direction, and thus the UE may determine that the subsequent RACH attempt 516 is also likely to include the same Doppler shift direction (positive). As a result, the UE may apply a negative frequency offset to the subsequent RACH attempt 516 according to Table 2 above.

[0154]

[0133] On the other hand, if the consecutive number Y of the RAPID mismatch due to the frequency offset in the same direction cannot be determined, the UE may determine which frequency offset direction is associated with more RAPID mismatches (e.g., whether K1 > K2 or K2 > K1). Following this determination, the UE may apply an offset to the subsequent RACH attempt 516 accordingly to compensate for this direction. For example, if K1 > K2, the UE may apply a negative frequency offset to each subsequent RACH attempt 516 as shown in Table 2 above, and if K2 > K1, the UE may apply a positive frequency offset to each subsequent RACH attempt 516 as shown in Table 3 above.

[0155]

[0134] For example, assuming K = 5 and Y = 3, the UE determines the RAPID inconsistency due to the CFO in the first to fifth RACH attempts with the following directions, i.e., the first, second, and fifth RACH attempts being positive (K1 = 3), and the third and fourth RACH attempts being negative (K2 = 2). In such a case, the UE may determine that there is no consecutive number Y of RAPID inconsistencies associated with the same Doppler shift direction (since in this example, there are only two consecutive RACH attempts in the same direction). Therefore, since K1 > K2 (there are more positive Doppler shifts), the UE may determine that the subsequent RACH attempt 516 is likely to also include the positive Doppler shift direction. As a result, the UE may apply a negative frequency offset to the subsequent RACH attempt 516 according to Table 2 above.

[0156]

[0135] As a result, if the UE is unable to determine the consecutive number Y of RAPID inconsistencies due to the frequency offset in the same direction, the UE can determine which frequency offset direction is associated with more RAPID inconsistencies (i.e., the majority direction) and which frequency offset direction is associated with fewer RAPID inconsistencies (i.e., the minority direction), and then the UE can apply CFO compensation accordingly. For example, if K1 > K2, the UE may determine that the majority direction is positive and the minority direction is negative, and if K2 > K1, the UE may determine that the majority direction is negative and the minority direction is positive. However, in some cases, the UE may also determine that the majority direction is not applied to the last RAPID inconsistency (e.g., the Kth RACH attempt). For example, if K1 > K2, the UE may sometimes determine that K1 does not include the last RAPID inconsistency, or if K2 > K1, the UE may sometimes determine that K2 does not include the last RAPID inconsistency. As a result, the UE may not be able to determine with a high likelihood whether the subsequent RACH attempt 516 is also associated with the majority decision direction (K1 or K2).

[0157]

[0136] For example, assuming N = 10 and K = 5, the second and fifth RACH attempts are positive (K1 = 2), and the first, third, and fourth RACH attempts are negative (K2 = 3). Here, since K2 > K1, the UE first applies a positive frequency offset to subsequent RACH attempt 516 according to Table 3 above. However, in this example, although the majority direction is negative (K2 > K1), the last K-th RAPID mismatch in the fifth RACH attempt is in the minority direction (positive or K1). Therefore, the UE may not be able to determine with a high likelihood that subsequent RACH attempts 516 also include the negative direction (e.g., they could be positive instead).

[0158]

[0137] Therefore, while the UE is applying CFO compensation to subsequent RACH attempts 516 in the majority direction, the UE may also monitor these subsequent RACH attempts to determine whether the offset direction should be switched (e.g., from the offset in Table 2 to Table 3, or vice versa). For example, the UE may determine whether a consecutive number Y of RAPID mismatches has occurred due to the CFO in the minority direction, including the RAPID mismatch associated with the last monitored subsequent RACH attempt (K2 if K1 > K2, or K1 if K2 > K1). If the UE determines that a consecutive number Y of RAPID mismatches in the minority direction exists in subsequent RACH attempts, the UE may determine that it was incorrect to apply the offset in the majority direction, and thus the UE may switch to the offset in the minority direction accordingly. For example, if K1 > K2, the UE may switch from applying the offset in Table 2 to the offset in Table 3, and if K2 > K1, the UE may switch from applying the offset in Table 3 to the offset in Table 2. The UE may also stop monitoring subsequent RACH attempts at this point.

[0159]

[0138] For example, assume that the UE starts applying CFO compensation according to Table 3 starting from the 6th subsequent RACH attempt. Further assume that Y = 3. In the above example, after performing the 1st to 5th RACH attempts, the UE determines RAPID mismatch using the following directions, i.e., negative for the 6th and 7th subsequent RACH attempts and positive for the 8th to 10th subsequent RACH attempts, regardless of the CFO compensation in the 6th to 10th subsequent RACH attempts. In such a case, three consecutive RACH attempts (including the last 10th subsequent RACH attempt) are associated with the positive Doppler shift direction, and thus the UE may determine that there is a high probability that additional RACH attempts (e.g., 11th and subsequent RACH attempts) will also include the same Doppler shift direction (positive). As a result, during additional RACH attempts (e.g., 11th and subsequent), the UE may switch from applying a positive frequency offset according to Table 3 to applying a negative frequency offset according to Table 2.

[0160]

[0139] Therefore, in any of the above examples, the UE may perform a plurality of subsequent RACH attempts using the applied carrier frequency offset in an attempt to compensate for the uplink Doppler shift effect on Message 1 or msgA. However, in some cases where the UE's wireless state is insufficient, the UE may not be able to perform subsequent RACH attempts. For example, when the reference signal received power (RSRP) of a non-HST cell serving an HST UE is below a configured RSRP threshold (e.g., -120 dBm by default or some other value), the UE may not perform more than N RACH attempts. Thus, in one example, the UE may perform the CFO compensation / offset, calculation, or determination described in any of the above examples in response to determining that the RSRP of the serving cell is greater than or equal to the RSRP threshold.

[0161]

[0140] Figure 8 shows an example 800 of a call flow between UE 802 and base station 804. UE 802 may correspond to HST UE 402 or UE 502, 602, 702 of FIGS. 4-7, and base station 804 may correspond to base stations 404, 504, 604 of FIGS. 4-6. First, the UE may receive a RACH configuration 806 from the base station. The RACH configuration may include the maximum number of preamble transmissions 807 (e.g., parameter maxPreambleTrans or another name). After receiving the RACH configuration, the UE may transmit one or more random access messages 808. The random access message 808 may correspond to the RACH messages 408, 508 of FIGS. 4 and 5 (e.g., in the 1st to Nth RACH attempts), and may each include a preamble 809 selected by the UE. In response to transmitting the random access message 808, the UE may receive one or more RARs 810 from the base station, where each RAR responds to the random access message. The RAR 810 may correspond to RARs 412, 510 (e.g., in the 1st to Nth RACH attempts), and may each include a RAPID 811 configured by the base station. The number of RARs (e.g., number N) may be a function of the maximum number of preamble transmissions 807.

[0162]

[0141] At 812, the UE 802 may determine whether the RAR 810 of the threshold number 813 contains an inconsistent RAPID. For example, the UE may determine whether K out of N RARs contain a RAPID different from the corresponding preamble. Further, the UE may determine whether each inconsistent RAPID among the K RARs is due to the uplink Doppler shift effect. For example, at 814, the UE may determine whether the frequency offset 816 (or Doppler shift) has affected each of the RARs, and at the same time determine the direction of the frequency offset. In one example, the UE may perform the determination at 814 based on the expected RAPID 818 as described above with respect to Equations 1-8. In another example, the UE may perform the determination at 814 based on the expected RAPID 818 and the timing advance 820 as described above with respect to Equations 9-17.

[0163]

[0142] If the UE 802 determines at 812 that the RAR 810 of the threshold number contains an inconsistent RAPID based on the frequency offset 816, at 822, the UE may offset the carrier frequency for subsequent random access messages 824 (e.g., in the N+1th and subsequent RACH attempts). The UE may offset the carrier frequency by transmitting the preamble 825 in each subsequent random access message 824 at a frequency offset from the carrier frequency for the random access message 808. The UE may apply the carrier frequency offset at 822 in response to determining at 826 that the RSRP of the serving cell of the base station 804 serving the UE is greater than or equal to the RSRP threshold.

[0164]

[0143] The carrier frequency offset applicable by the UE to subsequent random access messages can be within a configured range 828 of positive or negative offsets. For example, the UE 802 can offset the carrier frequency for each subsequent random access message by the positive value described above in Table 3 or by the negative value shown above in Table 2. In one example, the range 828 can be a function of the random access preamble subcarrier spacing 830. In another example, the range 828 can be a function of the frequency offset 816 determined at 814. In a further example, the range 828 can be a function of the maximum Doppler shift 832 in the HST.

[0165]

[0144] In response to identifying at 834 the sequence number of RAPID mismatches in a threshold number of RARs 810, the UE 802 can determine at 822 the direction (e.g., positive or negative) in which the frequency offset should be applied. For example, the UE can identify whether Y consecutive RARs contain a RAPID mismatch due to the CFO. If Y consecutive mismatches are identified, the UE can offset the carrier frequency of each subsequent random access message 824 based on the direction of the frequency offset associated with each consecutive mismatch. For example, if the mismatch is based on a positive CFO, the UE can apply a negative frequency offset at 822, and if the mismatch is based on a negative CFO, the UE can apply a positive frequency offset at 822.

[0166] Instead, if UE 802 receives an additional RAR 836 in response to a subsequent random access message 824 and each additional RAR includes a RAPID 837 that is inconsistent with a corresponding one of the subsequent preambles 825 (e.g., due to an incorrect frequency offset direction applied at 822), the UE may determine, at 838, whether Y consecutive inconsistencies are identified in the RAPIDs of these additional RARs 836. If the UE determines that Y consecutive inconsistencies are identified in these additional inconsistent RAPIDs, at 840, the UE may offset the carrier frequency for an additional random access message 842 that the UE transmits to the base station in a direction opposite to the direction applied at 822. For example, if the UE applied a positive frequency offset to a subsequent random access message 824 at 822 (e.g., according to Table 3), at 840, the UE may apply a negative frequency offset to the additional random access message 842 (e.g., according to Table 2). Similarly, if the UE applied a negative frequency offset to a subsequent random access message 824 at 822 (e.g., according to Table 2), at 840, the UE may apply a positive frequency offset to the additional random access message 842 (e.g., according to Table 3). In this way, the likelihood of success of the RACH attempt can be further increased.

[0167]

[0146] Figure 9 is a flowchart 900 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104, 350, 402, 502, 602, 702, 802, device 1002). Optional aspects are indicated by dashed lines. The method enables a UE to apply CFO compensation to improve the RACH success rate in response to determining an inconsistent RAPID in a previous RACH attempt caused by an uplink Doppler shift effect (e.g., in an HST).

[0168]

[0147] In 902, the UE acquires one or more RARs, where each of the one or more RARs includes a RAPID, and each of the one or more RARs responds to a random access message that includes a preamble. For example, referring to FIG. 8, the UE 802 may acquire RARs 810 each including a RAPID 811. The RARs may be acquired in response to a random access message 808 that includes a preamble 809 and is transmitted by the UE to the base station 804. The UE (or a component of the UE) may acquire the RARs by, for example, receiving the RARs from base stations 310, 404, 504, 604, 804 and demodulating the data of the received RARs. For example, the RX processor 356 of the UE 350 may receive the RARs from the base station through one or more antennas 352, and the controller / processor 359 of the UE 350 may demodulate the data of the received RARs and identify the RAPID.

[0169]

[0148] In one example, the number of one or more RARs may be based on the maximum number of preamble transmissions. For example, referring to FIG. 8, the UE 802 may acquire a number N of RARs 810, where the number N is a function of the maximum number of preamble transmissions 807 configured for the UE. For example, N may be the minimum value between the maximum number of preamble transmissions 807, represented by the formula N = minimum(preambleTransMax, 10), and a preconfigured or configured value (e.g., 10).

[0170]

[0149] In 904, the UE determines that in each of one or more RARs of a threshold number, the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message. For example, referring to FIG. 8, UE 802 may determine at 812 that each RAR 810 of the RARs 810 of the threshold number 813 includes a RAPID that is different from the preamble of the corresponding one of the random access messages 808. For example, referring to FIG. 5, UE 502 may determine that K RACH attempts within N consecutive RACH attempts each include a mismatched RAPID. The UE (or a component of the UE) may perform this determination, for example, by identifying the RAPID in one of N RARs (e.g., message 2 or msgB), comparing the RAPID with the corresponding preamble in one of N random access messages (e.g., message 1 or msgA), identifying a mismatch between the RAPID and the preamble, and repeating the identification and comparison for different RAPIDs until K mismatches are identified. For example, following the reception of RAR 510 of the first RACH attempt from RX processor 356, controller / processor 359 of UE 350 may identify the RAPID in that RAR, compare that RAPID with the preamble in the RACH message 508 previously transmitted during the first RACH attempt, and identify that the RAPID and the preamble are different (e.g., the selected preamble included in RACH message 508 was actually preamble 9 or some other different value, but the RAPID configured in RAR 510 may indicate preamble 21 or some other value). Controller / processor 359 may similarly repeat the above process of identifying RAPID mismatches in the second, third, etc. RACH attempts until K RAPID mismatches are identified.

[0171]

[0150] In one example, each of one or more RARs of the threshold number may include an inconsistent RAPID based on the frequency offset of the PRACH received at the base station. For example, referring to FIG. 8, at 814, UE 802 may determine that the frequency offset 816 (e.g., positive or negative Doppler shift) has affected each of the RARs 810, where the UE has determined an inconsistent RAPID at 812. For example, referring to FIG. 6, UE 602 may determine that the PRACH 606 carrying each RACH preamble (e.g., in the random access message 808 of FIG. 8) has been received by the base station 604 following an uplink Doppler shift in either the positive direction (at a frequency higher than the transmitted frequency, such as PRACH1 in FIG. 6) or the negative direction (at a frequency lower than the transmitted frequency, such as PRACH2 in FIG. 6). As a result of this frequency offset or uplink Doppler shift in PRACH 606, the UE may determine that the base station has mis-identified each PRACH as including a preamble different from what was actually transmitted by the UE.

[0172]

[0151] In one example, the frequency offset may be determined based on the expected RAPID received at the base station. For example, referring to FIG. 8, at 814, UE 802 may determine the presence of the frequency offset 816 that caused the inconsistent RAPID and the direction (positive or negative) of the frequency offset 816 based on the expected RAPID 818 that the UE expected the base station 804 to receive as a result of the uplink Doppler shift. For example, the UE may apply the above equations 1 to 7 to identify the expected RAPID (e.g., in one example RAPID pos or RAPID neg ) and may apply the above equation 8 to determine the presence and direction of the offset 816 in response to this expected RAPID.

[0173]

[0152] In one example, the frequency offset may be further determined based on the timing advance. For example, referring to FIG. 8, at 814, UE 802 may determine the presence of a frequency offset 816 that caused an inconsistent RAPID based on the timing advance 820 reported by the base station 804 and the predicted RAPID 818, and at the same time determine the direction of the frequency offset 816. For example, the UE may use the timing advance (e.g., T NW ), the predicted RAPID (e.g., in one example,

[0174]

number

[0175] or

[0176]

number

[0177] ), and the cyclic shift of the predicted RAPID (e.g., in one example, I D ) to identify, apply the above equations 9 to 16, and in response to these parameters, apply the above equation 17 to determine the presence and direction of the frequency offset 816.

[0178]

[0153] In 906, in response to the decision, the UE offsets the carrier frequency for each of one or more subsequent random access messages. For example, referring to FIG. 8, at 812, in response to determining the number of mismatch RAPID thresholds 813 by frequency offset 816, at 822, the UE may offset the carrier frequency for subsequent random access message 824 to compensate for frequency offset 816. For example, referring to FIG. 7, UE 702 may offset the carrier frequency for each RACH preamble by transmitting each preamble in PRACH 704 with a different (positive or negative) frequency offset, for example, to compensate for the Doppler shift effect. Referring to FIG. 5, UE 502 may apply offset 520 to carrier frequency 514 for each subsequent RACH message 518. As an example, if the UE transmits a random access message 808 at a carrier frequency of 3.8 GHz, the UE may apply an offset of 600 Hz or -600 Hz (or some other positive or negative value) to the 3.8 GHz frequency when transmitting subsequent random access messages 824 (for example, in one example, such that the messages are transmitted at offset carrier frequencies of 3.8000006 GHz or 3.7999994 GHz, respectively). The offset may be, for example, one of the CFO compensation values identified in Table 2 or Table 3 above. The UE (or a component of the UE) may perform the offsetting by, for example, identifying the offset to be applied to the carrier frequency for each subsequent random access message and transmitting each subsequent random access message at the offset carrier frequency.For example, in response to determining the number of mismatch RAPID thresholds due to a frequency offset, the controller / processor 359 of the UE 350 may identify an offset for each subsequent random access message from either Table 2 or Table 3 (e.g., depending on the direction of the frequency offset), and the TX processor 368 may transmit subsequent random access messages at the offset carrier frequency identified by the controller / processor 359 for each subsequent random access message to the base station 310 via one or more antennas 352.

[0179]

[0154] In one example, each of the carrier frequencies may be offset only by values within a range based on the random access preamble sub-carrier spacing. For example, referring to FIG. 8, the offset may be within a range 828 of configured positive or negative values. The range 828 may be a function of the random access preamble sub-carrier spacing 830. For example, referring to FIG. 5, each offset 520 (e.g., corresponding to one of the values in Table 2 or Table 3 above) may be limited to within a configured range based on the preamble sub-carrier spacing Δf RA . For example, the range may be one of the above ranges (18) or (19) that is a function of RA_SCS (Δf RA ).

[0180]

[0155] In one example, the range may be a function of the frequency offset of the PRACH received at the base station. For example, referring to FIGS. 6 and 8, the range 828 may be based on the frequency offset 816 that affected the PRACH 606 carrying the RACH preamble received by the base stations 604, 804, and which frequency offset the UE 802 determined at 814. For example, referring to FIG. 5, either of the above ranges (18) or (19) may be a function of L, the value of which may depend on whether the frequency offset 816 is as large as one PRACH sub-carrier (e.g., L = 0), or as large as two PRACH sub-carriers (e.g., L = 1).

[0181]

[0156] In one example, the range may be further based on the maximum Doppler shift in HST deployment. For example, referring to FIG. 8, range 828 may be based on the maximum Doppler shift 832 in HST (e.g., range 828 may be a function of the maximum value of the frequency offset 816 in FIG. 8). For example, referring to FIG. 5, either of the above ranges (18) or (19) may be a function of L or RA_SCS, and either value thereof may be further optimized to depend on the maximum uplink Doppler shift observed in HST. For example, the maximum uplink Doppler shift may be twice the maximum Doppler shift normally observed in HST (e.g., for an HST of 350 km / h, 2×1230 Hz = 2460 Hz, i.e., assuming Δf RA = 1.25 kHz, approximately two PRACH subcarriers). An example of HST deployment is shown in FIG. 4.

[0182]

[0157] In one example, each of the carrier frequencies may be offset in response to the RSRP associated with the serving cell exceeding a threshold. For example, referring to FIG. 8, UE 802 may offset the carrier frequency at 822 in response to determining at 826 that the RSRP of the serving cell of base station 804 serving the UE is greater than or equal to the RSRP threshold. For example, referring to FIGS. 4 and 5, UEs 402, 502 may apply an offset 520 to the carrier frequency 514 for each subsequent RACH message 518 if the RSRP of a non-HST cell serving the HST UE (e.g., the cell in which base station 404 serves HST UE 402) is greater than or equal to a configured RSRP threshold (e.g., -120 dbM or some other value).

[0183]

[0158] In one example, each of the carrier frequencies can be offset by a different value. For example, referring to FIGS. 5, 7, and 8, UEs 502, 702, 802 can apply an offset 520 to a carrier frequency 514 for a subsequent RACH message 518 (e.g., at 822) according to either (or both) of the configurations of Table 2 or Table 3 described above, where each offset is different for each subsequent RACH message as shown in FIG. 7. For example, a subsequent RACH message at the N+1-th RACH attempt can be offset by one value -O*M (or its positive version in other tables), and the next subsequent RACH message at the N+2-th RACH attempt can be offset by a different value -(O+1)*M (or its positive version), and so on, where M represents a configurable offset per RACH attempt, such as M = 200 Hz or some other value, and O represents

[0184]

Number

[0185] or some other function, etc., representing a configurable starting frequency for the offset. Further, at least one of the different values can be a function of the maximum number (X) of one or more subsequent random access messages. For example, a subsequent RACH message at the N+X-2-th RACH attempt can be offset by another different value -(O+X-3)*M (or its positive version), and the next subsequent RACH message at the N+X-1-th RACH attempt can be offset by an even different value -(O+X-2)*M (or its positive version), and so on, where X represents the maximum number of RACH attempts to which CFO compensation can be applied. The value of X can depend on the values of O and M. For example, X is

[0186]

Number

[0187] Or it may be equal to some other value.

[0188]

[0159] In one example, one or more of the carrier frequencies can be offset by the same value. For example, referring to FIGS. 5 and 8, UEs 502, 802 can apply an offset 520 to a carrier frequency 514 for a subsequent RACH message 518 (e.g., at 822) according to either (or both) of the configurations of Table 2 or Table 3 above, where one or more of the offsets are the same for subsequent RACH messages. For example, both the N+1th and N+2th RACH attempts can be associated with the same offset O*M (or its negative version in other tables) instead of different offsets O*M and (O+1)*M (or their negative versions in other tables). The UE can apply the same offset to multiple RACH attempts, for example, when M is a large value (e.g., M = 600 Hz). Similarly, the same value can be a function of the maximum number (X) of one or more subsequent random access messages. For example, both the N+X-2th and N+X-1th RACH attempts can be associated with the same offset -(O+X-3)*M instead of different offsets -(O+X-3)*M and -(O+X-2)*M.

[0189]

[0160] In 908, the UE may identify a threshold amount of consecutive mismatches between the RAPID and the preamble, where the carrier frequency is offset by only one of a positive value or a negative value in response to the identification. For example, referring to FIG. 8, at 834, the UE may identify a threshold amount Y of consecutive RAPID mismatches between the RAPID 811 and the preamble 809. If Y consecutive mismatches are identified at 834, at 822, the UE may offset the carrier frequency of each subsequent random access message 824 by a positive or negative value according to the frequency offset 816 determined at 814. For example, referring to FIG. 5, if the UE 502 determines that all Y consecutive RAPID mismatches within the RACH attempts 1 to K are due to a positive frequency offset (for example, for PRACH1 in FIG. 6, the frequency offset 816 in FIG. 8 is positive), the UE may apply the negative frequency offset in Table 2 to each subsequent RACH attempt 516. Alternatively, if the UE determines that all Y consecutive RAPID mismatches within the RACH attempts 1 to K are due to a negative frequency offset (for example, the frequency offset 816 in FIG. 8 is negative for PRACH2 in FIG. 6, etc.), the UE may apply the positive frequency offset in Table 3 to each subsequent RACH attempt 516. The value of Y may be configurable by the base station or preconfigured for the UE (for example, Y = 3 or some other value). The UE (or a component of the UE) may, for example, count each instance where the RAPID 811 is different from the preamble 809 within the RACH attempts 1 to K, determine to sum at least the threshold amount (Y) in consecutive RACH attempts when counting, and determine that all the counted instances receive the same direction frequency offset, thereby performing the identification of the threshold amount of consecutive mismatches between the RAPID and the preamble. For example, the controller / processor 359 of the UE 350 may identify (assuming K = 5 and Y = 3) that the 3rd, 4th, and 5th consecutive RACH attempts include a mismatched RAPID due to a positive frequency offset.

[0190]

[0161] At 910, the UE may obtain an additional RAR, where each of the additional RARs includes an additional RAPID and responds to one of the subsequent random access messages including a subsequent preamble. For example, referring to FIG. 8, the UE 802 may obtain an additional RAR 836 from the base station 804 in response to a subsequent random access message 824 transmitted by the UE together with a subsequent preamble 825. Each of the additional RARs may include an additional RAPID 837 configured by the base station. The UE (or a component of the UE) may obtain the additional RAR, for example, by receiving the additional RAR and demodulating the data in the additional RAR. For example, the RX processor 356 may receive the additional RAR via one or more antennas 352, and the controller / processor 359 may demodulate the data received from the RX processor 356.

[0191]

[0162] In 912, the UE may further determine a threshold amount of consecutive mismatches between an additional RAPID and a subsequent preamble. For example, referring to FIG. 8, in 838, the UE may determine a threshold amount Y of consecutive RAPID mismatches between an additional RAPID 837 and a subsequent preamble 825. The threshold amount Y may be the same as or different from the threshold amount Y referred to above in 908 (and 834 in FIG. 8). The UE (or a component of the UE) may perform the further determination, for example, according to the following process. First, if the controller / processor 359 of the UE 350 cannot determine at 834 that all Y consecutive RAPID mismatches are due to frequency offsets in the same direction, the controller / processor 359 may determine a majority direction of frequency offsets and a minority direction of frequency offsets. Next, the controller / processor 359 may receive an additional RAR 836 including the additional RAPID 837, and the controller / processor 359 may compare Y consecutive additional RAPIDs with a subsequent preamble 825 of a corresponding subsequent random access message 824. The controller / processor 359 may then determine whether these additional RAPID mismatches are due to frequency offsets in the minority direction.

[0192]

[0163] Finally, at 914, in response to a further determination, the UE may offset the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value, where the carrier frequency for one or more subsequent random access messages is offset by only the other of a positive value or a negative value. For example, referring to FIG. 8, if the UE determines at 838 that Y consecutive mismatches are identified in the additional RAPID 837 of the additional RAR 836, at 840, the UE may offset the carrier frequency for an additional random access message 842 that the UE may transmit to the base station 804. The UE may offset these carrier frequencies in a direction opposite to the direction applied at 822. For example, if the UE applied a positive frequency offset to the subsequent random access message 824 at 822 (e.g., according to Table 3), at 840, the UE may apply a negative frequency offset to the additional random access message 842 (e.g., according to Table 2). Similarly, if the UE applied a negative frequency offset to the subsequent random access message 824 at 822 (e.g., according to Table 2), at 840, the UE may apply a positive frequency offset to the additional random access message 842 (e.g., according to Table 3). The UE (or a component of the UE) may perform the offset of the carrier frequency for each additional random access message, for example, by identifying the offset to be applied to the carrier frequency for each additional random access message and transmitting each additional random access message at the offset carrier frequency.For example, in response to further determining the additional RAPID threshold number of mismatches due to the minority direction frequency offset, the controller / processor 359 of the UE 350 may identify an offset for each additional random access message from either Table 2 or Table 3 (e.g., in the opposite direction applied to subsequent random access messages), and the TX processor 368 may transmit the additional random access messages at the offset carrier frequencies identified by the controller / processor 359 for each additional random access message to the base station 310 via one or more antennas 352.

[0193]

[0164] FIG. 10 is a diagram 1000 showing an example of a hardware implementation form for apparatus 1002. Apparatus 1002 is a UE and includes a cellular baseband processor 1004 (also called a modem) coupled to cellular RF transceivers 1022 and one or more subscriber identity module (SIM) cards 1020, an application processor 1006 coupled to a secure digital (SD) card 1008 and a screen 1010, a Bluetooth module 1012, a wireless local area network (WLAN) module 1014, a global positioning system (GPS) module 1016, and a power supply 1018. The cellular baseband processor 1004 communicates with the UE 104 and / or the BS 102 / 180 through the cellular RF transceiver 1022. The cellular baseband processor 1004 may include a computer-readable medium / memory. The computer-readable medium / memory may be non-transitory. The cellular baseband processor 1004 is responsible for general processing including the execution of software stored in the computer-readable medium / memory. The software, when executed by the cellular baseband processor 1004, causes the cellular baseband processor 1004 to perform the various functions described above. The computer-readable medium / memory may also be used to store data that is manipulated by the cellular baseband processor 1004 when executing the software. The cellular baseband processor 1004 further includes a receiving component 1030, a communication manager 1032, and a transmitting component 1034. The communication manager 1032 includes one or more of the illustrated components. The components within the communication manager 1032 may be stored in the computer-readable medium / memory and / or configured as hardware within the cellular baseband processor 1004. The cellular baseband processor 1004 may be a component of the UE 350 and may include at least one of the memory 360, and / or the TX processor 368, the RX processor 356, and the controller / processor 359.In one configuration, apparatus 1002 is a modem chip and may include only baseband processor 1004. In another configuration, apparatus 1002 is the entire UE (see, e.g., 350 of FIG. 3) and may include the additional modules described previously for apparatus 1002.

[0194]

[0165] Communication manager 1032 includes, for example, RAR component 1040 configured to obtain one or more RARs as described with respect to 902. Each of the one or more RARs includes a RAPID and each of the one or more RARs responds to a random access message including a preamble. Communication manager 1032 further includes, for example, decision component 1042 configured to receive an input in the form of one or more RARs from RAR component 1040 and to determine that, for each of a threshold number of the one or more RARs, the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message. Communication manager 1032 further includes, for example, offset component 1044 configured to receive an input in the form of a decision from decision component 1042 and to offset the carrier frequency for each of one or more subsequent random access messages in response to the decision.

[0195]

[0166] Communication manager 1032 may further include, for example, identification component 1046 configured to receive an input in the form of a RAPID and a preamble from RAR component 1040 and to identify a threshold amount of consecutive mismatches between the RAPID and the preamble. Each carrier frequency may be offset (by offset component 1044) by only one of a positive value or a negative value in response to the identification by identification component 1046.

[0196]

[0167] The RAR component 1040 may be further configured to obtain additional RARs, for example, as described with respect to 910, where each of the additional RARs includes an additional RAPID and responds to one of the subsequent random access messages including a subsequent preamble. The determination component 1042 may receive an input in the form of an additional RAR from the RAR component 1040, for example, as described with respect to 912, and may be further configured to further determine a threshold amount of consecutive mismatches between the additional RAPID and the subsequent preamble. The offset component 1044 may receive an input in the form of a further determination from the determination component 1042 and may be further configured to offset the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value in response to the further determination, where, for example, as described with respect to 914, the carrier frequency for one or more subsequent random access messages is offset by only the other of a positive value or a negative value.

[0197]

[0168] The apparatus may include additional components that implement each of the blocks of the algorithms in the above-described flowcharts of FIGS. 8 and 9. Accordingly, each block in the above-described flowcharts of FIGS. 8 and 9 may be implemented by one component, and the apparatus may include one or more of those components. The components may be one or more hardware components specifically configured to perform the described process / algorithm, implemented by a processor configured to perform the described process / algorithm, stored in a computer-readable medium for implementation by the processor, or some combination thereof.

[0198]

[0169] In one configuration, the apparatus 1002, particularly the cellular baseband processor 1004, includes means for obtaining one or more RARs, where each of the one or more RARs includes a RAPID and each of the one or more RARs responds to a random access message that includes a preamble. The apparatus 1002, particularly the cellular baseband processor 1004, also includes means for determining, at each of a threshold number of the one or more RARs, that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message. The apparatus 1002, particularly the cellular baseband processor 1004, further includes means for offsetting the carrier frequency for each of one or more subsequent random access messages in response to the determination.

[0199]

[0170] In one configuration, the apparatus 1002, particularly the cellular baseband processor 1004, may include means for identifying a threshold amount of consecutive mismatches between the RAPID and the preamble, where the carrier frequency is offset by only one of a positive value or a negative value in response to the identification.

[0200]

[0171] In one configuration, the means for obtaining may be further configured to obtain additional RARs, where each of the additional RARs includes an additional RAPID and responds to one of subsequent random access messages that include a subsequent preamble. The means for determining may be further configured to further determine a threshold amount of consecutive mismatches between the additional RAPID and the subsequent preamble. The means for offsetting may be further configured to offset the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value in response to the further determination, where the carrier frequency for one or more subsequent random access messages is offset by only the other of a positive value or a negative value.

[0201]

[0172] The above means can be one or more of the above components of the apparatus 1002 configured to implement the functions implemented by the above means. As described above, the apparatus 1002 can include a TX processor 368, an RX processor 356, and a controller / processor 359. Thus, in one configuration, the above means can be the TX processor 368, the RX processor 356, and the controller / processor 359 configured to implement the functions implemented by the above means.

[0202]

[0173] Accordingly, aspects of the present disclosure enable a UE to apply CFO compensation to improve the RACH success rate in response to determining a RAPID of an inconsistency in a RACH attempt prior to that typically caused by the uplink Doppler shift effect in HST. When attempting to perform a RACH with a base station, the UE may obtain one or more RARs each including a RAPID in response to each transmitting a random access message including a preamble. If the UE determines a RAPID inconsistency at each of a threshold number of these RARs, such an inconsistency is caused by the frequency offset (uplink Doppler shift) of the PRACH received at the base station, and the UE may offset the carrier frequency for each subsequent random access message it transmits. When the inconsistent RAPID is caused by such an uplink Doppler shift, offsetting the carrier frequency may be able to resolve the RAPID inconsistency, thereby enabling an improvement in the RACH success rate. Further, to determine the frequency direction to be applied at the offset to resolve the RAPID inconsistency, the UE may identify whether there is a threshold amount of consecutive inconsistencies between the RAPID and the preamble, and the UE may offset the carrier frequency for a subsequent random access message by only one of a positive value or a negative value in response to the identification. If there is no consecutive RAPID inconsistency of this threshold amount, and if a subsequent random access message includes a consecutive additional RAPID inconsistency of a threshold amount caused by a frequency offset in the opposite direction, the UE may determine to change the direction of the offset in the additional random access message (e.g., from positive to negative, or vice versa). As a result, the RACH success rate may be further improved.

[0203] It should be understood that the particular order or hierarchy of blocks within the disclosed process / flowchart is illustrative of exemplary approaches. Based on design preferences, it should be understood that the particular order or hierarchy of blocks within the process / flowchart may be rearranged. Additionally, some blocks may be combined or omitted. The appended method claims present the elements of the various blocks in an illustrative order and are not limited to the particular order or hierarchy presented.

[0204]

[0175] The foregoing description is provided to enable a person of ordinary skill 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 general principles defined herein may be applied to other aspects. Accordingly, the claims are not to be limited to the aspects shown herein but are to be accorded the widest scope consistent with the language of the claims and not inconsistent therewith, and references to singular elements are not to be construed as meaning “sole and exclusive” unless so stated, but rather “one or more.” Terms such as “if,” “when,” and “while” are not to be construed as implying an immediate temporal relationship or reaction, but rather are to be interpreted to mean “under the condition that.” That is, these phrases, for example, “when,” do not imply an immediate action in response to or during the occurrence of an action, but rather simply imply that an action occurs if the condition is met, without the need for a specific or immediate time constraint as to when the action should occur. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” should not necessarily be construed as preferred or advantageous over other aspects. Unless otherwise specified, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” include any combination of A, B, and / or C and may include multiple As, multiple Bs, or multiple Cs.Specifically, combinations such as "at least one of A, B, or C", "one or more of A, B, or C", "at least one of A, B, and C", "one or more of A, B, and C", and "A, B, C, or any combination thereof" can be only A, only B, only C, A and B, A and C, B and C, or A and B and C, where any such combination can include one or more members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure are known or will become known to those of ordinary skill in the art and are hereby expressly incorporated by reference into this specification and are intended to be covered by the claims. Further, what is disclosed herein is not intended to be dedicated to the public whether or not such disclosure is expressly recited in the claims. The words "module", "mechanism", "element", "device", etc. may not be used as a substitute for the word "means". Accordingly, no claim element should be construed as a means-plus-function unless the element is expressly recited using the phrase "means for".

[0205]

[0176] The following examples are illustrative only and not limiting, but may be combined with other embodiments or aspects of the teachings described herein.

[0206]

[0177] Example 1 is a method of wireless communication in a user equipment (UE), the method comprising: obtaining one or more random access responses (RARs), wherein each of the one or more RARs includes a random access preamble identifier (RAPID), and each of the one or more RARs responds to a random access message including a preamble; for each of the one or more RARs of a threshold, determining that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message; and in response to the determination, offsetting the carrier frequency for each of the one or more subsequent random access messages.

[0207]

[0178] Example 2 is the method according to Example 1, wherein the number of one or more RARs is based on the maximum number of preamble transmissions.

[0208]

[0179] Example 3 is the method according to Example 1 or 2, wherein each of the one or more RARs of a threshold includes a mismatched RAPID based on a frequency offset of a physical random access channel (PRACH) received at a base station.

[0209]

[0180] Example 4 is the method according to Example 3, wherein the frequency offset is determined based on an expected RAPID received at a base station.

[0210]

[0181] Example 5 is the method according to Example 4, wherein the frequency offset is further determined based on a timing advance.

[0211]

[0182] Example 6 is the method according to any one of Examples 1 to 5, wherein each of the carrier frequencies is offset by a value within a range based on a random access preamble subcarrier spacing.

[0212]

[0183] Example 7 is the method according to Example 6, wherein the range is a function of a frequency offset of a physical random access channel (PRACH) received at a base station.

[0213]

[0184] Example 8 is the method according to Example 6 or 7, wherein the range is further based on the maximum Doppler shift in high-speed train (HST) deployment.

[0214]

[0185] Example 9 is the method according to any one of Examples 1 to 8, wherein each of the carrier frequencies is offset in response to the reference signal received power (RSRP) associated with the serving cell exceeding a threshold.

[0215]

[0186] Example 10 is the method according to any one of Examples 1 to 9, wherein each of the carrier frequencies is offset by a different value.

[0216]

[0187] Example 11 is the method according to Example 10, wherein at least one of the different values is a function of the maximum number of subsequent random access messages.

[0217]

[0188] Example 12 is the method according to any one of Examples 1 to 9, wherein one or more of the carrier frequencies are offset by the same value.

[0218]

[0189] Example 13 further includes identifying a threshold amount of continuous mismatches between the RAPID and the preamble, wherein each of the carrier frequencies is offset by only one of a positive value or a negative value in response to the identification, and is the method according to any one of Examples 1 to 12.

[0219]

[0190] Example 14 further comprises obtaining additional RARs, where each of the additional RARs includes an additional RAPID and responds to one of the subsequent random access messages including a subsequent preamble, further determining a threshold amount of consecutive mismatches between the additional RAPID and the subsequent preamble, and in response to the further determination, offsetting the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value, where the carrier frequency for one or more subsequent random access messages is offset by only the other of the positive value or the negative value, and is the method according to any one of Examples 1 to 12.

[0220]

[0191] Example 15 is a device for wireless communication, the device comprising a processor, a memory coupled to the processor, and instructions stored in the memory, which when executed by the processor cause the device to obtain one or more random access responses (RARs), where each of the one or more RARs includes a random access preamble identifier (RAPID), and where each of the one or more RARs responds to a random access message including a preamble, determining in each of one or more RARs of a threshold number that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message, and in response to the determination, offsetting the carrier frequency for each of one or more subsequent random access messages.

[0221]

[0192] Example 16 is the device according to Example 15, where each of one or more RARs of a threshold number includes a mismatched RAPID based on a frequency offset of a physical random access channel (PRACH) received at a base station.

[0222]

[0193] Example 17 is the device according to Example 16, where the frequency offset is determined based on an expected RAPID received at a base station.

[0223]

[0194] Example 18 is the apparatus according to Example 17, wherein the frequency offset is further determined based on the timing advance.

[0224]

[0195] Example 19 is the apparatus according to any one of Examples 15 to 18, wherein each of the carrier frequencies is offset by a value within a range based on the random access preamble subcarrier spacing.

[0225]

[0196] Example 20 is the apparatus according to Example 19, wherein the range is a function of the frequency offset of the physical random access channel (PRACH) received at the base station.

[0226]

[0197] Example 21 is the apparatus according to Example 19 or 20, wherein the range is further based on the maximum Doppler shift in a high-speed train (HST) deployment.

[0227]

[0198] Example 22 is the apparatus according to any one of Examples 15 to 21, wherein each of the carrier frequencies is offset in response to the reference signal received power (RSRP) associated with the serving cell exceeding a threshold.

[0228]

[0199] Example 23 is the apparatus according to any one of Examples 15 to 22, wherein each of the carrier frequencies is offset by a different value, wherein at least one of the different values is a function of the maximum number of subsequent random access messages.

[0229]

[0200] Example 24 is the apparatus according to any one of Examples 15 to 22, wherein one or more of the carrier frequencies are offset by the same value.

[0230]

[0201] Example 25 causes the apparatus, when the instruction is executed by the processor, to further identify a threshold amount of continuous mismatches between the RAPID and the preamble, where the carrier frequency is offset by only one of a positive value or a negative value in response to the identification, and is an apparatus according to any one of Examples 15 to 24.

[0231]

[0202] Example 26 causes the apparatus, when the instruction is executed by the processor, to obtain additional RARs, where each of the additional RARs includes an additional RAPID and responds to one of subsequent random access messages including the additional RAPID and a subsequent preamble, to further determine a threshold amount of continuous mismatches between the additional RAPID and the subsequent preamble, and in response to the further determination, to offset the carrier frequency of each of one or more subsequent random access messages by only one of a positive value or a negative value, where the carrier frequency of one or more subsequent random access messages is offset by only the other of a positive value or a negative value, and is an apparatus according to any one of Examples 15 to 24.

[0232]

[0203] Example 27 is an apparatus for wireless communication, comprising means for obtaining one or more random access responses (RARs), where each of the one or more RARs includes a random access preamble identifier (RAPID) and each of the one or more RARs responds to a random access message including a preamble, means for determining, in each of one or more RARs of a threshold number, that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message, and means for offsetting the carrier frequency of each of one or more subsequent random access messages in response to the determination.

[0233]

[0204] Example 28 further comprises means for identifying a threshold amount of successive mismatches between a RAPID and a preamble, wherein the carrier frequency is offset by only one of a positive value or a negative value in response to the identification, and is the apparatus according to Example 27.

[0234]

[0205] Example 29 is such that the means for obtaining is further configured to obtain additional RARs, wherein each of the additional RARs includes an additional RAPID and responds to one of subsequent random access messages including a subsequent preamble, the means for determining is further configured to determine a threshold amount of successive mismatches between the additional RAPID and the subsequent preamble, and the means for offsetting is further configured to offset the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value in response to the further determination, and the carrier frequency for one or more subsequent random access messages is offset by only the other of a positive value or a negative value, and is the apparatus according to Example 27.

[0235]

[0206] Example 30 is a computer-readable medium storing computer-executable code, which, when executed by a processor, causes the processor to obtain one or more random access responses (RARs), wherein each of the one or more RARs includes a random access preamble identifier (RAPID) and each of the one or more RARs responds to a random access message including a preamble, determine, in each of one or more of the RARs of a threshold number, that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message, and offset the carrier frequency for each of one or more subsequent random access messages in response to the determination. The invention described in the claims of the present application at the time of filing is appended below. [C1] A method for wireless communication in a user equipment (UE), comprising: acquiring one or more random access responses (RARs), wherein each of the one or more RARs includes a random access preamble identifier (RAPID), and each of the one or more RARs responds to a random access message including a preamble; determining, for each of the threshold number of the one or more RARs, that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message; offsetting the carrier frequency for each of one or more subsequent random access messages in response to the determination. A method comprising the above steps. [C2] The method according to [C1], wherein the number of the one or more RARs is based on the maximum number of preamble transmissions. [C3] The method according to [C1], wherein each of the threshold number of the one or more RARs includes a mismatched RAPID based on a frequency offset of a physical random access channel (PRACH) received at a base station. [C4] The method according to [C3], wherein the frequency offset is determined based on an expected RAPID received at the base station. [C5] The method according to [C4], wherein the frequency offset is further determined based on a timing advance. [C6] The method according to [C1], wherein each of the carrier frequencies is offset by a value within a range based on a random access preamble subcarrier spacing. [C7] The method according to [C6], wherein the range is a function of a frequency offset of a physical random access channel (PRACH) received at a base station. [C8] The method according to [C6], wherein the range is further based on a maximum Doppler shift in a high-speed train (HST) deployment. [C9] The method according to [C1], wherein each of the carrier frequencies is offset in response to a serving cell-related reference signal received power (RSRP) exceeding a threshold. [C10] The method according to [C1], wherein each of the carrier frequencies is offset by a different value. [C11] The method according to [C10], wherein at least one of the different values is a function of the maximum number of the one or more subsequent random access messages. [C12] The method according to [C1], wherein one or more of the carrier frequencies are offset by the same value. [C13] The method further comprises identifying a threshold amount of consecutive mismatches between the RAPID and the preamble, wherein the carrier frequency is offset by only one of a positive value or a negative value in response to the identification, according to the method of [C1]. [C14] The method obtaining additional RARs, wherein each of the additional RARs includes an additional RAPID and responds to one of the subsequent random access messages including a subsequent preamble, further determining a threshold amount of consecutive mismatches between the additional RAPID and the subsequent preamble, offsetting the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value in response to the further determination, further comprising wherein the carrier frequency for the one or more subsequent random access messages is offset by only the other of the positive value or the negative value, according to the method of claim 1 of [C1]. [C15] An apparatus for wireless communication, comprising a processor, a memory coupled to the processor, instructions stored in the memory, wherein the instructions, when executed by the processor, cause the apparatus to obtain one or more random access responses (RARs), wherein each of the one or more RARs includes a random access preamble identifier (RAPID) and each of the one or more RARs responds to a random access message including a preamble, determine, in each of the one or more RARs of a threshold number, that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message, offset the carrier frequency for each of one or more subsequent random access messages in response to the determination, an apparatus operable to perform. [C16] The apparatus according to [C15], wherein each of the one or more RARs of the threshold number includes a mismatched RAPID based on a frequency offset of a physical random access channel (PRACH) received at a base station. [C17] The apparatus according to [C16], wherein the frequency offset is determined based on an expected RAPID received at the base station. [C18] The apparatus according to [C17], wherein the frequency offset is further determined based on a timing advance. [C19] The apparatus according to [C15], wherein each of the carrier frequencies is offset by a value within a range based on a random access preamble sub-carrier spacing. [C20] The apparatus according to [C19], wherein the range is a function of a frequency offset of a physical random access channel (PRACH) received at a base station. [C21] The apparatus according to [C19], wherein the range is further based on a maximum Doppler shift in a high-speed train (HST) deployment. [C22] The apparatus according to [C15], wherein each of the carrier frequencies is offset in response to a reference signal received power (RSRP) associated with a serving cell exceeding a threshold. [C23] The apparatus according to [C15], wherein each of the carrier frequencies is offset by a different value, and at least one of the different values is a function of a maximum number of subsequent random access messages. [C24] The apparatus according to [C15], wherein one or more of the carrier frequencies are offset by the same value. [C25] When executed by the processor, the instruction causes the apparatus to further identify a threshold amount of consecutive mismatches between the RAPID and the preamble, wherein each of the carrier frequencies is offset by only one of a positive value or a negative value in response to the identification. The apparatus according to [C25]. [C26] When executed by the processor, the instruction causes the apparatus to acquire additional RARs, wherein each of the additional RARs includes an additional RAPID and responds to one of the subsequent random access messages including a subsequent preamble, further determine a threshold amount of consecutive mismatches between the additional RAPID and the subsequent preamble, In response to said further determination, offset the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value, and further cause, the carrier frequency for said one or more subsequent random access messages to be offset by only the other of said positive value or said negative value, the apparatus according to [C15]. [C27] An apparatus for wireless communication, means for obtaining one or more random access responses (RARs), wherein each of said one or more RARs includes a random access preamble identifier (RAPID), and each of said one or more RARs responds to a random access message including a preamble, means for determining, in each of a threshold number of said one or more RARs, that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message, means for offsetting the carrier frequency for each of one or more subsequent random access messages in response to said determination, comprising an apparatus. [C28] The apparatus, further comprises means for identifying a threshold amount of consecutive mismatches between said RAPID and said preamble, the carrier frequency is offset by only one of a positive value or a negative value respectively in response to said identification, the apparatus according to [C27]. [C29] The means for obtaining is further configured to obtain additional RARs, wherein each of said additional RARs includes an additional RAPID and responds to one of said subsequent random access messages including a subsequent preamble, the means for determining is further configured to determine a threshold amount of consecutive mismatches between said additional RAPID and said subsequent preamble, the means for offsetting is further configured to offset the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value in response to said further determination, the carrier frequency for said one or more subsequent random access messages is offset by only the other of said positive value or said negative value, the apparatus according to [C27]. A computer-readable medium storing computer-executable code, which, when executed by a processor, causes the processor to obtain one or more random access responses (RARs), where each of the one or more RARs includes a random access preamble identifier (RAPID), and each of the one or more RARs responds to a random access message including a preamble, at each of a threshold number of the one or more RARs, determine that the RAPID of the corresponding RAR is different from the preamble of the corresponding random access message, in response to the determination, offset a carrier frequency for each of one or more subsequent random access messages, A computer-readable medium that causes the above to be performed.

Claims

1. A method for wireless communication in a user equipment (UE), comprising: obtaining, by the UE, one or more random access responses (RARs), wherein each of the one or more RARs includes a random access preamble identifier (RAPID), and each of the one or more RARs responds to a random access message including a preamble; determining, by the UE, for each of a threshold number of the one or more RARs, that the RAPID of the corresponding RAR is different from an identifier associated with a preamble sequence transmitted by the UE; offsetting, by the UE, a carrier frequency for each of one or more subsequent random access messages in response to the determination; A method comprising the above.

2. The method according to claim 1, wherein the number of the one or more RARs is based on a maximum number of preamble transmissions.

3. The method according to claim 1, wherein each of the threshold number of the one or more RARs includes a mismatched RAPID based on a frequency offset of a physical random access channel (PRACH) received at a base station.

4. The method according to claim 3, wherein the frequency offset is determined based on an expected RAPID received at the base station.

5. The method according to claim 4, wherein the frequency offset is further determined based on a timing advance.

6. The method according to claim 1, wherein each of the carrier frequencies is offset by a value within a range based on a random access preamble sub-carrier spacing.

7. The method according to claim 6, wherein the range is a function of a frequency offset of a physical random access channel (PRACH) received at a base station.

8. The method according to claim 6, wherein the range is further based on a maximum Doppler shift in a high-speed train (HST) deployment.

9. The method according to claim 1, wherein each of the carrier frequencies is offset in response to a serving cell associated reference signal received power (RSRP) exceeding a threshold.

10. The method according to claim 1, wherein each of the carrier frequencies is offset by a different value.

11. The method according to claim 10, wherein at least one of said different values is a function of a maximum number of said one or more subsequent random access messages.

12. The method according to claim 1, wherein one or more of said carrier frequencies are each offset by the same value.

13. The method further comprises identifying a threshold amount of consecutive mismatches between said RAPID and said preamble, wherein said carrier frequency is each offset by only one of a positive value or a negative value in response to said identification, the method according to claim 1.

14. The method obtaining additional RARs, wherein each of said additional RARs includes an additional RAPID and responds to one of said subsequent random access messages including a subsequent preamble, further determining a threshold amount of consecutive mismatches between said additional RAPID and said subsequent preamble, offsetting a carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value in response to said further determination, further comprising wherein said carrier frequency for said one or more subsequent random access messages is offset by only the other of said positive value or said negative value, the method according to claim 1.

15. An apparatus for wireless communication, comprising a processor, a memory coupled to the processor, instructions stored in the memory, wherein the instructions, when executed by the processor, cause the apparatus to obtain one or more random access responses (RARs), wherein each of said one or more RARs includes a random access preamble identifier (RAPID) and each of said one or more RARs responds to a random access message including a preamble, determine that in each of said threshold number of said one or more RARs, the RAPID of the corresponding RAR is different from an identifier associated with a preamble sequence transmitted by the apparatus, offset a carrier frequency for each of one or more subsequent random access messages in response to said determination, an apparatus operable to perform.

16. The apparatus according to claim 15, wherein each of the one or more RARs of the threshold number includes a mismatched RAPID based on a frequency offset of a Physical Random Access Channel (PRACH) received at a base station.

17. The apparatus according to claim 16, wherein the frequency offset is determined based on an expected RAPID received at the base station.

18. The apparatus according to claim 17, wherein the frequency offset is further determined based on a timing advance.

19. The apparatus according to claim 15, wherein each of the carrier frequencies is offset by a value within a range based on a random access preamble sub-carrier spacing.

20. The apparatus according to claim 19, wherein the range is a function of a frequency offset of a Physical Random Access Channel (PRACH) received at a base station.

21. The apparatus according to claim 19, wherein the range is further based on a maximum Doppler shift in a High-Speed Train (HST) deployment.

22. The apparatus according to claim 15, wherein each of the carrier frequencies is offset in response to a serving cell associated Reference Signal Received Power (RSRP) exceeding a threshold.

23. The apparatus according to claim 15, wherein each of the carrier frequencies is offset by a different value, and at least one of the different values is a function of a maximum number of subsequent random access messages.

24. The apparatus according to claim 15, wherein one or more of the carrier frequencies are offset by the same value.

25. When executed by the processor, the instruction causes the apparatus to further identify a threshold amount of consecutive mismatches between the RAPID and the preamble, The apparatus according to claim 15, wherein each of the carrier frequencies is offset by only one of a positive value or a negative value in response to the identification.

26. When executed by the processor, the instruction causes the apparatus to acquire additional RARs, where each of the additional RARs includes an additional RAPID and responds to one of the subsequent random access messages including a subsequent preamble, further determine a threshold amount of consecutive mismatches between the additional RAPID and the subsequent preamble, In response to said further determination, offset the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value, and further cause, for said one or more subsequent random access messages, the carrier frequency to be offset by only the other of said positive value or said negative value, the apparatus according to claim 15. **Claim 27** An apparatus for wireless communication, means for obtaining one or more random access responses (RARs), wherein each of said one or more RARs includes a random access preamble identifier (RAPID), and each of said one or more RARs responds to a random access message including a preamble, means for determining, in each of a threshold number of said one or more RARs, that the RAPID of the corresponding RAR is different from an identifier associated with a preamble sequence transmitted by the apparatus, means for offsetting the carrier frequency for each of one or more subsequent random access messages in response to said determination, comprising an apparatus. **Claim 28** The apparatus further comprises means for identifying a threshold amount of consecutive mismatches between said RAPID and said preamble, wherein the carrier frequency is offset by only one of a positive value or a negative value in response to said identification, the apparatus according to claim 27. **Claim 29** The means for obtaining is further configured to obtain additional RARs, wherein each of said additional RARs includes an additional RAPID and responds to one of said subsequent random access messages including a subsequent preamble, the means for determining is further configured to determine a threshold amount of consecutive mismatches between said additional RAPID and said subsequent preamble, the means for offsetting is further configured to offset the carrier frequency for each of one or more additional random access messages by only one of a positive value or a negative value in response to said further determination, for said one or more subsequent random access messages, the carrier frequency to be offset by only the other of said positive value or said negative value, the apparatus according to claim 27. **Claim 30** A computer-readable medium storing computer-executable code, which, when executed by a processor of a user equipment (UE), causes the processor to obtain, by the UE, one or more random access responses (RARs), wherein each of the one or more RARs includes a random access preamble identifier (RAPID), and each of the one or more RARs responds to a random access message including a preamble, determine, by the UE, at each of the threshold number of the one or more RARs, that the RAPID of the corresponding RAR is different from an identifier associated with a preamble sequence transmitted by the UE, offset, by the UE, a carrier frequency for each of one or more subsequent random access messages in response to the determination, A computer-readable medium that causes the above to be performed.

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