Prioritize random access channelless Layer 1 / Layer 2 trigger mobility.

Abstract

In general, the present subject matter relates to prioritizing random access channel layer-less (RACH-less) Layer 1 / Layer 2 triggered mobility (LTM). In some implementations, prioritizing RACH-less LTM may include receiving, at a serving distribution unit (DU) of a base station, information indicating RACH-less handover configurations for multiple LTM target cells of the base station or timing advance information for each of the multiple LTM target cells from an aggregation unit control plane of the base station; identifying, at the serving DU, at least one target cell to which a RACH-less handover of a service for a user equipment (UE) may be performed based on the received information; and selecting, at the serving DU, one of the identified at least one target cell for handover from the serving DU of the service for the UE and triggering a handover of the service to the selected target cell.

Description

Technical Field

[0001] In some implementations, the present subject matter relates to communication systems, and more particularly, to prioritizing random access channel layer-less (RACH less) layer 1 / layer 2 trigger mobility (LTM).

Background Art

[0002] In today's world, cellular networks provide on-demand communication capabilities to individuals and business entities. Typically, a cellular network is a wireless network that can be distributed across land areas called cells. Each such cell is served by at least one fixed-position transceiver represented as a cell site or base station. Each cell can use a different set of frequencies from its neighboring cells to avoid interference and provide improved services within each cell. By combining cells, wireless coverage over a wide geographic area is provided such that a large number of mobile phones and / or other wireless devices or portable transceivers can communicate with each other and with fixed transceivers and phones anywhere in the network. Such communication is carried out through the base station and is realized even when the mobile transceiver in communication passes through more than one cell. Major wireless communication providers have deployed such cell sites around the world, enabling mobile phones and mobile computing devices to connect to the public switched telephone network and the public Internet.

[0003] A mobile phone is a portable phone capable of receiving and / or making phone and / or data calls via a cell site or communication tower by using radio waves to transmit signals to and from a mobile phone. From the perspective of a large number of mobile phone users, current mobile phone networks provide limited and shared resources. In this regard, cell sites and handsets can change frequencies and use low-power transmitters to allow simultaneous use of the network by many callers with less interference. Cell site coverage can depend on a particular geographical location and / or the number of users who could potentially use the network. For example, in a city, a cell site may have a range of up to about half a mile. In suburban areas, the range can be as much as 5 miles. In some areas, users can receive signals from cell sites as far as 25 miles away.

[0004] The following are some examples of digital cellular technologies used by telecommunications providers: Global System for Mobile Communications (“GSM”), General Packet Radio Service (“GPRS”), cdmaOne, CDMA2000, Evolution-Data Optimized (“EV-DO”), Enhanced Data Rates for GSM Evolution (“EDGE”), Universal Mobile Telecommunications System (“UMTS”), Digital Enhanced Cordless Telecommunications (“DECT”), Digital AMPS (“IS-136 / TDMA”), and Integrated Digital Enhanced Network (“iDEN”). Long Term Evolution, or 4G LTE, developed by the Third Generation Partnership Project (“3GPP”) standardization body, is a standard for high-speed data wireless communication for mobile phones and data terminals. Currently, 5G standards are under development and deployment. 3GPP cellular technologies such as LTE and 5G NR are evolutions of previous generation 3GPP technologies such as GSM / EDGE and UMTS / HSPA digital cellular technologies, enabling increased capacity and speed through improvements to the core network and the use of different radio interfaces.

[0005] A cellular network can be divided into a radio access network and a core network. The radio access network (RAN) may include network functions capable of handling radio layer communication processing. The core network may include network functions capable of handling higher layer communications (e.g., Internet Protocol (IP), transport layer, and application layer). In some cases, the RAN functions can be divided into baseband unit functions and radio unit functions. Here, radio units connected to baseband units via a fronthaul network may handle lower layer processing of the radio physical layer, for example, while baseband units may handle higher layer radio protocols (e.g., MAC, RLC, etc.). [Overview of the project] [Problems that the invention aims to solve]

[0006] A base station for a 5G cellular network may include an aggregation unit (CU), one or more distributed units (DUs) responsively coupled to the CU, and one or more radio units (RUs), each responsively coupled to at least one of the one or more DUs, and each responsively coupled to one or more cellular and / or other user equipment (UEs). A CU may logically be divided into a control plane portion (CU-CP) and one or more user plane portions (CU-UP). During the responsive coupling of an UE to a base station, the DU supporting the UE may change. Time synchronization is established in the Random Access Channel (RACH) procedure between the UE and the new support DU to ensure that communication takes place properly between the UE and the new support DU. However, such a handover from one DU to the other requires more time if a competition-based RACH procedure must be taken instead of a competition-free RACH procedure. The increased time required to implement such a handover increases handover latency and user plane interruption time. [Means for solving the problem]

[0007] In some implementations, the subject relates to computer implementation methods. The method may include the Serving Distribution Unit (DU) of a base station receiving information from the Base Station Aggregation Unit Control Plane (CU CP) indicating a random access channelless (RACH-less) handover configuration for multiple Layer 1 / Layer 2 Trigger Mobility (LTM) target cells of the base station, or timing advance (TA) information for each of the multiple LTM target cells of the base station. The method may also include the Serving DU identifying, based on the received information, at least one target cell in which a RACH-less handover of the service currently served by the Serving DU to a User Equipment (UE) can be performed. The method may also include the Serving DU selecting one of the at least one target cells identified for the handover of the service to the UE from the Serving DU to the selected target cell and triggering the handover of the service to the UE from the Serving DU to the selected target cell.

[0008] The method may allow RACH-less handover from one cell to another to be preferred over RACH-based HO for UEs that are communicably coupled to a base station of the wireless communication system.

[0009] In some implementations, the subject may include one or more of the following optional features:

[0010] In some implementations, identification may include determining whether one or more of the target cells have (a) the same TA as the serving cell, (b) a zero TA, or (c) a RACH-less handover configuration prepared therein.

[0011] In some implementations, the received information may also include the handover priority for each of the multiple target cells. Identifying can identify one or more target cells in which a RACH-less or RACH-based handover may be performed. Selecting may include selecting one or more target cells with a RACH-less configuration and the highest priority.

[0012] In some implementations, the method may also include determining in the serving DU whether one or more of the target cells have radio quality exceeding a predetermined radio quality threshold. The selection may be made from one or more of the determined target cells.

[0013] In some implementations, the CU-CP may receive information from one or more target DUs of a base station containing multiple LTM target cells, indicating a RACH-less handover configuration for multiple LTM target cells, or TA information for each of the multiple LTM target cells.

[0014] In some implementations, triggering may involve sending a Media Access Control (MAC) Control Element (CE) message from the Serving Duty Unit (DU) to the UE.

[0015] In some implementations, the base station may have a disaggregated architecture.

[0016] In some implementations, a base station may include a Next Generation Radio Access Network (NG-RAN) node. Furthermore, an NG-RAN node may include a gNodeB or eNodeB.

[0017] In some implementations, the base station may include at least one processor and at least one non-temporary storage medium capable of storing instructions that cause at least one processor to execute a method when executed by at least one processor.

[0018] Also described are non-temporary computer program products (i.e., physically embodied computer program products) that store instructions causing at least one data processor to perform the operations described herein when executed by one or more data processors in one or more computing systems. Similarly, computer systems that may include one or more data processors and memory coupled to one or more data processors are also described. The memory may temporarily or permanently store instructions causing at least one processor to perform one or more of the operations described herein. In addition, the method may be implemented by one or more data processors within a single computing system or distributed across two or more computing systems. Such computing systems are connected and can exchange data and / or commands or other instructions via one or more connections (including, but not limited to, connections on a network (e.g., the Internet, a wireless wide area network, a local area network, a wide area network, a wired network, etc.)) such as direct connections between one or more multi-computing systems.

[0019] Details of one or more variations of the subject matter described herein are presented in the accompanying drawings and the following description. Other features and advantages of the subject matter described herein will become apparent from the description, drawings, and claims. [Brief explanation of the drawing]

[0020] The following accompanying drawings, which are integrated into and form part of this specification, illustrate certain aspects of the subject matter disclosed herein and, together with the description, help to illustrate some of the principles relating to the disclosed implementation.

[0021] Figure 1a shows an exemplary conventional "long term evolution" ("LTE") communication system.

[0022] Figure 1b shows further details of the exemplary LTE system shown in Figure 1a.

[0023] Figure 1c shows additional details of the "evolved packet core" of the exemplary LTE system shown in Figure 1a.

[0024] Figure 1d shows an exemplary "evolved Node B" of the exemplary LTE system shown in Figure 1a.

[0025] Figure 2 illustrates further details of the "evolved Node B" shown in Figures 1a - d.

[0026] Figure 3 shows an exemplary virtual radio access network according to some implementations of the present subject matter.

[0027] Figure 4 shows an exemplary 3GPP split architecture for providing the use of higher frequency bands to its users.

[0028] Figure 5a shows an exemplary 5G wireless communication system.

[0029] Figure 5b shows an exemplary layer architecture of a split gNB and / or split ng-eNB (e.g., "next generation eNB" which may be connected to 5GC).

[0030] Figure 5c shows an exemplary functional split in the gNB architecture shown in Figures 5a - b.

[0031] Figure 6a shows an exemplary system according to some implementations of the present subject matter.

[0032] Figure 6b shows an exemplary alternative configuration of the system of Figure 6a according to some implementations of the present subject matter.

[0033] Figure 7 shows an exemplary method according to some implementations of the present subject matter.

[0034] Figure 8a shows other exemplary systems relating to several implementations of the current subject.

[0035] Figure 8b shows other illustrative methods relating to several implementations of the current subject.

[0036] Figure 9 shows yet another exemplary system relating to some implementations of the current subject.

[0037] Figure 10 shows yet another illustrative method relating to some implementations of the current subject. [Modes for carrying out the invention]

[0038] The present subject can provide systems and methods that can be implemented in wireless communication systems. Such systems may include a variety of wireless communication systems, including 5G New Radio communication systems, "long term evolution" communication systems, and so on.

[0039] In general, the current topic concerns prioritizing RACH-less LTM.

[0040] In some implementations of the current subject, a RACH-less (or "RACH-free") handover (HO) from one cell to another may be preferred over a RACH-based HO for user equipment (UE) that is communicatively coupled to a base station of a wireless communication system. An HO from one cell to another requires less time because a competition-free RACH procedure may be taken instead of a competition-based RACH procedure. This reduces handover latency and user plane downtime.

[0041] 3GPP standards that define one or more aspects that may be relevant to the current subject include 3GPP TS 38.321 “NR; Medium Access Control (MAC) protocol specification”, 3GPP TS 38.331 “NR; Radio Resource Control (RRC) protocol specification”, 3GPP TS 38.463 “NG-RAN; E1 Application Protocol (E1AP)”, and 3GPP TS 38.473 “NG RAN F1 application protocol (F1AP)”. O-RAN Alliance standards may also be relevant to one or more aspects of the current subject.

[0042] One or more aspects of the current subject can be integrated into the transmitter and / or receiver components of base stations (e.g., gNodeB, eNodeB, etc.) in such communication systems. The following is a general discussion of long-term evolutionary communication systems and 5G New Radio communication systems. I. "Long Term Evolution" Communication System

[0043] Figures 1a-c and 12 illustrate an exemplary conventional long-term evolution ("LTE") communication system 100 with its various components. The LTE system, or 4G LTE, conforms to the standards for high-speed data wireless communication for mobile phones and data terminals, as is commercially known. The standards are an evolution of GSM / EDGE ("Global System for Mobile Communications" / "Enhanced Data rates for GSM Evolution") and UMTS / HSPA ("Universal Mobile Telecommunications System" / "High Speed ​​Packet Access") network technologies. The standards were developed by 3GPP ("3rd Generation Partnership Project").

[0044] As shown in Figure 1a, System 100 may include an "evolved universal terrestrial radio access network" ("EUTRAN") 102, an "evolved packet core" ("EPC") 108, and a "packet data network" ("PDN") 101, which EUTRAN 102 and EPC 108 provide for communication between user devices 104 and PDN 101. EUTRAN 102 may include multiple "evolved Node B" ("eNodeB" or "ENODEB" or "enodeb" or "eNB") or base stations 106 (a, b, c) (as shown in Figure 1b) that provide communication capabilities to multiple user devices 104 (a, b, c). User devices 104 may be mobile phones, smartphones, tablets, personal computers, personal digital assistants ("PDAs"), servers, data terminals, and / or any other type of user device, and / or any combination thereof. The user device 104 can connect to the EPC 108 and subsequently to the PDN 101 via any eNodeB 106. Typically, the user device 104 can connect to the eNodeB 106 closest in terms of distance. In the LTE system 100, the EUTRAN 102 and EPC 108 work together to provide connectivity, mobility, and services to the user device 104.

[0045] Figure 1b illustrates further details of the network 100 shown in Figure 1a. As previously mentioned, EUTRAN 102 includes multiple eNodeB 106, also known as cell sites. The eNodeB 106 provides radio functionality and performs key control functions, including scheduling of airlink resources or radio resource management, active mode mobility or handover, and admission control for service. The eNodeB 106 is responsible for selecting which mobility management entity (MME, as shown in Figure 1c) serves the user equipment 104, and for protocol features such as header compression and encryption. The eNodeB 106 constituting EUTRAN 102 cooperate with each other for radio resource management and handover.

[0046] Communication between user equipment 104 and eNodeB 106 occurs via air interface 122 (also known as the “LTE-Uu” interface). As shown in Figure 1b, air interface 122 provides communication between user equipment 104b and eNodeB 106a. Air interface 122 uses orthogonal frequency division multiple access (“OFDMA”) and single-carrier frequency division multiple access (“SC-FDMA”), OFDMA variants, on the downlink and uplink, respectively. OFDMA enables the use of multiple known antenna techniques, such as “Multiple Input Multiple Output” (“MIMO”).

[0047] The air interface 122 uses various protocols, including Radio Resource Control ("RRC") for signaling between user equipment 104 and eNodeB 106, and Non-Access Layer ("NAS") for signaling between user equipment 104 and MME (as shown in Figure 1c). In addition to signaling, user traffic is forwarded between user equipment 104 and eNodeB 106. Both signaling and traffic in system 100 are carried by physical layer ("PHY") channels.

[0048] Multiple eNodeB106s can be interconnected using X2 interfaces 130(a, b, c). As shown in Figure 1b, X2 interface 130a provides interconnection between eNodeB106a and eNodeB106b, X2 interface 130b provides interconnection between eNodeB106a and eNodeB106c, and X2 interface 130c provides interconnection between eNodeB106b and eNodeB106c. The X2 interface can be established between two eNodeBs to provide signal exchange, which may include load or interference-related information and handover-related information. The eNodeB106 communicates with the "evolved packet core" 108 via S1 interfaces 124(a, b, c). S1 interface 124 can be divided into two interfaces. One is the control plane (shown as the control plane interface (S1-MME interface) 128 in Figure 1c), and the other is the user plane (shown as the user plane interface (S1-U interface) 125 in Figure 1c).

[0049] The EPC108 establishes and enables "Quality of Service" ("QoS") for user services, allowing user equipment 104 to maintain a consistent Internet Protocol ("IP") address while in transit. Each node in network 100 has its own IP address. The EPC108 is designed to work with legacy wireless networks. The EPC108 is also designed to separate the control plane (i.e., signaling) and the user plane (i.e., traffic) in the core network architecture, enabling greater flexibility in implementation and independent scalability of control and user data functions.

[0050] The architecture of EPC108 is for packet data and is shown in more detail in Figure 1c. EPC108 includes a Serving Gateway (S-GW) 110, a PDN Gateway (P-GW) 112, a Mobility Management Entity ("MME") 114, a Home Subscriber Server ("HSS") 116 (subscriber database for EPC108), and a Policy Control and Billing Rule Function ("PCRF") 118. Some of these (S-GW, P-GW, MME, HSS, etc.) are often combined into a node according to the manufacturer's implementation.

[0051] S-GW110 functions as an IP packet data router and is the bearer path anchor for user equipment in EPC108. Therefore, as user equipment moves from one eNodeB106 to another during mobility operations, S-GW110 remains the same, and the bearer path toward EUTRAN102 is switched to speak with the new eNodeB106 serving user equipment 104. If user equipment 104 moves to the domain of another S-GW110, MME114 forwards all of the user equipment's bearer paths to the new S-GW. S-GW110 establishes bearer paths toward one or more P-GW112 for the user equipment. When downstream data is received for idle user equipment, S-GW110 buffers the downstream packets and requests MME114 to identify and re-establish the bearer paths toward and through EUTRAN102.

[0052] P-GW112 is the gateway between EPC108 (and user devices 104 and EUTRAN102) and PDN101 (shown in Figure 1a). P-GW112 acts as a router for user traffic, performing functions on behalf of the user devices. These include assigning IP addresses to user devices, packet filtering of downstream user traffic to ensure it is placed on the appropriate bearer path, and enabling downstream QoS, including data rates. Depending on the services used by the subscriber, there may be multiple user data bearer paths between user device 104 and P-GW112. Subscribers can use services on the PDN served by different P-GWs. In this case, user devices have at least one bearer path established to each P-GW112. If the S-GW110 also changes during a handover of user devices from one eNodeB to another, the bearer path from P-GW112 is switched to the new S-GW.

[0053] The MME114 manages user devices 104 within the EPC108 (including managing subscriber authentication, maintaining context for authenticated user devices 104, establishing data bearer paths in the network for user traffic, and continuing to track the location of idle mobile devices that are not disconnected from the network). For idle user devices 104 that need to be reconnected to the access network to receive downstream data, the MME114 initiates paging to identify the user device and re-establish the bearer path to and through the EUTRAN102. The MME114 for a particular user device 104 is selected by the eNodeB106 from which the user device 104 initiates system access. MMEs are typically part of a collection of MMEs in the EPC108 for load sharing and redundancy purposes. In establishing the user's data bearer path, the MME114 is responsible for selecting the P-GW112 and S-GW110 that constitute the ends of the data path through the EPC108.

[0054] PCRF118 is responsible for policy control decision-making and controlling the flow-based billing function within the policy control enablement function ("PCEF") located within P-GW110. PCRF118 determines how specific data flows are handled in PCEF and provides QoS authorization (QoS class identifier ("QCI") and bitrate) to ensure that this is in line with the user's subscription profile.

[0055] As previously mentioned, IP service 119 is provided by PDN101 (shown in Figure 1a).

[0056] Figure 1d shows an exemplary configuration of eNodeB106. eNodeB106 may include at least one “remote radio head” (“RRH”) 132 (typically there may be three RRHs) and a baseband unit (“BBU”) 134. The RRH 132 may be connected to the antenna 136. The RRH 132 and BBU 134 may be connected using an optical interface compliant with the “common public radio interface” (“CPRI”) / “enhanced CPRI” (“eCPRI”) 142 standard, using a custom control and user plane framing method specific to the RRH or a control and user plane framing method compliant with the O-RAN Alliance. The operation of the eNodeB106 can be characterized using the following standard parameters (and specifications): radio frequency band (Band 4, Band 9, Band 17, etc.), bandwidth (5, 10, 15, 20 MHz), access scheme (downlink: OFDMA; uplink: SC-OFDMA), antenna technology (single-user and multi-user MIMO; uplink: single-user and multi-user MIMO), number of sectors (up to 6), maximum transmit rate (downlink: 150 Mb / s; uplink: 50 Mb / s), S1 / X2 interface (1000Base-SX, 1000Base-T), and mobile environment (up to 350 km / h). The BBU134 can handle digital baseband signal processing, S1 line termination, X2 line termination, call processing, and monitoring control processing. IP packets received from EPC108 (not shown in Figure 1d) can be modulated into digital baseband signals and transmitted to RRH132. Conversely, digital baseband signals received from RRH132 can be demodulated into IP packets for transmission to EPC108.

[0057] The RRH132 can transmit and receive radio signals using antenna 136. The RRH132 can convert digital baseband signals from BBU134 into radio frequency ("RF") signals (using converter ("CONV") 140) and amplify the power for transmission to user equipment 104 (not shown in Figure 1d) (using amplifier ("AMP") 138). Conversely, RF signals received from user equipment 104 are amplified (using AMP 138) and converted into digital baseband signals for transmission to BBU134 (using CONV 140).

[0058] Figure 2 shows additional details of an exemplary eNodeB106. The eNodeB106 comprises multiple layers ("LTE Layer 1" 202, "LTE Layer 2" 204, "LTE Layer 3" 206). LTE Layer 1 includes the physical layer ("PHY"). LTE Layer 2 includes Media Access Control ("MAC"), Radio Link Control ("RLC"), and Packet Data Convergence Protocol ("PDCP"). LTE Layer 3 includes various functions and protocols, including Radio Resource Control ("RRC"), Dynamic Resource Allocation, eNodeB Measurement Configuration and Provisioning, Radio Admission Control, Connectivity Mobility Control, and Radio Resource Management ("RRM"). The RLC protocol is an "automatic repeat request" ("ARQ") fragmentation protocol used on the cellular air interface. The RRC protocol handles LTE Layer 3 control plane signaling between user equipment and EUTRAN. RRC includes functions for connection establishment and release, broadcasting system information, establishing / reconfiguring and releasing radio bearers, RRC connection mobility procedures, paging notifications and releases, and outer loop power control. PDCP performs IP header compression and decompression, user data transfer, and maintaining sequence numbers for radio bearers. BBU134, shown in Figure 1d, may include LTE layers L1-L3.

[0059] One of the main functions of eNodeB106 is radio resource management, including scheduling of both uplink and downlink air interface resources for user equipment 104, bearer resource control, and admission control. As an agent for EPC108, eNodeB106 is responsible for forwarding paging messages used to identify idle mobiles. eNodeB106 also communicates common control channel information for the radio, header compression, encryption and decryption of user data transmitted over the radio, and establishes handover reporting and trigger criteria. As previously mentioned, eNodeB106 can collaborate with other eNodeB106s on the X2 interface for handover and interference management purposes. eNodeB106 communicates with the EPC's MME via the S1-MME interface and with the S-GW on the S1-U interface. Furthermore, eNodeB106 exchanges user data with the S-GW on the S1-U interface. eNodeB106 and EPC108 have a many-to-many relationship to support load sharing and redundancy between MMEs and S-GWs. eNodeB106 selects an MME from a group of MMEs so that the load can be shared by multiple MMEs to avoid congestion. II.5G NR Wireless Communication Network

[0060] In some implementations, the current subject concerns the 5G New Radio ("NR") communication system. 5G NR is the successor communication standard to the 4G / IMT-Advanced standard. 5G networks offer higher capacity than current 4G, accommodating more mobile broadband users per unit area and enabling greater and / or unlimited data consumption in gigabytes per month and per user. This could allow users to stream high-definition media on their mobile devices for much of the day (even when it's not possible to do the same on a Wi-Fi network). 5G networks also offer improved support for device-to-device communication, lower costs, lower latency than 4G equipment, lower battery consumption, and more. Such networks offer data rates of tens of megabits per second for a large number of users, 100 Mb / s for metropolitan areas, 1 Gb / s for simultaneous users in restricted areas (e.g., office floors), numerous simultaneous connections for wireless sensor networks, improved spectral efficiency, improved coverage, improved signaling efficiency, 1-10 ms latency, and reduced latency compared to existing systems.

[0061] Figure 3 shows an exemplary virtual radio access network 300. The network 300 can provide communication between various components, including base stations (e.g., eNodeB, gNodeB) 301, radio equipment 303, aggregation units 302, digital units 304, and radio devices 306. Components in system 300 may be communicatively coupled to the core using backhaul links 305. An aggregation unit ("CU") 302 may be communicatively coupled to a distributed unit ("DU") 304 using a midhaul connection 308. A radio frequency ("RU") component 306 may be communicatively coupled to a DU 304 using a fronthaul connection 310.

[0062] In some implementations, CU302 can provide intelligent communication capabilities to one or more DU units 304. Units 302, 304 may include one or more base stations, macro base stations, micro base stations, "remote radio heads," etc., and / or any combination thereof.

[0063] In lower layer-split architecture environments, CPRI bandwidth requirements for NR can be several hundred Gb / s. CPRI compression can be implemented in DU and RU (shown in Figure 3). In 5G communication systems, compressed CPRI on Ethernet frames is represented as eCPRI and is the recommended fronthaul network. The architecture can enable fronthaul / midhaul standardization, which may include fronthaul with higher layer-split architectures (e.g., "Option 2" or "Option 3-1" (higher / lower RLC split architectures)) and L1 split architectures ("Option 7").

[0064] In some implementations, a lower layer-split architecture (e.g., "Option 7") may include joint processing across multiple transmit points (TPs) for both receivers in the uplink and DL / UL, as well as transport bandwidth and latency requirements for ease of deployment. Furthermore, the lower layer-split architecture of the present subject may include a split between cell-level and user-level processing, including cell-level processing at remote units ("RUs") and user-level processing at DUs. Moreover, by using the lower layer-split architecture of the present subject, frequency-domain samples that can be compressed to reduce fronthaul bandwidth may be transmitted over the Ethernet fronthaul.

[0065] Figure 4 shows an exemplary communication system 400 that can implement 5G technology and provide users with the use of higher frequency bands (e.g., above 10 GHz). System 400 may include macrocells 402 and small cells 404, 406.

[0066] The mobile device 408 may be configured to communicate with one or more small cells 404, 406. System 400 may enable the separation of the control plane (C-plane) and user plane (U-plane), which utilize different frequency bands, between the macrocell 402 and the small cells 404, 406. In particular, the small cells 404, 406 may be configured to utilize higher frequency bands when communicating with the mobile device 408. The macrocell 402 can utilize existing cellular bands for C-plane communication. The mobile device 408 may be communicatively coupled via the U-plane 412. Here, the small cell (e.g., small cell 406) can provide higher data rates and more flexible / cost-effective / energy-efficient operations. The macrocell 402 can maintain good connectivity and mobility via the C-plane 410. Furthermore, in some cases, LTE and NR may be transmitted on the same frequency.

[0067] Figure 5a shows an exemplary 5G wireless communication system 500 relating to several implementations of the present subject. System 500 may be configured to have a lower layer-split architecture in accordance with "Option 7-2". System 500 may include a core network 502 (e.g., 5G Core) and one or more gNodeBs (or gNBs) which may have aggregation units gNB-CUs. A gNB-CU may be logically separated into a control plane portion (gNB-CU-CP) 504 and one or more user plane portions (gNB-CU-UP) 506. The control plane portion 504 and the user plane portion 506 may be configured to be communicatively coupled using an E1 communication interface 514 (as defined in the 3GPP standard). The control plane portion 504 may be configured to be responsible for executing the RRC and PDCP protocols of the radio stack.

[0068] The control plane and user plane portions 504, 506 of the gNB aggregation unit may be configured to communicate with one or more distributed units (DUs) 508, 510 according to a higher layer-split architecture. The distributed units 508, 510 may be configured to run the upper layers of the RLC, MAC, and PHY layer protocols of the radio stack. The control plane portion 504 may be configured to communicate with the distributed units 508, 510 using an F1-C communication interface 516, and the user plane portion 506 may be configured to communicate with the distributed units 508, 510 using an F1-U communication interface 518. The distributed units 508, 510 can communicate with one or more remote radio units (RUs) 512 via a fronthaul network 520 (which may include switches, links, etc.) and communicate with one or more user devices (not shown in Figure 5a). The remote radio unit 512 may be configured to perform lower-level parts of the PHY layer protocol and provide antenna capabilities to the remote unit for communication with user equipment (similar to the above discussion regarding Figures 1a-2).

[0069] Figure 5b shows an exemplary layer architecture 530 of a split gNB. Architecture 530, which can be configured as a virtualized and decomposed radio access network (RAN) architecture (where layers L1, L2, L3 and radio processing can be virtualized and decomposed in the aggregate unit, distributed unit and radio unit), can be implemented in the communication system 500 shown in Figure 5a. As shown in Figure 5b, the gNB-DU 508 can be communicatively coupled with the gNB-CU-CP control plane portion 504 (also shown in Figure 5a) and the gNB-CU-UP user plane portion 506. Each of components 504, 506, and 508 can be configured to include one or more layers.

[0070] The gNB-DU508 may include RLC, MAC, and PHY layers, as well as various communication sublayers. These may include the F1 Application Protocol (F1-AP) sublayer, the GPRS Tunneling Protocol (GTPU) sublayer, the Stream Controlled Transmit Protocol (SCTP) sublayer, the User Datagram Protocol (UDP) sublayer, and the Internet Protocol (IP) sublayer. As previously stated, the distributed unit 508 may be communicatively coupled to the control plane portion 504 of the aggregation unit, which may include the F1-AP, SCTP, and IP sublayers, radio resource control, and PDCP control (PDCP-C) sublayers. Furthermore, the distributed unit 508 may be communicatively coupled to the user plane portion 506 of the aggregation unit of the gNB. The user plane portion 506 may include the Service Data Adaptation Protocol (SDAP), PDCP User (PDCP-U), GTPU, UDP, and IP sublayers.

[0071] Figure 5c shows an exemplary functional split in the gNB architecture shown in Figures 5a and 5b. As shown in Figure 5c, gNB-DU508 may be communicatively coupled with gNB-CU-CP504 and GNB-CU-UP506 using the F1-C communication interface. gNB-CU-CP504 and GNB-CU-UP506 may be communicatively coupled using the E1 communication interface. The higher portion of the PHY layer (or Layer 1) may be performed by gNB-DU508, and the lower portion of the PHY layer may be performed by RU (not shown in Figure 5c). As shown in Figure 5c, the RRC and PDCP-C portions may be performed by the control plane portion 504, and the SDAP and PDCP-U portions may be performed by the user plane portion 506.

[0072] Some of the functions of the PHY layer in a 5G communication network may include error detection on the transport channel and suggestion to higher layers, FEC encoding / decoding of the transport channel, hybrid ARQ soft synthesis, rate matching of coded transport channels to physical channels, mapping of coded transport channels onto physical channels, power weighting of physical channels, modulation and demodulation of physical channels, frequency and time synchronization, radio characteristics measurement and suggestion to higher layers, MIMO antenna processing, digital and analog beamforming, RF processing, and other functions.

[0073] The Layer 2 MAC sublayer can perform beam management, random access procedures, mapping between logical and transport channels, concatenation of multiple MAC service data units (SDUs) belonging to a single logical channel into a transport block (TB), multiplexing / demultiplexing of SDUs belonging to logical channels to / from TBs delivered to / from the physical layer over transport channels, scheduling of information reporting, error correction via HARQ, priority handling between logical channels of a single UE, priority handling between UEs through dynamic scheduling, transport format selection, and other functions. The functions of the RLC sublayer may include forwarding upper layer packet data units (PDUs), error correction via ARQ, sorting of data PDUs, duplication and protocol error detection, and re-establishment. The PDCP sublayer may be responsible for forwarding user data, various functions during re-establishment procedures, retransmission of SDUs, discarding SDUs on the uplink, forwarding control plane data, and others.

[0074] The Layer 3 RRC sublayer can perform functions such as broadcasting system information to NAS and AS, establishing, maintaining, and releasing RRC connections, security, establishing, configuring, maintaining, and releasing point-to-point radio bearers, mobility functions, reporting, and other functions. III. Prioritize RACH-less LTM

[0075] In some implementations of the current subject, RACH-less handover (HO) from one cell to another may be preferred for user equipment (UE) that is communicatively coupled to a base station of a wireless communication system.

[0076] Layer 1 / Layer 2 triggered mobility (LTM) inter-cell handovers at a base station can occur by performing a Serving Cell Change (SSC) from the serving cell to the target cell. Multiple target cells can be strong target cell options for a handover (HO) if they satisfy the radio conditions or handover criteria required for the UE to receive the SSC. One or more strong target cells may require a RACH-based HO with a competition-based or competition-free RACH procedure, for example, because the timing advance (TA) of the serving cell and the TA of the target cell are different. The timing advance represents the time offset between the start times of the downlink subframes received and the uplink subframes transmitted at the UE. This offset at the UE is necessary to ensure that the downlink and uplink subframes are synchronized at the base station. This is a base station-to-UE media access control (MAC) layer (Layer 2) control element (CE) used in controlling the timing of uplink signal transmission (e.g., from the UE to the base station). One or more other strong target cells may allow a RACH-less HO, for example, because the target cell's TA is zero, or the serving cell's TA is the same as the target cell's TA. Prioritizing RACH-less HOs over RACH-based HOs is configured to allow a handover to one of the target cells that allows a RACH-less HO procedure.

[0077] For a UE, as initial access to a radio communication system including a base station, or as a handover from one cell to another, the base station can receive signals on a communication channel (e.g., an uplink communication channel established between the base station and one or more UEs) using one or more antennas, such as antenna 136 in Figure 1d. The interface may be, for example, the air interface 122 in Figure 1 using OFDMA and SC-FDMA, or other communication channels. Signals may include frames containing multiple symbols, including one or more symbol groups. Generally, OFDM symbols may include a random access preamble containing a cyclic prefix (CP) portion and data symbols. Symbol groups may include a CP portion and multiple data symbols, which can reduce overhead by allowing one CP portion to be used for multiple data symbols instead of using one CP portion for only one data symbol. Random access is based on the UE transmitting a random access preamble on a random access channel (RACH) for access to the base station (initial access or handover). Only a certain number of random access preambles may be available to the cell. For example, under 3GPP, an LTE cell may have 64 available preambles. Therefore, multiple UEs may each randomly select the same preamble, and the cell may receive signals containing the same preamble from multiple UEs at the same time, resulting in a collision, referred to as a "contradiction." While a conflict-based RACH procedure can be performed to resolve the collision, it can delay the HO (Handover) because the collision must be resolved before the UEs can properly communicate with the cell, for example, by requiring each UE to use a different preamble.

[0078] Conversely, in a competition-free RACH procedure, the UE does not select a preamble. Instead, the cell selects a preamble for the UE and sends it to the UE. In this way, the cell can ensure that no collisions occur by assigning preambles so that a particular preamble is assigned to only one UE, and can reduce HO latency compared to a competition-based RACH procedure because it saves uplink synchronization time, which can be at least 20ms.

[0079] In some implementations of the current subject, a base station (e.g., a next-generation RAN (NG-RAN) node such as gNodeB, eNodeB, or gNodeB in Figure 5a) of a wireless communication system (e.g., a 5G wireless communication system, a 6G or later generation wireless communication system) may have a disaggregated architecture in which the base station includes one gNB-CU-CP (e.g., gNB-CU-CP504 in Figures 5a-5c), one or more CU-UPs (e.g., gNB-CU-UP506 in Figures 5a-5c), and gNB-DUs (e.g., gNB-DU508, 510 in Figures 5a-5c). The base station may be configured to prioritize RACH-less LTM when a UE is handed off from one cell of the base station (serving cell) to the other cell of the base station (target cell).

[0080] Figure 6a shows an exemplary system 600 configured to provide RACH-less LTM. The base station 624 in this exemplary implementation is a gNB configured in a 5G wireless communication system similar to the 5G wireless communication system 500 in Figure 5a described above, but other base stations may be configured and used similarly when providing RACH-less LTM. In the exemplary implementation of Figure 6a, the base station 624 includes multiple CU-UPs 606a, 606b, and 606c. The base station 624 includes three CU-UPs 606a, 606b, and 606c in this exemplary implementation, but may include other multiple CU-UPs. The CUs of the base station 624, including the multiple CU-UPs 606a, 606b, and 606c, are configured to be communicatively coupled to a core network (not shown in Figure 6a), such as the 5GC502 in Figure 5a.

[0081] The CU of base station 624 also includes a CU-CP604 configured to communicately couple to the user plane portions 606a, 606b, and 606c of the CU using an E1 communication interface 614. The E1 interface 614 includes three communication links, reflecting that there are three CU-UP606a, 606b, and 606c that the CU-CP604 may be configured to communicate with.

[0082] Base station 624 also includes multiple DU608,610. In this exemplary implementation, base station 624 includes two DU608,610, but may include multiple other DUs. CU-CP604 is configured to communicately couple to DU608,610 using F1-C communication interface 616. CU-UP606a,606b,606c are configured to communicately couple to DU608,610 using F1-U communication interface 618. The F1-U interface 618 associated with each of the DU608,610 includes three communication links, reflecting that there are three CU-UP606a,606b,606c that each DU608,610 may be configured to communicate with.

[0083] Base station 624 also includes multiple RU612s. In this exemplary implementation, base station 624 includes five RU612s, but may include other RUs. The RU612s are configured to be communicatively coupled to DU608, 610 via the fronthaul network 620. In addition, each RU612 is configured to be communicatively coupled to one or more UE622s. In this exemplary implementation, two RU612s are shown as communicatively coupled to one UE622, two RU612s are shown as communicatively coupled to two UE622s, and one RU612 is shown as communicatively coupled to three UE622s, but each RU612 may be coupled to any other number of UEs, either the same or different from any other RU612s.

[0084] A RACH-less LTM priority may be configured when one of the UEs, which is communicatively coupled to base station 624, is handed off from one DU608,610 of base station 624 to the other DU608,610 of the same base station 624. The DU608,610 currently servicing UE622 is referred to as the "serving DU" because it is currently servicing UE622 (for example, by serving UE622). The other DU608,610 to which the UE's service is handed off is referred to as the "target DU" because it will be the target for servicing UE622.

[0085] A system that can be configured to prioritize RACH-less LTM is further described with respect to Figure 6b. Figure 6b illustrates CU-CP604 and CU-UP606a, 606b, 606b of Figure 6a, but in the example implementation of Figure 6b, base station 624 contains more than two DUs. In the example implementation of Figure 6b, base station 624 contains 66 DU626, 628. Three of DU628a, 628b, and 628c are macrocells (labeled macro1, macro2, and macro3 in Figure 6b), and 63 DU626 are small cells (of which nine are labeled gNB-DU10, gNB-DU20, gNB-DU30, gNB-DU40, gNB-DU50, gNB-DU60, gNB-DU70, gNB-DU80, and gNB-DU90 in Figure 6b). Base station 624 may include other numbers of macrocells and / or other numbers of subcells. Twenty-one subcells DU626, including macro 1DU628a, macro 2DU628b, gNB-DU10, gNB-DU20, and gNB-DU30, are configured to be served by the first CU-UP606a (labeled CU-UP1 in Figure 6b). Twenty-one subcells DU626, including macro 1DU628a, macro 2DU628b, macro 3DU628c, gNB-DU40, gNB-DU50, and gNB-DU60, are configured to be served by the second CU-UP606b (labeled CU-UP2 in Figure 6b). The 21 subcells DU626, including macros 2DU628b, 3DU628c, gNB-DU70, gNB-DU80, and gNB-DU90, are configured to be served by the third CU-UP606c (labeled CU-UP3 in Figure 6b).

[0086] In the implementation shown in Figure 6b, each CU-UP 606a, 606b, and 606c serves a subset of DUs 626, 628a, 628, and 628c for all services. However, a CU-UP can serve a subset of DUs for other services (e.g., V2X (vehicle-to-everything) or URLLC (ultra-reliable low latency communication)) while serving all DUs at the base station for one service (e.g., eMBB (enhanced mobile broadband)).

[0087] Figure 7 shows exemplary methods 700 relating to several implementations of the present subject. Method 700 is described in relation to the exemplary system 800 shown in Figure 8a, but can be similarly implemented in other systems, such as system 100 in Figures 1a-1c and 2, system 400 in Figure 4, system 500 in Figure 5a, and systems in Figures 6a and 6b. Although system 800 in Figure 8a is a 5G system, as mentioned above, the RACH-less LTM preference described herein can also be implemented in other types of wireless communication systems, such as LTE wireless communication systems and 6G or later generation wireless communication systems.

[0088] In system 800, a UE802 (e.g., UE104 in Figures 1a-1c, UE622 in Figure 6a, etc.) is configured with LTMs (810) with one or more target cells in one or more DU804, 806 (e.g., DU508 in Figures 5a-5c, DU510 in Figure 5a, DU608 in Figure 6a, DU610 in Figure 6a, DU626 in Figure 6b, DU628 in Figure 6b, etc.) of a base station such as a gNB (gNodeB in Figure 5a, gNodeB624 in Figures 6a and 6b, etc.). For convenience of explanation, system 800 is shown in Figure 8a with one UE802 communicably coupled to a base station and a base station containing two DU804, 806, but more than one UE may be communicably coupled to a base station, and / or the base station may contain more than two DUs. The base station of system 800 includes a CU containing a CU-CP808 (e.g., gNB-CU-CP504 in Figures 5a-5c, CU-CP604 in Figures 6a and 6b, etc.) and one or more CU-UPs (e.g., gNB-CU-UP506 in Figures 5a-5c, CU-UP606a, 606b, 606c, etc. in Figures 6a and 6b) (not shown in Figure 8a), and also includes multiple RUs (e.g., RU512 in Figure 5a, RU612 in Figure 6a, etc.) (not shown in Figure 8a). UE802 is currently served by serving DU804. In addition, the base station in Figure 8a is coupled to the core network (e.g., EPC108 in Figures 1a-1c and 2, 5GC502 in Figure 5a, etc.) (not shown in Figure 8a) for communication.

[0089] Method 700 provides an implementation of an intra-DU LTM serving cell change scenario, which includes serving DU 804 determining that a cell change is necessary for UE 802 (702). The serving DU's determination 702 may include serving DU 804 analyzing an in-frequency L1 measurement report transmitted to serving DU 804 by UE 802 (812) in accordance with the 3GPP standard (814). In accordance with the 3GPP standard, the in-frequency L1 measurement report may include Layer 1 (L1) measurement results that UE 802 can analyze when making resource control decisions, which may include a serving cell change served by a different DU (e.g., target DU 806) for at least one service.

[0090] Upon determining that a serving cell change should occur (702), the serving DU 804 notifies the UE 802 of the serving cell change (704). As shown in Figure 8a, the notification 704 to the UE 802 may include the serving DU 804 sending a serving cell change command (e.g., MAC CE) to the UE 802 (816).

[0091] Furthermore, upon determining that a cell service change should occur (702), the serving DU 804 notifies the CU-CP 808 that a serving cell change has occurred for UE 802 (704). In this way, notification 704 identifies UE 802 to CU-CP 808 in accordance with the 3GPP standard by identifiers known to the serving DU 804, etc. As shown in Figure 8a, notification 704 to CU-CP 808 may include the serving DU 804 sending a serving cell change notification message to CU-CP 808 using the F1 communication interface (818). Also, as shown in Figure 8a, the serving cell change notification message includes a cell ID (identification) that uniquely identifies UE 802 after the serving cell change.

[0092] Upon receiving a serving cell change command 704 from serving DU804, UE802 sends a radio resource control (RRC) reconfiguration confirmation message to CU-CP808 (820). From the RRC reconfiguration confirmation message, CU-CP808 recognizes that UE802, uniquely identified to CU-CP808 by serving DU804, has confirmed the success (completion) of the serving cell change.

[0093] Furthermore, upon receiving a Layer 3 RRC measurement configuration, UE802 transmits an RRC measurement report to CU-CP808 in accordance with the 3GPP standard (822). In accordance with the 3GPP standard, the RRC measurement report may include Layer 3 (L3) measurement results that can be analyzed by CU-CP808 when making resource control decisions, which may include deciding to prepare at least one target DU cell for LTM such that at least one target cell from target DU806 is available to serve UE802 in place of serving DU804 for at least one service (824).

[0094] In accordance with the decision to prepare at least one target cell for the LTM (824), CU-CP808 prepares at least one target cell for the LTM (706). As shown in Figure 8a, in this exemplary embodiment, each of the at least one target cell is an inter-DU target cell (e.g., a portion of the DU that is the same base station as serving DU804 but different from serving DU804). Also, in this exemplary embodiment, since there are only two gNB-DUs, the at least one target cell contains only target DU806, but as previously stated, a base station may contain more than two target cells. Currently, according to the 3GPP standard, up to eight LTM target cells can be prepared for a given UE.

[0095] Preparing at least one target DU cell for LTM (706) may include notifying at least one target DU that at least one target DU may be notified later to initiate service provision to UE802 for at least one service. Thus, target DU806 can reserve the necessary resources for UE802. As shown in Figure 8a, in this exemplary embodiment, preparation 706 of at least one target cell, which is only target DU806, may include CU-CP808 sending a UE CONTEXT SETUP REQUEST message to target DU806 using the F1 communication interface (826) in accordance with the 3GPP standard.

[0096] The CU-CP808 is assumed to recognize the timing advances (TAs) of the base station's DU804 and 806, respectively, in accordance with the 3GPP standard. Therefore, the CU-CP808 can determine whether each of at least one target cell is a candidate for a RACH-less HO from the serving DU804 based on whether the target cell's TA is zero or the serving cell's TA is the same as the target cell's TA. Alternatively, the CU-CP808 can request the serving DU804 to provide the TA of the UE in the serving cell. This may be passed transparently to the target DU806 to enable the determination of the possibility of a RACH-less handover. If the target cell's TA is zero or the serving cell's TA is the same as the target cell's TA, the target cell is a candidate for a RACH-less HO. Preparation 706 of at least one target cell may include notifying each of one or more target cells whether the target cell is a candidate for a RACH-less HO. As shown in Figure 8a, this notification may include a UE context setup request message indicating RACHless ON (the target cell is a candidate for RACHless HO) or RACHless OFF (the target cell is not a candidate for RACHless HO) using an information element (IE), etc. In this way, if a target cell is later notified by UE802 to start a service to UE802 instead of serving DU804 for at least one service, each of the one or more target cells can recognize the necessary RACH procedure.

[0097] In response to receiving a UE context setup request message from CU-CP808, target DU806 prepares each of at least one target cells for LTM (828). For example, target DU806 reserves the necessary resources for UE802 and notifies CU-CP808 that preparation 828 is complete. In this exemplary embodiment, at least one target cell includes only one target DU806 that prepares one target cell (828). As shown in Figure 8a, notification to CU-CP808 may include target DU806 sending a UE context setup response message to CU-CP808 using the F1 communication interface in accordance with the 3GPP standard (830). Also as shown in Figure 8a, the UE context setup response message includes integrated cell group configuration information for the target cells prepared in target DU806.

[0098] CU-CP808 notifies Serving DU804 of at least one LTM-prepared target cell by identifying each of the one or more LTM-prepared target cells and including information about each of the one or more target DUs (708). In some implementations, one or more of the at least one LTM-prepared target cells may belong to a different DU than Serving DU806. For example, referring to the system in Figure 6b, Serving DU may be subcell 626 of macro 1DU628a, and one or more target cells may be subcells 626 of macro 2DU628b and / or macro 3DU628c. In some implementations, one or more of the at least one target cells may belong to the same DU as Serving DU806. For example, referring to the system in Figure 6b, Serving DU may be gNB-DU70, and at least one target cell may include gNB-DU80 and gNB-DU90.

[0099] As shown in Figure 8a, notification 708 to serving DU 804 may include CU-CP 808 sending a UE CONTEXT MODIFICATION REQUEST message to serving DU 804 using the F1 communication interface (832). Also, as shown in Figure 8a, the UE CONTEXT MODIFICATION REQUEST message may include, for each of one or more target DUs, cell identification information (e.g., a unique cell ID that identifies the target DU, such as a physical cell identifier (PCI)) or an index corresponding to the cell ID, TA information for the target DU (e.g., the TA value for target DU 806), and priority information. In this way, serving DU 804 can recognize the TA for one or more prepared target cells, which is information that the serving DU does not conventionally possess. Recognizing the TA for each of the one or more target cells identified to serving DU 804 enables serving DU 804 to identify which of the one or more target cells is a candidate for RACH-less HO, as will be discussed further below. Notification 708 to serving DU804 may include information indicating a RACH-less HO configuration for target DU806 instead of TA information. As previously mentioned, CU-CP808 recognizes the candidateness of target DUs for RACH-less handovers. Since serving DU804 learns from CU-CP808 whether a RACH-less HO is possible via information about the RACH-less HO configuration, serving DU804 does not need target cell TA information to determine whether a RACH-less HO is possible.

[0100] The priority information provided to Serving DU804 by CU-CP808 indicates the ranking of one or more target cells configured for RACH-less handover for selection by Serving DU804 as the target DU for handover. Thus, the priority information for a particular target cell may include a ranking (e.g., 1, 2, 3, etc.) indicating the target cell's rank in the ranking of all target cells that are RACH-less handover eligible, as identified by CU-CP808 to Serving DU804. CU-CP808 can determine rankings in various arbitrary ways. In some implementations, CU-CP808 can determine rankings based on resource availability, load, slice compatibility, and / or any other RRM criteria. The priority information can help Serving DU804 select one or more target cells for RACH-less HO, as will be discussed further below.

[0101] If there is only one target cell eligible for RACH-less handover, as in this exemplary embodiment where target DU806 is the only option, then it is the candidate for serving cell change, and since there is only one possible option for the HO identified for serving DU804, priority information may be omitted from the message to serving DU804 from CU-CP808.

[0102] In response to the notification of at least one LTM-prepared target DU cell (708), serving cell 804 stores received information relating to at least one LTM target cell (834). For example, serving cell 804 stores a list of LTM-prepared target cells and their respective TAs (or RACH-less HO configurations), and, if provided to serving DU 804, their respective priority information. Also in response to the notification of at least one target DU (708), serving cell 804 sends a UE CONTEXT MODIFICATION RESPONSE message to CU-CP 808 using the F1 communication interface (836). As shown in Figure 8a, the UE CONTEXT MODIFICATION RESPONSE message may include integrated cell group configuration information for each of the one or more target cells identified by CU-CP 808 for UE 802. The UE CONTEXT MODIFICATION RESPONSE message and the UE CONTEXT MODIFICATION RESPONSE message are defined by 3GPP, respectively. In this way, the serving DU804 can receive information about at least one target cell from the CU-CP808 and can acknowledge receipt to the CU-CP808 using a message already sent for HO in accordance with the 3GPP standard.

[0103] Upon receiving the UE context change response message, CU-CP808 sends an RRC reconfiguration message to UE802 in accordance with the 3GPP standard (838). The RRC reconfiguration message also includes LTM target cell configuration information (for example, provided from target DU806 to CU-CP808 in the transmitted (830) UE context setup response message).

[0104] Upon receiving the target cell configuration in the RRC reconfiguration message, UE802 transmits an L1 measurement report to serving DU804 in accordance with the 3GPP standard (840). The L1 measurement report provides serving DU804 with radio condition information measured by the UE of the configured target cell.

[0105] In response to receiving the (840)L1 measurement report transmitted from UE802, serving cell 804 selects a target cell capable of RACH-less HO from among the one or more LTM-prepared target cells identified for serving DU804 (710, 842). In this exemplary embodiment, since there is only one target cell identified by CU-CP808 as an LTM-prepared target cell for serving DU804 (target DU806), the selection of the serving cell (710, 842) is straightforward (serving DU804 selects target DU806 (710, 842)). If there are multiple LTM-prepared target cells that satisfy the handover criteria in serving DU804, serving DU804 is configured to select a target cell (if available) configured for RACH-less handover, as discussed here. If there are no LTM-prepared target cells that are candidates for RACH-less HO, a target cell may be selected according to conventional 3GPP procedures.

[0106] In implementations where multiple target cells are identified for the serving DU804 by CU-CP808, the serving cell's target cell selection (710, 842) may include determining whether one or more of the target cells have radio quality above a predetermined radio quality threshold. The predetermined radio quality threshold is determined by the radio conditions of the UE received by the serving DU804 from the UE802 in the L1 measurement report. In this way, the serving DU804 can take into account the specific needs of a particular UE802 involved in the HO when selecting target cells for HO (710, 842). In addition, the (840) L1 measurement report transmitted by the UE802 to the serving DU804 reports L1 measurement results, which may include RSRP (reference signal received power) as defined by 3GPP, for each of the multiple target cells known to the UE802, since it is provided to the UE802 in the RRC reconfiguration message by CU-CP808. Therefore, the serving DU804 can analyze the L1 measurement report received from the UE802 to determine whether one or more of the target cells have a radio quality that exceeds a predetermined radio quality threshold.

[0107] If only one of several target cells satisfies the UE's radio conditions, for example, if the radio quality of only one target cell exceeds a predetermined radio quality threshold, serving cell 804 selects that target cell (710, 842). If more than one target cell satisfies the UE's radio conditions, for example, if the radio quality of each of several target cells exceeds a predetermined radio quality threshold, any one of these target cells can meet the UE's needs. Therefore, serving cell 804 considers the timing advances of these target cells, transmitted from CU-CP 808 to serving DU 804 (832), in order to determine whether RACH-less HO is possible for any of these target cells. Such determination involves determining whether one or more of these target cells have (a) the same TA as serving cell 804, (b) a zero TA, or (c) a RACH-less handover configuration prepared therein. If the notification 708 from CU-CP 808 to serving DU 804 includes TA information, then (a) or (b) may occur. If notification 708 from CU-CP808 to serving DU804 includes RACH-less HO configuration information, then (c) may occur.

[0108] If RACH-less HO is possible for only one target cell that satisfies the UE's radio conditions, the serving DU804 selects that target cell (710, 842). Thus, the serving DU804 does not need to select a target cell with better report radio quality than the selected (710, 842) target cell in order to prioritize RACH-less handover. The implementation illustrated in Figure 8a provides an example of this scenario by showing that although both the first and second cells A and B satisfy the UE's radio conditions, RACH-less HO may be selected for the first cell A but not for the second cell B (710, 842).

[0109] If a RACH-less HO is possible for more than one target cell that satisfies the UE's radio conditions, the serving DU 804 takes into account priority information received from the CU-CP 808 (because there is more than one target cell prepared for LTM, priority information is sent from the CU-CP 808 to the serving DU 804 (832)). In particular, the serving DU 804 selects the target cell with the highest priority among the target cells that have radio quality above a predetermined radio quality threshold and are candidates for RACH-less handover (710, 842). Thus, the serving DU 804 does not have to select a target cell with better report radio quality than the selected (710, 842) target cell in order to prioritize RACH-less handover. In implementations where the serving DU 804 does not receive priority information from the CU-CP 808, the serving DU can randomly select a target cell from among the target cells that have radio quality above a predetermined radio quality threshold and are candidates for RACH-less handover (710, 842).

[0110] A serving DU804 that has selected a target cell (e.g., target DU806 in the implementation illustrated in Figure 8a) (710, 842) triggers a serving cell change (712) for the selected (710, 842) target cell. As shown in Figure 8a, triggering a serving cell change (712) may include the serving DU804 sending a MAC CE to the UE802 (844) that includes a serving cell change command and identifies the selected (710, 842) target cell to the UE802 via PCI or the like. Figure 8a reflects the aforementioned example by showing the PCI that identifies the first cell A (844) sent to the UE802.

[0111] The UE's receipt of the MAC CE indicates to the UE802 that an LTM Serving Cell Change (SCC) must be performed for the target cell identified for the UE802 (e.g., target DU806 in the example implementation in Figure 8a). Therefore, upon receiving the MAC CE from serving cell 804, the UE802 initiates a RACH-less HO to the target cell (714). As shown in Figure 8a, the UE802 initiating a RACH-less HO to the target cell (714) may include the UE802 accessing the target cell for a RACH-less HO without taking the RACH procedure for target DU806 in accordance with the 3GPP standard (846). In response to the UE802 accessing the target cell, target DU806 sends a Serving Cell Change Notice to CU-CP808 via the F1 communication interface, identifying target DU806 as the new current serving cell for the UE802 for at least one service by a unique identifier in accordance with the 3GPP standard (848). Furthermore, upon receiving a MAC CE from serving cell 804, UE802 sends an RRC reconfiguration acknowledgment message to CU-CP808 (850). Thus, CU-CP808 receives acknowledgments from both UE802 (via the RRC reconfiguration acknowledgment message indicating that RRC reconfiguration was successful in UE802) and target DU806 (via a serving cell change notification indicating that target DU806, which was handed over from serving DU804, is serving UE802 for at least one service).

[0112] In some implementations, such as those illustrated in Figure 8a, the CU-CP808 receives TA information from each of the one or more candidate target cells as part of the HO process (particularly after the CU-CP808 has decided to prepare one or more candidate target cells for LTM (824)). In this way, the CU-CP808 receives TA information on demand for possible HOs, whenever needed. Such on-demand UE-HO-related reception of TA information can alleviate the storage requirements of the CU-CP808 because the TA information is received only when needed and does not necessarily need to be stored for later use.

[0113] In some implementations, instead of the CU-CP808 receiving TA information from one or more candidate target cells as part of the HO process, the CU-CP808 receives TA information from the cell during the F1 setup procedure, in which the F1 communication interface is set up between the CU-CP808 and the cell. This procedure may be more granular, corresponding to each beam or beam group. Thus, a single cell may have multiple TAs, each corresponding to one or more beams / beam groups within the cell. This procedure is also feasible for smaller cells where the TAs do not fluctuate significantly. Therefore, the CU-CP808 receives and holds the TA information before the UE's HO needs are known, and is ready to transmit it to the serving cell during the HO process, as previously described with respect to Figures 7 and 8a.

[0114] Figure 8b illustrates the system of Figure 8a, which is configured to provide TA information from the cell to the CU-CP808 during the F1 setup procedure, relating to several implementations of the present subject. The F1 communication interface is set up between the DU and the CU-CP808 in accordance with the 3GPP standard.

[0115] As shown in Figure 8b, in the F1 setup procedure in which the F1 communication interface is set up between CU-CP808 and Serving DU804, Serving DU804 sends an "F1: setup request" to CU-CP808 containing TA information for all beam / beamgroups for each cell of Serving DU804 (852). Although Serving DU804 is shown in Figure 8b as having multiple cells including cell 1, cell 2, etc., Serving DU804 may consist of a single cell or two or more cells. Upon receiving the "F1: setup request" from Serving DU804, CU-CP808 sends an "F1: setup response" to Serving DU804 (854).

[0116] Furthermore, as shown in Figure 8b, in the F1 setup procedure in which the F1 communication interface is set up between CU-CP808 and target DU806, target DU806 sends an "F1: setup request" to CU-CP808 containing TA information for all beams / beam groups of each cell of target DU806 (856). In Figure 8b, target DU806 is shown as having multiple cells, including cell 1, cell 2, etc., but target DU806 may contain a single cell or two or more cells. In response to receiving the "F1: setup request" from target DU806, CU-CP808 sends an "F1: setup response" to target DU806 (858).

[0117] Figure 8b shows the F1 communication interface being set up between serving DU804 and CU-CP808 before the F1 communication interface is set up between target DU806 and CU-CP808, however, the F1 communication interface may be set up between target DU806 and CU-CP808 before the F1 communication interface is set up between serving DU804 and CU-CP808.

[0118] In some implementations, the subject may be configured to be implemented in system 900 as shown in Figure 9. System 900 may include one or more of the following: a processor 910, memory 920, storage device 930, and input / output device 940. Each of the components 910, 920, 930, and 940 may be interconnected using a system bus 950. The processor 910 may be configured to process instructions for execution within system 600. In some implementations, the processor 910 may be a single-threaded processor. In alternative implementations, the processor 910 may be a multi-threaded processor. The processor 910 may be further configured to process instructions stored in memory 920 or storage device 930, including receiving or transmitting information through the input / output device 940. Memory 920 can store information within system 900. In some implementations, memory 920 may be computer-readable media. In alternative implementations, memory 920 may be a volatile memory unit. Furthermore, in some implementations, memory 920 may be a non-volatile memory unit. Storage device 930 may provide mass storage for system 900. In some implementations, storage device 930 may be a computer-readable medium. In alternative implementations, storage device 930 may be a floppy disk device, a hard disk device, an optical disk device, a tape device, a non-volatile solid-state memory, or any other type of storage device. Input / output device 940 may be configured to provide input / output operations for system 900. In some implementations, input / output device 940 may include a keyboard and / or a pointing device. In alternative implementations, input / output device 940 may include a display unit for displaying a graphical user interface.

[0119] Figure 10 shows an exemplary method 1000 for prioritizing RACH-less LTM, relating to several implementations of the current subject. Method 1000 may be performed using, for example, the implementations shown and described with respect to Figures 1-8b.

[0120] Method 1000 includes receiving information from the base station's aggregate unit control plane (e.g., gNB-CU-CP504 in Figures 5a-5c, CU-CP604 in Figures 6a-6b, CU-CP808 in Figures 8a-8b, etc.) indicating a RACH-less handover configuration for multiple LTM target cells of the base station, or timing advance (TA) information for each of multiple target cells of the base station (e.g., DU508, 510 in Figure 5a, DU608, 610 in Figure 6a, 626, 628 in Figure 6b, target DU806 in Figures 8a-8b, etc.) at the base station's serving DU (e.g., serving DU804 in Figures 8a-8b, etc.). The method may also include, in the serving DU, identifying, based on the received information, at least one target cell in which a RACH-less handover of service to a user device currently being served by a serving cell (e.g., UE104 in Figures 1a-1c, UE622 in Figure 6a, etc.) can be performed. The method may also include, in the serving DU, selecting one of the at least one target cell identified for the handover of service to a UE from the serving DU to the selected target cell, and triggering the handover of service to the UE from the serving DU to the selected target cell.

[0121] In some implementations, the subject may include one or more of the following optional features:

[0122] In some implementations, identification may include determining whether one or more of the target cells have (a) the same TA as the serving cell, (b) a zero TA, or (c) a RACH-less handover configuration prepared therein.

[0123] In some implementations, the received information may also include the handover priority for each of the multiple target cells. Identifying can identify one or more target cells in which a RACH-less or RACH-based handover may be performed. Selecting may include selecting one or more target cells with a RACH-less configuration and the highest priority.

[0124] In some implementations, the method may also include determining in the serving DU whether one or more of the target cells have radio quality exceeding a predetermined radio quality threshold. The selection may be made from one or more of the determined target cells.

[0125] In some implementations, the CU-CP may receive information from one or more target DUs of a base station containing multiple LTM target cells, indicating a RACH-less handover configuration for multiple LTM target cells, or TA information for each of the multiple LTM target cells.

[0126] In some implementations, triggering this may involve sending a MAC CE message from the Serving DU to the UE.

[0127] In some implementations, the base station may have a disaggregated architecture (for example, as shown in Figures 6a and 6b).

[0128] In some implementations, a base station may include a Next Generation Radio Access Network (NG-RAN) node. Furthermore, an NG-RAN node may include a gNodeB (e.g., gNodeB in Figure 5a, gNodeB624 in Figure 6a or 6b, gNodeB in Figures 8a and 8b, etc.) or an eNodeB (e.g., eNodeB106 in Figures 1b-2, etc.). A serving cell and multiple target cells may each include a distributed unit of the base station (e.g., DU304 in Figure 3, DU508 in Figures 5a-5c, DU510 in Figure 5a, DU608 in Figure 6a, DU610 in Figure 6a, DU626 in Figure 6b, DU628 in Figure 6b, DU804, 806 in Figures 8a and 8b, etc.).

[0129] In some implementations, the base station may include at least one processor and at least one non-temporary storage medium (e.g., memory 920, storage device 930, etc., in Figure 9) that can store instructions causing at least one processor to execute method 1000 when executed by at least one processor (e.g., processor 910, etc., in Figure 9).

[0130] The systems and methods disclosed herein can be embodied in various forms, including, for example, data processors such as computers, which may also include databases, digital electronic circuits, firmware, software, or combinations thereof. Furthermore, the aforementioned features and other aspects and principles of the disclosed implementations can be implemented in various environments. Such environments and associated applications may be specifically configured to perform various processes and operations relating to the disclosed implementations, or they may include general-purpose computers or computing platforms that are selectively activated or reconfigured by code to provide the necessary functions. The processes disclosed herein are not inherently related to any particular computer, network, architecture, environment, or other device, and can be implemented by an appropriate combination of hardware, software, and / or firmware. For example, various general-purpose devices may be used with programs written in accordance with the teachings of the disclosed implementations, or they may be more convenient for configuring dedicated devices or systems to perform the necessary methods and techniques.

[0131] The systems and methods disclosed herein may be implemented as computer program products (i.e., computer programs tangibly embodied in information carriers (e.g., machine-readable storage devices or propagating signals) for execution by or control of the operation of data processing devices (e.g., programmable processors, computers, or multicomputers)). Computer programs may be written in any form of programming language, including compiled or interpreted languages, and may be deployed in any form, including standalone programs or modules, components, subroutines, or other units appropriate for use in a computing environment. Computer programs may be deployed to run on a single computer or multicomputers, distributed across multiple sites and interconnected by a communication network, either at a single site or across multiple sites.

[0132] As used herein, the term “user” can refer to any entity, including a person or a computer.

[0133] While sequential numbers such as "1st," "2nd," etc., may indicate order in some contexts, the sequential numbers used in this document do not necessarily imply order. For example, sequential numbers may simply be used to distinguish one item from another. For instance, distinguishing the first event from the second event does not necessarily imply a temporal order or a fixed reference system (just as the first event in one paragraph of the description may differ from the first event in another paragraph of the description).

[0134] The above description is for illustrative purposes only and is not intended to limit the scope of the invention as defined by the attached claims. Other implementations are also within the scope of the following claims.

[0135] These computer programs, software, software applications, applications, components, or code, which may also be referred to as programs, contain machine instructions for a programmable processor and may be implemented in high-level procedural and / or object-oriented programming languages ​​and / or assembly / machine languages. As used herein, the term “machine-readable medium” refers to any computer program product, apparatus and / or device (e.g., magnetic disks, optical disks, memory, programmable logic devices (PLDs)) used to provide machine instructions and / or data to a programmable processor, and includes machine-readable medium that receives machine instructions as machine-readable signals. The term “machine-readable signals” refers to any signals used to provide machine instructions and / or data to a programmable processor. Machine-readable medium may store such machine instructions non-temporarily (e.g., non-temporarily solid-state memory or magnetic hard drives or any equivalent storage medium). Alternatively, machine-readable medium may store such machine instructions in a temporary manner (e.g., processor cache or other random-access memory associated with one or more physical processor cores).

[0136] To provide user interaction, the subject described herein may be implemented on a computer having a display device such as a cathode ray tube (CRT) or liquid crystal display (LCD) monitor for displaying information to the user, and a pointing device such as a keyboard and mouse or trackball to which the user can provide input to the computer. Other types of devices may also be used to provide user interaction. For example, the feedback provided to the user may be any form of sensory feedback, such as visual feedback, auditory feedback, or haptic feedback. Input from the user may be received in any form, including but not limited to acoustic, speech, or haptic input.

[0137] The subject matter described herein may be implemented in a computing system that includes one or more backend components such as data servers, or one or more middleware components such as application servers, or one or more frontend components such as client computers having a graphical user interface or web browser on which users can interact with the implementation of the subject matter described herein, or any combination of such backend, middleware, or frontend components. The components of the system may be interconnected by digital data communication in any form or medium such as a communication network. Examples of communication networks include, but are not limited to, a local area network ("LAN"), a wide area network ("WAN"), and the internet.

[0138] A computing system may include clients and servers. Clients and servers are generally (but not limited to) separate from each other and typically interact through a communication network. The client-server relationship arises from computer programs running on each computer, and these programs have a client-server relationship with each other.

[0139] The implementations presented in the above description do not represent all implementations consistent with the subject matter described herein. Rather, they are merely some examples consistent with aspects related to the subject matter described herein. A few variations have been described in detail prior to this, but other modifications or additions are possible. In particular, further features and / or variations may be provided in addition to those presented herein. For example, the implementations described herein may be directed toward various combinations and subcombinations of the disclosed features, and / or combinations and subcombinations of some of the further features disclosed above. In addition, the logical flows shown in the accompanying diagrams and / or described herein do not necessarily require a specific order or sequence shown to achieve the desired result. Other implementations may also be within the scope of the following claims.

Claims

1. In a base station's serving distribution unit (DU), information is received from the base station's aggregation unit control plane (CU CP) indicating a random access channelless (RACH-less) handover configuration for multiple Layer 1 / Layer 2 trigger mobility (LTM) target cells of the base station, or timing advance (TA) information for each of the multiple LTM target cells of the base station. In the Serving DU, based on the received information, at least one of the target cells in which a RACH-less handover of the service currently being served by the Serving DU can be performed is identified. In the serving DU, select one of the at least one target cell identified for the handover of the service from the serving DU to the UE, and trigger the handover of the service from the serving DU to the selected target cell to the UE. A device comprising the serving DU configured to perform an operation comprising the following:

2. The apparatus according to claim 1, wherein the identification includes determining whether one or more of the plurality of target cells have (a) the same TA as the serving cell, (b) a zero TA, or (c) a RACH-less handover configuration prepared therein.

3. The received information includes the handover priority for each of the multiple target cells, The aforementioned identification identifies more than one of the target cells in which a RACH-less or RACH-based handover can be performed. The aforementioned selection includes selecting one of the more than one of the target cells that has a RACH-less configuration and the highest priority. The apparatus according to claim 1.

4. The operation further comprises determining in the serving DU whether one or more of the plurality of target cells have a radio quality that exceeds a predetermined radio quality threshold. The selection is made from the one or more determined target cells. The apparatus according to claim 1.

5. The apparatus according to claim 1, wherein the CU-CP receives the information indicating the RACH-less handover configuration for the plurality of LTM target cells, or the TA information for each of the plurality of LTM target cells, from one or more target DUs of the base station including the plurality of LTM target cells.

6. The apparatus according to claim 1, wherein the triggering includes transmitting a media access control (MAC) control element (CE) message from the serving DU to the UE.

7. The device according to claim 1, wherein the base station has a disaggregated architecture.

8. The apparatus according to claim 1, wherein the base station includes a Next Generation Radio Access Network (NG-RAN) node.

9. The apparatus according to claim 8, wherein the NG-RAN node includes a gNodeB or an eNodeB.

10. The apparatus according to claim 1, wherein the base station includes the at least one processor and the at least one non-temporary storage medium.

11. In a base station's serving distribution unit (DU), information is received from the base station's aggregation unit control plane (CU CP) indicating a random access channelless (RACH-less) handover configuration for multiple Layer 1 / Layer 2 trigger mobility (LTM) target cells of the base station, or timing advance (TA) information for each of the multiple LTM target cells of the base station. In the Serving DU, based on the received information, at least one of the target cells in which a RACH-less handover of the service currently being served by the Serving DU can be performed is identified. In the serving DU, select one of the at least one target cell identified for the handover of the service from the serving DU to the UE, and trigger the handover of the service from the serving DU to the selected target cell to the UE. A computer implementation method comprising the following:

12. The method according to claim 11, wherein the identification includes determining whether one or more of the plurality of target cells have (a) the same TA as the serving cell, (b) a zero TA, or (c) a RACH-less handover configuration prepared therein.

13. The received information includes the handover priority for each of the multiple target cells, The aforementioned identification identifies more than one of the target cells in which a RACH-less or RACH-based handover can be performed. The aforementioned selection includes selecting one of the more than one of the target cells that has a RACH-less configuration and the highest priority. The method according to claim 11.

14. The serving DU further includes determining whether one or more of the multiple target cells have a wireless quality exceeding a predetermined wireless quality threshold. The selection is made from the one or more determined target cells. The method according to claim 11.

15. The method according to claim 11, wherein the base station includes a Next Generation Radio Access Network (NG-RAN) node.

16. In a base station's serving distribution unit (DU), information is received from the base station's aggregation unit control plane (CU CP) indicating a random access channelless (RACH-less) handover configuration for multiple Layer 1 / Layer 2 trigger mobility (LTM) target cells of the base station, or timing advance (TA) information for each of the multiple LTM target cells of the base station. In the Serving DU, based on the received information, at least one of the target cells in which a RACH-less handover of the service currently being served by the Serving DU can be performed is identified. In the serving DU, select one of the at least one target cell identified for the handover of the service from the serving DU to the UE, and trigger the handover of the service from the serving DU to the selected target cell to the UE. A program that causes one or more computers to perform an operation that includes [specific features / functions].

17. The program according to claim 16, wherein the identification includes determining whether one or more of the plurality of target cells have (a) the same TA as the serving cell, (b) a zero TA, or (c) a RACH-less handover configuration prepared therein.

18. The received information includes the handover priority for each of the multiple target cells, The aforementioned identification identifies more than one of the target cells in which a RACH-less or RACH-based handover can be performed. The aforementioned selection includes selecting one of the more than one of the target cells that has a RACH-less configuration and the highest priority. L as described in claim 16.

19. The operation further comprises determining in the serving DU whether one or more of the plurality of target cells have a radio quality that exceeds a predetermined radio quality threshold. The selection is made from the one or more determined target cells. L as described in claim 16.

20. The program according to claim 16, wherein the base station includes a Next Generation Radio Access Network (NG-RAN) node.

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