Layer 1 / layer 2 triggered mobility enabling random access-free channels

Abstract

In general, the current subject matter relates to implementing Layer 1 / Layer 2 triggered mobility (LTM) without random access channel layer (RACH-free). In some implementations, implementing RACH-free LTM may include receiving, at at least one LTM target cell of a base station, information indicating whether a handover (HO) of a service of a user equipment (UE) currently served by a serving DU of the base station can be a random access channel-free (RACH-free) HO to the at least one target cell or a RACH-based HO to the at least one LTM target cell, and preparing the at least one LTM target cell for one of the RACH-free HO and the RACH-based HO based on the information received at the at least one LTM target cell.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of Indian Patent Application No. 202221056932 filed on October 4, 2022, titled “Method and system to realize RACH-less HO for LLM in inter gNB-DU scenario”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] In some implementations, the present subject matter relates to telecommunication systems, and more particularly to implementing Layer 1 / Layer 2 Triggered Mobility (LTM) without a Random Access Channel (without RACH). Background Art

[0004] In today's world, cellular networks provide on-demand communication capabilities for individuals and business entities. Typically, a cellular network is a wireless network that can be distributed over land areas (called cells). Each such cell is served by at least one fixed-position transceiver, which is called a cell site or base station. Each cell can use a different set of frequencies from its neighboring cells to avoid interference and provide better service within each cell. When cells are linked together, they provide radio coverage over a wide geographic area, which enables a large number of mobile phones and / or other wireless devices or portable transceivers to communicate with each other and with fixed transceivers and phones anywhere in the network. Such communications are performed through base stations and can be completed even if the mobile transceiver passes through more than one cell during transmission. Major wireless communication providers have deployed such cell sites around the world, allowing communicating mobile phones and mobile computing devices to connect to the public switched telephone network and the public Internet.

[0005] A mobile phone is a portable telephone that is capable of receiving and / or making telephone and / or data calls through a cell site or transmission tower by transmitting signals to and from the mobile phone using radio waves. Given the large number of mobile phone users, current mobile phone networks provide limited and shared resources. In this regard, cell sites and mobile phones can change frequencies and use low-power transmitters to allow many callers to use the network simultaneously with less interference. The coverage area of ​​a cell site can depend on the specific geographic location and / or the number of users who may potentially use the network. For example, in cities, the range of a cell site can be up to about 1 / 2 mile; in rural areas, this range can be up to 5 miles; in some areas, users can receive signals from cell sites up to 25 miles away.

[0006] The following are some examples of digital cellular technologies that are being used by communications 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), Data AMPS (IS-136 / TDMA), and Integrated Digital Enhanced Network (iDEN). Long Term Evolution or 4G LTE, developed by the 3rd Generation Partnership Project (3GPP) standards body, is a standard for high-speed data wireless communications for mobile phones and data terminals. 5G standards are currently being developed and deployed. 3GPP cellular technologies such as LTE and 5G NR are evolutions of earlier 3GPP technologies such as GSM / EDGE and UMTS / HSPA digital cellular technologies and allow for increased capacity and speed by using different radio interfaces and core network improvements.

[0007] A cellular network can be divided into a radio access network and a core network. The radio access network (RAN) may include network functions that may handle radio layer communication processing. The core network may include network functions that may handle higher layer communications, such as Internet Protocol (IP), transport layer, and application layer. In some cases, the RAN functions may be split into baseband unit functions and radio unit functions, where, for example, a radio unit connected to a baseband unit via a fronthaul network may be responsible for lower layer processing of a radio physical layer, while the baseband unit may be responsible for higher layer radio protocols, such as MAC, RLC, etc.

[0008] A base station for a 5G cellular network may include a centralized unit (CU), one or more distributed units (DUs) communicatively coupled to the CU, and one or more radio units (RUs), each RU being communicatively coupled to at least one of the one or more DUs, and each RU being configured to be communicatively coupled to one or more mobile phones and / or other user equipment (UEs). The CU may be logically split into a control plane portion CU-CP and one or more user plane portions (CU-UPs). During the communication coupling process between the UE and the base station, the DU supporting the UE may change. Time synchronization is established during the random access channel (RACH) process between the UE and the newly supported DU so that communication between the UE and the newly supported DU proceeds correctly. However, when a contention-based RACH process rather than a contention-free RACH process must occur, such a switch from one DU to another DU requires more time. This increase in the time to complete the switch increases the switching delay and thereby increases the user plane interruption time. Summary of the invention

[0009] In some implementations, the current subject matter relates to a computer-implemented method. The method may include receiving information at at least one Layer 1 / Layer 2 Triggered Mobility (LTM) target distributed unit (DU) of a base station, the information indicating that a handover (HO) of a service of a user equipment (UE) currently served by a serving DU of the base station can be a random access channel-less (RACH-less) HO to at least one LTM target cell of the target DU or a RACH-based HO to at least one LTM target cell. The method may also include preparing at least one LTM target cell for one of a RACH-less HO and a RACH-based HO based on the information received at the at least one LTM target cell.

[0010] The method may allow HO from one cell of the base station to another cell of the base station to take less time, because HO from the serving cell to one of the at least one target cell may have been prepared at each of the one or more target cells to include a contention-free RACH procedure (for RACH-free HO) or a contention-based RACH procedure (for RACH-based HO). Therefore, handover delay may be reduced, and thus user plane interruption time may be reduced.

[0011] In some implementations, the current subject matter can include one or more of the following optional features.

[0012] In some implementations, the information may include timing advance (TA) information of the UE in the serving DU, the TA information of the UE in the serving cell is either (a) the same TA as the TA in the at least one LTM target cell, or (b) the TA is zero, which may indicate that the HO to the at least one LTM target cell can be a RACH-free HO, and the TA information of the UE in the serving cell is neither (a) the same TA as the TA in the at least one LTM target cell, nor (b) the TA is zero, which may indicate that the HO to the at least one LTM target cell can be a RACH-based HO. In addition, at least one LTM target DU may receive the TA information of the UE in the serving DU in a message from the serving DU, and the method may include the at least one LTM target DU indicating to the serving DU whether the prepared LTM target cell configuration is a RACH-free configuration or a RACH-based configuration, or the at least one LTM target DU may receive the TA information of the UE in the serving DU in a message from a centralized unit control plane (CU-CP) of the base station, and the method may include the at least one LTM target DU indicating to the CU-CP whether the prepared LTM target cell configuration is a RACH-free configuration or a RACH-based configuration. In addition, during the establishment of the F1 communication interface between the service DU and the CU-CP, the CU-CP can receive the TA information of the UE in the service DU from the service DU, or after the F1 communication interface has been established between the service DU and the CU-CP, the CU-CP can receive the TA information of the UE in the service DU from the service DU.

[0013] In some implementations, at least one LTM target cell may be included in at least one DU of the base station that is not a serving DU.

[0014] In some implementations, the service DU may select one of the prepared at least one LTM target cells for handover of the UE's service from the service DU, and the service DU may trigger handover of the UE's service from the service DU to the selected LTM target cell. In addition, the service DU may determine which one or more of the at least one LTM target cells have a radio quality higher than a predetermined threshold radio quality, and the selection may be made among the determined one or more LTM target cells; and / or the triggering may include the service DU sending a media access control (MAC) control element (CE) message to the UE.

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

[0016] In some implementations, the base station may include a next generation radio access network (NG-RAN) node. In addition, the NG-RAN node may include a gNodeB or an ng-eNodeB.

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

[0018] A non-transient computer program product (i.e., a physically embodied computer program product) storing instructions is also described, which when executed by one or more data processors of one or more computing systems causes at least one data processor to perform the operations described herein. Similarly, a computer system is also described, which may include one or more data processors and a memory coupled to the one or more data processors. The memory may temporarily or permanently store instructions that cause 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 between two or more computing systems. Such computing systems may be connected via one or more connections, and data and / or commands or other instructions may be exchanged, including but not limited to connections made via a network (e.g., the Internet, a wireless wide area network, a local area network, a wide area network, a wired network, etc.), connections made via direct connections between one or more computing systems in a plurality of computing systems, etc.

[0019] The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate certain aspects of the subject matter disclosed herein and, together with the description, help explain some of the principles associated with the disclosed implementations.

[0021] Figure 1a An exemplary conventional Long Term Evolution (LTE) communication system is illustrated;

[0022] Figure 1b Pictured Figure 1a Additional details of the exemplary LTE system shown;

[0023] Figure 1c Pictured Figure 1a Further details of the Evolved Packet Core of the exemplary LTE system are shown;

[0024] Figure 1d Pictured Figure 1a An exemplary evolved Node B of an exemplary LTE system is shown;

[0025] Figure 2 Pictured Figure 1a-1dOther details of the eNodeB shown;

[0026] Figure 3 illustrates an exemplary virtual radio access network according to some implementations of the current subject matter;

[0027] Figure 4 An exemplary 3GPP split architecture is illustrated to provide use of higher frequency bands to its users;

[0028] Figure 5a An exemplary 5G wireless communication system is illustrated;

[0029] Figure 5b An exemplary layer architecture of a split gNB and / or split ng-eNB (e.g., a next generation eNB that may be connected to a 5GC) is illustrated;

[0030] Figure 5c Pictured Figure 5a-Figure 5b Example functional split in the gNB architecture shown;

[0031] Figure 6a An exemplary system according to some implementations of the current subject matter is illustrated;

[0032] Figure 6b Illustration of some implementations based on the current topic Figure 6a Exemplary alternative configurations of systems;

[0033] Figure 7 An exemplary method according to some implementations of the current subject matter is illustrated;

[0034] Figure 8a Another exemplary system according to some implementations of the current subject matter is illustrated;

[0035] Figure 8b Another exemplary system according to some implementations of the current subject matter is illustrated;

[0036] Figure 8c illustrates yet another exemplary system according to some implementations of the current subject matter;

[0037] Figure 8d illustrates yet another exemplary system according to some implementations of the current subject matter;

[0038] Figure 8e Another exemplary system according to some implementations of the current subject matter is illustrated;

[0039] Fig. 9 illustrates yet another exemplary system according to some implementations of the current subject matter; and

[0040] Fig.10 Yet another exemplary method according to some implementations of the current subject matter is illustrated. DETAILED DESCRIPTION

[0041] The current subject matter can provide systems and methods that can be implemented in wireless communication systems. Such systems can include various wireless communication systems, including 5G new radio communication systems, long term evolution communication systems, etc.

[0042] In general, the present subject matter relates to implementing LTM without RACH.

[0043] In some implementations of the current subject matter, a timing advance (TA) of a serving cell of a base station of a wireless communication system may be used to prepare at least one target cell of the base station for LTM. For example, by receiving the TA of the serving cell from a CU-CP of a base station communicatively coupled to the serving cell and the at least one target cell, the TA of the serving cell may be notified to the at least one target cell. Notifying the at least one target cell of the TA of the serving cell may allow each of the one or more target cells to prepare for a RACH-less (also referred to as RACH-free) handover (HO) or RACH-based HO of a user equipment (UE) communicatively coupled to the base station from the serving cell. Therefore, a HO from one cell of the base station to another cell of the base station may require less time because the HO from the serving cell to one of the at least one target cells has been prepared at each of the one or more target cells to include a contention-free RACH procedure (for RACH-less HO) or a contention-based RACH procedure (for RACH-based HO). Therefore, handover delays may be reduced, and user plane interruption time may thereby be reduced.

[0044] Layer 1 / Layer 2 Triggered Mobility (LTM) is an updated term for Lower Layer Mobility (LLM). RAN2 has agreed on a definition of LTM. In general, LTM is a mobility procedure that allows the network to switch a UE from a source cell to a target cell without necessarily having to have a synchronized reconfiguration. In particular, based on the received L1 measurements, the network may indicate in L2 signaling (e.g. messages such as MAC CE) the beams belonging to LTM candidate cells to which the UE should perform an LTM cell switching procedure. Before performing the LTM cell switching procedure, at least one LTM candidate cell configuration is provided to the UE by the network.

[0045] 3GPP standards that define one or more aspects that may be relevant to the present subject matter 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)”. Standards of the O-RAN Alliance may also be relevant to one or more aspects of the present subject matter.

[0046] One or more aspects of the current subject matter may be incorporated into a transmitter and / or receiver component of a base station (e.g., gNodeB, eNodeB, etc.) in such a communication system. The following is a general discussion of long term evolution communication systems and 5G new radio communication systems.

[0047] Ⅰ. Long Term Evolution Communication System

[0048] Figure 1a-Figure 1c and Figure 2 An exemplary conventional Long Term Evolution (LTE) communication system 100 and its various components are illustrated. As is known in the business, the LTE system or 4G LTE is governed by a standard for high-speed data wireless communications for mobile phones and data terminals. The standard is 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 standard is developed by 3GPP (3rd Generation Partnership Project).

[0049] like Figure 1a As shown, the 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, wherein the EUTRAN 102 and the EPC 108 provide communication between a user equipment 104 and the PDN 101. The EUTRAN 102 may include a plurality of evolved Node Bs (eNodeBs or ENODEBs or eNodeBs or eNBs) or base stations 106 (a, b, c) (e.g., Figure 1b104). The user equipment 104 may be a mobile phone, a smart phone, a tablet computer, a personal computer, a personal digital assistant (PDA), a server, a data terminal and / or any other type of user equipment, and / or any combination thereof. The user equipment 104 may be connected to the EPC 108 via any eNodeB 106, and ultimately to the PDN 101. Typically, the user equipment 104 may be connected to the eNodeB 106 that is closest in distance. In the LTE system 100, the EUTRAN 102 and the EPC 108 work together to provide connectivity, mobility, and services for the user equipment 104.

[0050] Figure 1b Pictured Figure 1a 102. As described above, EUTRAN 102 includes multiple eNodeBs 106, also known as cell sites. The eNodeBs 106 provide radio functions and perform key control functions, including scheduling of air link resources or radio resource management, active mode mobility or handover, and admission control of services. The eNodeBs 106 are responsible for selecting which mobility management entities (MMEs, such as Figure 1c The eNodeBs 106 (shown in FIG. 1 ) will serve the user equipment 104 and are responsible for protocol features such as header compression and encryption. The eNodeBs 106 that make up the EUTRAN 102 cooperate with each other to perform radio resource management and handover.

[0051] Communication between the user equipment 104 and the eNodeB 106 is performed via an air interface 122 (also referred to as an LTE-Uu interface). Figure 1b As shown, the air interface 122 provides communication between the user equipment 104b and the eNodeB 106a. The air interface 122 uses orthogonal frequency division multiple access (OFDMA) and single carrier frequency division multiple access (SC-FDMA), a variant of OFDMA, on the downlink and uplink, respectively. OFDMA allows the use of a variety of known antenna technologies, such as multiple input multiple output (MIMO).

[0052] The air interface 122 uses various protocols, including radio resource control (RRC) for signaling between the user equipment 104 and the eNodeB 106 and non-access stratum (NAS) for signaling between the user equipment 104 and the MME (eg, Figure 1c In addition to signaling, user traffic is transmitted between user equipment 104 and eNodeB 106. Both signaling and traffic in system 100 are carried by physical layer (PHY) channels.

[0053] Multiple eNodeBs 106 may be interconnected with each other using X2 interfaces 130 (a, b, c). Figure 1bAs shown, X2 interface 130a provides interconnection between eNodeB 106a and eNodeB 106b; X2 interface 130b provides interconnection between eNodeB 106a and eNodeB 106c; X2 interface 130c provides interconnection between eNodeB 106b and eNodeB 106c. X2 interface can be established between two eNodeBs to provide signal exchange, which may include load or interference related information and handover related information. eNodeB 106 communicates with evolved packet core 108 via S1 interface 124 (a, b, c). S1 interface 124 can be split into two interfaces: one interface is used for control plane (such as Figure 1c The control plane interface (S1-MME interface) 128 in FIG. 128 ) and the other interface is used for the user plane (such as Figure 1c The user plane interface (S1-U interface) 125 is shown in FIG.

[0054] The EPC 108 establishes and enforces quality of service (QoS) for user services and allows the user device 104 to maintain a consistent Internet Protocol (IP) address when moving. It should be noted that each node in the network 100 has its own IP address. The EPC 108 is designed to interoperate with traditional wireless networks. The EPC 108 is also designed to separate the control plane (i.e., signaling) and the user plane (i.e., business) in the core network architecture, which allows for greater flexibility and independent scalability of control and user data functions.

[0055] The EPC 108 architecture is dedicated to packet data and is Figure 1c 1. The EPC 108 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 of the EPC 108), and a policy control and charging rules function (PCRF) 118. Some of them (such as S-GW, P-GW, MME, and HSS) are usually combined into nodes according to the manufacturer's implementation.

[0056] The S-GW 110 acts as an IP packet data router and is the bearer path anchor for the user equipment in the EPC 108. Therefore, when the user equipment moves from one eNodeB 106 to another during mobility operation, the S-GW 110 remains unchanged and the bearer path toward the EUTRAN 102 is switched to talk to the new eNodeB 106 serving the user equipment 104. If the user equipment 104 moves to the domain of another S-GW 110, the MME 114 transfers all the bearer paths of the user equipment to the new S-GW. The S-GW 110 establishes a bearer path to one or more P-GWs 112 for the user equipment. If downlink data for an idle user equipment is received, the S-GW 110 buffers the downlink packets and requests the MME 114 to locate and reestablish the bearer path to and through the EUTRAN 102.

[0057] P-GW 112 is the interface between EPC 108 (and user equipment 104 and EUTRAN 102) and PDN 101 (such as Figure 1a 112). P-GW 112 acts as a router for user traffic and performs functions on behalf of user equipment. These include allocating IP addresses to user equipment, packet filtering of downstream user traffic to ensure that it is placed on the appropriate bearer path, and implementing downstream QoS (including data rate). Depending on the services the subscriber is using, there may be multiple user data bearer paths between the user equipment 104 and the P-GW 112. A subscriber may use services on PDNs served by different P-GWs, in which case the user equipment has at least one bearer path established to each P-GW 112. During a handover of a user equipment from one eNodeB to another, if the S-GW 110 is also changing, the bearer path from the P-GW 112 is switched to the new S-GW.

[0058] The MME 114 manages the user equipment 104 within the EPC 108, including managing subscriber authentication, maintaining the context of the authenticated user equipment 104, establishing data bearer paths for user traffic in the network, and tracking the location of idle mobile devices that have not yet been detached from the network. For idle user equipment 104 that needs to be reconnected to the access network to receive downstream data, the MME 114 initiates paging to locate the user equipment and reestablishes the bearer path to and through the EUTRAN 102. The MME 114 for a particular user equipment 104 is selected by the eNodeB 106, from which the user equipment 104 initiates system access. For the purpose of load sharing and redundancy, the MME is usually part of a set of MMEs in the EPC 108. When establishing a user's data bearer path, the MME 114 is responsible for selecting the P-GW 112 and S-GW 110, which will constitute the end of the data path through the EPC 108.

[0059] PCRF 118 is responsible for policy control decisions and controls flow-based charging functions in the Policy Control Enforcement Function (PCEF) located in P-GW 110. PCRF 118 provides QoS authorization (QoS Class Identifier (QCI) and bit rate) which determines how a particular data flow will be handled in the PCEF and ensures that this complies with the user's subscription profile.

[0060] As described above, IP services 119 are provided by PDN 101 (e.g. Figure 1a shown).

[0061] Figure 1dAn exemplary structure of an eNodeB 106 is illustrated. The eNodeB 106 may include at least one remote radio head (RRH) 132 (typically there may be three RRHs 132) and a baseband unit (BBU) 134. The RRH 132 may be connected to an antenna 136. The RRH 132 and the BBU 134 may be connected using an optical interface compliant with the Common Public Radio Interface (CPRI) / Enhanced CPRI (eCPRI) 142 standard specification, or using RRH-specific customized control and user plane framing methods, or using control and user plane framing methods compliant with the O-RAN Alliance. The operation of the eNodeB 106 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 transmission 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 BBU 134 can be responsible for digital baseband signal processing, termination of S1 lines, termination of X2 lines, and call processing and monitoring control processing. From the EPC 108 ( Figure 1d IP packets received by the RRH 132 (not shown) may be modulated into digital baseband signals and transmitted to the RRH 132. Conversely, digital baseband signals received from the RRH 132 may be demodulated into IP packets for transmission to the EPC 108.

[0062] RRH 132 may use antenna 136 to send and receive wireless signals. RRH 132 may convert (using converter (CONV) 140) the digital baseband signal from BBU 134 into a radio frequency (RF) signal and power amplify (using amplifier (AMP) 138) it for transmission to user equipment 104 ( Figure 1d Conversely, RF signals received from user equipment 104 are amplified (using AMP 138 ) and converted (using CONV 140 ) to digital baseband signals for transmission to BBU 134 .

[0063] Figure 2Additional details of an exemplary eNodeB 106 are illustrated. The eNodeB 106 includes multiple layers: LTE Layer 1 202, LTE Layer 2 204, and LTE Layer 3 206. LTE Layer 1 includes the physical layer (PHY). LTE Layer 2 includes Media Access Control (MAC), Radio Link Control (RLC), 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, Connection Mobility Control, and Radio Resource Management (RRM). The RLC protocol is an automatic repeat request (ARQ) segmentation protocol used on the cellular air interface. The RRC protocol handles the control plane signaling of LTE Layer 3 between user equipment and EUTRAN. RRC includes functions such as connection establishment and release, system information broadcast, radio bearer establishment / reconfiguration and release, RRC connection mobility procedures, paging notification and release, and outer loop power control. PDCP performs IP header compression and decompression, transmission of user data, and maintenance of sequence numbers for radio bearers. As Figure 1d As shown, the BBU 134 may include LTE layers L1-L3.

[0064] One of the main functions of eNodeB 106 is radio resource management, which includes scheduling both uplink and downlink air interface resources for user equipment 104, controlling bearer resources and admission control. As an agent of EPC 108, eNodeB 106 is responsible for the transmission of paging messages used to locate mobile devices when the mobile device is idle. eNodeB 106 also transmits common control channel information, header compression, encryption and decryption of user data sent over the air, and establishes switching reports and triggering criteria over the air. As described above, eNodeB 106 can collaborate with other eNodeBs 106 via the X2 interface to perform switching and interference management. eNodeB 106 communicates with the MME of EPC via the S1-MME interface and communicates with the S-GW using the S1-U interface. In addition, eNodeB 106 exchanges user data with the S-GW via the S1-U interface. eNodeB 106 and EPC 108 have a many-to-many relationship to support load sharing and redundancy between MME and S-GW. The eNodeB 106 selects an MME from a group of MMEs so that multiple MMEs can share the load to avoid congestion.

[0065] II.5G NR Wireless Communication Network

[0066] In some implementations, the current subject matter relates to a 5G New Radio (NR) communication system. 5G NR is the next telecommunication standard beyond the 4G / IMT Advanced standard. 5G networks provide higher capacity than current 4G, allowing more mobile broadband users per unit area, and allowing higher and / or unlimited gigabytes of data to be consumed per month and per user. This can allow users to stream high-definition media for hours a day using mobile devices, even when Wi-Fi networks are not possible. 5G networks have improved support for inter-device communication, lower costs, lower latency than 4G devices, lower battery consumption, and the like. Compared to existing systems, such networks have data rates of tens of megabits per second for a large number of users, data rates of 100Mb / s for metropolitan areas, data rates of 1Gb / s for users in limited areas (e.g., office buildings) at the same time, a large number of simultaneous connections for wireless sensor networks, enhanced spectrum efficiency, improved coverage, enhanced signaling efficiency, 1-10ms latency, and reduced latency.

[0067] Figure 3 An exemplary virtual radio access network 300 is illustrated. The network 300 can provide communications between various components, including base stations (e.g., eNodeBs, gNodeBs) 301, radio equipment 303, centralized units 302, digital units 304, and radio equipment 306. The components in the system 300 can be communicatively coupled to a core using backhaul links 305. The centralized unit (CU) 302 can be communicatively coupled to a distributed unit (DU) 304 using a midhaul connection 308. The radio frequency (RU) component 306 can be communicatively coupled to the DU 304 using a fronthaul connection 310.

[0068] In some implementations, the CU 302 can provide smart communication capabilities to one or more DU units 304. The units 302, 304 can include one or more base stations, macro base stations, micro base stations, remote radio heads, etc., and / or any combination thereof.

[0069] In a lower layer split architecture environment, the CPRI bandwidth requirement for NR can be 100s of Gb / s. CPRI compression can be implemented in the DU and RU (e.g. Figure 3 ). In the 5G communication system, compressed CPRI on Ethernet frames is called eCPRI and is the recommended fronthaul network. This architecture can achieve standardization of fronthaul / midhaul, which can include higher layer split (e.g., option 2 or option 3-1 (upper / lower RLC split architecture)) and fronthaul with L1 split architecture (option 7).

[0070] In some implementations, a lower layer split architecture (e.g., Option 7) may include a receiver in the uplink, joint processing of multiple transmission points (TPs) for both DL / UL, and transmission bandwidth and latency requirements to facilitate deployment. In addition, the lower layer split architecture of the current subject matter may include a split between cell-level processing and user-level processing, which may include cell-level processing in a remote unit (RU) and user-level processing in a DU. In addition, using the lower layer split architecture of the current subject matter, frequency domain samples may be transmitted via Ethernet fronthaul, where the frequency domain samples may be compressed to reduce the fronthaul bandwidth.

[0071] Figure 4 An exemplary communication system 400 is illustrated that can implement 5G technology and can provide its users with the use of higher frequency bands (e.g., greater than 10 GHz). The system 400 can include a macro cell 402 and small cells 404, 406.

[0072] The mobile device 408 can be configured to communicate with one or more of the small cells 404 and 406. The system 400 can allow the control plane (C-plane) and the user plane (U-plane) to be split between the macro cell 402 and the small cells 404 and 406, where the C-plane and the U-plane use different frequency bands. In particular, the small cells 404 and 406 can be configured to utilize higher frequency bands when communicating with the mobile device 408. The macro cell 402 can utilize existing cellular frequency bands for C-plane communications. The mobile device 408 can be communicatively coupled via the U-plane 412, where the small cell (e.g., the small cell 406) can provide higher data rates and more flexible / cost-effective / energy-efficient operation. The macro cell 402 can maintain good connectivity and mobility via the C-plane 410. In addition, in some cases, LTE and NR can be transmitted on the same frequency.

[0073] Figure 5a An exemplary 5G wireless communication system 500 according to some implementations of the current subject matter is illustrated. According to option 7-2, the system 500 can be configured to have a lower layer split architecture. The system 500 may include a core network 502 (e.g., a 5G core) and one or more gNodeBs (or gNBs), wherein the gNB may have a centralized unit gNB-CU. The gNB-CU may be logically split 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 specified in the 3GPP standard). The control plane portion 504 may be configured to be responsible for executing the RRC protocol and the PDCP protocol of the radio stack.

[0074] In accordance with a higher layer split architecture, the control plane and user plane portions 504, 506 of the centralized unit of the gNB may be configured to be communicatively coupled to one or more distributed units (DU) 508, 510. The distributed units 508, 510 may be configured to execute the upper portions of the RLC, MAC, and PHY layer protocols of the radio stack. The control plane portion 504 may be configured to be communicatively coupled to the distributed units 508, 510 using an F1-C communication interface 516, and the user plane portion 506 may be configured to be communicatively coupled to the distributed units 508, 510 using an F1-U communication interface 518. The distributed units 508, 510 may be coupled to one or more remote radio units (RU) 512 via a fronthaul network 520 (which may include one or more switches, links, etc.), which in turn communicate with one or more user equipment (UE) devices. Figure 5a The remote radio unit 512 may be configured to execute the lower portion of the PHY layer protocol and provide antenna capabilities to the remote unit for communication with the user equipment (similar to the above in conjunction with Figure 1a-Figure 2 for discussion).

[0075] Figure 5b An exemplary layer architecture 530 for split gNB is illustrated. The architecture 530 may be Figure 5a The communication system 500 shown is implemented in a virtualized decomposed radio access network (RAN) architecture, whereby layers L1, L2, L3 and radio processing can be virtualized and decomposed in (multiple) centralized units, (multiple) distributed units and (multiple) radio units. Figure 5b As shown, the gNB-DU 508 can be communicatively coupled to the gNB-CU-CP control plane portion 504 (also in Figure 5a ) and a gNB-CU-UP user plane part 506. Each of components 504, 506, 508 may be configured to include one or more layers.

[0076] The gNB-DU 508 may include an RLC layer, a MAC layer, and a PHY layer, as well as various communication sublayers. These may include an F1 Application Protocol (F1-AP) sublayer, a GPRS Tunneling Protocol (GTPU) sublayer, a Stream Control Transmission Protocol (SCTP) sublayer, a User Datagram Protocol (UDP) sublayer, and an Internet Protocol (IP) sublayer. As described above, the distributed unit 508 may be communicatively coupled to a control plane portion 504 of the centralized unit, which may also include F1-AP, SCTP, and IP sublayers, as well as a Radio Resource Control and PDCP Control (PDCP-C) sublayer. In addition, the distributed unit 508 may also be communicatively coupled to a user plane portion 506 of the centralized unit of the gNB. The user plane portion 506 may include a Service Data Adaptation Protocol (SDAP), a PDCP User (PDCP-U), GTPU, UDP, and IP sublayers.

[0077] Figure 5c Pictured Figure 5a-Figure 5b Example functional split in the gNB architecture shown in Figure 1. Figure 5c As shown, the gNB-DU 508 may be communicatively coupled to the gNB-CU-CP 504 and the gNB-CU-UP 506 using an F1-C communication interface. The gNB-CU-CP 504 and the gNB-CU-UP 506 may be communicatively coupled using an E1 communication interface. The higher portion of the PHY layer (or Layer 1) may be performed by the gNB-DU 508, while the lower portion of the PHY layer may be performed by the RU ( Figure 5c Execute as shown in the figure. Figure 5c As shown, the RRC and PDCP-C parts may be performed by the control plane part 504 , and the SDAP and PDCP-U parts may be performed by the user plane part 506 .

[0078] Some of the functions of the PHY layer in a 5G communication network may include error detection on transport channels and indication to higher layers, FEC encoding / decoding of transport channels, hybrid ARQ soft combining, rate matching of coded transport channels to physical channels, mapping of coded transport channels to physical channels, power weighting of physical channels, modulation and demodulation of physical channels, frequency and time synchronization, radio characteristic measurement and indication to higher layers, MIMO antenna processing, digital and analog beamforming, RF processing, and other functions.

[0079] The MAC sublayer of layer 2 can perform beam management, random access procedures, mapping between logical channels and transport channels, concatenation of multiple MAC service data units (SDUs) belonging to one logical channel into a transport block (TB), multiplexing / demultiplexing of SDUs belonging to logical channels on transport channels to / from the physical layer for TB delivery, scheduling information reporting, error correction through HARQ, priority handling between logical channels of one UE, priority handling between UEs with the help of dynamic scheduling, transport format selection, and other functions. The functions of the RLC sublayer may include transmission of higher layer packet data units (PDUs), error correction through ARQ, reordering of data PDUs, duplication and protocol error detection, reconstruction, etc. The PDCP sublayer may be responsible for transmission of user data, various functions during reconstruction, retransmission of SDUs, SDU discard in uplink, transmission of control plane data, etc.

[0080] The RRC sublayer of Layer 3 may perform broadcasting system information to NAS and AS, establishment, maintenance, and release of RRC connections, security, establishment, configuration, maintenance, and release of point-to-point radio bearers, mobility functions, reporting, and other functions.

[0081] III. Implementing LTM without RACH

[0082]

[0013] In some implementations of the current subject matter, for a UE communicatively coupled to a base station of a wireless communication system, a RACH-less HO from one cell to another can be implemented.

[0083] Layer 1 / Layer 2 Triggered Mobility (LTM) inter-cell handover at the base station can be achieved by performing a serving cell change (SSC) from a serving cell to a target cell. Multiple target cells may meet the radio conditions or handover criteria required for the UE to perform SSC and are therefore viable target cell options for HO. One or more of the viable target cells may require RACH-based HO, which involves a contention-based RACH process or a contention-free RACH process, for example, because the timing advance (TA) of the UE's serving cell and the TA of the target cell are different. Timing advance refers to the time offset between the start of the received downlink subframe and the start of the transmitted uplink subframe at the UE. This offset at the UE is necessary to ensure synchronization of the downlink and uplink subframes at the base station. This is a media access control (MAC) layer (Layer 2) control element (CE) from the base station to the UE, which is used to control the uplink (e.g., UE to base station) signal transmission timing. One or more of the other possible target cells may allow RACH-less HO, for example, because the TA of the target cell for the UE is zero, or because the TA of the serving cell is the same as the TA of the target cell for the UE. RACH-less HO is implemented over RACH-based HO to allow handover to one of the target cells that allow a RACH-less HO procedure.

[0084] As a UE's initial access to a wireless communication system including a base station, or as a handover from one cell to another, the base station may, for example, utilize one or more antennas (such as Figure 1d(multiple) antennas 136) receive signals on a communication channel (e.g., an uplink communication channel established between a base station and one or more UEs). The interface may be, for example, the air interface 122 of FIG. 1 using OFDMA and SC-FDMA, or may be another communication channel. The signal may include a frame including a plurality of symbols, the plurality of symbols including one or more symbol groups. Typically, an OFDM symbol may include a random access preamble, which includes a cyclic prefix (CP) portion and a data symbol. A symbol group may include a CP portion and a plurality of data symbols, which may reduce overhead by allowing a CP portion to be used with a plurality of data symbols (rather than using a CP portion with only one data symbol). Random access is based on a UE sending a random access preamble on a random access channel (RACH) to access a base station, either for initial access or for switching. Only a certain number of random access preambles are available for a cell. For example, under 3GPP, an LTE cell may have 64 available preambles. As a result, multiple UEs may each randomly select the same preamble, and a cell may receive signals from multiple UEs simultaneously, each of which includes the same preamble, resulting in collisions, known as "contention". A contention-based RACH procedure may be performed to resolve the collisions, which may delay HO because the collisions must be resolved, for example, because each UE must use a different preamble before the UEs can all communicate correctly with the cell.

[0085] In contrast, in a contention-free RACH procedure, the UE does not select a preamble. Instead, the cell selects a preamble for the UE and sends the preamble to the UE. Therefore, the cell can ensure that no collision occurs by allocating preambles so that a specific preamble is only allocated to one UE, which can reduce HO delays compared to a contention-based RACH procedure because it can save uplink synchronization time of no less than 20ms.

[0086] In some implementations of the current subject matter, a timing advance (TA) of a UE served by a serving cell of a base station of a wireless communication system may be used to prepare a configuration of at least one target cell of at least one target DU of the base station for LTM. The at least one target DU may be notified of the TA of the serving cell of the UE. Notifying the at least one target cell of the TA of the serving cell may allow each of the one or more target DUs to prepare for a RACH-free HO or a RACH-based HO from the serving cell for a UE communicatively coupled to the base station. Therefore, a HO from one cell of the base station to another cell of the base station may require less time because a HO from the serving cell to one of the at least one target cells has been prepared at each of the one or more target DUs to include a contention-free RACH procedure (for RACH-free HO) or a contention-based RACH procedure (for RACH-based HO). Therefore, a handover delay may be reduced, and thereby a user plane interruption time may be reduced.

[0087] In some implementations of the current subject matter, at least one target DU may be informed of the TA of the UE's serving cell by receiving the TA of the UE's serving cell from a CU-CP of a base station communicatively coupled to the serving cell and at least one target cell. The TA information is layer 1 (L1) information and is therefore not information used by the CU.

[0088] In some implementations of the current subject matter, a base station (e.g., Figure 5a gNodeB, Next Generation RAN (NG-RAN) node, such as eNodeB or gNodeB, etc.) can have a split architecture in which the base station includes a gNB-CU-CP (e.g., Figure 5a-5c gNB-CU-CP 504, etc.) and more than one CU-UP (e.g., Figure 5a to Figure 5c gNB-CU-UP 506, etc.) and gNB-DU (e.g., Figure 5a to Figure 5c The base station may be configured to implement LTM without RACH when the UE switches from one cell of the base station (the serving cell) to another cell of the base station (the target cell).

[0089] Figure 6a An exemplary system 600 is illustrated that is configured to implement LTM without RACH in an inter-DU scenario. In the illustrated implementation, the base station 624 is configured in a manner similar to that described above. Figure 5a The 5G wireless communication system 500 is a gNB in ​​the 5G wireless communication system, but other base stations can also be similarly configured and used to implement LTM without RACH. Figure 6aIn the illustrated implementation, the base station 624 includes a plurality of CU-UPs 606a, 606b, 606c. In the illustrated implementation, the base station 624 includes three CU-UPs 606a, 606b, 606c, but may also include other plurality of CU-UPs. The CU of the base station 624 including the plurality of CU-UPs 606a, 606b, 606c is configured to communicate with the core network ( Figure 6a Not shown, for example Figure 5a 5GC 502, etc.) are communicatively coupled.

[0090] The CU of the base station 624 also includes a CU-CP 604 configured to be communicatively coupled to the user plane portions 606a, 606b, 606c of the CU using an E1 communication interface 614. In the illustrated implementation, the E1 interface 614 includes three communication links to reflect that the CU-CP 604 can be configured to communicate with three CU-UPs 606a, 606b, 606c.

[0091] The base station 624 also includes a plurality of DUs 608, 610. In the illustrated implementation, the base station 624 includes two DUs 608, 610, but may also include other plurality of DUs. The CU-CP 604 is configured to be communicatively coupled to the DUs 608, 610 using an F1-C communication interface 616. The CU-UPs 606a, 606b, 606c are configured to be communicatively coupled to the DUs 608, 610 using an F1-U communication interface 618. In the illustrated implementation, the F1-U interface 618 associated with each of the DUs 608, 610 includes three communication links to reflect that each DU 608 and 610 may be configured to communicate with three CU-UPs 606a, 606b, 606c.

[0092] The base station 624 also includes a plurality of RUs 612. In the illustrated implementation, the base station 624 includes five RUs 612, but may include other plurality of RUs. The RUs 612 are configured to be communicatively coupled to the DUs 608, 610 via the fronthaul network 620. In addition, each of the RUs 612 is configured to be communicatively coupled to one or more UEs 622. In the illustrated implementation, two of the RUs 612 are shown communicatively coupled to one UE 622, two of the RUs 612 are shown communicatively coupled to two UEs 622, and one of the RUs 612 is shown communicatively coupled to three UEs 622, but each of the RUs 612 may be coupled to other numbers of UEs that are the same or different than any other RU 612.

[0093] Implementing LTM without RACH in an inter-DU scenario may be configured to occur when one of the UEs communicatively coupled to a base station 624 is handed off from one of the DUs 608, 610 of the base station 624 to another of the DUs 608, 610 that is also of the same base station 624. One of the DUs 608, 610 currently serving the UE 622 is referred to as a "serving DU" because it is currently providing service to the UE 622, e.g., is currently serving the UE 622. One of the DUs 608, 610 to which the UE's service is being handed off is referred to as a "target DU" because it is directed to provide service to the UE 622.

[0094] refer to Figure 6b A system is further described in which LTM without RACH in an inter-DU scenario can be configured. Figure 6b Pictured Figure 6a CU-CP 604 and CU-UP 606a, 606b, 606b, but in Figure 6b In the illustrated implementation, base station 624 includes more than two DUs. Figure 6b In the illustrated implementation, base station 624 includes 66 DUs. Three of DUs 628a, 628b, and 628c are macro cells (in Figure 6b 1, macro2, and macro3), and 63 of the DUs 626 are small cells (nine of which are in Figure 6b The base station 624 may include other numbers of macro cells and / or other numbers of small cells. The macro1 DU 628a, macro2 DU 628b, and 21 small cell DUs 626 including gNB-DU10, gNB-DU20, and gNB-DU30 are configured to be provided by the first CU-UP 606a (in FIG. Figure 6b The macro1 DU 628a, macro2 DU 628b, macro3 DU 628c, and 21 small cell DUs 626 including gNB-DU40, gNB-DU50, and gNB-DU60 are configured to be served by the second CU-UP 606b ( Figure 6b The macro2 DU 628b, macro3 DU 628c, and 21 small cell DUs 626 including gNB-DU70, gNB-DU80, and gNB-DU90 are configured to be served by the third CU-UP 606c (in Figure 6b 3) services marked as CU-UP.

[0095] exist Figure 6b In the illustrated implementation, each CU-UP 606a, 606b, 606c serves a subset of DUs 626, 628a, 628, 628c for all services. However, a CU-UP may serve all DUs of a base station for one service (e.g., enhanced mobile broadband (eMBB)) while serving a subset of DUs for another service (e.g., vehicle-to-everything (V2X) or ultra-reliable low latency communications (URLLC)).

[0096] Figure 7 An exemplary method 700 according to some implementations of the current subject matter is illustrated. The method 700 is related to Figure 8a The exemplary system 800 is shown, but may be similarly implemented using other systems, such as, Figure 1a-Figure 1c and Figure 2 System 100, Figure 4 System 400, Figure 5a System 500, Figure 6a and Figure 6b systems, etc. Figure 8a The system 800 is a 5G system, but as described above, the implementation of RACH-free LTM in the inter-DU scenario described in this article can be performed using other types of wireless communication systems, such as an LTE wireless communication system or a 6G or higher generation wireless communication system.

[0097] In system 800, UE 802 (e.g., Figure 1a-Figure 1c UE 104, Figure 6a UE 622, etc.) is configured 810 with a base station (e.g., gNB (e.g., Figure 5a gNodeB, Figure 6a and Figure 6b gNodeB 624, etc.) of one or more DUs 804, 806 (e.g., Figure 5a-5c DU 508 Figure 5a DU 510 Figure 6a DU 608 Figure 6a DU 610 Figure 6b DU 626 Figure 6b For ease of explanation, Figure 8a800 is illustrated in FIG, wherein one UE 802 is communicatively coupled to a base station and the base station includes two DUs 804, 806, but more than one UE may be communicatively coupled to the base station and / or the base station may include more than two DUs. The base station of system 800 also includes a CU that includes a CU-CP 808 (e.g., Figure 5a-5c gNB-CU-CP 504, Figure 6a and Figure 6b CU-CP604, etc.) and one or more CU-UPs (e.g., Figure 5a-5c gNB-CU-UP 506, Figure 6a and Figure 6b CU-UP 606a, 606b, 606c, etc.) ( Figure 8a ), and multiple RUs (e.g., Figure 5a RU 512, Figure 6a RU 612, etc.) ( Figure 8a UE 802 is currently being served by serving DU 804. Figure 8a Base stations and core networks (for example, Figure 1a-Figure 1c and Figure 2 EPC 108 Figure 5a 5GC 502, etc.) ( Figure 8a ) are communicatively coupled.

[0098] The method 700 illustrates an implementation of an inter-DU LTM serving cell change scenario that includes a serving DU 804 determining 702 that a cell change is required for a UE 802. The serving DU's determination 702 may include the serving DU 804 analyzing 814 an intra-frequency L1 measurement report sent 812 by the UE 802 to the serving DU 804 in accordance with 3GPP standards. In accordance with 3GPP standards, the intra-frequency L1 measurement report may include layer 1 (L1) measurements that may be analyzed by the serving DU 804 in making resource control decisions, which may include a serving cell change in which the UE 802 is to be served by a DU (e.g., a target DU 806) (rather than the serving DU 804) for at least one service.

[0099] In response to determining 702 that a serving cell change should occur, the serving DU 804 notifies 704 the UE 802 of the serving cell change. Figure 8a As shown, the notification 704 to the UE 802 may include the serving DU 804 sending 816 a serving cell change command, such as a MAC CE, to the UE 802 .

[0100] Likewise, in response to determining 702 that a cell service change should occur, the serving DU 804 notifies 704 the CU-CP 808 that a serving cell change has occurred for the UE 802. Thus, the notification 704 may identify the UE 802 to the CU-CP 808, such as in accordance with 3GPP standards, using an identifier known to the serving DU 804 that uniquely identifies the UE 802 to the CU-CP 808. Figure 8a As shown, the notification 704 to the CU-CP 808 may include the serving DU 804 sending 818 a serving cell change notification message to the CU-CP 808 using the F1 communication interface. Figure 8a As shown, the serving cell change notification message includes a cell identification (ID) that uniquely identifies the UE 802 that has undergone a serving cell change.

[0101] In response to receiving the serving cell change command 704 from the serving DU 804, the UE 802 sends 820 a radio resource control (RRC) reconfiguration confirmation message to the CU-CP 808. The CU-CP 808 learns from the RRC reconfiguration confirmation message that the UE 802 uniquely identified by the serving DU 804 is confirmed to the CU-CP 808 that a successful serving cell change is completed.

[0102] Likewise, in response to receiving the Layer 3 RRC measurement configuration, the UE 802 sends 822 an RRC measurement report in accordance with 3GPP standards to the CU-CP 808. In accordance with 3GPP standards, the RRC measurement report may include Layer 3 (L3) measurements that may be analyzed by the CU-CP 808 in making resource control decisions, which may include deciding 824 to prepare at least one target DU cell for LTM such that at least one target cell from the target DU 806 (rather than the serving DU 804) is ready to serve the UE 802 for at least one service.

[0103] In response to deciding 824 to prepare at least one target cell for LTM, the CU-CP 808 prepares 706 at least one target cell for LTM. Figure 8a As shown, in the illustrated implementation, each of the at least one target cell is an inter-DU target cell, e.g., is part of a different DU than the serving DU 804, where the same CU (e.g., a CU including a CU-CP 808) serves each DU 804, 806. Also, in the illustrated implementation, since there are only two gNB-DUs, the at least one target cell includes only the target DU 806, but as described above, the base station may include more than two target cells. Currently, according to the 3GPP standard, up to eight LTM target cells may be prepared for a given UE.

[0104] Preparing 706 at least one target cell for LTM may include notifying at least one target DU 806 that at least one target DU 806 may then be notified to start providing services to UE 802 for at least one service. Thus, the target DU 806 may reserve necessary resources for UE 802. Figure 8a As shown, the preparation 706 of at least one target cell (only the target DU 806 in this illustrated implementation) may include the CU-CP 808 sending 832 a UE context setup request message to the target DU 806 using the F1 communication interface in accordance with the 3GPP standard.

[0105] The preparation 706 of at least one target cell may include providing information indicating whether the HO is a RACH-free HO or a RACH-based HO (contention-free RACH (CFRA) or contention-based RACH (CBRA)) to the at least one target DU 806. In an exemplary implementation, the information includes timing advance (TA) information of the UE in the serving DU 804. The TA information of the UE in the serving cell 804 is either (a) the same TA as the TA of the target cell receiving the TA information, or (b) the TA is zero indicating that the HO to the target cell can be a RACH-free HO, thereby allowing the target cell to prepare for the RACH-free HO. The TA information of the UE in the serving cell 804 is neither (a) the same TA as the TA of the target cell receiving the TA information, nor (b) the TA is zero indicating that the HO to the target cell can be a RACH-based HO, thereby allowing the target cell to prepare for the RACH-based HO. In the case where the at least one target cell includes more than one target cell, zero or more of the target cells may be RACH-free HO, and the remaining target cells may be RACH-based HO. The information indicating whether the HO is a RACH-less HO or a RACH-based HO may be provided to the at least one target DU 806 in various ways.

[0106] In some implementations, the CU-CP 808 sends information, e.g., TA information of the serving cell 804 of the UE, in the preparation 706 of at least one target cell 806, e.g., as a parameter in a UE context setup request message sent 832 to the target DU 806. The CU-CP 808 may receive the TA information prior to the target cell preparation 706.

[0107] In some implementations, where the CU-CP 808 receives the serving cell TA information before the target cell preparation 706, the CU-CP 808 may retrieve 826 the serving cell TA information from the serving cell 804 before sending 832 the UE context setup request message to the target DU 806. Thus, the retrieval 826 of the serving cell 804 TA information may occur after the F1 setup process, in which the F1 communication interface is established between the CU-CP 808 and the serving cell 804. Figure 8a This implementation is illustrated.

[0108] like Figure 8a As shown, the CU-CP 808 retrieving 826 the TA information of the serving cell 804 may include the CU-CP sending 828 a message to the serving cell 804, the message requesting the serving cell 804 to provide the TA information of the serving cell 804 to the CU-CP 808; and the serving cell 804 sending 830 the TA information as a response to the CU-CP 808. The CU-CP 808 decision 824 to prepare at least one target cell may trigger the CU-CP to transmit 828 a message requesting TA information because the CU-CP 808 is now aware of the HO situation. Retrieving the TA information of the serving cell 804 after knowing that UE HO is required may allow the CU-CP 808 to have the latest TA information of the serving cell. As needed, when it is known that UE HO is required, the reception of TA information associated with UE HO may simplify the storage requirements of the CU-CP 808 because the TA information is only received when needed and does not necessarily have to be stored for later use. As Figure 8a As shown, the message sent 828 by the CU-CP 808 to request the serving cell TA information may be a UE context modification request message, and the message sent 830 by the serving cell 804 as a response may be a UE context setup response message. The UE context modification request message and the UE context setup response message are defined by 3GPP, so the process can utilize existing CU and DU functions.

[0109] In response to receiving the UE context setup request message from the CU-CP 808, the target DU 806 prepares 834 each target cell in the at least one target cell for LTM. In the illustrated implementation, the at least one target cell includes only the target DU 806 that prepares 834 one target cell. Figure 8a As shown, preparation 834 may include the target cell reserving necessary resources for UE 802 and verifying the RACH-free feasibility of HO. The target DU receiving the serving cell TA information from CU-CP 808 allows such verification because the target DU already knows the TA of its own cell and now also knows the TA of the serving cell.

[0110] The target DU 806 notifies the CU-CP 808 that the preparation 834 is complete. Figure 8a As shown, the notification to the CU-CP 808 may include the target DU 806 sending 836 a UE context establishment response message to the CU-CP 808 using the F1 communication interface according to the 3GPP standard. Figure 8a As shown, the UE context setup response message includes the merged cell group configuration information of the target cell prepared at the target DU 806. The merged cell group configuration information includes information on the configuration type, for example, RACH-based configuration or RACH-free configuration.

[0111] The CU-CP 808 notifies 708 the serving DU 804 of at least one LTM prepared target cell and its configuration type by identifying each of the one or more LTM prepared target cells and including information about each of the one or more target DUs. In the inter-DU LTM scenario, one or more of the at least one LTM prepared target cells belong to a different DU than the serving DU 806. For example, referring to Figure 6b In a system of FIG. 6A , the serving DU may be a small cell 626 of a macro1 DU 628a, and one or more of the target cells may be one or more small cells 626 of a macro2 DU 628b and / or a macro3 DU 628c.

[0112] like Figure 8a As shown, the notification 708 to the serving DU 804 may include the CU-CP 808 sending 838 a UE context modification request message to the serving DU 804 using the F1 communication interface. The UE context modification request message may include cell identification information (e.g., a unique cell ID identifying the target DU, such as a physical cell identifier (PCI)) or an index corresponding to the cell ID, and priority information for each of the one or more target DUs. The notification 708 to the serving DU 804 may include information indicating the RACH-free HO configuration of the target DU 806. As described above, the CU-CP 808 is aware of the candidacy of the target DU for RACH-free handover.

[0113] The priority information provided by the CU-CP 808 to the service DU 804 indicates the sorting order of one or more target cells configured for RACH-free switching, for the service DU 804 to select as the target DU for switching. Therefore, the priority information of a particular target cell may include a sequence number (e.g., one, two, three, etc.) indicating the ranking of the target cell in the ranking of all target cells eligible for RACH-free switching identified by the CU-CP 808 to the service DU 804. The CU-CP 808 may determine the sorting order in any of a variety of ways. In some implementations, the CU-CP 808 may determine the sorting order based on resource availability, load, slice compatibility, and / or any other RRM criteria. As discussed further below, the priority information may help the service DU 804 select one of the one or more target cells for RACH-free HO.

[0114] If there is only one target cell that is eligible for RACH-free handover and is a candidate for a serving cell change, as in the illustrated implementation where the target DU 806 is the only choice, the priority information may be omitted from the message from the CU-CP 808 to the serving DU 804 since there is only one possible choice for the HO identified to the serving DU 804.

[0115] In response to being notified 708 of at least one LTM prepared target DU cell, the serving cell 804 stores the received information about at least one LTM target cell, for example, a list of (multiple) target cells prepared by LTM, and if provided to the serving DU 804, its corresponding priority information is stored. Similarly, in response to being notified 708 of at least one target DU, the serving cell 804 sends 840 a UE context modification response message to the CU-CP 808 using the F1 communication interface. The UE context modification response message may include merged cell group configuration information for each of the one or more target cells identified by the CU-CP 808 to the UE 802. Both the UE context modification request message and the UE context modification response message are defined by 3GPP. Therefore, the serving DU 804 can receive information about at least one target cell from the CU-CP 808, and can confirm the reception to the CU-CP 808 using a message that has been sent for HO according to the 3GPP standard.

[0116] In response to receiving the UE context modification response message, the CU-CP 808 sends 842 an RRC reconfiguration message to the UE 802 according to the 3GPP standard. Figure 8aAs shown, the RRC reconfiguration message includes LTM target cell configuration information, such as information provided from the target DU 806 to the CU-CP 808 in the UE context setup response message sent 830. Thus, the UE may be informed whether RACH-less HO (LTM SCC) is possible. If RACH-less HO is not possible, the UE may perform CBRA on the target cell 806 because the preamble is not reserved for CFRA.

[0117] In response to receiving the target cell configuration in the RRC reconfiguration message, the UE 802 sends 844 an L1 measurement report according to the 3GPP standard to the serving DU 804. The L1 measurement report provides the serving DU 804 with UE-measured radio condition information of the configured target cell.

[0118] In response to receiving the L1 measurement report sent 844 from the UE 802, the serving cell 804 selects 710, 846 a target cell from one or more LTM prepared target cells identified to the serving DU 804 where RACH-free HO is possible. In the illustrated implementation, only one target cell (target DU 806) is identified by the CU-CP 808 to the serving DU 804 as an LTM prepared target cell, so the selection 710, 846 of the serving cell is direct, where the serving DU 804 selects 710, 846 the target DU 806. As described herein, if there are multiple LTM prepared target cells at the serving DU 804 that meet the handover criteria, the serving DU 804 is configured to select a target cell configured for RACH-free handover when available. If there is no LTM prepared target cell that is a candidate for RACH-free HO, the target cell can be selected according to the conventional procedures of 3GPP.

[0119] In implementations where multiple target cells are identified by the CU-CP 808 to the serving DU 804, the target cell selection 710, 846 of the serving cell may include determining which one or more of the multiple target cells have a radio quality above a predetermined threshold radio quality. The predetermined threshold radio quality is defined by the radio conditions of the UE received by the serving DU 804 from the UE 802 in an L1 measurement report. Thus, when selecting 710, 846 a target cell for the HO, the serving DU 804 may take into account the specific needs of the specific UE 802 involved in the HO. In addition, the L1 measurement report sent 844 by the UE 802 to the serving DU 804 may report L1 measurements of each of the multiple target cells, which may include a reference signal received power (RSRP) defined by 3GPP, and the UE 802 knows the identities of these target cells provided by the CU-CP 808 to the UE 802 in an RRC reconfiguration message. Therefore, the serving DU 804 may analyze the L1 measurement report received from the UE 802 to determine which target cell or cells among the plurality of target cells have a radio quality above a predetermined threshold radio quality.

[0120] If only one of the multiple target cells meets the radio condition of the UE, for example, only one of the target cells has a radio quality above a predetermined threshold radio quality, the serving cell 804 selects 710, 846 the target cell. If more than one of the multiple target cells meet the radio condition of the UE, for example, the radio quality of the target cells are all above a predetermined threshold radio quality, any one of the target cells may be able to serve the needs of the UE, and one of the target cells may be selected based on priority information (if received), randomly, or based on another desired criterion.

[0121] In selecting 710, 846 a target cell (e.g., Figure 8a After the target DU 806 in the illustrated implementation is received, the serving DU 804 triggers 712 the serving cell to change to the selected 710, 846 target cell. Figure 8a As shown, triggering 712 a serving cell change may include the serving DU 804 sending 848 a MAC CE to the UE 802, the MAC CE including a serving cell change command and identifying the selected 710, 846 target cell to the UE 802, such as via a PCI.

[0122] The UE's reception of the MAC CE indicates to the UE 802 that the identified target cell (eg, Figure 8aThe target DU 806 in the illustrated implementation performs an LTM serving cell change (SCC). Thus, in response to receiving a MAC CE from the serving cell 804, the UE 802 initiates 714, 850 a RACH-free HO to the target cell. Figure 8a As shown, the UE 802 starting 714, 850 a RACH-free HO to the target cell may include the UE 802 accessing 852 the target cell without a RACH procedure to the target DU 806 (according to the 3GPP standard) for the RACH-free HO. In response to the UE 802 accessing the target cell, the target DU 806 sends 854 a serving cell change notification to the CU-CP 808 via the F1 communication interface, which identifies the target DU 806 as a new current serving cell for at least one served UE 802, for example, by a unique identifier per 3GPP. Similarly, in response to receiving a MAC CE from the serving cell 804, the UE 802 sends 856 an RRC reconfiguration confirmation message to the CU-CP 808. Thus, CU-CP 808 receives confirmation from UE 802 via an RRC reconfiguration confirmation message, which indicates a successful RRC reconfiguration at UE 802; and receives confirmation from target DU 806 via a serving cell change notification, confirming that target DU 806 is now serving UE 802 for at least one service that has been switched from serving DU 804.

[0123] In some implementations, the serving DU 804, which has been informed by the CU-CP 808 that the configuration of the multiple target cells is a RACH-free configuration or a RACH-based configuration, can be configured to configure the UE 802 to perform uplink (UL) synchronization (sync) with the selected 710, 846 target cell while still acting as a serving cell and before the serving cell change. The serving DU 804 can configure the UE 802 to perform uplink synchronization, for example, by sending a command to the UE 802 before the transmission 848 of the MAC CE to the UE 802, and thus before the serving cell change has occurred. The UE 802 performing UL synchronization before the serving cell change can help the UE 802 to acquire the timing advance of the selected 710, 846 target cell and adjust if there is any change in the UE's serving cell TA due to further mobility of the UE 802 between the target cell preparation time and the serving cell change execution. The UE 802 may be configured to report to the serving DU 804 the target cell TA acquired by the UE 802 during UL synchronization with the target DU 806. The serving DU 804 may be configured to compare the TA of the UE 802 in the serving cell (determined at the serving DU 804) with the selected 710, 846 target cell (acquired during UL synchronization), and thereby determine whether a previously configured RACH-less HO may be performed on the given target cell. In the event that a change in the serving cell TA renders RACH-less HO not feasible, the serving DU 804 may be configured to indicate to the UE 802 in the sent 848 serving cell change command that a RACH-based HO should be performed on the target cell.

[0124] In some implementations, based on a target cell preparation request from the CU-CP 808, e.g., a UE context setup request sent 832 from the CU-CP 808, together with preparing a RACH-free target cell configuration, the target DU 806 may be configured to retain the RACH preamble for a RACH-based serving cell change. In the case where the UE 802 experiences continuous mobility in the serving DU / cell, and a RACH-free HO is not feasible due to a change in the TA of the UE at the serving DU 804, the UE 802 may use the retained RACH preamble for contention-free RACH access (CFRA) as a fallback solution.

[0125] As described above, the CU-CP 808 may receive the serving cell TA information before the target cell is prepared 706. In some implementations, the CU-CP 808 may receive the serving cell TA information from the cell during the F1 establishment process, in which the F1 communication interface is established between the CU-CP 808 and the cell. The process may be more refined and corresponds to each beam or beam group. A cell is divided into different beams / beam groups or regions, which may be assigned specific TAs. Afterwards, when it is found that the UE reports a specific beam group or region in its L3 measurement, a fixed TA may be mapped to the UE. Therefore, a single cell may have multiple TAs, each corresponding to one or more beams / beam groups of the cell. This process is also applicable to smaller cells where the TA does not vary much. Therefore, the CU-CP 808 may receive the TA information before knowing any UE HO requirements, and thereby make the TA information available and ready to be sent to the target cell. Figure 8b and Figure 8c This implementation is illustrated. Figure 8b Similar to Figure 8a , except that, after the CU-CP 808 has been notified 818 of the serving cell change, instead of retrieving 826 the serving cell TA information from the serving cell 804 during the HO process, the CU-CP 808 checks 858 the previously received serving cell TA information to identify that there is no RACH target cell candidate.

[0126] Figure 8c Illustration of some implementations based on the current topic Figure 8b The system is configured to provide TA information from the cell to the CU-CP 808 during the F1 establishment process. This can be updated using the F1:gNB-DU configuration update procedure. The F1 communication interface is established between the DU and the CU-CP 808 according to the 3GPP standard.

[0127] like Figure 8c As shown, in the F1 establishment process, in which an F1 communication interface is established between the CU-CP 808 and the service DU 804, the service DU 804 sends 860F1: establishment request to the CU-CP 808, and the request includes TA information of all beams / beam groups of each cell of the service DU 804. The service DU 804 Figure 8c 804, but the serving DU 804 may include a single cell. In response to receiving the F1: setup request from the serving DU 804, the CU-CP 808 sends 862 an F1: setup response to the serving DU 804.

[0128] like Figure 8cAs shown, in the F1 establishment process, an F1 communication interface is established between the CU-CP 808 and the target DU 806, and the target DU 806 sends 864F1: establishment request to the CU-CP 808, which includes TA information of all beams / beam groups of each cell of the target DU 806. Figure 8b 806, but the target DU 806 may include a single cell. In response to receiving the F1: setup request from the target DU 806, the CU-CP 808 sends 866 an F1: setup response to the target DU 806.

[0129] Figure 8c The diagram illustrates that the F1 communication interface is established between the serving DU 804 and the CU-CP 808 before the F1 communication interface is established between the target DU 806 and the CU-CP 808, but the F1 communication interface may be established between the target DU 806 and the CU-CP 808 before the F1 communication interface is established between the serving DU 804 and the CU-CP 808.

[0130] In some implementations, where the CU-CP 808 receives the TA information before the target cell preparation 706, the serving DU 804 may proactively provide the TA information to the CU-CP 808 without receiving a request for the TA information from the CU-CP 808. Thus, the CU-CP 808 may store the service cell TA information and prepare for later provision to the target DU 806. Figure 8d This implementation is illustrated. Figure 8d Similar to Figure 8a , except that, after the CU-CP 808 has been notified 818 of the serving cell change, instead of retrieving 826 the serving cell TA information from the serving cell 804 during the HO process, the CU-CP 808 checks 876 the previously received serving cell TA information to identify that there is no RACH target cell candidate.

[0131] like Figure 8d As shown, after the serving SU 804 has determined 702 that a cell change is required for the UE 802, in response to receiving an L1 measurement report sent 870 to the serving DU 804 from the UE 802, the serving DU 804 receives a cell change from a neighboring DU (at Figure 8d In the illustrated implementation, this includes only one DU 806 identifying 872 one or more potential candidate target cells for HO without RACH. The serving DU 804 then sends 874 a message identifying the one or more potential candidate target cells to the CU-CP 808 via the F1 communication interface. The serving DU 804 may be configured to only send 874 such a message to the CU-CP 808 if one or more potential candidate target cells are identified.

[0132] In some implementations, such as described above with respect to Figure 8a-8d In various implementations discussed, each of the one or more candidate target cells receives the UE's serving cell TA information from the CU-CP. In other implementations, the DUs of the base station may directly share their TA information with each other. Such DU-to-DU communication is not possible in 5G wireless communication systems, but will be possible in 6G or later wireless communication systems. Figure 8e This implementation is illustrated. Figure 8e Similar to Figure 8a , except that the service DU 804 executes the CU-CP 808 in Figure 8a The various functions described as being performed in the implementation of the solution include: termination of the RRC protocol at the DU and CU-CP, delivery of intra-gNB L3 measurements to the DU, delivery of inter-gNB and inter-radio access technology (RAT) measurements to the CU-CP, and autonomous decision by the DU to perform intra-gNB handover.

[0133] like Figure 8e As shown, in response to receiving the serving cell change command 704 from the serving DU 804, the UE 802 sends 878 an RRC reconfiguration confirm message to the serving DU 804. The serving DU 804 knows from the RRC reconfiguration confirm message that the UE 802 confirms the successful completion of the serving cell change.

[0134] Likewise, in response to receiving the Layer 3 RRC measurement configuration, the UE 802 sends 880 an RRC measurement report to the serving DU 804. The RRC measurement report may include L3 measurements that may be analyzed by the serving DU 804 in making resource control decisions, which may include deciding 882 to prepare at least one target DU cell for LTM such that at least one target cell from the target DU 806 (rather than the serving DU 804) is ready to serve the UE 802 for at least one service.

[0135] In response to deciding 882 to prepare at least one target cell for LTM, the serving DU 804 prepares at least one target cell for LTM. Preparing at least one target cell for LTM may include notifying at least one target DU 806 that at least one target DU 806 may then be notified to start providing services to UE 802 for at least one service. Thus, the target DU 806 may reserve necessary resources for the UE 802. Figure 8e As shown, the preparation of at least one target cell (only the target DU 806 in this illustrated implementation) may include the serving DU 804 sending 884 a UE context setup request message to the target DU 806 .

[0136] Similar to the above, the preparation of at least one target cell may include providing information indicating whether the HO is a RACH-free HO or a RACH-based HO (CFRA or CBRA) to at least one target DU 806. Figure 8e As shown, the information includes serving cell TA information sent 884 from the serving DU 804 to the target DU 806 in a UE context setup request message.

[0137] In response to receiving the UE context setup request message from the serving DU 804, the target DU 806 prepares 886 each of the at least one target cell for LTM, similar to the above with respect to Figure 8a The target DU 806 notifies the serving DU 804 that the preparation 886 has been completed. Figure 8e As shown, the notification to the serving DU 804 may include the target DU 806 sending 888 a UE context establishment response message to the serving DU 804. Figure 8e As shown, the UE context setup response message includes the merged cell group configuration information of the target cells prepared at the target DU 806. In response to being notified of at least one LTM prepared target DU cell, the serving cell 804 stores the received information about the at least one LTM target cell, for example, stores a list of LTM prepared (multiple) target cells and, if provided to the serving DU 804, stores their corresponding priority information.

[0138] In response to receiving the UE context modification response message, the serving cell 804 sends 890 an RRC reconfiguration message to the UE 802. Figure 8e As shown, the RRC reconfiguration message includes LTM target cell configuration information, such as the information provided from the target DU 806 to the serving cell 804 in the UE context setup response message sent 888. Thus, the UE may be informed whether RACH-less HO (LTM SCC) is possible. If RACH-less HO is not possible, the UE may perform CBRA on the target cell 806 because the preamble is not reserved for CFRA. In response to receiving the target cell configuration in the RRC reconfiguration message, the UE 802 sends 844 an L1 measurement report to the serving DU 804, and the process continues similar to that described above with respect to Figure 8a The process of discussion.

[0139] In some implementations, such as Fig. 9As shown, the current subject matter can be configured to be implemented in a system 900. The system 900 may include one or more of a processor 910, a memory 920, a storage device 930, and an 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 the system 600. In some implementations, the processor 910 may be a single-threaded processor. In an alternative implementation, the processor 910 may be a multi-threaded processor. The processor 910 may also be configured to process instructions stored in the memory 920 or on the storage device 930, including receiving or sending information through the input / output device 940. The memory 920 may store information within the system 900. In some implementations, the memory 920 may be a computer-readable medium. In an alternative implementation, the memory 920 may be a volatile memory unit. In some other implementations, the memory 920 may be a non-volatile memory unit. The storage device 930 may be capable of providing mass storage for the system 900. In some implementations, the storage device 930 may be a computer readable medium. In alternative implementations, the storage device 930 may be a floppy disk device, a hard disk device, an optical disk device, a magnetic tape device, a non-volatile solid-state memory, or any other type of storage device. The input / output device 940 may be configured to provide input / output operations to the system 900. In some implementations, the input / output device 940 may include a keyboard and / or a pointing device. In alternative implementations, the input / output device 940 may include a display unit for displaying a graphical user interface.

[0140] Fig.10 An exemplary method 1000 for implementing LTM without RACH according to some implementations of the current subject matter is illustrated. For example, the method 1000 may use the method described with respect to FIG. Figure 8b to perform as shown and described.

[0141] Method 1000 includes at least one LTM target cell (e.g., Figure 5a DU 508, 510, Figure 6a DU 608, 610, Figure 6b Cells 626, 628a, 628b, 628c, Figure 8a-8e 806, etc.), receives 1002 information indicating that the base station (e.g., Figure 1b-Figure 2 eNodeB 106, Figure 5a gNodeB, Figure 6a and Figure 6b gNodeB 624, Figure 8a-8e base station, etc.) of the service DU (for example, Figure 8a-8eThe method may further include preparing 1004 at least one LTM target cell for one of the RACH-free HO and the RACH-based HO based on the information received at the at least one LTM target cell.

[0142] In some implementations, the current subject matter can include one or more of the following optional features.

[0143] In some implementations, the information may include timing advance (TA) information of the UE in the serving DU, the TA information of the UE in the serving cell being either (a) the same TA as the TA in the at least one LTM target cell, or (b) the TA being zero may indicate that the HO to the at least one LTM target cell can be a RACH-free HO, and the TA information of the UE in the serving cell is neither (a) the same TA as the TA in the at least one LTM target cell, nor (b) the TA being zero may indicate that the HO to the at least one LTM target cell can be a RACH-based HO. In addition, the at least one LTM target cell may receive the serving DU (e.g., Figure 8e TA information of the UE in the service DU 804, etc.); and the method may include at least one LTM target cell indicating to the service DU whether the prepared LTM target cell configuration is a RACH-free configuration or a RACH-based configuration; or at least one LTM target cell may be in a CU-CP (e.g., Figure 5a-5c gNB-CU-CP 504, Figure 6a and Figure 6b CU-CP 604, Figure 8a-8d 808, etc.); and the method may include at least one LTM target cell indicating to the CU-CP whether the prepared LTM target cell configuration is a RACH-free configuration or a RACH-based configuration. In addition, during the establishment of the F1 communication interface between the service DU and the CU-CP, the CU-CP may receive the TA information of the UE in the service DU from the service DU; or after the F1 communication interface has been established between the service DU and the CU-CP, the CU-CP may receive the TA information of the UE in the service DU from the service DU.

[0144] In some implementations, at least one LTM target cell may be included in at least one DU of the base station that is not a serving DU.

[0145] In some implementations, the service DU may select one of the prepared at least one LTM target cells for handover of the UE's service from the service DU, and the service DU may trigger handover of the UE's service from the service DU to the selected LTM target cell. In addition, the service DU may determine which one or more of the at least one LTM target cells have a radio quality higher than a predetermined threshold radio quality, and the selection may be made among the determined one or more LTM target cells; and / or the triggering may include the service DU sending a media access control (MAC) control element (CE) message to the UE.

[0146] In some implementations, the base station may have a split architecture.

[0147] In some implementations, the base station may include a Next Generation Radio Access Network (NG-RAN) node. In addition, the NG-RAN node may include a gNodeB (e.g., Figure 5a gNodeB, Figure 6a or Figure 6b gNodeB 624, Figure 8a and Figure 8b gNodeB, etc.) or ng-eNodeB.

[0148] In some implementations, a base station may include at least one processor (e.g., Fig. 9 processor 910, etc.) and at least one non-transitory storage medium storing instructions (e.g., Fig. 9 920, storage device 930, etc.), when the instruction is executed by at least one processor, the at least one processor executes the above method 1000.

[0149] The systems and methods disclosed herein can be embodied in various forms, including, for example, data processors, such as computers, which also include databases, digital electronic circuit systems, firmware, software, or a combination thereof. In addition, the above-mentioned features and other aspects and principles of the implementation of the present disclosure can be implemented in various environments. Such an environment and related applications can be specially constructed to perform various processes and operations according to the disclosed implementation, or it can include a general-purpose computer or computing platform that is selectively activated or reconfigured by code to provide necessary functions. The process disclosed herein has no inherent relationship with any specific computer, network, architecture, environment, or other device, and can be implemented by a suitable combination of hardware, software, and / or firmware. For example, various general-purpose machines can be used with programs written according to the teachings of the disclosed implementation, or it can be more convenient to build a special device or system to perform the required methods and techniques.

[0150] The systems and methods disclosed herein may be implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, for example, in a machine-readable storage device or a propagated signal, for execution by a data processing apparatus (e.g., a programmable processor, a computer, or multiple computers) or for controlling its operation. The computer program may be written in any form of programming language, including compiled or interpreted languages, and may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for a computing environment. The computer program may be deployed to be executed on one computer or multiple computers, which are located at one site or distributed between multiple sites and interconnected by a communication network.

[0151] As used herein, the term "user" may refer to any entity, including a person or a computer.

[0152] Although in some cases, ordinal numbers such as first, second, etc. can be related to order; as used in this document, ordinal numbers do not necessarily indicate order. For example, ordinal numbers can only be used to distinguish one item from another item. For example, to distinguish a first event from a second event, but need not imply any time order or fixed reference system (such that the first event in one paragraph of the specification can be different from the first event in another paragraph of the specification).

[0153] The above description is intended to illustrate but not limit the scope of the present invention, which is defined by the scope of the appended claims. Other implementations are within the scope of the following claims.

[0154] These computer programs (also referred to as programs, software, software applications, applications, components or codes) include machine instructions for programmable processors and can be implemented in high-level programs 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, device and / or equipment for providing machine instructions and / or data to a programmable processor, such as, for example, a disk, an optical disk, a memory and a programmable logic device (PLD), including a machine-readable medium that receives machine instructions as a machine-readable signal. The term "machine-readable signal" refers to any signal for providing machine instructions and / or data to a programmable processor. A machine-readable medium can store such machine instructions in a non-transient manner, such as, for example, a non-transient solid-state memory or a magnetic hard drive or any equivalent storage medium. A machine-readable medium can alternatively or additionally store such machine instructions in a transient manner, such as, for example, a processor cache or other random access memory associated with one or more physical processor cores.

[0155] To provide interaction with a user, the subject matter described herein can be implemented on a computer having a display device for displaying information to the user, such as, for example, a cathode ray tube (CRT) or a liquid crystal display (LCD) monitor; and a keyboard and pointing device, such as, for example, a mouse or trackball, through which the user can provide input to the computer. Other types of devices can also be used to provide interaction with the user. For example, the feedback provided to the user can be any form of sensory feedback, such as, for example, visual feedback, auditory feedback, or tactile feedback; and the input from the user can be received in any form, including but not limited to sound, voice, or tactile input.

[0156] The subject matter described herein may be implemented in a computing system that includes a back-end component, such as, for example, one or more data servers; or includes a middleware component, such as, for example, one or more application servers; or includes a front-end component, such as, for example, one or more client computers with a graphical user interface or a web browser, through which a user can interact with an implementation of the subject matter described herein; or includes any combination of such back-end components, middleware components, or front-end components. The components of the system may be interconnected by any form or medium of digital data communication, such as, for example, 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.

[0157] A computing system may include clients and servers. Clients and servers are typically (but not limited to) remote from each other and typically interact through a communication network. The relationship of client and server arises from computer programs running on the respective computers and having a client-server relationship to each other.

[0158] The implementations set forth in the above description do not represent all implementations consistent with the subject matter described herein. Instead, they are merely some examples consistent with aspects related to the described subject matter. Although some variations are described in detail above, other modifications or additions are possible. In particular, other features and / or variations may be provided in addition to those described herein. For example, the above implementations may be directed to various combinations and subcombinations of the disclosed features and / or combinations and subcombinations of several other features described above. In addition, the logical flows described in the accompanying drawings and / or herein do not necessarily require the specific order shown or in a sequential order to achieve the desired results. Other implementations may be within the scope of the following claims.

Claims

1. A device comprising: at least one processor, and at least one non-transitory storage medium storing instructions that, when executed by the at least one processor, cause the at least one processor to perform operations comprising: receiving, at at least one layer 1 / layer 2 triggered mobility (LTM) target distributed unit (DU) of a base station, information indicating that a handover (HO) of a service of a user equipment (UE) currently served by a serving DU of the base station can be a random access channel-less (RACH-less) HO to at least one LTM target cell of the target DU or can be a RACH-based HO to the at least one LTM target cell; and The at least one LTM target cell is prepared for one of a RACH-less HO and a RACH-based HO based on the information received at the at least one LTM target cell.

2. The apparatus according to claim 1, wherein the information comprises: Timing Advance (TA) information of the UE in the serving DU; The TA information of the UE in the serving cell is either (a) the same TA as the TA in the at least one LTM target cell, or (b) the TA is zero indicating that the HO to the at least one LTM target cell can be a RACH-less HO; and The TA information of the UE in the serving cell is neither (a) the same TA as the TA in the at least one LTM target cell nor (b) TA is zero, indicating that the HO to the at least one LTM target cell can be a RACH-based HO.

3. The apparatus of claim 2, wherein the at least one LTM target DU receives the TA information of the UE in the serving DU in a message from the serving DU; and The operations also include: The at least one LTM target DU indicates to the serving DU whether the prepared LTM target cell configuration is a RACH-free configuration or a RACH-based configuration.

4. The apparatus of claim 2, wherein the at least one LTM target DU receives the TA information of the UE in the serving DU in a message from a centralized unit control plane (CU-CP) of the base station; and The operations also include: The at least one LTM target DU indicates to the CU-CP whether the prepared LTM target cell configuration is a RACH-free configuration or a RACH-based configuration. 5 . The apparatus of claim 4 , wherein during establishment of an F1 communication interface between the serving DU and the CU-CP, the CU-CP receives the TA information of the UE in the serving DU from the serving DU. 6 . The apparatus according to claim 4 , wherein after an F1 communication interface has been established between the serving DU and the CU-CP, the CU-CP receives the TA information of the UE in the serving DU from the serving DU. 7 . The apparatus according to claim 1 , wherein the at least one LTM target cell is included in at least one DU of the base station that is not the serving DU.

8. The apparatus according to claim 1, wherein the serving DU selects one of the at least one prepared LTM target cells for handover of the service of the UE from the serving DU, and the serving DU triggers handover of the service of the UE from the serving DU to the selected LTM target cell.

9. The apparatus according to claim 8, wherein the serving DU determines which one or more of the at least one LTM target cells have a radio quality above a predetermined threshold radio quality; and The selection is performed in the determined one or more LTM target cells.

10. The apparatus of claim 8, wherein the trigger comprises: The serving DU sends a medium access control (MAC) control element (CE) message to the UE. The apparatus of claim 1 , wherein the base station has a split architecture.

12. The apparatus of claim 1, wherein the base station comprises a Next Generation Radio Access Network (NG-RAN) node.

13. The apparatus of claim 12, wherein the NG-RAN node comprises a gNodeB or an ng-eNodeB.

14. The apparatus according to claim 1, wherein the base station comprises: The at least one processor and the at least one non-transitory storage medium.

15. A computer-implemented method comprising: receiving, at at least one layer 1 / layer 2 triggered mobility (LTM) target distributed unit (DU) of a base station, information indicating that a handover (HO) of a service of a user equipment (UE) currently served by a serving DU of the base station can be a random access channel-less (RACH-less) HO to at least one LTM target cell of the target DU or can be a RACH-based HO to the at least one LTM target cell; as well as The at least one LTM target cell is prepared for one of a RACH-less HO and a RACH-based HO based on the information received at the at least one LTM target cell.

16. The method of claim 15, wherein the information comprises: Timing Advance (TA) information of the UE in the serving DU; The TA information of the UE in the serving cell is either (a) the same TA as the TA in the at least one LTM target cell, or (b) the TA is zero indicating that the HO to the at least one LTM target cell can be a RACH-less HO; and The TA information of the UE in the serving cell is neither (a) the same TA as the TA in the at least one LTM target cell nor (b) TA is zero, indicating that the HO to the at least one LTM target cell can be a RACH-based HO.

17. At least one non-transitory storage medium storing instructions that, when executed by at least one processor, cause the at least one processor to perform operations comprising: receiving, at at least one layer 1 / layer 2 triggered mobility (LTM) target distributed unit (DU) of a base station, information indicating that a handover (HO) of a service of a user equipment (UE) currently served by a serving DU of the base station can be a random access channel-less (RACH-less) HO to at least one LTM target cell of the target DU or can be a RACH-based HO to the at least one LTM target cell; as well as The at least one LTM target cell is prepared for one of a RACH-less HO and a RACH-based HO based on the information received at the at least one LTM target cell.

18. The storage medium according to claim 17, wherein the information comprises: Timing Advance (TA) information of the UE in the serving DU; The TA information of the UE in the serving cell is either (a) the same TA as the TA in the at least one LTM target cell, or (b) the TA is zero indicating that the HO to the at least one LTM target cell can be a RACH-less HO; and The TA information of the UE in the serving cell is neither (a) the same TA as the TA in the at least one LTM target cell nor (b) TA is zero, indicating that the HO to the at least one LTM target cell can be a RACH-based HO.

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