Layer 1 / Layer 2 Triggered Mobility for User Plane Relocation of Base Station Centralized Units

Abstract

Generally, the present subject matter relates to Layer 1 / Layer 2 (L1 / L2) triggered mobility (LTM) for intra-base station centralized unit user plane (CU-UP) relocation. In some implementations, a target distributed unit (DU) of a base station for serving a user equipment (UE) can determine that it is being served by a target CU-UP of the base station. A serving CU-UP of the base station can serve a serving DU of the base station that is currently serving the UE. A centralized unit control plane (CU-CP) of the base station can be used to prepare the target CU-UP for Layer 1 / Layer 2 triggered mobility (LTM), and the CU-CP can be used to prepare the target DU for LTM.

Description

[Technical Field]

[0001] In some implementations, the present subject matter relates to telecommunications systems, and in particular to Layer 1 / Layer 2 triggered mobility (LTM) for intra-base station centralized unit user plane (CU-UP) relocation. [Background technology]

[0002] In today's world, cellular networks provide individuals and businesses with on-demand communication capabilities. Typically, cellular networks are wireless networks that can be distributed over a terrestrial area called a cell. Each such cell is served by at least one fixed-location transceiver called a cell site or base station. Each cell may use a different set of frequencies from its neighboring cells to avoid interference and provide improved service within each cell. When cells are combined together, they provide wireless coverage over a wide geographic area, allowing numerous 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 communication is performed through base stations and is accomplished even when a mobile transceiver is traveling through two or more cells during transmission. Major wireless communication providers have deployed such cell sites worldwide, allowing mobile phones and mobile computing devices to connect to the public switched telephone network and the public Internet.

[0003] A mobile phone is a portable telephone that can receive and / or make telephone and / or data communications through a cell site or transmission tower by using radio waves to transfer signals to and from the mobile phone. Given the large number of mobile phone users, current mobile phone networks offer limited shared resources. In that regard, cell sites and handsets may change frequencies and use low-power transmitters to allow simultaneous use of the network by many callers with less interference. Coverage by a cell site may depend on the particular geographic location and / or the number of users who can use the network. For example, in cities, cell sites may have a range of up to about 1 / 2 mile, while in suburban areas, the range may be as much as 5 miles, and in some areas, users may be able to receive signals from cell sites 25 miles away.

[0004] The following are some examples of digital cellular technologies used by communication providers: Global System for Mobile Communications ("GSM"), General Packet Radio Service ("GPRS"), cdmaOne, CDMA2000, Evolution Data Optimized ("EV-DO"), GSM Evolution Improved Data Rates ("EDGE"), Universal Mobile Telecommunications System ("UMTS"), Digital Improved Cordless Communications ("DECT"), Digital AMPS ("IS-136 / TDMA"), and Integrated Digital Improved Network ("iDEN"). 4G LTE, developed by the Long Term Evolution, or 3rd Generation Partnership Project ("3GPP®") standards organization, is a high-speed data wireless communication standard 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 generations of 3GPP technologies such as GSM / EDGE and UMTS / HSPA digital cellular technologies, and enable increased capacity and speeds by using different air interfaces along with improvements to the core network.

[0005] A cellular network can be divided into a radio access network and a core network. The radio access network (RAN) can include network functions capable of handling radio layer communication processing. The core network can include network functions capable of handling higher layer communication, such as internet protocol (IP), transport layer, and application layer. In some cases, the RAN function can be divided into baseband unit function and radio unit function; for example, a radio unit connected to a baseband unit via a fronthaul network can be responsible for lower layer processing of the radio physical layer, and the baseband unit can be responsible for higher layer radio protocols, such as MAC, RLC, etc.

[0006] 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 communicatively coupled to at least one of the one or more DUs and each configured to be communicatively coupled to one or more mobile phones and / or other user equipment (UE). The CU may be logically divided into a control plane portion (CU-CP) and one or more user plane portions (CU-UPs). In a non-aggregated architecture, a base station includes two or more CU-UPs. During the course of a UE's communicative coupling with a base station, the CU-UP of the base station providing support for the UE may change from one CU-UP of the base station to another CU-UP of the base station. However, cell service changes according to current standards are triggered by Layer 3 (L3) measurements and therefore require resets at the lower layers Layer 1 (L1) and Layer 2 (L2), which results in higher latency, higher overhead and longer interruptions. Summary of the Invention [Means for solving the problem]

[0007] In some implementations, the subject matter relates to a computer-implemented method. The method can include determining that a target distributed unit (DU) of a base station for serving a user equipment (UE) is served by a target centralized unit user plane (CU-UP) of the base station. The serving CU-UP of the base station can serve a serving DU of the base station that is currently serving the UE. The method can also include preparing the target CU-UP for layer 1 / layer 2 triggered mobility (LTM) using a centralized unit control plane (CU-CP) of the base station and preparing the target DU for LTM using the CU-CP.

[0008] This method may enable the base station to provide LTM when a UE undergoes relocation from one CU-UP of the base station to another CU-UP of the base station for one or more services.

[0009] In some implementations, the present subject matter can include one or more of the following optional features.

[0010] In some implementations, preparing the target CU-UP may include fetching security keys from the target CU-UP using the CU-CP, and preparing the target DU may include sending the security keys from the CU-CP to the target DU. Further, the security keys configured by the target CU-UP may be sent from the CU-CP to the target DU in a UE CONTEXT SETUP REQUEST message, and / or fetching the security keys may include the CU-CP sending a BEARER CONTEXT SETUP REQUEST message to the target CU-UP and the CU-UP sending a BEARER CONTEXT SETUP RESPONSE message to the CU-CP, where the BEARER CONTEXT SETUP RESPONSE message may include security keys that may correspond to UEs served by the target CU-UP. Further, the BEARER CONTEXT SETUP REQUEST message may include an information element (IE) that notifies the target CU-UP of the LTM.

[0011] In some implementations, preparing the target CU-UP may include sending an information element (IE) from the CU-CP to the target CU-UP that notifies the target CU-UP of the LTM to reserve resources for the UE.

[0012] In some implementations, the method may also include triggering the serving CU-UP to initiate data transfer to the target CU-UP after the target CU-UP prepares and the target DU prepares. Furthermore, the triggering may include sending a control packet data unit (PDU) from the serving DU to the serving CU-UP, and then the serving CU-UP sending unsent and unacknowledged data PDUs to the target CU-UP. Furthermore, the method may also include sending information from the CU-CP to the serving DU to identify a change in the serving CU-UP of the LTM before sending the control PDU to trigger the data transfer. Furthermore, this information may be sent from the CU-CP to the serving DU in a UE CONTEXT MODIFICATION REQUEST message.

[0013] In some implementations, the method may also include, after preparing the target CU-UP and preparing the target DU, triggering the target CU-UP to start serving the UE via the target DU. Further, the triggering may include sending a control packet data unit (PDU) from the target DU to the target CU-UP to start downlink data transmission, and then the target CU-UP sending a data PDU to the target DU, or the triggering may include sending a first message from the serving DU to the CU-CP, and then the CU-CP sending a second message to the serving CU-UP, and then the serving CU-UP sending a third message to the target CU-UP, and / or serving the UE may include sending a first message from the target DU to the CU-CP, and then the CU-CP sending a second message to the target CU-UP, and then the target CU-UP starting downlink data transmission toward the target DU.

[0014] In some implementations, determining may include using the CU-CP to analyze radio resource control (RRC) measurement reports received at the CU-CP from the UE.

[0015] In some implementations, the serving CU-UP and the target CU-UP may be different entities.

[0016] In some implementations, the base station may be a new generation radio access network (NG-RAN) node.

[0017] In some implementations, a base station may include at least one processor and at least one non-transitory storage medium.

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

[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 to explain some of the principles associated with the disclosed implementations. [Brief explanation of the drawings]

[0021] [Figure 1a] FIG. 1 illustrates an exemplary conventional Long Term Evolution (“LTE”) communication system. [Figure 1b]It is a diagram showing further details of an exemplary LTE system shown in FIG. 1a. [Figure 1c] It is a diagram showing further details of the evolved packet core of the exemplary LTE system shown in FIG. 1a. [Figure 1d] It is a diagram showing an exemplary evolved Node B of the exemplary LTE system shown in FIG. 1a. [Figure 2] It is a diagram showing further details of the evolved Node B shown in FIGS. 1a to 1d. [Figure 3] It is a diagram showing an exemplary virtual radio access network according to some implementations of the present subject matter. [Figure 4] It is a diagram showing an exemplary 3GPP split architecture for providing its user with the use of a higher frequency band. [Figure 5a] It is a diagram showing an exemplary 5G wireless communication system. [Figure 5b] It is a diagram showing an exemplary layer architecture of a split gNB and / or a split ng-eNB (for example, a next-generation eNB that can be connected to a 5GC). [Figure 5c] It is a diagram showing an exemplary functional split in the gNB architecture shown in FIGS. 5a to 5b. [Figure 6a] It is a diagram showing an exemplary system according to some implementations of the present subject matter. [Figure 6b] It is a diagram showing an exemplary alternative configuration of the system of FIG. 6a according to some implementations of the present subject matter. [Figure 7] It is a diagram showing an exemplary method according to some implementations of the present subject matter. [Figure 8] It is a diagram showing another exemplary system according to some implementations of the present subject matter. [Figure 9] It is a diagram showing yet another exemplary system according to some implementations of the present subject matter. [Figure 10] It is a diagram showing another exemplary method according to some implementations of the present subject matter.

Modes for Carrying Out the Invention

[0022] The present subject matter may provide systems and methods that may be implemented in wireless communication systems. Such systems may include various wireless communication systems, including 5G New Radio communication systems, Long Term Evolution communication systems, etc.

[0023] Generally, the present subject matter relates to Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) for intra-base station centralized unit user plane (CU-UP) relocation.

[0024] In some implementations of the present subject matter, a base station of a wireless communication system can have a distributed architecture in which the base station includes two or more CU-UPs. The base station can be configured to provide LTM when a UE communicatively coupled to the base station undergoes relocation from one CU-UP of the base station to another CU-UP of the base station for one or more services of the UE.

[0025] 3GPP standards that define one or more aspects that may be related 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)." O-RAN Alliance standards may also be related to one or more aspects of the present subject matter.

[0026] One or more aspects of the present subject matter may be incorporated into transmitter and / or receiver components of base stations (e.g., gNodeBs, eNodeBs, etc.) within such communication systems. The following is a general discussion of Long Term Evolution and 5G New Radio communication systems.

[0027] I. Long Term Evolution Communication System 1a-1c and 2 illustrate an exemplary conventional Long Term Evolution ("LTE") communication system 100 along with its various components. The LTE system, or 4G LTE, as it is commercially known, is governed by a high-speed data wireless communication standard 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 was developed by 3GPP ("Third Generation Partnership Project").

[0028] As shown in FIG. 1a, system 100 may include an Evolved Universal Terrestrial Radio Access Network (“EUTRAN”) 102, an Evolved Packet Core (“EPC”) 108, and a Packet Data Network (“PDN”) 101, where EUTRAN 102 and EPC 108 provide communications between user equipment 104 and PDN 101. EUTRAN 102 may include multiple Evolved Node Bs (“eNodeB” or “ENODEB” or “enodeb” or “eNB”) or base stations 106(a, b, c) (as shown in FIG. 1b) that provide communications capabilities to multiple user equipment 104(a, b, c). User equipment 104 may be a mobile phone, a smartphone, a tablet, 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. A user equipment 104 can connect to the EPC 108 and ultimately to the PDN 101 through any eNodeB 106. Typically, the user equipment 104 can connect 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.

[0029] Figure 1b shows further details of the network 100 shown in Figure 1a. As mentioned above, the EUTRAN 102 includes multiple eNodeBs 106, also known as cell sites. The eNodeBs 106 provide radio functionality and perform important control functions, including air link resource scheduling or radio resource management, active mode mobility or handover, and admission control for services. The eNodeBs 106 are responsible for selecting which mobility management entity (MME shown in Figure 1c) will serve the user equipment 104, as well as protocol functions such as header compression and encryption. The eNodeBs 106 that make up the EUTRAN 102 cooperate with each other regarding radio resource management and handover.

[0030] Communication between the user equipment 104 and the eNodeB 106 occurs over an air interface 122 (also known as the "LTE-Uu" interface). As shown in FIG. 1b, 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"), an OFDMA variant, on the downlink and uplink, respectively. OFDMA allows the use of multiple known antenna technologies, such as Multiple Input Multiple Output ("MIMO").

[0031] 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 (shown in FIG. 1c). In addition to signaling, user traffic is transferred between the user equipment 104 and the eNodeB 106. Both signaling and traffic in the system 100 are carried by physical layer ("PHY") channels.

[0032] Multiple eNodeBs 106 may be interconnected with each other using X2 interfaces 130(a, b, c). As shown in FIG. 1b, X2 interface 130a provides interconnection between eNodeB 106a and eNodeB 106b, X2 interface 130b provides interconnection between eNodeB 106a and eNodeB 106c, and X2 interface 130c provides interconnection between eNodeB 106b and eNodeB 106c. The X2 interfaces may be established between two eNodeBs to provide for the exchange of signals, which may include information related to loading or interference, as well as information related to handover. The eNodeBs 106 communicate with the evolved packet core 108 via S1 interfaces 124(a, b, c). The S1 interface 124 may be split into two interfaces, one for the control plane (shown in FIG. 1c as control plane interface (S1-MME interface) 128) and the other for the user plane (shown in FIG. 1c as user plane interface (S1-U interface) 125).

[0033] The EPC 108 establishes and enforces quality of service ("QoS") for user services and enables user equipment 104 to maintain a consistent Internet Protocol ("IP") address while moving. Note that each node in the network 100 has its own IP address. The EPC 108 is designed to interwork with legacy wireless networks. The EPC 108 is also designed to separate the control plane (i.e., signaling) and user plane (i.e., traffic) in the core network architecture, which allows for more flexibility in implementation and independent scalability of control and user data functions.

[0034] The EPC 108 architecture is dedicated to packet data and is shown in more detail in Figure 1c. 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 (the subscriber database for the EPC 108), and a Policy Control and Charging Rules Function ("PCRF") 118. Some of these (such as the S-GW, P-GW, MME, and HSS) are often embedded in nodes, depending on the manufacturer's implementation.

[0035] The S-GW 110 functions as an IP packet data router and is the bearer path anchor for user equipment within the EPC 108. Thus, when a user equipment moves from one eNodeB 106 to another during mobility operation, the S-GW 110 remains the same and the bearer path towards the EUTRAN 102 is switched to communicate with 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 of the user equipment's bearer path to the new S-GW. The S-GW 110 establishes a bearer path for the user equipment to one or more P-GWs 112. When downstream data is received for an idle user equipment, the S-GW 110 buffers the downstream packets and requests the MME 114 to find and re-establish a bearer path to and through the EUTRAN 102.

[0036] The P-GW 112 is the gateway between the EPC 108 (and user equipment 104 and EUTRAN 102) and the PDN 101 (shown in FIG. 1a). The P-GW 112 acts as a router for user traffic and performs functions on behalf of the user equipment. These include IP address allocation to the user equipment, packet filtering of downstream user traffic to ensure that it is placed on the appropriate bearer path, and enforcement of downstream QoS, including data rate. Depending on the services a 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 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.

[0037] The MME 114 manages user equipment 104 within the EPC 108, including managing subscriber authentication, maintaining context for authenticated user equipment 104, establishing a data bearer path within the network for user traffic, and tracking the location of idle mobiles that have not detached from the network. In the case of an idle user equipment 104 that needs to reconnect to the access network to receive downstream data, the MME 114 initiates paging to locate the user equipment and reestablishes a bearer path to and through the EUTRAN 102. The MME 114 for a particular user equipment 104 is selected by the eNodeB 106 through which the user equipment 104 initiates system access. The MME is typically part of a group of MMEs within the EPC 108 for load sharing and redundancy purposes. In establishing a user's data bearer path, the MME 114 is responsible for selecting the P-GW 112 and S-GW 110 that constitute the termination points of the data path through the EPC 108.

[0038] The PCRF 118 is responsible for controlling policy control decision-making and flow-based charging functionality within the Policy Control Enforcement Function ("PCEF") residing within the P-GW 110. The PCRF 118 provides QoS authorizations (QoS Class Identifier ("QCI") and bitrate) that determine how a particular data flow is treated within the PCEF, ensuring that this is consistent with the user's subscription profile.

[0039] As mentioned above, IP services 119 are provided by PDN 101 (shown in FIG. 1a).

[0040] 1d shows an example structure of an eNodeB 106. 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 RRHs 132 may be connected to an antenna 136. The RRHs 132 and BBU 134 may be connected using an optical interface that conforms to the Common Public Radio Interface (“CPRI”) / enhanced CPRI (“eCPRI”) 142 standard specification, either using RRH-specific custom control and user plane framing methods or using O-RAN Alliance-compliant control and user plane framing methods. 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 method (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 speed (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, S1 line termination, X2 line termination, call processing, and monitoring and control processing. IP packets (not shown in FIG. 1d) received from the EPC 108 can 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.

[0041] The RRH 132 can transmit and receive wireless signals using the antenna 136. The RRH 132 can convert digital baseband signals from the BBU 134 (using a converter (“CONV”) 140) to radio frequency (“RF”) signals and power amplify them (using an amplifier (“AMP”) 138) for transmission to the user equipment 104 (not shown in FIG. 1d). Conversely, RF signals received from the user equipment 104 are amplified (using AMP 138) and converted (using CONV 140) to digital baseband signals for transmission to the BBU 134.

[0042] Figure 2 shows additional details of an exemplary eNodeB 106. 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 medium access control ("MAC"), radio link control ("RLC"), and packet data convergence protocol ("PDCP"). LTE Layer 3 includes various functions and protocols, including radio resource control ("RRC"), dynamic resource allocation, eNodeB measurement configuration and provisioning, radio admission control, connection mobility control, and radio resource management ("RRM"). The RLC protocol is an automatic repeat request ("ARQ") fragmentation protocol used over the cellular air interface. The RRC protocol handles LTE Layer 3 control plane signaling between user equipment and the EUTRAN. The RRC includes functions for 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. The PDCP performs IP header compression and decompression, user data transfer, and radio bearer sequence number maintenance. The BBU 134 shown in FIG. 1d may include LTE layers L1-L3.

[0043] One of the primary functions of the eNodeB 106 is radio resource management, including scheduling of both uplink and downlink air interface resources for the user equipment 104, control of bearer resources, and admission control. As an agent for the EPC 108, the eNodeB 106 is responsible for forwarding paging messages used to locate a mobile when it is idle. The eNodeB 106 also communicates common control channel information over the air, performs header compression, encryption and decryption of user data sent over the air, and establishes handover reporting and trigger criteria. As mentioned above, the eNodeB 106 can cooperate with other eNodeBs 106 via the X2 interface for handover and interference management purposes. The eNodeB 106 communicates with the MME of the EPC via the S1-MME interface and with the S-GW using the S1-U interface. Additionally, the eNodeB 106 exchanges user data with the S-GW via the S1-U interface. The eNodeBs 106 and the EPC 108 have a many-to-many relationship to support load sharing and redundancy between MMEs and S-GWs. The eNodeB 106 selects one MME from a group of MMEs so that it can distribute the load across multiple MMEs to avoid congestion.

[0044] II. 5G NR wireless communication network In some implementations, the present subject matter relates to 5G new radio ("NR") communication systems. 5G NR is the next communication standard beyond the 4G / IMT-Advanced standard. 5G networks offer higher capacity than current 4G, allowing for more mobile broadband users per area unit, and enabling higher and / or unlimited data consumption in gigabytes per month and per user. This may allow users to stream high-definition media for hours per day using their mobile devices, even when Wi-Fi networks do not allow. 5G networks have improved support for device-to-device communication, lower costs, lower latency and lower battery consumption than 4G equipment, etc. Such networks will have data rates of tens of megabits per second for many users, data rates of 100 Mb / s for large metropolitan areas, simultaneous 1 Gb / s to users within a limited area (e.g., an office floor), many simultaneous connections for wireless sensor networks, increased spectral efficiency, improved coverage, enhanced signaling efficiency, 1-10 ms latency, and reduced latency compared to existing systems.

[0045] 3 illustrates an exemplary virtual radio access network 300. The network 300 can provide communication between various components, including a base station (e.g., eNodeB, gNodeB) 301, radio equipment 303, a centralized unit 302, a digital unit 304, and wireless devices 306. The components within 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 midhaul connections 308. The radio frequency ("RU") component 306 can be communicatively coupled to the DU 304 using fronthaul connections 310.

[0046] In some implementations, the CU 302 can provide intelligent 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.

[0047] In a lower layer split architecture environment, the CPRI bandwidth requirement for NR can be several hundred Gb / s. CPRI compression can be implemented in the DU and RU (as shown in Figure 3). In 5G communication systems, compressed CPRI over Ethernet frames is referred to as eCPRI and is the recommended fronthaul network. This architecture can enable standardization of fronthaul / midhaul, which can include upper layer splitting (e.g., Option 2 or Option 3-1 (upper / lower RLC split architecture)) and fronthaul using an L1 split architecture (Option 7).

[0048] In some implementations, a lower layer split architecture (e.g., Option 7) may include receiver in the uplink and joint processing across multiple transmission points (TPs) for both DL / UL and transport bandwidth and latency requirements to facilitate deployment. Additionally, the subject lower layer split architecture may include splitting of cell-level and user-level processing, which may include cell-level processing in a remote unit ("RU") and user-level processing in a DU. Additionally, using the subject lower layer split architecture, frequency-domain samples may be transported over the Ethernet fronthaul, and the frequency-domain samples may be compressed for reduced fronthaul bandwidth.

[0049] 4 illustrates an example communication system 400 that can implement 5G technology and provide users with access to higher frequency bands (e.g., greater than 10 GHz). The system 400 can include a macro cell 402 and small cells 404, 406.

[0050] The mobile device 408 may be configured to communicate with one or more of the small cells 404, 406. The system 400 may enable splitting of the control plane (C-plane) and user plane (U-plane) between the macro cell 402 and the small cells 404, 406, with the C-plane and U-plane utilizing different frequency bands. Specifically, the small cells 404, 406 may be configured to utilize higher frequency bands when communicating with the mobile device 408. The macro cell 402 may utilize existing cellular bands for C-plane communications. The mobile device 408 may be communicatively coupled via the U-plane 412, and the small cells (e.g., the small cell 406) may provide higher data rates and more flexible / cost / energy-efficient operation. The macro cell 402 can maintain good connectivity and mobility via the C-plane 410. Furthermore, in some cases, LTE and NR may be transmitted on the same frequency.

[0051] FIG. 5a illustrates an exemplary 5G wireless communication system 500 according to some implementations of the present subject matter. The system 500 may be configured to have a lower-layer split architecture according to Option 7-2. The system 500 may include a core network 502 (e.g., 5G Core) and one or more gNodeBs (or gNBs), where the gNBs may have a centralized unit gNB-CU. The gNB-CU may be logically divided 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 (defined in the 3GPP standard). The control plane portion 504 may be configured to be responsible for executing the RRC and PDCP protocols of the radio stack.

[0052] The control plane portion 504 and user plane portion 506 of the centralized unit of the gNB may be configured to be communicatively coupled to one or more distributed units (DUs) 508, 510 according to an upper layer split architecture. The distributed units 508, 510 may be configured to execute 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 (RUs) 512 via a fronthaul network 520 (which may include one or more switches, links, etc.), which communicate with one or more user equipment (not shown in FIG. 5a). The remote radio unit 512 may be configured to execute lower portions of the PHY layer protocol and provide antenna capabilities to the remote unit for communication with user equipment (similar to the description above in connection with Figures 1a-2).

[0053] Figure 5b shows an example layer architecture 530 for a split gNB. The architecture 530 may be implemented within the communication system 500 shown in Figure 5a, which may be configured as a virtualized split radio access network (RAN) architecture, whereby layers L1, L2, L3 and radio processing may be virtualized and dissociated across centralized, distributed, and radio units. As shown in Figure 5b, the gNB-DU 508 may be communicatively coupled to the gNB-CU-CP control plane portion 504 (also shown in Figure 5a) and the gNB-CU-UP user plane portion 506. Each of the components 504, 506, 508 may be configured to include one or more layers.

[0054] The gNB-DU 508 may include RLC, MAC, and PHY layers, 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 the control plane portion 504 of the centralized unit, which may also include the F1-AP, SCTP, and IP sublayers, as well as the Radio Resource Control and PDCP Control (PDCP-C) sublayers. Furthermore, the distributed unit 508 may also be communicatively coupled to the user plane portion 506 of the centralized unit of the gNB. The user plane portion 506 may include the Service Data Adaptation Protocol (SDAP), PDCP User (PDCP-U), GTPU, UDP, and IP sublayers.

[0055] Figure 5c shows an example functional division in the gNB architecture shown in Figures 5a-5b. As shown in Figure 5c, 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. An upper portion of the PHY layer (or Layer 1) may be performed by the gNB-DU 508, and a lower portion of the PHY layer may be performed by the RU (not shown in Figure 5c). As shown in Figure 5c, the RRC and PDCP-C portions may be performed by the control plane portion 504, and the SDAP and PDCP-U portions may be performed by the user plane portion 506.

[0056] 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.

[0057] The MAC sublayer of Layer 2 may 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 transport blocks (TBs), multiplexing / demultiplexing of SDUs belonging to logical channels to / from TBs passed to / from the physical layer on transport channels, scheduling information reporting, error correction using HARQ, priority handling between logical channels for one UE, priority handling between UEs using dynamic scheduling, transport format selection, and other functions. The RLC sublayer's functions may include forwarding upper-layer packet data units (PDUs), error correction using ARQ, reordering of data PDUs, duplication and protocol error detection, reestablishment, etc. The PDCP sublayer may be responsible for forwarding user data, various functions during reestablishment procedures, retransmission of SDUs, discarding SDUs in the uplink, forwarding of control plane data, etc.

[0058] The RRC sublayer of Layer 3 may perform functions such as broadcasting system information to the NAS and AS, establishing, maintaining, and releasing RRC connections, security, establishing, configuring, maintaining, and releasing point-to-point radio bearers, mobility functions, reporting, and other functions.

[0059] III. LTM for CU-UP Relocation within Base Station In some implementations of the present subject matter, a base station (e.g., a gNodeB in FIG. 5a) of a wireless communication system (e.g., a 5G wireless communication system, a 6G or later generation wireless communication system, etc.) can have a distributed architecture in which the base station includes two or more CU-UPs (e.g., gNB-CU-UP 506 in FIGS. 5a-5c). The base station can be configured to provide LTM when a UE communicatively coupled to the base station undergoes relocation from one CU-UP of the base station to another CU-UP of the base station with respect to one or more services.

[0060] FIG. 6a shows an example system 600 configured to provide LTM for intra-base station CU-UP relocation. The base station 624 in this illustrated implementation is a gNB configured to be in a 5G wireless communication system similar to the 5G wireless communication system 500 of FIG. 5a described above, although other base stations may be similarly configured and used in providing LTM for intra-base station CU-UP relocation. In the illustrated implementation of FIG. 6a, the base station 624 includes multiple CU-UPs 606a, 606b, and 606c. The base station 624 includes three CU-UPs 606a, 606b, and 606c in this illustrated implementation, but may include multiple other CU-UPs. The CUs of the base station 624, including the multiple CU-UPs 606a, 606b, and 606c, are configured to be communicatively coupled with a core network (not shown in FIG. 6a), such as the 5G 5G communication system 502 of FIG. 5a.

[0061] 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. The E1 interface 614 includes three communication links in this illustrated implementation to reflect that there are three CU-UPs 606a, 606b, 606c with which the CU-CP 604 may be configured to communicate.

[0062] The base station 624 also includes multiple DUs 608, 610. The base station 624 includes two DUs 608, 610 in this illustrated implementation, but may include multiple other 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. The F1-U interface 618 associated with each of the DUs 608, 610 includes three communication links in this illustrated implementation to reflect the three CU-UPs 606a, 606b, 606c with which each DU 608, 610 may be configured to communicate.

[0063] The base station 624 also includes multiple RUs 612. In this illustrated implementation, the base station 624 includes five RUs 612, but may include a different number of RUs. The RUs 612 are configured to be communicatively coupled to the DUs 608, 610 via a fronthaul network 620. Furthermore, each of the RUs 612 is configured to be communicatively coupled to one or more UEs 622. In this 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 another number of UEs, the same or different from any of the other RUs 612.

[0064] Intra-base-station CU-UP relocation may be configured to occur when one of the UEs 622 communicatively coupled with the base station 624 undergoes relocation from one of the CU-UPs 606a, 606b, 606c to another of the CU-UPs 606a, 606b, 606c with respect to one or more services. One of the CU-UPs 606a, 606b, 606c currently serving the UE 622 is referred to as the "serving CU-UP" because it currently serves the UE 622. One of the CU-UPs 606a, 606b, 606c to which the UE's services are being moved upon relocation is referred to as the "target CU-UP" because it is targeted to serve the UE 622.

[0065] For example, an intra-base station CU-UP relocation scenario may occur when one of the UEs 622 is being served by a first one of the DUs 608 (via one of the RUs 612), which is being served by a first one of the CU-UPs 606a, and is moving at least one service (via the same one of the RUs 612 or a different one of the RUs 612) to a second one of the DUs 612, which is being served by a second one of the CU-UPs 606b. The DU 608 currently serving the UE 622 is referred to as the "serving DU," e.g., because it currently serves the UE 622. The DU 610 to which the UE's service is being moved is referred to as the "target DU," because it is targeted to serve the UE 622. Each of the CU-UPs 606a, 606b, 606c has a different security key used when securely communicating with the DU. Therefore, the target DU 610 needs the security key of the second CU-UP 606b before the DU 610 can provide services to the UE 622.

[0066] For example, in a scenario where one of the UEs 622 is being served by one of the first and second DUs 608, 610, which are in turn served by one of the CU-UPs 606a, 606b, 606c, and is moving at least one service to another of the DUs 608, 610 that is also served by the same one of the CU-UPs 606a, 606b, 606c, no intra-base station CU-UP relocation needs to occur. Thus, one of the DUs 608, 610 serving the UE 622 may have changed, but the CU-UP 606a, 606b, 606c serving the UE 622 has not changed.

[0067] Scenarios in which intra-base station CU-UP relocation is configured to or not to occur are further described with respect to Figure 6b. Figure 6b shows the CU-CP 604 and CU-UPs 606a, 606b, 606b of Figure 6a, but in the illustrated implementation of Figure 6b, the base station 624 includes three or more DUs. In the illustrated implementation of Figure 6b, the base station 624 includes 66 DUs 626, 628. Three of the DUs 628a, 628b, and 628c are macro cells (labeled macro1, macro2, and macro3 in FIG. 6b), and 63 of the DUs 626 are small cells (nine of which are labeled gNB-DU10, gNB-DU20, gNB-DU30, gNB-DU40, gNB-DU50, gNB-DU60, gNB-DU70, gNB-DU80, and gNB-DU90 in FIG. 6b). The base station 624 may include a different number of macro cells and / or a different number of small cells. Twenty-one of the small cells DUs 626, including macro1 DU 628a, macro2 DU 628b, and gNB-DU10, gNB-DU20, and gNB-DU30, are configured to be served by a first CU-UP 606a (labeled CU-UP1 in FIG. 6b). Twenty-one of the small cells DUs 626, including macro1 DU 628a, macro2 DU 628b, macro3 DU 628c, and gNB-DU40, gNB-DU50, and gNB-DU60, are configured to be served by a second CU-UP 606b (labeled CU-UP2 in FIG. 6b). Twenty-one of the small cells DUs 626, including macro2 DU 628b, macro3 DU 628c, and gNB-DU70, gNB-DU80, and gNB-DU90, are configured to be served by a third CU-UP 606c (labeled CU-UP3 in FIG. 6b).

[0068] An example of a scenario in which intra-base station CU-UP relocation is not configured to occur is when at least one service of a UE moves from one macrocell served by a particular CU-UP to another macrocell also served by that CU-UP, for example, moving from Macro 1 DU 628a served by a first CU-UP 606a to Macro 2 DU 628b also served by the first CU-UP 606a, moving from Macro 3 DU 628c served by a second CU-UP 606b to Macro 2 DU 628b also served by the second CU-UP 606b, etc. Another example of a scenario in which intra-base station CU-UP relocation is not configured to occur is when at least one service of UE 622 moves from one small cell served by a particular CU-UP to another small cell, for example, moving from gNB-DU10 626 to gNB-DU20 626, moving from gNB-DU50 626 to gNB-DU40 626, moving from gNB-DU50 626 to gNB-DU60 626, moving from gNB-DU70 626 to gNB-DU80 626, moving from gNB-DU80 626 to gNB-DU70 626, etc.

[0069] An example of a scenario in which intra-base station CU-UP relocation is configured to occur is when at least one service of one of the UEs moves from one macrocell served by a particular CU-UP to another macrocell served by another CU-UP, e.g., moves from a Macro 1 DU 628a served by a first CU-UP 606a to a Macro 3 DU 628c served by a second CU-UP 606b, moves from a Macro 3 DU 628a served by a second CU-UP 606a to a Macro 3 DU 628c served by a third CU-UP 606c, etc. Another example of a scenario in which intra-base station CU-UP relocation is configured to occur is when at least one service of a UE moves from one small cell served by a particular CU-UP to another small cell served by another small cell, for example, moving from gNB-DU10 626 served by a first CU-UP 606a to gNB-DU40 626 served by a second CU-UP 606b, moving from gNB-DU80 626 served by a third CU-UP 606b to gNB-DU40 626 served by a second CU-UP 606b, moving from gNB-DU90 626 served by a third CU-UP 606c to gNB-DU30 626 served by the first CU-UP 606a, or moving from gNB-DU50 626 served by the second CU-UP 606b to gNB-DU20 626 served by the first CU-UP 606a. Move to 626, etc.

[0070] 6b, each CU-UP 606a, 606b, 606c serves a subset of DUs 626, 628a, 628, 628c for all services. However, a CU-UP can 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)).

[0071] The scenarios described above with respect to Figures 6a and 6b illustrate examples of intra-base station CU-UP relocation. The intra-base station CU-UP relocation described herein also applies to L1 / L2-based inter-cell mobility, which covers intra-CU inter-DU scenarios. An example of such a scenario is when at least one service of a UE moves from one small cell served by a particular CU-UP to another small cell served by that CU-UP, for example, moving from gNB-DU10 626 served by a first CU-UP 606a to gNB-DU20 626 served by the first CU-UP 606a, moving from gNB-DU40 626 served by a second CU-UP 606b to gNB-DU60 626 served by the second CU-UP 606b, moving from gNB-DU90 626 served by a third CU-UP 606c to gNB-DU80 626 served by the third CU-UP 606c, etc.

[0072] In some implementations, providing LTM for intra-base station CU-UP relocation may include a preparation stage and a data transfer stage that occurs after the preparation stage. In some implementations, the preparation stage may include a CU-CP (e.g., gNB-CU-CP 504 in FIGS. 5a-5c, CU-CP 604 in FIGS. 6a-6b, etc.) of a base station (e.g., gNodeB in FIG. 5a, gNB 624 in FIG. 6a, etc.) preparing a target DU (e.g., DU 508 in FIGS. 5a-5c, DU 510 in FIG. 5a, DU 608 in FIG. 6a, DU 610 in FIG. 6a, DU 626 in FIG. 6b, DU 628 in FIG. 6b, etc.) and a target CU-UP (e.g., gNB-CU-UP 506 in FIGS. 5a-5c, CU-UP 606a, 606b, 606c in FIGS. 6a-6b, etc.) for the LTM.

[0073] Preparing the target DU may include the CU-CP providing the target DU with security keys for the UE provided by the target CU-UP, thereby enabling the target DU to communicate securely with the UE and the target CU-UP using the security keys. The CU-CP may provide the security keys to the target DU before a serving cell change occurs and at least one service of the UE (e.g., UE 622 in FIG. 6a) is relocated to the target CU-UP, so that the target DU can communicate securely with the UE and the target CU-UP without delay once the serving cell change occurs. In some implementations, the CU-CP may be configured to provide the security keys to the target DU in an F1:UE CONTEXT SETUP REQUEST message. The F1:UE CONTEXT SETUP REQUEST message is defined by 3GPP. Thus, the security keys may be sent from the CU-CP to the target DU using a message already sent from the CU-CP to the target DU according to the 3GPP standard.

[0074] Target CU-UP preparation can include the CU-CP notifying the target CU-UP that relocation will occur for a given UE. The notification can enable the CU-CP to receive security keys for the UE's target CU-UP from the target CU-UP, for example, in response to the notification, so that the CU-CP can provide the security keys to the target DU during LTM target cell preparation. In some implementations, the CU-CP can be configured to provide the notification to the target CU-UP in a BEARER CONTEXT SETUP REQUEST message, such as an information element (IE) of the BEARER CONTEXT SETUP REQUEST message. 3GPP defines the BEARER CONTEXT SETUP REQUEST message. Thus, the notification can be sent from the CU-CP to the target CU-UP using a message already sent from the CU-CP to the target CU-UP according to the 3GPP standards. The same message can be used to reserve resources required for the UE's CU-UP relocation.

[0075] In some implementations, the data forwarding stage may include a serving DU (e.g., DU 508 of FIGS. 5a-5c, DU 510 of FIG. 5a, DU 608 of FIG. 6a, DU 610 of FIG. 6a, DU 626 of FIG. 6b, DU 628 of FIG. 6b, etc.) that indicates to a serving CU-UP (e.g., gNB-CU-UP 506 of FIGS. 5a-5c, CU-UPs 606a, 606b, 606c of FIGS. 6a and 6b, etc.) when to initiate data forwarding to the target CU-UP. The data forwarding stage may also include a CU-CP that identifies a target CU-UP of a given target cell to the serving DU, thereby enabling the serving DU to identify the target CU-UP corresponding to the target cell in the target DU to the serving CU-UP so that the serving CU-UP can communicate with the target CU-UP for the purpose of triggering data forwarding to the target CU-UP. In some implementations, the CU-CP can be configured to identify the target CU-UP of a given target cell to the serving DU in a UE CONTEXT MODIFICATION REQUEST message. The UE CONTEXT MODIFICATION REQUEST message is specified by 3GPP. Thus, the identification of the target CU-UP of a given target cell can be provided from the CU-CP to the serving DU using a message already sent from the CU-CP to the serving DU according to the 3GPP standards.

[0076] FIG. 7 illustrates an example method 700 in accordance with some implementations of the present subject matter. As shown in FIG. 7, method 700 includes a preparation stage 716 and a data transfer stage 718. Method 700 is described with respect to an example system 800 shown in FIG. 8, but may be similarly implemented in other systems, such as the systems of FIGS. 6a and 6b. While system 800 of FIG. 8 is a 5G system, as noted above, the LTM for intra-base station CU-UP relocation described herein may be performed in other types of wireless communication systems, such as 6G or later generation wireless communication systems.

[0077] In system 800, a UE 802 (e.g., UE 622 in FIG. 6a) is configured 814 with an LTM having one or more target cells within one or more DUs 804, 806 (e.g., DU 508 in FIGS. 5a-5c, DU 510 in FIG. 5a, DU 608 in FIG. 6a, DU 610 in FIG. 6a, DU 626 in FIG. 6b, DU 628 in FIG. 6b, etc.) of a base station, such as a gNodeB (e.g., gNodeB in FIG. 5a, gNodeB 624 in FIGS. 6a and 6b). For ease of explanation, the system 800 is shown in FIG. 8 with one UE 802, two DUs 804, 806, and two CU-UPs 810, 812 of the base station (e.g., gNB-CU-UP 506 in FIGS. 5a-5c, CU-UPs 606a, 606b, 606c in FIGS. 6a and 6b, etc.) communicatively coupled to the base station, but more than one UE can be communicatively coupled to the base station, a base station can include more than two DUs, and a base station can include more than two CU-UPs. The base station of the system 800 also includes a CU-CP 808 (e.g., gNB-CU-CP 504 in FIGS. 5a-5c, CU-CP 604 in FIGS. 6a and 6b, etc.) and multiple RUs (e.g., RU 512 in FIG. 5a, RU 612 in FIG. 6a, etc.) (not shown in FIG. 8). The UE 802 is currently served by the serving DU 804 and serving CU-UP 810.

[0078] The method 700 includes a CU-CP 808 determining 702 that a target DU 806 of a UE 802 is served by a different CU-UP (target CU-UP 812) than a serving CU-UP 810 currently serving a serving DU 804. The CU-CP's determination 702 may include the CU-CP 808 analyzing 818 a radio resource control (RRC) measurement report sent 816 by the UE 802 to the CU-CP 808 in accordance with 3GPP standards. 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 a service change whereby the UE 802 will be served by a DU other than the serving DU 804, e.g., the target DU 806, for at least one service. According to the 3GPP standard, the CU-CP 808 is aware of the serving CU-UP 810 currently serving the serving DU 804 and the CU-UP 812 currently serving the target DU 806. Therefore, the CU-CP 808 is aware that the LTM of the intra-base station CU-UP relocation is properly performed in this scenario since the CU-UP serving the UE 802 is changed.

[0079] In response to determining 702 that the target DU 806 of the UE 802 is served by a different CU-UP 810 (target CU-UP) than the serving CU-UP 812 currently serving the serving DU 804, the CU-CP 808 prepares the target CU-UP 812 for LTM. Preparing the target CU-UP 812 may include the CU-CP 808 requesting the target CU-UP 812 to reserve necessary resources for the UE 802 and fetching 704 security keys for the UE 802 from the target CU-UP 812. As shown in FIG. 8 , preparing the target CU-UP 812 for LTM and fetching security keys 704 may include the CU-CP 808 sending 820 an E1:BEARER CONTEXT SETUP REQUEST message to the target CU-UP 812 using the E1 communication interface. As further shown in FIG. 8, the E1:BEARER CONTEXT SETUP REQUEST message may include an IE that notifies the target CU-UP 812 that CU-UP relocation is occurring so that the target CU-UP 812 can reserve resources for the UE 802.

[0080] In response to receiving the E1:BEARER CONTEXT SETUP REQUEST message, for example, in response to receiving an IE indicating that CU-UP relocation is occurring, the target CU-UP 812 sends an E1:BEARER CONTEXT SETUP RESPONSE message to the CU-CP 808 at 822, which includes the security keys of the target CU-UP of the UE 802. The E1:BEARER CONTEXT SETUP RESPONSE message is specified in 3GPP. Thus, the security keys may be sent from the target CU-UP 808 to the CU-CP 812 using a message already sent from the target CU-UP 812 to the CU-CP 808 according to the 3GPP standards.

[0081] After fetching the security key of the target CU-UP of the UE 802 in 704, the CU-CP 808 transmits the security key of the UE 802 to the target DU 806 in 706 to prepare the target DU 806 for LTM. As shown in FIG. 8 , transmitting the security key to the target DU 806 in 706 may include the CU-CP 808 transmitting a UE CONTEXT SETUP REQUEST message in 824 using the F1 communication interface, the UE CONTEXT SETUP REQUEST message including the security key of the target CU-UP of the UE 802. In response to receiving the F1:UE CONTEXT SETUP REQUEST message, the target DU 806 reserves necessary resources and transmits an F1:UE CONTEXT SETUP RESPONSE message in 826. As shown in FIG. 8 , the F1:UE CONTEXT SETUP RESPONSE message may include cell group configuration information of the target DU 806. The F1:UE CONTEXT SETUP REQUEST message and the F1:UE CONTEXT SETUP RESPONSE message are respectively defined by 3GPP, so that the security key can be sent from the CU-CP 808 to the target DU 806 and acknowledged by the target DU 806 to the CU-CP 808 using messages already sent according to the 3GPP standard.

[0082] The CU-CP 808 also notifies the serving DU 804 of the change in the CU-UP of the given target cell at 708 by identifying the target CU-UP 812 and the corresponding target cell or target DU 806 to the serving DU 804. As shown in Figure 8, notifying the serving DU 804 may include the CU-CP 808 sending a UE CONTEXT MODIFICATION REQUEST message to the serving DU 804 at 828 using the F1 communication interface. As further shown in Figure 8, the UE CONTEXT MODIFICATION REQUEST message may include cell identification information and target CU-UP mapping information.

[0083] In response to receiving the UE CONTEXT MODIFICATION REQUEST message, the serving DU 804 stores information identifying the received target CU-UP 812 at 830 and sends a UE CONTEXT MODIFICATION RESPONSE message to the CU-CP 808 at 832. As shown in Figure 8, the UE CONTEXT MODIFICATION RESPONSE message includes aggregated cell group configuration information for all target cells identified for the UE 802 by the CU-CP 808. The UE CONTEXT MODIFICATION REQUEST message and the UE CONTEXT MODIFICATION RESPONSE message are each defined by 3GPP. Thus, the serving DU 804 can receive information about the target CU-UP 812 from the CU-CP and acknowledge its receipt to the CU-CP 808 using messages already sent according to the 3GPP standard.

[0084] At 710, the CU-CP 808 also notifies the UE 802 of the security key change (indirectly, the CU-UP change) corresponding to the target cell. As shown in FIG. 8, this notification to the UE 802 may include the CU-CP 808 sending an RRC reconfiguration message at 834 to the UE 802 in accordance with 3GPP standards. As further shown in FIG. 8, the RRC reconfiguration message includes target cell configuration information, including the security key corresponding to the target cell, as provided from the target DU 806 to the CU-CP 808 in, for example, a UE CONTEXT SETUP RESPONSE message. The RRC reconfiguration message including the target cell configuration information (LTM preparation) indicates to the UE 802 that the security keys of the new target cell served by the target CU-UP 812 are different. In this scenario, the packet data convergence protocol (PDCP) entity needs to be reset.

[0085] In response to receiving the RRC reconfiguration message, the UE 802 sends an intra-frequency or inter-frequency L1 measurement report to the serving DU 804 at 836 according to the 3GPP standard. The intra-frequency or inter-frequency L1 measurement report provides the UE measured radio condition information to the serving DU 804 and indicates when the serving DU 804 should trigger the serving CU-UP 810 to perform data transfer to the target DU 806.

[0086] Thereafter, according to an intra- or inter-frequency L1 measurement report indicating a predetermined threshold configured as a criterion for when triggering should occur, the serving DU 804 triggers data transfer from the serving CU-UP 810 to the target CU-UP 812 by notifying the serving CU-UP 810 when to start data transfer to the target CU-UP 812 at 712. As shown in FIG. 8 , the serving DU 804 can notify the serving CU-UP 810 at 712 by sending a control packet data unit (PDU) to the serving CU-UP 810 at 840 in accordance with the 3GPP standard. The control PDU is not a control signaling message, as it is a user plane data packet containing control plane information. As also shown in FIG. 8 , the control PDU includes information identifying the target CU-UP 812 and information indicating that data transfer to the target CU-UP 812 should be started, for example, by including the ID of the CU-UP 812 when provided to the serving DU 804 in a UE CONTEXT MODIFICATION REQUEST message.

[0087] In response to the serving CU-UP 810 being notified by the serving DU 804 at 712 to initiate data transfer, the serving CU-UP 810 initiates data transfer to the target CU-UP 812 at 714 by sending any unsent and unacknowledged data PDUs to the target CU-UP 812 at 842. The serving CU-UP 810 knows which base station's CU-UP to contact as the target CU-UP 810 by the CU-UP ID provided to the serving CU-UP 812 by the serving DU 804.

[0088] In some implementations, instead of the serving DU 804 sending a control PDU to the serving CU-UP 810 at 840, the serving DU 804 can send a signaling message to the CU-CP 808 using the F1-C communication interface, which then initiates the data transfer to the target CU-UP 812 by sending a message to the serving CU-UP 810 using the E1 communication interface, which then initiates the data transfer to the target CU-UP 812. This alternative implementation uses one more message transmission than the implementation shown in FIG. 8, but unlike the implementation shown in FIG. 8, it utilizes the E1-C communication interface in triggering the data transfer.

[0089] 7, after the serving DU 804 triggers data forwarding, e.g., after the serving DU 804 sends a control PDU to the serving CU-UP 810 (or CU-CP 808 in an alternative implementation) at 840, the serving DU 804 notifies the UE 802 at 716 that a serving cell change, e.g., an LTM secondary component carrier (SCC), must be performed for the UE's target DU 806. As shown in FIG. 8, the UE notification at 716 may include the serving DU 804 sending a MAC Control Element (MAC CE) to the UE 802 at 844, which includes a serving cell change command. As further shown in FIG. 8, the MAC CE may include a security key change indication, which may be a one-bit indicator within the MAC CE.

[0090] In response to receiving the MACCE, the UE 802 transmits a random access channel (RACH) message to the target DU 812 at 846, and the UE 802 transmits an RRC reconfiguration acknowledgement message to the CU-CP 808 at 852, in accordance with 3GPP standards. In response to successful completion of the RACH procedure, the target DU 812 transmits a control PDU to the target CU-UP 812 at 848, and the target DU 812 transmits a serving cell change notification message to the CU-CP 808 at 850 using the F1 communication interface. As shown in FIG. 8, the control PDU may include the SCC and the RACH completion notification. This notification initiates the transmission of downlink data to the UE 802. As further shown in FIG. 8, the serving cell change notification message may include the ID of the target DU 812.

[0091] The base station of Figure 8 is communicatively coupled to a core network (not shown in Figure 8). The method 700 may also include performing a path switching procedure toward the core network, which may be performed in accordance with 3GPP standards, such as in an intra-gNB CU-UP relocation scenario.

[0092] In some implementations, the present subject matter can be configured to be implemented in a system 900, as shown in FIG. 9 . The system 900 can 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 can be interconnected using a system bus 950. The processor 910 can be configured to process instructions for execution within the system 600. In some implementations, the processor 910 can be a single-threaded processor. In alternative implementations, the processor 910 can be a multi-threaded processor. The processor 910 can further be configured to process instructions stored in the memory 920 or the storage device 930, including receiving or transmitting information through the input / output device 940. The memory 920 can store information within the system 900. In some implementations, the memory 920 can be a computer-readable medium. In alternative implementations, the memory 920 can be a volatile memory unit. Further, in some implementations, memory 920 may be a non-volatile memory unit. Storage device 930 may be capable of providing mass storage for system 900. In some implementations, storage device 930 may be a computer-readable medium. In alternative implementations, storage device 930 may be a floppy disk device, a hard disk device, an optical disk device, a tape device, a non-volatile solid-state memory, or any other type of storage device. Input / output device 940 may be configured to provide input / output operations to system 900. In some implementations, input / output device 940 may include a keyboard and / or a pointing device. In alternative implementations, input / output device 940 may include a display unit for displaying a graphical user interface.

[0093] 10 illustrates an example method 1000 of LTM for intra-base station CU-UP relocation in accordance with some implementations of the present subject matter. Method 1000 may be performed, for example, using the implementations shown in and described with respect to FIGS.

[0094] The method 1000 includes determining 1002 that a target distributed unit (e.g., DU 508 in Figures 5a to 5c, DU 510 in Figures 5a, DU 608 in Figures 6a, DU 610 in Figures 6a, DU 626 in Figure 6b, DU 628 in Figure 6b, target DU 806 in Figure 8, etc.) of a base station (e.g., gNodeB in Figure 5a, gNodeB 624 in Figures 6a and 6b, gNodeB in Figure 8, etc.) serving a user equipment (e.g., UE 622 in Figure 6a, UW 802 in Figure 8, etc.) is served by a target centralized unit user plane (e.g., gNB-CU-UP 506 in Figures 5a to 5c, CU-UP 606a, 606b, 606c in Figures 6a and 6b, target CU-UP 812, etc.) of the base station. The base station's serving CU-UP (e.g., gNB-CU-UP 506 in Figures 5a to 5c, CU-UPs 606a, 606b, 606c, serving CU-UP 810 in Figures 6a and 6b, etc.) serves the base station's serving DU (e.g., DU 508 in Figures 5a to 5c, DU 510 in Figure 5a, DU 608 in Figure 6a, DU 610 in Figure 6a, DU 626 in Figure 6b, DU 628 in Figure 6b, serving DU 804 in Figure 8, etc.) that is currently serving the UE. The method 1000 also includes preparing 1004 a target CU-UP for the LTM using a centralized unit control plane of the base station (e.g., gNB-CU-CP 504 in Figures 5a to 5c, CU-CP 604, CU-CP 808 in Figures 6a and 6b, etc.), and preparing 1006 a target DU for the LTM using the CU-CP.

[0095] In some implementations, the present subject matter can include one or more of the following optional features.

[0096] In some implementations, preparing the target CU-UP may include fetching security keys from the target CU-UP using the CU-CP, and preparing the target DU may include sending the security keys from the CU-CP to the target DU. Further, the security keys configured by the target CU-UP may be sent from the CU-CP to the target DU in a UE CONTEXT SETUP REQUEST message, and / or fetching the security keys may include the CU-CP sending a BEARER CONTEXT SETUP REQUEST message to the target CU-UP and the CU-UP sending a BEARER CONTEXT SETUP RESPONSE message to the CU-CP, where the BEARER CONTEXT SETUP RESPONSE message may include security keys that may correspond to UEs served by the target CU-UP. Further, the BEARER CONTEXT SETUP REQUEST message may include an information element (IE) that notifies the target CU-UP of the LTM.

[0097] In some implementations, preparing the target CU-UP may include sending an information element (IE) from the CU-CP to the target CU-UP that notifies the target CU-UP of the LTM to reserve resources for the UE.

[0098] In some implementations, the method may also include triggering the serving CU-UP to initiate data transfer to the target CU-UP after the target CU-UP prepares and the target DU prepares. Further, the triggering may include sending a control packet data unit (PDU) from the serving DU to the serving CU-UP to initiate downlink data transmission, and the serving CU-UP then sending untransmitted and unacknowledged data PDUs to the target CU-UP. Furthermore, the method may also include sending information from the CU-CP to the serving DU to identify a change in the serving CU-UP of the LTM before sending the control PDU to trigger the data transfer. Furthermore, this information may be sent from the CU-CP to the serving DU in a UE CONTEXT MODIFICATION REQUEST message.

[0099] In some implementations, the method may also include, after preparing the target CU-UP and preparing the target DU, triggering the target CU-UP to start serving the UE via the target DU. Further, the triggering may include sending a control packet data unit (PDU) from the target DU to the target CU-UP, and then the target CU-UP sending a data PDU to the target DU, or the triggering may include sending a first message from the serving DU to the CU-CP, then the CU-CP sending a second message to the serving CU-UP, and then the serving CU-UP sending a third message to the target CU-UP, and / or serving the UE may include sending a first message from the target DU to the CU-CP, then the CU-CP sending a second message to the target CU-UP, and then the target CU-UP starting downlink data transmission toward the target DU.

[0100] In some implementations, determining may include using the CU-CP to analyze a radio resource control (RRC) measurement report received at the CU-CP from the UE.

[0101] In some implementations, the serving CU-UP and the target CU-UP may be different entities.

[0102] In some implementations, the base station may be a new generation radio access network (NG-RAN) node (e.g., gNodeB).

[0103] In some implementations, a base station may include at least one processor and at least one non-transitory storage medium.

[0104] The systems and methods disclosed herein may be embodied in various forms, including, for example, a data processor such as a computer, including a database, digital electronic circuitry, firmware, software, or any combination thereof. Furthermore, the above-described features and other aspects and principles of the implementations of the present disclosure may be implemented in various environments. Such environments and associated applications may be specially constructed to perform the various processes and operations in accordance with the disclosed implementations, or they may comprise general-purpose computers or computing platforms selectively activated or reconfigured by code to provide the required functionality. The processes disclosed herein are not inherently related to any particular computer, network, architecture, environment, or other apparatus, but may be implemented by any suitable combination of hardware, software, and / or firmware. For example, various general-purpose machines may be used with programs written in accordance with the teachings of the disclosed implementations, or it may be more convenient to construct specialized apparatus or systems to perform the required methods and techniques.

[0105] 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, e.g., a machine-readable storage device or a propagated signal, for execution by or to control the operation of a data processing apparatus, e.g., a programmable processor, computer, or multiple computers. The computer program may be written in any type 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 use in a computing environment. The computer program may be deployed to be executed on one computer, or on multiple computers at one site or distributed across multiple sites and interconnected by a communications network.

[0106] As used herein, the term "user" may refer to any entity, including a person or a computer.

[0107] Although ordinal numbers such as first, second, etc. may relate to order in some circumstances, as used in this document, ordinal numbers do not necessarily imply order. For example, ordinal numbers may be used simply to distinguish one item from another. For example, distinguishing a first event from a second event need not imply any chronological order or fixed frame of reference (the first event in one paragraph of description may be different from the first event in another paragraph of description).

[0108] The foregoing description is intended to illustrate, but not to limit, the scope of the invention, which is defined by the appended claims. Other implementations are within the scope of the following claims.

[0109] These computer programs, which may also be referred to as programs, software, software applications, applications, components, or code, include machine instructions for a programmable processor and may be implemented in a high-level procedural and / or object-oriented programming language and / or in assembly / machine language. As used herein, the term “machine-readable medium” refers to any computer program product, apparatus, and / or device used to provide machine instructions and / or data to a programmable processor, such as, for example, a magnetic 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 used to provide machine instructions and / or data to a programmable processor. A machine-readable medium may non-transitory store such machine instructions, such as, for example, a non-transitory solid-state memory or a magnetic hard drive or any equivalent storage medium. Alternatively or additionally, a machine-readable medium may temporarily store such machine instructions, such as, for example, a processor cache or other random access memory associated with one or more physical processor cores.

[0110] To provide for user interaction, the subject matter described herein may be implemented on a computer having a display device, such as a cathode ray tube (CRT) or liquid crystal display (LCD) monitor, for displaying information to the user, and a keyboard and pointing device, such as a mouse or trackball, by which the user can provide input to the computer. Other types of devices may also be used to provide for user interaction. For example, feedback provided to the user may be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback, and input from the user may be received in any form, including, but not limited to, acoustic, speech, or tactile input.

[0111] The subject matter described herein may be implemented in a computing system that includes back-end components, such as, for example, one or more data servers, or middleware components, such as, for example, one or more application servers, or front-end components, such as, for example, one or more client computers having a graphical user interface or web browser through which a user can interact with an implementation of the subject matter described herein, or any combination of such back-end, middleware, 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 communications network. Examples of communications networks include, but are not limited to, a local area network ("LAN"), a wide area network ("WAN"), and the Internet.

[0112] A computing system may include clients and servers. Clients and servers are typically, but not exclusively, remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

[0113] The implementations described in the foregoing description do not represent all implementations consistent with the subject matter described herein. Rather, they are merely some examples consistent with aspects related to the subject matter described. While several variations have been described in detail above, other modifications or additions are possible. In particular, additional features and / or variations may be provided in addition to those described herein. For example, the implementations described above may be directed to various combinations and subcombinations of the disclosed features and / or combinations and subcombinations of certain additional features disclosed above. In addition, the logic flow illustrated in the accompanying figures and / or described herein does not necessarily require the particular order shown, or sequential order, to achieve desirable results. Other implementations may be within the scope of the following claims.

Claims

1. 1. An apparatus comprising: at least one processor; 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: determining that a target distributed unit (DU) of a base station serving a user equipment (UE) is served by a target centralized unit user plane (CU-UP) of the base station, wherein the serving CU-UP of the base station serves the serving DU of the base station that is currently serving the UE; preparing the target CU-UP for Layer 1 / Layer 2 triggered mobility (LTM) using a centralized unit control plane (CU-CP) of the base station; preparing the target DU for LTM using the CU-CP; a non-transitory storage medium for causing the operation to be performed, the non-transitory storage medium including: An apparatus comprising:

2. Preparing the target CU-UP includes fetching a security key from the target CU-UP using the CU-CP; Preparing the target DU includes transmitting the security key from the CU-CP to the target DU; The apparatus of claim 1 , comprising:

3. The apparatus of claim 2 , wherein the security keys configured by the target CU-UP are sent from the CU-CP to the target DU in a UE CONTEXT SETUP REQUEST message.

4. fetching the security key includes the CU-CP sending a BEARER CONTEXT SETUP REQUEST message to the target CU-UP, and the CU-UP sending a BEARER CONTEXT SETUP RESPONSE message to the CU-CP; The apparatus of claim 2 , wherein the BEARER CONTEXT SETUP RESPONSE message includes the security key corresponding to the UE served by the target CU-UP.

5. The apparatus of claim 4 , wherein the BEARER CONTEXT SETUP REQUEST message includes an information element (IE) that notifies the target CU-UP of the LTM.

6. The apparatus of claim 1, wherein preparing the target CU-UP includes transmitting an information element (IE) from the CU-CP to the target CU-UP that notifies the target CU-UP of the LTM to reserve resources for the UE.

7. The apparatus of claim 1 , wherein the operation further includes triggering the serving CU-UP to initiate data transfer to the target CU-UP after the preparation of the target CU-UP and the preparation of the target DU.

8. 8. The apparatus of claim 7, wherein the triggering includes transmitting a control packet data unit (PDU) from the serving DU to the serving CU-UP, and then the serving CU-UP transmitting untransmitted and unacknowledged data PDUs to the target CU-UP.

9. The apparatus of claim 1 , wherein the operation further includes, after the preparation of the target CU-UP and the preparation of the target DU, triggering the target CU-UP to start service to the UE via the target DU.

10. 10. The apparatus of claim 9, wherein the triggering includes transmitting a control packet data unit (PDU) from the target DU to the target CU-UP to initiate downlink data transmission, and then the target CU-UP transmitting a data PDU to the target DU.

11. 10. The apparatus of claim 8, wherein the operation further includes transmitting information from the CU-CP to the serving DU to identify a change in the serving CU-UP of an LTM before the transmission of the control PDU to trigger data transfer.

12. The apparatus of claim 11 , wherein the information is sent from the CU-CP to the serving DU in a UE-CONTEXT MODIFICATION REQUEST message.

13. 10. The apparatus of claim 9, wherein the triggering includes sending a first message from the serving DU to the CU-CP, then the CU-CP sending a second message to the serving CU-UP, and then the serving CU-UP sending a third message to the target CU-UP.

14. 10. The apparatus of claim 9, wherein serving the UE includes transmitting a first message from the target DU to the CU-CP, then the CU-CP transmitting a second message to the target CU-UP, and then the target CU-UP starting downlink data transmission toward the target DU.

15. The apparatus of claim 1 , wherein the determining includes using the CU-CP to analyze a radio resource control (RRC) measurement report received in the CU-CP from the UE.

16. The apparatus of claim 1 , wherein the serving CU-UP and the target CU-UP are different entities.

17. The apparatus of claim 1 , wherein the base station is a New Generation Radio Access Network (NG-RAN) node.

18. The apparatus of claim 1 , wherein the base station includes the at least one processor and the at least one non-transitory storage medium.

19. 1. A computer-implemented method comprising: determining that a target distributed unit (DU) of a base station serving a user equipment (UE) is served by a target centralized unit user plane (CU-UP) of the base station, wherein the serving CU-UP of the base station serves the serving DU of the base station that is currently serving the UE; Using a centralized unit control plane (CU-CP) of the base station, prepare a target CU-UP for Layer 1 / Layer 2 triggered mobility (LTM); preparing the target DU for LTM using the CU-CP; 11. A computer-implemented method comprising:

20. at least one non-transitory storage medium storing instructions that, when executed by at least one processor, cause the at least one processor to: Determining that a target distributed unit (DU) of a base station serving a user equipment (UE) is served by a target centralized unit user plane (CU-UP) of the base station, wherein the serving CU-UP of the base station serves the serving DU of the base station that is currently serving the UE; Using a centralized unit control plane (CU-CP) of a base station, preparing a target CU-UP for Layer 1 / Layer 2 triggered mobility (LTM); preparing the target DU for LTM using the CU-CP; At least one non-transitory storage medium that causes the device to perform operations including:

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