Target cell prioritization for layer 1 / layer 2 triggered mobility

Abstract

In general, the current subject matter relates to target cell prioritization for Layer 1 / Layer 2 triggered Mobility (LTM). In some implementations, target cell prioritization for LTM may include receiving, at a serving distributed unit (DU) of a base station, information from a centralized unit control plane (CU-CP) of the base station, the information indicating a handover prioritization of a plurality of Layer 1 / Layer 2 triggered mobility (LTM) target cells of a second DU of the base station, and transmitting, at the serving DU, a handover prioritization of a plurality of Layer 1 / Layer 2 triggered mobility (LTM) target cells of the second DU of the base station based on the received information. In one embodiment, one of a plurality of LTM target cells is selected for handover of service for a user equipment (UE) from a serving DU, and handover of service for the UE from the serving DU to the selected target cell is triggered. Each of the plurality of LTM target cells from which the serving DU selects satisfies a handover criterion.

Description

Technical Field

[0001] In some implementations, the present subject matter relates to telecommunication systems, and more particularly, to target cell prioritization for Layer 1 / Layer 2 Triggered Mobility (LTM). Background Art

[0002] In today's world, cellular networks provide on-demand communication capabilities to individuals and businesses. 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-location transceiver, called a cell site or base station. Each cell can use a different set of frequencies than its neighboring cells to avoid interference and provide improved service within each cell. When cells are connected together, they provide radio coverage over a wide geographic area, enabling 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 accomplished even if a mobile transceiver moves through more than one cell during transmission. Major wireless communication providers have deployed such cell sites throughout the world, allowing communicating 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 capable of receiving and / or making telephone and / or data calls through a cell site or transmission tower by using radio waves to transmit signals to and from the mobile phone. Given the large number of mobile phone users, current mobile phone networks offer limited, shared resources. To this end, cell sites and handsets can change frequencies and use low-power transmitters to allow many callers to use the network simultaneously with less interference. The coverage provided by a cell site may depend on the specific geographic location and / or the number of users who could potentially use the network. For example, in cities, a cell site has a range of up to about 1 / 2 mile; in rural areas, the range can be up to 5 miles; and in some areas, users can receive signals from cell sites up to 25 miles away.

[0004] The following are examples of some digital cellular technologies 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"), Digital 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 wireless communications for high-speed data 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, along with core network improvements.

[0005] A cellular network can be divided into a radio access network and a core network. The radio access network (RAN) may include network functions capable of handling radio layer communication processing. The core network may include network functions capable of handling higher layer communications, such as Internet Protocol (IP), transport layer, and application layer. In some cases, the RAN functions may be divided into baseband unit functions and radio unit functions, for example, where a radio unit connected to a baseband unit via a fronthaul network may be responsible for lower layer processing of the radio physical layer, while the baseband unit may 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 radio unit communicatively coupled to at least one of the one or more DUs and each radio unit configured to be communicatively coupled to one or more mobile phones and / or other user equipment (UEs). The CU may be logically divided into a control plane part CU-CP and one or more user plane parts (CU-UPs). During the process of communicatively coupling the UE with the base station, the DU supporting the UE may change (e.g., be switched) from one DU (serving DU) to one or more other DUs (target DUs). Multiple target cells at one or more DUs may be prepared for switching. However, if the configuration of the prepared target cell does not match the source configuration, the user experience may be affected even if the prepared target cell meets the radio conditions required for the UE to perform a serving cell change (SSC). Summary of the Invention

[0007] In some implementations, the present subject matter relates to a computer-implemented method. The method may include: receiving, at a serving DU of a base station, information from a CU-CP of the base station indicating a handover priority ranking of a plurality of LTM target cells of a second DU of the base station, and, at the serving DU, selecting, based on the received information, one of the plurality of LTM target cells for handover of a service for a UE from the serving DU, and triggering handover of the service for the UE from the serving DU to the selected target cell. Each of the plurality of LTM target cells selected by the serving DU satisfies a handover criterion.

[0008] This approach may allow a target cell to be selected for handover, allowing for as little service interruption and / or reduced quality of service for the UE as possible, thereby improving the user experience.

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

[0010] In some implementations, handover prioritization may be based on a target cell configuration for each of the plurality of LTM target cells. Furthermore, the target cell configuration for each of the plurality of LTM target cells may include at least one of: a configuration regarding GBR allocation for GBR DRBs, a configuration regarding PDU session-to-DRB mapping, a configuration regarding carrier configuration for carrier aggregation, a configuration regarding slice mapping for UE services, and a configuration regarding accepted DRBs for the UE; and / or the handover prioritization may be based on the configuration of each of the plurality of LTM target cells compared to the configuration of the serving cell. Furthermore, at least one target DU including the plurality of LTM target cells may provide the target cell configuration for each of the plurality of LTM target cells to the CU-CP in an F1 message, and / or the handover prioritization may be recalculated whenever an LTM target cell is added, reconfigured, or removed for the UE. Furthermore, the at least one target DU may also provide a list of changes for the plurality of LTM target cells compared to the serving cell configuration.

[0011] In some implementations, the handover criteria may include: a predetermined threshold radio quality, and the operation may also include: at the serving DU, determining which one or more of the multiple target cells have a radio quality higher than the predetermined threshold radio quality, and the selection may be only among the one or more determined target cells.

[0012] In some implementations, the triggering may include sending a MAC CE message from the serving DU to the UE.

[0013] In some implementations, a base station may have a disaggregated architecture.

[0014] In some implementations, the base station may comprise a Next Generation Radio Access Network (NG-RAN) node. Additionally, the NG-RAN node may comprise a gNodeB or an ng-eNodeB.

[0015] 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 method.

[0016] A non-transitory computer program product (i.e., a physically embodied computer program product) is also described, which stores instructions that, when executed by one or more data processors of one or more computing systems, cause the 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 the 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 by one or more data processors 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.), via direct connections between one or more computing systems, and the like.

[0017] 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

[0018] 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.

[0019] Figure 1a An exemplary conventional Long Term Evolution ("LTE") communication system is shown;

[0020] Figure 1b Shown Figure 1a Further details of the exemplary LTE system shown in;

[0021] Figure 1c Shown Figure 1aAdditional details of the Evolved Packet Core of the exemplary LTE system shown in;

[0022] Figure 1d Shown Figure 1a An exemplary evolved Node B of the exemplary LTE system shown in FIG;

[0023] Figure 2 Shown Figure 1a - Further details of the eNodeB shown in d;

[0024] Figure 3 An exemplary virtual radio access network according to some implementations of the current subject matter is shown;

[0025] Figure 4 An exemplary 3GPP split architecture is shown that provides use of higher frequency bands to its users;

[0026] Figure 5a An exemplary 5G wireless communication system is shown;

[0027] Figure 5b An exemplary layer architecture for a split gNB and / or split ng-eNB (e.g., a next-generation eNB that can be connected to a 5GC) is shown.

[0028] Figure 5c Shown Figure 5a - An exemplary functional split in the gNB architecture shown in b;

[0029] Figure 6a illustrates an exemplary system according to some implementations of the current subject matter;

[0030] Figure 6b Shows some implementations according to the current topic Figure 6a Example alternative configurations of systems;

[0031] Figure 7 Exemplary methods according to some implementations of the current subject matter are shown;

[0032] Figure 8 Another exemplary system according to some implementations of the current subject matter is shown;

[0033] Figure 9 illustrates an exemplary system according to some implementations of the current subject matter; and

[0034] Figure 10 Exemplary methods according to some implementations of the current subject matter are shown. DETAILED DESCRIPTION

[0035] The present 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.

[0036] Generally speaking, the present subject matter relates to target cell prioritization for Layer 1 / Layer 2 Triggered Mobility (LTM).

[0037] In some implementations of the current subject matter, for a user equipment (UE) communicatively coupled to a base station of a wireless communication system, a target cell may be prioritized upon handover (HO) from one cell (serving cell) to another cell (target cell). The prioritization may be based on the configuration of the target cell. Multiple target cells may meet the HO criteria required for the UE to perform a serving cell change (SSC) and, therefore, be viable target cell options for HO. However, one or more of the target cells that meet the HO criteria may have a configuration that is more similar to the configuration of the serving cell currently serving the UE than the other target cell(s) in the target cells. Therefore, prioritizing the target cells based on the configuration of the target cells may allow the target cells to be selected for HO, thereby allowing as little service interruption and / or degradation of service quality as possible for the UE, thereby improving the user experience.

[0038] 3GPP standards that define one or more aspects that may be relevant to the present subject matter include 3GPP TS 38.473 “NGRAN F1 application protocol (F1AP).” Standards of the O-RAN Alliance may also be relevant to one or more aspects of the present subject matter.

[0039] One or more aspects of the current subject matter may be incorporated into transmitter and / or receiver components 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.

[0040] I. Long Term Evolution Communication System

[0041] Figure 1a Figures 1-c and 2 show an exemplary conventional Long Term Evolution ("LTE") communication system 100 and its various components. The LTE system, or 4G LTE as it is commercially known, is governed by a standard for wireless communication of high-speed data 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").

[0042] like Figure 1a As shown in FIG, 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 EUTRAN 102 and EPC 108 provide communication between user equipment 104 and PDN 101. EUTRAN 102 may include multiple evolved Node Bs (“eNodeBs” or “ENODEBs” or “enodeb” or “eNBs”) or base stations 106 (a, b, c) (e.g., Figure 1b 100 ), which provides communication capabilities to multiple user devices 104 (a, b, c). User devices 104 may be mobile phones, smartphones, tablets, personal computers, personal digital assistants ("PDAs"), servers, data terminals, and / or any other type of user equipment, and / or any combination thereof. User devices 104 may connect to EPC 108 and ultimately to PDN 101 via any eNodeB 106. Typically, user devices 104 connect to the eNodeB 106 that is closest in terms of distance. In LTE system 100, EUTRAN 102 and EPC 108 work together to provide connectivity, mobility, and services for user devices 104.

[0043] Figure 1b It further shows Figure 1a As mentioned above, EUTRAN 102 includes multiple eNodeBs 106, also known as cell sites. The eNodeBs 106 provide radio functions and perform key 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 Entities (MMEs, such as Figure 1c The eNodeBs 106 that make up the EUTRAN 102 cooperate with each other for radio resource management and handover.

[0044] Communication between user equipment 104 and eNodeB 106 occurs via an air interface 122 (also referred to as an "LTE-Uu" interface). Figure 1b As shown, air interface 122 provides communication between user equipment 104b and eNodeB 106a. Air interface 122 uses Orthogonal Frequency Division Multiple Access ("OFDMA") and Single Carrier Frequency Division Multiple Access ("SC-FDMA") (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").

[0045] 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 (e.g., Figure 1c ). In addition to signaling, user traffic is also transmitted between user equipment 104 and eNodeB 106. Both signaling and traffic in system 100 are carried by physical layer ("PHY") channels.

[0046] Multiple eNodeBs 106 may be interconnected using X2 interfaces 130 (a, b, c). Figure 1b As shown, 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. An X2 interface may be established between two eNodeBs to provide for signal exchange, which may include load or interference related information and handover related information. The eNodeB 106 communicates with the evolved packet core 108 via S1 interfaces 124 (a, b, c). The S1 interface 124 may be divided into two interfaces: one for the control plane (in Figure 1c is shown as a control plane interface (S1-MME interface) 128), and another for the user plane (in Figure 1c is shown as user plane interface (S1-U interface) 125).

[0047] The EPC 108 establishes and enforces quality of service ("QoS") for user services and allows user devices 104 to maintain a consistent Internet Protocol ("IP") address while 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 user plane (i.e., traffic) in the core network architecture, which allows for greater flexibility in implementation and independent scalability of control and user data functions.

[0048] The EPC 108 architecture is dedicated to packet data and is Figure 1cThe 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 (a 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 typically combined into nodes depending on the manufacturer's implementation.

[0049] S-GW 110 acts as an IP packet data router and is the bearer path anchor point for user equipment in EPC 108. Therefore, when a user equipment moves from one eNodeB 106 to another during mobility operations, S-GW 110 remains the same, and the bearer path toward 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, MME 114 transfers all bearer paths for the user equipment to the new S-GW. S-GW 110 establishes a bearer path for the user equipment to one or more P-GWs 112. If downstream data is received for an idle user equipment, S-GW 110 buffers the downstream packets and requests MME 114 to locate and reestablish the bearer path to and through EUTRAN 102.

[0050] P-GW 112 is the interface between EPC 108 (and user equipment 104 and EUTRAN 102) and PDN 101 (e.g. Figure 1a 112). 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 for the user equipment, packet filtering of downstream user traffic to ensure it is placed on the appropriate bearer path, and enforcement of 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 the user equipment from one eNodeB to another, if the S-GW 110 is also changing, the bearer path from the P-GW 112 will be switched to the new S-GW.

[0051] The MME 114 manages user devices 104 within the EPC 108, including managing subscriber authentication, maintaining context for authenticated user devices 104, establishing data bearer paths within the network for user traffic, and tracking the location of idle mobile devices that have not yet detached from the network. For idle user devices 104 that need to reconnect to the access network to receive downstream data, the MME 114 initiates paging to locate the user device and reestablish a bearer path to and through the EUTRAN 102. The MME 114 for a particular user device 104 is selected by the eNodeB 106 from which the user device 104 initiates system access. For load sharing and redundancy purposes, an MME is typically part of a set of MMEs within the EPC 108. During the establishment of a user's data bearer path, the MME 114 is responsible for selecting the P-GW 112 and S-GW 110, which will form the endpoints of the data path through the EPC 108.

[0052] PCRF 118 is responsible for policy control decisions and controls flow-based charging functions residing in the Policy Control Enforcement Function ("PCEF") in P-GW 110. PCRF 118 provides QoS authorization (QoS Class Identifier ("QCI") and bit rate) that determines how a certain data flow will be handled in the PCEF and ensures that this complies with the user's subscription profile.

[0053] As mentioned above, IP services 119 are provided by PDN 101 (e.g. Figure 1a shown).

[0054] Figure 1dAn exemplary structure of an eNodeB 106 is shown. 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, using either RRH-specific custom control and user plane framing methods or 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 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 mobility 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, call processing, and monitoring and 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 sent 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.

[0055] The RRH 132 may transmit and receive wireless signals using an antenna 136. The RRH 132 may convert (using a converter ("CONV") 140) the digital baseband signal from the BBU 134 into a radio frequency ("RF") signal and power amplify (using an amplifier ("AMP") 138) the signal for transmission to the user equipment 104 ( Figure 1d 134 ). Conversely, the RF signal received from the user equipment 104 is amplified (using AMP 138 ) and converted (using CONV 140 ) to a digital baseband signal for transmission to the BBU 134 .

[0056] Figure 2Additional details of an exemplary eNodeB 106 are shown. 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") segmentation protocol used over the cellular air interface. The RRC protocol handles the control plane signaling of LTE Layer 3 between user equipment and the EUTRAN. RRC includes functions for connection establishment and release, broadcast of system information, 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, delivery of user data, and maintenance of sequence numbers for radio bearers. Figure 1d The BBU 134 shown in FIG may include LTE layers L1 - L3 .

[0057] One of the primary functions of the eNodeB 106 is radio resource management, which includes scheduling both uplink and downlink air interface resources, control of bearer resources, and admission control for user equipment 104. The eNodeB 106 acts as a proxy for the EPC 108 and is responsible for delivering paging messages, which are used to locate mobile devices when they are idle. The eNodeB 106 also handles over-the-air transmission of common control channel information, header compression, encryption and decryption of user data sent over the air, and establishment of handover reporting and triggering criteria. As described above, the eNodeB 106 can collaborate with other eNodeBs 106 via the X2 interface for handover and interference management purposes. The eNodeB 106 communicates with the EPC's MME via the S1-MME interface and with the S-GW using the S1-U interface. Furthermore, the eNodeB 106 exchanges user data with the S-GW via the S1-U interface. The eNodeB 106 and EPC 108 have a many-to-many relationship to support load sharing and redundancy between the MME and S-GW. The eNodeB 106 selects an MME from a group of MMEs, so the load can be shared by multiple MMEs to avoid congestion.

[0058] II.5G NR Wireless Communication Network

[0059] In some implementations, the present subject matter relates to 5G New Radio ("NR") communication systems. 5G NR is the next telecommunications standard beyond the 4G / IMT-Advanced standard. 5G networks offer higher capacity than current 4G, allowing for a higher number of mobile broadband users per area unit and higher and / or unlimited data consumption per user in gigabytes per month. This can allow users to stream high-definition media for hours a day using their mobile devices, even when unable to connect to a Wi-Fi network. 5G networks offer improved support for device-to-device communications, lower costs, lower latency than 4G devices, and lower battery consumption. Such networks offer data rates of tens of megabits per second for large numbers of users, 100 Mbps for metropolitan areas, and 1 Gbps for users within a limited area (e.g., an office floor). They offer enhanced spectral efficiency, improved coverage, enhanced signaling efficiency, 1-10 ms latency, and reduced latency compared to existing systems for large numbers of simultaneous connections to wireless sensor networks.

[0060] Figure 3 An exemplary virtual radio access network 300 is shown. 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. Components in system 300 can be communicatively coupled to a core using backhaul links 305. Centralized units ("CUs") 302 can be communicatively coupled to distributed units ("DUs") 304 using mid-haul connections 308. Radio frequency ("RU") components 306 can be communicatively coupled to DUs 304 using fronthaul connections 310.

[0061] 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.

[0062] In a lower layer split architecture environment, the CPRI bandwidth requirement for NR can be 100Gb / s. CPRI compression can be implemented in DU and RU (e.g. Figure 3 In 5G communication systems, CPRI compressed over Ethernet frames is called eCPRI and is the recommended fronthaul network. This architecture can allow for standardization of fronthaul / midhaul, which can include higher layer splits (e.g., Option 2 or Option 3-1 (upper / lower RLC split architecture)) and fronthaul with an L1-split architecture (Option 7).

[0063] In some implementations, a lower layer split architecture (e.g., Option 7) can include a receiver in the uplink, joint processing for both DL / UL across multiple transmission points (TPs), and transmission bandwidth and latency requirements for ease of deployment. Furthermore, the lower layer split architecture of the current subject matter can include a split between cell-level and user-level processing, which can include cell-level processing in a remote unit ("RU") and user-level processing in a DU. Furthermore, using the lower layer split architecture of the current subject matter, frequency domain samples can be transmitted via an Ethernet fronthaul, where the frequency domain samples can be compressed to reduce the fronthaul bandwidth.

[0064] Figure 4 An exemplary communication system 400 is shown that can implement 5G technology and can provide its users with access to higher frequency bands (e.g., greater than 10 GHz). System 400 can include a macro cell 402 and small cells 404, 406.

[0065] 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 user plane (U-plane) to be divided between the macro cell 402 and the small cells 404 and 406, where the C-plane and the U-plane are utilizing different frequency bands. Specifically, the small cells 404 and 406 can be configured to utilize a higher frequency band 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 cells (e.g., the small cell 406) can provide higher data rates and more flexible / cost-saving / 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.

[0066] Figure 5a An exemplary 5G wireless communication system 500 is shown according to some implementations of the present subject matter. System 500 can be configured with a lower-layer split architecture according to Option 7-2. System 500 can include a core network 502 (e.g., a 5G core) and one or more gNodeBs (or gNBs), wherein the gNBs can have a centralized unit (gNB-CU). The gNB-CU can 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 can be configured to be communicatively coupled using an E1 communication interface 514 (as specified in the 3GPP standard). The control plane portion 504 can be configured to be responsible for executing the RRC and PDCP protocols of the radio stack.

[0067] The control plane and user plane portions 504, 506 of the centralized unit of the gNB may be configured to be communicatively coupled with one or more distributed units (DUs) 508, 510 according to a higher layer split architecture. The distributed units 508, 510 may be configured to 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 (RUs) 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 (UEs). Figure 5a The remote radio unit 512 may be configured to execute the lower portion of the PHY layer protocol, as well as provide antenna capabilities to the remote unit for communicating with user equipment (similar to the above description regarding Figure 1a-2 discussion).

[0068] Figure 5b An exemplary layer architecture 530 for a split gNB is shown. The architecture 530 may be Figure 5a The communication system 500 shown in FIG5 may be implemented as a virtualized disaggregated radio access network (RAN) architecture, whereby layers L1, L2, L3 and radio processing may be virtualized and disaggregated in centralized unit(s), distributed unit(s) and radio unit(s). Figure 5b As shown, the gNB-DU 508 may be communicatively coupled to the gNB-CU-CP control plane portion 504 (also shown in FIG. Figure 5a ) and the gNB-CU-UP user plane portion 506. Each of components 504, 506, 508 may be configured to include one or more layers.

[0069] The gNB-DU 508 may include RLC, MAC, and PHY layers, as well as various communication sublayers. These may include the F1 Application Protocol (F1-AP) sublayer, the GPRS Tunneling Protocol (GTPU) sublayer, the Stream Control Transmission Protocol (SCTP) sublayer, the User Datagram Protocol (UDP) sublayer, and the 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 gNB's centralized unit. The user plane portion 506 may include the Service Data Adaptation Protocol (SDAP), PDCP User (PDCP-U), GTPU, UDP, and IP sublayers.

[0070] Figure 5c Shown Figure 5a -Example functional split in the gNB architecture shown in Figure 2. 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 (not shown) is executed. Figure 5c As shown in , the RRC and PDCP-C parts may be performed by the control plane part 504 , while the SDAP and PDCP-U parts may be performed by the user plane part 506 .

[0071] Some 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 measurements and indication to higher layers, MIMO antenna processing, digital and analog beamforming, RF processing, and other functions.

[0072] The MAC sublayer of Layer 2 can perform beam management, random access procedures, mapping between logical channels and transport channels, concatenating multiple MAC service data units (SDUs) belonging to one logical channel into a transport block (TB), multiplexing SDUs belonging to logical channels onto TBs transmitted to the physical layer on transport channels / demultiplexing SDUs belonging to logical channels from TBs transmitted from the physical layer on transport channels, scheduling information reporting, error correction through HARQ, priority handling between logical channels of one UE, priority handling between UEs through dynamic scheduling, transport format selection, and other functions. The functions of the RLC sublayer may include delivery of upper-layer packet data units (PDUs), error correction through ARQ, reordering of data PDUs, duplication and protocol error detection, and reestablishment. The PDCP sublayer may be responsible for delivery of user data, various functions during the reestablishment process, retransmission of SDUs, discarding of SDUs in the uplink, delivery of control plane data, and the like.

[0073] The RRC sublayer of layer 3 may perform broadcasting of 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.

[0074] III. Target Cell Prioritization for L1 / L2 Triggered Mobility (LTM)

[0075] Various implementations of target cell prioritization for LTM described herein may include prioritizing a target cell in a handover (HO) of a user equipment (UE) communicatively coupled to a base station of a wireless communication system from one cell (serving cell) to another cell (target cell). Prioritization may be based on a configuration of the target cell.

[0076] Layer 1 / Layer 2 Triggered Mobility (LTM) inter-cell HO at the base station may occur by performing a serving cell change (SSC) from a serving cell to a target cell. Multiple target cells may meet the HO criteria required for the UE to perform SSC and are therefore viable target cell options for HO. However, one or more of the target cells that meet the HO criteria may have a configuration that is more similar to the configuration of the serving cell currently serving the UE than the other target cell(s). Therefore, prioritizing target cells based on their configuration may allow target cells to be selected for HO, allowing for as little service interruption and / or degradation in service quality as possible for the UE, thereby improving the user experience.

[0077] Prioritizing the target cells may include ranking each of the plurality of candidate target cells for HO based on the configuration of the plurality of candidate target cells. Currently, according to 3GPP standards, up to eight LTM target cells may be prepared for a given UE. Therefore, in currently available scenarios, ranking may include ranking the up to eight target cells in order of HO preference.

[0078] When prioritizing the target cell, one or more aspects of the cell configuration may be taken into account. One example of a cell configuration is the configuration of GBR allocations for guaranteed bit rate (GBR) data radio bearers (DRBs). DRBs carry data or user plane traffic. The GBR bearers of the UE may or may not be allowed by the target cell, such as because different vendors may configure their equipment differently, because of resource availability at the time of target cell preparation, and / or because of one or more other factors. Considering the GBR allocation of the target cell to GBR DRBs compared to the source (e.g., serving cell) configuration can help ensure that the UE does not receive a lower GBR from the target cell when switching from the serving cell to the target cell, relative to the GBR allocation for GBR DRBs. Therefore, even if the user experience is not improved, it can be maintained.

[0079] Another example of cell configuration is the configuration regarding packet data unit (PDU) session to DRB mapping. DRBs are mapped to quality of service (QoS) flow identifiers (QFIs). Each QFI can be mapped to more than one DRB. Therefore, a UE with one or more PDU sessions with QFIs can be mapped to one or more DRBs in the RAN. The source configuration may or may not be accepted by the target cell, such as because different vendors may have different RRM algorithms regarding PDU session to DRB mapping, because of resource availability when the target cell is prepared, and / or because of one or more other factors. Considering the PDU session to DRB mapping may help to ensure that the DRB mapping at the target cell will not adversely affect the user experience.

[0080] Another example of cell configuration is the configuration of carrier configuration for carrier aggregation. A source cell may have N carriers configured for a UE with carrier aggregation. A target cell may have N or more carriers that may be allocated to the UE, in which case the user experience may be maintained even if the user experience is not improved if the service is handed over from the source cell to the target cell. However, the target call may have fewer than N carriers that may be allocated for the UE, in which case the user experience may be adversely affected if the service is handed over from the source cell to the target cell. Considering carrier configuration for carrier aggregation may help ensure that the same or a greater number of carriers may be allocated for the UE by the target cell than allocated for the UE by the serving cell.

[0081] Another example of cell configuration is the configuration of slice mapping for UE services. A particular network slice that is available to a UE via a serving cell may not be available to the UE via a target cell because the target cell may not have access to that slice. Therefore, handing over the UE's service to the target cell may cause a poor user experience because the UE will no longer have access to that network slice and slice remapping must be performed. For example, a network slice may be available only to certain UEs, such as if a company, university or other educational institution or other entity has a network slice that is available to UEs registered by or otherwise associated with its employees and / or students, but not to other UEs. The serving cell may have access to such a network slice, while one or more target cells may not have access to that slice. Therefore, considering slice mapping for UE services may help prevent slice remapping, and this helps prevent a degraded user experience.

[0082] Another example of cell configuration is the configuration of DRBs accepted by the UE. The serving cell may have different DRBs for the UE than the DRBs accepted for the UE at the target cell. Therefore, considering the UE DRBs accepted by the target cell compared to the serving cell currently serving the UE may help ensure that all DRBs for the UE currently served by the serving cell are accepted by the target cell, thereby helping to prevent a degraded user experience.

[0083] In some implementations of the current subject matter, a base station (e.g., Figure 5a A gNodeB, a next generation RAN (NG-RAN) node (such as an eNodeB or gNodeB, etc.) may have a decomposed architecture, where the base station includes a gNB-CU-CP (e.g., Figures 5a-5c gNB-CU-CP504, etc.) and more than one CU-UP (e.g., Figures 5a-5c gNB-CU-UP 506, etc.) and gNB-DU (e.g., Figures 5a-5c In general, the ng-eNodeB is enhanced as a next-generation (NG) device to connect a 5G UE to a 5G core network. When a UE is handed over from one cell of the base station (the serving cell) to another cell of the base station (the target cell), the base station can be configured to prioritize the target cell as described above.

[0084] Figure 6a An exemplary system 600 is shown that is configured to prioritize target cells. In this illustrated implementation, a base station 602 is configured to be located similar to the above-described Figure 5a The 5G wireless communication system 500 is a gNB in the 5G wireless communication system, but other base stations can be similarly configured and used to provide RACH-free LTM. Figure 6a In the illustrated implementation, the base station 602 includes a plurality of CU-UPs 606a, 606b, 606c. In the illustrated implementation, the base station 602 includes three CU-UPs 606a, 606b, 606c, but may include another plurality of CU-UPs. The CUs of the base station 602 including the plurality of CU-UPs 606a, 606b, 606c are configured to communicate with the core network ( Figure 6a ) communicatively coupled, e.g. Figure 5a 5GC 502, etc.

[0085] The CU of the base station 602 also includes a CU-CP 604, which is 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 the illustrated implementation to reflect the presence of three CU-Ups 606a, 606b, 606c with which the CU-CP 604 can be configured to communicate.

[0086] The base station 602 also includes a plurality of DUs 608, 610. In the illustrated implementation, the base station 602 includes two DUs 608, 610, but may include another 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. The F1-U interface 618 associated with each of the DUs 608, 610 includes three communication links in the illustrated implementation to reflect the presence of three CU-UPs 606a, 606b, 606c with which each DU 608, 610 may be configured to communicate.

[0087] The base station 602 also includes a plurality of RUs 612. The base station 602 includes five RUs 612 in the illustrated implementation, but may include another plurality of RUs. The RUs 612 are configured to be communicatively coupled to the DUs 608, 610 via a 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 another number of UEs that is the same as or different from any of the other RUs 612.

[0088] Target cell prioritization may be configured to occur when one of the UEs communicatively coupled to the base station 602 is handed over from one of the DUs 608, 610 of the base station 602 to another of the DUs 608, 610 also of the same base station 602. The one of the DUs 608, 610 currently providing service to the UE 622 is referred to as a "serving DU" because it currently provides service to the UE 622, e.g., currently serves the UE 622. The one of the DUs 608, 610 to which the UE's service is handed over is referred to as a "target DU" because it is targeted to provide service to the UE 622.

[0089] Prioritization of target cells can be configured in the system in which it occurs with respect to Figure 6b is further described. Figure 6b Shown Figure 6a CU-CP 604 and CU-UP 606a, 606b, 606b in, but in Figure 6b In the implementation shown in FIG, base station 624 includes more than two DUs. Figure 6b In the implementation shown in FIG, base station 624 includes sixty-six DUs. Three of DUs 628a, 628b, and 628c are macro cells (in Figure 6b 1, macro2, and macro3), and sixty-three of the DUs 626 are small cells (nine of which are in Figure 6bThe base station 624 may include another number of macro cells and / or another number of small cells. The macro1 DU 628a, macro2 DU 628b, and 21 small cell DUs of the small cell DU 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 6280c, and 21 small cell DUs in the small cell DU 626 including gNB-DU40, gNB-DU50, and gNB-DU60 are configured to be served by the second CU-UP 606b (in Figure 6b The macro2 DU 628b, macro3 DU 628c, and 21 small cell DUs in the small cell DU 626 including gNB-DU70, gNB-DU80, and gNB-DU90 are configured to be served by the third CU-UP 606c (in Figure 6b are marked as CU-UP3) services.

[0090] exist Figure 6b In the illustrated implementation, each CU-UP 606a, 606b, 606c is serving a subset of the DUs 626, 628a, 628b, 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 communication (URLLC)).

[0091] Figure 7 An exemplary method 700 according to some implementations of the current subject matter is shown. Figure 8 The exemplary system 800 shown in FIG is described, but can be similarly applied to other systems (e.g., Figures 1a-1c and 2 systems 100, Figure 4 System 400, Figure 5a System 500, Figure 6a and 6b systems, etc.) are implemented together. Figure 8The system 800 is a 5G system, but as mentioned above, the prioritization of target cells as described herein can be performed using other types of wireless communication systems, such as an LTE wireless communication system or a 6G or later generation wireless communication system.

[0092] In system 800, UE 802 (e.g., Figures 1a-1c UE 104, Figure 6a UE 622, etc.) is configured 810 with an LTM having a base station (e.g., a gNB (e.g., Figure 5a gNodeB, Figure 6a and 6b gNodeB 624, etc.)) of one or more DUs 804, 806 (e.g., Figures 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 8 A system 800 is shown in which 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., Figures 5a-5c gNB-CU-CP 504, Figure 6a and 6b CU-CP 604, etc.) and one or more CU-UPs (e.g., Figures 5a-5c gNB-CU-UP 506, Figure 6a and 6b CU-UP 606a, 606b, 606c, etc.) Figure 8 ), and multiple RUs (e.g., Figure 5a RU 512, Figure 6a RU 612, etc.)( Figure 8 ). UE 802 is currently served by serving DU 804. In addition, Figure 8 a's base station and core network (e.g. Figures 1a-1c and EPC 108 of 2, Figure 5a 5GC 502, etc.) communication coupling ( Figure 8 not shown).

[0093] Method 700 illustrates an implementation of an inter-DU LTM serving cell change scenario, which includes a serving DU 804 determining 702 that a cell change is required for a UE 802, but method 700 is also applicable to intra-DU LTM serving cell change scenarios and combined inter-DU and intra-DU serving cell change scenarios. The serving DU determination 702 may include the serving DU 804 analyzing 814 intra-frequency L1 measurement reports sent 812 by the UE 802 to the serving DU 804 in accordance with 3GPP standards. According to 3GPP standards, the intra-frequency L1 measurement reports may include layer 1 (L1) measurements that may be analyzed by the serving DU 804 when making resource control decisions, such as a serving cell change in which the UE 802 will be served by a DU other than the serving DU 804 (e.g., a target DU 806) for at least one service.

[0094] 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 8 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 .

[0095] Additionally, 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 with an identifier known to the serving DU 804 according to 3GPP standards that uniquely identifies the UE 802 to the CU-CP 808. Figure 8 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 8 As shown, the serving cell change notification message includes a cell identification (ID) that may be associated with the UE 802 undergoing the serving cell change.

[0096] In response to receiving the serving cell change command 704 from the serving DU 804 and executing the serving cell change command, the UE 802 sends 820 a radio resource control (RRC) reconfiguration confirm message to the CU-CP 808. The CU-CP 808 understands from the RRC reconfiguration confirm message that the UE 802 (uniquely identified to the CU-CP 808 by the serving DU 804) confirms the completion of the successful serving cell change.

[0097] Additionally, 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, which may be analyzed by the CU-CP 808 when 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 is prepared to serve the UE 802 instead of serving the serving DU 804 for the at least one service.

[0098] 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 8 As shown, in the illustrated implementation, each of the at least one target cell is an inter-DU target cell, e.g., 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 only includes the target DU 806, but as described above, the base station can include more than two target cells. Currently, according to 3GPP standards, up to eight LTM target cells can be prepared for a given UE.

[0099] Preparing 706 at least one target cell for LTM may include notifying at least one target DU 806, which may later be notified to begin providing services to UE 802 for at least one service. Thus, the target DU 806 may reserve necessary resources for UE 802. Figure 8 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 826 a UE context setup request message to the target DU 806 using the F1 communication interface in accordance with the GPP standard.

[0100] In response to receiving the UE context setup request message from the CU-CP 808, the target DU 806 prepares 828 each of the at least one target cell for LTM. In the illustrated embodiment, the at least one target cell includes only the target DU 806 preparing 828 the target cell. The preparation 828 may include the target cell reserving necessary resources for the UE 802. The preparation 828 may also include identifying HO preparation inputs, which include configurations for each target cell. The configurations for each target cell include one or more of the above-described configurations, such as configuration regarding GBR allocation for GBR DRBs, configuration regarding PDU session to DRB mapping, configuration regarding carrier configuration for carrier aggregation, configuration regarding slice mapping for UE services, and configuration regarding accepted DRBs.

[0101] The target DU 806 notifies the CU-CP 808 that the preparation 828 has been completed. Figure 8 As shown, the notification to the CU-CP 808 may include the target DU 806 sending 830 a UE context setup response message to the CU-CP 808 using the F1 communication interface according to the 3GPP standard. Figure 8 As shown, the UE context setup response message includes the merged cell group configuration information for one or more target cells prepared at the target DU 806 and also includes HO preparation input. Therefore, the CU-CP 808 can understand the configuration of each of the one or more prepared 828 target cells and any changes to the serving cell configuration.

[0102] The CU-CP 808 determines 708, 832 an LTM HO priority for each of the one or more prepared 828 target cells. If there is only one prepared 828 target cell, the CU-CP 808 omits determinations 708, 832 because there is only one target cell candidate. If there are multiple prepared 828 target cells, the CU-CP 808 performs determinations 708, 832 because there are at least two candidate target cells available for HO prioritization. Determinations 708, 832 may include comparing each of the received target cell configurations with a serving cell configuration as reflected by the expected UE service requirements, e.g., based on received L3 measurement reports. Different vendors may decide to give higher weight to certain configuration factors than other configuration factors based on which factors the vendor considers to be more important for maintaining the best user experience at HO, for example, maintaining GBR allocation for GBR DRBs is considered to be more important than maintaining the configuration regarding PDU session to DRB mapping and therefore deserves higher priority, configuration regarding carrier configuration for carrier aggregation is considered to be more important than configuration regarding slice mapping for UE services and therefore deserves higher priority, giving lower priority to a target cell in which multiple QFIs are mapped to the same DRB or the number of configured secondary carriers (SCells) is reduced or some DRBs of a slice are remapped to a default slice compared to a target cell in which the source cell configuration is not downgraded or is enhanced, etc.

[0103] The CU-CP 808 assigns a priority value to each of the target cells based on the determined priorities 708, 832. The priority value may be a number (e.g., 1 for highest priority, 2 for second highest priority, etc.), an alphabetic value (e.g., A for highest priority, B for second highest priority, etc.), or another format.

[0104] The CU-CP 808 may be configured to receive updated target cell information and readjust the LTM HO priority based on the updated information. If the configuration of the target cell changes (upgraded or downgraded), the target DU 806 may send updated target cell configuration information to the CU-CP 808. If the target cell becomes unavailable for LTM HO, the target DU 806 may send an update to the CU-CP 808 indicating that the target cell is no longer available for LTM HO. If the target cell becomes available for LTM HO, the target DU 806 may send an update to the CU-CP 808 including the configuration information of the target cell and indicating that the target cell is available for LTM HO.

[0105] The CU-CP 808 notifies 710 the serving DU 804 of at least one LTM prepared target cell by identifying each of the one or more LTM prepared target cells and its LTM HO priority. In an 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. 5 , 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.

[0106] like Figure 8 As shown, the notification 710 to the serving DU 804 may include the CU-CP 808 sending 834 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 cell, such as a physical cell identifier (PCI)) and LTM HO priority information (e.g., a numerical, alphabetical, or other ranking assigned to each target cell indicating the priority of the target cell for HO) for each of the one or more target DUs. If there is only one candidate target cell, the priority information may be omitted from the message from the CU-CP 808 to the serving DU 804 because there is only one possible choice for the HO identified by the serving DU 804.

[0107] In response to being notified 710 of at least one LTM prepared target DU cell, the serving cell 804 stores 836 the received information about the at least one LTM target cell, for example, storing a list of (multiple) LTM prepared target cells and their corresponding LTM HO priority information. In addition, in response to being notified 710 of the at least one target DU, the serving cell 804 sends 838 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. The UE context modification request message and the UE context modification response message are each defined by 3GPP. Therefore, the serving DU 804 can receive information about the at least one target cell from the CU-CP 808 and can confirm receipt to the CU-CP 808 using the message that has been sent for HO in accordance with the 3GPP standard.

[0108] In response to receiving the UE context modification response message, the CU-CP 808 sends 840 an RRC reconfiguration message to the UE 802 according to the 3GPP standard. Figure 8 As shown, the RRC reconfiguration message includes the LTM target cell configuration information, eg, as provided from the target DU 806 to the CU-CP 808 in a sent 830 UE context setup response message.

[0109] In response to receiving the target cell configuration in the RRC reconfiguration message, the UE 802 sends 842 an L1 measurement report according to 3GPP standards 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.

[0110] In response to receiving the L1 measurement report sent 842 from the UE 802, the serving cell 804 selects 712, 844 a target cell from the one or more LTM-prepared target cells identified to the serving DU 804. When there is only one target cell identified by the CU-CP 808 to the serving DU 804 as an LTM-prepared target cell, the selection 710, 844 of the serving cell is simple and the serving DU 804 selects 710, 844 one candidate target cell.

[0111] When there are multiple target cells identified by the CU-CP 808 to the serving DU 804, target cell selection 710, 846 for 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, the serving DU 804 can consider the specific needs of the specific UE 802 involved in the HO when selecting 712, 844 the target cell for HO. In addition, the L1 measurement report sent 842 by the UE 802 to the serving DU 804 reports L1 measurements for each of the multiple target cells, which may include reference signal received power (RSRP) defined by 3GPP, the identities of which are known to the UE 802 because they have been provided to the UE 802 by the CU-CP 808 in the RRC reconfiguration message. Thus, the serving DU 804 may analyze the L1 measurement report received from the UE 802 to determine which one or more target cells among the plurality of target cells have a radio quality above a predetermined threshold radio quality.

[0112] If only one target cell among the multiple target cells satisfies the radio condition of the UE, for example, only one target cell has a radio quality higher than a predetermined threshold radio quality, the serving cell 804 selects 712, 844 the target cell. If more than one target cell among the multiple target cells satisfies the radio condition of the UE, for example, each of the radio qualities of the target cells is higher than a predetermined threshold radio quality, any one of the target cells will be able to meet the needs of the UE and one of the target cells may be selected by selecting one of the target cells with the highest priority ranking (cells satisfying the radio condition) according to the LTM HO priority information received by the serving DU 804 from the CU-CP 808. Figure 8 In the illustrated implementation, target cell A of target DU 806 and target cell B of target DU 806 have each been identified by serving DU 804 as satisfying radio conditions, and target cell A is selected 712, 844 as the target cell for HO because target cell A has a higher priority ranking than target cell B in the LTM HO priority received by serving DU 804 and thus will cause less impairment to user experience than target cell B. Therefore, even though target cell B has better radio conditions than target cell A, target cell A is selected for HO because target cell A has a higher LTM HO priority.

[0113] After selecting 712, 844 the target cell, the serving DU 804 triggers 714 the serving cell to change to the selected 713, 844 target cell. Figure 8 As shown in , triggering 712 a serving cell change may include the serving DU 804 sending 846 a MAC CE to the UE 802, the MAC CE including a serving cell change command and identifying the selected 712, 844 target cell to the UE 802, e.g., via PCI.

[0114] The UE receives the MAC CE indicating to the UE 802 that an LTM serving cell change (SCC) must be performed on the identified target cell for the UE 802. Thus, in response to receiving the MAC CE from the serving cell 804, the UE 802 initiates 716, 848 a HO to the target cell. Figure 8As shown in FIG, , UE 802 initiating 716, 848 HO to the target cell may include UE 802 accessing 848 the target cell using a RACH message, which may be performed in accordance with 3GPP standards. In response to UE 802 accessing the target cell, target DU 806 sends 850 a serving cell change notification to CU-CP 808 via the F1 communication interface, the serving cell change notification identifying UE 802 for at least one service as the new current serving cell, for example, by a unique identifier according to 3GPP. In addition, in response to receiving a MAC CE from serving cell 804, UE 802 sends 852 an RRC reconfiguration confirm message to CU-CP 808. Thus, CU-CP 808 receives confirmation from both UE 802 (via the RRC reconfiguration confirm message indicating a successful RRC reconfiguration at UE 802) and target DU 806 (via the serving cell change notification that target DU 806 is now serving UE 802 for at least one service switched from serving DU 804).

[0115] In some implementations, the current subject matter can be configured to be implemented in system 900, such as Figure 9 As shown in . 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 components 910, 920, 930, and 940 may be interconnected using a system bus 950. Processor 910 may be configured to process instructions for execution within system 600. In some implementations, processor 910 may be a single-threaded processor. In alternative implementations, processor 910 may be a multi-threaded processor. Processor 910 may also be configured to process instructions stored in memory 920 or on storage device 930, including receiving or sending information via input / output device 940. Memory 920 may store information within system 900. In some implementations, memory 920 may be a computer-readable medium. In alternative implementations, memory 920 may be a volatile memory unit. In still other 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, the storage device 930 can be a computer-readable medium. In alternative implementations, the storage device 930 can 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 can be configured to provide input / output operations for the system 900. In some implementations, the input / output device 940 can include a keyboard and / or a pointing device. In alternative implementations, the input / output device 940 can include a display unit for displaying a graphical user interface.

[0116] Figure 10An exemplary method 1000 for prioritizing target cells for LTM according to some implementations of the current subject matter is shown. For example, the method 1000 may use Figure 6a-8 Shown in and about Figure 6a-8 The described implementation is performed.

[0117] The method 1000 includes receiving 1002, at a serving DU of a base station, information indicating a handover priority ranking of a plurality of LTM target cells of a second DU of the base station from a CU-CP of the base station, and selecting 1004, at the serving DU, one of the plurality of LTM target cells for handover of a service for the UE from the serving DU based on the received information, and triggering handover of the service for the UE from the serving DU to the selected target cell. Each of the plurality of LTM target cells selected by the serving DU satisfies a handover criterion.

[0118] In some implementations, the current subject matter can include one or more of the following optional features.

[0119] In some implementations, handover prioritization may be based on a target cell configuration for each of the plurality of LTM target cells. Furthermore, the target cell configuration for each of the plurality of LTM target cells may include at least one of: a configuration regarding GBR allocation for GBR DRBs, a configuration regarding PDU session-to-DRB mapping, a configuration regarding carrier configuration for carrier aggregation, a configuration regarding slice mapping for UE services, and a configuration regarding accepted DRBs for the UE; and / or the handover prioritization may be based on the configuration of each of the plurality of LTM target cells compared to the configuration of the serving cell. Furthermore, at least one target DU including the plurality of LTM target cells may provide the target cell configuration for each of the plurality of LTM target cells to the CU-CP in an F1 message, and / or the handover prioritization may be recalculated whenever an LTM target cell is added, reconfigured, or removed for the UE. Furthermore, the at least one target DU may also provide a list of changes for the plurality of LTM target cells compared to the serving cell configuration.

[0120] In some implementations, the handover criteria may include a predetermined threshold radio quality, and the operation may further include: at the serving DU, determining which one or more of the multiple target cells have a radio quality higher than the predetermined threshold radio quality, and the selection may be only among the one or more determined target cells.

[0121] In some implementations, the triggering may include sending a MAC CE message from the serving DU to the UE.

[0122] In some implementations, a base station may have a disaggregated architecture.

[0123] In some implementations, the base station may comprise a Next Generation Radio Access Network (NG-RAN) node. Additionally, the NG-RAN node may comprise a gNodeB or an ng-eNodeB.

[0124] 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 method.

[0125] The systems and methods disclosed herein can be embodied in various forms, including, for example, data processors (such as computers that also include a database), digital electronic circuit systems, firmware, software, or combinations 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 environments and related applications can be specially constructed to perform various processes and operations according to the disclosed implementation, or they can include general-purpose computers or computing platforms that are selectively activated or reconfigured by code to provide necessary functions. The processes disclosed herein are not inherently related to any particular computer, network, architecture, environment, or other device, and can be implemented by appropriate combinations of hardware, software, and / or firmware. For example, various general-purpose machines can be used together with programs written according to the teachings of the disclosed implementation, or special-purpose devices or systems can be more conveniently constructed to perform the required methods and techniques.

[0126] 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 in a propagated signal, for execution by a data processing apparatus (e.g., a programmable processor, a computer, or multiple computers) or for controlling the operation of a data processor. 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 use in a computing environment. The computer program may be deployed to be executed on one computer or multiple computers at one site, or distributed across multiple sites and interconnected by a communications network.

[0127] As used herein, the term "user" may refer to any entity, including a person or a computer.

[0128] Although ordinal numbers (such as first, second, etc.) can in some cases be associated with order, as used herein, they do not necessarily imply order. For example, ordinal numbers can be used simply to distinguish one item from another, such as to distinguish a first event from a second event, without necessarily implying any temporal order or fixed reference system (such that the first event in one paragraph of a description may be different from the first event in another paragraph of the description).

[0129] The foregoing description is intended to illustrate but not limit the scope of the invention, which is defined by the scope of the appended claims. Other implementations are within the scope of the following claims.

[0130] These computer programs (which may also be referred to as programs, software, software applications, applications, components or codes) include machine instructions for programmable processors and can be implemented in high-level procedural and / or object-oriented programming languages and / or assembly / machine languages. As used herein, the term "machine-readable medium" refers to any computer program product, device and / or equipment used to provide 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 used to provide machine instructions and / or data to a programmable processor. A machine-readable medium can store such machine instructions non-transiently, 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 temporary manner, such as, for example, a processor cache or other random access memory associated with one or more physical processor cores.

[0131] To provide for interaction with a user, the subject matter described herein can be implemented on a computer having a display device, such as, for example, 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, 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 for 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 acoustic, voice, or tactile input.

[0132] The subject matter described herein can be realized in a computing system, and this computing system includes back-end components (such as, for example, one or more data servers), or includes middleware components (such as, for example, one or more application servers) or includes front-end components (such as, for example, one or more client computers with a graphical user interface (GUI) or a Web browser), and the user can interact with the realization of the subject matter described herein by any combination of this graphical user interface (GUI) or a Web browser or these back ends, middleware or front-end components.The component of system can be interconnected by the digital data communication of any form or medium, such as, for example, a communication network.The example of a communication network includes, but is not limited to, a local area network ("LAN"), a wide area network ("WAN") and the internet.

[0133] A computing system may include clients and servers. A client and server are typically, but not exclusively, remote from each other and typically interact through a communication network. The relationship of client and server arises by computer programs running on the respective computers and having a client-server relationship to each other.

[0134] The implementations set forth in the foregoing 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 subject matter. Although some variations have been described in detail above, other modifications or additions are possible. Specifically, in addition to the features and / or variations set forth herein, additional features and / or variations may also be provided. For example, the implementations described above may be directed to various combinations and subcombinations of the disclosed features and / or combinations and subcombinations of several additional features disclosed above. In addition, the logical flows depicted in the accompanying drawings and / or described herein do not necessarily require the specific order or sequential order shown 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 a serving distributed unit (DU) of a base station, information from a centralized unit control plane (CU-CP) of the base station, the information indicating handover prioritization of a plurality of layer 1 / layer 2 triggered mobility (LTM) target cells of a second DU of the base station, and At the serving DU, based on the received information, one of a plurality of LTM target cells is selected for handing over a service for a user equipment (UE) from the serving DU, and the handover of the service for the UE from the serving DU to the selected target cell is triggered, wherein each of the plurality of LTM target cells selected by the serving DU satisfies a handover criterion. 2 . The apparatus of claim 1 , wherein the handover priority ranking is based on a target cell configuration of each of the plurality of LTM target cells.

3. The apparatus according to claim 2, wherein the target cell configuration of each LTM target cell in the plurality of LTM target cells comprises at least one of the following: Regarding the configuration of guaranteed bit rate (GBR) allocations for data radio bearers (DRBs), Regarding the configuration of packet data unit (PDU) session to DRB mapping, Regarding the configuration of carrier configuration for carrier aggregation, Regarding the configuration of slice mapping for UE services, and Regarding the configuration of the DRBs accepted by the UE. 4 . The apparatus according to claim 3 , wherein at least one target DU including the plurality of LTM target cells provides the target cell configuration for each of the plurality of LTM target cells to the CU-CP in an F1 message.

5. The apparatus of claim 4, wherein the at least one target DU further provides a list of changes for the plurality of LTM target cells compared to a serving cell configuration.

6. The apparatus of claim 2, wherein the handover prioritization is based on the configuration of each of the plurality of LTM target cells compared to a configuration of the serving cell. 7 . The apparatus of claim 6 , wherein the handover priority ranking is recalculated each time an LTM target cell is added, reconfigured, or removed for the UE.

8. The apparatus of claim 1 , wherein the switching criteria comprises: predetermined threshold radio quality; The operations further include: determining, at the serving DU, which one or more target cells of the plurality of target cells have a radio quality above the predetermined threshold radio quality; as well as The selection is only among the one or more determined target cells.

9. The apparatus of claim 1 , wherein the trigger comprises: A medium access control (MAC) element (CE) message is sent from the serving DU to the UE.

10. The apparatus of claim 1, wherein the base station has a disaggregated architecture.

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

12. The apparatus of claim 11, wherein the NG-RAN node comprises a gNodeB or an ng-eNodeB.

13. 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.

14. 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 a serving distributed unit (DU) of a base station, information from a centralized unit control plane (CU-CP) of the base station, the information indicating handover prioritization of a plurality of layer 1 / layer 2 triggered mobility (LTM) target cells of a second DU of the base station, and At the serving DU, based on the received information, one of a plurality of LTM target cells is selected for handing over a service for a user equipment (UE) from the serving DU, and the handover of the service for the UE from the serving DU to the selected target cell is triggered, wherein each of the plurality of LTM target cells selected by the serving DU satisfies a handover criterion. 15 . The storage medium of claim 14 , wherein the handover priority ranking is based on a target cell configuration of each of the plurality of LTM target cells.

16. The storage medium of claim 15, wherein the target cell configuration of each LTM target cell in the plurality of LTM target cells comprises at least one of the following: Regarding the configuration of guaranteed bit rate (GBR) allocations for data radio bearers (DRBs), Regarding the configuration of packet data unit (PDU) session to DRB mapping, Regarding the configuration of carrier configuration for carrier aggregation, Regarding the configuration of slice mapping for UE services, and Regarding the configuration of the DRBs accepted by the UE.

17. A computer-implemented method comprising: receiving, at a serving distributed unit (DU) of a base station, information from a centralized unit control plane (CU-CP) of the base station, the information indicating handover prioritization of a plurality of layer 1 / layer 2 triggered mobility (LTM) target cells of a second DU of the base station, and At the serving DU, based on the received information, one of a plurality of LTM target cells is selected for handing over a service for a user equipment (UE) from the serving DU, and the handover of the service for the UE from the serving DU to the selected target cell is triggered, wherein each of the plurality of LTM target cells selected by the serving DU satisfies a handover criterion.

18. The method of claim 17, wherein the handover prioritization is based on a target cell configuration of each of the plurality of LTM target cells.

19. The method according to claim 18, wherein the target cell configuration of each LTM target cell in the plurality of LTM target cells comprises at least one of the following: Regarding the configuration of guaranteed bit rate (GBR) allocations for data radio bearers (DRBs), Regarding the configuration of packet data unit (PDU) session to DRB mapping, Regarding the configuration of carrier configuration for carrier aggregation, Regarding the configuration of slice mapping for UE services, and Regarding the configuration of the DRBs accepted by the UE.

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