Target Cell Prioritization for Layer 1 / Layer 2 Triggered Mobility

Abstract

Generally, the present disclosure relates to target cell prioritization for Layer 1 / Layer 2 triggered mobility (LTM). In some implementations, the target cell prioritization for LTM may include receiving, at a serving distribution unit (DU) of the base station, information indicating handover priorities of multiple Layer 1 / Layer 2 triggered mobility (LTM) target cells of a second DU of the base station from a centralized unit control plane (CU-CP) of the base station; and, based on the received information, selecting, at the serving DU, one of multiple LTM target cells for handover of a service for a user equipment (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 multiple LTM target cells selected by the serving DU satisfies handover criteria.

Description

[Technical Field]

[0001] In some implementations, the present disclosure relates to telecommunications systems, and more particularly, to target cell prioritization for layer 1 / layer 2 triggered mobility (LTM). [Background technology]

[0002] In today's world, cellular networks provide on-demand communication capabilities to individuals and businesses. 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, 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 communication 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 phone 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 for 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 Rate (EDGE), Universal Mobile Telecommunications System (UMTS), Digital Improved Cordless Communications (DECT), Digital AMPS (IS-136 / TDMA), and Integrated Digital Improved Network (iDEN). Long Term Evolution, or 4G LTE, developed by the 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, enabling 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 communications processing. The core network can include network functions capable of handling higher layer communications, such as Internet Protocol (IP), transport layers, and application layers. In some cases, the RAN functions can be divided into baseband unit functions and radio unit functions; for example, a radio unit connected to a baseband unit via a fronthaul network can handle lower layer processing of the radio physical layer, and the baseband unit can handle 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 of the radio units (RUs) is communicatively coupled to at least one of one or more DUs, and each is 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 part (CU-CP) and one or more user plane parts (CU-UP). During a UE's communicative coupling with the base station, the DU supporting the UE may be changed (e.g., handed over) from one DU (serving DU) to one or more other DUs (target DUs). For handover, multiple target cells may be prepared in one or more DUs. However, if the configuration of the prepared target cell does not match the source configuration, the user experience may be impaired even if the prepared target cell meets the radio conditions required for the UE to make (or undergo) a Serving Cell Change (SSC). Summary of the Invention

[0007] Some implementations of the present disclosure relate to a computer-implemented method. The method may include receiving, at a serving DU of the base station, information indicating handover priorities of multiple LTM target cells of a second DU of the base station from a CU-CP of the base station, and selecting, at the serving DU, one LTM target cell from the multiple LTM target cells for handing over a service for the UE from the serving DU based on the received information, where each of the multiple LTM target cells selected by the serving DU satisfies a handover criterion.

[0008] The method may ensure that a target cell is selected for handover that causes as little interruption and / or degradation of service quality to the UE as possible, thereby improving the user experience.

[0009] Some implementations of the present disclosure may include one or more of the following optional features.

[0010] In some implementations, the handover priority can be based on the target cell configuration of each of the multiple LTM target cells. Furthermore, the target cell configuration of each of the multiple LTM target cells can include at least one of a configuration for GBR allocation to GBR DRBs, a configuration for PDU sessions to map to DRBs, a configuration for carrier aggregation, a configuration for slice mapping for UE service, and a configuration for the UE's accepted DRBs, and / or the handover priority can be based on the configuration of each of the multiple LTM target cells compared to the configuration of the serving cell. Furthermore, at least one target DU including the multiple LTM target cells can provide the target cell configuration of each of the multiple LTM target cells to the CU-CP in an F1 message, and / or the handover priority can be recalculated each time an LTM target cell is added, reconfigured, or deleted for the UE. Furthermore, the at least one target DU can also provide a list of changes in the multiple 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 operations may further include determining, at the serving DU, which one or more target cells among the plurality of target cells have a radio quality above the predetermined threshold radio quality, and the selection scope 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, the base station may have a disaggregated architecture.

[0014] In some implementations, the base station may include a Next Generation Radio Access Network (NG-RAN) node, which may further include 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 a method.

[0016] Non-transitory computer program products (i.e., physically embodied computer program products) that store instructions, 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. Similarly, computer systems are described that may include one or more data processors and memory coupled to the one or more data processors. The memory may temporarily or permanently store instructions that cause at least one processor to perform one or more of the operations described herein. 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.

[0017] The details of one or more variations of the disclosure described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the disclosure described herein will be apparent from the description and drawings, and from the claims.

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate certain aspects of the disclosure described herein and, together with the description, serve to explain some of the principles associated with the disclosed implementations. [Brief explanation of the drawings]

[0019] [Figure 1a] FIG. 1 illustrates an exemplary conventional Long Term Evolution (LTE) communication system.

[0020] [Figure 1b] FIG. 1b illustrates further details of the exemplary LTE system shown in FIG. 1a.

[0021] [Figure 1c] FIG. 1b illustrates further details of the evolved packet core of the exemplary LTE system shown in FIG. 1a.

[0022] [Figure 1d] FIG. 1B illustrates an exemplary evolved Node B for the exemplary LTE system shown in FIG. 1a.

[0023] [Figure 2] FIG. 2 shows further details of the evolved Node B shown in FIGS. 1a to 1d.

[0024] [Figure 3] FIG. 1 illustrates an example virtual radio access network, in accordance with some implementations of the present disclosure.

[0025] [Figure 4] FIG. 1 illustrates an exemplary 3GPP split architecture for providing users with access to higher frequency bands.

[0026] [Figure 5a] FIG. 1 illustrates an exemplary 5G wireless communication system.

[0027] [Figure 5b] A diagram illustrating an example layer architecture of a split gNB and / or a split ng-eNB (e.g., a next-generation eNB that may be connected to 5GC).

[0028] [Figure 5c]FIG. 5a to FIG. 5b is a diagram showing an exemplary functional split in the gNB architecture.

[0029] [Figure 6a] FIG. 6 is a diagram showing an exemplary system according to some implementations of the present disclosure.

[0030] [Figure 6b] FIG. 7 is a diagram showing an exemplary alternative configuration of the system of FIG. 6a according to some implementations of the present disclosure.

[0031] [Figure 7] FIG. 8 is a diagram showing an exemplary method according to some implementations of the present disclosure.

[0032] [Figure 8] FIG. 9 is a diagram showing another exemplary system according to some implementations of the present disclosure.

[0033] [Figure 9] FIG. 10 is a diagram showing an exemplary system according to some implementations of the present disclosure.

[0034] [Figure 10] FIG. 11 is a diagram showing an exemplary method according to some implementations of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present disclosure can provide systems and methods that can be implemented in a wireless communication system. Such systems can include various wireless communication systems, including a 5G New Radio communication system, a Long Term Evolution communication system, and the like.

[0036] Generally, the present disclosure relates to target cell prioritization for layer 1 / layer 2 triggered mobility (LTM).

[0037] In some implementations of the present disclosure, target cells may be prioritized during a handover (HO) from one cell (serving cell) to another cell (target cell) for a user equipment (UE) communicatively coupled with a base station of a wireless communication system. The prioritization may be based on the configuration of the target cells. Multiple target cells may meet the HO criteria required for the UE to undergo a serving cell change (SSC) and thus be viable target cell options for the HO. However, one or more target cells that meet the HO criteria may have a configuration that is more similar to that of the serving cell currently serving the UE than the other(s) of the target cells. Thus, by prioritizing target cells based on their configuration, a target cell that causes as little interruption and / or degradation of service to the UE as possible may be selected for the HO, thereby improving the user experience.

[0038] 3GPP standards that define one or more aspects that may be relevant to the present disclosure include 3GPP TS 38.473 "NG-RAN F1 Application Protocol (F1AP)." O-RAN Alliance standards may also be relevant to one or more aspects of the present disclosure.

[0039] One or more aspects of the present disclosure 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 description of a Long Term Evolution communication system and a 5G New Radio communication system.

[0040] I. Long Term Evolution Communication System 1a-1c and 2 illustrate a typical conventional Long Term Evolution (LTE) communication system 100 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. This standard is an evolution of GSM / EDGE (Global System for Mobile communications / GSM Evolution Improved Data Rates) and UMTS / HSPA (Universal Mobile Telecommunications System / High-Speed ​​Packet Access) network technologies. This standard was developed by 3GPP (3rd Generation Partnership Project).

[0041] 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 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 (106a, 106b, 106c) that provide communication capabilities to multiple user equipment 104 (104a, 104b, 104c) (as shown in FIG. 1b). 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. User equipment 104 can connect to the EPC 108 and ultimately to the PDN 101 through any eNodeB 106. Typically, 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 to user equipment 104.

[0042] 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 service. The eNodeBs 106 are responsible for selecting which mobility management entity (MME shown in Figure 1c) will serve the user equipment 104 and for 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.

[0043] 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).

[0044] 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 within the system 100 are carried by physical layer (PHY) channels.

[0045] Multiple eNodeBs 106 may be interconnected with each other using X2 interfaces 130 (130a, 130b, 130c). As shown in FIG. 1b, the X2 interface 130a provides interconnection between the eNodeBs 106a and 106b, the X2 interface 130b provides interconnection between the eNodeBs 106a and 106c, and the X2 interface 130c provides interconnection between the eNodeBs 106b and 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 handovers. The eNodeBs 106 communicate with the evolved packet core 108 via S1 interfaces 124 (124a, 124b, 124c). 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).

[0046] 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.

[0047] 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 (a subscriber database for the EPC 108), and a policy control and charging rules function (PCRF) 118. Some of these (e.g., S-GW, P-GW, MME, HSS) are often integrated into the node, depending on the manufacturer's implementation.

[0048] The S-GW 110 functions as an IP packet data router and is the bearer path anchor for the user equipment in the EPC 108. Thus, when the 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 a different 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.

[0049] The P-GW 112 is the gateway between the EPC 108 (as well as the 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 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 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.

[0050] The MME 114 manages user equipment 104 in the EPC 108, including managing subscriber authentication, maintaining context for authenticated user equipment 104, establishing a data bearer path in the network for user traffic, and tracking the location of idle mobiles that have not detached from the network. For 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 from which the user equipment 104 initiates system access. An MME is typically part of a collection of MMEs in 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 ends of the data path through the EPC 108.

[0051] The PCRF 118 is responsible for policy control decision making and controlling the flow-based charging functionality with the policy control enforcement function (PCEF) residing in the P-GW 110. The PCRF 118 provides QoS authorization (QoS Class Identifier (QCI) and bit rate) that determines how a particular data flow is treated by the PCEF and ensures that this is in line with the user's subscription profile.

[0052] As mentioned above, IP services 119 are provided by PDN 101 (shown in FIG. 1a).

[0053] 1d shows a typical 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 compliant with the Common Public Radio Interface (CPRI) / enhanced CPRI (eCPRI) 142 standard specification, either using an RRH-specific custom control and user plane framing method or using an O-RAN Alliance compliant control and user plane framing method. 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 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.

[0054] The RRH 132 can transmit and receive wireless signals using an antenna 136. The RRH 132 can convert (using a converter (CONV) 140) digital baseband signals from the BBU 134 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.

[0055] Figure 2 shows additional details of a typical 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 the 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.

[0056] 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 the MMEs and the S-GWs. The eNodeB 106 selects one MME from a group of MMEs so that the load can be distributed across multiple MMEs to avoid congestion.

[0057] II. 5G NR Wireless Communication Network Some implementations of the present disclosure relate 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. 5G networks have improved support for device-to-device communication, lower costs, lower latency than 4G devices, and less battery consumption. 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, enhanced spectral efficiency, improved coverage, enhanced signaling efficiency, 1-10 ms latency, and reduced latency compared to existing systems.

[0058] 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 a wireless device 306. The components within the system 300 can be communicatively coupled to a core using a backhaul link 305. The centralized unit (CU) 302 can be communicatively coupled to a distributed unit (DU) 304 using a midhaul connection 308. The radio frequency (RU) component 306 can be communicatively coupled to the DU 304 using a fronthaul connection 310.

[0059] 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.

[0060] 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 called 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 with L1 split architecture (Option 7).

[0061] In some implementations, a lower layer split architecture (e.g., Option 7) may include a 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 lower layer split architecture of the present disclosure may include splitting of cell-level processing and user-level processing, which may include cell-level processing in a remote unit (RU) and user-level processing in a DU. Additionally, using the lower layer split architecture of the present disclosure, frequency-domain samples may be transported over the Ethernet fronthaul, and the frequency-domain samples may be compressed to reduce the fronthaul bandwidth.

[0062] 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.

[0063] The mobile device 408 may be configured to communicate with any 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 macrocell 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 macrocell 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-efficient, and energy-efficient operation. The macrocell 402 may maintain good connectivity and mobility via the C-plane 410. Furthermore, in some cases, LTE and NR may be transmitted on the same frequency.

[0064] FIG. 5a illustrates a typical 5G wireless communication system 500 according to some implementations of the present disclosure. 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.

[0065] 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).

[0066] Figure 5b shows an exemplary 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 disaggregated radio access network (RAN) architecture, whereby layers L1, L2, L3 and radio processing may be virtualized and disaggregated across centralized, distributed, and radio units. As shown in Figure 5b, the gNB-DU 508 may be communicatively coupled to a gNB-CU-CP control plane portion 504 (also shown in Figure 5a) and a gNB-CU-UP user plane portion 506. Each of the components 504, 506, 508 may be configured to include one or more layers.

[0067] The gNB-DU 508 may include RLC, MAC, and PHY layers, as well as various communications 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 radio resource control and PDCP control (PDCP-C) sublayers. Furthermore, the distributed unit 508 may be communicatively coupled to the user plane portion 506 of the 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.

[0068] 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. The upper portion of the PHY layer (or Layer 1) may be performed by the gNB-DU 508, and the lower portion of the PHY layer may be performed by the RU (not shown in Figure 5c). As shown in Figure 5c, the RRC portion and the PDCP-C portion may be performed by the control plane portion 504, and the SDAP portion and the PDCP-U portion may be performed by the user plane portion 506.

[0069] 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.

[0070] The MAC sublayer of Layer 2 may perform beam management, random access procedures, mapping of logical channels to 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 via HARQ, priority handling between logical channels for one UE, priority handling between UEs via dynamic scheduling, transport format selection, and other functions. The RLC sublayer's functions may include forwarding upper-layer packet data units (PDUs), error correction via 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, SDU retransmission, SDU discard in the uplink, forwarding of control plane data, and others.

[0071] 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.

[0072] III. Target Cell Prioritization for L1 / L2 Triggered Mobility (LTM) Various implementations of target cell prioritization for LTM described herein can include prioritizing target cells upon handover (HO) from one cell (serving cell) to another cell (target cell) for a user equipment (UE) communicatively coupled with a base station of a wireless communication system. The prioritization can be based on a configuration of the target cell.

[0073] A Layer 1 / Layer 2 triggered mobility (LTM) inter-cell HO in a base station can be performed by performing a serving cell change (SSC) from a serving cell to a target cell. Multiple target cells can meet the HO criteria required for a UE to undergo SSC and thus be viable target cell options for HO. However, one or more target cells that meet the HO criteria may have a configuration that is more similar to that of the serving cell currently serving the UE than the other cell(s) in the target cell. Thus, by prioritizing target cells based on their configuration, a target cell that causes as little service interruption and / or degradation of service quality to the UE as possible can be selected for HO, thereby improving the user experience.

[0074] Prioritizing the target cells may include ranking each of multiple candidate target cells for HO based on the target cell configuration. Currently, according to 3GPP standards, up to eight LTM target cells may be prepared for a given UE. Therefore, in currently available scenarios, the ranking may include ranking up to eight target cells in order of HO priority.

[0075] One or more aspects of a cell's configuration may be considered in prioritizing a target cell. One example of a cell configuration is its configuration for guaranteed bit rate (GBR) allocation to GBR data radio bearers (DRBs). DRBs carry data or user plane traffic. A UE's GBR bearers may or may not be permitted by the target cell because, for example, different vendors may configure their devices differently, because of resource availability at the time of target cell preparation, and / or because of one or more other factors. Regarding GBR allocation to GBR DRBs, considering the target cell's GBR allocation to GBR DRBs compared to the source (e.g., serving cell) configuration can help ensure that a UE does not receive a lower GBR from the target cell when handed over from the serving cell to the target cell. Thus, the user experience may be maintained, if not improved.

[0076] Another example of a cell configuration is a configuration for packet data unit (PDU) sessions to map to DRBs. A DRB maps a quality of service (QoS) flow identifier (QFI). Each QFI may be mapped to two or more DRBs. Thus, a UE with one or more PDU sessions with a QFI may be mapped to one or more DRBs in the RAN. The source configuration may or may not be honored by the target cell due to, for example, resource availability at the time of target cell preparation (because different vendors may have different RRM algorithms for PDU sessions to map to DRBs), and / or one or more other factors. Considering PDU sessions to map to DRBs can help ensure that DRB mapping at the target cell does not adversely affect the user experience.

[0077] Another example of cell configuration is a configuration related to 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 can be assigned to a UE, and the user experience may be maintained, if not improved, when service is handed over from the source cell to the target cell. However, a target call may have fewer than N carriers that can be assigned to a UE, and the user experience may be adversely affected when service is handed over from the source cell to the target cell. Considering the carrier configuration for carrier aggregation may help ensure that the same or more carriers can be assigned to the UE by the target cell compared to the number of carriers assigned to the UE by the serving cell.

[0078] Another example of cell configuration is a configuration related to slice mapping of UE services. A particular network slice 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. Thus, when the UE's service is handed over to the target cell, the UE no longer has access to that network slice, and slice remapping must occur, potentially resulting in a poor user experience. For example, a network slice may be available only to certain UEs, such as when a company, university, or other educational institution, or other organization has a network slice available to UEs registered with or otherwise associated with its employees and / or students but not to other UEs. The serving cell can access such a network slice, but one or more target cells cannot access the slice. Therefore, considering slice mapping of UE services helps prevent slice remapping, which helps prevent a poor user experience.

[0079] Another example of cell configuration is the configuration regarding accepted DRBs for a UE. The serving cell may have DRBs for the UE that are different from those accepted in the target cell. Therefore, considering the DRBs for the UE accepted by the target cell compared to the serving cell currently serving the UE helps ensure that all of the DRBs for the UE currently served by the serving cell can be accepted by the target cell, thereby helping to prevent degradation of the user experience.

[0080] In some implementations of the present disclosure, a base station (e.g., a Next Generation RAN (NG-RAN) node such as a gNodeB, eNodeB, or 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 disaggregated architecture in which the base station includes one gNB-CU-CP (e.g., gNB-CU-CP 504 in FIGS. 5a-5c) and two or more CU-UPs (e.g., gNB-CU-UP 506 in FIGS. 5a-5c) and gNB-DUs (e.g., gNB-DUs 508, 510 in FIGS. 5a-5c). Generally, the ng-eNodeB is enhanced as a Next Generation (ng) device to be configured to connect a 5G UE to a 5G core network. The base station can be configured to prioritize target cells as described above when a UE is handed off from one cell (serving cell) of the base station to another cell (target cell) of the base station.

[0081] FIG. 6a shows an example system 600 configured to prioritize target cells. The base station 602 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 may be used in providing RACH-less LTM. In the illustrated implementation of FIG. 6a, the base station 602 includes multiple CU-UPs 606a, 606b, and 606c. In this illustrated implementation, the base station 602 includes three CU-UPs 606a, 606b, and 606c, but may include multiple other CU-UPs. The CUs of the base station 602, 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 GC 502 of FIG. 5a.

[0082] The CU of the base station 602 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.

[0083] The base station 602 also includes multiple DUs 608, 610. The base station 602 includes two DUs 608, 610 in this illustrated implementation, but may include multiple additional 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 fact that there are three CU-UPs 606a, 606b, 606c with which each DU 608, 610 may be configured to communicate.

[0084] The base station 602 also includes multiple RUs 612. In this illustrated implementation, the base station 602 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. Additionally, 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.

[0085] Target cell prioritization may be configured to occur when one EU of a UE communicatively coupled to the base station 602 is handed off from one DU of the DUs 608, 610 of the base station 602 to another DU of the DUs 608, 610 of the same base station 602. The one DU of the DUs 608, 610 currently serving the UE 622 is referred to as the "serving DU" because it currently serves the UE 622, e.g., currently serving the UE 622. The one DU of the DUs 608, 610 to which the UE's service is being handed off is referred to as the "target DU" because it is intended to serve the UE 622.

[0086] A system that can be configured to prioritize target cells is further described with reference to Figure 6b. Figure 6b shows the CU-CP 604 and CU-UPs 606a, 606b, and 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. Three of the DUs 628a, 628b, and 628c are macro cells (labeled macro1, macro2, and macro3 in Figure 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 Figure 6b). The base station 624 may include another number of macro cells and / or another number of small cells. 21 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). 21 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 cell 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).

[0087] 6b, each CU-UP 606a, 606b, 606c serves a subset of 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 communications (URLLC)).

[0088] Figure 7 illustrates an example method 700 according to some implementations of the present disclosure. Method 700 is described with reference to example system 800 shown in Figure 8, but may be similarly implemented in other systems, such as system 100 of Figures 1a-1c and 2, system 400 of Figure 4, system 500 of Figure 5a, and systems of Figures 6a and 6b, etc. System 800 of Figure 8 is a 5G system, but as noted above, the target cell prioritization described herein may be performed in other types of wireless communication systems, such as an LTE wireless communication system or a 6G or later generation wireless communication system.

[0089] In the system 800, a UE 802 (e.g., UE 104 of FIGS. 1a-1c, UE 622 of FIG. 6a, etc.) is configured 810 with one or more target cells within one or more DUs 804, 806 (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, DUs 628a, 628b, 628c of FIG. 6b, etc.) of a base station, e.g., a gNB (e.g., gNodeB of FIG. 5a, gNodeB 624 of FIGS. 6a and 6b, etc.). For ease of explanation, the system 800 is shown in FIG. 8 with one UE 802 communicatively coupled to the base station and the base station includes two DUs 804, 806, although multiple UEs may be communicatively coupled to the base station and / or the base station may include more than two DUs. The base station of the system 800 also includes a CU including a CU-CP 808 (e.g., the gNB-CU-CP 504 of FIGS. 5a-5c, the CU-CP 604 of FIGS. 6a and 6b, etc.) and one or more CU-UPs (e.g., the gNB-CU-UP 506 of FIGS. 5a-5c, the CU-UPs 606a, 606b, 606c of FIGS. 6a and 6b, etc.) (not shown in FIG. 8a), and multiple RUs (e.g., the RU 512 of FIG. 5a, the RU 612 of FIG. 6a, etc.) (not shown in FIG. 8a). The UE 802 is currently served by the serving DU 804. Furthermore, the base station of FIG. 8a is communicatively coupled to a core network (e.g., the EPC 108 of FIGS. 1a-1c and 2, the 5GC 502 of FIG. 5a, etc.) (not shown in FIG. 8a).

[0090] Although the method 700 illustrates an implementation of an inter-DU LTM serving cell change scenario, including a serving DU 804 determining 702 that a cell change is necessary for the UE 802, the method 700 also applies to an intra-DU LTM serving cell change scenario and a combined inter- and intra-DU serving cell change scenario. The serving DU determination 702 may include the serving DU 804 analyzing an intra-frequency L1 measurement report 814 transmitted 812 by the UE 802 to the serving DU 804 in accordance with 3GPP standards. In accordance with 3GPP standards, the intra-frequency L1 measurement report may include Layer 1 (L1) measurements that may be analyzed by the serving DU 804 when making resource control decisions, which may include a serving cell change where 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.

[0091] In response to determining 702 that a serving cell change should occur, the serving DU 804 notifies the UE 802 of the serving cell change at step 704. As shown in FIG. 8 , notifying the UE 802 at step 704 may include the serving DU 804 sending a serving cell change command, e.g., a MAC CE, to the UE 802 at 816.

[0092] Also, in response to determining 702 that a cell service change should occur, the serving DU 804 notifies the CU-CP 808 in step 704 that a serving cell change has occurred for the UE 802. Thus, the notification (step 704) may identify the UE 802 to the CU-CP 808 using an identifier, such as in accordance with 3GPP standards, that uniquely identifies the UE 802 to the CU-CP 808 and that is known to the serving DU 804. As shown in FIG. 8, the notification to the CU-CP 808 (step 704) may include the serving DU 804 sending a serving cell change notification message at 818 to the CU-CP 808 using the F1 communication interface. As further shown in FIG. 8, the serving cell change notification message includes a cell identity (ID) that may be associated with the UE 802 that has made the serving cell change.

[0093] The UE 802 receives the serving cell change command from the serving DU 804 in step 704, and in response to executing the serving cell change command, sends a radio resource control (RRC) reconfiguration confirm message to the CU-CP 808 at 820. The CU-CP 808 becomes aware from the RRC reconfiguration confirm message that the UE 802, which is uniquely identified to the CU-CP 808 by the serving DU 804, has confirmed successful completion of the serving cell change.

[0094] Also, in response to receiving the layer 3 RRC measurement configuration, the UE 802 sends an RRC measurement report 822 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 when making a resource control decision, which may include determining 824 to prepare at least one target DU cell for LTM such that at least one target cell from the target DU 806 is ready to serve the UE 802 instead of the serving DU 804 for at least one service.

[0095] In response to determining at 824 to prepare at least one target cell for LTM, the CU-CP 808 prepares at least one target cell for LTM in step 706. As shown in FIG. 8 , in this illustrated implementation, each of the at least one target cell is an inter-DU target cell, e.g., part of a DU different from the serving DU 804 where the same CU (e.g., the CU including the CU-CP 808) serves each DU 804, 806. Also, in this illustrated implementation, because there are only two gNB-DUs, the at least one target cell includes only the target DU 806; however, as described above, a base station can include three or more target cells. Currently, according to 3GPP standards, up to eight LTM target cells may be prepared for a given UE.

[0096] The step 706 of preparing at least one target cell for LTM may include notifying the at least one target DU 806 that the at least one target DU 806 may later be notified to start serving the UE 802 for at least one service. Thus, the target DU 806 may reserve necessary resources for the UE 802. As shown in FIG. 8 , the step 706 of preparing at least one target cell may include the CU-CP 808, which in this illustrated implementation is only the target DU 806, sending a UE Context Setup Request message at 826 to the target DU 806 using the F1 communication interface in accordance with the 3GPP standard.

[0097] In response to receiving the UE context setup request message from the CU-CP 808, the target DU 806 prepares each of the at least one target cell for LTM at 828. In this illustrated implementation, the at least one target cell includes only the target DU 806 preparing the target cell at 828. The preparation at 828 may include the target cell reserving necessary resources for the UE 802. The preparation at 828 may also include identifying HO preparation inputs including configurations for each target cell. The configurations for each target cell include one or more of the configurations described above, such as a configuration for GBR allocation for GBR DRBs, a configuration for PDU sessions to map to DRBs, a configuration for carrier configuration for carrier aggregation, a configuration for slice mapping for a UE service, and a configuration for accepted DRBs.

[0098] The target DU 806 notifies the CU-CP 808 that the preparation is complete at 828. As shown in FIG. 8, notifying the CU-CP 808 may include the target DU 806 sending a UE context setup response message at 830 to the CU-CP 808 using the F1 communication interface in accordance with the 3GPP standard. As further shown in FIG. 8, the UE context setup response message includes consolidated cell group configuration information of one or more target cells prepared by the target DU 806, and also includes HO preparation input. Thus, the CU-CP 808 is aware of each configuration of the target cell(s) prepared at 828 and any changes to the serving cell configuration.

[0099] The CU-CP 808 determines the LTM HO priority for each of the one or more target cells prepared at 828 at step 708, 832. If there is only one target cell prepared at 828, the CU-CP 808 skips the determination at step 708, 832 since there is only one target cell candidate. If there are multiple target cells prepared at 828, there are two candidate target cells available for HO priority, so the CU-CP 808 performs the determination at step 708, 832. The determination at step 708, 832 may include comparing each of the received target cell configurations to a serving cell configuration reflected by the expected UE service requirements, for example, based on received L3 measurement reports. Different vendors may decide to give higher weight to some configuration factors than others, based on which factors the vendor considers more important to maintain than others in order to maintain the best user experience during HO, for example, by considering that maintaining GBR allocation for GBR DRBs is more important and therefore deserves a higher priority than maintaining the configuration regarding PDU sessions to map to DRBs, considering that the configuration regarding carrier configuration for carrier aggregation is more important and therefore configuration regarding slice mapping for UE services is given a higher priority, giving lower priority to target cells where multiple QFIs are mapped to the same DRB or where the number of configured secondary carriers (SCells) is reduced or where some DRBs of a slice are remapped to a default slice compared to target cells with a degraded or enhanced source cell configuration, etc.

[0100] The CU-CP 808 assigns a priority value to each target cell based on the priority determined in step 708, 832. The priority values ​​may be numeric (e.g., 1 for highest priority, 2 for second highest priority, etc.), alphabetic (e.g., A for highest priority, B for second highest priority, etc.), or may be in another format.

[0101] 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 target cell's configuration changes (improves or deteriorates), 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 (information) 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 (information) to the CU-CP 808 including the target cell's configuration information and indicating that the target cell is available for LTM HO.

[0102] The CU-CP 808 notifies 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 their LTM HO priorities in step 710. In an inter-DU LTM scenario, one or more target cells of the at least one LTM-prepared target cell belong to a DU different from the serving DU 806. For example, referring to the system of FIG. 6b, the serving DU may be a small cell 626 of the macro1 DU 628a, and one or more target cells of the target cells may be one or more small cells 626 of the macro2 DU 628b and / or macro3 DU 628c.

[0103] 8, the notification to the serving DU 804 in step 710 may include the CU-CP 808 sending a UE context modification request message at 834 to the serving DU 804 using the F1 communication interface. The UE context modification request message may include, for each one or more target DUs, cell identification information (e.g., a unique cell ID identifying a 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). 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 HO identified to the serving DU 804.

[0104] In response to being notified of at least one LTM-prepared target DU cell in step 710, the serving cell 804 stores received information about the at least one LTM target cell at 836. For example, the serving cell 804 stores a list of LTM-prepared target cells and their respective LTM HO priority information. Also, in response to being notified of at least one target DU in step 710, the serving cell 804 sends a UE context modification response message to the CU-CP 808 using the F1 communication interface at 838. The UE context modification response message may include aggregated cell group configuration information for each of one or more 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 at least one target cell from the CU-CP 808 and acknowledge the receipt to the CU-CP 808 using a message already sent for HO according to the 3GPP standard.

[0105] In response to receiving the UE Context Modification Response message, the CU-CP 808 sends an RRC Reconfiguration message to the UE 802 at 840 in accordance with 3GPP standards. As shown in FIG. 8 , the RRC Reconfiguration message includes the LTM target cell configuration information provided to the CU-CP 808 from the target DU 806, for example, in the UE Context Setup Response message sent at 830.

[0106] In response to receiving the target cell configuration in the RRC reconfiguration message, the UE 802 sends an L1 measurement report to the serving DU 804 at 842, in accordance with 3GPP standards. The L1 measurement report provides the serving DU 804 with UE measured radio condition information of the configured target cell.

[0107] In response to receiving the L1 measurement report sent from the UE 802 at 842, the serving cell 804 selects one target cell from among one or more LTM-prepared target cells identified for the serving DU 804 at step 712, 844. If there is only one target cell identified to the serving DU 804 by the CU-CP 808 as an LTM-prepared target cell, the serving cell selection at step 710, 844 is straightforward, and the serving DU 804 selects the one candidate target cell at step 710, 844.

[0108] If there are multiple target cells identified by the CU-CP 808 for the serving DU 804, the target cell selection of the serving cell in step 710, 846 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 UE radio conditions received by the serving DU 804 from the UE 802 in the L1 measurement report. Thus, the serving DU 804 can consider the specific needs of the particular UE 802 involved in the HO when selecting a target cell for HO in step 712, 844. Furthermore, the L1 measurement report sent by the UE 802 to the serving DU 804 in 842 reports L1 measurements that may include a Reference Signal Received Power (RSRP) defined by 3GPP for each of the multiple target cells, the identity of which is known by the UE 802 as provided to the UE 802 by the CU-CP 808 in the RRC reconfiguration message. Therefore, the serving DU 804 can analyze the L1 measurement report received from the UE 802 to determine which one or more target cells among the multiple target cells have a radio quality that exceeds a predetermined threshold radio quality.

[0109] If only one target cell among the multiple target cells satisfies the radio conditions of the UE, for example, if only one of the radio qualities of the target cells exceeds a predetermined threshold radio quality, the serving cell 804 selects the target cell in step 712, symbol 844. If two or more target cells among the multiple target cells satisfy the radio conditions of the UE, for example, if the radio qualities of the target cells each exceed a predetermined threshold radio quality, any one of these target cells can serve the needs of the UE, and the one of these target cells can be selected according to the LTM HO priority information received by the serving DU 804 from the CU-CP 808 by selecting one of the target cells having the highest priority (satisfying the radio conditions). 8 , target cell A of target DU 806 and target cell B of target DU 806 are each identified by the serving DU 804 as meeting radio conditions, and target cell A is selected as the target cell for HO in step 712, 844, because it has a higher priority ranking than target cell B in the LTM HO priority received by the serving DU 804 and therefore provides a less impaired user experience than target cell B. Thus, even if target cell B has better radio conditions than target cell A, target cell A is selected for HO because of its higher LTM HO priority.

[0110] Upon selecting the target cell in step 712 844, the serving DU 804 triggers a serving cell change in step 714 to the target cell selected in step 713 844. As shown in FIG. 8 , triggering the serving cell change in step 712 may include the serving DU 804 sending a MAC CE to the UE 802, e.g., by PCI, 846, including a serving cell change command and identifying the target cell selected for the UE 802 in step 712 844.

[0111] The UE's receipt of the MAC CE indicates to the UE 802 that an LTM serving cell change (SCC) should be performed to the target cell identified for the UE 802. Accordingly, in response to receiving the MAC CE from the serving cell 804, the UE 802 initiates an HO to the target cell at step 716, 848. As shown in FIG. 8 , the UE 802 initiating an HO to the target cell at step 716, 848 may include the UE 802 accessing the target cell at 848 using a RACH message, which may be performed in accordance with the 3GPP standards. In response to the UE 802 accessing the target cell, the target DU 806 transmits a serving cell change notification at 850 to the CU-CP 808 over the F1 communication interface, identifying the target cell as the new current serving cell for the UE 802 for at least one service, e.g., by a unique identifier according to 3GPP. Also, in response to receiving the MAC CE from the serving cell 804, the UE 802 sends an RRC Reconfiguration Acknowledge message to the CU-CP 808 at 852. Thus, the CU-CP 808 receives acknowledgements from both the UE 802 via the RRC Reconfiguration Acknowledge message indicating successful RRC reconfiguration at the UE 802 and from the target DU 806 via the serving cell change notification that the target DU 806 is now serving the UE 802 for at least one service handed over from the serving DU 804.

[0112] Some implementations of the present disclosure may be configured to be implemented in a system 900, as shown in FIG. 9 . The system 900 may include one or more of a processor 910, a memory 920, a storage device 930, and an input / output device 940. Each of the components 910, 920, 930, and 940 may be interconnected using a system bus 950. The processor 910 may be configured to process instructions for execution within the system 600. In some implementations, the processor 910 may be a single-threaded processor. In alternative implementations, the processor 910 may be a multi-threaded processor. The processor 910 may further be configured to process instructions stored in the memory 920 or the storage device 930, including receiving or sending information through the input / output device 940. The memory 920 may store information within the system 900. In some implementations, the memory 920 may be a computer-readable medium. In alternative implementations, the memory 920 may 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.

[0113] 10 illustrates an example method 1000 of target cell prioritization for LTM according to some implementations of the present disclosure. Method 1000 may be performed, for example, using the implementations shown in and described with respect to FIGS.

[0114] The method 1000 includes step 1002 of receiving, at a serving DU of the base station, information indicating handover priorities of multiple LTM target cells of a second DU of the base station from a CU-CP of the base station, and step 1004 of selecting, at the serving DU, one LTM target cell from the multiple LTM target cells for handing over a service for the UE from the serving DU based on the received information, and triggering handover of a service for the UE from the serving DU to the selected target cell, where each of the multiple LTM target cells selected by the serving DU satisfies a handover criterion.

[0115] Some implementations of the present disclosure can include one or more of the following optional features.

[0116] In some implementations, the handover priority can be based on the target cell configuration of each of the multiple LTM target cells. Furthermore, the target cell configuration of each of the multiple LTM target cells can include at least one of a configuration for GBR allocation to GBR DRBs, a configuration for PDU sessions to map to DRBs, a configuration for carrier aggregation, a configuration for slice mapping for UE services, and a configuration for accepted DRBs for the UE, and / or the handover priority can be based on the configuration of each of the multiple LTM target cells compared to the configuration of the serving cell. Furthermore, at least one target DU including the multiple LTM target cells can provide the target cell configuration of each of the multiple LTM target cells to the CU-CP in an F1 message, and / or the handover priority can be recalculated each time an LTM target cell is added, reconfigured, or deleted for the UE. Furthermore, the at least one target DU can also provide a list of changes in the multiple LTM target cells compared to the serving cell configuration.

[0117] In some implementations, the handover criteria may include a predetermined threshold radio quality, and the operation may further include determining, at the serving DU, which one or more target cells among the plurality of target cells have a radio quality above the predetermined threshold radio quality, and the selection range may be only among the one or more determined target cells.

[0118] In some implementations, the triggering may include sending a MAC CE message from the serving DU to the UE.

[0119] In some implementations, the base station may have a non-aggregated architecture.

[0120] In some implementations, the base station may include a Next Generation Radio Access Network (NG-RAN) node, which may further include a gNodeB or an ng-eNodeB.

[0121] In some implementations, the base station may include at least one processor and at least one non-transitory storage medium that stores instructions that, when executed by the at least one processor, cause the at least one processor to perform a method.

[0122] 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.

[0123] 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 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.

[0124] As used herein, the term "user" may refer to any entity, including a person or a computer.

[0125] Although ordinal numbers such as first, second, etc. may relate to order in some circumstances, as used herein, 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 (just as a first event in one paragraph of description may differ from a first event in another paragraph of description).

[0126] 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.

[0127] 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, magnetic disks, optical disks, memories, and programmable logic devices (PLDs), including machine-readable media that receive machine instructions as machine-readable signals. 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.

[0128] To provide for user interaction, the disclosure 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.

[0129] The disclosure described herein may be implemented in a computing system including back-end components, such as one or more data servers, or middleware components, such as one or more application servers, or front-end components, such as one or more client computers having a graphical user interface or web browser through which a user can interact with an implementation of the disclosure 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.

[0130] A computing system may include clients and servers. Clients and servers are often, 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.

[0131] The implementations described in the foregoing description do not represent all implementations consistent with the disclosure set forth herein. Rather, they are merely some examples consistent with aspects related to the disclosure set forth herein. 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. Additionally, the logic flow illustrated in the accompanying drawings 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; and at least one non-transitory storage medium having instructions stored thereon, the instructions, when executed by the at least one processor, causing the at least one processor to perform operations, the operations including: receiving, from a centralized unit control plane (CU-CP) of a base station, information indicating handover priorities of a plurality of Layer 1 / Layer 2 triggered mobility (LTM) target cells of a second DU of the base station, at a serving distributed unit (DU) of the base station; and selecting, in the serving DU, one LTM target cell among 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 the handover of the service for the UE from the serving DU to the selected target cell, wherein each of the plurality of LTM target cells selected by the serving DU satisfies handover criteria.

2. The apparatus of claim 1 , wherein the handover priority is based on a target cell configuration of each of the plurality of LTM target cells.

3. The target cell configuration of each of the plurality of LTM target cells comprises: A configuration for Guaranteed Bit Rate (GBR) allocation for GBR Data Radio Bearers (DRBs); A configuration for packet data unit (PDU) sessions for mapping to DRBs; A configuration related to a carrier configuration for carrier aggregation; a configuration for slice mapping for a UE service; and a configuration for accepted DRBs for the UE.

4. The apparatus of claim 3 , wherein at least one target DU including the plurality of LTM target cells provides the target cell configuration of 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 provides a list of changes to the multiple LTM target cells compared to a serving cell configuration.

6. The apparatus of claim 2 , wherein the handover priority is based on the configuration of each of the plurality of LTM target cells compared to the configuration of the serving cell.

7. The apparatus of claim 6 , wherein the handover priority is recalculated each time a LTM target cell is added, reconfigured, or removed for the UE.

8. the handover criteria include a predetermined threshold radio quality; The operations further include determining, in the serving DU, which one or more target cells among the plurality of target cells have a radio quality that exceeds the predetermined threshold radio quality; The apparatus of claim 1 , wherein the range of selection is only among the one or more determined target cells.

9. The apparatus of claim 1 , wherein the triggering includes transmitting a Medium Access Control (MAC) Control Element (CE) message from the serving DU to the UE.

10. The apparatus of claim 1 , wherein the base station has a non-aggregated 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 of claim 1 , wherein the base station includes 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, including: receiving, from a centralized unit control plane (CU-CP) of a base station, information indicating handover priorities of a plurality of Layer 1 / Layer 2 triggered mobility (LTM) target cells of a second DU of the base station, at a serving distributed unit (DU) of the base station; A non-transitory storage medium comprising: based on the received information, selecting, in the serving DU, one LTM target cell among the plurality of LTM target cells for handover of a service for the UE from the serving DU, and triggering the handover of the service for the user equipment (UE) from the serving DU to the selected target cell, wherein each of the plurality of LTM target cells selected by the serving DU satisfies handover criteria.

15. The storage medium of claim 14 , wherein the handover priority is based on a target cell configuration of each of the plurality of LTM target cells.

16. The target cell configuration of each of the plurality of LTM target cells comprises: A configuration for Guaranteed Bit Rate (GBR) allocation for GBR Data Radio Bearers (DRBs); A configuration for packet data unit (PDU) sessions for mapping to DRBs; A configuration related to a carrier configuration for carrier aggregation; a configuration for slice mapping for a UE service; and a configuration regarding accepted DRBs for the UE.

17. 1. A computer-implemented method comprising: receiving, from a centralized unit control plane (CU-CP) of a base station, information indicating handover priorities of a plurality of Layer 1 / Layer 2 triggered mobility (LTM) target cells of a second DU of the base station, at a serving distributed unit (DU) of the base station; and selecting, in the serving DU based on the received information, one LTM target cell among the plurality of LTM target cells for handover of a service for the UE from the serving DU, and triggering the handover of the service for the UE from the serving DU to the selected target cell, wherein each of the plurality of LTM target cells selected by the serving DU satisfies handover criteria.

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

19. The target cell configuration of each of the plurality of LTM target cells comprises: A configuration for Guaranteed Bit Rate (GBR) allocation for GBR Data Radio Bearers (DRBs); A configuration for packet data unit (PDU) sessions for mapping to DRBs; A configuration related to a carrier configuration for carrier aggregation; a configuration for slice mapping for a UE service; and a configuration for accepted DRBs for the UE.

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