Lower Layer Triggered Mobility Resources

Abstract

In a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, the base station distributed unit determines a CFRA resource for the user equipment to access the target cell from a pool of contention-free random access (CFRA) resources reserved for lower layer triggered mobility, and the base station distributed unit transmits information to the user equipment indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell, thereby improving performance of the lower layer mobility.

Description

[Technical Field]

[0001] The present invention relates to lower layer triggered mobility, and more particularly to controlling resources for radio access in a target cell. [Background technology]

[0002] This section is intended to provide a background or context for the claimed invention. The description herein may include concepts that could be pursued, but not necessarily concepts that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the material described in this section is not prior art to the description and claims of this application, and is not admitted to be prior art by inclusion in this section.

[0003] One of the goals of the 3GPP Release 18 work item on mobility enhancements includes support for lower layer triggered mobility (LTM) to improve the interruption time and execution delay of switching between cells of the same Distributed Unit (DU) or between cells controlled by the same Centralized Unit (CU) but of different DUs.

[0004] Unlike L3-based mobility, where handover decisions are made based on Layer 3 (L3) cell quality measurements, handover in LTM is triggered by the DU based on measurements below L3, e.g., Layer 1 (L1) beam measurements.

[0005] By reserving CFRA resources in the target cell, the target cell can be prepared for LTM to facilitate dynamic switching of UEs to the target cell. To improve LTM interruption time and execution delay, the CFRA resource reservation can be increased. However, this limits the number of UEs that can utilize LTM. In particular, one target cell may be prepared for LTM by different source nodes for different UEs, in which case the target cell may need to reserve at least one CFRA preamble for each UE. Therefore, CFRA resource reservation can be high, especially in high-density networks with a large number of DUs. Summary of the Invention

[0006] The scope of protection sought for various embodiments of the invention is defined by the independent claims. If any, the embodiments, examples, and features described herein that do not fall within the scope of the independent claims are to be interpreted as examples that serve to understand various embodiments of the invention.

[0007] According to a first aspect, there is provided an apparatus comprising one or more processors, the apparatus, when executed by the one or more processors, comprising: - determining, in a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, to change the user equipment from the source cell to the target cell; - determining, by the base station distributed unit, contention free random access (CFRA) resources for accessing the target cell by the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility; sending, by the base station distributed unit, information to the user equipment indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell; and a memory storing instructions to cause the device to:

[0008] According to a second aspect, there is provided an apparatus comprising one or more processors, the apparatus, when executed by the one or more processors, comprising: - receiving, by a base station distributed unit configured for lower layer triggered mobility of the user equipment from a source cell to a target cell, information indicating a contention-free random access, CFRA resource allocated to the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility; - preparing, in the base station distributed unit, a random access channel based on the received information indicating a CFRA resource for changing the user equipment from the source cell to the target cell; and a memory storing instructions to cause the device to:

[0009] According to a third aspect, there is provided an apparatus, comprising: one or more processors; and, when executed by the one or more processors, the apparatus: - determining, by a base station centralized unit configured for lower layer triggered mobility of the user equipment from a contention-free random access (CFRA) resource pool reserved for lower layer triggered mobility, CFRA resources for accessing the target cell by the user equipment; and sending, by the base station centralized unit, information indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell to the base station distributed unit of the target cell; and a memory storing instructions to cause the device to:

[0010] According to a fourth aspect, - determining, in a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, to change the user equipment from the source cell to the target cell; - determining, by the base station distributed unit, contention-free random access (CFRA) resources for accessing the target cell by the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility; sending, by the base station distributed unit, information to the user equipment indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell; A method is provided comprising:

[0011] According to a fifth aspect, - receiving, by a base station distributed unit configured for lower layer triggered mobility of the user equipment from a source cell to a target cell, information indicating a contention-free random access, CFRA resource allocated to the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility; - preparing, in the base station distributed unit, a random access channel based on the received information indicating a CFRA resource for changing the user equipment from the source cell to the target cell; A method is provided comprising:

[0012] According to a sixth aspect, - determining, by a base station centralized unit configured for lower layer triggered mobility of the user equipment from a contention-free random access (CFRA) resource pool reserved for lower layer triggered mobility, CFRA resources for accessing the target cell by the user equipment; and sending, by the base station centralized unit, information indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell to the base station distributed unit of the target cell; A method is provided comprising:

[0013] According to a seventh aspect, - determining, in a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, to change the user equipment from the source cell to the target cell; - determining, by the base station distributed unit, contention-free random access (CFRA) resources for accessing the target cell by the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility; sending, by the base station distributed unit, information to the user equipment indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell; There is provided a computer program comprising computer readable program code means adapted to perform at least the steps of:

[0014] According to an eighth aspect, - receiving, by a base station distributed unit configured for lower layer triggered mobility of the user equipment from a source cell to a target cell, information indicating a contention-free random access, CFRA resource allocated to the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility; - preparing, in the base station distributed unit, a random access channel based on the received information indicating a CFRA resource for changing the user equipment from the source cell to the target cell; There is provided a computer program comprising computer readable program code means adapted to perform at least the steps of:

[0015] According to a ninth aspect, - determining, by a base station centralized unit configured for lower layer triggered mobility of the user equipment from a contention-free random access (CFRA) resource pool reserved for lower layer triggered mobility, CFRA resources for accessing the target cell by the user equipment; and sending, by the base station centralized unit, information indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell to the base station distributed unit of the target cell; There is provided a computer program comprising computer readable program code means adapted to perform at least the steps of:

[0016] One or more of the above aspects may comprise at least some of the following features from the following list: receiving physical layer measurements at a base station distributed unit; Deciding, by the base station distribution unit, to change the user equipment from the source cell to the target cell based on the received physical layer measurements; sending, by the base station distributed unit, a request for CFRA resources for accessing the target cell by the user equipment to the base station centralized unit based on the determined changes; receiving, by the base station distributed unit, from the base station centralized unit, a pool of CFRA resources reserved for lower layer triggered mobility; sending, by the base station distributed unit, information indicating the determined CFRA resources for accessing the target cell by the user equipment to the base station centralized unit; receiving, at the base station distributed unit, information indicating completion of a radio access procedure for the user equipment; In the base station distributed unit, releasing CFRA resources based on received information indicating completion of the user equipment radio access procedure; sending, by the base station distributed unit, information indicating the release of CFRA resources to a base station node managing a pool of CFRA resources reserved for lower layer triggered mobility; The determined CFRA resource is sent in a cell change command; the information indicating the determined CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; o sending, by the base station distributed unit, a message to release allocated CFRA resources to the centralized unit based on completion of the radio access procedure of the user equipment; the received information indicating a CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; o sending, by the base station distributed unit, a message to the user equipment for triggering a change of the user equipment from the source cell to the target cell, such as a Medium Access Control (MAC) Control Element (CE) or downlink control information (DCI); receiving, by a base station centralized unit, a request by a user equipment for CFRA resources to access a target cell; receiving, by the base station centralized unit, information from one or more base station distributed units indicating one or more CFRA resources for lower layer triggered mobility; generating, by the base station centralized unit, a pool of CFRA resources reserved for lower layer triggered mobility based on the received information; o requesting, by the base station centralized unit, from one or more base station distributed units, information indicating one or more CFRA resources for lower layer triggered mobility when configuring the base station distributed units for lower layer triggered mobility; transmitting, by the base station centralized unit, to the base station distributed unit, a pool of CFRA resources reserved for lower layer triggered mobility when configuring the base station distributed unit for lower layer triggered mobility; sending a message by the base station centralized unit to one or more other base station distributed units to cause the one or more other base station distributed units to refrain from configuring the determined CFRA resources for other user equipments attempting to access the target cell; receiving, at the base station centralization unit, information indicating completion of a radio access procedure of the user equipment to the target cell; In the base station centralized unit, releasing CFRA resources based on received information indicating completion of the user equipment radio access procedure; allocating, by the base station centralization unit, one or more physical radio access channel mask indices to each CFRA resource of the pool; The information indicating the determined CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index.

[0017] At least some embodiments improve lower layer mobility performance.

[0018] For a more complete understanding of the exemplary embodiments of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 illustrates an example of a communication system in accordance with at least some embodiments described herein. [Figure 2] FIG. 1 illustrates an example method according to at least some embodiments. [Figure 3] FIG. 1 illustrates an example method according to at least some embodiments. [Figure 4] FIG. 1 illustrates an example method according to at least some embodiments. [Figure 5]FIG. 10 illustrates an example sequence according to at least some embodiments. [Figure 6] FIG. 10 illustrates an example sequence according to at least some embodiments. [Figure 7] FIG. 10 illustrates an example sequence according to at least some embodiments. [Figure 8] FIG. 10 illustrates an example sequence according to at least some embodiments. [Figure 9] FIG. 1 illustrates an example of an apparatus according to at least some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following embodiments are illustrative. Although the specification may refer to "an," "one," or "some" embodiments in several places, this does not necessarily mean that each such reference refers to the same embodiment or that a feature applies only to a single embodiment. Single features of different embodiments may be combined to provide other embodiments.

[0021] The use of ordinal numbers such as "first," "second," "third," etc. to modify a recited feature in the claims and description does not, by itself, imply any priority, precedence, or ordering of one recited feature over another, or any temporal order in which the acts of a method are performed, but is merely used as a label to distinguish one recited feature having a particular name from another recited feature having the same name (except for the use of the ordinal number) to distinguish the recited features.

[0022] As used herein, "at least one of the following:" and "at least one of:" and similar phrases, when a list of two or more elements is joined by "and" or "or," mean at least any one of the elements, or at least any two or more of the elements, or at least all of the elements.

[0023] In a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, the base station distributed unit determines a CFRA resource for the user equipment to access the target cell from a pool of contention-free random access (CFRA) resources reserved for lower layer triggered mobility, and the base station distributed unit transmits information to the user equipment indicating the determined CFRA resource for the user equipment to change from the source cell to the target cell, thereby improving lower layer mobility performance. In this manner, sufficient CFRA resources can be provided in the target cell to improve cell switch interruption time and execution delay. The CFRA resource is selected from a pool controlled by the base station centralized unit. Furthermore, upon completion of the radio access procedure by the user equipment, a message to release the CFRA resource is transmitted to the base station centralized unit. In this manner, dynamic CFRA resource management controlled by the base station centralized unit is provided.

[0024] As used herein, lower layer triggered mobility refers to a mobility procedure in which a user equipment changes or switches from a source cell of a radio access network to a target cell based on a base station distributed unit serving the user equipment's source cell sending a message, e.g., a medium access control (MAC) control element (CE) or downlink control information (DCI), to the user equipment. Examples of mobility procedures include at least one of a cell switch, a handover, or a cell change. The LTM procedure may be performed between cells of the same radio access node or between cells of different radio access nodes. Lower layer triggered mobility (LTM) may refer to a mobility procedure initiated based on processing in any of the lower layers of the radio protocol stack of the radio access network. The lower layers of the radio protocol stack include at least one of a physical layer, i.e., Layer 1 (L1), or a baseband layer for real-time processing, i.e., Layer 2 (L2). A layer above the lower layers of the radio protocol stack, e.g., Layer 3 (L3), may include at least a baseband layer for non-real-time processing. Thus, in LTM, processing performed in at least one of L1 and L2 may trigger a mobility procedure. An example of an LTM procedure is a cell switch triggered based on an L1 measurement report.

[0025] As examples that are helpful in understanding the examples described herein, reference may be made to 3GPP TS38.331NR, Radio Resource Control (RRC), Protocol Specification, Version 17.3.0, and 3GPP TS38.321, NR, Medium Access Control (MAC) Protocol Specification, Version 17.3.0.

[0026] FIG. 1 illustrates an example of a communication system in accordance with at least some embodiments described herein.

[0027] 1 shows user devices 100 and 102 configured to be wirelessly connected over one or more communication channels within an access node (e.g., NodeB) 104 serving a cell. The physical link from the user devices to the NodeB (e.g.,) is referred to as the uplink (UL) or reverse link, and the physical link from the NodeB (e.g.,) to the user devices is referred to as the downlink (DL) or forward link. It should be understood that the NodeB (e.g.,) or their functionality may be implemented using any node, host, server, or access point, or other entity suitable for such use.

[0028] A communication system typically includes multiple (e.g.,) NodeBs, which may be configured to communicate with each other via wired or wireless links designed for that purpose. These links may be used for signaling purposes. A (e.g.,) NodeB is a computing device configured to control radio resources of the communication system to which it is coupled. A NodeB may also be referred to as a base station, an access point, or any other type of interface device, including a relay station operable in a wireless environment. A (e.g.,) NodeB includes or is coupled to a transceiver. The (e.g.,) NodeB's transceiver provides a connection to an antenna unit that establishes a bidirectional radio link to a user device. The antenna unit may include multiple antennas or antenna elements. A (e.g.,) NodeB is further connected to a core network 110 (CN or Next Generation Core NGC). Depending on the system, the CN counterpart may be a Serving Gateway (S-GW, routing and forwarding of user data packets), a Packet Data Network Gateway (P-GW) for providing connectivity between user devices (UEs) and external packet data networks, or a mobile management entity (MME). The CN may comprise nodes that may be referred to as network entities or management entities. Examples of network entities include at least an Access and Mobility Management Function (AMF).

[0029] A user device, also referred to as user equipment (UE), user terminal, terminal device, wireless device, mobile station (MS), etc., refers to a type of device to which resources over the air interface are allocated and assigned, and thus any features described herein with respect to a user device may be implemented by corresponding network devices such as relay nodes, eNBs, and gNBs. An example of such a relay node is a Layer 3 relay (self-backhaul relay) to a base station.

[0030] A user device typically refers to a portable computing device, including wireless mobile communication devices that operate with or without a subscriber identification module (SIM). Portable computing devices include, but are not limited to, types of devices such as mobile stations (mobile phones), smartphones, personal digital assistants (PDAs), handsets, devices that use wireless modems (such as alarms or measurement devices), laptop and / or touchscreen computers, tablets, game consoles, notebooks, and multimedia devices. It should be understood that a user device may also be an almost exclusively uplink-only device, an example of which is a camera or video camera that loads images or video clips onto a network. A user device may also be a device capable of operating in an Internet of Things (IoT) network, a scenario in which objects are provided with the ability to transfer data over a network without the need for human-to-human or human-to-computer interaction. Thus, a user device may be an IoT device. A user device may also utilize the cloud. In some applications, a user device may comprise a small portable device with wireless components (such as a watch, earphones, or glasses) and computations are performed in the cloud. A user device (or in some embodiments a Layer 3 relay node) is configured to perform one or more of the user equipment functions. A user device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal, or user equipment (UE), which are just a few of the names or devices.

[0031] The various techniques described herein may also be applied to cyber-physical systems (CPSs), which are systems in which computational elements cooperate to control physical entities. CPSs enable the implementation and utilization of a large number of interconnected ICT devices (sensors, actuators, processors, microcontrollers, etc.) embedded in physical objects in various locations. Mobile cyber-physical systems are a subcategory of cyber-physical systems because the physical systems in question possess inherent mobility. Examples of mobile physical systems include mobile robots and electronic devices transported by humans or animals.

[0032] Furthermore, although the device is depicted as a single entity, it may be implemented with different units, processors, and / or memory units (not all of which are shown in FIG. 1).

[0033] 5G enables the use of multiple input-multiple output (MIMO) antennas and many more base stations or nodes than LTE (the so-called small cell concept). This includes macro sites operating in conjunction with smaller stations, employing various radio technologies depending on service needs, use cases, and / or available spectrum. Access nodes in the wireless network form transmission / reception points (TRPs), and UEs are expected to access multiple, at least partially overlapping, TRP networks, such as macro cells, small cells, pico cells, femto cells, remote radio heads, and relay nodes. Access nodes may be equipped with massive MIMO antennas, i.e., very large antenna arrays consisting of, for example, tens or hundreds of antenna elements, implemented in a single antenna panel or multiple antenna panels, capable of using multiple simultaneous radio beams to communicate with the UE. UEs may be provided with MIMO antennas with antenna arrays consisting of multiple antenna elements, also known as patches, implemented in a single antenna panel or multiple antenna panels. Thus, a UE may use one beam to access one TRP, may use multiple beams to access one TRP, may use one (common) beam to access multiple TRPs, or may use multiple beams to access multiple TRPs.

[0034] 5G mobile communications will support a wide range of use cases and related applications, including video streaming, augmented reality, various data sharing methods, and various forms of machine-type applications (e.g., massive machine-type communications, mMTC) including vehicle safety, various sensors, and real-time control. 5G is expected to have multiple air interfaces, namely, sub-6 GHz, cmWave, and mmWave, and may also be integrated with existing conventional radio access technologies such as LTE. Integration with LTE, at least initially, may be implemented as a system in which macro coverage is provided by LTE and 5G air interface access is provided from small cells by aggregation to LTE. In other words, 5G is expected to support both inter-RAT (e.g., LTE-5G) and inter-RI (inter-air interface operation between sub-6 GHz, cmWave, mmWave, etc.). One of the concepts being considered for use in 5G networks is network slicing, in which multiple independent and dedicated virtual subnetworks (network instances) are created within the same infrastructure to run services with different requirements in terms of latency, reliability, throughput, and mobility.

[0035] The current architecture of LTE networks is fully distributed in the radio and fully centralized in the core network. Low-latency applications and services in 5G require content to be closer to the radio, leading to local breakout and multi-access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the source of the data. This approach must leverage resources that may not be continuously connected to the network, such as laptops, smartphones, tablets, and sensors. MEC provides a distributed computing environment for hosting applications and services. It also has the ability to store and process content closer to cellular subscribers for faster response times. Edge computing covers a wide range of technologies, including wireless sensor networks, mobile data acquisition, mobile signature analysis, cooperative distributed peer-to-peer ad-hoc networking and processing (which can also be categorized as local cloud / fog computing and grid / mesh computing), dew computing, mobile edge computing, cloudlets, distributed data storage and retrieval, autonomous self-healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (where large-scale connectivity and / or latency are critical), and critical communications (autonomous vehicles, road safety, real-time analytics, time-critical control, healthcare applications).

[0036] The communications system may also communicate with and use services provided by other networks, such as the public switched telephone network or the Internet 112. The communications network may also be capable of supporting the use of cloud services, e.g., at least some of the core network operations may be performed as cloud services (this is depicted in FIG. 1 by "cloud" 114). The communications system may also comprise a central control entity that provides facilities for networks of different operators to cooperate, for example in spectrum sharing.

[0037] By utilizing network function virtualization (NFV) and software defined networking (SDN), an edge cloud can be introduced into the radio access network (RAN). The use of an edge cloud may mean that access node operations will be performed at least in part in a server, host, or node operatively coupled to a remote radio head or base station comprising the radio components. It is also possible to distribute node operations across multiple servers, nodes, or hosts. The application of the cloudRAN architecture allows RAN real-time functions to be performed on the RAN side (e.g., in the distributed unit DU) and non-real-time functions to be performed centrally (e.g., in the centralized unit CU108).

[0038] It should also be understood that the distribution of labor between core network operations and base station operations may be different from that of LTE, and may even not be distributed at all. Some other technological advancements that will likely be used include big data and all-IP, which may change the way networks are built and managed. 5G (or new radio (NR)) networks are designed to support multiple tiers where MEC servers can be placed between the core and base stations or NodeBs (gNBs). It should be understood that MEC is also applicable to 4G networks. A gNB is a next-generation NodeB (or new NodeB) that supports a 5G network (i.e., NR).

[0039] 5G may also utilize non-terrestrial nodes 106, e.g., access nodes, to extend or complement the reach of 5G services by, for example, providing backhaul, wireless access to wireless devices, service continuity for machine-to-machine (M2M) communications, service continuity for Internet of Things (IoT) devices, and service continuity for passengers aboard vehicles, ensuring service availability for critical communications, and / or ensuring service availability for future rail, maritime, and aviation communications. The non-terrestrial nodes may have fixed locations relative to the Earth's surface, or they may be mobile non-terrestrial nodes that may move relative to the Earth's surface. The non-terrestrial nodes may comprise satellites and / or High Altitude Platforms Stations (HAPS). Satellite communications may utilize geostationary earth orbit (GEO) satellite systems as well as low earth orbit (LEO) satellite systems, particularly megaconstellations (systems in which hundreds of nano-satellites are deployed). Each satellite in the megaconstellation may cover multiple satellite-enabled network entities that form ground cells, which may be formed through terrestrial relay nodes 104 or by gNBs located on the ground or within the satellites.

[0040] Those skilled in the art will appreciate that the depicted system is only an example of a part of a wireless access system, and that in practice the system may include multiple (e.g.) NodeBs, a user device may access multiple radio cells, and the system may also include other devices such as physical layer relay nodes or other network elements, where at least one of the (e.g.) NodeBs may be a Home (e.g.) NodeB.

[0041] Furthermore, (for example) a NodeB or base station may be divided into a radio unit (RU) including a radio transceiver (TRX), i.e., a transmitter (TX) and a receiver (RX), a distributed unit (DU) that can be used for so-called Layer 1 (L1) processing and real-time Layer 2 (L2) processing, and a centralized unit (CU) or central unit that can be used for non-real-time L2 and Layer 3 (L3) processing. Such division may enable the CU to be centralized at the cell site and the DU, while the DU may be more distributed or even remain at the cell site. The CU and DU together may be referred to as a baseband or baseband unit (BBU). The CU and DU may be connected by an F1 interface. The RU and DU may also constitute a radio access point (RAP). A cloud computing platform may also be used to run the CU or DU. The CU may run on the cloud computing platform (vCU, virtualized CU). In addition to the vCU, there is also a virtualized DU (vDU) that runs on the cloud computing platform. Furthermore, there may be combinations where the DU may use so-called bare metal solutions, such as application-specific integrated circuits (ASICs) or customer-specific standard product (CSSP) system-on-a-chip (SoC) solutions. It should also be understood that the distribution of labor between the above-mentioned base station units, i.e., the various core network operations and the base station operations, may differ.

[0042] Furthermore, a geographical area of ​​a wireless communication system may be provided with not only a plurality of radio cells but also a plurality of radio cells of different types. The radio cells may be macrocells (or umbrella cells), which are large cells typically reaching tens of kilometers in diameter, or smaller cells such as microcells, femtocells, picocells, or so-called small cells. A Node B (for example) in FIG. 1 may provide any of these cell types. A cellular wireless system may be implemented as a multi-tier network including multiple types of cells. Typically, in a multi-tier network, one access node provides one or more cells of one type, and therefore multiple Node Bs (for example) are required to provide such a network structure.

[0043] 2 illustrates an example method according to at least some embodiments that improves performance of LTM and may be performed by a base station distributed unit that hosts a source cell of lower layer triggered mobility.

[0044] Phase 202 comprises, in a base station distributed unit configured for lower layer triggered mobility of user equipment from a source cell to a target cell, deciding to change user equipment from a source cell to a target cell.

[0045] Phase 204 comprises determining, by the base station distributed unit, contention-free random access, CFRA resources for accessing the target cell by the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility.

[0046] Phase 206 comprises transmitting, by the base station distribution unit, information to the user equipment indicating the determined CFRA resources for changing the user equipment from the source cell to the target cell.

[0047] In an example according to at least some embodiments, phase 202 comprises receiving, at the base station distribution unit, physical layer measurements and determining, by the base station distribution unit, to change user equipment from the source cell to the target cell based on the received physical layer measurements.

[0048] In an example according to at least some embodiments, phase 202 comprises transmitting, by the base station distributed unit, a request for CFRA resources for the user equipment to access the target cell to the base station centralized unit based on the determined changes.

[0049] In an example according to at least some embodiments, phase 204 comprises receiving, by the base station distributed unit, from the base station centralized unit, a pool of CFRA resources reserved for lower layer triggered mobility, and transmitting, by the base station distributed unit, information to the base station centralized unit indicating the determined CFRA resources for the user equipment to access the target cell.

[0050] In an example according to at least some embodiments, phase 206 comprises transmitting the determined CFRA resources in a cell change command.

[0051] In an example according to at least some embodiments, phase 206 comprises receiving, at the base station distributed unit, information indicating completion of a radio access procedure for the user equipment; and releasing, at the base station distributed unit, CFRA resources based on the received information indicating completion of the radio access procedure for the user equipment.

[0052] In an example according to at least some embodiments, phase 206 comprises transmitting, by the base station distributed unit, information indicating the release of CFRA resources to a base station node that manages a pool of CFRA resources reserved for lower layer triggered mobility.

[0053] In an example according to at least some embodiments, phase 206 comprises the information indicating the determined CFRA resource comprising at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index. Examples of a CFRA resource are a Physical Random Access Channel (PRACH) preamble or a combination of a PRACH preamble and a PRACH mask index.

[0054] 3 illustrates an example method according to at least some embodiments that improves performance of LTM and may be performed by a base station distributed unit that hosts a target cell of lower layer triggered mobility.

[0055] Phase 302 comprises receiving, by a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, information indicating contention-free random access, CFRA resources allocated to the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility.

[0056] Phase 304 comprises, at the base station distribution unit, preparing a random access channel based on the received information indicating CFRA resources for changing the user equipment from the source cell to the target cell.

[0057] In an example according to at least some embodiments, phase 304 comprises transmitting, by the base station distributed unit, a message to release allocated CFRA resources to the base station centralized unit based on completion of the user equipment radio access procedure.

[0058] In an example according to at least some embodiments, phase 302 comprises the received information indicating a CFRA resource comprising at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index. Examples of a CFRA resource include a PRACH preamble or a combination of a PRACH preamble and a PRACH mask index.

[0059] 4 illustrates an example method according to at least some embodiments for improving LTM performance, which may be performed by a base station centralized unit.

[0060] Phase 402 comprises determining, by a base station centralization unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, contention-free random access, CFRA resources for accessing the target cell by the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility.

[0061] Phase 404 comprises transmitting, by the base station centralized unit, information indicating the determined CFRA resources for changing the user equipment from the source cell to the target cell to the base station distributed unit of the target cell.

[0062] In an example according to at least some embodiments, phase 404 comprises receiving, by the base station centralization unit, a request for CFRA resources for accessing the target cell by the user equipment.

[0063] In an example according to at least some embodiments, phase 402 comprises receiving, by the base station centralized unit, information from one or more base station distributed units indicating one or more CFRA resources for lower layer triggered mobility, and generating, by the base station centralized unit, a pool of CFRA resources reserved for the lower layer triggered mobility based on the received information.

[0064] In an example according to at least some embodiments, phase 402 comprises the base station centralized unit requesting, from one or more base station distributed units, information indicating one or more CFRA resources for lower layer triggered mobility upon configuration of the base station distributed units for lower layer triggered mobility.

[0065] In an example according to at least some embodiments, phase 402 comprises transmitting, by the base station centralized unit, a pool of CFRA resources reserved for lower layer triggered mobility to the base station distributed unit upon configuration of the base station distributed unit for lower layer triggered mobility.

[0066] In an example according to at least some embodiments, phase 402 comprises transmitting a message by the base station centralized unit to one or more other base station distributed units to cause the one or more other base station distributed units to refrain from configuring the determined CFRA resources for other user equipment attempting to access the target cell.

[0067] In an example according to at least some embodiments, phase 404 comprises receiving, at the base station centralization unit, information indicating completion of a radio access procedure for the user equipment to the target cell, and releasing, at the base station centralization unit, CFRA resources based on the received information indicating completion of the radio access procedure for the user equipment.

[0068] In an example according to at least some embodiments, phase 402 comprises allocating one or more physical radio access channel mask indices to each CFRA resource of the pool.

[0069] In an example according to at least some embodiments, phase 404 comprises the information indicating the determined CFRA resource comprising at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index. Examples of a CFRA resource include a PRACH preamble or a combination of a PRACH preamble and a PRACH mask index.

[0070] Figure 5 illustrates an example sequence according to at least some embodiments. This sequence provides for configuring a base station distributed unit for lower layer triggered mobility. In this sequence, the CU may be responsible for allocating CFRA resources from a pool of CFRA resources. Thus, the base station node that manages the pool of CFRA resources is the CU. Then, in connection with a cell switch of a user equipment from a source cell to a target cell, the DU hosting the source cell may request CFRA resources from the CU for the UE to access the target cell, and the CU may allocate CFRA resources to the UE to change the UE from the source cell to the target cell.

[0071] Phases 501 and 502 comprise sending L3 measurement reports from the UE to the centralized unit CU via the distributed unit DU1.

[0072] Phase 503 comprises determining, by the CU, to prepare one or more target cells, in this case cells in the distributed unit DU2, for L1 / L2 inter-cell mobility. The target cell determined in DU2, Cell 2, may be configured for lower layer triggered mobility of the user equipment.

[0073] Phase 504 comprises the CU sending a UE context setup request to DU2. The UE context setup request comprises a request for CFRA resources for LTM. In one example, the UE context setup request may comprise a specific number of CFRA resources for LTM. The CU may estimate the number of CFRA preambles required based on the current connected mode users with LTM mobility enabled and an estimated number of LTM mobility events based on previous mobility history events. For example, DU2 may allocate a specific number of CFRA preambles along with the RACH resource configuration as part of LTM preparation. Additionally or alternatively, DU2 may allocate one or more different PRACH mask indices associated with each of the CFRA preambles. The number of CFRA preambles may be provided per cell or per beam used for LTM. Examples of beams include at least a synchronization signal block beam and a channel status information beam. Furthermore, it should be noted that the CU may provide the source cell to DU1.

[0074] Phase 505 comprises the CU sending a UE context setup response to the CU, the UE context setup response comprising a CFRA preamble for the LTM of one or more cells of DU2, in this case the UE context setup response comprising a CFRA preamble for cell 2 of DU2.

[0075] Phase 506 comprises the CU sending a UE context modification request to DU1. The UE context modification request comprises a request for CFRA resources for LTM. In one example, the UE context setup modification request may comprise a specific number of CFRA resources for LTM. The CU may estimate the number of CFRA preambles required based on current connected mode users with LTM mobility enabled and an estimated number of LTM mobility events based on previous mobility history events. For example, DU1 may allocate a specific number of CFRA preambles along with a RACH resource configuration as part of LTM preparation. Additionally or alternatively, DU1 may allocate one or more different PRACH mask indices associated with each of the CFRA preambles. The number of CFRA preambles may be provided per cell or per beam used for LTM. Examples of beams include at least a synchronization signal block beam and a channel status information beam. Additionally, note that the CU may provide the source cell to DU2.

[0076] Phase 507 comprises the CU sending a UE context setup response to the CU, the UE context setup response comprising a CFRA preamble for the LTM of one or more cells of DU1. In this case, the UE context setup response comprises a CFRA preamble for cell 1 of DU1.

[0077] Phase 508 comprises preparing a Radio Resource Control protocol (RRC) configuration by the CU.

[0078] Phase 509 comprises transmitting, by the CU, an RRC Reconfiguration message to the UE via DU1. The RRC Reconfiguration message comprises the CFRA resources for cell 1 and cell 2 received in phases 505 and 507. Thus, the RRC Reconfiguration message provided to the UE for LTM mobility includes a CFRA RACH configuration and a CFRA pool for LTM, which may differ from the CFRA pool broadcast in each target cell.

[0079] For example, note that in phase 508, the base station centralized unit may assign each CFRA resource an index that will be referenced in the LTM switch command by the source cell, in this case cell 1. Alternatively or additionally, a PRACH mask index may also be assigned and indicated in the LTM switch command to the UE.

[0080] Phase 510 comprises sending, by the UE, an RRC reconfiguration complete message to the CU via DU1.

[0081] Figure 6 illustrates an example sequence according to at least some embodiments, which improves LTM performance. This sequence may be performed after the base station distributed unit is configured for lower layer triggered mobility, for example, as described in Figure 5. This sequence is described with reference to the entities described in Figure 5.

[0082] Phase 611 comprises the UE sending an L1 measurement report to DU1.

[0083] Phase 612 comprises DU1 deciding to switch the serving cell of the UE. Thus, DU1 decides to change the UE from a source cell in DU1, i.e., cell 1, to a target cell in DU2, i.e., cell 2, based on the received L1 measurement report.

[0084] Phase 613 comprises DU1 sending, based on the determined switch, a request to the CU for CFRA resources for the UE to access the target cell, in this case cell 2 in DU2. The request may comprise an identifier of the UE (UE ID) and the target cell.

[0085] Phase 614 comprises the CU determining a CFRA resource, e.g., Y1, from a pool based on the received request and transmitting the determined CFRA resource, e.g., Y1, for the UE to access cell 2 in DU2. In this manner, the determined CFRA resource may be assigned to the UE for LTM to cell 2. In an example, phase 614 comprises the CU allocating a unique CFRA resource, e.g., a PRACH preamble or a combination of a PRACH preamble and a PRACH mask index, such that no collision occurs between LTM mobility from different source cells to the same target cell, i.e., such that the CFRA resource is reserved for the serving DU until the UE performs a cell switch.

[0086] Phase 615 comprises the CU transmitting information, e.g., a UE ID, to DU2 indicating the UE attempting random access using the determined CFRA resource, e.g., Y1. In this way, the determined CFRA resource, e.g., Y1, can be reserved in DU2 for the UE.

[0087] Phase 616 comprises DU2 sending an acknowledgement to the CU in response to the information received in phase 615.

[0088] Phase 617 comprises DU1 transmitting an LTM switch command to the UE comprising a medium access control (MAC) control element (CE) comprising the determined CFRA resource, e.g., Y1. Alternatively or additionally, a PRACH mask index is also assigned and indicated in the LTM switch command to the UE. Note that the LTM switch command may be transmitted by DU1 based on DU1 determining that the CU has notified DU2 hosting the target cell of the CFRA resource assigned to the UE. DU1 may determine that the CU has notified DU2 about the CFRA resource assigned to the UE based on receiving the CFRA determined in phase 614.

[0089] Phase 618 comprises the UE performing a random access procedure to cell 2 based on the determined CFRA resource, eg, Y1.

[0090] Phase 619 comprises DU2 activating UE contexts for UEs in DU2.

[0091] Phase 620 comprises DU2 sending a Random Access Response (RAR) to the UE.

[0092] Phase 621 comprises the UE sending an RRC Reconfiguration Complete message to the CU via DU2. The CU may release CFRA resources allocated to the UE based on the RRC Reconfiguration Complete. In this manner, the allocated CFRA can be released back to the pool and reallocated to the LTM. Note that in phase 621, the CU may determine whether the random access procedure for the UE has completed successfully based on the RRC Reconfiguration Complete message. Alternatives to the RRC Reconfiguration Complete message include at least one of the CU allocating an UL grant to the UE in response to receiving the CFRA preamble or the CU receiving a transmission by the UE via the allocated UL grant.

[0093] It should be noted that alternatively or additionally, the target cell, or the DU2 hosting the target cell, may send information to the CU, for example in phase 619, indicating that the UE's random access procedure has been successfully completed.

[0094] FIG. 7 illustrates an example sequence according to at least some embodiments. This sequence provides for configuring a base station distributed unit for lower layer triggered mobility. In connection with preparing a DU for LTM, the CU may provide each DU with a pool of CFRA resources, thereby enabling each DU to allocate CFRA resources from the pool. Thus, base station nodes, herein the base station distributed units, may each manage their own pool of CFRA resources. Then, in connection with a cell switch of a user equipment from a source cell to a target cell, the DU hosting the source cell may allocate a CFRA resource, e.g., Y2, for changing the UE from the source cell to the target cell and notify the CU of the selected CFRA resource. The CU may notify other prepared cells about the unavailability or reservation of the selected CFRA resource, e.g., Y2, so that the other prepared cells may refrain from selecting the same selected CFRA resource, e.g., Y2, when attempting to handover another UE to the same target cell.

[0095] Phases 701 and 702 comprise transmitting L3 measurement reports from the user equipment to the centralized unit CU via the distributed unit DU1.

[0096] Phase 703 comprises the determination by the CU to prepare one or more target cells, in this case cells in the distributed units DU1 and DU2, for L1 / L2 inter-cell mobility. The determined target cells in DU2 and DU3 may be configured for lower layer triggered mobility of user equipment from the source cell to the target cell.

[0097] Phase 704 comprises the target cell in DU2 being configured for lower layer triggered mobility of user equipment from the source cell to the target cell.

[0098] Phase 704 comprises the CU sending a UE context setup request to DU2. The UE context modification request comprises CFRA resources to be used for LTM for each other prepared target cell. Each other prepared target cell comprises a cell hosted by the same DU or a different DU. For example, the CFRA resources received in DU2 may comprise a CFRA preamble allocated to the target cell prepared for LTM. Additionally or alternatively, the CFRA resources received in DU2 may comprise one or more different PRACH mask indices allocated by the CU associated with each of the allocated CFRA preambles. In this way, DU2 can assign a CFRA resource to the UE comprising a PRACH preamble to the target cell and a PRACH mask index for LTM, even if the PRACH preamble is reserved for LTM of another UE.

[0099] Phase 705 comprises DU2 sending a UE context setup response to the CU.

[0100] Phase 706 comprises the CU sending a UE context modification request to one or more other DUs. The UE context modification request comprises CFRA resources to be used for LTM for each other prepared target cell. For example, the CFRA resources received in one or more other DUs may comprise CFRA preambles allocated to the prepared target cells for LTM. Additionally or alternatively, the CFRA resources received in one or more other DUs may comprise one or more different allocated PRACH mask indices associated with each of the allocated CFRA preambles. The PRACH mask indices may be used by one or more other DUs as described for DU2 in phase 704.

[0101] Phase 707 comprises one or more other DUs sending a UE context modification response to the CU.

[0102] Phase 708 comprises the CU sending a UE context modification request to DU1. The UE context modification request comprises CFRA resources to be used for LTM for each other prepared target cell. For example, the CFRA resources received at DU1 may comprise CFRA preambles allocated to the prepared target cell for LTM. Additionally or alternatively, the CFRA resources received at DU1 may comprise one or more different PRACH mask indices allocated by the CU associated with each of the allocated CFRA preambles. In this way, DU1 is provided with information to assign a CFRA resource to the UE comprising a PRACH preamble to the target cell and a PRACH mask index for LTM, even if the PRACH preamble is reserved for LTM of another UE.

[0103] Phase 709 comprises DU1 sending a UE context modification response to the CU.

[0104] Phase 710 comprises preparing a Radio Resource Control protocol (RRC) configuration by the CU.

[0105] Phase 711 comprises sending, by the CU, an RRC reconfiguration message to the UE via DU1. The RRC reconfiguration message comprises CFRA resources of the target cell.

[0106] Phase 712 comprises sending, by the UE, an RRC reconfiguration complete message to the CU via DU1.

[0107] Figure 8 illustrates an example sequence according to at least some embodiments that improves LTM performance. This sequence may be performed after the distributed unit is configured for lower layer triggered mobility, for example, as described in Figure 5.

[0108] Phase 813 comprises DU1 determining, based on the L1 measurement report, to change the UE from the source cell in DU1 to the target cell in DU2. DU1 may determine CFRA resources for cell 2 from the pool.

[0109] Phase 814 comprises DU1 determining, based on the L1 measurement report, to change the UE from the source cell in DU1, i.e., cell 1, to the target cell in DU2, i.e., cell 2. DU1 further allocates a CFRA resource, Y2, to the UE.

[0110] Phase 815 comprises DU1 transmitting information, e.g., a UE ID, to the CU indicating a UE attempting random access to cell 2 using the allocated CFRA resource, Y2. In this manner, the CFRA resource, Y2, may be reserved for the UE.

[0111] Phase 816 comprises the CU transmitting information, e.g., a UE ID, to DU2 indicating the UE attempting random access using the allocated CFRA resource. In this way, a CFRA resource, Y2, can be reserved in DU2 for the UE.

[0112] Phase 817 comprises DU2 sending an acknowledgement to the CU, thus indicating to the CU that the allocated CFRA resource, Y2, is reserved.

[0113] Phase 818 comprises the CU sending a message to one or more other DUs, causing the one or more other DUs to refrain from configuring the CFRA resource, Y2, assigned / determined for the other UEs attempting to switch to cell 2. In one example, the CU may send information to one or more other CUs indicating the CFRA resource and cell 2. In this way, the CFRA assigned for the RACH may be prevented from being used in the cells of the one or more other DUs.

[0114] Phase 819 comprises one or more other DUs sending an acknowledgement to the CU, thus indicating to the CU that one or more other DUs are refraining from using the allocated CFRA resource, Y2.

[0115] Phase 820 comprises the CU sending an acknowledgement to DU1, in which case DU1 is indicated that the allocated CFRA resource, Y2, has been reserved in DU2 for the UE.

[0116] Phase 821 comprises DU1 transmitting an LTM switch command to the UE comprising a medium access control (MAC) control element (CE) comprising the allocated CFRA resource, Y2. Alternatively or additionally, a PRACH mask index is also assigned and indicated in the LTM switch command to the UE. Note that the LTM switch command may be sent by DU1 based on DU1 determining that the CU has notified DU2 hosting the target cell of the CFRA resource allocated to the UE. DU1 may determine that the CU has notified DU2 of the CFRA resource allocated to the UE based on receiving an acknowledgment in phase 820.

[0117] Phase 822 comprises the UE performing a random access procedure to cell 2 based on the allocated CFRA resource, eg, Y2.

[0118] Phase 823 comprises DU2 activating the UE context of the UE in DU2.

[0119] Phase 824 comprises DU2 sending a random access response (RAR) to the UE.

[0120] Phase 825 comprises the UE sending an RRC Reconfiguration Complete message to the CU via DU2. Note that in phase 825, the CU may determine whether the UE's random access procedure has completed successfully based on the RRC Reconfiguration Complete message. Alternatives to the RRC Reconfiguration Complete message include the CU allocating an UL grant to the UE in response to receiving the CFRA preamble, or the CU receiving a transmission by the UE via the allocated UL grant.

[0121] It should be noted that alternatively or additionally, the target cell, or DU2 hosting the target cell, may transmit information to the CU indicating that the UE's random access procedure has been successfully completed, for example in connection with phase 823.

[0122] 9 illustrates an example of an apparatus according to at least some embodiments. The apparatus may be a radio access network node, such as a base station, a base station distribution unit, or a base station centralized unit. The apparatus includes at least one processor 902 and at least one transceiver 904. The processor is operatively connected to the transceiver for controlling the transceiver. The apparatus may include at least one memory 906. The memory may be operatively connected to the processor. It should be understood that the memory may be a separate memory or may be included in the processor and / or the transceiver.

[0123] 9 includes a CFRA module 908 operatively connected to the processor. The CFRA module may be configured to effect one or more functions described in one or more examples described herein, and includes at least the following functions: a. in a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, determining to change the user equipment from the source cell to the target cell; determining, by the base station distributed unit, a CFRA resource for the user equipment to access the target cell from a pool of contention-free random access (CFRA) resources reserved for lower layer triggered mobility; and transmitting, by the base station distributed unit, information indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell to the user equipment; or b. receiving, by a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, information indicating a contention-free random access, CFRA resource allocated to the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility; and preparing, in the base station distributed unit, a random access channel based on the received information indicating the CFRA resource for changing the user equipment from the source cell to the target cell; or c. determining, by a base station centralized unit configured for lower layer triggered mobility of a user equipment from a pool of contention-free random access, CFRA resources reserved for lower layer triggered mobility, a CFRA resource for the user equipment to access the target cell, and transmitting, by the base station centralized unit, information indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell to a base station distributed unit of the target cell.

[0124] The embodiment is - determining, in a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, to change the user equipment from the source cell to the target cell; - determining, by the base station distributed unit, contention-free random access (CFRA) resources for the user equipment to access the target cell from a pool of CFRA resources reserved for lower layer triggered mobility; - transmitting, by the base station distributed unit, information to the user equipment indicating the determined CFRA resources for changing the user equipment from the source cell to the target cell.

[0125] The embodiment is - receiving, by a base station distributed unit configured for lower layer triggered mobility of the user equipment from a source cell to a target cell, information indicating CFRA resources allocated to the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility; - preparing a random access channel based on the received information indicating CFRA resources for changing the user equipment from the source cell to the target cell, in the base station distributed unit.

[0126] The embodiment is - determining, by a base station centralized unit configured for lower layer triggered mobility of the user equipment from a pool of contention-free random access (CFRA) resources reserved for lower layer triggered mobility, CFRA resources for accessing the target cell by the user equipment; and - transmitting, by the base station centralized unit, information indicating the determined CFRA resources for changing the user equipment from the source cell to the target cell to the base station distributed units of the target cell.

[0127] The embodiment provides a network entity with at least: - determining, in a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, to change the user equipment from the source cell to the target cell; - determining, by the base station distributed unit, contention-free random access (CFRA) resources for the user equipment to access the target cell from a pool of CFRA resources reserved for lower layer triggered mobility; - transmitting, by the base station distributed unit, information to the user equipment indicating the determined CFRA resources for changing the user equipment from the source cell to the target cell.

[0128] The embodiment provides a network entity with at least: - receiving, by a base station distributed unit configured for lower layer triggered mobility of the user equipment from a source cell to a target cell, information indicating CFRA resources allocated to the user equipment from a pool of CFRA resources reserved for lower layer triggered mobility; and - preparing, at the base station distributed unit, a random access channel based on the received information indicating CFRA resources for changing the user equipment from the source cell to the target cell.

[0129] The embodiment provides a network entity with at least: - determining, by a base station centralized unit configured for lower layer triggered mobility of the user equipment from a pool of contention-free random access (CFRA) resources reserved for lower layer triggered mobility, CFRA resources for accessing the target cell by the user equipment; and - transmitting, by the base station centralized unit, information indicating the determined CFRA resources for changing the user equipment from the source cell to the target cell to the base station distributed units of the target cell.

[0130] Embodiments may be implemented in software, hardware, application logic, or a combination of software, hardware, and application logic. The software, application logic, and / or hardware may reside on memory or any computer medium. In an exemplary embodiment, the application logic, software, or instruction set is maintained on any of various conventional computer-readable media. In the context of this specification, a "memory" or a "computer-readable medium" may be any medium or means that can contain, store, communicate, propagate, or transfer instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer.

[0131] Where relevant, references to a "computer readable medium," "computer program product," "tangibly embodied computer program," etc., or to a "processor" or "processing circuitry," etc., should be understood to encompass computers having different architectures, such as single / multi-processor architectures and sequencer / parallel architectures, as well as specialized circuitry, such as field programmable gate arrays (FPGAs), application specific circuits (ASICs), signal processing devices, and other devices. References to computer readable program code means, computer programs, computer instructions, program instructions, instructions, computer code, etc., should be understood to represent software, such as programmable processor firmware, as instructions to a processor, or the programmable content of a hardware device, as configured or configured settings of a fixed function device, gate array, programmable logic device, etc.

[0132] In general, various embodiments of the present invention may be implemented in hardware or special purpose circuits, or any combination thereof. Although various aspects of the present invention may be illustrated and described using block diagrams or other graphical representations, it is well understood that these blocks, apparatus, systems, techniques, or methods described herein may be implemented in, by way of non-limiting example, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controllers, or other computing devices, or combinations thereof.

[0133] Embodiments of the present invention may be implemented in a variety of components, such as integrated circuit modules, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), microcontrollers, microprocessors, combinations of these modules, etc. The design of integrated circuits is generally a highly automated process. Complex and powerful software tools are available for converting logic-level designs into semiconductor circuit designs ready to be etched onto semiconductor substrates.

[0134] Programs such as those offered by Synopsys, Inc. of Mountain View, Calif., and Cadence Design of San Jose, Calif., use well-established design rules and pre-stored libraries of design modules to automatically route conductors and determine the location of components on a semiconductor chip. Once the design of a semiconductor circuit is complete, the resulting design in a standardized electronic format (e.g., Opus, GDSII, etc.) can be sent to a semiconductor manufacturing facility, or "fab," for fabrication.

[0135] The term "circuitry" as used in this application may refer to one or more or all of the following: (a) a hardware-only circuit implementation (e.g., an analog and / or digital-only implementation); and (b) A combination of hardware circuitry and software (if applicable), such as: (i) a combination of analog and / or digital hardware circuitry and software / firmware; and (ii) any portion of a hardware processor (including a digital signal processor) with software, software, and memory that operates in conjunction to cause a device, such as a mobile phone or server, to perform various functions; and (c) Hardware circuits and processors, such as microprocessors or portions of microprocessors, that require software (e.g., firmware) to operate, but the software may be absent if not necessary for operation.

[0136] This definition of circuit applies to all uses of the term in this application, including any claims. As a further example, the term circuit as used in this application covers implementations of only a hardware circuit or processor(s), or of portions of a hardware circuit or processor and its(their) accompanying software and / or firmware. The term circuit also covers, for example, baseband or processor integrated circuits for mobile devices, or similar integrated circuits in servers, cellular network devices, or other computing or network devices, if applicable to certain claim elements.

[0137] The foregoing description has provided a complete and informative description of exemplary embodiments of the present invention, by way of illustrative and non-limiting examples. However, various modifications and adaptations will become apparent to those skilled in the relevant art in view of the above description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of the present invention.

[0138] List of acronyms AMF Access and Mobility Management Functions BLER Block Error Rate CE Control Elements CFRA Contention-Free Random Access CN Core Network CPS Cyber-Physical System CU Centralized Unit DL Downlink DU Distributed Unit GEO geostationary orbit HAPS High Altitude Platform Station IoT Internet of Things IP Internet Protocol LEO low orbit LTE Long Term Evolution LTM Lower Layer Triggered Mobility M2M Machine to Machine MAC Media Access Control MEC Multi-Access Edge Computing MIMO Multiple Input Multiple Output MME Mobile Management Entity mMTP Large-scale Machine Type Communication MS mobile station MTP Machine Type Communication NFV Network Functions Virtualization NGC Next Generation Core NR New Radio PDA Personal Digital Assistant PDCP Packet Data Convergence Protocol P-GW Packet Data Network Gateway PHY physical layer PRACH Physical Random Access Channel RAN Radio Access Network RF radio frequency RRC Radio Resource Control RU Wireless Unit SDN Software Defined Network S-GW Serving Gateway SIM Subscriber Identity Module TDD Time Division Duplex TRP Sending / Receiving Point TRX Send / Receive UE User Equipment UL Uplink

Claims

1. 1. An apparatus, comprising: one or more processors; and, when executed by the one or more processors, the apparatus: - in a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, deciding (202) to change said user equipment from said source cell to said target cell; - determining (204) by the base station distributed unit a contention-free random access, CFRA resource for the user equipment to access the target cell from a pool of CFRA resources reserved for the lower layer triggered mobility, wherein the CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; transmitting (206) by the base station distributed unit to the user equipment information indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell; a memory for storing instructions for causing the An apparatus comprising:

2. receiving physical layer measurements at said base station distributed unit; determining, by the base station distribution unit, to change the user equipment from the source cell to the target cell based on the received physical layer measurements; The apparatus of claim 1 .

3. The apparatus according to claim 1 or 2, causing the base station distributed unit to transmit, based on the determined change, a request for CFRA resources for the user equipment to access the target cell to a base station centralized unit.

4. receiving, by the base station distributed unit, the pool of CFRA resources reserved for the lower layer triggered mobility from a base station centralized unit; transmitting, by the base station distributed unit, information indicating the determined CFRA resource for the user equipment to access the target cell to the base station centralized unit; The apparatus according to claim 1 or 2,

5. receiving, at the base station distributed unit, information indicating completion of a radio access procedure of the user equipment; in the base station distributed unit, releasing the CFRA resources based on the received information indicating completion of the radio access procedure of the user equipment; The apparatus according to any one of claims 1 to 4,

6. The apparatus of claim 5, further comprising: causing the base station distributed unit to transmit information indicating the release of the CFRA resources to a base station node that manages the pool of CFRA resources reserved for the lower layer triggered mobility.

7. The apparatus according to any one of claims 1 to 6, wherein the determined CFRA resource is transmitted in a cell change command.

8. The apparatus of any one of claims 1 to 7, causing the base station distributed unit to send to the user equipment a message, for example a medium access control, MAC, control element, CE, or downlink control information, DCI, to trigger the change of the user equipment from the source cell to the target cell.

9. 1. An apparatus, comprising: one or more processors; and, when executed by the one or more processors, the apparatus: - receiving (302) by a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, information indicating a contention-free random access, CFRA resource allocated to the user equipment from a pool of CFRA resources reserved for said lower layer triggered mobility, wherein said CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; preparing (304) in the base station distributed unit a random access channel based on the received information indicating the CFRA resource for changing the user equipment from the source cell to the target cell; a memory for storing instructions for causing the An apparatus comprising:

10. The apparatus of claim 9, further comprising: causing the base station distributed unit to send a message to a centralized unit to release the allocated CFRA resources based on completion of a radio access procedure of the user equipment.

11. 1. An apparatus, comprising: one or more processors; and, when executed by the one or more processors, the apparatus: - determining (402) by a base station centralized unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, from a pool of contention-free random access, CFRA resources reserved for said lower layer triggered mobility, a CFRA resource for said user equipment to access said target cell, wherein said CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; sending, by the base station centralized unit, information indicating the determined CFRA resource for transferring the user equipment from the source cell to the target cell to a base station distributed unit of the target cell (404); a memory for storing instructions for causing the An apparatus comprising:

12. The apparatus of claim 11, further comprising: causing the base station centralization unit to receive a request for the CFRA resources for accessing the target cell by the user equipment.

13. receiving, by the base station centralized unit, information from one or more base station distributed units indicating one or more CFRA resources for lower layer triggered mobility; generating, by the base station centralization unit, the pool of CFRA resources reserved for the lower layer triggered mobility based on the received information; 13. The apparatus according to claim 11 or 12,

14. The apparatus according to any one of claims 11 to 13, wherein the base station centralized unit requests, from one or more base station distributed units, information indicating one or more CFRA resources for lower layer triggered mobility when configuring the base station distributed units for the lower layer triggered mobility.

15. The apparatus according to any one of claims 11 to 14, wherein the base station centralized unit is configured to transmit the pool of CFRA resources reserved for the lower layer triggered mobility to the base station distributed unit when the base station centralized unit is configured for the lower layer triggered mobility.

16. the apparatus according to any one of claims 11 to 15, causing the base station centralized unit to send a message to one or more other base station distributed units, in order to cause the one or more other base station distributed units to refrain from configuring the determined CFRA resources for other user equipments attempting to access the target cell.

17. receiving, at the base station central unit, information indicating completion of a radio access procedure of the user equipment to the target cell; in the base station central unit, releasing the CFRA resources based on the received information indicating completion of the radio access procedure of the user equipment; The apparatus according to any one of claims 11 to 16,

18. An arrangement according to any one of claims 11 to 17, causing the base station centralisation unit to allocate one or more physical radio access channel mask indices to each CFRA resource of the pool.

19. 19. The apparatus of claim 11, wherein the information indicating the determined CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index.

20. - in a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, deciding (202) to change said user equipment from said source cell to said target cell; - determining (204) by the base station distributed unit a contention-free random access, CFRA resource for the user equipment to access the target cell from a pool of CFRA resources reserved for the lower layer triggered mobility, wherein the CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; transmitting (206) by the base station distributed unit to the user equipment information indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell; A method comprising:

21. - receiving (302) by a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, information indicating a contention-free random access, CFRA resource allocated to the user equipment from a pool of CFRA resources reserved for said lower layer triggered mobility, wherein said CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; preparing (304) in the base station distributed unit a random access channel based on the received information indicating the CFRA resource for changing the user equipment from the source cell to the target cell; A method comprising:

22. - determining (402) by a base station centralized unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, from a pool of contention-free random access, CFRA resources reserved for said lower layer triggered mobility, a CFRA resource for said user equipment to access said target cell, wherein said CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; sending, by the base station centralized unit, information indicating the determined CFRA resource for transferring the user equipment from the source cell to the target cell to a base station distributed unit of the target cell (404); A method comprising:

23. - in a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, deciding (202) to change said user equipment from said source cell to said target cell; - determining (204) by the base station distributed unit a contention-free random access, CFRA resource for the user equipment to access the target cell from a pool of CFRA resources reserved for the lower layer triggered mobility, wherein the CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; transmitting (206) by the base station distributed unit to the user equipment information indicating the determined CFRA resource for changing the user equipment from the source cell to the target cell; 1. A computer program comprising computer readable program code means adapted to perform at least the steps of:

24. - receiving (302) information by a base station distributed unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell indicating CFRA resources allocated to the user equipment from a pool of CFRA resources reserved for said lower layer triggered mobility, wherein said CFRA resources comprise at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; preparing (304) in the base station distributed unit a random access channel based on the received information indicating the CFRA resource for changing the user equipment from the source cell to the target cell; 1. A computer program comprising computer readable program code means adapted to perform at least the steps of:

25. - determining (402) by a base station centralized unit configured for lower layer triggered mobility of a user equipment from a source cell to a target cell, from a pool of contention-free random access, CFRA resources reserved for said lower layer triggered mobility, a CFRA resource for said user equipment to access said target cell, wherein said CFRA resource comprises at least one of a CFRA preamble or a combination of a CFRA preamble and a physical radio access channel mask index; sending, by the base station centralized unit, information indicating the determined CFRA resource for transferring the user equipment from the source cell to the target cell to a base station distributed unit of the target cell (404); 1. A computer program comprising computer readable program code means adapted to perform at least the steps of:

26. one or more processors, and when executed by the one or more processors, the apparatus - receiving (617) from the source cell a Medium Access Control, MAC, Control Element, MAC-CE indicating contention-free random access, CFRA, resources for accessing the target cell; performing a random access procedure to access the target cell on the indicated CFRA resource (618); a memory for storing instructions for causing the An apparatus comprising:

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