Patent Description:
A unified air interface, which utilizes licensed, unlicensed, and shared license radio spectrum, in multiple frequency bands, is one aspect of enabling the capabilities of <NUM> and <NUM> systems. The <NUM> and <NUM> air interface utilizes radio spectrum in bands below <NUM> (sub-gigahertz), below <NUM> (sub-<NUM>), and above <NUM>. Radio spectrum above <NUM> includes millimeter wave (mmWave) frequency bands that provide wide channel bandwidths to support higher data rates for wireless broadband.

To increase data rates, throughput, and reliability for a user equipment, various forms of wireless connectivity that use multiple radio links between base stations and the user equipment are supported in <NUM> and <NUM> systems. Techniques such as dual connectivity or coordinated multipoint communications, often coupled with beamformed signals, can improve data rates, throughput, and reliability, especially as received signal strengths decrease for the user equipment near the edge of cells. The use of these radio link configurations increases the complexity of mobility management to maintain high data rates and reliability for the user equipment.

Conventional mobility management techniques are based on base station neighbor relationships and use handovers to maintain connectivity for the user equipment. However, conventional handover techniques based on base station neighbor relationships disconnect radio bearers and establish new bearers during a handover, which can interrupt data communication for the user equipment during the handover thus affecting data throughput and latency for the user equipment.

<CIT> relates to a radio station communicating control information for multipoint cooperating communication, in which a plurality of radio stations takes part in data transmission/reception of a terminal, with another radio station taking part in the multipoint cooperating communication and/or a control station that manages the radio station.

Aspects of an active coordination set for mobility management are described with reference to the following drawings. The same numbers are used throughout the drawings to reference like features and components:.

This document describes methods, devices, systems, and means for an active coordination set for mobility management. A user equipment (UE) evaluates a link quality measurement for one or more base stations and determines to include at least a first base station of the base stations in an Active Coordination Set (ACS). The user equipment sends a message, including an indication to add the at least the first base station to the ACS, to an ACS Server that causes the ACS Server to store the ACS associated with the user equipment and send a copy of the stored ACS to a master base station. The user equipment communicates via one or more of the base stations included in the ACS. The user equipment can transmit an uplink ACS sounding signal to evaluate base stations to include in the ACS.

The evolution of wireless communication systems to fifth generation (<NUM>) New Radio (<NUM> NR) and Sixth Generation (<NUM>) technologies provides higher data rates to users. By employing techniques, such as Coordinated MultiPoint (CoMP) or Dual Connectivity (DC) over beamformed wireless connections, higher data rates can be provided at the edges of <NUM> and <NUM> cells. However, the management of user equipment (UE) mobility and handovers becomes increasingly complex in these environments.

Conventional techniques, such as neighbor relation tables, are used to describe neighbor cells of a serving cell that may be potential target base stations to receive the user equipment in a handover. These techniques are base-station-specific, do not fully account for the changing radio-channel environment of a user equipment, and interrupt data communication for the user equipment during the handover. In aspects, the Active Coordination Set combines the selection of base stations of a mobile-assisted handover with beamforming. Each time an ACS is updated the selection of base stations and beamforming weights are updated in the ACS associated with the user equipment.

In aspects, an Active Coordination Set (ACS) is a user equipment-specific set of <NUM> and/or <NUM> base stations that are determined by the user equipment to be usable for wireless communication. More specifically, the base stations in the ACS are usable for joint transmission and/or reception (joint communication) between the user equipment and one or more of the base stations in the ACS. The joint transmission and/or reception techniques includes CoMP, Single Radio Access Technology (RAT) Dual Connectivity (single-RAT DC), and/or Multi-Radio Access Technology Dual Connectivity (MR-DC). Joint communication includes communication between the user equipment and multiple base stations, or communication between the user equipment and multiple sectors of a single base station. The joint communication includes communication in a single radio frequency band or communication in multiple radio frequency bands.

The user equipment determines which base stations to include in the ACS and updates the ACS as the base stations that provide usable link quality change. The user equipment also determines beamforming parameters for the base stations included in the ACS, such as beamforming weights, codebook indices, and the like. The user equipment communicates the ACS and changes to the ACS to an ACS Server that maintains ACSs for UEs in a wireless network. The UE communicates with the ACS using Radio Resource Control messaging, Non-Access Stratum messaging, or application layer messaging.

The ACS is provided to a master base station that coordinates joint transmission and/or reception for the user equipment. The master base station uses the ACS to schedule air interface resources for the set of base stations communicating with the user equipment. By using this joint scheduling for communications with the UE, scheduling efficiency is increased, and inter-cell interference (ICI) is reduced in the wireless network.

As channel conditions change for the user equipment, the user equipment can add or remove base stations from the ACS while concurrently communicating with base stations in the ACS that provide usable link quality. Based on these changes to the ACS, the master base station can add or remove base stations from the joint communication with the user equipment without performing a handover that interrupts data communication with the user equipment. By using the ACS for communication management, the master base station can select optimal routing for data communication with the UE and maintain the highest data throughput for the user equipment without interruptions caused by a handover.

While features and concepts of the described systems and methods for an active coordination set for mobility management can be implemented in any number of different environments, systems, devices, and/or various configurations, aspects of an active coordination set for mobility management are described in the context of the following example devices, systems, and configurations.

<FIG> illustrates an example environment <NUM> in which various aspects of an active coordination set for mobility management can be implemented. The example environment <NUM> includes a user equipment <NUM> (UE <NUM>) that communicates with one or more base stations <NUM> (illustrated as base stations <NUM> and <NUM>), through one or more wireless communication links <NUM> (wireless link <NUM>), illustrated as wireless links <NUM> and <NUM>. In this example, the user equipment <NUM> is implemented as a smartphone. Although illustrated as a smartphone, the user equipment <NUM> may be implemented as any suitable computing or electronic device, such as a mobile communication device, a modem, cellular phone, gaming device, navigation device, media device, laptop computer, desktop computer, tablet computer, smart appliance, or vehicle-based communication system. The base stations <NUM> (e.g., an Evolved Universal Terrestrial Radio Access Network Node B, E-UTRAN Node B, evolved Node B, eNodeB, eNB, Next Generation Node B, gNode B, gNB, a <NUM> node B, or the like) may be implemented in a macrocell, microcell, small cell, picocell, and the like, or any combination thereof.

The base stations <NUM> communicate with the user equipment <NUM> via the wireless links <NUM> and <NUM>, which may be implemented as any suitable type of wireless link. The wireless links <NUM> and <NUM> can include a downlink of data and control information communicated from the base stations <NUM> to the user equipment <NUM>, an uplink of other data and control information communicated from the user equipment <NUM> to the base stations <NUM>, or both. The wireless links <NUM> may include one or more wireless links or bearers implemented using any suitable communication protocol or standard, or combination of communication protocols or standards such as 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE), Fifth Generation New Radio (<NUM> NR), <NUM>, and so forth. Multiple wireless links <NUM> may be aggregated in a carrier aggregation to provide a higher data rate for the user equipment <NUM>. Multiple wireless links <NUM> from multiple base stations <NUM> may be configured for Coordinated Multipoint (CoMP) communication with the user equipment <NUM>. Additionally, multiple wireless links <NUM> may be configured for single-radio access technology (RAT) (single-RAT) dual connectivity (single-RAT-DC) or multi-RAT dual connectivity (MR-DC).

The base stations <NUM> are collectively a Radio Access Network <NUM> (RAN, Evolved Universal Terrestrial Radio Access Network, E-UTRAN, <NUM> NR RAN or NR RAN). The base stations <NUM> and <NUM> in the RAN <NUM> are connected to a core network <NUM>, such as a Fifth Generation Core (5GC) or <NUM> core network. The base stations <NUM> and <NUM> connect, at <NUM> and <NUM> respectively, to the core network <NUM> via an NG2 interface (or a similar <NUM> interface) for control-plane signaling and via an NG3 interface (or a similar <NUM> interface) for user-plane data communications. In addition to connections to core networks, base stations <NUM> may communicate with each other via an Xn Application Protocol (XnAP), at <NUM>, to exchange user-plane and control-plane data. The user equipment <NUM> may also connect, via the core network <NUM>, to public networks, such as the Internet <NUM> to interact with a remote service <NUM>.

<FIG> illustrates an example device diagram <NUM> of the user equipment <NUM> and the base stations <NUM>. The user equipment <NUM> and the base stations <NUM> may include additional functions and interfaces that are omitted from <FIG> for the sake of clarity. The user equipment <NUM> includes antennas <NUM>, a radio frequency front end <NUM> (RF front end <NUM>), an LTE transceiver <NUM>, a <NUM> NR transceiver <NUM>, and a <NUM> transceiver <NUM> for communicating with base stations <NUM> in the RAN <NUM>. The RF front end <NUM> of the user equipment <NUM> can couple or connect the LTE transceiver <NUM>, the <NUM> NR transceiver <NUM>, and the <NUM> transceiver <NUM> to the antennas <NUM> to facilitate various types of wireless communication. The antennas <NUM> of the user equipment <NUM> may include an array of multiple antennas that are configured similarly to or differently from each other. The antennas <NUM> and the RF front end <NUM> can be tuned to, and/or be tunable to, one or more frequency bands defined by the 3GPP LTE, <NUM> NR, and <NUM> communication standards and implemented by the LTE transceiver <NUM>, the <NUM> NR transceiver <NUM>, and/or the <NUM> transceiver <NUM>. Additionally, the antennas <NUM>, the RF front end <NUM>, the LTE transceiver <NUM>, the <NUM> NR transceiver <NUM>, and/or the <NUM> transceiver <NUM> may be configured to support beamforming for the transmission and reception of communications with the base stations <NUM>. By way of example and not limitation, the antennas <NUM> and the RF front end <NUM> can be implemented for operation in sub-gigahertz bands, sub-<NUM> bands, and/or above <NUM> bands that are defined by the 3GPP LTE, <NUM> NR, and <NUM> communication standards.

The user equipment <NUM> also includes processor(s) <NUM> and computer-readable storage media <NUM> (CRM <NUM>). The processor <NUM> may be a single core processor or a multiple core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. The computer-readable storage media described herein excludes propagating signals. CRM <NUM> may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or Flash memory useable to store device data <NUM> of the user equipment <NUM>. The device data <NUM> includes user data, multimedia data, beamforming codebooks, applications, and/or an operating system of the user equipment <NUM>, which are executable by processor(s) <NUM> to enable user-plane communication, control-plane signaling, and user interaction with the user equipment <NUM>.

In some implementations, the CRM <NUM> may also include an active coordination set (ACS) manager <NUM>. The ACS manager <NUM> can communicate with the antennas <NUM>, the RF front end <NUM>, the LTE transceiver <NUM>, the <NUM> NR transceiver <NUM>, and/or the <NUM> transceiver <NUM> to monitor the quality of the wireless communication links <NUM>. Based on this monitoring, the ACS manager <NUM> can determine to add or remove base stations <NUM> from the ACS and/or trigger the transmission of an uplink ACS sounding signal.

The device diagram for the base stations <NUM>, shown in <FIG>, includes a single network node (e.g., a gNode B). The functionality of the base stations <NUM> may be distributed across multiple network nodes or devices and may be distributed in any fashion suitable to perform the functions described herein. The base stations <NUM> include antennas <NUM>, a radio frequency front end <NUM> (RF front end <NUM>), one or more LTE transceivers <NUM>, one or more <NUM> NR transceivers <NUM>, and/or one or more <NUM> transceivers <NUM> for communicating with the UE <NUM>. The RF front end <NUM> of the base stations <NUM> can couple or connect the LTE transceivers <NUM>, the <NUM> NR transceivers <NUM>, and/or the <NUM> transceivers <NUM> to the antennas <NUM> to facilitate various types of wireless communication. The antennas <NUM> of the base stations <NUM> may include an array of multiple antennas that are configured similarly to or differently from each other. The antennas <NUM> and the RF front end <NUM> can be tuned to, and/or be tunable to, one or more frequency band defined by the 3GPP LTE, <NUM> NR, and <NUM> communication standards, and implemented by the LTE transceivers <NUM>, one or more <NUM> NR transceivers <NUM>, and/or one or more <NUM> transceivers <NUM>. Additionally, the antennas <NUM>, the RF front end <NUM>, the LTE transceivers <NUM>, one or more <NUM> NR transceivers <NUM>, and/or one or more <NUM> transceivers <NUM> may be configured to support beamforming, such as Massive-MIMO, for the transmission and reception of communications with the UE <NUM>.

The base stations <NUM> also include processor(s) <NUM> and computer-readable storage media <NUM> (CRM <NUM>). The processor <NUM> may be a single core processor or a multiple core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. CRM <NUM> may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or Flash memory useable to store device data <NUM> of the base stations <NUM>. The device data <NUM> includes network scheduling data, radio resource management data, beamforming codebooks, applications, and/or an operating system of the base stations <NUM>, which are executable by processor(s) <NUM> to enable communication with the user equipment <NUM>.

CRM <NUM> also includes a joint communication scheduler <NUM>. Alternately or additionally, the joint communication scheduler <NUM> may be implemented in whole or part as hardware logic or circuitry integrated with or separate from other components of the base stations <NUM>. In at least some aspects, the joint communication scheduler <NUM> configures the LTE transceivers <NUM>, the <NUM> NR transceivers <NUM>, and the <NUM> transceiver(s) <NUM> for communication with the user equipment <NUM>, as well as communication with a core network, such as the core network <NUM>, and routing user-plane and control-plane data for joint communication. Additionally, the joint communication scheduler <NUM> may allocate air interface resources and schedule communications for the UE <NUM> and base stations <NUM> in the ACS when the base station <NUM> is acting as a master base station for the base stations <NUM> in the ACS.

The base stations <NUM> include an inter-base station interface <NUM>, such as an Xn and/or X2 interface, which the joint communication scheduler <NUM> configures to exchange user-plane and control-plane data between other base stations <NUM>, to manage the communication of the base stations <NUM> with the user equipment <NUM>. The base stations <NUM> include a core network interface <NUM> that the joint communication scheduler <NUM> configures to exchange user-plane and control-plane data with core network functions and/or entities.

<FIG> illustrates an air interface resource that extends between a user equipment and a base station and with which various aspects of an active coordination set for mobility management can be implemented. The air interface resource <NUM> can be divided into resource units <NUM>, each of which occupies some intersection of frequency spectrum and elapsed time. A portion of the air interface resource <NUM> is illustrated graphically in a grid or matrix having multiple resource blocks <NUM>, including example resource blocks <NUM>, <NUM>, <NUM>, <NUM>. An example of a resource unit <NUM> therefore includes at least one resource block <NUM>. As shown, time is depicted along the horizontal dimension as the abscissa axis, and frequency is depicted along the vertical dimension as the ordinate axis. The air interface resource <NUM>, as defined by a given communication protocol or standard, may span any suitable specified frequency range, and/or may be divided into intervals of any specified duration. Increments of time can correspond to, for example, milliseconds (mSec). Increments of frequency can correspond to, for example, megahertz (MHz).

In example operations generally, the base stations <NUM> allocate portions (e.g., resource units <NUM>) of the air interface resource <NUM> for uplink and downlink communications. Each resource block <NUM> of network access resources may be allocated to support respective wireless communication links <NUM> of multiple user equipment <NUM>. In the lower left corner of the grid, the resource block <NUM> may span, as defined by a given communication protocol, a specified frequency range <NUM> and comprise multiple subcarriers or frequency sub-bands. The resource block <NUM> may include any suitable number of subcarriers (e.g., <NUM>) that each correspond to a respective portion (e.g., <NUM>) of the specified frequency range <NUM> (e.g., <NUM>). The resource block <NUM> may also span, as defined by the given communication protocol, a specified time interval <NUM> or time slot (e.g., lasting approximately one-half millisecond or <NUM> orthogonal frequency-division multiplexing (OFDM) symbols). The time interval <NUM> includes subintervals that may each correspond to a symbol, such as an OFDM symbol. As shown in <FIG>, each resource block <NUM> may include multiple resource elements <NUM> (REs) that correspond to, or are defined by, a subcarrier of the frequency range <NUM> and a subinterval (or symbol) of the time interval <NUM>. Alternatively, a given resource element <NUM> may span more than one frequency subcarrier or symbol. Thus, a resource unit <NUM> may include at least one resource block <NUM>, at least one resource element <NUM>, and so forth.

In example implementations, multiple user equipment <NUM> (one of which is shown) are communicating with the base stations <NUM> (one of which is shown) through access provided by portions of the air interface resource <NUM>. The joint communication scheduler <NUM> (shown in <FIG>) may determine a respective data-rate, type of information, or amount of information (e.g., data or control information) to be communicated (e.g., transmitted) by the user equipment <NUM>. For example, the joint communication scheduler <NUM> can determine that each user equipment <NUM> is to transmit at a different respective data rate or transmit a different respective amount of information. The joint communication scheduler <NUM> then allocates one or more resource blocks <NUM> to each user equipment <NUM> based on the determined data rate or amount of information.

Additionally, or in the alternative to block-level resource grants, the joint communication scheduler <NUM> may allocate resource units at an element-level. Thus, the joint communication scheduler <NUM> may allocate one or more resource elements <NUM> or individual subcarriers to different user equipment <NUM>. By so doing, one resource block <NUM> can be allocated to facilitate network access for multiple user equipment <NUM>. Accordingly, the joint communication scheduler <NUM> may allocate, at various granularities, one or up to all subcarriers or resource elements <NUM> of a resource block <NUM> to one user equipment <NUM> or divided across multiple user equipment <NUM>, thereby enabling higher network utilization or increased spectrum efficiency.

The joint communication scheduler <NUM> can therefore allocate air interface resource <NUM> by resource unit <NUM>, resource block <NUM>, frequency carrier, time interval, resource element <NUM>, frequency subcarrier, time subinterval, symbol, spreading code, some combination thereof, and so forth. Based on respective allocations of resource units <NUM>, the joint communication scheduler <NUM> can transmit respective messages to the multiple user equipment <NUM> indicating the respective allocation of resource units <NUM> to each user equipment <NUM>. Each message may enable a respective user equipment <NUM> to queue the information or configure the LTE transceiver <NUM>, the <NUM> NR transceiver <NUM>, and/or the <NUM> transceiver <NUM> to communicate via the allocated resource units <NUM> of the air interface resource <NUM>.

In aspects, an active coordination set for mobility management is described with which the user equipment <NUM> measures the link quality of candidate base stations <NUM> to determine which base stations <NUM> and associated beamforming parameters to include in the ACS. <FIG> illustrates an example environment <NUM> in which a user equipment <NUM> is moving through a radio access network (RAN) that includes multiple base stations <NUM>, illustrated as base stations <NUM>-<NUM>. These base stations may utilize different technologies (e.g., LTE, <NUM> NR, <NUM>) at a variety of frequencies (e.g., sub-gigahertz, sub-<NUM>, and above <NUM> bands and sub-bands).

For example, the user equipment <NUM> follows a path <NUM> through the RAN <NUM>. The user equipment <NUM> periodically measures the link quality (e.g., of base stations that are currently in the ACS and candidate base stations that the UE <NUM> may add to the ACS. For example, at position <NUM>, the ACS at <NUM> includes the base stations <NUM>, <NUM>, and <NUM>. As the UE <NUM> continues to move, at position <NUM>, the UE <NUM> has deleted base station <NUM> and base station <NUM> from the ACS and added base stations <NUM>, <NUM>, and <NUM>, as shown at <NUM>. Continuing along the path <NUM>, the UE <NUM>, at position <NUM>, has deleted the base stations <NUM> and <NUM> and added the base station <NUM>, as shown in the ACS at <NUM>.

<FIG> illustrates an example environment <NUM> in which various aspects of an active coordination set for mobility management can be implemented. The user equipment <NUM> is engaged in joint transmission and/or reception (joint communication) with the three base stations <NUM>, <NUM>, and <NUM>. The base station <NUM> is acting as a master base station for the joint transmission and/or reception. Which base station is the master base station is transparent to the UE <NUM>, and the master base station can change as base stations are added and/or removed from the ACS. The master base station coordinates control-plane and user-plane communications for the joint communication with the UE <NUM> via the Xn interfaces <NUM> (or a similar <NUM> interface) to the base stations <NUM> and <NUM> and maintains the user-plane context between the UE <NUM> and the core network <NUM>. The coordination may be performed using proprietary or standards-based messaging, procedures, and/or protocols.

The master base station schedules air interface resources for the joint communication for the UE <NUM> and the base stations <NUM>, <NUM>, and <NUM>, based on the ACS associated with the UE <NUM>. The master base station (base station <NUM>) connects, via an N3 interface <NUM> (or a <NUM> equivalent interface), to the User Plane Function <NUM> (UPF <NUM>) in the core network <NUM> for the communication of user plane data to and from the user equipment <NUM>. The master base station distributes the user-plane data to all the base stations in the joint communication via the Xn interfaces <NUM>. The UPF <NUM> is further connected to a data network, such as the Internet <NUM> via the N6 interface <NUM>.

UE <NUM> downlink data can be sent from all of the base stations <NUM> in the ACS or any subset of the base stations <NUM> in the ACS. The master base station <NUM> determines which combination of base stations <NUM> in the ACS to use to transmit downlink data to the UE <NUM>. The selection of base stations <NUM> to use to transmit downlink data can be based on one or more factors, such as application quality of service (QoS) requirements, location of the UE <NUM>, velocity of the UE <NUM>, a Reference Signal Received Power (RSRP), a Received Signal Strength Indicator (RSSI), interference, or the like. UE <NUM> uplink data can be received by all of the base stations <NUM> in the ACS or any subset of the base stations <NUM> in the ACS.

Similarly to downlink data, the master base station <NUM> determines which combination of base stations <NUM> in the ACS to use to receive uplink data from the UE <NUM>. The selection of base stations <NUM> to use to receive uplink data can be based on one or more factors, such as application QoS requirements, location of the UE <NUM>, velocity of the UE <NUM>, RSRP, RSSI, interference, or the like. Typically, the combination of base stations <NUM> for downlink transmission and uplink reception will be identical, although different combinations of base stations <NUM> may be used for downlink transmission and uplink reception.

When the user equipment <NUM> creates or modifies an ACS, the user equipment <NUM> communicates the ACS or the ACS modification to an ACS Server <NUM> that stores the ACS for each user equipment <NUM> operating in the RAN <NUM>. Although shown in the core network <NUM>, alternatively the ACS Server <NUM> may be an application server located outside the core network <NUM>. The user equipment <NUM> communicates the ACS or ACS modification via the master base station (base station <NUM>) which is connected to the ACS Server <NUM> via an N-ACS interface <NUM>. Optionally or alternatively, the user equipment <NUM> communicates the ACS or ACS modification to the ACS Server <NUM> via the Access and Mobility Function <NUM> (AMF <NUM>) which is connected to the master base station (base station <NUM>) via an N2 interface <NUM>. The AMF <NUM> relays ACS-related communications to and from the ACS Server <NUM> via an ACS-AMF interface <NUM>. ACS data between the user equipment <NUM> and the ACS Server <NUM> can be communicated via Radio Resource Control (RRC) communications, Non-Access Stratum (NAS) communications, or application-layer communications.

The ACS Server <NUM> may be implemented as a single network node (e.g., a server). The functionality of the ACS Server <NUM> may be distributed across multiple network nodes and/or devices and may be distributed in any fashion suitable to perform the functions described herein. The ACS Server <NUM> includes processor(s) and computer-readable storage media. The processor may be a single core processor, or a multiple core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. CRM may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), hard disk drives, or Flash memory useful to ACS and related data. The CRM includes applications and/or an operating system of the ACS Server <NUM> which are executable by the processor(s) to enable communication with the user equipment <NUM>, the master base station <NUM>, and the AMF <NUM>. The ACS Server <NUM> includes one or more network interfaces for communication with the master base station <NUM>, the AMF <NUM>, and other devices in the core network <NUM>, the user equipment <NUM>, and/or devices in the RAN <NUM>.

Whenever there is a change to the contents of the ACS for any particular user equipment <NUM>, the ACS Server <NUM> sends a copy of the modified ACS to the master base station (base station <NUM>) for that UE. The copy of the ACS stored in the ACS Server <NUM>, can be considered to be the master copy of the ACS for the UE <NUM>. Optionally, in addition to adding and removing base stations <NUM> and beamforming weights from the ACS, the UE <NUM> can query the ACS Server <NUM>, via one or more of the base stations <NUM>, to retrieve a copy of the ACS. The master base station uses the ACS to schedule air interface resources for joint communication with the user equipment <NUM>. For example, when a new base station is added to the ACS or an existing base station in the ACS is deleted, the master base station allocates air interface resources for the new base station to participate in the joint communication or deallocates resources for the deleted base station. The master base station relays user-plane data based on the ACS received from the ACS Server <NUM>. Continuing with the example, the master base station starts routing user-plane data to the new base station added to the ACS or terminates relaying data to the existing base station that was removed from the ACS. If the master base station <NUM> is removed from the ACS, a different base station <NUM> is designated as the master base station. This change of master base stations is transparent to the UE <NUM>. For example, when the ACS Server <NUM> determines that the current master base station is to be removed from the ACS, the ACS Server <NUM> and/or other core network functions, such as the AMF <NUM>, determines which base station <NUM> in the updated ACS will be the new master base station. A message indicating the change of the master base station is communicated to the current and new master base stations, which is effective to move the functions of managing communication in the ACS from the current master base station to the new master base station.

In aspects, the initial ACS for the user equipment <NUM> can be established by the UE <NUM> during or after the UE <NUM> performs the attach procedure to connect to the RAN <NUM>. For example, the UE <NUM> can initialize the ACS with the base stations <NUM> included in the neighbor relation table of the base station through which the UE <NUM> attaches to the RAN <NUM>. In another example, the UE <NUM> considers the base stations <NUM> included in the neighbor relation table as candidates for the ACS and then measures the link quality of each candidate base station before adding a candidate base station to the ACS. In a further example, the user equipment <NUM> queries the ACS Server <NUM> for the last ACS used by the user equipment <NUM> or an ACS used by this or another UE <NUM> at the current location of the UE <NUM>. The UE <NUM> then validates the entries in the last-used ACS to determine which, if any, entries of the last-used ACS are usable for communication and inclusion in the ACS. In another example, the UE <NUM>, measures the link quality of any base stations <NUM> from the previous ACS that are within communication range and populates the ACS with one or more of the base stations <NUM> that exceed a threshold for inclusion (e.g., above a threshold for a Received Signal Strength Indicator (RSSI), a Reference Signal Received Power (RSRP), or a Reference Signal Received Quality (RSRQ)).

The user equipment <NUM> adds or deletes a base station <NUM> from the ACS by sending an ACS modification message to the ACS Server <NUM>. The ACS modification message includes an identifier for a base station to add or delete from the ACS along with an indicator to either add or delete the identified base station. When adding a base station to the ACS, the ACS modification message can also include beamforming parameters for the base station being added. Optionally, or additionally, the ACS modification message may include identifiers of multiple base stations with corresponding add/delete indicators for each base station. Other information useful to the management of the ACS may be stored in or with the ACS, such as timestamps for entries in the ACS, geographic location information from the UE, an identifier for the UE <NUM>, identification information for the current master base stations, and the like.

The ACS Server <NUM> receives the ACS modification message from the UE <NUM> (via the current master base station) and performs the requested modification to an ACS record for the UE <NUM> that is stored by the ACS server <NUM>. After receiving the ACS modification message, the ACS Server <NUM> sends a modified copy of the ACS for the UE <NUM> to the master base station (base station <NUM>) via the N-ACS interface <NUM>. Optionally or alternatively, the ACS Server <NUM> may send only the modification of the ACS to the master base station which causes the master base station to update its copy of the ACS. The joint communication scheduler <NUM> in the master base station uses the updated or modified ACS to modify the scheduling of resources and joint communications for the base stations <NUM> in the ACS. The master base station can perform real-time scheduling of resources within the ACS of the user equipment <NUM> to respond to changing channel conditions or communication requirements with low latency requirements.

<FIG> and <FIG> illustrate an example of control transactions <NUM> and <NUM> between devices in accordance with aspects of an active coordination set for mobility management. The user equipment <NUM> attaches to the RAN <NUM> by performing an attach procedure at <NUM>. In one alternative, the UE <NUM> may receive a System Information Block (SIB) that includes information describing neighboring base stations (e.g., SIB3 or SIB4). In this alternative, the UE <NUM> can use the neighboring base stations as candidate base stations to include in the ACS or to further evaluate for inclusion in the ACS. Optionally or alternatively, at <NUM>, the master base station <NUM> may transmit a list of neighboring base stations to the UE <NUM> specifically for the purpose of providing the UE <NUM> with candidate base stations for potential inclusion in the ACS.

Optionally or alternatively, the UE <NUM> may use a previous ACS (e.g., the last ACS used by the UE <NUM> before detaching from the RAN <NUM> or an ACS used by this or another UE <NUM> at or near the current geographic location of the UE <NUM>) as a list of candidate base stations for the ACS or as an initial ACS. For example, based on the base station identifiers included in the ACS or based on optional geographic location information stored with the ACS of the UE's last location before detaching from the RAN <NUM>, the UE <NUM> can use, or evaluate for use, the previous ACS as the current ACS or the ACS of another UE used at the current geographic location of the UE <NUM>. In this example, the ACS Server <NUM> sends the previous ACS to the master base station <NUM> at <NUM>, which the master base station <NUM> forwards to the UE <NUM> at <NUM>. The ACS Server <NUM> may be triggered to send the previous ACS by the attach process, such as by receiving a message from the AMF <NUM>, or the UE <NUM> may message the ACS Server <NUM> to request the previous ACS.

At <NUM>, the user equipment <NUM> sends an ACS-Modify message to the master base station <NUM> to add the base station <NUM> to the ACS, which the master base station <NUM> relays to the ACS Server <NUM> at <NUM>. The ACS Server <NUM> updates the copy of the ACS stored by the ACS Server <NUM> to add the master base station <NUM> to the ACS associated with the UE <NUM>. If there is no copy of an ACS associated with the UE <NUM> stored in the ACS Server <NUM>, the ACS Server <NUM> creates an ACS for the UE <NUM>, associates the ACS with the UE <NUM>, and adds the master base station <NUM>, to the ACS associated with the UE <NUM>, as the initial master base station for the ACS. Based on receiving the ACS-Modify message, the ACS Server <NUM> sends, at <NUM>, an updated ACS to the master base station <NUM>. The master base station <NUM> uses the copy of the updated ACS to allocate resources and schedule communications between the UE <NUM> and any base stations <NUM> included in the ACS.

At <NUM>, the UE <NUM> measures the link quality (e.g., RSRP) of candidate base stations for inclusion in the ACS. The measurement of link quality can include performing a beam search or beam scan procedure to determine the link quality of beams transmitted by the candidate base stations. The UE <NUM> may identify candidate base stations in any suitable manner, such as from a received neighboring base station list, a previous ACS, by listening for broadcast transmission within the RAN <NUM>, performing a frequency search, from a neighbor advertisement, and so forth.

Based on the performed measurements, the UE <NUM> identifies one or more additional base stations <NUM> to add to the ACS. At <NUM>, the UE <NUM> sends another ACS-Modify message including identifiers of the additional base stations <NUM> to the master base station <NUM>. The identifiers of the additional base stations can include associated beamforming parameters for each of the additional base stations. The master base station relays the ACS-Modify message to the ACS Server <NUM>, at <NUM>. The ACS Server <NUM> updates the stored ACS of the UE <NUM> to include the identifiers of the additional base stations <NUM> and at <NUM> sends an updated version of the ACS to the master base station <NUM>.

At <NUM>, based on receiving the updated ACS, the master base station <NUM> schedules resources for joint communication with the UE <NUM> by one or more of the base stations <NUM> in the ACS. The master base station <NUM> communicates the resource schedule via the Xn interfaces <NUM> between the master base station <NUM> and the additional base stations <NUM> to enable joint communication with the UE at <NUM>.

Continuing at <NUM> in <FIG>, the user equipment <NUM> evaluates whether any base station <NUM> in the ACS has fallen below a threshold for link quality (e.g., a threshold value for a minimum RSRP level). For example, the UE <NUM> may evaluate the base stations <NUM> periodically in time using either a standard time period or a dynamically changing time period, based on communication performance metrics (e.g., dropped frame rate, retransmission rate, or the like), based on a change in the location of the UE <NUM> exceeding a distance threshold or a velocity threshold, or the like.

If the UE <NUM> determines that a base station has fallen below the link quality threshold, the UE <NUM> removes that base station from the ACS. For example, the UE <NUM> determines that the base station <NUM> has fallen below the link quality threshold and sends, at <NUM>, an ACS-Modify message to remove the base station <NUM> from the ACS. The master base station <NUM> and/or other base stations in the ACS receive the ACS-Modify message, and the master base station <NUM> forwards the ACS-Modify message to the ACS Server <NUM> at <NUM>. The ACS Server <NUM> modifies the ACS, stores the modified ACS, and at <NUM> sends the modified ACS to the master base station <NUM>. Optionally or additionally, the ACS-Modify message can indicate a change in beamforming parameters for a base station already included in the ACS. For example, the ACS-Modify message can indicate adding a base station that is already included in the ACS but with new beamforming parameters or the ACS-Modify message can indicate an update to the beamforming parameters of the base station in the ACS.

At <NUM>, the master base station <NUM> modifies the resource allocations and scheduling based on the modified ACS and communicates the modified schedule to the base stations in the modified ACS and communicates the deallocation of scheduled resources to the base station <NUM> that has been removed from the ACS. At <NUM>, the master base station <NUM> and the base stations <NUM> in the modified ACS continue joint communication with the UE.

As described above, the user equipment <NUM> can determine which base stations <NUM> to include in the ACS based on the measurement of radio frequency (RF) signals transmitted from the candidate base stations. In another aspect, the user equipment can evaluate candidate base stations <NUM> by transmitting an uplink sounding signal to measure uplink performance. The uplink sounding may be used in place of, or in addition to, downlink measurements when the UE <NUM> determines which base stations <NUM> to include in the ACS. For example, uplink sounding may be used for a Time Division Duplex (TDD) radio link due to the link reciprocity in a TDD radio channel; however, uplink sounding may be applied in Frequency Division Duplex (FDD) systems as well.

<FIG> illustrates an example of control transactions <NUM> between devices in accordance with aspects of an active coordination set for mobility management that generally relate to uplink sounding. At <NUM>, the user equipment <NUM> evaluates whether any base station <NUM> in the ACS has fallen below a threshold for link quality (e.g., a threshold value for a minimum RSRP level).

Optionally at <NUM>, the user equipment <NUM> sends an ACS Update Request or another signal such as a Random Access Channel (RACH) signal to the master base station <NUM> and/or other base stations <NUM> in the ACS indicting that the user equipment <NUM> will be transmitting an uplink ACS sounding signal. Time, frequency, and code resources for the uplink ACS sounding signal can be semi-statically allocated in the RAN <NUM>. Optionally or additionally, the master base station <NUM> notifies candidate base stations <NUM> (that may not be included in the ACS currently being used by the UE <NUM>) that the UE <NUM> will be transmitting an uplink ACS sounding signal. An indication of the time, frequency, and code resources for the uplink ACS sounding signal may be included in the notification.

At <NUM>, the user equipment <NUM> transmits the uplink ACS sounding signal to the master base station <NUM> and other base stations <NUM> in the ACS. At <NUM>, the master base station <NUM> and other base stations <NUM> in the ACS decode the uplink ACS sounding signal and report link quality metrics (e.g., RSSI) for the decoded uplink ACS sounding signal. The base stations <NUM> report the decode results to the master base station <NUM> at <NUM>, and the master base station <NUM> forwards those decode results along with its own decode result to the UE <NUM> at <NUM>.

At <NUM>, the user equipment <NUM> evaluates the received decode results and determines which base stations <NUM> to include in the ACS. Optionally or alternatively, the master base station <NUM> can evaluate the decode results and determine which base stations <NUM> to include in the ACS and communicate a new ACS or changes in the ACS to the UE <NUM> and the ACS Server <NUM>. In another option or alternative, the decode results can be forwarded to the ACS Server <NUM> for the evaluation and determination of which base stations <NUM> to include in the ACS and the ACS Server <NUM> communicates a new ACS or changes in the ACS to the UE <NUM> and the master base station <NUM>. Optionally or additionally, other uplink and/or downlink signals, such as a Physical Uplink Shared Channel (PUSCH), a Physical Uplink Control Channel (PUCCH), or a Physical Random Access Channel (PRACH) can be evaluated to determines which base stations <NUM> to include in an ACS.

At <NUM>, the user equipment <NUM> sends an ACS-Modify message to the master base station <NUM> indicting which base stations <NUM> to add to and/or remove from the ACS. The UE <NUM> may also choose to remove from the ACS one or more base stations <NUM> that did not return a decode result. At <NUM>, the master base station <NUM> forwards the ACS-Modify message to the ACS Server <NUM>. The ACS Server <NUM> modifies the ACS, stores the modified ACS, and at <NUM> sends the modified ACS to the master base station <NUM>.

Example methods <NUM> and <NUM> are described with reference to <FIG> and <FIG> in accordance with one or more aspects of an active coordination set for mobility management. The order in which the method blocks are described are not intended to be construed as a limitation, and any number of the described method blocks can be skipped or combined in any order to implement a method or an alternate method. Generally, any of the components, modules, methods, and operations described herein can be implemented using software, firmware, hardware (e.g., fixed logic circuitry), manual processing, or any combination thereof. Some operations of the example methods may be described in the general context of executable instructions stored on computer-readable storage memory that is local and/or remote to a computer processing system, and implementations can include software applications, programs, functions, and the like. Alternatively or in addition, any of the functionality described herein can be performed, at least in part, by one or more hardware logic components, such as, and without limitation, Field-programmable Gate Arrays (FPGAs), Application-specific Integrated Circuits (ASICs), Application-specific Standard Products (ASSPs), System-on-a-chip systems (SoCs), Complex Programmable Logic Devices (CPLDs), and the like.

<FIG> illustrates example method(s) <NUM> of an active coordination set for mobility management as generally related to the user equipment <NUM> determining base stations <NUM> for inclusion in the ACS. At block <NUM>, a user equipment (e.g., the user equipment <NUM>) evaluates a link quality measurement for each of one or more base stations (e.g., the base stations <NUM>). For example, the user equipment evaluates a link quality parameter, such as RSRP, for downlink RF signals received from each of the one or more base stations.

At block <NUM>, the user equipment determines whether to include at least a first base station of the one or more base stations in the ACS. For example, the user equipment compares the received downlink RF signals to a threshold for a minimum acceptable value for the link quality parameter.

At block <NUM>, the user equipment sends a message to an ACS Server (e.g., the ACS Server <NUM>) including an indication to add the at least first base station to the ACS. For example, the user equipment sends an ACS-Modify message to the ACS Server that causes the ACS Server to store the ACS for the user equipment that includes the indicated base station(s) and sends a copy of the stored ACS to a master base station (e.g., the master base station <NUM>).

At block <NUM>, the user equipment communicates via one or more of the base stations included in the ACS. For example, the user equipment communicates via wireless channels with one, two, or more of the base stations included in the ACS.

<FIG> illustrates example method(s) <NUM> of an active coordination set for mobility management as generally related to the user equipment <NUM> maintaining an ACS by evaluating candidate base stations to include in the ACS. At block <NUM>, the user equipment (e.g., the user equipment <NUM>) determines that one or more base stations (e.g., the base stations <NUM>) in the ACS has fallen below a threshold for a link quality parameter. For example, the user equipment determines that a downlink quality parameter has dropped below a threshold for a minimum acceptable value for the link quality parameter.

At block <NUM>, the user equipment transmits an uplink ACS sounding signal to candidate base stations. For example, the user equipment transmits the uplink ACS using semi-statically allocated resources for the uplink ACS sounding signal to candidate base stations that receive and decode the uplink ACS sounding signal.

At block <NUM>, the user equipment receives decoding results for the uplink ACS sounding signal from the candidate base stations. For example, the candidate base stations transmit the decoding results directly to the user equipment or send the decoding results to the master base station (e.g., the master base station <NUM>) via the Xn interface <NUM> which then passes on the set of decoding results to the UE wirelessly.

At block <NUM>, the user equipment uses the decoding results to determine which of the candidate base stations to include in the ACS. For example, the user equipment adds one or more of the candidate base stations to the ACS that reported a decoding result greater than a threshold value for decoding results. As another example, the UE removes one or more of the candidate base stations from the ACS that reported a decoding result lower than a threshold value or did not report any decoding results.

At block <NUM>, the user equipment sends a message to an ACS Server that includes an indication of which of the candidate base stations to include in the ACS. For example, the user equipment sends an ACS-Modify message to the ACS Server that causes the ACS Server to store the ACS, for the user equipment, that includes the indication of the base stations to include and/or remove from the ACS and sends a copy of the ACS to the master base station. The copy of the ACS stored in the ACS Server <NUM> can be considered to be the master copy of the ACS. In alternatives, the copy of the ACS stored in the UE <NUM> or stored in the master base station <NUM> can be considered to be the master copy of the ACS.

Claim 1:
A method (<NUM>) for maintaining an Active Coordination Set, ACS, (<NUM>, <NUM>, <NUM>), by a user equipment (<NUM>), for wireless communication between the user equipment and base stations (<NUM>; <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) in the ACS, the method comprising:
determining (<NUM>; <NUM>), by the user equipment, that a link quality parameter for one or more of the base stations in the ACS has fallen below a threshold for the link quality parameter;
based on the determining that the link quality parameter for one or more of the base stations in the ACS has fallen below a threshold for the link quality parameter, transmitting (<NUM>; <NUM>) an uplink ACS sounding signal that is effective to cause candidate base stations to receive and decode the uplink ACS sounding signal;
receiving (<NUM>; <NUM>) decoding results for the uplink ACS sounding signal from the candidate base stations;
determining (<NUM>; <NUM>), using the decoding results, which of the candidate base stations to include in the ACS;
sending (<NUM>, <NUM>; <NUM>) a message to an ACS Server, the message including an indication of which candidate base stations to include in the ACS; and
jointly communicating (<NUM>) with one or more of the base stations included in the ACS.