Patent Description:
The evolution of wireless communication systems to fifth generation (<NUM>) New Radio (NR) and Sixth Generation (<NUM>) technologies provides higher data rates to users. By employing techniques, such as Coordinated MultiPoint (CoMP) over beamformed wireless connections within an ACS, still higher data rates can be provided at the edges of <NUM> and <NUM> cells. UE mobility, however, can cause changes in the base stations included in an ACS. [0002a] <CIT> relates to a communication apparatus that includes: a channel estimating unit for acquiring a channel estimation value between the communication apparatus and a cell base station of a cell which the communication apparatus is located; a transmitter for transmitting the channel estimation value; a receiver for receiving a coordinated multipoint (CoMP) message indicating a codebook or precoding matrix used by the base cell station; a channel matrix forming unit; and a decoder.

<CIT> relates to a communication method and apparatus for coordinated multi-point (CoMP) transmission. In this method the size of codebooks for a plurality of base stations may be adjusted based on the status of channels between a target base station and a plurality of base stations.

<NPL>) discusses potential coordination schemes for closed-loop coordinated transmission.

This summary is provided to introduce simplified concepts of dynamic codebooks for active coordination sets. The simplified concepts are further described below in the Detailed Description. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter. Based on the configurations of base stations in the ACS and changes in the set of base stations participating in the ACS, codebooks for a specific ACS need to be sent to the UE to enable the UE to perform precoding feedback.

In accordance with the invention, there is provided: a method for determining a joint-codebook as recited by claim <NUM>; and a base station as recited by claim <NUM>.

In aspects, methods, devices, systems, and means for determining a joint-codebook for wireless communication with a user equipment (UE) by a base station in an active coordination set (ACS) describe a base station receiving capability information from one or more other base stations in the ACS. The base station generates a joint-codebook for the ACS based on the received capability information and sends the joint-codebook to the one or more other base stations in the ACS. The base station and the other base stations in the ACS jointly-transmit the joint-codebook to the UE and receive Precoding Matrix Indicator (PMI) feedback from the UE. The base station and the other base stations in the ACS jointly-process downlink data for the UE using the PMI feedback and the j oint-codebook and jointly-transmit the downlink data to the UE.

Aspects of dynamic codebooks for active coordination sets 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 determining a joint-codebook for wireless communication with a user equipment (UE) by a base station in an active coordination set (ACS) in which a base station receives capability information from one or more other base stations in the ACS. The base station generates a joint-codebook for the ACS based on the received capability information and sends the joint-codebook to the one or more other base stations in the ACS. The base station and the other base stations in the ACS jointly-transmit the joint-codebook to the UE and receive Precoding Matrix Indicator (PMI) feedback from the UE. The base station and the other base stations in the ACS jointly-process downlink data for the UE using the PMI feedback and the j oint-codebook and j ointly-transmit the downlink data to the UE.

UE mobility (changes in UE location) can dynamically change the set of base stations included in an ACS. As the composition of the ACS changes, the phase coherence capabilities and the antenna configuration (e.g., a number of antenna ports, a number of antenna panels, a number of beams available for azimuth and/or elevation, etc.) for base stations in the ACS can change as well. For a UE to be able to perform precoding feedback, a coordinating base station sends a joint-codebook that includes UE-specific precoding matrices for the ACS to the UE.

The j oint-codebook for an ACS with a set of base stations may not have any particular relationship with individual codebooks for each base station. For example, for phase coherence, the joint-codebook can require each base station to apply a different phase shift and the amount of phase shift can depend on the number of base stations in the ACS. A joint-codebook includes a respective set of precoding matrices for each base station in the ACS. The precoding matrices of the joint-codebook are such that, when each base station in the ACS processes downlink data in accordance with a precoding matrix selected from its respective set of precoding matrices, joint transmission of downlink data to the UE is improved (as compared to a scenario in which each base station processes downlink data in accordance with an individual codebook whose precoding matrices are independent of those of other base stations in the ACS).

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

<FIG> illustrates an example environment <NUM> in which various aspects of dynamic codebooks for active coordination sets 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 future evolutions. 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, determine PMI feedback, and/or determine beams to use for communication with base stations.

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 nomenclature for this distributed base station functionality varies and includes terms such as Central Unit (CU), Distributed Unit (DU), Baseband Unit (BBU), Remote Radio Head (RRH), Radio Unit (RU), and/or Remote Radio Unit (RRU). 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 base station manager <NUM>. Alternately or additionally, the base station manager <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 base station manager <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 base station manager <NUM> may allocate air interface resources, schedule communications, and generate joint-precoding-matrix codebooks for the UE <NUM> and base stations <NUM> in the ACS when the base station <NUM> is acting as a coordinating 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 base station manager <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 base station manager <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 dynamic codebooks for active coordination sets 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 seven 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 base station manager <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 base station manager <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 base station manager <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 base station manager <NUM> may allocate resource units at an element-level. Thus, the base station manager <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 base station manager <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 base station manager <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 base station manager <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>.

<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). An ACS is a set of base stations, determined by a UE, that perform coordinated communication with the UE, such as by using joint-transmission and/or joint-reception by the base stations in the ACS to communicate with the UE.

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 dynamic codebooks for active coordination sets 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 coordinating base station for the joint transmission and/or reception. Which base station is the coordinating base station is transparent to the UE <NUM>, and the coordinating base station can change as base stations are added and/or removed from the ACS. The coordinating 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.

In joint-transmission, multiple transmitters (of the base stations <NUM>) coordinate transmission of signals for the same set of data to increase transmit power, as compared to a single transmitter, and improve the link budget to a receiver. In joint-reception, multiple-receivers (of the base stations <NUM>) each receive transmitted signals for the same set of data and accumulate the I/Q samples from each of the receivers to decode the combined I/Q samples into the set of data. By using joint-reception, the receivers provide increased receiver sensitivity, as compared to a single receiver, and improve the link budget for receiving the data from a transmitter.

The coordinating 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 coordinating 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 coordinating 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 coordinating 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 coordinating 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 coordinating 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 coordinating 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.

Whenever there is a change to the constituent base stations in the ACS for any particular user equipment <NUM>, the ACS Server <NUM> sends a copy of the modified ACS configuration to the coordinating base station (base station <NUM>) for that UE. The copy of the ACS configuration stored in the ACS Server <NUM>, can be considered to be the master copy of the ACS configuration for the UE <NUM>. Optionally, in addition to adding and removing base stations <NUM> and beamforming parameters 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 configuration of the ACS. The coordinating base station uses schedules air interface resources for joint communication between the ACS and 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 coordinating 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 coordinating base station relays user-plane data based on the ACS received from the ACS Server <NUM>. Continuing with the example, the coordinating 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 coordinating base station <NUM> is removed from the ACS, a different base station <NUM> is designated as the coordinating base station. This change of coordinating base stations is transparent to the UE <NUM>. For example, when the ACS Server <NUM> determines that the current coordinating 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 coordinating base station. A message indicating the change of the coordinating base station is communicated to the current and new coordinating base stations, which is effective to move the functions of managing communication in the ACS from the current coordinating base station to the new coordinating 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 an 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 coordinating base stations, and the like.

The ACS Server <NUM> receives the ACS modification message from the UE <NUM> (via the current coordinating 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 coordinating 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 coordinating base station which causes the coordinating base station to update its copy of the ACS. The base station manager <NUM> in the coordinating 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 coordinating 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.

In aspects, base stations within an ACS communicate and coordinate with each other to provide a joint-codebook for the UE <NUM>. For example, base stations <NUM> and <NUM> each send capability information to the coordinating base station <NUM>. The coordinating base station <NUM> generates the joint-precoding-matrix codebook for the ACS that is UE-specific for communication between the ACS and the UE <NUM>.

Phase coherence between base stations in the ACS is an important factor for joint-communication between the ACS and the UE. The base stations in the ACS send their phase coherence capability to the coordinating base station <NUM> to use as a factor in generating the joint-codebook. For example, the phase coherence capability indicates the source of the phase reference used by a base station, such as a Global Navigation Satellite System (GNSS), IEEE <NUM> Precision Time Protocol (PTP), or Synchronous Ethernet (SyncE).

When the base stations in the ACS use a common phase reference, the base stations in the ACS can use the same air interface resources for joint transmission. In the event that different phase references are used by base stations in the ACS, the coordinating base station <NUM> can select a portion of the available antenna elements at the base stations in the ACS and/or schedule air interface resources for the base stations in the ACS to mitigate a scenario where non-phase-coherence leads to destructive addition or cancellation of transmitted signals. For example, the coordinating base station <NUM> schedules a first subset of base stations in the ACS that share a first phase reference to transmit in a first time slot and schedules a second subset of base stations in the ACS that share a second phase reference to transmit in a second time slot to maintain phase coherence in the first and second time slots, respectively.

The joint-precoding-matrix codebook for a UE <NUM> can be determined based on the phase coherence capabilities among base stations <NUM> in the ACS. For example, a subset of base stations <NUM> in an ACS can be phase coherent (e.g., the RF components of the base stations are disciplined to a first common timebase) while another subset of base stations <NUM> in the ACS may not be phase coherent (e.g., the RF components of the base stations are not disciplined to the first common timebase). For example, when there is no phase coherence between certain base stations in the ACS, then coherent beamforming may not be possible using the non-phase coherent base stations. In this case, the j oint-codebook can define selective transmission among a few subsets of phase-coherent base stations. This is determined by the amount of synchronization between base stations <NUM> in the ACS. For example, whether the base stations can maintain frequency synchronization by being disciplined to a common clock (timebase). Each base station can be synchronized to the common clock using SyncE or PTP to discipline each base station's clock to the common clock. Alternatively, a second base station can be calibrated to a first base station based on RF transmissions of the first base station. For example, the second base station receives an RF calibration signal from the first base station, and then measures the phase of the received RF calibration signal to adjust its timebase to maintain phase coherence with the first base station.

An ACS can maintain phase coherence for joint transmission and/or joint reception by maintaining stable RF phase and frequency alignment that drifts less than the Doppler frequency shift caused by UE mobility. Using the joint codebook, the UE <NUM> feeds back an indication of a desired phase vector (precoding matrix) that will be applied by the ACS. As long as the base stations' clocks within ACS do not drift to the point of making the UE feedback outdated, phase coherence can be maintained.

In another aspect, the joint-codebook can depend on the antenna configuration of the base stations forming the ACS, such as a number of antenna ports, a number of antenna panels, and a number of beams for each row and each column of antenna elements used for azimuth and elevation beamforming, respectively. For example, a base station in a first ACS may configure part of the available antenna elements (e.g., one sub-panel) for the first ACS, and the base station can use other sub-panels for a second ACS, as one base station can concurrently participate in multiple ACSs.

From the UE perspective, joint-codebooks are dynamically changing as the UE <NUM> can select different ACS constituents (e.g., base stations with different capabilities) at different times due to UE mobility. From the infrastructure point of view, base stations can communicate with each other to negotiate the joint-codebook once the set of base stations in the ACS is formed for a particular UE. For example, it is possible for a first base station to use a first joint-codebook with a second base station while serving a first UE, and later, for the same UE, the first base station can use a second joint-codebook with a third base station when the base stations included in the ACS for the UE changes from the first base station and the second base station to the first base station and the third base station.

In an aspect, the ACS or the coordinating base station of the ACS can send a joint-codebook via Radio Resource Control (RRC) or Non-Access Stratum (NAS) messages to the UE. The ACS or the coordinating base station of the ACS also sends a Channel State Information-Reference Signal (CSI-RS) configuration to the UE along with the joint-codebook. Alternatively, the CSI-RS configuration can be sent in a separate message from the joint-codebook message. The joint-codebook includes a set of precoding matrices for the ACS. In one alternative, there can be a predefined joint-codebook that is shared between the ACS and the UE where the ACS sends an index of the predefined j oint-codebook to the UE <NUM>. The UE <NUM> measures Channel State Information-Reference Signals (CSI-RS) received from the base stations in the ACS to determine a precoding matrix for joint communication with the ACS. Typically, the UE <NUM> tries multiple precoding matrix hypotheses to choose a precoding matrix such that the UE-expected downlink (DL) signal-to-interference-plus-noise ratio (SINR) is maximized. After selecting a precoding matrix, the UE <NUM> sends a Precoding Matrix Indicator (PMI) to the ACS to indicate the precoding matrix that the UE has selected from the joint-codebook.

The coordinating base station <NUM> uses any suitable generating procedure, such as Fast Fourier Transfer (FFT) matrix-based precoding, and the capability information received from the other base stations, such as phase coherence capability, a number of antenna ports, a number of antenna panels, and a number of beams for each row and each column of antenna elements used for azimuth and elevation beamforming, respectively, to generate the precoding vectors that are included in the joint-codebook. The coordinating base station <NUM> dynamically generates new joint-codebooks as needed, based on UE mobility as mentioned previously.

To reduce signaling overhead, the coordinating base station <NUM> can communicate (e.g., using RRC or NAS messages) only the precoding vectors that have changed in the new joint-codebook relative to the previous joint-codebook. The UE <NUM> receives the changes to the codebook and adds and deletes (or inactivates) a subset of precoding vectors from the old joint-codebook to derive the new joint-codebook. For example, when a constituent base station is removed from an ACS, the coordinating base station <NUM> can indicate to the UE the indices of precoding matrices in the joint-codebook to delete (or inactivate) to generate a revised joint-codebook that no longer includes the removed base station. In another example, when a base station is added to an existing ACS, the coordinating base station <NUM> can send precoding matrices for the new base station to the UE such that the UE can add the new precoding matrices to the existing joint-codebook to generate a revised joint-codebook.

Base stations in the ACS can negotiate to determine a start-time at which to start using a new joint-codebook. The ACS then sends an indication of the determined timing to the UE to indicate when the UE should generate precoding index (PMI) feedback. The timing can be indicated using a system frame number and/or slot number. The coordinating base station <NUM> can trigger use of the new joint-codebook using a Medium Access Control (MAC) Control Element (CE) or Layer <NUM> DL control channel signaling.

<FIG> illustrates an example of data and control transactions <NUM> between devices in accordance with aspects of dynamic codebooks for active coordination sets. The messaging diagram <NUM> illustrates generation and communication of a joint-codebook for the UE <NUM>.

At <NUM>, the coordinating base station <NUM> and one or more other base stations <NUM> form an ACS for the UE <NUM> as described above with respect to <FIG> and <FIG>. At <NUM>, the one or more other base stations <NUM> in the ACS send capability information including a phase coherence capability, and MIMO and antenna configuration information, such as a number of antenna ports, a number of antenna panels, and a number of beams for each row and each column of antenna elements used for azimuth and elevation beamforming, respectively.

At <NUM>, the coordinating base station <NUM> generates a joint-precoding-matrix codebook for the UE <NUM> using any suitable generating procedure, such as Fast Fourier Transfer (FFT) matrix-based precoding, and the parameters received from the other base stations. At <NUM>, the coordinating base station <NUM> sends the joint-codebook to the one or more other base stations in the ACS. At <NUM>, the coordinating base station <NUM> and the other base stations <NUM> jointly-transmit the joint-codebook and a CSI-RS configuration to the UE <NUM>. At <NUM>, the coordinating base station <NUM> and the other base stations <NUM> jointly-transmit an indication of a start-time to the UE <NUM> to direct the UE <NUM> to begin using the joint-codebook at the indicated start-time. In some implementations, any or both of messages <NUM>, <NUM> may be jointly-transmitted without coherent beamforming.

At <NUM>, the UE receives and measures Channel State Information-Reference Signals (CSI-RS) from the ACS to determine a precoding matrix from the joint-codebook. At <NUM>, the UE <NUM> transmits PMI feedback to the ACS that is jointly-received by the coordinating base station <NUM> and the one or more other base stations <NUM> in the ACS. At <NUM>, each base station in the ACS receives the PMI feedback signaling and demodulates the PMI feedback transmission. The base stations <NUM> send the demodulated PMI feedback, using the Xn interface, to the coordinating base station <NUM> that aggregates and jointly-processes the demodulated PMI feedback into decoded PMI feedback results. The process at <NUM>, and described above, can also be used to in the ACS to jointly-process other received uplink control and data signals.

At <NUM> the coordinating base station <NUM> and the one or more other base stations <NUM> in the ACS jointly-process downlink data using the joint-codebook for the UE <NUM>. At <NUM>, the coordinating base station <NUM> and the one or more other base stations <NUM> in the ACS jointly-transmit the downlink control and data signals to the UE <NUM> based on the PMI feedback results. Joint-codebook PMI feedback enables phase-coherent beamformed transmissions from the base stations in the ACS. The phase-coherent beamformed transmissions provide an improved signal-to-noise ratio and increased reception signal strength at the UE that increases range, power efficiency, and data throughput.

Example method <NUM> is described with reference to <FIG> in accordance with one or more aspects of dynamic codebooks for active coordination sets. <FIG> illustrates example method(s) <NUM> of dynamic codebooks for active coordination sets as generally related to the base station <NUM> generating and communicating a joint-codebook to the UE <NUM>.

At block <NUM>, a base station receives capability information from one or more other base stations in an ACS. For example, a base station (e.g., the coordinating base station <NUM>) receives (at <NUM>) capability information from one or more other base stations (e.g., the base stations <NUM> and <NUM>) in the ACS. The capability information includes a phase coherence capability, and MIMO and antenna configuration information, such as a number of antenna ports, a number of antenna panels, and a number of beams for each row and each column of antenna elements used for azimuth and elevation beamforming, respectively.

At block <NUM>, the base station generates a joint-codebook for the ACS based on the received capability information. For example, the base station (at <NUM>) generates a joint-codebook specific to a UE (e.g., the UE <NUM>) for the ACS based on the received capability information. The base station can use any suitable generation technique such as Fast Fourier Transfer (FFT) matrix-based precoding.

At block <NUM>, the base station sends the joint-codebook to the one or more other base stations in the ACS. For example, the base station sends the joint-codebook (at <NUM>) to the other base stations using the Xn interface (e.g., the Xn interface <NUM>).

At block <NUM>, the base station jointly-transmits the joint-codebook to the UE. For example, the base station and the other base stations in the ACS jointly-transmit (at <NUM>) the joint-codebook to the UE. The transmission of the j oint-codebook directs the UE to determine PMI feedback (at <NUM>).

At block <NUM>, the base station receives Precoding Matrix Indicator (PMI) feedback from the UE. For example, based on transmitting the joint-codebook to the UE (at <NUM>) and optionally transmitting a start-time indication (at <NUM>), the base station receives PMI feedback from the UE (at <NUM>). The coordinating base station <NUM> receives the demodulated PMI feedback signals from the other base stations in the ACS that have demodulated the received PMI feedback and sent that demodulated feedback to the coordinating base station <NUM>. The coordinating base station <NUM> aggregates and jointly-processes (at <NUM>) the received, demodulated PMI feedback along with demodulated PMI feedback that the coordinating base station <NUM> received to obtain the jointly-received decoded PMI feedback result. As noted previously, the process of receiving and jointly-processing <NUM> uplink signals may be used for not only the PMI feedback but also other control and data signals.

At block <NUM>, the base station jointly-processes downlink data for the UE using the PMI feedback and the joint-codebook and sends a PMI feedback result to the other base stations in the ACS. For example, based on the PMI feedback, the base station and the other base stations in the ACS select a precoding vector to jointly-process (at <NUM>) downlink data for the UE. The base station sends the PMI feedback to other base stations using the Xn interface. In addition to the PMI feedback, the base station sends downlink data, air interface resource allocations, and/or timing advance information for joint-transmission to the other base stations in the ACS.

At block <NUM>, the base station jointly-transmits the downlink data to the UE. For example, the base station and the other base stations in the ACS jointly-transmit (at <NUM>) the downlink data to the UE.

At optional block <NUM>, the base station receives a request from the UE for a new joint-codebook or receives an updated PMI indication. For example, the UE measures a low SINR for received downlink data and transmits a request to the ACS for a new joint-codebook. The ACS jointly-receives the request and the method flow transitions to block <NUM> to generate the new joint-codebook. Alternatively, if the base station receives an updated PMI indication, the method skips back to block <NUM> and sends the updated PMI indication to the other base stations in the ACS.

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.

Claim 1:
A method for determining a joint-codebook for wireless communication with a user equipment, UE (<NUM>), by a base station (<NUM>) in an active coordination set, ACS, the method comprising the base station:
receiving (<NUM>) capability information from one or more other base stations in the ACS;
generating (<NUM>) a joint-codebook for the ACS based on the received capability information;
sending (<NUM>) the joint-codebook to the one or more other base stations (<NUM>) in the ACS;
jointly-transmitting (<NUM>) the joint-codebook to the UE (<NUM>);
receiving (<NUM>) Precoding Matrix Indicator, PMI, feedback from the UE;
jointly-processing (<NUM>) downlink data for the UE using the PMI feedback and the joint-codebook; and
jointly-transmitting (<NUM>) the downlink data to the UE (<NUM>).