Release of conditional primary secondary cell addition/modification configurations

A wireless terminal includes processor circuitry configured to establish, using a first master key, a first security context on a first radio connection with a master access node, and receiver circuitry configured to receive a re-configuration message including one or more conditional secondary cell configurations and at least one counter. Each conditional secondary cell configuration may include an identity of a candidate primary secondary cell and at least one triggering condition, the candidate primary secondary cell being used for Dual-Connectivity. The at least one counter and the first master key may be used for derivation of a second master key to be used for an establishment of a second security context with one of candidate primary secondary cells. The processor circuitry is further configured to invalidate the one or more conditional secondary cell configurations upon a change of the first master key.

TECHNICAL FIELD

The technology relates to wireless communications, and particularly to conditional handovers in a radio access network.

BACKGROUND ART

A radio access network typically resides between wireless devices, such as user equipment (UEs), mobile phones, mobile stations, or any other device having wireless termination, and a core network. Example of radio access network types includes the GRAN, GSM radio access network; the GERAN, which includes EDGE packet radio services; UTRAN, the UMTS radio access network; E-UTRAN, which includes Long-Term Evolution; and g-UTRAN, the New Radio (NR).

A radio access network may comprise one or more access nodes, such as base station nodes, which facilitate wireless communication or otherwise provides an interface between a wireless terminal and a telecommunications system. A non-limiting example of a base station can include, depending on radio access technology type, a Node B (“NB”), an enhanced Node B (“eNB”), a home eNB (“HeNB”), a gNB (for a New Radio [“NR”] technology system), or some other similar terminology.

The 3rd Generation Partnership Project (“3GPP”) is a group that, e.g., develops collaboration agreements such as 3GPP standards that aim to define globally applicable technical specifications and technical reports for wireless communication systems. Various 3GPP documents may describe certain aspects of radio access networks. Overall architecture for a fifth generation system, e.g., the 5G System, also called “NR” or “New Radio”, as well as “NG” or “Next Generation”, is shown inFIG.1, and is also described in 3GPP TS 38.300. The 5G NR network is comprised of NG RAN (Next Generation Radio Access Network) and 5GC (5G Core Network). As shown, NGRAN is comprised of gNBs (e.g., 5G Base stations) and ng-eNBs (i.e. LTE base stations). An Xn interface exists between gNB-gNB, between (gNB)-(ng-eNB) and between (ng-eNB)-(ng-eNB). The Xn is the network interface between NG-RAN nodes. Xn-U stands for Xn User Plane interface and Xn-C stands for Xn Control Plane interface. An NG interface exists between 5GC and the base stations (i.e. gNB & ng-eNB). A gNB node provides NR user plane and control plane protocol terminations towards the UE, and is connected via the NG interface to the 5GC. The 5G NR (New Radio) gNB is connected to AMF (Access and Mobility Management Function) and UPF (User Plane Function) in 5GC (5G Core Network).

In typical cellular mobile communication systems, handover (HO) procedures are adopted to manage the mobility of a wireless terminal (e.g. User Equipment, UE). In general, there are two types of handovers: (1) make after break and (2) make before break. In make after break HO, a connection between a wireless terminal and a current (source) base station is temporarily disconnected before establishing a new connection between the wireless terminal and a target base station. In contrast, in make before break HO the new connection is prepared before breaking the connection with the current base station.

3GPP has completed the basic feature for new radio (NR) systems in Release 15 specification. 3GPP Release 15 describes only basic handover, i.e., make after break. The basic make after break handover described in 3GPP Release 15 is mainly based on LTE handover mechanism in which the network controls UE mobility based on UE measurement reporting. In the basic make after break handover described in 3GPP Release 15, similar to LTE, a source gNB triggers handover by sending a HO request to target gNB. After receiving an acknowledgement, ACK, from the target gNB, the source gNB initiates handover by sending a HO command to the UE, the HO command including the target cell configuration. The UE then performs an initial access to the target cell in order to establish a connection with the with target cell.

In 3GPP Release 16, standardization of several HO improvements is ongoing. Conditional handover (CHO) is one of such 3GPP Release 16 improvement aimed for increasing reliability and robustness of handovers. In CHO, the gNB of the source cell provides CHO configuration parameters including candidate target cells and triggering conditions to the UE in RRC_CONNECTED state. After receipt of the CHO configuration parameters, the UE may perform measurements of radio signals from the source cell as well as the candidate target cells, and may autonomously initiate a handover to one of the candidate cells whose triggering conditions are met.

What is needed, therefore, are apparatus, methods, and procedures to efficiently and effectively implement conditional handover to a secondary cell group (SCG).

SUMMARY OF INVENTION

In one example, a wireless terminal comprising: processor circuitry configured to establish, using a first Access Stratum (AS) master key, a first security context on a first radio connection with a master access node; receiver circuitry configured to receive a re-configuration message comprising one or more conditional secondary cell group (SCG) configurations and at least one counter, each conditional SCG configuration comprising an identity of a candidate target primary cell of SCG (PSCell) and at least one triggering condition, the candidate target PSCell being used for Dual-Connectivity (DC), the at least one counter and the first AS master key being used for derivation of a second AS master key to be used for establishment of a second security context with a candidate target PSCell comprised in one of the one or more conditional SCG configurations; and the processor circuitry further configured to store the one or more conditional SCG configurations, wherein: the stored one or more conditional secondary cell configurations are released upon a change of the first AS master key.

In one example, a method for a wireless terminal comprising: establishing, using a first Access Stratum (AS) master key, a first security context on a first radio connection with a master access node; receiving a re-configuration message comprising one or more conditional secondary cell group (SCG) configurations and at least one counter, each conditional SCG configuration comprising an identity of a candidate target primary cell of SCG (PSCell) and at least one triggering condition, the candidate target PSCell being used for Dual-Connectivity (DC), the at least one counter and the first AS master key being used for derivation of a second AS master key to be used for establishment of a second security context with one of a candidate target PSCell comprised in one of the one or more conditional SCG configurations; and storing the one or more conditional SCG configurations wherein: the stored one or more conditional SCG configurations are released upon a change of the first AS master key.

In one example, an access node comprising: processor circuitry configured to establish, using a first Access Stratum (AS) master key, a first security context on a first radio connection with a wireless terminal; transmitter circuitry configured to transmit a re-configuration message comprising one or more conditional secondary cell group (SCG) configurations and at least one counter, each conditional SCG configuration comprising an identity of a candidate target primary cell of SCG (PSCell) and at least one triggering condition, the candidate target PSCell being used for Dual-Connectivity (DC), the at least one counter and the first AS master key being used for derivation of a second AS master key to be used for establishment of a second security context with a candidate target PSCell comprised in one of the one or more conditional SCG configurations; wherein: the one or more conditional SCG configurations are released upon a change of the first master key.

In one example, a method for an access node comprising: establishing, using a first Access Stratum (AS) master key, a first security context on a first radio connection with a wireless terminal; transmitting a re-configuration message comprising one or more conditional secondary cell group (SCG) configurations and at least one counter, each conditional SCG configuration comprising an identity of a candidate target primary cell for SCG (PSCell) and at least one triggering condition, the candidate target PSCell being used for Dual-Connectivity (DC), the at least one counter and the first master key being used for derivation of a second AS master key to be used for establishment of a second security context with a candidate target PSCell comprised in one of the one or more conditional SCG configurations; wherein: the one or more conditional SCG configurations are released upon a change of the first AS master key.

DESCRIPTION OF EMBODIMENTS

The foregoing and other objects, features, and advantages of the technology disclosed herein will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the technology disclosed herein.

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the technology disclosed herein. However, it will be apparent to those skilled in the art that the technology disclosed herein may be practiced in other embodiments that depart from these specific details. That is, those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the technology disclosed herein and are included within its spirit and scope. In some instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the technology disclosed herein with unnecessary detail. All statements herein reciting principles, aspects, and embodiments of the technology disclosed herein, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

As used herein, the term “core network” can refer to a device, group of devices, or sub-system in a telecommunication network that provides services to users of the telecommunications network. Examples of services provided by a core network include aggregation, authentication, call switching, service invocation, gateways to other networks, etc.

As used herein, the term “wireless terminal” can refer to any electronic device used to communicate voice and/or data via a telecommunications system, such as (but not limited to) a cellular network. Other terminology used to refer to wireless terminals and non-limiting examples of such devices can include user equipment terminal, UE, mobile station, mobile device, access terminal, subscriber station, mobile terminal, remote station, user terminal, terminal, subscriber unit, cellular phones, smart phones, personal digital assistants (“PDAs”), laptop computers, tablets, netbooks, e-readers, wireless modems, etc.

As used herein, the term “access node”, “node”, or “base station” can refer to any device or group of devices that facilitates wireless communication or otherwise provides an interface between a wireless terminal and a telecommunications system. A non-limiting example of a base station can include, in the 3GPP specification, a Node B (“NB”), an enhanced Node B (“eNB”), a home eNB (“HeNB”), a gNB (for a New Radio [“NR”] technology system), or some other similar terminology.

As used herein, the term “telecommunication system” or “communications system” can refer to any network of devices used to transmit information. A non-limiting example of a telecommunication system is a cellular network or other wireless communication system.

As used herein, the term “cellular network” or “cellular radio access network” can refer to a network distributed over cells, each cell served by at least one fixed-location transceiver, such as a base station. A “cell” may be any communication channel that is specified by standardization or regulatory bodies to be used for International Mobile Telecommunications-Advanced (“IMTAdvanced”). All or a subset of the cell may be adopted by 3GPP as licensed bands (e.g., frequency band) to be used for communication between a base station, such as a Node B, and a UE terminal. A cellular network using licensed frequency bands can include configured cells. Configured cells can include cells of which a UE terminal is aware and in which it is allowed by a base station to transmit or receive information. Examples of cellular radio access networks include E-UTRAN, and any successors thereof (e.g., NUTRAN).

Any reference to a “resource” herein means “radio resource” unless otherwise clear from the context that another meaning is intended. In general, as used herein a radio resource (“resource”) is a time-frequency unit that can carry information across a radio interface, e.g., either signal information or data information. An example of a radio resource occurs in the context of a “frame” of information that is typically formatted and prepared, e.g., by a node. A frame, which may have both downlink portion(s) and uplink portion(s), is communicated between the base station and the wireless terminal. Each frame may comprise plural subframes, and a subframe may be divided into slots. The transmitted signal in each slot is described by a resource grid comprised of resource elements (RE). Each column of the two dimensional grid represents a symbol (e.g., an OFDM symbol on downlink (DL) from node to wireless terminal; an SC-FDMA symbol in an uplink (UL) frame from wireless terminal to node). Each row of the grid represents a subcarrier. A resource element (RE) is the smallest time-frequency unit for downlink transmission in the subframe. That is, one symbol on one sub-carrier in the sub-frame comprises a resource element (RE) which is uniquely defined by an index pair (k,l) in a slot (where k and l are the indices in the frequency and time domain, respectively). In other words, one symbol on one sub-carrier is a resource element (RE). Each symbol comprises a number of sub-carriers in the frequency domain, depending on the channel bandwidth and configuration. The smallest time-frequency resource supported by the standard today is a set of plural subcarriers and plural symbols (e.g., plural resource elements (RE)) and is called a resource block (RB). A resource block may comprise, for example, 84 resource elements, i.e., 12 subcarriers and 7 symbols, in case of normal cyclic prefix.

As described herein, both an access node and a wireless terminal may manage respective Radio Resource Control (RRC) state machines. The RRC state machines transition between several RRC states including RRC_IDLE, RRC_INACTIVE and RRC_CONNECTED.FIG.2depicts the state transition diagram of the RRC states. From the vantage point of a wireless terminal e.g., user equipment (UE), the RRC states may be briefly characterized as follows:RRC_IDLEA UE specific DRX (discontinuous reception) may be configured by upper layers;UE controlled mobility based on network configuration;The UE:Monitors a Paging channel;Performs neighboring cell measurements and cell (re-)selection;Acquires system information.RRC_INACTIVEA UE specific DRX may be configured by upper layers or by RRC layer;UE controlled mobility based on network configuration;The UE stores the Access Stratum (AS) context;The UE;Monitors a Paging channel;Performs neighboring cell measurements and cell (re-)selection;Performs RAN-based notification area updates when moving outside the RAN-based notification area;Acquires system information.RRC_CONNECTEDThe UE stores the AS context.Transfer of unicast data to/from UE.At lower layers, the UE may be configured with a UE specific DRX;Network controlled mobility, i.e. handover within NR and to/from E-UTRAN;The UEMonitors a Paging channel;Monitors control channels associated with the shared data channel to determine if data is scheduled for it;Provides channel quality and feedback information;Performs neighboring cell measurements and measurement reporting;Acquires system information.

FIG.3shows a procedure/scenario of a basic handover in a cellular communication system. During RRC_CONNECTED state, depicted by act3-0, as act3-1the wireless terminal, e.g., UE, may receive RRCReconfiguration message from the gNB of the current serving cell (source cell). The RRCReconfiguration message of act3-1may comprise configuration parameters (a) for radio signal measurements and (b) reporting of measurement results (measurement configuration). The RRCReconfiguration message of act3-1may be acknowledged with an RRCReconfigurationComplete message, as shown by act3-2. Thereafter, the UE may start measurements and, as shown by act3-3a, act3-3b, and act3-3i, may transmit the results of the measurements to the gNB of the source cell based on the configuration parameters which were received in the RRCReconfiguration message of act3-1. The configuration parameters may include radio resources (frequencies, sub-carrier spacing, etc.) for measurements and conditions to trigger reporting. Upon receiving one of the measurement reports of acts3-3x, as act3-4the gNB of the source cell may determine whether or not to handover the UE to another cell. For example, when the measurement report indicates that signal quality from a neighbor cell (Target cell inFIG.3) is better than the one from the source cell, the gNB of the source cell may initiate a handover to the target cell. As shown by act3-5, the gNB may then conduct a coordination procedure to the gNB of the target cell. After the coordination depicted by act3-5is completed, as shown by act3-6the gNB may send to the UE a RRCReconfiguration message. The RRCReconfiguration message of act3-6may include a command to handover to the target cell. Upon receiving RRCReconfiguration message of act3-6with the handover command, the UE may start an initial access to the target cell by sending Random Access Preamble as shown by act3-7. In response to it sending of the Random Access Preamble as shown by act3-7, the UE should receive a Random Access Response message as shown by act3-8. The handover procedure is then completed by the UE sending a RRCReconfigurationComplete message to the gNB of the target cell, as shown by act3-9.

In one configuration, the measurement configuration, which may be realized by the parameters of the RRCReconfiguration message of act3-1, may comprise the parameters which are illustrated inFIG.4as “measurement objects”, “reporting configurations”, “measurement identities”, “quantity configurations”, and “measurement gaps”, each of which are described below.1. Measurement objects: A list of objects on which the UE shall perform the measurements.For intra-frequency and inter-frequency measurements a measurement object (MO) indicates the frequency/time location and subcarrier spacing of reference signals to be measured. Associated with this measurement object, the network may configure a list of cell specific offsets, a list of ‘blacklisted’ cells and a list of ‘whitelisted’ cells. Blacklisted cells are not applicable in event evaluation or measurement reporting. Whitelisted cells are the only ones applicable in event evaluation or measurement reporting.The measObjectId of the MO which corresponds to each serving cell is indicated by servingCellMO within the serving cell configuration.For inter-RAT E-UTRA measurements a measurement object is a single E-UTRA carrier frequency. Associated with this E-UTRA carrier frequency, the network can configure a list of cell specific offsets, a list of ‘blacklisted’ cells and a list of ‘whitelisted’ cells. Blacklisted cells are not applicable in event evaluation or measurement reporting. Whitelisted cells are the only ones applicable in event evaluation or measurement reporting.2. Reporting configurations: A list of reporting configurations where there can be one or multiple reporting configurations per measurement object. Each reporting configuration may comprise the following:Reporting criterion: The criterion that triggers the UE to send a measurement report. This can either be periodical or a single event description.Reference Signal (RS) type: The RS that the UE uses for beam and cell measurement results (synchronization signal SS/Physical Broadcast Channel PBCH block or Channel State Information-Reference Signal CSI-RS).Reporting format: The quantities per cell and per beam that the UE includes in the measurement report, e.g. received signal received power, RSRP and other associated information such as the maximum number of cells and the maximum number beams per cell to report.3. Measurement identities: A list of measurement identities where each measurement identity links one measurement object with one reporting configuration. By configuring multiple measurement identities, it is possible to link more than one measurement object to the same reporting configuration, as well as to link more than one reporting configuration to the same measurement object. The measurement identity is also included in the measurement report that triggered the reporting, serving as a reference to the network.4. Quantity configurations: The quantity configuration defines the measurement filtering configuration used for all event evaluation and related reporting, and for periodical reporting of that measurement. For NR measurements, the network may configure up to 2 quantity configurations with a reference in the NR measurement object to the configuration that is to be used. In each configuration, different filter coefficients can be configured for different measurement quantities, for different RS types, and for measurements per cell and per beam.5. Measurement gaps: Periods that the UE may use to perform measurements.

A UE in RRC_CONNECTED state may maintain a measurement object list, a reporting configuration list, and a measurement identities list. The measurement object list may possibly include New Radio, NR, measurement object(s) and inter-RAT objects. Similarly, the reporting configuration list may include NR and inter-RAT reporting configurations. Any measurement object can be linked to any reporting configuration of the same RAT type. Some reporting configurations may not be linked to a measurement object. Likewise, some measurement objects may not be linked to a reporting configuration.

The measurement procedures may distinguish the three types of cells: the serving cell(s), the listed cell(s), and the detected cell(s). The listed cells are cells listed within the measurement object(s). The detected cells are cells that are not listed within the measurement object(s) but are detected by the UE on the synchronization signal block, SSB, frequency(ies) and subcarrier spacing(s) indicated by the measurement object(s).

For measurement object(s), the UE measures and reports on the serving cell(s), listed cells and/or detected cells. For inter-RAT measurements object(s) of E-UTRA, the UE measures and reports on listed cells and detected cells.

Listing 1 shows an example implementation of the measurement configuration, per 3GPP TS 38.331 v15.5.1.

Listing 2 shows an example procedure of measurement report triggering.

Listing 2Event A1:Serving becomes better than absolute threshold;Event A2:Serving becomes worse than absolute threshold;Event A3:Neighbour becomes amount of offset better than PCell/PSCell;Event A4:Neighbour becomes better than absolute threshold;Event A5:PCell/PSCell becomes worse than absolute threshold1 ANDNeighbour/SCell becomes better than another absolute threshold2;Event A6:Neighbour becomes amount of offset better than SCell.1>for each measId included in the measIdList within VarMeasConfig:2>if the corresponding reportConfig includes a reportType set to eventTriggeredor periodical:3>if the corresponding measObject concerns NR:4>if the eventA1 or eventA2 is configured in the correspondingreportConfig:5>consider only the serving cell to be applicable;4>if the eventA3 or eventA5 is configured in the correspondingreportConfig:5>if a serving cell is associated with a measObjectNR and neighbours areassociated with another measObjectNR, consider any serving cellassociated with the other measObjectNR to be a neighbouring cell as well;4>for measurement events other than eventA1 or eventA2:5>if useWhiteCellList is set to true:6> consider any neighbouring cell detected based on parametersin the associated measObjectNR to be applicable when the concernedcell is included in the whiteCellsToAddModList defined within theVarMeasConfig for this measId;5>else:6> consider any neighbouring cell detected based on parametersin the associated measObjectNR to be applicable when the concernedcell is not included in the blackCellsToAddModList defined within theVarMeasConfig for this measId;3>else if the corresponding measObject concerns E-UTRA:4>consider any neighbouring cell detected on the associated frequency tobe applicable when the concerned cell is not included in theblackCellsToAddModListEUTRAN defined within the VarMeasConfig forthis measId;2>else if the corresponding reportConfig includes a reportType set to reportCGI:3>consider the cell detected on the associated measObject which has aphysical cell identity matching the value of the cellForWhichToReportCGIincluded in the corresponding reportConfig within the VarMeasConfig to beapplicable;2>if the reportType is set to eventTriggered and if the entry condition applicablefor this event, i.e. the event corresponding with the eventId of the correspondingreportConfig within VarMeasConfig, is fulfilled for one or more applicable cells forall measurements after layer 3 filtering taken during timeToTrigger defined forthis event within the VarMeasConfig, while the VarMeasReportList does notinclude a measurement reporting entry for this measId (a first cell triggers theevent):3>include a measurement reporting entry within the VarMeasReportListfor this measId;3>set the numberOfReportsSent defined within the VarMeasReportListfor this measId to 0;3>include the concerned cell(s) in the cellsTriggeredList defined withinthe VarMeasReportList for this measId;3>initiate the measurement reporting procedure;2>else if the reportType is set to eventTriggered and if the entry conditionapplicable for this event, i.e. the event corresponding with the eventId of thecorresponding reportConfig within VarMeasConfig; is fulfilled for one or moreapplicable cells not included in the cellsTriggeredList for all measurements afterlayer 3 filtering taken during timeToTrigger defined for this event within theVarMeasConfig (a subsequent cell triggers the event):3>set the numberOfReportsSent defined within the VarMeasReportListfor this measId to 0;3>include the concerned cell(s) in the cellsTriggeredList defined withinthe VarMeasReportList for this measId;3>initiate the measurement reporting procedure;2>else if the reportType is set to eventTriggered and if the leaving conditionapplicable for this event is fulfilled for one or more of the cells included in thecellsTriggeredList defined within the VarMeasReportList for this measId for allmeasurements after layer 3 filtering taken during time To Trigger defined withinthe VarMeasConfigtor this event:3>remove the concerned cell(s) in the cellsTriggeredList defined withinthe VarMeasReportList for this measId;3>if reportOnLeave is set to true for the corresponding reportingconfiguration:4>initiate the measurement reporting procedure;3>if the cellsTriggeredList defined within the VarMeasReportList forthis measId is empty:4>remove the measurement reporting entry within theVarMeasReportList for this measId;4>stop the periodical reporting timer for this measId, if running;2>if reportType is set to periodical and if a (first) measurement result is available:3>include a measurement reporting entry within the VarMeasReportListfor this measId;3>set the numberOfReportsSent defined within the VarMeasReportListfor this measId to 0;3>if the reportAmount exceeds 1:4>initiate the measurement reporting procedure, as specified in 5.5.5,immediately after the quantity to be reported becomes available for the NRSpCell;3>else (i.e. the reportAmount is equal to 1):4>initiate the measurement reporting procedure, immediately after thequantity to be reported becomes available for the NR SpCell and for thestrongest cell among the applicable cells;2>upon expiry of the periodical reporting timer for this measId:3>initiate the measurement reporting procedure.2>if reportType is set to reportCGI:3>if the UE acquired the SIB1 or SystemInformationBlockType1 for therequested cell; or3>if the UE detects that the requested NR cell is not transmitting SIB1(see TS 38.213 [13], clause 13):4>stop timer T321;4>include a measurement reporting entry within the VarMeasReportListfor this measId;4>set the numberOfReportsSent defined within the VarMeasReportListfor this measId to 0;4>initiate the measurement reporting procedure;2>upon the expiry of T321 for this measId:3>include a measurement reporting entry within the VarMeasReportListfor this measId;3>set the numberOfReportsSent defined within the VarMeasReportListfor this measId to 0;3>initiate the measurement reporting procedure.

In the measurement reporting procedure described above, the UE may transmit the MeasurementReport message to the gNB of the serving cell (source cell). The MeasurementReport message may comprise measId that triggered the measurement reporting, measurement result(s) of serving cell(s), best neighboring cells, and/or cells that triggered reporting event(s), as illustrated by way of example inFIG.5. It should be noted that for event-driven (eventTriggered) reporting, there are two conditions: entry condition and leaving condition. The entry condition is met when a specific event occurs, whereas the leaving condition is met when the condition of the specific event no longer exists. In addition, a parameter for hysteresis may be involved in determining the entry/leaving conditions to avoid ping-pong effects. For example, for Event A1, the entry condition is met when the signal strength of the serving cell is better than a1-threshold+hysteresis, whereas the leaving condition is met when the signal strength is lower than a1-threshod−hysteresis. When the entry condition is met, the UE may generate and send MeasurementReport. On the other hand, when the leaving condition is met, whether or not to send MeasurementReport may depend on the parameter reportOnLeave associated with a concerned event.

Listing 3 shows an example implementation of a MeasurementReport.

Five basic example embodiments and modes of conditional handover configurations and techniques according to the technology disclosed herein are described below in general, non-limiting fashion.

1: Conditional Handover Configurations and Reporting

FIG.6shows an example communications system20wherein a source radio access node22communicates over air or radio interface24(e.g., Uu interface) with wireless terminal26. The source radio access node may also communication with a target radio access node28over an appropriate interface, such as either the radio interface24in the case of a backhaul configuration or Xninterface in the manner shown inFIG.1.

As mentioned above, the radio access node22may be any suitable node for communicating with the wireless terminal26, such as a base station node, gNodeB (“gNB”) or eNodeB (“eNB”), for example. For sake of simplicity, the source radio access node22may herein briefly be referred to as the source node22, or source gNodeB22, or source gNB22. Similarly, the target radio access node28may herein briefly be referred to as the target node28, or target gNodeB28, or target gNB28.

The source gNodeB22comprises node processor circuitry (“node processor30”) and node transceiver circuitry32. The node transceiver circuitry32typically comprises node transmitter circuitry34and node receiver circuitry36, which are also called node transmitter and node receiver, respectively. In addition, source gNodeB22may comprise inter-node interface circuitry38for communicating with target gNodeB28. Although not shown as such, it should be understood that he target gNodeB28may similarly have its own node processor30, node transceiver circuitry32, and inter-node interface circuitry38.

The wireless terminal26comprises terminal processor40and terminal transceiver circuitry42. The terminal transceiver circuitry42typically comprises terminal transmitter circuitry44and terminal receiver circuitry46, which are also called terminal transmitter44and terminal receiver46, respectively. The wireless terminal26also typically comprises user interface48. The terminal user interface48may serve for both user input and output operations, and may comprise (for example) a screen such as a touch screen that can both display information to the user and receive information entered by the user. The user interface48may also include other types of devices, such as a speaker, a microphone, or a haptic feedback device, for example.

For both the radio access node22and radio interface24, the respective transceiver circuitries22include antenna(s). The respective transmitter circuits36and46may comprise, e.g., amplifier(s), modulation circuitry and other conventional transmission equipment. The respective receiver circuits34and44may comprise, e.g., amplifiers, demodulation circuitry, and other conventional receiver equipment.

In general operation, source gNodeB22and wireless terminal26communicate with each other across radio interface24using predefined configurations of information. By way of non-limiting example, the source gNodeB22and wireless terminal26may communicate over radio interface24using “frames” of information that may be configured to include various channels. For example, a frame, which may have both downlink portion(s) and uplink portion(s), may comprise plural subframes, with each subframe in turn being divided into slots. The frame may be conceptualized as a resource grid (a two dimensional grid) comprised of resource elements (RE). Each column of the two dimensional grid represents a symbol (e.g., an OFDM symbol on downlink (DL) from node to wireless terminal; an SC-FDMA symbol in an uplink (UL) frame from wireless terminal to node). Each row of the grid represents a subcarrier. The frame and subframe structure serves only as an example of a technique of formatting of information that is to be transmitted over a radio or air interface. It should be understood that “frame” and “subframe” may be utilized interchangeably or may include or be realized by other units of information formatting, and as such may bear other terminology (such as blocks, for example).

To cater to the transmission of information between source gNodeB22and wireless terminal26over radio interface24, the node processor30and terminal processor40ofFIG.6are shown as comprising respective information handlers. For an example implementation in which the information is communicated via frames, the information handler for source gNodeB22is shown as node frame/signal scheduler/handler50, while the information handler for wireless terminal26is shown as terminal frame/signal handler52.

The node processor30of source gNodeB22also includes message generator54, RRC state machine56, and handover controller60. The RRC state machine56may operate in a manner understood fromFIG.2, and may interact with message generator54for the generation of RRC messages such as RRCReconfiguration messages, for example. The handover controller60may comprise measurement analyzer62, conditional handover (CHO) determination unit64, and conditional handover configuration information generator66.

The terminal processor40of wireless terminal26also includes message processor70, handover unit72, and measurement controller80. The measurement controller80in turn further comprises measurement initiation unit82; measurement results unit84; and measurement report control unit86.

FIG.7illustrates an example scenario in which the communications system ofFIG.6may execute a conditional handover. Some acts ofFIG.7which are similar to those ofFIG.3have similar suffixed act numbers, for example, act7-0, like act2-0shows that the UE is in RRC_CONNECTED state. Similarly, act7-1, like act3-1, shows that the wireless terminal26may be configured by the gNB22of the serving cell (source cell) with the measurement configuration. The measurement configuration of act7-1may be similar to the measurement configuration of Listing 1. Based on the measurement configuration received in act7-1, the wireless terminal26may send measurement reports7-3. The timing of the measurements made by wireless terminal26may be governed by measurement initiation unit82, the measurement results analysed by measurement results unit84, and the measurement reports may be generated by86. The measurement reports may be similar to the example implementation shown in Listing 3. Example logic for triggering the decision of act7-4, e.g., a procedure for measurement report triggering, may be understood with reference to Listing 1.

FIG.7further shows that, in this particular scenario, as act7-4the gNB22makes a decision to send the conditional handover (CHO) configuration to the wireless terminal26. The decision of act7-4, which may be made by conditional handover (CHO) determination unit64, is triggered by the measurement result(s) of the target cell, i.e., a measurement report7-3, as assessed by measurement analyzer62. Act7-5shows a handover coordination procedure which is performed after the decision of act7-4. The handover coordination procedure of act7-5is performed to prepare both source gNodeB22and target gNodeB28for the possibility of the handover. The communications involved in the handover coordination procedure of act7-5may be transmitted over the inter-node interface34.

In one example implementation, after the handover decision of act7-4and the handover coordination procedure of act7-5, as shown by act7-6a message may be sent to wireless terminal26to carry the conditional handover CHO configuration information. The conditional handover configuration information for the message of act7-6may be generated by conditional handover configuration information generator66. In one example implementation the message of act7-6may be an RRCReconfiguration message. In another example implementation (not illustrated), another suitable message (e.g., RRCCHOConfiguration) may be used to send the conditional handover configuration information. Upon successful receipt of the message of act7-6, i.e., the message that includes and sends the conditional handover configuration information to wireless terminal26, a response or acknowledgement message is returned to source gNodeB22as shown by act7-6′.

In an example implementation, the message used for act7-6, e.g., the message that includes the CHO configuration information, may comprise the following parameters:Identification(s) of candidate target cell(s)Event(s) to trigger execution of CHORACH configuration(s) of the candidate target cell(s)UL/DL configuration(s) of the candidate target cell(s)New UE identity(ies) (e.g. RNTI) to be used for the candidate target cell(s).

FIG.8generically shows various general information elements or types of information that may be included in the conditional handover configuration message of act7-6, including but not limited to: reference signal type (e.g. SSB or CSI-RS); identifier(s) of candidate target nodes; handover conditions; measurement instructions; periodic values for periodic reporting, and leaving conditions. The last three aforementioned information elements may be optional and may be discussed in conjunction with other example embodiments and modes.

Listing 4 shows an information element CHOConfig, which is an example implementation of an information element (IE) to be included in the message of act7-6which is used for the CHO configuration. In this example implementation, the condition(s) to trigger measurement report (EventTriggerConfigCHO) may be configured separately from the conditions included in measConfig (EventTriggerConfig).

After receiving the CHO configuration in the message of act7-6ofFIG.7, the wireless terminal26could, as in previous practice, continue the measurement procedure based on the measurement configuration received earlier, e.g., the measurement configuration received in act7-1before the handover decision of act7-4. The earlier measurement configuration, e.g., the pre-conditional measurement configuration information, may include a measurement object that includes the measurement parameters covering the candidate target cell(s). Additionally, the measurement object of the pre-conditional measurement configuration information may also include the candidate target cell(s) in the whitelisted cells. In such a case, the measurement object could trigger a measurement report based on the associated (linked) report configuration. However, the serving cell, e.g., source gNodeB22, has already negotiated with each of the candidate target cell(s), and the wireless terminal26is allowed to autonomously execute a handover to one of the candidate target cell(s) as long as the CHO configuration remains valid. Therefore, once the CHO configuration is provided in the message of act7-5, it may be wasteful to send a measurement report with regard to any of the candidate target cell(s).

In view of the foregoing, as one of its features and advantages, the wireless terminal26ofFIG.6may suppress measurement reports with regard to a candidate target cell included in the CHO configuration, when the measurement result of the signal from the candidate target cell satisfies the reporting condition specified in the corresponding reporting configuration. In other words, the wireless terminal26may transmit a measurement report when the measurement results available in the UE include the result(s) from cell(s) other than the one(s) configured as candidate target cell(s). Accordingly, the measurement report control unit86of wireless terminal26is labeled as a measurement report control unit86which may suppress the reporting of measurements for candidate target gNodeBs.

To reflect the foregoing,FIG.7shows as act7-3′ the wireless terminal26sending a measurement report which is based on the conditional handover configuration. For example, assume that one measurement object is linked to an event-triggered reporting configuration. If the measurement with regard to this measurement object results in finding a cell that meets the triggering condition in the reporting configuration, the wireless terminal26ofFIG.6may send a measurement report if the identification of the found cell (e.g. physical cell ID) is for none of the candidate target cell(s) in the CHO configuration. Otherwise the UE may determine not to send the measurement report. If measurement results for cells other than the candidate target cell(s) are available, the wireless terminal26may be allowed to include in the measurement report the results from the candidate target cell(s) along with the results from the cells other than the candidate target cells.

Act7-4′ shows that the wireless terminal26may make a determination that the conditional handover conditions of the conditional handover configuration information are satisfied, and that a handover to a candidate target gNodeB28should occur. The determination of act7-4′ may be made by handover unit72of wireless terminal26. Thereafter, the wireless terminal26may seek access to target gNodeB28by engaging in a random access procedure, as shown by act7-7and act7-8. Act7-7comprises wireless terminal26sending a Random Access Preamble to target gNodeB28. Upon successful receipt and recognition by target gNodeB28of the Random Access Preamble of act7-7, the wireless terminal26should receive a Random Access Response message as shown by act7-8. The handover procedure is then completed by the wireless terminal26sending an RRCReconfigurationComplete message to the target gNodeB28, as shown by act7-9.

The source gNodeB22ofFIG.6thus provides wireless terminal26with conditional handover configuration information which the wireless terminal26may use for controlling generation and/or content of measurement reports. Example, representative, basic acts performed by source gNodeB22ofFIG.6are shown inFIG.9. Act9-1comprises receiving a measurement report from a wireless terminal. The measurement report of act9-1may be a report message such as message7-3ofFIG.7. Act9-2comprises making a determination for reconfiguring the wireless terminal based on the measurement report. The determination of act9-2may be made by conditional handover (CHO) determination unit64of source gNodeB22, and may further be reflected by act7-4ofFIG.7. Act9-3comprises transmitting to the wireless terminal a configuration message to configure a conditional handover, the configuration message being configured for use by the wireless terminal in making a decision regarding transmission of a wireless terminal measurement report to the source gNodeB22.

Example, representative, basic acts performed by wireless terminal26ofFIG.6are shown inFIG.10. Act10-1comprises receiving from the wireless access node a configuration message to configure a conditional handover. The conditional handover configuration message of act10-1may be the message of act7-5as described above. Act10-2comprises the wireless terminal26performing a measurement. The measurement may be initiated by measurement initiation unit82of wireless terminal26. Act10-3comprises the wireless terminal26making a decision, based on the configuration message of act10-2, to send a measurement report including the measurement result. Act10-4comprises transmitting the measurement report to source gNodeB22.

Listing 5 is an example procedure of measurement report triggering, based on Listing 2 with revisions for supporting the embodiment and mode ofFIG.6andFIG.7marked as bold text.

Listing 51>for each measId included in the measIdList within VarMeasConfig:2>if the corresponding reportConfig includes a reportType set to eventTriggeredor periodical:3>if the corresponding measObject concerns NR:4>if the eventA1 or eventA2 is configured in the correspondingreportConfig:5>consider only the serving cell to be applicable;4>if the eventA3 or eventA5 is configured in the correspondingreportConfig:5>if a serving cell is associated with a measObjectNR and neighbours areassociated with another measObjectNR consider any serving cellassociated with the other measObjectNR to be a neighbouring cell as well;4>for measurement events other than eventA1 or eventA2:5>if use WhiteCellList is set to true:6>consider any neighbouring cell detected based on parametersin the associated measObjectNR to be applicable when the concernedcell is included in the whiteCellsToAddModList defined within theVarMeasConfig for this measId;5>else:6>consider any neighbouring cell detected based on parametersin the associated measObjectNR to be applicable when the concernedcell is not included in the blackCellsToAddModList defined within theVarMeasConfig for this measId;3>else if the corresponding measObject concerns E-UTRA:4>consider any neighbouring cell detected on the associatedfrequency to be applicable when the concerned cell is not includedin the blackCellsToAddModListEUTRAN defined within theVarMeasConfig for this measId;2>else if the corresponding report Config includes a reportType set to reportCGI:3>consider the cell detected on the associated measObject which has aphysical cell identity matching the value of the cellForWhichToReportCGIincluded in the corresponding reportConfig within the VarMeasConfig tobe applicable;2>if the reportType is set to eventTriggered if the entry condition applicablefor this event, i.e. the event corresponding with the eventId of the thecorresponding reportConfig within VarMeasConfig, is fulfilled for one or moreapplicable cells for all measurements after layer 3 filtering taken duringtimeToTrigger defined for this event within the VarMeasConfig, while theVarMeasReportList does not include a measurement reporting entry for thismeasId (a first cell triggers the event):3>include a measurement reporting entry within the VarMeasReportList forthis measId;3>set the numberOfReportsSent defined within the VarMeasReportList forthis measId to 0;3>include the concerned cell(s) in the cellsTriggeredList defined within theVarMeasReportList for this measId;3> if cellsTriggeredList includes cells other than the candidate target cell(s)configured by CHOConfig;4>initiate the measurement reporting procedure;2>else if the reportType is set to eventTriggered and if the entry conditionapplicable for this event, i.e. the event corresponding with the eventId of thecorresponding reportConfig within VarMeasConfig; is fulfilled for one or moreapplicable cells not included in the cellsTriggeredList for all measurementsafter layer 3 filtering taken during timeToTrigger defined for this eventwithin the VarMeasConfig (a subsequent cell triggers the event):3>set the numberOfReportsSent defined within the VarMeasReportList forthis measId to 0;3>include the concerned cell(s) in the cellsTriggeredList defined within theVarMeasReportList for this measId;3> if cellsTriggeredList includes cells other than the candidate target cell(s)configured by CHOConfig;4>initiate the measurement reporting procedure;2>else if the reportType is set to eventTriggered and if the leaving conditionapplicable for this event is fulfilled for one or more of the cells included in thecellsTriggeredList defined within the VarMeasReportList for this measId forall measurements after layer 3 filtering taken during timeToTrigger definedwithin the VarMeasConfig for this event:3>remove the concerned cell(s) in the cellsTriggeredList defined within theVarMeasReportList for this measId;3>if reportOnLeave is set to true for the corresponding reportingconfiguration:4>initiate the measurement reporting procedure;3>if the cellsTriggeredList defined within the VarMeasReportList for thismeasId is empty:4>remove the measurement reporting entry within theVarMeasReportList for this measId;4>stop the periodical reporting timer for this measId, if running;2>if reportType is set to periodical and if a (first) measurement result isavailable:3>include a measurement reporting entry within the VarMeasReportList forthis measId;3>set the numberOfReportsSent defined within the VarMeasReportList forthis measId to 0;3>if the reportAmount exceeds 1:4>initiate the measurement reporting procedure, as specified in5.5.5, immediately after the quantity to be reported becomesavailable for the NR SpCell;3>else (i.e. the reportAmount is equal to 1):4>initiate the measurement reporting procedure, immediately afterthe quantity to be reported becomes available for the NR SpCelland for the strongest cell among the applicable cells;2>upon expiry of the periodical reporting timer for this measId:3>initiate the measurement reporting procedure.2>if reportType is set to reportCGI:3>if the UE acquired the SIB1 or SystemInformationBlockType1 for therequested cell; or3>if the UE detects that the requested NR cell is not transmitting SIB1 (seeTS 38.213 [13], clause 13):4>stop timer T321;4>include a measurement reporting entry within theVarMeasReportList for this measId;4>set the numberOfReportsSent defined within theVarMeasReportList for this measId to 0;4>initiate the measurement reporting procedure;2>upon the expiry of T321 for this measId:3>include a measurement reporting entry within the VarMeasReportList forthis measId;3>set the numberOfReportsSent defined within the VarMeasReportList forthis measId to 0;3>initiate the measurement reporting procedure.
2: Measurement Reporting after Conditional Handover Configuration

In the example embodiment and mode ofFIG.11, the wireless terminal26may be permitted to periodically transmit a measurement report for the configured candidate target cell(s). One reason for permitting the wireless terminal26to transmit a measurement report on a periodic basis is that the source cell, the serving cell of source gNodeB22, may use this measurement report to determine whether or not to release the CHO configuration. Since each of the candidate target cell(s), such as target gNodeB28, reserves radio resources for a potential CHO, the radio access network may not desire to maintain the reserved resources forever. Therefore, the radio access network may force the wireless terminal26to continue reporting the measurement results of the candidate target cells.

The source gNodeB22, wireless terminal26, and node processor30of the communications system20ofFIG.11are similar to those ofFIG.6, with like units and functionalities having like reference numbers. As shown inFIG.11, the source gNodeB22comprises node processor circuitry (“node processor30”) and node transceiver circuitry32, with node transceiver circuitry32comprising node transmitter34and node receiver36. The node processor30comprises node frame/signal scheduler/handler50, message generator54, RRC state machine56, and handover controller60, with the handover controller60in turn comprising measurement analyzer62, conditional handover (CHO) determination unit64, and conditional handover configuration information generator66(11). A difference between the example embodiment ofFIG.6and the example embodiment and mode ofFIG.11is that the conditional handover configuration information generator66(11) includes in the conditional handover configuration information a conditional handover instruction which, rather than suppressing the reporting of measurements for candidate target gNodeBs, instead permits periodic reporting of the measurements for candidate target gNodeBs. The instruction of the conditional handover configuration information that permits the periodic reporting of the measurement results for the candidate target gNodeBs may be included in the “measurements instruction” information element, shown as the fourth information element of the conditional handover configuration message ofFIG.8, for example. Moreover, a value of the periodicity for the permitted reporting of the measurement results for the candidate target gNodeBs may be included in the “periodic value” information element, shown as the fifth information element of the conditional handover configuration message ofFIG.8, for example.

As in theFIG.6example embodiment and mode, the wireless terminal26of the example embodiment and mode ofFIG.11comprises terminal processor40and terminal transceiver circuitry42, with terminal transceiver circuitry42in turn comprising terminal transmitter44and terminal receiver46. The terminal processor40comprises terminal frame/signal handler52, message processor70, handover unit72, and measurement controller80, with the measurement controller80in turn comprising measurement initiation unit82, measurement results unit84, and measurement report control unit86. Since, in the example embodiment and mode ofFIG.11, the wireless terminal26is permitted to periodically transmit the measurement results for a candidate target gNodeB, the measurement report control unit86ofFIG.11is labeled for periodic candidate reporting.

FIG.12illustrates an example scenario of the example embodiment and mode ofFIG.11, wherein after receiving the CHO configuration the wireless terminal26may periodically transmit the measurement report including the measurement results of some or all of the candidate target cell(s). The acts ofFIG.12which are similar to those ofFIG.7have similar suffixes, e.g., act12-0ofFIG.12is similar to act7-0ofFIG.7, act12-1ofFIG.12is similar to act7-1ofFIG.7, and so forth. A difference in the example embodiment and mode ofFIG.11andFIG.12is that, after the conditional handover coordination of act12-5, periodic reporting of measurement results for the candidate target gNodeB(s) is permitted. For example,FIG.12shows that the reporting of measurement results for the candidate target gNodeB(s) does not occur in the first two measurement reporting messages12-3′-11(1) and12-3′-11(2), but does occur in the third measurement reporting message12-3′-11(3).

In the example situation shown inFIG.12, it may occur as a result of the third measurement reporting message12-3′-11(3) that as act12-10the network, e.g., source gNodeB22, determines that the conditional handover configuration, which resulted from the conditional handover decision of act12-4, should be released. Such determination may be made by conditional handover (CHO) determination unit64, for example. After the conditional handover release decision of act12-10, as act12-11the source gNodeB22may engage in a handover release operation with target gNodeB28, as reflected by act12-11. In other words, as act12-10the source cell22may decide to release the CHO configuration, and in accordance with such decision may as act12-11negotiate with the candidate target cell(s), such as target gNodeB28, to release the reserved resources. Thereafter as act12-12the source gNodeB22may send a conditional handover de-configuration message to the wireless terminal26. Upon successful receipt of the conditional handover de-configuration message, as act12-13the wireless terminal26replies to source gNodeB22with a RRCReconfigurationComplete message.

The source gNodeB22ofFIG.11thus permits the wireless terminal26to periodically report measurement results for the candidate target gNodeB(s). Example, representative, basic acts performed by source gNodeB22ofFIG.11are shown inFIG.13. Act13-1comprises receiving a measurement report from a wireless terminal. Act13-2comprises making a determination for reconfiguring the wireless terminal based on the measurement report. The determination of act13-2may be made by conditional handover (CHO) determination unit64of source gNodeB22, and may further be reflected by act12-4ofFIG.12. Act13-3comprises transmitting to the wireless terminal a configuration message to configure a conditional handover, the configuration message being configured to permit periodic reporting of measurement results for a candidate target gNodeB(s).

Example, representative, basic acts performed by wireless terminal26ofFIG.11are shown inFIG.14. Act14-1comprises receiving from the wireless access node a configuration message to configure a conditional handover. The conditional handover configuration message of act14-1may be the message of act12-6as described above. Act14-2comprises the wireless terminal26performing a measurement. The measurement may be initiated by measurement initiation unit82of wireless terminal26. Act14-3comprises the wireless terminal26making a decision, based on the configuration message of act14-2and permitted periodicity, to send a measurement report including the measurement result. Act14-4comprises transmitting the measurement report to source gNodeB22.

In one example implementation, the CHO configuration may indicate if the wireless terminal26is required to transmit the measurement report for some or all of the candidate target cell(s), and the periodicity of the reporting. Listing 6 shows an example format of the CHO configuration based on Listing 4, where an optional field reportPeriodicity, configured separately from the reporting configuration, indicates the periodicity of the reporting of the concerned target cell(s). The presence of this optional field may indicate that the UE is forced to periodically transmit the measurement report, whereas the absence of this field may indicate that the UE should suppress the measurement report as disclosed in the first example embodiment and mode. The reportPeriodicity field may correspond to the period value information element shown inFIG.8.

Listing 7 is an example procedure of measurement report triggering, based on Listing 2 with revisions for supporting the present embodiment marked as bold text.

Listing 71>for each measId included in the measIdList within VarMeasConfig:2>if the corresponding reportConfig includes a reportType set to eventTriggeredor periodical:3>if the corresponding measObject concerns NR:4>if the eventA1 or eventA2 is configured in the correspondingreportConfig:5>consider only the serving cell to be applicable;4>if the eventA3 or eventA5 is configured in the correspondingreportConfig;5>if a serving cell is associated with a measObjectNR and neighbours areassociated with another measObjectNR, consider any serving cellassociated with the other measObjectNR to be a neighbouring cell as well;4>for measurement events other than eventA1 or eventA2:5>if useWhiteCellList is set to true:6>consider any neighbouring cell detected based on parametersin the associated measObjectNR to be applicable when the concernedcell is included in the whiteCellsToAddModList defined within theVarMeasConfig for this measId;5>else:6>consider any neighbouring cell detected based on parametersin the associated measObjectNR to be applicable when the concernedcell is not included in the blackCellsToAddModList defined within theVarMeasConfig for this measId;3>else if the corresponding measObject concerns E-UTRA:4>consider any neighbouring cell detected on the associatedfrequency to be applicable when the concerned cell is not includedin the blackCellsToAddModListEUTRAN defined within theVarMeasConfig for this measId;2>else if the corresponding report Config includes a reportType set to reportCGI:3>consider the cell detected on the associated measObject which has aphysical cell identity matching the value of the cellForWhichToReportCGIincluded in the corresponding reportConfig within the VarMeasConfig tobe applicable;2>if the reportType is set to eventTriggered and if the entry condition applicablefor this event, i.e. the event corresponding with the eventId of thecorresponding reportConfig within VarMeasConfig, is fulfilled for one or moreapplicable cells for all measurements after layer 3 filtering taken duringtimeToTrigger defined for this event within the VarMeasConfig, while theVarMeasReportList does not include a measurement reporting entry for thismeasId (a first cell triggers the event):3>include a measurement reporting entry within the VarMeasReportList forthis measId;3>set the numberOfReportsSent defined within the VarMeasReportList forthis measId to 0;3>include the concerned cell(s) in the cellsTriggeredList defined within theVarMeasReportList for this measId;3>initiate the measurement reporting procedure;2>else if the reportType is set to eventTriggered and if the entry conditionapplicable for this event, i.e. the event corresponding with the eventId of thecorresponding reportConfig within VarMeasConfig, is fulfilled for one or moreapplicable cells not included in the cellsTriggeredList for all measurementsafter layer 3 filtering taken during timeToTrigger defined for this eventwithin the VarMeasConfig (a subsequent cell triggers the event):3>set the numberOfReportsSent defined within the VarMeasReportList forthis measId to 0;3>include the concerned cell(s) in the cellsTriggeredList defined within theVarMeasReportList for this measId;4>initiate the measurement reporting procedure;2>else if the reportType is set to eventTriggered and if the leaving conditionapplicable for this event is fulfilled for one or more of the cells included in thecellsTriggeredList defined within the VarMeasReportList for this measId forall measurements after layer 3 filtering taken during timeToTrigger definedwithin the VarMeasConfig for this event:3>remove the concerned cell(s) in the cellsTriggeredList defined within theVarMeasReportList for this measId;3>if reportOnLeave is set to true for the corresponding reportingconfiguration:4>initiate the measurement reporting procedure;3>if the cellsTriggeredList defined within the VarMeasReportList for thismeasId is empty:4>remove the measurement reporting entry within theVarMeasReportList for this measId;4>stop the periodical reporting timer for this measId, if running;2>if reportType is set to periodical and if a (first) measurement result isavailable,or:2>if a measurement result is available for one of the candidate target cell(s)configured by CHOConfig, and reportPeriodicity is included in CHOConfig:3>include a measurement reporting entry within the VarMeasReportList forthis measId;3>set the numberOfReportsSent defined within the VarMeasReportList forthis measId to 0;3>if the reportAmount exceeds 1:4>initiate the measurement reporting procedure, as specified in5.5.5, immediately after the quantity to be reported becomesavailable for the NR SpCell;3>else (i.e. the reportAmount is equal to 1):4>initiate the measurement reporting procedure, immediately afterthe quantity to be reported becomes available for the NR SpCelland for the strongest cell among the applicable cells;2>upon expiry of the periodical reporting timer for this measId,or:2>upon expiry ofreportPeriodicity included in CHOConfig:3>initiate the measurement reporting procedure.2>if reportType is set to reportCGI:3>if the UE acquired the SIB1 or SystemInformationBlockType1 for therequested cell; or3>if the UE detects that the requested NR cell is not transmitting SIB1 (seeTS 38.213 [13], clause 13):4>stop timer T321;4>include a measurement reporting entry within theVarMeasReportList for this measId;4>set the numberOfReportsSent defined within theVarMeasReportList for this measId to 0;4>initiate the measurement reporting procedure;2>upon the expiry of T321 for this measId:3>include a measurement reporting entry within the VarMeasReportList forthis measId;3>set the numberOfReportsSent defined within the VarMeasReportList forthis measId to 0;3>initiate the measurement reporting procedure.

In another example implementation, the indication in the CHO configuration indicating if the wireless terminal26is required to transmit the measurement report for some or all of the candidate target cell(s) may be a Boolean type field (or a present/absence type field), associated with no designated periodicity. In this case, after receiving the CHO configuration, the wireless terminal may send a measurement report (even for candidate target cell(s)) in accordance with the reporting configuration in the pre-conditional measurement configuration if the Boolean type field is set to true (or false) (or the presence/absence type field is present (or absent)), otherwise, the wireless terminal may suppress measurement reports with regard to the candidate target cell(s) in accordance with the previous embodiment.

3: Leaving Condition for Conditional Handover Configuration

In the example embodiment and mode ofFIG.15, the source gNodeB22may provide the wireless terminal26with validity information, or conversely invalidity information, that informs the wireless terminal26of the validity or currency of the conditional handover configuration information that the wireless terminal26receives from the source gNodeB22One reason for providing the wireless terminal26with such (in)validity information is to preclude continued pendency of aged conditional handover configuration information, and/or to force the wireless terminal26to report measurement results for a candidate target gNodeB upon occurrence of one or more leave condition(s).

The source gNodeB22, wireless terminal26, and node processor30of the communications system20ofFIG.15are similar to those ofFIG.6andFIG.11, with like units and functionalities having like reference numbers. As shown inFIG.15, the source gNodeB22comprises node processor circuitry (“node processor30”) and node transceiver circuitry32, with node transceiver circuitry32comprising node transmitter34and node receiver36. The node processor30comprises node frame/signal scheduler/handler50, message generator54, RRC state machine56, and handover controller60, with the handover controller60in turn comprising measurement analyzer62, conditional handover (CHO) determination unit64, and conditional handover configuration information generator66(15). A difference between the previous example embodiments and the example embodiment and mode ofFIG.15is that the conditional handover configuration information generator66(15) includes, in the conditional handover configuration information, (in)validity information, also known as “leave condition(s)”, which may be used by wireless terminal26to assess how long the conditional handover condition is to be in effect or when the conditional handover condition is to be exited. By way of non-limiting example, the leaving conditions may be provided in the last illustrated information element, “leaving conditions”, of the conditional handover configuration message ofFIG.8.

As in the preceding example embodiments and modes, the wireless terminal26of the example embodiment and mode ofFIG.15comprises terminal processor40and terminal transceiver circuitry42, with terminal transceiver circuitry42in turn comprising terminal transmitter44and terminal receiver46. The terminal processor40comprises terminal frame/signal handler52, message processor70, handover unit72, and measurement controller80, with the measurement controller80in turn comprising measurement initiation unit82, measurement results unit84, and measurement report control unit86. In the example embodiment and mode ofFIG.15, the wireless terminal26is provided with information which specifies the (in)validity of or leaving conditions for the conditional handover. Accordingly, the measurement report control unit86(15) ofFIG.15functions to determine, using the (in)validity information and/or leaving conditions, whether the measurement results for the candidate target gNodeB(s) are to be reported.

The example embodiment ofFIG.15discloses validity of CHO configurations that wireless terminal26has previously received and associated reporting. In one example implementation, the validity of a CHO configuration may be valid until the wireless terminal26actually executes a handover. In another example implementation, the validity may terminate upon the source cell explicitly de-configuring the CHO configuration by sending a message to the UE (as in the example embodiment and mode ofFIG.11). In yet another example implementation, the validity may be managed by at least one timer. In this timer implementation, the wireless terminal26may release the CHO configuration at the expiry of the timer, while the radio network (the source/candidate target cells) may release the reserved radio resources at the expiry.

In theFIG.15example embodiment, de-configuring CHO configurations may be based on one or more leaving conditions. The leaving conditions may specify events upon which the UE leaves from the CHO configuration.

FIG.16illustrates an example scenario which may be performed by the system20ofFIG.15. In one example implementation shown inFIG.16, the UE wireless terminal26may use EventTriggeringConfig configured with MeasConfig. Accordingly, the UE may continue the measuring procedure based on the information element measIds in MeasConfig. For each measId, if the UE detects that one of the candidate target cell meets the leaving condition/event (e.g. measurement result<threshold−hysteresis) specified in the corresponding reportConfig, the wireless terminal26may send a measurement report including the measurement result of the candidate target cell, based on a flag reportOnLeave associated with the condition/event. The source cell may release the handover coordination with the candidate target cell and may further send a message for CHO de-configuration. This scenario is illustrated inFIG.16.

The acts ofFIG.16which are similar to those ofFIG.7andFIG.12, have similar suffixes, e.g., act16-0ofFIG.16is similar to act7-0ofFIG.7, act16-1ofFIG.16is similar to act7-1ofFIG.7, and so forth. A difference in the example embodiment and mode ofFIG.16relative to previous example embodiments and modes is that, after the conditional handover coordination of act16-5, the wireless terminal26continues to check if the invalidity or leave conditions specified in the conditional handover configuration information of message16-5is satisfied. If the invalidity or leave conditions specified in the conditional handover configuration information of message16-5are not satisfied, then the measurement report control unit86of wireless terminal26continues to suppress the measurement reporting of the measurement results of the candidate target eNode(s), in a manner similar to that of the example embodiment ofFIG.6andFIG.7. In other words, measurement reports such as those of act7-3′ ofFIG.6, which suppress the reporting of measurement results for the candidate target eNode(s), may be transmitted. However, in the example scenario ofFIG.16, as act16-4′ the wireless terminal26detects that the invalidity or leaving conditions specified in the conditional handover configuration information are met. Upon making the determination of act16-4that the invalidity or leaving conditions specified in the conditional handover configuration information are met by current conditions and/or events, thereafter the wireless terminal26sends measurement reports which include the candidate target cell, as reflected by act16-3′-16. Based on the receipt of the unsuppressed measurement report of act16-3′-16or other information, as act16-14the source gNodeB22makes a decision to release the conditional handover. Accordingly, a conditional handover release procedure is performed between source gNodeB22and the target gNodeB28, as shown by act16-15. Thereafter as act16-16the source gNodeB22may send a conditional handover de-configuration message to the wireless terminal26. Upon successful receipt of the conditional handover de-configuration message, as act16-17the wireless terminal26replies to source gNodeB22with a RRCReconfigurationComplete message.

The source gNodeB22ofFIG.15thus provides the wireless terminal26with certain (in)validity information or leaving condition information to apprise the wireless terminal26how long reports of measurement results for the candidate target gNodeB(s) should be suppressed, if the report suppression is configured as described in the previous embodiment. Example, representative, basic acts performed by source gNodeB22ofFIG.15are shown inFIG.17. Act17-1comprises receiving a measurement report from a wireless terminal. Act17-2comprises making a determination for reconfiguring the wireless terminal based on the measurement report. The determination of act17-2may be made by conditional handover (CHO) determination unit64of source gNodeB22, and may further be reflected by act16-4ofFIG.16. Act17-3comprises transmitting to the wireless terminal a configuration message to configure a conditional handover, the configuration message being configured to provide (in)validity or leaving condition information for a conditional handover.

Example, representative, basic acts performed by wireless terminal26ofFIG.15are shown inFIG.18. Act18-1comprises receiving from the wireless access node a configuration message to configure a conditional handover. The conditional handover configuration message of act18-1may be the message of act16-6as described above. Act18-2comprises the wireless terminal26performing a measurement. The measurement may be initiated by measurement initiation unit82of wireless terminal26. Act18-3comprises the wireless terminal26making a decision, based on the configuration message of act14-2and the (in)validity and/or leaving condition information, whether to send a measurement report including the measurement result for a candidate target gNodeB(s). Act18-4comprises transmitting the measurement report to source gNodeB22.

In another example implementation, the CHO configuration may include one or more leaving condition(s), separately from the condition(s) configured in MeasConfig. For example, the CHO configuration may include leaving offset(s) for each condition/event as shown in Listing 8. The wireless terminal26may consider that the leaving condition is met when the measurement result of the concerned candidate target cell goes below ax_Threshold−ax_LeavingOffset, where ax is one of A1, A2, A3, A4, A5 and A6 or any other events (not specified). Similar to the previous implementation, each condition may be associated with reportOnLeave, instructing the UE whether to transmit a measurement report when the leaving condition is met.

Typical wireless systems may be required to protect user/signalling data from security attacks by applying encryptions and integrity protections. For this purpose, security contexts may be established among terminals and network entities. In general, a security context is a secure relationship between two or more entities using one or more keys. In the LTE/5G systems, the UE establishes an Access Stratum (AS) security context with eNB(s) and/or gNB(s). The AS security context may be setup in conjunction with a Non-Access Stratum (NAS) security context (established with Mobility Management Entity (MME) for LTE, or Access and Mobility management Function (AMF) for 5G). The security contexts may comprise one or more security keys derived from some shared secrets stored in the UE and a network entity. The AS security context may be firstly established immediately after an RRC connection establishment (i.e. Initial AS security context), while the NAS security context may be firstly established during a registration process.

FIG.19shows an example communications system20wherein security contexts may be employed in conjunction with handovers.FIG.19shows system20as comprising source gNodeB22, wireless terminal26, and candidate target node28. The source gNodeB22, wireless terminal26, and node processor30of the communications system20ofFIG.19are similar to those ofFIG.6,FIG.11, andFIG.15, with like units and functionalities having like reference numbers. As shown inFIG.19, the source gNodeB22comprises node processor circuitry (“node processor30”) and node transceiver circuitry32, with node transceiver circuitry32comprising node transmitter34and node receiver36. The node processor30comprises node frame/signal scheduler/handler50, message generator54, RRC state machine56, and handover controller60, with the handover controller60in turn comprising measurement analyzer62, conditional handover (CHO) determination unit64, and conditional handover configuration information generator66(19). A difference between the previous example embodiments and the example embodiment and mode ofFIG.19is that node processor30further comprises source node security context manager90. The security context manager90in turn comprises first security context generator91and key set generator92for target cell(s).

As in the preceding example embodiments and modes, the wireless terminal26of the example embodiment and mode ofFIG.19comprises terminal processor40and terminal transceiver circuitry42, with terminal transceiver circuitry42in turn comprising terminal transmitter44and terminal receiver46. The terminal processor40comprises terminal frame/signal handler52, message processor70, handover unit72, and measurement controller80. Although not specifically shown inFIG.19, it should be understood that, in like manner withFIG.15, measurement controller80may in turn comprises a measurement initiation unit, a measurement results unit, and a measurement report control unit. In addition, the terminal processor40ofFIG.19is shown as comprising terminal security context manager94. The terminal security context manager94comprises terminal first context generator95and terminal second context generator96for target cell(s).

The example embodiment and mode ofFIG.19takes into consideration various aspects of context generation and handling in conjunction with handovers. For example, the example embodiment and mode ofFIG.19takes into consideration that, in some conditions, such as upon a handover, the security context may be altered/updated. A handover, either conditional or non-conditional, may be categorized into one of the following types:Inter-gNB handover: the target cell is controlled by a gNB different from the gNB that controls the currently serving cell.Intra-gNB handover: the target cell is controlled by the same gNB that controls the currently serving cell.Intra-cell handover: some configuration parameter changes while the UE stays in the currently serving cell. This may be considered as a handover without mobility.

A non-conditional handover herein refers to a conventional (regular) handover, wherein the UE immediately attempts to access to a target cell once directed to do so. On the other hand, a conditional handover is a handover configured prospectively, e.g., for which the wireless terminal is configured for a potential handover in advance of an actual handover trigger or event, as explained in the previous embodiments.

While the UE stays in RRC_CONNECTED (or possibly in RRC_INACTIVE), the AS security context may have to be updated due to the UE's mobility or some other reasons. The AS security context update may be triggered by the Radio Access Network (RAN). When triggered, the UE and the currently serving gNB (source gNB) may generate a fresh set of security keys. If the UE performs a handover to a target cell, the fresh set of security keys may be shared by the target gNB controlling the target cell. Herein a set of parameters or information used for generating the security keys used for a non-conditional handover may be referred as a first security configuration. In some example configurations, the first security configuration may be provided to the UE by a handover command upon directing a handover or anytime the security keys need to be updated.

In a non-conditional handover, the currently serving gNB may send a handover command to the UE. In one configuration, RRCReconfiguration may be used to trigger the non-conditional handover. Listing 9 shows an example format of RRCReconfiguration used for the non-conditional handover.

When receiving RRCReconfiguration as shown by way of example in Listing 9 above, the UE may perform the a procedure as specified in 3GPP TS 38.331 and shown, at least in part, in Listing 10.

LISTING 101>:2>if the nas-Container is included in the received masterKeyUpdate:3>forward the nas-Container to the upper layers;2>if the keySetChangeIndicator is set to true:3>derive or update the KgNBkey based on the KAMFkey, as specified in TS 33.501[11];2>else:3>derive or update the KgNBkey based on the current KgNBkey or the NH, using thenextHopChainingCount value indicated in the received masterKeyUpdate, asspecified in TS 33.501 [11];2>store the nextHopChainingCount value;2>derive the keys associated with the KgNBkey as follows:3>if the securityAlgorithmConfig is included in SecurityConfig:4>derive the KRRCencand KUPenckeys associated with the cipheringAlgorithmindicated in the securityAlgorithmConfig, as specified in TS 33.501 [11];4>derive the KRRCintand KUPintkeys associated with the integrityProtAlgorithmindicated in the securityAlgorithmConfig, as specified in TS 33.501 [11];3>else:4>derive the KRRCencand KUPenckeys associated with the currentcipheringAlgorithm, as specified in TS 33.501 [11];4>derive the KRRCintand KUPintkeys associated with the currentintegrityProtAlgorithm, as specified in TS 33.501 [11].

In one configuration, the MasterKeyUpdate information element (IE) (and possibly combined with securityAlgorithmConfig IE) shown by way of example in Listing 10 may be considered to be one example implementation of the first security configuration. In addition, the ReconfigurationWithSync IE may comprise RACH configurations, indicating that this handover involves mobility (cell change and/or gNB change).

If indicated by the handover command (e.g., by the presence of the first security configuration), the UE may be requested to update the security context. For an intra-gNB or an inter-gNB handover, the updated security context may be used for the target cell upon/after the handover procedure execution. For example, the UE may derive KgNB, a master key used for the AS security context, using parameters including KAMF, one of the keys used for NAS security context, nextHopChainingCount (NCC), received in RRCReconfiguration, as shown inFIG.20, per 3GPP TS 33.501, which is incorporated herein by reference. The derived KgNBmay be used to further generate subsequent keys (such as KRRcintand KRRcenper TS 33.501). An example procedure of the key derivation, according to 3GPP TS 33.501, is described at least in part in Listing 11.

Whenever an initial AS security context needs to be established between UE and gNB/ng-eNB, AMF and the UE shall derive a KgNBand a Next Hop parameter (NH). The KgNBand the NH are derived from the KAMF. A NH Chaining Counter (NCC) is associated with each KgNBand NH parameter. Every KgNBis associated with the NCC corresponding to the NH value from which it was derived. At initial setup, the KgNBis derived directly from KAMF, and is then considered to be associated with a virtual NH parameter with NCC value equal to zero. At initial setup, the derived NH value is associated with the NCC value one.NOTE 1: At the UE, the NH derivation associated with NCC=1 could be delayed until the first handover performing vertical key derivation.NOTE 1a: In N2 handover, when the KgNBis updated either due to KAMFchange or synchronising the AS security context with the NAS security context, the KgNBis derived as specified in clauses 6.9.2.3.3 and 6.9.2.3.4 of the present document. In inter-RAT handover, the KgNBis derived as specified in clause 8.4 of the present document. In UE context modification, the KgNBis derived as specified in clause 6.9.2.2.

Whether the AMF sends the KgNBkey or the {NH, NCC} pair to the serving gNB/ng-eNB is described in detail in sub-clauses 6.9.2.2 and 6.9.2.3. The AMF shall not send the NH value to gNB/ng-eNB at the initial connection setup. The gNB/ng-eNB shall initialize the NCC value to zero after receiving NGAP Initial Context Setup Request message.NOTE 2: Since the AMF does not send the NH value to gNB/ng-eNB at the initial connection setup, the NH value associated with the NCC value one cannot be used in the next Xn handover or the next intra-gNB/intra-ng-eNB-CU handover, for the next Xn handover or the next intra-gNB-CU/intra-ng-eNB handover the horizontal key derivation (see Figure 6.9.2.1.1-1) will apply.NOTE 3: One of the rules specified for the AMF in sub-clause 6.9.2.3.3 of the present document states that the AMF always computes a fresh {NH, NCC} pair that is given to the target gNB/ng-eNB. An implication of this is that the first {NH, NCC} pair will never be used to derive a KgNB. It only serves as an initial value for the NH chain.

The UE and the gNB/ng-eNB use the KgNBto secure the communication between each other. On handovers, the basis for the KgNBthat will be used between the UE and the target gNB/ng-eNB, called KNG RAN*, is derived from either the currently active KgNBor from the NH parameter. If KNG RAN* is derived from the currently active KgNBthis is referred to as a horizontal key derivation (see Figure 6.9.2.1.1-1) and if the KNG RAN* is derived from the NH parameter the derivation is referred to as a vertical key derivation (see Figure 6.9.2.1.1-1).

As NH parameters are only computable by the UE and the AMF, it is arranged so that NH parameters are provided to gNB/ng-eNBs from the AMF in such a way that forward security can be achieved.

On handovers with vertical key derivation the NH is further bound to the target PCI and its frequency ARFCN-DL before it is taken into use as the KgNBin the target gNB/ng-eNB. On handovers with horizontal key derivation the currently active KgNBis further bound to the target PCI and its frequency ARFCN-DL before it is taken into use as the KgNBin the target gNB/ng-eNB.

In addition, in some configurations, an intra-cell handover may be instructed to the UE just to update the AS security context. This act may be referred as “Key change on the fly”, which may be categorized in one of the following two cases: Key re-keying and Key refresh.

The case of Key re-keying is initiated by the AMF. The AMF may create a new KgNBfrom the current KAMFusing a fresh uplink NAS COUNT, a counter handled by the Non-Access Stratum (NAS) layer, which is shared by the UE and the AMF. The derived KgNBmay be sent to the gNB. The gNB may then send an RRC message (e.g., RRCReconfiguration) with the first security configuration comprising (1) an indication indicating a need to generate a fresh KAMFand/or (2) indication indicating a need to generate a fresh KgNBbased on the KAMF(e.g. KeySetChangeIndicator=TRUE).

The case of Key refresh is initiated by the currently serving gNB. The gNB may generate a new KgNBfrom the Next Hop parameter, NH), if an unused {NH, NCC} pair is available, given by the AMF, known as “vertical derivation”. Otherwise the gNB may generate a new KgNBfrom the currently used KgNB(known as “horizontal derivation”). The vertical derivation is performed in the vertical direction inFIG.20, whereas the horizontal derivation is performed in the horizontal direction inFIG.20. The gNB may then send an RRC message (e.g. RRCReconfiguration) including the first security configuration (e.g., nextHopChainingCount used for the key derivation and KeySetChangeIndicator=FALSE). The UE receiving the RRC message may generate a new KgNBwith either the vertical or horizontal derivation, based on the received NCC value and the saved NCC value. That is, the vertical derivation may be performed if the received NCC value is different from the saved NCC value, otherwise, the horizontal derivation may be performed.

If the handover command does not comprise the first security configuration, the UE is supposed to continue using the current AS security context, i.e., the current AS keys, after the handover. In some systems, such as the 5G system, the AS key update may not be required for an intra-gNB handover. In such a case, for example, the UE may determine if the AS key update is needed by the presence of MasterKeyUpdate, and possibly also securityAlgorithmConfig, in RRCReconfiguration.

As mentioned before, “a first security configuration” was described as a set of parameters or information used for generating the security keys used for a non-conditional handover. On the other hand, and as used herein, a “second security configuration(s)” comprises a set of parameters or information which will be used for generating a security context to be established upon or after performing a conditional handover to one of the candidate target cells configured in the CHO configurations. In an example first implementation of the example embodiment and mode ofFIG.19, the CHO configurations disclosed in the previous embodiments, e.g., the example embodiments and modes described with reference to one or more ofFIG.6,FIG.11, and/orFIG.15, may further comprise second security configuration(s), which will be used for generating a security context to be established upon or after performing a conditional handover to one of the candidate target cells configured in the CHO configurations. In other example implementations of the example embodiment and mode ofFIG.19, the second security configuration may be a part of a message comprising the CHO configurations but not a part of the CHO configuration information element per se (e.g., in a different information element included in the message). For example,FIG.21shows an example format of at least portions of a representative conditional handover configuration message which includes second security configuration information. In either case, and as shown by way of example inFIG.22, the second security configuration may comprise:Security algorithm to be used (e.g. securityAlgorithmConfig)Next hop chaining count (e.g. nextHopChainingCoun6An indication indicating a need to generate a fresh AS key set (e.g., KeySetChangeIndicator)

Similar to the first security configuration, the second security configuration for a candidate target cell may be optionally included in the CHO configurations. If the second security configuration is absent, then the UE may continue using the master key and the subsequent keys being used in the currently serving cell after performing a CHO to the candidate target cell.

In one example configuration, illustrated by way of example inFIG.23A, a common second security configuration may be used for all of the candidate target cell(s) in the CHO configurations.

In another example configuration, illustrated by way of example inFIG.23B, a cell-specific second security configuration may be configured for each of the candidate target cell(s).

In yet another example configuration, illustrated by way of example inFIG.23C, a plurality of second security configurations is configured, wherein each of the second security configurations may be used for one or a group of candidate target cells.

Listing 12-1 shows an example format of the CHO configurations comprising a cell-specific second security configuration for each of the candidate target cells.

Listing 12-2 is an alternative format for the cell-specific second security configuration, wherein the CHO configurations, CHOConfig, may comprise one common second security configuration, masterKeyUpdate, each of the CHO configurations, e.g., CHOConfigNR, comprising a flag to indicate whether or not it is associated with the second common security configuration.

In the example embodiment and mode ofFIG.19, the source gNodeB22comprises node processor30and node transmitter34. The node processor30, and particularly first security context generator91, is configured to establish, using a first key set, a first security context with the wireless terminal26. The node processor30, e.g., conditional handover configuration information generator66(19), is configured to generate a configuration message comprising (1) one or more conditional handover configurations and (2) an indication, by whether or not each of the one or more conditional handover configurations is configured with a security configuration, of a key set to be used by a wireless terminal to establish a second security context upon or after a handover configured by the each of the one or more conditional handover configurations. Each of the one or more conditional handover configurations comprises at least one identity of a candidate target cell, and at least one triggering condition. The key set to be used by a wireless terminal to establish a second security context upon or after a handover configured by the each of the one or more conditional handover configurations may be generated by key set generator92for target cell(s).

Thus, the source gNodeB22ofFIG.19performs example, basic, representative acts of steps as shown inFIG.24. Act24-1comprises establishing, using a first key set, a first security context with a wireless terminal. Act24-1may be performed at least in part by first security context generator91. Act24-2comprises configuration message. The configuration message of act24-2, which may be generated by key set generator92for target cell(s), may comprise (1) the one or more conditional handover configurations and (2) the indication, by whether or not each of the one or more conditional handover configurations is configured with a security configuration, of a key set to be used by a wireless terminal to establish a second security context upon or after a handover configured by the each of the one or more conditional handover configurations.

In the example embodiment and mode ofFIG.19, the wireless terminal26, sometimes referred to as the UE, comprises terminal processor40and terminal receiver46. The terminal processor40of the wireless terminal26, and particularly terminal security context manager94, is configured to establish, using a first key set, a first security context with a first wireless access node. The terminal processor40, particularly handover unit72, is configured to perform a conditional handover to a candidate target cell configured by one of the one or more conditional handover configurations, in a case that the at least one triggering condition associated with the candidate target cell is met The terminal processor40, and particularly terminal second context generator96for target cell(s), is further configured to establish a second security context with a second wireless access node that serves the candidate target cell, based on whether or not a security configuration associated with the candidate target cell is configured by the configuration message.

Thus, the wireless terminal26ofFIG.19performs example, basic, representative acts of steps as shown inFIG.25. Act25-1comprises establishing, using a first key set, a first security context with a first wireless access node. Act25-2comprises performing a conditional handover to a candidate target cell configured by one of the one or more conditional handover configurations, in a case that the at least one triggering condition associated with the candidate target cell is met. Act25-3comprises establishing a second security context with a second wireless access node that serves the candidate target cell, based on whether or not a security configuration associated with the candidate target cell is configured by the configuration message.

FIG.26shows an example procedure for the UE for which security configurations are provided for handover. Accordingly, as act26-0the UE may establish a first security context with a first (source) gNB. The first security context may comprise a first key set used for encryptions and integrity protection. As act26-1the UE may receive a configuration message from the first gNB, the configuration message comprising one or more conditional handover configurations. Each of the conditional handover configurations may comprise at least one identity of a candidate target cell and at least one triggering condition. The configuration message of act26-1may further comprise optional security configuration(s). Each of the security configuration(s), if present, may be associated with at least one of the conditional handover configurations. Act26-2comprises making a determination if the at least one triggering condition associated with the candidate target cell is met. If it is determined at act26-2that the at least one triggering condition associated with the candidate cell is met, as act26-3the UE may perform a conditional handover to a candidate target cell. Upon or after executing the conditional handover of act26-3, as act26-4the UE may check the presence of the security configuration associated with the candidate target cell. If the check of act26-4is positive, as act26-5the UE may establish a second security context with a node, e.g., a target gNB, that controls the candidate target cell using a second key set derived from the associated security configuration. If the check of act26-4is negative, as act26-6the UE may continue using the first key set to establish a second security context with the second gNB.

FIG.27shows an example procedure for the gNB of this embodiment. Act27-1shows that the gNB may establish a first security context with the UE. The first security context may comprise a first key set used for encryptions and integrity protection. As act27-1the gNB may determine candidate target cell(s) for CHO to be configured to the UE. As act27-2the gNB may further determine, for each of the candidate target cell(s), a key set to be used, either the first key set or an updated key set. As act27-3, for each of the candidate target cell(s), the gNB may prospectively perform a handover coordination with a node that controls the each of the candidate target cell(s). During the handover coordination for each of the candidate target cell(s), if an updated key set is to be used, the gNB may generate a second key set and provide the second key set to the node. As act27-4the gNB may then generate and transmit a configuration message comprising CHO configurations and optional second security configuration(s). Each of the conditional handover configurations may comprise at least one identity of a candidate target cell and at least one triggering condition. Each of the second security configuration(s), if present, may be associated with at least one of the conditional handover configurations. For each of the CHO configurations, if associated with one of the optional security configuration(s), the gNB may instruct the UE to derive the second key set upon or after a conditional handover, otherwise the gNB may instruct the UE to continue using the first key set.

5: Releasing CHO Configurations Based on Security Configuration

As described in the previous section and embodiment ofFIG.19, a series of access stratum, AS, security contexts may be generated and established in a chained process as shown by way of example inFIG.20. In addition, a second security configuration may be for a future use; e.g., not to be consumed immediately, but to be used only after a conditional handover is triggered.

There may be situations in which, after a second security configuration has been created, for one more reasons yet another new security configuration must be created. In such event where the yet another new security context has to be created, creation of the yet another security configuration breaks into the key chaining, as creation of a new key set for the yet another security configuration may invalidate the previously configured (unused) second security configuration. In such situation involving creation of the yet another security configuration, therefore, the previously created other CHO configurations may have to be released (de-configured), or suspended (inactivated).

FIG.28shows an example communications system20wherein security contexts may also be employed in conjunction with handovers, and wherein validity of handover configurations may be checked based on security configurations for reasons such as those basically described above.FIG.28shows system20as comprising source gNodeB22, wireless terminal26, and candidate target node28. The source gNodeB22, wireless terminal26, and node processor30of the communications system20ofFIG.28are similar to those ofFIG.6,FIG.11,FIG.15, andFIG.19, with like units and functionalities having like reference numbers. As shown inFIG.28, the source gNodeB22comprises node processor circuitry (“node processor30”) and node transceiver circuitry32, with node transceiver circuitry32comprising node transmitter34and node receiver36. The node processor30comprises node frame/signal scheduler/handler50, message generator54, RRC state machine56, handover controller60, security context manager90. As in previous example embodiment and modes, the handover controller60may comprise measurement analyzer62, conditional handover (CHO) determination unit64, and conditional handover configuration information generator66(28). A difference between the previous example embodiments and the example embodiment and mode ofFIG.28is that node processor30further comprises node conditional handover validity checker97. The node conditional handover validity checker97may comprises or be included in handover controller60, and may communicate and/or interact with security context manager90. The security context manager90comprises first security context generator91and second key set generator92(28) which derives a second key set for establishing a second security context between the wireless terminal and a second wireless access node that serves the target cell.

As in the preceding example embodiments and modes, the wireless terminal26of the example embodiment and mode ofFIG.28comprises terminal processor40and terminal transceiver circuitry42, with terminal transceiver circuitry42in turn comprising terminal transmitter44and terminal receiver46. The terminal processor40comprises terminal frame/signal handler52, message processor70, handover unit72, and measurement controller80. Although not specifically shown inFIG.28, it should be understood that, in like manner withFIG.15andFIG.19, measurement controller80may in turn comprises a measurement initiation unit, a measurement results unit, and a measurement report control unit. In addition, the terminal processor40ofFIG.28is shown as comprising terminal conditional handover validity checker98. The terminal security context manager94comprises terminal first context generator95and terminal second key generator96(28). The terminal second key generator96(28) uses a security configuration to derive a second key set for establishing a second security context with a second wireless access node that serves the target cell.

The example embodiment and mode ofFIG.28takes into consideration various aspects of context generation and handling in conjunction with handovers, and particularly checks for validity of conditional handover configurations as described herein. For example, the example embodiment and mode ofFIG.19takes into consideration various examples and scenarios, as the example scenarios 5-1 through 5-4 below and correspondingFIGS.29through33illustrate example situations in which CHO configurations need to be released or can be preserved. The acts ofFIG.34andFIG.35may also be performed by the system of the example embodiment and mode ofFIG.28.

FIG.29shows an example scenario where the UE experiences a radio link failure (RLF) with the currently serving cell (Source Cell) after a CHO is configured with a candidate target cell by the currently serving cell. How the CHO is configured for the UE with respect to the candidate target cell is reflected by acts29-0through29-6′, which are similar to acts7-0through7-6′ ofFIG.7, respectively, and hence not described further herein.

In the scenario ofFIG.29, after detecting an RLF the UE may perform a cell selection procedure, which results in finding Cell A, also referred to herein as cell29. As shown by acts29-7and29-8, the UE may perform a RACH procedure, e.g., Random Access Preamble/Response procedure, and thereafter as act29-9may send a RRCReestablishmentRequest message to Cell A. Cell A may then, as act29-10, communicate with the Source Cell to retrieve the connection context for the UE, e.g., the UE context. Upon a successful retrieval of the UE context, as act29-11Cell A may respond to the UE with a RRCReestablishment message. The RRCReestablishment message of act29-11may comprise a nextHopChainingCount information element that the UE will use for Cell A. Using the nextHopChainingCount information element, as shown by act29-12the UE may then update KgNBby either the vertical or horizontal key derivation and the subsequent keys. Act29-13shows the UE then sending a RRCReestablishmentComplete message to cell A.

In some systems, such as LTE and 5G RAN, the key update such as shown by act29-13always has to occur after a connection re-establishment, e.g., after act29-12. In such a case, the second security configuration for each of the candidate target cells configured by the CHO configurations may have to be invalidated. Thus, in the scenario ofFIG.29, the UE may release all of the CHO configurations, e.g., for all candidate target cells. In parallel, the gNB serving the Source Cell may also need to cancel the CHO coordination, e.g., the resource allocations, made to the candidate target cell(s). In one example configuration, upon receiving a context retrieval request from Cell A, as act29-15the gNB serving the Source Cell may send a CHO/HO cancellation command to each of the gNBs that control the candidate target cell(s).

Upon or after receiving the RRCReestablishment message, as act29-13the UE may perform the horizontal or vertical key derivation to create a fresh AS master key, i.e., KgNB, and the subsequent keys based on comparing the received and saved (currently used) NCC values, as described in the previous embodiment.

Cell A may be a cell different from the Source Cell or may be the same cell as the Source Cell. In the latter case, the UE context retrieval may take place as internal signalling. In addition, if Cell A is one of the candidate target cells configured in the CHO configuration, the UE may perform a conditional handover (CHO), as shown by way of example inFIG.7, instead of a connection re-establishment.

The scenarioFIG.30has similar initial acts30-0through30-6′ as the scenario ofFIG.29. But in the scenario ofFIG.30, after receiving in act30-6the CHO configurations from the currently serving cell (Source Cell), the UE is instructed by the currently serving cell to perform a non-conditional handover to a target cell, Cell B, also known as cell29′, that is not included in the CHO configurations. The case ofFIG.30may happen when a measurement report sent by the UE, such as that depicted by act30-3′ inFIG.30, indicates that the signal from a cell not listed as a candidate target cell becomes strong. The coordination of the non-conditional handover to the target cell (Cell B) that is not included in the CHO configurations is reflected by act30-7. If Cell B is under control of another gNB, Cell B and the UE may have to use a fresh AS master key, and thus a RRCReconfiguration procedure as indicated by act30-8is performed to instruct that the non-conditional handover may include a first security configuration and thus to force the UE to update the key, e.g., to generate a new AS master key and the subsequent keys. Generation of the new AS master key, which is a form of key update, is reflected by act30-9. As described in the previous example scenario ofFIG.29, the UE may generate the AS master key by either the horizontal key derivation or the vertical key derivation based on the value of NCC included in RRCReconfiguration, and the saved (currently used) NCC.

Similar to Example Scenario 5-1, in a case that as act30-9the UE derives a new master key due to the non-conditional inter-gNB handover, any second security configuration that the UE received in the CHO configurations may become invalid, which may result in invalidating the CHO configurations for all of the candidate target cell(s). The UE may release the saved CHO configurations. Likewise, as shown by act30-10, the Source Cell may send the CHO/HO cancellation command to each of the each of the gNBs that control the candidate target cell(s). Thereafter the UE may engage in a random access procedure to cell B, as shown by the Random Access Preamble, the Random Access Response, and the RRCReconfigurationComplete message of respective acts30-11through30-13, respectively.

Example Scenario 5-3: Key Change-On-the-Fly

In some cases, the network, e.g., the gNB or a core network entity, such as AMF, may initiate a key update. This procedure may be also known as an intra-cell handover without mobility, or key change/update-on-the-fly procedure. There are two types of network-initiated key update-on-the-fly procedures:

A Key re-keying procedure may be initiated by the currently serving AMF. The AMF may create a new KgNBfrom the current KAMFusing a fresh uplink NAS COUNT (a counter handled by the Non-Access Stratum (NAS) layer, shared by the UE and the AMF). The derived KgNBmay be sent to the currently serving gNB, which may then send an RRC message (e.g. RRCReconfiguration) comprising (1) an indication indicating a need to generate a fresh KAMF(e.g. a field KAMFchange flag included in nas-Container) and/or (2) indication indicating a need to generate a fresh KgNBbased on the KAMF(e.g. KeySetChangeIndicator=TRUE).

A Key refresh procedure may be initiated by the currently serving gNB. The gNB may generate a new KgNBfrom NH if an unused {NH, NCC} pair is available, given by the AMF, i.e. vertical derivation. Otherwise the currently serving gNB may generate a new KgNBfrom the currently used KgNB, i.e., horizontal derivation. The gNB may then send an RRC message, e.g. RRCReconfiguration, including NCC and KeySetChangeIndicator=FALSE. The UE receiving the RRC message may generate a new KgNBwith either the vertical or horizontal derivation, based on the received NCC value and the saved NCC value.

FIG.31illustrates an example scenario, wherein after configuring the CHO to a candidate target cell (Cell A), as act31-7the currently serving cell (Source Cell) may send a RRCReconfiguration message including a masterKeyUpdate information element comprising at least a value for the NCC and KeySetChangeIndicator. The US then then may respond with a RRCReconfigurationComplete message as shown by act31-8. As act31-9the UE may then release all of the CHO configurations, e.g., CHO configuration for Cell A and others, if any. In parallel, as act31-10the Source Cell may initiate a HO cancellation procedure to release the reserved CHO coordination in the candidate target cell(s), e.g., Cell A. In the example scenario ofFIG.31, act31-0through31-6-are essentially the same as comparable acts of other scenarios, such as act29-0through29-6′.

An intra-gNB/eNB handover is a handover between two cells controlled by one gNB22(32). As shown inFIG.32, the handover may be between source cell23and cell A, also known as cell29. In the example scenario ofFIG.32, it is assumed that the UE has already been configured with the CHO configurations with one or more candidate target cells. In other words, act32-0through32-6, which are essentially the same as act29-0through29-6′, respectively, have already been executed. Act32-4shows that the gNB22(32) had made a handover decision for a handover to cell A29. As a result, cell A performs handover coordination as shown by act32-5. In the example scenario ofFIG.32, however, a key update on KgNBmay take place upon the intra-gNB handover. In other words, act32-7shows that in a message advising of handover that an information element such as masterKeyChange is included and provides the key update on KgNB. After receipt of the message advising of handover, a RACH procedure is performed as reflected by the RandomAccess Preamble message of act32-8and the RandomAccessResponse message of act32-9. Thereafter, after the UE sends the RRCReconfigurationComplete message of act32-11, the cell A29may cancel the conditional handover coordination, if previously configured, by engaging in handover cancellation act32-12.

In other deployment scenarios, the network operation policy may allow to keep using the same KgNBand the subsequent keys after the intra-gNodeB handover.

In the example intra-gNB scenarios described herein it is assumed that the UE has already been configured with the CHO configurations with one or more candidate target cells. In other words, act32-0through32-7, which are essentially the same as act29-0through29-7, respectively, have already been executed. Upon successfully performing a handover to a target cell, which may be one of the candidate target cells (for a conditional handover) or may be another cell (for a non-conditional handover), if the UE is allowed to use the current KgNBand the subsequent keys, the UE of this embodiment and mode may preserve (not release) the CHO configurations. In this case, the gNB may also keep the CHO configurations as valid configurations. Although the UE/gNB may just release the CHO configuration for the target cell to which the UE successfully performed a conditional handover, and may preserve the remaining CHO configurations. On the other hand, if a key update is required, the UE/gNB may release all the CHO configurations upon performing the handover in the same manner as previously disclosed for the inter-gNB handover.

For example, consider that the CHO configurations contain Cell A and Cell B as candidate target cells, both of Cell A and Cell B being under control of one gNB, and no key update is required for Cell A or Cell B. If the UE successfully performs a conditional handover to Cell A, the UE/gNB may keep the CHO configuration for Cell B while releasing the CHO configuration for Cell A. The CHO configuration for Cell A may be released because the prospectively allocated radio resource(s) for the UE at Cell A may be no longer reserved after the conditional handover. Furthermore, if the UE, before executing a conditional handover to Cell A or Cell B, successfully performs a non-conditional handover to Cell C, which is also under control of the gNB but not a candidate target cell, the UE/gNB may keep the CHO configurations for Cell A and Cell B after the non-conditional handover.

In one configuration, the UE may determine if the current KgNBis to be used after a handover (and therefore the CHO configurations can be preserved) by the presence of the first or second security configuration. Accordingly, if a candidate target cell configured in the CHO configurations is associated with a second security configuration, the UE may consider that a key update is needed for a handover to the candidate target cell. On the other hand, if a second security configuration is not associated with the candidate target cell, the UE may perform no key update after a handover to the cell. Furthermore, in a case that the UE receives a handover command (e.g. RRCReconfiguration) from the currently serving gNB (i.e. a regular handover, or a non-CHO handover), if the handover command comprises a first security configuration, the UE may perform a key update to generate a fresh KgNB, otherwise, the UE will continue using the current key after the handover.

FIG.33illustrates an example UE procedure, e.g., a procedure performed by terminal processor40ofFIG.28, Act33-0comprises the UE establishing a first security context with a first (source) gNB, using a first key set.

Act33-1comprises the UE receiving the CHO configurations from the first gNB.

Act33-2comprises the UE checking if it is experiencing a radio link failure (RLF).

Act33-3comprises the UE performing a cell selection procedure. After a successful selection, the UE performs the re-establish procedure, which will result in receiving from a target cell RRCReestablishment comprising security configuration for the target cell.

Act33-4comprises the UE checking if it received RRCReconfiguration from the currently serving gNB, which may trigger an intra-cell, intra-gNB or inter-gNB handover.

Act33-5comprises the UE checking if one of the triggering conditions configured in the CHO configurations is met.

Act33-6comprises the UE performing a non-conditional or conditional handover.

For the non-conditional handover, the UE follows the configuration of the target cell given by the received RRCReconfiguration. For the conditional handover, the UE follows the configuration of the candidate target cell for which the triggering condition is met.

Act33-7comprises the UE checking if security configuration is available, which forces the UE to generate a fresh KgNB(or KeNB) and the subsequent keys (a second key set). In the case of the regular handover, the security configuration may be optionally present in the received RRCReconfiguration. In the case of the conditional handover, the security configuration for the target cell may be optionally present in the CHO configurations.

Act33-8comprises the UE establishing a second security context using the second key set.

Act33-9comprises the UE releasing all the CHO configurations.

Act33-10comprises the UE establishing a second security context using the first key set.

Act33-11comprises the UE releasing CHO configuration only for the target cell and preserve the CHO configurations for other candidate target cells.

FIG.34shows an example procedure performed by a source gNodeB22, e.g., a currently serving gNB, for the example embodiment and mode ofFIG.28.

Act34-0comprises the gNB establishing a first security context with a UE, using a first key set.

Act34-1comprises the gNB determining candidate target cell(s) for CHO to be configured to the UE.

Act34-2comprises the gNB determining, for each of the candidate target cell(s), a key set to be used, either the first key set or a new key set.

Act34-3comprises, for each of the candidate target cell(s), the gNB prospectively performing a handover coordination with a node that controls the each of the candidate target cell(s).

Act34-4comprises the gNB transmitting CHO configurations to the UE. The CHO configurations comprise resource configuration, triggering condition(s) and optional security configuration for each of the candidate target cell(s).

Act34-5comprises the gNB checking if the UE has performed the re-establishment procedure (due to an RLF). The gNB can recognize the presence of the reestablishment procedure initiated by the UE when it receives a UE context retrieval request received from another node (inter-gNB re-establishment), or RRCReestablishmentRequest from the UE (intra-gNB re-establishment).

Act34-6comprises the gNB determining if a (non-conditional) handover is needed. This handover may be either an intra-cell, intra-gNB or inter-gNB handover.

Act34-7comprises the gNB transmitting RRCReconfiguration to trigger the (non-conditional) handover for the UE.

Act34-8comprises the gNB checking if the (non-conditional) handover is associated with a security configuration.

Act33-9comprises the gNB checking if the UE has successfully performed a conditional handover to one of the candidate target cell(s). The gNB can recognize a successful conditional handover if it receives a CHO success notification from one of the other gNBs (inter-gNB CHO) or it receives RRCReconfigurationComplete from one of the candidate target cell(s) under control of the (currently serving) gNB.

Act34-10comprises the gNB releasing all the CHO configurations configured to the UE, and performs handover cancellation for all the other gNBs.

Act34-11comprises the gNB releasing the CHO configuration for the target cell of the (non-conditional) handover, if the target cell is one of the candidate target cell(s).

In the example embodiment and mode ofFIG.28, the source gNodeB22comprises node processor30and node transmitter34. The node processor30, and particularly first security context generator91, is configured to establish, using a first key set, a first security context with the wireless terminal26. The node transmitter34is configured to transmit a configuration message comprising one or more conditional handover configurations. Each of the one or more conditional handover configurations may comprise at least one identity of a candidate target cell, and at least one triggering condition. The node processor30, for example node conditional handover validity checker97, is configured to determine, upon the wireless terminal performing a handover to a target cell, validity of the conditional handover configurations, based on whether or not the handover to the target cell is configured with a security configuration. The node processor30, for example second key set generator92(28), is further configured to use the security configuration to derive a second key set for establishing a second security context between the wireless terminal and a second wireless access node that serves the target cell.

Thus, the source gNodeB22ofFIG.28performs example, basic, representative acts of steps as shown inFIG.35. Act35-1comprises establishing a first security context with a wireless terminal using a first key set. Act35-2comprises transmitting a configuration message comprising one or more conditional handover configurations. Each of the one or more conditional handover configurations may comprise at least one identity of a candidate target cell, and at least one triggering condition. Act35-3comprises determining, upon the wireless terminal performing a handover to a target cell, validity of the conditional handover configurations, based on whether or not the handover to the target cell is configured with a security configuration. Act35-4comprises using the security configuration to derive a second key set for establishing a second security context between the wireless terminal and a second wireless access node that serves the target cell.

In the example embodiment and mode ofFIG.28, the wireless terminal26, sometimes referred to as the UE, comprises terminal processor40and terminal receiver46. The terminal processor40of terminal processor40, and particularly terminal security context manager94, is configured to establish, using a first key set, a first security context with a first wireless access node. The terminal receiver46is configured to receive the configuration message comprising one or more conditional handover configurations. The terminal processor40, e.g., handover unit72, is configured to perform a handover to a target cell. The terminal processor40, for example, terminal conditional handover validity checker98, is configured to determine validity of the conditional handover configurations, based on whether or not the handover to the target cell is configured with a security configuration. The terminal processor40is further configured, e.g., using terminal second key generator96(28), to use the security configuration to derive a second key set for establishing a second security context with a second wireless access node that serves the target cell.

Thus, the wireless terminal26ofFIG.28performs example, basic, representative acts of steps as shown inFIG.36. Act36-1comprises establishing, using a first key set, a first security context with a first wireless access node. Act36-2comprises receiving a configuration message comprising one or more conditional handover configurations. Each of the one or more conditional handover configurations may comprise at least one identity of a candidate target cell, and at least one triggering condition. Act36-3comprises determining validity of the conditional handover configurations, based on whether or not the handover to the target cell is configured with a security configuration. Act36-4comprises using the security configuration to derive a second key set for establishing a second security context with a second wireless access node that serves the target cell.

6: Providing Secondary Cell Group Configuration for Dual Connectivity

An example embodiment and mode described with reference toFIG.37discloses Dual Connectivity (DC) scenarios in which a Master gNodeB22provides a secondary cell group (SCG) configuration to a wireless terminal for immediate use by the wireless terminal upon reception. An example illustration of Dual Connectivity (DC) is depicted inFIG.38.FIG.38shows that, when a UE is configured with a DC operation, the UE may be configured with a group of one or more cells served by a master node (MN), Master Cell Group (MCG) and a group of one or more cells served by a secondary node (SN), Secondary Cell Group (SCG). InFIG.38, the cells belonging to the Master Cell Group (MCG) are shown by solid lines, whereas the cells belonging to the Secondary Cell Group (SCG) are shown in dotted lines. The depictions ofFIG.38are merely for sake of an example illustration and are not intended to specify any particular placement or number of cells.

In a Dual Connectivity mode, a special cell may be defined among one or more cells in each of the cell groups (MCG or SCG). Such a special cell may be used for obtaining timing reference to be used for the corresponding cell group. The special cell for the MCG may be referred as PCell (Primary Cell), whereas the special cell for the SCG may be referred as PSCell (primary cell of SCG), or SpCell (Special Cell) of a SCG. The PCell may be a serving cell, operating a primary frequency, in which the UE may perform an initial connection establishment procedure and/or a connection reestablishment procedure. In addition, the PSCell may be a serving cell in which the UE may perform a random access procedure (e.g., in a case that the UE performs a reconfiguration with synchronization procedure). The cell(s) other than the special cell in each of the cell groups may be referred as SCell(s) (Secondary Cell(s)). Thus, with respect to dual connectivity, secondary cell group (SCG) is a term given to a group of serving cells which are associated with a secondary RAN node.

FIG.37shows an example communications system20(37) which provides a secondary cell group (SCG) configuration to a wireless terminal for immediate use by the wireless terminal upon reception.FIG.37shows system20(37) as comprising source gNodeB22, wireless terminal26, and a secondary cell group (SCG). In the example embodiment and mode ofFIG.37, the source gNodeB22serves as the Master node (MN), and thus may also be referred to as Master gNodeB22. The Master gNodeB22with its node processor30and wireless terminal26with its terminal processor40ofFIG.37are similar to those ofFIG.6,FIG.11,FIG.15,FIG.19, andFIG.28, with like units and functionalities having like reference numbers. As shown inFIG.37, the Master gNodeB22comprises node processor circuitry (“node processor30”) and node transceiver circuitry32, with node transceiver circuitry32comprising node transmitter34and node receiver36. The node processor30comprises node frame/signal scheduler/handler50; message generator54; RRC state machine56; handover controller60; security context manager90(37). As in previous example embodiment and modes, the handover controller60may comprise measurement analyzer62, conditional handover (CHO) determination unit64, and handover configuration information generator66. In theFIG.37embodiment and mode, the message generator54may also be known as configuration message generator54since it generates a configuration message that includes configuration information for immediate handover to one or more cells of the secondary cell group (SCG) to which wireless terminal26may belong or have access.

In serving as the master node, gNodeB22may control connectivity of wireless terminals served thereby, including wireless terminal26. For this reason the node processor30of gNodeB22is shown as comprising master node connectivity controller120. The master node connectivity controller120may execute an instance of a connectivity control logic, program or a connective control routine for each wireless terminal26served thereby. When providing dual connectivity (DC) such as that illustrated by way of example inFIG.38, for example, for each wireless terminal26the instance of the connectivity control program may include master cell group connectivity logic122and secondary cell group connectivity control logic124. Since certain aspects of the technology disclosed herein concern the secondary cell group (SCG),FIG.37further shows that the secondary cell group connectivity control logic124may comprise, or have access to, network plan or network topological information126. The network plan or network topological information126may comprise a data base of nodes that may be eligible for inclusion, or actually be included in, the secondary cell group (SCG) to which wireless terminal26has access.

The security context manager90(37) of the Master gNodeB22comprises first security context generator91and second key generator92(37) which derives a second key for establishing a second security context and thus one or more security keys used for the radio connection with one or more secondary cells included in the secondary cell configuration.

As in the preceding example embodiments and modes, the wireless terminal26of the example embodiment and mode ofFIG.37comprises terminal processor40and terminal transceiver circuitry42, with terminal transceiver circuitry42in turn comprising terminal transmitter44and terminal receiver46. The terminal processor40comprises terminal frame/signal handler52, message processor70, handover unit72, and measurement controller80. Although not specifically shown inFIG.37, it should be understood that, in like manner withFIG.15,FIG.19, andFIG.28, measurement controller80may in turn comprises a measurement initiation unit, a measurement results unit, and a measurement report control unit. In addition, the terminal processor40ofFIG.37is shown as terminal security context manager94.

The wireless terminal26comprises connection controller130, which may be realized or comprised by terminal processor40. Since the wireless terminal26ofFIG.37may be capable of operating with dual connectivity, the connection controller130as shown as comprising master cell group connectivity logic132and secondary cell group connectivity control logic134. As explained previously, the secondary cell group (SCG) may comprise a PSCell and other cells, e.g., SCells. As an example aspect of the technology disclosed herein, the Master gNodeB22prompts the wireless terminal26to perform an immediate handover to one or more of the cells of the secondary cell group (SCG). Information pertinent to the immediate handover of each cell in the secondary cell group (SCG) may be provided by the Master gNodeB22to the wireless terminal26in a configuration message138generated by message generator54. The configuration message138may also be referred to as the re-configuration message138. The Master gNodeB22provides the configuration message138so that the secondary cell group connectivity control logic134may direct the handover unit72to perform the handover upon receipt by the wireless terminal of the configuration message138. Such information may herein also be known as configuration information. The configuration information for the secondary cell group (SCG) may be stored in secondary cell group configuration memory140(37), to which the secondary cell group connectivity control logic134has access. For one or more cells of the secondary cell group (SCG) to which wireless terminal26belongs, the secondary cell group configuration memory140(37) comprises fields or records which are shown inFIG.37as including configuration identification field142; PSCell field144, and, an optional security key-utilizing counter field148.

The wireless terminal26further comprises terminal security context manager94. The terminal security context manager94in turn comprises terminal first context generator95and terminal second key generator96(37). The terminal second key generator96(37) derives one or more security keys used for the radio connection with one or more secondary cells included in the conditional secondary cell configuration.

The Master gNodeB22thus comprises message generator54that may generate and transmit to the wireless terminal26the configuration message138that may include an SCG configuration with a PSCell configuration. The SCG configuration is preferably stored in secondary cell group configuration memory140(37). The secondary cell group connectivity control logic134of the UE that receives the configuration message may start synchronization with the configured PSCell, and then establish radio connection/bearers with the SCells in the SCG.

FIG.39is a flowchart which shows representative, generic, steps or acts performed by Master gNodeB22ofFIG.37. Act39-1comprises establishing a first radio connection with a wireless terminal, e.g., with wireless terminal26. Act39-2comprises transmitting a re-configuration message comprising a secondary cell group configuration. An example of the re-configuration message, also known as “configuration message”, is configuration message138shown inFIG.37. As previously explained, the configuration message138may be generated by message generator54, and transmitted via transmitter circuitry34to wireless terminal26. The configuration message138is received by receiver circuitry46of wireless terminal26, processed by message processor70, which stores contents of the configuration message138in conditional secondary cell configuration memory140(37). The configuration message138may include a secondary cell group configuration which in turn comprises an identity of a primary secondary cell (stored in PSCell field144) which may be used for Dual-Connectivity (DC). The secondary cell group configuration included in the configuration message138is configured to instruct the wireless terminal26to establish a second radio connection with a secondary access node serving the primary secondary cell included in the secondary cell configuration upon receipt of the configuration message138.

FIG.40is a flowchart which shows representative, generic, steps or acts performed by wireless terminal26ofFIG.37. Act40-1comprises establishing a first radio connection with a master access node, e.g., with Master gNodeB22.

Act40-2comprises receiving a re-configuration message comprising a secondary cell group configuration. The secondary cell group configuration may comprise an identity of a primary secondary cell (stored in PSCell field144) which may be used for Dual-Connectivity (DC). The secondary cell group configuration may be configured to instruct the wireless terminal to establish a second radio connection with a secondary access node serving the primary secondary cell upon reception of the configuration message138, e.g., essentially immediately upon receiving and processing the configuration message138.

Example circumstances of generation of the configuration message138, also known as re-configuration message138, are described below, as well as examples of how the configuration message138may be structured or encapsulated in other messages. For example,FIG.41and Table 1 provide an example circumstance/procedure for adding a secondary node, whileFIG.42and Table 2 provide an example circumstance/procedure for modifying the current SCG configuration within the same SN.

3GPP TS 37.340 specifies a procedure for adding (newly configure) a secondary node (i.e. adding a new SCG configuration) as shown inFIG.41. Messages, acts and signal ofFIG.40are basically described in Table 1 below:

TABLE 11.The MN decides to request the target SN to allocate resources for one or more specific PDUSessions/QoS Flows, indicating QoS Flows characteristics (QoS Flow Level QoS parameters, PDUsession level TNL address information, and PDU session level Network Slice info). In addition, forbearers requiring SCG radio resources, MN indicates the requested SCG configurationinformation, including the entire UE capabilities and the UE capability coordination result. In thiscase, the MN also provides the latest measurement results for SN to choose and configure theSCG cell(s). The MN may request the SN to allocate radio resources for split SRB operation. InNGEN-DC and NR-DC, the MN always provides all the needed security information to the SN(even if no SN terminated bearers are setup) to enable SRB3 to be setup based on SN decision.For MN terminated bearer options that require Xn-U resources between the MN and the SN, theMN provides Xn-U UL TNL address information. For SN terminated bearers, the MN provides alist of available DRB IDs. The S-NG-RAN node shall store this information and use it whenestablishing SN terminated bearers. The SN may reject the request.For SN terminated bearer options that require Xn-U resources between the MN and the SN, theMN provides in step 1 a list of QoS flows per PDU Sessions for which SCG resources arerequested to be setup upon which the SN decides how to map QoS flows to DRB.NOTE 1:For split bearers, MCG and SCG resources may be requested of such an amount, that theQoS for the respective QoS Flow is guaranteed by the exact sum of resources provided bythe MCG and the SCG together, or even more. For MN terminated split bearers, the MNdecision is reflected in step 1 by the QoS Flow parameters signalled to the SN, which maydiffer from QoS Flow parameters received over NG.NOTE 2:For a specific QoS flow, the MN may request the direct establishment of SCG and/or splitbearers, i.e. without first having to establish MCG bearers. It is also allowed that all QoSflows can be mapped to SN terminated bearers, i.e. there is no QoS flow mapped to anMN terminated bearer.2.If the RRM entity in the SN is able to admit the resource request, it allocates respective radioresources and, dependent on the bearer type options, respective transport network resources.For bearers requiring SCG radio resources the SN triggers UE Random Access so thatsynchronisation of the SN radio resource configuration can be performed. The SN decides for thePSCell and other SCG SCells and provides the new SCG radio resource configuration to the MNwithin an SN RRC configuration message contained in the SN Addition Request Acknowledgemessage. In case of bearer options that require Xn-U resources between the MN and the SN, theSN provides Xn-U TNL address information for the respective DRB, Xn-U UL TNL addressinformation for SN terminated bearers, Xn-U DL TNL address information for MN terminatedbearers. For SN terminated bearers, the SN provides the NG-U DL TNL address information forthe respective PDU Session and security algorithm. If SCG radio resources have been requested,the SCG radio resource configuration is provided.NOTE 3:In case of MN terminated bearers, transmission of user plane data may take place afterstep 2.NOTE 4:In case of SN terminated bearers, data forwarding and the SN Status Transfer may takeplace after step 2.NOTE 5:For MN terminated NR SCG bearers for which PDCP duplication with CA is configured theMN allocates 2 separate Xn-U bearers.For SN terminated NR MCG bearers for which PDCP duplication with CA is configured theSN allocates 2 separate Xn-U bearers.2a.For SN terminated bearers using MCG resources, the MN provides Xn-U DL TNL addressinformation in the Xn-U Address Indication message.3.The MN sends the MN RRC reconfiguration message to the UE including the SN RRCconfiguration message, without modifying it.4.The UE applies the new configuration and replies to MN with MN RRC reconfiguration completemessage, including an SN RRC response message for SN, if needed. In case the UE is unable tocomply with (part of) the configuration included in the MN RRC reconfiguration message, itperforms the reconfiguration failure procedure.5.The MN informs the SN that the UE has completed the reconfiguration procedure successfully viaSN Reconfiguration Complete message, including the SN RRC response message, if receivedfrom the UE.6.If configured with bearers requiring SCG radio resources, the UE performs synchronisationtowards the PSCell configured by the SN. The order the UE sends the MN RRC reconfigurationcomplete message and performs the Random Access procedure towards the SCG is not defined.The successful RA procedure towards the SCG is not required for a successful completion of theRRC Connection Reconfiguration procedure.7.In case of SN terminated bearers using RLC AM, the MN sends SN Status Transfer.8.In case of SN terminated bearers using RLC AM, and dependent on the bearer characteristics ofthe respective QoS Flows, the MN may take actions to minimise service interruption due toactivation of MR-DC (Data forwarding).9-12.For SN terminated bearers, the update of the UP path towards the 5GC is performedvia PDU Session Path Update procedure.

TS37.340 also describes a procedure for modifying the current SCG configuration within the same SN as shown inFIG.42and the text of Table 2.

TABLE 21.The MN sends the SN Modification Request message, which may contain user plane resourceconfiguration related or other UE context related information, data forwarding addressinformation (if applicable), PDU session level Network Slice info and the requested SCGconfiguration information, including the UE capabilities coordination result to be usedas basis for the reconfiguration by the SN. In case a security key update in the SN isrequired, a new SN Security Key is included.2.The SN responds with the SN Modification Request Acknowledge message, which may containnew SCG radio configuration information within an SN RRC reconfiguration message, and dataforwarding address information (if applicable).NOTE 1:For MN terminated NR SCG bearers to be setup forwhich PDCP duplication with CA isconfigured the MN allocates 2 separate Xn-U bearersFor SN-terminated NR MCG bearers to be setup forwhich PDCP duplication with CA isconfigured the SN allocates 2 separate Xn-U bearers.2a.For SN terminated MCG bearers, the MN provides Xn-U DL TNL address information in the Xn-UAddress Indication message.3/4.The MN initiates the RRC reconfiguration procedure, including an SN RRC reconfigurationmessage. The UE applies the new configuration, synchronizes to the MN (if instructed, in case ofintra-MN handover) and replies with MN RRC reconfiguration complete message, including an SNRRC response message, if needed. In case the UE is unable to comply with (part of) theconfiguration included in the MN RRC reconfiguration message, it performs the reconfigurationfailure procedure.5.Upon successful completion of the reconfiguration, the success of the procedure is indicated inthe SN Reconfiguration Complete message.6.If instructed, the UE performs synchronisation towards the PSCell of the SN as described in SNaddition procedure. Otherwise, the UE may perform UL transmission after having applied thenew configuration.7.If PDCP termination point is changed for bearers using RLC AM, and when RRC full configurationis not used, the MN sends the SN Status transfer.8.If applicable, data forwarding between MN and the SN takes place (FIG. 10.3.2-1 depicts thecase where a user plane resource configuration related context is transferred from the MN to theSN).9.The SN sends the Secondary RAT Data Usage Report message to the MN and includes the datavolumes delivered to and received from the UE as described in clause 10.11.2.NOTE 2:The order the SN sends the Secondary RAT DataUsage Report message and performsdata forwarding with MN is not defined. The SNmay send the report when thetransmission of the related QoS flow is stopped.10.If applicable, a PDU Session path update procedure is performed.

As shown in Step3ofFIG.41/FIG.42, RRCReconfiguration message (i.e. MN RRCReconfiguration message) may be used for configuring the UE with a new/modified SCG. Furthermore, as described in Step2ofFIG.41/FIG.42, the MN RRCReconfiguration message may encapsulate another RRCReconfiguration message provided by the SN (i.e. SN RRCReconfiguration Message) that comprises the SCG configuration. Listing 13 is an example format of the RRCReconfiguration message.

In this example, it should be understood that for the MN RRCReconfiguration message the information element mrdc-SecondaryCellGroupConfig may be used to encapsulate the SN RRCReconfiguration message, whereas the encapsulated SN RRCReconfiguration message may include the information element secondaryCellGroup for the SCG configuration.

As mentioned in Section 4, SECURITY CONFIGURATIONS FOR CONDITIONAL HANDOVER CONFIGURATION, terminals and network entities may be required to protect user/signalling data from security attacks by applying encryptions and integrity protections. This may be the case for the radio bearers using the SCG as well. One example configuration of security mechanisms for the secondary cell group (SCG) may comprise, as specified in 3GPP TS 33.401 and/or TS 33.501, an access stratum, AS, key derivation scheme for a secondary node, SN, to derive a master AS key for the secondary node, e.g., key KSN.

FIG.43shows an example key derivation scheme for KSN. The example scheme ofFIG.43may be used when the Master gNodeB22decides to newly add an secondary node, SN160, or to newly add a secondary cell group, SCG, or when the Master gNodeB22updates the security keys used in the currently active SN/SCG.FIG.43shows Master gNodeB22, for example secondary key generator92(37) of Master gNodeB22, which computes KSN. As shown inFIG.43, the secondary key generator92(37) may comprise secondary key derivation function150which may receive inputs in the form of the currently active AS master key152for Master gNodeB22, KgNB, and a counter, such as SK Counter154, as an input for a key derivation function (KDF). The secondary key derivation function150uses the inputs of the currently active AS master key152and the SK Counter154to derive secondary node key KSN156. The SK Counter154may be also referred as an SN Counter or an SCG Counter. The SK Counter154may be selected by Master gNodeB22and be used as freshness input into KSNderivations to guarantee that other security keys further derived from KSNin the SN are not re-used with the same input parameters. The other security keys may be used for encryption and integrity protection of radio bearers for the SN. The secondary node key KSN156derived in the Master gNodeB22may be sent to the secondary node160using the SN Addition Request for SN addition, as shown in by way of example inFIG.41, or the SN Modification Request for SN key updates as shown by way of example inFIG.42.

The Master gNodeB22may send the SK Counter to the wireless terminal26using the RRCReconfiguration message (see Listing 13).FIG.43further shows wireless terminal26, and secondary key generator96(37) in particular, as comprising key derivation function170. The key derivation function170receives inputs including the SK Counter172, received from Master gNodeB22, e.g., in the RRCReconfiguration message, and the currently active AS key KgNB174. Upon reception of the RRCReconfiguration message the secondary key generator96(37) may use the currently active AS key, KgNB174, shared with Master gNodeB22, and the received SK Counter172as inputs to the key derivation function170to derive secondary key KSN,176, which may be used for deriving other security key to be used for encryption and integrity protection of radio bearers for the secondary node SN160.

FIG.37andFIG.43thus show that a secondary cell group configuration is associated with a designated a counter, such as the SK Counter, and that the counter may be used for computing one or more security keys used for the radio connection with the secondary cell included in the secondary cell group configuration. For example,FIG.43shows how in Master gNodeB22the input SK Counter154may be used by secondary key derivation function150to compute secondary node key KSN156, and how in wireless terminal26the SK Counter172may be used by key derivation function170to compute secondary key KSN,176.

7: Configuration of a Conditional PSCell Addition/Modification

Some of the previous example embodiments and modes discuss conditional handovers, where one or more candidate target cells (candidate PCells) may be configured to the UE with associated one or more triggering conditions. The example embodiment and mode ofFIG.37describes, e.g., providing secondary cell group (SCG) configuration for dual connectivity, wherein a handover involving the secondary cell group (SCG) occurs automatically upon receipt of a configuration message that carries the secondary cell group (SCG) configuration information. The example embodiment and mode ofFIG.44-FIG.46, on the other hand, discloses configurations for conditional PSCell addition/modification. For the conditional PSCell addition, the Master gNodeB22may configure wireless terminal26with a candidate PSCell associated with at least one triggering condition. When the triggering condition is met, the UE may perform the aforementioned SN addition procedure. For the conditional PSCell modification (change) of theFIG.44example embodiment and mode, the wireless terminal26that is currently establishing SCG radio connection/bearers with a SN may be configured with a candidate PSCell associated with at least one triggering condition. In the case ofFIG.44, the wireless terminal26may perform the aforementioned SN modification procedure at a time when it is determined that the triggering condition is met. In one example implementation of theFIG.44embodiment and mode, the triggering condition may be one or a combination of the previously disclosed triggering conditions for conditional handover, CHO. Furthermore, for the conditional PSCell modification, the candidate PSCell may be served by the SN that the UE is currently communicating with (intra-SN PSCell) or served by a different SN (inter-SN PSCell).

The configuration for conditional PSCell addition/modification as exemplified by the example embodiment and mode ofFIG.44-FIG.46for one secondary cell group (SCG) comprises one PSCell and zero or more SCells. In a sense the PSCell addition/modification may also be considered as a “handover” to a secondary cell group (SCG), so at some junctures the terminologies “PSCell addition/modification” and “handover to a SCG” may be used interchangeably herein, as well as the terminologies “configuration . . . for conditional PSCell addition/modification” and “configuration . . . for conditional handover to the SCG”.

FIG.44shows an example communications system20(42) which provides a configuration for conditional PSCell addition/modification.FIG.44shows system20(44) as comprising source gNodeB22, wireless terminal26, and a secondary cell group (SCG). In the example embodiment and mode ofFIG.44, the source gNodeB22serves as the Master node (MN), and thus may also be referred to as Master gNodeB22. The Master gNodeB22with its node processor30and wireless terminal26with its terminal processor40ofFIG.44are similar to those ofFIG.6,FIG.11,FIG.15,FIG.19,FIG.28, andFIG.37, with like units and functionalities having like reference numbers. As shown inFIG.44, the Master gNodeB22comprises node processor circuitry (“node processor30”) and node transceiver circuitry32, with node transceiver circuitry32comprising node transmitter34and node receiver36. The node processor30comprises node frame/signal scheduler/handler50; message generator54; RRC state machine56; handover controller60; security context manager90(44). As in previous example embodiment and modes, the handover controller60may comprise measurement analyzer62, conditional handover (CHO) determination unit64, and conditional handover configuration information generator66. In theFIG.44embodiment and mode, the message generator54may also be known as conditional configuration message generator54since it generates a configuration message that includes configuration information for conditional handover to the SCG, e.g. PSCell addition/modification, for the PSCell and optionally SCells, if configured, of the secondary cell group (SCG) to which wireless terminal26may belong or have access.

In serving as the master node, gNodeB22may control connectivity of wireless terminals served thereby, including wireless terminal26. For this reason the node processor30of gNodeB22is shown as comprising master node connectivity controller120. The master node connectivity controller120may execute an instance of a connectivity control logic, program or a connective control routine for each wireless terminal26served thereby. When providing dual connectivity (DC) such as that illustrated by way of example inFIG.38, for example, for each wireless terminal26the instance of the connectivity control program may include master cell group connectivity logic122and secondary cell group connectivity control logic124. Since certain aspects of the technology disclosed herein concern the secondary cell group (SCG),FIG.44further shows that the secondary cell group connectivity control logic124may comprise, or have access to, network plan or network topological information126. The network plan or network topological information126may comprise a data base of nodes that may be eligible for inclusion, or actually be included in, the secondary cell group (SCG) to which wireless terminal26has access. The secondary cell group connectivity control logic124may also comprise conditional handover trigger logic128. The conditional handover trigger logic128may comprise intelligence for generating the conditions for the handover to the SCG, e.g., the triggering criteria, for one or more secondary cells included in the secondary cell group (SCG) for the wireless terminal26. Such triggering conditions may be the same or different for different cells included in the secondary cell group (SCG).

The security context manager90(44) of the Master gNodeB22comprises first security context generator91and second key generator92(44) which derives a second key for establishing a second security context and thus one or more security keys used for the radio connection with one or more secondary cells included in the conditional secondary cell configuration.

As in the preceding example embodiments and modes, the wireless terminal26of the example embodiment and mode ofFIG.44comprises terminal processor40and terminal transceiver circuitry42, with terminal transceiver circuitry42in turn comprising terminal transmitter44and terminal receiver46. The terminal processor40comprises terminal frame/signal handler52, message processor70, handover unit72, and measurement controller80. Although not specifically shown inFIG.44, it should be understood that, in like manner withFIG.15,FIG.19,FIG.28, andFIG.37, measurement controller80may in turn comprise a measurement initiation unit, a measurement results unit, and a measurement report control unit. In addition, the terminal processor40ofFIG.44is shown as terminal security context manager94(42).

The wireless terminal26comprises connection controller130, which may be realized or comprised by terminal processor40. Since the wireless terminal26ofFIG.44may be capable of operating with dual connectivity, the connection controller130as shown as comprising master cell group connectivity logic132and secondary cell group connectivity control logic134. As explained previously, the secondary cell group (SCG) may comprise a PSCell and other cells, e.g., SCells. As an example aspect of the technology disclosed herein, the Master gNodeB22may permit and/or authorize the wireless terminal26to perform a conditional handover to the SCG, and the conditional handover to the SCG may involve the PSCell and optionally SCells, if configured, of the secondary cell group (SCG). Information pertinent to the conditional handover to the SCG for each cell in the secondary cell group (SCG) may be provided by the Master gNodeB22to the wireless terminal26in a configuration message138(44) generated by message generator54. The configuration message138(44) may also be referred to as the re-configuration message138(44), or the conditional configuration message. The Master gNodeB22provides the configuration message138(44) so that the secondary cell group connectivity control logic134may direct the handover unit72to perform the conditional handover to the SCG upon occurrence of condition(s) specified in the configuration message138(44). Such information may herein also be known as conditional configuration information. The configuration information for each cell of the secondary cell group (SCG) may be stored in conditional secondary cell configuration memory140(44) to which the secondary cell group connectivity control logic134has access. For one or more cells of the secondary cell group (SCG) to which wireless terminal26belongs, the conditional secondary cell configuration memory140(44) comprises fields or records which are shown inFIG.44as including configuration identification field142; PSCell field144, triggering condition field146, and, an optional security key-utilizing counter field148.

The wireless terminal26further comprises terminal security context manager94. The terminal security context manager94in turn comprises terminal first context generator95and terminal second key generator96(44). The terminal second key generator96(44) derives one or more security keys used for the radio connection for one or more secondary cells included in the conditional secondary cell configuration.

The Master gNodeB22thus comprises message generator54that may generate and transmit to the wireless terminal26the configuration message138(44) that may include an SCG configuration with a PSCell configuration. The SCG configuration is preferably stored in conditional secondary cell configuration memory140(44). The secondary cell group connectivity control logic134of the UE that receives the configuration message may start synchronization with the configured PSCell, and then establish radio connection/bearers with the SCells in the SCG after the wireless terminal26determines that the triggering condition associated with the SCG configuration is satisfied.

FIG.45is a flowchart which shows representative, generic, steps or acts performed by Master gNodeB22ofFIG.44. Act45-1comprises establishing a first radio connection with a wireless terminal, e.g., with wireless terminal26. Act45-2comprises transmitting a re-configuration message comprising a conditional secondary cell configuration. An example of the re-configuration message, also known as “configuration message”, is configuration message138(44) shown inFIG.44. As previously explained, the configuration message138(44) may be generated by message generator54, and transmitted via transmitter circuitry34to wireless terminal26. The configuration message138(44) is received by receiver circuitry46of wireless terminal26, processed by message processor70, which stores contents of the configuration message138(44) in conditional secondary cell configuration memory140(44). The configuration message138(44) may include a conditional secondary cell configuration which in turn may comprise an identity of a candidate primary secondary cell (stored in PSCell field144) which may be used for Dual-Connectivity (DC). Moreover, the conditional secondary cell configuration may be associated with at least one triggering condition, stored in triggering condition field146.

The conditional secondary cell configuration included in the configuration message138(44) is configured to instruct the wireless terminal26to establish a second radio connection with a secondary access node serving the candidate primary secondary cell included in the conditional secondary cell configuration in a case that the at least one triggering condition associated with the conditional secondary cell configuration is met.

FIG.46is a flowchart which shows representative, generic, steps or acts performed by wireless terminal26ofFIG.44. Act46-1comprises establishing a first radio connection with a master access node, e.g., with Master gNodeB22.

Act46-2comprises receiving a re-configuration message comprising a conditional secondary cell configuration. The conditional secondary cell configuration may comprise an identity of a candidate primary secondary cell (stored in PSCell field144) which may be used for Dual-Connectivity (DC). The conditional secondary cell configuration may be associated with at least one triggering condition (stored in triggering condition field146). The conditional secondary cell configuration may be configured to instruct the wireless terminal to establish a second radio connection with a secondary access node serving the candidate primary secondary cell included in the conditional secondary cell configuration in a case that the at least one triggering condition associated with the conditional secondary cell configuration is met. Act46-3thus comprises the wireless terminal26establishing a second radio connection with a secondary access node serving the candidate primary secondary cell included in the conditional secondary cell configuration in a case that the at least one triggering condition associated with the conditional secondary cell configuration is met.

As understood from the foregoing, the configuration message138(44) of the embodiment and mode ofFIG.44pertains to conditional configuration of a secondary cell group (SCG), whereas the configuration of the secondary cell group (SCG) for theFIG.37embodiment and mode occurred upon receipt of the configuration message138. Nevertheless, example circumstances of generation of the configuration message138(44), as well as examples of how the configuration message138(44) may be structured or encapsulated in other messages, are also understood from the preceding example embodiment and mode ofFIG.37. For example,FIG.41and Table 1 provide an example circumstance/procedure for adding a secondary node, whileFIG.44and Table 2 provide an example circumstance/procedure for modifying the current SCG configuration within the same SN.

Listing 14 shows an example format of the configuration for conditional PSCell addition/modification, where the MN RRCReconfiguration message that encapsulates the SN RRCReconfiguration message may comprise a list of triggering conditions. It should be understood that the MN RRCReconfiguration message may be essentially as disclosed for theFIG.37embodiment and mode, but additionally includes the list of triggering conditions.

In one example implementation of theFIG.44embodiment and mode, the wireless terminal26, upon receiving the MN RRCReconfiguration message, may perform a regular, e.g., non-conditional, legacy or essentially immediate, PSCell addition/modification in a case that the message includes no triggering condition. Otherwise, the wireless terminal26may store in conditional secondary cell configuration memory140(44) the configuration for PSCell addition/modification along with the triggering condition(s), without activating the configuration, and perform the designated PSCell addition/modification when at least one of the triggering condition(s) is met.

In another configuration, the (MN or SN) RRCReconfiguration message may comprise a separate information element, which is not shown in Listing 14, and which indicates whether or not the configuration for PSCell addition/modification is conditional. In this case the wireless terminal26may determine whether or not to perform the regular PSCell addition/modification or the conditional PSCell addition/modification based on the separately supplied information element.

In one example implementation, the system30(44) of the embodiment and mode ofFIG.44also includes a mechanism of provisioning of the security configuration, such as, for example, the SK Counter, disclosed in the embodiment and mode ofFIG.37andFIG.43, may be used for a candidate PSCell. That is, the MN RRCReconfiguration message138(44) may comprise an information element corresponding to sk-Counter to be applied to the conditional PSCell addition/modification configuration included in the encapsulated SN RRCReconfiguration message. The wireless terminal26that receives the MN RRCReconfiguration message may store the received SK Counter in security key-utilizing counter field148of conditional secondary cell configuration memory140(44), and compute KSNfor the candidate PSCell as disclosed, for example, inFIG.43and descriptions herein thereof, before or upon executing the configured PSCell addition/modification.

8: Configuration for Conditional PSCell Addition/Modification for Multiple Candidate PSCells

FIG.47shows an example embodiment and mode wherein a wireless terminal26may be configured with multiple candidate PSCells for conditional PSCell addition/modification. For sake of simplified illustration,FIG.47shows two secondary cell groups (SCGs), a first secondary cell group (SCG) comprising unprimed PSCell and two unprimed Scells, and a second secondary cell group (SCG) comprising primed PSCell and two unprimed Scells. In one example implementation of theFIG.47embodiment and mode, each candidate PSCell configuration may be associated with one or more designated triggering conditions. In another example implementation of theFIG.47embodiment and mode, one triggering condition may be shared by all or some of the multiple candidate PSCells, e.g., by both the primed and unprimed PSCells. When configured, the wireless terminal26may evaluate the triggering condition(s) and perform a PSCell addition/modification, as disclosed in theFIG.44embodiment and mode, for the PSCell whose triggering condition(s) is met.

FIG.47shows system20(47) as comprising source gNodeB22, wireless terminal26, and multiple secondary cell groups (SCG). In the example embodiment and mode ofFIG.47, the source gNodeB22serves as the Master node (MN), and thus may also be referred to as Master gNodeB22. The Master gNodeB22with its node processor30and wireless terminal26with its terminal processor40ofFIG.47are similar to those ofFIG.6,FIG.11,FIG.15,FIG.19,FIG.28,FIG.37, andFIG.44, with like units and functionalities having like reference numbers. As shown inFIG.47, the Master gNodeB22comprises node processor circuitry (“node processor30”) and node transceiver circuitry32, with node transceiver circuitry32comprising node transmitter34and node receiver36. The node processor30comprises node frame/signal scheduler/handler50; message generator54; RRC state machine56; handover controller60; security context manager90(47). As in previous example embodiment and modes, the handover controller60may comprise measurement analyzer62, conditional handover (CHO) determination unit64, and conditional handover configuration information generator66. In theFIG.47embodiment and mode, the message generator54may also be known as conditional configuration message generator54since it generates a configuration message that includes configuration information for conditional handover to the SCG for one or more cells of one of the multiple secondary cell groups (SCG) to which wireless terminal26may belong or have access.

In serving as the master node, gNodeB22may control connectivity of wireless terminals served thereby, including wireless terminal26. For this reason the node processor30of gNodeB22is shown as comprising master node connectivity controller120. The master node connectivity controller120may execute an instance of a connectivity control logic, program or a connective control routine for each wireless terminal26served thereby. When providing dual connectivity (DC) such as that illustrated by way of example inFIG.38, for example, for each wireless terminal26the instance of the connectivity control program may include master cell group connectivity logic122and secondary cell group connectivity control logic124. Since certain aspects of the technology disclosed herein concern the secondary cell group (SCG),FIG.47further shows that the secondary cell group connectivity control logic124may comprise, or have access to, network plan or network topological information126. The network plan or network topological information126may comprise a data base of nodes that may be eligible for inclusion, or actually be included in, the secondary cell group(s) (SCG) to which wireless terminal26has access. The secondary cell group connectivity control logic124may also comprise conditional handover trigger logic128. The conditional handover trigger logic128may comprise intelligence for generating the conditions for handover to the SCG, e.g., the triggering criteria, to one or more secondary cells included in the multiple secondary cell groups (SCG) for the wireless terminal26. Such triggering conditions may be the same or different for different cells included in the multiple secondary cell groups (SCG).

The security context manager90(47) of the Master gNodeB22comprises first security context generator91and second key generator92(47) which derives a second key for establishing a second security context and thus one or more security keys used for the radio connection with one or more secondary cells included in the conditional secondary cell configuration.

As in the preceding example embodiments and modes, the wireless terminal26of the example embodiment and mode ofFIG.47comprises terminal processor40and terminal transceiver circuitry42, with terminal transceiver circuitry42in turn comprising terminal transmitter44and terminal receiver46. The terminal processor40comprises terminal frame/signal handler52, message processor70, handover unit72, and measurement controller80. Although not specifically shown inFIG.47, it should be understood that, in like manner withFIG.15,FIG.19,FIG.28,FIG.37, andFIG.44, measurement controller80may in turn comprise a measurement initiation unit, a measurement results unit, and a measurement report control unit. In addition, the terminal processor40ofFIG.47is shown as terminal security context manager94(47).

The wireless terminal26comprises connection controller130, which may be realized or comprised by terminal processor40. Since the wireless terminal26ofFIG.47may be capable of operating with dual connectivity, the connection controller130as shown as comprising master cell group connectivity logic132and secondary cell group connectivity control logic134. As explained previously, each of the multiple secondary cell groups (SCGs) may comprise a PSCell and other cells, e.g., SCells. As an example aspect of the technology disclosed herein, the Master gNodeB22may permit and/or authorize the wireless terminal26to perform a conditional handover to the SCG, and the conditional handover to the SCG may involve any one of the cells of the involved secondary cell groups (SCGs). Information pertinent to the conditional handover to the SCG of each of the multiple secondary cell groups (SCGs) may be provided by the Master gNodeB22to the wireless terminal26in a configuration message138(47) generated by message generator54. The configuration message138(47) may also be referred to as the re-configuration message138(47), or the conditional configuration message. The Master gNodeB22provides the configuration message138(47) so that the secondary cell group connectivity control logic134may direct the handover unit72to perform the conditional handover to the SCG upon occurrence of condition(s) specified in the configuration message138(47). Such information may herein also be known as conditional configuration information. The configuration information for each of the multiple secondary cell groups (SCGs), and for each cell of each secondary cell group (SCG), may be stored in conditional secondary cell configuration memory140(47), to which the secondary cell group connectivity control logic134has access. For one or more cells of the multiple secondary cell groups (SCG) to which wireless terminal26belongs, the conditional secondary cell configuration memory140(47) comprises fields or records which are shown inFIG.44as including configuration identification field142; PSCell field144, triggering condition field146, and, an optional security key-utilizing counter field148.FIG.47particularly shows that conditional secondary cell configuration memory140(47) comprises fields or records associated with the unprimed secondary cell group (SCG) and fields or records associated with the primed secondary cell group (SCG), and thus accommodates storage of multiple secondary cell group (SCG) configurations.

The wireless terminal26further comprises terminal security context manager94. The terminal security context manager94in turn comprises terminal first context generator95and terminal second key generator96(47). The terminal second key generator96(47) derives one or more security keys used for the radio connection with one or more secondary cells included in the conditional secondary cell configuration.

The Master gNodeB22thus comprises message generator54that may generate and transmit to the wireless terminal26the configuration message138(47) that may include one or multiples SCG configurations with a PSCell configuration. The SCG configuration is preferably stored in conditional secondary cell configuration memory140(47). The secondary cell group connectivity control logic134of the UE that receives the configuration message may start synchronization with the configured PSCell, and then establish radio connection/bearers with the SCells in the SCG after the wireless terminal26determines that the triggering condition associated with the SCG configuration is satisfied.

FIG.48is a flowchart which shows representative, generic, steps or acts performed by Master gNodeB22ofFIG.47. Act48-1comprises establishing a first radio connection with a wireless terminal, e.g., with wireless terminal26. Act48-2comprises transmitting a re-configuration message comprising one or more conditional secondary cell configurations. An example of the re-configuration message, also known as “configuration message”, is configuration message138(47) shown inFIG.47. As previously explained, the configuration message138(47) may be generated by message generator54, and transmitted via transmitter circuitry34to wireless terminal26. The configuration message138(47) is received by receiver circuitry46of wireless terminal26, processed by message processor70, which stores contents of the configuration message138(47) in conditional secondary cell configuration memory140(47). The configuration message138(47) may include configurations for one or more of the multiple secondary cell groups (SCGs), each of which may comprise an identity of a candidate primary secondary cell (stored in PSCell field144) which may be used for Dual-Connectivity (DC). Moreover, each of the one or more conditional secondary cell configurations may be associated with at least one triggering condition, stored in triggering condition field146.

Each of the one or more conditional secondary cell configurations included in the configuration message138(47) is configured to instruct the wireless terminal26to establish a second radio connection with a secondary access node serving the candidate primary secondary cell included in the each of the one or more conditional secondary cell configurations in a case that the at least one triggering condition associated with the each of the one or more conditional secondary cell configurations is met.

FIG.49is a flowchart which shows representative, generic, steps or acts performed by wireless terminal26ofFIG.47. Act49-1comprises establishing a first radio connection with a master access node, e.g., with Master gNodeB22.

Act49-2comprises receiving a re-configuration message comprising one or more conditional secondary cell configurations. Each of the one or more conditional secondary cell configurations may comprise an identity of a candidate primary secondary cell (stored in PSCell field144) which may be used for Dual-Connectivity (DC). Each of the one or more conditional secondary cell configurations may be associated with at least one triggering condition (stored in triggering condition field146). Each of the one or more conditional secondary cell configurations may be configured to instruct the wireless terminal to establish a second radio connection with a secondary access node serving the candidate primary secondary cell included in the each of the one or more conditional secondary cell configurations in a case that the at least one triggering condition associated with the each of the one or more conditional secondary cell configurations is met. Act49-3thus comprises the wireless terminal26establishing a second radio connection with a secondary access node serving the candidate primary secondary cell included in one of the one or more conditional secondary cell configurations in a case that the at least one triggering condition associated with the one of the one or more conditional secondary cell configurations is met.

As understood from the foregoing, the configuration message138(47) of the embodiment and mode ofFIG.47pertains to conditional configuration of one or multiple secondary cell groups (SCGs). The example circumstances of generation of the configuration message138(47), as well as examples of how the configuration message138(47) may be structured or encapsulated in other messages, are also understood from the preceding example embodiment and mode ofFIG.37. For example,FIG.41and Table 1 provide an example circumstance/procedure for adding a secondary node, whileFIG.44and Table 2 provide an example circumstance/procedure for modifying the current SCG configuration within the same SN.

Thus, one or more conditional secondary cell configurations may be included in an addition/modification list, e.g., an add/mod list, with the addition/modification list indicating whether the each of the one or more conditional secondary cell configurations in the addition/modification list is a new conditional secondary cell configuration or an updated configuration of a conditional secondary cell configuration stored in the wireless terminal. In addition, an identifier(s) of one or more conditional secondary cell configurations previously configured to the wireless terminal may be included in a release list, with the release list indicating that the conditional secondary cell configuration(s) identified by the identifier(s) in the release list needs to be released. Thus, the configuration message138(47) may be formatted in a manner to express a “list” of conditional secondary cell configurations, with the nature of the list, e.g., addition/modification or release, being specified in the configuration message138(47) as well, or by another message.

Listing 15 shows an example format of the configuration for conditional PSCell addition/modification with multiple candidate PSCells, wherein the information element condPSCellAddModList comprises a list of conditional PSCell configurations CondPSCellConfig, whereas condPSCellReleaseList may be used by the MN to instruct the UE to release some of the conditional PSCell configurations. The information element condPSCellConfigId may be used to identify a specific CondPSCellConfig. If the current UE configuration (i.e. the configuration for conditional PSCell addition/modification saved in the UE) includes CondPSCellConfig with the given condPSCellConfigId in condPSCellAddModList, the UE may modify the current UE configuration with the received CondPSCellConfig, otherwise the UE may add the received CondPSCellConfig to the current UE configuration. If the current UE configuration includes CondPSCellConfig with the given condPSCellConfigId in condPSCellReleaseList, the UE may release the CondPSCellConfig from the current UE configuration.

It was mentioned above that, in one example implementation of theFIG.47embodiment and mode, each candidate PSCell configuration (e.g. each SCG configuration with a candidate PSCell) may be associated with one or more designated triggering conditions. Such is shown in the conditional secondary cell configuration memory140(147) ofFIG.47, wherein the unprimed PSCell is associated with an unprimed trigger value in its associated triggering condition field146, and the primed PSCell is associated with a primed trigger value in its associated triggering condition field146. However, in another example implementation of theFIG.47embodiment and mode, one triggering condition may be shared by all or some of the multiple candidate PSCells, e.g., by both the primed and unprimed PSCells.

It should be noted that CondPSCellConfig may comprise a SK Counter, sk-Counter, understood with reference toFIG.43, for example, which may be associated with one candidate PSCell. This SK counter may be used in a case that Master gNodeB22decides to differentiate the value of SK counters among multiple candidate PSCells. In such a case, the SK Counter in the information element RRCReconfigurationv1560-IEs may be omitted or ignored.

9: Releasing Conditional PSCell Addition/Modification Configurations Based on Security Configuration

The example embodiments and modes ofFIG.37,FIG.44, andFIG.47disclose techniques wherein a security key for a secondary node, SN, may be generated and used for candidate PSCell(s). In those techniques a currently active access stratum (AS) key, KgNB, is used as an input to a key derivation function (KDF) for deriving a secondary key, e.g., key KSN, as illustrated by way of example inFIG.43. In actual use, the secondary key KSNmay need to be updated in a case that the currently active key K gNB gets updated. As a consequence, a conditional PSCell addition/modification configuration which is always tied a secondary key KSNwhich is derived from the current key KgNB, may become invalid upon a KgNBupdate.

The fifth section hereof, “RELEASING CHO CONFIGURATIONS BASED ON SECURITY CONFIGURATION”, discloses that the cases where KgNBgets updated, as follows:Re-establishment after RLFInter-gNB handoverKey change on the flyIntra-gNB handover

According to one example aspect of the technology disclosed herein, should the currently active access stratum (AS) key KgNBbe updated during any of the cases listed above or any other case, the wireless terminal26may release the conditional PSCell addition/modification configuration(s).

According to one example implementation of this example aspect, the Master gNodeB22that has configured the conditional PSCell addition/modification may coordinate with the secondary node(s), SN(s), to cancel the PSCell addition/modification configuration(s).

According to another example implementation of this aspect, the wireless terminal26may suspend (e.g. inactivate) the conditional PSCell addition/modification configuration(s). In this “suspension” implementation, the Master gNodeB22may coordinate with the secondary node(s), SN(s), to update KSNwhile preserving other configuration parameters, and then send to the wireless terminal26the MN RRCReconfiguration message with a new SK Counter so that the wireless terminal26may derive the updated KSNand resume the conditional PSCell addition/modification configuration(s). The wireless terminal26may keep (e.g. not release) the suspended conditional PSCell addition/modification configuration(s), and may release the suspended conditional PSCell addition/modification configuration(s) when explicitly instructed by the Master gNodeB22using a signaling message such as, e.g. RRCReconfiguration comprising the aforementioned release list, or when a timer expires. The timer may be pre-configured or configured by the Master gNodeB22. It should be noted that the mode and operation of suspension for PSCell addition/modification configurations may be also applied to the release of CHO configuration(s) disclosed in the fifth section. Accordingly, after the CHO configuration(s) is suspended (inactivated), the wireless terminal may keep the CHO configuration(s) until explicitly instructed by the source gNB to release the CHO configuration(s) or until a timer expires.

FIG.50shows system20(50) wherein one or more conditional secondary cell configurations are invalidated upon a change of a first master key.FIG.50shows system20(50) as comprising source gNodeB22, wireless terminal26, and multiple secondary cell groups (SCG). In the example embodiment and mode ofFIG.50, the source gNodeB22serves as the Master node (MN), and thus may also be referred to as Master gNodeB22. The Master gNodeB22with its node processor30and wireless terminal26with its terminal processor40ofFIG.50are similar to those ofFIG.6,FIG.11,FIG.15,FIG.19,FIG.28,FIG.37,FIG.44, andFIG.47, with like units and functionalities having like reference numbers. As shown inFIG.50, the Master gNodeB22comprises node processor circuitry (“node processor30”) and node transceiver circuitry32, with node transceiver circuitry32comprising node transmitter34and node receiver36. The node processor30comprises node frame/signal scheduler/handler50; message generator54; RRC state machine56; handover controller60; security context manager90(50). As in previous example embodiment and modes, the handover controller60may comprise measurement analyzer62, conditional handover (CHO) determination unit64, and conditional handover configuration information generator66. In theFIG.50embodiment and mode, the message generator54may also be known as conditional configuration message generator54since it generates a configuration message that includes configuration information for conditional handover to the SCG for one or more cells of one of the multiple secondary cell groups (SCG) to which wireless terminal26may belong or have access.

In serving as the master node, gNodeB22may control connectivity of wireless terminals served thereby, including wireless terminal26. For this reason the node processor30of gNodeB22is shown as comprising master node connectivity controller120. The master node connectivity controller120may execute an instance of a connectivity control logic, program or a connective control routine for each wireless terminal26served thereby. When providing dual connectivity (DC) such as that illustrated by way of example inFIG.38, for example, for each wireless terminal26the instance of the connectivity control program may include master cell group connectivity logic122and secondary cell group connectivity control logic124. Since certain aspects of the technology disclosed herein concern the secondary cell group (SCG),FIG.50further shows that the secondary cell group connectivity control logic124may comprise, or have access to, network plan or network topological information126. The network plan or network topological information126may comprise a data base of nodes that may be eligible for inclusion, or actually be included in, the secondary cell group(s) (SCG) to which wireless terminal26has access. The secondary cell group connectivity control logic124may also comprise conditional handover trigger logic128. The conditional handover trigger logic128may comprise intelligence for generating the conditions for handover to the SCG, e.g., the triggering criteria, to one or more secondary cells included in the multiple secondary cell groups (SCG) for the wireless terminal26. Such triggering conditions may be the same or different for different cells included in the multiple secondary cell groups (SCG).

The security context manager90(50) of the Master gNodeB22comprises first security context generator91and second key generator92(50) which derives a second key for establishing a second security context and thus one or more security keys used for the radio connection with one or more secondary cells included in the conditional secondary cell configuration. As shown inFIG.50, security context manager90(50) comprises the first security context generator91and second key generator92(50). The second key generator92(50) may derive the second key for a secondary node in the manner understood fromFIG.43. For theFIG.50example embodiment and mode security context manager90(50) further comprises secondary cell group (SCG) configuration invalidator180, e.g., SCG invalidator180. As described used herein, “invalidation” encompasses both “cancellation” and “suspension” of a secondary cell group (SCG) configuration.

As in the preceding example embodiments and modes, the wireless terminal26of the example embodiment and mode ofFIG.50comprises terminal processor40and terminal transceiver circuitry42, with terminal transceiver circuitry42in turn comprising terminal transmitter44and terminal receiver46. The terminal processor40comprises terminal frame/signal handler52, message processor70, handover unit72, and measurement controller80. Although not specifically shown inFIG.50, it should be understood that, in like manner withFIG.15,FIG.19,FIG.28,FIG.37,FIG.44, andFIG.47, measurement controller80may in turn comprise a measurement initiation unit, a measurement results unit, and a measurement report control unit. In addition, the terminal processor40ofFIG.50is shown as terminal security context manager94(50).

The wireless terminal26comprises connection controller130, which may be realized or comprised by terminal processor40. Since the wireless terminal26ofFIG.50may be capable of operating with dual connectivity, the connection controller130as shown as comprising master cell group connectivity logic132and secondary cell group connectivity control logic134. As explained previously, each of the multiple secondary cell groups (SCGs) may comprise a PSCell and other cells, e.g., SCells. As an example aspect of the technology disclosed herein, the Master gNodeB22may permit and/or authorize the wireless terminal26to perform a conditional handover to the SCG, and the conditional handover to the SCG may involve any one of the cells of the involved secondary cell groups (SCGs). Information pertinent to the conditional handover to the SCG of each of the multiple secondary cell groups (SCGs) may be provided by the Master gNodeB22to the wireless terminal26in a configuration message138(50) generated by message generator54. The configuration message138(50) may also be referred to as the re-configuration message138(50), or the conditional configuration message. The Master gNodeB22provides the configuration message138(50) so that the secondary cell group connectivity control logic134may direct the handover unit72to perform the conditional handover to the SCG upon occurrence of condition(s) specified in the configuration message138(50). Such information may herein also be known as conditional configuration information. The configuration information for each of the multiple secondary cell groups (SCGs), and for each cell of each secondary cell group (SCG), may be stored in conditional secondary cell configuration memory140(50), to which the secondary cell group connectivity control logic134has access. For one or more cells of the multiple secondary cell groups (SCG) to which wireless terminal26belongs, the conditional secondary cell configuration memory140(50) comprises fields or records which are shown inFIG.44as including configuration identification field142; PSCell field144, triggering condition field146, and, an optional security key-utilizing counter field148.FIG.50particularly shows that conditional secondary cell configuration memory140(50) comprises fields or records associated with the unprimed secondary cell group (SCG) and fields or records associated with the primed secondary cell group (SCG), and thus accommodates storage of multiple secondary cell group (SCG) configurations.

The wireless terminal26further comprises terminal security context manager94(50). The terminal security context manager94(50) in turn comprises terminal first context generator95; terminal second key generator96(50); key change detector182; and secondary cell group (SCG) configuration invalidator184. The terminal second key generator96(50) derives one or more security keys used for the radio connection with one or more secondary cells included in the conditional secondary cell configuration. The manner of derivation of the second key for a secondary node SN, e.g., key KSN, is understood with reference toFIG.43. As described herein, the key change detector182detects a change in the current first master key, e.g., key KgNB, and notifies secondary cell group (SCG) configuration invalidator184. The secondary cell group (SCG) configuration invalidator184in turn “invalidates” one or more of the secondary cell group (SCG) configurations in conditional secondary cell configuration memory140(50) having a secondary key KSNthat is derived from the changed master key KgNB.

The Master gNodeB22thus comprises message generator54that may generate and transmit to the wireless terminal26the configuration message138(50) that may include one or multiples SCG configurations with a PSCell configuration. The SCG configuration is preferably stored in conditional secondary cell configuration memory140(50). The secondary cell group connectivity control logic134of the UE that receives the configuration message may start synchronization with the configured PSCell, and then establish radio connection/bearers with the SCells in the SCG after the wireless terminal26determines that the triggering condition associated with the SCG configuration is satisfied.

FIG.51is a flowchart which shows representative, generic, steps or acts performed by Master gNodeB22ofFIG.50. Act51-1comprises establishing, using a first master key, a first security context on a first radio connection with a wireless terminal. Act51-2comprises transmitting a re-configuration message comprising one or more conditional secondary cell configurations and at least one counter to the wireless terminal26. The re-configuration message may be configuration message138(50), for example. Each conditional secondary cell configuration may comprise an identity of a candidate primary secondary cell and at least one triggering condition. The candidate secondary cell may be used for Dual-Connectivity (DC). The at least one counter and the first master key are used for derivation of a second master key to be used for establishment of a second security context with one of the candidate primary secondary cells. Act51-3comprises invalidating the one or more conditional secondary cell configurations upon a change of the first master key.

In the case of the invalidation of the configuration being a cancellation, act51-3may comprise the Master gNodeB22coordinating with the secondary node(s), SN(s), to cancel the PSCell addition/modification configuration(s). In the case of the invalidation being a “suspension” of the configuration, the Master gNodeB22may coordinate with the secondary node(s), SN(s), to update KSNwhile preserving other configuration parameters, and then send to the wireless terminal26the MN RRCReconfiguration message with a new SK Counter so that the wireless terminal26may derive the updated KSNand resume the conditional PSCell addition/modification configuration(s). The invalidation of either the cancellation case or the suspension case may be executed by node processor30, e.g., processor circuitry of Master gNodeB22, such as SCG invalidator180, for example.FIG.50shows by arrow186an example of SCG invalidator180coordinating with a secondary node(s), SN. The coordination between Master gNodeB22and such secondary node may be through an appropriate interface not expressly shown inFIG.50.

FIG.52is a flowchart which shows representative, generic, steps or acts performed by wireless terminal26ofFIG.50. Act52-1comprises establishing, using a first master key, a first security context on a first radio connection with a master access node. Act52-2comprises receiving a re-configuration message comprising one or more conditional secondary cell configurations and at least one counter. The reconfiguration message may be configuration message138(50), for example. As understood herein, each conditional secondary cell configuration may comprise an identity of a candidate primary secondary cell and at least one triggering condition, and the candidate primary secondary cell may be used for Dual-Connectivity (DC). The at least one counter and the first master key may be used for derivation of a second master key to be used for establishment of a second security context with one of the candidate primary secondary cell. Act52-3comprises invalidating the one or more conditional secondary cell configurations upon a change of the first master key.FIG.50shows by arrow188the secondary cell group (SCG) configuration invalidator184invalidating a secondary cell group (SCG) in conditional secondary cell configuration memory140(50).

Act52-3thus subsumes detecting a change of the first master key. As mentioned above, a change of the first master key may occur during a connection re-establishment procedure to recover the first radio connection from a radio link failure (RLF); upon or after a handover of the first radio connection; or upon receiving a message instructing the first master key change.

In the case of the invalidation being a “suspension” of the configuration, as mentioned above the Master gNodeB22may coordinate with the secondary node(s), SN(s), to update KSNwhile preserving other configuration parameters, and then send to the wireless terminal26the MN RRCReconfiguration message with a new SK Counter so that the wireless terminal26may derive the updated KSNand resume the conditional PSCell addition/modification configuration(s). In the case of a suspension, the wireless terminal26may release the suspended conditional PSCell addition/modification configuration(s) when explicitly instructed by the Master gNodeB22using a signaling message such as, e.g. RRCReconfiguration, or when a timer expires. The timer may be pre-configured or configured by the Master gNodeB22.

The technology disclosed herein thus proposes, e.g., methods and apparatus for a UE to handle measurement reports associated with conditional handover configurations. Specifically:The UE may suppress measurement reports for cells configured as candidate target cells for conditional handovers. The suppression may be configured by the gNB of the serving cell.The UE may continue measurement reports in a periodic manner for cells configured as candidate target cells for conditional handovers. The periodicity may be configured by the gNB of the serving cell.The gNB may configure the UE with leaving condition(s) associated with conditional handover configurations. The UE may discard the conditional handover configurations when some of the leaving condition(s) is/are met.The conditional handover configurations may be associated with a second security configuration(s). The security configuration(s) may be used for establishing a security context after performing a conditional handover.The conditional handover configurations may be released upon a mobility event, such as a handover and re-establishment, based on the second security configurations, and a first security configuration configured for the mobility event.Configuration mechanism for conditional PSCell addition/modification is disclosed, including configuration for multiple candidate PSCells as well as security configuration for PSCell(s).The PSCell addition/modification configurations may be invalidated in a case that the master security key for the master node (MN) has changed.

Certain units and functionalities of the systems20may be implemented by electronic machinery. For example, electronic machinery may refer to the processor circuitry described herein, such as node processor(s)30, and terminal processor(s)40. Moreover, the term “processor circuitry” is not limited to mean one processor, but may include plural processors, with the plural processors operating at one or more sites. Moreover, as used herein the term “server” is not confined to one server unit, but may encompasses plural servers and/or other electronic equipment, and may be co-located at one site or distributed to different sites. With these understandings,FIG.53shows an example of electronic machinery, e.g., processor circuitry, as comprising one or more processors190, program instruction memory192; other memory194(e.g., RAM, cache, etc.); input/output interfaces196and197, peripheral interfaces198; support circuits199; and busses200for communication between the aforementioned units. The processor(s)190may comprise the processor circuitries described herein, for example, node processor(s)30and terminal processor(s)40.

An memory or register described herein may be depicted by memory194, or any computer-readable medium, may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, flash memory or any other form of digital storage, local or remote, and is preferably of non-volatile nature, as and such may comprise memory. The support circuits199are coupled to the processors190for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like.

Although the processes and methods of the disclosed embodiments may be discussed as being implemented as a software routine, some of the method steps that are disclosed therein may be performed in hardware as well as by a processor running software. As such, the embodiments may be implemented in software as executed upon a computer system, in hardware as an application specific integrated circuit or other type of hardware implementation, or a combination of software and hardware. The software routines of the disclosed embodiments are capable of being executed on any computer operating system, and is capable of being performed using any CPU architecture.

The functions of the various elements including functional blocks, including but not limited to those labeled or described as “computer”, “processor” or “controller”, may be provided through the use of hardware such as circuit hardware and/or hardware capable of executing software in the form of coded instructions stored on computer readable medium. Thus, such functions and illustrated functional blocks are to be understood as being either hardware-implemented and/or computer-implemented, and thus machine-implemented.

In terms of hardware implementation, the functional blocks may include or encompass, without limitation, digital signal processor (DSP) hardware, reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) [ASIC], and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions.

In terms of computer implementation, a computer is generally understood to comprise one or more processors or one or more controllers, and the terms computer and processor and controller may be employed interchangeably herein. When provided by a computer or processor or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, use of the term “processor” or “controller” may also be construed to refer to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above.

Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, the technology disclosed herein may additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

The technologies of the various example embodiments and modes described herein may be implemented either singly or in combination with one another. For example, one or more features of the example embodiment and mode ofFIG.6, one or more features of the example embodiment and mode ofFIG.11, one or more features of the example embodiment and mode ofFIG.15, one or more features of the example embodiment and mode ofFIG.19, one or more features of the example embodiment and mode ofFIG.28, one or more features of the example embodiment and mode ofFIG.37, one or more features of the example embodiment and mode ofFIG.44, one or more features of the example embodiment and mode ofFIG.47, and one or more features of the example embodiment and mode ofFIG.50may be combined for use with one or more of each other.

It will be appreciated that the technology disclosed herein is directed to solving radio communications-centric issues and is necessarily rooted in computer technology and overcomes problems specifically arising in radio communications. Moreover, the technology disclosed herein improves basic function of a providing a wireless terminal with configuration information for one or more secondary cell groups (SCGs), in order to operate the network20effectively and to reduce congestion in such operation.

One or more of the following documents may be pertinent to the technology disclosed herein (all of which are incorporated herein by reference in their entirety):

SUMMARY

In one of its example aspects, the technology disclosed herein concerns structure and operation of a wireless terminal which receives one or more secondary cell group (SCG) configurations from an access node. In an example embodiment and mode, the wireless terminal comprises processor circuitry and receiver circuitry. The processor circuitry is configured to establish a first radio connection with a master access node. The receiver circuitry is configured to receive a re-configuration message comprising one or more conditional secondary cell configurations. Each of the one or more conditional secondary cell configurations may comprise an identity of a candidate primary secondary cell, each of the one or more conditional secondary cell configurations being associated with at least one triggering condition, the candidate primary secondary cell being used for Dual-Connectivity (DC). The processor circuitry is further configured in accordance with the one or more conditional secondary cell configurations to establish a second radio connection with a secondary access node serving the candidate primary secondary cell included in the each of the one or more conditional secondary cell configurations in a case that the at least one triggering condition associated with the each of the one or more conditional secondary cell configurations is met. Methods of operation of such wireless terminals are also provided.

In one of its example aspects, the technology disclosed herein concerns structure and operation of an access node which provides one or more secondary cell group (SCG) configurations to a wireless terminal. The processor circuitry is configured to establish a first radio connection with a wireless terminal. The transmitter circuitry is configured to transmit a re-configuration message comprising one or more conditional secondary cell configurations. Each of the one or more conditional secondary cell configurations may comprise an identity of a candidate primary secondary cell, each of the one or more conditional secondary cell configurations being associated with at least one triggering condition, the candidate primary secondary cell being used for Dual-Connectivity (DC). Each of the one or more conditional secondary cell configurations is configured to instruct the wireless terminal to establish a second radio connection with a secondary access node serving the candidate primary secondary cell included in the each of the one or more conditional secondary cell configurations in a case that the at least one triggering condition associated with the each of the one or more conditional secondary cell configurations is met. Methods of operation of such access node are also provided.

In one of its example aspects, the technology disclosed herein concerns structure and operation of a wireless terminal wherein secondary cell group (SCG) configurations are invalidated upon change of a master key. In an example embodiment and mode, the wireless terminal comprises processor circuitry and receiver circuitry. The processor circuitry is configured to establish, using a first master key, a first security context on a first radio connection with a master access node. The receiver circuitry is configured to receiver circuitry configured to receive a re-configuration message comprising one or more conditional secondary cell configurations and at least one counter. Each conditional secondary cell configuration may comprise an identity of a candidate primary secondary cell and at least one triggering condition, the candidate primary secondary cell being used for Dual-Connectivity (DC). The at least one counter and the first master key may be used for derivation of a second master key to be used for establishment of a second security context with one of the candidate primary secondary cells. The processor circuitry is further configured to invalidate one or more conditional secondary cell configurations upon a change of the first master key. Methods of operation of such wireless terminals are also provided.

In one of its example aspects, the technology disclosed herein concerns structure and operation of an access node for a dual connectivity system wherein secondary cell group (SCG) configurations are invalidated upon change of a master key. In an example embodiment and mode, the access node comprises processor circuitry and receiver circuitry. The processor circuitry is configured to establish, using a first master key, a first security context on a first radio connection with a wireless terminal. The transmitter circuitry is configured to transmit, to a wireless terminal, a reconfiguration message comprising one or more conditional secondary cell configurations and at least one counter. Each conditional secondary cell configuration may comprise an identity of a candidate primary secondary cell and at least one triggering condition, the candidate primary secondary cell being used for Dual-Connectivity (DC). The at least one counter and the first master key may be used for derivation of a second master key to be used for establishment of a second security context with one of the candidate primary secondary cells. The wireless terminal is configured to invalidate one or more conditional secondary cell configurations upon a change of the first master key. Methods of operation of such access node are also provided.