User equipment security key updates without random access

Abstract

Embodiments include methods for a user equipment (UE) configured for mobility between cells of a radio access network (RAN). Such methods include receiving, from the RAN via a first cell, a first message that includes an indication to perform a security key update and updating one or more access stratum (AS) security keys based on the indication. Such methods include transmitting, to the RAN via a second cell, a second message that indicates a security key update has been performed. The second message is transmitted without the UE performing a random access (RA) to the second cell in conjunction with the security key update. Other embodiments include complementary methods for a RAN node, as well as UEs and RAN nodes configured to perform such methods. Figure 9 is selected for publication.

Description

[0001] USER EQUIPMENT SECURITY KEY UPDATES WITHOUT RANDOM ACCESS

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to wireless networks and more specifically to techniques for improving security of user equipment (UEs) operating in a radio access network (RAN), particularly in relation to RAN control of UE updates to security keys used for communication with the RAN.

[0004] BACKGROUND

[0005] The fifth generation (5G) of cellular systems has been standardized within the Third- Generation Partnership Project (3GPP). 5G was developed for maximum flexibility to support many different use cases including enhanced mobile broadband (eMBB), machine type communications (MTC), ultra-reliable low latency communications (URLLC), side-link device- to-device (D2D), and several other use cases. 5G was initially specified in 3GPP Release 15 (Rel-15) and continues to evolve through subsequent releases.

[0006] Figure 1 shows an exemplary 5G network architecture, including a Next Generation Radio Access Network (NG-RAN, 199) and a 5G Core (5GC, 198). The NG-RAN can include one or more gNodeB’s (gNBs) connected to the 5GC via one or more NG interfaces, such as gNBs (100, 150) connected via respective interfaces (102, 152). More specifically, the gNBs can be connected to one or more Access and Mobility Management Functions (AMFs) in the 5GC via respective NG-C interfaces and to one or more User Plane Functions (UPFs) in 5GC via respective NG-U interfaces. The 5GC can include various other network functions (NFs), such as Session Management Function (SMF).

[0007] In addition, the gNBs can be connected to each other via one or more Xn interfaces, such as Xn interface (140) between gNBs (100, 150). The radio technology for the NG-RAN is often referred to as “New Radio” (NR). With respect to the NR interface to UEs, each of the gNBs can support frequency division duplexing (FDD), time division duplexing (TDD), or a combination thereof. Each of the gNBs can serve a geographic coverage area including one or more cells and, in some cases, can also use various directional beams to provide coverage in the respective cells. In general, a DL “beam” is a coverage area of a network-transmitted reference signal (RS) that may be measured or monitored by a UE.

[0008] NG RAN logical nodes (e.g., gNB 100) include a Central Unit (CU or gNB-CU, e.g., 110) and one or more Distributed Units (DU or gNB-DU, e.g., 120, 130). CUs are logical nodes that host higher-layer protocols and perform various gNB functions such controlling the operation of DUs. DUs are decentralized logical nodes that host lower layer protocols and can include, depending on the functional split option, various subsets of the gNB functions. Each CU and DU can include various circuitry needed to perform their respective functions, including processing circuitry, communication interface circuitry (e.g., transceivers), and power supply circuitry.

[0009] A gNB-CU connects to one or more gNB-DUs over respective Fl logical interfaces (e.g., 122 and 132 shown in Figure 1). However, each gNB-DU can be connected to only one gNB-CU. The gNB-CU and its connected gNB-DU(s) are only visible to other gNBs and the 5GC as a gNB. In other words, the Fl interface is not visible beyond gNB-CU.

[0010] Access stratum (AS) security in the 5G network includes integrity protection and ciphering of radio resource control (RRC) signaling radio bearers (SRBs) and user data radio bearers (DRBs). Each gNB applies four different AS security keys: one for integrity protection of RRC signaling (KRRCint), one for ciphering of RRC signaling (KRRCenc), one for integrity protection of user data (Kupint) and one for ciphering of user data (Kupenc). All four AS keys are derived from the KgNB key of the gNB, which is based on the KAMF key handled by upper layers as specified in 3GPP TS 33.501 (vl8.0.0). RRC also handles configuration of AS security parameters such as integrity protection algorithm, ciphering algorithm, and other security parameters used by the UE. For example, a counter (COUNT) is configured and maintained independently in each direction for each DRB / SRB, and provides fresh input for ciphering and integrity protection for the associated DRB / SRB.

[0011] Seamless mobility is a key feature of 3GPP radio access technologies (RATs). In general, a RAN (e.g., NG-RAN) configures a UE to perform and report radio resource management (RRM) measurements to assist network-controlled mobility decisions, such as for handover from a serving cell to a neighbor cell. Seamless handovers ensure that the UE moves around in the coverage area of different cells without excessive interruption to data transmission.

[0012] Conventionally, serving cell change is triggered by layer 3 (L3, e.g., RRC) measurements and involves RRC signaling to change PCell and PSCell (e.g., when DC is configured) and to release / add SCells. L3 serving cell change - also referred to as handover (HO) - also involves LI and L2 resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching. Certain L3 mobility operations may also involve changes to integrity protection and ciphering algorithms as well the AS keys KSNB, KRRCint, KRRCenc, KuPint and KuPenc-

[0013] Even so, HO and other L3 mobility operations can have various robustness problems. For example, a HO command is normally sent when UE’s connection is degraded, such as near cell borders. As such, the HO command may need to be segmented (e.g., to allow for redundancy to protect against errors) and / or retransmitted one or more times before it reaches the UE. The HO command may not reach the UE in time (or at all) before the degraded connection is dropped. Failure of HO to a target cell may lead to the UE declaring radio link failure (RLF) in the serving cell and reestablishing its connection in another cell.

[0014] 3GPP Rel-16 and Rel-17 support conditional HO (CHO) and other conditional mobility procedures. A main principle is that transmission and execution of a mobility (e.g., HO) command are separated. This allows the mobility command to be sent to UE when the radio conditions are still good, thus increasing the likelihood of successful reception. The UE executes the mobility command later based on an associated execution condition. These conditional mobility procedures are facilitated by a conditional reconfiguration framework in which the network provides a UE with one or more reconfigurations, each with associated execution condition(s). 3GPP Rel-18 also supports subsequent L3 mobility, in which a UE may perform multiple L3 mobility procedures without intermediate reconfiguration by the RAN.

[0015] 3GPP Rel-18 includes further NR mobility enhancements, including layer- 1 / layer-2 (L1 / L2) triggered mobility (LTM). Conventional L3 inter-cell mobility also involves complete LI and L2 resets, which increases latency, signaling overhead, and interruptions compared to intra-cell beam switching. A goal of Rel-18 L1 / L2 mobility enhancements is to facilitate serving cell changes via L1 / L2 signaling to address these problems and / or difficulties.

[0016] In LTM, a UE is pre-configured by its serving RAN node with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration.” The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN node, based on which the RAN node sends the UE an LTM cell switch command to trigger UE execution of an LTM cell switch to one of the configured LTM candidate cells.

[0017] According 3 GPP agreements, a UE may perform multiple LTM cell switch procedures without the need of being reconfigured by the RAN. For example, after the UE has performed an LTM cell switch from a serving cell to a first LTM candidate cell, the UE may perform another LTM cell switch - also called “subsequent LTM” - to a second LTM candidate cell based on a previously received RRCReconfiguration message.

[0018] Rel-18 LTM also supports the split CU / DU architecture of Figure 1, including intra-DU and inter-DU / intra-CU cell switches. In the inter-DU / intra-CU scenario, the candidate cell is served by a neighbor DU to the (serving or source) DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). In the intra-DU scenario, the candidate cell is served by the same DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). In either case, the LTM candidate cell configurations and other LTM-related configurations for a UE (e.g., measurement and reporting, early UL / DL synchronization configuration, etc.) are only used within a single CU and one or more DUs of a single gNB. SUMMARY

[0019] According to 3 GPP agreements, Rel-19 will support inter-CU LTM as well as conditional LTM, which is analogous to L3 CHO. Both of these features - along with subsequent LTM and subsequent L3 mobility - require the support of new security-related functionality that is not part earlier releases. For example, security key updated is needed whenever the UE’s CU changes but may also be initiated by the RAN as needed during intra-CU / inter-cell mobility or intra-cell operation. Conventionally, inter-cell L3 handover may be used to trigger security key update. As mentioned above, however, L3 handover introduces undesirable latency, signaling overhead, and interruptions. Moreover, L3 handover is unnecessary for intra-cell security key updates since the UE is already synchronized to and should remain in its current serving cell.

[0020] An object of embodiments of the present disclosure is to provide techniques for intra-cell security key updates for UEs without the need for UE random access (RA), such as by enabling and / or facilitating solutions to exemplary problems summarized above and described in more detail below.

[0021] Embodiments include methods (e.g., procedures) for a UE configured for mobility between cells of a radio access network (RAN, e.g., E-UTRAN, NG-RAN).

[0022] These exemplary methods include receiving, from the RAN via a first cell, a first message that includes an indication to perform a security key update. These exemplary methods also include updating one or more AS security keys based on the indication. These exemplary methods also include transmitting, to the RAN via a second cell, a second message that indicates a security key update has been performed. The second message is transmitted without performing a RA to the second cell in conjunction with the security key update.

[0023] In some embodiments, the updated one or more AS security keys include a master RAN node security key and the following security keys derived from the master RAN node security key: a first key for integrity protection of signaling, a second key for ciphering of signaling, a third key for integrity protection of user data, and a fourth key for ciphering of user data. In some embodiments, these exemplary methods also include, prior to transmitting the second message, performing encryption and / or integrity protection of the second message based on at least one of the updated AS security keys.

[0024] In some embodiments, the first message also includes a security configuration, and the one or more AS security keys are updated further based on the security configuration.

[0025] In other embodiments, these exemplary methods also include receiving, from the RAN via the first cell, a third message that includes a security configuration for the UE. The one or more AS security keys are updated further based on the security configuration. In some of these embodiments, the third message is an RRCReconfiguration message that includes an LTM candidate configuration for the second cell, and the first message is a command to perform LTM cell switch from the first cell to the second cell.

[0026] Other embodiments include exemplary methods (e.g., procedures) for a RAN node configured to facilitate mobility by UEs between cells of a RAN. In general, these exemplary methods can be complementary to the exemplary methods for a UE summarized above.

[0027] These exemplary methods include sending, to a UE via a first cell, a first message that includes an indication to perform a security key update. These exemplary methods also include receiving, from the UE via a second cell, a second message that indicates a security key update has been performed by the UE based on the indication. The second message is received without a RA by the UE to the second cell in conjunction with the security key update.

[0028] In some embodiments, the security key update performed by the UE is to one or more AS security keys, and these exemplary methods also include updating one or more corresponding AS security keys used by the RAN node. In some embodiments, the updated one or more corresponding AS security keys include a master RAN node security key and the following security keys derived from the master RAN node security key: a first key for integrity protection of signaling, a second key for ciphering of signaling, a third key for integrity protection of user data, and a fourth key for ciphering of user data.

[0029] In some of these embodiments, these exemplary methods also include performing decryption and / or integrity checking on the second message based on at least one of the updated corresponding AS security keys.

[0030] In some embodiments, these exemplary methods also include receiving, from a core network node (e.g., AMF), an updated security configuration for the UE. The first message is responsive to the received updated security configuration.

[0031] In other embodiments, these exemplary methods also include sending, to the UE via the first cell, a third message that includes a security configuration for the UE. The one or more AS security keys are updated further based on the security configuration. In some of these embodiments, the third message is an RRCReconfiguration message that includes an LTM candidate configuration for the second cell, and the first message is a command to perform LTM cell switch from the first cell to the second cell.

[0032] The following summary of features applies to UE and RAN node embodiments summarized above.

[0033] In some embodiments, the first cell is the same as the second cell. In other words, the UE performs the security key update without RA and without changing cells.

[0034] In some embodiments, the first message is a medium access control (MAC) control element (CE) or a radio resource control (RRC) message. In some embodiments, the first message also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2 (L2) reset. In some of these embodiments, the first message is a command to perform an LTM cell switch from the first cell to the second cell.

[0035] In some embodiments, the first message also includes the security configuration, the security key update is performed by the UE further based on the security configuration, and the indication to perform security key update is either implicit from the security configuration being included in the first message or an explicit indication separate from the security configuration.

[0036] In some embodiments, the security configuration (in the first message or the third message) includes one of more of the following:

[0037] • an indication whether horizontal or vertical key derivation should be used;

[0038] • a next-hop (NH) parameter;

[0039] • a next-hop chaining counter (NCC) value; and

[0040] • a container of non-access stratum (NAS) information.

[0041] Other embodiments and variants of the exemplary methods summarized above are described herein. Other embodiments include UEs (e.g., wireless devices) and RAN nodes (e.g., base stations, eNBs, gNBs, ng-eNBs, etc.) configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments include non-transitory, computer- readable media storing program instructions that, when executed by processing circuitry, configure such UEs and RAN nodes to perform operations corresponding to any of the exemplary methods described herein.

[0042] These and other embodiments described herein may provide various advantages, benefits, and / or solutions to problems. For example, embodiments may facilitate UE and RAN security key update without need for RA by the UE, which provides reduced latency, signaling, and / or interruptions compared to the conventional approach of triggering security key update by L3 handover. This may be especially beneficial for security key updates in conjunction with LTM as well as for intra-cell security key updates (e.g., after UE mobility to a target cell). As such, embodiments may facilitate necessary updates for encryption and integrity protection as the UE moves between and within cells in the RAN, thereby increasing security of signaling and user data carried by radio bearers secured in this manner.

[0043] These and other objects, features, and advantages of embodiments of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 shows an exemplary 5G network architecture.

[0045] Figure 2 shows an example NG-RAN node arranged in a split CU / DU architecture.

[0046] Figure 3 shows exemplary 5G user plane (UP) and control plane (CP) protocol layers.

[0047] Figure 4 illustrates security key derivation for handover and other UE mobility procedures.

[0048] Figure 5 shows a signaling diagram for an exemplary two-stage L3 handover for a UE.

[0049] Figure 6 shows an example system in which some embodiments of the present disclosure may be implemented.

[0050] Figure 7 shows a signaling diagram for an exemplary inter-CU LTM procedure in accordance with some of the embodiments of the present disclosure.

[0051] Figure 8 shows a signaling diagram for an exemplary intra-cell security key update procedure in accordance with some of the embodiments of the present disclosure.

[0052] Figure 9 shows a flow diagram of an exemplary method for a UE (e.g., wireless device), according to various embodiments of the present disclosure.

[0053] Figure 10 shows a flow diagram of an exemplary method for a RAN node (e.g., base station, eNB, gNB, DU, etc.), according to various embodiments of the present disclosure.

[0054] Figure 11 shows a communication system according to various embodiments of the present disclosure.

[0055] Figure 12 shows a UE according to various embodiments of the present disclosure.

[0056] Figure 13 shows a network node according to various embodiments of the present disclosure.

[0057] Figure 14 is a block diagram of a virtualization environment in which functions implemented by some embodiments of the present disclosure may be virtualized.

[0058] DETAILED DESCRIPTION

[0059] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided as examples to convey the scope of the subject matter to those skilled in the art.

[0060] In general, all terms used herein are to be interpreted according to their ordinary meaning to a person of ordinary skill in the relevant technical field, unless a different meaning is expressly defined and / or implied from the context of use. All references to a / an / the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise or clearly implied from the context of use. The operations of any methods and / or procedures disclosed herein do not have to be performed in the exact order disclosed, unless an operation is explicitly described as following or preceding another operation and / or where it is implicit that an operation must follow or precede another operation. Any feature of any embodiment disclosed herein can apply to any other disclosed embodiment, as appropriate. Likewise, any advantage of any embodiment described herein can apply to any other disclosed embodiment, as appropriate.

[0061] Furthermore, the following terms are used throughout the description given below:

[0062] • Radio Access Node: As used herein, a “radio access node” (or equivalently “radio network node,” “radio access network node,” or “RAN node”) can be any node in a radio access network (RAN) that operates to wirelessly transmit and / or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., gNB in a 3 GPP 5G / NR network or an enhanced or eNB in a 3GPP LTE network), base station distributed components (e.g., CU and DU), a high-power or macro base station, a low-power base station (e.g., micro, pico, femto, or home base station, or the like), an integrated access backhaul (IAB) node, a transmission point (TP), a transmission reception point (TRP), a remote radio unit (RRU or RRH), and a relay node.

[0063] • Core Network Node: As used herein, a “core network node” is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a serving gateway (SGW), a PDN Gateway (P-GW), a Policy and Charging Rules Function (PCRF), an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a Charging Function (CHF), a Policy Control Function (PCF), an Authentication Server Function (AUSF), a location management function (LMF), or the like.

[0064] • Wireless Device: As used herein, a “wireless device” (or “WD” for short) is any type of device that is capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other wireless devices. Communicating wirelessly can involve transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information through air. Unless otherwise noted, the term “wireless device” is used interchangeably herein with the term “user equipment” (or “UE” for short), with both of these terms having a different meaning than the term “network node”.

[0065] • Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0066] • Network Node: As used herein, a “network node” is any node that is either part of the radio access network (e.g., a radio access node or equivalent term) or of the core network (e.g., a core network node discussed above) of a cellular communications network. Functionally, a network node is equipment capable, configured, arranged, and / or operable to communicate directly or indirectly with a wireless device and / or with other network nodes or equipment in the cellular communications network, to enable and / or provide wireless access to the wireless device, and / or to perform other functions (e.g., administration) in the cellular communications network.

[0067] • Node: As used herein, the term “node” (without prefix) can be any type of node that can in or with a wireless network (including RAN and / or core network), including a radio access node (or equivalent term), core network node, or wireless device. However, the term “node” may be limited to a particular type (e.g., radio access node, IAB node) based on its specific characteristics in any given context.

[0068] The above definitions are not meant to be exclusive. In other words, various ones of the above terms may be explained and / or described elsewhere in the present disclosure using the same or similar terminology. Nevertheless, to the extent that such other explanations and / or descriptions conflict with the above definitions, the above definitions should control.

[0069] Note that the description given herein focuses on a 3 GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system and can be applied to any communication system that may benefit from them.

[0070] Figure 2 shows an example NG-RAN node (e.g., gNB or ng-eNB) arranged in the split CU / DU architecture, such as shown in Figure 1. This logical architecture separates the CU into control plane (CP) and user plane (UP) functionality, called CU-C (or CU-CP) and CU-U (or CU- UP) respectively. Furthermore, each of the NG, Xn, and Fl interfaces is split into a CP interface (e.g., NG-C) and a UP interface (e.g., NG-U). Moreover, the CU-U and CU-C can communicate via an El interface. Each DU may be connected to only one CU-C, and each CU-U may be connected to only one CU-C. However, a single DU may be connected to multiple CU-Us under the control of the same CU-C, or a single CU-U may be connected to multiple DUs under the control of the same CU-C. Note that the terms “Central Entity” and “Distributed Entity” in Figure 2 refer to physical network nodes.

[0071] Figure 3 shows exemplary 5G UP and CP protocol layers between a UE (310), a gNB (320), and an AMF (330). Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP) layers between UE and gNB are common to UP and CP. PDCP provides ciphering / deciphering, integrity protection, sequence numbering, reordering, and duplicate detection for both CP and UP, as well as header compression and retransmission for UP data. On the UP side, Internet protocol (IP) packets arrive to PDCP as service data units (SDUs), and PDCP creates protocol data units (PDUs) to deliver to RLC. The Service Data Adaptation Protocol (SDAP) layer handles quality-of-service (QoS) including mapping between QoS flows and Data Radio Bearers (DRBs) and marking QoS flow identifiers (QFI) in UL and DL packets. RLC transfers PDCP PDUs to MAC through logical channels (LCH). RLC provides error detection / correction, concatenation, segmentation / reassembly, sequence numbering, reordering of data transferred to / from the upper layers. MAC provides mapping between LCHs and PHY transport channels, LCH prioritization, multiplexing into or demultiplexing from transport blocks (TBs), hybrid ARQ (HARQ) error correction, and dynamic scheduling (in gNB). PHY provides transport channel services to MAC and handles transfer over the NR radio interface, e.g., via modulation, coding, antenna mapping, and beam forming.

[0072] On the CP side, the non-access stratum (NAS) layer between UE and AMF handles UE / gNB authentication, mobility management, and security control. RRC sits below NAS in the UE but terminates in the gNB rather than the AMF. RRC controls communications between UE and gNB at the radio interface as well as the mobility of a UE between cells in the NG-RAN. RRC also broadcasts system information (SI) and performs establishment, configuration, maintenance, and release of DRBs and Signaling Radio Bearers (SRBs) and used by UEs. Additionally, RRC controls addition, modification, and release of carrier aggregation (CA) and dual -connectivity (DC) configurations for UEs, and performs various security functions such as key management.

[0073] After a UE is powered ON it will be in the RRC IDLE state until an RRC connection is established with the network, at which time the UE will transition to RRC CONNECTED state (e.g., where data transfer can occur). The UE returns to RRC IDLE after the connection with the network is released. In RRC IDLE state, the UE’s radio is active on a discontinuous reception (DRX) schedule configured by upper layers. During DRX active periods (also referred to as “DRX On durations”), an RRC IDLE UE receives SI broadcast in the cell where the UE is camping, performs measurements of neighbor cells to support cell reselection, and monitors a paging channel on PDCCH for pages from 5GC via gNB. An NR UE in RRC IDLE state is not known to the gNB serving the cell where the UE is camping. However, NR RRC includes an RRC_INACTIVE state in which a UE is known (e.g., via UE context) by the serving gNB. RRC INACTIVE has some properties similar to a “suspended” condition used in LTE.

[0074] 3 GPP Rel-10 introduced support for channel bandwidths larger than 20 MHz in LTE networks. To remain compatible with UEs from earlier releases (e.g., LTE Rel-8), a wideband LTE Rel-10 carrier appears as multiple component carriers (CCs), each having the same structure as an LTE Rel-8 carrier. A Rel-10 UE can receive the multiple CCs based on Carrier Aggregation (CA). The CCs can also be considered “cells,” such that a UE in CA has one primary cell (PCell) and one or more secondary cells (SCells) that are referred to collectively as a “cell group.”

[0075] 3 GPP Rel-12 introduced LTE dual connectivity (DC), whereby a UE can be connected to two network nodes simultaneously. In particular, a master node (MN) provides a master cell group (MCG) for the UE and a secondary node (SN) provides a secondary cell group (SCG). Each cell group includes a primary cell (PCell for MCG, PSCell for SCG) and may include one or more secondary cells (SCells). 5G also supports DC, including NR-DC that is similar to LTE-DC except that both the MN and SN use the NR interface to communicate with the UE. In addition, 5G supports various multi-RAT DC (MR-DC) scenarios in one of the MN and SN uses the NR radio interface and the other uses the LTE radio interface to communicate with the UE.

[0076] As mentioned above, RRC also handles configuration of AS security parameters such as integrity protection algorithm, ciphering algorithm, and parameters keySetChangelndicator and nextHopChainingCount used by the UE to determine its AS security keys upon reconfiguration with sync (with key change), RRC connection re-establishment, and RRC connection resume. The integrity protection algorithm is common for SRB1, SRB2, SRB3 (if configured), SRB4 (if configured) and DRBs configured with integrity protection, with the same keyToUse value. The ciphering algorithm is common for SRB1, SRB2, SRB3 (if configured), SRB4 (if configured) and DRBs configured with the same keyToUse value. Neither integrity protection nor ciphering is used for SRBO.

[0077] RRC integrity protection and ciphering are always activated together, i.e., in one message / procedure. RRC integrity protection and ciphering for SRBs are never de-activated. However, it is possible to switch to a 'NULL' ciphering algorithm (neaO). The 'NULL' integrity protection algorithm (niaO) is used only for SRBs and for the UE in limited service mode, as specified in 3GPP TS 33.501 (V18.0.0). When used for SRBs, integrity protection is disabled for DRBs. In case the 'NULL' integrity protection algorithm is used, 'NULL' ciphering algorithm is also used. Additionally, lower layers discard RRC messages for which the integrity protection check has failed and indicate the integrity protection verification check failure to RRC.

[0078] The AS applies four different security keys: one for integrity protection of RRC signaling (KRRCint), one for ciphering of RRC signaling (KRRCenc), one for integrity protection of user data (Kupint) and one for ciphering of user data (KuPenc). All four AS keys are derived from the KSNB key of the gNB, which is based on the KAMF key handled by upper layers as specified in 3GPP TS 33.501 (vl8.0.0). The integrity protection and ciphering algorithms can only be changed with reconfiguration with sync. The four AS keys change upon reconfiguration with sync (if masterKeyUpdate is included), and upon RRC connection re-establishment and RRC connection resume. For each DRB or SRB an independent counter (COUNT) is maintained for each direction and is used in an initialization vector (IV) input to ciphering and integrity protection algorithms applied to each packet of data. Specifically, COUNT is used to ensure fresh IVs when other, semistable parameters remain the same. However, it is not allowed to use the same COUNT value more than once for a given security key. In order to avoid such re-use, the network may use different RB identities for RB establishments, change the AS security key, or cause the UE to perform an RRC CONNECTED to RRC IDLE / RRC INACTIVE transition and then return to RRC CONNECTED. The network ensures that DL IVs are fresh and that the UE can generate fresh UL IVs. For example, since the UE cannot change DRB IDs or initiate re-keying, the gNB must ensure that such actions are taken when the UL COUNT for a DRB approaches wrap-around.

[0079] In order to limit the signaling overhead, individual messages / packets include a short PDCP sequence number (PDCP-SN). In addition, the hyper frame number (HFN) is used as an overflow counter mechanism. HFN needs to be synchronized between the UE and the network. Further details are specified in 3GPP TS 38.323 (vl8.0.0). For each SRB, the value provided by RRC to lower layers to derive the 5-bit BEARER parameter used as input for ciphering and for integrity protection is the value of the corresponding srb-Identity with the MSBs padded with zeroes.

[0080] As described in 3GPP TS 38.501 (vl8.4.0), whenever an initial AS security context needs to be established between a UE and a gNB, the AMF and the UE derive KSNB and a Next Hop parameter (NH) from KA F provided by the AMF. A NH Chaining Counter (NCC) is associated with each KSNB and NH parameter, and each KSNB is associated with the NCC corresponding to the NH value from which the KSNB was derived. At initial setup, KSNB is 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. The UE and the gNB use KSNB to secure the communication between each other, including derivation of the four keys mentioned above.

[0081] Seamless mobility is a key feature of 3GPP radio access technologies (RATs). When the UE moves between the coverage areas of two cells, a serving cell change needs to be performed at some point. Currently, serving cell change is triggered by L3 (e.g., RSRP) measurements and involves RRC signaling to change PCell and PSCell (e.g., when dual connectivity is configured), as well as release / add SCells (e.g., when CA is configured).

[0082] In general, a RAN (e.g., NG-RAN) configures a UE in RRC_CONNECTED state to perform and report radio resource management (RRM) measurements to assist network- controlled mobility decisions, such as for handover from a serving cell to a target cell (e.g., PCell change). Upon the reported measurements meeting a certain condition or threshold, the serving RAN node may send a handover command to the UE, indicating a target cell for the handover. In NR, the handover command is an RRCReconfiguration message with a reconfigurationWithSync field. The procedure to perform a handover is sometimes also referred to as “L3 mobility”, as it is controlled by layer 3 (L3, i.e., RRC) and the messages exchanged are part of L3.

[0083] These reconfigurations are prepared in advance by a target RAN node serving the target cell, upon a request from the UE’s serving RAN node. This request is transmitted over the Xn interface in case the serving and target RAN nodes are part of the NG-RAN. The reconfiguration provided by the target RAN node contains all information the UE needs to access the target cell, e.g., random access configuration, a new cell radio network temporary identifier (C-RNTI) assigned to the UE in the target cell, and parameters enabling the UE to calculate security keys that it can use when communicating with the target cell (including sending a handover complete message).

[0084] In general, UE nobility in RRC CONNECTED state is network-based since the network has the most information about conditions such as cell loading (UEs and / or traffic), available node resources (e.g., processing), available frequencies, etc. However, there will be scenarios when the network fails to handover the UE to the “correct” neighbor cell in time, which can cause the UE will declare radio link failure (RLF) or handover failure (HOF).

[0085] As briefly mentioned above, conditional handover (CHO) was introduced in 3GPP Rel- 16 to improve robustness of UE handover. The key idea in CHO is separation of transmission and execution of the handover command. This allows the handover command to be sent to a UE earlier when the radio conditions are still good, thus increasing the likelihood that the message is successfully transferred. The execution of the handover command is done later in time based on an associated execution condition.

[0086] The execution condition is typically based on a threshold. For example, a signal strength of candidate target cell becomes X dB better than the serving cell (so called “A3 event ”). A preceding measurement reporting event could use a threshold Y that is selected to be lower than X used as the handover execution condition. This allows the serving cell to prepare the handover upon reception of an early measurement report and to provide the RRCConnectionReconfiguration with mobilityControlInfo (for LTE), or a RRCReconfiguration with either a reconfigurationWithSync or a CellGroupConfig (for NR) at a time when the radio link between the source cell and the UE is still relatively stable.

[0087] As used herein, a cell for which conditional handover (or other conditional mobility procedure) is configured is called a “candidate target cell” or “potential target cell”. Similarly, a RAN node controlling a candidate / potential target cell is called “candidate target node” or “potential target node”. Once the conditional mobility execution condition has been fulfilled for a candidate / potential target cell and mobility execution towards this cell has been triggered, this cell is no longer “potential” or a “candidate” in the normal senses of the words, since it is now certain that the mobility operation will be executed towards it. Rather, the candidate / potential target cell can then be referred to as the “target cell”.

[0088] On UE handovers and transitions from RRC INACTIVE to RRC CONNECTED, the basis for KSNB used between the UE and the target NG-RAN node (e.g., gNB) - called KNG-RAN* - is derived from either the currently active KSNB or from the NH parameter. Deriving KNG-RAN* from the currently active KSNB this is referred to as a “horizontal key derivation” while deriving KNG-RAN* from the NH parameter is referred to as “vertical key derivation.” To facilitate horizontal key derivation, the UE must receive an indication of the NH value currently being used by the source RAN node. This indication is an NCC value (e.g., eight bits) that points to an NH value, and is secured by the source RAN node using one or more of the existing AS keys.

[0089] These horizontal and vertical key derivations are illustrated by Figure 4, which shows exemplary security key derivation for HO and other UE mobility procedures. Since NH parameters are only computable by the UE and the AMF, the AMF provides NH parameters to RAN nodes in 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 DL frequency (ARFCN-DL) before it is used for KSNB in the target RAN node. On handovers with horizontal key derivation, the currently active KSNB is further bound to the target PCI and its frequency ARFCN-DL before it is used for KSNB in the target RAN node.

[0090] In some cases, however, the RAN may use both horizontal and vertical key derivation to achieve desired “key separation” between source and target RAN nodes for a UE handover. Figure 5 shows a signaling diagram for an exemplary two-stage L3 handover for a UE from a source cell provided by a source RAN node (gNB#l) to a target cell provided by a target RAN node (gNB#2). The first and target RAN nodes are connected via an Xn interface and both are coupled to an AMF and a UPF in the 5GC.

[0091] Initially, the source RAN node triggers inter-cell, Xn-based L3 handover of the UE to the target cell provided by the target RAN node. The source RAN node includes a masterKeyUpdate information element (IE) in the handover command to trigger security key update by the UE. During this procedure, the UE and the target RAN node perform horizontal key derivation, which facilitates initial secure communication between UE and target RAN node in the target cell. Subsequently, the target RAN sends a path switch request to AMF / UPF and receives in response a new {NH, NCC} pair for the UE. The target RAN node informs the source RAN node to release its context for the UE and then triggers an intra-cell L3 handover for the UE, during which the UE and the target RAN node perform vertical key derivation based on the new {NH, NCC} pair.

[0092] The CHO procedure discussed above can be generalized into a generic conditional reconfiguration framework, wherein a UE may be configured in advance with other types of reconfigurations that can be executed by an RRCReconfiguration message (in NR) or an RRCConnectionReconfiguration message (in LTE) when associated execution condition(s) is(are) triggered. Each such message is prepared by a candidate target RAN node, associated with a candidate target cell, and includes execution conditions that can be represented by one or more identifiers of measurement configuration(s). This conditional reconfiguration framework can be applied to the following mobility operations:

[0093] • CHO (e.g., target candidate RRCReconfiguration message contains a reconfiguration with sync for the MCG);

[0094] • Conditional PSCell Addition (CPA e.g., target candidate RRCReconfiguration message contains an SCG configuration which contains a reconfiguration with sync for a cell to be the PSCell of the SCG);

[0095] • Conditional PSCell Change (CPC, e.g., target candidate RRCReconfiguration message includes an SCG configuration that contains a reconfiguration with sync for a new target candidate cell to be the PSCell of the SCG);

[0096] • Conditional PSCell Release (e.g., source RRCReconfiguration message to be conditionally applied contains an SCG release indication); or

[0097] • Conditional PSCell Suspend (e.g., source RRCReconfiguration message to be conditionally applied contains an SCG suspend indication).

[0098] An SN-initiated intra-SN CPC procedure was specified in 3GPP Rel-16. In this procedure, a UE operating in MR-DC receives a conditional reconfiguration that includes an RRCReconfiguration message containing an SCG configuration (e.g., a secondaryCellGroup field of a CellGroupConfig information element) with an associated execution condition (e.g., an A3 / A5 event configuration). When the UE detects that the execution condition is fulfilled (i.e., finds a neighbor cell better than current PSCell by a configured amount), the UE performs PSCell change. The intra-SN solution for Rel-16 is only for scenarios where the (candidate) target PSCells are provided by the UE’s current SN. Similar to CHO, when a UE successfully connects (e.g., completes RA) to a target cell during intra-SN CPC, it releases all the conditional reconfigurations that it has stored.

[0099] 3GPP Rel-17 introduces support for Conditional PSCell Addition (CPA) and inter-SN CPC. The CPA procedure is used to add a PSCell / SCG to a UE currently configured with only an MCG, when associated execution conditions are fulfilled. CPA is initiated after the MN requests and receives an SCG configuration from a candidate target SN (T-SN), which the MN then provides to the UE as part of a conditional reconfiguration together with the associated execution condition(s). An inter-SN CPC procedure can be initiated by the MN or by the source SN (S-SN), with the MN handling the signaling toward the T-SN and the UE in either case.

[0100] 3GPP Rel-18 includes support a feature known as subsequent conditional PSCell addition / change (CP AC), but may be more generally thought of as a type of subsequent L3 mobility. In subsequent CP AC, a UE performs a further (or subsequent) PSCell / SCG change or addition after an initial PSCell / SCG change or addition, without the need of being reconfigured by the RAN. This is realized by the UE retaining its received CP AC configurations for candidate cells after applying one of them during CPA or CPC execution.

[0101] This retention is different than behavior specified in Rel-17, where the UE releases other CPC configurations after applying one of them during execution of a PSCell change. Instead, a Rel-18 UE can perform one or more subsequent PSCell / SCG changes based on one of those retained CPC configurations, without additional reconfiguration signaling by the RAN. Relative to Rel-17, Rel-18 subsequent CPAC reduces interruption time and signaling overhead for subsequent PSCell / SCG changes, especially for frequent PSCell / SCG changes that may occur while a UE is operating in NR frequency range 2.

[0102] 3GPP Rel-18 also includes an NR mobility enhancement known L1 / L2 triggered mobility (LTM). Current L3 -based inter-cell mobility procedures involve LI and L2 resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intracell beam switching. Thus, Rel-18 LTM is intended to facilitate serving cell changes via L1 / L2 signaling that reduce latency, signaling overhead, and interruptions.

[0103] In LTM, a UE is pre-configured by its serving RAN with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration”. This configuration may be an RRCReconfiguration message or a portion thereof, such as one or more lEs / fields / parameters (e.g., CellGroupConfig IE). The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN, which triggers the execution of a LTM cell switch procedure by the UE to one of the configured LTM candidate cells. This triggering is done by transmitting an LTM cell switch command to the UE in lower layer signaling (e.g., DCI or MAC CE). Based on this command, the UE connects to the associated LTM candidate cell and uses the previously received RRC configuration for this cell.

[0104] Since a goal of LTM is to reduce interruption time for UE data transmissions, the UE needs to be ready to communicate with an LTM candidate cell upon (or shortly after) receiving the L1 / L2 signaling for mobility execution from the source cell. For example, the UE must be able to transmit UL data or a scheduling request (SR) to the LTM candidate cell and / or monitor a DL control channel (e.g., PDCCH) from the LTM candidate cell. In other words, UE needs to know the cell that it is moving to so it can apply the corresponding configuration, including the correct timing alignment and / or TCI state for the cell. Likewise, in the case of inter-DU LTM, when the source DU transmits the L1 / L2 signaling for mobility execution, the target DU needs to be prepared for scheduling UL and DL transmissions for the UE in the target cell, and for receiving SR from the UE.

[0105] Accordingly, before receiving an LTM cell switch command, the UE performs early UL and DL synchronization with its configured LTM candidate cells. For early UL synchronization, the UE transmits a contention-free random access (CFRA) preamble towards an LTM candidate cell in response to a physical DL control channel (PDCCH) order received via the source cell. In order to minimize the data interruption of the source cell due to CFRA towards the LTM candidate cell, the UE does not receive a RA response (with TA) from the LTM candidate cell. Instead, the TA for the LTM candidate cell is indicated in a subsequent LTM cell switch command.

[0106] The LTM cell switch command from the source RAN node (or DU) is a MAC control element (CE) that includes an identifier (e.g., index) of the corresponding LTM candidate cell configuration previously provided to the UE. The MAC CE may also include an identifier of a beam by which the UE should access the target cell. For example, the beam indication is given as a transmission configuration indicator (TCI) state identifier (ID) associated with the LTM candidate cell. Upon receiving the LTM cell switch command, the UE monitors PDCCH on the indicated beam of the target cell. In other words, the UE considers the TCI state for the indicated beam / TCI state to be “activated” when performing the LTM cell switch. The UE also applies the LTM candidate cell configuration identified in the MAC CE. Note that since the UE previously performed early UL synchronization, it does not need to perform RA at LTM cell switch.

[0107] The split CU / DU architecture shown in Figure 1 also supports Rel-18 LTM, including for intra-DU and inter-DU / intra-CU cell changes. In the inter-DU / intra-CU scenario, the candidate cell for LTM is a cell served by a neighbor DU to the (serving or source) DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). In the intra-DU scenario, the candidate cell for LTM is a cell served by the same DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC).

[0108] According to 3 GPP agreements, a UE may perform multiple LTM cell switch procedures without the need of being reconfigured by the RAN. For example, after the UE has performed an LTM cell switch from a serving cell to a first target cell (e.g., a first LTM candidate cell), the UE may perform another LTM cell switch - referred to as “subsequent LTM” - to a second target cell (e.g., a second LTM candidate cell previously configured) without receiving another RRCReconfiguration message in the first target cell. 3GPP Rel-19 will support inter-CU LTM as well as conditional LTM, which is analogous to L3 CHO described above. In conditional LTM, an LTM candidate configuration for an LTM candidate cell includes an execution condition, such as “LTM candidate cell becomes offset better than PCell” or “beam of LTM candidate cell becomes offset better than serving beam”. Instead of executing LTM in response to an LTM cell switch command, the UE executes an LTM cell switch to an LTM candidate cell when the associated execution condition is fulfilled. As such, an LTM candidate cell with an associated execution condition may be referred to as a conditional LTM candidate cell, and corresponding LTM procedure may be referred to as a conditional LTM cell switch. It is expected that Rel-19 will support both intra- and inter-CU conditional LTM.

[0109] However, inter-CU LTM, conditional LTM, subsequent LTM, and subsequent CHO require the support of new security -related functionality that is not part of Rel-18. For example, security key updated is needed whenever the UE’s CU changes but may also be initiated by the RAN as needed during intra-CU / inter-cell mobility or intra-cell operation. Conventionally, intercell L3 handover may be used to trigger security key update, such as illustrated in Figure 5. Handovers (including CHO) and other L3 mobility procedures involve the UE performing RA to the target cell establish UL synchronization, which also helps establish the precise timing for when an updated security key will be used by the UE and the target RAN node.

[0110] As mentioned above, L3 handover introduces undesirable latency, signaling overhead, and interruptions, thereby motivating the use of LTM. However, a UE performs RA to an LTM candidate cell at some unknown time after configuration but before LTM cell switch, such that the RA cannot be used to establish the precise timing for a security key update during LTM. Moreover, L3 handover is unnecessary for intra-cell security key updates since the UE is already synchronized to and should remain in its current serving cell.

[0111] Accordingly, embodiments of the present disclosure address these problems and / or issues by flexible and efficient techniques for a UE, a source RAN node, and (optionally) a target RAN node to perform security key changes without requiring the UE to perform RA to a serving or target cell. At a high level, the UE synchronizes security configuration with the RAN via transmi ssion(s) over physical uplink control channel (PUCCH) and / or physical uplink control channel (PUSCH). Certain embodiments may involve network control of UE security key change, layer-2 (L2) reset, and / or RA.

[0112] In some embodiments, a UE may perform a security key update in conjunction with a mobility procedure to a target cell. For example, when the mobility procedure is an LTM cell switch, the UE may determine whether to perform a security key update based on one or more fields in an LTM candidate cell configuration and / or an LTM cell switch command. In some variants, the UE may perform the security key update before accessing the target cell, such that the UE’s initial control plane (e.g., RRC) and / or user plane (e.g., PDCP) transmission to encrypted and / or integrity protected based on the updated security key(s). In other variants, the UE may perform the security key update after accessing the target cell.

[0113] In other embodiments, the UE may perform a security key update in response to a message from its serving RAN node, which may be unrelated to any mobility procedure. In some variants, the message may be a MAC CE that includes an NCC for security key update and, optionally, an indication of whether the UE should perform RA and / or L2 reset. In other variants, the message may by an RRC message with similar content.

[0114] Embodiments of the present disclosure may provide various advantages and / or benefits. For example, embodiments may facilitate UE and RAN security key update without need for RA, which provides reduced latency, signaling, and / or interruptions compared to the conventional approach of triggering security key update by L3 handover. This may be especially beneficial for security key updates in conjunction with LTM as well as for intra-cell security key updates (e.g., after UE mobility to a target cell). As such, embodiments may facilitate necessary updates for encryption and integrity protection as the UE moves between and within cells in the RAN, thereby increasing security of signaling and user data carried by radio bearers secured in this manner.

[0115] In the present disclosure, the following terms may be used interchangeably: “L1 / L2 based inter-cell mobility”, “L1 / L2 mobility,” “LI -mobility,” “LI based mobility,” “Ll / L2-centric inter-cell mobility,” “L1 / L2 inter-cell mobility,” “inter-cell beam management,” “inter-DU L1 / L2 based inter-cell mobility”, and “L1 / L2 triggered mobility” (or LTM). These terms refer to a scenario in which a UE receives lower layer (i.e., below RRC, such as MAC or PHY) signaling from a network indicating for the UE to change of its serving cell (e.g., PCell) from a source cell to a target cell.

[0116] The content of the lower layer signaling may be referred to as “LTM cell switch command.” Exemplary lower layer signaling includes LI DL control information (DCI) and L2 MAC control element (CE). Compared to conventional RRC signaling, lower layer signaling reduces processing time and interruption time during mobility and may also increase mobility robustness since the network can respond more quickly to changes in the UE’s channel conditions.

[0117] The term “LTM candidate cell” refers to a cell for which the UE is configured for LTM, specifically a cell the UE can move to in a LTM cell switch procedure in response to receiving an LTM cell switch command. An LTM candidate cell may also be referred to herein as “candidate cell”, “(LTM) candidate, “mobility candidate”, “non-serving cell”, “additional cell”, “(LTM) target candidate cell”, “(LTM) target candidate”, and comparable terms. A UE may perform and report measurements (e.g., CSI measurements) on an LTM candidate cell, based on which the UE’s serving RAN node may make an informed decision about which beam (or TCI state) and / or cell to switch the UE. An LTM candidate cell may be a candidate to be a target PCell or PSCell, or an SCell of a cell group (e.g., MCG SCell). In the case of LTM fast recovery, when a failure is detected and the UE selects an LTM candidate cell, the UE performs an LTM cell switch towards the selected LTM candidate cell (e.g., by applying the associated LTM candidate cell configuration) rather than performing RRC re-establishment.

[0118] The change of serving cell (e.g., PCell) may also lead to a change in SCell(s) of the same cell group, e.g., in case an LTM cell switch command triggers the UE to change to another cell group configuration of the same type (e.g., another MCG configuration). For example, an LTM cell switch may include a change in SpCell (e.g., PCell for MCG, PSCell for SCG) and a change (e.g., addition, modification and / or release) in SCells of the same cell group. This may happen when the command triggers the UE to change to another cell group configuration of the same type (e.g., another SCG configuration).

[0119] Before the UE receives the LTM cell switch command, the UE is configured by the network with one or more “LTM candidate cell configurations” via an RRCReconfiguration message. The terms “(LTM) candidate configuration”, “(LTM) candidate target cell configuration”, and “(LTM) target candidate (cell) configuration” may be used interchangeably with LTM candidate cell configuration.

[0120] An LTM candidate cell configuration may be included in an RRC IE such as CellGroupConfig, SpCellConfig, or SCellConfig and / or an embedded RRCReconfiguration message for an LTM candidate cell. An LTM candidate cell configuration includes configuration parameters the UE needs to operate in that LTM candidate cell when it performs an LTM cell switch procedure, e.g., upon reception of the LTM cell switch command. As some more specific examples, an LTM candidate cell configuration can include a PCell configuration and one or more SCell configurations of an MCG, or a PSCell configuration and one or more SCell configurations of an SCG. The exact content and / or structure of the IE and / or embedded message for an LTM candidate cell configuration may be called “RRC model for the candidate configuration” or more simply “RRC model”.

[0121] A UE may receive an LTM candidate cell configuration in a complete form or as a delta (or difference) relative to a reference configuration (which may be signaled separately). In the latter case, the actual LTM candidate configuration is a combination of the delta configuration and the reference configuration.

[0122] The lower layer signaling from the RAN may include an identifier (or index) associated with an LTM candidate cell configuration. The identifier may be sent together with an LTM cell switch command, indicating for the UE to perform an LTM cell switch to the associated LTM candidate cell. The term “mobility configuration” refers to a data structure that is used for or related to a UE mobility procedure, and may include one or more of the following elements (non-exclusive):

[0123] • a candidate configuration, i.e., for a mobility candidate cell;

[0124] • lower layer information, such as PHY configuration, MAC configuration, RLC configuration, cell group configuration, and / or serving cell configuration;

[0125] • higher layer information, such as RRC parameters (e.g., timer values), PDCP configuration, radio bearer configuration, or measurement configuration

[0126] • configuration of measurements for future candidate cells;

[0127] • measurement reporting configuration;

[0128] • CSI resource configuration;

[0129] • CSI reporting configuration;

[0130] • configuration for early DL synchronization, e.g., for early TCI state activation;

[0131] • a configuration for early UL synchronization, e.g., for PDCCH ordered preamble transmission and reception of timing advance (TA);

[0132] • configuration for execution of a mobility procedure according to the candidate configuration, such as indications whether to perform RA, RLC reestablishment, MAC reset, PDCP recovery, etc. as well as RA resources, UL configured grants, timer values, etc.; and

[0133] • information related to security key refresh, e.g., RRC MasterKeyUpdate IE and / or RRC RadioBearerConfig IE that includes SecurityConfig field with SecurityAlgorithmConfig.

[0134] The term “part of a mobility configuration” may refer to a subset of the elements in the above list, and / or a subset of items comprising any of the elements present (e.g., subset of configurations for DL pre-sync).

[0135] The term “mobility procedure” refers to a UE procedure for changing serving cell from a source cell to a target cell, which was a mobility candidate cell prior to execution of the mobility procedure. Examples of mobility procedures include L3 procedures such as HO, PSCell change, SCG change, SN change, CHO, CPC, CPA, and CP AC, as well as L1 / L2 procedures such as intra-CU LTM, inter-CU LTM, and conditional LTM. When the UE performs a mobility procedure to a candidate cell, the UE applies the received candidate configuration (of the mobility configuration) associated with that candidate cell when communicating with that candidate cell. The UE may also use other parts of the mobility configuration in preparing for the mobility procedure, such as performing and reporting measurements, early UL / DL synchronization, etc. A non-conditional mobility procedure may be triggered by a command from the RAN, while a conditional mobility procedure may be triggered by UE measurements meeting an execution condition associated with a candidate cell. The term “subsequent mobility procedure” refers to a further or follow-on mobility procedure performed by the UE after an initial mobility procedure from a source cell to a candidate / target cell, without a reconfiguration or other intermediate intervention by a serving RAN node. The mobility configuration used for the subsequent mobility procedure may have been received by the UE while in in the source cell, prior to the initial mobility procedure.

[0136] The phrase “LTM cell switch procedure” refers to the process of a UE switching (or changing) from a source cell to a target cell (i.e., an LTM candidate cell) using LTM. An LTM cell switch procedure may also be referred to as “L1 / L2 based inter-cell mobility execution”, “LTM execution”, “dynamic switch”, “LTM switch”, “(LTM) cell switch”, “(LTM) serving cell change”, or “(LTM) cell change”. Similarly, the phrase “switching to an LTM candidate cell configuration” means that the UE applies an LTM candidate cell configuration such that the associated LTM candidate cell becomes its new special cell (SpCell, e.g., PCell for LTM in MCG or PSCell for LTM in SCG) or its new SCell. In other words, an LTM candidate cell can be a candidate for the UE’s PCell, PSCell, or SCell.

[0137] Furthermore, an LTM cell switch may involve a UE switching (or changing) from a source cell group to a target cell group using LTM. For example, this may involve a change in the SpCell for a cell group (e.g., PCell for MCG, PSCell for SCG), a change in SCells of the cell group (e.g., addition, modification, and / or release of one or more SCells), and / or a swap between SpCell and SCell roles for two cells in the same cell group.

[0138] The terms “CHO,” “CHO execution,” and “CHO execution procedure” refer to the process of a UE evaluating certain conditions configured by the RAN and, upon the fulfilling of such criteria, switching (or changing) from a source cell to a CHO candidate cell (which becomes a target cell) without further involvement of the source cell (e.g., signaling). In switching to the CHO candidate cell, the UE applies an CHO candidate configuration such that the CHO candidate cell becomes the UE’s new special cell (SpCell, e.g., PCell for LTM in MCG or PSCell for LTM in SCG) or its new SCell. In other words, a CHO candidate cell can be a candidate for the UE’s PCell, PSCell, or SCell. Further, when the CHO candidate cell is the PSCell, CHO may also be referred to as CPA, CPC, CP AC, or subsequent CP AC.

[0139] Furthermore, CHO execution witch may involve a UE switching (or changing) from a source cell group to a target cell group using CHO. For example, this may involve a change in the SpCell for a cell group (e.g., PCell for MCG, PSCell for SCG), a change in SCells of the cell group (e.g., addition, modification, and / or release of one or more SCells), and / or a swap between SpCell and SCell roles for two cells in the same cell group.

[0140] The term “security key” may refer to an integrity protection key for CP, an integrity protection key for UP, an encryption key for CP, an encryption key for UP, or an intermediate key used for derivation of any of these key (e.g., KSNB). The term “security configuration” refers to one or more parameters used to control security key derivation performed by a UE, and may include one or more of the following:

[0141] • a first identifier associated to a candidate cell;

[0142] • a second identifier associated to a source cell the UE is connected to when the mobility procedure is executed;

[0143] • a key set change indicator;

[0144] • a next hop chaining counter (NCC);

[0145] • a non-access stratum (NAS) container (NASC);

[0146] • an indication, indicating that mobility from current serving cell to a certain candidate target cell requires security key refresh;

[0147] • an indication, indicating that mobility towards a certain target cell requires security key refresh (or does not require security key refresh);

[0148] • an indication, indicating that security key refresh is required (or is not required) for subsequent mobility towards a certain cell; and

[0149] • an indication that security key refresh is to be performed without RA.

[0150] An example security configuration is the masterKeyUpdate IE.

[0151] The term “security key refresh,” “security key update,” “AS key refresh” or similar terms refer to a procedure by which a UE changes or updates one or more AS security keys, including during a mobility procedure such as an LTM cell switch procedure. A security key refresh may include at least one of the following operations:

[0152] • UE receives a masterKeyUpdate IE included in a mobility configuration, e.g., in the candidate cell configuration;

[0153] • When a NAS indication (e.g., NASC) is received masterKeyUpdate IE, the UE forwards the NAS indication to UE NAS layer and updates its NAS security context according to 3GPP TS 33.501 clause 6.9.2.3.4;

[0154] • When a key set change indication (e.g., keySetChangelndicator) is received and / or is set to ‘true’ (e.g., within masterKeyUpdate IE), the UE derives or updates KSNB based on KAMF, as specified in 3GPP TS 33.501;

[0155] • UE derives or updates KSNB for the candidate cell configuration based on the current KSNB or the NH, using the NCC value indicated in the received masterKeyUpdate IE, as specified in 3GPP TS 33.501; • UE derives KRRCenc and Kupenc associated with a ciphering algorithm (e.g., cipheringAlgorithm indicated in securityAlgorithmConfig), as specified in 3 GPP TS 33.501;

[0156] • UE derives KRRCint and Kupint associated with an integrity protection algorithm (e.g., integrityProtAlgorithm indicated in securityAlgorithmConfig), as specified in 3 GPP TS 33.501;

[0157] • UE receives a security algorithm configuration included in a mobility configuration, based on which the UE derives UP security keys (e.g., Kupenc and Kupint) and / or CP security keys (e.g., KRRCenc and KRRCint) for encryption and / or integrity protection;

[0158] • UE uses its current security algorithm configuration, based on which the UE derives UP security keys (e.g., Kupenc and Kupint) and / or CP security keys (e.g., KRRCenc and KRRCint) for encryption and / or integrity protection;

[0159] • UE applies the provided ciphering algorithm and associated security key during a PDCP entity re-establishment procedure; and

[0160] • UE applies the provided integrity protection algorithm and associated security key during a PDCP entity re-establishment procedure;

[0161] • UE derives the security key(s) when it receives a mobility configuration, which it may user for a subsequent mobility procedure.

[0162] Figure 6 shows an example system in which some embodiments of the present disclosure may be implemented. UE (601) is a wireless terminal, such as a cellular smartphone. The UE may be connected to the first RAN node (602) over a first wireless interface (604) and, in some cases, to a second RAN node (603) over a second wireless interface (605).

[0163] The first RAN node provides a first cell (607), which may be referred to as the UE’s source cell in the context of mobility (e.g., LTM or L3 HO), or the UE’s serving cell, Special Cell (SpCell), PCell, or PSCell in the context of CA and / or DC. The second RAN node provides a second cell (608), which may be referred to as neighbor cell to the serving cell or, in the context of mobility, as target cell, candidate cell, LTM candidate cell, or inter-CU LTM candidate cell.

[0164] The first RAN node and the second RAN node may be gNBs of an NG-RAN, and may be interconnected over an interface (606), which may be an Xn or Xn-C type of interface. However, the first RAN node and the second RAN node are not necessarily interconnected.

[0165] In the context of mobility, the first RAN node may be referred to as source RAN node since it provides the source cell for UE mobility. Likewise, the second RAN node may be referred to as target or candidate RAN node since it provides the target or candidate cell for UE mobility. In some cases, such as during intra-gNB or intra-CU mobility, the first RAN node and the second RAN node may be a single RAN node. In case of a distributed CU / DU RAN architecture, the first RAN node and / or the second RAN node 603 may be divided into a CU and one or more DUs. As shown in Figure 6, first RAN node includes a first CU (609) and a first DU (610), which may be referred to as serving CU / DU or source CU / DU for the UE. Likewise, the second RAN node includes a second CU (612) and a second DU (613), which may be referred to as target CU / DU or candidate CU / DU for the UE. In some cases, such as during intra-gNB or intra-CU mobility, first / source CU and second / target CU may be a single CU.

[0166] The first CU and the first DU are connected over an interface (611), which may be an Fl type of interface in case of NG-RAN. Correspondingly, the second CU and the second DU are connected over an interface (614), which may also be an Fl type of interface in case of NG-RAN.

[0167] The first RAN node and the second RAN node may be connected to a third network node (615 over respective interfaces (616 and 617). The third network node may be a core network node, such as a UPF or an AMF. In the latter case, the respective interfaces are both NG interfaces and / or N2 reference points. Sometimes the third network node may comprise two different network nodes, such as a source AMF connected with the first RAN node and a target AMF connected with the second RAN node. These two network nodes are inter-connected over an interface, such as an N14 reference point or an Namf type of service-based interface.

[0168] Some embodiments include enhancements to LTM to facilitate intra-cell security key update. In these embodiments, there is a need to be able to indicate the TA to use by the UE in order to avoid RA. In some embodiments, the LTM cell switch command (e.g., MAC CE) can include a Timing Advance Command (TAC) field of which a particular value indicates that the UE should continue to use the same TA for the target cell (e.g., SpCell) as was being used in the source cell before the LTM cell switch. For example, the particular value can correspond to “keep” or “source”. Alternately, 3GPP specifications can be modified to include procedural text that instructs the UE to continue to use the same TA as before an LTM cell switch in which the source cell (e.g., SpCell) and target cell are the same.

[0169] In some of these embodiments, the LTM cell switch command may indicate an LTM candidate cell that is identical to the UE’s current source / serving cell, such that the UE performs a security key update triggered by the LTM cell switch command without actually changing cells. For example, the UE may have previously performed a mobility procedure to arrive in the serving cell, after which the UE receives the LTM cell switch that triggers the security key update.

[0170] In other of these embodiments, the LTM cell switch command may indicate an LTM candidate cell that is different than the UE’s current source / serving cell, such that the UE performs a security key update in conjunction with changing cells (e.g., before or after the LTM cell switch). For example, the RAN node (e.g., DU) that sends the LTM cell switch command may provide UE’s source / serving cell and the indicated LTM candidate cell.

[0171] In some of these embodiments, prior to triggering a security key update, the UE’s serving RAN node may send an RRCReconfiguration message that includes a masterKeyUpdate IE, which includes the NCC value to apply for security key derivation in the next security key update. This NCC value effectively controls whether the UE uses vertical or horizontal key derivation for next security key change. The masterKeyUpdate IE can be included in the RRCReconfiguration message at the top level, as part of an LTM-Config IE, as part of the LTM-Candidate IE within LTM-Config, or as part of an RRCReconfiguration message contained in an LTM-Candidate IE. Note that masterKeyUpdate IE is only exemplary and the NCC value (and / or related information) may be in a different IE that may or may not be related to LTM.

[0172] Subsequently, the serving RAN node triggers the security key update based on an LTM cell switch command, which may be a MAC CE, downlink control information (DCI), or an RRC message. Upon receiving the LTM cell switch command, the UE determines whether to perform security key update, L2 reset, and / or RA based on one or more of the following:

[0173] • whether the LTM candidate configuration ID included in the LTM cell switch command points to the UE’s current serving cell (e.g., SpCell) as LTM candidate cell;

[0174] • whether the LTM cell switch command includes a valid LTM candidate configuration ID (e.g., as opposed to being absent or having a value that exceeds the maximum number of LTM candidate cell configurations that can be configured at the UE);

[0175] • one or more explicit indications (e.g., flags, Booleans, etc.) in the LTM cell switch command, of whether to perform security key change, L2 reset, and / or RA;

[0176] • one or more explicit indications (e.g., masterKeyUpdate field) in the LTM candidate configuration whose ID is included in the LTM cell switch command and / or that is applied during LTM cell switch. The explicit indication(s) may always trigger the associated actions and may override any other indications used to control security key change, L2 reset, and / or RA. For example, the explicit indication(s) may indicate any of the following: o whether to perform security key update, L2 reset, and / or RA; o whether security key update is required when performing mobility to an LTM candidate (target) cell, which may or may not be identical to the current serving cell; o whether security key update is required when performing subsequent mobility to an LTM candidate (target) cell, which may or may not be identical to the current serving cell; o whether security key update is required when performing mobility from the UE’s current serving cell to an LTM candidate (target) cell, which may or may not be identical to the current serving cell; o whether security key update with or without RA is required when performing mobility from the UE’s current serving cell to an LTM candidate (target) cell, which may or may not be identical to the current serving cell.

[0177] Alternately, instead of relying on an earlier RRCReconfiguration message, the LTM cell switch command can include the necessary information to control security key update, L2 reset, and / or RA. For example, the LTM cell switch command can include a new field containing NCC value that controls horizontal / vertical key derivation, with the presence of this field causing the UE to update the security keys. In some variants, the presence of the NCC field also triggers L2 reset required for security key change and whether the UE performs RA. In other variants, another field is included in the LTM cell switch command to control L2 reset and RA. In other variants, another field is included in the LTM cell switch command to indicate security key update according to the NCC field (e.g., horizontal or vertical).

[0178] Figure 7 shows a signaling diagram for an exemplary inter-CU LTM procedure in accordance with some of the embodiments described above. The procedure involves a UE (710), a source RAN node (720), a target RAN node (730), and an AMF / UPF (740). Although the operations shown in Figure 7 are given numerical labels, this is done to facilitate the following explanation rather than to require or imply any particular operational order, unless expressly stated otherwise.

[0179] The source RAN node provides a serving cell for the UE, while the target RAN node provides one or more neighbor cells to the serving cell. In operation 1, the source RAN node obtains from the target RAN node an LTM candidate cell configuration for one of the neighbor cells, and provides this to the UE as part of an LTM configuration (which may include other LTM candidate cell configurations).

[0180] In operation 2, the UE sends lower-layer measurement reports for configured LTM candidate cells to the source RAN node, based on which the source RAN node decides to trigger an inter-CU LTM cell switch for the UE from the serving / source cell to the neighbor LTM candidate cell provided by the target RAN node (operation 3). The source RAN node sends an LTM cell switch command to the UE (operation 4) and an indication of LTM cell switch execution to the target RAN node that provides the LTM candidate cell (operation 5). This message to the target RAN node may include security information for the UE. In operations 6-8, the UE executes the LTM cell switch to the LTM candidate (target) cell, transmits initial UL data to the target RAN node, and then sends an RRCReconfigurationComplete message indicating that the LTM cell switch has been completed.

[0181] In operations 9-10, the target RAN node indicates to the source RAN node that the UE has successfully accessed the target cell and the source RAN node responds with SN STATUS TRANSFER. In operation 11, the target RAN node transmits an NGAP PATH SWITCH REQUEST message to the AMF to initiate switch of the UE data path from the source RAN node to the target RAN node. In operation 12, the AMF sends the target RAN node an NGAP PATH SWITCH REQUEST ACKNOWLEDGE message that includes new security context information for the UE. For example, this information may be carried in a Security Context IE and may include an NCC value, an NH parameter (including a new security key), and optionally a New Security Context Indicator IE.

[0182] In operation 13, the target RAN node transmits a UE CONTEXT RELEASE message to the source RAN node. In operation 14, based on the security context information received in operation 12, the target RAN node determines that a security key update (e.g., AS key refresh) should be performed for the UE.

[0183] In operation 15 (optional), the target RAN node provides an updated LTM configuration to the UE. This LTM configuration may include information needed to update one or more security keys, such as a masterKeyUpdate IE that includes the NCC value to apply for security key derivation, which effectively controls whether the UE performs vertical or horizontal key derivation. The masterKeyUpdate IE may be provided in any of the forms discussed above. The LTM configuration may also contain one or more fields that indicating whether to perform security key update, L2 reset, and / or random access, such as in any of the forms discussed above.

[0184] In operation 16, the target RAN node transmits an LTM cell switch command MAC CE to the UE to trigger security key update. The command includes an indication of an intra-cell LTM cell switch, e.g., based on including an ID of an LTM candidate cell configuration for the UE’s current serving SpCell. This LTM candidate cell configuration may have been updated in operation 15 to include information needed to derive a new security key. Alternately, the LTM cell switch command may include information needed to derive a new security key, such as the NCC value. The LTM cell switch may also contain one or more fields that indicating whether to perform security key update, L2 reset, and / or random access, such as in any of the forms discussed above. For example, the indication of whether to perform RA is a particular TA value that indicates the UE should continue to use the same TA for the target cell (e.g., SpCell) as was being used in the source cell before the LTM cell switch. As another example, the LTM cell switch command includes an explicit indication to perform LTM cell switch without RA (i.e., “RACH-less”).

[0185] In operation 17, the UE executes the intra-cell LTM cell switch procedure and performs security key update, L2 reset, and / or RA according to the received LTM cell switch command (operation 16) and the LTM configuration (if received in operation 15). For example, the UE determines not to perform RA based on the LTM cell switch command including a particular TA value that indicates the UE should continue to use the same TA for the target cell (e.g., SpCell) as was being used in the source cell before the LTM cell switch. As another example, the security key update performed by the UE is based on the NCC value received in operation 15 or 16 and on a UE derived NH parameter. In operations 18-19, the UE transmits to the target RAN node initial UL data without RA in the current serving cell (e.g., SpCell) and an RRCReconfigurationComplete message to confirm that the UE has successfully executed the intra-cell LTM cell switch (i.e., without cell change) and security key update.

[0186] Other embodiments include new messages that facilitate intra-cell security key update without an accompanying LTM cell switch. In various embodiments, these new messages can be MAC CEs or RRC messages. In some of these embodiments, the message includes an NCC and one or more indications (e.g., flags, Booleans, etc.) of whether to perform security key change, L2 reset, and / or RA. The indications may be explicit or implicit. For example, the MAC CE can include a Timing Advance Command (TAC) field of which a particular value indicates that the UE should continue to use the same TA. For example, the particular value can correspond to “keep” or “source”. As another example, the type of the MAC CE can implicitly indicate that a security key change should be performed without RA.

[0187] In some of these embodiments, when the message is a MAC CE, the UE MAC layer interprets it and performs (or initiates) the indicated security key change, L2 reset, and / or RA directly without reference to any previously received RRC information, such as an LTM candidate configuration. This interpretation can be based on the content (e.g., explicit indications) and / or type of the MAC CE.

[0188] In other of these embodiments, when the message is a MAC CE, the UE MAC layer interprets it and indicates to the UE RRC layer that security key update, L2 reset, and / or RA should be performed. This interpretation can be based on the content (e.g., explicit indications) and / or type of the MAC CE. Based on the indication from the UE MAC layer, the UE RRC layer performs the corresponding actions, which may also be based on information in a previous RRC message received from the serving RAN node. For example, the previous RRC message may be an RRCReconfiguration that indicates ciphering and / or integrity protection algorithms, such as in SecurityAlgorithmConfig field within RadioBearerConfig IE.

[0189] In other embodiments, the message may be a MAC CE that includes security information that updates security information received previously in an RRC configuration, but does not necessarily trigger a security key updates. In this case, the security key update may be indicated by control information included in an LTM candidate cell configuration as described above. In other embodiments, the message may be an RRCReconfiguration message with a reconfigurationWithSync IE that includes a new field indicating whether to perform security key change, L2 reset, and / or RA. For example, the new field may indicate for the UE to perform a reconfiguration with sync procedure without RA. As another example, the new field may be a RACH-lessHO field indicating targetNTA as source, which means that the UE should perform reconfiguration with sync to access the target cell but apply the same TA as in the source cell rather than performing RA to the target cell.

[0190] Figure 8 shows a signaling diagram for an exemplary intra-cell security key update procedure in accordance with some of the embodiments described above. The procedure involves a UE (810), a serving RAN node (820), and an AMF / UPF (830). Although the operations shown in Figure 8 are given numerical labels, this is done to facilitate the following explanation rather than to require or imply any particular operational order, unless expressly stated otherwise.

[0191] In operation 1 (optional), the UE may execute an inter-CU mobility procedure (e.g., L3 handover or LTM) from a source cell provided by a source RAN node to a target cell provided by serving RAN node. Prior to operation 2, the AMF decides to update security key(s) for the UE (e.g., AS re-keying). Although not shown, this may involve an initial NAS SMC procedure towards the UE to update the NAS related security information (e.g., a fresh NAS COUNT). In operation 2, the AMF then derives a new AS security key (e.g., KSNB) and transmits an NGAP UE CONTEXT MODIFICATION REQUEST message to the serving RAN node. The message includes the new AS security key, e.g., in a Security Key IE.

[0192] In operation 3, the serving RAN node responds to the AMF in an NGAP UE CONTEXT MODIFICATION RESPONSE message. In operation 4, the serving RAN node decides to perform a security key update for the UE (e.g., key change on-the-fly) based on the new security key received from the AMF in operation 2. In operation 5, the serving RAN node transmits a security key command message to the UE to trigger the security key update. In some embodiments, the message is a MAC CE, such as a new security key command MAC CE. In other embodiments, the message is an RRC message, such as an RRCReconfiguration message including a reconfigurationWithSync field.

[0193] The message transmitted to the UE in operation 5 includes information indicating whether or not to perform security key change, L2 reset and random access. In one example, the message includes an indication to perform a key change on-the-fly procedure. In one example, the message includes an NCC value. In one example, the message includes an indication to derive a new AS security key. In one example, the message includes an indication to perform a RACH-less procedure. In operation 6, the UE performs security key update, L2 reset, and / or RA according to the message received in operation 5. For example, the UE determines to not perform RA based on the message including a particular TA value that indicates the UE should continue to use the same TA. As another example , the security key update performed by the UE is based on the NCC value received in operation 5 and on a UE derived NH parameter.

[0194] In operation 7, the UE transmits to the target RAN node initial UL data without RA in the current serving cell (e.g., SpCell), using the updated security key(s) derived in operation 6 for encryption and / or integrity protection. Optionally, the UE also transmits a response to the message received in operation 5, such as an RRCReconfigurationComplete message to confirm that the UE has performed security key update.

[0195] Other embodiments include techniques to synchronize the timing of security key update between the UE and the RAN (i.e., when the new security key will be used). Different example techniques are described below.

[0196] In some embodiments, the LTM candidate configuration or the message (e.g., RRC) may include a configured grant for UE transmission of an RRCReconfigurationComplete message. Receiving a transmission from the UE on the granted resources indicates that the UE has updated security keys, such that the RAN node should also use updated security keys to decrypt and / or integrity check the RRCReconfigurationComplete message on the link layer. Alternately, the RAN node may blindly decrypt and integrity check the received RRC message using both old and the new security key, but only pass to RRC layer the decrypted version that passes integrity check (i.e., with matching checksums).

[0197] In other embodiments, the message (e.g., MAC CE) may include a configured grant for UE transmission of the initial UL message (e.g., PDCP PDU) protected by the updated security key(s). Receiving a transmission from the UE on the granted resources indicates that the UE has updated security keys, such that the RAN node should also use updated security keys to decrypt and / or integrity check the initial UL message on the link layer. Alternately, the RAN node may blindly decrypt and integrity check the received UL message using both old and the new security key, but only pass to higher layers the decrypted version that passes integrity check (i.e., with matching checksums).

[0198] In other embodiments, the LTM candidate configuration may include or indicate a set of PUCCH resources specifically for transmitting a SR for the RRCReconfigurationComplete message. Receiving an SR from the UE on these granted PUCCH resources indicates that the UE has updated security keys, such that the RAN node should also use updated security keys to decrypt and / or integrity check the subsequent RRCReconfigurationComplete message on the link layer. In other embodiments, receiving the message causes the UE to switch to a different PUCCH resource allocation for SR transmission. For example, the message may be an RRC message that includes a new RRC configuration with a different PUCCH resource allocation, Receiving an SR from the UE in PUCCH resources from this allocation indicates that the UE has updated security keys, such that the RAN node should also use updated security keys to decrypt and / or integrity check subsequent messages scheduled based on the received SR.

[0199] In other embodiments, the LTM cell switch command or the message may include explicit timing information for when a security key update shall be applied. For example, the timing information may include a System Frame Number (SFN), a subframe number, a timeslot number, etc. of the serving RAN node’s radio interface. Each of these may be an absolute value or an offset / differential value. As a more specific example, the SFN value may be an offset from the SFN in which the UE receives the LTM cell switch command or message. Alternately, the timing information may be in terms of real time, such as an absolute Universal Time Coordinate (UTC) or an offset from when the UE receives the LTM cell switch command or message.

[0200] In other embodiments, both the UE and the RAN node apply the security key update at a specified, pre-configured, and / or hard-coded time after transmission / reception of the LTM cell switch command or the message.

[0201] In other embodiments, the UE transmits an acknowledgement (e.g., HARQ ACK) of successful reception of the LTM cell switch command or the message (e.g., MAC CE), and both the UE and the RAN node apply the security key update at a specified, pre-configured, and / or hard-coded time after transmission / reception of the acknowledgement. In some variants, the UE transmits acknowledgements only for intra-cell LTM cell switch commands or only for intra-cell LTM cell switch commands that indicate a security key update. In any case, reception of acknowledgement indicates to the RAN node that the UE will perform the security key update.

[0202] In other embodiments, the UE indicates to the serving RAN node its security key update capability, including the minimum duration needed to apply a security key update after reception of the LTM cell switch command or the message. In some variants, the UE and RAN node directly apply their corresponding security key updates after this indicated minimum duration. In other variants, the RAN node indicates in the LTM cell switch command or the message when the security key update should be applied (e.g., according to embodiments described above), based on the security key update capability provided by the UE.

[0203] Various features of the embodiments summarized above correspond to various operations illustrated in Figures 9-10, which show exemplary methods (e.g., procedures) for a UE and a RAN node, respectively. In other words, various features of the operations described below correspond to various embodiments described above. Furthermore, the exemplary methods shown in Figures 9-10 can be used cooperatively to provide various benefits, advantages, and / or solutions to problems described herein. Although Figures 9-10 show specific blocks in particular orders, the operations of the exemplary methods can be performed in different orders than shown and can be combined and / or divided into blocks having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

[0204] In particular, Figure 9 shows an exemplary method (e.g., procedure) for a UE configured for mobility between cells of a RAN, according to various embodiments of the present disclosure. The exemplary method can be performed by a UE (e.g., wireless device) such as described elsewhere herein.

[0205] The exemplary method includes the operations of block 920, where the UE receives, from the RAN via a first cell, a first message that includes an indication to perform a security key update. The exemplary method also includes the operations of block 930, where the UE updates one or more access stratum (AS) security keys based on the indication. The exemplary method also includes the operations of block 940, where the UE transmits, to the RAN via a second cell, a second message that indicates a security key update has been performed. The second message is transmitted without the UE performing a RA to the second cell in conjunction with the security key update.

[0206] In some embodiments, the first cell is the same as the second cell. In other words, the UE performs the security key update without RA and without changing cells.

[0207] In some embodiments, the updated one or more AS security keys include a master RAN node security key and the following security keys derived from the master RAN node security key: a first key for integrity protection of signaling, a second key for ciphering of signaling, a third key for integrity protection of user data, and a fourth key for ciphering of user data. In some embodiments, the exemplary method also includes the operations of block 935, where before transmitting the second message in block 940, the UE performs encryption and / or integrity protection of the second message using at least one of the updated AS security keys. In other words, the second message is secured using at least one of the updated AS security keys.

[0208] In some embodiments, the first message is one of the following: a medium access control (MAC) control element (CE), or a radio resource control (RRC) message. In some of these embodiments, the first message also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2 (L2) reset.

[0209] In some variants of these embodiments, the first message is a MAC CE and the further indication of whether the UE should perform RA to the second cell is a Timing Advance Command (TAC) field having a particular value indicating the UE should use its current timing advance (TA) with respect to the first cell for an initial transmission to the second cell. In other variants of these embodiments, the first message is an RRCReconfiguration message, with the indication and the further indication being included in a reconfigurationWithSync information element (IE) of the RRCReconfiguration message.

[0210] In some of these embodiments, the first message includes a grant of resources in the second cell for transmission of the second message via the second cell, and transmitting the second message via the granted resources in the second cell (e.g., block 940) indicates that the security key update has been performed by the UE. In some variants of these embodiments, the second message is one of the following: a scheduling request (SR), an RRCReconfigurationComplete message, or a protocol data unit (PDU).

[0211] In some of these embodiments, the first message is a command to perform an LTM cell switch from the first cell to the second cell. In some of these embodiments, the second message is an acknowledgement (e.g., HARQ) that the LTM cell switch command was received successfully.

[0212] In some embodiments, the first message also includes a security configuration and the one or more AS security keys are updated further based on the security configuration. In some of these embodiments, the indication to perform security key update is one of the following: implicit from the security configuration being included in the first message, or an explicit indication separate from the security configuration.

[0213] In other embodiments, the exemplary method also includes the operations of block 910, where the UE receives, from the RAN via the first cell, a third message that includes a security configuration for the UE. The one or more AS security keys are updated further based on the security configuration. In some of these embodiments, the third message is an RRCReconfiguration message that includes an LTM candidate configuration for the second cell, and the first message is a command to perform LTM cell switch from the first cell to the second cell. In some variants of these embodiments, the security configuration is included in a masterKeyUpdate IE of the RRCReconfiguration message.

[0214] In some variants of these embodiments, the LTM cell switch command also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and an L2 reset. In some further variants, the indication and the further indication are based on one or more explicit indications in the LTM cell switch command. In other further variants, the indication and the further indication are based on an identifier of the LTM candidate configuration for the second cell in the LTM cell switch command, and one of the following:

[0215] • the second cell being the same as the first cell; or

[0216] • one or more explicit indications in the LTM candidate configuration for the second cell. In some of these embodiments, the security configuration (i.e., in the first message or the third message) includes one of more of the following:

[0217] • an indication whether horizontal or vertical key derivation should be used;

[0218] • a next-hop (NH) parameter;

[0219] • a next-hop chaining counter (NCC); and

[0220] • a container of non-AS (NAS) information.

[0221] In addition, Figure 10 shows an exemplary method (e.g., procedure) for a RAN node configured to facilitate mobility between cells by UEs, according to various embodiments of the present disclosure. The exemplary method can be performed by a RAN node (e.g., base station, eNB, gNB, ng-eNB, DU, etc.) such as described elsewhere herein.

[0222] The exemplary method includes the operations of block 1030, where the RAN node sends, to a UE via a first cell, a first message that includes an indication to perform a security key update. The exemplary method also includes the operations of block 1040, where the RAN node receives, from the UE via a second cell, a second message that indicates a security key update has been performed by the UE based on the indication. The second message is received without a RA by the UE to the second cell in conjunction with the security key update.

[0223] In some embodiments, the first cell is the same as the second cell. In other words, the UE performs the security key update without RA and without changing cells.

[0224] In some embodiments, the security key update performed by the UE is to one or more AS security keys, and the exemplary method also includes the operations of block 1050, where the RAN node updates one or more corresponding AS security keys.

[0225] In some of these embodiments, the first message is sent in block 1030 in conjunction with or responsive to updating the one or more corresponding AS security keys in block 10509. In other of these embodiments, updating the one or more corresponding AS security keys in block 1050 is responsive to the second message in block 1040.

[0226] In some of these embodiments, the updated corresponding AS security keys include a master RAN node security key and the following security keys derived from the master RAN node security key: a first key for integrity protection of signaling, a second key for ciphering of signaling, a third key for integrity protection of user data, and a fourth key for ciphering of user data. In some of these embodiments, the exemplary method also includes the operations of block 1060, where the RAN node performs decryption and / or integrity checking on the second message based on the updated corresponding AS security keys.

[0227] In some embodiments, the exemplary method also includes the operations of block 1010, where the RAN node receives, from a core network node (e.g., AMF), an updated security configuration for the UE. The first message in block 1030 is responsive to the received updated security configuration.

[0228] In some embodiments, the first message is a MAC CE or an RRC message. In some embodiments, the first message also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and an L2 reset.

[0229] In some variants of these embodiments, the first message is a MAC CE and the further indication of whether the UE should perform RA to the second cell is a Timing Advance Command (TAC) field having a particular value indicating the UE should use its current TA with respect to the first cell for an initial transmission to the second cell. In other variants of these embodiments, the first message is an RRCReconfiguration message, with the indication and the further indication being included in a reconfigurationWithSync IE of the RRCReconfiguration message.

[0230] In some of these embodiments, the first message includes a grant of resources in the second cell for transmission of the second message via the second cell, and receiving the second message via the granted resources in the second cell (e.g., block 1040) indicates that the security key update has been performed by the UE. In some variants of these embodiments, the second message is one of the following: a scheduling request (SR), an RRCReconfigurationComplete message, or a protocol data unit (PDU).

[0231] In some of these embodiments, the first message is a command to perform an LTM cell switch from the first cell to the second cell. In some of these embodiments, the second message is an acknowledgement (e.g., HARQ) that the LTM cell switch command was received successfully by the UE.

[0232] In some embodiments, the first message also includes a security configuration and the security key update is performed by the UE (as indicated by the second message) further based on the security configuration. In some of these embodiments, the indication to perform security key update is one of the following: implicit from the security configuration being included in the first message, or an explicit indication separate from the security configuration.

[0233] In other embodiments, the exemplary method also includes the operations of block 1020, where the RAN node sends, to the UE via the first cell, a third message that includes a security configuration for the UE. The security key update is performed by the UE (as indicated by the second message) further based on the security configuration. In some of these embodiments, the third message is an RRCReconfiguration message that includes an LTM candidate configuration for the second cell, and the first message is a command to perform LTM cell switch from the first cell to the second cell. In some variants of these embodiments, the security configuration is included in a masterKeyUpdate IE of the RRCReconfiguration message.

[0234] In some variants of these embodiments, the LTM cell switch command also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and an L2 reset. In some further variants, the indication and the further indication are based on one or more explicit indications in the LTM cell switch command. In other further variants, the indication and the further indication are based on an identifier of the LTM candidate configuration for the second cell in the LTM cell switch command, and one of the following:

[0235] • the second cell being the same as the first cell; or

[0236] • one or more explicit indications in the LTM candidate configuration for the second cell.

[0237] In some of these embodiments, the security configuration (i.e., in the first message or the third message) includes one of more of the following:

[0238] • an indication whether horizontal or vertical key derivation should be used;

[0239] • a next-hop (NH) parameter;

[0240] • a next-hop chaining counter (NCC) value; and

[0241] • a container of non-AS (NAS) information.

[0242] Although various embodiments are described above in terms of methods, techniques, and / or procedures, the person of ordinary skill will readily comprehend that such methods, techniques, and / or procedures can be embodied by various combinations of hardware and software in various systems, communication devices, computing devices, control devices, apparatuses, non-transitory computer-readable media, computer program products, etc.

[0243] Figure 11 shows an example of a communication system 1100 in accordance with some embodiments. In this example, communication system 1100 includes a telecommunication network 1102 that includes an access network 1104 (e.g., RAN) and a core network 1106, which includes one or more core network nodes 1108. Access network 1104 includes one or more access network nodes, such as network nodes l l lOa-b (one or more of which may be referred to as network nodes 1110), or any other similar 3GPP access nodes or non-3GPP access points. Moreover, as will be appreciated by those of skill in the art, a network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor.

[0244] Thus, it will be understood that network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, telecommunication network 1102 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 1102 that supports an ORAN specification (e.g., a specification published by the O-RAN Alliance, or any similar organization) and may operate alone or together with other nodes to implement one or more functionalities of any node in telecommunication network 1102, including one or more network nodes 1110 and / or core network nodes 1108.

[0245] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O-CU- CP) or an O-CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an 0-2 interface defined by the 0-RAN Alliance or comparable technologies. Network nodes 1110 facilitate direct or indirect connection of UEs, such as by connecting UEs 1112a-d (one or more of which may be referred to as UEs 1112) to core network 1106 over one or more wireless connections.

[0246] Example wireless communications over a wireless connection include transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, communication system 1100 may include any number of wired or wireless networks, network nodes, UEs, and / or any other components or systems that may facilitate or participate in the communication of data and / or signals whether via wired or wireless connections. Communication system 1100 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0247] UEs 1112 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with network nodes 1110 and other communication devices. Similarly, network nodes 1110 are arranged, capable, configured, and / or operable to communicate directly or indirectly with UEs 1112 and / or with other network nodes or equipment in telecommunication network 1102 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in telecommunication network 1102. In the depicted example, core network 1106 connects network nodes 1110 to one or more hosts, such as host 1116. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. Core network 1106 includes one or more core network nodes (e.g., 1108) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and / or hosts, such that the descriptions thereof are applicable to the corresponding components of core network node 1108. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0248] Host 1116 may be under the ownership or control of a service provider other than an operator or provider of access network 1104 and / or telecommunication network 1102, and may be operated by the service provider or on behalf of the service provider. Host 1116 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio / video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

[0249] As a whole, communication system 1100 of Figure 11 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

[0250] In some examples, telecommunication network 1102 is a cellular network that implements 3 GPP standardized features. Accordingly, telecommunication network 1102 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 1102. For example, telecommunication network 1102 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC) / Massive loT services to yet further UEs.

[0251] In some examples, UEs 1112 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to access network 1104 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 1104. Additionally, a UE may be configured for operating in single- or multi-RAT or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e., being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

[0252] In the example, hub 1114 communicates with access network 1104 to facilitate indirect communication between one or more UEs (e.g., 1112c and / or 1112d) and network nodes (e.g., 1110b). In some examples, hub 1114 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 1114 may be a broadband router enabling access to core network 1106 for the UEs. As another example, hub 1114 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 1110, or by executable code, script, process, or other instructions in hub 1114. As another example, hub 1114 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, hub 1114 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 1114 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 1114 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, hub 1114 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0253] Hub 1114 may have a constant / persistent or intermittent connection to network node 1110b. Hub 1114 may also allow for a different communication scheme and / or schedule between hub 1114 and UEs (e.g., 1112c and / or 1112d), and between hub 1114 and core network 1106. In other examples, hub 1114 is connected to core network 1106 and / or one or more UEs via a wired connection. Moreover, hub 1114 may be configured to connect to an M2M service provider over access network 1104 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 1110 while still connected via hub 1114 via a wired or wireless connection. In some embodiments, hub 1114 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to network node 1110b. In other embodiments, hub 1114 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1110b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0254] In some embodiments, any of UEs 1112 may be configured to perform operations attributed to a UE in various methods or procedures described above, including the exemplary method shown in Figure 9. In some embodiments, any of network nodes 1110 may be configured to perform operations attributed to a RAN node in various methods or procedures described above, including the exemplary method shown in Figure 10.

[0255] Figure 12 shows a UE 1200 in accordance with some embodiments. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by 3 GPP, including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0256] A UE may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and / or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

[0257] UE 1200 includes processing circuitry 1202 that is operatively coupled via a bus 1204 to an input / output interface 1206, a power source 1208, a memory 1210, a communication interface 1212, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 12. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc. Processing circuitry 1202 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in memory 1210. Processing circuitry 1202 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general -purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, processing circuitry 1202 may include multiple central processing units (CPUs).

[0258] In the example, input / output interface 1206 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into UE 1200. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

[0259] In some embodiments, power source 1208 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. Power source 1208 may further include power circuitry for delivering power from power source 1208 itself, and / or an external power source, to the various parts of UE 1200 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging power source 1208. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1208 to make the power suitable for the respective components of UE 1200 to which power is supplied.

[0260] Memory 1210 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, memory 1210 includes one or more application programs 1214, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1216. Memory 1210 may store, for use by UE 1200, any of a variety of various operating systems or combinations of operating systems.

[0261] Memory 1210 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and / or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ Memory 1210 may allow UE 1200 to access instructions, application programs and the like, stored on transitory or non- transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in memory 1210, which may be or comprise a device-readable storage medium.

[0262] Processing circuitry 1202 may be configured to communicate with an access network or other network using communication interface 1212. Communication interface 1212 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1222. Communication interface 1212 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1218 and / or a receiver 1220 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 1218 and receiver 1220 may be coupled to one or more antennas (e.g., antenna 1222) and may share circuit components, software, or firmware, or alternatively be implemented separately.

[0263] In the illustrated embodiment, communication functions of communication interface 1212 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / internet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0264] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1212, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0265] As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or to a robotic arm performing a medical procedure according to the received input.

[0266] A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or Virtual Reality (VR), a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence of the intended application of the loT device in addition to other components as described in relation to UE 1200 shown in Figure 12.

[0267] As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and / or measurements, and transmits the results of such monitoring and / or measurements to another UE and / or a network node. The UE may in this case be an M2M device, which may in a 3 GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0268] In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g., by controlling an actuator) to increase or decrease the drone’s speed. The first and / or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

[0269] In some embodiments, UE 1200 may be configured to perform operations attributed to a UE in various methods or procedures described above, including the exemplary method shown in Figure 9.

[0270] Figure 13 shows a network node 1300 in accordance with some embodiments. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (e.g., radio base stations, Node Bs, eNBs, gNBs), and 0-RAN nodes or components of an 0-RAN node (e g., 0-RU, 0-DU, O-CU).

[0271] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units, distributed units (e.g., in an 0-RAN access node) and / or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[0272] Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell / multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and / or Minimization of Drive Tests (MDTs).

[0273] Network node 1300 includes processing circuitry 1302, memory 1304, communication interface 1306, and power source 1308. Network node 1300 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which network node 1300 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, network node 1300 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1304 for different RATs) and some components may be reused (e.g., a same antenna 1310 may be shared by different RATs). Network node 1300 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1300, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 1300.

[0274] Processing circuitry 1302 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 1300 components, such as memory 1304, to provide network node 1300 functionality.

[0275] In some embodiments, processing circuitry 1302 includes a system on a chip (SOC). In some embodiments, processing circuitry 1302 includes one or more of radio frequency (RF) transceiver circuitry 1312 and baseband processing circuitry 1314. In some embodiments, RF transceiver circuitry 1312 and baseband processing circuitry 1314 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1312 and baseband processing circuitry 1314 may be on the same chip or set of chips, boards, or units.

[0276] Memory 1304 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computer-executable memory devices that store information, data, and / or instructions that may be used by processing circuitry 1302. Memory 1304 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions (collectively denoted computer program 1304a, which may be in the form of a computer program product) capable of being executed by processing circuitry 1302 and utilized by network node 1300. Memory 1304 may be used to store any calculations made by processing circuitry 1302 and / or any data received via communication interface 1306. In some embodiments, processing circuitry 1302 and memory 1304 is integrated.

[0277] Communication interface 1306 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, communication interface 1306 comprises port(s) / terminal(s) 1316 to send and receive data, for example to and from a network over a wired connection. Communication interface 1306 also includes radio frontend circuitry 1318 that may be coupled to, or in certain embodiments a part of, antenna 1310. Radio front-end circuitry 1318 comprises filters 1320 and amplifiers 1322. Radio front-end circuitry 1318 may be connected to an antenna 1310 and processing circuitry 1302. The radio front-end circuitry may be configured to condition signals communicated between antenna 1310 and processing circuitry 1302. Radio front-end circuitry 1318 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1318 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1320 and / or amplifiers 1322. The radio signal may then be transmitted via antenna 1310. Similarly, when receiving data, antenna 1310 may collect radio signals which are then converted into digital data by radio front-end circuitry 1318. The digital data may be passed to processing circuitry 1302. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0278] In certain alternative embodiments, network node 1300 does not include separate radio front-end circuitry 1318, instead, processing circuitry 1302 includes radio front-end circuitry and is connected to antenna 1310. Similarly, in some embodiments, all or some of RF transceiver circuitry 1312 is part of communication interface 1306. In still other embodiments, communication interface 1306 includes one or more ports or terminals 1316, radio front-end circuitry 1318, and RF transceiver circuitry 1312, as part of a radio unit (not shown), and communication interface 1306 communicates with baseband processing circuitry 1314, which is part of a digital unit (not shown). Antenna 1310 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. Antenna 1310 may be coupled to radio front-end circuitry 1318 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, antenna 1310 is separate from network node 1300 and connectable to network node 1300 through an interface or port.

[0279] Antenna 1310, communication interface 1306, and / or processing circuitry 1302 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment. Similarly, antenna 1310, communication interface 1306, and / or processing circuitry 1302 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipment.

[0280] Power source 1308 provides power to the various components of network node 1300 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1308 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1300 with power for performing the functionality described herein. For example, network node 1300 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of power source 1308. As a further example, power source 1308 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0281] Embodiments of network node 1300 may include additional components beyond those shown in Figure 13 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, network node 1300 may include user interface equipment to allow input of information into network node 1300 and to allow output of information from network node 1300. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1300.

[0282] In some embodiments, network node 1300 may be configured to perform operations attributed to a RAN node in various methods or procedures described above, including the exemplary method shown in Figure 10.

[0283] Figure 15 is a block diagram illustrating a virtualization environment 1500 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1500 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 1500 includes components defined by the O-RAN Alliance, such as an O-Cloud environment orchestrated by a Service Management and Orchestration Framework via an 0-2 interface.

[0284] Applications 1502 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1500 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein. In some embodiments, one or more virtual nodes 1502 may be configured to perform operations attributed to a RAN node in various methods or procedures described above, including the exemplary method shown in Figure 10.

[0285] Hardware 1504 includes processing circuitry, memory that stores software and / or instructions (collectively denoted computer program 1504a, which may be in the form of a computer program product) executable by hardware processing circuitry, and / or other hardware devices as described herein, such as a network interface, input / output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1506 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1508a-1508b (one or more of which may be referred to as VMs 1508), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. Virtualization layer 1506 may present a virtual operating platform that appears like networking hardware to the VMs 1508.

[0286] VMs 1508 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1506. Different embodiments of the instance of a virtual appliance 1502 may be implemented on one or more of VMs 1508, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

[0287] In the context of NFV, each VM 1508 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each VM 1508, and that part of hardware 1504 that executes that VM, be it hardware dedicated to that VM and / or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 1508 on top of the hardware 1504 and corresponds to the application 1502.

[0288] Hardware 1504 may be implemented in a standalone network node with generic or specific components. Hardware 1504 may implement some functions via virtualization. Alternatively, hardware 1504 may be part of a larger cluster of hardware (e.g., such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration function 1510, which, among others, oversees lifecycle management of applications 1502. In some embodiments, hardware 1504 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system 1512 which may alternatively be used for communication between hardware nodes and radio units.

[0289] The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the spirit and scope of the disclosure. Various embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art.

[0290] The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and / or electronic devices and can include, for example, electrical and / or electronic circuitry, devices, modules, processors, memories, logic solid state and / or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and / or displaying functions, and so on, as such as those that are described herein. Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according to one or more embodiments of the present disclosure.

[0291] As described herein, device and / or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and / or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

[0292] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0293] In addition, certain terms used in the present disclosure, including the specification and drawings, can be used synonymously in certain instances (e.g., “data” and “information”). It should be understood that although such terms may be used synonymously herein, there may be instances when such terms are not intended to be used synonymously. Embodiments of the techniques and apparatus described herein also include, but are not limited to, the following enumerated examples:

[0294] Al . A method for a user equipment (UE) configured for mobility between cells of a radio access network (RAN), the method comprising: receiving, from the RAN via a first cell, a first message that includes an indication to perform a security key update; updating one or more access stratum (AS) security keys based on the indication; and transmitting, to the RAN via a second cell, a second message that indicates a security key update has been performed, wherein the second message is transmitted without performing a random access (RA) to the second cell in conjunction with the security key update.

[0295] Ala. The method of embodiment Al, wherein the first cell is the same as the second cell.

[0296] Alb. The method of any of embodiments Al-Ala, wherein the updated one or more AS security keys include a master RAN node security key and the following security keys derived from the master RAN node security key: a first key for integrity protection of signaling, a second key for ciphering of signaling, a third key for integrity protection of user data, and a fourth key for ciphering of user data.

[0297] Ale. The method of any of embodiments Al -Alb, wherein the second message is secured using at least one of the updated AS security keys.

[0298] A2. The method of any of embodiments Al -Ale, wherein the first message is one of the following: a medium access control (MAC) control element (CE), or a radio resource control (RRC) message.

[0299] A2a. The method of embodiment A2, wherein the first message also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2 (L2) reset.

[0300] A2b. The method of embodiment A2a, wherein the first message is a MAC CE and the further indication of whether the UE should perform RA to the second cell is a Timing Advance Command (TAC) field having a particular value indicating the UE should use its current timing advance (TA) with respect to the first cell for an initial transmission to the second cell.

[0301] A2c. The method of embodiment A2a, wherein the first message is an RRCReconfiguration message, with the indication and the further indication being included in a reconfigurationWithSync information element (IE) of the RRCReconfiguration message.

[0302] A2d. The method of any of embodiments A2-A2c, wherein the first message includes a grant of resources in the second cell for transmission of the second message via the second cell, and transmitting the second message via the granted resources in the second cell indicates that the security key update has been performed by the UE.

[0303] A2e. The method of embodiment A2d, wherein the second message is one of the following: a scheduling request (SR), an RRCReconfigurationComplete message, or a protocol data unit (PDU).

[0304] A2f. The method of any of embodiments A2-A2b, wherein the first message is a command to perform a layer-l / layer-2 triggered mobility (LTM) cell switch from the first cell to the second cell.

[0305] A2g. The method of embodiment A2f, wherein the second message is an acknowledgement that the LTM cell switch command was received successfully.

[0306] A3. The method of any of embodiments Al-A2g, wherein the first message also includes a security configuration, and the one or more AS security keys are updated further based on the security configuration.

[0307] A3a. The method of embodiment A3, wherein the indication to perform security key update is one of the following: implicit from the security configuration being included in the first message, or an explicit indication separate from the security configuration.

[0308] A4. The method of any of embodiments Al -Ale, further comprising receiving, from the RAN via the first cell, a third message that includes a security configuration for the UE, wherein the one or more AS security keys are updated further based on the security configuration.

[0309] A4a. The method of embodiment A4, wherein the third message is an RRCReconfiguration message that includes a layer-l / layer-2 triggered mobility (LTM) candidate configuration for the second cell, and the first message is a command to perform LTM cell switch from the first cell to the second cell.

[0310] A4b. The method of embodiment A4a, wherein the security configuration is included in a masterKeyUpdate information element (IE) of the RRCReconfiguration message.

[0311] A4c. The method of any of embodiments A4a-A4b, wherein the LTM cell switch command also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2 (L2) reset.

[0312] A4d. The method of embodiment A4c, wherein the indication and the further indication are based on one of the following: one or more explicit indications in the LTM cell switch command; or an identifier of the LTM candidate configuration for the second cell in the LTM cell switch command, and one of the following: one or more explicit indications in the LTM candidate configuration for the second cell, or the second cell being the same as the first cell.

[0313] A4e. The method of any of embodiments A3-A4d, wherein the security configuration includes one of more of the following: an indication whether horizontal or vertical key derivation should be used; a next-hop (NH) parameter; a next-hop chaining counter (NCC) value; and a container of non-AS (NAS) information.

[0314] BL A method for a radio access network (RAN) node configured to facilitate mobility between cells by user equipment (UEs), the method comprising: sending, to a UE via a first cell, a first message that includes an indication to perform a security key update; and receiving, from the UE via a second cell, a second message that indicates a security key update has been performed by the UE based on the indication, wherein the second message is received without a random access (RA) by the UE to the second cell in conjunction with the security key update.

[0315] Bia. The method of embodiment Bl, wherein the first cell is the same as the second cell.

[0316] Bib. The method of any of embodiments Bl-Bla, wherein the security key update performed by the UE is to one or more access stratum (AS) security keys, and the method further comprises updating one or more corresponding AS security keys based on the security key update performed by the UE.

[0317] Bic. The method of embodiment Bib, wherein the one or more AS security keys include a master RAN node security key and the following security keys derived from the master RAN node security key: a first key for integrity protection of signaling, a second key for ciphering of signaling, a third key for integrity protection of user data, and a fourth key for ciphering of user data.

[0318] Bld. The method of any of embodiments Blb-Blc, wherein the second message is secured using at least one of the updated AS security keys, and the method further comprises performing decryption and / or integrity checking on the second message based on the updated corresponding AS security keys.

[0319] Ble. The method of any of embodiments Bl -Bld, further comprising receiving, from a core network node, an updated security configuration for the UE, wherein the first message is responsive to the received updated security configuration.

[0320] B2. The method of any of embodiments Bl -Ble, wherein the first message is one of the following: a medium access control (MAC) control element (CE), or a radio resource control (RRC) message.

[0321] B2a. The method of embodiment B2, wherein the first message also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2 (L2) reset.

[0322] B2b. The method of embodiment B2a, wherein the first message is a MAC CE and the further indication of whether the UE should perform RA to the second cell is a Timing Advance Command (TAC) field having a particular value indicating the UE should use its current timing advance (TA) with respect to the first cell for an initial transmission to the second cell.

[0323] B2c. The method of embodiment B2a, wherein the first message is an RRCReconfiguration message, with the indication and the further indication being included in a reconfigurationWithSync information element (IE) of the RRCReconfiguration message.

[0324] B2d. The method of any of embodiments B2-B2c, wherein the first message includes a grant of resources in the second cell for transmission of the second message via the second cell, and receiving the second message via the granted resources in the second cell indicates that the security key update has been performed by the UE.

[0325] B2e. The method of embodiment B2d, wherein the second message is one of the following: a scheduling request (SR), an RRCReconfigurationComplete message, or a protocol data unit (PDU).

[0326] B2f. The method of any of embodiments B2-B2b, wherein the first message is a command to perform a layer-l / layer-2 triggered mobility (LTM) cell switch from the first cell to the second cell.

[0327] B2g. The method of embodiment B2f, wherein the second message is an acknowledgement that the LTM cell switch command was received successfully by the UE.

[0328] B3. The method of any of embodiments Bl-B2g, wherein the first message also includes a security configuration, and the security key update is performed by the UE further based on the security configuration.

[0329] B3a. The method of embodiment B3, wherein the indication to perform security key update is one of the following: implicit from the security configuration being included in the first message, or an explicit indication separate from the security configuration.

[0330] B4. The method of any of embodiments Bl-Ble, further comprising sending, to the UE via the first cell, a third message that includes a security configuration for the UE, wherein the security key update is performed by the UE further based on the security configuration.

[0331] B4a. The method of embodiment B4, wherein the third message is an RRCReconfiguration message that includes a layer-l / layer-2 triggered mobility (LTM) candidate configuration for the second cell, and the first message is a command to perform LTM cell switch from the first cell to the second cell.

[0332] B4b. The method of embodiment B4a, wherein the security configuration is included in a masterKeyUpdate information element (IE) of the RRCReconfiguration message.

[0333] B4c. The method of any of embodiments B4a-B4b, wherein the LTM cell switch command also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2 (L2) reset.

[0334] B4d. The method of embodiment B4c, wherein the indication and the further indication are based on one of the following: one or more explicit indications in the LTM cell switch command; or an identifier of the LTM candidate configuration for the second cell in the LTM cell switch command, and one of the following: one or more explicit indications in the LTM candidate configuration for the second cell, or the second cell being the same as the first cell.

[0335] B4e. The method of any of embodiments B3-B4d, wherein the security configuration includes one of more of the following: an indication whether horizontal or vertical key derivation should be used; a next-hop (NH) parameter; a next-hop chaining counter (NCC) value; and a container of non-AS (NAS) information.

[0336] CL User equipment (UE) configured for mobility between cells of a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate with RAN nodes; and processing circuitry operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of embodiments Al-A4e. C2. User equipment (UE) configured for mobility between cells of a radio access network (RAN), the UE being further configured to perform operations corresponding to the methods of any of embodiments Al-A4e.

[0337] C3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of user equipment (UE) configured for mobility between cells of a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments Al-A4e.

[0338] C4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of user equipment (UE) configured for mobility between cells of a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments Al-A4e.

[0339] DI . Radio access network (RAN) node configured to facilitate mobility between cells by user equipment (UEs), the RAN node comprising: communication interface circuitry configured to communicate with UEs; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of embodiments Bl-B4e.

[0340] D2. Radio access network (RAN) node configured to facilitate mobility between cells by user equipment (UEs), the RAN node being further configured to perform operations corresponding to the methods of any of embodiments Bl-B4e.

[0341] D3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a radio access network (RAN) node configured to facilitate mobility between cells by user equipment (UEs), configure the RAN node to perform operations corresponding to the methods of any of embodiments Bl-B4e.

[0342] D4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a radio access network (RAN) node configured to facilitate mobility between cells by user equipment (UEs), configure the RAN node to perform operations corresponding to the methods of any of embodiments Bl-B4e.

Claims

CLAIMS1. A method for a user equipment, UE, configured for mobility between cells of a radio access network, RAN, the method comprising: receiving (920), from the RAN via a first cell, a first message that includes an indication to perform a security key update; updating (930) one or more access stratum, AS, security keys based on the indication; and transmitting (940), to the RAN via a second cell, a second message that indicates a security key update has been performed, wherein the second message is transmitted without the UE performing a random access, RA, to the second cell in conjunction with the security key update.

2. The method of claim 1, wherein the first cell is the same as the second cell.

3. The method of any of claims 1-2, wherein the updated one or more AS security keys include a master RAN node security key and the following security keys derived from the master RAN node security key: a first key for integrity protection of signaling, a second key for ciphering of signaling, a third key for integrity protection of user data, and a fourth key for ciphering of user data.

4. The method of any of claims 1-3, further comprising, before transmitting (940) the second message, performing (935) encryption and / or integrity protection of the second message using at least one of the updated AS security keys.

5. The method of any of claims 1-4, wherein: the first message is one of the following: a medium access control, MAC, control element, CE, or a radio resource control, RRC, message; and the first message also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2, L2, reset.

6. The method of claim 5, wherein the first message is a MAC CE and the further indication of whether the UE should perform RA to the second cell is a Timing AdvanceCommand, TAC, field having a particular value indicating the UE should use its current timing advance, TA, with respect to the first cell for an initial transmission to the second cell.

7. The method of claim 5, wherein the first message is an RRCReconfiguration message, with the indication and the further indication being included in a reconfigurationWithSync information element, IE, of the RRCReconfiguration message.

8. The method of any of claims 5-7, wherein the first message includes a grant of resources in the second cell for transmission of the second message via the second cell, and transmitting (940) the second message via the granted resources in the second cell indicates that the security key update has been performed by the UE.

9. The method of claim 8, wherein the second message is one of the following: a scheduling request, SR; an RRCReconfigurationComplete message; or a protocol data unit, PDU.

10. The method of any of claims 5-6, wherein: the first message includes a command to perform a layer-l / layer-2 triggered mobility, LTM, cell switch from the first cell to the second cell; and the second message is an acknowledgement that the LTM cell switch command was received successfully.

11. The method of any of claims 1-10, wherein: the first message also includes a security configuration; the one or more AS security keys are updated further based on the security configuration; and the indication to perform security key update is one of the following: implicit from the security configuration being included in the first message, or an explicit indication separate from the security configuration.

12. The method of any of claims 1-4, further comprising receiving (910), from the RAN via the first cell, a third message that includes a security configuration for the UE, wherein the one or more AS security keys are updated further based on the security configuration.

13. The method of claim 12, wherein:the third message is an RRCReconfiguration message that includes a layer-l / layer-2 triggered mobility, LTM, candidate configuration for the second cell; the security configuration is included in a masterKeyUpdate information element, IE, of the RRCReconfiguration message; and the first message is a command to perform LTM cell switch from the first cell to the second cell.

14. The method of claim 13, wherein the LTM cell switch command also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2, L2, reset.

15. The method of claim 14, wherein the indication and the further indication are based on one of the following: one or more explicit indications in the LTM cell switch command; or an identifier of the LTM candidate configuration for the second cell in the LTM cell switch command, and one of the following: one or more explicit indications in the LTM candidate configuration for the second cell, or the second cell being the same as the first cell.

16. The method of any of claims 11-15, wherein the security configuration includes one of more of the following: an indication whether horizontal or vertical key derivation should be used; a next-hop, NH, parameter; a next-hop chaining counter, NCC, value; and a container of non-access stratum, NAS, information.

17. A method for a radio access network, RAN, node configured to facilitate mobility between cells by user equipment, UEs, the method comprising: sending (1030), to a UE via a first cell, a first message that includes an indication to perform a security key update; and receiving (1040), from the UE via a second cell, a second message that indicates a security key update has been performed by the UE based on the indication, wherein the second message is received without a random access, RA, by the UE to the second cell in conjunction with the security key update.

18. The method of claim 17, wherein the first cell is the same as the second cell.

19. The method of any of claims 17-18, wherein the security key update performed by the UE includes updates to one or more access stratum, AS, security keys, and the method further comprises updating (1050) one or more corresponding AS security keys20. The method of claim 19, wherein one of the following applies: the first message is sent in conjunction with or responsive to updating (1050) the one or more corresponding AS security keys; or updating (1050) the one or more corresponding AS security keys is responsive to the second message.

21. The method of any of claims 19-20, wherein the updated corresponding AS security keys include a master RAN node security key and the following security keys derived from the master RAN node security key: a first key for integrity protection of signaling, a second key for ciphering of signaling, a third key for integrity protection of user data, and a fourth key for ciphering of user data.

22. The method of any of claims 19-21, further comprising performing (1060) decryption and / or integrity checking on the second message using at least one of the updated corresponding AS security keys.

23. The method of any of claims 17-22, further comprising receiving (1010) from a core network node an updated security configuration for the UE, wherein the first message is responsive to the received updated security configuration.

24. The method of any of claims 17-23, wherein: the first message is one of the following: a medium access control, MAC, control element, CE, or a radio resource control, RRC, message; and the first message also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2, L2, reset.

25. The method of claim 24, wherein the first message is a MAC CE and the further indication of whether the UE should perform RA to the second cell is a Timing Advance Command, TAC, field having a particular value indicating the UE should use its current timing advance, TA, with respect to the first cell for an initial transmission to the second cell.

26. The method of claim 24, wherein the first message is an RRCReconfiguration message, with the indication and the further indication being included in a reconfigurationWithSync information element, IE, of the RRCReconfiguration message.

27. The method of any of claims 24-26, wherein the first message includes a grant of resources in the second cell for transmission of the second message via the second cell, and receiving the second message via the granted resources in the second cell indicates that the security key update has been performed by the UE.

28. The method of claim 27, wherein the second message is one of the following: a scheduling request, SR; an RRCReconfigurationComplete message; or a protocol data unit, PDU.

29. The method of any of claims 24-25, wherein: the first message includes a command to perform a layer-l / layer-2 triggered mobility, LTM, cell switch from the first cell to the second cell; and the second message is an acknowledgement that the LTM cell switch command was received successfully by the UE.

30. The method of any of claims 17-29, wherein: the first message also includes a security configuration; the security key update is performed by the UE further based on the security configuration; and the indication to perform security key update is one of the following: implicit from the security configuration being included in the first message, or an explicit indication separate from the security configuration.

31. The method of any of claims 17-23, further comprising sending (1020), to the UE via the first cell, a third message that includes a security configuration for the UE, wherein the security key update is performed by the UE further based on the security configuration.

32. The method of claim 31, wherein: the third message is an RRCReconfiguration message that includes a layer-l / layer-2 triggered mobility, LTM, candidate configuration for the second cell; the security configuration is included in a masterKeyUpdate information element, IE, of the RRCReconfiguration message; and the first message is a command to perform LTM cell switch from the first cell to the second cell.

33. The method of claim 32, wherein the LTM cell switch command also includes a further indication of whether the UE should perform one or more of the following in conjunction with the security key update: RA to the second cell, and a layer-2, L2, reset.

34. The method of claim 33, wherein the indication and the further indication are based on one of the following: one or more explicit indications in the LTM cell switch command; or an identifier of the LTM candidate configuration for the second cell in the LTM cell switch command, and one of the following: one or more explicit indications in the LTM candidate configuration for the second cell, or the second cell being the same as the first cell.

35. The method of any of claims 29-34, wherein the security configuration includes one of more of the following: an indication whether horizontal or vertical key derivation should be used; a next-hop, NH, parameter; a next-hop chaining counter, NCC, value; and a container of non-access stratum, NAS, information.

36. User equipment, UE (310, 601, 710, 810, 1112, 1200) configured for mobility between cells of a radio access network, RAN (199, 1104), the UE comprising: communication interface circuitry (1212) configured to communicate with RAN nodes (100, 320, 602, 603, 720, 730, 820, 1110, 1300, 1402); andprocessing circuitry (1202) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive, from the RAN via a first cell, a first message that includes an indication to perform a security key update; update one or more access stratum, AS, security keys based on the indication; and transmit, to the RAN via a second cell, a second message that indicates a security key update has been performed, wherein the second message is transmitted without performing a random access, RA, to the second cell in conjunction with the security key update.

37. The UE of claim 36, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 2-16.

38. User equipment, UE (310, 601, 710, 810, 1112, 1200) configured for mobility between cells of a radio access network, RAN (199, 1104), the UE being further configured to: receive, from the RAN via a first cell, a first message that includes an indication to perform a security key update; update one or more access stratum, AS, security keys based on the indication; and transmit, to the RAN via a second cell, a second message that indicates a security key update has been performed, wherein the second message is transmitted without performing a random access, RA, to the second cell in conjunction with the security key update.

39. The UE of claim 38, being further configured to perform operations corresponding to the methods of any of claims 2-16.

40. Non-transitory, computer-readable medium (1210) storing computer-executable instructions that, when executed by processing circuitry (1201) of user equipment, UE (310, 601, 710, 810, 1112, 1200) configured for mobility between cells of a radio access network, RAN (199, 1104), configure the UE to perform operations corresponding to the methods of any of claims 1-16.

41. Computer program product (1214) comprising computer-executable instructions that, when executed by processing circuitry (1201) of user equipment, UE (310, 601, 710, 810, 1112, 1200) configured for mobility between cells of a radio access network, RAN (199, 1104), configure the UE to perform operations corresponding to the methods of any of claims 1-16.

42. Radio access network, RAN, node (100, 320, 602, 603, 720, 730, 820, 1110, 1300, 1402) configured to facilitate mobility between cells by user equipment, UEs (310, 601, 710, 810,1112, 1200), the RAN node comprising: communication interface circuitry (1306, 1404) configured to communicate with UEs; and processing circuitry (1302, 1404) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: send, to a UE via a first cell, a first message that includes an indication to perform a security key update; and receive, from the UE via a second cell, a second message that indicates a security key update has been performed by the UE based on the indication, wherein the second message is received without a random access, RA, by the UE to the second cell in conjunction with the security key update.

43. The RAN node of claim 42, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 18-35.

44. Radio access network, RAN, node (100, 320, 602, 603, 720, 730, 820, 1110, 1300, 1402) configured to facilitate mobility between cells by user equipment, UEs (310, 601, 710, 810,1112, 1200), the RAN node being further configured to: send, to a UE via a first cell, a first message that includes an indication to perform a security key update; and receive, from the UE via a second cell, a second message that indicates a security key update has been performed by the UE based on the indication, wherein the second message is received without a random access, RA, by the UE to the second cell in conjunction with the security key update.

45. The RAN node of claim 44, being further configured to perform operations corresponding to the methods of any of claims 18-35.

46. Non-transitory, computer-readable medium (1304, 1404) storing computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a radio access network, RAN, node (100, 320, 602, 603, 720, 730, 820, 1110, 1300, 1402) configured to facilitate mobility between cells by user equipment, UEs (310, 601, 710, 810, 1112, 1200), configure the RAN node to perform operations corresponding to the methods of any of claims 17-35.

47. Computer program product (1304a, 1404a) comprising computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a radio access network, RAN, node (100, 320, 602, 603, 720, 730, 820, 1110, 1300, 1402) configured to facilitate mobility between cells by user equipment, UEs (310, 601, 710, 810, 1112, 1200), configure the RAN node to perform operations corresponding to the methods of any of claims 17-35.

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