Patent Description:
Integrated access and backhaul (IAB), where part of the wireless spectrum is used for the backhaul connection of base stations instead of fiber, allows a more flexible and cheaper deployment of dense networks as compared to deployments where there is a dedicated fiber link to the base stations. A full-fledged, multi-hop, IAB solution that is based on split architecture (i.e., Centralized Unit (CU) and Distributed Unit (DU) architecture) has been specified for NR.

<NPL> provides a discussion for PCI reconfiguration signalling.

The present application is directed to subject-matter as disclosed by the appended claims.

A wireless transmit/receive unit (WTRU) operating in CONNECTED mode may be configured tc receive an indication/configuration from a network regarding changes in information related to the serving cell's identity (e.g., physical cell identity (PCI), cell global identity (CGI), etc.), which may contain additional information such as the conditions when this change becomes effective (e.g., delta time or specific slot/frame). Upon the reception of this indication, and if a condition is also specified, fulfillment of the condition, the WTRU may consider the new PCI/CGI as the serving cell's PCI/CGI, consider the old PCI as belonging to a neighbor cell, and/or update the security keys that are used for encryption and integrity protection based on the new PCI.

A WTRU that is operating in CONNECTED mode, after detecting a change in serving cell information according to example solutions above and updating the security keys, may be configured to use the new security keys for encrypting/decrypting and integrity protection/verification of UL/DL packets in the PDCP in one of the following ways: (<NUM>) use the new keys for the UL (i.e., encryption and integrity protection) immediately after the computation of the new keys; (<NUM>) use the new keys for the DL (i.e. decryption and integrity verification) immediately after the computation of the new keys; (<NUM>) use the new keys for the UL (i.e., encryption and integrity protection) a specified duration (e.g., delta time from the computation of the keys, specific frame/slot number, etc.) after the computation of the new keys; (<NUM>) use the new keys for the DL (i.e. decryption and integrity verification) a specified duration (e.g., delta time from the computation of the keys, specific frame/slot number, etc.) after the computation of the new keys; and/or (<NUM>) keep using the old keys in the UL and DL, until a reception of a DL packet that is not associated with the new key (e.g., integrity verification with the old key fails, but integrity verification with the new key succeeds).

A WTRU that is operating in CONNECTED mode, may be configured to receive an indication/configuration from the network regarding changes in information related to a neighbor cell's identity (e.g., PCI, CGI, etc.), which may contain additional information such as the conditions when this change becomes effective (e.g., delta time or specific slot/frame). The WTRU, upon the reception of this indication (or if a condition is also specified, from the fulfillment of the condition), may consider the new PCI/CGI as the neighbor cell's PCI/CGI and/or may update the measurements associated with the neighbor cell to reflect the change in PCI (e.g., change the cell identity index in the measurement report from the old PCI to the new PCI).

A WTRU that is operating in CONNECTED mode may receive configuration information from the network indicating a set of equivalent identities for the serving cell (e.g., list of PCIs, list of CGls, etc.). If the WTRU is not able to detect the current PCI associated with the serving cell (e.g., in the SSBs it is measuring), the WTRU may be configured to not consider a radio link failure and instead try to detect the other equivalent PCIs. Upon the detection of one of the equivalent PCIs, the WTRU may be configured to consider the new PCI as the serving cell's PCI, consider the old PCI as belonging to a neighbor cell, and/or updates the security keys that are used for encryption and integrity protection based on the new PCI.

A WTRU that is operating in INACTIVE mode, may be configured such that upon being suspended to INACTIVE state, to receive a RAN notification area (RNA). Further, while in INACTIVE state, the WTRU may be configured to receive an indication (e.g., broadcast signaling) from the network indicating a change of the identity of the cell that the WTRU is currently camping on (e.g., PCI, CGI, TAC, etc.). The WTRU may be configured to refrain from triggering RAN area update (RANU), even if the new PCI/TAC is not in the WTRU's RNA configuration and/or updates the RNA configuration to include the new PCI/TAC.

For example, the communications systems <NUM> may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique-word discrete Fourier transform Spread OFDM (ZT-UW-DFT-S-OFDM), unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bank multicarrier (FBMC), and the like.

As shown in <FIG>, the communications system <NUM> may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) <NUM>, a core network (CN) <NUM>, a public switched telephone network (PSTN) <NUM>, the Internet <NUM>, and other networks <NUM>, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a station (STA), may be configured to transmit and/or receive wireless signals and may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like.

Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN <NUM>, the Internet <NUM>, and/or the other networks <NUM>. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a NodeB, an eNode B (eNB), a Home Node B, a Home eNode B, a next generation NodeB, such as a gNode B (gNB), a new radio (NR) NodeB, a site controller, an access point (AP), a wireless router, and the like.

In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR Radio Access , which may establish the air interface <NUM> using NR.

The WTRU <NUM> may include a full duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for both the UL (e.g., for transmission) and DL (e.g., for reception) may be concurrent and/or simultaneous. In an embodiment, the WTRU <NUM> may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for either the UL (e.g., for transmission) or the DL (e.g., for reception)).

The AP may have access or an interface to a Distribution System (DS) or another type of wired/wireless network that carries traffic in to and/or out of the BSS. 11e DLS or an <NUM>.

The primary channel may be a fixed width (e.g., <NUM> wide bandwidth) or a dynamically set width. In certain representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) may be implemented, for example in <NUM> systems.

11af and <NUM>. 11af and <NUM>. 11n, and <NUM>. 11af supports <NUM>, <NUM>, and <NUM> bandwidths in the TV White Space (TVWS) spectrum, and <NUM>. 11ah may support Meter Type Control/Machine-Type Communications (MTC), such as MTC devices in a macro coverage area.

11n, <NUM>. 11ac, <NUM>. 11af, and <NUM>. If the primary channel is busy, for example, due to a STA (which supports only a <NUM> operating mode) transmitting to the AP, all available frequency bands may be considered busy even though a majority of the available frequency bands remains idle.

The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using subframe or transmission time intervals (TTls) of various or scalable lengths (e.g., containing a varying number of OFDM symbols and/or lasting varying lengths of absolute time).

For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling of different protocol data unit (PDU) sessions with different requirements), selecting a particular SMF 183a, 183b, management of the registration area, termination of non-access stratum (NAS) signaling, mobility management, and the like. For example, different network slices may be established for different use cases such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for MTC access, and the like. The AMF 182a, 182b may provide a control plane function for switching between the RAN <NUM> and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and/or non-3GPP access technologies such as WiFi.

As discussed above, integrated access and backhaul (IAB), where part of the wireless spectrum is used for the backhaul connection of base stations instead of fiber, allows a more flexible and cheaper deployment of dense networks as compared to deployments where there is a dedicated fiber link to the base stations. A full-fledged, multi-hop, IAB solution that is based on split architecture (i.e. Centralized Unit (CU) and Distributed Unit (DU) architecture) has been specified for NR.

<FIG> illustrates an IAB user plane (UP) protocol architecture <NUM>, according to an embodiment. <FIG> illustrates an IAB control plane (CP) protocol architecture <NUM>, according to an embodiment. The UP architecture <NUM> and the CP architecture <NUM> may comprise a mobile termination (MT) part <NUM>, which may be used to communicate with a parent node, and a DU part <NUM>, which may be used to communicate with a child node or a normal WTRU (e.g., WTRU <NUM>). Both the UP and CP architectures may employ a routing/forwarding approach inspired by IP networks, where each IAB node is assigned an IP address that is routable from a donor base station (and associated L2 addresses), and intermediate IAB nodes forward the packets transparently based on route identifiers/destination addresses. The IAB node may terminate the DU functionality. A base station, which may be referred to as an IAB-donor <NUM>, may terminate the CU functionality <NUM>. Thus, the IAB node and donor CU <NUM> may form one logical base station unit employing CU/DU split architecture regardless of how many hops apart the IAB node and donor CU are physically from each other. The IAB node serving a WTRU (e.g., IAB node <NUM> serving WTRU <NUM> in <FIG>), may be referred to as the access IAB node while the nodes between the IAB donor DU and the access IAB node (e.g., IAB node <NUM> in <FIG>) may be referred to as intermediate IAB nodes. In some embodiments, an IAB node may play the role of both an access IAB node (for the WTRUs that are directly connected to it) and an intermediate IAB node (for WTRUs that are served by its descendant IAB nodes).

Hop-by-hop RLC may be used between the IAB nodes, instead of an End to End (E2E) RLC between the donor DU <NUM> and the WTRU <NUM>. An adaption layer, referred to as backhaul adaptation protocol (BAP), may be used to enable efficient multi-hop forwarding. The IAB-donor <NUM> may assign a unique L2 address (BAP address) to each IAB node that it controls (e.g., IAB node <NUM> and IAB node <NUM>). In case of multiple paths, multiple route IDs may be associated to each BAP address. The BAP of the origin node (IAB-donor DU for the DL traffic, and the access IAB node for the UL) may add a BAP header to packets they are transmitting, which may include a BAP routing ID (e.g., BAP address of the destination/source IAB node and the path ID). If a packet arrives that has a BAP routing ID that contains a BAP address that is equal to the IAB nodes BAP address, it knows the packet is destined for it and passes it on to higher layers for processing (i.e., an F1-C/U message destined for the IAB node's DU, an F1-C message that contains SRB data for a WTRU directly connected to the IAB node, or an F1-U message that contains DRB data for a WTRU directly connected to the IAB node). Otherwise, the IAB node may employ routing/mapping tables to determine where to forward the data to. Each IAB node may have a routing table (configured by the IAB donor CU) containing the next hop identifier for each BAP routing ID. Separate routing tables are kept for the DL and UL direction, where the DL table is used by the DU part of the IAB node, while the MT part of the IAB node uses the UL table.

Backhaul (BH) RLC channels may be used for transporting packets between IAB nodes (or between an IAB-donor DU and an IAB node). A BH RLC channel configuration contains the associated RLC and logical channel configuration. Either many-to-one (N:<NUM>) or one-to-one (<NUM>:<NUM>) mapping may be performed between WTRU radio bearers and BH RLC channels. N:<NUM> mapping multiplexes several WTRU radio bearers into a single BH RLC channel based on specific parameters, such as QoS profile of the bearers, and is suitable for bearers that do not have very strict requirements such as best effort bearers. The <NUM>:<NUM> mapping, on the other hand, may map each WTRU radio bearer onto a separate BH RLC channel, and is designed to ensure finer QoS granularity at WTRU radio bearer level. <NUM>:<NUM> mapping is suitable for bearers with strict throughput or/and latency requirements, such as GBR (Guaranteed Bit Rate) bearers or VoIP bearers.

When an IAB node detects a BH radio link failure (RLF), the IAB node may send a BH RLF indication (which is a BAP control PDU) to its descendant nodes. Upon receiving such an indication form a parent node, the IAB node may initiate procedures such as re-establishment to another parent or pause transmission/reception with the concerned parent.

In a multi-hop IAB network, data congestion may occur on intermediate IAB node, which may lead to packet drops if left unresolved. Though higher layer protocols such as TCP may be used to assure reliability, TCP congestion avoidance and slow start mechanisms may be very costly to overall end to end performance (e.g., throughput degradation). Therefore, IAB networks employ flow control. For the DL, both end-to-end (E2E) and hop-by-hop (H2H) flow control mechanisms are available.

The DL E2E flow control may be based on the DL Data Delivery Status (DDDS) specified for CU/DU split architecture. In DDDS, the DU (in the context of IAB networks, the DU part of the access IAB node) reports to the CU (in the context of IAB networks, the donor CU, specifically, the CU-UP) information such as the desired buffer size per DRB, desired data rate per DRB, the highest successfully delivered PDCP SN, lost packets (i.e. not ACKed by the DU at RLC level), etc. In some embodiments, only access IAB nodes perform DDDS (i.e., IABs report only information concerning the DRBs of the WTRUs that they are directly serving) and no information is provided regarding the BH RLC channels.

For DL H2H flow control, an IAB node generates a flow control message (which is also a BAP control PDU) when its buffer load exceeds a certain level or when it receives a flow control polling message from a peer BAP entity (e.g., a child node). In some embodiments, the H2H flow control information indicates the available buffer size and may be at the granularity of BH RLC channels (e.g., available buffer = value_1 for BH RLC channel #<NUM>, available buffer = value_2 or per BH RLC channel #<NUM>, etc.) or destination routing ID (e.g., available buffer= value_1 for destination routing ID = address1, available buffer = value2 for destination routing ID =addres2, etc.). The node receiving the flow control message may use the information to control the traffic flow towards the sender (e.g., throttle or pause the traffic associated with certain BH RLC channel or/and destination if the flow control message indicated a low available buffer for the concerned traffic, increase the traffic flow if the flow control was indicating a high available buffer value, etc). The exact actions taken on flow control and the configurations/values of thresholds and other parameters to trigger flow control message (e.g., buffer threshold values, polling timers, etc.) may be left to IAB/network implementation.

Pre-emptive buffer status reporting (BSR) has been specified, where an IAB node may trigger BSR to its parent node(s) even before new data has arrived in its UL buffer, based on the BSR that it has received from its child nodes or WTRUs, or scheduling grants it has provided to them (i.e. an indication of anticipated data). Legacy NR mechanisms are applied where an IAB node controls the flow of UL data from its children nodes and WTRUs by the providing them with proper UL scheduling grants based on the BSR received from them. In some embodiments, IAB nodes are static nodes. However, handover of IAB nodes (also referred to as migration or relocation) from one donor to another is supported for load balancing and also for handling radio link failures (RLFs) due to blockage, e.g., due to moving objects, such as vehicles, seasonal changes (foliage), or infrastructure changes (new buildings). Intra-donor CU handover is supported (i.e. the target and the source parent DUs of the IAB node are controlled by the same donor CU) and inter-donor CU handover is expected to be specified.

IAB connectivity via MR-DC is supported. For example, an IAB node may be connected to the network via EN-DC, where the master node is an LTE node and the secondary node is an NR node.

In some embodiments, from a WTRU's point of view, IAB nodes appear to be normal base stations).

The master information block (MIB) may be transmitted on the broadcast channel (BCH) with a periodicity of <NUM> and repetitions made within <NUM> and it includes parameters that are needed to acquire SIB1 from the cell. The first transmission of the MIB is scheduled in subframes and repetitions are scheduled according to the periodicity of the SSB (synchronization signal block).

Two types of synchronization signals are defined for NR: primary synchronization signal (PSS) and the Secondary Synchronization Signal (SSS). The synchronization signal/PBCH block (SSB) includes a PSS, SSS and Physical Broadcast Channel (PBCH).

The WTRU may identify each cell via the physical-layer cell identity (PCI), which is derived from the PCI group number included in the SSS and the physical layer identity included in the PSS. There are <NUM> unique PCIs defined in <NUM> NR, double of that in LTE (<NUM>). The NR PCIs are divided into <NUM> unique PCI groups and each group including three different identities.

Limiting the number of PCIs makes the initial PCI detection by the WTRUs during cell search easier. However, the limited number of PCIs inevitably leads to the reuse of the same PCI values in different cells controlled by different gNBs. Therefore, a PCI might not uniquely identify a neighbor cell, and each cell additionally broadcasts, as a part of the system information (SI), a globally unique cell global identifier (CGI). The CGI is constructed from the PLMN identity the cell belongs to and the NR Cell Identity (NCI) of the cell. The gNB Identifier (gNB ID) is contained with the NCI and is used to identify the gNBs within a PLMN.

When a new base station is brought into the field, a PCI needs to be selected for each of its supported cells. The PCI assignment may fulfill the following two conditions: Collision-free and confusion-free. In collision-free, the PCI may be unique in the area that the cell covers for a given carrier frequency. In confusion-free, a cell may not have more than one neighboring cell with identical PCI that are using the same carrier frequency.

Using an identical PCI for two neighboring cells may create collision. Such a collision means that a WTRU moving from one of the cells to the other may fail to detect the candidate cell since it cannot detect a new PCI. In fact, the reception situation is similar to the case when the WTRU receives multiple copies of a transmitted signal that has traveled along different paths. A PCI collision may be solved only by restarting at least one of the cells and reassigning it a different PCI, causing service interruption for all the WTRUs that were connected to it.

PCI confusion, on the other hand, may occur if the cells using the same PCI are not neighboring each other but have a common neighbor. Thus, handover measurements, which are based on the PCI, may become ambiguous leading to confusing measurement reports. This may lead to handover failures (HOF) or even Radio Link Failure (RLF).

Traditionally, a proper PCI is derived from radio network planning and is part of the initial configuration of the node. The network planning tool calculates the possible PCIs for the new cell(s) based on estimated neighbor relations of the new cells, as estimated by cell coverage area predictions. However, prediction errors, due to imperfections in map and building data, and to inaccuracies in propagation models, have forced operators to resort to drive/walk tests to ensure proper knowledge of the coverage region and identify all relevant neighbors and handover regions. The drive/walk tests may also be inaccurate, as some factors such as seasonal changes (the falling of leaves or snow melting) may alter the propagation conditions. In addition, the inaccuracy of cell coverage and neighbor relation assessment increases with time as the live network and its surroundings evolve.

NR supports a feature known as WTRU Automatic Neighbor Relations (ANR), which enables the serving gNB to request the WTRU to decode and report the CGI of a given cell associated with a given PCI.

In SIB1, a cell broadcasts the CellAccessRelatedInfo IE, which includes the PLMN-IdentityInfoList. <FIG> illustrates an IE PLMN-IdentityInfoList, according to an embodiment. The IE PLMN-IdentitylnfoList <NUM> includes a list of PLMN identity information. <FIG> illustrates IE CellIdentity <NUM>, according to an embodiment, which may be used to unambiguously identify a cell within a PLMN.

Each gNB in the network may need information about its neighbor gNBs and the cells hosted by the neighbors, primarily for handover and dual connectivity purposes. WTRUs may use PCIs to identify cells, as well as to report measurement results. If the gNB receives a measurement report from a WTRU that includes a PCI that it does not recognize, it may request the WTRU read the CGI from SIB1 of the concerned cell. From the CGI report (i.e., gNB id included in the CGI), the gNB may be able to identify the gNB hosting the cell. If there is a possibility to setup an x2/xn connection with that neighbor, the gNB may initiate the establishment of such a connection, if not done already.

gNBs may maintain neighbor relations tables (NRTs) that contain information such as the PCI/CGI of neighboring cells/nodes as well as information such as whether a direct X2/Xn connection is available towards that neighbor. When there is a need for handover (e.g., a WTRU sends a measurement result indicating that it has a better signal from a cell with a certain PCI), the gNB may then lookup the gNB controlling that cell from the NRT, determine the handover type available (e.g., directly via X2/Xn, CN based handover via S1/NG, etc.), and send the appropriate HO request to it.

RRC_INACTIVE is a state where a WTRU remains in CM-CONNECTED and may move within an area configured by NG-RAN, the RAN notification area (RNA), without notifying NG-RAN. The RRC_INACTIVE state is a compromise between the ACTIVE/CONNECTED state and the IDLE state, where the WTRU has almost the same power saving benefits of the IDLE state, but may be brought back quickly to connected sate when the need arises (e.g., when UL/DL data concerning that WTRU arrives).

When a WTRU is suspended to an INACTIVE state, it may be allocated an I-RNTI by the last serving gNB. The I-RNTI may include a WTRU specific part (e.g., CRNTI used in the cell where the WTRU got suspended) and a network specific part (e.g., ID of the gNB that was hosting the cell where the WTRU got suspended). The last serving gNB node keeps the WTRU context and the WTRU-associated NG connection with the serving AMF and UPF.

A WTRU in the RRC_INACTIVE state may be configured by the last serving gNB with an RNA, where: (<NUM>) the RNA may cover a single or multiple cells, and may be contained within the CN registration area; and/or (<NUM>) a RAN-based notification area update (RNAU) is periodically sent by the WTRU and is also sent when the cell reselection procedure of the WTRU selects a cell that does not belong to the configured RNA.

The RNAU may be performed via a two-step resume procedure. For example, in some embodiments, a WTRU may send an RRC Resume Request with a cause value indicating RANU, and the network may respond immediately with an RRC Release.

There are several different alternatives on how the RNA may be configured. In some embodiments, a WTRU is provided an explicit list of one or more cells that constitute the RNA.

In other embodiments, a WTRU is provided at least one RAN area ID, where the at least one RAN area is a subset of a CN Tracking Area (TA) or equal to a CN TA. A RAN area is specified by one RAN area ID, which includes a TAC and optionally a RAN area code. A cell broadcasts one or more RAN area IDs in the system information.

If the last serving gNB receives DL data from the UPF or DL WTRU-associated signaling from the AMF the WTRU is in RRC_INACTIVE, it pages in the cells corresponding to the RNA and may send XnAP RAN Paging to neighbor gNB(s) if the RNA includes cells of neighbor gNB(s).

When the WTRU resumes (e.g., in a cell/gNB different from where it was suspended), it may provide the I-RNTI in the resume request and the target gNB may be able to identify the source gNB from the network specific part of the C-RNTI and send the context fetch request to the source node.

The migrations of an IAB node from one parent node to another (possibly involving a change of the donor DU or even donor CU) are specified for load balancing or backhaul RLF handling. Such a migration of an IAB node may also be referred to as topology adaptation.

<FIG> and <FIG> illustrate inter-CU topology adaptation 600A, 600B, according to an embodiment. In some embodiments, topology adaptation may comprise establishment of new route/resources via the new parent CU/path. For example, in the embodiment illustrated in <FIG>, adapt route A <NUM> is established between IAB-node <NUM>, IAN-node <NUM>, IAB-node <NUM>, and IAB-donor DU <NUM>. During the topology adaptation new adapt route B <NUM> may be established between IAB-node <NUM>, IAB-node <NUM>, IAB-node <NUM>, and IAB-donor DU <NUM>, as illustrated in <FIG>.

In some embodiments, topology adaptation may further comprise redirection of F1-U tunnels and F1--AP onto new route. For example, in the embodiment illustrated in <FIG>, tunnel connection for F1 <NUM> is established between IAB-donor DU <NUM> and IAB-donor CU <NUM>; F1-C <NUM> is established between the DU of IAB-node <NUM> and the CU-CP of IAB-donor CU <NUM>; and F1-U1 <NUM> is established between the DU of IAB-node <NUM> and the CU-UP of IAB-donor CU <NUM>, as illustrated in <FIG>. Tunnel connection for F1 <NUM> may be redirected to tunnel connection for F1 <NUM> between IAB-donor DU <NUM> and IAB-donor <NUM>. Similarly, F1-C <NUM> and F1-U1 <NUM> may be redirected to F1-C <NUM> and F1-C <NUM>, as illustrated in <FIG>.

In some embodiments, topology adaptation may further comprise the release of old route/resources. For example, the following routes/resources are released in the embodiment illustrated in <FIG>: adapt route A <NUM>, tunnel connection for F1 <NUM>, F1-C <NUM>, and F1-U1 <NUM>.

<FIG> illustrates the keys of the key hierarchy generation in NR <NUM>, according to an embodiment. As shown in <FIG>, the key hierarchy may include the following keys: KAUSF <NUM>, KSEAF <NUM>, KAMF <NUM>, KNASint <NUM>, KNASenc <NUM>, KN3IWF <NUM>, KgNB <NUM>, KRRCint <NUM>, KRRCenc <NUM>, KUPint <NUM> and KUPenc <NUM>. Discussed below are the keys that are related to the access stratum.

KgNB <NUM> may be a key derived by ME and AMF from KAMF <NUM>. KgNB <NUM> is further derived by ME and source gNB when performing horizontal or vertical key derivation. The KgNB <NUM> may be used as KeNB (not shown) between ME and ng-eNB.

KUPenc <NUM> may be a key derived by ME and gNB from KgNB<NUM>, which may be used for the protection of UP traffic with a particular encryption algorithm.

KUPint <NUM> may be a key derived by ME and gNB from KgNB<NUM>, which may be used for the protection of UP traffic between ME and gNB with a particular integrity algorithm.

KRRCint <NUM> may be a key derived by ME and gNB from KgNB<NUM>, which may be used for the protection of RRC signaling with a particular integrity algorithm.

KRRCenc <NUM> may be a key derived by ME and gNB from KgNB <NUM>, which may be used for the protection of RRC signaling with a particular encryption algorithm.

Next hop parameter (NH) <NUM> may be a key derived by ME and AMF to provide forward security.

KNG-RAN * (KgNB* if the target is a gNB or KeNB* if the target is an eNB) may be a key derived by ME and NG-RAN (i.e., gNB or ng-eNB) when performing a horizontal or vertical key derivation.

When an initial AS security context needs to be established between the WTRU and gNB, AMF and the WTRU derive a KgNB and a NH. The KgNB and the NH may be derived from the KAMF. A NH Chaining Counter (NCC) may be associated with each KgNB and NH parameter. Every KgNB may be associated with the NCC corresponding to the NH value from which it was derived. At initial setup, the KgNB may be derived directly from KAMF, and then may be considered to be associated with a virtual NH parameter with NCC value equal to zero. At initial setup, the derived NH value may be associated with the NCC value one. On handovers, the basis for the KgNB that may be used between the WTRU and the target gNB, called KgNB*, is derived from either the currently active KgNB or from the NH parameter. If KgNB* is derived from the currently active KgNB, this is referred to as a horizontal key derivation and is indicated to WTRU with an NCC that does not increase. If the KgNB* is derived from the NH parameter, the derivation is referred to as a vertical key derivation and is indicated to WTRU with an NCC increase. Finally, KRRCint, KRRCenc, KUPint and KUPenc may be derived based on KgNB after a new KgNB is derived.

With such key derivation, a gNB with knowledge of a KgNB, shared with a WTRU, may be unable to compute any previous KgNB that has been used between the same WTRU and a previous gNB, therefore providing backward security. Similarly, a gNB with knowledge of a KgNB, shared with a WTRU, may be unable to predict any future KgNB that may be used between the same WTRU and another gNB after n or more handovers (since NH parameters are only computable by the WTRU and the AMF).

On handovers with vertical key derivation the NH may be further bound to the target PCI and its frequency ARFCN-DL before it is taken into use as the KgNB in the target gNB. On handovers with horizontal key derivation the currently active KgNB may be further bound to the target PCI and its frequency ARFCN-DL before it is taken into use as the KgNB in the target gNB. That is, when deriving the KgNB, the PCI and the ARFCN (i.e. absolute frequency of SSB of the target cell), may be used as input to the security key derivation function (KDF).

When an IAB node performs relocation, specifically inter-CU relocation, the PCIs/CGIs of the cells that it is hosting may be changed. In some embodiments, the PCIs/CGIs of the cells that it is hosting may be changed as the DU of the IAB node, and thus the cells hosted by the DU may belong to the target CU. This may lead to several issues as described below.

First, the WTRUs or IAB nodes that are directly connected to the migrating IAB node may detect a new PCI the next time they read the SSBs of their serving cells. Thus, they may consider their serving cell as a neighbor cell, and unable to find an SSB that is broadcasting the PCI associated with their serving cell, may consider this as an RLF and trigger unnecessary re-establishment and may be reconnected to the same cell afterwards. This may cause considerable service interruption to the bearers of the WTRUs that are being directly or indirectly served by the migrating IAB node (e.g., WTRUs served by a child of the migrating IAB node).

Second, the measurement results by WTRUs or IAB MTs that were being served by neighbors of the migrating IAB node and currently measuring the cells of the migrating IAB node may become invalidated as the associated PCI is not detected anymore (e.g., previous results that were collected for the concerned cells may be removed from the measurement results, and subsequent results gathered as if they are for a new cell).

Third, idle or inactive WTRUs or IAB-MTs that are camping in one of the cells of the migrating IAB node may be forced to perform an unnecessary cell re-selection, which could be the same cell as before with the new PCI, or a different cell.

Fourth, idle or inactive WTRUs or IAB-MTs that are camping in one of the cells of the migrating IAB node may be forced to perform an unnecessary RAN area update procedure (e.g., start a two-step resume to let the network know that the inactive WTRU has now moved to a new RAN area), if: (<NUM>) the new PCI of the migrating IAB node is not within the list of cells provided in the RAN area list provided to the WTRU or IAB-MT when it was sent to INACTIVE state; or (<NUM>) the new TAC of the migrating IAB node is not within the list of TACs provided in the RAN area list provided to the WTRU or IAB-MT when it was sent to INACTIVE state.

The issues described above cover the multi-hop IAB scenario, wherein an IAB node migrates from one parent to another (e.g., inter-CU relocation), resulting on the need for the IAB node's cell information (e.g., PCI, CGI, TAC, etc.) to be updated. However, the embodiments described below are equally applicable to other scenarios (e.g., non IAB scenario with CU/DU split, or a non CU-DU split architecture where the gNB is terminated in one node) where the cell's information/identity need to be changed on the fly (e.g., dynamic PCI update due to detection of PCI collision/confusion).

The terms IAB node, MT part of an IAB node or DU part of an IAB node, and WTRU may be used interchangeably.

Most of the implementation described herein are related to PCI/CGI change. However, the implementation are applicable also to scenarios where the change is related to other network identities such as tracking area identity (TAI), tracking area code (TAC), PLMN identity, etc..

In one implementation, a WTRU may be provided with a configuration update information regarding a change of information of the current serving cell (e.g., PCI, CGI, TAC). After the reception of this information, the WTRU may replace the new information for the serving instead of the old ones. For example, if the update indicates a change of a PCI, the WTRU may not look for the old PCI in the SSBs of the serving cell but instead may check the new PCI. If a WTRU detects an SSB that contains the old PCI, it may consider it as a neighbor cell. In one implementation, the WTRU may consider the change of the serving cell information effective immediately after the reception of the configuration update.

In one implementation, the WTRU may consider the change of the serving cell information effective a certain duration after the reception of the configuration update. The duration could be a certain time (e.g., x ms) after the reception of the update message or it could be an exact time in the future (e.g., frame/slot number). The duration may be included within the configuration update message or it may be after a duration specified in 3GPP standards.

The WTRU may be provided with the serving cell update information via a dedicated signaling (e.g., RRC Reconfiguration, MAC CE) or via broadcast signaling (e.g., SIB).

In one implementation, a WTRU may be provided with a configuration update information regarding a change of information of a neighbor cell (e.g., PCI, CGI, TAC). After the reception of this information, the WTRU may replace the new information for the neighbor cell instead of the old ones. For example, if the update indicates a change of a PCI, the WTRU may update all current measurement results associated/indexed with the old PCI to the new PCI. For example, if a WTRU detects an SSB that contains the old PCI, it may consider it as a new neighbor cell.

In some embodiments, the neighbor cell configuration update contains the old and new (set of) neighbor cell information. For example, the content of a configuration update message may be: (<NUM>) {current PCI = PCI_current, new PCI= PCI_new} or (<NUM>) {current PCI = PCI_current, new TAC= TAC_new}.

In some embodiments, the neighbor cell configuration update may include the old and new (set of) cell information for multiple cells. For example, [cell_1 info: {current PCI = PCI_current, new PCI= PCI_new}, cell_2 info:{current PCI = PCI_current, new PCI= PCI_new}].

In some embodiments, the WTRU may consider the change of the neighbor cell information effective immediately after the reception of the configuration update.

In some embodiments, the WTRU may consider the change of the neighbor cell information effective a certain duration after the reception of the configuration update. The duration may be a certain time (e.g., x ms) after the reception of the update message or it could be an exact time in the future (e.g., frame/slot number). The duration may be included within the configuration update message or it may be after a duration specified in 3GPP standards. If the configuration contains information for more than one neighbor cell, the same duration may be applied to all the cells included in the update, or a different duration may be included for each cell.

The WTRU may be provided with the neighbor cell update information via a dedicated signaling (e.g., RRC Reconfiguration, MAC CE) or via broadcast signaling (e.g., SIB). Note that in the case of broadcast signaling, the signaling could be from the serving cell or the neighbor cell (e.g., SIB change).

In some embodiments, cells may broadcast more than one set of cell information (e.g., PCI, CGI, TAC), and the WTRU may consider them all equivalent. For example, a cell may indicate in MIB or SIBx (e.g., SIB1) the possible PCIs that it may be associated with. The WTRU may then store all the possible PCIs indicated therein and associate them with the PCI that the cell is broadcasting in the SSB, and from thereon may consider all these PCIs are equivalent.

If the concerned cell is a serving cell, the WTRU, on not being able to detect the PCI that was being used by the current serving cell in the SSB, may try to detect any of the PCIs that it has associated with the cell. If one of them is detected, then that SSB may be considered as the SSB of the serving cell. Otherwise, as in legacy behavior, the WTRU may consider a radio link failure has been detected.

If the concerned cell is a neighbor cell, the WTRU, upon detecting a PCI that is associated with a neighbor cell in an SSB, may associate all previous measurement results associated with the old PCI used by the neighbor cell with the new PCI.

As discussed above, the PCI may be one of the parameters that is used to compute the security key (KgNB), and that the KgNB may be used to compute the user plane and control plane security keys that are used by PDCP for encryption and integrity protection (i.e., KUPenc , KUPint, KRRCenc ,KRRCint).

In some embodiments, the WTRU may continue using the same security keys (KgNB, KUPenc , KUPint KRRCenc ,KRRCint) as before detecting the PCI change of the serving cell by the reception of the cell configuration update information. Since the network also knows that the change of the PCI of the cell, the gNB may keep using the same keys as before, even though the PCI of the serving cell has changed.

In some embodiments, the WTRU updates the security keys to reflect the change of PCI. That is, it may derive the new KgNB using the new PCI and update the KUPenc, KUPint, KRRCenc, and KRRCint, using the newly derived KgNB. In some embodiments, the WTRU may immediately start using the newly derived UP and CP encryption and integrity protection keys immediately after the PCI change has become effective.

In some embodiments, the WTRU may try to use both the old and newly derived UP and CP keys for decoding incoming DL packets for a certain duration after the key change. For example, the WTRU may try to use the old keys first and if that doesn't succeed, instead of declaring radio link failure as in the legacy case, it may try to the new keys (or vice versa). This may enable the proper reception of any outstanding packets (e.g., retransmissions) that were sent by the gNB before the change of the PCI and thus encrypted or integrity protected using the old keys. The duration where the WTRU tries to use both the old and the new keys may be included in the cell configuration update information, specified in 3GPP standards, or left to WTRU implementation. For example, the WTRU may stop using the old keys once it has received packets that are integrity protected with the new keys.

It should be noted that one advantage of operating with the two security keys simultaneously for a certain duration after the change of the PCI is that it avoids the need for retransmissions. If a re-establishment or normal HO was triggered due to the change of PCI, the packets that were pending transmission or those that were transmitted but waiting acknowledgement at the gNB may have to be re-encoded with the new security keys and retransmitted (the WTRU may have to do the same for UL packets).

In some embodiments, a WTRU that is INACTIVE mode may refrain from triggering a RAN area update (RANU), upon detecting a PCI/TAC change in the serving cell, even if that PCI/TAC does not belong to the WTRU's RNA configuration, if it notices that the new PCI/TAC belongs to the same serving cell, using any of the solutions discussed above (e.g., from equivalent PCIs, from SIB signaling indicating that the PCI/TAC of the current serving cell has changed, etc).

In some embodiments, a WTRU that is INACTIVE mode, when determining that PCI/TAC of the current serving cell has changed (e.g., SIB signaling indicating the change) or could change (e.g., SIB signaling indicating equivalent PCIs/TACs), the WTRU may update the RNA configuration to include the new PCI/TAC or the possible set of equivalent PCIs/TACs.

In some embodiments, a WTRU that is INACTIVE or IDLE mode may refrain from triggering a cell re-selection procedure, upon detecting a PCI/TAC change in the serving cell, if it notices that the new PCI/TAC belongs to the same serving cell, using any of the solutions discussed above (e.g., from equivalent PCIs, from SIB signaling indicating that the PCI/TAC of the current serving cell has changed, etc.).

<FIG> is a flow diagram of a method for detecting change in serving cell identity and considering the new cell identity as the identity of the serving cell, without triggering RLF/re-establishment, according to an embodiment. At <NUM>, WTRU <NUM> operating in CONNECTED mode receives an indication from the network <NUM> regarding changes in the serving cell's identity (e.g., PCI, CGI, etc.) and associated WTRU behavior. In some embodiments, the associated WTRU behavior may comprise WTRU security handling behavior upon identity changes. In some embodiments, the WTRU <NUM> may further receive one or more conditions for serving cell identity change. At <NUM>, the WTRU <NUM> may send an indication to the network <NUM> that reconfiguration is complete.

If one or more conditions are specified at <NUM>, the WTRU <NUM> may determine if the one or more conditions are met at <NUM>. If the one or more conditions are met, the WTRU <NUM> may consider the indicated cell identity as the serving cell's identity at <NUM>, and may derive new security keys for encryption and integrity protection based on the new cell identity at <NUM>. The one or more conditions may comprise a specified duration (e.g., delta time or a specific slot/frame) and/or failure of old identity. The failure of old identity condition may comprise the WTRU searching for a cell with a new cell identity if the WTRU cannot detect a cell with the identity of the current serving cell, and upon the WTRU discovering an equivalent identity of the current serving cell in another cell, considering the another cell as the new serving cell.

If one or more conditions for switching to the new security keys are fulfilled at <NUM>, then the WTRU <NUM> may begin using the new security keys at <NUM>. If the conditions for switching to the new security keys are not fulfilled, then the WTRU <NUM> may continue using the old security keys at <NUM>.

The WTRU <NUM> may be configured to use the new security keys for encrypting/decrypting and integrity protection/verification of UL/DL packets in the PDCP in one of the following ways: (<NUM>) use the new keys for the UL (i.e., encryption and integrity protection) immediately after the computation of the new keys; (<NUM>) use the new keys for the DL (i.e. decryption and integrity verification) immediately after the computation of the new keys; (<NUM>) use the new keys for the UL (i.e., encryption and integrity protection) according to a specified duration (e.g., delta time from the computation of the keys, specific frame/slot number, etc.) after the computation of the new keys; (<NUM>) use the new keys for the DL (i.e. decryption and integrity verification) according to a specified duration (e.g., delta time from the computation of the keys, specific frame/slot number, etc.) after the computation of the new keys; and/or (<NUM>) keep using the old keys in the UL and DL, until a reception of a DL packet that is not associated with the new key (e.g., integrity verification with the old key fails, but integrity verification with the new key succeeds).

In some embodiments, a WTRU operating in CONNECTED mode may receive configuration information from the network regarding changes in information related to a neighbor cell's identity (e.g., PCI, CGI, etc.) and associated WTRU behavior. In some embodiments, the configuration information comprises conditions for these changes, such as specified duration (e.g., delta time or specific slot/frame). In some embodiments, the associated WTRU behavior may comprise the handling of neighbor measurements. Upon receipt of an indication from the network comprising the handling of neighbor measurements, and if one or more conditions are also specified, the fulfillment of the one or more conditions, the WTRU may consider the new identity an as the neighbor cell's identity. The WTRU may then update the measurements associated with the neighbor cell to reflect the change in identity. For example, in some embodiments, the WTRU may update the cell identity index in the measurement report.

In some embodiments, a WTRU operating in CONNECTED mode may receive configuration information from the network indicating a set of equivalent identities for the serving cell (e.g., list of PCIs, list of CGls, etc.). If the WTRU is not able to detect the current PCI associated with the serving cell (e.g., in the SSBs it is measuring), the WTRU may be configured to not consider a radio link failure and instead try to detect the other equivalent PCIs. Upon the detection of one of the equivalent PCIs, the WTRU may be configured to consider the new PCI as the serving cell's PCI, consider the old PCI as belonging to a neighbor cell, and/or updates the security keys that are used for encryption and integrity protection based on the new PCI.

In some embodiments, a WTRU in INACTIVE mode may receive an indication (e.g., broadcast signaling) from the network indicating a change of the identity of the cell that the WTRU is currently camping on (e.g., PCI, CGI, TAC, etc.). Upon receipt of such indicating, the WTRU may: (<NUM>) refrain from triggering RAN area update (RANU), even if the PCT/TAC is not in the WTRU's RNA configuration; and/or (<NUM>) update the RNA configuration to include the new PCI/TAC.

Claim 1:
A method performed by a wireless transmit receive unit, WTRU, the method comprising:
receiving (<NUM>) configuration information including information regarding a change in an identity of a serving cell, one or more conditions for the change in the identity of the serving cell, and associated WTRU behavior;
monitoring (<NUM>) the one or more conditions for the change in the identity of the serving cell;
on a condition that the one or more conditions for the change in the identity of the serving cell are fulfilled, changing (<NUM>) the identity of the serving cell to a new cell identity;
deriving (<NUM>) one or more new security keys based on the new cell identity; anc
using (<NUM>,<NUM>) the one or more new security keys according to a configured security key handling behavior for communication with the serving cell.