Patent Description:
In a typical wireless communication network, user equipment (UE), also known as wireless communication devices, mobile stations, stations (STA) and/or wireless devices, communicate via a Radio Access Network (RAN) to one or more core networks belonging to different network operators. The RAN covers a geographical area which is divided into areas or cell areas, with each area or cell area being served by a radio network node, e.g., a Wi-Fi access point, a RAN node or a Radio Base Station (RBS), which in some networks may also be called, for example, a NodeB, eNodeB or a gNodeB. The area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the UE within range of the radio network node.

A Universal Mobile Telecommunications System (UMTS) is a third generation telecommunication network, which evolved from the second generation (<NUM>) Global System for Mobile Communications (GSM). The UMTS Terrestrial Radio Access Network (UTRAN) is essentially a RAN using Wideband Code Division Multiple Access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipment. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a Radio Network Controller (RNC) or a Base Station Controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. The RNCs are typically connected to one or more core networks.

Specifications for the Evolved Packet System (EPS) have been completed within the 3GPP and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP Radio Access Technology (RAT) wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially "flat" architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs.

With the emerging <NUM> technologies such as New Radio (NR), the use of a large number of transmit- and receive-antenna elements is of great interest as it makes it possible to utilize beamforming, such as transmit-side and receive-side beamforming. Transmit-side beamforming means that the transmitter can amplify the transmitted signals in a selected direction or directions, while suppressing the transmitted signals in other directions. Similarly, on the receive-side, a receiver can amplify signals coming from a selected direction or directions, while suppressing unwanted signals coming from other directions.

When a UE is located at the border between two RATs, the UE performs a Tracking Area Update (TAU) /Attach/Registration Area Update/Registration request procedure every time it toggles between the two RATs. This is harmful for the communication and negatively impacts both the UE battery life time and the overall network signalling overhead.

3GPP DRAFT; R2-<NUM> relates to allowing inter-RAT/inter-system RAN Notification Areas as a way to reduce unnecessary battery consuming signalling and to procedures for how it can be supported also for UEs in LTE/EPC.

3GPP DRAFT; R2-<NUM> discloses a solution to support inter-RAT mobility in Inactive mode to allow for fast connection configuration while maintaining UE power saving.

An object of embodiments herein is to provide a mechanism that handles communication in a more efficient manner.

According to an aspect the object is achieved by providing a method performed by a UE for handling communication with a first RAN node associated with a first RAT and a second RAN node associated with a second RAT. The UE, the first RAN node and the second RAN node operate in a wireless communication network. The UE is located on or close to a radio coverage border of the first RAT and the second RAT and is in inactive state in the first RAT when being registered through the first RAN node. The UE performs a registration through the second RAN node while retaining a stored inactive context related to the first RAN node, wherein a dual registration timer is used for retaining the stored inactive context, thereby having a dual registration to the first and second RAN nodes. The UE further enters a state in the second RAT while remaining in the inactive state in the first RAT.

According to another aspect the object is achieved by providing a method performed by a first RAN node for handling communication with a UE. The first RAN node is associated with a first RAT and a second RAN node is associated with a second RAT. The UE, the first RAN node and the second RAN node operate in a wireless communication network. The UE is located on or close to a radio coverage border of the first RAT and the second RAT and is in inactive state in the first RAT when being registered through the first RAN node. The first RAN node configures the UE with a dual registration timer for dual registration, that the UE will use to retain an inactive context in the first RAT when registering through the second RAN node. The first network RAN node then retains the inactive context for the UE until the timer is expired.

According to yet another aspect of embodiments herein, the object is achieved by providing a UE for handling communication with a first RAN node associated with a first RAT and a second RAN node associated with a second RAT. The UE, the first RAN node and the second RAN node operate in a wireless communication network. The UE is located on or close to a radio coverage border of the first RAT and the second RAT and is in inactive state in the first RAT when being registered through the first RAN node. The UE is configured to perform a registration through the second RAN node while retaining a stored inactive context related to the first RAN node, wherein a dual registration timer is used for retaining the stored inactive context, thereby having a dual registration to the first and second RAN nodes. The UE is further configured to enter a state in the second RAT while remaining in the inactive state in the first RAT.

According to still another aspect of embodiments herein, the object is achieved by providing a first RAN node for handling communication with a UE. The first RAN node is associated with a first RAT and a second RAN node is associated with a second RAT. The UE, the first RAN node and the second RAN node operate in a wireless communication network. The UE is located on or close to a radio coverage border of the first RAT and the second RAT and is in inactive state in the first RAT when being registered through the first RAN node. The first RAN node is configured to configure the UE with a dual registration timer for dual registration, that the UE will use to retain the inactive context in the first RAT when registering through the second RAN node. The first RAN is further configured to retain the inactive context until the timer is expired.

It is furthermore provided herein a non-claimed computer program product comprising instructions, which, when executed on at least one processor, cause the at least one processor to carry out the method above, as performed by the UE or the first RAN node, respectively. It is additionally provided herein a computer-readable storage medium, having stored thereon a computer program product comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to the method above, as performed by the UE or the first RAN node, respectively.

Embodiments herein are based on the realisation that as the UE retains the stored inactive context related to the first RAN node when performing a registration to the second RAN node, dual registration to the first and second RAN nodes is enabled and the UE does not need to initiate a registration every time it enters the coverage of the other RAT. Thereby, the communication is handled in a more efficient manner and the power consumption of the UE is decreased. Even though some embodiments have been summarized above, the claimed subject matter is de-fined in the attached claims <NUM>-<NUM>.

Hereinafter, <FIG> and <FIG> provide embodiments of the invention, whereas the other figures are presented for a better understanding of the invention.

In all the embodiments according to the invention, the UE is located on or close to a radio coverage border of the first RAT and the second RAT.

First the technology according to prior-art will be described.

The following section relates to Inter-Radio Access Technology (RAT), Intra-<NUM> Core (5GC) and Inter-core interworking in LTE and NR. <FIG> is a schematic overview depicting a network architecture for an EPS, e.g. E-UTRAN and EPC, and 5GS, e.g. NG-RAN and 5GC.

3GPP introduces both a new core network, e.g. 5GC, and a RAT, e.g. NR, in the <NUM> system (5GS). However, the core network will also support other RATs than NR, such as E-UTRA. As shown in <FIG>, the network architecture for EPS comprises an E-UTRAN comprising LTE nodes, e.g. eNBs, which are connected to EPC. <FIG> also shows the network architecture for 5GS comprising an NG-RAN comprising LTE nodes, e.g. ng-eNBs, and NR nodes, e.g. gNBs, which are connected to 5GC.

The LTE nodes connected to EPC can be interconnected through the X2 interface, while the NG-RAN nodes can be interconnected through the Xn interface. 3GPP has also introduced an interface between the Mobility Management Entity (MME) in EPC and the Access and Mobility Management Function (AMF) in 5GC called N26, which enables interworking between EPC and 5GC. <FIG> shows the N26 interface between one MME and AMF, however, the N26 interface may exist between many MMEs and AMFs.

<FIG> is a state diagram illustrating a UE state machine and state transitions between NR/5GC, E-UTRA/EPC and E-UTRA/5GC. A Radio Resource Control (RRC)_INACTIVE state and the associated state transitions are only available for NR/5GC and E-UTRA/5GC. The RRC state RRC_INACTIVE was introduced in 3GPP Release-<NUM> for both NR and LTE/5GC. In RRC_INACTIVE state, the UE stores certain configurations, e.g. Data Radio Bearer (DRB) configurations and physical layers parameters. When the UE needs to resume the connection to the network, it transmits an RRCConnectionResumeRequest or RRCResumeRequest/RRCResumeRequest1. The UE may then reuse the stored settings and reduce the time and signaling needed to properly operate in RRC_CONNECTED, as when in RRC_INACTIVE state the security and CN connection are restored upon resume. Thus when in RRC_INACTIVE, the connection from RAN to CN for the UE is kept. At resume it is possible to reduce the time and signaling needed to operate in RRC_CONNECTED.

In NR, an RRC Connection Resume procedure may be initiated with an RRCResumeRequest, including a short I-Radio Network Temporary Identifier (I-RNTI) of <NUM> bits, or an RRCResumeRequest1, including a full I-RNTI of <NUM> bits. The I-RNTI is used to identify the UE context in RRC_INACTIVE. A UE may select an RRCResumeRequest1, sent on the logical Common Control Channel (CCCH1), if the cell where the UE is camped on broadcasts System information Block (SIB1) with presence of useFullResumelD IE (true). Otherwise, the UE may initiate an RRC Connection Resume procedure with RRCResumeRequest, sent on the CCCH.

A UE in RRC_INACTIVE state in one RAT and performing cell reselection to another RAT may trigger the UE to release its Access Stratum (AS) context, enter an RRC_IDLE state in the reselected RAT and perform a registration area update.

The following section concerns RRC Release and Radio access node Notification Areas (RNAs).

To suspend a UE from RRC_CONNECTED state to RRC_INACTIVE state, the last serving node prepares an RRC Release message which contains configurations for the RRC_INACTIVE state. In NR, this message is the RRC Release message with the suspendConfig which contains configurations for a RNA, which comprises one of the following choices:.

The list of "RAN Area Config" can either be:.

The "RAN Area Config" is encoded in RRC NR as follows:
<IMG>.

The first choice is between cellList or ran-AreaConfigList. In the case of cellList, it is possible to signal a common Public Land Mobile Network (PLMN) for a list of cells, or different PLMNs per cell.

Each RAN area configuration in the list has a TAC. Hence, the NG-RAN may configure the UE with a list of Tracking Area Identifiers TAls, i.e. a TAC and a PLMN, or a list of RAN Area Identifiers where each RAN Area Identifier comprises a TAC and a RANAC. The TAI comprises a Mobile Country Code (MCC), a Mobile Network Code (MNC), and a TAC. <IMG>
<IMG>.

Whenever a UE in RRC_INACTIVE state reselects to a new cell, e.g. based on measurements on signals from the cells, the UE checks whether the target cell belongs to the configured RNA by checking the system information, e.g. SIB1, broadcasted from the target cell. If the SIB1 contains the cell identity or the RANAC included in the RNA list of cells or RANACs respectively, the UE will remain in RRC_INACTIVE state without performing any signaling. Since the NG-RAN is aware that the UE is configured with a set of cells and/or RANACs, the UE does not need to inform the network as long as it remains within the RNA. If the network needs to page the UE, e.g. due to an incoming downlink data or a voice call, the core network will address the source node, which suspended the UE, and the source node may perform a RAN paging across the cells inside the RNA. In the case the RNA is made up of cells belonging to different NG-RAN nodes, the source NG-RAN node will send an XnAP paging message to the other NG-RAN nodes serving the RNA so that these NG-RAN nodes can page the UE within their own cells. Since the NG-RAN node only pages in the RNA, it is advantageous for the NG-RAN to know when the UE moves outside the configured RNA configuration for reachability purposes.

However, if the UE reselects a new NR cell which does not belong to the RNA configuration at the UE, e.g. based on cell Id or TAC/RANAC, the UE may initiate an RRC Connection Resume procedure by sending an RRCResumeRequest/RRCResumeRequest1 either to perform a RAN Area Update, i.e. with ResumeCause value ranAreaUpdate, or to perform a Non-Access Stratum (NAS) procedure, e.g. Tracking/Registration Area Update, by transmitting a resume message with the ResumeCause in accordance with the NAS message, which may occur in case the UE leaves a cell and enters both a new RAN area and new registration area. In either case, the network may decide upon reception of the Resume Request message whether to keep the UE in RRC_CONNECTED state, or to release the UE to move back to RRC_INACTIVE state with updated configurations or to transition the UE to RRC_IDLE state. Other options are also possible, e.g. to reject the UE with wait time, in case of overload.

Regarding RRC Release messages in NR, as can be seen below, the RRCRelease message in NR comprises a suspendConfig Information Element (IE). The suspendConfig includes the configuration of an RAN Notification Area (RNA) which comprises either a list of cells, or a list of RAN Area Config, which in turns contains a Tracking Area Code and optionally a RANAC. See RRCRelease in NR, TS. <NUM> v <NUM>. <NUM> below:.

Regarding the current inter-working mechanism for RRC_IDLE state and RRC_INACTIVE state between 3GPP systems, it has been discussed in 3GPP Release <NUM> what kind of inter-RAT mobility would be supported when the UEs are in RRC_IDLE state and/or RRC_INACTIVE state.

Regarding Inter-RAT mobility in RRC_IDLE state, a UE in RRC_IDLE state in NR and connected to 5GC, upon reselecting to an LTE cell, may enter RRC_IDLE state in LTE.

If the target LTE cell is connected to 5GC with only a 5GC TAC associated, that TAC may either be part of the UE's TAI list or not. In other words, the UE may either trigger a Registration Area Update or not, depending whether the LTE cell is in its TAI list.

In the case the target LTE cell is connected to EPC only, and not included in the UE's TAI list, there may always be a Tracking Area Update since the cell is served by a different core network. EPC NAS only supports a <NUM> bits TAC, while 5GC has a <NUM> bits TAC. In other words, upon entering RRC_IDLE state in EPC, there may always be a Tracking Area Update. No paging between the core networks is supported between 5GC and EPC.

In the case the target cell is an LTE cell connected to both EPC and 5GC, as long as at least one of the TACs is in the UE's TAI list, there may be no Registration/Tracking Area Updates, i.e., no signalling.

Regarding Inter-RAT mobility in RRC_INACTIVE state, a UE in RRC_INACTIVE state in NR, upon reselecting to an LTE cell, may enter RRC_IDLE state in LTE.

If the target LTE cell is connected to 5GC, with only a 5GC TAC associated, that may either be part of the UE's TAI list or not. In other words, the LTE cell is in its TAI list.

In the case the UE is in RRC_INACTIVE state in NR and performs inter-RAT cell reselection to an LTE cell, the UE always transition to RRC_IDLE state in LTE, regardless if that is an LTE EPC only cell, or LTE 5GC only cell or both LTE 5GC/EPC cell.

According to current proceedings regarding Inter-RAT Cell reselection in RRC_INACTIVE state, upon cell reselection to an E-UTRA/EPC cell, the UE which is suspended to RRC_INACTIVE state discards the stored UE Access Stratum (AS) inactive context and any configuration for RRC_INACTIVE state in current TS <NUM>. The UE performs tracking area update or registration update in EPC.

Location management in mobile communication systems is concerned with those network functions necessary to allow the UE to be reached whenever it is idle, e.g. in RRC_IDLE state, but located in the network coverage area. The challenge mainly comes when the idle UE is moving around. In case of multi-RAT nodes, for example, the same geographical node location may belong to two RATs, e.g. NR and E-UTRA. The current design of tracking areas in LTE and NR takes the idle and/or inactive UEs of these two RATs separately. However, there may be an inactive UE performing a Tracking Area Update just because it is located at the border between the two RATs and in most cases in the coverage of a dual RAT node, e.g. eNB/gNB. Therefore, the challenge may not only be due to the idle UEs movement, but it may happen to a stationary UE while facing a change in some physical radio property, also referred to as radio conditions.

A UE in the RRC_INACTIVE state, upon cell reselection to another RAT, may discard the stored AS inactive context and any configuration for RRC_INACTIVE state. This is unreasonably costly in cases when the conditions for cell reselection are valid for a short period of time.

Moreover, when the UE resides at the border between two RATs, e.g. between NR and E-UTRA/EPC or between NR and E-UTRA/5GC, the UE may perform the TAU/Attach/Registration Area Update/Registration request procedure every time it toggles between two RATs. This negatively impacts both the UE battery life time and the overall network signaling overhead.

Embodiments herein relate to wireless communications networks in general. <FIG> is a schematic overview depicting a wireless communications network, such as a wireless communications network <NUM>. The wireless communications network <NUM> comprises one or more Radio Access Networks (RANs) and one or more Core Networks (CNs). The wireless communications network <NUM> may use one or a number of different technologies. Embodiments herein relate to recent technology trends that are of particular interest in a New Radio (NR) context, however, embodiments are also applicable in further development of existing wireless communications systems such as e.g. LTE or Wideband Code Division Multiple Access (WCDMA).

In the wireless communications network <NUM>, a UE <NUM> is comprised. The UE <NUM>, may e.g. be a wireless device such as a mobile station, a non-access point (non-AP) station (STA), a STA and/or a wireless terminal, communicating via e.g. one or more Access Networks (ANs), e.g. RANs, to one or more CNs. It should be understood by the skilled in the art that "UE" is a non-limiting term which means any terminal, wireless communications terminal, user equipment, Narrowband Internet of Things (NB-IoT) device, Machine Type Communication (MTC) device, Device to Device (D2D) terminal, or node e.g. smart phone, laptop, mobile phone, sensor, relay, mobile tablets or even a small base station capable of communicating using radio communication with a radio network node within an area served by the radio network node.

The wireless communication network <NUM> comprises a first RAN node <NUM> providing radio coverage over a geographical area, a service area, e.g. a cell <NUM>, of a first RAT, such as NR, LTE or similar. The wireless communication network <NUM> further comprises a second RAN node <NUM> providing radio coverage over a geographical area, a service area, e.g. a cell <NUM>, of a second RAT, such as NR, LTE or similar. Each of the first RAN node <NUM> and the second RAN node <NUM> may provide a transmission point and a reception point, and may be implemented as an access node, an access controller, a base station, e.g. a radio base station such as a gNodeB (gNB), an evolved Node B (eNB, eNode B), a NodeB, a base transceiver station, a radio remote unit, an Access Point Base Station, a base station router, a Wireless Local Area Network (WLAN) access point or an Access Point Station (AP STA), a transmission arrangement of a radio base station, a stand-alone access point or any other network unit or node capable of communicating with a wireless device within the area served by the first or second RAN nodes, <NUM> and <NUM> respectively, depending e.g. on the RAT and terminology used. The first RAN node <NUM> and the second RAN node <NUM> may be referred to as a serving radio network node wherein the service area may be referred to as a serving cell, and the serving network node communicates with the wireless device in form of downlink (DL) transmissions to the wireless device and uplink (UL) transmissions from the wireless device. It should be noted that a service area may be denoted as cell, beam, beam group or similar to define an area of radio coverage.

The first RAN node <NUM> and/or the second RAN node <NUM> may be an AMF, which controls the base stations. The wireless communication network <NUM> comprises a core node, which may be an MME which is a control node for an LTE access network, a Serving Gateway (SGW), and a Packet Data Network Gateway (PGW). An MME is amongst other responsible for tracking and paging procedures including retransmissions. The MME and the AMF may communicate via the N26 interface, as shown in <FIG>.

Methods according to embodiments herein may be respectively performed by the first RAN node <NUM>, the second RAN node <NUM> and/or the UE <NUM>. As an alternative, a Distributed Node (DN) and functionality, e.g. comprised in a cloud <NUM> as shown in <FIG> may be used for performing or partly performing the methods and actions described herein.

According to embodiments herein the UE <NUM> is in an inactive state in the first RAT when being registered through the first RAN node <NUM>. When the UE moves to the second RAT the UE <NUM> performs a registration through the second RAN node <NUM> while retaining a stored inactive context related to the first RAN node <NUM>, thereby having a dual registration by being registered through both the first- and second RAN nodes <NUM> and <NUM>, respectively, at the same time. The UE <NUM> further enters a state, e.g. an inactive state or an idle state, in the second RAT while remaining in the inactive state in the first RAT. The registration through the second RAN node <NUM> may be handled by the core node. Further, the registration through the first RAN node <NUM> and the registration through the second RAN node <NUM> may be created by the same core node or by two different core nodes depending on the implementation.

Some actions that may be performed by the UE <NUM> for handling the communication with a first RAN node <NUM> associated with a first RAT and a second RAN node <NUM> associated with a second RAT according to embodiments herein, will now be described with reference to a flowchart depicted in <FIG> and with further reference to the communication scenario in <FIG>. The UE <NUM>, the first RAN node <NUM> and the second RAN node <NUM> are operating in the wireless communication network <NUM>. The UE <NUM> is in inactive state in the first RAT when being registered through the first RAN node <NUM>. The actions do not have to be taken in the order stated below, but may be taken in any suitable order. Optional actions that may be performed in some embodiments are marked with dashed boxes.

Action <NUM>. When the UE <NUM> is in the radio coverage area, e.g. the cell <NUM>, of the first RAN node <NUM> associated with the first RAT and moves to the radio coverage area, e.g. the cell <NUM>, of the second RAN node <NUM> associated with the second RAT, the UE <NUM> may select, or reselect, the cell of the second RAN node <NUM>. This is performed prior to performing the registration through the second RAN node <NUM>.

Action <NUM>. In some embodiments, when the first RAT is related to <NUM> and the second RAT is related to <NUM>, the UE <NUM> may initiate a Tracking Area Update (TAU) request procedure. The TAU is initiated when the UE <NUM> moves to a new tracking area which is not included in its list of tracking areas with which the UE <NUM> is registered.

Action <NUM>. In some embodiments, when the first RAT is related to <NUM> and the second RAT is related to <NUM>, the UE <NUM> may initiate a Mobility Registration Update (MRU) request procedure. The MRU is initiated as the UE <NUM> leaves the area it is registered to and enters another area which it is not registered to.

Action <NUM>. The UE <NUM> then performs a registration through the second RAN node <NUM> while retaining a stored inactive context related to the first RAN node <NUM>, wherein a dual registration timer is used for retaining the stored inactive context. Thereby the UE <NUM> has a dual registration through the first RAN node <NUM> and the second RAN node <NUM>. Storing the inactive context relating to the first RAN node <NUM> thus enables the dual registration through both the first RAN node <NUM> and the second RAN node <NUM>. This enables the communication of the UE <NUM> in the wireless communication network to be handled in a more efficient manner, which in turn could reduce the power consumption of the UE <NUM>.

Performing the registration through the second RAN node <NUM> may comprise maintaining a list of the second RAT in addition to maintaining a list of the first RAT. The registration may be handled, e.g. created and stored, in a core node. Further, the registration through the first RAN node <NUM> and the registration through the second RAN node <NUM> may be created by the same core node or by two different core nodes depending on the implementation.

In some embodiments, when the first RAT is related to <NUM> and the second RAT is related to <NUM>, the maintained list of the second RAT is a tracking area list and the maintained list of the first RAT is based on a Radio access node Notification Area (RNA).

In some embodiments, when the first RAT is related to <NUM> and the second RAT is related to <NUM>, the maintained list of the second RAT is based on the RNA and the maintained list of the first RAT is the tracking area list.

In some embodiments, the inactive context is an Access Stratum (AS) inactive context.

Action <NUM>. The UE <NUM> then enters a state in the second RAT while remaining in the inactive state in the first RAT. The entered state in the second RAT may be the idle state or the inactive state.

Performing the registration through the second RAN node <NUM> and entering the state in the second RAT may be performed when the UE <NUM> is located on or close to a radio coverage border of, e.g. between, the first RAT and the second RAT.

According to some embodiments, when the UE <NUM> is registered to the reselected network, the UE <NUM> may be released to RRC_INACTIVE state after registration. This means that the UE <NUM> may concurrently be in RRC_INACTIVE state in two RATs with two stored separate contexts. The UE <NUM> may thus concurrently be in:.

The method actions performed by the first RAN node <NUM> for handling communication with the UE <NUM> according to embodiments herein will now be described with reference to a flowchart depicted in <FIG> and with further reference to the communication scenario in <FIG>. The first RAN node <NUM> is associated with the first RAT and the second RAN node <NUM> is associated with the second RAT. The first RAN node <NUM>, the second RAN node <NUM> and the UE <NUM> are operating in the wireless communication network <NUM>. The UE <NUM> is in the inactive state in the first RAT when being registered through the first RAN node <NUM>. The actions do not have to be taken in the order stated below, but may be taken in any suitable order.

Action <NUM>. When transitioning the UE <NUM> to inactive state, the first RAN node <NUM> configures the UE <NUM> with a dual registration timer for dual registration that will be used by the UE <NUM> to retain the inactive context in the first RAT when registering through the second RAN node <NUM>. The timer may be a dual registration timer.

Action <NUM>. The first RAN node <NUM> then retains the inactive context until the timer is expired. The inactive context may be an AS inactive context. An additional condition for not retaining, e.g. not keeping, the inactive context may be that the UE <NUM> initiates the indication of, e.g. t380Dual expiration, or an uplink request to a cell which is far from the border between two RATs. Another additional condition for not retaining the inactive context may be that the UE <NUM> reselects to a cell which is not included in the TAI list in the E-UTRA RAT or new RNA in NR RAT. A further condition for not retaining the inactive context may be that the UE <NUM> responds to paging to a cell which is far from the border between two RATs.

Some of the embodiments herein, as mentioned above, will now be further described and exemplified. The text below is applicable to and may be combined with any suitable embodiment(s) described above.

Embodiments herein describe how the UE <NUM> is reachable in a network in one RAT when the UE <NUM> is in RRC_INACTIVE state, either E-UTRA or NR, and RRC_IDLE or RRC_INACTIVE state in another RAT. The embodiments herein are useful e.g. when the UE <NUM> toggles between different RATs, also known as ping pong effect. To address the aforementioned problem in a simple structure, it is assumed that the UE <NUM> being in the inactive state in the first RAT, e.g. is released to RRC_INACTIVE state in NR, and that the UE <NUM> may reside on the border between the NR and E-UTRA RATs.

According to embodiments herein, when the NR/5GC RRC_INACTIVE UE <NUM> reselects an E-UTRA/LTE cell, the UE <NUM> may initiate the TAU request procedure and it subscribes itself to E-UTRA/LTE network as dual registration. <NUM> section <NUM>. <NUM> describes mobility for UEs in dual-registration mode.

Embodiments herein may be considered according to the following UE and network perspectives:.

Furthermore, the UE <NUM> may override the periodic RNA update timer, e.g. t380, to t380Dual, that may be a configurable timer sent to the UE <NUM> or a fixed defined timer. Upon expiration of the t380Dual timer the UE may send the indication of t380Dual expiration towards the camping RAT on which it is camped on to update its location.

Embodiments herein enhance the concept of lists, e.g. cell/TA code or RANAC lists, from one RAT to two RATs. When the UE <NUM> registers to a new RAT, it can keep a combination of two RATs list, either as one list or multiple ones.

<FIG> illustrates an example of inter-RAT mobility between cells of different RATs for the UE <NUM>. The UE <NUM> is in RRC_INACTIVE state in the first RAT when being registered through the first RAN node <NUM>. The UE <NUM> is located on or close to a radio coverage border of the first RAT <NUM> and the second RAT <NUM>, where the second RAT is shown as TA3. The first RAT may be either <NUM> or <NUM>, i.e. either NR or E-UTRA. The UE <NUM> may thus be in RRC_INACTIVE state in NR or E-UTRA. In this example, the first RAT <NUM> is related to <NUM> and the second RAT <NUM> is related to <NUM>. The UE <NUM> selects or reselect to Inter-RAT (I-RAT) cells connected to E-UTRA core network, i.e. the UE <NUM> moves from the first RAT related to <NUM> to the second RAT related to <NUM>.

In accordance with embodiments herein, the UE <NUM> keeps two concurrent states, e.g. inactive state such as RRC_INACTIVE and/or idle state such as RRC_IDLE. As will be explained further below, the UE <NUM> keeps its old state whenever it reselects the new RAT and can concurrently be in two different RRC states with separate contexts in <NUM>, e.g. NR-RAN, and <NUM>, e.g. E-UTRA RAN. The UE <NUM> is released to RRC_INACTIVE state in one RAT and then moves towards the I-RAT border. When the UE <NUM> enters the other RAT for the first time, the UE <NUM> registers in the new system by initiating a Tracking Area Update, if moving from <NUM> to <NUM> or initiating a Mobility Registration Update, if moving from <NUM> to <NUM>. As mentioned above, embodiments herein may be considered according to a network perspective and a UE perspective, which will be further explained below:.

Furthermore, the UE <NUM> may consider E-UTRA, or NR, tracking area list into its E-UTRA, or NR, context. Therefore, every time the UE <NUM> toggles between the two RATs, it skips the TAU procedure within the neighbour E-UTRA, or NR, tracking area.

In addition, the UE <NUM> may override the periodic RNA update timer, e.g. t380, to e.g. t380Dual. With expiration of the timer, which may optionally be either a fixed defined timer in the UE <NUM> or a configurable timer in SuspendConfig, the UE <NUM> may initiate an indication to the camped cell, either in the <NUM> or <NUM> network. The UE <NUM> may initiate RRCResumeRequest/ RRCResumeRequest1 with resumeCause set to rna-update or new cause value, when it moves back to NR coverage or an indication to the E-UTRA network.

The UE <NUM> is not required to be able to receive paging in 5GC/NR when camping on E-UTRA/EPC.

<FIG> and <FIG> illustrate a combined flowchart and signalling scheme according to some embodiments herein for handling the communication in the communication network <NUM>, where <FIG> is a continuation of <FIG> and <FIG> comprise the following actions:.

The dual registration may be torn down due to the following conditions:.

<FIG> is a block diagram depicting the UE <NUM> for communication with the first RAN node <NUM> associated with the first RAT and the second RAN node <NUM> associated with the second RAT according to embodiments herein. The UE <NUM> is in the inactive state in the first RAT when being registered to the first RAN node <NUM>.

The UE <NUM> may comprise processing circuitry <NUM>, e.g. one or more processors, configured to perform the methods herein.

The UE <NUM> may comprise a selecting or reselecting unit <NUM>. The UE <NUM>, the processing circuitry <NUM>, and/or the selecting or reselecting unit <NUM> may be configured to select or reselect the cell of the second RAN node <NUM>.

The UE <NUM> may comprise an initiating unit <NUM>. The UE <NUM>, the processing circuitry <NUM>, and/or the initiating unit <NUM> may be configured to initiate the TAU request procedure.

The UE <NUM>, the processing circuitry <NUM>, and/or the initiating unit <NUM> may be configured to initiate the MRU request procedure.

The UE <NUM> may comprise a performing unit <NUM>. The UE <NUM>, the processing circuitry <NUM>, and/or the performing unit <NUM> is configured to perform the registration through the second RAN node <NUM> while retaining the stored inactive context related to the first RAN node <NUM>, wherein a dual registration timer is used for retaining the stored inactive context, thereby having the dual registration through the first RAN node <NUM> and through the second RAN node <NUM>.

The UE may be configured to perform the registration through the second RAN node <NUM> by maintaining the list of the second RAT in addition to maintaining the list of the first RAT.

The maintained list of the second RAT may be the tracking area list and the maintained list of the first RAT may be based on the Radio access node Notification Area, RNA.

The maintained list of the second RAT may be based on the RNA and the maintained list of the first RAT may be the tracking area list.

The inactive context may be the AS inactive context.

The UE <NUM> may comprise an entering unit <NUM>. The UE <NUM>, the processing circuitry <NUM>, and/or the entering unit <NUM> is configured to enter the state in the second RAT while remaining in the inactive state in the first RAT.

Entering the state in the second RAT may comprise entering the idle state in the second RAT.

Entering the state in the second RAT may comprise entering the inactive state in the second RAT.

The UE <NUM> may be located on or close to the radio coverage border of the first RAT and the second RAT.

The UE <NUM> further comprises a memory <NUM>. The memory <NUM> comprises one or more units to be used to store data on, such as radio signals, inactive context, tracking area lists, RNA lists, input/output data, metadata, etc. and applications to perform the methods disclosed herein when being executed, and similar. The UE <NUM> may further comprise a communication interface comprising e.g. one or more antenna or antenna elements.

The methods according to the embodiments described herein for the UE <NUM> are respectively implemented by means of e.g. a computer program product <NUM> or a computer program, comprising instructions, i.e., software code portions, which, when executed on at least one processor, cause the at least one processor to carry out the actions described herein, as performed by the UE <NUM>. The computer program product <NUM> may be stored on a computer-readable storage medium <NUM>, e.g. a disc, a universal serial bus (USB) stick or similar. The computer-readable storage medium <NUM>, having stored thereon the computer program product, may comprise the instructions which, when executed on at least one processor, cause the at least one processor to carry out the actions described herein, as performed by the UE <NUM>. In some embodiments, the computer-readable storage medium may be a transitory or a non-transitory computer-readable storage medium.

<FIG> is a block diagram depicting the first RAN node <NUM> for handling communication with the UE <NUM>, wherein the first RAN node <NUM> is associated with the first RAT and the second RAN node <NUM> is associated with the second RAT, according to embodiments herein.

The first RAN node <NUM> may comprise processing circuitry <NUM>, e.g. one or more processors, configured to perform the methods herein.

The first RAN node <NUM> may comprise a configuring unit <NUM>. The first RAN node <NUM>, the processing circuitry <NUM>, and/or the configuring unit <NUM> is configured to configure the UE <NUM> with a dual registration timer for dual registration, that the UE <NUM> will use to retain the inactive context in the first RAT when registering through the second RAN node <NUM>. The timer may be the dual registration timer.

The first RAN node <NUM> may comprise a retaining unit <NUM>. The first RAN node <NUM>, the processing circuitry <NUM>, and/or the retaining unit <NUM> is configured to retain the inactive context until the timer is expired. The inactive context may be the AS inactive context.

The first RAN node <NUM> further comprises a memory <NUM>. The memory <NUM> comprises one or more units to be used to store data on, such as radio signals, inactive context, tracking area lists, RNA lists, input/output data, metadata, etc. and applications to perform the methods disclosed herein when being executed, and similar. The first RAN node <NUM> may further comprise a communication interface comprising e.g. one or more antenna or antenna elements.

The methods according to the embodiments described herein for first RAN node <NUM> are respectively implemented by means of e.g. a computer program product <NUM> or a computer program, comprising instructions, i.e., software code portions, which, when executed on at least one processor, cause the at least one processor to carry out the actions described herein, as performed by the first RAN node <NUM>. The computer program product <NUM> may be stored on a computer-readable storage medium <NUM>, e.g. a disc, a universal serial bus (USB) stick or similar. The computer-readable storage medium <NUM>, having stored thereon the computer program product, may comprise the instructions which, when executed on at least one processor, cause the at least one processor to carry out the actions described herein, as performed by the first RAN node <NUM>. In some embodiments, the computer-readable storage medium may be a transitory or a non-transitory computer-readable storage medium.

In some embodiments a more general term "radio network node" is used and it can correspond to any type of radio-network node or any network node, which communicates with a wireless device and/or with another network node. Examples of network nodes are gNodeB, eNodeB, NodeB, MeNB, SeNB, a network node belonging to Master cell group (MCG) or Secondary cell group (SCG), base station (BS), multistandard radio (MSR) radio node such as MSR BS, eNodeB, network controller, radio-network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, Remote radio Unit (RRU), Remote Radio Head (RRH), nodes in distributed antenna system (DAS), etc..

In some embodiments the non-limiting term wireless device or user equipment (UE) is used and it refers to any type of wireless device communicating with a network node and/or with another wireless device in a cellular or mobile communication system. Examples of UE are target device, device to device (D2D) UE, proximity capable UE (aka ProSe UE), machine type UE or UE capable of machine to machine (M2M) communication, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles etc..

Embodiments are applicable to any radio access technology (RAT) or multi-RAT systems, where the devices receives and/or transmit signals, e.g. data, such as New Radio (NR), Wi-Fi, Long Term Evolution (LTE), LTE-Advanced, Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations.

As will be readily understood by those familiar with communications design, that functions means or circuits may be implemented using digital logic and/or one or more microcontrollers, microprocessors, or other digital hardware. In some embodiments, several or all of the various functions may be implemented together, such as in a single application-specific integrated circuit (ASIC), or in two or more separate devices with appropriate hardware and/or software interfaces between them. Several of the functions may be implemented on a processor shared with other functional components of a UE or RAN node, for example.

Alternatively, several of the functional elements of the processing units discussed may be provided through the use of dedicated hardware, while others are provided with hardware for executing software, in association with the appropriate software or firmware. Thus, the term "processor" or "controller" as used herein does not exclusively refer to hardware capable of executing software and may implicitly include, without limitation, digital signal processor (DSP) hardware and/or program or application data. Designers of communications devices will appreciate the cost, performance, and maintenance trade-offs inherent in these design choices.

It will be appreciated that the foregoing description and the accompanying drawings represent non-limiting examples of the methods and apparatus taught herein. As such, the apparatus and techniques taught herein are not limited by the foregoing description and accompanying drawings. Instead, the embodiments herein are limited only by the following claims and their legal equivalents.

<FIG> shows a Telecommunication network connected via an intermediate network to a host computer in accordance with some embodiments. Access network <NUM> comprises a plurality of base stations 3212a, 3212b, 3212c, such as NBs, eNBs, gNBs or other types of wireless access points being examples of the RAN nodes12 and <NUM> above, each defining a corresponding coverage area 3213a, 3213b, 3213c. Each base station 3212a, 3212b, 3212c is connectable to core network <NUM> over a wired or wireless connection <NUM>. A first UE <NUM> located in coverage area 3213c is configured to wirelessly connect to, or be paged by, the corresponding base station 3212c. A second UE <NUM> in coverage area 3213a is wirelessly connectable to the corresponding base station 3212a. While a plurality of UEs <NUM>, <NUM> are illustrated in this example being examples of the wireless device <NUM> above, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station <NUM>.

<FIG> shows a host computer communicating via a base station and with a user equipment over a partially wireless connection in accordance with some embodiments.

It is noted that host computer <NUM>, base station <NUM> and UE <NUM> illustrated in <FIG> may be similar or identical to host computer <NUM>, one of base stations 3212a, 3212b, 3212c and one of UEs <NUM>, <NUM> of <FIG>, respectively.

Wireless connection <NUM> between UE <NUM> and base station <NUM> is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to UE <NUM> using OTT connection <NUM>, in which wireless connection <NUM> forms the last segment. More precisely, the teachings of these embodiments may increase the performance of the UE as the UE may not need to perform the TAU/Attach/Registration Area Update/Registration request procedure every time it toggles between two RATs. This improves the UE battery life time and the overall network signalling overhead.

<FIG> shows methods implemented in a communication system including a host computer, a base station and a user equipment in accordance with some embodiments.

For simplicity of the present disclosure, only drawing references to Fig. <NUM> will be included in this section.

<FIG> show methods implemented in a communication system including a host computer, a base station and a user equipment in accordance with some embodiments.

Claim 1:
A method performed by a User Equipment, UE, (<NUM>) for handling communication with a first Radio Access Network, RAN, node (<NUM>) associated with a first Radio Access Technology, RAT, and a second RAN node (<NUM>) associated with a second RAT, wherein the UE (<NUM>), the first RAN node (<NUM>) and the second RAN node (<NUM>) are operating in a wireless communication network, and wherein the UE (<NUM>) is in inactive state in the first RAT when being registered through the first RAN node (<NUM>), the method comprising:
- performing (<NUM>) a registration through the second RAN node (<NUM>) while retaining a stored inactive Access Stratum, AS, context related to the first RAN node (<NUM>), wherein a dual registration timer is used for retaining the stored inactive context, thereby having a dual registration to the first RAN node (<NUM>) and the second RAN node (<NUM>); and
- entering (<NUM>) a state in the second RAT while remaining in the inactive state in the first RAT, wherein the UE (<NUM>) is located on or close to a radio coverage border of the first RAT and the second RAT.