Patent Description:
In response to a power-on, a user equipment (also referred to as mobile device or end device) will generally search and attach to the wireless communication network (also referred to as mobile or cellular network) of the mobile network operator the user equipment has subscribed to (this network is also referred to as Home Public Land Mobile Network or short HPLMN). In case the user equipment is at a location, where the HPLMN is not available (for instance, when the user equipment is abroad), the user equipment will perform a roaming procedure and attach to a visiting PLMN (VPLMN). Thus, generally a user equipment having only a single RF chain or a single instance of higher layer control protocols, such as RRC (Radio Resource and Control), is not capable of attaching to more than one mobile network at the same time. A conventional user equipment that needs to manage its connectivity states (e.g., IDLE, CONNECTED) for more than one mobile networks will face a number of issues, such as the appropriate allocation of the communication resources of the user equipment and the different mobile networks, different parameterization of mobile network timers and the like.

Dual-SIM user equipments are known, which are capable of attaching to two different mobile networks. Dual-SIM user equipments, however, do not allow managing the connectivity to more than two networks at the same time, which would be desirable, for instance, in a V2X environment, i.e. a mobile wireless communication environment comprising vehicles and infrastructure.

Further suggested approaches, like pre-registering to multiple mobile networks, can minimize the switching time from one mobile network operator to another. However, how to efficiently manage the connection to more than one mobile network operator, for instance, when crossing the border between geographical areas still remains a problem.

<CIT> discloses an approach based on a database of registration information associating UEs with cells under control of different network operators. The registration information is used to coordinate between a first network operator and a second network operator to facilitate establishment of a direct communication link between the first UE and the second UE.

Some approaches have been suggests about how to select a specific PLMN when roaming. Usually, this involves the pre-configuration of the SIM card of the UE with a prioritized list of PLMNs to be used when the US needs to perform roaming. <CIT> discloses a method for selecting from a prioritized list of PLMNs as well the most suitable access technology to be used. This kind of solutions is not suitable for dynamic environments of moving devices that require multi connectivity and focus only on single operator aspects.

Thus, current technical approaches are not capable of tackling the problem of supporting user equipments, which allows managing their connectivity to multiple mobile networks. Therefore, there is a need for improved user equipments and network entities as well as corresponding methods allowing user equipments to attach to more than one mobile network.

<CIT> discloses a node of a cellular network which detects the entry of a vehicle-to-vehicle communication device into a cell of the cellular network. The node allocates resources to the vehicle-to-vehicle communication device, and sends channel information to the vehicle-to-vehicle communication device. The channel information can be included in a handover command to the vehicle-to-vehicle communication device. The channel information indicates the allocated resources. The vehicle-to-vehicle communication device uses the allocated resources for sending of vehicle-to-vehicle communication messages.

<CIT> discloses D2D communications considering different network operators. Therein, a database of registration information associating UEs with cells under control of different network operators is maintained. In response to an inquiry from a first network operator that a first UE desires direct communications with a second UE, the registration information is used to coordinate between the first network operator and the second network operator to facilitate establishment of a direct communication link between the first UE and the second UE.

<CIT> discloses a cellular communication system, wherein pre-coding MIMO parameters are assigned for transmission of device-to-device (D2D) signals between D2D mobile devices to minimize interference at unintended recipient devices (receiving proximate devices). The pre-coding MIMO parameters are transmitted from a base station to a transmitting D2D mobile device over a subset of defined downlink cellular communication resources defined by a communication specification for downlink transmission from base stations to mobile wireless devices. The pre-coding MIMO parameters are determined based on channel characteristics of at least an Interference channel where the Interference channel is between a D2D transmitting device and a proximate receiving mobile device (unintended recipient device). The precoding MIMO parameters are determined to facilitate interference management at the receiving proximate mobile device when the pre-coded transmission signal Is received through the interference channel.

<CIT> discloses the scheduling and controlling of device-to-device (D2D) communication. Therein, device parameters and uplink parameters are received from a first communication device and at least one second communication device, respectively. Further, based on the device parameters and the uplink parameters, transmission format of a D2D communication link for allowing D2D communication between the first communication device and the at least one second communication device is determined. Further, an uplink transmit grant and an uplink listen grant are transmitted to the first communication device and the at least one second communication device, respectively, based on the determination, wherein the uplink transmit grant and the uplink listen grant indicate at least the transmission format and time of transmission on the D2D communication link to the first communication device and the at least one second communication device.

<CIT> discloses a method for setting a direct mode communication channel of a group of terminals in a wide band radio communication system. The setting of the channel being assisted by at least one base station at which terminals of the group are recorded. The method includes transmitting a setting request to the base station by a terminal of the group recorded at said base station, setting a direct mode communication channel by the base station by allocating free resource blocks, transmitting a setting message by the base station to the terminals, and accessing direct mode communication channel by each of said terminals for directly communicating with the other terminals of the group.

<CIT> discloses measures for supporting multiple subscriber identities in a wireless communication device. The wireless communication device communicates with a first wireless network and with a second wireless network and shares mobility management tasks between first and second wireless cellular protocol software stacks when the first and second subscriber identity modules are each associated with the same wireless network provider either as a serving carrier or as a roaming carrier.

It is an object of the invention to provide improved user equipments and network entities as well as corresponding methods allowing user equipments to attach to more than one mobile network.

The present invention is defined by a user equipment according to independent claim <NUM>, a method for operating a user equipment according to independent claim <NUM>, a network entity according to independent claim <NUM> a method for operating a network entity according to claim <NUM> and computer program of claim <NUM>.

According to a first aspect the invention relates to a user equipment configured to be connected to a first cellular communication network and additionally to a second cellular communication network, wherein the user equipment comprises: a communication interface configured to transmit a first message to the second cellular communication network, when the user equipment is connected to the first cellular communication network and is triggered to connect additionally to the second cellular communication network, wherein the first message comprises information about the first cellular communication network. The first and second cellular communication networks can be physically or logically independent networks.

Thus, an improved user equipment is provided, which is capable of attaching to more than one mobile network. Embodiments of the invention support the ability of user equipments to have multiple connectivity options with different (logical or physical) networks even if a UE has only one RF chain or a single instance of higher layer control protocols e.g., RRC in LTE. This may be of particular advantage is use cases like V2X communication, where the UE often receives information from more than one operator, or network slicing, where the UE has to simultaneously connect to more than one slice.

The invention can be implemented in hardware and/or software.

In the various figures, identical reference signs will be used for identical or at least functionally equivalent features.

In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the present invention may be placed. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the present invention is defined be the appended claims.

<FIG> shows a schematic diagram illustrating a wireless communication system <NUM> comprising a user equipment <NUM> according to an embodiment, which is configured to be connected to and communicate with a first mobile or cellular communication network <NUM> and a second mobile or cellular communication network <NUM>. The first and second cellular communication networks <NUM>, <NUM> can be physically or logically independent networks. For instance, the first and second cellular communication networks <NUM>, <NUM> can be implemented on different network infrastructure operated by different network operators. Alternatively, the first and second cellular communication networks <NUM>, <NUM> can be logically independent networks implemented on the same network infrastructure (also known as network slices. As shown in <FIG>, respective network entities <NUM>, <NUM>, for instance, in the form of management servers, can be provided in the first and second cellular communication networks <NUM>, <NUM>, respectively.

Usually, when the UE <NUM> is registered to one of the cellular communication networks <NUM>, <NUM>, this does not necessarily mean that the UE <NUM> is able to communicate with other devices. To do this, according to current standards it must be in a usually called CONNECTED state, where network communication resources, in particular resource blocks, have been allocated to the UE <NUM>. If no communication resources have been allocated to the UE <NUM>, it is considered to be in a typically called IDLE state, where the UE <NUM> has to be triggered to request for communication resources.

Embodiments of the invention allow managing the states of the UE <NUM> through the proper processing of different events and the transition between these states. Embodiments of the invention enable the simultaneous communication of the UE <NUM> with the first and second cellular communication network <NUM>, <NUM> at the same time by means of control protocols being associated with one state machine in the UE <NUM> and independent control plane state machines in first and second cellular communication network <NUM>, <NUM> (or the corresponding network entities <NUM>, <NUM> thereof). According to embodiments of the invention, the UE <NUM> can be in the IDLE state in a subset of cellular communication networks and CONNECTED in the rest of the cellular communication networks.

According to an embodiment which is not a part of the claimed invention, when the UE <NUM> is in the IDLE state, it can either execute typical actions as specified in the corresponding telecommunication standards (e.g., monitoring the frequency of broadcasting or paging channels) or it may adopt a different behavior (e.g., faster monitoring of the downlink channels) according to particular triggering events (e.g., entering a specific geographical area, network load notification, etc.).

According to an embodiment which is not a part of the claimed invention, when the UE <NUM> is CONNECTED to more than one of the
cellular communication networks <NUM>, <NUM>, it is configured to provide these networks appropriate information. For instance, the UE <NUM> can be connected to the first cellular communication network <NUM> and communication resources have been allocated to the UE <NUM> by the first cellular communication network <NUM>. If the UE <NUM> becomes CONNECTED to the second cellular communication network <NUM>, while remaining CONNECTED to the first cellular communication network <NUM>, according to an embodiment the UE <NUM> is configured to inform the second cellular communication network <NUM> about potential restrictions it will have for the allocation of communication resources. In other words, according to an embodiment the UE <NUM> is configured to provide the second cellular communication network <NUM> with information allowing the second cellular communication network <NUM> (or the network entity <NUM> thereof) not to allocate communication resources, for instance, during the same time interval in both networks <NUM>, <NUM>, since the UE <NUM> may have only one RF chain and cannot transmit data in different networks possibly operating in different spectrum bands, as will be described in more detail further below.

As can be taken from the detailed view of <FIG>, the UE <NUM> comprises a processor <NUM> and a communication interface <NUM> for communicating with the first and second cellular communication networks <NUM>, <NUM> (and the corresponding network entities <NUM>, <NUM> thereof).

As will be described in more detail further below, the communication interface <NUM> is configured to transmit a first message to the second cellular communication network <NUM>, when the user equipment <NUM> is connected to the first cellular communication network <NUM> and is triggered to connect additionally to the second cellular communication network <NUM>, wherein the first message comprises information about the first cellular communication network <NUM>.

In an embodiment, the communication interface <NUM> is configured to transmit a second message to the second cellular communication network <NUM>, when the user equipment <NUM> is connected to the first cellular communication network <NUM> and the second cellular communication network <NUM>, wherein the second message comprises information about the first cellular communication network <NUM>.

In an embodiment which is not a part of the claimed invention, the first message and/or the second message further comprises information about the allocation of at least one of a plurality of communication resources, in particular time-frequency resource blocks, to the user equipment <NUM> by the first cellular communication network <NUM>.

In an embodiment, the first message is a "Connection Request" message and the communication interface <NUM> is configured to transmit the "Connection Request" message to the second cellular communication network <NUM>, when the user equipment <NUM> is triggered to connect additionally to the second cellular communication network <NUM>.

In an embodiment, the processor <NUM> of the UE <NUM> is configured to be in one of a plurality of states, including a first state and a second state, wherein in the first state of the processor <NUM> the UE <NUM> is connected to the first cellular communication network <NUM> but not to the second cellular communication network <NUM> and wherein in the second state of the processor <NUM> the UE <NUM> is connected to the first cellular communication network <NUM> and the second cellular communication network <NUM>.

As can be taken from the detailed view of <FIG>, both the network entity <NUM> and the network entity <NUM> comprise a processor <NUM>, <NUM> and a communication interface <NUM>, <NUM>. In the exemplary case that the UE <NUM> is already connected to the first cellular communication <NUM> the network entity <NUM> of the second cellular communication network <NUM> is configured to receive a message from the UE <NUM> via its communication interface <NUM>, wherein the message comprises information about the first cellular communication network <NUM> the UE <NUM> is already connected to. The processor <NUM> of the network entity <NUM> is configured to allocate at least one of the plurality of communication resources to the UE <NUM> for communicating over the second cellular communication network <NUM> on the basis of the information about the first cellular communication network <NUM> the UE <NUM> is already connected to.

As already described above, embodiments of the invention allow managing the connections of the user equipment <NUM> with multiple mobile networks by having one higher layer radio control protocol which undertakes responsibilities similar to the ones that the Radio Resource Control protocol according to the current LTE standard undertakes. In particular, the radio control protocol provided by embodiments of the invention relates to connection management, downlink channels monitoring (such as Paging Channel in LTE), and resource control.

<FIG> shows a state diagram of a state machine <NUM> implemented in the network entities <NUM>, <NUM> according to an embodiment. When the network entity <NUM>, <NUM> receives a Connection Request message from the UE <NUM> that is in the IDLE state (reference sign <NUM>), the network entity <NUM>, <NUM> processes this request and changes the status of the UE <NUM> to the CONNECTED state (reference sign <NUM>). In an embodiment, the Connection Request message contains further information regarding the cellular networks that the UE <NUM> is already connected to and its restrictions for communication, such as information about timing restrictions, physical communication resources and the like. When being in the CONNECTED state, if the UE <NUM> is inactive for a certain amount of time or when a Tracking Area Update (TAU) Accept message, i.e. a message related to the UE Tracking Area List for mobility management purposes, is send to the UE <NUM>, it will turn to the IDLE state. Additionally, when the UE <NUM> is in the CONNECTED state, it may send a Reconfiguration Request to the network entity <NUM>, <NUM> for several purposes, such as establishing/modifying/releasing radio bearers and/or performing a handover.

With respect to the UE <NUM>, as already described above, embodiments of the invention provide an enhanced radio control protocol, which can be represented using various state machine diagrams (or short state diagrams). In the following three embodiments of a state machine implemented in the UE <NUM> will be described in more detail. In brief, the state machines of these functionally similar embodiments of the UE <NUM> can be characterized as follows.

In the first embodiment the UE <NUM> comprises a state machine, which is based on the state machine as defined by the LTE standard and further takes into account the number of cellular communication networks <NUM>, <NUM> to which the UE <NUM> is connected to.

In the second embodiment the UE <NUM> comprises a state machine, which is based on the state machine as defined by the LTE standard and comprises a further state referred to as "MULTI-CONNECTED" state. In this "MULTI-CONNECTED" state the UE <NUM> is connected with more than one cellular communication network <NUM>, <NUM>. This embodiment also allows keeping track of the number of cellular communication networks <NUM>, <NUM> to which the UE <NUM> is connected to.

In the third embodiment which is not a part of the claimed invention, the UE <NUM> is configured to implement multiple instances of a state machine, which is based on the state machine as defined by the LTE standard. In this third embodiment the UE <NUM> can comprise a state machine selection function for defining which instance of the state machine will be used at each specific point in time. <FIG> shows a state diagram of the state machine <NUM> implemented in the UE <NUM> according to the first embodiment. As already mentioned above, in this first embodiment the state machine implemented in the UE <NUM> is based on the RRC state machine defined by the LTE standard in that it comprises the same states as the RRC state machine defined by the LTE standard, namely an IDLE state (reference sign <NUM>) and a CONNECTED state (reference sign <NUM>). Furthermore, the state machine <NUM> implemented in the UE <NUM> according to this first embodiment comprises a counter for tracking the number of cellular communication networks <NUM>, <NUM> the UE <NUM> is connected (CONNECTED state) to or in an IDLE state relative thereto.

As illustrated in <FIG>, once the UE <NUM> according to the first embodiment is powered on, it switches to the IDLE state with respect to all the mobile networks <NUM>, <NUM>. Then, on the basis of the UE's configuration (which may be fixed in a SIM card of the UE <NUM>, periodically updated, or updated in every other way) the UE <NUM> will start registering itself to each of the individual mobile networks <NUM>, <NUM>. The registration may take place sequentially (i.e., the UE <NUM> registers itself to a new mobile network once a previous registration has finished) or simultaneously (the registration procedure can be initiated to all the networks at the same time), as far as this is possible due to potential limitations of the physical layer of the UE <NUM>. For registering itself in one of the mobile networks <NUM>, <NUM> the UE <NUM> has to switch to the CONNECTED state with respect to that mobile network. To this end, in an embodiment, the UE <NUM> is configured to send a "Connection Request" message, in particular a "Radio Control Connection Setup" message to the first mobile network to which it wants to register on the basis of the UE's configuration, for instance, the first mobile network <NUM>. As a result thereof, the UE <NUM> will be CONNECTED with the first mobile network <NUM> and IDLE with respect to all the other mobile networks; the UE <NUM>, thus, will be in the CONNECTED state. In order to register with the other mobile networks the UE <NUM> is configured to send further "Radio Control Connection Setup" messages to these mobile networks and it will remain in the CONNECTED state.

In an embodiment which is not a part of the claimed invention, the UE <NUM> comprises a counter for the number of mobile networks <NUM>, <NUM> to which the UE <NUM> is already CONNECTED to (herein also referred to as "Connected Networks Counter"). This counter is configured to enable the UE <NUM> to decide whether to remain in the CONNECTED state or to switch to the IDLE state. For instance, in an embodiment, if the counter is larger than or equal to <NUM>, the UE <NUM> remains in the CONNECTED state. Otherwise, i.e. if the counter is equal to <NUM>, the UE <NUM> switches to the IDLE state. Such an embodiment will be further illustrated by means of the following exemplary scenario.

In an exemplary scenario the UE <NUM> can be CONNECTED to a mobile network A (e.g. the first mobile network <NUM> of <FIG>) and in the IDLE state with respect to mobile networks B (e.g. the second mobile network <NUM> of <FIG>) and C; the UE will be in the CONNECTED state in his local state diagram. Once the UE <NUM> wants to be CONNECTED to the mobile network B as well, it will send a "Connection Request" message, in particular a "Radio Control Connection Setup" message, to the mobile network B, while being in the CONNECTED state in its state machine. As a result thereof, the UE <NUM> will be CONNECTED to the mobile networks A and B and it will be IDLE with respect to the mobile network C in the respective network state diagrams. Moreover, the UE <NUM> will increment the Connected Networks Counter from <NUM> to <NUM>. Once inactivity is detected with respect to one of the two connected mobile networks, by way of example with respect to mobile network B, the UE <NUM> will switch to the IDLE state relative to the mobile network B in the state diagram of the mobile network B, but it will remain in the CONNECTED state, since it is in the CONNECTED state for at least one network, namely the mobile network A. Accordingly, the UE <NUM> will decrement the Connected Networks Counter from <NUM> to <NUM>. Once inactivity of the UE <NUM> is detected with respect to the mobile network A as well, the UE <NUM> will turn to IDLE for the mobile network A (i.e. the state diagram of mobile network A) as well. As correspondingly, the UE <NUM> will be IDLE for all mobile networks with the Connected Networks Counter having been decremented once more to <NUM>, the UE <NUM> will turn to its IDLE state. In an embodiment, the same process can be followed for the reception of TAU Accept messages.

When the UE <NUM> is in the CONNECTED state, according to an embodiment it can send Radio Control Reconfiguration Messages to the mobile networks <NUM>, <NUM> that the UE <NUM> is already connected to. These Radio Control Reconfiguration Messages can be used for establishing or modifying bearers or for performing handovers or any other similar procedures that are part of similar protocols such as the RRC in LTE and are captured by the RRC reconfiguration request process.

When the UE <NUM> is in the IDLE state with respect to one or more mobile networks <NUM>, <NUM>, according to an embodiment the way that it behaves is configurable in terms of which downlink channel it should monitor and how often (e.g., Paging Channel in LTE) for each of the mobile networks <NUM>, <NUM>. This configuration can depend on the capabilities of the UE <NUM> and is configurable by the network entities <NUM>, <NUM> of the mobile networks <NUM>, <NUM>. As will be appreciated, if, for instance, the UE <NUM> has multiple RF chains, it has the capability to remain inactive during the switching from one mobile network to another. This can be the case, for instance, when two mobile networks <NUM>, <NUM> operate with communication resources at different frequencies or having different waveforms. Thus, in an embodiment, the UE <NUM>, when it is in IDLE state in the network state diagram, it may have a different configuration compared to other networks to which it is IDLE as well. In other words, the UE <NUM> can be IDLE with respect to more than one network and can have different configurations in the different networks. In an embodiment, the configuration of the UE <NUM> may be provided by a mobile network, when the UE <NUM> performs its initial registration or during other operations such as the Tracking Area Update (TAU) process. In other embodiments, such updates could be provided by means of periodic updates provided by the mobile networks or upon requests from the UE <NUM> or even can be preconfigured on a SIM card of the UE <NUM>.

<FIG> shows a state diagram of the state machine <NUM> implemented in the UE <NUM> according to the second embodiment. As already mentioned above, in this second embodiment the state machine implemented in the UE <NUM> is based on the state machine as defined by the LTE standard and comprises a further state referred to as "MULTI-CONNECTED" state (reference sign <NUM>). In this "MULTI-CONNECTED" state the UE <NUM> is connected with more than one mobile network <NUM>, <NUM>. This embodiment also allows keeping track of the number of mobile networks <NUM>, <NUM> to which the UE <NUM> is connected to.

As illustrated in <FIG>, the mobile network <NUM>, <NUM> may still update the IDLE mode operation of the UE <NUM>. For this embodiment the Connected Networks Counter provides the information about when the UE <NUM> should be in the MULTI-CONNECTED state or in the CONNECTED state.

<FIG> shows a state diagram of the state machine <NUM> implemented in the UE <NUM> according to the third embodiment. As already mentioned above, in this third embodiment the UE <NUM> is configured to implement multiple instances of a state machine, which is based on the state machine as defined by the LTE standard. In the embodiment illustrated in <FIG> the UE <NUM> comprises a state machine selection function <NUM> for defining which instance of the state machine will be used at each specific point in time.

<FIG> shows a schematic diagram illustrating multiple interactions between the UE <NUM> according to an embodiment and the cellular communication networks <NUM>, <NUM> as well as their network entities <NUM>, <NUM>. In the embodiment shown in <FIG>, a radio control protocol 111a and a scheduling function 111b are implemented on the processor <NUM> of the UE <NUM>. Likewise, corresponding radio control protocols 123a, 133a and scheduling functions 123b, 133b are implemented on the processor <NUM>, <NUM> of the network entity <NUM>, <NUM> of the first and second cellular communication network <NUM>, <NUM>, respectively.

In an embodiment which is not a part of the claimed invention, when the UE <NUM> wants to connect with multiple mobile networks <NUM>, <NUM> at the same time, it is configured to provide to each individual mobile network <NUM>, <NUM> information about its capabilities and/or restrictions regarding its wireless connections. In an embodiment, this information can include the availability of multiple RF chains in the UE <NUM>, possible waveforms, other active connections, or any other type of restrictions including timing restrictions, band restrictions, energy saving requirements for multiple connections, etc. This information can be used by the scheduling function 123b, 133b of each mobile network <NUM>, <NUM> for avoiding overlaps in the scheduling (Uplink, Downlink, Sidelink) of the UE <NUM>. These overlaps may refer to frequency bands (if common spectrum is used), or time overlaps (if the UE <NUM> uses one RF chain it will not be possible to access both networks simultaneously), codes (if certain CDMA schemes are used). According to an embodiment, this information can be provided in the Radio Control Protocol Connection Setup Messages and Radio Control Protocol Reconfiguration Requests that the UE <NUM> sends to the mobile networks <NUM>, <NUM>.

In an embodiment which is not a part of the claimed invention, more detailed information may be provided in the case of dynamic scheduling, where the UE <NUM> is configured to provide with high granularity information regarding its capabilities and/or restrictions (e.g., timing restrictions, occupied or already scheduled TTls, etc.). The detailed restrictions can be provided in the Status Reporting of the UE <NUM> to each scheduling function 123b, 133b of each mobile network <NUM>, <NUM> along with, for instance, a channel status, a buffer status and/or power headroom reports.

<FIG> illustrates both cases, where the UE <NUM> provides generic restrictions in the Radio Control Connection Setup message (i.e., restrictions related to scheduling information, timing restrictions, carrier and frequency restrictions, device capabilities; provided with the message in block <NUM> of <FIG>) and more detailed restrictions (e.g., timing restrictions; provided with the message in block <NUM> of <FIG>) via direct interactions with the scheduling function 133b of the new network to which it wants to connect, i.e. the second mobile network <NUM>. In an embodiment, this detailed information can be provided by the scheduling function 111b of the UE <NUM>, which can be configured to provide this information to the other mobile network to which the UE is already connected as well, namely mobile network <NUM>. In the embodiment shown in <FIG>, the processor <NUM> of the UE <NUM> implements the radio control protocol 111a and the scheduling function 111b. Likewise, the respective processors <NUM>, <NUM> of the respective network entities <NUM>, <NUM> of the first and second mobile network <NUM>, <NUM> implement a respective radio control protocol 123a, 133a and a respective scheduling function 123b, 133b. In addition to the steps already described above <FIG> shows the following steps: a step <NUM> of communication between the UE <NUM> and the first mobile network <NUM>; a step <NUM> of triggering a connection to the second mobile network <NUM>; a step <NUM> of forwarding the scheduling restrictions received in step <NUM> to the scheduling function 133b of the network entity <NUM> of the second mobile network <NUM>; a step <NUM> of sending a Radio Control Connection Setup Response from the radio control protocol 133a of the network entity <NUM> of the second mobile network <NUM> to the UE <NUM>; and a step <NUM> of allocating communication resources by the scheduling function 133b of the network entity <NUM> of the second mobile network 130to the UE <NUM>.

Another embodiment which is not a part of the claimed invention, of the invention relates to the timings of the mobile networks <NUM>, <NUM>. As the mobile networks <NUM>, <NUM> generally might not be synchronized, in an embodiment the UE <NUM> is configured to synchronize with each mobile network <NUM>, <NUM> for transmission and reception. To this end, in an embodiment the UE <NUM> comprises a timing function configured to provide a temporal alignment or coordination among the multiple networks <NUM>, <NUM>. This timing function allows the UE <NUM> to synchronize faster with the other network or to achieve energy gains by avoiding having to listen to the synchronization channels all the time. In an embodiment, the functionalities of the timing function of the UE <NUM> include time shifting for being able to synchronize to a new transmission/reception, and even more complicated actions including sleeping and waking up for certain time periods.

The triggering events for the transition among the states of the Radio Control Protocol implemented by embodiments of the invention can include: new incoming or outgoing data traffic; UE Inactivity; activation, sensing, notification and/or identification of a new mobile network; entering/leaving special geographical areas; reception of certain messages for reconfiguration of the operation of the UE <NUM> and/or reception of certain messages related to the location tracking of the UE <NUM>.

<FIG> shows a schematic diagram illustrating a method <NUM> of operating the user equipment <NUM> according to an embodiment. The method <NUM> comprises the step <NUM> of transmitting a first message to the second cellular communication network <NUM>, when the user equipment <NUM> is triggered to connect additionally to the second cellular communication network <NUM>, wherein the first message comprises information about the first cellular communication network <NUM>.

<FIG> shows a schematic diagram illustrating a method <NUM> of operating the network entity <NUM> according to an embodiment. The method <NUM> comprises the steps of: receiving a message from the user equipment <NUM>, wherein the message comprises information about the further cellular communication network <NUM> the user equipment is connected to; and allocating at least one of the plurality of communication resources to the user equipment <NUM> for communicating over the cellular communication network <NUM> on the basis of the information about the further cellular communication network <NUM> the user equipment <NUM> is connected to.

While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms "coupled" and "connected", along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.

Claim 1:
A user equipment (<NUM>), comprising:
a processor (<NUM>) configured to determine, in response to detecting a second communication network (<NUM>) or a change of a geographical position of the user equipment, that the user equipment is to connect to the second communication network in addition to a first communication network (<NUM>) to which the user equipment is currently connected; and
a communication interface (<NUM>) configured to transmit, in response to the determination that the user equipment is to additionally connect to the second communication network, a first message to the second communication network, while the user equipment is connected to the first communication network, wherein the first message comprises timing restrictions and/or carrier and frequency restrictions for communication between the user equipment and the second communication network to inform the second communication network regarding the timing restrictions and/or carrier and frequency restrictions for communication between the user equipment and the second communication network,
wherein the user equipment is further configured to establish, after transmission of the first message, the additional connection to the second communication network while the user equipment is connected to the first communication network, wherein the additional connection to the second communication network is subject to the timing restrictions and/or carrier and frequency restrictions in the first message;
wherein the processor is further configured to manage a plurality of states of the user equipment, including a first state and a second state, wherein in the first state the user equipment is connected to the first communication network but not to the second communication network, and wherein in the second state the user equipment is connected to both the first communication network and the second communication network; and
wherein the communication interface is configured to transmit a second message intermittently to the second communication network while the user equipment is connected to both the first communication network and the second communication network, wherein the second message comprises one or more additional restrictions for communication between the user equipment and the second communication network.