TECHNICAL FIELD

Various examples generally relate to prioritizing frequencies for communicating between a wireless communication device and multiple communication networks. Various examples specifically relate to multi-subscriber identity wireless commu nication devices communicating with multiple communication networks.

BACKGROUND

Mobile communication using wireless communication devices is widespread. Some wireless communication devices (user equipment, UE) are capable of con necting to at least one communication network using multiple identities. Such UEs can have, e.g., multiple subscriber identity modules (SIMs). Hence, sometimes, these UEs are capable of connecting to at least one communication network us ing multiple identities are referred to multi-SIM UEs.

Sometimes, multi-SIM UEs have a capability of contemporaneously transmitting on multiple frequencies (dual transmission capability). For example, multiple an alog front ends and multiple digital front ends may be available to handle the communication towards the multiple communication networks associated with multiple identities.

It has been observed that contemporaneously transmitting on multiple frequen cies can result in interference between the multiple frequencies (inter-frequency interference), in particular when the transmit power is high. SUMMARY

Accordingly, there is a need for advanced techniques of operating multi-SIM UEs. There is a need for advanced techniques of communicating on multiple frequen cies.

This need is met by the features of the independent claims. The features of the dependent claims define embodiments.

A method of operating a wireless communication device is provided. The wireless communication device includes a wireless interface. The wireless interface has dual transmission capability. The method includes communicating with a first net work on one or more first frequencies. The method also includes, in accordance with a level of interference between the one or more first frequencies and one or more second frequencies, prioritizing at least one preferred frequency of the one or more second frequencies for communication with a second network.

A computer program or a computer program product or a computer-readable stor age medium includes program code. The program code can be executed by at least one processor of a control circuitry of a wireless communication device. The wireless communication device includes a wireless interface having dual trans mission capability. Executing the program code causes the at least one processor to perform a method. The method includes communicating with a first network on one or more first frequencies. The method also includes, in accordance with a level of interference between the one or more first frequencies and one or more second frequencies, prioritizing at least one preferred frequency of the one or more second frequencies for communication with a second network.

A wireless communication device includes control circuitry and a wireless inter face. The wireless interface has dual transmission capability. The control circuitry is configured to control the wireless interface to communicate with a first network on one or more first frequencies. The control circuitry is also configured to control the wireless interface to prioritize at least one preferred frequency of one or more second frequencies for communication with a second network in accordance with a level of interference between the one or more first frequencies and the one or more second frequencies.

A method of operating an access node of a network includes receiving, from a wireless communication device, a request to communicate on at least one pre ferred frequency when the wireless communication device operates in a con nected mode towards the network. The method also includes controlling commu nication with the wireless communication device in accordance with the at least one preferred frequency.

A method of operating an access node of a network includes receiving, from a wireless communication device, a request for a list of one or more frequencies of the network when the wireless communication device operates in connected mode towards the network. The method also includes transmitting, to the wireless communication device, the list of the one or more frequencies.

A computer program or a computer program product or a computer-readable stor age medium includes program code. The program code can be executed by at least one processor of a control circuitry of an access node of a network. Execut ing the program code causes the at least one processor to perform a method The method includes receiving, from a wireless communication device, a request to communicate on at least one preferred frequency when the wireless communica tion device operates in a connected mode towards the network. The method also includes controlling communication with the wireless communication device in accordance with the at least one preferred frequency.

A computer program or a computer program product or a computer-readable stor age medium includes program code. The program code can be executed by at least one processor of a control circuitry of an access node of a network. Execut ing the program code causes the at least one processor to perform a method The method includes receiving, from a wireless communication device, a request for a list of one or more frequencies of the network when the wireless communication device operates in connected mode towards the network. The method also in cludes transmitting, to the wireless communication device, the list of the one or more frequencies.

An access node of a network includes control circuitry configured to: receive, from a wireless communication device, a request to communicate on at least one pre ferred frequency when the wireless communication device operates in a con- nected mode towards the network; and control communication with the wireless communication device in accordance with the at least one preferred frequency.

An access node of a network includes control circuitry configured to: receive, from a wireless communication device, a request for a list of one or more frequencies of the network when the wireless communication device operates in connected mode towards the network; and transmit, to the wireless communication device, the list of the one or more frequencies.

It is to be understood that the features mentioned above and those yet to be explained below may be used not only in the respective combinations indicated, but also in other combinations or in isolation without departing from the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a cellular network according to various examples.

FIG. 2 schematically illustrates a multi-Sim UE communicating using multiple identities with multiple cellular networks according to various examples. FIG. 3 schematically illustrates inter-frequency interference according to various examples.

FIG. 4 schematically illustrates a time-frequency resource grid including time-fre- quency resources that are allocated to multiple channels according to various examples.

FIG. 5 schematically illustrates multiple modes in which a UE can operate ac cording to various examples.

FIG. 6 schematically illustrates a base station according to various examples. FIG. 7 schematically illustrates a UE according to various examples FIG. 8 is a flowchart of a method according to various examples.

FIG. 9 is a flowchart of a method according to various examples.

FIG. 10 is a signaling diagram of communication according to various examples.

FIG. 11 is a signaling diagram of communication according to various examples. FIG. 12 is a flowchart of a method according to various examples. FIG. 13 is a flowchart of a method according to various examples.

DETAILED DESCRIPTION OF EMBODIMENTS

Some examples of the present disclosure generally provide for a plurality of cir- cuits or other electrical devices. All references to the circuits and other electrical devices and the functionality provided by each are not intended to be limited to encompassing only what is illustrated and described herein. While particular la bels may be assigned to the various circuits or other electrical devices disclosed, such labels are not intended to limit the scope of operation for the circuits and the other electrical devices. Such circuits and other electrical devices may be com bined with each other and/or separated in any manner based on the particular type of electrical implementation that is desired. It is recognized that any circuit or other electrical device disclosed herein may include any number of microcon trollers, a graphics processor unit (GPU), integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electri cally programmable read only memory (EPROM), electrically erasable program mable read only memory (EEPROM), or other suitable variants thereof), and soft ware which co-act with one another to perform operation(s) disclosed herein. In addition, any one or more of the electrical devices may be configured to execute a program code that is embodied in a non-transitory computer readable medium programmed to perform any number of the functions as disclosed.

In the following, embodiments of the invention will be described in detail with ref erence to the accompanying drawings. It is to be understood that the following description of embodiments is not to be taken in a limiting sense. The scope of the invention is not intended to be limited by the embodiments described herein after or by the drawings, which are taken to be illustrative only.

The drawings are to be regarded as being schematic representations and ele ments illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to a person skilled in the art. Any connection or coupling be tween functional blocks, devices, components, or other physical or functional units shown in the drawings or described herein may also be implemented by an indirect connection or coupling. A coupling between components may also be established over a wireless connection. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof. Various aspects relate to a communication system. For example, the communi cation system may be implemented by a UE and a BS of a communication net work, e.g., of a cellular network. The communication system may include a wire less link between the UE and the BS. Downlink (DL) signals may be transmitted by the BS and received by the UE. Uplink (UL) signals may be transmitted by the UE and received by the BS.

Various examples described herein relate to UEs that are capable of connecting to the cellular network using two or more identities of the UE. As a general rule, the term identity of the UE as used herein may refer to an identity associated with a subscriber associated with the UE, i.e. , a subscriber identity. The identity may include a temporary identity assigned to the UE.

For example, such UEs capable of connecting to the cellular network using two or more identities could comprise multiple SIM chip cards or embedded SIMs hereinafter, such UEs that are capable of connecting to the cellular network using multiple identities will be referred to as multi-SIM UEs.

As a general rule, multi-SIM UEs can connect to the same cellular network or to different cellular networks using their multiple identities. For instance, some sce narios are described herein in which a multi-SIM UE connects to multiple cellular networks.

The different identities of a multi-SIM UE are typically associated with different subscriptions at respective cellular network. Such subscriptions are associated with a unique identity, e.g., the International Mobile Subscriber Identity (IMSI), and a unique service agreement. For example, policies and charging and/or traf fic shaping for telephone calls, short messaging services and packet data or other services can be dependent on the respective service model. As a general rule, if the multi-SIM UE connects to at least one cellular network using a first identity, then a respective IP address, a unique mobile station international subscriber directory number (MSISDN), and a unique data connection with the cellular net work can be provisioned. Hence, it can be said that a multi-SIM UE, from a net work perspective, will be perceived as two independent UEs.

As a general rule, multi-SIM UEs can have a communication interface having dual transmission capability. In particular, UEs not having dual transmission capability are sometimes called “single radio”. Then, to be able to communicate with more than one cellular network, time multiplexing is needed. Multi-SIM UEs that have dual transmit capability are sometimes called "multi-radio". Such multi-radio multi- SIM UEs can contemporaneously transmit on multiple frequencies. Thus, fre quency multiplexing is possible.

Various techniques are based on the finding that contemporaneous transmitting and/or receiving (communicating) on multiple frequencies can suffer from inter frequency interference. For example, higher-order harmonics of a first frequency may be excited at a significant power spectral density by an analog front end and can then interfere with a second frequency used for communicating with a second network. Further, side lobes of a frequency band can also be excited at a signifi cant power spectral density and may, again, interfere with a second frequency used for communicating with a second network. Then, such inter-frequency inter ference can cause conflicts between the communication towards the first and second networks.

Such conflicts due to inter-frequency interference are mitigated by the techniques described herein. According to examples, when the multi-radio multi-SIM UE communicates with a first network on one or more first frequencies, it is possible to prioritize at least one preferred frequency of one or more second frequencies for communication with a second network, wherein such prioritizing is in accord ance with a level of interference between the one or more first frequencies and the one or more second frequencies. Thereby, it would be possible to prioritize the at least one preferred frequency that exhibits a limited or reduced inter-frequency interference with the one or more first frequencies. Thus, conflicts between the communication with the first network and the communication with the second network are mitigated.

Such prioritization of the at least one preferred frequency can be implemented by logic that is centric at the multi-radio multi-SIM UE. For example, often multiple communication networks are not aware and cannot control the frequency of an other network. Thus, according to the techniques described herein, if multiple frequencies (or more specifically multiple frequency bands) are available for com municating with the second network, it is possible to prioritize, at the multi-radio multi-SIM UE, the at least one preferred frequency so as to minimize the inter frequency interference between the signals communicated between the multi-ra dio multi-SIM UE and the first network and the second network.

As a general rule, various examples are described hereinafter in which the multi radio multi-SIM UE communicates with a first network: For example, the multi radio multi-SIM UE could be in connected mode towards the first network. I.e. , a data connection may be set up between the UE and the first network and UL data and/or DL data may be communicated along this data connection. Then, the UE may prioritize the at least one preferred frequency from the one or more second frequencies that are in principle available for communication with the second net work. In this regard, it would be possible that the UE uses the at least one pre ferred frequency in connection with an initial Public Land Mobile Network (PLMN) search for the second network, and/or when operating in idle mode towards the second network, and/or when operating in connected mode towards the second network. As will be appreciated, the prioritization of the at least one preferred frequency can be applicable in various modes of operating the multi-radio multi- SIM UE towards the second network.

Furthermore, while various examples will be described hereinafter in which the prioritization of the at least one preferred frequency is implemented with respect to the one or more second frequencies for communication with the second net work, it would alternatively or additionally be possible to implement such prioriti zation of at least one further preferred frequency of the one or more first frequen cies for communication with the first network. In other words, three scenarios are conceivable: In the first scenario, the communication towards the first network is not adapted by prioritizing the at least one further preferred frequency in view of the inter-frequency interference and the prioritizing is with respect to the at least one preferred frequency of the one or more second frequencies for communica tion with the second network, only. Here, a hierarchy between communicating between the multi-radio multi-SIM UE and the first network and the communi cating between the multi-radio multi-SIM UE and the second network exists. The communication between the multi-radio multi-SIM UE and the second network has to adapt to certain constraints imposed by the inter-frequency interference from the one or more first frequencies used for communicating between the multi radio multi-SIM UE and the first network. A second scenario pertains to the in verted situation: here, the prioritization is implemented with respect to the at least one further preferred frequency of the one or more first frequencies, but not with respect to the one or more second frequencies. Also in this second scenario there is a hierarchy between communicating with the first network and the second net work. The third scenario does not rely on such a hierarchy. Here, it would be possible to prioritize, both, the at least one preferred frequency of the one or more second frequencies, as well as the at least one further preferred frequency of the one or more first frequencies. Then, the communication between the multi-radio multi-SIM UE and, both, the first network, as well as the second network is af fected by the inter-frequency interference mitigation. On the other hand, interfer ence mitigation can be more powerful, because it is possible to adjust two de grees of freedom (i.e. , the communication frequency towards a first network, as well as the communication frequency towards the second network).

Accordingly, while, hereinafter, various techniques will be described in connec tion with the prioritizing of the at least one preferred frequency of the one or more second frequencies for communication between the multi-radio multi-SIM UE and the second network, similar techniques may be readily applied alternatively or additionally to prioritizing the at least one further preferred frequency of the one or more first frequencies for communication between the multi-radio multi-SIM UE and the first network.

FIG. 1 schematically illustrates a cellular network 100. The example of FIG. 1 illustrates the cellular network 100 according to the 3GPP 5G architecture. Details of the 3GPP 5G architecture are described in 3GPP TS 23.501, version 15.3.0 (2017-09). While FIG. 1 and further parts of the following description illustrate techniques in the 3GPP 5G framework of a cellular network, similar techniques may be readily applied to other communication protocols. Examples include 3GPP LTE 4G - e.g., in the MTC or NB-IOT framework - and even non-cellular wireless systems, e.g., an IEEE Wi-Fi technology. In the scenario of FIG. 1, a UE 101 is connectable to the cellular network 100. For example, the UE 101 may be one of the following: a cellular phone; a smart phone; an IOT device; a MTC device; a sensor; an actuator; etc.

The UE 101 is a multi-SIM UE 101 : the UE 101 is capable of connecting to mul- tiple cellular networks (in FIG. 1 only a single cellular network is illustrated) - in accordance with two identities 451, 452. For instance, the UE 101 could use the first identity 451 to register at and/or request communication and/or communicate with a first network; the UE 101 could use the second identity 452 to register at and/or request communication and/or communicate with a second network that is different from the first network.

The UE 101 is connectable to a core network (CN) 115 of the cellular network 100 via a RAN 111 , typically formed by one or more BSs 112 (only a single BS 112 is illustrated in FIG. 1 for sake of simplicity). A wireless link 114 is established between the RAN 111 - specifically between one or more of the BSs 112 of the RAN 111 - and the UE 101. The CN 115 includes a user plane (UP) 191 and a control plane (CP) 192. Appli cation data is typically routed via the UP 191. For this, there is provided a UP function (UPF) 121. The UPF 121 may implement router functionality. Application data may pass through one or more UPFs 121. In the scenario of FIG. 1 , the UPF 121 acts as a gateway towards a data network 180, e.g., the Internet or a Local

Area Network. Application data can be communicated between the UE 101 and one or more servers on the data network 180.

The cellular network 100 also includes an Access and Mobility Management Function (AMF) 131; a Session Management Function (SMF) 132; a Policy Con trol Function (PCF) 133; an Application Function (AF) 134; a Network Slice Se lection Function (NSSF) 134; an Authentication Server Function (AUSF) 136; and a Unified Data Management (UDM) 137. FIG. 1 also illustrates the protocol ref erence points N1-N22 between these nodes.

The AMF 131 provides one or more of the following functionalities: connection management sometimes also referred to as registration management; NAS ter mination; connection management; reachability management; mobility manage ment; connection authentication; and connection authorization. For example, the AMF 131 controls CN-initiated paging of the UE 101, if the respective UE 101 operates in idle mode. The AMF 131 may trigger transmission of paging signals to the UE 101; this may be time-aligned with POs. After UE registration to the network, the AMF 131 creates a UE context 459 and keeps this UE context, at least as long as the UE 101 is registered to the network. The AMF 131 also pro- vides the UE 101 with a temporary identity, the TMSI.

A data connection 189 is established by the SMF 132 if the respective UE 101 operates in a connected mode. The data connection 189 is characterized by UE subscription information hosted by the UDM 137. To keep track of the current mode of the UE 101 , the AMF 131 sets the UE 101 to CM-CONNECTED or CM- IDLE. During CM-CONNECTED, a non-access stratum (NAS) connection is maintained between the UE 101 and the AMF 131. The NAS connection imple ments an example of a mobility control connection. The NAS connection may be set up in response to paging of the UE 101.

The SMF 132 provides one or more of the following functionalities: session man agement including session establishment, modify and release, including bearers set up of UP bearers between the RAN 111 and the UPF 121 ; selection and con trol of UPFs; configuring of traffic steering; roaming functionality; termination of at least parts of NAS messages; etc. As such, the AMF 131 and the SMF 132 both implement CP mobility management needed to support a moving UE.

The data connection 189 is established between the UE 101 via the RAN 111 and the UP 191 of the CN 115 and towards the DN 180. For example, a connec tion with the Internet or another packet data network can be established. To es tablish the data connection 189, i.e. , to connect to the cellular network 100, it is possible that the respective UE 101 performs a random access (RACFI) proce dure, e.g., in response to reception of a paging signal. A server of the DN 180 may host a service for which payload data is communicated via the data connec tion 189. The data connection 189 may include one or more bearers such as a dedicated bearer or a default bearer. The data connection 189 may be defined on the RRC layer, e.g., generally Layer 3 of the OSI model.

FIG. 2 schematically illustrates aspects with respect to the multiple identities 451 , 452. In the scenario of FIG. 2, two cellular networks 100-1 , 100-2 are provided. The UE 101 is configured to communicate with the cellular network 100-1 on a first wireless link 114-1 using the identity 451 ; and is configured to communicate with the cellular network 100-2 on a second wireless link 114-2 using the identity 452.

Each of the cellular networks 100-1 , 100-2 can be configured in accordance with the cellular network 100 of FIG. 1. Each cellular network 100-1 , 100-2 can store a respective UE context 459 associated with the respective identity 451 , 452. Details with respect to the wireless links 114-1 and 114-2 are illustrated in con nection with FIG. 3. FIG. 3 schematically illustrates aspects with respect to the configuration of the wireless link 114-1 and the configuration of the wireless link 114-2 in frequency domain. More specifically, FIG. 3 schematically illustrates multiple frequency bands 901-903 allocated to the first wireless link 114-1; and multiple frequency bands 905-908 allocated to the second wireless link 114-2. As illustrated in FIG. 3, the frequency bands 901-903 are offset, in frequency domain, from the fre quency bands 905-908, to reduce inter-frequency interference.

Nonetheless, there can be (residual) inter-frequency interference 911-912, even though the frequency bands 901-903 and 905-907 are offset from each other in frequency domain. For example, there can be inter-frequency interference 911 between the neighboring frequency bands 901 and 905, e.g., because transmis sion by the UE 101 on frequencies in the frequency band 901 can also be ex tended to side lobes (i.e. , power spectral density can be significant in a side lobe, i.e. , side-lobe leaking) that extend into the frequency band 905. The inter-fre- quency interference 912 can be due to non-lineararity effects and coupling to higher-order harmonics. For example, a transceiver hardware of an analog front end of a wireless interface of the multi-radio multi-SIM UE 101 can experience such non-linearities. As a general rule, various options are available to estimate or determine the level of interference. For instance, based on an analytical model or simulations or cal ibration measurements, a lookup table could be provided that specifies the level of interference for the various available frequencies. Then, it would be possible that the level of interference is determined based on a comparison of the first frequency bands 901 -903 and the second frequency bands 905-908, and the cor responding lookup in the table. Alternatively, an analytical model may be loaded and the comparison of the frequency bands 901-903 and 905-907 may be pro vided as an input to the analytical model. In an alternative embodiment, it would also be possible to communicate pilot signals and determine the level of interfer ence based on channel measurements. Here, in one example strategy for chan nel measurements, it would be possible to implement silent durations on, e.g., the first frequency bands 901-903 and then transmit, during the silent durations, pilot signals on the second frequency bands 905-908. Then, the power spectral density due to the pilot signals can be measured on the first frequency bands 901 -903, to determine the inter-frequency interference. There are other strategies available to perform such channel measurements. For instance, there may be simultaneous transmission on both frequency bands 901-903 and 905-908. For instance, pilot signals may be transmitted on the frequency bands 905-908while there is payload data communicated on the frequency bands 901-903. Then, the degradation of the communication on the frequency bands 905-908 due to the inter-frequency interference 911-912 can be observed based on the channel measurements, e.g., based on a receive property - e.g., amplitude and/or phase - of the pilot signals. Thus, channel measurements are a tool to determine the level of inter-frequency interference.

As a general rule, the wireless links 114-1 and 114-2 supported by the RANs 111 of the cellular networks 100-1 , 100-2 can each include one or more carriers, e.g., each carrier providing for Orthogonal Frequency Division Multiplex (OFDM) mod ulation. Details with respect to a corresponding time-frequency resource grid are illustrated in FIG. 4.

FIG. 4 schematically illustrates aspects with respect to a time-frequency resource grid 200 including multiple time-frequency resource elements 210. Such a time- frequency resource grid 200 could be defined on each one of the frequency bands 901-903 and 905-907, respectively. The time-frequency resource elements 210 are defined by symbols and subcarriers according to the OFDM modulation. Fur ther, the time-frequency resource elements 210 are structured in time domain. For this, frames 201-203 of a protocol implemented by the respective wireless link 114 are provided. The give an example, the frames 201-203 may be imple mented by transmission frames, subframes, or timeslots. Typically, a transmis sion frame includes multiple subframes and a given subframe includes multiple timeslots.

As a general rule, each frame 201-203 has a certain sequence number. The se quence numbers of the frames 201-203 can implement a time reference for the respective cellular network 100-1 , 100-2. Synchronization signals indicative of the time reference can be communicated in a respective channel (not illustrated in FIG. 3).

FIG. 4 also illustrates aspects with respect to multiple channels 261-263. In par ticular, different channels 261-263 can be associated with different time-fre quency resource elements 210. Different channels 261-263 can be used for dif- ferent types of signals. Different channels can use different modulation and cod ing schemes. Some of the channels may be used for UL communication, while other channels may be used for DL communication.

A first channel (dashed line in FIG. 4) - e.g., implemented as the Physical DL Control Channel (PDCCH) 261 - may carry paging indicators, which enable the cellular network 100 - e.g., the AMF 131 - to page a UE 101 during a PO. The PDCCH 261 may also carry scheduling grants/assignments, sometimes referred to as DL control information (DCI). Further, a second channel (dashed-dotted line in FIG. 4 - e.g., implemented by the Physical DL Shared Channel (PDSCH) 262 - is associated with a payload DL messages carrying higher-layer data. Higher-layer messages may include Radio Resource Control (RRC) control messages, e.g., paging messages. The paging messages can be indicative of the identities of the particular UE to be paged. The PDSCH 262 can also carry messages including payload data from the UP 191. While in the scenario of FIG. 4 only the PDSCH 262 for DL messages is illus trated, the time-frequency resource grid 200 can also include time-frequency re sources 210 allocated to a Physical UL Shared Channel (PUSCH) (not illustrated in FIG. 3). For example, payload UL messages carrying higher-layer data or UP 191 payload data can be communication on the PUSCFI.

Further, a third channel (dotted line in FIG. 4) - e.g., implemented by the Physical UL Control Channel (PUCCH) 263 - is an UL control channel. The PUCCH 263 could e.g. include scheduling requests, e.g., implemented by a buffer status re port (BSR). This can trigger scheduling at the BS 112. Then, a scheduling grant on the PDCCFI 261 can be used to indicate allocations 220 on the PUSCFI. On the other hand, for scheduling DL data, a DL notification can be transmitted on the PDCCFI; and an associated allocation 220 on the PDSCFI 262 can be indi cated.

FIG. 5 illustrates aspects with respect to different modes 301 - 303 in which the UE 101 can operate. Example implementations of the operational modes 301 - 303 are described, e.g., in 3GPP TS 38.300, e.g., version 15.0.0.

Before initially connecting to a network 100-1 , 100-2, a PLMN search mode 303 is executed. Flere, multiple candidate frequencies are searched and the UE 101 attempts to acquire synchronization signals to obtain the time reference of the respective cellular network 100-1 , 100-2. At this time, the AMF 131 may not hold a context of the UE 101. Once obtaining the time reference, and identity of the cellular network 100-1 , 100-2 may be checked, e.g., in a broadcast information block. Then, the data connection 189 may be set up, by performing a random access procedure. This triggers a transition into a connected mode 301.

During the connected mode 301 , the data connection 189 is set up. For example, a default bearer and optionally one or more dedicated bearers may be set up between the UE 101 and the cellular network 100. A wireless interface of the UE 101 may persistently operate in an active state, or may implement a discontinu ous reception (DRX) cycle.

To achieve a power reduction, it is possible to implement the idle mode 302. When operating in the idle mode 302, the UE 101 is configured to monitor for paging indicators and, optionally, paging messages in accordance with a timing of POs. The timing of the POs may be aligned with a DRX cycle in idle mode 302. This may help to further reduce the power consumption - e.g., if compared to the connected mode 301. In the idle mode 302, the data connection 189 is not main- tained, but released.

FIG. 6 schematically illustrates the BS 112. The BS 112 includes an interface 1125. For example, the interface 1125 may include an analog front end and a digital front end. The interface 1125 can also be used for signaling towards the CN 115. The BS 112 further includes control circuitry 1122, e.g., implemented by means of one or more processors and software. For example, program code to be executed by the control circuitry 1122 may be stored in a non-volatile memory 1123. In the various examples disclosed herein, various functionality may be im plemented by the control circuitry 1122 by executing the program code, e.g.: re- ceiving a request for a list of one or more frequencies for communication; trans mitting the list; receiving a request for at least one preferred frequency; communi cating in accordance with the at least one preferred frequency.

FIG. 7 schematically illustrates the UE 101. In the example of FIG. 7, the UE 101 is a dual-radio UE and a wireless interface 1015 having two radios 1018, 1019. Accordingly, the UE 101 has dual transmission capability. For example, each ra dio 1018, 1019 of the interface 1015 may include an analog front end and a digital front end. The UE 101 can transmit on the radio 1018 and, at the same time, transmit on the radio 1019 (dual transmission capability). For example, the UE 101 may be configured to connect to a cellular network 100, 100-1 , 100-2 and to communicate using the respective identity 451 , 452. Frequency-duplexing can be employed. The UE 101 also includes control circuitry 1012, e.g., implemented by means of one or more processors and software. For example, program code to be executed by the control circuitry 1012 may be stored in a non-volatile memory 1013. In the various examples disclosed herein, various functionality may be im plemented by the control circuitry 1012 by executing the program code, e.g.: com- municating with a first network on one or more first frequencies; communicating with a second network on one or more second frequencies; prioritizing at least one preferred frequency of the one or more second frequencies for communica tion with the second network, e.g., in accordance with a level of interference be tween the one or more first frequencies and the one or more second frequencies; determining the level of interference; selecting the at least one preferred fre quency from a list of the one or more second frequencies; etc.

As a general rule, when transmitting on the radio 1018 and on the radio 1019 on different frequencies in accordance with the dual transmission capability, there may be inter-frequency interference between the radios 1018 and 1019.

FIG. 8 is a flowchart of a method according to various examples. The method of FIG. 8 can be executed by a UE. For example, the method according to FIG. 8 could be executed by the control circuitry 1012 of the UE 101, e.g., upon load respective program code from the memory 1013 (of. FIG. 7). Various examples will be described hereinafter for a scenario in which the method according to FIG. 8 is executed by the UE 101 for sake of simplicity, but similar techniques may be readily employed for other scenarios in which the method according to FIG. 8 is executed by other devices or nodes.

At box 1001, the UE 101 communicates with the first network. For example, the UE 101 can receive data from the first network 100-1 and/or can transmit data to the first network 100-1. The UE 101 can communicate with the first network on one or more of the frequency bands 901-903 of the respective wireless link 114- 1 (of. FIG. 3). For example, it would be possible that, at box 1001 , the UE 101 is in connected mode 301 towards the first network 100-1 .

Next, at box 1002, the UE 101 prioritizes at least one preferred frequency of the one or more second frequency bands 905-907 for communication with the sec ond network 100-2. For example, considering the scenario of FIG. 3 - in which there is inter-frequency interference 911 between the frequency band 901 and the frequency band 905 and in which there is also inter-frequency interference 912 between the frequency band 901 and the frequency band 907, it would be possible to prioritize the frequency band 906. This is because the frequency band 906 experiences the lowest level of inter-frequency interference if compared to all available frequency bands 905-907.

Then, at box 1003, the UE 101 can communicate with the second network 100-2 in accordance with the at least one preferred frequency 906.

As a general rule, the method of FIG. 8 may be of particular relevance for multi radio multi-SIM UE such as the UE 101. As a general rule, it would also be pos sible that such techniques are broadly employed for non-subscriber-identity-re- lated techniques in which multiple frequencies are used to communicate with mul tiple networks.

As a general rule, there are various options available for implementing the prior itization of the at least one preferred frequency at box 1002. Some options of how to implement such prioritization are explained next in connection with FIG. 9.

FIG. 9 is a flowchart of a method according to various examples. FIG. 9 illustrates an example implementation of box 1002 of FIG. 8. FIG. 9 illustrates aspects with respect to prioritizing at least one preferred frequency. Optional boxes are marked with dashed lines in FIG. 9. Initially, at box 2001 , it would be possible to transmit a request for a list of the one or more second frequency bands 905-907. For instance, such a request may be helpful when operating in the connected mode 301 towards the second network 100-2. Then, it would be possible that the list of the one or more second fre- quency bands 905-907 is received on, e.g., the PDCCFI 261 from the second network 100-2. Such techniques are based on the finding that, conventionally, the control of the employed frequencies resides at the network when the UE 101 operates in the connected mode 301. Thus, conventionally, the network would not provide a list of all available frequencies to the UE 101 while the UE 101 operates in the connected mode 301 ; but rather select the appropriate frequency at the network (e.g., depending on decision criteria such as load-balancing, avail able resources, etc.). Thus, when operating in the connected mode 301, it can be helpful to request the list from the network. Then, at box 2002, the list is obtained, e.g., received from the second network 100 2

There are other options available for establishing the list of the second frequency bands 905-907, beyond receiving the list of the second frequency bands 905-907 from the second network 100-2. For instance, it would be possible, at 2003, to perform a band scan to determine the list. The band scan can generally relate to scanning the entire spectrum (e.g., from a lower end 991 to an upper end 993 (of. FIG. 3), listening for reference signal such as synchronization signals and broad casted system information blocks and, thereby, identify the available frequency bands 905-907. These techniques mitigate downlink control signaling. Moreover, such techniques can be helpful when operating in the idle mode 302. Flere, the PDCCFI 261 may not be readily established for transmission of the list and, thereby, the UE may not be easily informed in a dedicated control signaling, ac cordingly.

Yet another option for establishing the list would include receiving a broadcasted system information block that includes the list. Next, at optional box 2003, the level of interference is estimated.

For example, the interference estimation could include comparing the frequency positions of the first frequency bands 901 -903 with the frequency positions of the second frequency bands 905-907. Then, a check could be made for, e.g., higher- order harmonics or adjacent frequency positions. Side-lobe leaking or non-line arity effects can be identified. Another option for implementing box 2003 would be that channel measurements are performed to determine the level of interference. This may be the case where there is transmission ongoing on both frequency bands 901-903, as well as 905- 907. Another option for implementing box 2003 includes a check of whether the UE 101 operates in the connected mode 301 towards the first network 100-1. Some times, only when operating in the connected mode 301 towards the first network 100-1 , the level of inter-frequency interference is significant. This is based on the finding that the amount of spectrum access during the connected mode 301 is typically magnitudes higher than during the idle mode 302. In particular, during the idle mode 302, it may be seldom that the UE 101 has to transmit. Rather, the UE 101 may have to occasionally monitor paging occasions for paging signals transmitted by the first network 100-1. This may cause no or no significant inter frequency interference 911-912 into the second frequency bands 905-907 of the second network 100-2. In other examples, inter-frequency interference mitigation may also be helpful for idle mode 302.

Other options are available for estimating the level of interference at box 2003. For example, it would be possible to detect contemporaneous transmission be- tween the UE 101 and the first network 100-1, and the UE 101 and the second network 100-2. When detecting such contemporaneous transmission, it may be judged that the level of interference is significant. For example, it could be checked whether a transmit chain of the radios 1018 and 1019 (cf. FIG. 7) are contemporaneously activated.

As will be appreciated, there are various options available to assess the level of inter-frequency interference at box 2003.

At optional box 2004, it is checked whether the level of inter-frequency interfer ence is significant. This is based on the estimation of box 2003. For example, a corresponding threshold may be predefined and the estimated inter-frequency interference can be compared against the threshold. The threshold could be de pendent on the required quality-of-service.

If, at box 2004, it is judged that there is significant inter-frequency interference, the method commences at box 2005. Otherwise the remaining boxes are not ex ecuted.

At box 2005, the at least one preferred frequency band 906 is selected from the list of available frequency bands 905-907. This selection depends on the esti mated level of interference that is lower for the preferred frequency band 906 than for the non-preferred frequency bands 905, 907.

Then, at box 2006, the prioritization is executed. The at least one preferred fre quency band 906 is prioritized in accordance with the level of interference.

Again, there are various options available for implementation of box 2006.

In particular, the implementation of box 2006 can depend on the mode 301 -302, 305 according to which the UE 101 operates towards the second network 100-2. In particular, an example state chart is represented by Table 1 .

Table 1 : State chart of operational modes towards the networks 100-1 , 100-2

For example, in Tab 1 , a first example is illustrated in row 1. Here, the UE 101 is in connected mode 301 or in idle mode 302 towards the first network 100-1 and performs a PLMN search in the PLMN search mode 303 with respect to the sec ond network 100-2. In such a scenario, the prioritization can be executed in box 2006 by prioritizing the network band scan on the preferred frequency band 906 over the network band scans on the non-preferred frequency bands 905, 907. There are various options available for prioritizing the network band scan on the preferred frequency band 906. For instance, the network band scan can initially commence on the preferred frequency band 906 and, later on, in case the net work band scan on the preferred frequency band 906 has not been successful, switch to the non-preferred frequency bands 905 and 907. In another option, where a repetitive band scan is implemented, it would be possible to visit the preferred frequency band 906 more often than the non-preferred frequency bands 905, 907.

Then, if the second network 100-2 is found, the UE 101 can camp on the respec tive frequencies (corresponding to a transition for the PLMN search mode 303 to the idle mode 302, cf. FIG. 5). Otherwise, when transitioning to the connected mode 301 towards the second network 100-2, it can be checked whether the level of interference is below a threshold such that the communication towards the first network 100-1 and the communication towards the second network 100-2 is not severely impacted.

A further scenario is illustrated in Tab. 1: row 2. Here, the UE 101 operates, to wards the first network 100-1 , in the connected mode 301 or in the idle mode 302. The UE 101 operates, towards the second network 100-2, in the idle mode 302. When the UE 101 operates, towards both networks 100-1 , 100-2, in the idle mode 302, paging occasions associated with each one of the networks 100-1 , 100-2 can be handled in time domain, e.g., by time multiplexing or time sharing.

Thus, next, a scenario will be discussed in which the UE 101 operates in the connected mode 301 towards the first network 100-1 and operates in the idle mode 302 towards the second network 100-2. Details with respect to such a sce nario are illustrated in FIG. 10.

FIG. 10 is a signaling diagram of communication between the UE 101 and the networks 100-1 and 100-2. For example, the communication between the UE 101 and the network 100-1 can be in accordance with the first subscriber identity 451 ; and the communication between the UE 101 and the second network 100-2 can be in accordance with the second subscriber identity 452.

As illustrated in FIG. 10, the UE 101 operates in the connected mode 301 towards the first network 100-1 for the entire illustrated time duration.

At some point, the UE 101 transitions from the connected mode 301 to the idle mode 302 towards the second network 100-2.

In the idle mode 302, the transmit chain of the respective radio 1019 of the wire less interface 1015 of the UE 101 are not active (unless there is mobile-originating UL data), and the receive chain is only active for short periods in accordance with the discontinuous reception cycle and the paging occasions. As a result of this, degraded radio performance cannot easily be measured based on channel meas urements. Therefore, channel sounding routines typically do not indicate the level of interference 911-912 to be expected. Thus, it can be helpful to estimate the interference based on a comparison of the first and second frequency bands 901 - 903, as well as 905-907 (as previously discussed in connection with box 2004 of FIG. 9). Then, the selection of the at least one preferred frequency band for camp ing that box 3005 can be based on this estimated level of interference. It would be possible that the at least one preferred frequency band 906 is selected from a list 4002 that is transmitted by the network 100-2 at 3002, e.g., in response to a respective request 4001 transmitted by the UE 101 at 3001. The communi cation at 3001 and 3002 could be implemented during the connected mode 301 towards the second network 100-2, e.g., on the PUSCH and the PDSCH 262, using Radio Resource Control (RRC) control signaling.

In the idle mode 302, the UE 101 can autonomously execute the prioritization in accordance with the camping at 3004. Thus, the UE 101 can camp on the pre ferred frequency band 906, but may avoid camping on the non-preferred fre quency bands 905, 907. This prioritization in connection with the camping at box 3004 does not need to be signaled to the network 100-2.

Nonetheless, it may be helpful to transmit, at 3003, a request 4011 for communi cating on the preferred frequency band 906 while still operating in the connected mode 301 , optionally triggered by the transition from operating in the connected mode to the idle mode 302. For example, the request 4011 could be included in a RRC Connection Release control message that triggers the transition from the connected mode 301 to the idle mode 302 towards the second network 100-2.

By means of the request 4011 , when the UE 101 , later on, transitions again to the connected mode 301 towards the second network 100-2, e.g., by implement ing a corresponding connection control signaling 4009 (e.g., including a random access procedure and paging) at 3005, it would be possible that the network 100- 2 is already aware of the preferred frequency band 906 and implements the com munication between the UE 101 and the second network 100-2 in accordance with the preferred frequency band 906: e.g., paging at 3005 may be shifted / im plemented on the preferred frequency band 906; and/or data transmission 4050 at 3006 on the PUSCH or PDSCH along the data connection 189 may be imple mented on the preferred frequency band 906. Thus, in other words, the indicated preference of the preferred frequency band 906 may be stored at the second network 100-2 - e.g., in the UE context at the AMF 131 - while the UE 101 oper ates in the idle mode 302 towards the second network 100-2.

As a general rule, when prioritizing the at least one preferred frequency - e.g., when prioritizing the frequency band 906 for camping at 3004 when the UE 101 operates in the idle mode 302 towards the second network 100-2 - it would be possible to take into account also further decision criteria, beyond the level of inter-frequency interference. For example, it would be possible to implement con ventional channel measurements for the available frequency bands 905-907, e.g., based on DL pilot signals and/or UL pilot signals. Then, the preferred fre quency band 906 can be prioritized also in accordance with such channel meas urements. These channel measurements may not be indicative or only indicative to a limited degree of inter-frequency interference 911-912.

While in the scenario of FIG. 10 the list 4002 of the available frequency bands 905-907 is received while still operating in the connected mode 301 towards the second network 100-2, this is an example only. In other examples, the list 4002 may also be received while the UE 101 operates in the idle mode 302, e.g., on a broadcast channel. Then, there does not need to be a request.

Furthermore, the request for the preferred frequency band 906 that is transmitted, in the example of FIG. 10, at 3003 while the UE 101 operates in the connected mode 301 towards the second network 100-2, may in other examples be trans mitted while the UE 101 operates in the idle mode 302 towards the second net work 100-2.

Referring again to Tab. 1 : row 3, a further scenario pertains to the UE 101 oper ating in the connected mode 301 towards the first network 100-1 , and operating in the connected mode 301 towards the second network 100-2. Typically, in the connected mode 301 , mobility and selection of carrier frequencies is handled by the respective network 100-1 , 100-2. Thus, the UE 101 may rely on the requests to implement the prioritization of the preferred frequency band 906. Such a sce nario is illustrated in FIG. 11.

FIG. 11 is a signaling diagram of communication between the UE 101 and each one of the networks 100-1 and 100-2. In the scenario of FIG. 11, the UE 101 persistently operates in the connected mode 301 towards both networks 100-1, 100 2

When the UE 101 operates in the connected mode 301 towards both networks 100-1, 100-2; accordingly, mobility is handled by the respective networks 100-1, 100-2 and it is assumed that the networks 100-1 , 100-2 are aware of the UE 101 being a multi-SIM UE. For example, a corresponding uplink control signaling could be used to inform the networks 100-1 , 100-2 accordingly. Also in such case, the frequencies should be prioritized to minimize inter-frequency interference 911-912 between the various frequency bands 901 -903, 905-907.

In the example of FIG. 11, this is accomplished by the UE 101, transmitting, at 3011, the request 4001 for the list of frequency bands 905-907 supported by the second network 100-2. The UE then receives, at 3012, the list 4002 and can transmit, at 3013, the request 4011 for communication on the preferred frequency band 906. The request 4011 could be indicative of the dual-transmission capabil ity of the UE 101. Then, the second network 100-2 can configure the communi cation between the UE 101 and the second network 100-2 in accordance with the preferred frequency band 906.

As a general rule, while in the scenario of FIG. 11 the UE 101 first receives the list 4002 and selects the preferred frequency band 906 from the list 4002, in other examples, it would be possible that the UE 101 determines all possible preferred frequencies and transmits these preferred frequencies to the network 100-2. Then, the network 100-2 can make a fine selection from these preferred frequen cies and implement the communication with the UE 101 accordingly. In such a scenario, it may not be required to implement 3011 and 3012. FIG. 12 is a flowchart of a method according to various examples. FIG. 12 illus trates schemes for prioritizing at least one preferred frequency for communication with multiple networks.

In particular, above, various examples have been described in which the UE 101 prioritizes frequency band 906 for the communication with the second network 100-2. In some examples, the prioritization is restricted to the frequency bands 905-907 of the second network 100-2; there is no prioritization with respect to the frequency bands 901 -903 of the first network 100-1.

In other examples, it is also possible to implement a prioritization with respect to both networks 100-1, 100-2. The corresponding example is illustrated in FIG. 12. Initially, the UE 101 prioritizes the preferred frequency band 906 for communi cating with the second network 100-2, box 2051. Thus, box 2051 corresponds to box 1002 (of. FIG. 8). Techniques as described above in connection with FIG. 9, FIG. 10, and FIG. 11 can be employed. Then, at optional box 2052, it can be checked whether the level of inter-frequency interference 911-912 is sufficiently low, taking into account the prioritization with respect to the frequency bands 905-907 of the second network 100-2. For exam ple, channel measurements may be performed. Considering that the estimated level of interference is sufficiently low, then, the communication with both net- works 100-1 and 100-2 can commence at box 2054 directly, without prioritizing any further preferred frequency band for communicating with the first network 100 1

However, if at box 2052 it is judged that the level of inter-frequency interference is insufficient, then it would be possible to also employ a prioritization of at least one further preferred frequency band for communication between the UE 101 and the first network 100-1 , at box 2053. For instance, referring to FIG. 3, it could be judged that the level of inter-frequency interference is even lower when the fre quency band 902 is prioritized vis-a-vis the frequency bands 901 and 903 for the communication between the UE 101 and the first network 100-1. Strategies for prioritizing as explained above in connection with, e.g., FIG. 11 (e.g., transmitting a corresponding request 4001 for a list of all frequency bands 901-903 to the network 100-1, receiving the list 4002, and requesting the com munication on the preferred frequency band 902) can be implemented also to wards the first network 100-1.

Then, at box 2054, the communication with both networks 100-1 and 100-2 can commence in accordance with the respectively preferred frequency bands 902 and 906. According to some examples, it would be possible to delay operating the UE 101 in the connected mode 301 towards the second network 100-2 for a correspond ing time duration 2059, until the prioritization of the preferred frequency band 902 for communication between the UE 101 and the first network 100-1 has been accomplished. This is to avoid overly strong inter-frequency interference. For ex- ample, the UE 101 may continue to operate in the idle mode 302 until this priori tization of the further preferred frequency band 902 has been completed. Thereby, a reduced quality of service due to significant inter-frequency interfer ence 911-912 can be avoided. FIG. 13 is a flowchart of a method according to various examples. The method of FIG. 13 can be executed by an access node of a network, e.g., by a base station of a cellular network. For example, the method according to FIG. 13 could be executed by the control circuitry 1122 of the base station 112, e.g., upon loading respective program code from the memory 1123 (of. FIG. 6). Various examples will be described hereinafter for a scenario in which the method according to FIG. 13 is executed by the base station 112 for sake of simplicity, but similar tech niques may be readily employed for other scenarios in which the method accord ing to FIG. 13 is executed by other devices or nodes. Optional boxes are labeled with the dashed lines in FIG. 13.

At optional box 2081 , the base station 112 receives the request 4001 for the list for 4002 of frequency bands 905-907 supported by the second network 100-2. Accordingly, at box 2082, the list 4002 is transmitted. Box 2081 and box 2082 of FIG. 13 thus generally correspond to 3001 and 3002 of FIG. 10 and 3011 and 3012 of FIG. 11. Furthermore, box 2081 and box 2082 are inter-related with box 2002 and box 2003 of FIG. 9.

Then, at box 2083, the base station receives a request 4011 for a preferred fre- quency band 906. At box 2084, the base station 112 then communicates with the UE 101 in accordance with the preferred frequency band 906, e.g., by disabling further frequency bands 905 and 907 for communication. Box 2083 and box 2084 thus corresponds to FIG. 10: 3003 and 3006, as well as FIG. 11: 3013 and 3014. Further, box 2083 and box 2084 are inter-related with box 2006 of FIG. 9.

The communication in accordance with the preferred frequency band at box 2084 can be implemented using techniques such as carrier switching, selective activa tion/deactivation of air carrier aggregation; etc. Summarizing, above techniques have been described that facilitate control of fre quency selection for communicating between a multi-radio multi-SIM UE and mul tiple networks. The techniques are versatile in that selection of the appropriate frequency is possible in different operational modes in which the UE can operate towards the multiple networks. For instance, UE-network signaling would allow the UE to be operating simultaneously and connected mode towards two net works. This would allow the two networks to predict and optimize the radio re source scheduling and prevent unintentional implicit performance degradation or lost coverage due to the inter-frequency interference. For this, the UE can signal to the network its multi-SIM capability. The UE can request a list of supported bands from each network. The network can then signal these lists. The UE can signal one or more preferred frequencies to each one of the networks. The net work can select the frequency bands for the communication in accordance with the one or more preferred frequencies.

Although the invention has been shown and described with respect to certain preferred embodiments, equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalents and modifications and is limited only by the scope of the appended claims.

For illustration, various examples have been described in which at least one pre ferred frequency is prioritized in accordance with a level of interference. As a general rule, it would be possible that in addition to such a prioritization in accord ance with the level of interference, one or more further decision criteria taken into account. For example, channel measurements can be taken into account that sound the respective channels not only in view of the inter-frequency interference, but also in view of path loss, obstructions, multi-path fading, etc. Alternatively or additionally, it would be possible to take into account a hardware capability of the wireless communication interface of the respective multi-radio UE when selecting the at least one preferred frequency. For instance, scenarios are conceivable where certain restrictions on the arrangement of multiple frequencies on which the radios of the wireless interface can communicate exists. Then, such re strictions or limitations can be taken into account when prioritizing the at least one preferred frequency.

For further illustration, various examples have been described in connection with a multi-SIM UE having the dual transmission capability. In other examples, it would be possible that the UE is not a multi-SIM UE, but communicates, e.g., with different types of networks. For instance, the UE could communicate with a first network, e.g., a 3GPP network, and a second network, e.g., a IEEE 802.11 WiFi network at different frequency bands; another example would be a 3GPP LTE network, and a 3GPP NR network at different frequency bands; yet another ex ample would be a WiFi network and a Bluetooth network. Other examples are conceivable.