METHOD AND APPARATUS FOR COMMUNICATION SYSTEMS INVOLVING INCORPORATING USER EQUIPMENT IDENTIFIERS INTO CONTROL CHANNEL TRANSMISSIONS

The apparatus includes at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to duplicate base station computation of an identifier value for a user equipment, and search for one or more control channel transmissions incorporating an identifier value matching the identifier value.

TECHNICAL FIELD

The present disclosure relates to apparatus, a method, and a computer program, and in particular but not exclusively to apparatus, methods and computer programs for communication systems involving the incorporation into control channel transmissions of identifiers by which a user equipment (UE) can identify control channel transmissions specific thereto.

BACKGROUND

Some communication systems involve a base station (e.g. eNB or gNB) making UE-specific control channel transmissions (e.g. physical downlink control channel PDCCH transmission) for a plurality of UEs. A control channel transmission specific to a UE may, for example, indicate the allocation of data channel resources (e.g. physical downlink shared channel PDSCH and/or physical uplink shared channel PUSCH resources) to uplink and/or downlink transmissions for the UE. A control channel transmission specific to a UE incorporates an identifier for the UE. The UE searches control channel transmission resources for a control channel transmission incorporating the identifier for the UE.

SUMMARY

A method comprising: duplicating, at a user equipment, base station computation of an identifier value for the user equipment; and searching, at the user equipment, for one or more control channel transmissions incorporating an identifier value matching the identifier value computed at the user equipment.

Duplicating base station computation of an identifier value for the user equipment may comprise computing an identifier value based on one or more input parameter values and one or more mathematical functions used at the base station to compute an identifier value for the user equipment.

Computation of an identifier value may be based at least partly on a value of a time-related parameter; and the computed identifier value may be effective for a time period related to the value of the time-related parameter.

The method may further comprise: duplicating, at the user equipment, base station computation of a further identifier value; and after expiry of the time period, searching at the user equipment for one or more control channel transmissions incorporating an identifier value matching the further identifier value computed at the user equipment.

The time-related parameter may be a system frame number.

Computation of an identifier value may be at least partly based on a security key value derived at least partly from a secret key shared between the base station and the user equipment.

Computation of an identifier value may be at least partly based on a start value included in a random access reply message.

The one or more control channel transmissions may indicate radio resources allocated to the user equipment for downlink and/or uplink transmissions.

A method comprising: duplicating, at a base station, user equipment computation of an identifier value for the user equipment; and incorporating the identifier value into one or more control channel transmissions specific to the user equipment.

Duplicating user equipment computation of an identifier value for the user equipment may comprise computing an identifier value based on one or more input parameter values and one or more mathematical functions used at the user equipment to compute an identifier value for the user equipment.

The method may further comprise: sending to the user equipment a base value for computation of an identifier value; and in response to thereafter determining that computation based on the base value generates an identifier value that clashes with one or more identifier values for one or more other user equipments sharing radio resources for control channel transmissions with the user equipment, sending a new base value to the user equipment.

A method comprising: recovering, at a user equipment, a sequence of identifier values for the user equipment from a radio transmission; and searching at the user equipment for one or more control channel transmissions incorporating an identifier value matching one of the sequence of identifier values.

The sequence of identifier values for the user equipment may comprise at least a first identifier value effective for a first time period, and a second identifier value effective for a second time period after the first time period; and the method may comprise: during the first time period searching at the user equipment for one or more control channel transmissions incorporating an identifier value matching the first identifier value; and during the second time period searching at the user equipment for one or more control channel transmissions incorporating an identifier value matching the second identifier value.

A method comprising: transmitting, from a base station, an indication of a sequence of identifier values for a user equipment; and incorporating one of the sequence of identifier values for the user equipment into one or more control channel transmissions specific to the user equipment.

The sequence of identifier values for the user equipment may comprise at least a first identifier value effective for a first time period, and a second identifier value effective for a second time period after the first time period; and the method may comprise: during the first time period making one or more control channel transmissions incorporating the first identifier value; and during the second time period making one or more control channel transmissions incorporating the second identifier value.

Apparatus comprising: means for duplicating base station computation of an identifier value for a user equipment; and means for searching for one or more control channel transmissions incorporating an identifier value matching the identifier value.

The means for duplicating base station computation of an identifier value for the user equipment may comprise means for computing an identifier value based on one or more input parameter values and one or more mathematical functions used at the base station to compute an identifier value for the user equipment.

Computation of an identifier value may be based at least partly on a value of a time-related parameter; and the computed identifier value may be effective for a time period related to the value of the time-related parameter.

The apparatus may further comprise: means for duplicating base station computation of a further identifier value; and means for, after expiry of the time period, searching for one or more control channel transmissions incorporating an identifier value matching the further identifier value.

The time-related parameter may be a system frame number.

Computation of an identifier value may be at least partly based on a security key value derived at least partly from a secret key shared between the base station and the user equipment.

Computation of an identifier value may be at least partly based on a start value included in a random access reply message.

The one or more control channel transmissions may indicate radio resources allocated to the user equipment for downlink and/or uplink transmissions.

Apparatus comprising: means for duplicating user equipment computation of an identifier value for the user equipment; and means for incorporating the identifier value into one or more control channel transmissions specific to the user equipment.

The means for duplicating user equipment computation of an identifier value for the user equipment may comprise means for computing an identifier value based on one or more input parameter values and one or more mathematical functions used at the user equipment to compute an identifier value for the user equipment.

The apparatus may comprise: means for sending to the user equipment a base value for computation of an identifier value; and means for, in response to thereafter determining that computation based on the base value generates an identifier value that clashes with one or more identifier values for one or more other user equipments sharing radio resources for control channel transmissions with the user equipment, sending a new base value to the user equipment.

Apparatus comprising: means for recovering a sequence of identifier values for a user equipment from a radio transmission; and means for searching for one or more control channel transmissions incorporating an identifier value matching one of the sequence of identifier values.

The sequence of identifier values for the user equipment may comprise at least a first identifier value effective for a first time period, and a second identifier value effective for a second time period after the first time period; and the apparatus may comprise: means for, during the first time period, searching for one or more control channel transmissions incorporating an identifier value matching the first identifier value, and, during the second time period, searching for one or more control channel transmissions incorporating an identifier value matching the second identifier value.

Apparatus comprising: means for transmitting an indication of a sequence of identifier values for a user equipment; and means for incorporating one of the sequence of identifier values for the user equipment into one or more control channel transmissions specific to the user equipment.

The sequence of identifier values for the user equipment may comprise at least a first identifier value effective for a first time period, and a second identifier value effective for a second time period after the first time period; and the apparatus may comprise: means for, during the first time period, making one or more control channel transmissions incorporating the first identifier value, and, during the second time period, making one or more control channel transmissions incorporating the second identifier value.

An apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus to perform:

duplicating base station computation of an identifier value for a user equipment; and searching for one or more control channel transmissions incorporating an identifier value matching the identifier value.

Duplicating base station computation of an identifier value for the user equipment may comprise computing an identifier value based on one or more input parameter values and one or more mathematical functions used at the base station to compute an identifier value for the user equipment.

Computation of an identifier value may be based at least partly on a value of a time-related parameter; and the computed identifier value may be effective for a time period related to the value of the time-related parameter.

The at least one memory and computer program code may be configured to, with the at least one processor, cause the apparatus to: duplicate base station computation of a further identifier value; and after expiry of the time period, search for one or more control channel transmissions incorporating an identifier value matching the further identifier value.

The time-related parameter may be a system frame number.

Computation of an identifier value may be at least partly based on a security key value derived at least partly from a secret key shared between the base station and the user equipment.

Computation of an identifier value may be at least partly based on a start value included in a random access reply message.

The one or more control channel transmissions may indicate radio resources allocated to the user equipment for downlink and/or uplink transmissions.

An apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus to perform: duplicating user equipment computation of an identifier value for a user equipment; and incorporating the identifier value into one or more control channel transmissions specific to the user equipment.

Duplicating user equipment computation of an identifier value for the user equipment may comprise computing an identifier value based on one or more input parameter values and one or more mathematical functions used at the user equipment to compute an identifier value for the user equipment.

The at least one memory and computer program code may be configured to, with the at least one processor, cause the apparatus to: send to the user equipment a base value for computation of an identifier value; and in response to thereafter determining that computation based on the base value generates an identifier value that clashes with one or more identifier values for one or more other user equipments sharing radio resources for control channel transmissions with the user equipment, send a new base value to the user equipment.

An apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus to perform: recovering a sequence of identifier values for a user equipment from a radio transmission; and searching for one or more control channel transmissions incorporating an identifier value matching one of the sequence of identifier values.

The sequence of identifier values for the user equipment may comprise at least a first identifier value effective for a first time period, and a second identifier value effective for a second time period after the first time period; and the at least one memory and computer program code may be configured to, with the at least one processor, cause the apparatus to: during the first time period, search for one or more control channel transmissions incorporating an identifier value matching the first identifier value; and during the second time period, search at the user equipment for one or more control channel transmissions incorporating an identifier value matching the second identifier value.

An apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus to perform: transmitting an indication of a sequence of identifier values for a user equipment; and incorporating one of the sequence of identifier values for the user equipment into one or more control channel transmissions specific to the user equipment.

The sequence of identifier values for the user equipment may comprise at least a first identifier value effective for a first time period, and a second identifier value effective for a second time period after the first time period; and the at least one memory and computer program code may be configured to, with the at least one processor, cause the apparatus to: during the first time period, make one or more control channel transmissions incorporating the first identifier value; and during the second time period. make one or more control channel transmissions incorporating the second identifier value.

Apparatus comprising: duplicating circuitry for duplicating base station computation of an identifier value for a user equipment; and searching circuitry for searching for one or more control channel transmissions incorporating an identifier value matching the identifier value.

Apparatus comprising: duplicating circuitry for duplicating user equipment computation of an identifier value for the user equipment; and incorporating circuitry for incorporating the identifier value into one or more control channel transmissions specific to the user equipment.

Apparatus comprising: recovering circuitry for recovering a sequence of identifier values for a user equipment from a radio transmission; and searching circuitry for searching for one or more control channel transmissions incorporating an identifier value matching one of the sequence of identifier values.

Apparatus comprising: transmitting circuitry for transmitting an indication of a sequence of identifier values for a user equipment; and incorporating circuitry for incorporating one of the sequence of identifier values for the user equipment into one or more control channel transmissions specific to the user equipment.

A computer readable medium comprising program instructions stored thereon for performing: duplicating, at a user equipment, base station computation of an identifier value for the user equipment; and searching, at the user equipment, for one or more control channel transmissions incorporating an identifier value matching the identifier value computed at the user equipment.

A computer readable medium comprising program instructions stored thereon for performing: duplicating, at a base station, user equipment computation of an identifier value for the user equipment; and incorporating the identifier value into one or more control channel transmissions specific to the user equipment.

A computer readable medium comprising program instructions stored thereon for performing: recovering, at a user equipment, a sequence of identifier values for the user equipment from a radio transmission; and searching at the user equipment for one or more control channel transmissions incorporating an identifier value matching one of the sequence of identifier values.

A computer readable medium comprising program instructions stored thereon for performing: transmitting, from a base station, an indication of a sequence of identifier values for a user equipment; and incorporating one of the sequence of identifier values for the user equipment into one or more control channel transmissions specific to the user equipment.

A computer program comprising computer executable code which when run on at least one processor is configured to cause an apparatus at least to: duplicate base station computation of an identifier value for a user equipment; and search for one or more control channel transmissions incorporating an identifier value matching the identifier value.

A computer program comprising computer executable code which when run on at least one processor is configured to cause an apparatus at least to: duplicate user equipment computation of an identifier value for a user equipment; and incorporate the identifier value into one or more control channel transmissions specific to the user equipment.

A computer program comprising computer executable code which when run on at least one processor is configured to cause an apparatus at least to: recover a sequence of identifier values for a user equipment from a radio transmission; and search for one or more control channel transmissions incorporating an identifier value matching one of the sequence of identifier values.

A computer program comprising computer executable code which when run on at least one processor is configured to cause an apparatus at least to: transmit an indication of a sequence of identifier values for a user equipment; and incorporate one of the sequence of identifier values for the user equipment into one or more control channel transmissions specific to the user equipment.

A non-transitory computer readable medium comprising program instructions stored thereon for performing: duplicating, at a user equipment, base station computation of an identifier value for the user equipment; and searching, at the user equipment, for one or more control channel transmissions incorporating an identifier value matching the identifier value computed at the user equipment.

A non-transitory computer readable medium comprising program instructions stored thereon for performing: duplicating, at a base station, user equipment computation of an identifier value for the user equipment; and incorporating the identifier value into one or more control channel transmissions specific to the user equipment.

A non-transitory computer readable medium comprising program instructions stored thereon for performing: recovering, at a user equipment, a sequence of identifier values for the user equipment from a radio transmission; and searching at the user equipment for one or more control channel transmissions incorporating an identifier value matching one of the sequence of identifier values.

A non-transitory computer readable medium comprising program instructions stored thereon for performing: transmitting, from a base station, an indication of a sequence of identifier values for a user equipment; and incorporating one of the sequence of identifier values for the user equipment into one or more control channel transmissions specific to the user equipment.

In the above, many different aspects have been described. It should be appreciated that further aspects may be provided by the combination of any two or more of the aspects described above. Various other aspects are also described in the following detailed description and in the attached claims.

DETAILED DESCRIPTION

The example ofFIG.1shows a part of an exemplifying radio access network. For example, the radio access network may support sidelink communications described below in more detail.

FIG.1shows devices100and102. The devices100and102are configured to be in a wireless connection on one or more communication channels with a node104. The node104is further connected to a core network106. In one example, the node104may be an access node such as (e/g)NodeB serving devices in a cell. In one example, the node104may be a non-3GPP access node. The physical link from a device to a (e/g)NodeB is called uplink or reverse link and the physical link from the (e/g)NodeB to the device is called downlink or forward link. It should be appreciated that (e/g)NodeBs or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage.

A communications system typically comprises more than one (e/g)NodeB in which case the (e/g)NodeBs may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used for signalling purposes. The (e/g)NodeB is a computing device configured to control the radio resources of communication system it is coupled to. The NodeB may also be referred to as a base station, an access point or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (e/g)NodeB includes or is coupled to transceivers. From the transceivers of the (e/g)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to devices. The antenna unit may comprise a plurality of antennas or antenna elements. The (e/g)NodeB is further connected to the core network106(CN or next generation core NGC). Depending on the deployed technology, the (e/g)NodeB is connected to a serving and packet data network gateway (S-GW+P-GW) or user plane function (UPF), for routing and forwarding user data packets and for providing connectivity of devices to one or more external packet data networks, and to a mobile management entity (MME) or access mobility management function (AMF), for controlling access and mobility of the devices.

Exemplary embodiments of a device are a subscriber unit, a user device, a user equipment (UE), a user terminal, a terminal device, a mobile station, a mobile device, etc

The device typically refers to a mobile or static device (e.g. a portable or non-portable computing device) that includes wireless mobile communication devices operating with or without an universal subscriber identification module (USIM), including, but not limited to, the following types of devices: mobile phone, smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop and/or touch screen computer, tablet, game console, notebook, and multimedia device. It should be appreciated that a device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. A device may also be a device having capability to operate in Internet of Things (loT) network which is a scenario in which objects are provided with the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction, e.g. to be used in smart power grids and connected vehicles. The device may also utilise cloud. In some applications, a device may comprise a user portable device with radio parts (such as a watch, earphones or eyeglasses) and the computation is carried out in the cloud.

The device illustrates one type of an apparatus to which resources on the air interface are allocated and assigned, and thus any feature described herein with a device may be implemented with a corresponding apparatus, such as a relay node. An example of such a relay node is a layer3relay (self-backhauling relay) towards the base station. The device (or in some embodiments a layer3relay node) is configured to perform one or more of user equipment functionalities.

FIG.2illustrates an example of operations at a device implementing user equipment functionality, hereafter referred to as UE (such as e.g. UE100ofFIG.1) and a device implementing base station functionality, hereafter referred to as BS (such as e.g. the e/gNB node104ofFIG.1). UE100makes a random access preamble transmission (OPERATION200ofFIG.2). The random access preamble transmission is successful, and BS104transmits a random access reply (RAR) message (OPERATION202ofFIG.2). The RAR message includes a base identifier value (hereafter referred to as base C-RNTI (cell-radio network temporary identifier) value) for UE100to use as a start value to compute identifier values for the UE100. UE100recovers the base C-RNTI value from the RAR message (OPERATION204ofFIG.2).

Later, both UE100and BS104separately perform the same pre-determined computation of an identifier value (hereafter referred to as dynamic C-RNTI or DC-RNTI value) for the UE100, using the base C-RNTI value as one input (OPERATIONS206aand206bofFIG.2). Duplicating BS computation of a DC-RNTI value for UE100at UE100uses the same one-way mathematical function(s) and inputs as the computation of a DC-RNTI value for UE100at BS104. In this example, the computation inputs also include; (i) a security key (here referred to as KRNTI) derived ultimately from a secret key pre-shared between UE100and a home subscriber server (HSS), which secret key is primarily used to authenticate the UE subscriber/user; and (ii) a time input related to the time at which both UE100and BS104are configured to compute the DC-RNTI value for UE100. In one example, this time input is the value, at the time of DC-RNTI computation, of the system frame number (SFN) (or alternatively the hyper frame number (HFN)) of the cell via which the UE100has the RRC connection.

In this example, KRNTIis derived from existing keys KeNBor KgNB, using the key derivation function (KDF) as mentioned in 3GPP TS 33.501, Annex A, with a further input comprising a FC-value from the FC number space controlled by TS 33.220, as mentioned at TS 33.501 A.1.2.

In this example, the DC-RNTI value is computed from the base C-RNTI value, the SFN/HFN and KRNTI using a one-way mathematical function, such as the ones specified in the Milenage and Tuak algorithm sets identified in TS35.205 and TS35.231.

The SFN (used in this example as one of the inputs to compute the DC-RNTI value for UE100) is broadcast by the cell, and has a value shared by all UEs served by the cell. An incremented SFN value is broadcast every10ms (in the physical broadcast channel (PBCH) for the cell). The SFN is10bits in length, and may therefore have1024different values. The SFN cycle (the time period over which the SFN value repeats) is 1024*10 ms=10.24 seconds.

In another example, a hyper frame number (HFN) of the kind implemented in LTE is used instead of SFN as an input for computation of the DC-RNTI value. The HFN value increments when the SFN value is equal to 0. The HFN is also 10 bits in length. The HFN cycle (the time period over which the HFN value repeats) is 1024*1024*10 ms=10485.76 second (about 7 days).

In another example, the timing reference broadcast in 5G NR as part of the 9th System Information Block (SIB9) is used instead of SFN or HFN as one input for computation of the DC-RNTI value.

BS104incorporates the DC-RNTI value computed at BS104for UE100into one or more control downlink channel transmissions (e.g. PDCCH transmissions) specific to UE100(OPERATION208ofFIG.2); and UE100searches a search space for control channel transmissions incorporating a DC-RNTI value matching the DC-RNTI value computed at UE100for UE100(OPERATION210ofFIG.2). In this example, incorporating the computed DC-RNTI value into a control channel transmission involves using the computed DC-RNTI value to modify the CRC (cyclic redundancy check) attached to the PDCCH payload (DCI (downlink control information) through a scrambling operation; and UE100searches the search space for a PDCCH transmission that it can correctly decode using the DC-RNTI value computed at UE100.

The computed DC-RNTI value is thus used by UE100and BS104to distinguish control channel transmissions specific to the UE100from control channel transmissions specific to other UEs searching the same search space for DCI messages specific thereto. A control channel transmission (e.g. PDCCH transmission) incorporating the computed DC-RNTI value for UE100indicates data channel radio resources allocated to uplink transmissions by UE100and/or downlink transmissions specific to UE100.

UE100is representative of a plurality of UEs searching the same search space for PDCCH transmissions incorporating a DC-RNTI value matching a DC-RNTI value computed at the respective UE based on a respective base C-RNTI value and a respective security key (KRNTI).

According to one example whose representation is shown inFIG.6, BS104periodically computes a fresh DC-RNTI for UE100, and UE100duplicates the periodic computation of fresh DC-RNTI, again using the same one-way mathematical function and input parameters as BS104. UE100and BS104may compute a fresh DC-RNTI (using e.g. the current SFN value as one input) at predetermined times (e.g. at predetermined values of SFN). The period between successive computations of a DC-RNTI value may, for example, be in the range of 10 ms to hours or days. There may be a pre-configured default timing for the fresh computing of-RNTI values, which UE100adopts unless UE100has received an overriding individual configuration from BS104.

With reference toFIG.6, UE100regularly determines whether the current SFN value is one for which the UE100is configured to compute a new DC-RNTI value (OPERATION60). If the determination is negative, UE100continues to search the PDCCH search space for PDCCH transmissions incorporating a DC-RNTI value matching the existing DC-RNTI value (i.e. the DC-RNTI value most recently computed at UE100) (OPERATION62). On the other hand, if the determination is positive, UE100computes a new DC-RNTI value using the current SFN value as one input, and subsequently searches the PDCCH search space for PDCCH transmissions incorporating a DC-RNTI value matching the new DC-RNTI value computed at UE100(OPERATION64ofFIG.6).

As mentioned above, one of the input parameters is the SFN value for the cell at the time of DC-RNTI computation, which is different to the SFN value used for the previous DC-RNTI computation and is also different to the SFN value that will be used for the subsequent DC-RNTI computation. In this way, control channel transmissions specific to UE100incorporate changing identifier values over time.

As mentioned above, UE100is representative of a plurality of UEs searching the same search space for control channel transmissions incorporating a DC-RNTI value matching the DC-RNTI value computed at UE100(based on the respective base C-RNTI value and respective security key value). According to this example embodiment, other UEs (or all UEs) of the plurality of UEs searching the same search space for PDCCH transmissions compute respective fresh DC-RNTI values at the same time. For example, the SFN/HFN values at which DC-RNTI computation is performed is the same for other UEs (e.g. all UEs searching the search space for control channel transmissions).

According to another example, BS104triggers the computation of a fresh DC-RNTI value. For example, the trigger may take the form of an encrypted RRC message.

FIG.3illustrates an example of operations at BS104aimed at avoiding DC-RNTI clashes between UEs searching the same search space for PDCCH transmissions. The operations are aimed at guaranteeing that the DC-RNTI value for UE100is unique to UE100at least among all UEs simultaneously searching the same search space for PDCCH transmissions.

BS104precomputes a sequence of DC-RNTI values for UE100based respectively on the predetermined SFN values at which UE100is configured to perform DC-RNTI computation (OPERATION300ofFIG.3). The computation of each DC-RNTI value of the sequence is also based on the base C-RNTI value for UE100and the KRNTI value for UE100. The sequence of DC-RNTI values may comprise a predetermined number of DC-RNTI values (for a predetermined number of DC-RNTI computations for UE100) or DC-RNTI values for a predetermined period of time. BS104does the same pre-computation for all other UEs sharing the same PDCCH search space as UE104. BS104determines (OPERATION302ofFIG.3) whether this pre-computation predicts one or more instances of DC-RNTI clashes with any other UE sharing the same PDCCH search space. If this pre-computation predicts no instances of any DC-RNTI clashes (i.e. predicts no instances of more than one UE computing the same DC-RNTI value for the same SFN value input), BS104takes no corrective action and uses the pre-computed DC-RNTI values for UE-specific PDCCH transmissions (OPERATION310ofFIG.3). On the other hand, if the precomputation of a sequence of DC-RNTIs for UE100predicts one or more instances of a DC-RNTI clash with one or more other UEs, BS104pre-computes a new sequence of DC-RNTI values for UE100based on a new base C-RNTI value (OPERATION304ofFIG.3) and determines (OPERATION306ofFIG.3) whether this pre-computation based on a new base C-RNTI value predicts one or more instances of DC-RNTI clashes with any other UE sharing the same PDCCH search space (OPERATION306). BS104repeats this pair of operations304and306until it finds a new base C-RNTI value for which the pre-computation does not predict any DC-RNTI clashes. BS104then directs UE100to use the new base C-RNTI value for the computation of DC-RNTIs (OPERATION308ofFIG.3). The new base C-RNTI value for UE100can be sent to the UE100via radio resources indicated to UE100by a PDCCH transmission incorporating the currently valid DC-RNTI value for UE100.

Another example technique for avoiding DC-RNTI clashes is as follows. Instead of precomputing a future sequence of DC-RNTI values for UE100(and respective future sequences of DC-RNTI values for other UEs sharing the same PDCCH search space with UE100), BS104checks for DC-RNTI clashes each time DC-RNTI values are about to be recomputed at UEs including UE100. If the precomputation at BS104of the next round of DC-RNTIs for the UEs predicts a DC-RNTI clash for UE100, BS104tries one or more new base C-RNTI values for UE100until BS104finds a new base C-RNTI value for which pre-computation of DC-RNTI values predicts no DC-RNTI clashes; and BS104sends the new base C-RNTI value to UE100.

The implementation described so far has the advantage that no new information has to be passed between UE100and BS104for the generation of DC-RNTI values, except when an individual configuration for changing the DC-RNTI value is required, and/or unless a precomputation of DC-RNTI values at BS104predicts a DC-RNTI clash. The inputs for computing DC-RNTI values for UE are already available to UE100. The base C-RNTI value is the C-RNTI value already included in the RAR message; the security key KRNTIderived from a key already used at UE for other existing purposes at UE100; and SFN values are already broadcast by the cell.

According to one example variation, BS104sends all parameters for computing the DC-RNTIs to UE100in an encrypted RRC message, such as, for example, the RRC reconfiguration message sent by BS104following the RRC security command procedure. For example, computation at the UE100may be based on: a KRNTIvalue included in the encrypted RRC message; a starting value (instead of the C-RNTI value included in the RAR message); and the SFN value.

According to another example embodiment, UE100does not duplicate the BS computation of DC-RNTI values, but instead receives from BS104a sequence of DC-RNTI values to use over a period of time.

FIGS.4and5show a representation of the operations at BS104and UE100according to this example embodiment. BS104sends to UE100a sequence of DC-RNTI values that do not clash with DC-RNTI values sent to other UEs sharing the same PDCCH search space. The sequence of DC-RNTI values for UE100may be sent to UE100in an encrypted RRC message via data channel resources (e.g. PDCCH resources) indicated by a PDCCH transmission incorporating the C-RNTI value included in the RAR message (OPERATION400ofFIG.4). UE100recovers the sequence of DC-RNTI values from the encrypted RRC message (OPERATION500ofFIG.5). In this example, the DC-RNTI values of the sequence of DC-RNTI values are valid for respective consecutive periods of time; and UE100and BS104selectively use the DC-RNTI values of the sequence of DC-RNTI values for the respective periods of time for which they are valid. As shown by operations402,404and406ofFIG.4, BS104incorporates an nth DC-RNTI value into PDCCH transmissions specific to UE100for as long as the nth DC-RNTI value is valid, and then switches to incorporating the (n+1)th DC-RNTI value of the set of values into PDCCH transmissions specific to UE100; and so on. As shown by operations502,504and506ofFIG.5: UE searches for PDCCH transmissions incorporating an nth DC-RNTI value for as long as the nth DC-RNTI value is valid, and then switches to searching for PDCCH transmissions incorporating the (n+1)th DC-RNTI value of the set of values; and so on.

For all techniques described above, either (i) the information necessary for duplicating base station computation of DC-RNTI at UE100or (ii) a set of DC-RNTI values for UE100, may be included in a RRC reconfiguration message sent to command or trigger a handover of UE100from a source cell to a target cell.FIG.7shows a representation of an example of a handover of UE100from a source cell to a target cell. UE100receives (OPERATION700ofFIG.7) via the source cell a RRC reconfiguration message including either (i) all the information UE100needs to duplicate base station computation of DC-RNTI value(s) at UE100or (ii) a sequence of DC-RNTI values. UE100performs handover (OPERATION702ofFIG.7) using a DC-RNTI value computed at UE100using the information included in the RRC reconfiguration message, or a first one of the provided sequence of DC-RNTI values included in the RRC reconfiguration message.

Sending such an encrypted RRC reconfiguration message also in the event of an intra-cell handover (for which the source cell and the target cell are the same and only the used channel is changed) provides an opportunity to securely re-set the computation of DC-RNTI at UE100or provide UE100with a new sequence of DC-RNTI values.

Also in the event of restoring a RRC connection via a serving cell (for example, in the event of Beam Failure Recovery), UE may use a DC-RNTI value computed at UE100(or one of a sequence of DC-RNTI values received previously in an encrypted message via the serving cell). For the example of computing a DC-RNTI value at UE100, the UE100reads the current SFN value from the master information block (MIB) broadcast by the serving cell.

The example embodiments described above can reduce the risk of a malicious third party being able to track the PDCCH transmissions specific to UE100, and thus can increase security against PDCCH-tracking based attacks, and against man-in-the-middle (MITM) attacks by fake base stations (FBSs).

For example, the example embodiments can reduce the effectiveness of attacks in which the attacker relies on being able to identify PDCCH transmissions related to a GUTI (Globally Unique Temporary Identifier) or SUCI (Subscription Concealed Identifier) included in a register request via data channel resources scheduled by a PDCCH transmission.

For example, the example embodiments can thus reduce the risk of a malicious third party (with the extra assistance of additional intelligence (like physical observation)) being able to identify the human subscriber using the UE that sent the register request including the GUTI or SUCI.

For example, the example embodiments can reduce the effectiveness of attacks involving a malicious attacker sending traffic (e.g. a series of silent short messages, or a series of messenger messages) to a public address of a human victim known by the attacker to have a UE served by a particular cell, and then exploiting the characteristics of the traffic resulting from the traffic originated by the malicious attacker (like number and length of messages, timing).

For example, the example embodiments can increase security in networks where the GUTI is not changed frequently, by increasing the difficulty of determining which PDCCH transmissions are related to a GUTI (i.e. specific to a UE having the GUTI).

For example, the example embodiments can reduce the effectiveness of malicious attacks involving the attacker finding (by monitoring both source and target cells for a handover of UE100(and having possibly also other intelligence)) the C-RNTI value used in a random access (RA) procedure for the UE.

For example, the example embodiments can increase security against IMP4GT (IMPersonation Attacks in 4G NeTworks) involving an attacker relying on being able to map PDCCH transmissions to a GUTI. IMP4GT is described in a paper entitled “IMP4GT: IMPersonation Attacks in 4G NeTworks by David Rupprecht et al (DO 1:10.14722/ndss.2020.24283).

For example, the example embodiments can reduce the effectiveness of attacks involving exploitation of unencrypted MAC control elements sent to a certain UE.

FIG.8illustrates an example of an apparatus for implementing the operations of a device implementing UE or BS functionality. The apparatus may comprise at least one processor602coupled to one or more interfaces608. In the case of a device implementing UE functionality, the one or more interfaces may be e.g. to other equipment for which the UE functionality provides radio communications. In the case of a device implementing base station functionality, the one or more interfaces may be e.g. to other devices implementing other network functionality such as devices implementing UPF (User Plane Function) functionality in a 5G system. The at least one processor602is also coupled to a radio unit604including one or more antennas etc. for making and receiving radio transmissions. The at least one processor602may also be coupled to at least one memory606. The at least one processor602may be configured to execute an appropriate software code to perform the operations described above. The software code may be stored in the memory606

FIG.9shows a schematic representation of non-volatile memory media1100a(e.g. computer disc (CD) or digital versatile disc (DVD)) and1100b(e.g. universal serial bus (USB) memory stick) storing instructions and/or parameters1102which when executed by a processor allow the processor to perform one or more of the steps of the methods described previously.

It is to be noted that embodiments of the present invention may be implemented as circuitry, in software, hardware, application logic or a combination of software, hardware and application logic. In an example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a “computer-readable medium” may be any media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as the base stations or user equipment of the above-described embodiments.

As used in this application, the term “circuitry” refers to all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) to combinations of circuits and software (and/or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as the user equipment or base stations of the above-described embodiments, to perform various functions) and (c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of ‘circuitry’ applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term “circuitry” would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term “circuitry” would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in server, a cellular network device, or other network device.

The described features, advantages, and characteristics of the invention can be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages can be recognized in certain embodiments that may not be present in all embodiments of the invention. One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention.