Obfuscating hardware-specific identification information

Abstract

It is provided a method for obfuscating hardware-specific identification information of a user equipment, UE, (2) in a communication network (9) to obstruct radio-frequency fingerprinting, RFF, of the UE, the method being performed by the UE (2) configured to obstruct RFF. The method comprises: upon receiving (40) a request (20) to transmit specific uplink data; transmitting (46), to a radio network node (1), obfuscated uplink data (22), the obfuscated uplink data (22) having been constructed by applying, to the specific uplink data, at least one parameter for obfuscating hardware-specific identification information, that could otherwise be used for RFF of the UE (2) based on uplink transmission by the UE (2). It is further disclosed a UE (2), a computer program (67, 91) and a computer program product (64, 90).

Description

OBFUSCATING HARDWARE-SPECIFIC IDENTIFICATION INFORMATIONTECHNICAL FIELD

[0001] The present invention relates generally to the field of a communication network, and more specifically to a method, a user equipment, a computer program and a computer program product for obfuscating hardware-specific identification information to obstruct Radio Frequency Fingerprinting (RFF) of a user equipment of such a communication network.BACKGROUND

[0002] In contemporary communication systems, the physical layer of the network has become an increasingly significant aspect in terms of security. Radio frequency fingerprinting (RFF) has emerged as a novel method for physical layer security, leveraging the intrinsic and device-unique hardware impairments present in radio transmitters to authenticate devices, thereby bolstering the trustworthiness of telecommunications infrastructure. RFF can thus be used for authenticating user equipment (UE) or any other radio device in a communication network.

[0003] The article entitled “Radio Frequency Fingerprinting via Deep Learning: Challenges and Opportunities” by Al-Hazbi et al, arXiv: 2310.16406vi, available at https: / / arxiv.0rg / abs / 2310.16406vi at the time of filing this patent application, discloses an overview of the current open problems that prevent real deployment of deep learning-based RFF systems while also discussing promising research opportunities to enhance the overall accuracy, robustness, and privacy of these systems.

[0004] Despite the ingenuity of RFF, it raises considerable privacy concerns, particularly in light of varying international legislations aimed at protecting user privacy. Traditional RFF techniques, while useful for security, inadvertently create a risk where device-specific signatures could be exploited for nefarious activities such as unauthorised tracking, profiling, and spoofing attacks.

[0005] There is no solution in the prior art that adequately addresses the vital aspect of protection against potential abuse by unauthorised or rogue networks.SUMMARY

[0006] One object is to protect the privacy of the user to prevent undesired exploitation of RFF.

[0007] According to a first aspect, it is provided a method for obfuscating hardwarespecific identification information of a user equipment, UE, in a communication network to obstruct radio-frequency fingerprinting, RFF, of the UE. The method is performed by the UE configured to obstruct RFF, the method comprises: upon receiving a request to transmit specific uplink data; transmitting, to a radio network node, obfuscated uplink data, the obfuscated uplink data having been constructed by applying, to the specific uplink data, at least one parameter for obfuscating hardware-specific identification information, that could otherwise be used for RFF of the UE based on uplink transmission by the UE.

[0008] The method may further comprise: determining that the UE is configured to obstruct RFF.

[0009] The method may further comprise: determining the at least one parameter for obfuscating hardware-specific identification information.

[0010] The request may be a request for RFF-based authentication issued by the radio network node.

[0011] The at least one parameter may comprise an offset for at least one quadrature amplitude modulation, QAM, symbol in either one or both of its in-phase, I, component and its quadrature, Q, component.

[0012] The at least one parameter may comprise an offset to a bias for a power amplifier, or an offset to a power level.

[0013] The at least one parameter may comprise digital pre-distortion, DPD, parameters that are determined such that they do not match a power amplifier used for uplink transmissions by the UE.

[0014] The at least one parameter may be determined based on a random, or pseudo-random, number source.

[0015] The method may further comprise: transmitting an uplink transmission comprising user data while applying the at least one parameter.

[0016] The method may further comprise: transmitting a privacy request to the network node to remove all RFF data for the UE.

[0017] The communication network may be a cellular network.

[0018] According to a second aspect, it is provided a user equipment, UE, for obfuscating hardware-specific identification information of the UE to obstruct radiofrequency fingerprinting, RFF, of the UE. The UE is configured to form part of a communication network. The UE comprises: processing circuitry; and memory circuitry storing instructions that, when executed by the processing circuitry, cause the UE to: upon receiving a request to transmit specific uplink data; transmit, to a radio network node, obfuscated uplink data, the obfuscated uplink data having been constructed by applying, to the specific uplink data, at least one parameter for obfuscating hardwarespecific identification information, that could otherwise be used for RFF of the UE based on uplink transmission by the UE.

[0019] The UE may further comprise instructions that, when executed by the processing circuitry, cause the UE to: determine that the UE is configured to obstruct RFF.

[0020] The UE may further comprise instructions that, when executed by the processing circuitry, cause the UE to: determine the at least one parameter for obfuscating hardware-specific identification information.

[0021] The request may be a request for RFF-based authentication issued by the radio network node.

[0022] The at least one parameter may comprise an offset for at least one quadrature amplitude modulation, QAM, symbol in either one or both of its in-phase, I, component and its quadrature, Q, component.

[0023] The at least one parameter may comprise an offset to a bias for a power amplifier, or an offset to a power back-off level.

[0024] The at least one parameter may comprise digital pre-distortion, DPD, parameters that are determined such that they do not match a power amplifier used for uplink transmissions by the UE.

[0025] The at least one parameter may be determined based on a random, or pseudo-random, number source.

[0026] The UE may further comprise instructions that, when executed by the processing circuitry, cause the UE to: transmit an uplink transmission comprising user data while applying the at least one parameter.

[0027] The UE may further comprise instructions that, when executed by the processing circuitry, cause the UE to: transmit a privacy request to the network node to remove all RFF data for the UE.

[0028] The communication network may be a cellular network.

[0029] According to a third aspect, it is provided a computer program for obfuscating hardware-specific identification information of a user equipment, UE, in a communication network to obstruct radio-frequency fingerprinting, RFF, of the UE. The computer program comprises computer program code which, when executed on a UE causes the UE to: upon receiving a request to transmit specific uplink data; transmit, to a radio network node, obfuscated uplink data, the obfuscated uplink data having been constructed by applying, to the specific uplink data, at least one parameter for obfuscating hardware-specific identification information, that could otherwise be used for RFF of the UE based on uplink transmission by the UE.

[0030] According to a fourth aspect, it is provided a computer program product comprising a computer program according to the third aspect and a computer readable means comprising non-transitory memory in which the computer program is stored.

[0031] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

[0033] Fig 1 is a schematic diagram illustrating environments in which embodiments presented herein can be applied;

[0034] Fig 2 is a schematic diagram illustrating a transmission chain of the UE of Fig 1 according to one embodiment;

[0035] Figs 3A-C are swimlane diagrams illustrating embodiments of methods for obfuscating hardware-specific identification information of a UE to obstruct RFF;

[0036] Fig 4 is a schematic diagram illustrating some components of the UE of Fig 1 according to one embodiment;

[0037] Fig 5 is a schematic diagram showing functional modules of the UE of Fig 1 according to one embodiment; and

[0038] Fig 6 shows one example of a computer program product comprising computer readable means.DETAILED DESCRIPTION

[0039] The aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0040] According to embodiments presented herein, RFF of a UE is obstructed by obfuscating hardware-specific identification information in the transmission chain ofthe UE. This prevents a receiver from deducing hardware-specific characteristics for identifying the UE.

[0041] Fig 1 is a schematic diagram illustrating environments in which embodiments presented herein can be applied. A communication network 9 comprises a core network 3 and one or more radio network nodes 1, here in the form of gNode Bs, also known as gNBs. The radio network node 1 could also be in the form of eNode Bs, Node Bs, etc. or any other suitable base station or access point. The radio network node 1 forms part of a radio access network (RAN), providing radio connectivity over a wireless interface 4 to one or more UEs 2. While applicable for multiple UEs, for ease of comprehension and clarity, the relationship with one radio network node 1 and one UE 2 is described hereinafter. The term UE 2 is also known as mobile communication terminal, wireless device, mobile terminal, user terminal, user agent, wireless terminal, machine-to- machine device, etc., and can be implemented, for example, in what today is commonly known as a mobile phone, smartphone, an loT device, or a tablet / laptop with wireless connectivity. The communication network 9 can be a cellular communication network or a non-cellular network, e.g. a Wi-Fi network.

[0042] The cellular network 9 can e.g. comply with any one or a combination of 5G (fifth generation), 6G (sixth generation), LTE (long term evolution), LTE Advanced, W- CDMA (Wideband Code Division Multiplex), IEEE 802.11 (Wi-Fi) or any other current or future wireless network, as long as the principles described hereinafter are applicable.

[0043] Over the wireless interface 4, downlink (DL) communication occurs from the radio network node 1 to the UE 2 and uplink (UL) communication occurs from the UE 2 to the radio network node 1. The quality of the wireless radio interface to each UE 2 can vary over time and depend on the position of the UE 2, due to effects such as fading, multipath propagation, interference, etc.

[0044] Depending on the RAN, the radio network node 1 can optionally be connected to the core network 3 for connectivity to central functions and a wide area network 7, such as the Internet.

[0045] Fig 2 is a schematic diagram illustrating a transmission chain 7 of the UE 2 of Fig 1 according to one embodiment. The transmission chain 7 comprises a baseband module 10 that performs digital-domain transmission processing of data to betransmitted. The next module is a digital-to-analogue converter (DAC) 11, that converts the digital domain signals to analogue signals. Once converted, the analogue signals are at baseband frequency. A mixer 12 upconverts the baseband analogue signals to analogue signals at radio frequency (RF). The RF signals are fed to a power amplifier 13 for suitable amplification, prior to transmission over the air using an antenna 14.

[0046] Figs 3A-C are swimlane diagrams illustrating embodiments of methods for obfuscating hardware-specific identification information of a UE 2 to obstruct RFF of the UE when RFF is attempted by a radio network node 1. The swimlane diagrams can be considered to comprise flow charts for methods performed by the UE 2 on the left, and flow charts for methods performed by the radio network node 1 on the right. Communication between the entities is also shown.

[0047] Looking first to Fig 3A, in a transmit UL tx (transmission) req. (request) step 140, the radio network node 1 transmits a UL transmission request 20 to the UE 2.

[0048] In a receive UL tx req. step 40, the UE 2 receives the request to transmit specific uplink data, i.e. the UL transmission request 20, comprising a specific configuration of the UL data to be transmitted. The UL transmission request 20 can e.g. be a request for RFF-based authentication, and UL transmission request 20 can be issued by the radio network node, in the transmit UL tx req. step 140 described above. The specific uplink data comprises data that is known to the radio network node 1, to allow the radio network node 1 to evaluate how the specific uplink data is transformed by the transmission chain 7, thereby revealing hardware-specific identification information, e.g. related to non-linearities in the transmission chain 7. For instance, the specific uplink data can comprise a reference signal or a non-linearity profile / signature to be transmitted by the UE. However, according to embodiments presented herein, the specific uplink data is obfuscated prior to transmission, as explained in more detail below.

[0049] Upon receiving the UL transmission request 20, in a transmit specific UL data step 46, the UE 2 transmits, to the radio network node 1, obfuscated uplink data 22. The obfuscated uplink data is constructed by applying, to the specific uplink data (generated in line with the UL transmission request 20), at least one parameter for obfuscating hardware-specific identification information, that could otherwise be used for RFF of the UE based on uplink transmission by the UE.

[0050] In one embodiment, the at least one parameter comprises an offset for at least one modulated symbol, e.g. a quadrature amplitude modulation (QAM), symbol in either one or both of its in-phase (I) component and its quadrature (Q) component. This offset can be applied in the digital domain, e.g. in the baseband module 10, or in the analogue domain, e.g. after the DAC n.

[0051] In one embodiment, the at least one parameter comprises an offset to a bias for a power amplifier 13, or an offset to a power level. The bias can affect linearity of the power amplifier 13, whereby any change in the bias will also affect RFF based on nonlinearity of the UE transmission chain. Adjusting the power back-off level also affects linearity, and thus also the ability to use RFF based on non-linearity of the UE transmission chain 7.

[0052] In one embodiment, the at least one parameter comprises digital predistortion (DPD) parameters that are determined such that they do not match a power amplifier used for uplink transmissions by the UE. Since DPD parameters are tailored for each UE to compensate for non-linearities in the power amplifier, any change in DPD parameters will result in a different non-linearity result.

[0053] In one embodiment, the at least one parameter is determined based on a random, or pseudo-random, number source. Randomising the at least one parameter increases the difficulty for any radio network node 1 to compensate for the obfuscation based on the at least one parameter.

[0054] The at least one parameter can be unique for each RFF-related request. This prevents the radio network node 1 from finding out the at least one parameter by tracking transmissions over time. Alternatively, the same at least one parameter can be applied for multiple RFF-related requests, e.g. during a certain time period, to avoid having to generate the at least one parameter for each RFF-related request.

[0055] In a receive specific UL data step 146, the radio network node 1 receives the obfuscated uplink data 22.

[0056] In an attempt RFF step 150, the radio network node 1 attempts to perform RFF based on the received obfuscated UL data 22, and with the knowledge of the specific UL data or CCDF (complementary cumulative distribution function) in line withwhat the radio network node 1 expects the UE 2 to transmit. However, due to the obfuscation, RFF will be obstructed, making the RFF very difficult, or even impossible, since the true hardware-specific variations will not be possible to be derived from the obfuscated uplink data 22.

[0057] Regarding CCDF, the UE perspective performs a Fourier transform for minimising PAPR (peak to average ratio) and corresponding linearity. In this way, the CCDF of the uplink signal for a given power is relatively uniform. If there is an RFF model already available for a given UE output power (and corresponding CCDF), any signal of that output power will have similar CCDF and thus similar non-linearity, allowing identification the UE.

[0058] Looking now to Fig 3B, only new or modified steps compared to those illustrated by Fig 3A are described.

[0059] In an optional conditional obstruct RFF step 42, the UE 2 determines whether the UE is configured to obstruct RFF. This can e.g. be based on a user configuration in the UE or an interactive prompt using the user interface of the UE for each instance of a request to transmit data for RFF. If the UE is configured to obstruct RFF, the method proceeds with obfuscation. Otherwise, the method proceeds to the transmit specific UL data 46, but without applying any obfuscation.

[0060] In an optional transmit privacy request step 43, the UE 2 transmits a privacy request 21 to the network node 1 to remove all RFF data for the UE 2.

[0061] In an optional receive privacy request step 143, the radio network node 1 receives the privacy request 21 and removes the RFF data for the UE 2. In this way, the network has removed the association between RFF parameters and the UE 2 for even greater privacy for the UE.

[0062] In an optional determine obfuscation parameter(s) step 44, the UE 2 determines the at least one parameter for obfuscating hardware-specific identification information. This step is optionally part of the transmit specific UL data 46, but can also be separated for determining the obfuscation parameter(s), described above.

[0063] Looking now to Fig 3C, only new or modified steps compared to those illustrated by Fig 3B are described.

[0064] In an optional transmit user UL data step 48, the UE 2 transmits an uplink transmission comprising user data 23 while applying the at least one parameter, i.e. applying the obfuscation. This can apply for all UL transmissions, to prevent a user from being tracked by passive RFF identification methods.

[0065] In an optional receive user UL data step 148, the radio network node 1 receives the user UL data 23. Since the obfuscation is applied also to the UL user data 23, the radio network node 1 is unable to perform RFF based on the UL user data 23.

[0066] Fig 4 is a schematic diagram illustrating some components of the UE 2 of Fig 1 according to one embodiment. Processing circuitry 60 is provided using any combination of one or more of a suitable central processing unit (CPU), graphics processing unit (GPU), multiprocessor, neural processing unit (NPU), microcontroller, digital signal processor (DSP), etc., capable of executing software instructions 67 stored in memory circuitry 64, which can thus be a computer program product. The processing circuitry 60 could alternatively be implemented using an application specific integrated circuit (ASIC), field programmable gate array (FPGA), etc. The processing circuitry 60 can be configured to execute the methods for the UE 2 described with reference to Figs 3A-C above.

[0067] The memory circuitry 64 can be any combination of random-access memory (RAM) and / or read-only memory (ROM). The memory circuitry 64 also comprises non- transitory persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid-state memory or even remotely mounted memory.

[0068] A data memory 66 is also provided for reading and / or storing data during execution of software instructions in the processing circuitry 60. The data memory 66 can be any combination of RAM and / or ROM.

[0069] An I / O interface 62 is provided for communicating with external and / or internal entities using wireless communication, e.g. Wi-Fi, Bluetooth, Bluetooth Low Energy, and / or a cellular network, complying with any one or a combination of sixth generation (6G) mobile networks, next generation mobile networks (fifth generation, 5G), LTE (Long Term Evolution), UMTS (Universal Mobile Telecommunications System) utilising W-CDMA (Wideband Code Division Multiplex), or any other currentor future wireless network, as long as the principles described hereinafter are applicable. The transmission chain 7 forms part of the I / O interface 62.

[0070] Other components of the UE 2 are omitted in order not to obscure the concepts presented herein.

[0071] Fig 5 is a schematic diagram showing functional modules of the UE 2 of Fig 1 according to one embodiment. The modules are implemented using software instructions such as a computer program executing in the UE 2. Alternatively or additionally, the modules are implemented using hardware, such as any one or more of an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or discrete logical circuits. The modules correspond to the steps in the methods illustrated in Figs 3A-C for the UE 2.

[0072] An UL Tx req. (request) receiver 70 corresponds to step 40. An RFF obstruction determiner 72 corresponds to step 42. A privacy request transmitter 73 corresponds to step 43. A parameter determiner 74 corresponds to step 44. A specific UL data transmitter 76 corresponds to step 46. A user UL data transmitter 78 corresponds to step 48.

[0073] Fig 6 shows one example of a computer program product 90 comprising computer readable means. On this computer readable means, a computer program 91 can be stored in a non-transitory memory. The computer program can cause processing circuitry to execute a method according to embodiments described herein. In this example, the computer program product 90 is in the form of a removable solid-state memory, e.g. a Universal Serial Bus (USB) drive. As explained above, the computer program product could also be embodied in a memory of a device, such as the computer program product 64 of Fig 4. While the computer program 91 is here schematically shown as a section of the removable solid-state memory, the computer program can be stored in any way which is suitable for the computer program product, such as another type of removable solid-state memory, or an optical disc, such as a CD (compact disc), a DVD (digital versatile disc) or a Blu-Ray disc.

[0074] The aspects of the present disclosure have mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible withinthe scope of the invention, as defined by the appended patent claims. Thus, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.

Claims

CLAIMS1. A method for obfuscating hardware-specific identification information of a user equipment, UE, (2) in a communication network (9) to obstruct radio-frequency fingerprinting, RFF, of the UE, the method being performed by the UE (2) configured to obstruct RFF, the method comprising: upon receiving (40) a request (20) to transmit specific uplink data; transmitting (46), to a radio network node (1), obfuscated uplink data (22), the obfuscated uplink data (22) having been constructed by applying, to the specific uplink data, at least one parameter for obfuscating hardware-specific identification information, that could otherwise be used for RFF of the UE (2) based on uplink transmission by the UE (2).

2. The method according to claim 1, further comprising: determining (42) that the UE (2) is configured to obstruct RFF.

3. The method according to claim 1 or 2, further comprising: determining (44) the at least one parameter for obfuscating hardware-specific identification information.

4. The method according to any one of the preceding claims, wherein the request is a request for RFF-based authentication issued by the radio network node (1).

5. The method according to any one of the preceding claims, wherein the at least one parameter comprises an offset for at least one quadrature amplitude modulation, QAM, symbol in either one or both of its in-phase, I, component and its quadrature, Q, component.

6. The method according to any one of the preceding claims, wherein the at least one parameter comprises an offset to a bias for a power amplifier, or an offset to a power level.

7. The method according to any one of the preceding claims, wherein the at least one parameter comprises digital pre-distortion, DPD, parameters that are determined such that they do not match a power amplifier used for uplink transmissions by the UE.

8. The method according to any one of the preceding claims, wherein the at least one parameter is determined based on a random, or pseudo-random, number source.

9. The method according to any one of the preceding claims, further comprising: transmitting (48) an uplink transmission comprising user data while applying the at least one parameter.

10. The method according to any one of the preceding claims, further comprising: transmitting (43) a privacy request to the network node (1) to remove all RFF data for the UE (2).

11. The method according to any one of the preceding claims, wherein the communication network is a cellular network.

12. A user equipment, UE, (2) for obfuscating hardware-specific identification information of the UE to obstruct radio-frequency fingerprinting, RFF, of the UE, the UE being configured to form part of a communication network (9), the UE (2) comprising: processing circuitry (60); and memory circuitry (64) storing instructions (67) that, when executed by the processing circuitry, cause the UE (2) to: upon receiving a request (20) to transmit specific uplink data; transmit, to a radio network node (1), obfuscated uplink data (22), the obfuscated uplink data (22) having been constructed by applying, to the specific uplink data, at least one parameter for obfuscating hardware-specific identification information, that could otherwise be used for RFF of the UE (2) based on uplink transmission by the UE (2).

13. The UE (2) according to claim 12, further comprising instructions (67) that, when executed by the processing circuitry, cause the UE (2) to: determine that the UE (2) is configured to obstruct RFF.

14. The UE (2) according to claim 12 or 13, further comprising instructions (67) that, when executed by the processing circuitry, cause the UE (2) to: determine the at least one parameter for obfuscating hardware-specific identification information.15- The UE (2) according to any one of claims 12 to 14, wherein the request is a request for RFF-based authentication issued by the radio network node (1).

16. The UE (2) according to any one of claims 12 to 15, wherein the at least one parameter comprises an offset for at least one quadrature amplitude modulation, QAM, symbol in either one or both of its in-phase, I, component and its quadrature, Q, component.

17. The UE (2) according to any one of claims 12 to 16, wherein the at least one parameter comprises an offset to a bias for a power amplifier, or an offset to a power back-off level.

18. The UE (2) according to any one of claims 12 to 17, wherein the at least one parameter comprises digital pre-distortion, DPD, parameters that are determined such that they do not match a power amplifier used for uplink transmissions by the UE.

19. The UE (2) according to any one of claims 12 to 18, wherein the at least one parameter is determined based on a random, or pseudo-random, number source.

20. The UE (2) according to any one of claims 12 to 19, further comprising instructions (67) that, when executed by the processing circuitry, cause the UE (2) to: transmit an uplink transmission comprising user data while applying the at least one parameter.

21. The UE (2) according to any one of claims 12 to 20, further comprising instructions (67) that, when executed by the processing circuitry, cause the UE (2) to: transmit a privacy request to the network node (1) to remove all RFF data for the UE (2).

22. The UE (2) according to any one of claims 12 to 21, wherein the communication network is a cellular network.

23. A computer program (67, 91) for obfuscating hardware-specific identification information of a user equipment, UE, (2) in a communication network (9) to obstruct radio-frequency fingerprinting, RFF, of the UE, the computer program comprising computer program code which, when executed on a UE (2) causes the UE (2) to: upon receiving a request (20) to transmit specific uplink data;transmit, to a radio network node (i), obfuscated uplink data (22), the obfuscated uplink data (22) having been constructed by applying, to the specific uplink data, at least one parameter for obfuscating hardware-specific identification information, that could otherwise be used for RFF of the UE (2) based on uplink transmission by the UE (2).

24. A computer program product (64, 90) comprising a computer program according to claim 23 and a computer readable means comprising non-transitory memory in which the computer program is stored.

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