Apparatus for increasing signal integrity in signal transmission network

Abstract

The invention relates to a device (Rx) for increasing the integrity of signals (S) in a signal transmission network, each signal comprising a sequence of one or more signal elements. The apparatus comprises an identification unit configured to identify any injection of a signal element into the received signal based on at least one of: a) a change in signal element amplitude, b) an inversion of a permutation operation applied to the received signal at the time of transmission, c) a signal fingerprint, d) a position of the transmitter, and e) an AI / ML, artificial intelligence / machine learning model. This allows reliable identification of injection of signal elements due to capture effects. In particular, not only over-obscuring attacks can be identified, but also under-obscuring attacks or other injection attacks can be identified. By processing the received signal based on any identified injection of signal elements, signal integrity in the network can be improved.

Description

Technical Field

[0001] The present invention relates to an apparatus, a system, a method and a computer program for increasing signal integrity in a signal transmission network or a sensing network. Background Art

[0002] If the transmitter sends the original signal and the third-party transmitter sends a stronger interfering signal, a receiver that receives the combination of these two signals may only get the interfering signal after demodulation or decoding. This is due to the capture effect, according to which, whenever a combination of signals is received, only the strongest of the combined signals will actually be selected for demodulation or decoding. More generally, the receiver gets a distorted signal that includes any combination of the wanted original signal and the unwanted interfering signal. For simplicity in this specification, we describe this arbitrary combination as being caused by the capture effect.

[0003] If a third party intentionally sends or "injects" a stronger interference signal, this is called an overshadow attack. Overshadow attacks may occur in various wireless communication networks (such as LTE, 5G, WiFi, etc.) and in wired communication networks (including fiber-based networks). These attacks and other injection attacks may also occur in wired sensing networks or wireless sensing networks, for example, in wireless sensing networks based on, for example, radar signals. In a wireless sensing network, wireless sensing signals are sent and received while reflecting on surrounding objects. In addition, integrated sensing and communication (ISAC) networks may also be subject to overshadow attacks and other injection attacks.

[0004] A variant of overshadow attacks is called undershadow attacks. In this variant, the capture effect is exploited as in overshadow attacks, but the interfering signal is consistent with the original signal only at different signal elements. Undershadow attacks may be more difficult to detect than overshadow attacks.

[0005] There is a need to increase signal integrity in signal transmission networks in the presence of known injection attacks such as over-masking attacks and under-masking attacks, whereby injection may be caused for malicious or non-malicious reasons. Interfering signals may affect the communication or sensing capabilities of a specific device or the overall communication / system sensing, for example, modifying the received signal or allowing the retrieval of private data. Summary of the invention

[0006] The object of the present invention is to increase signal integrity in a signal transmission network. An apparatus for increasing signal integrity in a signal transmission network is proposed, wherein each signal comprises a sequence of one or more signal elements. The apparatus comprises an identification unit configured to identify any injection of a signal element into a received signal based on at least one of: a) a signal element amplitude change, and b) an inversion of a permutation operation applied to the received signal when transmitting.

[0007] Since the signal element needs to have a relatively high amplitude in order to be successfully injected into the attacked signal by the attacker, it has been recognized that the change in the amplitude of the signal element is a good basis for identifying any injection of the signal element into the received signal and thereby increasing the signal integrity in the signal transmission network. In addition, it has been recognized that the signal element injection depends on the assumed order of the signal to be attacked. The assumed order can be reliably detected by applying a permutation operation to the signal when sending and reversing the permutation operation when receiving the signal. Therefore, it has been found that the signal integrity in the signal transmission network can also be increased in this way. In particular, it has been recognized that based on any one or combination of a) signal element amplitude change and b) inversion of the permutation operation applied to the received signal when sending, not only over-shielding attacks can be identified, but also under-shielding attacks can be identified.

[0008] The signal transmission network may include one or more nodes that act as a transmitter and / or receiver for signals whose integrity will be increased. Exemplary signal transmission networks include communication networks, sensing networks, and integrated sensing and communication networks. In particular, in communication networks and integrated sensing and communication networks, signals can be understood as corresponding to messages transmitted in the network. For example, a signal can transmit a message, in which case the signal can be understood as an information carrier, and the message can be understood as the information carried. The signal in the signal transmission network can be considered to be exchanged, that is, exchanged between one or more nodes of the network. However, the signal can also be sent and received by the same node. This may be particularly true in sensing networks and integrated sensing and communication networks. When referring to a signal in a signal transmission network or simply "the network" in this article, it should be understood that it refers to a signal exchanged or otherwise sent (i.e., propagated in the network) via a network.

[0009] A signal element may refer to a symbol of a signal, for example, wherein a bit is understood herein as a specific case of a symbol. A sequence of signal elements in a signal may also be referred to as a sequence of time slots in the signal and the corresponding signal content in the time slots. A sequence of signal elements is not necessarily a time sequence, but may also be, for example, a sequence in the spectral domain. In other words, the time slots of a signal may be individualized, i.e., separated from each other, for example, in time and / or frequency. A signal element may refer to a feature in a modulation scheme or a multiple access scheme, such as a signal carrier, a modulation of a carrier, a polarization of a signal, an angular momentum of a signal, and the like.

[0010] The signal element amplitude may, for example, indicate the energy of the signal element. In particular, the signal element amplitude may refer to the energy of the signal element. However, more generally, the signal element amplitude may be any quantity that can be considered as the amplitude of the signal element. For example, the signal element amplitude may be the strength, polarization, intensity, phase, frequency shift or power of the signal element. Exemplary quantities of the above kind that are frequently used in practice in relevant applications are, for example, received signal strength indicator (RSSI), signal-to-noise ratio (SNR) and error vector magnitude (EVM).

[0011] The apparatus may comprise a measuring unit configured to measure a signal element amplitude for each signal element of the received signal.Signal element amplitude variations may then be detected in the measured signal element amplitudes.

[0012] Signal element amplitude variations may be variations of signal element amplitudes across and / or within a signal. That is, signal element amplitude variations may be variations of signal element amplitudes of corresponding signal elements in different received signals and / or amplitude variations of a sequence of signal elements of a single signal.

[0013] The recognition unit (which may also be referred to as a recognizer) may be configured to detect only signal element amplitude changes, or, if the change exceeds a predetermined threshold, it is considered significant. For example, a uniform distribution may be assumed for the amplitude of the signal element across and / or within the signal, wherein the signal element injection may be identified based on any significant deviation from the uniform distribution. For example, the presence of a significant deviation may be determined based on a p-test (i.e., a statistical test resulting in, for example, a p-value). The recognition unit may also rely on an artificial intelligence (AI) model, particularly a machine learning (ML) model, to detect an attack or interference signal. That is, the recognition unit may be configured to identify any injection of a signal element in a received signal based on a trained AI or ML model, wherein the model has been trained to receive a signal as an input and provide a corresponding output, wherein the corresponding output indicates any injection of a signal element in a corresponding signal received as an input. The ML / AI model may be configured to identify any injection of a signal element in a signal according to a signal element amplitude change (such as by training it accordingly). Once detected, the ML / AI model may also be configured to enable extraction of a received signal, such as an actual signal and an interference signal.

[0014] The ML / AI model may have been centrally trained and deployed to the receivers of the network so that it can be used for inference, i.e., to infer whether a signal is under or under obscured. The ML / AI model may also be trained locally based on locally received and decoded / demodulated signals. The ML / AI model may be based on supervised learning or unsupervised learning. The ML / AI model may also be distributed, for example, such as in a federated learning approach.

[0015] The injection of the signal element to be identified may in particular be performed by a third party on the received signal after the received signal has been transmitted. An injection of the signal element throughout the entire signal will correspond to an over-masking attack, whereas an under-masking attack will correspond to an injection of the signal element only at selected positions of the signal. The injection of the signal element identified into the received signal may in particular comprise locating the injected signal element in the received signal. The injected signal element may be located in the received signal by detecting where in a sequence of signal elements of the received signal the amplitude of the signal element changes, i.e. for example exceeds a predetermined degree.

[0016] The apparatus may be configured to discard or drop the received signal if any injected signal element has been identified in the received signal. Additionally or alternatively, the apparatus may be configured to trigger an alarm upon detection of any signal element injection. On the other hand, it may be preferred that the apparatus further comprises a processing unit or "processor" configured to process the received signal. In particular, the processing unit may be configured to process the received signal based on any identified injection of a signal element. As will be described in further detail below, this allows the received signal to be corrected for signal element injection.

[0017] More generally, it can be determined in a policy configured by a management entity (such as a base station or a network function in a core network) which action to take when identifying the injection of one or more signal elements. For example, the policy can determine that when an attack is detected, the receiver of the network should send an alarm to the base station or management entity of the network. However, in the same way, any signal processing implemented as a countermeasure against the attack can also be performed by the processing unit independently of any identified signal element injection, in particular any signal correction. Therefore, the policy can determine that a predefined part of the received signal, only the received signal that has been identified as including the injected signal element (i.e., has been attacked), or all received signals should be subjected to a predefined correction process. When an injection is detected, the signal can still be successfully extracted / demodulated / obtained, and further provided for further processing or presentation. In the case of a sensing signal, a sensing signal that may have been identified as injected can be processed, presented or shown together with the state, so that further evaluation (e.g., by a user) is feasible.

[0018] Any one of the measuring unit, the identification unit and the processing unit may preferably be included in a receiver of the network. Thus, the device may in particular be or include a receiver. However, the device may also be separate from the receiver, wherein the receiver may then forward any received signals to the device. Furthermore, the measuring unit, the identification unit and the processing unit may also be distributed in a network, for example, in which case the device may be understood as a distributed device or system.

[0019] It should be understood that the terms "receiver" and "transmitter" may simply refer to different functions of the same device (which may be referred to as a "transceiver"), wherein the device may perform the functions of "receiving" and "transmitting" at different times. However, with respect to certain services of the network or predefined signal types, there may be a fixed allocation between a) receiving functions and transmitting functions and b) devices in the network. This also means that the device may provide a receiving function for some services of the network or for some signals, but a transmitting function for other signal situations.

[0020] Optionally, the configuration of the device or a configuration for the device (which can also be understood as a policy) can be sent to a receiver or transmitter of the network. For example, if the device is separated from any receiver or transmitter of the network that is receiving or respectively sending a signal (which is the object of the configuration of the device), the configuration of the device can be sent to these receivers or transmitters. On the other hand, if the device is or includes a corresponding receiver or transmitter, the configuration can be forwarded to other receivers or transmitters in the network, and / or the device can receive its configuration from a management entity of the network.

[0021] As mentioned above, the signal element amplitude variation may be a variation of the signal element amplitude across the signal and / or within the signal. In particular, in order to identify any injection of a signal element into the received signal based on the signal element amplitude variation, the identification unit may be configured to detect the signal element amplitude variation in at least one of: a) a sequence of signal elements of the received signal and b) a sequence of signal elements comprising the signal element of the received signal and one or more corresponding signal elements of a previous repetition of the received signal.

[0022] In case the received signal corresponds to a current repetition of a repeatedly received signal, the signal element amplitude may specifically refer to an average signal element amplitude calculated from said current repetition and a predetermined number of previous repetitions of the received signal. Identifying signal element injections based on the average signal element amplitude may improve reliability, as random fluctuations of the signal element amplitude are less likely to result in false alarms.

[0023] For example, if the last N repetitions of a signal S are represented by S[n], S[n-1], ..., S[n-N+1], then a corresponding set of average signal element amplitudes A=[A[0], A[1], ..., A[L-1]] can be calculated, where L is the number of signal elements in S (i.e., each repetition thereof), and A[j]=(1 / N)(S[n,j]+S[n-1,j]+ ...+S[n-N+1,j]), where S[m,j] refers to the jth signal element in the sequence of signal elements of the mth repetition of S. Note that N can be any natural number, including 1, where, in the case of N=1, no average is calculated, but only the signal element amplitudes of S[n] are used.

[0024] Known examples of repeatedly received signals are periodically transmitted signals, such as signals forming a master information block (MIB) or a system information block (SIB1), or sensing signals, such as radar signals or preambles for measuring channel state information. A periodic signal is understood in this context as a repetitive signal which is repeated, for example, at constant time intervals.

[0025] As described above, the uniform distribution assumed for signal element amplitudes for the purpose of identifying signal element injections may refer to a uniform distribution within and / or across signals. A uniform distribution within a signal is understood to refer to uniformity of signal elements of any given signal, but not necessarily uniformity of signal elements of different signals. A uniform distribution across signals is understood to refer to uniformity of corresponding signal elements of different signals, but not necessarily uniformity of signal elements of any given signal itself. Signal element correspondence between different signals may refer to, for example, a correspondence of positions in the corresponding signals.

[0026] The concept of assuming uniform distribution within and / or across signals translates to the above example, where average signal element amplitudes are used to identify signal element injections (i.e., attacks), rather than the amplitudes of the signal elements themselves. In this case, with reference to the above discussion, a uniform distribution may be assumed for each of the N averages A[j] for any given j measured repeatedly over time, and / or for the L averages A measured for a given received signal at any given point in time.

[0027] It may be preferred that the identification unit and / or the processing unit is configured to invert a transmission transform applied to the received signal when transmitting. A transmission transform to be distinguished from the permutation operation may correspond to, for example, modulation or coding, wherein the inversion of the transform may correspond to demodulation or decoding, respectively. Thus, when a transmitter in the network transmits a signal by modulating or encoding information to be transmitted on a carrier signal, the apparatus when acting as a receiver or in combination with a receiver may demodulate or decode the received signal, respectively.

[0028] The identification unit and / or the processing unit may be configured to apply the inverted transmission transform to the received signal, regardless of whether the received signal has been identified by the identification unit as comprising an injected signal element. In fact, attacks such as over-shading attacks and under-shading attacks that exploit the capture effect rely on the transmitter and the receiver to encode / modulate the signal and decode / demodulate the signal, respectively. In particular, these types of transmission transforms (i.e., those transmission transforms on which the attack relies and which can therefore also be regarded as "ordinary" transmission transforms) can be performed regardless of any identified signal element injection. However, as will be further described below, further or subsequent applications of the transmission transform and / or its inversion may be beneficial, particularly at the receiver end, wherein these further applications of the transmission transform and / or its inversion may also be performed regardless of any identified signal element injection.

[0029] Furthermore, it may be preferred that the processing of the received signal (i.e. the processing performed by the processing unit in accordance with or independently of any identified signal element injection) comprises scaling the signal elements of the received signal in accordance with whether the signal elements of the received signal have been identified as injected signal elements. The scaling of the signal elements may refer to the scaling of the amplitudes of the respective signal elements. Furthermore, the scaling may be applied after applying the inverted transmission transform to the received signal, in particular after applying the "normal" inverted transmission transform or the first inverted transmission transform. In particular, the processing unit may be configured to copy the received signal, apply the inverted transmission transform to the first copy, and scale the signal elements of the transformed first copy. In this way, an unprocessed version of the received signal still exists, i.e. the second copy. Thus, any further processing may use both the processed first copy and the unprocessed second copy.

[0030] Preferably, the processing of the received signal comprises thresholding the signal elements to a number of predefined signal element levels, the predefined signal element levels comprising at least an injected level indicating an injected signal element amplitude and a non-injected level indicating a non-injected signal element amplitude, wherein the signal elements are scaled in dependence on their signal element levels. The processing unit may in particular be configured to apply the thresholding to the respective received signal before applying a "normal" or first inverted transmission transform and / or before copying the received signal. Thus, for example, the processing unit may be configured to apply the thresholding as an initial processing step. Alternatively, the thresholding may also be applied to the received signal before the received signal is handed over to the processing unit, i.e., for example, even before reaching the identification unit or even the measurement unit.

[0031] Thresholding of a signal element may refer to: determining which amplitude interval of a predefined set of amplitude intervals the corresponding signal element falls into, and then replacing the amplitude of the signal element with an amplitude level, wherein the amplitude level represents the amplitude interval into which the signal element has been determined to fall. The amplitude level may be predefined as a multiple of the minimum signal element amplitude measured for the corresponding signal. In addition, the amplitude level may be normalized relative to the lowest or highest of the amplitude levels. In the case of binary thresholding (e.g., thresholding that is only divided into the injected level and the uninjected level), the signal element amplitude level of a given signal will be 1 or k, where k>1 is a thresholding parameter. The uninjected level is preferably predetermined so that it is the lowest signal element level. In addition, the uninjected level is preferably predefined so that it corresponds to the amplitude interval into which the amplitude of the intact or undamaged signal element is expected to fall, and the injected level is preferably predefined so that it corresponds to the amplitude interval into which the signal element amplitude of the injection of the expected attacker attempts to fall. For example, if the complete signal element is expected to have an amplitude between I and I+ΔI, and all potential injected signal elements are expected to have amplitudes between kI and (k+Δk)I, k>1, then the corresponding (binary) thresholded amplitude levels can be the respective lower interval boundaries, i.e. I and kI, so that after normalization with respect to the lower of the two (i.e. I), for each signal element in the received signal result, the above-given example of possible amplitude levels 1 and k is obtained, where k is 1.

[0032] Although the thresholding can be extended to signals whose symbols are received at multiple amplitude levels, it may be preferred that the thresholding is a binary thresholding of the signal elements to a lower signal element level and an upper signal element level. In the case of binary thresholding, the thresholding parameter k can be selected so that any attacking signal ends up completely at the upper signal element level, while all unattacked signals end up completely at the lower signal element level.

[0033] Preferably, the processing involves forming a difference signal based on an unprocessed version of the received signal (i.e. the second copy) and a processed version of the received signal corresponding to the received signal (i.e. the first copy) resulting from the thresholding and the scaling, wherein the scaling comprises scaling the signal elements at the injected level to above a level difference indicating an amplitude difference between the injected level and the uninjected level. It has been found that in this way, recovery of an uncorrupted signal from the received signal is facilitated, wherein the received signal may include signal elements injected by an attacker.

[0034] In particular, when the signal element at the lower signal element level or the non-injected level is scaled by a factor a (where preferably 0≤a≤1), and the signal element at the higher signal element level (i.e., the injected level) is scaled by a factor b, the factor b may be selected to satisfy b>k-1. As described above, k may indicate a signal element amplitude ratio between the injected signal element and the signal element from the original signal, more specifically, the ratio between the amplitude of the signal element at the injected level and the amplitude of the signal element at the non-injected level. Thus, the scaling factor b is selected to be above the level difference k-1, which in this case is the normalized level difference.

[0035] The above given condition for the scaling factor b corresponds to the following observation: namely, the signal elements of the first copy of the received signal are preferably scaled so that when the scaled first copy is subtracted from the second copy of the received signal, the amplitude of the signal elements of the original signal part corresponding to the second copy in the superposition is greater than the difference between a) the amplitude of the signal elements of the injected / attack signal part corresponding to the second copy in the superposition and b) the scaled signal elements of the injected / attack part of the first copy of the received signal.

[0036] The processing unit is preferably configured to apply an inverted transmission transform to the difference signal. As mentioned above, if an inverted transmission transform has been applied before forming the difference signal, for example as an initial processing step, the processing unit is therefore configured to apply the inverted transmission transform twice. By applying the inverted transmission transform to the difference signal, signal elements that have been replaced by injected signal elements can be restored, thereby correcting the received signal for injection attacks by third parties, such as under-shadowing.

[0037] Between applying the inverted transmission transform to the received signal (i.e. for the first time) and applying the inverted transmission transform to the difference signal, the processing unit may be configured to apply a non-inverted transmission transform, i.e. the transmission transform that was applied to the received signal when transmitting. For example, the first copy of the received signal (i.e. the version of the received signal that was processed until the difference signal was formed based thereon and the hitherto unprocessed version of the received signal) may be processed in the following order: 1) applying the inverted transmission transform, 2) applying the non-inverted transmission transform, 3) applying the scaling. An alternative order would be: 1) applying the inverted transmission transform, 2) applying the scaling, 3) applying the non-inverted transmission transform. Regardless of the order, the inverted transmission transform is preferably applied to the difference signal obtained from the resulting version of the first copy and the second "saved" copy. As previously mentioned, the transmission transform may correspond in particular to modulation or coding, so that the inverted transmission transform may correspond in particular to demodulation or decoding.

[0038] In practice, it has been found that the inversion of a transformation on the received signal that has been applied to the signal when transmitting can also be used to identify the injected signal elements. To this end, the transformation may in particular correspond to a permutation of the signal elements in the received signal, since this allows a mismatch to be created between the order of the signal elements assumed by the attacker and the actual order of the signal elements that temporarily exist between transmission and reception. In particular, it may be preferred that, in order to identify any injection of signal elements into the received signal based on the inversion of the permutation operation applied to the received signal when transmitting, the identification unit is configured to permute the received signal according to the inverted permutation operation and to perform an integrity check on the permuted received signal. The integrity check may be a known integrity check, in particular an integrity check known to return a negative result for a signal comprising signal elements of an incorrect order or randomly distributed erroneous signal elements (such as caused by interference or noise). For example, the identification unit may be configured to perform a cyclic redundancy check (CRC).

[0039] The permutation operation may in particular be a random permutation operation, wherein "randomness" is understood herein to also encompass "pseudo-randomness". For example, a secure pseudo-random sequence of signal elements may be obtained by first determining a random seed and then applying a secure pseudo-random function (e.g., a key derivation function, SHAKE, ...) thereto.

[0040] Just as the method of identifying injected signal elements based on changes in the amplitude of signal elements, the method of using integrity checking in combination with signal permutation is also based in part on the observation that current wireless communication standards (such as LTE or 5G) lack integrity protection in the lower communication layers. Whether integrity protection can be enabled is currently being studied. For example, the solution to the second key problem (KI#2) mentioned by the Third Generation Partnership Project (3GPP) in Technical Report (TR) 33.809 (titled "Study on 5G security enhancement against False Base Stations (FBS)") discusses how to protect broadcast 5G system information. Similarly, if a message integrity code (MIC) is added to the message (e.g., a message between a UE and a base station), integrity protection in unicast messages can be enabled. However, applying integrity protection to each message can be expensive.

[0041] Fortunately, performing integrity checks on all received signals may not be necessary to identify injected signal elements with sufficient probability. Therefore, the identification unit can be configured to perform integrity checks on a predetermined portion of the signal in the network, wherein, for a given signal to be sent, it is randomly determined whether to perform integrity checks on the signal based on the predetermined portion. This can allow for a reduction in computational workload. In other words, efficiency can be improved by integrity protection only for certain messages (e.g., a portion f of the message, where, for example, f = 50% or less). A given message can be (randomly) selected for integrity protection with a probability f, and if protected, it includes a digital signature or a message integrity check (MIC), or more generally, any integrity check. If an integrity check is included, the receiver must check the integrity of the received message. Then, if an attacker attempts to manipulate the signal, the attacker will not always be successful, and the attack can therefore be detected. The probability f can correspond to the previously mentioned predetermined portion. In an example, performing the integrity check can include checking whether the signal structure (which can be given based on the signal element) conforms to a standard structure. For example, the standard structure can correspond to a communication protocol.

[0042] For any signal for which an integrity check is to be performed, an integrity indication signal portion may be sent in conjunction with the signal, wherein the identification unit may be configured to check the integrity of the signal based on the integrity indication signal portion when the signal is received. For example, the combination of the integrity indication signal portion sent and the signal is formed by including the integrity indication signal portion in the corresponding signal, wherein a lack of integrity is concluded when the signal is received if it is determined that the amplitude of one or more signal elements of the integrity indication signal portion exceeds a predetermined threshold. The integrity indication signal portion may in particular correspond to a digital signature or a MIC. The signal elements of the integrity indication signal portion may be of the same type as the signal elements of the signal itself. Thus, for example, it may correspond to bits or other symbols.

[0043] For example, the integrity indication signal part can be included in the corresponding signal by appending the integrity (check) indication signal part at the end of the signal or by inserting the integrity (check) indication signal part in front of the signal. However, if the integrity check is appended at the end of the message, the attacker may try to mask the end of the message. To solve this problem, the integrity check can be placed at the beginning of the message so that when the integrity check is sent, the sending of the rest of the message is shifted. Alternatively, the integrity check can be appended to the end of the message, but if the energy of the symbol occupied by the integrity check is too high, especially compared to the rest of the message, a negative integrity check result is returned.

[0044] In other words, it may be preferred that: a) the combination of the transmitted integrity indication signal portion and the signal is formed by inserting the integrity indication signal portion in front of the signal, or b) the combination of the transmitted integrity indication signal portion and the signal is formed by appending the integrity indication signal portion at the end of the signal, wherein if it is determined that the size of one or more signal elements of the integrity indication signal portion exceeds a predetermined threshold, a conclusion is drawn that the signal lacks integrity when it is received.

[0045] In practice, it may also be preferred that: a) only a predetermined part of the signal in the network is permuted according to a permutation operation before transmission, wherein, for a given signal to be transmitted, whether the signal is permuted is randomly determined based on the predetermined part, and / or b) a combination of the transmitted permutation indication signal part and the permuted signal is formed by inserting a permutation indication signal part in front of the permuted signal, and / or according to an indication made by means of a different message (e.g., a configuration message).

[0046] It should be emphasized that, alternatively, any integrity check of the above type can be implemented independently of whether the signal is permuted. Including integrity checks in the signal itself can allow more attacks to be detected and thus increase signal integrity in the signal transmission network. This is particularly applicable to networks operating according to wireless communication standards (such as LTE or 5G), which, as mentioned above, lack integrity protection in the lower communication layers.

[0047] So far, various aspects of attack detection by identifying signal element injections and correspondingly processing received signals to increase signal integrity in a signal transmission network have been discussed, wherein it should be emphasized that these aspects may be implemented individually or in combination.

[0048] On the other hand, it has been recognised that, while for example processing any received signal in which injected signal elements have been identified so as to correct the injected signal elements by restoring the signal elements which have been replaced by the injected signal elements, provides an effective means for increasing the overall integrity of signals in signal transmission networks subject to third party injection attacks (such as under-masking), these attacks may alternatively be avoided entirely with the aid of some attack avoidance measures.

[0049] For attack detection, but also for attack avoidance, for example, at least some of the signals in the network may be permuted before transmission according to a permutation operation, wherein the permutation operation may be reversed after the signal is received. Thus, the processing unit may be configured to reverse the permutation operation for at least some of the received signals, wherein the signal has been permuted before or when transmitted according to the permutation operation. Third-party attacks, such as under-masking attacks, may be prevented in this way as long as the attacker is unaware of the permutation operation. Since it may not always be possible to completely avoid attacks, signal correction and attack avoidance measures may be implemented side by side, i.e. both may be implemented in the same network. Furthermore, either or both of these measures may be implemented, for example by identifying signal element injection in the received signal, regardless of whether an attack has been previously detected. Such an implementation may be considered to be of a preventive nature, although possibly at the expense of additional computational effort.

[0050] Therefore, the present disclosure also relates to a system for increasing signal integrity in a signal transmission network, each signal comprising a sequence of one or more signal elements, wherein the system comprises: a) an apparatus described above as a receiving device or receiver for signals in the network, and / or b) a sending device or transmitter for signals in the network, wherein the sending device comprises a permutation unit configured to permute the signal to be sent according to a permutation operation.

[0051] Therefore, a device for increasing signal integrity in a signal transmission network is also proposed, wherein each signal comprises a sequence of one or more signal elements, and wherein the device optionally comprises: means for identifying any injection of signal elements into the received signal based on at least one of a signal element amplitude variation and an inversion of a permutation operation applied to the received signal when transmitting, in particular for any of: a) measuring a signal element amplitude for each signal element of the received signal, the signal element amplitude being indicative of signal element energy, b) identifying any injection of signal elements into the received signal by detecting a signal element amplitude variation based on the measured signal element amplitude, and / or c) processing the received signal based on any identified injection of signal elements, but wherein the device comprises d) means for permuting, such as a permutation unit or "permutator", configured to permute at least some signals in the network according to a permutation operation before transmission, wherein after receiving the signal, the permutation operation may be inverted, such as by the processing unit of another device in the system. If the device implements only option d), it may in particular be a transmitter.

[0052] It should be understood that while aspects of correcting the received signal for an identified attack may be accomplished solely by a receiver (i.e., a receiving device implementing the apparatus as initially described), attack avoidance by means of, for example, permutations of the signal is preferably accomplished by collaboration of a transmitter and receiver (i.e., a transmitting device implementing the apparatus implementing option d) above) and a further receiver (i.e., a receiving device implementing the apparatus as initially described).

[0053] Attack avoidance measures (e.g. permuting signal elements in the signal according to a certain permutation operation) may be initiated not only by the sender but also by the receiver. In an example, the receiver may request the sender to take attack avoidance measures, in particular to start permuting signal elements of the signal sent by the sender to the receiver according to a certain permutation operation. Such a request may be sent once the receiver has identified an injection of one or more signal elements in the received signal, i.e. once an attack has been detected.

[0054] In any case, i.e. whether implemented for the purpose of attack detection or attack avoidance, whether implemented without implementing the same or other measures for the corresponding other purpose or signal correction purpose, etc., it may be preferred that for each permuted signal to be sent, the permutation operation is encoded as a permutation indication signal portion, and the permuted signal is sent in combination with the permutation indication signal portion, wherein the permuted signal is received in combination with the permutation indication signal portion, and after receiving the signal, the permutation is inverted based on the permutation indication signal portion. Preferably, the combination of the permutation indication signal portion and the permuted signal sent may be formed by a) appending the permutation indication signal portion at the end of the permuted signal, or by b) inserting the permutation indication signal portion in front of the permuted signal. Additionally or alternatively, the permutation indication signal portion may also be sent in a different configuration message or signal.

[0055] In another embodiment, the permutation operation may be encoded in some physical parameter of the signal. For example, the initiator and the responder (which may correspond to a transmitter and a receiver, respectively, or vice versa) may exchange data encoded in the phase of the carrier signal, in particular an encryption key. The responder may encode a permutation operation for permuting the transmitted data, instead of exchanging a key.

[0056] In a variant, the permutation operation according to which the first signal to be transmitted is permuted can be encoded as a permutation indication signal portion, which is sent in combination with the second permuted signal. In addition, the combination of the permutation indication signal portion sent and the second permuted signal can be formed by a) appending the permutation indication signal portion at the end of the second permuted signal, or by b) inserting the permutation indication signal portion in front of the second permuted signal. The second permuted signal may have been permuted according to a permutation operation different from the permutation operation according to which the first signal is permuted. The first signal and the second signal may have any predefined relationship with respect to each other. For example, they may be signals that are sent subsequently, i.e. the second signal may be sent directly after the first signal.

[0057] In another embodiment, the permutation operation may not be encoded in any signal portion transmitted with any permuted signal combination. Instead, the permutation operation may be defined, for example, based on one or more communication parameters accessible or known to the transmitter and receiver in the network. The communication parameters defining the permutation operation may be understood as global parameters of the network. Preferably, the communication parameters are selected so that they are difficult or impractical to be guessed by a potential attacker.

[0058] The above embodiments are particularly, but not exclusively, applicable to signals transmitted by a transmitter (e.g., a transmitter of a base station or access point) before a receiver (e.g., a user equipment) has established a connection with the transmitter. For example, the signal may be a master information block (MIB) or a system information block SIB1 initially sent by a 5G base station to allow a user equipment to perform an initial random access procedure in a 5G network. If a connection is already available, the permutations may also be exchanged or agreed upon in a secure manner, for example, by securely exchanging secret permutations using a secure channel between the transmitter and the receiver / responder, which will be applied to signals exchanged later. Here, a secure channel may refer to a confidentiality protected channel and / or an integrity protected channel and / or a replay protected channel, and the like.

[0059] The above embodiments are also applicable to signals that encode configuration parameters and are generally unprotected, such as DCI, UCI or SCI messages. The permutations applied to these messages can be configured in a secure manner, for example, through protected RRC messages, and then the transmitter and receiver can apply the protected secret permutations. The receiver can then undo the secret permutations and verify the integrity check (e.g., CRC) to verify the message.

[0060] While it may be sufficient to pursue an avoidance strategy in conjunction with a correction strategy or even in its own right, the additional effort (even if relatively small) that must be taken to do so may not be necessary if it is known that there is no ongoing attack. Therefore, it is beneficial to first identify any injection of signal elements into the received signal by detecting signal element amplitude changes (such as, based on previously measured signal element amplitudes) for at least some of the received signals. In other words, it may be preferred that the signal in the network is permuted according to a permutation operation before transmission only if the injected signal element has been identified in the received signal. In particular, the permutation unit can be configured to permutate the signal to be transmitted only if the injected signal element has been identified in the received signal based on the signal element amplitude changes. Subsequently, the permutation can be used to detect attacks more accurately. According to another aspect that can be used independently of the same purpose of increasing signal integrity in a signal transmission network, a node participating in a process dialogue with a peer can measure some physical (layer) parameters of each transmitted signal received by the node from the peer. These measurements can be combined into a "fingerprint" that represents the signal sent from the peer node as seen / sensed by the first node. The receiving node can obtain the signal to be measured and any information being measured through configuration messages, pre-configuration. If the conversation is interrupted / modified / etc. by a transmission from a third node, whether intentionally (e.g., an over-obstruction attack) or unintentionally, the measurements obtained by the first node will be combined together to form a fingerprint that is significantly different from what was expected. The first node can use this information to take appropriate action. For example, it can simply discard the signal without attempting to read it. For example, it can reissue the last signal it sent to the peer. For example, it can instruct the peer to abort or restart an ongoing process.

[0061] In one embodiment, the physical parameters include one or more measurements related to location. For example, an estimate of the distance between two nodes. For example, a measurement of the angle of arrival of an incoming signal from a peer-to-peer mode. The first node may use multiple antennas to collect more detailed information. In another example, the physical parameters may include measurements of characteristics of the signal itself. For example, a measurement of the received signal strength or received signal quality of the signal or its components. For example, a measurement of carrier frequency.

[0062] In a related embodiment, due to the fact that the transmitter of the desired signal S and the transmitter of the unexpected interference signal I will be at different positions and their signals will arrive at each receiving antenna position in different proportions, the use of multiple antennas at different positions can be used to distinguish between the desired signal S and the unexpected interference signal I.

[0063] In a related embodiment, a measure of the distance between the fingerprint of the most recent received signal and a weighted average of previous fingerprints is calculated. If the calculated distance exceeds a threshold, the first node can assume that the signal has not arrived from the peer node, that is, a malicious device is interfering with the communication. The weighting used can take into account the operating environment. For example, if both nodes are relatively static, the weighted average can be used to eliminate measurement noise. In this case, each signal can be weighted equally. In another example, if one or both nodes are in motion, the weighting can favor more recent signals. Alternatively, in the event of motion or other system changes, the previous fingerprint can be used to predict the expected fingerprint for the next signal.

[0064] A fingerprint comprising multiple parameters can be represented as a multi-dimensional object. The representation can additionally define a measure of distance that can be used to compare fingerprints. Alternatively, some or all parameters can be processed to reduce the dimensionality. In the extreme case, the fingerprint can be represented as a single graph.

[0065] In another embodiment, more than one threshold may be used to determine an appropriate response. For example, a distance exceeding a first threshold may cause the signal to be discarded without further action. A distance exceeding a second threshold may cause the first node to abandon or restart an ongoing process.

[0066] In another embodiment, the first node may initiate a transaction by first determining some physical characteristics of the peer node (e.g., the precise location of the peer node) to determine if the peer node is in a "validity zone" for the transaction. For example, if the first node is a point of sale terminal, the peer node should be within a small footprint corresponding to the owner in front of the terminal. At least a portion of the location information may then form part of a fingerprint. Subsequent signals may then be checked to ensure that: a) the peer device stays in the zone for the duration of the transaction, and b) all signals are from the peer device.

[0067] In another embodiment, the fingerprint is alternatively or additionally used to determine whether the peer device is in motion relative to the first device.A detected change in motion may be used to trigger a mitigation mechanism, such as a change in antenna beam configuration or a handover procedure.

[0068] In another embodiment variant, the fingerprint may be determined by using a ranging process between two UEs, or by using a positioning process, or by using a wireless sensing process.

[0069] An example of benefiting from the described technology refers to receiving a rejection message, for example, a rejection message sent by a UE when a potential rejection reason is detected. This can occur, for example, in the context of a UE to a network relay when the relay receives a direct communication request message whose integrity cannot be verified and / or which includes parameters that cannot be verified. In this case, it may be beneficial that the relay can send a rejection message to notify the remote UE of the fact that it has not been accepted. Typically, it may be beneficial that the rejection message is integrity protected (e.g., by MIC) to ensure that an attacker cannot inject a false rejection message that interferes with normal communication. However, if it is not integrity protected, the remote UE can apply the technology in the previous embodiment, wherein the remote UE checks that the received rejection message is associated with a fingerprint similar to the fingerprint of the message previously exchanged with the UE to the network relay. In this way, the remote UE can obtain a certain level of assurance about the source of the received rejection message. This principle is applicable to other settings, in which the first device verifies that it is still communicating with the second device by comparing the fingerprint of the received message. Similar techniques can be applied to other communication / sensing processes involving other devices. For example, a user device receives a rejection message from a base station.

[0070] Exemplary procedures that may benefit from the described procedures may include (but are not limited to) random access procedures, (conditional) handover procedures, where, for example, either the gNB or the UE may want to determine that the other has a suitable signal / fingerprint.

[0071] In general, the above embodiments describe a device (Rx) for increasing the integrity of a signal (S) in a signal transmission network, each signal (S) comprising a sequence of one or more signal elements, wherein the device (Rx) comprises an identification unit configured to identify any injection (kI) of a signal element or interference into the received signal based on at least one of: a) a signal element amplitude variation, b) a signal fingerprint, c) a location of the transmitter, and d) a reversal of a permutation operation (P) applied to the received signal when transmitting.

[0072] According to another aspect of the same purpose of increasing signal integrity in a signal transmission network, it has been recognized that an attacker may wish to attack a wireless system, such as a wireless sensing system. Such a wireless sensing system (which may also be understood as a network) may be based on the measurement of a radar signal or a pilot sensing signal. The wireless sensing signal may be attacked by means of an over-shading attack or an under-shading attack or by injecting a signal. The radar signal may consist of a chirp, for example, transmitted in a periodic manner. The chirp may be a periodic signal, for example, with an increasing or decreasing frequency over time. For example, a radar signal may be transmitted every Tt seconds, and the radar signal itself may have a duration of Ts seconds, which contains N chirps of duration Tc=Ts / N, wherein during the duration of each chirp, the frequency increases linearly between a frequency fa and a frequency fb. For example, the transmitted signal has a frequency fa+(k*t mod(fb-fa)), where fa is the initial frequency, k is the increasing speed, t is time, and mod refers to a modulo operation. If the attacker knows the parameters of the radar signal, the attacker can determine how to inject a new signal similar to the reflected radar signal to create a new non-existent object or mask the actual measured features of the object. To solve this problem, the chirps in the radar signal can follow a permuted "pattern" or "signature" as in the previous embodiment. In addition or alternatively, they can also follow a seemingly random "pattern", for example, the N chirps can be of increasing / decreasing frequency type. Therefore, as an addition or alternative to permuting signal elements based on the permutation operation as described above, the signal elements can be modified in the frequency domain in a predetermined, possibly random manner. Similarly, it may be preferred that the manner in which the signal is changed (i.e., in this case, the modification of the signal elements in the frequency domain) is known to the corresponding transmitter and the corresponding receiver, but not to any potential attacker. It should also be noted again that the term "random" is understood in this article to also cover "pseudo-random". As already mentioned further above, a secure pseudo-random sequence of signal elements can be obtained by first determining a random seed and then applying a secure pseudo-random function (e.g., a key derivation function, SHAKE, ...) thereon.

[0073] The permutation mentioned above may be a random permutation applied to a standard wireless sensing signal (e.g., a given well-known chirp pattern), wherein the permutation may be applied to the wireless sensing signal before transmission. Likewise, the permutation may be a random permutation applied to the standard wireless sensing signal upon reception. Furthermore, the permutation operation may be applied only to a portion of the wireless sensing signal. For example, the chirp signal may be transmitted as usual in a portion f of time, and a random permutation may be used in a portion 1-f of the time. This has the advantage of reducing computational overhead in transmission and reception.

[0074] In fact, in order to increase the integrity of wireless (sensing) signals in the signal transmission network, the wireless sensing signal can be characterized or identified by a "signature" or "pattern", which can be, for example, (i) a given randomized / permuted arrangement of chirps as described above, and / or (ii) a given modulation (e.g., amplitude, phase, frequency...) of one or more chirps. In this second case, the modulation can include modulating the amplitude (or other characteristics) of a chirp of duration Tc, for example, Tc can be divided into M intervals of duration Tc / M, each of which is modulated by a different amplitude (or other characteristics). Another example of this second case is that the frequency can be modulated, for example, instead of having a chirp with a frequency of each chirp increasing linearly between a frequency fa and a frequency fb, it is feasible to have a chirp whose frequency follows a non-constant pattern and changes continuously between fa and fb (i.e., without jumps) but is still difficult to be guessed by an attacker. For example, the transmitted signal may have a frequency fa+(k(t)*t mod(fb-fa)), where k(t) refers to an increasing speed that may vary over time and is not constant, for example, k(t) may be k*sin(fm*t), where fm is the frequency that determines the rate of change.

[0075] The "signature" or "pattern" may be updated following a given schedule (eg, every T_up seconds).

[0076] In an embodiment, the wireless sensing signal may be characterized / identified by a "signature" or "pattern" as defined above, which is location-specific or direction-specific, i.e., specific to a specific direction DIR relative to, for example, a transmitter. This limits the scope of potential injection attacks, since the attacker must be able to monitor the "signature" or "pattern" included in the wireless sensing signal in a given direction DIR. A malicious attacker injecting a fake wireless sensing signal will only succeed if the attacker injects a signal from the direction DIR that includes the appropriate "signature" or "pattern" or "fingerprint".

[0077] In an embodiment, if a first signal (e.g., a communication signal) is received immediately following a second signal (e.g., a ranging signal, or a wireless sensing signal such as a radar chirp), and whereby the second signal allows the receiver to verify the location of the transmitter, the receiver can verify the integrity of the first signal.

[0078] To implement any of the above measures, one or more wireless sensing transmitters of the network may be configured to transmit wireless (sensing) signals as described above.

[0079] In another embodiment, if the corresponding wireless sensing receiver detects that an object at a distance d is the nearest object, or if the wireless sensing receiver wants to limit the feasible distance for performing an attack to d or less (i.e., an attacker at a distance > d cannot perform an injection attack), the wireless sensing receiver can request the wireless sensing transmitter (alternatively, the wireless sensing transmitter can be configured accordingly) to adapt the period of the wireless sensing signal to at least d / c, in particular, using a "pattern" or "signature" whose duration is at least d / c, where c is the speed of light.

[0080] In addition, the wireless (sensing) receiver can receive a wireless (sensing) signal as described above, and compare (or integrity check) the pattern (e.g., permuted pattern, random pattern, ...) of the received wireless (sensing) signal and the transmitted wireless (sensing) signal, wherein the comparison may require that the received wireless (sensing) signal follows the same "signature" / "pattern" as the transmitted wireless (sensing) signal. In addition, the comparison (integrity check) step may require, for example, detecting a change in the amplitude of a signal element and / or the inversion of a (permutation) operation (P) applied to the received signal when transmitting. In addition, the comparison (integrity check) step may be direction-dependent.

[0081] In another embodiment, if an operation (e.g., permutation) is applied to the sensing signal when it is transmitted, it is necessary to synchronize the receiver when the sensing signal arrives before applying the inversion of the (permutation) operation. For example, a wireless sensing system that receives a chirp (e.g., FMWC chirp) that has been permuted before transmission requires a synchronization module that is able to detect the permuted chirp sequence. When the permuted chirp sequence is detected, the synchronization module triggers a detection event that triggers a second module responsible for performing the inversion of the (permutation) operation on the received signal. This is necessary because the target may be at any distance and therefore the reflected wireless sensing signal may arrive at any point in time, so that before the inversion of the operation can be performed on the sensing signal, it is first necessary to determine when the inversion operation should start. The synchronization module can detect the signal, for example, by analyzing the correlation of the received signal with the transmitted permuted sensing signal or by a matched filter. When the correlation peak is determined, the inversion operation can then be applied to the received sensing signal, which is then fed to a wireless sensing receiver (e.g., a radar receiver).

[0082] Note that the synchronization step described above is also required if not all sensing (chirp) signals are exactly equal, or if some features of the chirp are mixed or varied depending on the operation applied to the transmitted sensing signal. Features that may also be varied or mixed may include: the slope or speed at which the frequency increases linearly between frequency fa and frequency fb, or the distance between chirps.

[0083] Note that the above synchronization step may not be required in the above embodiment where the "signature" or "pattern" may be a given modulation, and therefore this embodiment may result in a simpler sensing receiver. For example, in the case of a receiver with a time-varying frequency rate, the sensing receiver may need to mix the received signal with a transmitted signal having a variable frequency between fa and fb and modulated according to k(t). When the signals are mixed, then a main peak will appear in the frequency domain at a frequency that depends on the distance, and smaller peaks will appear next to it, with the specific position depending on the modulation frequency in k(t). The sensing receiver can determine the presence of the injected signal by monitoring the correct or incorrect position of those smaller peaks that depend on k(t).

[0084] If an operation is applied to the transmitted sensing signal in a portion of the time, the above pipeline only needs to be executed in a portion of the time, thereby reducing the required resources.

[0085] In another embodiment, if an operation is applied to the transmitted sensing signal in a portion of time, an attacker may try to attack the system when the sensing signal is predictable. Therefore, the receiver should verify that the reading r1[n] of the received sensing (radar) signal when the operation is applied to the transmitted sensing signal and the reading r2[n] of the received sensing (radar) signal when the operation is not applied remain consistent, for example, no new targets are detected when no operation is applied to the transmitted sensing signal, or for example, the readings r1[n] and r2[n] are equal, where n refers to the discrete time n.

[0086] In another embodiment, the portion of the time in which the sent sensing signal is subjected to the (permutation) operation is context-dependent. If the environment is friendly (e.g., no attacker is detected when comparing the readings of the received sensing (radar) signal when the operation is applied to the sent sensing signal and when the operation is not applied), the (permutation) operation is applied to a small portion of the sent sensing signal. If the readings show inconsistency, the operation is applied to a larger portion / part f' of the sent sensing signal. This embodiment provides a compromise between resource requirements and robustness. In particular, f at time n may depend on the coherence between the readings obtained from the sent sensing signal with and without the (permutation) operation. For example, if r1[n-1]==r2[n-1], then f[n] moves towards a low value f0, but if r1[n-1]!=r2[n-1], then f[n] moves towards a higher value f1.

[0087] Configuration parameters (including the use of "patterns" or "signatures" to limit the injection of spurious sensing signals, timing characteristics, whether the "patterns" or "signatures" are direction-specific, update times, etc.) can be configured in the wireless sensing transmitter or wireless sensing receiver by a management entity (such as a core network or network function) responsible for wireless sensing or (external) application functions. It should also be noted that the wireless sensing transmitter and / or the wireless sensing receiver can be a base station or a user equipment.

[0088] In some cases, an attacker may exploit wireless sensing signals with the intent of passively monitoring a target device, such as a person. This may be done, for example, if the attacker is monitoring a wireless sensing signal (e.g., a radar-based sensing signal) from a transmitter (e.g., a base station) and receiving the sensing signal reflected by an object (e.g., a person). This may be done if the attacker himself is able to send wireless sensing signals to monitor an object (e.g., a person). Features that an attacker may want to monitor include, but are not limited to, location, speed, health information, quantity, etc. Therefore, another object of the present invention is to address this privacy issue. This is achieved by means of an embodiment that monitors the integrity of the received signal and prevents unwanted / unauthorized parties from injected signals (such as sensing signals).

[0089] In another embodiment, a Personal Sensing Firewall (PSF) - whose purpose is to prevent unwanted / unauthorized parties from performing sensing - can be used in a Region of Interest (ROI), either by a person or by an object. For example, the ROI can be a house. For example, an object can be a UE. For example, a person can carry the PSF. The PSF processes the received signals to ensure their integrity, i.e., as in other embodiments, only signals received from trusted senders are processed to remove injected signals / interference. Additionally or alternatively, the PSF can also modify the received signals to ensure that they do not leak information. This is done by Fig.10 1, wherein a transmitting device 1000 transmits a signal 1003. The signal is received by a user device 1002 which may include a PSF function 1007. The user device / PSF may reflect / generate / return a signal 1004 to the receiving device 1001. A (malicious) transmitter / receiver 1005 may transmit a signal 1006, the goal or effect of which is to interfere with the operation of the user device 1002 and the reception of the signal 1003 and / or the reflection / transmission of the signal 1004.

[0090] In another embodiment, the PSF may be integrated into the UE. Alternatively, it may be associated with the UE in other ways. For example, it may be integrated into a phone housing for holding the UE, and may be additionally linked to the UE via a proximity mechanism such as NFC, allowing the PSF to operate under instructions received from the UE or from the network. For example, it may be integrated in a home (e.g., in a home base station providing coverage for the home), and the PSF may be active when the UE is in the home area. The PSF may also be integrated in a router (such as a wireless router), for example, for use in a Wi-Fi network.

[0091] The PSF may monitor incoming signals and determine whether an authorized incoming signal is being received. For example, the PSF may monitor whether an incoming wireless sensing signal (1003 or 1006) that may be used, for example, for wireless sensing is being received. The PSF may monitor whether a signal is authorized. For example, signal 1003 is authorized, and the access device (usually, the transmitter) may have notified the UE / PSF (1002, 1007) of it. For example, signal 1006 may not be authorized, and the UE / PSF may not know it. Therefore, when signal 1003 or 1006 is detected, the UE / PSF may have a strategy or configuration to apply the relevant embodiments in the present invention to prevent leakage.

[0092] In another embodiment, the PSF may be based on / include one or more backscattering devices adapted to modulate the backscattered wireless (sensing) signal. The PSF may also refer to a smart repeater that is capable of changing certain parameters of the retransmitted signal (e.g., phase, delay, or amplitude to simulate the perceived wireless channel or distortion in the received signal).

[0093] In another embodiment, the PSF may rely on or include one or more radio and / or receiving / transmitting units, such as a backscatter radio unit, which is capable of, for example, reflecting and / or modulating the received wireless (sensing) signal, wherein the modulation may be at least one of FSP, PSK or ASK. The radio unit may also be capable of generating a wireless sensing signal, for example, when the PSF receives / senses a wireless sensing signal, the PSF may be capable of determining parameters of the wireless sensing signal and reproducing / retransmitting the wireless sensing signal (e.g. with a given delay).

[0094] In another embodiment, the PSF modulates the (reflected / backscattered) wireless sensing signal following a pattern, wherein the pattern is generated by the PSF, for example, when the PSF may want to achieve that monitoring of an object / person / ROI is not performed or monitoring becomes more difficult (monitoring can be done with the help of wireless sensing).

[0095] In another embodiment, the pattern is a random pattern.

[0096] In another embodiment, the randomized pattern is unpredictable in the sense that an attacker monitoring the pattern over a period of time cannot guess the value of the pattern at the next moment. In particular, if the pattern can be a sequence of symbols where each symbol can take two values ​​(1 and 0) that appear with equal chance, then an attacker cannot guess whether the next symbol will be 1 or 0 with a chance higher than 0.5 (between 0 and 1).

[0097] In another embodiment, the PSF FSK-modulates the (reflected / backscattered / received) wireless sensing signal according to a pattern so that a receiver (e.g., an attacker's receiver) cannot determine the position / movement / acceleration of the object because the (reflected / backscattered) signal hides the smaller / weaker reflection of the passive object. For example, it can use a random pattern to determine a random frequency fs for FSK modulation of the backscattered / reflected wireless sensing signal (creating fake objects at different locations). For example, it can use a random pattern to determine a set of frequencies fsi to modulate the backscattered / reflected wireless sensing signal with a different set of frequencies fsi (creating different fake objects at different locations).

[0098] In another embodiment, the PSF (PSK / ASK-)modulates the (reflected / backscattered) wireless sensing signal according to a pattern such that the wireless communication channel appears randomized and a receiver (e.g., an attacker's receiver) cannot determine the object's velocity (e.g., related to heart rate / respiration rate) because the (reflected / backscattered) signal hides the smaller / weaker reflections of passive objects.

[0099] In another embodiment, the PSF and the trusted (sensing) device (e.g., gNB or receiver) agree on a pattern (e.g., a randomized pattern). This allows the trusted (sensing) device to access information of the received (reflected) wireless sensing signals even if the PSF applies the pattern. Consider Fig.10 , the trusted (sensing) device may refer to a sending device 1000 and a receiving device 1001 which may be co-located or at different locations.

[0100] In another embodiment, the PSF securely receives a pattern (or parameters used to generate the pattern) from an access device (e.g., a gNB) or a wireless sensing transmitter or a wireless sensing receiver.

[0101] In another embodiment, the PSF generates a random pattern of a given length from a seed with the aid of a cryptographically secure pseudo-random number generator, for example by applying a deterministic random bit generator or a function such as SHAKE256 (part of the SHA-3 hash function family).

[0102] In an alternative embodiment, the PSF is arranged to optimize the propagation path between the transmitter of the sensing signal and one or more authorized sensing receivers. In addition to providing gain for the sensing receivers (and potentially allowing lower transmit power), the PSF also directs energy away from the attacker's receiver.

[0103] In another embodiment, multiple PSFs in the vicinity may coordinate themselves or be coordinated by the network to monitor different parts of the spectrum. This is beneficial in the case where the PSFs are narrowband and can use wireless sensing signals in different (wide) frequency bands. When one of the PSFs detects a potential malicious wireless sensing signal, the PSF may report it to the network and / or other PSFs. The PSFs may then monitor / configure themselves (be configured) to act in that particular frequency band.

[0104] In another embodiment, when it is noted that an incoming signal (e.g., signal 1006) is received from a different location than a previously received signal (e.g., signal 1003), typically when the fingerprint of the incoming signal (e.g., signal 1006) is different from the fingerprint of the previously received signal (e.g., signal 1003), the PSF may apply one of the protection measures, for example, applying the random pattern to modulate the signal.

[0105] In another embodiment, the PSF may apply protection measures as described in the present invention. For example, the PSF may apply AI / ML mechanisms to reduce or cope with the interference signal. The PSF may also coordinate the application of the countermeasures with a management entity (such as a RAN entity (e.g., a base station), a network function, or an application) based on a control command or configuration.

[0106] Another possible threat to sensing protection is under-shading, which occurs when an attacker sends a signal that interferes with the sensing signal at the receiver, resulting in symbol errors or signal quality degradation. In one embodiment variant, such an attack may be detectable (and possibly correctable) at the symbol or block level by an error coding system used in a layer above the physical layer. For example, the receiver may employ a cyclic redundancy check (CRC) code, a forward error correction (FEC) code, or other form of integrity check to identify and correct errors in the received signal. Alternatively or additionally, the receiver may use artificial intelligence (AI) or machine learning (ML) techniques to analyze error patterns and / or help detect and correct errors. For example, the receiver may use an error correction neural network to learn a mapping between a corrupted signal and an original signal, or use a classifier to distinguish between legitimate and malicious signals based on their characteristics.

[0107] In another embodiment variant, the device may employ one or more of the following techniques to expose interference or attacks to the sensing signal. One technique is to send an empty or known pseudo symbol, where interference may be expected, such as in the presence of noise, interference, or a spoofed signal. By comparing the received symbol with the expected symbol, the device can detect any difference indicating interference or attack. Another technique is to change the modulation of the sensing signal, especially for sensing signals with different symbol rates or carrier spacings, which can also expose interference or attacks. For example, the device can switch from quadrature phase shift keying (QPSK) modulation to amplitude shift keying (ASK) modulation, or from narrowband to broadband modulation. By doing so, the device can change the spectral characteristics of the sensing signal, which makes it more difficult for an attacker to match or interfere with it. The device can also observe the effect of the modulation change on the quality or error rate of the received signal, which can reveal any anomalies caused by interference or attacks. Depending on the network conditions and sensing requirements, the device can apply these techniques periodically, randomly, or adaptively.

[0108] Different embodiments may be combined with each other as appropriate.

[0109] In the general definition of this embodiment, a method for sensing protection is proposed, which can be implemented in a device suitable for the following operations:

[0110] - receiving or determining (sensing) the presence of a signal,

[0111] - receiving a configuration of countermeasures for increasing the integrity of received signals and a strategy for determining when to apply said countermeasures, e.g. said configuration of a mode,

[0112] - applying the countermeasure, e.g., retrieving or generating a pattern, and using the pattern when at least one of the following occurs:

[0113] - modulate the received sensing signal which is backscattered or reflected, or

[0114] - Sending a time delayed / scaled / modulated copy of the received sensing signal.

[0115] The present invention also relates to a method for increasing signal integrity in a signal transmission network, each signal comprising a sequence of one or more signal elements, wherein the method comprises identifying any injection of signal elements into the received signal based on at least one of a) a signal element amplitude variation and b) an inversion of a permutation operation applied to the received signal when transmitting. As explained above for the corresponding device, the method may for example comprise identifying any injection of signal elements in the received signal by detecting signal element amplitude variations, such as by measuring the signal element amplitude for each signal element of the received signal, the signal element amplitude possibly indicating the signal element energy, and detecting the signal element amplitude variation based on the measured signal element amplitude, and possibly processing the received signal based on any identified injection of the signal element. As described above, the processing may in particular comprise correction of the received signal for the detected attack.

[0116] Furthermore, the present invention relates to a computer program for increasing signal integrity in a signal transmission network, wherein the program comprises instructions for causing a device (in particular the first device) to execute the method.

[0117] Similarly, a method and a corresponding computer program are provided, according to which: a) in order to avoid a successful attack, at least some of the signals in the network are modified before transmission according to a permutation operation and / or a frequency modification operation, the corresponding operations being determined as described above, and / or b) an integrity check is performed on a predetermined portion of the signals in the network, wherein, for a given signal to be transmitted, it is randomly determined whether an integrity check is to be performed on the signal based on the predetermined portion, wherein the integrity check can be performed and / or is of a type as further indicated above.

[0118] It shall be understood that the apparatus of claim 1, the system of claim 13, the method of claim 14 and the computer program of claim 15 have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0119] It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or the above-described embodiments with the respective independent claim.

[0120] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0121] In the following figures:

[0122] Figure 1 schematically and exemplarily shows a communication network,

[0123] Figure 2 Schematically and exemplarily showing an over-shadow attack,

[0124] Figure 3 Schematically and exemplarily showing the use of successive interference cancellation to remove interfering signals, for example, against over-obstruction attacks,

[0125] Figure 4 Schematically and exemplarily showing an under-masking attack,

[0126] Figure 5 schematically and exemplarily shows an apparatus for increasing the integrity of signals exchanged in a signal transmission network,

[0127] Figure 6 schematically and exemplarily illustrating processing of a received signal to correct for an under-shadowing attack,

[0128] Figure 7 Schematically and exemplarily illustrating the processing of a received signal to remove an interfering signal, for example, to avoid a successful under-obstruction attack,

[0129] Figure 8 schematically illustrates an exemplary permutation operation applied to a signal to avoid interfering with the signal (e.g., to avoid a successful under-obstruction attack),

[0130] Fig. 9 schematically illustrates the AI / ML process for removing interfering signals, and

[0131] Fig.10 The use of the present invention is schematically shown. DETAILED DESCRIPTION

[0132] Figure 1 Schematically and exemplarily, a communication network is shown in which the embodiments disclosed herein may be implemented. The exemplary network shown is a cellular telecommunication network, such as a 4G or 5G network, whose terminal / terminal device (referred to as user equipment, or UE for short, in 5G) implements the apparatus according to the disclosed embodiments. Figure 1In the 5G network, the terminals / terminal devices are indicated as receivers Rx, since this is their function to which the subsequent detailed description mainly refers, but it should be understood that they also act as transmitters in the network. Similarly, the base stations of the network (also called gNodeBs or simply gNBs in 5G) are located in the Figure 1 In the example, the terminals / terminal devices are indicated as transmitters Tx because this is their function to which the subsequent detailed description mainly refers, but it should be understood that they also act as receivers in the network. For example, a terminal / terminal device can access different types of services, including voice services and data services, by exchanging signals with a base station of the network.

[0133] Each base station serves and communicates with terminals / terminal devices present in a predetermined area (also called a cell). Figure 1 The base stations are connected to the core network CN managed by the network operator or management entity and control the delivery of services. Each cell is served by a base station, which serves as an interface between the terminal / terminal device and the core network 120. Figure 1 As shown, when multiple terminals / terminal devices are mobile devices that can travel from one network cell to another, therefore, the interface used by a given terminal / terminal device may change over time.

[0134] The terminal / terminal device may communicate with the base station on various radio channels, uplink (from the device to the corresponding base station) and downlink (from the corresponding base station to the device). For example, there may be other radio channels between the terminal / terminal device (e.g., sidelink channels) and between the base stations (e.g., X2 interface), but for simplicity, the radio channels are described in detail in the following. Figure 1 Each terminal / terminal device may perform its functions along any of its channels. However, the main interest may be on the channel connecting it to the respective base station. In particular, the downlink channel may be of interest, in which case the terminal / terminal device may implement an apparatus according to the present disclosure in the form of a receiver Rx, and the base station may implement another apparatus according to the present disclosure in the form of a transmitter Tx.

[0135] Cellular telecommunication networks will evolve to include wireless sensing capabilities, so that the resulting system is capable of both wireless communication and sensing. In such a system, a base station may be able to send and / or receive wireless sensing signals. Similarly, a terminal / terminal device may also be able to send and / or receive wireless signals.

[0136] Figure 2An over-masking attack is schematically depicted, where a transmitter Tx sends a message / signal S, and the attacker sends an interfering, stronger signal kI, so that the receiver Rx receives the signal S+kI. It is assumed that the interfering signal is k times stronger than the signal S, where k>1. Therefore, it is assumed that the amplitudes of S and I are the same. Furthermore, as a characteristic of an over-masking attack, the interfering signal has the same length as the original signal S, i.e. the same number of signal elements, and its timing is determined so that it is received by the receiver Rx at the same time as the signal S. The signal S+kI received by the receiver Rx is the superposition of the signals S and kI, as shown in Figure 2. Figure 2 As shown, signal S appears in front of signal kI, although there is actually no "front" or "back" in the superposition.

[0137] Figure 2 The signal S in is a modulated or coded signal. Thus, as is usual for conveying information via signals, the transmitter Tx has applied a transmission transformation in the form of a modulation or coding operation to the corresponding carrier or base signal. Figure 2 As shown, in order to extract the information conveyed via the signal S, the receiver Rx applies a demodulation or encoding operation, respectively, to the received signal, which in this case is the superimposed signal S+kI. A receiver that receives and demodulates / decodes the signal S+kI will typically obtain a signal whose phase and amplitude are different from the signal S, depending on the relative proportions of S and I at the receiver. In an extreme example where S is a phase- or frequency-modulated signal and the amplitude of kI is sufficiently greater than S, the receiver will tend to obtain the signal I due to the capture effect, where the obtained signal I corresponds to a demodulated or decoded version of the signal kI sent by the attacker, which is down-modulated to the amplitude of the signal S sent by the transmitter Tx.

[0138] An exemplary case of an over-obscuration attack would be that an attacker attacks a broadcast message sent by an LTE base station acting as a transmitter Tx by modifying the broadcast message over the air by injecting a strong signal, which can be represented as kI as described above. Therefore, any user equipment (UE) device that receives such a broadcast as a receiver Rx is affected because they will decode the wrong signal. In this case, an over-obscuration attack may be used to modify certain fields in an LTE or 5G broadcast message, especially in low-signal transport layers or during initial communications because they are not integrity protected. It has been shown that any downlink service in an LTE system can be over-obscured. Conversely, an attacker may also attack a base station that receives a message sent by a UE. In this case, the UE can be a transmitter Tx and the base station can be a receiver Rx.

[0139] It has been discovered that a signal that has been hit by an over-obstruction attack can be recovered using a technique called Successive Interference Cancellation (SIC). SIC is the basis for the non-orthogonal multiple access that has been discussed for use in 5G. The original SIC concept was first proposed in Figure 3 Shown in.

[0140] As far as extracting signal I from the superimposed signal S+kI is concerned, Figure 3 Corresponds to Figure 2 However, in this case, the receiver Rx is configured to modulate or encode the signal I again, respectively, and to subtract the resulting signal from the original received signal S+kI. Figure 3 As shown, two signal processing chains can be formed in the receiver, wherein the signal S+kI can be demodulated / decoded along the first signal processing chain and then modulated / encoded again, and before being demodulated / decoded along the first signal processing chain, the signal S+kI is saved along the second signal processing chain. The two signal processing chains can be combined by subtracting the signal generated by the first signal processing chain from the signal generated by the second processing chain, wherein the second processing chain is only the received signal S+kI. The signal resulting from this subtraction is the signal S originally sent by the transmitter Tx, that is, the undisturbed signal. As shown Figure 3 As shown, a demodulation or decoding operation may then be applied to the signal in order to extract the information to be conveyed therefrom.

[0141] Split the signal processing chain into Figure 3 The first signal processing chain and the second signal processing chain shown are examples of what has been further described above as copying the received signal into a first copy and a second copy. Figure 3 shown and in Figure 6 Signal subtraction can be achieved by first inverting the signal to be subtracted (ie, obtaining its opposite version) and then adding the signals, by repeating accordingly in .

[0142] As already mentioned at the beginning, just like the over-masking attack, the under-masking attack also exploits the capture effect, but the interference signal of the under-masking attack coincides with the original signal only at different signal elements. Figure 4 An under-masking attack is schematically and exemplarily shown, where it can be seen that, compared to an over-masking attack, in the under-masking attack the injected signal kI affects only certain bits / symbols of S, i.e., only certain signal elements in a sequence of signal elements co-occurring in signal S.

[0143] It has been found that under-masking attacks may be more difficult to detect than over-masking attacks, since the total energy of the interfering signal may be relatively low, in particular lower than the total energy of the original signal. In contrast to over-masking attacks, the corrupted signal is therefore indistinguishable from the uncorrupted signal in terms of its total energy. In addition, Figure 3The SIC shown can no longer be successfully applied, since by this subtraction the complete / original signal element will be lost. It has therefore been proposed to use digital signatures in the Master Information Block (MIB) used in LTE to avoid under-obscuration attacks, and / or to modify the SIC in order to correct for under-obscuration attacks. However, there remains a need to increase the integrity of the signal in networks subject to attacks such as over-obscuration, and in particular under-obscuration attacks. Reference Figures 5 to 8 , a specific embodiment that addresses this need will be described. However, it should be noted that reference has been made to Figure 3 The described apparatus for processing a signal by SIC in order to correct an identified over-shadowing attack can increase signal integrity in a signal transmission network, e.g. Figure 1 Such an arrangement therefore forms another embodiment and may in fact be regarded as a "basic" embodiment.

[0144] Figure 5 A device for increasing signal integrity in a signal transmission network is schematically and exemplarily shown. The specific device shown (which may be a receiver of the network or a part of a receiver of the network) includes a measuring unit, an identification unit and a processing unit, although each of the three units may be unnecessary in other embodiments. The measuring unit (which may include a sensor) is configured to measure the amplitude of the signal elements of the received signal and forward them to the identification unit or provide them for access by the identification unit. The identification unit is configured to identify any injection of the signal elements in the received signal, in this case, based on the signal element amplitude change (i.e., the change of the signal element amplitude measured by the measuring unit). The processing unit is configured to process the received signal based on any identified injection of the signal element, i.e., in this case, if the injected signal element has been identified by the identification unit, and if identified, based on the injected signal element, such as, for example, based on their amplitude and / or position in the signal element sequence.

[0145] Figure 6 A device for increasing signal integrity in a signal transmission network is also schematically and exemplarily shown in the form of a receiver Rx, wherein each signal comprises a sequence of one or more signal elements, and wherein the device comprises a processing unit configured to process any received signal. The processing unit (also referred to as a processor) is Figure 6 Not shown in the figure, but the processing steps implemented by the processing unit are shown. Figure 6 can be understood as Figure 5 A more contextual description of an apparatus of the type shown, wherein Figure 6 The focus is on the processing steps that may be performed by the processing unit, which may also be understood and implemented independently of the measuring steps and the identifying steps that may be performed by the measuring unit and the identifying unit, respectively. Figure 5 and Figure 6 The receiver is shown as an exemplary arrangement, rather than being located in the receiver Rx, but the processing unit may also be located partly or completely elsewhere, wherein the receiver then forwards the received signal to the processing unit, possibly after some initial processing steps including demodulation or decoding.

[0146] The processing unit is configured to process the received signal based on any identified injection of the signal element. In particular, while Figure 6 The processing steps indicated in are shown as if they were fixed, i.e. as if they were always performed and for all received signals, which may not be the case. Instead, the processing unit may be configured to perform the processing steps shown only upon request, such as upon request by the transmitter Tx or a central management entity in the core network CN, and / or only when an injection of one or more signal elements in a signal previously sent via the network (in particular, a signal previously received by the receiver Rx) has been identified. Furthermore, in order to identify the injection of signal elements (such as due to an over- or under-masking attack), the receiver Rx may (although as already indicated, not necessarily) comprise: Figure 5 As shown, a measuring unit is configured to measure, for each signal element of the received signal, a signal element amplitude, said signal element amplitude being indicative of a signal element energy or a related quantity; and further, an identification unit is configured to identify any injection of signal elements into the received signal by detecting signal element amplitude changes based on the measured signal element amplitudes. The signal element amplitudes used as a basis may refer to amplitudes of signal elements within a single received signal or across signals. Thus, for example, the signal element amplitudes of at least one of the following may be compared with each other to detect significant amplitude changes: a) a given sequence of signal elements of the received signal and b) a sequence of signal elements comprising a signal element of the received signal and one or more corresponding signal elements of previous repetitions of the received signal. Although Figure 3 and Figure 6 , but the measuring unit and the identifying unit may be located before the elements indicated for the receiver in the signal processing chain. For example, the identifying unit may be configured to identify the presence of an over-masking attack if all measured signal element amplitudes of the received signal measured by the measuring unit deviate from the expected signal element amplitudes by at least a predetermined amount; and to identify the presence of an under-masking attack if one or more measured signal element amplitudes of the received signal measured by the measuring unit deviate from the expected signal element amplitudes by at least a predetermined amount.

[0147] In order to identify under-masking attacks on a repetitive signal S, the measuring unit may be configured to measure the signal element amplitudes over several repetitions of the signal S, wherein the identification unit may be configured to calculate an average signal element amplitude for each signal element over several repetitions of the signal S, and to identify any injection of the signal element based on a variation of the average signal element amplitude, wherein the variation may be detected based on a statistical test of whether the average signal element amplitude corresponds to an assumed uniform distribution. If the signal is a non-repetitive signal, only the signal element amplitudes of the respective signal itself may be used, i.e. without an average value. The identification unit may also be based on an AI / ML model integrated in the signal receiver, wherein the model may be designed to classify the received signal / signal element as being subject to interference.

[0148] Figure 6 To some extent corresponds to Figure 3 , i.e., the original signal sent by the transmitter Tx is again represented by S, and the interference signal sent by, for example, an attacker is again represented by kI. Figure 6 In the example, the combined (i.e., superimposed) signal S+kI of the two signals S and kI received by the receiver Rx is represented by S2, i.e., S2=S+kI. Figure 3 , in the embodiment shown, the receiver Rx is configured to subtract the processed version of the signal S2 from the signal S2 itself, optionally in case the presence of an attack (which is now an under-shaded attack) has been identified.

[0149] Again similar to Figure 3 , the subsequent processing is performed by means of two separate signal processing chains, wherein a first signal processing chain actually processes the signal S2, a second signal processing chain saves the signal S2, and the two signal processing chains are combined by subtracting the processed version of the signal S2 from the saved (or unprocessed) version of the signal S2. Figure 6 In an embodiment, the processing applied along the first signal processing chain differs from Figure 3 The processing shown, although still the same with respect to the first demodulation / decoding step. The subsequent processing can also be based on an AI / ML model that is able to process the incoming signal and perform demodulation / decoding in a way that ignores interfering signals.

[0150] exist Fig. 9 In the exemplary embodiment shown, an apparatus may be used in a wireless transceiver. Fig. 9, 905 represents an antenna for receiving transmission information, 902 represents a modulation / demodulation block, 903 represents a MIMO block for implementing transmission / reception through multiple antennas, 904 represents a reception / transmission processor, 906 represents a data source / data sink, and 901 represents one or more AI / ML models for managing 902, 903, and 904, wherein control is managed by block 900. The apparatus may be applicable to wireless communication devices, such as 3GPP wireless communication devices. A first AI / ML model may be trained to distinguish / infer whether an original received signal includes two or more overlapping signals, for example, based on the output of block 902. A second AI / ML model may be trained to distinguish whether a signal is received from multiple different directions, for example, based on the output of block 903. A third AI / ML model may be trained to separate two or more signals given the inferred information from the first model and / or the second model.

[0151] In a variant embodiment, the first AI / ML model is able to distinguish whether one, two or more signals are received by analyzing the modulation constellation (e.g., 16-QAM) and analyzing whether there are one, two or more overlapping modulation constellations. These analyses can also return relative received signal strengths, which in turn can allow one signal to be extracted from another signal.

[0152] In another embodiment variation, the second AI / ML model may be able to distinguish between reception directions of different signals.

[0153] In another embodiment variation, the third AI / ML model may be capable of extracting one or more signals from the original received signal.

[0154] In another embodiment variation, the AI / ML model may be able to determine whether the one or more signals contained in the original received signal are multipath signals arriving with different phases / delays / signal strengths based on the corresponding path channels, and the AI / ML model may be able to indicate the relative signal strength, phase, delay, ..., so that box 904 performs alignment of the signal.

[0155] In another embodiment variation, the AI / ML model may be able to distinguish the type of interference, for example, injection attacks (such as over-shading or under-shading attacks), or multipath, etc., and return an indication of the cause.

[0156] In another embodiment variation, the AI / ML model may have been trained with a data set representing the situation to be inferred, for example, with a data set including over-obscuration attacks, under-obscuration attacks, multi-path, etc.

[0157] In another embodiment variant, the apparatus may receive an indication regarding application of one or more AI / ML models from a management entity such as an access device (e.g., a base station such as a 5G gNB) or a network function or an operation, management, and maintenance function in a core network, wherein the indication may include an identifier indicating the AI / ML model to be applied.

[0158] In another embodiment variant, the device may be capable of receiving an AI / ML model from a management entity as previously defined.

[0159] In another embodiment variation, the AI / ML model may be a neural network, such as a convolutional neural network (CNN) or a recurrent neural network (RNN). A convolutional neural network may allow the received symbol to be determined in a modulation. If interference occurs and a symbol is hidden by the interference, the CNN may still allow the symbol to be recovered because it is trained or adapted to recognize symbols of a given size / strength. Symmetrically, the RNN maintains a memory of the output of previous calculations. The RNN may also keep track of the received signal strength of the signal so that the inference of the next processed symbol may take it into account to remove the interfering signal and / or give an indication of the interfering signal.

[0160] In another embodiment, a device implementing the technology described in the present invention and allowing determination of the potential injection of interference signals or the impact of interference and a technology allowing removal of the interference can be applied when a management entity (e.g., RAN equipment (such as access equipment), NF in a core network, OAM, etc.) is configured, wherein the application can be completed for:

[0161] - for requests based on measurements provided by said device, and / or

[0162] - Where the configured policy determines the conditions for the technology to be applied, an analysis of whether the conditions are met by the device.

[0163] In another embodiment, the measurements / conditions sent to the management entity or triggering the execution of the configured policy may include one or more of the following:

[0164] -degrade the quality of communication,

[0165] - an increase in the amount of communication errors,

[0166] - detect changes in the fingerprint of the received signal,

[0167] -An unexpected signal was detected.

[0168] exist Figure 6 In the exemplary embodiment schematically shown, the demodulated / decoded signal is referred to as S3=d (-1)S+dI. In this notation, d is a binary signal with a length of S, such that d is 1 in the time slots (e.g., time / frequency) that affect S (when I has a value different from 0) and 0 otherwise. Signal d (-1) is the inversion signal of d, and therefore explicitly sets the value of S affected by I to 0, and sets the value not affected by I to S. The term "inversion" refers to binary inversion or complement, so that d (-1) It is zero when d is 1, and vice versa.

[0169] Depending on whether a signal element of the signal S3 (which may in particular be a symbol) has been identified as an injected signal element by the identification unit based on, for example, a change in the signal element amplitude (which may in particular be the symbol energy), the signal element of the signal S3 is scaled. In case the injected signal element is identified based on the signal element amplitude, it can also be said that the signal element is scaled based on the signal element amplitude of the signal element. In this way, the identification of the injected signal element can be considered to remain implicit.

[0170] The result of this scaling operation is Figure 6 S4 = ad (-1) S+bdI represents. Thus, the signal elements that have been identified as originating from the transmitter Tx are scaled by a predefined factor a, while the signal elements that have been identified as originating from the attacker are scaled by a different predefined factor b. Preferably, the factors a and b are selected such that 0≤a<1 and b>k-1.

[0171] In order to obtain a and b, it is necessary to normalize the signal S2 by dividing the signal element amplitude of each signal element of the signal S2 by the signal element amplitude of the signal element with the lowest signal element amplitude. If each symbol in S2 can be received with two energy levels, as is the case when binary thresholding of the received signal is performed, then after normalization, the energy level of each symbol in S2 is either 1 or k. In the above description, in particular Figure 6In , a signal S2 that has undergone binary thresholding and normalization is assumed and shown. This assumption is reasonable because the processing unit can be configured so that the processing of the received signal includes thresholding the signal elements to predefined signal element levels, the predefined signal element levels at least including: an injection level indicating the injected signal element amplitude and an uninjected level indicating the uninjected signal element amplitude, wherein the signal elements are scaled according to their signal element levels. The injection level can be selected to include all reasonable signal element amplitudes that will be applied by the attacker, and the uninjected level can be selected to include all signal element amplitudes of the usual signal traffic in the network. The normalization can be performed relative to a lower uninjected level so that a factor k will appear, which indicates the ratio between the representative amplitude of the injected level and the representative amplitude of the uninjected level, respectively.

[0172] according to Figure 6 In an embodiment, before the second demodulation / decoding, a scaled version of S3 is subtracted from S2, ie, S4=ad (-1) S+bdI, we get S5=S+kI–(ad (-1) S+bdI)=(1-ad (-1) )S+(k-bd)I. Thus, a difference signal S5 is formed based on an unprocessed version S2 of the received signal and a processed version S4 of the received signal corresponding to the received signal resulting from the thresholding and scaling. If S3 is scaled according to the condition b>k-1, the signal element at the injected level is scaled to be above the level difference k-1, which indicates the amplitude difference between the injected level and the uninjected level. This has the following effect: in the difference signal S5, at the positions in the sequence of signal elements where signal elements have been injected by the attacker, the amplitude of the part coming from the original signal S will be higher than the amplitude from the injected part. In this way, again similar to SIC, the original signal S can be retrieved in a second and final demodulation / decoding step. In Figure 6 , the result of this last demodulation / decoding corresponding to the original signal S is denoted by S6, i.e. S6=S in this case. Note that if a valid signal S6 is recovered, this (also) gives a detection indication, i.e. an indication of an ongoing attack. This illustrates that the processing unit and the identification unit may in practice be a single unit.

[0173] As a reference above Figure 3 and Figure 6In addition or as an alternative to the described processing of the received signal, in order to counter attacks such as over-shading attacks and under-shading attacks, avoidance strategies may be implemented. For this purpose, a device in the form of a receiver Rx may again be used, in particular in combination with a corresponding device, which may be in the form of a transmitter Tx comprising a permutation unit for permuting the signal to be transmitted. A specific way of avoiding the attack is to permute the signal according to a permutation operation known to the transmitter and the receiver but unknown to the attacker.

[0174] Figure 7 and Figure 8 Schematically and exemplarily, the case where the permutation operation is encoded as a permutation indication signal portion is shown. In this case, the permutation indication signal portion corresponds to a permutation mask M (which is at least one bit long) and determines the bit arrangement in the signal S. The permuted version of the signal S can be represented as P(S, M), i.e. a function P according to the original signal S and the permutation mask M. In other words, according to the illustrated embodiment, the physical (e.g., time / frequency) arrangement of signal elements (such as symbols / bits) in the transmitted signal / message S is based on the mask M, wherein the signal S in its permuted form is transmitted in combination with the mask M. The permutation mask can also be based on a codebook, wherein the permutation mask field includes an identifier indicating the permutation used.

[0175] Preferably, the mask M is appended to the end of the signal. In this case, as shown in the figure, the combined transmitted signal can be expressed as S1=P(S,M)|M. In a variant, the mask M is included at the beginning of the signal, which can have the following advantages: the receiver does not need to buffer the entire signal before processing the signal. In another variant, one or more masks M can be added to the signal, wherein each of the masks indicates a permutation performed only on the corresponding part of the signal. For example, if a signal containing N symbols is sent, the first (group, not necessarily continuous) N / 2 symbols can be subjected to a permutation determined by a first mask, and the second (group, not necessarily continuous) N / 2 symbols can be subjected to a second permutation determined by a second mask.

[0176] Furthermore, preferably, the mask M is set randomly, in particular individually for each signal. However, the mask M can also be set according to predefined regulations accessible to the sender and the receiver, but at least not open to attackers. The random mask M can also be retained for a predetermined period of time, wherein only after the period of time has passed, a new mask M to be used is randomly selected.

[0177] When M is sent at the end of S1 and is set randomly, the attacker injecting the signal does not know how / when to modify the bits, and the attacker must guess how to under-mask the signal S. If M is 1 bit long, this leads to a 50% success rate. If this is applied to multiple messages, the communication is unstable, causing the receiver (Rx) to discard the communication. Since the receiver may notice that 50% of the messages are decoded in an unsuccessful way, the attacker will be forced to over-mask the entire signal, in particular including the mask M. These over-masking attacks can then be detected again, for example by analyzing the measurement of the transmitted power (i.e. the overall amplitude of the received signal).

[0178] Figure 7 It is shown how the transceiver Tx sends a combined signal S1, wherein an attacker tries to inject a signal kI that interferes with S1. This results in a signal S2 = P(S, M) | M + kI, wherein the interfering signal kI affects, for example, certain symbols of S1.

[0179] After demodulation / decoding, the receiver (Rx) obtains the signal S3 = d from S2 (-1) P(S,M)|M+dI. S3 is then permuted or restored by the receiver according to the received mask M, which results in a signal S4=P (-1) (S3',M), where S3' is equal to S3, until the permutation mask at the end is removed and P (-1) refers to the inverse function of P. S3' can also be written as d (-1) P(S,M)+dI, such as Figure 7 shown.

[0180] S4 shows how to permute or restore the permutation of the injected signal I based on M. This will turn the injected signal I back into a pure interference signal. That is, without knowing the permutation mask M, the attacker will no longer be able to inject the bits at the expected position. On the contrary, the injected bits will be permuted, which will destroy the meaning / correctness of the attacked signal like an ordinary interference signal, which may cause signal reception interruption. For example, the receiver can be configured to perform an integrity test (such as a cyclic redundancy check (CRC)) on, for example, the received signal and discard any signal that does not pass the integrity test. Due to the (reversal) permutation, signal S4 will not pass a check such as a CRC.

[0181] The mask M may affect the signal S at different steps of the modulation / coding process. For example, it may refer to a permutation of the incoming bit string corresponding to the signal at the physical layer, or to a permutation at a different layer in the communication stack. For example, it may refer to a permutation in the mapping of the Orthogonal Frequency Division Multiplexing (OFDM) carrier or the Quadrature Amplitude Modulation (QAM) symbols used in the transmission of S.

[0182] Figure 8 An exemplary message S comprising 8 bits is shown at the top. The sender transforms the message S by appending a mask bit M at the end of the message. In the example shown, when M=1 (which corresponds to Figure 8 In the middle case of ), S1 = Rotate(S)|M, where the Rotate() loop rotates S. In this example, when M = 0 (which corresponds to Figure 8 In the bottom case, S1 = S|M. Therefore, in this particular case,

[0183]

[0184] As further mentioned above, the permutation operation can not only be encoded as a permutation indication signal part like a mask M, wherein the permuted signal is sent in combination with the permutation indication signal part. Additionally or alternatively, the permutation operation can be encoded into the physical parameters of the corresponding signal and / or defined according to one or more communication parameters of the network. In addition, the permutation operation according to which the first signal to be sent is permuted can be encoded as a permutation indication signal part, which is sent in combination with the second permutation signal. Thus, for example, when the transmitter Tx continuously sends a first signal S to the receiver Rx and then sends a second signal S' to the receiver Rx, the mask M for S can be sent in combination with S', and vice versa.

[0185] In another embodiment, the transmitted signal may be transmitted in a default known frequency / time resource, but with a given frequency / time offset known only to the transmitter and the responder. For example, if the resources allocated for transmitting the signal are in a time resource block between t0 and t1 and in a frequency resource block between f0 and f1, the actual frequency resource used may be between f0+df and f1+df. Similarly, the actual time resource used may be between t0+dt and t1+dt. In this case, dt and df may be securely exchanged or agreed upon between the transmitter and the receiver, or securely assigned to the transmitter and the receiver. Similarly, dt and df may also be variable parameters, i.e., they may change each time a signal is exchanged between the transmitter and the receiver. Here, "securely" refers to confidentiality protection and / or integrity protection and / or replay protection, etc.

[0186] In a different embodiment related to the previous embodiment, frequency and / or time resources used to exchange signals between a transmitter and a receiver (e.g., frequency resource blocks between f0 and f1 and time resource blocks t0 and t1) can be securely exchanged or agreed upon between the transmitter and the receiver, or securely allocated to the transmitter and the receiver.

[0187] In addition, the shift of the signal element in time and / or frequency can be performed by a permutation unit of the transmitter Tx and thereafter reversed by the receiver Rx (particularly the identification unit). These shifts can be considered as special cases of permutation. In addition, it should be emphasized that no signal permutation measurement is necessarily taken constantly. On the contrary, it is more effective to configure the permutation unit so that the permutation unit permutes the signal to be transmitted only when the injected signal element is identified in the received signal based on the signal element amplitude change. The corresponding notification or request can be sent from the receiver Rx to the transmitter Tx.

[0188] refer to Figure 7 and Figure 8 , specific ways for permuting a signal have been described. In fact, it has been found that all of these ways are not only suitable for avoiding attacks, but also for detecting attacks. Therefore, in addition to using the change in the amplitude of the signal element as the basis for detecting any injection I of the signal element in the received signal, the identification unit can also be configured to use the inversion of the permutation operation applied to the received signal when sending as its basis. The identification unit is then preferably configured to permute the received signal according to the inverted permutation operation and to perform an integrity check on the permuted received signal. Whether the integrity check returns a positive result or a negative result can then be regarded as an indicator of any attack launched on the received signal (in particular, on a selected signal element in the signal element sequence of the signal) without knowing that the signal has been permuted.

[0189] Although integrity checks may be used particularly in conjunction with permutations of signals for detecting attacks, it may be equally beneficial to perform integrity checks in their own right. Regardless of whether they are performed in conjunction with signal permutations, the identification units may be configured to perform integrity checks on predetermined portions of signals S in the network, wherein, for a given signal S to be sent, a random determination is made as to whether an integrity check is to be performed on the signal based on the predetermined portion. The receiver Rx and the transmitter Tx may collaboratively agree on whether an integrity check is to be performed on a given signal. Then, for any signal S for which an integrity check is to be performed, an integrity indication signal portion may be sent in conjunction with the signal S, wherein the identification unit may be configured to verify the integrity of the signal S upon receipt of the signal based on the integrity indication signal portion. Similar to the method described by Figure 8The permutation indication signal portion exemplified by the mask M shown in , the integrity indication signal portion may be formed by additional signal elements, such as bits or symbols included in the corresponding signal in addition to bits or symbols encoding the actual message to be transmitted with the signal. In a specific example, the combination of the transmitted integrity indication signal portion and the signal S may be formed by including the integrity indication signal portion in the corresponding signal, wherein if it is determined that the amplitude of one or more signal elements of the integrity indication signal portion exceeds a predetermined threshold, a conclusion of lack of integrity may be drawn when the signal is received.

[0190] The embodiments disclosed herein have been discovered based on the following recognition: there are no good solutions in the prior art to 1) detect, 2) avoid or 3) deal with / recover from interference signals, for example, interference signals injected by an attacker with the aid of over-masking attacks and / or under-masking attacks. Attacks based on signal injection (such as over-masking attacks and under-masking attacks, i.e., attacks in which an attacker injects a signal that over-masks / under-masks a message sent by a transmitter so that a receiver decodes the modified message) are becoming increasingly important in wireless communication systems (such as LTE and 5G). Such injection attacks are also expected to be applicable to wireless sensing systems. These techniques may also be applicable when dealing with other interference signals (e.g., due to multipath or due to interference).

[0191] Detecting an attack may refer to, for example, detecting that there is an ongoing attack, avoiding an attack may refer to, for example, making it infeasible for an attacker to perform the attack, and countering an attack may refer to, for example, being able to receive the actual message, i.e., the original signal, in the event of an attack. According to the disclosed embodiments, 1) the presence of an attack may be detected by monitoring the traffic for a persistent signal with a higher signal amplitude (higher "received signal") over the entire signal (message) or certain elements (portions) of the signal or using an AI / ML model, 2) the attack may be prevented (i.e., avoided) from occurring or its impact may be limited by including in the signal a mask that determines the arrangement of bits / symbols in the signal, wherein the mask may indicate a permutation, and / or 3) the desired signal may be recovered (thereby countering the attack) by performing successive interference cancellation (SIC) on the received signal and additionally using the primary signal (i.e., the received signal), by scaling on a signal element-by-signal basis, or by removing the attacker's signal (particularly, which may be an over-obscured / under-obscured signal) using an AI / ML model trained to recover the interfered signal. It has been found that any single method of these methods 1) to 3) and any combination thereof can improve the security of wired and wireless communications, especially when subjected to over-shading and / or under-shading attacks.

[0192] When the above embodiments are implemented on a receiver, the receiver may perform a test to determine whether the symbols or other signal elements in one or more received signals follow an expected distribution and / or whether the original received signal contains multiple signal components. If the test is negative, the receiver may be able to trigger an action based on a configured policy. The receiver may be configured to receive a configuration policy sent by a management entity (e.g., a 5G core network or a radio access network). In addition, the receiver may be configured to activate the policy when the policy is received, or to activate a policy or a portion thereof, such as certain rules, when a given situation is detected. The action may include applying an AI / ML model to remove interference signals and / or SIC when decoding at least one of the received signals, wherein the previously decoded signal is scaled element by element. The scaling factor for scaling may depend on a normalized version of the received signal in an element-by-element manner. The action triggered when the test is negative may include requesting the transmitter to permute the transmitted signal based on a permutation indicator (which may be considered a mask). For example, a mask may be attached to the transmitted signal. Alternatively, the action triggered in the event of a negative test may include applying a permutation indicator (mask) to permute any signal sent by the receiver itself when acting as a transmitter. In addition, for example, the permutation indicator used by the receiver when acting as a transmitter may be appended to the signal. In another alternative, the action triggered by a negative test may include rejecting the received signal or triggering an alarm.

[0193] Any countermeasures against attacks such as over-masking attacks and / or under-masking attacks may be taken generally or only in the case where the presence of such attacks is actually detected. Therefore, some of the above-described embodiments are intended to detect over-masking attacks / under-masking attacks by monitoring, for example, changes in the received SNR between different messages S. If an attacker injects a signal I or several signals I1,…,IM to modify (certain symbols of) S or several signals S1,…SM, the receiver will receive those messages affected by the signal I (or I1,…,IM), which have higher energy levels than those signals S (or S1,…,SM) (signal elements in, i.e., for example, symbols) that are not affected by I. Therefore, specific methods for implementing these embodiments include: a) tracking the energy of each symbol from a plurality of received signals S, and b) calculating whether the energy level of the signal symbol follows a uniform distribution, for example by means of a statistical test (e.g., a p test). These embodiments may be performed by the receiving device if the receiving device performs the above-described checks / tests itself.

[0194] It should be understood that the techniques described with reference to any of the above embodiments may be combined. For example, according to a first combination option, a) the receiver may be configured to measure the amplitude of a signal element of the received signal, and to detect the presence of an attacker, test whether the amplitude of the measured signal element within and / or across the received signal or its time average satisfies an expected distribution. This input may also be used as an input to an AI / ML model for determining the presence of an interfering signal. If an attacker is detected in this manner, the receiver may be configured to apply continuous interference cancellation or an AI / ML model, in particular with reference to Figure 6 The adaptation form described above is used to recover a desired signal that is being modified by an attacker or is noisy when received. In addition, upon detecting an attacker, the receiver can be configured to process the received signal itself based on a predefined permutation operation to prevent the attacker from interfering with the signal exchanged with the transmitter (which can be a user equipment (UE)), and / or request the transmitter to utilize the same permutation operation when transmitting a signal.

[0195] According to a second exemplary combination option, the receiver may be configured to apply successive interference cancellation and / or an AI / ML model, in particular with reference to Figure 6 The adaptation form described above is used to recover the desired signal modified by the attacker. Then, if one or more potential desired signals (i.e., one or more signals that appear to be uncorrupted) are detected, the receiver can test whether the measured signal element amplitudes or their time averages of one (or more) potential desired signals within and / or across one (or more) received signals satisfy the expected distribution to confirm that the received signal is indeed uncorrupted or has actually been attacked. Additionally, when an attacker is detected, the receiver can be configured to process the received signal itself based on a predefined permutation operation to prevent the attacker from interfering with the signals exchanged with the transmitter (which may be a user equipment (UE)), and / or request the transmitter to utilize the same permutation operation when sending a signal.

[0196] In a particular embodiment, a system in the form of one or more UEs is proposed, wherein the device acting as a receiver is configured to collect information or statistics about the received signal S and send them to a management agency (e.g., a base station or network function in a core network) so that the system can determine the presence of an attacker. The collected relevant information may include any parameters involved in the embodiments disclosed herein, raw or processed, such as the signal strength of each symbol or the results of a statistical test related to the uniformity of the energy of the received signal symbols. The network / core network can use the received information to provide a specific configuration to the UE, which determines the type of technology to be applied to deal with the interfering signal, for example, applying a given permutation or using a given AI / ML model customized for a specific type of interference.

[0197] Once again, when testing whether the signal elements in one or more received signals follow the expected distribution, any of the above actions that the receiver can take when a negative test result is obtained can also be taken independently of any test. In other words, actions can be taken continuously alternatively. Then, only tests corresponding to the identification of any injected signal elements can be optionally added. Choosing between taking actions independently or according to tests (i.e., independently or according to whether an attack has been detected) can be considered a compromise between security and efficiency. This desired compromise can be specified in a policy that may have been configured in the corresponding device. The test can also refer to a test of whether the received signal includes an interfering signal (not necessarily with malicious intent).

[0198] Furthermore, although the above embodiments have been described focusing on over-masking and under-masking attacks, these embodiments may equally well be applied as measures against any other attack that works similarly to over-masking and under-masking attacks, in particular based on signal element injection exploiting capture effects, for example in the context of wireless communications or sensing.

[0199] The above-described embodiments may be applied to different types of multiple access, such as Orthogonal Frequency Division Multiple Access (OFDMA) or Rate Division Multiple Access (RSMA) or Orthogonal Angular Momentum (OAM) systems.

[0200] The above embodiments can be applied to different types of networks, such as cellular systems, Wi-Fi networks, ultra-wideband systems. The above embodiments can also be applied to different types of networking infrastructures, such as terrestrial networks and non-terrestrial networks, using smart repeaters or reflective smart surfaces for range extension, etc.

[0201] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0202] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. Furthermore, it should be understood that expressions involving the phrase "at least one of..." and the following one or more elements or features are to be understood in an inclusive disjunctive sense. For example, the expression "at least one of A, B and C" is to be understood to mean "A and / or B and / or C".

[0203] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0204] Processes such as measurement of signal element amplitudes, identification of signal element injections, any further processing of received signals, permutations of signals to be transmitted, etc., which are performed by one or several units or devices, may be performed by any other number of units or devices. These processes may be implemented as program code units of a computer program and / or dedicated hardware. However, these processes and any methods following any combination thereof are also disclosed herein independently of how they are implemented.

[0205] The computer program may be stored / distributed on suitable media (such as optical storage media or solid-state media) provided together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0206] Any reference signs in the claims should not be construed as limiting the scope.

[0207] The present invention relates to a device for increasing signal integrity in a signal transmission network, each signal comprising a sequence of one or more signal elements. The device comprises an identification unit configured to identify any injection of a signal element into a received signal based on at least one of: a) a change in the amplitude of the signal element, and b) an inversion of a permutation operation applied to the received signal when transmitting. This allows injection of signal elements due to capture effects to be reliably identified. In particular, not only over-masking attacks can be identified, but also under-masking attacks or other injection attacks or interferences can be identified. By processing the received signal based on any identified injection / interference of the signal element, the signal integrity in the network can be improved.

Claims

1. A device (Rx) for increasing the integrity of a signal (S) in a signal transmission network, each signal (S) comprising a sequence of one or more signal elements, wherein: The device (Rx) comprises an identification unit configured to identify any injection (kI) or interference into a signal element in the received signal based on at least one of: a) a signal element amplitude change, b) an inversion of a permutation operation (P) applied to the received signal when transmitting, c) a signal fingerprint, d) the location of the transmitter, and e) an AI / ML, artificial intelligence / machine learning model.

2. The apparatus (Rx) according to claim 1, further comprising a processing unit configured to process the received signal based on any identified injections or interferences of signal elements.

3. The device (Rx) according to claim 2, wherein The processing of the received signal comprises scaling signal elements of the received signal depending on whether the signal elements of the received signal have been identified as injected signal elements.

4. The device (Rx) according to claim 2 or 3, wherein: The processing of the received signal includes using an AI / ML model to recover the interfered signal.

5. The device (Rx) according to claim 2 or 3, wherein: The processing of the received signal comprises thresholding the signal elements to predefined signal element levels, the predefined signal element levels comprising at least an injected level indicating an injected signal element amplitude and a non-injected level indicating a non-injected signal element amplitude, wherein the signal elements are scaled according to the signal element levels of the signal elements.

6. The device (Rx) according to claim 5, wherein The processing involves forming a difference signal (S5) based on an unprocessed version of the received signal and a processed version of the received signal corresponding to the received signal resulting from the thresholding and scaling, wherein the scaling comprises scaling the signal elements at the injected level to above a level difference indicating an amplitude difference between the injected level and the uninjected level.

7. The device (Rx) according to any of the preceding claims, wherein In order to identify signal elements or any injection of interference (kI) in the received signal based on signal element amplitude changes, the identification unit is configured to detect the signal element amplitude changes in at least one of the following: a) the sequence of signal elements of the received signal, and b) a signal element sequence comprising the signal element of the received signal and one or more corresponding signal elements of previous repetitions of the received signal.

8. The device (Rx) according to any of the preceding claims, wherein In order to identify signal elements or any injection of interference (kI) in the received signal based on the inversion of the permutation operation (P) applied to the received signal when sending, the identification unit is configured to permute the received signal according to the inverted permutation operation and to perform an integrity check on the permuted received signal.

9. The device (Rx) according to any of the preceding claims, wherein The identification unit is configured to perform an integrity check on a predetermined portion of a signal (S) in the network, wherein for a given signal (S) to be transmitted, whether to perform the integrity check on the signal is randomly determined based on the predetermined portion.

10. The device (Rx) according to claim 9, wherein For any signal (S) for which an integrity check is to be performed, an integrity indication signal portion is sent in combination with the signal (S), wherein the identification unit is configured to check the integrity of the signal (S) based on the integrity indication signal portion when receiving the signal.

11. The device (Rx) according to claim 10, wherein The combination of the transmitted integrity indication signal portion and the signal (S) is formed by including the integrity indication signal portion in the corresponding signal, wherein a lack of integrity is concluded when the signal is received if the amplitude of one or more signal elements of the integrity indication signal portion is determined to exceed a predetermined threshold.

12. A system for increasing the integrity of signals (S) in a signal transmission network, each signal (S) comprising a sequence of one or more signal elements, wherein: The system comprises: a) an apparatus (Rx) according to any one of claims 1 to 11, as a receiving device for the signal in the network, and / or b) A transmitting device (Tx) for the signal (S) in the network, wherein the transmitting device comprises a permutation unit configured to permute the signal (S) to be transmitted according to a permutation operation.

13. The system of claim 12, wherein: a) the permutation operation (P) is encoded as a permutation indication signal part (M), and the permuted signal is transmitted in combination with the permutation indication signal part, b) said permutation operation (P) is encoded as a physical parameter of the corresponding signal (S), c) the permutation operation (P) is encoded as a permutation indication signal portion, wherein, according to the permutation operation (P), the first signal to be transmitted is permuted, the permutation indication signal portion is transmitted in combination with the second permuted signal, and / or d) The permutation operation (P) is defined according to one or more communication parameters of the network.

14. The system according to claim 12 or 13, wherein: The permutation unit is configured to permute the signal (S) to be transmitted only if an injected signal element has been identified in the received signal based on a signal element amplitude variation.

15. A method for increasing the integrity of a signal (S) in a signal transmission network, each signal (S) comprising a sequence of one or more signal elements, wherein: The method includes identifying any injection (kI) of a signal element into a received signal based on at least one of: a) a change in the amplitude of the signal element, and b) an inverse of a permutation operation (P) applied to the received signal when transmitting, c) a signal fingerprint, d) the location of the transmitter, and e) an AI / ML, artificial intelligence / machine learning model.

16. A computer program for increasing the integrity of a signal (S) in a signal transmission network, wherein: The program comprises instructions for causing the apparatus (Rx) according to any one of claims 1 to 13 to execute the method according to claim 15 .

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