Method and device for determining jamming characteristics

Abstract

A method for determining one or more characteristics of a potential jamming signal. The method comprises obtaining input regarding the potential jamming signal from at least two receivers (121, 122), each of the receivers monitoring a respective frequency band (f1, f2); determining first time duration between time instant at which the potential jamming signal is detected at frequency band monitored by the first receiver and time instant at which the potential jamming signal is detected at frequency band monitored by the second receiver; determining second time duration between time instant at which the potential jamming signal is detected at frequency band monitored by one of the first or the second receivers, and a subsequent time instant at which the potential jamming signal is detected at frequency band monitored by the same one of the first or the second receivers; and determining one or more characteristics of the potential jamming signal.

Description

[0001] METHOD AND DEVICE FOR DETERMINING JAMMING CHARACTERISTICS

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to techniques for determining one or more characteristics of a potential jamming signal.

[0004] BACKGROUND

[0005] Wireless communication has grown rapidly, both in terms of number of users and carried data volume, over the last few decades and is expected to continue to grow as Fifth Generation (5G) is being deployed. In addition to consumer mobile broadband (MBB) applications, a wide range of business and mission-critical applications (such as, public safety communication, smart manufacturing and industrial automation) are starting to emerge with 5G new radio (NR) access network deployments. Many of these applications demand fast, reliable and secure communications. Disturbances or outage in such type of communication can have catastrophic consequences.

[0006] Of the new services, smart manufacturing is developing rapidly. For instance, Worcester Bosch factory in the UK has launched a 5G private network infrastructure that is provided by Ericsson and manned by British Telecom (Robert Bosch UK, "Leading in 5G Technology," 2020. [Online]. Available: https: / / www.bosch.co.uk / intemet-of-things / leading-in-5g-technology / ). Schneider Electric and Orange have jointly conducted trials of a 5G indoor private network in the Le Vaudreuil factory on experimental frequencies (Orange, "Orange and Schneider Electric Run Industrial 5G trials in French Factory," 28 September 2020. [Online], Available: https: / / www.orange.com / en / newsroom / press-releases / 2020 / orange-and-schneider-electric- run-industrial-5g-trials-french-factory). Such connectivity systems may (as most radio-based connectivity systems) face different kinds of attacks that lead to application service interruption, including communication denial, for example, cloning of SIM cards, tracking of users, DNS spoofing, denial -of-service (DoS) attacks, and injection of manipulated broadcast messages with adequate power to overshadow the legitimate ones. Radio jamming has been identified as a potential threat.

[0007] Although the use of communication jammers is prohibited by law in most countries, wireless systems are still vulnerable to malicious electromagnetic threats from unlawful activity, primarily due to the broadcast nature of the wireless medium. Nowadays, commercial off-the- shelf (COTS) radio jammers may be bought by any individual from a variety of internet sites and may be used to target the above-mentioned critical applications. These jammers typically do not require any skill to operate. Measurements show that many COTS jammers are chirp jammers (T. Kraus, R. Bauemfeind, and B. Eissfeller, “Survey of In-Car Jammers - Analysis and Modeling of the RF signals and IF samples (suitable for active signal cancellation),” in ION GNSS, Portland, Oregon, USA, 2011) and (R. H. Mitch, R. C. Dougherty, M. L. Psiaki, S. P. Powell, B. W. O'Hanlon, J. A. Bhatti, and T. E. Humphreys, “Signal Characteristics of Civil GPS Jammers,” in ION GNSS, Portland, Oregon, USA, 2011).

[0008] Moreover, one may also lawfully buy components on the market, e.g., software-defined radio (SDR) kits intended for research and assemble and use them in an unlawful manner to harm wireless communication.

[0009] Reduction of the transmission rate, as a result of a jamming attack, may increase the end-to- end latency of communication links. This may cause an anticipated message to be delayed, so that it is not delivered in the expected timebound in the context of industrial applications or public safety alerts utilizing the wireless connectivity. Jamming attacks may lead to increased number of retransmissions. Retransmissions increase the latency. Increased latency may not be acceptable, especially for applications relying on ultra-reliable low-latency communication, as the electromagnetic threats on the spectrum may lead to significant financial losses via production damage.

[0010] Consider a scenario with a radio access network, e.g., 2G, 3G, 4G, 5G, or Wi-Fi or Low-Power Wide Area Network (LPWAN), in operation. For performance reasons and / or safety reasons and / or concern for the equipments that are using the network, early detection and classification of electro-magnetic threats (EMTs) may be important to mitigate the impact of jamming attacks on the communications performance.

[0011] Existing solutions for detection of electromagnetic attacks are often highly specialized, expensive stand-alone systems that do not lend themselves to easy integration with the communication system. Furthermore, the detection methods described in the literature often employ spectrum analysis techniques that are computationally burdensome.

[0012] SUMMARY According to a first aspect, there is provide a method for determining one or more characteristics of a potential jamming signal. The method comprises obtaining input regarding a potential jamming signal from at least two receivers, each of the receivers monitoring a respective frequency band. The method comprises determining, based on the obtained input, a first time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver. The method comprises determining, based on the obtained input, a second time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by one of the first receiver or the second receiver, and a subsequent time instant at which the potential jamming signal is detected at the frequency band monitored by the same one of the first receiver or the second receiver. The method comprises determining one or more characteristics of the potential jamming signal based on the first time duration and the second time duration.

[0013] In an embodiment according to the first aspect, the method comprises determining, based on the obtained input, the second time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver, and a subsequent time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver. The method further comprises determining, based on the obtained input, a third time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver. The method further comprises determining, based on the obtained input, a fourth time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver. The determining of the one or more characteristics of the potential jamming signal is additionally based on the third time duration and the fourth time duration.

[0014] In an embodiment according to the first aspect, the obtained input comprises input from a third receiver monitoring a frequency band located between the frequency bands monitored by the first and the second receiver. The method further comprises determining, based on the obtained input, a fifth time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the third receiver; and / or determining, based on the obtained input, a sixth time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the third receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver. The determining of the one or more characteristics of the potential jamming signal is additionally based on the fifth time duration and / or the sixth time duration.

[0015] In an embodiment according to the first aspect, the method comprises indicating to a communication node, the one or more characteristics of the potential jamming signal for enabling detection of the potential jamming signal as a jamming signal.

[0016] In an embodiment according to the first aspect, the method comprises determining that the potential jamming signal is a jamming signal; and sending, to a communication node, an indication that the potential jamming signal is a jamming signal.

[0017] In an embodiment according to the first aspect, the method comprises transmitting a signal for controlling at least one of the receivers to monitor a different frequency band than the frequency band previously monitored by that receiver.

[0018] In an embodiment according to the first aspect, the signal for controlling is transmitted in response to the potential jamming signal not being detected at the frequency band previously monitored by that receiver.

[0019] In an embodiment according to the first aspect, the different frequency band is closer, than the frequency band previously monitored by that receiver, to a frequency band at which the jamming signal has been detected.

[0020] In an embodiment according to the first aspect, the potential jamming signal is a chirp signal comprising a waveform according to at least one of the following: a triangle, a saw-tooth, and a sinusoid.

[0021] In an embodiment according to the first aspect, the potential jamming signal is a periodic signal of a time period equal to sum of the first time duration, second time duration, third time duration and the fourth time duration.

[0022] In an embodiment according to the first aspect, at least one of the receivers monitors a frequency band in a guard band of a carrier. In an embodiment according to the first aspect, at least one of the receivers monitors a frequency band located at an edge of a carrier bandwidth.

[0023] In an embodiment according to the first aspect, at least one of the receivers monitors a frequency band located within a carrier bandwidth.

[0024] In an embodiment according to the first aspect, the one or more characteristics of the potential jamming signal includes at least one of: a center frequency, a bandwidth and a shape of the potential jamming signal.

[0025] In an embodiment according to the first aspect, the obtained input indicates time instants at which the potential jamming signal is detected at the respective frequency bands monitored by the receivers.

[0026] In an embodiment according to the first aspect, the method is performed by Radio Access Network, RAN, equipment or a RAN node.

[0027] According to a second aspect, there is provided a device for determining one or more characteristics of a potential jamming signal, the device comprising a memory and a processor, the memory containing instructions which when executed on the processor, cause the device to: obtain input regarding a potential jamming signal from at least two receivers, each or the receivers monitoring a respective frequency band; determine, based on the obtained input, a first time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver; determine, based on the obtained input, a second time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by one of the first receiver or the second receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the same one of the first receiver or the second receiver; and determine one or more characteristics of the potential jamming signal based on the first time duration and the second time duration.

[0028] In an embodiment according to the second aspect, the memory containing instructions which when executed on the processor, cause the device to perform the method according to the first aspect. According to a third aspect, there is provided a computer program comprising instructions which, when executed on a device, cause the device to carry out the method according to one or more embodiments of the first aspect.

[0029] According to a fourth aspect, there is provided a computer program product comprising a computer readable storage means on which the computer program according to the third aspect is stored.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 illustrates a jammer interfering with wireless communication according to one or more embodiments.

[0032] Figure 2a illustrates an example sawtooth signal pattern.

[0033] Figure 2b illustrates the detection of the sawtooth signal in Figure 2a by two receivers.

[0034] Figure 3a illustrates a method with some optional method steps according to one or more embodiments.

[0035] Figure 3b illustrates optional method steps for the method in Figure 3a, according to one or more embodiments.

[0036] Figure 4a illustrates an example triangular signal pattern.

[0037] Figure 4b illustrates the detection of the triangular signal in Figure 4a by two receivers.

[0038] Figure 5a illustrates an example sinusoidal signal pattern.

[0039] Figure 5b illustrates the detection of the sinusoidal signal in Figure 5a by two receivers.

[0040] Figure 6a illustrates an example exponential signal pattern.

[0041] Figure 6b illustrates the detection of the exponential signal in Figure 6a by three receivers.

[0042] Figure 7 illustrates an RC circuit with a common resistor for charge and recharge, used for generating the exponential signal pattern of Figure 6a according to one or more embodiments.

[0043] Figure 8 illustrates an RC circuit with different resistors for charge and discharge, used for generating the exponential signal pattern of Figure 6a according to one or more embodiments. Figure 9a illustrates an example triangular signal pattern that sweeps past the frequency of only one of the two receivers according to one or more embodiments.

[0044] Figure 9b illustrates the detection of the triangular signal in Figure 9a by only one of the receivers.

[0045] Figure 9c illustrates reconfiguring of one of the two receivers to detect the triangular signal in Figure 9a.

[0046] Figure 9d illustrates the detection of the triangular signal in Figure 9a by both the receivers.

[0047] Figure 10 illustrates a device for determining one or more characteristics of a potential jamming signal, according to one or more embodiments.

[0048] DETAILED DESCRIPTON

[0049] The COTS jammers, mentioned in the background section above, may be referred to as barrage jammers meaning that the jammer transmits a jamming signal in a certain frequency band without any deeper knowledge about the structure of the signals to be jammed. Barrage jamming may be realized by transmitting noise, a single tone, a comb-like pattern of multiple tones or a chirp. A chirp is a signal in which the frequency increases (up-chirp) or decreases (down-chirp) with time. The increase and decrease of the instantaneous frequency are repeated according to some pattern. The chirp jammer is advantageous for an attacker in the sense that it may generate sufficient power over a large enough bandwidth to adversely impact the targeted communication system.

[0050] Cellular networks feature adaptive modulation and coding, whereby the transmission rate is dynamically changed to match the quality of the propagation channel between a transmitter and a receiver. Such a feature may handle the inherent propagation fading effects in a wireless medium and, to some extent, the interference that exists in the channels (for example, cochannel interference from other cells), by means of adaptive modulation and coding. However, reducing the transmission rate may increase the end-to-end latency of communication links, which causes the anticipated message to not be delivered in the expected timebound in the context of industrial applications or public safety alerts utilizing the wireless connectivity. Increased number of retransmissions could be a result of a jamming attack. Retransmissions increase the latency which may not be acceptable, especially for applications relying on ultra- reliable low-latency communication, as the electromagnetic threats on the spectrum may lead to significant financial losses via production damage.

[0051] Figure 1 illustrates an example scenario of a jamming attack carried out in a communication network 100. Consider a user equipment (UE) 110 transmitting a signal 111 to a device 120 (for example a radio access network node) in the communication network 100. The UE 110 may be transmitting the signal 111 at a particular frequency or in a particular frequency band. Now consider a jamming device such as the jammer 130 that intends to maliciously interfere with the ongoing communication between the UE 110 and the device 120 and thus transmits a signal 131 to cause the interference. Such interfering signal 131 may herein be referred to as a jamming signal. The jammer 130 typically transmits a jamming signal 131 in a certain frequency band without any deeper knowledge about the structure of the signals to be jammed. Some examples of such jamming signals 131 include a noise signal, a single tone, a comb-like pattern of multiple tones or a chirp (sometimes also referred to as a sweep signal).

[0052] The jammer 130 transmitting the jamming signal 131 may generate sufficient power over a large enough bandwidth to adversely impact the device 120 or the communication between the device 120 and the UE 110. Thus, to avoid adverse impacts on the device 120 or on the communication between the UE 110 and the device 120, it is beneficial to detect the presence of the jamming signal 131 and / or understand one or more characteristics of the jamming signal 131.

[0053] The jamming signal 131 is not known in detail in advance and thus classical matched filter receivers may typically not be used. Furthermore, model based jamming detection with parameter estimation is challenging due to the large variations in expected jamming signals. One additional challenge with detecting the jamming signal 131 is to distinguish the jamming signal 131 from other radio signals used for radio communication.

[0054] Simply detecting high interference is not sufficient to conclude that the communication system is jammed. Interference from radio signals traffic and / or signaling in adjacent cells may dominate in the received signal even under normal operation.

[0055] Simple energy detection may not be able to distinguish the jamming signal 131 from other types of interference such as intra and inter cell interference. Thus, it may be challenging to detect a jamming signal 131 unless jamming signal specific features are identified. A technique to perform detection of the jamming signal 131 may, for example, be to analyse the long-term statistics of the interference power and / or communication system key performance indicators (KPIs) and performance counters. These methods may be useful to identify communication performance issues in general. However, such techniques typically rely on averaging performance measurements over time and are often considered to be too slow for many applications. Furthermore, methods based on KPIs, and performance counters may have limited capabilities to discriminate jamming signals from interference.

[0056] In at least some embodiments, the invention utilizes two or more comparably narrow-band receivers. The narrow-band receivers may, for example, have a bandwidth in the range of few kilohertz to few thousand kilohertz. The terms ‘receivers’ and ‘narrow-band receivers’ may be used interchangeably in this text. The narrow-band receivers’ center frequencies are configured to pick-up the jamming signal 131 in different frequency regions within the expected frequency band of the jamming signal 131.

[0057] The frequency sweep of the jamming signal 131 may appear as pulses in each narrow-band receiver as the jamming signal 131 sweeps past the frequency band of the receivers. The pulse time pattern from the different narrow-band receivers may then be used to identify and classify the jamming signal 131. For example, in case of a COTS barrage jammer with high enough power, then the output of each narrow-band threat detection receivers may include many pulses in each communication symbol time-duration.

[0058] The jamming signal 131 may be expected to sweep the frequency bands of the receivers faster than the communication symbol rate. The fast sweeping of the jamming signal 131 may be used to distinguish the jamming signal from any interference signal generated by communication signal.

[0059] The narrow-band receiver may, for example, use energy detection or any other detection method. If the one or more narrow-band receivers are configured to be located in the guard bands of the communication signal, then the jamming signal 131 may be relatively stronger compared to other interfering signals, and the detection of the jamming signal may be easier. If the one or more narrow-band receivers are configured to be located within the bandwidth of the communication signal, then the one or more narrow-band receivers may be able to distinguish between the communication signal 111 and the jamming signal 131. A combination of at least one narrow-band receiver located in the communication bandwidth and at least one narrow-band receiver located in the guard band of the communication bandwidth may be useful to further increase the sensitivity of the jammer detector.

[0060] Thus, it is proposed herein to use at least two receivers such as the receiver 121 and the receiver 122, preferably narrow-band receivers, to detect the presence of the jamming signal 131 and thereby detect the presence of the jammer 130 in the communication network 100. As indicated in Figure 1, the receivers 121, 122 may for example be comprised in the device 120, or the device 120 may employ external receivers 121, 122 to detect the jamming signal 131. At least some embodiments proposed herein exploit knowledge of signal structure of the jamming signal 131 to establish that the detected signal is indeed a jamming signal. One or more parameters of the detected signal may be used to determine the characteristics of the jamming signal 131, such as bandwidth of the jamming signal 131, center frequency of the jamming signal 131, and / or sweep period of the jamming signal 131, as will be described later in the application. For example, a chirp jamming signal (i.e., a jamming signal sweeping across a frequency band) with a bandwidth extending across the frequencies monitored by the receivers 121, 122 may give rise to pulses at the frequencies monitored by the receivers 121, 122. The duration and relative timing of the pulses may depend on the chirp jamming signal as well as the parameters of the receivers 121, 122. For a chirp jamming signal having up-chirps and down-chirps, the pulses detected at the monitoring frequencies of the receivers 121, 122, may be divided into two sets, one set of detections for the up-chirp and the other set of detections for the down-chirp. The time duration between the detections at the receivers may be used to determine the characteristics of the jamming signal.

[0061] The average durations over a number of periods may be used to determine properties / characteristics of the chirp signal, for example including which chirp signal sweep pattern (e.g., triangular, sawtooth, sinusoidal, and exponential) was detected as the pulses at the receivers 121, 122. At least some embodiments proposed herein use more than two receivers (for example three receivers) to detect a jamming signal of a certain type (for example, a sawtooth signal pattern) and to differentiate that signal type (for example, the sawtooth signal pattern) from other jamming signal patterns (for example, a triangular signal pattern).

[0062] In some embodiments, the receivers 121,122 may be triggered at different time instances. The trigger signals are used to 1) alert the communication system about the presence of the jammer 130, 2) estimate the jammer parameters, and 3) estimate the pattern of the pulsed output from the one or more receivers and use the pattern to identify and classify different jammer equipment.

[0063] It is conceivable that a strong jamming signal saturates the automatic gain control (AGC) of the communication system. If the jamming signal is in the range of the AGC, then the communication system may receive, digitalize, and process the complete received signal, but if the jamming signal is so strong that the AGC saturates, then the communication system may no longer do the normal signal processing. The receivers as described above, may still detect the jamming signal 131.

[0064] In this way, at least some embodiments proposed herein provide an efficient method for detecting and determining the presence of a jammer 130 in a communication network 100.

[0065] At least some of the embodiments provide the following advantages:

[0066] - Information of the detection of the potential jamming signal may be integrated in automated radio access network (RAN) security protocols that automatically take appropriate mitigation actions, trigger further jamming detection systems, and / or provide warnings to network operators.

[0067] The detection system / detection receivers may be operated in a stand-alone manner without the need to be integrated with the communication system.

[0068] The trigger information from the detection system can be used to provide basic frequency information to determine sweep directions and / or jammer center frequency. The sensitivity of the detection receivers may be selected such that they can receive and / or detect the jamming signal even if the AGC is saturated.

[0069] Figure 2a shows a graph of an example jamming signal having a sawtooth chirp signal pattern. As may be seen in Figure 2a, the horizontal axis represents time and the vertical axis represents frequency. The chirp signal is a signal in which the frequency increases with time, i.e. up-chirp, and / or decreases with time, i.e. down-chirp. The increase and / or decrease of the instantaneous frequency is repeated according to some pattern. The sawtooth chirp signal sweeps through frequencies in a proportional manner with time (either proportionally increasing with time or proportionally decreasing with time). In a sawtooth chirp signal comprising only up-chirps, there is a pattern of signals which have an increasing frequency with time. Similarly, in a sawtooth chirp signal comprising only down-chirps, there is a pattern of signals which have a decreasing frequency with time. A sawtooth chirp signal pattern comprising up-chirps is illustrated in Figure 2a as an example of a jamming signal (or a potential jamming signal). Consider a scenario where the sawtooth chirp signal in Figure 2a is employed as a jamming signal 131 to interfere with the communication of the device 120 (e.g. communicating in the radio frequency ranges) in the communication network 100 shown in Figure 1. Let the bandwidth of the communication signal 111 (or the carrier) be the Be, referred to herein as the communication bandwidth. Let Bg denote the guard band of the communication signal (or the carrier). The receivers 121, 122 are configured (for example tuned) to monitor narrow frequency bands centered around frequencies fl and f2 respectively. That is, receiver 121 (herein ‘first receiver’) is configured to monitor a narrow-band of frequencies centered at fl. Similarly, receiver 122 (herein ‘second receiver’) is configured to monitor a narrow-band of frequencies centered at f2. In the example depicted in Figure 2a, frequency f2 is higher than frequency fl . Let the difference between the frequencies f2 and fl be denoted by Br, and let the center frequency located between the frequencies fl and f2 be denoted by fcr. The frequencies fl, f2 monitored by the receivers 121, 122 are herein referred to as ‘monitored frequencies’. The receivers 121, 122 may be configured to monitor at the monitored frequencies such that the Br is the difference between the monitored frequencies fl and f2.

[0070] In Figure 2a, the receivers 121, 122 are depicted as configured in the guard band of the communication bandwidth to monitor frequencies close to the edge of the communication bandwidth. It will be appreciated that the receivers 121, 122 may be configured to monitor different frequencies. In some embodiments, at least one of the narrow-band receivers 121,122 may monitor frequencies (or frequency bands) located at the edge of the communication bandwidth. In some embodiments, at least one of the narrow-band receivers 121,122 may monitor frequencies (or frequency bands) located within the communication bandwidth. In some embodiments, at least one of the narrow-band receivers 121,122 may monitor frequencies (or frequency bands) known to have low usage.

[0071] The following figures will be explained with the example of the receivers 121,122 being located just outside the edges in the guard band of the communication bandwidth. To limit the interference from other communication signals and increase the sensitivity of the receivers, it may be advantageous to configure the receivers to monitor frequencies in the guard band. It may thus be easier for the receivers 121 , 122 to detect the energy of the j amming signal, because no other signals are expected in those frequency regions. It may further be noted that the receivers may, in some embodiments, be configured to monitor frequencies in different regions of the communication bandwidth as described above in the previous paragraph, and that the methods described herein in relation to different figures may be applicable to such embodiments as well.

[0072] The sawtooth chirp signal sweeps through a relatively large bandwidth to cause jamming in the network 100. In the example illustrated in Figure 2a, the sawtooth chirp signal sweeps across the monitored frequencies fl and f2.

[0073] The receivers 121, 122 are capable of detecting a signal transmitted with a frequency sweeping the monitored frequencies and thus detect the sawtooth chirp signal at frequencies fl and f2 as shown in Figure 2b. The receivers 121, 122 detect an increased energy when the sawtooth signal chirp signal is present at the monitored frequencies. The receivers 121, 122 may detect an energy pulse for a time instant (or very short time duration corresponding to the narrow frequency band of the receiver) at the monitored frequencies indicating that the sawtooth chirp signal enters or leaves the bandwidth located between the monitored frequencies. Let tl be the time duration between a detection at the first receiver 121 at frequency fl and a subsequent detection at the second receiver 122 at frequency f2. Between these two detections, the sawtooth chirp signal may be located within the communication bandwidth, tl may herein be referred to as ‘first time duration’. Let t2 be the time duration between a first detection by the receiver 122 at frequency f2 and a second subsequent detection by the receiver 122 at frequency f2.

[0074] The knowledge of the energy detections due to the sawtooth chirp signal being detected at the monitored frequencies may be exploited to determine the time durations tl and t2. For example, the time instants of detections at the receivers 121, 122 maybe obtained and the time durations tl and t2 may be determined. Time duration tl may be obtained by determining the difference between the time instant of detection of a symbol at the frequency f2 by the second receiver 122 and the time instant of detection of the same symbol at the frequency fl by the first receiver 121. Time duration t2 (also referred herein as ‘second time duration’) may be obtained by determining the difference between the time instant of detection of a symbol at the frequency f2 by the second receiver 122 and the time instant of detection of a subsequent symbol at the frequency f2 by the second receiver 122. Alternatively, t2 may be obtained by determining the difference between the time instant of detection of a symbol at the frequency fl by the first receiver 121 and the time instant of detection of a subsequent symbol at the frequency fl by the first receiver 121. Based on the determined time durations tl and t2 and the knowledge of the receivers’ 121, 122 frequency parameters (such as fl, f2, Br, fcr), one or more characteristics of the sawtooth chirp signal may be determined, as will now be explained. The characteristics of the sawtooth chirp signal may, for example, be the period, bandwidth and center frequency of the sawtooth chirp signal. Let the sawtooth chirp signal have a period tp, bandwidth Bj and a center frequency fcj as shown in Figure 2a.

[0075] Br is given by,

[0076] Br = f2 - fl. (1)

[0077] The center frequency fcr located between the monitored frequencies is given by

[0078] Typically, the parameters Br and fcr may already be known or pre-defined based on the receivers 121, 122 that are used for monitoring the presence of the jamming signal (or the potential jamming signal).

[0079] The sawtooth chirp signal shown in Figure 2a only has up-chirps, and jumps back down in frequency without passing thorough the monitored frequencies. As a result, the sawtooth chirp signal is only detected by the receivers 121, 122 on its way upwards at the monitored frequencies. The period tp of the sawtooth chirp signal is equal to t2, tp = t2 (3)

[0080] The difference between the monitored frequencies Br, the period tp and the time duration tl may be used to determine the bandwidth Bj of the sawtooth chirp signal as where * denotes a multiplication operation.

[0081] Furthermore, the bandwidth Bj of the sawtooth chirp signal overlaps with the bandwidth between the monitored frequencies . Thus, the center frequency fcj of the sawtooth chirp signal may be determined as being within the range fcr — (Br + Bj) / 2 < fcj < fcr + Br + Bjj / 2 (5)

[0082] If Bj is much larger than Br, the term Br may be omitted to obtain an approximate determination of fcj as being within the range, fcr — Bj / 2 < fcj < fcr + Bj / 2 (6) In this way, one or more characteristics of the sawtooth chirp signal in Figure 2a may be determined.

[0083] Figure 3a illustrates a flowchart of a method 200 for determining one or more characteristics of a potential jamming signal. The method 200 may for example be performed by the device 120 in Figure 1, using the receivers 121, 122. While the reference numbers from Figure 1 will be used in the description of the method 200, it will be appreciated that Figure 1 only serves as an example, and that the method 200 need not necessarily be performed by the device 120. The method 200 comprises several steps, some of which steps are optional.

[0084] The method 200 comprises obtaining 201 (for example receiving) input regarding a potential jamming signal from at least two receivers. Each of the receivers monitors a respective frequency band. The receivers may, for example be, the receivers 121, 122 described above in relation to Figures 1, 2a and 2b. The receivers 121, 122 may, for example, be monitoring narrow frequency bands between which monitored frequencies a UE 110 is communicating with a network 100. The receivers 121, 122 may, for example, be comprised in the device 120. As another example, the receivers 121, 122 and the device 120 may be comprised in a communication system 100, but the receivers 121, 122 may be arranged separately from the device 120. The receivers 121 , 122 may detect presence of a signal at the monitored frequencies fl and f2 respectively. This detected signal is referred to as a ‘potential jamming signal’ since it has not yet been determined if the detected signal is indeed a jamming signal. A jammer 130 intending to interfere with the communication of the UE 110 and the network 100 may transmit a jamming signal 131 that is now detected by the receivers 121, 122 as the potential jamming signal. The receivers 121, 122 may thus detect the potential jamming signal and provide input regarding the potential jamming signal.

[0085] In an embodiment, the potential jamming signal is the sawtooth signal described above in relation to Figure 2a.

[0086] The receivers 121, 122 may provide the input to the device 120. The input may, for example, be obtained at the device 120. The input may, for example, be obtained at a communication system 100 comprising the device 120.

[0087] The input obtained from the receivers 121, 122 at step 201 may, for example, comprise data samples of the potential jamming signal at the monitored frequencies. The input obtained from the receivers 121, 122 may, for example, comprise data samples of energy detected at the monitored frequencies, such as the energy of the potential jamming signal at the monitored frequencies. As another example, the obtained input may be an indication that a potential jamming signal is detected (or not detected) at the monitored frequencies. The input may, for example, be energy (or amplitude) samples of the potential jamming signal. The energy (or amplitude) samples of the potential jamming signal may be filtered to reduce the impact of noise. For this purpose, a filter such as a square filter or raised cosine filter may be used. As another example, the obtained input may be an indication of one or more time instants at which the potential jamming signal is detected.

[0088] In some embodiments, two or more receivers detect the potential jamming signal at the respective monitoring frequencies and provide the detections to a pulse generator (not shown in Figure). The pulse generator takes the detection input of each receiver and generates a sequence of pulses. The pulse sequences may be post-processed and sent as the input to the device 120.

[0089] The potential jamming signal may sweep past the monitored frequencies on a periodic basis. This is a typical feature of a chirp jammer which may be exploited to determine or estimate the presence of a jamming signal.

[0090] The method 200 comprises determining 202, based on the obtained input, a first time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver.

[0091] The first time duration referred to at step 202 may for example be tl as described above in relation to Figure 2a. The first time duration may correspond to the duration of the time spent by the potential jamming signal between the monitored frequencies. The potential jamming signal may sweep up or down in frequency within a single time period. So, the first time duration may correspond to the duration of the time spent by, for example, the up-chirp of the potential jamming signal between the monitored frequencies fl and f2 as exemplified by tl in Figure 2a.

[0092] The receivers 121, 122 may for example detect the potential jamming signal at the monitored frequencies based on an increased energy at the monitored frequencies. Further, the receivers 121, 122 may detect that the energy decreases when the potential jamming signal sweeps past the monitored frequencies. The time instant of detection of the energy pulse at the first receiver 121 and the time instant of successive detection of the energy pulse at the second receiver 122 may be used to determine the first time duration. As an example, in case of using two receivers the input may be divided into two sets SI and S2. The SI set corresponds to the detections by the first receiver 121 and includes the time instants of detection at the first receiver 121. Similarly, the S2 set corresponds to the detections by the second receiver 122 and includes the time instants of detection at the second receiver 122. The SI and S2 sets include multiple occurrences of detections of the potential jamming signal at the monitored frequencies. T1 may be obtained, for example, by determining the difference between a time instant of detection from the S2 set and a time instant of detection from the SI set.

[0093] The method 200 comprises determining 203, based on the obtained input, a second time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by one of the first or the second receiver, and a subsequent time instant at which the potential jamming signal is detected at the frequency band monitored by the same one of the first or the second receiver. For example, the second time duration may be the duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a subsequent (for example the next) time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver. For example, the second time duration may be the duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver, and a subsequent (for example the next) time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver. The frequency bands monitored by the receivers may, for example, be narrow frequency bands.

[0094] The second time duration may for example be the t2 described above in relation to Figure 2a. The second time duration may correspond to the duration of the time between a first detection of the potential jamming signal at frequency £2 at receiver 122 and a second subsequent detection of the potential jamming signal at frequency £2 at receiver 122. Alternatively, the second time duration may correspond to the duration of the time between a first detection of the potential jamming signal at frequency fl at receiver 121 and a second subsequent detection of the potential jamming signal at frequency fl at receiver 121..

[0095] In some embodiments, the time instant of detection of the energy pulse at the second receiver 122 and the time instant of successive detection of the energy pulse at the second receiver 122 may be used to determine the second time duration. This may be the case when the potential jamming signal is of the sawtooth signal pattern of Figure 2a. In case of dividing the input into sets S 1 and S2 as described above, the second time duration t2 is obtained by determining the difference between two successive time instants of detection from the SI set or from the SI set. The second time duration may thus correspond to the time period of the potential jamming signal.

[0096] The first time duration and the second time duration may be sufficient to determine one or more characteristics of the potential jamming signal such as the sawtooth signal of Figure 2a. The method 200 comprises determining 208 one or more characteristics of the potential jamming signal based on the first time duration and the second time duration determined at steps 202 and 203 respectively. The first time duration and the second time duration may, for example, be used to determine one or more characteristics of the potential jamming signal such as center frequency, bandwidth and / or period. As exemplified in the above paragraphs including equations 3-6, it is possible to determine the bandwidth Bj and period tp of the sawtooth shaped jamming signal in Figure 2a using the first time duration tl and the second time duration t2, and it is also possible to get a rough estimate of where the center frequency fcj of the jamming signal may be located using the first duration tl and the second duration t2.

[0097] As will be described further below, by determining characteristics of the potential jamming signal, one may also identify the signal pattern and / or type of the potential jamming signal, at least in some scenarios. The potential jamming signal may, for example, have a chirp signal pattern of the type sawtooth as shown in Figure 2a. As another example, the potential jamming signal may have a triangular chirp signal pattern as shown in Figure 4a. As still another example, the potential jamming signal may have a sinusoid chirp signal pattern as shown in Figure 5a. As yet another example, the potential jamming signal may have an exponential chirp signal pattern as shown in Figure 6a.

[0098] As exemplified above with reference to Figure 2a, it may be sufficient to determine the first and the second time durations (as in steps 202-203) in order to determine certain characteristics of the potential jamming signal, for example in case of symmetric potential jamming signals. However, it is possible to determine additional characteristics of the potential jamming signal by determining further time durations, such as a third time duration and a fourth time duration. For example, such additional time durations may be employed to distinguish between different chirp signal patterns, for example differentiate between triangular, sinusoidal and exponential chirp signals.

[0099] Let us now consider the example of triangular chirp signal pattern shown in Figure 4a. It may be seen that the triangular chirp signal comprises an up-chirp as well as a down-chirp within a single period tp of the triangular chirp signal. The triangular chirp signal would be detected by the receivers 121, 122 twice each at the monitored frequencies per period tp, i.e. for each receiver one detection during the up-chirp and one detection during the down-chirp, as shown in Figure 4b. For this reason, there are two time durations, i.e. the first time duration tl and the third time duration t3, during which the triangular chirp signal sweeps in between the monitored frequencies fl and 12. Furthermore, there are two durations, i.e. the second time duration t2 and the fourth time duration t4, during which the triangular chirp signal sweeps outside of the monitored frequencies fl and f2.

[0100] Therefore, the period tp of the triangular chirp signal may be seen as the sum of four durations - first time duration tl, second time duration t2, third time duration t3 and fourth time duration t4, as shown in Figure 4a. That is, tp = tl + t2 + t3 + 14, (7) wherein + denotes a summation operation.

[0101] The knowledge of the energy detections at the receivers 121, 122 due to the triangular chirp signal sweeping the monitored frequencies may be exploited to determine the four time durations. The first and the second time durations may, for example, be determined according to similar procedures as described above for the sawtooth chirp signal of Figure 2a. The first and the second durations may, for example, be determined according to the steps 202 and 203 of Figure 3a respectively.

[0102] The third time duration t3 and the fourth time duration t4 may for example be determined in a similar way as the first and the second time durations. During the downchirp part of the triangular signal, the triangular signal is first detected at the receiver 122 and then subsequently detected at the receiver 121.

[0103] Optionally, the method 200 comprises determining 204, based on the obtained input, a third time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver. The third time duration may be determined by obtaining the difference between the time instant of detection at the receiver 122 and the time instant of successive detection at the receiver 121. For example, referring to Figure 4a and Figure 4b, the third time duration is the time duration between when the potential jamming signal is detected at the frequency f2 by the receiver 122 and when the potential jamming signal is detected at the frequency fl by the receiver 121.

[0104] Optionally, the method 200 comprises determining 205 based on the received input, a fourth time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver. The fourth time duration may be determined by obtaining the difference between the time instant of detection at the receiver 121 and the time instant of successive detection at the same receiver 121. For example, referring to Figure 4a and Figure 4b, the fourth time duration is the time duration between when the potential jamming signal is detected at the frequency fl by the receiver 121 and when the potential jamming signal is successively detected at the frequency fl by the receiver 121.

[0105] Once the four time durations, i.e. tl, t2, t3 and t4 have been determined, various characteristics of the triangular chirp signal may further be determined (step 208). The first time duration tl and the third time duration t3 may be used to determine the linear sweep rates as follows: r2 = (9) where rl indicates the linear sweep rate for the up-chirp part of the triangular chirp signal and r2 indicates the linear sweep rate for the down-chirp part of the triangular chirp signal. Br as described above is the difference between the monitored frequencies f2 and fl .

[0106] The bandwidth Bj of the triangular chirp signal may thus be determined by where * denotes multiplication and tp is the period of the triangular chirp signal.

[0107] If the center frequency fcj of the triangular chirp signal is not equal to the center frequency fcr, then the time durations t2 and t4 will be unequal. The frequency offset fo between fcj and fcr may be determined by (t2-C4)*gj

[0108] / o = tp*2 (11)

[0109] The center frequency of the triangular chirp signal may be determined by fcj = fcr ± fo (12)

[0110] In this way one or more characteristics of the triangular chirp signal may be determined, such as the center frequency fcr, the bandwidth Bj and the period tp.

[0111] Figure 5a illustrates a frequency-time graph of a jamming signal in the form of a sinusoid signal pattern according to one or more embodiments.

[0112] The procedure of the method steps described above in relation to Figure 3a and Figure 3b, namely the method steps 201, 202, 203, 204, 205 and 208 may also be applicable to embodiments involving jamming signals of the type shown in Figure 5a. For example, the determination of tl, t2, t3 and t4 may be performed according to the method steps 202, 203, 204, and 205, respectively, of Figure 3a. The determining at step 208 may include determining the one or more characteristics of the sinusoid signal as follows:

[0113] Referring to Figure 5a, let,

[0114] The period tp of the sinusoid signal is obtained by summing the first, second, third and fourth time durations, as tp = tl + t2 + t3 + t4. (15)

[0115] Further, let the sweep rates be,

[0116] Further, Br is given by

[0117] Br = rl — r2 (18) Inserting equations (16) and (17) in (18), the bandwidth of the sinusoid signal (or the jamming signal) Bj may be determined by,

[0118] The center frequency fcj of the sinusoid signal may be determined by, fcj = fcr ± ^ (20)

[0119] Thus, the device may determine one or more jamming characteristics of the sinusoid signal (or the jamming signal) such as the center frequency, bandwidth and the period based on equations (20), (19) and (18) described above. The determination may, thus, be based on the four time durations tl, t2, t3 and t4.

[0120] Figure 6a illustrates a frequency-time graph of a jamming signal in the form of an exponential signal pattern according to one or more embodiments.

[0121] In some optional embodiments, it may be desired to further distinguish between the triangular signal of Figure 4a and the exponential signal such as in Figure 6a. In such embodiments, it may be advantageous to employ an additional third receiver 123 along with the two receivers 121, 122 to distinguish between the two signals, as shown in Figure 6a. The third receiver 123 may be configured to monitor a mid-band frequency f3 situated in-between the lowest monitoring frequency fl of the first receiver 121 and the highest monitoring frequency f2 of the second receiver 122. With three receivers, the sawtooth signal in Figure 6a may be detected three times during the up-chirp and three times during the down-chirp within a single period. Thus, it is possible to determine further time durations, i.e. a fifth time duration t5 and a sixth time duration t6, which may be employed to determine characteristics of the sawtooth signal.

[0122] Optionally, the input obtained at 201 further comprises input from a third receiver 123. The third receiver 123 monitors a frequency band f3 located between the frequency bands located between the frequency bands monitored by the first and the second receiver. This is depicted, for example in Figure 6a and 6b.

[0123] Thus, the method 200, optionally comprises, determining 206 based on the obtained input, a fifth time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the third receiver. The fifth time duration may thus be determined by obtaining the difference between the time instant of detection at the first receiver 121 and the time instant of successive detection at the third receiver 123. For example, the fifth time duration in step 206 of method 200 is exemplified in Figure 6a and 6b as t5.

[0124] The method 200, optionally comprises, determining 207, based on the obtained input, a sixth time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the third receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver. The sixth time duration may thus be determined by obtaining the difference between the time instant of detection at the third receiver 123 and the time instant of successive detection at the second receiver 122. For example, the sixth time duration in step 207 of method 200 is exemplified in Figure 6a and 6b as t6.

[0125] Once the fifth time duration and the sixth duration are determined, the determining at step 208 includes determining one or more characteristics of the exponential signal further based on the fifth and the sixth time durations. This will be explained now in relation to Figure 6a.

[0126] Referring to Figure 6a, measurements show that several commercial jammers have exponential sweep characteristics. Such sweeps may typically be generated by Resistor-Capacitor (RC) circuits. Figure 7 illustrates one such example of an RC circuit comprising a resistor R and a capacitor C, connected to a voltage supply and a voltage-controlled oscillator (VCO). Figure 8 illustrates another example of an RC circuit wherein a resistor Rc is used for charging procedure while a different resistor Rd is used for the discharging procedure. If different resistors are used for charging and discharging procedures, then more general values of the one or more jamming characteristics, such as jammer bandwidth, are possible.

[0127] Now referring to Figure 7, the RC circuit is described as follows.

[0128] If the switch S has been in the lower position, i.e. in SI, for a long time, then the capacitor C will be completely discharged. At time t=0, the switch S is moved to the upper i.e. S2 and the capacitor starts to charge. The voltage over the capacitor at time t>0 is given by

[0129] Fc - Vs * (1 — exp (-t / r)), (21) where Vs is the voltage of the voltage supply and r is the time constant T = R*C. At time t=5* r, Vc = 0.99 Vs and we can consider the capacitor fully charged. If the switch S has been in S2 position for a long time, the capacitor is fully charged i.e. Vc = Vs. If the switch S is moved to the lower position SI at time t=0, then the voltage over the capacitor at time t>0 will be given by

[0130] Vc = Vs * exp —t / c). (22)

[0131] Now at time t=5* T, VC=0.01 VS and we can consider the capacitor discharged.

[0132] The voltage over the capacitor is fed to the VCO. The VCO outputs an instantaneous frequency given by

[0133] / (t) = fo + K * Vin, (23) where fD is the quiescent (dormant) frequency, K is a constant and Vin is the input voltage. Here Vin = Vc. Let fs be the frequency swing of the VCO if the RC circuit is allowed to reach fully charged and discharges states, then fs = K*Vs. Assume that the capacitor is completely charged and discharged before the switch position is changed, the up-sweep frequency may determined as, u(t) = fO + fs * ((1 - exp (— t / r)). (24)

[0134] The down-sweep frequency may be determined as

[0135] In Figure 8, there are two different resistors Rc and Rd for charging and discharging, respectively. In comparison to Figure 7, two different time constants, Tcfor charging and Td for discharging, are obtained. The up-sweep frequency and down-sweep frequency may thus be determined by replacing T in (24) and (25) with TCand Td respectively.

[0136] In the description above, it was assumed that the capacitor is allowed to charge and discharge completely. If this is not the case, i.e., if, for example, the position of the switch is changed with a frequency greater than 1 / (5* T), then the capacitor will not charge and discharge fully. The input voltage to the VCO may not reach its end values (0 and Vs), and the output frequency swing may not be the full frequency range.

[0137] As seen in Figure 6a, the slope of the frequency change (and corresponding voltage change) is largest just after the switch position is changed (e.g. from charging to discharging) and the slope changes within the receiver bandwidth. If the center frequency between the monitoring frequencies is changed (re-configured), the parameters of the RC circuit may be estimated and the bandwidth of the jamming signal may be determined by fitting the determined time durations (for eg. tl, t2, t3, t4, t5, and / or t6) to the exponential curves shown in Figure 6a. Retuning may also be used to determine the jamming center frequency.

[0138] It may be noted that the procedure of the method steps described above in relation to Figure 3a and Figure 3b, namely the method steps 201 , 202, 203, 204, 205 and 208 may also be applicable to embodiments involving jamming signals of the type shown in Figure 6a. For example, the determination of the first, the second, the third, and the fourth time durations may be performed according to the method steps 202, 203, 204, and 205 respectively, of Figure 3a.

[0139] Now referring to method 200, in one or more embodiments, the method 200 comprises an optional step of sending 209, to a communication node, the one or more characteristics of the potential jamming signal for enabling detection of the potential jamming signal as a jamming signal. The communication node may be a different node from the device 120. The communication node may be comprised in the same communication network as the device 120. The communication node may, for example, use the information of the one or more characteristics of the potential jamming signal for determining that the potential jamming signal is indeed a jamming signal. The communication node may, for example, use the information of the one or more characteristics of the potential jamming signal for classifying different types of jammers.

[0140] In some embodiments, the method 200 comprises the optional step of determining 210 that the potential jamming signal is a jamming signal. The device 120 may, for example, use the information of the one or more characteristics of the potential jamming signal and compare the characteristics with different types of jamming signal patterns, and determine that the potential jamming signal is indeed a jamming signal. The determination at step 210 may, for example, be based on some or all of the durations determined at steps 202, 203, 204, 205, 206 and 207 (such as tl, t2, t3, t4, t5 and / or t6). For example, if these durations are not compatible with the expected jamming signal pattem(s) (for example one or more of the chirp signal patterns in Figure 2a, Figure 4a, Figure 5a and Figure 6a), it may be determined that the potential jamming signal is not to be considered as a jamming signal. The determination step 210 may for example be carried out concurrently with, or as part of, steps 202, 203, 204, 205, 206, 207 and / or 208. In some embodiments, the method 200 comprises the optional step of sending 211, to a communication node, an indication that the potential jamming signal is a jamming signal. The jamming signal may be of the form a triangular chirp, a saw-tooth chirp, a sinusoidal chirp or an exponential chirp. The communication node may for example use the indication to raise a security alert in the communication system (for example the communication system 100) and take actions to mitigate the signal interference caused by the jammer.

[0141] In some scenarios, it may be that the jamming signal (or the potential jamming signal) sweeps past only one of the monitoring frequencies and fails to sweep past the other monitoring frequency. In other words, the jamming signal is partially detected by only one of the receivers. This is illustrated in Figure 9a, wherein the triangular jamming signal sweeps past the monitoring frequency fl of the first receiver 121 but not the monitoring frequency 12 of the second receiver 122. This leads to the jamming signal being detected only at a single receiver, as illustrated in Figure 9b, causing an incomplete determination of the signal pattern of the potential jamming signal and thereby leading to faulty jammer detections in the system. To overcome these problems, it is herein proposed to employ re-configurable (or re-tunable) receivers that may be re-configured to different monitoring frequencies in a dynamic fashion.

[0142] Thus, the receiver 122 monitoring the frequency 12 may be reconfigured to a frequency within the communication bandwidth, as shown in Figure 9c. The jamming signal may be detected by the receivers 121 , 122 at four different instances as shown in Figure 9d. In this way, the reconfigurable receivers may be used to re-configure to different monitoring frequencies to enable the determination of the signal patterns of the potential jamming signal.

[0143] Thus, in some embodiments, the method 200 comprises the optional step of transmitting 212 a signal for controlling at least one of the receivers to monitor a different frequency band than the frequency band previously monitored by that receiver. The signal may for example be transmitted to the individual receivers 121, 122, 123 or to the device 120 comprising the receivers.

[0144] The signal for controlling may for example be transmitted in response to the potential jamming signal not being detected at the frequency band previously monitored by that receiver. This may be the case, for example, when no input is obtained at step 201 or the input obtained at step 201 is zero / empty for at least one of the receivers.

[0145] Further, it may be that the different frequency band is advantageously selected such that it is closer, than the frequency band previously monitored by that receiver, to a frequency band at which the jamming signal has been detected. For example, in Figure 9a, the receiver 122 monitoring the frequency f2 may be re-configured to monitor a frequency located closer to the frequency fl where the potential jamming signal has already been detected by the other receiver 121.

[0146] In some embodiments, the method 200 comprises the optional step of determining a signal pattern of the potential jamming signal based on at least the durations tl, t2, t3 and t4. These time durations enable different jamming signal patterns to be distinguished from each other. For example, the asymmetric shape of the triangular chirp signal in Figure 4a causes tl to differ from t3 and t2 to differ from t4, which is not compatible with the sawtooth chirp signal in Figure 2a nor the sinusoidal chirp signal of Figure 5a.

[0147] Figure 10 illustrates a device 120 for determining one or more jamming characteristics of a potential jamming signal. The device 120 comprises one or more processor(s) 1203 and memory 1201. The memory 1201 contains instructions which when executed on the one or more processor(s) 1203 cause the device 120 to perform a method described in relation to Figures 1 -9d (for example, method steps of Figure 3a and / or Figure 3b). The memory 1201 or computer readable storage medium 1202 may be configured to store data, programmatic software code and / or other information described herein. The instructions may be software (SW) or computer program 1204 associated with the device 120.

[0148] Thus, the device 120 may further comprise SW or computer program 1204, which is stored in, for example, the memory 1201 or the computer readable storage medium 1202 at the device 120, or stored in external memory, e.g., database, accessible by the device 120. The SW or computer program 1204 may be executable by the one or more processors 1203.

[0149] The device may comprise at least two receivers / transmitter (TX / RX) 1205, for example, the receivers 121, 122, 123. The receivers 121, 122, 123, may monitor respective narrow frequency bands and detect the presence / absence of the potential jamming signal in the monitored frequencies. The receivers 121, 122, 123 may send an input regarding the potential jamming signal to the device 120.

[0150] The device 120 according to Figure 10 may have storage and / or processing capabilities. The device 120 may include one or more processors 1203 and a memory 1201 or a computer readable storage medium 1202. In particular, in addition to a traditional processor and memory, the device 120 may comprise integrated circuitry for processing and / or control, e.g., one or more processors and / or processor cores and / or Field Programmable Gate Array (FPGAs) and / or Application Specific Integrated Circuitry (ASICs) adapted to execute instructions. The processor(s) 1203 may be configured to access, e.g., write to and / or read from) the memory

[0151] 1201 or the computer readable storage medium 1202, which may comprise any kind of volatile and / or nonvolatile memory, e.g., cache and / or buffer memory and / or Random Access Memory (RAM) and / or Read-Only Memory (ROM) and / or optical memory and / or Erasable Programmable Read-Only Memory (EPROM).

[0152] A computer program product in the form of a computer readable storage medium 1202 may comprise any form of volatile or non-volatile computer readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, RAM, ROM, mass storage media, for example: a hard disk, removable storage media for example: a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD), and / or any other volatile or non-volatile, non-transitory device 120 readable and / or computerexecutable memory devices that store information, data, and / or instructions that may be used by one or more processors 1203. Computer readable storage medium 1202 may store any suitable instructions, data or information, including a computer program 1204, software, an application including one or more of logic, rules, code, tables, etc. and / or other instructions capable of being executed by one or more processors 1203. Computer readable storage medium

[0153] 1202 may be used to store any calculations made by one or more processors 1203. In some embodiments, one or more processors 1203 and computer readable storage medium 1202 may be considered to be integrated.

[0154] The device 120 may, for example, be a radio network node capable of transmitting and receiving a communication message. The device 120 may, for example, be a Third Generation Partnership Project (3GPP) cellular communication node such as a Sixth Generation (6G) node, a Fifth Generation (5G) node, a Long-Term Evolution (LTE) node, a Third Generation node (3G) or a Second Generation node (2G). More specifically, the device 120 may be a communication node in the radio access network (RAN) of any one of the above communication networks. In an embodiment, the device 120 is a gNodeB (gNB). The device 120 may for example be implemented in a RAN node.

[0155] The device 120 may also be a communication node operating in an Internet of Things (loT) network or a Low Power Wide Area Network (LPWAN). In other words, the device 120 may, for example, operate in any one of the 3GPP Narrowband loT (NB-loT), SigFox, LoRaWAN communication networks. Additionally or alternatively, the device 120 may be a communication node in the RAN of any of the above communication networks.

[0156] In some embodiments, the device 120 may be an edge node. In some embodiments where the device 120 is a gNB, the gNB may comprise both the gNB-Control Unit (gNB-CU) and the gNB-Distributed Unit (gNB-DU) in the device 120. In another embodiment, the device 120 is the gNB-DU wherein the gNB-CU resides in another radio node. In yet another embodiment, the device 120 is the gNB-CU wherein the gNB-DU is deployed separately and the gNB-DU interacts with a user equipment (UE). In each of the embodiments, the gNB-DU and the gNB- CU communicate with each other over the Fl interface. In one or more embodiments, the device 120 may communicate with one or more radio base stations to obtain input on the potential jamming signal. In some other embodiments the device 120 may directly monitor the communication band for the detecting the potential jamming signal.

Claims

CLAIMS:

1. A method (200) for determining one or more characteristics of a potential jamming signal, the method comprising:- obtaining (201) input regarding a potential jamming signal from at least two receivers (121, 122), each of the receivers monitoring a respective frequency band (fl, f2); determining (202), based on the obtained input, a first time duration (tl) between a time instant at which the potential jamming signal is detected at the frequency band (fl) monitored by the first receiver (121), and a time instant at which the potential jamming signal is detected at the frequency band (f2) monitored by the second receiver (122);- determining (203), based on the obtained input, a second time duration (t2, t4) between a time instant at which the potential jamming signal is detected at the frequency band monitored by one of the first receiver or the second receiver, and a subsequent time instant at which the potential jamming signal is detected at the frequency band monitored by the same one of the first receiver or the second receiver; and determining (208) one or more characteristics of the potential jamming signal based on the first time duration and the second time duration.

2. The method according to claim 1, comprising: determining (203), based on the obtained input, the second time duration (t2) between a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver, and a subsequent time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver; determining (204), based on the obtained input, a third time duration (t3) between a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver;determining (205), based on the obtained input, a fourth time duration (t4) between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver; and wherein the determining of the one or more characteristics of the potential jamming signal is additionally based on the third time duration and the fourth time duration.

3. The method according to any one of claims 1-2, wherein the obtained input comprises input from a third receiver (123) monitoring a frequency band (f3) located between the frequency bands monitored by the first and the second receiver, the method further comprising: determining (206), based on the obtained input, a fifth time duration (t5) between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the third receiver; and / or- determining (207), based on the obtained input, a sixth time duration (t6) between a time instant at which the potential jamming signal is detected at the frequency band monitored by the third receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver; and wherein the determining of the one or more characteristics of the potential jamming signal is additionally based on the fifth time duration and / or the sixth time duration.

4. The method according to any one of claims 1-3, comprising indicating (209), to a communication node, the one or more characteristics of the potential jamming signal for enabling detection of the potential jamming signal as a jamming signal.

5. The method according to any one of claims 1-4, comprising:determining (210) that the potential jamming signal is a jamming signal; and sending (211), to a communication node, an indication that the potential jamming signal is a jamming signal.

6. The method according to any of claims 1-5, comprising transmitting (212) a signal for controlling at least one of the receivers to monitor a different frequency band than the frequency band previously monitored by that receiver.

7. The method according to claim 6, wherein the signal for controlling is transmitted in response to the potential jamming signal not being detected at the frequency band previously monitored by that receiver.

8. The method according to any of claims 6-7, wherein the different frequency band is closer, than the frequency band previously monitored by that receiver, to a frequency band at which the jamming signal has been detected.

9. The method according to any of claims 1-8, wherein the potential jamming signal is a chirp signal comprising a waveform according to at least one of the following: a triangle, a saw-tooth, and a sinusoid.

10. The method according to any of claims 1-9, wherein the potential jamming signal is a periodic signal of a time period equal to sum of the first time duration, second time duration, third time duration and the fourth time duration.

11. The method according to any of claims 1-10, wherein at least one of the receivers monitors a frequency band in a guard band of a carrier.

12. The method according to any of claims 1-11, wherein at least one of the receivers monitors a frequency band located at an edge of a carrier bandwidth.

13. The method according to any of claims 1-12, wherein at least one of the receivers monitors a frequency band located within a carrier bandwidth.

14. The method according to any of claims 1-13, wherein the one or more characteristics of the potential jamming signal includes at least one of: a center frequency, a bandwidth and a shape of the potential jamming signal.

15. The method according to any of claims 1-14, wherein the obtained input indicates time instants at which the potential jamming signal is detected at the respective frequency bands monitored by the receivers.

16. The method according to any of claims 1-15, wherein the method is performed by Radio Access Network, RAN, equipment or a RAN node.

17. A device (120) for determining one or more characteristics of a potential jamming signal, the device comprising a memory (1201) and a processor (1203), the memory containing instructions which when executed on the processor, cause the device to: obtain input regarding a potential jamming signal from at least two receivers, each or the receivers monitoring a respective frequency band;- determine, based on the obtained input, a first time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by the first receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the second receiver; determine, based on the obtained input, a second time duration between a time instant at which the potential jamming signal is detected at the frequency band monitored by one of the first receiver or the second receiver, and a time instant at which the potential jamming signal is detected at the frequency band monitored by the same one of the first receiver or the second receiver; and determine one or more characteristics of the potential jamming signal based on the first time duration and the second time duration.

18. The device according to claim 17, the memory containing instructions which when executed on the processor, cause the device to perform the method according to one or more claims 2-16.

19. A computer program (1204) comprising instructions which, when executed on a device, cause the device to carry out the method according to one or more claims 1- 16.

20. A computer program product comprising a computer readable storage means on which the computer program according to claim 19 is stored.

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