Sensing with a wireless communications network

Abstract

A method for sensing in a wireless communications network. The method comprises calculating (402) a first channel filter based on channel characteristics of a first reference radio signal originating from a first wireless communications device and received by a radio access node of the wireless communications network. The method further comprises calculating (404) a second channel filter based on channel characteristics of a second reference radio signal originating from an identifiable second wireless communications device and received by the radio access node. The method further comprises filtering (406), with the first channel filter and the second channel filter, a third reference radio signal originating from the first wireless communications device and received by the radio access node.

Description

[0001] SENSING WITH A WIRELESS COMMUNICATIONS NETWORK

[0002] TECHNICAL FIELD

[0003] Embodiments disclosed herein relate to a method and a network node for sensing, such as detecting moving objects, with a wireless communications network. In particular, embodiments disclosed herein relate to detecting an unknown intruder in an environment with trusted persons. A corresponding computer program and a computer program carrier are also disclosed.

[0004] BACKGROUND

[0005] In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and / or User Equipments (UE), communicate via a Local Area Network such as a Wi-Fi network or a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, which may also be referred to as a beam or a beam group, with each service area or cell area being served by a radio access node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a NodeB, eNodeB (eNB), or gNB as denoted in 5G. A service area or cell area is a geographical area where radio coverage is provided by the radio access node. The radio access node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio access node.

[0006] Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network also referred to as 5G New Radio (NR). The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E- UTRAN / LTE is a variant of a 3GPP radio access network wherein the radio access nodes are directly connected to the EPC core network rather than to RNCs used in 3G networks. In general, in E-UTRAN / LTE the functions of a 3G RNC are distributed between the radio access nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio access nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio access nodes, this interface being denoted the X2 interface.

[0007] Wireless communication systems in 3GPP

[0008] Figure 1 illustrates a simplified wireless communication system with a UE 12, which communicates with one or multiple access nodes 103-104, which in turn is connected to a network node 106. The access nodes 103-104 are part of a radio access network 10.

[0009] For wireless communication systems pursuant to 3GPP Evolved Packet System, (EPS), also referred to as Long Term Evolution, LTE, or 4G, standard specifications, such as specified in 3GPP TS 36.300 and related specifications, the access nodes 103-104 corresponds typically to a Evolved NodeBs (eNBs) and the network node 106 corresponds typically to either a Mobility Management Entity (MME) and / or a Serving Gateway (SGW). The eNB is part of the radio access network 10, which in this case is the E-UTRAN (Evolved Universal Terrestrial Radio Access Network), while the MME and SGW are both part of the EPC (Evolved Packet Core network). The eNBs are interconnected via the X2 interface, and connected to EPC via the S1 interface, more specifically via S1-C to the MME and S1-U to the SGW.

[0010] For wireless communication systems pursuant to 3GPP 5G System, 5GS (also referred to as New Radio, NR, or 5G) standard specifications, such as specified in 3GPP TS 38.300 and related specifications, on the other hand, the access nodes 103-104 corresponds typically to an 5G NodeB (gNB) and the network node 106 corresponds typically to either a Access and Mobility Management Function (AMF) and / or a User Plane Function (UPF). The gNB is part of the radio access network 10, which in this case is the NG-RAN (Next Generation Radio Access Network), while the AMF and UPF are both part of the 5G Core Network (5GC). The gNBs are inter-connected via the Xn interface, and connected to 5GC via the NG interface, more specifically via NG-C to the AMF and NG-U to the UPF.

[0011] To support fast mobility between NR and LTE and avoid change of core network, LTE eNBs may also be connected to the 5G-CN via NG-U / NG-C and support the Xn interface. An eNB connected to 5GC is called a next generation eNB (ng-eNB) and is considered part of the NG-RAN. LTE connected to 5GC will not be discussed further in this document; however, it should be noted that most of the solutions / features described for LTE and NR in this document also apply to LTE connected to 5GC. In this document, when the term LTE is used without further specification it refers to LTE-EPC.

[0012] Joint communication and sensing (JCAS)

[0013] Use of communication jointly with sensing (such as radar) is an efficient way of improving the performance of communication systems or of providing additional services, such as surveillance. Recently there has been a great interest in the field of Integrated Sensing and Communication (ISAC) sometimes also called JCAS, where the wireless communication system is also used to sense objects or events in the surroundings.

[0014] JCAS is a key technology envisioned for 6G. Millimeter wave / sub-THz frequencies are of particular interest for implementing JCAS, due to large bandwidths and sharp beams enabling high 3D resolution of localization and mapping. A basic idea with JCAS is reusing parts of or all of the radio hardware and signalling used for data communication to also support radar functionality.

[0015] To this end, communication signals (carrying data transmissions) may be reused as radar signals. Other signals, such as various reference signals (e.g. CSI-RS, SSB, DM RS) may also be used as radar signals. There are two basic setups for radar: monostatic and bistatic / multistatic radar. In monostatic radar, transmitter and receiver are co-located. In bi / multistatic radar, the receiver is not co-located with the transmitter, i.e. receiver and transmitter are part of different units, for instance in different base-stations or different user equipments (UEs).

[0016] 3GPP SA1 has compiled a set of use cases in TR 22.837. A first of the use cases listed in TR 22.837 is regarding intruder detection in smart homes where 5G customerpremises equipment (CPE) in rooms may be used to detect movement when there is not supposed to be one. It is readily understood that intruder detection may be applied to factories, warehouses and other areas besides smart homes.

[0017] In short, through Doppler and beamforming analysis of reference signals in existing communication systems, location and movement patterns of objects in the surrounding may be determined. For example, Sounding Reference Signal (SRS) transmissions from stationary User Equipment (UE) may be used to sense moving objects (such as cars, buses, etc) in a cell, and the speed of these objects may be determined from processing the received SRS signals in a base station. However, there are some problems related to existing JCAS technology. For example, radio-based sensing is generally blind to an identity of the sensed object. Such identity mapping is expected to be added by a higher layer, matching the sensed object and a known object by positioning. In situations where the location is not known, or is inaccurate, this matching has shortcomings, which may be severe in situations when this sensing is used in for example intrusion detection.

[0018] Classically, intrusion detection systems are turned off when trusted persons enter a surveillance area. However, in large areas there may be risk that intruders may enter, and still be unnoticed. Thus, smarter surveillance will be needed where the system separates movement from known sources and alerts of movement from unknown sources.

[0019] SUMMARY

[0020] There is thus a need for a more efficient approach for object detection using JCAS, especially detection that separates movement from known sources and alerts of movement from unknown sources.

[0021] An object of embodiments disclosed herein may be to obviate some of the problems mentioned above related to JCAS.

[0022] According to a first aspect, the object is achieved by a method for sensing, such as detecting a moving object, in a wireless communications network. The method comprises calculating a first channel filter based on channel characteristics of a first reference radio signal originating from a first wireless communications device and received by a radio access node of the wireless communications network.

[0023] The method further comprises calculating a second channel filter based on channel characteristics of a second reference radio signal originating from an identifiable second wireless communications device and received by the radio access node.

[0024] The method further comprises filtering, with the first channel filter and the second channel filter, a third reference radio signal originating from the first wireless communications device and received by the radio access node.

[0025] According to a second aspect, the object is achieved by a network node for sensing, such as detecting a moving object, in a wireless communications network.

[0026] The network node is configured to calculate a first channel filter based on channel characteristics of a first reference radio signal originating from a first wireless communications device and received by a radio access node of the wireless communications network.

[0027] The network node is further configured to calculate a second channel filter based on channel characteristics of a second reference radio signal originating from an identifiable second wireless communications device and received by the first radio access node.

[0028] The network node is further configured to filter, with the first channel filter and the second channel filter, a third reference radio signal originating from the first wireless communications device and received by the radio access node.

[0029] According to a further aspect, the object is achieved by a computer program comprising instructions, which when executed by a processor, causes the processor to perform actions according to any of the aspects above.

[0030] According to a further aspect, the object is achieved by a carrier comprising the computer program of the aspect above, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium.

[0031] Since the third reference radio signal is filtered with the first channel filter and the second channel filter channel effects due to the environment and the second identifiable second wireless communications device are removed from the third reference radio signal thereby enabling detection of moving objects while still allowing for movement of the second identifiable second wireless communications device, which may be associated with a known / trusted object / person, within the premises of the detection system without triggering an alarm.

[0032] Thus, embodiments herein allow intrusion detection systems to run while still allowing for movement of known / trusted objects / persons within the premises of the detection system without triggering an alarm.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In the figures, features that appear in some embodiments are indicated by dashed lines. The various aspects of embodiments disclosed herein, including particular features and advantages thereof, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0035] Figure 1 is a block diagram schematically illustrating a prior art wireless communications network,

[0036] Figure 2 is a block diagram schematically illustrating a wireless communications network according to some embodiments herein,

[0037] Figure 3 is a block diagram schematically illustrating some embodiments herein, Figure 4 is a flowchart illustrating embodiments of a method according to some embodiments herein,

[0038] Figure 5 is a block diagram schematically illustrating some embodiments herein,

[0039] Figure 6 is a block diagram schematically illustrating some embodiments herein,

[0040] Figure 7 is a graph illustrating Doppler data,

[0041] Figure 8 is a block diagram schematically illustrating some embodiments herein,

[0042] Figure 9 is a block diagram schematically illustrating some embodiments herein,

[0043] Figure 10 is a block diagram schematically illustrating some embodiments herein, Figure 11 is a block diagram schematically illustrating some embodiments herein, Figure 12 is a block diagram schematically illustrating some embodiments herein, Figure 13 is a block diagram schematically illustrating some embodiments herein, Figure 14 is a graph illustrating Doppler data after filtering according to embodiments herein,

[0044] Figure 15 is a flowchart illustrating embodiments of a method according to some further embodiments herein,

[0045] Figure 16 is a block diagram schematically illustrating a network node according to some embodiments herein.

[0046] DETAILED DESCRIPTION

[0047] Embodiments disclosed herein relate to methods for performing filtering of sensing signals based on reception of radio signals from a transmitter associated with a trusted object or person.

[0048] Consider, without loss of generality, that sensing is done based on SRS transmissions in a 5G setup. A remote, SRS transmitting node is scheduled to transmit an SRS, which is then received at a gNB and used for sensing, herein called sensing-SRS. A known object, such as a person, is equipped with a terminal device, which also transmits an SRS signal with a known UE-id. The SRS from the known terminal device may be referred to as a trusted-SRS. Characteristics from the trusted-SRS is used to filter the sensing-SRS, to remove the sensing signature of the trusted object / person.

[0049] This is possible as the radio channel from the reflection of signals from the sensing- SRS on the trusted object to the gNB is to a large extent affected by the same radio channel as the signal of the trusted-SRS.

[0050] Embodiments herein relate to wireless communications networks in general. Figure 2 is a schematic overview depicting a wireless communications network 100 wherein embodiments herein may be implemented.

[0051] The wireless communications network 100 may be a telecommunications network, such as a cellular network. For example, the wireless communications network 100 may comprise one or more Radio Access Networks (RAN) and one or more Core Networks (ON).

[0052] The wireless communications network 100 may use a number of different technologies, such as Wi-Fi, Long Term Evolution (LTE), LTE-Advanced, 5G, New Radio (NR), Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications / enhanced Data rate for GSM Evolution (GSM / EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations. Embodiments herein relate to recent technology trends that are of particular interest in a 5G context, however, embodiments are also applicable in further development of the existing wireless communication systems such as e.g. WCDMA and LTE and in future wireless communication systems, such as 6G systems.

[0053] Access nodes, such as a radio access node 111, operate in the RAN of the wireless communications network 100. The radio access node 111 provides radio coverage over a geographical area, a service area referred to as a cell 115, which may also be referred to as a beam or a beam group of a first radio access technology (RAT), such as 5G, LTE, Wi-Fi or similar. There may also be further cells for which radio coverage is provided by the radio access node 111 , such as a second cell 116.

[0054] There may also be further radio access nodes, such as a second radio access node (not shown). The second radio access node may provide radio coverage over a third cell and / or a fourth cell (not shown).

[0055] The radio access node 111 and the second radio access node may each be a NR- RAN node, transmission and reception point e.g. a base station, a radio access node such as a Wireless Local Area Network (WLAN) access point or an Access Point Station (AP STA), an access controller, a base station, e.g. a radio base station such as a NodeB, an evolved Node B (eNB, eNode B), a gNB, a base transceiver station, a radio remote unit, an Access Point Base Station, a base station router, a transmission arrangement of a radio base station, a stand-alone access point or any other network unit capable of communicating with a wireless device within the service area depending e.g. on the radio access technology and terminology used. The respective first and second radio access node may be referred to as a serving radio access node and communicates with a UE with Downlink (DL) transmissions to the UE and Uplink (UL) transmissions from the UE.

[0056] A number of wireless communications devices operate in the wireless communications network 100, such as a first wireless communications device 121 and a second wireless communications device 122. The first and second wireless communications devices 121, 122 may each be a UE. The first and second wireless communications devices 121, 122 may each be identifiable by the wireless communications network 100. For example, the first and second wireless communications devices 121, 122 may each be identifiable by a respective UE-ID. A UE-ID uniquely identifies a UE and is used to establish secure communication between the UE and the network. The UE ID may be a temporary identifier, such as a Subscription Concealed Identifier (SUCI), or a permanent identifier, such as a Subscription Permanent Identifier (SUPI), and it is used in various network procedures, such as registration, authentication, and key agreement.

[0057] Further, the respective wireless communications device 121 , 122 may be a mobile station, a non-access point (non-AP) STA, a STA, a user equipment and / or a wireless terminal, that communicates via one or more Access Networks (AN), e.g. RAN, e.g. via the radio access node 111 to one or more core networks (CN) e.g. comprising a CN node 112, for example comprising an Access Management Function (AMF). It should be understood by the skilled in the art that “UE” is a non-limiting term which means any terminal, wireless communication terminal, user equipment, Machine Type Communication (MTC) device, Device to Device (D2D) terminal, or node e.g. smart phone, laptop, mobile phone, sensor, relay, mobile tablets or even a small base station communicating within a cell. Methods herein may be performed by a network node, such as the radio access node 111 , the second radio access node or the CN node 112. As an alternative, a Distributed Node (DN) and functionality, e.g. comprised in a cloud 140 as shown in Figure 2, may be used for performing or partly performing the methods.

[0058] Embodiments herein will now be described in more detail. Embodiments herein discloses a method for sensing and possibly detecting unknown objects in an environment with known objects. Details of the embodiments below will be explained through usage of a 5G system transmission of SRS signals for intrusion detection. It should be readily understood that other systems than 5G and radio signals other than SRS may be used instead.

[0059] Embodiments disclosed herein are based on radio signals, sent by a network node, such as the second radio access node, possibly reflected by a moving object in the environment, and received by another network node, such as the radio access node 111, and some level of elaborate signal processing on the radio signals. The processing may for example be performed in the radio access node 111 or in the cloud 140 dependent on a requirement for real-time detection.

[0060] Figure 3 illustrates a scenario in which embodiments disclosed herein may be used advantageously. Figure 3 illustrates the wireless communications network 100 including the radio access node 111. Figure 3 further illustrates an object 130, such as an intruder. The object 130 is a moving object.

[0061] Detection of the moving object 130, which in some scenarios may be described as intrusion detection, may in a reference solution be accomplished by sending a reference signal from the first wireless communications device 121 which is scattered against the object 130 and detected by the radio access node 111. The radio access node 111 may for example detect changes in the scattered signal from the first wireless communications device 121 due to the reflection from the moving object 130. However, if there are trusted objects, like a person using the second wireless communications device 122, in the same environment which is covered by such an object detection system, these will also be detected. Embodiments herein aim at filtering out detection of the trusted objects such that only unknown objects are detected.

[0062] The environment in which the first and second wireless communications devices

[0063] 121 , 122 operate may be an indoor environment. Embodiments will now be described with reference to a flowchart in Figure 4.

[0064] Figure 4 illustrates a flowchart of a method for sensing, such as detecting a moving object 130, in the wireless communications network 100. The moving object 130 to be detected may be a passive object without any radio transmitter. The method may be performed by a network node of the wireless communications network 100, such as the radio access node 111 or the CN node 112. The method actions of Figure 4 may be performed in any suitable order.

[0065] Action 401

[0066] Action 401 may be performed in a setup / calibration phase illustrated in Figure 5. In some embodiments herein the method comprises receiving a first reference radio signal from the first wireless communications device 121. The radio access node 111 may receive the first reference radio signal. In some embodiments herein the radio access node 111 receives a multiple of first reference radio signals from a multiple of first wireless communications devices.

[0067] In some embodiments herein the first wireless communications device 121 is stationary.

[0068] The first reference radio signal may have been scattered against a static environment before reception. This is illustrated by scattering against a building in Figure 5. In some embodiments herein the environment which scatters the first radio signal may be an indoor environment even though Figure 5 illustrates scattering of the first radio signal against a fagade of the building.

[0069] As illustrated in Figure 5 the static environment may not comprise the moving object 130 to be detected nor the identifiable second wireless communications device 122. In some embodiments herein the setup phase is a phase when it is guaranteed that there will be no motion of objects that scatter the first radio signal.

[0070] Figure 6 illustrates a spatial profile plot of the received first reference radio signal. A cross indicates receive directions of the first reference radio signal.

[0071] The first reference radio signal may be an SRS or another known uplink reference signal, such as a Demodulation Reference Signal (DMRS). Different parameters of the first reference radio signal may be set. These parameters may affect the result of the sensing. For example, a higher bandwidth provides higher resolution of determining a delay based on the reference signal. A higher periodicity provides possibilities to detect Doppler in finer granularity. Action 402

[0072] The method further comprises calculating a first channel filter based on channel characteristics of a first reference radio signal originating from the first wireless communications device 121 and received by the radio access node 111 of the wireless communications network 100.

[0073] The first channel filter is adapted to remove a first channel characteristics from the third reference radio signal, which first channel characteristics are associated with propagation between the first wireless communications device 122 and the radio access node 111.

[0074] The first channel filter may be referred to as a static sensing filter which may be used to filter out contributions to the radio channel from the static environment. The first channel filter may be implemented by for example beamforming / nulling, Doppler filtering, delay gating, etc.

[0075] Figure 7 illustrates a Doppler spectrum indicating both a moving intruder and a moving second wireless communications device 122.

[0076] In case there are multiple first reference radio signals from multiple first wireless communications devices the calculation of the first channel filter may comprise calculations of multiple first channel filters: a respective first channel filter for each first radio signal.

[0077] Action 403

[0078] The method may further comprise receiving a second reference radio signal from the identifiable second wireless communications device 122. The second wireless communications device 122 may be a trusted device carried by a trusted person / object. The trusted device may be labelled trusted based on e.g. a user-ID in a list of trusted user-IDs. The second reference radio signal may be an SRS and may be referred to as a trusted-SRS. The second reference radio signal may also be another known uplink reference signal, such as a second DMRS.

[0079] The second reference radio signal may be received by the radio access node 111. This is illustrated in Figure 8. Figure 9 illustrates a spatial profile plot of the received second reference radio signal. A cross indicates a receive direction of the second reference radio signal.

[0080] In some embodiments herein the second wireless communications device 122 is moving and in some other embodiments disclosed herein it is stationary. The second reference radio signal may be received in an operational phase.

[0081] The received second reference radio signal may comprise a series of radio signals at different time instances.

[0082] Action 404

[0083] The method further comprises calculating a second channel filter based on channel characteristics of the second reference radio signal originating from the identifiable second wireless communications device 122 and received by the radio access node 111.

[0084] The first and second channel characteristics of the obtained reference radio signal may be any one or more of: spatial characteristics, time characteristics, frequency characteristics and polarization characteristics.

[0085] In some embodiments herein the spatial characteristics include any one or more of: signal strength of the obtained reference radio signal, direction of arrival of the obtained reference radio signal, and receive precoders used for receiving the obtained reference radio signal.

[0086] The second channel filter may be adapted to remove a second channel characteristics from the third reference radio signal, which second channel characteristics are associated with propagation between the identifiable second wireless communications device 122 and the radio access node 111. Thus, after application of the second channel filter the resulting channel profile, such as a spatial profile, may not contain any channel information, such as spatial directions, indicating motion unless there is an intruder. The higher movement speed of the second wireless communications device 122, the higher the update frequency of the filter for the second reference radio signal is needed to remove it from the third reference signal to detect. The SRS periodicities in the standard are designed to handle walking speeds without issues.

[0087] Since the second channel filter hasn’t been applied for the Doppler spectrum of Figure 7 the motion of the second wireless communications device 122 will also be visible in it.

[0088] Action 405

[0089] In some embodiments disclosed herein the method further comprises receiving a third reference radio signal originating from the first wireless communications device 121.

[0090] In some embodiments herein the third reference radio signal have been scattered against the moving object 130. The third reference radio signal may have been scattered before reception against the static environment and an object on which the identifiable second wireless communications device 122 is arranged.

[0091] Figure 10 illustrates a first scenario in which embodiments disclosed herein may be applied. Figure 10 illustrates reception of the second and third reference signals by the radio access node 111 in a scenario where there are no unknown moving objects scattering the first reference radio signal. A periodicity of the second and third reference signals may be chosen short enough such that the position of the second wireless communications device 122 within a period of the reference signals hasn’t changed substantially in a way that it affects the channel from the second wireless communications device 122 to the radio access node 111. Periodicity of the reference signals, such as SRS, may be on the order of a fraction of a second.

[0092] Figure 11 illustrates a spatial profile plot of the received first and second reference radio signals in the operational phase. A cross indicates a receive direction of the respective first and second reference radio signal.

[0093] Action 406

[0094] The method further comprises detecting the moving object 130 by filtering, with the first channel filter and the second channel filter, the third reference radio signal originating from the first wireless communications device 121 and received by the radio access node 111. In some embodiments herein at least some radio waves that carry the third reference radio signal interact with the moving object 130. Then the method may further comprise detecting the moving object 130 by the filtering.

[0095] The respective channel filter may comprise any one or more of a spatial filter, a time filter, a frequency filter, or a polarization filter.

[0096] For example, Figure 11 further illustrates spatial channel filters as circles around the crosses illustrating the receive directions of the reference signals.

[0097] Figure 12 illustrates a second scenario in which embodiments disclosed herein may be applied. Figure 12 illustrates reception of the second and third reference signals by the radio access node 111 in a scenario where the unknown moving object 130 scatters the first reference radio signal.

[0098] Figure 13 illustrates spatial channel filters as circles around the crosses illustrating the receive directions of the reference signals. As can be seen in Figure 13 the spatial filters filter out signal directions from which there has not been scattering by the moving object 130. That is the spatial filters filter out signal directions which are associated with the static environment and with the second wireless communications device 122.

[0099] In some embodiments herein the respective channel filter comprises a Doppler filter based on time variations of the respective radio channel.

[0100] The received third reference radio signal may comprise a series of radio signals at different time instances. Then detecting the moving object 130 is performed by detecting a difference in channel characteristics of the filtered third reference radio signal between at least two of the time instances. The reference signals may be periodic.

[0101] In situations where there is motion detected in the filtered third reference radio signal, for example based on changes over time, e.g. in the Doppler spectrum, an intrusion detection may trigger an alarm. For example, Figure 14 illustrates a Doppler spectrum after filtering the third reference radio signal with the first channel filter and the second channel filter. Doppler data indicating motion of the intruder is indicated with the arrow.

[0102] Figure 15 illustrates a flowchart comprising some optional actions of the method for sensing, such as detecting the moving object 130. The optional actions of Figure 15 may for example be performed after the actions of Figure 4.

[0103] Action 1501

[0104] In some embodiments the respective channel filter comprises a delay filter and then the method may further comprise obtaining an estimation of a position of the identifiable second wireless communications device 122. The estimation of the position of the identifiable second wireless communications device 122 may be used below in action 1503 to filter the third reference signal.

[0105] Action 1502

[0106] In some embodiments the method further comprises obtaining an estimation of a change of the position of the identifiable second wireless communications device 121.

[0107] Action 1503

[0108] Filtering the third reference radio signal may be further based on the estimated position of the identifiable second wireless communications device 122. Action 1504

[0109] Filtering the third reference radio signal may be further based on the estimated change of position of the identifiable second wireless communications device 122.

[0110] As mentioned above, the channel profiles and channel filters may be based on spatial directions as e.g. estimated by and implemented using an antenna array at the radio access node 111. But the radio channel may also be estimated over time, frequency, and polarization, which may provide additional degrees of freedom for determining profiles of trusted and untrusted objects and persons. In one embodiment, time variations of the radio channel is considered, e.g. via the Doppler frequencies of the (second wireless communications device 122 to radio access node) channel, the (first wireless communications device 121 to second wireless communications device 122 to radio access node 111) channel and the (first wireless communications device 121 to intruder to radio access node 111) channel. It is important to note that the Doppler frequencies of the (first wireless communications device 121 to second wireless communications device 122 to radio access node 111) channel may be different than the Doppler frequencies of the (second wireless communications device 122 to radio access node 111) channel, since the former is additionally affected by the relative movement of the second wireless communications device 122 compared to the path (including any possible multipath) between the first wireless communications device 121 and second wireless communications device 122. However, this additional Doppler shift may in some cases be determined using knowledge of the physical movement of the second wireless communications device 122, either via side information or by estimation of this physical movement based on radio signals, e.g. positioning. The side information may originate from apps periodically signaling a position. Knowing the (approximate) Doppler shifts of the (first wireless communications device 121 to second wireless communications device 122 to radio access node 111) channel may enable construction of a more efficient filter compared to if only spatial information, such as directional information, is used, thereby resulting in an overall more robust and reliable detection.

[0111] In another embodiment, frequency variations of the radio channel is considered. As known in the art, the frequency response of the channel may be used to estimate the time delay or path length to the second wireless communications device 122 (via e.g. an Inverse Fast Fourier Transform (IFFT)). Knowing the difference in path length between the channel reflected on the trusted object (associated with the second wireless communications device 122) from the sensing-SRS and the channel from the trusted SRS may enable an even more efficient filter e.g. via delay gating (i.e. filtering) of the sensing- SRS to further suppress the contributions of the second wireless communications device 122 to the sensing-SRS channel. As in the case of Doppler frequencies, the (second wireless communications device 122 to radio access node 111) channel contains only partial information relevant for the delay of the (first wireless communications device 121 to second wireless communications device 122 to radio access node 111) channel. However, this may be used to establish delay regions that may be used in the filter design. For example, estimation of the position of the identifiable second wireless communications device 122 may be used to filter the third reference signal by suppressing signal components that have a certain delay.

[0112] Figure 16 illustrates further optional details of a network node 1601, such as the radio access node 111 or the CN node 112. The network node 1601 is configured to perform the method actions of Figures 4 and 15 above. The network node 1601 is configured for sensing in the wireless communications network 100. The network node 1601 may be part of an intrusion detection system.

[0113] The embodiments herein may be implemented through a processor or one or more processors, such as the processor 1604 of a processing circuitry in the network node 1601 and depicted in Figure 16 together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the network node 1601. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server or a cloud and downloaded to the network node 1601.

[0114] The network node 1601 may further comprise a memory 1602 comprising one or more memory units. The memory comprises instructions executable by the processor in the network node 1601.

[0115] The respective memory 1602 is arranged to be used to store e.g. information, data, configurations, and applications to perform the methods herein when being executed in the network node 1601. In some embodiments, a computer program 1603 comprises instructions, which when executed by the at least one processor, cause the at least one processor of the network node 1601 to perform the actions above.

[0116] In some embodiments, a carrier 1605 comprises the computer program, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer- readable storage medium.

[0117] The network node 1601 may further comprise an input and output interface, I / O, 1606 configured to communicate with other devices. The input and output interface 1606 may comprise one or more transceivers, such as a wireless transceiver.

[0118] The network node 1601 is configured to calculate the first channel filter based on channel characteristics of the first reference radio signal originating from the first wireless communications device 121 and received by the radio access node 111 of the wireless communications network 100.

[0119] The network node 1601 is further configured to calculate the second channel filter based on channel characteristics of the second reference radio signal originating from an identifiable second wireless communications device 122 and received by the first radio access node 121.

[0120] The network node 1601 is further configured to filter, with the first channel filter and the second channel filter, the third reference radio signal originating from the first wireless communications device 121 and received by the radio access node 111.

[0121] In some embodiments disclosed herein at least some radio waves that carry the third reference radio signal interact with the moving object 130 and then the network node 111 , 112 may be further configured to detect the moving object 130 by being configured to filter with the first channel filter and the second channel filter, the third reference radio signal.

[0122] The received third reference radio signal may comprise the series of radio signals at different time instances and then the network node 111 , 112 may be further configured to detect the moving object by detecting the difference in channel characteristics of the filtered third reference radio signal between at least two of the time instances. In some embodiments disclosed herein the respective channel filter comprises the delay filter and then the network node 111, 130 may be further configured to obtain the estimation of the position of the identifiable wireless communications device 121 and filter the third reference radio signal further based on the estimated position of the identifiable wireless communications device 121.

[0123] In some embodiments disclosed herein the respective channel filter comprises the Doppler filter and then the network node 111, 112 may be further configured to obtain the estimation of the change of the position of the identifiable wireless communications device 121 and filter the third reference radio signal further based on the estimated change of position of the identifiable wireless communications device 121.

[0124] The first channel filter may be adapted to remove first channel characteristics from the third reference radio signal. The first channel characteristics are associated with propagation between the first wireless communications device 122 and the radio access node 111. The second channel filter may be adapted to remove second channel characteristics from the third reference radio signal. The second channel characteristics may be associated with propagation between the identifiable second wireless communications device 122 and the radio access node 111.

[0125] Those skilled in the art will also appreciate that the units described above may refer to a combination of analog and digital circuits, and / or one or more processors configured with software and / or firmware, e.g. stored in the network node, that when executed by the respective one or more processors such as the processors described above cause the one or more processors to carry out actions described herein, such as the method actions described above in relation to Figure 4 or Figure 15.

[0126] One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuitry (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC).

[0127] When using the word "comprise" or “comprising” it shall be interpreted as nonlimiting, i.e. meaning "consist at least of". The embodiments herein are not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used.

Claims

CLAIMS1. A method for sensing in a wireless communications network (100), the method comprising: calculating (402) a first channel filter based on channel characteristics of a first reference radio signal originating from a first wireless communications device (121) and received by a radio access node (111) of the wireless communications network (100); calculating (404) a second channel filter based on channel characteristics of a second reference radio signal originating from an identifiable second wireless communications device (122) and received by the radio access node (111); and filtering (406), with the first channel filter and the second channel filter, a third reference radio signal originating from the first wireless communications device (121) and received by the radio access node (111).

2. The method according to claim 1 , wherein at least some radio waves that carry the third reference radio signal interact with a moving object (130) and wherein the method further comprises detecting the moving object (130) by the filtering.

3. The method according to claim 2, wherein the received third reference radio signal comprises a series of radio signals at different time instances and detecting the moving object is performed by detecting a difference in channel characteristics of the filtered third reference radio signal between at least two of the time instances.

4. The method according to claim 3, wherein the received second reference radio signal comprises a series of radio signals at different time instances.

5. The method according to any of the claims 1-4, wherein the first and second channel characteristics of the obtained reference radio signal is any one or more of: spatial characteristics, time characteristics, frequency characteristics and polarization characteristics.

6. The method according to any of the claims 1-5, wherein the respective channel filter comprises any one or more of a spatial filter, a time filter, a frequency filter, or a polarization filter.

7. The method according to any of the claims 1-6, wherein the respective channel filter comprises a delay filter and wherein the method further comprises: obtaining (1501) an estimation of a position of the identifiable second wireless communications device (122); and filtering (1503) the third reference radio signal further based on the estimated position of the identifiable second wireless communications device (122).

8. The method according to any of the claims 1-7, wherein the respective channel filter comprises a Doppler filter based on time variations of a respective radio channel.

9. The method according to claim 8, wherein the method further comprises: obtaining (1502) an estimation of a change of a position of the identifiable second wireless communications device (121); and filtering (1504) the third reference radio signal further based on the estimated change of position of the identifiable second wireless communications device (122).

10. The method according to any of the claims 1-9, wherein the first channel filter is adapted to remove first channel characteristics from the third reference radio signal, which first channel characteristics are associated with propagation between the first wireless communications device (122) and the radio access node (111) and wherein the second channel filter is adapted to remove second channel characteristics from the third reference radio signal, which second channel characteristics are associated with propagation between the identifiable second wireless communications device (122) and the radio access node (111).

11. The method according to any of the claims 1-10, wherein the first reference radio signal has been scattered against a static environment before reception.

12. The method according to claim 11, wherein the static environment doesn’t comprise the moving object (130) to be detected nor the identifiable second wireless communications device (122).

13. The method according to any of the claims 1-12, wherein the third reference radio signal has been scattered before reception against the static environment and an object on which the identifiable second wireless communications device (122) is arranged.

14. The method according to any of the claims 1-13, wherein the first wireless communications device (121) is stationary.

15. The method according to any of the claims 2-14, wherein the moving object (130) to be detected is a passive object without any radio transmitter.

16. The method according to any of the claims 1-15, wherein the method is performed by a network node (111, 112) of the wireless communications network (100), such as the radio access node (111).

17. A network node (111, 112) for sensing in a wireless communications network (100), the network node (111 , 112) being configured to: calculate a first channel filter based on channel characteristics of a first reference radio signal originating from a first wireless communications device (121) and received by a radio access node (111) of the wireless communications network (100); calculate a second channel filter based on channel characteristics of a second reference radio signal originating from an identifiable second wireless communications device (122) and received by the first radio access node (121); and filter, with the first channel filter and the second channel filter, a third reference radio signal originating from the first wireless communications device (121) and received by the radio access node (111).

18. The network node (111, 112) according to claim 17, wherein at least some radio waves that carry the third reference radio signal interact with a moving object (130) and wherein the network node (111, 112) is further configured to detect the moving object (130) by being configured to filter, with the first channel filter and the second channel filter, the third reference radio signal.

19. The network node (111, 112) according to claim 18, wherein the received third reference radio signal comprises a series of radio signals at different time instances and wherein the network node (111, 112) is configured to detect the moving object by detecting a difference in channel characteristics of the filtered third reference radio signal between at least two of the time instances.

20. The network node (111, 112) according to any of the claims 17-19, wherein the respective channel filter comprises a delay filter and wherein the network node (111, 130) is further configured to: obtain an estimation of a position of the identifiable wireless communications device (121) and filter the third reference radio signal further based on the estimated position of the identifiable wireless communications device (121).

21. The network node (111, 112) according to any of the claims 17-20, wherein the respective channel filter comprises a Doppler filter and wherein the network node (111, 112) is further configured to: obtain an estimation of a change of a position of the identifiable wireless communications device (121) and filter the third reference radio signal further based on the estimated change of position of the identifiable wireless communications device (121).

22. The network node (111, 112) according to any of the claims 17-21, wherein the first channel filter is adapted to remove a channel associated with propagation between the first wireless communications device (122) and the radio access node (111) and wherein the second channel filter is adapted to remove a channel associated with propagation between the identifiable wireless communications device (121) and the first radio access node (121).

23. The network node (111, 112) according to any of the claims 17-22, wherein the network node is a radio access node (111).

24. A computer program (503), comprising computer readable code units which when executed on a computer causes the computer to perform the method according to any one of claims 1-16.

25. A carrier (505) comprising the computer program according to claim 24, wherein the carrier (505) is one of an electronic signal, an optical signal, a radio signal and a computer readable medium.

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