Time shift of FFT processing window for detection of sensing signal

Abstract

Time shift of FFT processing window for detection of sensing signal For sensing at least one target in an environment of a node of a wireless communication system, the node receives a wireless signal which comprises a sequence of Orthogonal Frequency Division Multiplexing, OFDM, symbols. Each of the OFDM symbols has a cyclic prefix, CP, and a length of the CP varies between at least some of the OFDM symbols. The node detects, based on Fast Fourier Transform, FFT, of the received wireless signal in an FFT processing window, a sensing signal modulated onto at least some of the OFDM symbols. For at least one of the OFDM symbols, the node applies a time shift relative to the OFDM symbol to the FFT processing window.

Description

[0001] P110928WO01

[0002] - 1 -

[0003] Time shift of FFT processing window for detection of sensing signal

[0004] Technical Field

[0005] The present invention relates to methods for wireless-signal based sensing and to corresponding devices, systems, and computer programs.

[0006] Background

[0007] Sensing based on wireless signals may be used to derive various information on the surrounding environment of wireless communication devices or wireless communication system, such as location, shape, or speed of objects in the surrounding. Examples of use cases of sensing in cellular communication systems include vehicular traffic monitoring, drone detection, gesture detection, motion detection, presence detection of objects or persons, vital sign detection, environment mapping, particle detection, pollution detection, or environmental reconstruction. The sensing typically involves measurements on wireless signals, also denoted as sensing signals, e.g., by measuring Time of Flight (ToF), or Doppler shift. In these measurements, the target to be sensed, e.g., object, is passive, i.e., is different from a source of the sensing signals and also different from the entity performing the measurements.

[0008] One reason why wireless sensing has received increased interest is that wireless signals used for performing sensing may be generated by the same hardware that is used for wireless communication. For example, a wireless signal carrying communication data can also be used for measurements related to sensing. When the same wireless signal, or at least the same hardware and spectrum, is used for both communication and wireless sensing, this is often referred to as joint communication and sensing (JCAS) or Integrated Sensing and Communication (ISAC).

[0009] ISAC may be regarded is a promising enhancement of cellular communication technologies, e.g., of the existing 5G (5th Generation) NR technology specified by 3GPP (3rd Generation Partnership Project) or of a future 6G (6th Generation) cellular communication technology. Here, the basic idea is to use base stations and / or UEs (user equipments) to sense the environment. This can be done by using wireless signals transmitted for purposes of communication, including wireless signals carrying communication data and control signals. Further, it is also possible to re-utilize device structures and configurations provided for communication purposes to transmit dedicated sensing signals. P110928WO01

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[0011] Sensing can be implemented as monostatic sensing, where a device transmits a wireless signal and the same device or co-located device performs the sensing-related measurements based on this wireless signal, e.g., by receiving an echo or reflection of this wireless signal. In monostatic sensing the sensing transmitter and sensing receiver are thus co-located, or even in the same device. Further, the sensing could be implemented as bistatic sensing, where a first device transmits a wireless signal and a second device at a different location performs the sensing-related measurements based on this wireless signal, e.g., by detecting the wireless signal after propagation through the environment, or by detecting an echo or reflection of the signal. Further, the sensing could be implemented as multistatic sensing, where a first device transmits a wireless signal and multiple second devices at different locations perform the sensing-related measurements based on this wireless signal, e.g., by detecting the signal after propagation through the environment, or by detecting an echo or reflection of the signal. In the case of bistatic or multistatic sensing, the sensing transmitter and the sensing receiver(s) are different devices in different locations. In some scenarios, multistatic sensing can also be based on utilizing multiple sensing transmitters and one sensing receiver.

[0012] One possibility to determine velocity of the target is to detect a Doppler signature, caused by Doppler-induced frequency shift due to movement of the target or parts of the target, in the received wireless signal. Knowing the Doppler signature of a target can also help in classifying targets. For example, a pedestrian has a very particular Doppler signature due to movements of legs and arms and is typically moving slower than a car. Doppler signatures can also help to differentiate reflected signals from stationary clutter and moving targets. The Doppler signatures can be determined by measurements based on a pulse train in the wireless signal. Related processing by the sensing receiver typically involves determination of cyclic correlation based on an FFT (Fast Fourier Transform) of the received wireless signal.

[0013] In a wireless communication technology which is based on OFDM (Orthogonal Frequency Division Multiplexing) a pulse of the pulse train may be generated by applying a sequence in frequency-domain to the allocated subcarriers of the OFDM modulator and then adding a cyclic prefix (CP) in accordance with the requirements of the technology. This may be done for each OFDM symbol or for only some OFDM-symbols, e.g., every N-th OFDM symbol, where N is an integer larger than one. This may however affect characteristics of the pulse train: By way of example, the NR technology supports different numerologies which have different subcarrier spacings and different OFDM symbol durations. Further, also the CP length may vary. Fig. 1A shows a table which lists exemplary numerologies of the NR technology and the respective OFDM symbol durations and CP length. P110928WO01

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[0015] In the NR technology, time-domain organization of OFDM symbols is based on slots and subframes, see for example 3GPP TS 38.211 V18.4.0 (2024-09). A subframe spans Tsf= 1 ms and contains Nsf= 2μ· 14 OFDM symbols, numbered l = 0,1,..., Nsf- 1. OFDM symbols with indices l = 2μ· 7 in a subframe have a longer CP (TCP,land NCP,l, l = 2μ· 7) than other symbols in a subframe TCP,land NCP,l, l ≠ 2μ· 7). TCP,l= NCP,l· Tcwith Tc= 1 / (480E3 · Nf) s and = 4096. These OFDM symbols occur every 0.5 ms, irrespective of the numerology. Such basic frame structure has been utilized from 3GPP Release 15 and can be expected to be also utilized in future evolutions of the NR technology.

[0016] The starting position of OFDM symbol I in a subframe is given by tstart,l= 0 for l = 0 and tstart,l= tstart,l-1+ (Nu+ NCP,l-1)Tcfor other l, Nu= 2048 · 64 · 2-μ

[0017]

[0018] 2 This pattern is repeated for each subframe. By way of example, Fig. 1B shows a table indicating the start time of the first 14 OFDM symbols for numerology / z = 1, which has 30 kHz subcarrier spacing, expressed in samples of duration 16Tc. The table shows both the start of the CP as well as the start of the main symbol tstart,l+ TCP,l. Fig. 1C shows a table which also indicates the time difference (expressed in samples of duration 16Tc) between the start samples of the current and preceding main part of the OFDM symbol, i.e., tstart,l+ TCP,l−(tstart,l-1+ TCP,l-1). The difference value for l = 0 is calculated as the start position of the main part of the OFDM symbol for l = 0 and the main symbol for l = 27 in the previous subframe.

[0019] As can be seen from the tables of Figs. 1 B and 1 C, due do the different CP lengths the OFDM symbols, when modulating the sensing sequence(s) onto the OFDM symbols, the pulses would occur at slightly irregular time instances: The CP of OFDM symbol l starts at tstart,land the main symbol duration at tstart,l+ TCP,l. The difference between start samples of the main part of the OFDM symbols is different for l = 0 compared to other OFDM symbols. For the considered example numerology μ = 1, such difference occurs for symbols l = 0 and l = 14 in a subframe. In more general terms, for numerology μ, such occurs for every 2μ· 7-th symbol in a subframe. Due to the above irregularity of the CP length, the pulses are not equidistantly spaced. This has the effect that, fora single target with constant velocity, side peaks may occur in the Doppler signature. These side peaks adversely affect the sensing accuracy and can for example mask the signatures of other targets.

[0020] Accordingly, there is a need for techniques which allow for efficiently processing sensing signals that are modulated onto OFDM symbols of a wireless signal with variations of CP length. P110928WO01

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[0022] Summary

[0023] According to an embodiment, a method of sensing at least one target in an environment of a node of a wireless communication system is provided. According to the method, the node receives a wireless signal which comprises a sequence of OFDM symbols. Each of the OFDM symbols has a CP, and a length of the CP varies between at least some of the OFDM symbols. The node detects, based on FFT of the received wireless signal in an FFT processing window, a sensing signal modulated onto at least some of the OFDM symbols. For at least one of the OFDM symbols, the node applies a time shift relative to the OFDM symbol to the FFT processing window.

[0024] According to a further embodiment, a method of sensing at least one target in the environment of a node of a wireless communication system is provided. According to the method, the node transmits a wireless signal which comprises a sequence of OFDM symbols. Each of the OFDM symbols has a CP, and a length of the CP varies between at least some of the OFDM symbols. The node modulates a sensing signal onto at least some of the OFDM symbols. For at least one of the OFDM symbols, the node sets a time-shift relative to the OFDM symbol, to be applied by a receiver of the wireless signal to an FFT processing window for FFT of the wireless signal. The node indicates the time-shift to the receiver of the wireless signal.

[0025] According to a further embodiment, a node for a wireless communication system is provided. The node is configured to receive a wireless signal comprising a sequence of OFDM symbols. Each of the OFDM symbols has a CP, and a length of the CP varies between at least some of the OFDM symbols. Further, the node is configured to detect, based on FFT of the received wireless signal in an FFT processing window, a sensing signal modulated onto at least some of the OFDM symbols of the sequence. Further, the node is configured to, for at least one of the OFDM symbols, apply a time shift relative to the OFDM symbol to the FFT processing window.

[0026] According to a further embodiment, a node for a wireless communication system is provided. The node comprises at least one processor and a memory. The memory contains instructions executable by said at least one processor, whereby the node is operative to receive a wireless signal comprising a sequence of OFDM symbols. Each of the OFDM symbols has a CP, and a length of the CP varies between at least some of the OFDM symbols. Further, the memory contains instructions executable by said at least one processor, whereby the node is operative to detect, based on FFT of the received wireless signal in an FFT processing window, a sensing signal modulated onto at least some of the OFDM symbols of the sequence. Further, P110928WO01

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[0028] the memory contains instructions executable by said at least one processor, whereby the node is operative to, for at least one of the OFDM symbols, apply a time shift relative to the OFDM symbol to the FFT processing window.

[0029] According to a further embodiment, a node for a wireless communication system is provided. The node is configured to transmit a wireless signal comprising a sequence of OFDM symbols. Each of the OFDM symbols has a CP, and a length of the CP varies between at least some of the OFDM symbols. Further, the node is configured to modulate a sensing signal onto the wireless signal of at least some of the OFDM symbols of the sequence. Further, the node is configured to, for at least one of the OFDM symbols of the sequence, set a time-shift relative to the OFDM symbol, to be applied by a receiver of the wireless signal for time-shifting an FFT processing window for FFT of the wireless signal. Further, the node is configured to indicate the time shift to the receiver of the wireless signal.

[0030] According to a further embodiment, a node for a wireless communication system is provided. The node comprises at least one processor and a memory. The memory contains instructions executable by said at least one processor, whereby the node is operative to transmit a wireless signal comprising a sequence of OFDM symbols. Each of the OFDM symbols has a CP, and a length of the CP varies between at least some of the OFDM symbols. Further, the memory contains instructions executable by said at least one processor, whereby the node is operative to modulate a sensing signal onto the wireless signal of at least some of the OFDM symbols of the sequence. Further, the memory contains instructions executable by said at least one processor, whereby the node is operative to, for at least one of the OFDM symbols of the sequence, set a time-shift relative to the OFDM symbol, to be applied by a receiver of the wireless signal for time-shifting an FFT processing window for FFT of the received wireless signal. Further, the memory contains instructions executable by said at least one processor, whereby the node is operative to indicate the time shift to a receiver of the wireless signal.

[0031] According to a further embodiment, a computer program or computer program product is provided, e.g., in the form of a non-transitory storage medium, which comprises program code to be executed by at least one processor of node of a wireless communication system. Execution of the program code causes the node to receive a wireless signal comprising a sequence of OFDM symbols. Each of the OFDM symbols has a CP, and a length of the CP varies between at least some of the OFDM symbols. Further, execution of the program code causes the node to detect, based on FFT of the received wireless signal in an FFT processing window, a sensing signal modulated onto at least some of the OFDM symbols of the sequence. P110928WO01

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[0033] Further, execution of the program code causes the node to, for at least one of the OFDM symbols, apply a time shift relative to the OFDM symbol to the FFT processing window.

[0034] According to a further embodiment, a computer program or computer program product is provided, e.g., in the form of a non-transitory storage medium, which comprises program code to be executed by at least one processor of node of a wireless communication system. Execution of the program code causes the node to transmit a wireless signal comprising a sequence of OFDM symbols. Each of the OFDM symbols has a CP, and a length of the CP varies between at least some of the OFDM symbols. Further, execution of the program code causes the node to modulate a sensing signal onto the wireless signal of at least some of the OFDM symbols of the sequence. Further, execution of the program code causes the node to, for at least one of the OFDM symbols of the sequence, set a time-shift relative to the OFDM symbol, to be applied by a receiver of the wireless signal for time-shifting an FFT processing window for FFT of the wireless signal. Further, execution of the program code causes the node to indicate the time shift to the receiver of the wireless signal.

[0035] Details of such embodiments and further embodiments will be apparent from the following detailed description of embodiments.

[0036] Brief Description of the Drawings

[0037] Figs. 1A, 1 B, and 1C show tables illustrating examples of OFDM symbol timing in the NR technology.

[0038] Fig. 2 schematically illustrates a wireless communication network in which sensing may be performed in accordance with an embodiment.

[0039] Fig. 2 schematically a communication network environment according to an embodiment.

[0040] Fig. 3A schematically illustrates a monostatic sensing scenario.

[0041] Fig. 3B schematically illustrates a bistatic sensing scenario.

[0042] Fig. 3C schematically illustrates a multistatic sensing scenario.

[0043] Fig. 4 schematically illustrates an example of a regular pulse train of a sensing signal modulated onto an OFDM signal. P110928WO01

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[0045] Fig. 5 schematically illustrates FFT-based reception (RX) processing of a sensing signal according to an embodiment.

[0046] Fig. 6 schematically illustrates an example for determination of time shifts of an RX FFT processing window according to an embodiment.

[0047] Fig. 7 shows a table indicating timing of the RX windows in the example of Fig. 7.

[0048] Fig. 8 schematically illustrates further details related to the time-shifting of the RX FFT processing window according to an embodiment.

[0049] Fig. 9 shows exemplary simulation results comparing the Doppler spectrum obtained based on the time-shifted RX FFT processing windows to the Doppler spectrum obtained without time-shifting of the RX FFT processing windows.

[0050] Fig. 10 shows a flowchart for schematically illustrating a method according to an embodiment.

[0051] Fig. 11 shows a flowchart for schematically illustrating a further method according to an embodiment.

[0052] Fig. 12 schematically illustrates structures of a wireless terminal according to an embodiment.

[0053] Fig. 13 schematically illustrates structures of a radio access node according to an embodiment.

[0054] Detailed Description

[0055] In the following, concepts in accordance with exemplary embodiments of the invention will be explained in more detail and with reference to the accompanying drawings. The illustrated embodiments relate to sensing of one or more targets in the environment of a node of a wireless communication system, by detecting a sensing signal modulated onto OFDM symbols of a wireless signal. The OFDM symbols of the wireless signal may carry communication payload, and in such cases the wireless signal may also be referred to as wireless communication signal. It is noted that in such cases the at least some OFDM symbols of the wireless signal would carry both communication payload and the sensing signal and / or some OFDM symbols of the wireless signal could carry the sensing signal while others carry communication payload. In some cases, the wireless signal could also be dedicated for P110928WO01

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[0057] sensing, but structures and configurations of the wireless communication system may be reutilized for transmission, and / or reception of the wireless signal. The wireless communication system may for example be based on a cellular technology, such as the 5G NR technology specified by 3GPP or a future 6G (6th Generation) technology. However, the illustrated concepts could also be applied to other technologies based on OFDM, e.g., a WLAN (Wireless Local Area Network) technology according to an IEEE 802.11 standard.

[0058] In the illustrated concepts, a sensing signal consisting of a given pulse sequence, herein also denoted as pulse train, is modulated onto at least some OFDM symbols of the wireless signal. The OFDM symbols each have a CP, and length of the CP is assumed to vary between at least some of the OFDM symbols. For detection of the sensing signal, RX processing of the received wireless signal corresponding to a given OFDM symbol involves FFT in an RX FFT processing window. A time shift relative to the OFDM symbol is applied to at least some of the RX FFT processing window(s) to compensate the variations of the length of the CP. For this purpose, the value of the time shift may also differ between the OFDM symbols, and / or the time shift may be applied to only a subset of the RX FFT processing windows. As a result, a more regular timing of the RX FFT processing windows, as compared to the timing of the OFDM symbols, can be obtained.

[0059] Accordingly, by the time shifting of the RX FFT processing window(s) relative to the timing of the corresponding OFDM symbol(s), side peaks in the FFT output can be significantly reduced without requiring change of the underlying OFDM structure of the wireless signal. Accordingly, usability of the wireless signal for purposes of sensing can be enhanced.

[0060] Due to the time shifting, it may occur that the RX FFT processing window captures part of the CP and part of the main part of the OFDM symbol, rather than capturing only the main part of the OFDM symbol, onto which the pulse of the sensing signal is modulated. A matched filter used for correlation of the received OFDM signal with the expected pulse train, may be adjusted to compensate for such misalignment.

[0061] The illustrated concepts may involve one or more of the following:

[0062] - For a sensing receiver, the RX FFT processing window is adjusted to reduce the variance of the time difference between start positions of subsequent RX FFT processing windows, by applying the time shift to one or more of the RX FFT processing windows.

[0063] - In addition, the matched filter used for correlation to the pulse train may be adjusted to compensate for the time difference between start of the RX FFT processing window and start P110928WO01

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[0065] of the main part of the OFDM symbol start, which is typically defined by the underlying OFDM structure, e.g., numerology, of the wireless signal.

[0066] - In addition or as an alternative, the received wireless signal may be cyclically shifted within the RX FFT processing window to compensate for the time difference between start of the RX FFT processing window and start of the main part of the OFDM symbol.

[0067] - In addition or as an alternative, the wireless signal may be adjusted by its transmitted, i.e., sensing transmitter, to compensate for the time difference between start of the RX FFT processing window and start of the main part of the OFDM symbol.

[0068] Fig. 2 illustrates exemplary structures of a wireless communication network which may be considered in the illustrated concepts. In particular, Fig. 2 shows UEs 10 which are served by access nodes 100 of the wireless communication network. Here, it is noted that the wireless communication network may actually include a plurality of access nodes 100 that may serve a number of cells within the coverage area of the wireless communication network. The access nodes 100 may be regarded as being part of a Radio access network (RAN) of the wireless communication network.

[0069] Further, Fig. 2 schematically illustrates a CN (Core Network) 210 of the wireless communication network. In Fig. 2, the CN 210 is illustrated as including a GW (gateway) 220 and one or more control node(s) 240. The GW 220 may be responsible for handling user plane data traffic of the UEs 10, e.g., by forwarding user plane data traffic from a UE 10 to a network destination or by forwarding user plane data traffic from a network source to a UE 10. Here, the network destination may correspond to another UE 10, to an internal node of the wireless communication network, or to an external node which is connected to the wireless communication network. Similarly, the network source may correspond to another UE 10, to an internal node of the wireless communication network, or to an external node which is connected to the wireless communication network. The GW 220 may for example correspond to a UPF (User Plane Function) of the 5G Core (5GC) or to an SGW (Serving Gateway) or PGW (Packet Data Gateway) of the 4G EPC (Evolved Packet Core). The control node(s) 240 may for example be used for controlling the user data traffic, e.g., by providing control information to the access nodes 100, the GW 220, and / or to the UE 10.

[0070] As illustrated by solid double-headed arrows, the access nodes 100 may send downlink (DL) wireless transmissions to at least some of the UEs 10, and some of the UEs 10 may send uplink (UL) wireless transmissions to the access node 100. P110928WO01

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[0072] The DL wireless transmissions and UL wireless transmissions may be used to provide various kinds of services to the UEs 10, e.g., a voice service, a multimedia service, or some other data service. Such services may be hosted in the CN 210, e.g., by a corresponding network node. By way of example, Fig. 2 illustrates an application service platform 250 provided in the CN 210. Further, such services may be hosted externally, e.g., by an AF (application function) connected to the CN 210. By way of example, Fig. 2 illustrates one or more application servers 300 connected to the CN 210. The application server(s) 300 could for example connect through the Internet or some other wide area communication network to the CN 210. The application service platform 250 may be based on a server or a cloud computing system and be hosted by one or more host computers. Similarly, the application server(s) 300 may be based on a server or a cloud computing system and be hosted by one or more host computers. The application server(s) 300 may include or be associated with one or more AFs that enable interaction with the CN 210 to provide one or more services to the UEs 10, corresponding to one or more applications. These services or applications may generate the user data traffic conveyed by the DL wireless transmissions and / or the UL wireless transmissions between the access nodes 100 and the respective UE 10. Accordingly, the application server(s) 300 may include or correspond to the above-mentioned network destination and / or network source for the user data traffic. In the respective UE 10, such service may be based on an application (or shortly “app”) which is executed on the UE 10. Such application may be pre-installed or installed by the user. Such application may generate at least a part of the user plane data traffic between the UE 10 and the access node 100.

[0073] In the illustrated concepts, it is assumed that the DL wireless transmissions and the UL wireless transmissions are carried by wireless signals based on OFDM. For wireless sensing of one or more targets 20 in the environment of the wireless communication network, a sensing signal is modulated onto at least some OFDM symbols of the wireless signal. The sensing signal may be defined by a certain pulse train, e.g., a Zadoff-Chu (ZC) sequence. A ZC sequence may be mapped to one pulse, corresponding to one OFDM symbol. The same or different ZC sequences may be mapped to multiple pulses. The pulse train thus consists of multiple pulses, and each pulse may be based on the same ZC sequence, or at least some of the pulses may be based on different ZC sequences.

[0074] The wireless signal onto which the sensing signal is modulated can be sent by any of the access nodes 100 or by any of the UEs 10. Similarly, the detection of the sensing signal can be accomplished by one or more of the access nodes 100 or by one or more of the UEs 10. Accordingly, in the illustrated concepts various nodes of the wireless communication network, either radio access node or UE, may act as sensing transmitter or a sensing receiver. Further, P110928WO01

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[0076] the sensing could be bistatic or multistatic. Further, in some scenarios the sensing could also be monostatic, i.e., the same node, either radio access node or UE, could act as the sensing transmitter and the sensing receiver for the same wireless signal. The one or more targets 20 may for example include vehicles, persons, or animals. Further, the one or more targets 20 could also include pollutants or other constituents of the surrounding atmosphere.

[0077] Fig. 3A schematically illustrates a monostatic sensing scenario, where a base station (BS), e.g., any of the above access nodes 100, acts as both the sensing transmitter and the sensing receiver. As can be seen, the sensing transmitter / receiver sends the sensing signal and receives an echo of the sensing signal, due to reflection by the target 20. The round-trip time (RTT) of the sensing signal, from sending of the sensing signal and reception of its echo, depends on the location of the target 20 relative to the sensing transmitter / receiver.

[0078] Fig. 3B schematically illustrates a bistatic sensing scenario, where a first base station (BS1), e.g., any of the above access nodes 100, acts as the sensing transmitter and a second base station (BS2), e.g., another access node 100, acts as the sensing receiver. As can be seen, the sensing transmitter sends the sensing signal and the sensing receiver receives an echo of the sensing signal, due to reflection by the target 20. The ToF of the sensing signal, from sending of the sensing signal and reception of its echo, depends on the location of the target 20 relative to the sensing transmitter and the sensing receiver.

[0079] Fig. 3C schematically illustrates a multistatic sensing scenario, where a first base station (BS1), e.g., any of the above access nodes 100, acts as the sensing transmitter, and a second base station (BS2) and a third base station (BS3), e.g., other access nodes 100, act as sensing receivers. As can be seen, the sensing transmitter sends the sensing signal and the sensing receivers each receive an echo of the sensing signal, due to reflection by the target 20. The ToFs of the sensing signal, from sending of the sensing signal and reception of its echo by the respective sensing receiver, depend on the location of the target 20 relative to the sensing transmitter and the sensing receivers.

[0080] In the following, information like RTT or ToF will also more generally be denoted as delay information, and it is noted that details of the evaluation of the delay information typically depend on the type of sensing, i.e., monostatic, bistatic or multistatic, and in the latter cases also on the underlying geometry.

[0081] In the case of monostatic sensing the distance between sensing transmitter / receiver and the target 20 is typically determined based on the RTT as r = c0RTT / 2 with RTT denoting the time P110928WO01

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[0083] span between transmission and reception of a pulse and and c0denoting the speed of light. Resolution of ranging is given by Rr= c0 / (2BW), i.e., targets that are further apart than Rrcan still be distinguished as separate objects. It can be seen the range resolution is inverse proportional to the sensing signal bandwidth BW. Similar relations also apply to bistatic sensing and multistatic sensing. In the case of bistatic sensing, distance measurements are typically based on measuring the ToF from the sensing transmitter via the target to the sensing receiver. All possible target positions for a measured ToF value are located on an ellipsis, or when considering three spatial coordinates, on an ellipsoid, with focal points of the ellipsis or ellipsoid given by the location of the sensing transmitter and the location of the sensing receiver. In addition to the ToF, the position of target 20 may be determined based on knowledge (or measurement) of the location of the sensing receiver, location of the sensing transmitter, and AoD (Angle of Departure) of the sensing signal from the sensing transmitter or AoA (Angle of Arrival) of the sensing signal at the sensing receiver. In the case of multistatic sensing, the measurements by the multiple sensing receivers may be evaluated in a similar manner as in the case of bistatic sensing and combined to obtain an estimate of the target position.

[0084] In the illustrated concepts, detection of the sensing signal may be based on correlation of the received sensing signal (echo) with the underlying pulse train to derive delay information and on FFT of the correlation output to determine Doppler-induced frequency shift. It is noted that this FFT of the correlation output would be performed in addition to the above-mentioned FFT of the received wireless signal, which would be applied on the input side of the correlation.

[0085] The Doppler-induced frequency shift, herein also denoted as Doppler shift, in the received sensing signal can be determined by measuring the phase difference between received pulses of the pulse train. For purposes of illustration, Fig. 4 shows an example of a regular pulse train, with pulses occurring every Trepseconds and each pulse having a CP. Assuming perfect phase and frequency synchronization between sensing transmitter and sensing receiver, and that the sensing transmitter, sensing receiver and target 20 are stationary, the distance transmitter-target-receiver does not change, and each received pulse has the same phase shift relative to its transmitted original, i.e. no phase difference is observed between consecutively received pulses.

[0086] When the target 20 is moving, the distance from sensing transmitter via the target 20 to the sensing receiver changes over time, which results in a phase change between consecutively received pulses. This phase change can in turn be used to determine the Doppler shift: The phase change can be determined as A<p = 2n ■ fd- Trep, with fddenoting the Doppler shift P110928WQ01

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[0088] induced by the movement of the target 20. The Doppler shift depends on the velocity of the target 20 as well as the direction relative to sensing transmitter and sensing receiver. For example, a target 20 moving with velocity v towards a monostatic sensing transmitter / receiver would lead to a Doppler shift of fd= 2vfc / c0, with c0denoting the speed of light and fcdenoting the carrier frequency. In a bistatic or multistatic sensing scenario, the Doppler shift would typically be less, depending on geometry of between sensing transmitter, sensing receiver, and target 20.

[0089] Quantities related to Doppler estimation include maximum unambiguous velocity vu= — - —

[0090] ^fc^rep and the velocity resolution vr= — - —, with M denoting the number of pulses in the pulse 2fcMTrep

[0091] train. The maximum unambiguous velocity is the highest velocity that can be unambiguously determined from -vuto vu, and with M pulses this range is divided into M velocity bins of size vr.

[0092] Fig. 5 schematically illustrates an example of reception processing of sensing signals corresponding to a pulse train like illustrated in Fig. 4, where each pulse has a CP: For each pulse, the sensing receiver performs a cyclic correlation of the received signal with the transmitted pulses (without CP). The outcome of the correlation (per pulse) is the cyclic convolution between the periodic autocorrelation function (ACF) of the transmitted pulses (without CP) and the impulse response between the sensing transmitter and the sensing receiver, which includes the effects caused by the target 20. The pulses may be designed in such a way that they have very good or even perfect ACFs. Here, a perfect ACF would have only one non-zero position and otherwise only zeros. One possibility to determine the cyclic correlation is to apply a frequency-domain matched filter which transforms the received signal (per pulse) into the frequency-domain using an FFT (Fast Fourier Transform), multiply the outcome of the frequency-domain matched filter with the conjugate complex of the frequencydomain representation, typically the FFT, of the transmitted pulse (without CP), and transform the result back to the time-domain, using an IFFT (Inverse FFT). The size of the FFT can be determined according to the pulse length (without CP) and the sampling rate used in the processing. The IFFT size can be selected based on the desired ranging granularity.

[0093] The output of the cyclic correlation, in a two-dimensional representation in coordinates of delay per cyclic correlator and number of sensing pulse, is called delay-time representation. Multiple FFTs, one per relevant cyclic correlator output sample, across different pulses for the same delay sample in each cyclic correlator output, are then used to convert the delay-time representation to a delay-Doppler representation. In the delay-Doppler representation, the target 20 can typically be identified by a corresponding peak at a certain combination of delay P110928WO01

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[0095] value and Doppler shift value. In the example of Fig. 5, it is assumed that three targets are detected, indicated by black squares in the delay-Doppler representation.

[0096] In some cases, the target 20 may also produce multiple peaks in the Doppler spectrum. The set of one or more peaks in the Doppler spectrum may also be denoted as Doppler signature. The Doppler signature may also help in classifying targets. For example, a pedestrian typically has a distinctive Doppler signature due to movements of legs and arms overlaid to movement of the overall body and is typically moving slower than a vehicle. The Doppler signature may also be used to differentiate reflected signals from stationary clutter and moving targets.

[0097] In the illustrated concepts, the sensing receiver, which may be a radio access node, e.g., any of the above access nodes 100, or a wireless terminal, e.g., any of the above UEs 10, can place the RX FFT processing window of the wireless communication signal depending on the timing of the OFDM symbols, onto which the sensing signal to be detected is modulated. This can be accomplished in such a way that the variation of the duration between subsequent RX FFT processing windows is reduced (as compared to the case where the RX FFT processing windows are exactly aligned with the OFDM symbols). As a result, a pattern of almost equidistant RX FFT processing windows can be achieved.

[0098] In the following, further details of calculating the starting positions of the time-shifted RX FFT processing windows are explained with reference to a specific example related to OFDM symbol timing in the NR technology. Further details concerning the OFDM symbol timing and the frame structure defined based on the numerology can for example be found in 3GPP TS 38.211 V18.4.0, specifically sections 4.2 and 4.3. It is however noted that similar concepts could also be applied to other frame structures or numerologies. Further, other methods could be used to reduce the variance of starting time differences between subsequent RX FFT processing windows.

[0099] As mentioned above, in the frame structure of the NR technology, OFDM symbols with longer CP occur every 0.5 ms or every Nsymb_0.5ms-th symbol, where Nsample_0.5ms. denotes the number of samples (with duration Tc) within a 0.5ms time interval. Based on this, Nsymbilsymbols of length Nsampieiland Nsymbi2symbols of length Nsampiei2can be constructed as follows:

[0100] Nsample O. Sms

[0101] ^sample,!

[0102] ^symb_0.5ms

[0103] Nsampl.e_0.5ms

[0104] ^sample, 2

[0105] ^symb_0.5ms

[0106] N

[0107]

[0108] symb, 2 mod(NSample_0.5>ms> Nsymb O. Sms) P110928WO01

[0109] - 15 -

[0110] symb,l ^symb O. Sms ^symb,2

[0111] The total number of samples ^sample, 1 ’ ^symb,l T ^sample, 2 ’Symb,2 sample _0.5ms and Nsymb.i + Nsymb,2= Nsymb_o.5ms. Nsample:1and Nsample 2include the samples of the CPs for the first and second OFDM symbol type which have length NCP 1= Nsampieil- Nuand NCP 2= N sample, 2 ~ Nu, respectively.

[0112] As illustrated in Fig. 6, for an NR subframe with 14 OFDM symbols, the first Nsymbi2starting positions of the RX FFT processing windows can be placed at samples (0-. Nsymb 2- 1) • Nsampie, 2 + ^CP,2. and the next Nsymb>starting positions can be placed at Nsymb,2■ ^sample,2+ (0-. Nsymb l- 1) • Nsampie l+ NCP 1, with “0" indicating the first sample in the subframe. The starting samples are denoted as nRX starti and the starting times of the RX FFT processing WindOWS tRXstart,lstart,l 'c-

[0113] Fig. 7 shows a table indicating the starting position of the RX FFT processing windows for the considered example when assuming NR numerology. = 1, expressed in units of 16TC. The table also indicates the deviation relative to the starting position of the main part of the OFDM symbol according to the NR frame structure, given by nRX starti - (tstart l+ TCP,0 / (167 / ), for the first 14 OFDM symbols of the subframe, expressed in units of 16TC. Further, the table shows the difference nRX start,i ~nRx start, i-i between the start samples of the current and the preceding RX FFT processing window, expressed in units of 16TC. As can be seen from the table of Fig. 7, the RX FFT processing windows have a very regular timing, deviating from a perfectly equidistant spacing by not more than one unit of 16TC.

[0114] For later RX FFT processing windows, i.e., for I > Nsymb 0.5ms, the pattern can be periodically extended. Another possibility would be to place the stating positions for the next 0.5ms interval 3

[0115]

[0116] t NSample_0.5ms T Nsymb-^ 1) • Nsampie-^ + NcP,} and Nsampiej) $ms+ Nsymb-^ ■ Nsampie-^ + (0: Nsymbi2- 1) • Nsampiei2+ NCP 2, again counting the samples from the beginning of subframe.

[0117] From the table of Fig. 7, it can also be seen that the RX FFT processing window of OFDM symbol I starts earlier than main symbol part of OFDM symbol I. The time difference is given by At(= tRX start>l- tstart>l+ TCP>1). The lowermost row in the table show 21^ / (167 / )). Fig. 8 further illustrates this time difference on the level of an individual OFDM symbol. As can be seen from Fig. 8, the RX FFT processing window starts within the CP, slightly before the beginning of the main part of the OFDM symbol. Since the CP contains the end of the main part of the OFDM symbol, the RX FFT processing window captures the content of OFDM P110928WO01

[0118] - 16 -

[0119] symbol I, but cyclically shifted to the right by |At(|. In the illustrated concepts, this shift may be compensated by adjusting the correlator of the sensing receiver, i.e., the matched filter for performing the correlation. If the transmitted sensing signal of symbol I is denoted by x((t), corresponding to a frequency-domain representation Xk i, with k denoting the subcarrier index, an adjusted time-domain correlator may correlate the received signal with the sequence %j(t) = %j((t + At() mod Nu■ Tc), where Nu■ Tcis the duration of the main part of the OFDM symbol. An adjusted frequency-domain correlator, may correlate the received signal with the sequence Xk t= Xk t■ exp (J2n ■ k ■tl / Nu■

[0120]

[0121] Alternatively, the correlator is left unchanged and the received signal within the RX FFT processing window may be cyclically shifted by |At(| to the left before fed into the correlator.

[0122] Fig. 9 illustrates exemplary simulation results based on the above example. In Fig. 9, a solid line shows the resulting Doppler spectrum with RX FFT processing windows placed according to NR frame structure (exactly aligned with the main parts of the OFDM symbols), and a broken line illustrates the resulting Doppler spectrum with the time-shifted RX FFT processing windows according to the above example. As can be seen, the Doppler spectrum without the time shifting exhibits a peak at about 20 m / s, which corresponds to the target of sensing, but also prominent side peaks. With the time-shifted RX FFT processing windows, these side peaks are significantly reduced, by more than 10 dB.

[0123] In the above explanations, placement of RX FFT processing windows and adjustment of correlation was described as being applied for all OFDM symbols in a subframe, and even over multiple subframes. It is however noted that in some scenarios the time-shifting and adjustment could also be applied to only some of the OFDM symbols, e.g., if the sensing signal is not modulated onto every OFDM symbol. For example, the sensing signal could be modulated onto only every R-th symbol of the wireless signal, and the time-shifted placement of the RX FFT processing window and adjustment of the correlator could be applied only to this subset of the OFDM symbols.

[0124] Further improvements could be achieved using higher sampling rate and / or applying a fractional delay using frequency domain multiplication to apply a linear phase shift for placement of the FFT processing windows and for adjusting the correlator of the sensing receiver. In this way, the placement of the RX FFT processing windows could be brought even closer to a perfect equidistant spacing.

[0125] In the above examples, it was assumed that the time offset between the RX FFT processing window and the main part of the OFDM symbol may be compensated by measures at the P110928WO01

[0126] - 17 -

[0127] sensing receiver, namely adjustment of the matched filter for correlation or (cyclic) shifting of the received signal within the RX FFT processing window. Alternatively or in addition, the time offset could also be compensated by measures at the sensing transmitter. For example, the sensing transmitter could apply a cyclic rotation in time-domain to the transmitted signal of the OFDM symbol, or could apply a linear phase ramp in frequency-domain to the transmitted signal of the OFDM symbol. In such cases, the sensing receiver could only time-shift the RX FFT processing windows to reduce the variance of the time difference between RX FFT processing window starting times, without further measures to compensate the time offset between the RX FFT processing window and the main part of the OFDM symbol. Since the needed cyclic time shift (or linear phase ramp) depends on the RX FFT processing window placement, the sensing transmitter and the sensing receiver may first agree on the RX FFT processing window placement. Such agreement could be based on pe-configuration, e.g., based on standardization, or on signaling between sensing transmitter and sensing receiver. For example, the sensing transmitter could determine the placement of the RX FFT processing windows relative to the timing of the OFDM symbols, i.e., set the time shift, and signal corresponding information to the sensing receiver. Alternatively, the sensing receiver could determine the placement of the RX FFT processing windows relative to the timing of the OFDM symbols, i.e., set the time shift, and signal corresponding information to the sensing transmitter. In some scenarios, the sensing receiver and the sensing receiver could also cooperatively set the time shift, e.g., by negotiation.

[0128] Fig. 10 shows a flowchart for illustrating a method, which may be utilized for implementing the illustrated functionalities of sensing based on a wireless signal. More specifically, the method of Fig. 10 may be used to implement the functionalities in a node of a wireless communication system which acts as a sensing receiver. Such node may correspond to a radio access node of the wireless communication system, e.g., to any of the above access nodes 100. Alternatively, such node could correspond to a wireless terminal, e.g., to any of the above UEs 10. The sensing may be monostatic, bistatic, or multistatic.

[0129] If a processor-based implementation of the node is used, at least some of the steps of the method of Fig. 10 may be performed and / or controlled by one or more processors of the node. Such node may also include a memory storing program code for implementing at least some of the below described functionalities or steps of the method of Fig. 10.

[0130] In the method of Fig. 10, it is assumed that the wireless signal comprises a sequence of OFDM symbols and the OFDM symbols each have a CP. The sequence may correspond to a frame, subframe, or slot defined by the technology of the wireless communication system. Further, P110928WO01

[0131] - 18 -

[0132] the length of the CP is assumed to vary between at least some of the OFDM symbols. The timing of the OFDM symbols and CP length may for example be defined by a standardized numerology, such as the numerologies specified by 3GPP for the NR technology. Details concerning the latter numerologies and related frame structures can be found in 3GPP TS 38.211 V18.4.0. Further, it is assumed that a sensing signal is modulated onto at least some of the OFDM symbols, e.g., in the form of a pulse train. The sensing signal may be based on a ZC sequence, but other types of sequences could be used as well.

[0133] At step 1010, if the sensing is bistatic or multistatic, the node may send information to a transmitter of the wireless signal, i.e., to the sensing transmitter. Alternatively or in addition, the node could receive information from the transmitter of the wireless signal, as indicated by step 1015. In accordance with the information sent at step 1010 and / or the information received at step 1015, the node may set, for at least one of the OFDM symbols of the sequence, a time shift relative to the OFDM symbol, as indicated by step 1020. The time shift is to be applied to an RX FFT processing window of the received wireless signal.

[0134] For example, the information of step 1010 could indicate the time shift to the transmitter of the wireless signal, or the information of step 1015 could indicate the time shift to the node. Further, the information of step 1010 and the information of step 1015 could be used to negotiate the time shift and / or indicate capabilities related to handling of the time shift. The time shift may be indicated in terms of a single value which specifies the time shift for a set of one or more RX FFT processing windows, each corresponding to a given OFDM symbol of the sequence, or in terms of multiple different values, respectively to be applied to a different RX FFT processing window, corresponding to a different OFDM symbol of the sequence.

[0135] If the sensing is monostatic, the node would also act as the sensing transmitter, i.e., transmit the wireless signal. In such case, the node may locally set the time shift, as indicated by step 1030. Further, the node may adjust the wireless signal depending on the time shift set at step 1030, as indicated by step 1040. Such adjustment may for example involve time-shifting a signal part corresponding to a main part of the OFDM symbol. Such time shifting of the signal part may be performed in a cyclic manner. Further, the adjustment could involve applying a linear phase ramp in frequency domain. The node may then transmit the wireless signal, as indicated by step 1045. The transmitted wireless signal carries the sensing signal modulated onto at least some of the OFDM symbols and may also include the adjustment of step 1040.

[0136] At step 1050, the node receives the wireless signal. In the case of bistatic sensing or multistatic sensing, the node receives the wireless signal from another node of the wireless P110928WO01

[0137] - 19 -

[0138] communication system which acts as the sensing transmitter. The received wireless signal may include a reflection or echo of the originally transmitted wireless signal, caused by the one or more targets in the environment of the node. In the case of monostatic sensing, the node receives a reflection or echo of the transmitted wireless signal originally transmitted by itself.

[0139] At step 1060, the node applies a time shift relative to the OFDM symbol time to the RX FFT processing window of the received wireless communication signal. This is done for at least one of the OFDM symbols of the sequence. In some scenarios, the time shifting may be done for a subset of the OFDM symbols of the sequence, or even for all OFDM symbols of the sequence. The time shift may be set at step 1020 or at step 1030. In some scenarios, the node may apply the time shift to multiple RX FFT processing windows, each corresponding to a different OFDM symbol of the sequence, and a value of the time shift may differ between at least some of the multiple RX FFT processing windows.

[0140] At step 1070, the node detects the sensing signal modulated onto the OFDM symbols. This is accomplished based on FFT of the received wireless signal in the RX FFT processing window(s) time shifted at step 1060.

[0141] In some scenarios, the detection of step 1070 may involve that, within the RX FFT processing window, the node time-shifts the received wireless signal depending on the time shift applied at step 1060. This time-shift may be cyclic, i.e., signal parts which are shifted out of the RX FFT processing window may be appended on the other side of the RX FFT processing window.

[0142] In some scenarios, the detection of step 1070 may involve that, based on a matched filter, the node correlates the received wireless signal to a pulse of the pulse sequence of the sensing signal. This correlation may also be performed in the RX FFT processing window. In such case, the node may also adjust the matched filter depending on the time shift applied at step 1060. For example, the node may adjust the matched filter by cyclic shifting.

[0143] In some scenarios, the node may use the detection of step 1070 to perform a Doppler measurement to estimate information on the at least one target. For example, this could involve estimating velocity of the at least one target or classifying the target, e.g., as corresponding to a vehicle or a pedestrian.

[0144] Fig. 11 shows a flowchart for illustrating a method, which may be utilized for implementing the illustrated functionalities of sensing based on a wireless signal. More specifically, the method of Fig. 11 may be used to implement the functionalities in a node of a wireless communication P110928WO01

[0145] - 20 -

[0146] system which acts as a sensing transmitter. Such node may correspond to a radio access node of the wireless communication system, e.g., to any of the above access nodes 100. Alternatively, such node could correspond to a wireless terminal, e.g., to any of the above UEs 10. The sensing may be bistatic or multistatic.

[0147] If a processor-based implementation of the node is used, at least some of the steps of the method of Fig. 11 may be performed and / or controlled by one or more processors of the node. Such node may also include a memory storing program code for implementing at least some of the below described functionalities or steps of the method of Fig. 11.

[0148] In the method of Fig. 11, it is assumed that the wireless signal comprises a sequence of OFDM symbols and the OFDM symbols each have a CP. The sequence may correspond to a frame, subframe, or slot defined by the technology of the wireless communication system. Further, the length of the CP is assumed to vary between at least some of the OFDM symbols. The timing of the OFDM symbols and CP length may for example be defined by a standardized numerology, such as the numerologies specified by 3GPP for the NR technology. Details concerning the latter numerologies and related frame structures can be found in 3GPP TS 38.211 V18.4.0. Further, it is assumed that a sensing signal is modulated onto at least some of the OFDM symbols, e.g., in the form of a pulse train. The sensing signal may be based on a ZC sequence, but other types of sequences could be used as well.

[0149] At step 1110, the node may send information to a receiver of the wireless signal, to the sensing receiver. Alternatively or in addition, the node could receive information from the receiver of the wireless signal, as indicated by step 1120. In accordance with the information sent at step 1110 and / or the information received at step 1120, the node may set, for at least one of the OFDM symbols of the sequence, a time shift relative to the OFDM symbol, as indicated by step 1130. The time shift is to be applied by a receiver of the wireless signal to an RX FFT processing window for FFT of the received wireless signal. For example, the information of step 1110 and the information of step 1120 could be used to negotiate the time shift and / or indicate capabilities related to handling of the time shift. In some scenarios, the node may set the time shift for multiple RX FFT processing windows, each corresponding to a different OFDM symbol of the sequence, and a value of the time shift may differ between at least some of the multiple RX FFT processing windows.

[0150] At step 1140, the node indicates the time shift to the receiver of the wireless signal. The time shift may be indicated in terms of a single value which specifies the time shift for a set of one or more RX FFT processing windows, each corresponding to a given OFDM symbol of the P110928WO01

[0151] - 21 -

[0152] sequence, or in terms of multiple different values, respectively to be applied to a different RX FFT processing window, corresponding to a different OFDM symbol of the sequence.

[0153] At step 1150, the node may adjust the wireless signal depending on the time shift set at step 1130. Such adjustment may for example involve time-shifting a signal part corresponding to a main part of the OFDM symbol. Such time shifting of the signal part may be performed in a cyclic manner. Further, the adjustment could involve applying a linear phase ramp in frequency domain. The node may then transmit the wireless signal, as indicated by step 1160. The transmitted wireless signal carries the sensing signal modulated onto at least some of the OFDM symbols and may also include the adjustment of step 1150.

[0154] Fig. 12 illustrates a processor-based implementation of a wireless terminal 1200 for a wireless communication system, which may be used for implementing the above-described concepts. The wireless terminal 1200 may for example correspond to any of the above UEs 10.

[0155] As illustrated, the wireless terminal 1200 may include wireless interface 1210, which may be used for wireless communication with one or more other nodes of the wireless communication system.

[0156] Further, the wireless terminal 1200 may include one or more processors 1250 coupled to the interface 1210 and a memory 1260 coupled to the processor(s) 1250. By way of example, the interface 1210, the processor(s) 1250, and the memory 1260 could be coupled by one or more internal bus systems of the wireless terminal 1200. The memory 1260 may include a read-only memory (ROM), e.g., a flash ROM, a random-access memory (RAM), e.g., a dynamic RAM (DRAM) or static RAM (SRAM), a mass storage, e.g., a hard disk or solid state disk, or the like. As illustrated, the memory 1260 may include software 1270 and / or firmware 1280. The memory 1260 may include suitably configured program code to be executed by the processor(s) 1250 so as to implement the above-described functionalities for sensing based on a wireless signal, such as explained in connection with Fig. 10.

[0157] It is to be understood that the structures as illustrated in Fig. 12 are merely schematic and that the wireless terminal 1200 may actually include further components which, for the sake of clarity, have not been illustrated, e.g., further interfaces or further processors. Also, it is to be understood that the memory 1260 may include further program code for implementing known functionalities of a UE or radio access node in a 3GPP system. According to some embodiments, also a computer program may be provided for implementing functionalities of the wireless terminal 1200, e.g., in the form of a physical medium storing the program code P110928WO01

[0158] - 22 -

[0159] and / or other data to be stored in the memory 1260 or by making the program code available for download or by streaming.

[0160] Fig. 13 illustrates a processor-based implementation of radio access node 1300 for operation in a wireless communication system, which may be used for implementing the abovedescribed concepts. The radio access node 1300 may correspond to any of the above-mentioned access nodes 100.

[0161] As illustrated, the radio access node 1300 may include wireless interface 1310, which may be used for wireless communication with one or more wireless devices, such as the above-mentioned UEs 10. Further, the radio access node 1300 may include a network interface 1320, which may be used for communication with other network nodes.

[0162] Further, the radio access node 1300 may include one or more processors 1350 coupled to the interfaces 1310, 1320 and a memory 1360 coupled to the processor(s) 1350. By way of example, the interfaces 1310, 1320, the processor(s) 1350, and the memory 1960 could be coupled by one or more internal bus systems of the radio access node 1300. The memory 1360 may include a ROM, e.g., a flash ROM, a RAM, e.g., a DRAM or SRAM, a mass storage, e.g., a hard disk or solid state disk, or the like. As illustrated, the memory 1360 may include software 1370 and / or firmware 1380. The memory 1360 may include suitably configured program code to be executed by the processor(s) 1350 so as to implement or configure the above-described functionalities sensing based on a wireless signal, such as explained in connection with Fig. 11.

[0163] It is to be understood that the structures as illustrated in Fig. 13 are merely schematic and that the radio access node 1300 may actually include further components which, for the sake of clarity, have not been illustrated, e.g., further interfaces or further processors. Also, it is to be understood that the memory 1360 may include further program code for implementing known functionalities of a radio access node in a 3GPP system. According to some embodiments, also a computer program may be provided for implementing functionalities of the radio access node 1300, e.g., in the form of a physical medium storing the program code and / or other data to be stored in the memory 1360 or by making the program code available for download or by streaming.

[0164] As can be seen, the concepts as described above may be used for enhancing sensing based on a wireless signal. The sensing signal can be efficiently modulated onto OFDM symbols of the wireless signal, and additional hardware requirements in the transmitter and receiver of P110928WO01

[0165] - 23 -

[0166] the wireless communication signal are low. Further, side peaks in the Doppler spectrum of the received wireless signal can be avoided or at least reduced, thereby improving sensing performance.

[0167] It is to be understood that the examples and embodiments as explained above are merely illustrative and susceptible to various modifications. For example, the illustrated concepts may be applied in connection with various kinds of wireless communication technologies based on OFDM. Moreover, it is to be understood that the above concepts may be implemented by using correspondingly designed software to be executed by one or more processors of an existing device or apparatus, or by using dedicated device hardware. Further, it should be noted that the illustrated apparatuses or devices may each be implemented as a single device or as a system of multiple interacting devices or modules.

Claims

P110928WO01- 24 -Claims1. A method of sensing at least one target (20) in an environment of a node (10; 100; 1200; 1300) of a wireless communication system, the method comprising:the node (10; 100; 1200; 1300) receiving a wireless signal comprising a sequence of orthogonal frequency division multiplexing, OFDM, symbols each having a cyclic prefix, CP, wherein a length of the CP varies between at least some of the OFDM symbols;the node (10; 100; 1200; 1300) detecting, based on Fast Fourier Transform, FFT, of the received wireless signal in an FFT processing window, a sensing signal modulated onto at least some of the OFDM symbols, andfor at least one of the OFDM symbols, the node (10; 100; 1200; 1300) applying a time shift relative to the OFDM symbol to the FFT processing window.

2. The method according to claim 1,wherein the node (10; 100; 1200; 1300) applies the time shift to multiple FFT processing windows for FFT of the received wireless signal, each corresponding to a different OFDM symbol of the sequence, and a value of the time shift differs between at least some of the multiple FFT processing windows.

3. The method according to claim 1 or 2, comprising:within the FFT processing window, the node (10; 100; 1200; 1300) time-shifting the received wireless signal depending on the time shift.

4. The method according to any of the preceding claims, comprising:based on a matched filter, the node (10; 100; 1200; 1300) correlating the received wireless signal to a pulse sequence of the sensing signal.

5. The method according to claim 4, comprising:the node (10; 100; 1200; 1300) adjusting the matched filter depending on the time shift.

6. The method according to claim 5,wherein the node (10; 100; 1200; 1300) adjusts the matched filter by cyclic shifting.

7. The method according to any of the preceding claims, comprising:the node (10; 100; 1200; 1300) setting the time shift based on information received from a transmitter of the wireless signal.P110928WO01- 25 -8. The method according to any of the preceding claims, comprising:the node (10; 100; 1200; 1300) indicating the time shift to a transmitter (10; 100; 1200; 1300) of the wireless signal.

9. The method according to claim 8, comprising:the node (10; 100; 1200; 1300) indicating multiple values of the time shift to the transmitter (10; 100; 1200; 1300) of the wireless signal, wherein each of the multiple values applies to the FFT processing window corresponding to a different OFDM symbol of the sequence.

10. The method according to any of claims 1 to 6, comprising:the node (10; 100; 1200; 1300) transmitting the wireless signal.

11. The method according to claim 10, comprising:the node (10; 100; 1200; 1300) adjusting the transmitted wireless signal depending on the time shift.

12. The method according to claim 11,wherein said adjusting comprises one or more of:- shifting the transmitted wireless signal in time-domain,- cyclic-shifting the transmitted wireless signal in time-domain, and- applying a linear phase ramp in frequency domain.

13. The method according to any of the preceding claims, comprising:based on the detected sensing signal, the node (10; 100; 1200; 1300) performing a Doppler measurement to estimate information the at least one target.

13. The method according to any of the preceding claims,wherein the sensing signal is based on a Zadoff-Chu sequence.

14. The method according to any of the preceding claims,wherein the node (10; 100; 1200; 1300) is a wireless terminal.

15. The method according to any of claims 1 to 13,wherein the node (10; 100; 1200; 1300) is a radio access node of the wireless communication system.P110928WO01- 26 -16. A method of sensing at least one target (20) in the environment of a node (10; 100; 1200; 1300) of a wireless communication system, the method comprising:the node (10; 100; 1200; 1300) transmitting a wireless signal comprising a sequence of orthogonal frequency division multiplexing, OFDM, symbols each having a cyclic prefix, CP, wherein a length of the CP varies between at least some of the OFDM symbols;the node (10; 100; 1200; 1300) modulating a sensing signal onto at least some of the OFDM symbols;for at least one of the OFDM symbols, the node (10; 100; 1200; 1300) setting a time shift relative to the OFDM symbol, to be applied by a receiver (10; 100; 1200; 1300) of the wireless signal to a Fast Fourier Transform, FFT, processing window for FFT of the received wireless signal; andthe node (10; 100; 1200; 1300) indicating the time shift to the receiver (10; 100; 1200; 1300) of the wireless signal.

17. The method according to claim 16,wherein the node (10; 100; 1200; 1300) sets the time shift for multiple FFT processing windows for FFT of the received wireless signal, each corresponding to a different OFDM symbol of the sequence and a value of the time shift differs between at least some of the multiple FFT processing windows.

18. The method according to claim 16 or 17, comprising:the node (10; 100; 1200; 1300) adjusting the transmitted wireless signal depending on the time shift.

19. The method according to claim 18,wherein said adjusting comprises one or more of:- shifting the transmitted wireless signal in time-domain,- cyclic-shifting the transmitted wireless signal in time-domain, and- applying a linear phase ramp in frequency domain.

20. The method according to any claims 16 to 19, comprising:the node (10; 100; 1200; 1300) setting the time shift based on information received from a receiver of the wireless signal.

21. The method according to any of claims 16 to 20,wherein the sensing signal is based on a Zadoff-Chu sequence.P110928WO01- 27 -22. The method according to any of claims 16 to 21,wherein the node (10; 100; 1200; 1300) is a wireless terminal.

23. The method according to any of claims 16 to 22,wherein the node (10; 100; 1200; 1300) is a radio access node of the wireless communication system.

24. A node (10; 100; 1200; 1300) for a wireless communication system, the node being configured to:receive a wireless signal comprising a sequence of orthogonal frequency division multiplexing, OFDM, symbols each having a cyclic prefix, CP, wherein length of the CP varies between at least some of the OFDM symbols;detect, based on Fast Fourier Transform, FFT, of the received wireless signal in an FFT processing window, a sensing signal modulated onto at least some of the OFDM symbols of the sequence; andfor at least one of the OFDM symbols, apply a time shift relative to the OFDM symbol to the FFT processing window.

25. The node (10; 100; 1200; 1300) according to claim 24,wherein the node (10; 100; 1200; 1300) is configured to perform a method according to any one of claims 2 to 15.

26. The node (10; 100; 1200; 1300) according to claim 24 or 25, comprising:at least one processor (1250; 1350), anda memory (1260; 1360) containing program code executable by the at least one processor (1250; 1350),whereby execution of the program code by the at least one processor (1250; 1350) causes the node (10; 100; 1200; 1300) to perform a method according to any one of claims 1 to 15.

27. A node (10; 100; 1200; 1300) for a wireless communication system, the node (10; 100; 1200; 1300) being configured to:transmit a wireless signal comprising a sequence of orthogonal frequency division multiplexing, OFDM, symbols each having a cyclic prefix, CP, wherein length of the CP varies between at least some of the OFDM symbols;modulate a sensing signal onto the wireless signal of at least some of the OFDM symbols of the sequence;P110928WO01- 28 -for at least one of the OFDM symbols of the sequence, set a time shift relative to the OFDM symbol, to be applied by a receiver (10; 100; 1200; 1300) of the wireless signal for time-shifting a Fast Fourier Transform, FFT, processing window for FFT of the received wireless signal; and indicate the time shift to the receiver (10; 100; 1200; 1300) of the wireless signal.

28. The node (10; 100; 1200; 1300) according to claim 27,wherein the node (10; 100; 1200; 1300) is configured to perform a method according to any one of claims 17 to 23.

29. The node (10; 100; 1200; 1300) according to claim 26 or 27, comprising:at least one processor (1250; 1350), anda memory (1260; 1360) containing program code executable by the at least one processor (1250; 1350),whereby execution of the program code by the at least one processor (1250; 1350) causes the node (10; 100; 1200; 1300) to perform a method according to any one of claims 16 to 23.

30. A computer program or computer program product comprising program code to be executed by at least one processor (1250; 1350) of a node (10; 100; 1200; 1300) of a wireless communication system, whereby execution of the program code causes the node (10; 100; 1200; 1300) to perform a method according to any one of claims 1 to 23.

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