Multi-static sensing of a target

Abstract

A method, performed by a receiving (Rx) node, for multi-static sensing of a target, wherein a transmitting (Tx) node transmits reference sensing signals for use in sensing the target. The method includes the Rx, node performing a first target sensing process. Performing the first target sensing process comprises: the Rx node producing a first sensing signal and determining, based on the first sensing signal, whether the target has been sensed and / or a quality of a sensing result. The method also includes providing first feedback for the Tx node, wherein the first feedback indicates a result of the first target sensing process.

Description

MULTI-STATIC SENSING OF A TARGETTECHNICAL FIELD

[0001] Disclosed are embodiments related to multi-static sensing of a target.BACKGROUND

[0002] Integrated Sensing and Communication (ISAC)

[0003] Radar technology for sensing and cellular technology for wireless telecommunication have coexisted for decades, and thanks to interference management efforts, including controlling interference by considering completely separated bands for sensing and communication, the two technologies have coexisted without causing interference to one another. But this interference management has caused additional costs for infrastructure and inefficiencies in spectrum usage. With Fifth Generation (5G) and beyond, however, we have access to wide bandwidth and large antenna systems, which are the key requirements for sensing functionalities.

[0004] Also, key radar bands for high resolution sensing are merging with the millimeter wave (mmw) communication bands. For instance, some of the popular radar bands like K (18 GHz-26.5GHz) and Ka (26.5 GHz - 40 GHz) are close to popular mmw communication bands. Also, possible use of sub-THz bands (100-300 GHz) in Sixth Generation (6G) makes it possible to perform accurate sensing using different wireless access points, e.g., 5G base station (gNBs). These open up opportunities for the so-called integrated sensing and communication (ISAC) systems, which was also known as joint communication and sensing (JCS) systems.

[0005] With ISAC, the objective is to share the spectrum more efficiently and / or reuse the existing cellular network infrastructure for sensing. In other words, the ISAC refers to the introduction of sensing capability as part of a wireless communication networks. Here, sensing refers to “radar-like” functionalities, i.e., the ability to detect the presence, and to track the movement, and other characteristics of connected or unconnected targets under the coverage of the wireless network. Compared to the deployment of a separate network for sensing functionality, the main benefit of ISAC is that the sensing capability can be introduced on largescale at a relatively low incremental cost by reusing the infrastructure that is deployed for communication purposes.

[0006] In general, as described in reference [1], sensing methods can be divided into two categories: Mono-static sensing and Multi-static sensing.

[0007] With mono-static sensing, the transmission of the sensing signal and the reception of the reflected signal are handled by the same node. In contrast, with multi-static sensing, the transmission and the reception can be handled by different collaborating nodes. The most common type of multi-static sensing is bi-static sensing where a first node transmits a sensing signal and a second node receives the reflections of the transmitted sensing signal.

[0008] Mono-static sensing typically requires full duplex capability at the sensing- capable node (e.g., base station). This is intuitively because in a typical sensing scenario the sensing range may be in the order of few to hundreds of meters and, thereby, the reflected wave may be received within a fraction of a microseconds which is shorter than in typical data communication systems with larger time scales (in the order of tens of microseconds). Full duplex, however, may be challenging as it requires high level of self-interference cancellation. With a multi-static sensing, on the other hand, full duplex is not required as the signal is transmitted and received by different nodes. On the other hand, multi-static sensing requires tight coordination and timing synchronization between the two or more nodes.

[0009] Automatic repeat request

[0010] Automatic repeat request (ARQ), such as, for example, Hybrid ARQ (HARQ), is a well-established technique in wireless communication networks. With ARQ, if data is not correctly decoded by the receiver, the receiver sends a negative acknowledgement (NACK) to the transmitter, which serves as a request for a retransmission of the data. This process continues for a number of rounds until the data is correctly decoded by the receiver or the maximum number of retransmissions is reached. Once the data is decoded correctly, the receiver sends to the transmitter a positive acknowledgement (ACK) to acknowledge the successful decoding of the transmitted data.

[0011] There are different state-of-the-art methods for ARQ in wireless communication networks. The simplest type of ARQ is the transmitter retransmitting the same signal and thereceiver decoding the data only based on the signal received in the last retransmission round (and ignoring the signals received in the previous rounds). With Chase combining HARQ, the transmitter retransmits the failed signal and the receiver performs maximum ratio combining of all received copies of the signal. Finally, with incremental redundancy (INR) HARQ, in each retransmission round, the transmitter sends new redundancy bits for the failed signal. Then, the receiver performs codeword concatenation of all received retransmissions to generate a longer codeword (with lower rate) and tries again to decode the data. Reference [2] provides additional details of different HARQ methods.SUMMARY

[0012] Certain challenges presently exist. For instance, when attempting to sense a target, the transmitter (Tx) node lacks knowledge about the sensing operation at the receiver (Rx) node. For example, the Tx node lacks information on the signal quality, signal strength, power delay profile of the at the Rx node and cannot update its configuration for transmitting the sensing signal.

[0013] Accordingly, in one aspect there is provided a method, performed by a receiving (Rx) node, for multi-static sensing of a target, wherein a transmitting (Tx) node transmits reference sensing signals for use in sensing the target. The method includes the Rx node performing a first target sensing process. Performing the first target sensing process comprises: the Rx node producing a first sensing signal and determining, based on the first sensing signal, whether the target has been sensed and / or a quality of a sensing result. The method also includes providing first feedback for the Tx node, wherein the first feedback indicates a result of the first target sensing process.

[0014] In another aspect there is provided a method, performed by a transmitting (Tx) node, for multi-static sensing of a target. The method includes the Tx node transmitting a first reference sensing signal for use in sensing the target. The method also includes the Tx node receiving first feedback from an Rx node configured for sensing the target, wherein the first feedback indicates that: the target was sensed, the target was lost, the target was not found, or the target was sensed with insufficient quality.

[0015] In another aspect there is provided an apparatus that is configured to perform the methods disclosed herein. The apparatus may include memory and processing circuitry coupled to the memory.

[0016] In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of an apparatus causes the apparatus to perform any of the methods disclosed herein. In one embodiment, there is provided a carrier containing the computer program wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

[0017] An advantage of the embodiments disclosed herein is that they enable multi-static sensing of non-cooperative targets with high accuracy and resolution. This enables an analysis of the coverage area in both short and long distances, which, in turn, helps the sensing and communication quality to meet minimum requirements. In this way, the embodiments address one of the points of interest in the Third Generation Partnership Project (3GPP) release 19 (Rel-19) as well as in 6G.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0019] FIG. 1 illustrates a multi-static sensing system according to an embodiment.

[0020] FIG. 2A is a flowchart illustrating a process according to an embodiment.

[0021] FIG. 2B is a flowchart illustrating a process according to an embodiment.

[0022] FIG. 3 A illustrates a first example sensing scenario.

[0023] FIG. 3B illustrates a second example sensing scenario.

[0024] FIG. 3C illustrates a third example sensing scenario.

[0025] FIG. 4 is a block diagram of a network node according to an embodiment.DETAILED DESCRIPTION

[0026] FIG. 1 illustrates a multi-static sensing system 100 according to an embodiment. In the embodiment shown, multi-static sensing system 100 is a bi-static system that includes a Txnode 102 and an Rx node 104. Tx node 102 and Rx node 104 work together to sense, that is, to detect, the presence or absence of a target 190, which in this example is a non-cooperative target. For example, Tx node 102 employs its antenna system 103, which may include one or more antenna arrays, to transmit a reference signal 150, which, depending on the location of the target and the direction in which the reference signal is transmitted, may reflect off the target. The reflected signal 152 may reach the antenna system 105 of Rx node 104.

[0027] Rx node 104 is configured to perform a target sensing process, which includes Rx node producing a sensing signal and, for example, comparing the sensing signal to a reference signal and / or comparing a power of the first sensing signal to a first threshold to determine, based on a result of the comparison, whether the target has been sensed and / or a quality of a sensing result. In one embodiment, the sensing signal is produced by performing a process that includes antenna system 105 converting the electromagnetic energy that it receives to an electrical signal, which is then processed by Rx node 104 so that Rx node can determine whether the target is present.

[0028] Tx node 102 may be a user equipment (UE), a base station, such as for example a 5G base station (gNB), an integrated access and backhaul (TAB) node, a fixed wireless access (FWA) node, or a device with similar functionalities. Similarly, Rx node 104 may be a UE, a gNB (or other base station), an IAB node, a FWA node, or a device with similar functionalities.

[0029] A noted above, there is a probability that Rx node 104 i) may not be able to sense target 190 reliably, ii) does not sense any target, or iii) loses the track of the target. In such cases, it is beneficial to follow the same procedure as in the HARQ methods used in wireless communications. That is, it is beneficial for Rx node 104 to inform Tx node 102 about a result of its sensing process. Based on this information, Tx node 102 may retransmit the sensing signals with proper reconfigurations, such as, for example proper power and / or transmit beam. Also, Rx node 104 can benefit from the combination of the signals received in different retransmission rounds to improve the sensing quality with applying a proper sensing method, e.g., combining different received signals. Accordingly, in one embodiment, the target sensing process mentioned above further includes Rx node 104 providing feedback for the Tx node 102,wherein the feedback indicates a result of the first target sensing process. The feedback may be sent via a feedback channel 160, which may be a wired and / or wireless channel.

[0030] FIG. 2A is a flowchart illustrating a process 200, according to an embodiment, that is performed by Tx node 102.

[0031] In step s202, which is optional, Tx node 102 receives a capability report comprising information about Rx node 104. The capability report may be included in: i) a radio resource control (RRC) message, ii) a MAC control element (MAC-CE), or iii) uplink control information (UCI) signaling. In one embodiment, Tx node 102 may receive the capability report from Rx node 104 itself, 0AM, higher layers or another network node.

[0032] In one embodiment, the capability report may include information about: support for different methods of retransmission -based sensing; number of antennas / panels, polarizations, antennas / panels coordinates, etc. in antenna system 105 of Rx node 104; The antenna constellations (X-by-Y) in antenna system 105 of Rx node 104; information about the pointing direction of the antennas or panels of antenna system 105 of Rx node 104; beamforming capabilities (number of beams, beam types, etc.) of Rx node 104; Rx node's ability to resolve targets with different position and velocity relative to Rx node 104; Rx node 104’s full-duplex operation capability; Rx node 104’s ISAC operation capability; internal sensing delay of Rx node 104; and / or the location ofRx node 104.

[0033] The sensing of a target may be based on single-polarization, dual-polarization, or alternating-polarization. Also, in one embodiment, Rx node 104 may be informed about the location of Tx node 102, as it may be required for sensing.

[0034] In step s203, which is optional, Tx node 102 transmits to Rx node 104 a transmission configuration, which identifies resources, such as, for example, time and / or frequency resources, that Tx node 102 will use to transmit reference sensing signals (which can also be called “sensing reference signals”) and also an indication of the reference sensing signal and / or transmits to Rx node 104 a receive configuration to be used by Rx node 104 to perform a sensing process.

[0035] In step s204, Tx node 102 transmits a reference sensing signal in accordance with the transmission configuration. The reference sensing signal may be any conventionalreference signal, such as, for example, a Zadoff-Chu sequence, a channel state information reference signal (CSI-RS), positioning reference signal (PRS), a synchronization signal, or any new reference signal such as any new reference signal defined in 6G. etc. During the time slot in which Tx node 102 transmits the reference sensing signal or shortly thereafter, Rx node 104 produces a sensing signal. For example, as is well known in the art of wireless communications, the antenna system 105 of Rx node 104 converts electromagnetic energy to an electrical signal and this electrical signal is processed by Rx node 104.

[0036] Based on the produced signal, Rx node determines whether or not a target has been detected and sends feedback to Tx node 102. That is, in step s206, Tx node 102 receives feedback from Rx node 104.

[0037] The feedback from Rx node 104 may include: i) information indicating that a target was sensed with high quality, such as, for example, high reliability, and no more retransmissions are required (this is referred to as an “ACK” feedback); ii) information indicating that a target that was previously sensed and being tracked is now lost (this is referred to as a “LOST” feedback); iii) information indicating that the target was not found, which means in one embodiment that no target is sensed or no reflected reference sensing signal is received in resource blocks that Rx node expects to receive the reflected reference signal (this is referred to as a “NOT-FOUND” feedback or “NF” feedback for short), or iv) information indicating the target was sensed with insufficient quality, for example, information indicating that reliability of the detection is low (this is referred to as a “NACK” feedback). Here, by quality one may consider different metrics such the positioning resolution, the positioning accuracy, the velocity resolution, the velocity accuracy, etc , or their combination. In one embodiment, Rx node 104 may inform Tx node 102 about the considered criterion related to the transmitted feedback. For example, if a NACK feedback is sent, then the feedback may further include information indicating the positioning resolution, the positioning accuracy, the velocity resolution, and / or velocity accuracy. As another example, if an ACK feedback is sent, then the feedback may further include information indicating the targets position, speed, and / or direction of travel.

[0038] In step s208, Tx node 102 determines whether it should transmit another reference sensing signal and, if another transmission is needed, whether the same transmissionconfiguration should be used or an adapted transmission configuration. Rx node 104 may also adapt its receive configuration, which may initially be provided to Rx node 104 from Tx node 102 or another node, such as, for example, a operational support node. Accordingly, Tx node 102 may adapt it transmit configuration (step s210) and retransmit at least one reference sensing signal with the adapted retransmission configuration and Rx node 104 receives its reflections with the adapted receive configuration. Moreover, Rx node 104 may adapt its sensing algorithm to exploit the additional signals and improve the sensing quality.

[0039] For instance, after the transmission configuration, receive configuration, and / or sensing process is adapted, Tx node 102 retransmits at least one reference sensing signal and Rx node 104 tries sensing the target, possibly by the combination of different produced sensing signals. The retransmission may continue until a maximum number of retransmissions is reached where the maximum number of retransmissions is determined by a specification and / or it is indicated by the transmission network node (or, other network nodes). Alternatively, the retransmissions continue until the required QoS is satisfied. In this way, one can exploit the retransmission-based sensing methods and feedback mechanism to improve the sensing quality. This results in an improved understanding of the environment and, in turn, improves the communication quality as well.

[0040] Determining whether to adapt the transmission configuration may be based on: a sensing QoS requirement; Rx node 104’ indicated method of sensing, Rx node 104’s capability report; the number of retransmitted signals; and / or the feedback received in step s206.

[0041] In one embodiment, adapting the transmit configuration for retransmissions to Rx node 104 may include: adjusting the beam configuration for the next transmission of the reference sensing signal; adjusting the time / frequency resource blocks with respect to each beam configuration for retransmission of the reference sensing signal(s); adjusting the polarization for a set of transmitting arrays / panels; turning on or off a set of transmitting arrays / panels in antenna system 103 of Tx node 102; adapting the transmission power; and / or adapting communication configurations in the cases with ISAC operation.

[0042] For example, depending on the received feedback from Rx node 104, Tx node 102 may use different beamwidths and / or cover different directions in the retransmissions. For instance, with an NF feedback, wider beams may be used, and the beams may cover newregions. On the other hand, with a NACK feedback, Tx node 102 may use narrow beams focusing on specific direction (because we already know the rough position of the non- cooperative target and the goal is to improve the sensing accuracy). With a LOST feedback, Tx node 102 may use a wide or semi-wide beam to cover a specific area predicted from the moving trajectory of the non-cooperative target before it gets lost.

[0043] In one alternative, with a LOST, NF, and / or NACK feedback, Tx node 102 may increase the Tx power gradually in the retransmissions. In another embodiment, the transmitter may generate diversities during the retransmissions where for instance different polarizations, beam directions, beam widths, etc. are used in the retransmissions. In yet another embodiment, Tx node 102 may retransmit the same sensing signal in different retransmission rounds. Then, Rx node 104 may only use the latest received signal or combine different copies of the received signal to sense the non-cooperative target.

[0044] The time / frequency resource block association indicates which beam(s) to be used in which time / frequency resource blocks. Here, the time resource may be indicated in terms of symbols, slots, sub-frames, frames, specific time period, etc. Also, the time resource may be indicated based on the beginning, ending, periodicity, duration, etc. of the desired period. In one embodiment, Tx node 102 may inform Rx node 104 about the time / frequency resources used for retransmission(s). Finally, in another embodiment, the retransmissions may be performed with pre-defined time resource offsets relative to the initial transmission, where the predefined offsets are defined by a specification.

[0045] In one embodiment, with the retransmissions, the parameters of the reference sensing signal may be updated. Here, the duration, the bandwidth, the periodicity of the reference sensing signal, the Tx power are among the parameters to be adapted properly. If we have specific sensing time resource, we can adjust the reference signal for sensing. Particularly, based on the considered sensing quality, one can design the reference sensing signal parameters. For instance, the duration, the bandwidth, the frequency and the periodicity of the sensing signal can be determined based on Table 1 below.Table 1. Determining the sensing signal parameters.

[0046] In some embodiments, the feedback received by the Tx node indicates that the target was lost, the target was not found, or the target was sensed with insufficient quality, and process 200 further comprises, as a result of receiving the feedback, retransmitting the first reference sensing signal or a second reference sensing signal.

[0047] In some embodiments, process 200 further comprises providing to the Rx node information indicating a time resource and a frequency resource used by the Tx node to retransmit the first reference sensing signal(s).

[0048] In some embodiments, the Tx node retransmits the first reference sensing signal until either i) the Tx node receives feedback indicating that the target has been sensed with sufficient quality or ii) a maximum number of retransmissions has been reached.

[0049] In some embodiments, the first reference sensing signal is: a Zadoff-Chu sequence, a channel state information reference signal (CSI-RS), a positioning reference signal, or a synchronization signal.

[0050] In some embodiments, process 200 further comprises: prior to transmitting the first reference sensing signal, receiving a capability report about the Rx node.

[0051] In some embodiments, receiving the capability report comprises: receiving a radio resource control (RRC) message comprising the capability report, receiving a medium accesscontrol element (MAC-CE) comprising the capability report, or receiving uplink control information (UCI) signaling comprising the capability report.

[0052] In some embodiments, the capability report comprises: information indicating support for different methods of retransmission-based sensing; information indicating number of antennas in an antenna system of the Rx node, information indicating number of antenna polarizations in the antenna system of the Rx node, information indicating an antenna constellation in the Rx node, information indicating a pointing direction of an antenna system of the Rx node, information indicating beamforming capabilities, information indicating the Rx node's ability to resolve objects with different position and velocity relative to the Rx node, information indicating a full-duplex operation capability, information indicating an integrated sensing and communication (ISAC) capability, information indicating an internal sensing delay of the Rx node, and / or information indicating the location of the Rx node.

[0053] In some embodiments, the Tx node transmits the first reference sensing signal based on first configuration information for use in sensing the target.

[0054] In some embodiments, the first configuration information indicates a beam configuration to be used for transmitting the first reference sensing signal.

[0055] In some embodiments, the beam configuration indicates a wide beam, a semi- wide beam, or a narrow beam.

[0056] In some embodiments, the first configuration information indicates a set of resource blocks that the Tx node will use to transmit the first reference sensing signal.

[0057] In some embodiments, the set of resource blocks includes a first resource block, and the first configuration information indicates that a first beam should be used in the first resource block.

[0058] In some embodiments, the first configuration information indicates a polarization for a transmitting antenna.

[0059] FIG. 2B is a flowchart illustrating a process 250, according to an embodiment, that is performed by Rx node 104.

[0060] In step s252, which is optional, Rx node 104 transmits to Tx node 102 the above described capability report comprising information about Rx node 104 and / or receives asensing configuration, such as, for example, the transmission configuration, which identifies resources, time and / or frequency resources, that Tx node 102 will use to transmit reference sensing signals and also an indication of the reference signal and / or a receive configuration.

[0061] In step s254, Rx node 104 performs a first target sensing process, as described above. For example, Rx node uses its antenna system 105, among other things such as a downconverter, filter, mixer, etc., to produce a sensing signal (e.g., which may be referred toas a first sensing signal) and, for example, compares the sensing signal to a reference signal and / or compares a power of the sensing signal to a first threshold. Rx node 104 then determines, based on a result of the comparison, whether the target has been sensed and / or a quality of a sensing result. In performing the target sensing process, Rx node 104 may employ different algorithmic approaches and various metrics, depending on the sensing application and its requirements.

[0062] In one example, Rx node 104 uses an energy detector to determine the energy of the sensing signal and then, based on the determined energy, determine whether the target is sensed reliably. For instance, if the determined energy or received echo strength indicator (RESI) derived using the determined energy, exceeds a first detection threshold, then Rx node 104 determines that the target has been sensed reliably and the feedback provided to Tx node 102 is an ACK feedback. Similarly, if the determined energy or RESI is less than a second detection threshold, which is lower than the first detection threshold, then Rx node 104 determines that the target is not found and the feedback provided to Tx node 102 is the NF feedback. And if the determined energy or RESI is greater than the second detection threshold, but less than the first detection threshold, then Rx node 102 determines that the target was sensed but with insufficient quality, and the feedback provided to Tx node 102 is the NACK feedback. In one embodiment, the RESI is defined as the E / N, where E is the determined energy and N is the expected noise level. Jointly processing previous sensing signals may lead to a LOST feedback, when the received energy abruptly drops to noise level (e g , below the second detection threshold). The design of such parameters affects the system’s performance and depends on the network’s desired characteristics, i.e., probability of detection, probability of false detection, etc.

[0063] In step s256, Rx node 104 provides first feedback for the Tx node, wherein the feedback indicates a result of the first target sensing process. The feedback may be transmitted via a Physical Uplink Control Channel (PUCCH) or a Physical Uplink Shared Channel(PUSCH), particularly in the case where Rx node 104 is a UE and Tx node 104 is a base station. In one embodiment, Rx node 104 may add an indication flag in the feedback to indicate Tx node 102 that the feedback is related to a sensing result and not the typical ACK / NACK related to communication functionalities.

[0064] As described above, in response to the feedback from Rx node 104, Tx node 102 may adapt it transmission configuration, and, also, based on the result of the sensing process, Rx node 104 may adapt its receive configuration and / or target sensing process (step s258).

[0065] That is, for example, adapting the receive configuration and / or the sensing process depends on the reported feedback and the sensing results in the previous retransmission rounds. In one embodiment, Rx node 104 may inform Tx node 102 about the adapted receive configuration and / or the sensing process. Also, in another embodiment, Rx node 104 may receive an indication from Tx node 102 about the considered retransmissionbased sensing configuration.

[0066] In one embodiment, adapting the receive configuration in Rx node 104 may include: adapting a configuration of a receive beam configurations; adapting time / frequency resource blocks with respect to each beam configuration; adapting the polarization for a set of receiving arrays / panels of antenna system 105, turning on or off a set of arrays / panels in antenna system 105 of Rx node 104; adjusting the number of receive beams and / or directions of the receive beams; and / or adapting a communication configuration in the cases with ISAC operation.

[0067] One may consider different methods to adapt the sensing process in Rx node 104 in different retransmission rounds. In one embodiment, configuring the sensing process in different retransmission rounds may include:

[0068] (1) sensing the non-cooperative target by using only the latest sensing signal(and, ignoring the previously produce sensing signals); this is a low-complexity method at the cost of low sensing quality and / or the need for multiple retransmissions;

[0069] (2) considering only a limited number of sensing signals for sensing purposes(for instance, in tracking the network node may only consider the few latest sensing signals);then, Rx node 104 may consider different methods for combining the sensing signals and improve the sensing quality; and / or

[0070] (3) sensing the non-cooperative target via the combination of different sensing signals produced in different retransmission rounds; this is of high computational complexity while the sensing quality can be improved significantly.

[0071] Sensing the non-cooperative target based on the combination of different signals received in different retransmission rounds may include: (1) triangulation methods based using different received signals; (2) line-of-sight (LOS), direction and / or multiple reflection estimation related to signals produced in different retransmission rounds, and ignoring the sensing signals estimated to be unreliable; here, different state-of-the-art methods can be used to understand if a signal is received directly from Tx node 102, is reflected directly from the non-cooperative target and / or it has reached Rx node 104 through multiple reflections of scatterers; (3) ignoring the sensing signal(s) in retransmission round(s) which is / are considerably different from other the sensing signals produced in other retransmission rounds; and / or (4) ignoring the sensing signals with low power.

[0072] In one embodiment, adapting the receive configuration and / or the sensing process may be based on: a sensing QoS requirement; Tx node 102’ s indicated method of retransmission; Rx node 104’s capabilities; the number of retransmitted reference signals; and or the feedback sent in step s256.

[0073] In some embodiments, the feedback provided by the Rx node to the Tx node indicates that: the target was sensed, the target was lost, the target was not found, or the target was sensed with insufficient quality.

[0074] In some embodiments, the Rx node performs the first target sensing process using first configuration information such as, for example, a transmission configuration or a receive configuration, the feedback indicates that the target was lost, the target was not found, or the target was sensed with insufficient quality, thereby triggering the Tx node to retransmit a reference sensing signal for sensing the target, and process 250 further comprises: performing a second target sensing process using second configuration information, wherein performing the second target sensing process comprises producing a second sensing signal and determining, based on the second sensing signal, whether the target has been sensed and / or a quality of asecond sensing result; and providing second feedback for the Tx node, wherein the second feedback indicates a result of the second target sensing process

[0075] In some embodiments, performing the first target sensing process comprises determining, based on the first sensing signal, a position of the target and determining an accuracy of the determined position, and if the accuracy of the determined position exceeds a threshold, then the first feedback indicates that the target was sensed.

[0076] In some embodiments, performing the first target sensing process comprises determining, based on the first sensing signal, a velocity of the target and determining an accuracy of the determined velocity, and if the accuracy of the determined velocity exceeds a threshold, then the first feedback indicates that the target was sensed.

[0077] In some embodiments, process 250 further comprises: prior to performing the first target sensing process, the Rx node sending a capability report to the Tx node.

[0078] In some embodiments, transmitting the capability report comprises: transmitting to the Tx node a radio resource control (RRC) message comprising the capability report, transmitting to the Tx node a medium access control element (MAC-CE) comprising the capability report, or transmitting to the Tx node uplink control information (UCI) signaling comprising the capability report.

[0079] In some embodiments, the capability report comprises: information indicating support for different methods of retransmission-based sensing; information indicating number of antennas in an antenna system of the Rx node, information indicating number of antenna polarizations in the antenna system of the Rx node, information indicating an antenna constellation in the Rx node, information indicating a pointing direction of an antenna system of the Rx node, information indicating beamforming capabilities, information indicating the Rx node's ability to resolve objects with different position and velocity relative to the Rx node, information indicating a full-duplex operation capability, information indicating an integrated sensing and communication (ISAC) capability, information indicating an internal sensing delay of the Rx node, and / or information indicating the location of the Rx node.

[0080] In some embodiments, the first sensing signal produced by the Rx node is produced as a result of the Rx node receiving a reflection of a reference sensing signaltransmitted by the Tx node, and determining whether the first sensing signal indicates that the target has been sensed comprises determining whether the first sensing signal has an expected characteristic.

[0081] In some embodiments, the Rx node performs the first target sensing process using first configuration information for use in sensing the target, and the first configuration information for use in sensing the target indicates a beam configuration to be used during the first target sensing process.

[0082] In some embodiments, the beam configuration indicates a wide beam, a semi- wide beam, or a narrow beam.

[0083] In some embodiments, the Rx node performs the first target sensing process using first configuration information for use in sensing the target, and the first configuration information for use in sensing the target indicates a set of resource blocks that the Tx node will use to transmit a reference sensing signal.

[0084] In some embodiments, the set of resource blocks includes a first resource block, and the first configuration information indicates that a first beam or a first beam configuration should be used in the first resource block.

[0085] In some embodiments, the Rx node performs the first target sensing process using first configuration information for use in sensing the target, and the first configuration information for use in sensing the target indicates a polarization for a receiving antenna.

[0086] In some embodiments, the Rx node performs the first target sensing process using first configuration information for use in sensing the target, and the first configuration information for use in sensing the target indicates that: the Rx node should use only the latest sensing signal for sensing purposes, the Rx node should use a limited number of sensing signals for sensing purposes, or the Rx node should use a combination of different sensing signals produced at different times for sensing purposes.

[0087] In some embodiments, performing the first target sensing process further comprises performing a triangulation process using different sensing signals.

[0088] In some embodiments, performing the first target sensing process further comprises: ignoring a second sensing signal as a result of determining that a difference betweenthe first sensing signal and the second sensing signal exceeds a threshold, ignoring the second sensing signal as a result of determining that the power of the second sensing signal is less than a power threshold, or ignoring the first sensing signal if a second sensing signal has higher quality than the first sensing signal.

[0089] In some embodiments, providing first feedback for the Tx node triggers the Tx node to retransmit a reference sensing signal.

[0090] In some embodiments, the Rx node obtains information indicating a time resource and a frequency resource used by the Tx node to retransmit the reference sensing signal.

[0091] In some embodiments, the Tx node retransmits the reference sensing signal until either i) the Tx node receives feedback indicating that the target has been sensed with sufficient quality or ii) a maximum number of retransmissions has been reached.

[0092] In some embodiments, the first feedback indicates that the target was not found or that the target was sensed with insufficient quality, thereby trigging the Tx node to retransmit the reference sensing signal, and process 250 further comprises: the Rx node producing a second sensing signal after the Tx node retransmits the reference sensing signal; and using both the first sensing signal and the second sensing signal to determine whether the target has been found.

[0093] In some embodiments, determining, based on the first sensing signal, whether the target has been sensed and / or a quality of a sensing result comprises comparing a power of the first sensing signal to a first threshold.

[0094] In some embodiments, it determined that the target has been sensed when the power of the first sensing signal exceeds the first threshold.

[0095] In some embodiments, process 250 further comprises, after determining that the target has been sensed, determining that the target has been lost if the power of a second sensing signal is lower than a second threshold.

[0096] In some embodiments, process 250 further comprises comparing the power of the first sensing signal to second threshold, it is determined that the target is not found if the power is lower than the second threshold, and it is determined that that the target is sensed with low quality, such as low reliability, if the power is less than the first threshold but greater than the second threshold.

[0097] In some embodiments, determining, based on the first sensing signal, whether the target has been sensed and / or a quality of a sensing result comprises comparing the first sensing signal to a reference signal.

[0098] In some embodiments, the comparison is in terms of any one or more of received power, received direction, travel time, etc.

[0099] Example Sensing Scenarios[000100] FIG. 3 A illustrates a first example sensing scenario. In this example, Rx node 104 initially receives no reflected reference sensing signal in the expected resources (via sensing scheduling noted above) and, thereby, informs the Tx node that no target is sensed via an NF feedback. As a result, the Tx node may adapt its transmission configurations, e.g., the Tx beams are widened and / or point in a new direction, and retransmit the reference sensing signal. At the same time, the Rx node may adapt its receive configuration, such as, for example, by using a wider receive beam. After this adjustment, Rx node 102 receives a reflected reference sensing signal and detects the target with good quality, thereby causing Rx node 104 to send an ACK feedback to Tx node 102. In response to the ACK feedback, Tx node may again readjust its transmission configuration by, for example, using a narrow beam pointing in the direction of the target as shown in FIG. 3 A.[000101] FIG. 3B illustrates a second example sensing scenario. In this example, an already sensed target may get lost during the tracking process due to, e.g., blockage, unpredicted trajectory, etc. As a result, the Rx node sends a LOST feedback to indicate the need for recalibrating the tracking parameters. Then, for instance, the Tx node may adjust the target’s trajectory prediction and utilize wider beams for retransmissions.[000102] FIG. 3C illustrates a third example sensing scenario. In this example, the Rx node may not be able to resolve the sensed targets’ velocities and, therefore, informs the Tx node via a NACK response, that, e.g., longer sensing interval is required. Accordingly, the transmission and / or reception / sensing methods may be adapted at the Tx and Rx nodes, respectively. The retransmissions continue until the target is properly sensed or the maximum number of retransmissions is reached.[000103] FIG. 4 is a block diagram of network node 400, according to some embodiments, which can implement TX node 41, RX node 121, and / or controller 501. As shown in FIG. 4, network node 400 may comprise: processing circuitry (PC) 402, which comprises one or more processors (P) 455 (e.g., one or more general purpose microprocessors and / or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (e g., network node 400 may be a distributed computing apparatus comprising two or more computers or a monolithic computing apparatus consisting of a single computer); at least one network interface 448 (e.g., a physical interface or air interface) comprising a transmitter (Tx) 445 and a receiver (Rx) 447 for enabling network node 400 to transmit data to and receive data from other nodes connected to network 110 (e.g., an Internet Protocol (IP) network) to which network interface 448 is connected (physically or wirelessly) (e.g., network interface 448 may be coupled to an antenna arrangement comprising one or more antennas for enabling network node 400 to wirelessly transmit / receive data); and a storage unit (a.k.a., “data storage system”) 408, which may include one or more nonvolatile storage devices and / or one or more volatile storage devices. In embodiments where PC 402 includes a programmable processor, a computer readable storage medium (CRSM) 442 may be provided. CRSM 442 may store a computer program (CP) 443 comprising computer readable instructions (CRI) 444. CRSM 442 may be a non-transitory computer readable medium, such as, magnetic media (e g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 444 of computer program 443 is configured such that when executed by PC 402, the CRI causes network node 400 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, network node 400 may be configured to perform steps described herein without the need for code. That is, for example, PC 402 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and / or software.[000104] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possiblevariations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.[000105] As used herein transmitting a message “to” or “toward” an intended recipient encompasses transmitting the message directly to the intended recipient or transmitting the message indirectly to the intended recipient (i.e., one or more other nodes are used to relay the message from the source node to the intended recipient). Likewise, as used herein receiving a message “from” a sender encompasses receiving the message directly from the sender or indirectly from the sender (i.e., one or more nodes are used to relay the message from the sender to the receiving node). Further, as used herein “a” means “at least one” or “one or more.”[000106] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.[000107] References[000108] [1] Behravan, A., et. al., "Introducing sensing into future wireless communication systems," 2nd IEEE International Symposium on Joint Communications & Sensing (JC&S), Seefeld, Austria, 1322, pp. 1-5.[000109] [2] Makki, B., et. al. “On the performance of MIMO-ARQ systems with channel state information at the receiver,” IEEE transactions on communications, 2014

Claims

CLAIMS1. A method (250) for multi-static sensing of a target (190), wherein a transmitting, Tx, node (102) transmits reference sensing signals for use in sensing the target, the method comprising: a receiving, Rx, node (104) performing (s254) a first target sensing process, wherein performing the first target sensing process comprises: the Rx node producing a first sensing signal; and determining, based on the first sensing signal, whether the target has been sensed and / or a quality of a sensing result; and providing (s256) first feedback for the Tx node, wherein the first feedback indicates a result of the first target sensing process.

2. The method of claim 1, wherein the first feedback indicates that: the target was sensed, the target was lost, the target was not found, or the target was sensed with insufficient quality.

3. The method of claim 1, wherein the Rx node performs the first target sensing process using first configuration information such as, for example, a transmission configuration or a receive configuration, the first feedback indicates that the target was lost, the target was not found, or the target was sensed with insufficient quality, thereby triggering the Tx node to retransmit a reference sensing signal for sensing the target, and the method further comprises: performing a second target sensing process using second configuration information, wherein performing the second target sensing process comprises producing a second sensing signal and determining, based on the second sensing signal, whether the target has been sensed and / or a quality of a second sensing result; andproviding second feedback for the Tx node, wherein the second feedback indicates a result of the second target sensing process4. The method of any one of claims 1-3, wherein performing the first target sensing process comprises determining, based on the first sensing signal, a position of the target and determining an accuracy of the determined position, and if the accuracy of the determined position exceeds a threshold, then the first feedback indicates that the target was sensed.

5. The method of any one of claims 1-3, wherein performing the first target sensing process comprises determining, based on the first sensing signal, a velocity of the target and determining an accuracy of the determined velocity, and if the accuracy of the determined velocity exceeds a threshold, then the first feedback indicates that the target was sensed.

6. The method of any one of claim 1-5, wherein the method further comprises: prior to performing a first target sensing process, the Rx node sending a capability report to the Tx node.

7. The method of claim 6, wherein transmitting the capability report comprises: transmitting to the Tx node a radio resource control (RRC) message comprising the capability report, transmitting to the Tx node a medium access control element (MAC-CE) comprising the capability report, or transmitting to the Tx node uplink control information (UCI) signaling comprising the capability report.

8. The method of claim 6 or 7, wherein the capability report comprises: information indicating support for different methods of retransmission-based sensing;information indicating number of antennas in an antenna system of the Rx node, information indicating number of antenna polarizations in the antenna system of the Rx node, information indicating an antenna constellation in the Rx node, information indicating a pointing direction of an antenna system of the Rx node, information indicating beamforming capabilities, information indicating the Rx node's ability to resolve objects with different position and velocity relative to the Rx node, information indicating a full-duplex operation capability, information indicating an integrated sensing and communication (ISAC) capability, information indicating an internal sensing delay of the Rx node, and / or information indicating the location of the Rx node.

9. The method of any one of claims 1-8, wherein the first sensing signal produced by the Rx node is produced as a result of the Rx node receiving a reflection of a reference sensing signal transmitted by the Tx node, and determining whether the first sensing signal indicates that the target has been sensed comprises determining whether the first sensing signal has an expected characteristic.

10. The method of any one of claims 1-9, wherein the Rx node performs the first target sensing process using first configuration information for use in sensing the target, and the first configuration information for use in sensing the target indicates a beam configuration to be used during the first target sensing process.

11. The method of claim 10, wherein the beam configuration indicates a wide beam, a semi-wide beam, or a narrow beam.

12. The method of any one of claims 1-11, wherein the Rx node performs the first target sensing process using first configuration information for use in sensing the target, andthe first configuration information for use in sensing the target indicates a set of resource blocks that the Tx node will use to transmit a reference sensing signal.

13. The method of claim 12, wherein the set of resource blocks includes a first resource block, and the first configuration information indicates that a first beam or a first beam configuration should be used in the first resource block.

14. The method of any one of claims 1-13, wherein the Rx node performs the first target sensing process using first configuration information for use in sensing the target, and the first configuration information for use in sensing the target indicates a polarization for a receiving antenna.

15. The method of any one of claims 1-14, wherein the Rx node performs the first target sensing process using first configuration information for use in sensing the target, and the first configuration information for use in sensing the target indicates that: the Rx node should use only the latest sensing signal for sensing purposes, the Rx node should use a limited number of sensing signals for sensing purposes, or the Rx node should use a combination of different sensing signals produced at different times for sensing purposes.

16. The method of any one of claims 1-15, wherein performing the first target sensing process further comprises performing a triangulation process using different sensing signals.

17. The method of any one of claims 1-16, wherein performing the first target sensing process further comprises: ignoring a second sensing signal as a result of determining that a difference between the first sensing signal and the second sensing signal exceeds a threshold,ignoring the second sensing signal as a result of determining that the power of the second sensing signal is less than a power threshold, or ignoring the first sensing signal if a second sensing signal has higher quality than the first sensing signal.

18. The method of any one of claims 1-17, wherein providing first feedback for the Tx node triggers the Tx node to retransmit a reference sensing signal.

19. The method of claim 18, wherein the Rx node obtains information indicating a time resource and a frequency resource used by the Tx node to retransmit the reference sensing signal.

20. The method of claim 18 or 19, wherein the Tx node retransmits the reference sensing signal until either i) the Tx node receives feedback indicating that the target has been sensed with sufficient quality or ii) a maximum number of retransmissions has been reached.

21. The method of claim 1, wherein the first feedback indicates that the target was not found or that the target was sensed with insufficient quality, thereby trigging the Tx node to retransmit the reference sensing signal, and the method further comprises: the Rx node producing a second sensing signal after the Tx node retransmits the reference sensing signal; and using both the first sensing signal and the second sensing signal to determine whether the target has been found.

22. The method of any one of claims 1-21, wherein determining, based on the first sensing signal, whether the target has been sensed and / or a quality of a sensing result comprises comparing a power of the first sensing signal to a first threshold.

23. The method of claim 22, wherein it determined that the target has been sensed when the power of the first sensing signal exceeds the first threshold.

24. The method of claim 23, wherein the method further comprises, after determining that the target has been sensed, determining that the target has been lost if the power of a second sensing signal is lower than a second threshold.

25. The method of claim 22, wherein the method further comprises comparing the power of the first sensing signal to second threshold, it is determined that the target is not found if the power is lower than the second threshold, and it is determined that that the target is sensed with low quality, such as low reliability, if the power is less than the first threshold but greater than the second threshold.

26. The method of any one of claims 1-25, wherein determining, based on the first sensing signal, whether the target has been sensed and / or a quality of a sensing result comprises comparing the first sensing signal to a reference signal.

27. The method of claim 26, wherein the comparison is in terms of received power, received direction, and / or travel time.

28. A method (200) for multi-static sensing of a target (190), the method comprising: a transmitting, Tx, node (102) transmitting a first reference sensing signal for use in sensing the target; and the Tx node receiving first feedback from a receiving, Rx, node (104) configured for sensing the target, wherein the first feedback indicates that: the target was sensed, the target was lost, the target was not found, or the target was sensed with insufficient quality.

29. The method of claim 28, whereinthe first feedback indicates that the target was lost, the target was not found, or the target was sensed with insufficient quality, and the method further comprises, as a result of receiving the first feedback, retransmitting the first reference sensing signal or a second reference sensing signal.

30. The method of claim 29, wherein the method further comprises providing to the Rx node information indicating a time resource and a frequency resource used by the Tx node to retransmit the first reference sensing signal(s).

31. The method of claim 29 or 30, wherein the Tx node retransmits the first reference sensing signal until either i) the Tx node receives feedback indicating that the target has been sensed with sufficient quality or ii) a maximum number of retransmissions has been reached.

32. The method of any one of claims 28-31, wherein the first reference sensing signal is: a Zadoff-Chu sequence, a channel state information reference signal (CSI-RS), a positioning reference signal, or a synchronization signal.

33. The method of any one of claim 28-32, wherein the method further comprises: prior to transmitting the first reference sensing signal, receiving a capability report about the Rx node.

34. The method of claim 33, wherein receiving the capability report comprises: receiving a radio resource control (RRC) message comprising the capability report, receiving a medium access control element (MAC-CE) comprising the capability report, or receiving uplink control information (UCI) signaling comprising the capability report.

35. The method of claim 33 or 34, wherein the capability report comprises:information indicating support for different methods of retransmission-based sensing; information indicating number of antennas in an antenna system of the Rx node, information indicating number of antenna polarizations in the antenna system of the Rx node, information indicating an antenna constellation in the Rx node, information indicating a pointing direction of an antenna system of the Rx node, information indicating beamforming capabilities, information indicating the Rx node's ability to resolve objects with different position and velocity relative to the Rx node, information indicating a full-duplex operation capability, information indicating an integrated sensing and communication (ISAC) capability, information indicating an internal sensing delay of the Rx node, and / or information indicating the location of the Rx node.

36. The method of any one of claim 28-35, wherein the Tx node transmits the first reference sensing signal based on first configuration information for use in sensing the target.

37. The method of claim 36, wherein the first configuration information indicates a beam configuration to be used for transmitting the first reference sensing signal.

38. The method of claim 37, wherein the beam configuration indicates a wide beam, a semi-wide beam, or a narrow beam.

39. The method of any one of claims 36-38, wherein the first configuration information indicates a set of resource blocks that the Tx node will use to transmit the first reference sensing signal.

40. The method of claim 39, wherein the set of resource blocks includes a first resource block, andthe first configuration information indicates that a first beam should be used in the first resource block.

41. The method of any one of claims 28-40, wherein the first configuration information indicates a polarization for a transmitting antenna.

42. A computer program (443) comprising instructions (444) which when executed by processing circuitry (402) of a receiving node causes the receiving node to perform the method of any one of claims 1-27.

43. A computer program (443) comprising instructions (444) which when executed by processing circuitry (402) of a transmitting, Tx, node (102) causes the Tx node to perform the method of any one of claims 28-41.

44. A carrier containing the computer program of claim Cl or C2, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium (442).

45. A receiving, Rx, node (104) for sensing a target (190), the Rx node being configured to perform a method comprising: performing (s254) a first target sensing process, wherein performing the first target sensing process comprises: producing a first sensing signal; and determining, based on the first sensing signal, whether the target has been sensed and / or a quality of a sensing result; and providing (s256) first feedback for a transmitting, Tx, node (102), wherein the first feedback indicates a result of the first target sensing process.

46. The Rx node of claim 45, wherein the Rx node is further configured to perform the method of any one of claims 2-27.

47. A transmitting, Tx, node (102), the Tx node being configured to perform a method comprising: transmitting a first reference sensing signal for use in sensing a target; and receiving first feedback from a receiving, Rx, node (104) configured for sensing the target, wherein the first feedback indicates that: the target was sensed, the target was lost, the target was not found, or the target was sensed with insufficient quality.

48. The Tx node of claim 47, wherein the Tx node is further configured to perform the method of any one of claims 29-41.

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