Anchor node configured to reflect an electromagnetic wave signal

Abstract

An anchor node (100) configured to reflect an electromagnetic wave signal, the anchor node comprising: an array (141) comprising a plurality of antennas (142); a plurality of phase shifters (143); a connector circuit (150) configured to provide signal connection such that each antenna is connected to at least one other antenna through at least one of said phase shifters; wherein the phase shifters are configured to obtain spatial sensitivity in a target direction to provide retro reflection upon the electromagnetic wave signal impinging the array in said target direction.

Description

[0001] ANCHOR NODE CONFIGURED TO REFLECT AN ELECTROMAGNETIC WAVE

[0002] SIGNAL

[0003] Technical field

[0004] This disclosure relates to the field of anchor nodes which are used for forwarding an electromagnetic wave signal by applying configured phase shifts using an array of antennas. Specifically, solutions are proposed for an anchor node which may be used for retro reflection.

[0005] Background

[0006] In wireless communication, a wireless channel is used to transfer information and data between different nodes acting as transmitter and receiver, using an electromagnetic wave signal. It is therefore beneficial if the wireless channel is constructed to ensure that the signal successfully reaches the receiver. Besides applying sufficient transmit power, an advantageous technology is so-called beamforming, whereby transmitted energy may be focused and directed towards an intended target or receiver position.

[0007] Beamforming and beam management have been more frequently considered since the development of the so-called 5G version of wireless communication under supervision of the 3rdGeneration Partnership Project (3GPP), and particularly for use in the mm wave spectrum. A reconfigurable antenna panel comprising an array of a plurality of antenna elements may e.g. be configured at a node, wherein the antenna elements may be suitably fed such that a combined bearer is obtained with suitable directional properties. Another type of device of similar technology is a panel station or forwarding station, configured to forward a signal from a transmitter towards a receiver. By way of example, such device is sometimes referred to as a Reconfigurable Intelligent Surface (RIS), alternatively a Large Intelligent Surface (LIS). Such a panel station comprises a reconfigurable antenna array to influence a received electromagnetic wave signal, wherein digitally configurable phase shifts are applied to its antenna elements such that signal components from the antenna elements combine constructively to relay the received signal in a certain direction, possibly with added gain. The panel station may apply a varying beamforming pattern to the antennas to obtain spatial sensitivity in selected directions, by means of the applied phase shifts, to obtain a beam sweep.

[0008] Panel stations have been suggested for enhancing coverage of a radio access network (RAN) of a wireless system, by being located to convey signals to and / or from a base station of the RAN to locations where the base station has poor coverage. Such panel stations may be technically complex and require access to electric power, and possibly communication or synchronization capability with respect to a served base station.

[0009] Summary

[0010] A general object is to provide an anchor node capable of providing local coverage to wireless devices. An aspect of this objective is to provide an anchor node of low technical complexity and / or low resource requirement for operation. Another aspect of the general objective is to provide an anchor node useful for positioning of wireless devices. Another aspect of the general objective is to provide an anchor node useful for providing position-based information to wireless devices. Another aspect of the general objective is to provide an anchor node useful for providing information to wireless devices located in a spatially limited area. Another aspect of the general objective is to provide information to wireless devices with minimum impact on other wireless communication nodes. Another aspect of the general objective is to provide an anchor node useful for allowing a wireless device to communicate, via the anchor node, with another radio node.

[0011] An anchor node configured to target these objectives is provided in accordance with the independent claim. Further aspects and details are set out in the dependent claims and in the description below.

[0012] The proposed solution thus relates to an anchor node configured to reflect an electromagnetic wave signal, the anchor node comprising: an array comprising a plurality of antennas; a plurality of phase shifters; a connector circuit configured to provide signal connection such that each antenna is connected to at least one other antenna through at least one of said phase shifters; wherein the phase shifters are configured to obtain spatial sensitivity in a target direction to provide retro reflection upon the electromagnetic wave signal impinging the array in said target direction.

[0013] By means of the configuration of the anchor node, full utilization of all antennas is obtained, while at the same time minimizing or avoiding interference in other directions than the target direction.

[0014] Brief description of the drawings

[0015] Various examples will be described with reference to the drawings, as briefly described below.

[0016] Fig. 1A schematically illustrates a general presentation of an anchor node according to various examples of the proposed solution.

[0017] Fig. IB schematically illustrates a context of use of the anchor node in retro reflection configuration with respect to a wireless device, and optionally to additionally relay communication between the wireless device and a further radio node.

[0018] Fig. 2 schematically illustrates functional elements of a first embodiment of the anchor node.

[0019] Fig. 3 schematically illustrates functional elements of a second embodiment of the anchor node.

[0020] Fig. 4A schematically illustrates pairwise connectivity between antennas in a third embodiment of the anchor node.

[0021] Fig. 4B schematically illustrates functional elements of the third embodiment of the anchor node.

[0022] Fig. 5A schematically illustrates a reflection pattern for the first embodiment in a retro reflection phase configuration at 0°.

[0023] Fig. 5B schematically illustrates a reflection pattern for the second embodiment in a retro reflection phase configuration at 0°.

[0024] Fig. 5C schematically illustrates a reflection pattern for the third embodiment in a retro reflection phase configuration at 0°.

[0025] Fig. 6 shows a diagram indicative of reflection along the main positive diagonal for the diagrams of Figs 5A-5C. Fig. 7 schematically illustrates various features of an anchor node according to the proposed solution, which is configured to insert information by energy harvesting of an incoming electromagnetic wave which is reflected.

[0026] Detailed description

[0027] In the following description, for purposes of explanation and not limitation, details are set forth herein related to various examples. However, it will be apparent to those skilled in the art that the present disclosure may be practiced in other examples that depart from these specific details. In some instances, detailed descriptions of well- known devices, circuits, and methods are omitted so as not to obscure the description of the present disclosure with unnecessary detail. The functions of the various elements including functional blocks, including but not limited to those labeled or described as “computer”, “processor” or “controller”, may be provided through the use of hardware such as circuit hardware and / or hardware capable of executing software in the form of coded instructions stored on computer readable medium. Thus, such functions and illustrated functional blocks are to be understood as being either hardware-implemented and / or computer-implemented and are thus machine-implemented. In terms of hardware implementation, the functional blocks may include or encompass, without limitation, digital signal processor (DSP) hardware, reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC), and (where appropriate) state machines capable of performing such functions. In terms of computer implementation, a computer is generally understood to comprise one or more processors or one or more controllers, and the terms computer and processor and controller may be employed interchangeably herein. When provided by a computer or processor or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, use of the term “processor” or “controller” shall also be construed to refer to other hardware capable of performing such functions and / or executing software, such as the example hardware recited above. The drawings provide performance plots and are otherwise to be regarded as being schematic, where representations and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to a person skilled in the art. Any connection or coupling between functional blocks, devices, components, or other physical or functional units shown in the drawings or described herein may also be implemented by an indirect connection or coupling. A coupling between components may also be established over a wireless connection. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof.

[0028] The proposed solution is related to a device which may be employed for reflecting an incoming electromagnetic wave signal, or signal for short. Herein, such a device is generally referred to as an anchor node. An alternative term may be panel station. Further, the anchor node as described herein can be seen as a new and special configuration of a RIS. In various examples, the anchor node may also add information to the signal that is reflected. The anchor node is configured, which in some examples means being configurable, to obtain spatial sensitivity in a target direction to provide retro reflection upon the signal impinging its array in said target direction. In certain embodiments of the proposed solution, the anchor node may further be configured to selectively reflect a signal which is incoming from a first direction, so as to leave the anchor node from a second direction.

[0029] Fig. 1A schematically illustrates a general presentation of an anchor node 100 according to various examples of the proposed solution. This drawing also shows various features that are optional in different embodiments.

[0030] The anchor node 100 comprises an array 141 comprising a plurality of antennas 142. The array 141 is thus a multi antenna array, sometimes referred to as an array antenna, which comprises is a set of multiple antennas 142 which work together as a single antenna, to transmit or receive electromagnetic wave signals, such as radio waves. The antennas 142 may alternatively be referred to as antenna elements or panel elements. In the drawing, the antennas 142 are shown in a 2D arrangement in the array. Alternative configurations may comprise a ID configuration ( a line of antennas 142) or a 3D configurations (antennas 142 further configured at different depth in the array A plurality of phase shifters 143 are connected to the antennas 142, operable to apply a certain phase shift to an incoming, or impinging, signal. This way, each antenna 142 is configured to reflect a signal component of the received signal, with the applied phase shift. The phase shifters 143 may be configured to apply phase shifts so that, dependent on the arrangement of the antennas 142 in the array 141 and on an angle (space angle) of reception, the reflected signal components combine constructively in a target direction. Function and operation of phase shifters 143 are, as such, well-known in the art, and in the context of antenna array. The phase shifter 143 serves to create a delay in a received signal that is small in comparison with the reciprocal of a baseband bandwidth. By way of examples, if the incoming signal is of bandwidth 20MHz at 6GHz, then one must create a (variable) delay by a duration that is small compared with l / 20e6, but the 6GHz does not matter. The phase shifter 143 may typically comprise a variable capacitor to implement the phase- shifting function.

[0031] A connector circuit 150 of the anchor node 100 is configured to provide signal connection such that each antenna 142 is connected to at least one other antenna 142 through at least one of said phase shifters 143. This means that between reception in one antenna 142 and transmission by another antenna 142, the signal is subjected at least once to a phase shift (which as such may be configured to be zero). In this context, a signal impinging an antenna 142 of the array is subjected to a phase shift by at least one phase shifter 143, before being transmitted by at least another antenna 142 of the array 141. In some examples, a signal component received in one antenna 142 will contribute to the signal transmitted from that very antenna 142. In some examples, each antenna 142 is connected, by the connector circuit 150, such that a signal impinging that antenna is subjected to a phase shift by a single phase shifter 143 (i.e., only one phase shift) before being transmitted by another antenna 142. In other examples, each antenna 142 is connected to one separate phase shifter 143, wherein a signal impinging the array 141 is, at each antenna 142, subjected once to a phase shift upon signal reception and once upon signal transmission. Each antenna receiving an incoming signal will thus also transmit a signal component. Optionally, the connector circuit 150 may further comprise an information insertion unit 151, such as a modulator or encoder, configured to insert information into the electromagnetic wave signal. This way, information may be inserted, by the anchor node 100, in a reflected signal. In some examples, the information may comprise information which is selected to be conveyed to wireless devices when located at an angle to the anchor node 100, corresponding to the target direction. The information may be indicative of said target direction. In some examples, the information may comprise an ID of the anchor node 100, or a beam ID for the target direction. In some examples, the information may comprise position information of the anchor node 100.

[0032] In some examples, the anchor node 100 comprises a control unit 160, which may be connected to the connector circuit 150 and / or to the phase shifters 143. In such examples, the control unit 160 may comprise logic circuitry that operates the phase setting of the phase shifters 143, and thus collectively of the array 141. The logic circuitry may include a processing device 161, including one or multiple processors, microprocessors, data processors, co-processors, and / or some other type of component that interprets and / or executes instructions and / or data. The processing device 161 may be implemented as hardware (e.g., a microprocessor, etc.) or a combination of hardware and software (e.g., a system-on-chip (SoC), an application-specific integrated circuit (ASIC), etc.). The processing device 161 may be configured to perform one or multiple operations based on an operating system and / or various applications or programs. The control unit 160 may further include memory storage 162, which may include one or multiple memories and / or one or multiple other types of storage media. For example, the memory storage 162 may include a random access memory (RAM), a dynamic random access memory (DRAM), a cache, a read only memory (ROM), a programmable read only memory (PROM), flash memory, and / or some other type of memory. The memory storage 162 may be configured for holding computer program code, which may be executed by the processing device 161, wherein the control unit 160 is configured to control the anchor node 100 to carry out any of the method steps or apply the configurations as provided herein. Software defined by said computer program code may include an application or a program that provides a function and / or a process. The software may include device firmware, an operating system (OS), or a variety of applications that may execute in the logic.

[0033] The control unit 160 may further comprise an interface 163 for obtaining input from a control node. The interface 163 may be a wireless input for communicating with the control node, such as a base station of a wireless network, with which the anchor node 100 is configured to operate. Alternatively, or additionally, the input may comprise a connector for wired input or manual input to the control unit 160. Input via the interface 163 may be used to configure the control unit 160 to determine and apply a certain phase pattern to the array of elements 142 (by control of the phase shifters 143 and / or the connector circuit 150), such as a static phase pattern or a dynamic phase pattern to perform a beam sweep.

[0034] The phase shifters 143 and their connections, provided by the connector circuit 150, are configured to obtain spatial sensitivity in a target direction to provide retro reflection upon the electromagnetic wave signal impinging the array in the target direction. The anchor node 100 may thus specifically be configured to be non- responsive to electromagnetic wave signals impinging the array from other directions than the target direction. In this context, when signals imping the array 141 from other directions than the target direction, signal components reflected from the antennas 142 of the array will not add up constructively in any particular direction. The anchor node 100 is thus configured to reduce parasitic reflections. In this context, only components of signals impinging in a configured direction are reflected, such as retro reflected, whereas signals impinging from all other directions are scattered. For any phase shifter setting that "looks" at a single direction, the architecture of the anchor node 100 provided by the connector circuit 150 ensures spatial selectivity. This is in contrast to more traditional RISs, where configuration of the phase shifters to a certain single direction anyways results in non-spatial sensitivity. By way of example, where a standard RIS is configured to reflect a signal incoming from 40 deg (azimuth) to -30 deg (azimuth), the phase shifters are configured to "look" at 40 deg (azimuth) and "send" to -30 (azimuth); thus, single directions. However, an incoming signal from 60 deg (azimuth) would be reflected into -10 deg (azimuth). Thus, a normal RIS works as a normal mirror: one may tilt the mirror so that the reflection is as desired (phase shifters are electromagnetic tilting), but after tilting the mirror, everything hitting the mirror is nevertheless reflected somewhere.

[0035] In some examples, the phase shifters 143 are statically configured, such as preconfigured, to obtain spatial sensitivity in the target direction (e.g., which respect to boresight of the array 141). In other examples, the phase shifters 143 are configurable by the control unit 160 to obtain spatial sensitivity in the target direction to provide retro reflection upon the electromagnetic wave signal impinging the array in the target direction. In such an example, the control unit may further control the phase shifters and / or the connector circuit 150 with spatial sensitivity such that a signal incoming from a certain source direction is constructively reflected to the target direction (and vice versa). These options will be outlined with respect to more detailed examples of embodiments. A common trait to the different examples of the proposed anchor node 100 is that a phase pattern is applied to the array 141, such that the panel elements 142 individually apply a phase shift by means of the phase shifters 143, so as to obtain beamforming. In this context, beamforming is intended to mean that a signal impinging on the array 141 from a certain source direction is selectively steered to the desired target direction (and may further configure shape / width of the beam in the target direction). Where retro reflection is configured, the source direction and the target direction are the same.

[0036] The anchor node of the proposed solution is usable by wireless devices which operate by electromagnetic wave communication, such as radio communication. Such wireless devices are commonly referred to as User Equipment (UE). UEs are typically configured to communicate, by transmission and / or reception, with a wireless network which comprises an access network. The access network may comprise a plurality of access nodes or base stations, configured to provide a wireless interface for connection to the UEs. The wireless network further includes a core network, to which the access network is connected. The core network is in turn connected to other communication networks, such as the Internet.

[0037] Fig. IB schematically illustrates a context of use of the anchor node 100 of the proposed solution. The setup of the drawing shows a UE 10 which moves along a trajectory. The anchor node 100 is located adjacent to the trajectory. A further radio node 20, such as another UE or a base station, is further shown. An objective in this context may be to determine the location of the UE 10. Alternatively, the objective may be to provide the UE 10 with position-based information. This scenario relates to UEs predominantly moving along fixed trajectories, such as roads, train tracks, pedestrians along pavements, etc. The proposed solution provides an anchor node 100, mounted in the environment and suitably configured to facilitate positioning and / or information sharing. As an example, the anchor node may be configured to obtain positiondependent information sharing. A simple case would be e.g., a car receives information about a speed-limit.

[0038] One foreseeable way of obtaining such objectives is to employ an anchor node which transmits power generated within the anchor node. Such an anchor node typically sweeps a number of beams. In each beam, the direction is encoded / embedded. Possibly also the location of the anchor node, if not known in advance. The UE determines which beam it can hear the strongest, and from the embedded information in said beam, it may deduce its position or exchange position associated information. Such a solution is indeed robust and merely requires that the UE receives signals - it does not need to transmit.

[0039] However, in various use cases (such as the one described with reference to Fig. IB), it is not the UEs that have power limitations, but rather the anchors. The general objective is thus to provide low complexity anchor nodes 10 which can operate with low energy consumption and possibly no power supply at all. The UE 10 may be a car or train, so that transmission of some minor power is not a limitation. The anchor node 10, on the other hand, may be placed in a remote area where power supply is not easily accommodated. Furthermore, with an active anchor, the anchor may need to always radiate power, which results in a large power waste when no UEs are present / need service. Such implementation additionally adds to the interference level, i.e., it “contaminates” the environment with signal transmission which may be interfering with radio reception in other UEs for other purposes.

[0040] The proposed solution is thus based on the more appealing alternative of a passive anchor node 10, which may only radiate impinging power by means of reflection. Based on the context of Fig. IB, where the UE 10 is in need of positioning assistance or position-based information obtainment, the energy radiated by the UE 10 is reflected by the anchor node 100. Based on the reflected signal, the UE 10 may determine its position and / or obtain position-based information. Ostensibly, this may come across as very limiting as full duplex operation is required at the UE 10. However, where the UE 10 is configured as a vehicle, such as a car, mounting two antennas - one for transmission (Tx) and one for reception (Rx) - is not limiting due to the form factor of the UE 10. This type of anchor node configuration virtually eliminates the need for power supply and allows the system to only radiate power whenever needed.

[0041] Returning to the drawing of Fig. IB as an example for reference, the anchor node 100 shall be configured to provide retro reflection in a target direction (with respect to the antenna array 141), such that the UE 10 may obtain a reflected signal back from the anchor node 100 upon the UE 10 transmitting from a location matching target direction. It may be argued that this may be obtained by configuring the anchor node as a so-called Van Atta array. However, such a solution is not truly spatially selective.

[0042] Instead of a Van Atta array, the anchor node could be built as a standard RIS. The anchor node can then perform a beam sweep, where each beam is configured to synthesize a retro reflection in a certain direction. E.g., with a beam sweep of length 11, the first beam may be a retro reflection in direction a = —40°, the second in a2= —50°, etc until the last a1= 50°. When the actual direction towards the anchor, p, coincides with the configured anchor direction, the UE detects this. Then, each anchor configuration may embed information on what the current beam direction is. The UE may subsequently determine its position based on the embedded information in the strongest reflection it hears (or obtain the position from a location node in the wireless network based on reporting the received beam information). However, there is a severe problem with this method. Namely, a RIS is not spatially selective. If the true direction is p but the current retro reflection is configured to a A p, then the signal from the UE will not be reflected back to itself. However, the signal does not vanish, but instead it is reflected elsewhere (with full beamforming gain). Other UEs may be interfered by this reflection. Expressed differently, in a beam sweep of length M, a UE radiating signal will cause « M — 1 instances of interferences, and 1 instance of useful signal (the one retro reflected when a = ?). An aspect of the objective of the proposed solution is to eliminate such a behavior.

[0043] Thus, to avoid causing interference, it is an objective to configure the anchor node such that it is “spatially selective”, i.e., it only reflects signals impinging from a given direction. Such behavior is what we herein term as a standard Network Controlled Repeater, or NCR for short. An NCR is a two-stage apparatus. The first stage is to apply phase changes to all receiving antennas. The phase rotated versions are then summed into a single scalar number which may be amplified. Said scalar number, possibly amplified, is then split into N signals (N being the number of transmit antennas). Each of the N signals is then phase rotated before being fed to the N antennas. The role played by the first set of phase rotations is to filter out a single direction from which signals are accepted. By controlling the phase shifter values, this direction may be controlled. The role of the second set of phase shifters is to spatially select a single direction in which the signal is being transmitted. Altogether, if the NCR is configured for retro reflection in a direction a, but the impinging signal arrives from direction p, then there will be no strong reflection from the anchor. With that, interference is eliminated, but the price to be paid for this is that only half of the antennas are involved in reception, and the other half is involved in transmission. Thus, the efficiency in retro reflection is less for a RIS.

[0044] Various examples of the proposed solution will now be described with reference to the drawings.

[0045] Fig. 2 shows a first embodiment of the anchor node 100, which can be seen as a first special version of the anchor node Fig. 1A. Herein, the connector circuit 150 comprises circuitry configured to obtain a summation signal from the antennas 142 and to distribute the summation signal to the antennas 142. In this context, the summation signal is a signal resulting from the combined signal components obtained from the antennas 142. The summation signal may be obtained by means of a signal combiner which combines the signal components from multiple antennas into a single feed line. The summation signal may alternatively be referred to as a combined signal or a composite signal.

[0046] Specifically, the array 141 comprises a first subset 144 of the antennas 142 and a second subset 145 of the antennas 142, wherein, for each of the subsets 144, 145, the circuitry is configured to distribute the summation signal to the other subset. For each subset, the included subset of antennas 142 form one panel array. However, since the summation signal collected from the antennas 142 of one subset 144 is split and distributed to each of the antennas 142 of the other subset 145, and vice versa from the subset 145 to the antennas 142 of the subset 144, all antennas 142 are active for both reception and transmission in retro reflection. This may be obtained when the first subset 144 and the second subset 145 of the antennas 142 are both configured for spatial sensitivity in the target direction. In some examples, where the first subset 144 and the second subset 145 of the antennas 142 are configured for spatial sensitivity in different directions, the anchor node 100 may be used for communication purposes, such as between the UE 10 and the radio node 20. Although, in the drawing, the subsets 144, 145 are indicated as physically separate entities, this shall only be seen as one illustrative and non-limiting example. Indeed, the antennas 142 of the respective subsets 144, 145 may be connected from one single antenna array and the subsets 144, 145 may even overlap. According to some examples, the circuitry of the connector circuit 150 may comprise multi-port circuits 152, 153 for each associated subset 144, 145, respectively, wherein each multiport circuit has a first port side with separate connections to the antennas 142 of the associated subset. Each multiport circuit further has a second port side with a single port, internally connected to each of the ports of the first port side. The second port side of the multiport circuits are in turn connected to each other, as illustrated. In this context, it may be noted that the + indicated at the first multi-port circuit 152 and the • indicated at the second multiport circuit 153 in Fig. 2 merely indicates signal connection from the first subset 144 to the second subset 145, but that the circuitry operates in both ways.

[0047] This embodiment is based on the notion of an NCR architecture. An important feature of what we term standard NCR is that of amplification and, at the very minimum, unidirectional behavior. That is, one panel array acts as receiver while the other panel array acts as transmitter. In the embodiment described with reference to Fig. 2, there is no amplifier which implies that signals impinging on one of the subsets (panels) 144 will be reflected from the other subset (panel) 145, and vice versa. Furthermore, the phase shifters at both panels are configured to the same direction, thereby synthesizing a retro reflection in the configured target direction. With that, there is full efficiency in the sense of beam forming gain per deployed antenna. Further, where the anchor node 100 comprises the control unit 160, the anchor node may be configured to act similar to a conventional NCR by configuring the phase shifters of the two panels to different directions, as noted above; but in that case, the efficiency is again reduced. In this context, the control unit 160 may be configured to selectively control the phase shifters 143 to obtain reflection of the electromagnetic wave signal between a first spatial direction and a second spatial direction.

[0048] Fig. 3 shows a second embodiment of the anchor node 100, which can be seen as a second special version of the anchor node Fig. 1A. Herein, the connector circuit 150 comprises circuitry configured to obtain a summation signal from the antennas 142 and to distribute the summation signal to the antennas 142. Specifically, the circuitry is configured to obtain a summation signal from each of the antennas 142 and to distribute the summation signal back to each antenna 142. In this embodiment, as in the first embodiment, each antenna 142 may be connected to one phase shifter 143, as indicated in the drawings. The signal components obtained from the respective antennas 142 are thus first subjected to a phase shift from the respective phase shifters 143 prior to summation, and the summation signal is subsequently again subjected to the same phase shift at each antenna 142. In other words, upon configuring the array for spatial sensitivity in a certain target direction, it is automatically configured for retro reflection in that target direction. In some examples, the circuitry is configured to reflect the summation signal back onto the antennas 142, under influence of the respective phase shifters 143.

[0049] In some examples, the circuitry of the connector circuit 150 may comprise a multi-port circuit 152 having a first port side with separate connections to each antenna 142. The multiport circuit 152 further has a second port side with a single port. The second port side may be non-terminated to obtain reflection back to the first port side. In some examples, the second port side may be non-terminated, i.e., not impedance matched. In some examples, as illustrated, the second port side is connected to a ground plane in which the reflection of the summation signal is obtained. In other examples, the second port side is left open.

[0050] Figs 4A and 4B show a third embodiment of the anchor node 100, which can be seen as a third special version of the anchor node Fig. 1A. The anchor node architecture is based on the concept of a normal RIS. As already indicated, the typical behavior of a RIS is that an impinging signal from a given direction is reflected to an arbitrary, but configurable, outgoing direction; this is commonly termed as an anomalous reflection. In other words, the RIS selects a spatial pair of directions and establishes a strong link between said two directions. However, a RIS is not spatially selective in the true sense, meaning that the only reflected signal is the one impinging from the configured input direction. Rather, a RIS reflects signals impinging from almost any direction, which may cause troublesome interference situations.

[0051] Based on this known drawback of prior art RIS design, the proposed solution according to the third embodiment involves an anchor node 100 which is based on a novel RIS implementation that only reflects signals from one given direction. By contemplating upon how this may possibly be done, one quickly reaches the conclusion that it cannot be done through means of ordinary signal processing, i.e., by adapting the phase configuration applied to the phase shifters. Rather, the hardware must be reengineered in such a way that the anchor node 100 is spatially selective. In standard RIS technology, the signal received at a certain element (antenna 142) is first phase rotated and then re-radiated from the very same element. However, according to the proposed solution, the phase-shifted signal is instead connected to leave the anchor node 100 from an element other than the one receiving it, as indicated in Fig. 4A. This way, the anchor node 100 naturally becomes spatially selective. This can be mathematically proved, as indicated in WO2023052335A1. That was the publication of PCT / EP2022 / 076782, which is herein incorporated by reference in its entirety. That application was filed on 27 September 2022 and claims priority from the Swedish application 2151196-9, filed on 29 September 2021.

[0052] It may be noted that for a single array 141 configuration, arbitrary combination of input and output directions with regard to the anchor node 100 (i.e., typically for radio communication purposes, such as between the UE 10 and the radio node 20), the connector circuit 150 will have to include circulators if the full array 141 is to be employed with full beamforming gain. However, by means of the connection indicated in Fig. 4A where only a single phase shifter is present for each pair of antennas 142, the permutation is symmetric. This provides for a less complex connector circuit 150, by avoiding the need of any circulators. For general reflection directions, i.e., not limited to retro-reflections, a symmetric circulator free permutation exacts a 4dB power penalty. However, whenever the reflection is configured to retro reflections, the power loss vanishes. Thus, we have full efficiency, i.e., beamforming gain, retro reflection, such as for positioning or for obtaining information in the UE 10 from the anchor node 100 based on a signal transmitted by the UE 10.

[0053] The embodiment of Figs 4A and 4B may thus be characterized in that the connector circuit 150 provides permuted antenna connections, that is, a signal received at antenna z leaves the anchor node 100 at antenna j. Specifically, the permutation pattern is symmetric, which further implies that the signal received at antenna j leaves the anchor node 100 from element z. Hence, only a single phase shifter 143 is adopted per pair of antennas 142, as is schematically illustrated in Fig. 4A (where only the connection of two antenna pairs are shown, for the sake of simplicity). For each of the antennas 142, the connector circuit 150 thus provides for single pairwise connection (154) via one phase shifter 143 to another one of the antennas 142.

[0054] Furthermore, a relative positional arrangement between the antennas of a first pairwise connection may be different from the relative positional arrangement between the antennas of a second pairwise connection. The difference in relative positional arrangement may comprise a difference in distance and / or direction between the antennas of the pairwise connections in x- or y-direction (in a plane of the array 141) or in z-direction (normal to the array 141). In this context, a first space vector between the positions of the antennas i, j of the first pairwise connection is different from a second space vector between the positions of the antennas k, I of the second pairwise connection. According to some examples, there is a non-systematic configuration of the relative positional arrangement of each pairwise connection. The non-systematic configuration may be random or pseudo-random. Specifically, the relative positional arrangement between the antennas of each pairwise connection may be different from the relative positional arrangement between the antennas of all other pairwise connections of the array 141. By means of the non-systematic configuration, a mechanism is obtained for suppressing contributions of different antennas 142 to add coherently for incoming-outgoing angle pairs different from the intended incomingoutgoing directions. Specifically, in retro reflection, the antenna array 141 is configured to act as mirror in the intended direction (also called target direction herein), whereas signals impinging in any other direction will not generate reflection of any constructive combination of signal components in any direction. Thereby, the anchor node 100 is configured to be truly spatially selective, in contrast to standard RIS configuration.

[0055] As indicated in Fig. 4B, the connector circuit 150 provides the pairwise connection 154, wherein the permutation plays a significant role. According to one example for an array 141 of 20 antennas 142, after brute force numerical search, a non- systematic pairwise configuration was found that appears particularly good, namely:

[0056] [1 2 3... 19 20] [17 18 20 16 13 11 14 19 12 15 6 9 5 7 104 1 2 8 3],

[0057] This permutation was found by randomly searching over 3xl04permutations, as well as S -random permutation which are known to be well performing in a variety of other contexts.

[0058] Figs 5A, 5B and 5C show reflection patterns synthesized based on the first, second and third embodiments, respectively. For simplicity of graphical illustration, a uniform linear array with N = 20 elements is considered in all cases. Thus, the reflection pattern may be expressed as A(0in, 0out) where 0in, 0outare directions of incoming and outgoing signals, respectively. It suffices to study a phase configuration according to 0in= 0out= 0, as any other retro reflective configuration would result in a translation of the reflection pattern for 0in= 0out= 0. The reflection patterns, normalized with normalized with A(0,0), are plotted in these drawings. The intensity scale, indicated to the right in the respective drawing, represents a dB value. The following can be noted:

[0059] • The gain for retro reflections are found along the main positive diagonal (southwest to northeast).

[0060] • All other points except said positive main diagonal correspond to interference.

[0061] • It can be clearly seen that the first and second embodiments have significantly superior side lobe suppression than the third embodiment.

[0062] • By inspection, the side lobe suppression in the third embodiment is 7.64dB, so it is not void of side lobe suppression.

[0063] • By DFT (Discrete Fourier Transform) and RIS theory, the side lobe suppression of the second embodiment is around 26dB (no matter N).

[0064] • By calculation, the side lobe closest to the main lobe of the first embodiment (i.e., start from the center and move northeast to the first lobe) is 6.5dB attenuated. Other sidelobes have around 26dB attenuation.

[0065] • The main lobe of the second embodiment is very narrow.

[0066] • The main lobe of the third embodiment is elongated in the direction of retro reflections.

[0067] • The main lobe of the first embodiment is elongated, but not in the direction of retro reflections.

[0068] • All main lobes reduce as N increases.

[0069] • The side lobes of the third embodiment decrease as N increases (unlike the first and second embodiments). So, at very large N, the third embodiment may be competitive even with respect to side lobe suppression.

[0070] The fact that the main lobe of the third embodiment is elongated in the direction of retro reflections is important. Fig. 6 shows the cut along the main positive diagonal, i.e., A(0in, 0out) bin=0Out plotted, again for a phase configuration to synthesize a retro reflection for 0in= 0out= 0. From this plot it can be observed that the main lobe of the third embodiment is much wider in comparison to the first and second embodiments. In some examples of the proposed anchor node, the control unit 160 is included and configured to control the phase shifters 143 to alter the spatial sensitivity according to a pattern to obtain a sweep of the target direction, i.e., a so-called beam sweep. The comparatively wider main lobe in the third embodiment has the implication that such a beam sweep at the anchor node 100 may be reduced, as fewer number of beams are needed to cover space. This is especially important as N increases.

[0071] Thus, various aspects of the embodiments may be summarized according to the table below.

[0072] Here, full gain refers to full beamforming gain in retro reflection. Further, dual operation relates to the capability of being configurable for both retro reflection (e.g., for positioning) and for reflection between different directions / angles (e.g., for communication). For the first and third embodiments, the anchor node 100 may comprise the control unit 160, which may be configured to to control the phase shifters 143 to apply equal spatial sensitivity for reception and transmission, i.e., for retro reflection. For communication purposes, the control unit 160 may alternatively control the phase shifters 143 to apply different spatial sensitivity for reception and transmission, but without full gain.

[0073] Moreover, indicated moderate implementation cost is due to presence of splitter / combiner circuitry 152, 153, and the amount of required phase shifters 143.

[0074] In some examples, the connector circuit is preconfigured to configure the phase shifters to apply equal spatial sensitivity for reception and transmission, hence, to obtain retro reflection. This is true by design for the second embodiment. Even for the first and third embodiment, the phase shifters may be preconfigured to only apply equal spatial sensitivity for reception and transmission, so as to only provide retro reflection. In such examples, wherein the anchor node 100 is preconfigured for retro reflection, the anchor node 100 may further be configured to introduce fixed losses in selected antennas 142, or optionally by switching in a resistive load. These fixed losses could synthesize, e.g., a Hamming window which would suppress side lobes.

[0075] In some examples, the phase shifters 143 are configured to statically obtain retro reflection in the target direction. In this context, there is no beam sweep. This further simplifies the construction of the anchor node 100.

[0076] As noted, the anchor node 100 may comprise an information insertion unit 151. The information insertion unit 151 may embed information in the reflected signal. The information insertion unit 151 may encode a reflected signal in power and / or phase and / or time domain, to include information in the reflected signal. In some examples, this may be obtained by modulation of the received signal. In some examples, the information insertion unit 151 may be configured to operate on a very low-complexity modulation, such as On-Off Keying (OOK) modulation, binary frequency shift keying (BFSK), and binary phase shift keying (BPSK). Other, more complex, modulation techniques are also plausible. In some examples, information on the target direction or other information of the anchor node 100 may be embedded for example, be done as follows. Let the current beam configuration be the vector c, where each element in c corresponds to the phase shift of its respective antenna 142. By keeping the beam direction constant, but invoking an overall phase shift over time, i.e., exp(it) c in the tth slot of the beam c, information can be embedded int.

[0077] The UE 10 which transmits a signal may be preconfigured to retrieve the embedded information from the retro reflected signal. The information may e.g., include positioning information, such as one or more of a position of the anchor node 100, an angle / direction of retro reflection, a beam ID, or other information. In other examples, the information may comprise position (direction)-based information, such as an ID of the anchor node or information relevant to convey at a position where a trajectory of the UE 10 (see Fig. IB) crosses the target direction at which the anchor node 100 provides retro reflection, such as traffic information or local regulatory information. In some examples of the anchor node 100 according to the proposed solution, power is required. This may relate to configurations where a beam sweep is carried out, where information is inserted, and / or where the anchor node 100 may be selectively reconfigured between retro reflection or reflection between different directions. The anchor node 100 may thus comprise an energy unit that provides energy to the other components of the anchor node 100. In some examples, the energy unit may comprise a capacitor or a battery, or a mains connector. In other examples, the anchor node 100 may be configured to obtain the required energy from received RF (radiofrequency) waves. This is schematically illustrated in Fig. 7. In some examples, the energy unit 700 is configured to harvest incoming radio frequency (RF) energy. The drawing provides a schematic overview of such an example, usable in the anchor node 100. The anchor node 100 is thereby configured to employ so-called backscatter communication. This may involve using a received RF signal for energy harvesting and using the energy for, e.g., modulating the signal to embed information. The energy unit 700 may comprise a power harvesting circuit, connected to the antennas of the array 141, a power management module and possibly an energy storage such as a capacitor. The information insertion unit 151 may comprise a modulator 710, which is powered by the energy unit 700, e.g., through the power management module. In some examples, the modulator 710 is connected directly to the antenna 314. The anchor node 100 may thus be configured to backscatter the received signal, using the same antenna array 141 for reception and reflection as proposed herein. The phase shifters are left out of this drawing but may be configured in accordance with any of the embodiments and examples provided herein. The control unit 160, where included, may further be powered by the energy unit 700.

[0078] Based on the example provided with reference to Fig. 7, the anchor node can be made power-independent, which allows for vertically unrestricted location opportunities in the environment.

[0079] As the anchor nodes 100 as provided herein are passive and merely present at certain geographical positions, a UE 10 may need to be informed on when it should initiate a transmission towards it. The following provides examples of associated protocols for this purpose:

[0080] A deployer of anchor nodes registers the anchor node(s) 100 to a wireless network, such as a cellular 3GPP network. • Each anchor node may be registered with one or more of the parameters {anchor-ID, location, duration / length of beam sweep}. Secondary parameters that may be included are {operating frequencies, interference properties, reflection pattern properties, positioning-precision-performance-metrics, dual operation mode}.

[0081] • A UE 10 that has been, e.g., by a base station of the wireless network, determined to be positioned in the vicinity of an anchor node 100 and classified as in the need or benefit of (i) improved position or, (ii) information held by the anchor node 100 (e.g., a speed limit, clearance signal, etc.) is provided time-frequency resources to transmit reference signals. Possibly, the base station indicates a direction to which the UE 10 should transmit, i.e., towards the anchor node 100.

[0082] • The UE 10 may indicate to the base station that it is capable of duplex operation, i.e., it is capable of transmitting a reference signal while, at the same time, monitoring received signals, i.e., reflections of the transmitted reference signal. A UE 10 could do this, e.g., by using different Rx and Tx panels; this is especially feasible for the case of large UEs, such as a car or a bus.

[0083] • Further information indicated to the UE 10 by the base station may include the duration during which the anchor node 100 maintains a given beam.

[0084] • The UE 10 monitors its receive antenna(s) during its transmission.

[0085] • Depending on application or use case there are several options on ensuing UE 10 operations. In some cases, the base station indicates to the UE 10 what the processing should be. In some cases, the anchor node 100 encodes (e.g. by modulation) its ID into its response, e.g., by applying a phase pattern to its reflection as described.

[0086] • The UE 10 reports the resources (i.e., anchors beams) in which it received the strongest reflection(s) as well as the anchor node ID. This is of interest in pure positioning applications. Based on this information, the base station (or a location node in the wireless network) may improve the positional estimate of the UE 10. This may require the anchor node 100 to encode a timestamp to each beam, or the beam-ID itself.

[0087] • The anchor node 100 may encode the current reflection direction in its response. This allows the UE 10 to directly obtain the positional estimate.

[0088] • The anchor node 100 may encode other information into its reflection, by the information insertion unit 151. In that case, the UE 10 can either decode this itself, or relay the information to the wireless network for handling the decoding. An example of a protocol for an anchor-aware-UE design is very similar to the above, but differs in its initiation:

[0089] • The UE 10 indicates to the base station that anchors nodes are available. It requests time-frequency resources for transmitting signals.

[0090] • The anchor nodes 100 may not be registered at the wireless network for this protocol. The UE 10 may need to inform the base station on interference properties of the anchor node(s) 100.

[0091] • The anchor nodes 100 encodes some application-specific information in its reflection.

[0092] • The UE 10 decodes the information and takes actions accordingly (application-specific).

[0093] Various details and aspects related to the proposed solution have been outlined in the foregoing. The proposed solution may further be embodied in accordance with any combination of the claims appended. The proposed solution relates to a passive anchor node 100 (i.e., it reflects rather than receives and transmits) which is preconfigured, or configurable, to provide retro reflection in a target direction. The antenna array 141 is further configured or controlled such that the anchor node 100 is truly spatially selective to only provide reflection in the target direction, such that potentially caused interference is minimized. This is obtained by the phase shifters and the connector circuitry being configured to obtain constructive combination of signal components from all antennas 142 solely in the target direction. This way, the anchor node 100 is configured to provide information to wireless devices 10 with minimum impact on other wireless communication nodes, such as other wireless devices. The proposed solution further provides full utilization of all antennas 142 of the array 141 in retro reflection.

Claims

CLAIMS1. An anchor node (100) configured to reflect an electromagnetic wave signal, the anchor node comprising: an array (141) comprising a plurality of antennas (142); a plurality of phase shifters (143); a connector circuit (150) configured to provide signal connection such that each antenna is connected to at least one other antenna through at least one of said phase shifters; wherein the phase shifters are configured to obtain spatial sensitivity in a target direction to provide retro reflection upon the electromagnetic wave signal impinging the array in said target direction.

2. The anchor node of claim 1, wherein the connector circuit comprises an information insertion unit (151), configured to insert information into the electromagnetic wave signal.

3. The anchor node of claim 2, wherein the information insertion unit comprises a signal modulator, configured to insert the information by modulation of the electromagnetic wave signal.

4. The anchor node of claim 2 or 3, wherein the information is indicative of said target direction.

5. The anchor node of any preceding claim, wherein the connector circuit is preconfigured to configure the phase shifters to apply equal spatial sensitivity for reception and transmission.

6. The anchor node of claim 5, wherein a fixed loss is configured at predetermined antennas to suppress side lobes.

7. The anchor node of any preceding claim, wherein the phase shifters are configured to statically obtain retro reflection in the target direction.

8. The anchor node of any of preceding claim, comprising a control unit configured to control said phase shifters.

9. The anchor node of claim 8, wherein the control unit is configured to control said phase shifters to alter the spatial sensitivity according to a pattern to obtain a sweep of the target direction.

10. The anchor node of claim 8 or 9, wherein the control unit is configured to selectively control said phase shifters to obtain reflection of the electromagnetic wave signal from a first spatial direction to a second spatial direction.

11. The anchor node of any preceding claim, wherein the connector circuit comprises circuitry configured to obtain a summation signal from the antennas and to distribute the summation signal to the antennas.

12. The anchor node of claim 11, wherein the circuitry is configured to obtain a summation signal from each of the antennas and distribute the summation signal back to each antenna.

13. The anchor node of claim 12, wherein the circuitry is configured to reflect the summation signal back onto the antennas.

14. The anchor node of claim 11, wherein the array comprises a first subset (144) and a second subset (145) of the antennas, wherein, for each of the subsets, the circuitry is configured to distribute the summation signal to the other subset.

15. The anchor node of any of claims 1-10, wherein each of said antennas has a single pairwise connection (154) via one phase shifter to another one of the antennas, and wherein a relative positional arrangement between the antennas of a first pairwise connection is different from the relative positional arrangement between the antennas of a second pairwise connection.

16. The anchor node of claim 15, comprising a non- systematic configuration of the relative positional arrangement of each pairwise connection.

17. The anchor node of claim 15 or 16, wherein each pairwise connection is circulator-free.

18. The anchor node of any preceding claim, wherein the phase shifters and the connector circuitry are configured to obtain constructive combination of signal components from all antennas solely in the target direction.

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