System and method for bidirectional integrated sensing and communication using shared frequency modulated continuous waveforms

Abstract

The present disclosure relates to a method for operating an integrated sensing and communication, ISAC, system. The method comprises: using the radar hardware equipment of the ISAC system for radar signal transmissions with frequency modulated continuous waveforms, FMCW; and encoding communication data symbols into the radar signals. Furthermore, a corresponding ISAC system is disclosed.

Description

[0001] SYSTEM AND METHOD FOR BIDIRECTIONAL INTEGRATED SENSING AND COMMUNICATION USING SHARED FREQUENCY MODULATED CONTINUOUS WAVEFORMS

[0002] The present invention relates to an integrated sensing and communication, ISAC, system, as well as to a method for operating an ISAC system.

[0003] Integrated Sensing and Communication (ISAC) technology marks a revolutionary advancement in wireless systems, seamlessly integrating cutting-edge communication capabilities with pervasive sensing functionalities. This transformative approach fosters unparalleled connectivity and intelligence across critical technological domains, reshaping the interaction between emerging systems and their environments.

[0004] A key technological challenge lies in balancing performance trade-offs between sensing and communication functions. As spectrum scarcity increasingly constrains emerging wireless technologies, there is a growing need to develop efficient strategies that merge traditionally distinct sensing and communication operations. By optimizing wireless systems through shared waveforms and hardware platforms, ISAC technology significantly improves spectral efficiency and overall system performance.

[0005] Existing research in ISAC predominantly follows two design paradigms: radar-centric and communication-centric systems. Communication-centric ISAC designs, often applied in Wi-Fi and cellular networks, aim to incorporate sensing functionalities within ongoing communication processes, thereby allocating fewer resources to sensing rather than communication. In contrast, radar-centric approaches emphasize enabling communication capabilities within sensing systems.

[0006] In this context, ISAC systems have evolved along four main architectural strategies. A first strategy relies on independent waveforms for both communication and sensing and thus suffers from inefficient spectrum utilization (for reference, see Lu, Haofan, et al. "A Millimeter Wave Backscatter Network for Two-Way Communication and Localization." Proceedings of the ACM SIGCOMM 2023 Conference. 2023). A second strategy employs dedicated dual-function waveforms, which requirespecialized radar development and active radios, making them impractical for resource-constrained loT devices (for reference, see Hassanien, Aboulnasr, et al. "Dual-function radar communication systems: A solution to the spectrum congestion problem." IEEE Signal Processing Magazine 36.5 (2019): 115-126) A third approach adapts existing communication waveforms, such as orthogonal frequency-division multiplexing (OFDM), for sensing purposes (for reference, see Barneto, Carlos Baquero, et al. "Full-duplex OFDM radar with LTE and 5G NR waveforms: Challenges, solutions, and measurements." IEEE Transactions on Microwave Theory and Techniques 67.10 (2019): 4042-4054). Finally, a fourth strategy - that is addressed in the present disclosure - involves embedding digital messages directly into radar waveforms, achieving a sophisticated integration of sensing and communication (for reference, see Okubo, Ryu, et al. "Integrated two-way radar backscatter communication and sensing with low-power loT tags." Proceedings of the ACM SIGCOMM 2024 Conference. 2024).

[0007] The solution proposed in the last cited reference leverages the frequency slope of chirp signals typical of frequency modulated continuous waveform (FMCW) radars to transmit data while sensing. However, this state-of-the-art solution is limited to binary transmissions, i.e. , it can embed only ones or zeroes in the signal which is strongly limiting the bitrate.

[0008] It is an objective of the present invention to improve and further develop a system and a method of the initially described type in such a way that the above-mentioned critical limitations of current ISAC systems are overcome or at least mitigated.

[0009] This objective is addressed by the subject-matter of the independent claims.

[0010] In accordance with the invention, the aforementioned object is accomplished by a method for operating an integrated sensing and communication, ISAC, system, the method comprising: using the radar hardware equipment of the ISAC system for radar signal transmissions with frequency modulated continuous waveforms, FMCW; and encoding communication data symbols into the radar signals.

[0011] Furthermore, the aforementioned object is accomplished by an integrated sensing and communication, ISAC, system, comprising a radar hardware equipmentconfigured to generate radar signal transmissions based on frequency modulated continuous waveforms, FMCW; and to encode communication data symbols into the radar signals.

[0012] The concept proposed herein overcomes critical limitations in current ISAC systems by introducing a novel modulation scheme that reuses standard radar hardware equipment to simultaneously transmit information and perform target localization and tracking. This is achieved by way of using frequency modulated continuous waveforms, FMCW, for the radar signals, wherein communication data symbols are encoded into these radar signals. The proposed concept can be implemented in a user-side compact and low-power hardware architecture and is applicable for different use cases depending on specific target characteristics. Furthermore, the proposed concept has the advantage that it is flexible in terms of the choice of operating frequency.

[0013] According to an example, the radar signals used for encoding communication data symbols include both up and down-chirps with variable steepness. Up and downchirps here refers to signals having a positive (up-chirp) and negative (down-chirp) time-frequency slope.

[0014] According to an example, the modulation order of the communication data symbols encoding into the FMCW radar signals can be defined by the total number of distinct chirp slope steepness. The number of distinct chirp slopes defines the number of different symbols that can be transmitted. This in turn reflects to the amount of information (number of bits) that can be transmitted through the transmission of a single symbol. For example, an M-ary modulation scheme with M = 4 can be realized with a maximum chirp rate |k_max| =2, i.e. including four different types of radar signals with k = 2, k = 1 , k = -1 and k = -2. For example, the bits could be assigned as follows in this scheme:

[0015] k_1 = k_max, corresponding to the bits 00,

[0016] k_2 = 0.5 k_max, corresponding to the bits 01 ,

[0017] k_3 = -0.5 k_max, corresponding to the bits 10, and

[0018] k_4 = -k_max, corresponding to the bits 11.According to an example, it may be provided that the modulation order is adjusted based on the quality level of the communication channel. To this end, the radar hardware equipment may include measuring components configured to determine the quality level of the communication channel and adaptation means for adjusting the modulation order based on the determined quality level of the communication channel. Specifically, the measuring components may be configured to measure a perceived channel quality, e.g., via Signal to Noise Ratio (SNR), Signal Strength Indicator (SSI), Channel Quality Indicator (CQI), or the like.

[0019] According to an example, the encoding of communication data symbols into the radar signals may comprise generating a M-ary modulation scheme based on FMCW radar chirp signals, where M is chosen as the highest value that can be currently supported by the communication channel. To determine the highest value that can be currently supported by the communication channel, the measuring components may perform various measurements including, but not limited to, exploiting feedback on the received SNR, analyzing signal quality indicators, checking attenuation of echos, and / or the like.

[0020] According to an example, the system may include at least on RX device configured to enable the reception and the decoding of the slope of a received chirped signal without disrupting the radar localization process. The RX device comprises an antenna configured to capture a chirped signal, one or more signal processing components configured to downconvert the frequency of the captured signal, an analog-to-digital converter, ADC, configured to digitize the signal and a micro controller unit, MCU, configured to create a spectrogram of the received signal. For instance, the MCU may create the spectrogram by performing a spectral analysis based on a short-time Fourier transform (STFT). Based on the spectrogram, the MCU may then determine the distance to the radar transmitter and Doppler velocity (if the radar is moving). Finally, the MCU may decode the data symbols of the M-ary communication.

[0021] According to an example, the one or more signal processing components of the RX device may include an envelope detector, preferably a RF Log Detector, configured to output a DC representation whose amplitude is inversely proportional to the power of the received chirp signal. Since the power consumption of a RF Log Detector israther low, this solution is particularly suitable for being implemented on devices that are designed to operate efficiently within limited power constraints (often incorporating internal energy storage). The output of the RF Log Detector can be sampled by the ADC and the digitized signal of the ADC can then be processed by the MCU, e.g. as described above.

[0022] According to an example, the one or more signal processing components of the RX device may include a mixer configured to self-mix a received radar signal for down converting the radar signal. Again, since the power consumption of a mixer is rather low, this solution is particularly suitable for being implemented on devices that are designed to operate efficiently within limited power constraints. Specifically, the mixer may be fed with signals from an RF splitter that divides the received signal into copies with halved power each. The output of the mixer can be sampled by the ADC and the digitized signal of the ADC can then be processed by the MCU, e.g. as described above.

[0023] According to an example, the one or more signal processing components of the RX device may include an RF splitter and at least two power detectors configured to estimate the slope monotonicity of the radar signal. In this solution, the spectral analysis can be offloaded to the hardware, i.e. computation can be partly offloaded from the MCU. Accordingly, this solution is particularly suitable for being implemented on devices equipped with low-computational power only. Specifically, the solution may include an RF splitter that splits the received input signal into two signals, one signal being the received input signal that serves as a reference, and the other signal being the received input signal with an intentionally introduced time delay, the delay producing phase shifts that vary predictably with the input frequency. Accordingly, the voltage produced becomes a direct representation of frequency deviation, wherein an upward frequency shift results in a proportional positive voltage change, while a downward shift generates a negative voltage. Each of these shifts is measured by a respective one of the two power detectors, wherein the outputs of the two power detectors can be further processed by the ADC und the MCU.

[0024] According to an example, the one or more signal processing components of the RX device include at least one diode, in particular a step recovery diode, SRD, configured to create a mixable and down convertible signal due to it switching characteristics.Specifically, the SRD may be adopted as a frequency multiplier for a waveform generator, WG. The output of the SRD may be routed through an LC filter in order to suppress unwanted replicas. The filtered output of the SRD may then be mixed and downconverted and can finally be processed by the ADC and the MCU, e.g. as described above.

[0025] According to an example, the RX device may be configured to further include a wave generator, WG, capable of generating a chirp signal for bidirectional communications. Accordingly, the device may be enabled to operate both in transmission mode and in reception mode. In transmission mode, the WG may be configured to generate the chirp signal with the desired chirp slope and monotonicity and to send the signal via a dedicated path to the antenna 20 of the module. When in reception mode, incoming signals may be sent to a mixer coupled with the WG, wherein the WG is configured to work as a local oscillator. By mixing the signal, it is downconverted to a suitable frequency, such that it can then be processed by the ADC and the MCU, e.g. as described above.

[0026] There are several ways how to design and further develop the teaching of the present invention in an advantageous way. To this end, it is to be referred to the dependent claims on the one hand and to the following explanation of preferred embodiments of the invention by way of example, illustrated by the figure on the other hand. In connection with the explanation of the preferred embodiments of the invention by the aid of the figure, generally preferred embodiments and further developments of the teaching will be explained. In the drawing

[0027] Fig. 1 is a diagram showing an example of a chirp signal (a), and representations of the frequency linear increments of the TX and RX signal and the offset caused by the doppler effect (b),

[0028] Fig. 2 is a diagram showing an example of a downchirp signal (a), and representations of the frequency linear increments of the TX and RX signal and the offset caused by the doppler effect (b),

[0029] Fig. 3 is a diagram showing an example of example of a 16-ary transmission and its spectral / time partitioning according to an example of the proposed concept,Fig. 4 is a diagram schematically illustrating an example of a typical application scenario of the proposed concept,

[0030] Fig. 5 is a diagram schematically illustrating an ideal ISAC equipment at a target according to an example of the proposed concept,

[0031] Fig. 6 is a diagram schematically illustrating an ideal system that implements bidirectional communication according to an example of the proposed concept,

[0032] Fig. 7 is a diagram schematically illustrating an ISAC RX with a log detector according to an example of the proposed concept,

[0033] Fig. 8 is a diagram schematically illustrating a self mixing approach according to an example of the proposed concept,

[0034] Fig. 9 is a diagram schematically illustrating a phase / power relation approach according to an example of the proposed concept,

[0035] Fig. 10 is a diagram schematically illustrating a step recovery diode approach according to an example of the proposed concept, and

[0036] Fig. 11 is a diagram schematically illustrating a bidirectional ISAC approach according to an example of the proposed concept.

[0037] The following description, along with the accompanying drawings, wherein like reference numerals refer to like or at least substantially similar parts throughout the various examples unless the context indicates otherwise, sets forth certain specific details in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that the disclosed embodiments may be practiced in various combinations, without one or more of these specific details, or with other methods, components, devices, etc. In some examples, well-known structures or components that are associated with the environment of thepresent disclosure, including but not limited to interfaces, physical component layout, etc., have not been shown or described in order to avoid unnecessarily obscuring descriptions of the embodiments. Additionally, the various embodiments may be methods, systems, or devices.

[0038] Generally, the present disclosure proposes a user-side compact and low-power hardware architecture for realizing simultaneous target localization, tracking, and bidirectional communication, via multi-symbol modulation based on frequency continuous waveforms aligned with the concept of Integrated Sensing and Communication (ISAC) framework. In various examples, the present disclosure provides hardware architectures for compact, low-power user devices designed to accurately demodulate the modulated radar signals. Such architectures enable multisymbol transmissions, thus increasing the achievable bitrate while minimizing the impact on sensing performances. Furthermore, the present disclosure proposes a bidirectional hardware architecture enabling communication between the radar and a target, thereby significantly advancing ISAC capabilities.

[0039] In a concrete example, According to the proposed concept, a method is provided for embedding information on radar waveforms, which are used for localization, thereby realizing ISAC with only equipment at the radar itself. In an example, the method may comprise the steps of

[0040] 1) Generation of a M-ary modulation scheme based on FMCW radar chirp signals, where M is chosen as the highest value that can be currently supported by the communication channel.

[0041] 2) Equip the RX devices with components to enable the reception and the decoding of the slope of chirped signal without disrupting the radar localization process.

[0042] 3) (optional) Equip the RX to be able to respond to the TX and realize bidirectional ISAC.

[0043] Frequency Modulated Continuous Wave (FMCW) is a radar technology that, unlike traditional radar systems, exploits a continuous signal whose frequency changes linearly over time, creating a distinctive sweeping pattern known as a chirp.The chirp signal is mathematically represented as a linear frequency modulation where the instantaneous frequency to(t) varies proportionally with time according to the function: to(t) = 2nf0+ kt, where f0represents the initial carrier frequency (with wavelength denoted by 20). defines the chirp rate (frequency slope), and t is the temporal variable. A simple example of a chirp is given in Fig. 1a. The chirp rate is defined as

[0044] > >

[0045]

[0046] with fstopdenoting the transmission frequency at the end of the slope, fstartdenoting the transmission frequency at the beginning of the slope, and T as the chirp duration.

[0047] When this coherent electromagnetic wave as shown in Fig. 1a is transmitted and subsequently reflected from a target, the received signal undergoes a time delay T, which is proportional to the target’s radial distance from the transmitter, whereas, if the target and / or the transmitter are moving, the relative velocity causes a doppler frequency shift (i.e., Doppler effect). The difference in frequency between the transmitted and received signals (briefly referred to as TX and RX, respectively) produces the beat frequency fbthat is directly related to the target’s range through the relationship: fb= (2R / c)k, where R represents the target’s range and c is the speed of electromagnetic propagation, while the doppler shift introduces an additional change on the beat frequency fd= 2v / 2. This is illustrated in Fig. 1b.

[0048] The spectral analysis of the beat frequency at the radar-side (i.e., the transmitter) enables simultaneous range and Doppler velocity estimation through advanced signal processing techniques. The chirp design translates into the achievable resolution in range and velocity. In particular, the resolution in range is proportional to the chirp bandwidth, i.e., AR = with c being the speed of light. A larger bandwidth results in

[0049]

[0050] a higher range resolution allowing for better discrimination between closely spaced objects. Instead, the resolution in speed is given by Av =

[0051]

[0052] (in the case of speed

[0053]

[0054]

[0055] measurements over Ncchirp repetitions, it becomes Av = but this case will not

[0056]

[0057] cT

[0058] be considered for simplicity). The maximum unambiguous range is — and the

[0059]

[0060] maximum unambiguous velocity Sensing properties of upchirp and downchirp radars are similar.

[0061] While the sensing capabilities of this method are well-regarded, in its conventional form, it is not possible to exploit it for realizing communication functions. To address this issue, according to the concept proposed herein, a method and a system are provided to convey information exploiting the spectral analysis at the target side (i.e. , the RX). In an example of the proposed scheme, the direction of the line representing the signal in the time-frequency diagram (e.g., Fig. 1b), will determine if the signal delivers a “1” or a “0”. For example, in Fig. 1, an upchirp is transmitted, that is, the increment in frequency over time will correspond to a “1”. On the other hand, a downchirp, shown in Fig. 2, which represents a signal with a decrement in frequency over time, corresponds to a “0”. Moreover, upchirp and downchirp present similar characteristics in terms of sensing performance.

[0062] While this solution can already transmit a simple message to a target equipped with the right RF components, which are discussed later, this modulation can clearly achieve only a moderate bitrate, given that it is comparable to an “ON / OFF keying” modulation. However, it is noted that this solution is more resilient to errors than the one proposed in Okubo, Ryu, et al. "Integrated two-way radar backscatter communication and sensing with low-power loT tags." Proceedings of the ACM SIGCOMM 2024 Conference. 202, as it presents an easier and clearer way to discriminate among ‘0’s and ‘1’s and it makes the proposed approach more robust in harsh environments. However, when operating in good conditions, even high bit rates can be achieved.

[0063] Assuming that a radar device consists of one or multiple high directivity antennas and that it can emit a significant amount of power, it is reasonable to assume that the target will receive this chirped signal with a good Signal to Noise Ratio (SNR). Therefore, the spectral / time space can be divided to create a number of M independent regions corresponding to M different data symbols (denoted as M-ary transmission herein). In an example, the present disclosure proposes to combine an up- and down-chirp selection scheme with a modulation based on the chirp rate (frequency slope) k.After a spectral analysis of an M-ary transmission at the RX-side, depending on where the decoded signal falls in the rate-monotonicity diagram, a symbol is decoded. This M-ary transmission can potentially achieve high bitrates while guaranteeing simultaneous sensing and tracking of the target from the radar. An illustrative example is given in Fig. 3 for M = 16.

[0064] The left-hand side of Fig. 3 shows two examples of possible modulated chirp signals for the scenario with M = 16 (i.e., 16 different symbols can be sent), while the righthand side of Fig. 3 represents how these different symbols could be decoded at the receiver. Accordingly, decoding could take place with 16 different decoding regions. The decoding regions are divided into two hemispheres, the upper one for Upchirps (positive monotonicity) and the bottom one for Downchirps (negative monotonicity). Both hemispheres can be split into 8 parts, which means that one can choose 8 different steepness levels for the signals, from 1 to 8 (referred to as the chip rate k). This creates the decoding regions, each one labeled with a symbol, from 1 to 16. Each decoding region corresponds to a unique signal with a defined chip rate k, i.e. there is a one-to-one relation that is predefined and known by both parties (sender and receiver).

[0065] In the first exemplary case illustrated in Fig. 3, represented by a line with circular markers, the chirp rate is equal to 1 , and the curve has a positive slope (Upchirp). Therefore, at the receiver (right-hand side of Fig. 3), this case is shown as a point in the upper hemisphere (i.e., positive slope) and inside the decoding region corresponding to the chirp rate of 1. Similarly, for the second example, which is represented by a line with triangular markers on the left-hand side of Fig. 3, this ends up in bin number 8 at the receiver side, since the respective signal is a Downchirp with rate equal to 5 (right-hand side of Fig. 3).

[0066] In an example, the value of M, i.e., the modulation order, may be determined depending on the instantaneous channel conditions. Indeed, high SNR scenarios may effectively support higher modulation orders and therefore higher bitrates, as is the case in conventional wireless communication scenarios. In this regard, an initial handshake / negotiation procedure between the TX and the RX is envisioned, which would agree on the order M of the modulation scheme, depending on the perceivedchannel quality, which can be measured, e.g., via SNR, Signal Strength Indicator (SSI), Channel Quality Indicator (CQI), etc.

[0067] Indeed, in practice, the SNR affects the ability of retrieving the slope of the chirp at the receiver (as explained in Serbes, A. (2018). A method for estimating chirp rate of a linear frequency modulated Signal. Balkan Journal of Electrical and Computer Engineering, 6(1), 9-12). While an accurate mapping would require the knowledge of the specific hardware implementation and estimation algorithm implemented to retrieve the chirp slope information at the receiver, it is possible to determine the theoretical limit by considering the Cramer-Rao bound (CRB) of the chirp slope 90 1 estimation, which, as per the above-referenced document, CRB = — , where

[0068]

[0069] N is the number of samples taken in during the chirp duration T, and Ts= l / fsis the sampling period. The resolution between two adjacent slopes is linked to the CRB as 6 = 2^ CRB [6] (as explained in Lee, H. B. (1992). The Cramer-Rao bound on frequency estimates of signals closely spaced in frequency. IEEE Transactions on Signal Processing, 40(6), 1507-1517), where an additional margin could be taken to reduce errors. 6 is then imposing a theoretical limit on the maximum order of modulation ^depending on the SNR. The higher the SNR, the higher is the possible modulation scheme order M.

[0070] Nonetheless, when designing the M-ary transmission scheme some considerations on their effect on the accuracy should be made: As described earlier, the velocity resolution and the maximum ambiguous velocity depend on the chirp duration T. In the present proposal, T is kept constant per each chirp transmission, hence not affecting those performance metrics. However, the absolute chirp rate |fc| influences the bandwidth of the chirp, which is constrained by the desired system performance and maximum allowed transmission bandwidth. This translates into the following design considerations. Considering a system with a maximum bandwidth Bmax> \k\T, and a minimum desired resolution Rmin< — 2kT, the value of k must satisfy < <

[0071]

[0072] To provide a practical example, the settings of a typical medium range radar are considered (e.g., a radar as described in Dham, V. (2017). Programming chirp parameters in Tl radar devices. Application Report SWRA553, Texas Instruments, 1457), with a 540 MHz bandwidth, 45 ps of chirp duration and N = 500 samples per chirp, which corresponds to a sampling period of Ts= 90 ns, and a frame duration of Tf= 7.04 ms. Moreover, the example settings consider a maximum variation of the chirp slope k of 0.1% from its maximum value (i.e., from the formulas above, the proposed approach sacrifices at most the 0.1% of the chirp bandwidth for implementing the proposed M-airy communication, or, in other words, it sacrifices a 0.1% of the range resolution). The example settings further consider an SNR at the receiver of OdB, and an allowed 3 with a margin of 10 times the statistical resolution, hence 6 = 20^CRBk— 422 Hz I ps.

[0073] With these settings, the maximum value of M is M = 10. The theoretically achievable

[0074]

[0075] data-rate with this setting is - - 73 kbps. It is noted that this is the theoretical limit,

[0076] Tr

[0077] however, practical performance might depend on the implementation itself, leading to a lower data rate. Nonetheless, the theoretical performance gives an idea of the huge potential of the proposed concept.

[0078] A typical use case for the proposed scheme, which is schematically illustrated in Fig. 4, is a radar 10 scanning an area for targets 12 and then exchanging information from a control tower or a vehicle (ship, airplane, etc.) where the radar 10 is mounted with the targets 12. A necessary condition for this to happen is that the target 12 is equipped with a basic ISAC module 14 that permits the successful decoding of the transmitted signal. In other words, an ISAC enabled RX of the target 12 is able to receive information decoded in the transmitted signal. The normal functioning of the radar 10 is not disrupted by this because the structure or the body of the target 12 will still scatter a prominent portion of the incident signal.

[0079] The proposed technique can be employed in several scenarios. For instance, in vehicle-to-vehicle communication, by embedding data within the radar signal, vehicles can exchange critical information such as braking intentions, road conditions, and hazard alerts without requiring additional communication hardware. Thisenhances traffic safety and coordination, particularly in low-visibility environments. In air traffic control and maritime navigation, communication between control towers and aircraft or ships traditionally depends on voice transmission. Embedding digital instructions within radar signals allows controllers to send clearance messages, weather warnings, and navigation updates directly, reducing reliance on voice channels. This not only optimizes communication efficiency but also frees up radio bandwidth for emergency situations, lowering the risk of miscommunication while saving valuable operational resources. For military and tactical applications, the proposed method enables military radars to transmit encrypted commands, target designations, or coordination signals without additional radio emissions. This allows aircraft, ships, and ground units to exchange vital information while minimizing exposure to electronic warfare threats such as signal jamming or interception.

[0080] An example of the design of the ISAC equipment 14 for reception is schematically illustrated in Fig. 5. As shown, the ISAC reception module comprises an antenna 20 configured to capture a chirped signal. The received signal is down converted in frequency by a downconverting module 22, meaning that it is scaled down in frequency such that an Analog Digital Converter (ADC) 24 can digitalize it and pass it to a Micro Controller Unit (MCU) 26. The downconverting operation, which is required since the ADC 24 cannot sample at the high frequencies that a radar usually employs (e.g., millimeter-wave (mmWave)), includes two components: a Local Oscillator (LO) that generates a signal of compatible frequency and a mixer to shift down the frequency to a suitable one for the ADC 24. The output of the mixers fo is composed of a sum and a difference: f0= fRF± fL0, where fRFis the input signal frequency and fi_o is the LO frequency; what interests here is the difference of the output, while the sum can be ignored and filtered out. The MCU 26 then implements an algorithm for spectral analysis, e.g. the short-time Fourier transform (STFT), to obtain a spectrogram. Based on an analysis of the spectrogram, the MCU 26 can determine the distance of the target 12 to the radar 10 and, if the radar 10 is moving, the Doppler velocity (denoted Vd in Fig. 5) and finally the data symbol(s) of the M-ary communication(denoted m in Fig. 5).

[0081] Furthermore, in an ideal implementation, the target 12 should implement also a system where a chirp signal is generated and then upconverted (if necessary) to allow a response of the target’s 12 RX to the radar 10. A schematic representation of ageneric bidirectional ISAC module 16 according to an example of the proposed concept is shown in Fig. 6. As shown, the module 16 includes a first switch 28 for switching between transmission and reception mode. When in reception mode, the chirped signal received via antenna 20 is processed in the same way as described above in connection with Fig. 5, i.e. by downconverting module 22, ADC 24 and MCU 26. On the other hand, when in transmission mode, a signal generated by a waveform generator 30 is directed to the antenna 20. For example, waveform generator 30 may be a digital waveform generator, where the desired signal is defined mathematically or as a series of discrete points, and a digital to analog converter may be employed to convert digital values to an analog signal with typical analog voltage values. Alternatively, an analog waveform generator may be used, where the desired signal is generated through analog circuits specifically designed for the respective scope. However, it should be noted that modem radar systems use sophisticated digital techniques and software tools to generate customizable waveforms. The generated signal may be directed to antenna 20 either directly or via an upconverting module 23, wherein the respective path is selectable by a second switch 32. The switch 32 is used to isolate the TX and the RX parts. This strategy allows to reuse the same hardware to enable transmission and reception while avoiding interference from other paths. The upconverting module 23 can be a separated module, or downconverting module 22 and upconverting module 23 can be integrated into a single device, as shown in Fig. 6.

[0082] In various examples, different approaches are proposed herein to circumvent the limitation of a traditional downconverter, for the reception only case and a case for the bidirectional case.

[0083] According to a first approach, which is schematically depicted in Fig. 7, a workaround for the down converting step is envisioned, which is implemented by an RF Log Detector (Radio Frequency Logarithmic Detector) 34, which is a type of signal detector that converts an RF signal into a DC voltage. More specifically, the RF Log Detector 34 measures the power level of the chirped RF signal received via antenna 22 and outputs a DC representation whose amplitude is inversely proportional to the logarithm of the input power. For example, the RF Log Detector 34 IC (Integrated Circuit) could be an AD8318, which is an analog device operating in a 1 MHz to 8 GHz, 60 dB dynamic range. The device has the advantage of being inexpensiveand consuming only little energy (circa 350mW when at use or 1 ,5mW when in sleep mode). The ADC 24 receives the output of the Log Detector 34 and samples it.

[0084] Although Log Detectors are compact, rather economical, and not power-consuming, the above solution is better suited for frequency ranges up to 2-3 GHz. An alternative, more flexible approach, which overcomes these limitations with regard to the operating frequency range, is schematically illustrated in Fig. 8. The approach involves an RF splitter 36 that divides the received signal into copies with halved power each, which are then sent into a mixer 38. By self-mixing the signal, the original signal can be downconverted to a frequency close to DC and, therefore, the ADC 24 can easily process it.

[0085] The system depicted in Fig. 8 is well suited for a wide range of frequencies, including mmWave. The system can be realized with the inclusion of passive components: for the RF split, an RF switch Single Put Double Through, such as SKY13348-374 LF for low frequency and MASW-011152-TR0500 for mmWave, and for the mixing part, components such as MAX2671 EUT+T for sub 6GHz and MAMX-011066-TR0100 for mmwave. All the mentioned components are passive; hence, their power consumption is negligible. In addition, all components sore rather cost-effective.

[0086] In a third proposed approach, the system consists of a frequency discriminator, i.e. , an electronic circuit designed to translate frequency variations into proportional voltage changes as depicted in Fig. 9. The core concept involves splitting, by RF splitter 40, the received input signal into two parallel paths with carefully engineered characteristics. One path (in Fig. 9 the upper path) serves as a reference, maintaining the original received signal, while the other path (in Fig. 9 the lower path) introduces a deliberate time delay. This delay creates phase shifts that vary predictably with the input frequency. The voltage produced becomes a direct representation of frequency deviation. An upward frequency shift results in a proportional positive voltage change, while a downward shift generates a negative voltage. To this end, the system includes two power detectors 42a, 42b, whose outputs are handled by the ADC 24 and MCU 26.

[0087] An advantage of this approach is that the complexity burden is offloaded from the MCU 26 to the other components since the MCU 26, contrary to the approachesdescribed before, does not need to elaborate the spectral analysis of the signal. As an example, the power detectors 42a, 42b can be implemented as MADT-011000, which can operate in a wide spectrum of frequencies (including mmWave) and consumes around 0.5 mW.

[0088] In a fourth proposed approach, a Step Recovery Diode (SRD) is utilized. Unlike conventional diodes, an SRD exhibits extraordinary behavior during its switching transitions, primarily due to its exceptional charge storage and rapid discharge properties. When forward biased, an SRD accumulates charge carriers, however, as the voltage switches from forward to reverse, the diode continues conducting until every single stored charge carrier is completely depleted. This discharge occurs with an abruptly sharp transition that happens in picoseconds, generating a rich harmonic spectrum. The sharp current discontinuity creates multiple frequency components above and below the input signal’s fundamental frequency. These harmonics can be selectively filtered and utilized for frequency multiplication.

[0089] According to this approach, which is schematically illustrated depicted in Fig. 10, the SRD 44 is adopted as a frequency multiplier for a waveform generator (WG) 30 that creates a pure sine wave, used as a local oscillator. Off-the-shelf WGs, such as ADF4159, can generate sine waves of a few GHz that would be sufficient for sub6GHz operations, but thanks to an SRD, the WG can be employed for mmWave operation, and it should be able to reach the terahertz spectrum (such as Macoom MMD837-C11 ). The output of the SRD 44 must pass through a filter, such as a classic LC filter 46 (which is an electronic filter composed of inductors (L) and capacitors (C) that are used to pass or block specific frequency ranges in a circuit), to supply undesired replicas. Accordingly, SRD 44 and LC filter 46 operate together to constitute the mmWave block 50 shown in Fig. 10. Finally, the upconverted signal is mixed with the received signal by mixer 38 and passed to the ADC 24. This solution is rather economical given the frequency it can support, as both SRD 44 and WG 30 are inexpensive components. The drawbacks are that the SRD 44 requires a proper reverse bias circuit (6-10 V) and it may introduce signal distortion.

[0090] Finally, a method is described for a Bidirectional ISAC module, which is conceptually, illustrated in Fig. 11. The module includes a first switch 28 for switching between transmission and reception mode. For transmissions, the module is equipped with aWave Generator 30, such as ADF4159, capable of creating chirp signals, which are compatible with the ones generated by the Radar. When the ISAC module is used to communicate, it generates the chirp with the desired chirp slope and monotonicity and sends it to the antenna 20 via a dedicated path. When the module is used in the RX mode, the incoming signal is sent to the mixer 38 and the WG 30 works as a local oscillator. Basically, the RX signal is mixed with a reference signal, downconverting it to a suitable frequency for the ADC 24. The reference signal used as input into the mixer 38 to downconvert the received signal to a frequency more suitable for the ADC 24 can be any signal, for example a sine wave with f close to the operating frequency.

[0091] The described method would work well for sub6GHz operations. However, according to an embodiment, it may be provided that a mmWave block like the mmWave block 48 included in the module of Fig. 10 is inserted in between the WG and the Switch, it would be possible to operate also at mmWave.

[0092] In summary, at least one of the examples of the present disclosure has at least one of the following features and / or at least one of the following advantages:

[0093] - The proposed hardware architectures for ISAC are meant for different use cases which depend on the target characteristics: e.g., on devices equipped with low-computational power, the spectral analysis can be offloaded to the hardware; on devices designed to operate efficiently within limited power constraints (often incorporating internal energy storage) more low-power solutions can be implemented.

[0094] - Flexibility in the choice of the operating frequency: the different examples disclosed herein detail schemes that are applicable to different frequency bands.

[0095] - Dynamic modulation scheme, whose order can be directly adjusted to match the current channel propagation conditions. In this way, one achieves reliability in harsh environments and high bitrates when the conditions are good.

[0096] When certain aspects are mentioned in relation to a device or system, they should also be considered as descriptions of the corresponding methods. For example, a block, component, or functional aspect of the device or system may correspond to a method step or feature of the related method. Therefore, aspects described regardinga method should also be understood as depicting a corresponding element, property, or functional feature of the corresponding device or system. In simpler terms, if something is described in relation to a device or system, it can also be applied to the corresponding method, and vice versa.

[0097] Many modifications and other embodiments of the invention set forth herein will come to mind to the one skilled in the art to which the invention pertains having the benefit of the teachings presented in the foregoing description and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.L i s t o f r e f e r e n c e s i g n s

[0098] 10 radar

[0099] 12 target

[0100] 14 ISAC reception module

[0101] 16 bidirectional ISAC module

[0102] 20 antenna

[0103] 22 downconverting module

[0104] 23 upconverting module

[0105] 24 Analog Digital Converter, ADC

[0106] 26 Micro Controller Unit, MCU

[0107] 28 first switch

[0108] 30 waveform generator

[0109] 32 second switch

[0110] 34 RF log detector

[0111] 36 RF splitter

[0112] 38 mixer

[0113] 40 RF splitter

[0114] a, 42b power detector

[0115] 44 Step Recovery Diode, SRD

[0116] 46 LC filter

[0117] 48 mm Wave block

Claims

C l a i m s1. A method for operating an integrated sensing and communication, ISAC, system, the method comprising:using the radar hardware equipment of the ISAC system for radar signal transmissions with frequency modulated continuous waveforms, FMCW; and encoding communication data symbols into the radar signals.

2. The method according to claim 1 , wherein the radar signals used for encoding communication data symbols include both up and down-chirps with variable steepness.

3. The method according to claim 2, wherein the modulation order of the communication data symbols encoding is defined by the total number of distinct chirp slope steepness.

4. The method according to claim 3, further comprising:adjusting the modulation order based on the quality level of the communication channel.

5. The method according to any of claims 1 to 4, wherein the encoding of communication data symbols into the radar signals comprises:generating a M-ary modulation scheme based on FMCW radar chirp signals, where M is chosen as the highest value that can be currently supported by the communication channel.

6. An integrated sensing and communication, ISAC, system, comprising a radar hardware equipment configuredto generate radar signal transmissions based on frequency modulated continuous waveforms, FMCW; andto encode communication data symbols into the radar signals.

7. The system according to claim 6, wherein the radar hardware equipment is configured to generate the radar signals used for encoding communication data symbols to include both up and down-chirps with variable steepness.

8. The system according to claim 6 or 7, further comprising measuring components configured to determine the quality level of the communication channel and adaptation means for adjusting a modulation order based on the determined quality level of the communication channel.

9. The system according to any of claims 6 to 8, wherein the radar hardware equipment is configured to perform the encoding of communication data symbols into the radar signals by generating a M-ary modulation scheme based on FMCW radar chirp signals, where M is chosen as the highest value that can be currently supported by the communication channel.

10. The system according to any of claims 6 to 9, further comprising at least on RX device (14) configured to enable the reception and the decoding of the slope of a received chirped signal without disrupting the radar localization process, wherein the RX device (14) comprises an antenna (20) configured to capture a chirped signal, one or more signal processing components configured to downconvert the frequency of the captured signal, an analog-to-digital converter (24), ADC, configured to digitize the signal and a micro controller unit (26), MCU, configured to create a spectrogram of the received signal.

11. The system according to claim 10, wherein the one or more signal processing components of the RX device (14) include an envelope detector, preferably a RF Log Detector (34), configured to output a DC representation whose amplitude is inversely proportional to the power of the received chirp signal.

12. The system according to claim 10 or 11, wherein the one or more signal processing components of the RX device (14) include a mixer (38) configured to selfmix a received radar signal for down converting the radar signal.

13. The system according to any of claims 10 to 12, wherein the one or more signal processing components of the RX device (14) include an RF splitter (36) and at leasttwo power detectors (42a, 42b) configured to estimate the radar signal’s slope monotonicity.

14. The system according to any of claims 10 to 13, wherein the one or more signal processing components of the RX device (14) include at least one diode, in particular a step recovery diode (44), SRD, configured to create a mixable and down convertible signal.

15. The system according to any of claims 10 to 14, wherein the RX device (16) further includes a wave generator (30) capable of generating a chirp signal for bidirectional communications.

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