A method for integrated sensing and communication frame in full duplex mode

Abstract

The present invention relates to a method, system, and computer program product for generating an Integrated Sensing and Communication (ISAC) frame operating in full duplex mode.

Description

[0001] DESCRIPTION

[0002] A METHOD FOR INTEGRATED SENSING AND COMMUNICATION FRAME IN FULL DUPLEX MODE

[0003] Technical Field

[0004] The present invention relates to a method, system, and computer program product for generating an Integrated Sensing and Communication (ISAC) frame operating in full duplex mode.

[0005] Prior Art

[0006] In designing waveforms for next generation wireless networks, a crucial aspect to consider is the seamless integration of both communication and sensing capabilities. A key challenge is how to minimize the interference between the two signals without affecting the performance of both functions. A separate transmission of the signal in different bands to avoid interference is not feasible as spectrum is becoming dense and there is no room for using frequency division duplexing to separate the signals, so sensing and communication signals interference is unavoidable. In designing such systems, using different chains also for sensing and communication is not also feasible as it increases the system complexity.

[0007] To address the problem of minimizing the interference between sensing signal and communication signals, several works in the literature addressed the issue of communication and sensing signal coexistence. In [1], a method for coexisting the orthogonal frequency division waveform (OFDM) with the FMCW waveform, by leveraging a repetitive chirp signal in time as sensing signal that can have a predicted pattern in frequency domain which can allow for orthogonal multiplexing of data and sensing signal. The others in [2], used a non-orthogonal transmission with power advantage for the sensing chirp signal over the communication OFDM signal and used the estimated channel using the sensing signal to reconstruct the data at the receiver. In [3] a chirped DFT-s-OFDM is proposed where a DFT spreading mechanism is used to modify the time frequency representation of the subcarrier such that when multiplied by a digital chirp samples different chirps with different rates appear on the OFDM symbol. Moreover, a full duplex joint radar-communication receiver is proposed in [4], where the frequency hopping based receivers are used to ensure minimum interference from backscattered signals along with di-chirping estimated parameters. For the work in [5], a full duplex waveform where a signal node sends a sensing signal and receives the objects echoes along with communication signal transmission, by dedicating a pulse radar signal with high correlation properties which opens a room for more spectral efficiency for communication signal. Finally, in [6] an ISAC system based on affine division multiplexing waveform is proposed where the same signal that is transmitted by the BS for communication is received back by the base station from the objects echoes, this reflected signal to the BS is low pass filtered only the to the frequency band of the signal pilot which allows a sub-Nyquist radar information extraction.

[0008] The proposed solutions in the literature suffer from different drawbacks, the use of a mixed chirp and OFDM signals for ISAC scenarios creates a severe interference on communication signal due to leakage of the chirp signals and if we multiplex them orthogonal chirp correlation properties will be degraded as it loses some of its frequency processing gain. For the full duplex between the sensing signal using pulse radar and communication signal requires a complex successive interference cancellation to separate the echoes of the sensing signal from the transmitted communication signals. Finally, using a multi-carrier chirp waveform like AFDM for both sensing and communication hinders sensing performance as high-power transmission will be limited due to peak to average power ratio which makes the reflecting echoes not detectable by the receiver.

[0009] As a result, all of the problem mentioned above has made it necessary to provide a novelty in the related field.

[0010] Brief Description and Objects of the Invention

[0011] The main object of the present invention is to establish a method for minimizing the interference between the two signals without affecting the performance of both functions in the integrated sensing and communication.

[0012] To achieve above-mentioned advantages, the present method leverages innovative waveform design and processing techniques to enable simultaneous sensing and communication functionalities while addressing interference challenges inherent in full duplex operations.

[0013] The method of the present invention involves designing an ISAC frame using Time Division Duplex (TDD) mode. A sensing signal, which is preferably generated with a high-power generalized multi-carrier chirp waveform, is transmitted during predefined periods, and a communication signal, employing an Orthogonal Frequency Division Multiplexing (OFDM) waveform, is multiplexed between consecutive sensing signals. This enables the simultaneous transmission and reception of sensing and communication signals in full duplex mode.

[0014] To resolve the interference challenges, the method incorporates waveform domain separability to distinguish received sensing echoes from self-interference caused by the communication signal. Furthermore, the selected carriers for the sensing signal can be configured to support low-data-rate transmissions for Internet of Things (loT) devices.

[0015] In another aspect, the invention includes detecting sensing echoes by correlating the received time-domain signal with the transmitted sensing signal. The correlated signal is transformed into the chirp domain using a generalized multi-carrier chirp transform, where noise and interference are filtered. Filtering includes canceling the chirp domain representation of the communication signal, substantially isolating the sensing signal while leaving only additive white Gaussian noise (AWGN) and channel effects.

[0016] Additional processing steps include transforming the filtered sensing signal from the chirp domain back to the time domain to extract sensing information. The time-domain sensing signal may then be reshaped into a square matrix, pre-coded using a Discrete Fourier Transform (DFT) matrix, and transformed into a Zak domain representation. The method also supports zeropadding of the reshaped matrix, which achieves sparsity in the Zak domain and enhances sensing target resolution proportionate to the zero-padding factor. Sensing parameters are estimated based on these resolved sensing targets.

[0017] The sensing signal waveform may comprise an Affine Frequency Division Multiplexing (AFDM) waveform as the generalized multi-carrier chirp waveform, providing further flexibility and efficiency in ISAC operations.

[0018] The invention extends to a processor device configured to execute the described method, a computer program comprising instructions for implementing the method, and a computer- readable data carrier storing the program. These embodiments ensure broad applicability and ease of deployment in various ISAC systems.

[0019] Description of the Figures of the Invention

[0020] The figures and related descriptions necessary for the subject matter of the invention to be understood better are given below.

[0021] Figure 1. A schematic view of the ISAC frame. Figure 2. A schematic self-interference representation in full duplex mode

[0022] Figure 3. Graph of sensing and communication signal representation in chirp domain.

[0023] Figure 4. Filtered signal reshaping and zero padding in time domain.

[0024] Figure 5. Flowchart of sensing parameters extraction process.

[0025] Figure 6. Graph of received sensing signal after zero padding and pre-coding with DFT matrix

[0026] Detailed Description of the Invention

[0027] This invention relates to the field of wireless communication and sensing systems and proposes an Integrated Sensing and Communication (ISAC) system that achieves high-resolution sensing and efficient communication in full duplex mode. The invention overcomes the challenges of interference between sensing and communication signals, spectral efficiency, and system complexity.

[0028] The invention comprises the generation of an ISAC frame capable of achieving both sensing and communication capabilities in full duplex mode. This ISAC frame is designed to minimize interference between the sensing signal and the communication signal, wherein a high-power radar multi-carrier chirp waveform is used for sensing, multiplexed in TDD mode with the communication signal, and duplexed in full duplex for transmission and reception. The received sensing echoes are resolved from the communication self-interference using waveform domain separability, and the estimated sensing parameters are tuned using a zero-padding technique of the received time domain signal.

[0029] The present invention relates to an integrated sensing and communication (ISAC) system, designed to enable simultaneous sensing and communication in a full duplex mode. This invention addresses the challenges of interference management and spectrum efficiency by employing a novel frame design and advanced signal processing techniques.

[0030] The invention involves designing an ISAC frame that operates in time division duplex (TDD) mode. A frame design using TDD is proposed where a sense signal is transmitted for a certain period of time and the communication signal is multiplexed between two successive sense signals as shown in Figure 1. In this frame, sensing and communication signals are multiplexed over time. Specifically, the sensing signal is transmitted during defined intervals, while the communication signal occupies the intermediate time slots. This structure minimizes mutual interference between the two signals. For sensing, a high-power generalized multi-carrier chirp waveform, such as affine frequency division multiplexing (AFDM), is utilized. This waveform is generated by selecting specific carriers from the available spectrum, which also serve a secondary purpose of supporting low-data-rate communication for loT applications. For communication, standard orthogonal frequency division multiplexing (OFDM) is employed, ensuring compatibility with existing systems. To mitigate interference between base stations, each base station is configured to use unique chirp carrier pairs, ensuring orthogonality of their respective sensing signals.

[0031] To be clearer, the parameters are in Fig. 1 are explained. Trrefers AFDM sensing signal duration, Tcrefers OFDM communication signal duration, Tgrefers Guard between AFDM and OFDM consecutive signals, Tp refers Complete duration of frame of AFDM and OFDM, ci and C2 are AFDM design parameters which designed based on maximum Doppler spread and Channel diversity, respectively. Furthermore, Xciand XC2 are AFDM rotational matrices in time and frequency respectively and SIC is successive interference cancelation and F represents the FFT transform.

[0032] Referring to Fig. 2; The system operates in full duplex mode, where both transmission and reception occur simultaneously. While this enables efficient operation, the received sensing echoes are contaminated by self-interference from the transmitted communication signal. To address this, the invention employs a multi-step signal processing approach.

[0033] Referring to Fig.3; Upon reception, the incoming signal is correlated with the transmitted sensing signal to detect the arrival of echoes. The correlated signal is then transformed into the chirp domain using a generalized multi-carrier chirp transform, which enhances noise suppression and isolates the desired components. As the transmitted communication signal is known at the base station, its chirp domain representation is generated and subtracted from the received signal. This step effectively cancels the self-interference, leaving the sensing signal clean, except for residual noise and channel effects as can be seen in Fig. 4.

[0034] The filtered sensing signal is subsequently processed to extract critical information. It is first transformed back into the time domain. To prepare for high-resolution sensing, the signal is reshaped into a square matrix form. This matrix is then zero-padded to a size of k N, where k represents the zero-padding factor and N is the matrix column length as illustrated in Fig. 5. Zero-padding creates a sparse representation of the chirp carriers in the Zak domain, which significantly enhances the resolution of the sensing process.

[0035] Referring to Fig. 6; A discrete Fourier transform (DFT) matrix is applied to the zero-padded matrix, followed by a transformation into the Zak domain. This transformation reveals a sparse representation, enabling precise detection and localization of sensing targets. The resolution achieved is directly proportional to the zero-padding factor, making it adaptable to various precision requirements.

[0036] The proposed ISAC system integrates three primary components: a transmitter, a receiver, and a processing unit. The transmitter generates both sensing and communication signals, ensuring that the sensing signal carriers are orthogonal across base stations to avoid inter-BS interference. The receiver is designed to simultaneously capture sensing echoes and communication signals, performing critical tasks such as correlation, chirp domain transformation, and interference cancellation. The processing unit carries out advanced signal processing, including time-domain transformation, reshaping, zero-padding, DFT pre-coding, and Zak domain transformation, while also handling self-interference mitigation.

[0037] This invention offers several advantages. It effectively separates sensing and communication signals, even in full duplex mode, through advanced interference mitigation techniques. Spectrum utilization is significantly improved by leveraging sensing carriers for low-data-rate communication. High-resolution sensing is achieved through the use of sparse Zak domain representations, enabling precise target detection and localization. The system is compatible with standard OFDM communication and supports diverse applications, including loT, radar sensing, and environmental monitoring.

[0038] References:

[0039] [1]: Boddapati, H. K., Kumar, K., Chavva, A. K. R., & Khan, M. S. (2023, October). Joint Communication and Sensing for MIMO Systems with Overlapped OFDM and FMCW. In 2023 IEEE 98th Vehicular Technology Conference (VTC2023-Fall) (pp. 1-5). IEEE. [2]: §ahin, M. M., & Arslan, H. (2020, November). Multi-functional coexistence of radarsensing and communication waveforms. In 2020 IEEE 92nd Vehicular Technology Conference (VTC2020-Fall) (pp. 1-5). IEEE.

[0040] [3]: Liu, Y., Guan, Y. L., & Yanikomeroglu, H. (2024). Chirped DFT-s-OFDM: A new singlecarrierwaveform with enhanced LMMSE noise suppression. arXiv preprint arXiv:2408.06796. [4]: Ni, Z., Zhang, J. A., Wu, K., Yang, K., & Liu, R. P. (2023). Receiver Design in Full-Duplex

[0041] Joint Radar-Communication Systems. IEEE Transactions on Communications, 71(7), 4234- 4246.

[0042] [5]: Xiao, Z., & Zeng, Y. (2022). Waveform design and performance analysis for full-duplex integrated sensing and communication. IEEE Journal on Selected Areas in Communications, 40(6), 1823-1837.

[0043] [6]: Bemani, A., Ksairi, N., & Kountouris, M. (2024). Integrated sensing and communications with affine frequency division multiplexing. IEEE Wireless Communications Letters.

Claims

CLAIMS1. A method for generating an Integrated Sensing and Communication (ISAC) frame in a full duplex mode, comprising: designing a frame using Time Division Duplex (TDD) mode such that a sensing signal is transmitted during a predefined period and a communication signal is multiplexed between consecutive sensing signals; generating the sensing signal using a high-power generalized multi-carrier chirp waveform by selecting specific carriers from an available carrier set; transmitting the communication signal using an Orthogonal Frequency Division Multiplexing (OFDM) waveform; simultaneously transmitting and receiving the sensing and communication signals in full duplex mode; resolving received sensing echoes from self-interference caused by the communication signal using waveform domain separability.

2. The method according to Claim 1, wherein the selected carriers for the sensing signal are further configured to support low-data-rate transmissions for Internet of Things (loT) devices.

3. The method according to Claim 1, wherein different pairs of chirp carriers are allocated to different base stations to ensure orthogonality and avoid inter-base station interference.

4. The method according to Claim 1, further comprising detecting the arrival of sensing echoes at a receiver by: correlating a received time-domain signal with the transmitted generalized multi-carrier chirp sensing signal; transforming the correlated signal to the chirp domain using a generalized multi-carrier chirp transform; filtering out noise and interference from the correlated signal in the chirp domain.

5. The method according to Claim 4, wherein the filtering step includes canceling the chirp domain representation of the communication signal from the received signal, the communication signal being known at the base station.

6. The method according to Claim 5, wherein the cancellation of the communication signal leaves the received sensing signal substantially free of interference from the communication signal, with only additive white Gaussian noise (AW GN) and channel effects remaining.

7. The method according to Claim 1, further comprising transforming the filtered sensing signal from the chirp domain back to the time domain to extract sensing information.

8. The method according to Claim 7, further comprising: reshaping the time-domain sensing signal into a square matrix form; pre-coding the reshaped matrix using a Discrete Fourier Transform (DFT) matrix; transforming the pre-coded matrix to a Zak domain representation.

9. The method according to Claim 7, further comprising zero-padding the reshaped matrix prior to the Zak domain transformation, whereinZero-padding the reshaped matrix to a size k N, where k is a zero-padding factor, and N is the column length of the reshaped matrix;Transforming the zero-padded matrix into a Zak domain using a discrete Fourier transform (DFT), wherein the zero-padding achieves sparsity in the chirp carriers in the Zak domain;Resolving sensing targets with a resolution proportional to the zero-padding factor k andEstimating sensing parameters based on the resolved sensing targets.

10. The method according to Claim 1, wherein the sensing signal comprises an Affine Frequency Division Multiplexing (AFDM) waveform as the generalized multi-carrier chirp waveform.

11. A processor device comprising means for carrying out the steps of the method of any of preceding claims.

12. A computer program comprising instructions which, when the program is executed by the processor device of claim 11, cause the computer to carry out the method of claim 1 to 10.

13. A computer-readable data carrier having stored thereon the computer program of claim12.

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