Extremely low-complexity integrated sensing and communication via OFDM signaling and method therefore

Abstract

This invention proposes a novel approach to designing a low complexity integrated sensing and communication (ISAC) transceiver for orthogonal frequency division multiplexing (OFDM) systems. High-resolution range- velocity profiles can be achieved. In the disclosed invention a novel pilot arrangement is proposed such that sensing is done over the whole OFDM frame (not one OFDM symbol). For example, 5G NR frame includes N0FDM = 140 x n slot_sub , where where n slot_sub is the number of the slots in one subframe.

Description

[0001] EXTREMELY LOW-COMPLEXITY INTEGRATED SENSING AND COMMUNICATION VIA OFDM SIGNALING AND METHOD THEREFORE

[0002] Technical Field:

[0003] This invention relates to an extremely low-complexity integrated sensing and communication via OFDM signaling and method therefore which can be used in any wireless communication device, including low-end simple devices, in all applications requiring communication, sensing or both communication and sensing.

[0004] State of The Art:

[0005] The range resolution, denoted as Ar, in wireless communication systems is determined by the available bandwidth, B. A larger bandwidth results in a higher range resolution, as given by the equation Ar = c / 2B, where c represents the speed of light. Achieving a high range resolution typically requires the use of high-speed ADC and DAC converters at the receiver and transmitter sides, respectively, for signal construction and reconstruction in OFDM systems [1], However, these devices are expensive and consume a substantial amount of energy. This poses challenges for widespread implementation, particularly in smart cities and autonomous environments where numerous sensors are required, such as in self-driving cars [2], Integrating multiple sensors under these constraints adds to the complexity and cost of the system. To overcome this, it is crucial to develop a solution that enables high resolution using low-cost, low-power sensors with low ADC sampling rates and reduced computational complexity. This would facilitate the realization of cutting-edge capabilities in the context of 6G networks.

[0006] On the other hand, the velocity resolution, denoted as Av, is inversely proportional to the available time duration of the signal, T. A larger time duration yields a higher velocity resolution, as indicated by the equation Av = c / (2fcT), where fc represents the carrier frequency. To extract Doppler information accurately, very long signals need to be acquired and processed at the receiver side. However, in wireless communication systems, it is challenging to fulfill the requirement of very long duration signals due to constraints related to latency and channel non-stationarity. Wireless communication typically operates within short time durations to meet these constraints. Therefore, achieving high velocity resolution becomes a significant challenge in such systems.

[0007] The studies in [3]-[6] explore low sampling rate techniques for OFDM radar while retaining the HRR sensing performance. In [3] symbols were divided into Msub subsymbols, with each sub-symbol being transmitted using a particular carrier frequency until the entire bandwidth was fully covered. This way a high range resolution is achieved with lower sampling rates at both DAC and ADC, at the expense of a lower maximal unambiguous velocity (vmax) and a fast-settling time of the phase locked loop (PLL) for synchronization, in addition to reduced data rate due to carrier-stepping. Similarly, [4] incorporates random non-equidistant frequency hopping pattern using narrowband OFDM to preserve the maximum ambiguities with low sampling rate utilizing compressed sensing (CS). Nevertheless, CS algorithms adds more computational complexity to the radar system. The work described in [5] uses a frequency comb composed of L carrier frequencies at both ends to upconvert (transmitter) and down convert (receiver) the signal, generating (L) sub bands identical OFDM signals that span the desired RF bandwidth. However, it elevates RF hardware complexity significantly for the sub-bands generation and power consumption, along with strict synchronization requirements. Another technique is proposed in [6], referred to as subcarrier aliasing OFDM (SA-OFDM), which leaves empty subcarriers between data subcarriers in each symbol, ensuring that when under-sampling a factor related to the empty subcarriers, the aliased subcarriers will slip into those empty subcarriers. Consequently, a low ADC sampling rate relative to p is achieved, at the expense of downgraded maximum unambiguous range and low data rate. Furthermore, there are other techniques [7], [8] for reducing the OFDM sampling rate, however they are related to the ones mentioned above and they differ only to the use of advanced algorithms or MIMO systems.

[0008] In order to achieve high Doppler resolution, multiple OFDM symbols are concatenated and reshaped into a 2D matrix form. Then, the DFT is taken over the time axis of this matrix. The disadvantages of the methods mentioned in the articles above are as follows: To achieves high range resolution they deploys large bandwidths with requires very fast expensive ADCs at the receiver, to achieve achieves high velocity resolution, data must be collected for long time durations with causes a problem of storage, high computational complexity are needed, does not requires obtaining the long frame for Doppler processing i.e., less storage and computation.

[0009] As a result, a new method is needed that can overcome the this mentioned disadvantages provide a low-complexity ISAC system capable of obtaining high-resolution rangevelocity profiles, and effectively utilize OFDM-based sensing even in low-capability devices.

[0010] References:

[0011] [1] M. Hasan, S. Ahmed, M. Y. A. Hashim, and M. I. Razzak, "High-performance automotive radar: A review of signal processing algorithms and modulation schemes," IEEE Access, vol. 7, pp. 18256-18278, 2019, doi: 10.1109 / ACCESS.2019.2894308.

[0012] [2] F. Li, S. Jia, C. Zhang and Y. Li, "A novel multi-objective artificial bee colony algorithm based on decomposition for feature selection," Expert Systems with Applications, vol. 156, p. 113816, Oct. 2020.

[0013] [3] B. Schweizer, C. Knill, D. Schindler, and C. Waldschmidt, “Stepped-carrier OFDM- radar processing scheme to retrieve high-resolution range-velocity profile at low sampling rate,” IEEE Transactions on Microwave Theory and Techniques, vol. 66, pp. 1610-1618, 3 2018.

[0014] [4] C. Knill, B. Schweizer, S. Sparrer, F. Roos, R. F. H. Fischer, and C. Waldschmidt, “High range and doppler resolution by application of compressed sensing using low baseband bandwidth OFDM radar,” IEEE Transactions on Microwave Theory and Techniques, vol. 66, pp. 3535-3546, 7 2018.

[0015] [5] B. Nuss, J. Mayer, S. Marahrens, and T. Zwick, “Frequency comb OFDM radar system with high range resolution and low sampling rate,” IEEE Transactions on Microwave Theory and Techniques, vol. 68, pp. 3861-3871, 9 2020. [6] O. Lang, R. Feger, C. Hofbauer, and M. Huemer, “OFDM radar with subcarrier aliasing — reducing the ADC sampling frequency without losing range resolution,” IEEE Transactions on Vehicular Technology, vol. 71, pp. 10 241-10 253, 10 2022. 2013, pp. 1-5.

[0016] [7] D. Schindler, B. Schweizer, C. Knill, J. Hasch, and C. Waldschmidt, “An integrated stepped-carrier OFDM mimo radar utilizing a novel fast frequency step generator for automotive applications,” IEEE Transactions on Microwave Theory and Techniques, vol. 67, no. 11, pp. 4559-4569, 2019.

[0017] [8] B. Nuss, L. G. de Oliveira, and T. Zwick, “Frequency comb mimo OFDM radar with no equidistant subcarrier interleaving,” IEEE Microwave and Wireless Components Letters, vol. 30, no. 12, pp. 1209-1212, 2020.

[0018] Description of The Invention:

[0019] The invention to realize all the objectives mentioned above and which will emerge from the detailed description below; the invention introduces a transceiver design for an ISAC OFDM system. A novel pilot structure is proposed at the transmitter, which enables high- resolution range and velocity profiles. Additionally, an extremely low-complexity sensing receiver, along with a simplified sensing process, is described. This approach eliminates the need for advanced and complex receivers typically required in similar systems. The disclosed invention provides an efficient solution for achieving high- resolution range and velocity profiles while maintaining simplicity and reducing complexity in the receiver design.

[0020] The disclosed invention aims to provide the following solutions:

[0021] - The invention introduces an ISAC system with low complexity that can achieve high- resolution range- velocity profiles. This is achieved by utilizing OFDM waveform, which ensures backward compatibility with existing systems.

[0022] - The proposed radar system provides enhanced capabilities while maintaining simplicity in its design. OFDM-based by employing this technique, even low- capability devices can effectively utilize OFDM-based sensing. The disclosed invention provides several advantages as follows:

[0023] - Compatibility: The proposed method is compatible with both 4G and 5G OFDM signaling, ensuring seamless integration with existing wireless communication systems.

[0024] - High range resolution: The invention achieves a high range resolution, allowing for precise localization and measurement of objects or targets.

[0025] - High velocity resolution: The method also achieves a high velocity resolution, enabling accurate detection and tracking of moving objects.

[0026] - Low-cost sensing receiver: The sensing receiver in this invention requires only ADC / DAC devices that sample at a few hundreds of KHz, resulting in extremely low-cost hardware implementation.

[0027] - Reduced computational complexity: The proposed method significantly reduces the computational complexity compared to conventional techniques, making it more efficient and practical for implementation.

[0028] - Reduced storage and computation: Unlike traditional approaches, the invention does not require obtaining long frames for Doppler processing. This results in lower storage requirements and computational load.

[0029] The structural and characteristic features and all advantages of the method subject to the invention will be understood more clearly thanks to the figures given below and the detailed explanation written by referring to these figures, and therefore the evaluation should be made by taking these figures and detailed explanation into consideration.

[0030] Description of the Figures:

[0031] The invention will be described with reference to the accompanying figures, so that the features of the invention will be more clearly understood and appreciated, but the purpose of this is not to limit the invention to these certain regulations. On the contrary, it is intended to cover all alternatives, changes and equivalences that can be included in the area of the invention defined by the accompanying claims. The details shown should be understood that they are shown only for the purpose of describing the preferred embodiments of the present invention and are presented in order to provide the most convenient and easily understandable description of both the shaping of methods and the rules and conceptual features of the invention. In these drawings;

[0032] Figure 1 A graphical view of the combined pilot structure used for all OFDM symbols.

[0033] Figure 2 A graphical view of pilot presetting such that each pilot turn is a continuous tone when CP is used.

[0034] Figure 3 An example schematic view of the detection receiver design.

[0035] The figures to help understand the present invention are numbered as indicated in the attached image and are given below along with their names.

[0036] Disclosure of References:

[0037] 100. Receiving The Signal

[0038] 105. Low-Noise Amplifier

[0039] 110. Signal Downconversion

[0040] 115. Low-Pass Filter

[0041] 120. Shift To the DF Band

[0042] 125. Sampling

[0043] 130. Reshaping The Sampled Data

[0044] 135. Digital Signal Processing

[0045] Detail Description of The Invention:

[0046] Before describing the invention subject method, a disclose of OFDM of mentioned in the description is given below:

[0047] OFDM: (Orthogonal Frequency Division Multiplexing) is a modulation technique widely used in modern communication systems. It divides a high-rate data stream into multiple lower-rate sub streams and transmits them simultaneously in parallel over a set of orthogonal subcarriers. Each subcarrier is modulated using a narrowband signal, allowing for efficient utilization of the available bandwidth.

[0048] The disclosed method presents a novel approach to designing a low-complexity OFDMbased ISAC system. It is composed of two main blocks, namely, transmitter and sensing receiver.

[0049] I. Transmitter:

[0050] The proposed scheme uses OFDM system with Nfftsubcarriers, Nppilots are employed in a comb structure in induces kp(0), kp(l), ... , kp(Np— 1) as seen in Figure 1. The pilot symbols are strategically inserted within the frequency domain, while X( / c) represents the data symbols in the frequency domain. The comb structure ensures that the pilot symbols are appropriately positioned to enable accurate estimation of the channel characteristics across the entire bandwidth. By leveraging these pilot symbols, the receiver can interpolate and extrapolate the channel response between pilot subcarriers, enabling estimation of the channel's behavior at other frequencies.

[0051] The data symbols, represented by X( / c) in the frequency domain, carry the information to be transmitted. These symbols undergo an inverse fast Fourier transform (IFFT) to convert them from the frequency domain to the time domain. The resulting time domain symbols, x(n), are then transmitted over the wireless channel.

[0052] In order to ensure the continuity of the tones of the pilots between each successive OFDM symbols, the pilot values are tuned in frequency domain as follows: j27ikpl-LCp

[0053] Xp{kp, l) = Xp{kp) - eNff , is the complex coeficient of the pilot on the Zc-th subcarrier, I denotes the number of the OFDM symbol and Lcpis the cyclic prefix (CP) length. Figure 2 depicts how this precoding impacts the signal in time domain. II. Extremely low-complexity Sensing receiver:

[0054] A low complexity radar receiver that utilizes mixing and sampling in the Doppler Frequency (DF) band is designed to simplify the signal processing and reduce computational requirements. This approach involves converting the received OFDM radar signal to a lower frequency Doppler Frequency before further processing.

[0055] Here's a high-level description of the low complexity OFDM radar receiver using mixing and sampling in the DF band which is depicted in Figure 3:

[0056] Signal Downconversion (110): The received OFDM radar signal is downconverted to the DF band through mixing with a local oscillator signal with step frequencies corresponding the pilot subcarriers (i.e., f = fc+ Xp(kp) f) where A is the subcarrier spacing. The LO signal is usually generated by a stable and tunable oscillator. Mixing involves multiplying the received signal with the LO signal, resulting in the desired frequency shift to the DF band (120).

[0057] Filtering: After downconversion, a lowpass filter (115) is applied to remove unwanted noise and interference outside the desired DF band. The filter's characteristics are chosen to match the bandwidth of the maximum Doppler frequency to preserve the relevant information.

[0058] Sampling (125): The downconverted and filtered signal is then sampled at a sufficiently high rate using an analog-to-digital converter (ADC). The sampling rate is chosen based on the Nyquist criterion to ensure accurate representation of the signal's bandwidth i.e., Fs= 2Fd maxwhere Fd maxis the maximum delay frequency that correspond to the target with the highest velocity. Generally, it is in the order of few KHz.

[0059] Reshaping the sampled data (130): The sampled data is in a matrix form each column is the output of one oscillator.

[0060] Digital Signal Processing (135): The sampled data is processed digitally to extract the desired information. Then it is converted to range-Doppler map

[0061] Detection and Estimation: Following digital signal processing, detection algorithms are applied to identify targets based on the processed data. Velocity estimation is performed by analyzing the frequency shift between the transmitted pilot tones and the received echoes. Range estimation is achieved by analyzing the frequency echos corresponding to the same time delays. The foregoing descriptions of specific embodiments of the present technology have been presented for the purposes of illustration and description. They are not intended to be exhaustive or to limit the present technology to the precise forms disclosed, and obviously many modifications and variations are possible considering the above teaching. The embodiments were chosen and described to best explain the principles of the present technology and its practical software, to thereby enable others skilled in the art to best utilize the present technology and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the software or implementation without departing from the spirit or scope of the claims of the present technology.

[0062] In a case that no conflict occurs, the embodiments in the present disclosure and the features in the embodiments may be mutually combined. The foregoing descriptions are merely specific implementations of the present disclosure but are not intended to limit the protection scope of the present disclosure. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in the present disclosure shall fail within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.

Claims

CLAIMS1- The invention relates to extremely low-complexity integrated sensing and communication via OFDM signaling and method therefore, its feature is; i. the received OFDM radar signal is mixed with a local oscillator signal with step frequencies corresponding to the pilot subcarriers and downconverted to the DF band, resulting in signal down conversion (110), ii. the application of a low-pass filter (115) to remove unwanted noise and interference outside the desired DF band, iii. sampling (125) the down-converted and filtered signal at a very slowrate using an analog-to-digital converter (ADC), iv. reshaping the sampled data (130) into a matrix form, v. including process steps of digitally processing and converting the sampled data into a range-Doppler map to extract the desired information.2- The method according to claim 1, is characterized by included of the comb structure is used to accurately estimate of channel characteristics across the entire bandwidth by appropriately positioning of the pilot symbols.3- The method according to claim 1, characterized in that ensure the continuity of the tones of the pilots between each successive OFDM symbols, the pilot values are tuned in frequency domain as the equation; j27ikpl-LCpXp{kp, l) = Xp{kp) - eNff ,is the complex coeficient of the pilot on the Zc-th subcarrier, I denotes the number of the OFDM symbol and Lcpis the cyclic prefix (CP) length.4- The method according to claim 1, characterized in that the received OFDM radar signal in step (i) is downconverted to the DF bandby mixing with stepped carriers that corresponds to the pilot frequencies. The carrier frequencies are given as ; fi = fc + kp(i )A ) for i = 0,1, ... ,Np- 1where A is the subcarrier spacing.5- The method according to claim 1, characterized in that in step (iii) the sampling rate is chosen according to the Nyquist criterion to ensure an accurate representation of the downconverted DFsignal, which is relatively small.

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