A system and method for adaptive transmission design based on the micro-doppler spread of rotors

Abstract

The invention relates to a system (1) and method for adaptive transmission design tailored to dynamically transmit a frame that emulates the periodic time-varying patterns of the micro-Doppler spread in scenarios involving devices performing rotational motion such as rotors.

Description

[0001] DESCRIPTION

[0002] A SYSTEM AND METHOD FOR ADAPTIVE TRANSMISSION DESIGN BASED ON THE MICRO-DOPPLER SPREAD OF ROTORS

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] The invention relates to a system and method for adaptive transmission design tailored to dynamically transmit a frame that emulates the periodic time-varying patterns of the micro¬ Doppler spread in scenarios involving devices exhibiting rotational motion such as rotors.

[0005] PRIOR ART

[0006] The micro-Doppler spread effect, commonly referred to as micro-Doppler signatures, has been extensively utilized by researchers to identify targets exhibiting micro-motions. These signatures have proven to be valuable tools in radar-based target recognition, with applications spanning defense and commercial domains.

[0007] Said micro-Doppler spread effect, resulting from the relative motion of specific target components such as rotating blades, oscillating mechanisms, or even vibrating surfaces produces unique frequency modulations. These modulations cany’ critical information about the physical characteristics, motion dynamics, and structural details of the target. The ability to analyze and interpret these effects has profound implications in both radar and communication systems, where understanding such fine-grained dynamics is crucial.

[0008] A general schematic model for a rotor with blades is illustrated in Figure 1. The model consists of K blades denoted as BK, with each blade having a length L and rotating at a frequency / j- The rotation elements of any rotating device may exhibit varying structural properties, dimensions, or rotational frequencies, resulting in diverse periodic micro¬ motions. These motions modulate the transmitted or reflected signal, producing distinct frequency shifts that give rise to the micro-Doppler spread effect. These frequency shifts, referred to as micro-Doppler signatures, provide valuable information about the device’s motion characteristics, including its rotation rate, structural properties, and dynamic behavior.

[0009] In addition, the micro-Doppler spread effect has demonstrated significant potential across various domains, offering unique opportunities for target recognition and classification. For ground-moving objects, such as humans, vehicles, and animals, micro-Doppler signatures have been effectively employed in applications like perimeter security, intelligent transportation systems, surveillance, and human gait analysis [1], Similarly, in the context of aerial targets, the micro-Doppler effect is instrumental in identifying micro-motion dynamics, such as the rotation of propellers in fixed-wing aircraft, fans and turbines in jet engines, helicopter blades, and drone rotors [2], Distinctive micro-Doppler signatures are also observed in space targets, enabling classification into warhead and decoy categories, as demonstrated in recent studies [3], Moreover, micro-Doppler-based recognition has proven useful in overcoming challenges like wind turbine clutter in airborne pulse-Doppler radar systems [4], Beyond traditional radar applications, micro-Doppler features play a key role in home automation, offering innovative solutions for security systems, including access control and alarms, as well as for gesture recognition and control [5], Additionally, the micro-motions caused by human heartbeat and breathing produce unique signatures that enable vital sign detection [6],

[0010] In wireless communication, the micro-Doppler spread contributes to dynamic multipath fading as moving or rotating objects introduce continuous changes in the reflected signal paths. This results in phase and frequency distortions that degrade the quality and reliability of the received signal. Unlike static Doppler shifts, the micro-Doppler spread imposes rapid, non-linear changes on the communication channel. These variations complicate channel state estimation, requiring more sophisticated algorithms to track and compensate for the dynamic behavior of the channel. Rotational dynamics can cause overlapping frequency components, leading to interference that reduces the separation of desired and undesired signals. This interference can decorrelate transmitted signals, making traditional equalization and demodulation techniques less effective. In advanced communication scenarios, such as fifth generation (5G), Internet of things (IoT), and vehicle-to-everything (V2X) systems, the micro-Doppler spread effect complicates the coexistence of communication and sensing. The dynamic effects can interfere with sensing accuracy while simultaneously disrupting communication links, creating an additional challenge.

[0011] The micro-Doppler effect is significantly influenced by the carrier frequency fc. Additionally, it depends on various factors, including the rotation rate ( fr), the number of blades, and the blade length (L). Taking all these dependencies into account, the maximum Doppler can mathematically expressed as fDmax= [(4 * n * L * fr* f.) / c] * cosp where c is the speed of light, and d is the elevation angle, as illustrated in the general geometric representation in Figure 2.

[0012] In traditional communication systems, the design is often based on the maximum Doppler spread of the channel, with parameters such as modulation, coding schemes, numerology, and waveform selected to accommodate the worst-case conditions. While this approach ensures a certain level of robustness, it fails to account for the time-varying nature of the Doppler spread, leading to inefficiencies and suboptimal performance.

[0013] Figure 3 illustrates the time-frequency representation of the micro-Doppler effect generated by a rotor. At an operating frequency of fc= 10 GHz, the micro-Doppler effect of a single blade is depicted in Figure 3-a. From the spectrogram, it can be observed that the micro- Doppler in the time-frequency domain exhibits a time-varying signal. The sinusoidal pattern confirms that the frequency variation follows a periodic behavior. Consequently, it can be concluded that the micro-Doppler spread is a periodic, time-varying effect.

[0014] To further validate the applicability and accuracy of the proposed method under varying operational conditions, experimental measurements were conducted in a controlled laboratory environment using a rotor with multiple blades operating at a frequency of fc= 120 GHz (Figure 3-b). Figure 3-b provides a detailed visualization of the micro-Doppler effect, illustrating how different frequency components evolve over time. For higher operating frequencies and contributions from multiple rotating blades, the micro-Doppler spread becomes more pronounced due to the superposition of multiple periodic components. From the spectrogram, it can be observed that the Doppler spread varies periodically over time, albeit with different periods T as shown in Figure 3-b. This observation confirms the presence of a distinct and unique pattern in the time-varying micro-Doppler spread.

[0015] While the micro-Doppler spread effect has been thoroughly studied and utilized in various dimensions for radar-based applications, there remains a significant gap of comprehensive research addressing its impact and potential in communication systems. This gap highlights the need for innovative approaches to analyze and harness the micro-Doppler spread effect within the context of modern wireless communication technologies. At the state of the art, the patent document numbered WO2023220912A1 mentions detecting or identifying targets or objects using wireless communications (e.g., radio frequency (RF) sensing). Aspects of this disclosure are related to systems and techniques for performing target or object detection or identification using micro-Doppler signatures. However, it does not account for the time-varying nature of the micro-Doppler spread that is variations of micro-Doppler effect in different symbols, which may cause errors in target detection or classification. Also, in this document, micro-Doppler effect has been utilized especially for radar-based applications, it does not present solutions generally for wireless communications.

[0016] References:

[0017] [1], Y. Kim and T. Moon, " Human Detection and Activity Classification Based on Micro- Doppler Signatures Using Deep Convolutional Neural Networks," in IEEE Geoscience and Remote Sensing Leters, vol. 13, no. 1, pp. 8-12, Jan. 2016.

[0018] [2], Victor Chen, The Micro-Doppler Effect in Radar, Artech, 2011.

[0019] [3], R. Nepal, et al., " Micro-Doppler radar signature identification within wind turbine clutter based on short-CPI airborne radar observations, " in IET Radar, Sonar & Navigation, vol.9, no.9, pp.1268-1275, 2015.

[0020] [4], A. R. Persico et al., " On Model, Algorithms, and Experiment for Micro-Doppler-Based Recognition of Ballistic

[0021] Targets," in IEEE Transactions on Aerospace and Electronic Systems, vol. 53, no. 3, pp.

[0022] 1088-1108, June 2017.

[0023] [5], Y. Kim and B. Toomajian, " Hand Gesture Recognition Using Micro-Doppler Signatures with Convolutional Neural Network," in IEEE Access, vol. 4, pp. 7125-7130, 2016.

[0024] [6], R. M. Narayanan, “Earthquake survivor detection using life signals from radar micro- Doppler,” in Proc. 1st Int. Conf. Wireless Technol. Hum. Relief (ACWR), p. 259, 2011.

[0025] The invention brings technical solutions to the technical problems in the state of the art stated above.

[0026] BRIEF DESCRIPTION OF THE INVENTION

[0027] The aim of the invention is to introduce an adaptive frame structure that effectively leverages the time-varying patterns of the micro-Doppler spread associated with devices exhibiting rotational motion such as rotors to enhance the performance, intelligence and robustness of wireless communication systems.

[0028] By overcoming the limitations of conventional approaches in radar literature, the adaptive transmission of frame exploits the time-varying characteristics of micro-Doppler, offering robust performance in dynamic and complex environments. This approach transforms the pattern of micro-Doppler spread into a valuable tool for smarter and more efficient communication systems in scenarios using rotors.

[0029] The subject-matter method and system of the invention addresses the limitation of accounting for the time-varying nature of the Doppler spread mentioned above by leveraging the dynamic variations in the Doppler spread observed across different symbols within the frame. Instead of applying static configurations, the system dynamically adapts key parameters — such as waveform, numerology, cyclic prefix, modulation, and coding schemes — based on the specific Doppler spread characteristics of each symbol. By synchronizing these parameters with the time-varying Doppler pattern, the proposed approach enhances the system’s efficiency, resilience, and adaptability, providing robust communication performance across diverse and dynamic environments.

[0030] Description of the Figures

[0031] Figure 1. A general schematic model for a rotor with blades

[0032] Figure 2. A general geometric representation of a rotor with blades

[0033] Figure 3. (a) The time-frequency representation of the micro-Doppler effect generated by a rotor, (b) A detailed visualization of the micro-Doppler effect, illustrating how different frequency components evolve over time

[0034] Figure 4. A schematic view of the system model for the invention

[0035] Figure 5. (a) Numerology selection for the micro-Doppler spread effect for an Orthogonal Frequency Division Multiplexing (OFDM) frame at the state of the art, (b) Numerology selection for the micro-Doppler spread effect for an Orthogonal Frequency Division Multiplexing (OFDM) frame in the invention

[0036] Figure 6. (a) Waveform selection for the micro-Doppler spread effect in conventional methods, (b) Waveform selection for the micro-Doppler spread effect in the invention Figure 7. (a) Coding / Modulation scheme selection for the micro-Doppler spread effect in conventional methods, (b) Coding / Modulation scheme selection for the micro-Doppler spread effect in the invention

[0037]

[0038] of the References in the

[0039] For a better understanding of the invention, the elements illustrated in the figures are numbered as follows:

[0040] 1. System

[0041] 1.1. Transmitter

[0042] 1.2. Receiver

[0043] 1.3. Antenna

[0044] 1.4. Two-way communication link

[0045] 1.5. Micro-Doppler spread pattern feedback mechanism

[0046] DETAILED DESCRIPTION OF THE INVENTION

[0047] The subject-matter system (1) of the invention comprises at least one transmitter (1.1), at least one receiver (1.2), at least two antennas (1.3), at least one two-way communication link (1.4) between the transmitter (1.1) and receiver (1.2) and at least one micro-Doppler spread pattern feedback mechanism (1.5) which is a wired or wireless link between the transmitter (1.1) and the receiver (1.2).

[0048] If a device performing a rotational motion and forming a micro-Doppler spread pattern (such as rotor etc.) is located on the transmitter (1.1) side, the transmitter (1.1) with the device will have prior knowledge of its micro-Doppler spread pattern, derived from the rotational motion properties causing the micro-Doppler effect without the need for the micro-Doppler spread pattern feedback mechanism (1.5) transmitting the pattern to the transmitter (1.1) (Case 1). Or, the device is located on the receiver (1.2) side and forms a micro-Doppler spread pattern (Case 2). Or, the device is located in the environment (Case 3). In case 2, the device generates a unique micro-Doppler spread pattern due to its micromotion, which is transmitted through the micro-Doppler spread pattern feedback mechanism (1.5) from the receiver (1.2) to the transmitter (1.1). In case 3, a signal from the device which has its micro- Doppler spread pattern is sent to the receiver (1.2), and the receiver (1.2) forwards it to the transmitter (1.1) through the micro-Doppler spread pattern feedback mechanism (1.5). In all three cases, the transmitter (1.1) designs a frame to synchronize with the micro-Doppler pattern across different symbol durations and communicates with the receiver (1.2) by transmitting this frame via the antennas (1.3) through the two-way communication link (1.4)..

[0049] In all three cases, the transmitter (1.1) selects the numerology or waveform or coding / modulation scheme according to the micro-Doppler spread pattern to design the frame to synchronize with the micro-Doppler pattern across different symbol durations.

[0050] For the selection of numerology: The entire frame duration T is divided into N OFDM symbol durations TNby the transmitter (1.1). Instead of applying a fixed parameter for the entire frame, each symbol is designed individually based on its own maximum micro- Doppler spread by the transmitter (1.1), i.e since fomaxi

[0051]

[0052] fomax. then the numerology applied in the symbol

[0053]

[0054] st symbol O2. The transmitter (1.1) adapts the OFDM symbols as Oj, O2... 0™ where 0™ represents the l -th OFDM symbol with a numerology m (m ---- 1,2... M ). The CP is also adapted for each symbol to align with its unique micro-Doppler characteristics as CP^, CP2... CP™ where CP™ represents the A7-th OFDM symbol CP with a numerology m. The transmitter (1.1) chooses smaller subcarrier spacing which are 15 kHz, 30 kHz or 60 kHz subcarrier spacing for low Doppler conditions to maximize data rates and larger spacing which are 120 kHz or 240 kHz subcarrier spacing for high Doppler environments to maintain robustness. By selecting the most suitable numerology, the system (1) can optimize spectral efficiency and minimize inter-carrier interference (ICI), resulting in more reliable data transmission. Furthermore, adaptive numerology selection enables the system (1) to balance throughput and latency. By adapting the CP length to the maximum Doppler spread for each symbol, the system (1) ensures that the CP is neither excessively long (which would waste bandwidth) nor too short (which would fail to handle two-way communication link (1.4) variations). This dynamic adjustment allows the system (1) to maintain orthogonality among subcarriers and ensures signal integrity even in challenging environments with significant Doppler effects. Moreover, an optimized CP length reduces overhead and power consumption, improving the overall efficiency of the system, particularly in scenarios involving fast-moving objects or devices with rotating components. By tailoring the design of each symbol to its specific maximum micro-Doppler spread, the system (1) achieves enhanced robustness and efficiency in handling the time-varying micro¬ Doppler effect across the frame.

[0055] For the selection of waveform: If the maximum Doppler spread fDmaxfor a given symbol exceeds a predefined maximum Doppler spread threshold fDmaxth.,r e- fomaxth < fc-max n thetransmitter (1.1) selects waveform W, where n = 1,2... N is the n-th symbol in N total symbols (Figure 6-b). The parameters of waveform W will be specifically defined to align with the maximum micro-Doppler spread characteristics of that particular symbol, ensuring optimal performance under the new conditions. Conversely, if the maximum Doppler spread for the symbol remains below the threshold, i.e fDmaxth > fsmax, n, the transmitter (1.1) retains an alternative waveform V for transmission. For low micro-Doppler spread which refers to micro-Doppler spreads less than the threshold, multicarrier waveforms like Cyclic Prefix OFDM (CP-OFDM) are applied by the transmitter (1.1) as it is ideal due to its efficiency and simplicity in handling stable two-way communication link (1.4) conditions. On the other hand, for high micro-Doppler spread conditions which refers to micro-Doppler spreads more than the threshold, more robust waveforms such as OFDM with wide subcarrier spacing, Filter Bank Multi-Carrier (FBMC) or Orthogonal Time-Frequency Space (OTFS) are applied. OFDM: with wide subcarrier spacing is a modified OFDM approach that increases subcarrier spacing to combat high Doppler-induced ICI, FBMC features enhanced frequency localization, reducing ICI in high Doppler conditions, while OTFS stands out by transforming signals into the delay-Doppler domain, offering exceptional robustness in rapidly changing environments like vehicular communication and drone networks. By selecting the appropriate waveform based on Doppler characteristics, the system can ensure reliable and efficient communication in both low and high Doppler environments.

[0056] For selection of coding / modulation scheme: Since the maximum micro-Doppler spread fsjmax varies across different symbols, each symbol will apply a coding and modulation scheme tailored to its own maximum micro-Doppler spread, i.e fDmaxi = f>max 2 then the scheme applied in the symbol

[0057]

[0058] symbol C2(see Figure 7-b). The transmitter (1.1) dynamically selects the most suitable coding / modulation scheme for each symbol from the predefined set k = l,2... as C^, C2,

[0059]

[0060] where represents the fc-th selected coding / modulation scheme for the AMh symbol. In low Doppler spread scenarios, where the two-way communication link (1.4) remains stable, high modulation order schemes such as Quadrature Phase Shift Keying (QPSK) or 16-Quadrature Amplitude Modulation (QAM) are applied by the transmitter (1.1) for achieving reliable communication and higher data rates, supported by a predetermined error correction method like convolutional coding, turbo coding, or Low-Density Parity-Check (LDPC), preferably % or3 / 4 coding rates may be selected. In high Doppler spread environments, where rapid and extreme two-way communication link variations occur, low order modulation schemes such as BPSK (Binary Phase Shift Keying) or reduced constellation QPSK (Quadrate Phase Shift Keying) are used by the transmitter (1.1), along with a predetermined error correction technique like Reed-Solomon codes, low-rate LDPC, or polar codes, ensuring signal reliability even in the most dynamic conditions, preferably V- or vi coding rates can be implemented (The micro-Doppler spread varies for each symbol. Based on these variations, the values are analyzed and categorized to decide whether the Doppler spread is considered low or high). This dynamic approach ensures that the communication system remains adaptive and efficient, optimizing performance by addressing the unique micro-Doppler characteristics of each symbol within the frame.

[0061] Finally, the transmitter (1.1) sends the designed adaptive frame structure to the receiver (1.2) via the antennas (1.3) through the two-way communication link (1.4).

[0062] In case 2, by receiving and analyzing the micro-Doppler pattern, the transmitter (1.1) gains detailed knowledge of the receiver's (1.2) rotational dynamics. Using this information, the transmitter (1.1) dynamically adapts its frame to match the time-varying micro-Doppler spread. The primary difference between the micro-Doppler spread pattern feedback mechanism in this invention and conventional systems lies in how the system (1) adapts to the time-varying Doppler spread. In conventional methods, the communication system operates based on a static design determined by the maximum Doppler spread of the two- way communication link. This results in fixed parameters, such as modulation, coding schemes, waveform, and numerology, being applied uniformly throughout the frame. While this ensures reliability for the worst-case Doppler conditions, it fails to account for variations in Doppler spread across different symbols, leading to inefficiencies and suboptimal resource utilization. In contrast, the proposed micro-Doppler spread pattern feedback mechanism (1.5) dynamically analyzes the Doppler spread for each symbol and provides real-time feedback to the transmitter (1.1). This feedback enables the transmitter (1.1) to adapt key communication parameters such as modulation, coding schemes, waveform, numerology, and cyclic prefix based on the specific Doppler characteristics of each symbol. By exploiting the time-varying nature of the micro-Doppler spread, the subject-matter system (1) and method ensures that each symbol is optimally configured to handle its unique Doppler environment. This dynamic, symbol -by-symbol adaptation not only enhances spectral and energy efficiency but also significantly improves system robustness and reliability in highly dynamic environments.

[0063] The method comprises the steps below:

[0064] Obtaining of the micro-Doppler spread pattern:

[0065] o If a device performing a rotational motion and forming a micro-Doppler spread patern (such as rotor etc.) is located on the transmitter (1.1) side, the transmitter (1.1) with the device will have prior knowledge of its micro- Doppler spread pattern, derived from the rotational motion properties causing the micro-Doppler effect (Case 1) or

[0066] o The device is located on the receiver (1.2) side (Case 2) and forms a micro- Doppler spread pattern or

[0067] o The device is located in the environment (Case 3) and forms a micro-Doppler spread pattern

[0068] Transmission of the micro-Doppler spread pattern:

[0069] o In case 1, the transmitter (1.1) already has the micro-Doppler spread pattern, o In case 2, the device generates a unique micro-Doppler spread pattern due to its micromotion, which is transmitted through the micro-Doppler spread pattern feedback mechanism (1.5) from the receiver (1.2) to the transmitter (1.1),

[0070] o In case 3, a signal from the device which has its micro-Doppler spread pattern is sent to the receiver (1.2), and the receiver (1.2) forwards it to the transmitter (1.1) through the micro-Doppler spread pattern feedback mechanism (1.5) In all three cases, the transmitter (1.1) designs a frame to synchronize with the micro- Doppler pattern across different symbol durations and communicates with the receiver (1.2) by transmitting this frame via the antennas (1.3) through the two-way communication link (1.4), Selection of the transmission parameters Numerology or Waveform or Coding / Modulation scheme and adaptive frame structure design by the transmitter (1.1):

[0071] o Numerology selection: The entire frame duration T is divided into N symbol durations TN. Instead of applying a fixed parameter for the entire frame, each symbol is designed individually based on its own maximum micro-Doppler spread by the transmitter (1.1), i.e. since fDmax ifomax

[0072]

[0073] the numerology applied in the symbol O symbol O2. The OFDM symbols are adapted as O;1, O2... 0™ where 0™ represents the IV -th OFDM symbol with a numerology m (m = 1,2... M). The CP is also adapted for each symbol to align with its unique micro-Doppler characteristics as CP11, CP22-- CP where CP™ represents the 7V-th OFDM symbol CP with a numerology m. The transmitter (1.1) chooses smaller subcarrier spacing which are 15 kHz, 30 kHz or 60 kHz subcarrier spacing for low Doppler conditions to maximize data rates and larger spacing which are 120 kHz or 240 kHz subcarrier spacing for high Doppler environments to maintain robustness (The micro- Doppler spread changes with each symbol. These variations are evaluated, and the values are sorted and categorized to determine whether the Doppler spread is low or high.)

[0074] or

[0075] o Waveform selection: If the maximum Doppler spread fDmaxfor a given symbol exceeds a predefined maximum Doppler spread threshold fDmaxtn> i.e. fomaxth < fnmax n, waveform W will be selected where n = 1,2... N is the n-th symbol in N total symbol s by the transmitter (1.1). The parameters of waveform W will be specifically defined to align with the maximum micro-Doppler spread characteristics of that particular symbol, ensuring optimal performance under the new conditions. Conversely, if the maximum Doppler spread for the symbol remains below the threshold, i.e fDmax th > fnmax, n, an alternative waveform V is retained for transmission by the transmitter (1.1). For low micro-Doppler spread which refers to micro- Doppler spreads less than the threshold, multicarrier waveforms like Cyclic Prefix OFDM (CP-OFDM) are applied by the transmitter (1.1) as it is ideal due to its efficiency and simplicity in handling stable two-way communication link (1.4) conditions. On the other hand, for high micro¬ Doppler spread conditions which refers to micro-Doppler spreads more than the threshold, more robust waveforms such as OFDM: with wide subcarrier spacing, Filter Bank Multi-Carrier (FBMC) or Orthogonal Time-Frequency Space (OTFS) are applied

[0076] or

[0077] o Coding / Modulation scheme selection: Since the maximum micro-Doppler spread fDmaxvaries across different symbols, each symbol will apply a coding and modulation scheme tailored to its own maximum micro-Doppler spread, i.e fDmax- = fomax2 then the scheme applied in the symbol symbol C2. The transmitter (1.1) dynamically selects the most suitable coding / modulation scheme for each symbol from the predefined set k = 1,2... K as C'i, C2,

[0078]

[0079] where represents the fc-th selected coding / modulation scheme for the / V-th symbol. In low Doppler spread scenarios, where the tvvo-vvay communication link (1.4) remains stable, high modulation order schemes such as Quadrature Phase Shift Keying (QPSK) or 16-Quadrature Amplitude Modulation (QAM) are applied by the transmitter (1.1) for achieving reliable communication and higher data rates, supported by a predetermined error correction method like convolutional coding, turbo coding, or Low-Density Parity-Check (LDPC), preferably % or % coding rates may be selected. In high Doppler spread environments, where rapid and extreme two-way communication link (1.4) variations occur, low order modulation schemes such as BPSK or reduced constellation QPSK are used by the transmitter (1.1), along with a predetermined error correction technique like Reed-Solomon codes, low-rate LDPC, or polar codes, ensuring signal reliability even in the most dynamic conditions, preferably ’A or % coding rates can be implemented. (The micro-Doppler spread changes with each symbol. These variations are evaluated, and the values are sorted and categorized to determine whether the Doppler spread is low or high.) The adaptive frame structure designed by the transmitter ( 1.1) i s sent to the receiver (1.2) via the antennas (1.3) through the two-way communication link (1.4). Figure 5-a indicates numerology selection for the micro-Doppler spread effect for an Orthogonal Frequency Division Multiplexing (OFDM) frame with a duration T. Unlike a simple frequency shift, the micro-Doppler effect is observed as a spread, as indicated by the thickness in the sinusoidal pattern. This visual representation highlights the time-varying nature and complexity of the Doppler spread, emphasizing its distinct characteristics in the time-frequency domain. The frame structure of OFDM system consists of N symbols, each preceded by a cyclic prefix (CP) to counteract inter-symbol interference and handle multipath propagation (Figure 5-a). 'I, T2... TNrepresents each symbol duration for N OFDM symbols. In the classical method, at the start of the frame, the maximum Doppler spread fDmax(Figure 5-a) is measured, reflecting the most extreme time-frequency variations expected due to motion or other dynamic factors affecting the two-way communication link. This measured maximum micro-Doppler spread is then used as a fixed parameter for the entire frame duration. Based on this value, a numerology is selected from a predefined set of nuraerologies m ----

[0080]

[0081] where M denotes the total number of available numerologies. The selected numerology, in remains fixed for the entire frame and dictates the subcarrier spacing and symbol duration applied uniformly to all symbols in the frame as 0, O™... O™ where 0™ represents the IV -th OFDM symbol with a fixed numerology in. The CP length is also configured to account for this maximum micro- Doppler spread, ensuring sufficient protection against two-way communication link variations while maintaining signal integrity as CP™, CP™... CP™ where CP™ represents the I -th OFDM symbol CP with a fixed numerology m. This approach simplifies the system design by treating the maximum micro-Doppler spread as a static parameter for the entire frame. However, it does not adapt to time-varying Doppler conditions within the frame, which could lead to inefficiencies in scenarios with significant temporal variations in the Doppler spread. To address this challenge, the proposed method detailed above is illustrated in Figure 5-b.

[0082] The waveform selection is depicted in Figure 6. In conventional methods, the maximum Doppler spread fDmaxis calculated observing the two-way communication link condition (Figure 6-a). Based on this value, a waveform with fixed parameters is selected to accommodate the micro-Doppler spread effects. Suppose we have a waveform W with a set of fixed parameters. This waveform is uniformly applied to all symbols within the frame of duration T for every symbol, regardless of variations in the micro-Doppler spread that may occur across different symbols. If the micro-Doppler spread increases during transmission, the waveform W wall remain unchanged, as the system does not adapt to the variations. This lack of responsiveness can lead to degraded performance, such as increased ICI (Inter¬ Carrier Interference) and reduced reliability in dynamic environments. Figure 6-b presents the proposed method designed to address this issue. The micro-Doppler spread exhibits variation across different symbols, as clearly demonstrated by the observed micro-Doppler pattern.

[0083] The selection of coding / modulation scheme is described in Figure 7. In conventional methods, the coding / modulation scheme is selected based on the maximum Doppler spread fDmaxobserved for the two-way communication link (Figure 7-a). The selection of an appropriate modulation and coding scheme is critical as it directly impacts the reliability, data rate, and robustness of the communication system. This chosen scheme is then uniformly applied to the entire frame with duration T and all the symbols within it, without accounting for variations in the Doppler spread across individual symbols. Based on this value, a scheme is selected from a predefined set of coding / modulation schemes k = 1,2... K where K denotes the total number of available schemes. The selected coding / modulation scheme fc, remains unchanged throughout the entire frame and across N symbols denoted as C (Figure 7-a). A well-suited scheme ensures that the system can maintain signal integrity and minimize errors under given two-way communication link conditions. However, by applying a single scheme uniformly across T without considering the variations in micro-Doppler spread across individual symbols, conventional methods fail to adapt dynamically to the two-way communication link’s time-varying characteristics. This lack of flexibility can lead to suboptimal performance, particularly in environments with significant Doppler fluctuations, where the chosen scheme may not adequately address the changing two-way communication link conditions. Figure 7-b illustrates the proposed method detailed above that overcomes this limitation.

[0084] The importance of the invention lies in its capability to dynamically leverage the micro-Doppler spread effect associated with rotating components such as rotors to enhance the performance and adaptability of next-generation wireless communication systems, including 4G, 5G, and future 6G networks for motion-rich communication scenarios. By introducing an adaptive frame structure that emulates the time-varying patterns of micro-Doppler signatures, the invention effectively addresses key challenges such as time-varying two-way communication link (1.4) conditions, interference mitigation, and maintaining signal integrity in dynamic environments.

[0085] The system (1) and method are broadly applicable to scenarios involving rotational motion, including but not limited to drones, vehicles, machinery, and other objects with rotational components. By exploiting the unique characteristics of micro-Doppler dynamics, the invention enables robust modulation techniques, improved two-way communication link (1.4) estimation, and efficient resource allocation, thereby enhancing the reliability and efficiency of data transmission. By enabling reliable connectivity in dynamic scenarios, the invention supports diverse applications, including smart manufacturing, autonomous vehicles, drone communication, aerial networks, and even space communication, positioning it as a transformative advancement in modem wireless technologies.

[0086] The invention is highly applicable across various industries that require reliable wireless communication in dynamic environments involving rotating components. It can be integrated into drones and unmanned aerial vehicles (UAVs) for defense, logistics, and agriculture; V2X systems for autonomous and connected vehicles; industrial loT for smart manufacturing and robotics; aerospace and aviation for aircraft communication, and maritime communication for shipping and offshore platforms. Additionally, it has potential applications in healthcare monitoring systems with moving devices and in next-generation telecommunications (5G and 6G) for optimizing data transmission in time-varying two-way communication links (1.4). By dynamically adapting frame structures to mitigate the microDoppler effect, the invention ensures robust and efficient communication, meeting the critical demands of these industries.

[0087] This invention solves critical technical problems below related to the micro-Doppler spread effect in rotors:

[0088] 1. Channel Degradation Due to Time- Varying Conditions: In environments with rotating or moving objects, time-varying channel conditions caused by micro- Doppler spread effects lead to signal degradation, including multipath fading, Doppler spread, and signal decorrelation. The invention introduces an adaptive frame structure that dynamically adjusts to the time-varying patterns of the micro-Doppler spread effect, ensuring robust and efficient data transmission even in challenging environments.

[0089] 2. Limitations in Channel Estimation: Conventional methods for channel state estimation struggle to account for the rapidly changing micro-Doppler dynamics, leading to inaccuracies and suboptimal communication performance. The proposed solution utilizes predictable micro-Doppler signatures to enhance channel state estimation accuracy, improving communication performance under dynamic conditions.

[0090] 3. Inefficiencies in Resource Allocation: Existing systems lack the ability to adapt resource allocation dynamically in response to the micro-Doppler-induced variations, resulting in inefficient use of bandwidth and power. Real-time dynamic resource allocation optimizes bandwidth and power usage, adapting to changes induced by micro-Doppler dynamics.

[0091] The invention offers several advantages and unique features that distinguish it from existing solutions in wireless communication, particularly in systems with rotors. Key advantages include:

[0092] 1. Enhanced Communication Robustness: The invention addresses the challenges of time-varying channel conditions caused by rotors, ensuring consistent and reliable data transmission in dynamic environments.

[0093] 2. Improved Channel Estimation: By utilizing the unique characteristics of micro- Doppler signatures, the invention significantly enhances channel state estimation accuracy, leading to better system performance.

[0094] 3. Optimized Resource Utilization: Dynamic resource allocation mechanisms enable efficient use of bandwidth and power, adapting in real-time to environmental variations.

[0095] 4. Adaptability Across Diverse Scenarios: Capable of addressing challenges in scenarios with rotors, such as drones, machinery, and vehicles, making it a versatile solution for modern communication systems.

[0096] 5. Broad Sector Applications: Extends beyond traditional communication systems to include applications in autonomous systems, industrial loT, and future smart city networks. In the description above, the word of “channel” refers to “two-way communication link (1.4)”.

[0097] The invention is not limited to the above exemplary embodiments, and a person skilled in the art can readily put forward embodiments of the invention. These are considered within the scope of the invention as claimed by the accompanying claims.

Claims

CLAIMS1. A system (1) for adaptive transmission design tailored to dynamically transmit a frame that emulates the periodic time-varying paterns of the micro-Doppler spread, comprising at least one receiver (1.2), at least two antennas (1.3), at least one two-way communication link (1.4) between the transmiter (1.1) and receiver (1.2) characterized by comprising:at least one micro-Doppler spread pattern feedback mechanism (1.5) which is a wired or wireless link between the transmitter (1.1) and the receiver (1.2) and which a micro- Doppler spread pattern generated by a device performing rotational motion is transmitted from the receiver (1.2) to the transmitter (1.1) through, if the device is located on the receiver (1.2) side or in the environment, andat least one transmitter (1.1) which has prior knowledge of its micro-Doppler spread pattern without the need for the micro-Doppler spread pattern feedback mechanism (1.5) transmitting the pattern to the transmitter (1.1) if the device is located on the transmitter (1.1) side, which selects the numerology or waveform or coding / modulation scheme according to the micro-Doppler spread pattern, for the selection of numerology, which divides the entire frame duration T into N OFDM symbol durations TN, designs each symbol individually based on its own maximum micro-Doppler spread, since fDmaxi = f Umax 2 then the numerology applied in the symbol O = symbol O2, adapts the OFDM symbols as O, O... 0™ where 0™ represents the? -th OFDM symbol with a numerology m (m = 1,2... M), adapts the CP for each symbol to align with its unique micro-Doppler characteristics as CPf, CPf... CP™ where CP™ represents the 'V-th OFDM symbol CP with a numerology m, ) chooses smaller subcarrier spacing which are 15 kHz, 30 kHz or 60 kHz subcarrier spacing for low Doppler conditions to maximize data rates and larger spacing which are 120 kHz or 240 kHz subcarrier spacing for high Doppler environments to maintain robustness, for the selection of waveform; which selects waveform W, where n = 1,2... N is the n-th symbol in N total symbols if the maximum Doppler spread fDmaxfor a given symbol exceeds a predefined maximum Doppler spread threshold fomaxth’e- fomaxtn < fomax n, retains an alternative waveform V for transmission if the maximum Doppler spread for the symbol remains below the threshold, i.e fBmax th > fomax, « •> applies multicarrier waveforms for low7micro-Doppler spread which refers to micro-Doppler spreads less than the threshold, applies OFDM! with wide subcarrier spacing, Filter Bank Multi-Carrier (FBMC) orOrthogonal Time-Frequency Space (OTFS) for high micro-Doppler spread conditions which refers to micro-Doppler spreads more than the threshold, for selection of coding / modulation scheme; which selects the most suitable coding / modulation scheme for each symbol from the predefined set k ~ 1,2... K as C*,C%, where represents the fc-th selected coding / modulation scheme for the A’-th symbol, applies high modulation order schemes supported by a predetermined error correction method in low Doppler spread scenarios, uses low order modulation schemes along with a predetermined error correction technique in high Doppler spread environments; which sends the designed adaptive frame structure to the receiver (1.2) via the antennas (1.3) through the two-way communication link (1.4).

2. A system (1) according to Claim 1, characterized by comprising the transmitter (1.1) which selects QPSK or QAM in low Doppler spread scenarios; BPSK or reduced constellation QPSK in high Doppler spread scenarios for selection of coding / modul tion scheme.

3. A method for adaptive transmission design tailored to dynamically transmit a frame that emulates the periodic time-varying patterns of the micro-Doppler spread, comprising the step of obtaining of the micro-Doppler spread pattern:o If a device performing a rotational motion and forming a micro-Doppler spread pattern (such as rotor etc.) is located on the transmitter (1.1) side, the transmitter (1.1) with the device will have prior knowledge of its micro- Doppler spread pattern, derived from the rotational motion properties causing the micro-Doppler effect (Case 1) oro The device is located on the receiver (1.2) side (Case 2) and forms a micro- Doppler spread pattern oro The device is located in the environment (Case 3) and forms a micro-Doppler spread pattern;characterized by comprising the following steps:Transmission of the micro-Doppler spread pattern:o In case 1, the transmitter (1.1) already has the micro-Doppler spread pattern, o In case 2, the device generates a unique micro-Doppler spread pattern due to its micromotion, which is transmitted through the micro-Doppler spread pattern feedback mechanism (1.5) from the receiver (1.2) to the transmittero In case 3, a signal from the device which has its micro-Doppler spread pattern is sent to the receiver (1.2), and the receiver (1.2) forwards it to the transmitter (1.1) through the micro-Doppler spread pattern feedback mechanism (1.5) In all three cases, the transmitter (1.1) designs a frame to synchronize with the micro- Doppler pattern across different symbol durations and communicates with the receiver (1.2) by transmitting this frame via the antennas (1.3) through the two-way communication link (1.4),Selection of the transmission parameters Numerology or Waveform or Coding / Modulation scheme and adaptive frame structure design by the transmitter (1.1):o Numerology selection: The entire frame duration T is divided into N symbol durations TN. Instead of applying a fixed parameter for the entire frame, each symbol is designed individually based on its own maximum micro-Doppler spread by the transmitter (1.1), i.e. since fDmax l* fDmax2 ^Qnthe numerology applied in the symbol O symbol O2The OFDM symbols are adapted as 0, O2... 0 where 0™ represents the N -th OFDM symbol with a numerology rn (m = 1,2,.. M). The CP is also adapted for each symbol to align with its unique micro-Doppler characteristics as CP^, CP2... CP^' where CP™ represents the TV -th OFDM symbol CP with a numerology m. The transmitter (1.1) chooses smaller subcarrier spacing which is 15 kHz, 30 kHz or 60 kHz subcarrier spacing for low Doppler conditions to maximize data rates and larger spacing which is 120 kHz or 240 kHz subcarrier spacing for high Doppler environments to maintain robustnessoro Waveform selection: If the maximum Doppler spread fDmaxfor a given symbol exceeds a predefined maximum Doppler spread threshold fDmax tfl, i.e. fomaxth < fomax n, waveform W will be selected where n = 1,2... N is the n-th symbol in N total symbols by the transmitter (1.1). The parameters of waveform W will be specifically defined to align with the maximum micro-Doppler spread characteristics of that particular symbol, ensuring optimal performance under the new conditions. Conversely, if the maximum Doppler spread for the symbol remains below the threshold, i.e fDmax th > fomax, n, an alternative waveform V is retained for transmission by thetransmitter (1.1). For low micro-Doppler spread which refers to micro¬ Doppler spreads less than the threshold, multicarrier waveforms are applied by the transmitter (1.1). On the other hand, for high micro-Doppler spread conditions which refers to micro-Doppler spreads more than the threshold, OFDM with wide subcarrier spacing, Filter Bank Multi-Carrier (FBMC) or Orthogonal Time-Frequency Space (OTFS) are applied by the transmitter (1.1)oro Coding / Modulation scheme selection: Since the maximum micro-Doppler spread fDmaxvaries across different symbols, each symbol will apply a coding and modulation scheme tailored to its own maximum micro-Doppler spread, i.e fDmax s= fDmax 2then the scheme applied in the symbol C symbol C2. The transmitter (1.1) dynamically selects the most suitable coding / modulation scheme for each symbol from the predefined set k = 1,2…K as C11, C22, CNkwhere C represents the fc-th selected coding / modulation scheme for the A7-th symbol. In low Doppler spread scenarios, high modulation order schemes are applied by the transmitter (1.1) for achieving reliable communication and higher data rates, supported by a predetermined error correction method. In high Doppler spread environments, low order modulation schemes are used by the transmitter (1.1), along with a predetermined error correction technique, The adaptive frame structure designed by the transmitter (1.1) is sent to the receiver (1.2) via the antennas (1.3) through the two-way communication link (1.4)., A method according to Claim 3, characterized by comprising the Coding / Modulation scheme selection step wherein the transmitter (1.1) selects Quadrature Phase Shift Keying (QPSK) or 16-Quadrature Amplitude Modulation (QAM) for low doppler scenarios; BPSK or reduced constellation QPSK for high doppler scenarios.

Images