Doppler-resilient universal filtered multicarrier modulation, dr-UFMC, apparatus and a method thereof

Abstract

A Doppler-resilient Universal Filtered Multicarrier Modulation (DR-UFMC) apparatus (102) is disclosed. The DR-UFMC apparatus (102) is configured to generate one or more DR-UFMC pilot signals (SDR-UFMC) based on Orthogonal Time Frequency Space (OTFS) pilot signals (SOTFS), wherein the OTFS pilot signals (SOTFS) are distorted prior to transmission to account for transmission distortion from the DR-UFMC modulation scheme. The DR-UFMC apparatus (102) can be used in various applications such as vehicular communications, satellite links, and other high-speed communication systems, offering improved spectral efficiency, reduced interference, and enhanced communication stability.

Description

[0001] DOPPLER-RESILIENT UNIVERSAL FILTERED MULTICARRIER MODULATION, DR-UFMC, APPARATUS AND A METHOD THEREOF TECHNICAL FIELD

[0002] The present disclosure relates generally to the field of wireless communication systems. Moreover, the present disclosure relates to a Doppler-resilient universal filtered multicarrier modulation, DR-UFMC, apparatus and a method thereof for improving signal transmission accuracy in environments with Doppler shifts and other transmission distortions, such as by designing pilots for delay-Doppler domain modulations.

[0003] BACKGROUND

[0004] In modem wireless communication systems, multicarrier modulation techniques such as Orthogonal Frequency Division Multiplexing (OFDM) are commonly used to improve data transmission efficiency. The OFDM modulation technique works by dividing a data stream into multiple subcarriers for parallel transmission, allowing for high data rates and resistance to frequency-selective fading. However, despite of widespread adoption of the OFDM modulation technique, the OFDM faces significant challenges such as poor spectral containment and degraded performance in high-mobility scenarios with large Doppler shifts.

[0005] Certain attempts have been made to address the limitations of the OFDM modulation techniques, which involves the introduction of Universal Filtered Multi-Carrier (UFMC) modulation and Orthogonal Time Frequency Space (OTFS) modulation. The UFMC uses a vector of information symbols that undergoes serial-to-parallel conversion, Inverse Fast Fourier Transform (IFFT) processing, and subband filtering, thereby providing better spectral containment and reducing out-of-band emissions. Moreover, OTFS arranges symbols in a delay-Doppler domain matrix, applies a 2D-IFFT transform, and then feeds the output to an OFDM modulator, thus enhancing the performance of communication in high-mobility scenarios with large Doppler shifts. Recently, a new modulation technique called Doppler-resilient Universal Filtered Multicarrier (DR-UFMC) has been proposed (DAndrea, C., Buzzi, S., Fresia, M., & Wu, X. (2023, June). Doppler-resilient universal filtered multicarrier (DR-UFMC): A beyond-OTFS modulation. In 2023 Joint European Conference on Networks and Communications & 6G Summit (EuCNC / 6G Summit) (pp. 150-155). IEEE), that combines the advantages ofbothUFMC and OTFS. The DR-UFMC aims to simultaneously address the spectral containment issue and improve performance in high-mobility scenarios. However, the introduction of DR-UFMC presents new challenges, particularly in channel estimation, as existing channel estimation methods and pilot designs for OTFS do not work well for DR-UFMC due to the subband filtering process. As a result, channel estimation for DR-UFMC cannot be performed in the same manner as OTFS. Thus, there exists a technical problem of how to design a pilot signal scheme that can enable an effective, simple, and well-performing channel estimation algorithm for DR-UFMC modulation.

[0006] Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with the conventional Doppler-resilient universal filtered multicarrier modulation (DR-UFMC) apparatus and conventional method for pilot signal generation.

[0007] SUMMARY

[0008] The present disclosure provides a Doppler-resilient Universal Filtered Multicarrier (DR-UFMC) apparatus and a method thereof. The present disclosure provides a solution to the existing problem of how to design a pilot signal scheme that can enable an effective, simple, and well-performing channel estimation algorithm for DR-UFMC modulation. An objective of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provides the improved DR-UFMC apparatus and the method thereof. One or more objectives of the present disclosure are achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.

[0009] In one aspect, the present disclosure provides a Doppler-resilient Universal Filtered Multicarrier Modulation (DR-UFMC) apparatus configured to generate one or more DR-UFMC pilot signals (SDR-UFMC) based on Orthogonal Time Frequency Space, OTFS, pilot signals (SOTFS). Furthermore, the OTFS, pilot signals (SOTFS) are distorted prior to transmission to account for transmission distortion from the DR-UFMC modulation scheme.

[0010] Advantageously, the DR-UFMC apparatus, improves communication performance in high-mobility environments. The apparatus reduces out-of-band emissions, enhancing spectral containment and minimizing interference with adjacent frequency bands. Additionally, the use of OTFS modulation provides resilience against Doppler shifts, ensuring stable and reliable signal transmission in environments with rapid motion, such as vehicular or satellite communication systems. A combination of UFMC modulation and OTFS modulation allows for improved spectral efficiency, enhanced signal quality, and better overall system reliability.

[0011]

[0012] The received power is concentrated to improve the accuracy of channel estimation by focusing signal power on the key propagation paths, ensuring that the receiver, such as a base station, can detect the signal more effectively, even in environments with significant movements, such as high-speed vehicles or aircraft.

[0013] In another implementation form, the DR-UFMC apparatus is further configured to utilize OTFS modulation and to transmit the one or more DR-UFMC pilot signals (SDR-UFMC) utilizing a UFMC transmitter in place of an OFDM transmitter according to the OTFS modulation.

[0014] The combination of the OTFS modulation and the UFMC transmitter allows the apparatus to perform well in dynamic environments, ensuring high data throughput and low error rates in wireless communication systems.

[0015] In yet another implementation form, the DR-UFMC apparatus is further configured to generate the one or more DR-UFMC pilot signals (SDR-UFMC) as in

[0016]

[0017] By using the equation for DR-UFMC pilot signals (SDR_UFMC), the apparatus ensures efficient and robust signal transmission, minimizing errors during high-mobility communication.

[0018] In yet another implementation form, the DR-UFMC apparatus is further configured to generate one or more pilot signals for more than one transmission channel, wherein a set of one or more pilot signals is generated for each of the transmission channels, wherein the DR-UFMC apparatus is further configured to shift a pilot symbol of one set of one or more pilot signals to not overlap a pilot symbol of another set of one or more pilot signals.

[0019] By preventing the overlap, the apparatus improves the accuracy of channel estimation and minimizes interference between users, ensuring efficient communication across multiple transmission channels.

[0020] In another implementation form, the DR-UFMC apparatus is further configured to shift a guard zone of one set of one or more pilot signals to not overlap a guard zone of another set of one or more pilot signals.

[0021] The shifting of the guard zones prevents interference between adjacent pilot signals, ensuring clearer signal reception and more accurate channel estimation. By maintaining distinct guard zones, the apparatus avoids signal distortion and improves the clarity of the received data, especially in multi-channel or multi-user environments.

[0022] In another implementation form, the OTFS pilot is arranged in a (K x N) dimensional matrix, K representing the delay domain and N representing the Doppler domain, wherein a pilot symbol is placed in position (fcp, np) of this (K x lV)-matrix and wherein the pilot symbol is surrounded by guard symbols, At and An.

[0023] The (K x lV)-dimensional matrix arrangement ensures that the pilot signal is well-structured and resilient to Doppler effects, making it easier to detect at the receiver. The use of guard symbols \t- and \,(prevents overlapping and interference, leading to more reliable communication in high-mobility scenarios.

[0024] In another implementation form, the apparatus is a communications network terminal.

[0025] The communications network terminal enables the apparatus to function in mobile networks, providing enhanced performance in high-mobility environments where traditional modulation schemes might fail.

[0026] In another implementation form, the apparatus is a processing chip.

[0027] The processing chip allows for deployment in a variety of communication devices, providing the same robustness against Doppler effects while minimizing size and power consumption, ideal for portable or embedded systems.

[0028] In another aspect, the present disclosure provides a method for the DR-UFMC apparatus. The method comprises generating one or more DR-UFMC pilot signals (SDR-UFMC) based on Orthogonal Time Frequency Space, OTFS, pilot signals (SOTFS). Moreover, the OTFS, pilot signals (SOTFS) are distorted prior to transmission to account for DR-UFMC transmission distortion. The method achieves all the advantages and technical effects of the DR-UFMC apparatus of the present disclosure.

[0029] It is to be appreciated that all the aforementioned implementation forms can be combined.

[0030] It has to be noted that all devices, elements, circuitry, units, and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application, as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity that performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements or any kind of combination thereof. It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.

[0031] Additional aspects, advantages, features, and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.

[0033] Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:

[0034] FIG. 1 is a block diagram that illustrates a Doppler-resilient Universal Filtered Multicarrier (DR-UFMC) apparatus, in accordance with an embodiment of the present disclosure;

[0035] FIG. 2 is a diagram that illustrates a DR-UFMC transmitter-channel-receiver chain, in accordance with an embodiment of the present disclosure; and

[0036] FIG. 3 is a flow chart that illustrates a method for pilot signal generation in the DR-UFMC apparatus, in accordance with an embodiment of the present disclosure.

[0037] In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.

[0038] DETAILED DESCRIPTION OF EMBODIMENTS

[0039] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.

[0040] FIG. 1 is a block diagram that illustrates an apparatus for Doppler-resilient Universal Filtered Multicarrier (DR-UFMC), in accordance with an embodiment of the present disclosure. With reference to FIG. 1, there is shown a diagram 100 of DR-UFMC apparatus 102 (herein referred to as the apparatus 102). The apparatus 102 includes a processor 104 communicatively connected to a Universal Filtered Multicarrier (UFMC) transmitter 106, an Inverse Fast Fourier Transform (IFFT) unit 108, a Fast Fourier Transform (FFT) unit 110, a filter bank 112, a pilot signal generator 114, a transmission interface 116, a modulation unit 118, and a demodulation unit 120. There is provided the Doppler-resilient Universal Filtered Multicarrier (DR-UFMC) apparatus 102 that provides enhanced communication performance in wireless networks, particularly in high-mobility environments where Doppler shifts affect signal transmission. Moreover, the apparatus 102 utilizes Orthogonal Time Frequency Space (OTFS) modulation and includes a Universal Filtered Multicarrier (UFMC) transmitter in place of the traditional OFDM transmitter. The combination of the OTFS modulation and the UFMC transmitter allows the apparatus 102 to take advantage of the robustness of the OFTS modulation against the Doppler effects and the improved spectral containment provided by the UFMC transmitters due to subband filtering. The apparatus 102 is configured to provide a pilot signal scheme that can enable an effective, simple, and well-performing channel estimation algorithm for DR-UFMC modulation. Thus, the apparatus 102 provides a significant advancement in wireless communication by addressing the limitations of traditional modulation schemes and improving overall communication performance in high-mobility environments.

[0041] The processor 104 refers to a computational element that is operable to respond to and process instructions that drive the apparatus 102. The processor 104 may refer to one or more individual processors, processing devices, and various elements associated with a processing device that may be shared by other processing devices. Additionally, the one or more individual processors, processing devices, and elements are arranged in various architectures for responding to and processing the instructions that drive the apparatus 102. Examples of the processor 104 may include but are not limited to, a hardware processor, a digital signal processor (DSP), a microprocessor, a microcontroller, a complex instruction set computing (CISC) processor, an application-specific integrated circuit (ASIC) processor, a reduced instruction set (RISC) processor, a very long instruction word (VLIW) processor, a state machine, a data processing unit, a graphics processing unit (GPU), and other processors or control circuitry.

[0042] The Universal Filtered Multicarrier (UFMC) transmitter 106 refers to an electronic device used in the UFMC modulation that is responsible for transmitting signals using UFMC modulation. In an implementation, the UFMC transmitter 106 is configured to apply subband filtering to groups of subcarriers, which improves spectral containment by reducing out-of-band emissions (OOB), thereby minimizing interference with adjacent frequency bands and allowing for more efficient use of the available spectrum. In another implementation, the UFMC transmitter 106 is further configured to integrate with the OTFS modulation scheme and provide resilience against Doppler shifts. Examples of the UFMC transmitter 106 may include but are not limited to, communication modules within wireless base stations, user equipment in mobile devices, and network terminals in vehicular communication systems. Such modules and hardware devices can be implemented in a variety of hardware configurations, such as digital signal processors (DSPs), application-specific integrated circuits (ASICs), or field-programmable gate arrays (FPGAs), each designed to handle UFMC modulation and subband filtering efficiently.

[0043] The Inverse Fast Fourier Transform (IFFT) unit 108 refers to an electronic component typically used in digital communications that is responsible for converting the signal from the frequency domain into the time domain, which is necessary for signal transmission over a wireless channel. In multicarrier modulation such as UFMC modulation, data is typically processed and manipulated in the frequency domain, where subcarriers are assigned specific frequency slots. The IFFT unit 108 is configured to take the frequency-domain data and perform an inverse transformation, converting the signal into a time-domain waveform, which is then filtered and transmitted to a receiver. Thus, the IFFT unit 108 ensures that the signal retains its structure and minimizes distortion during the conversion process by creating the time-continuous signal that will be transmitted by an antenna. Examples of the IFFT module 108 may include but are not limited to, hardware implementations within digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and the like. The Fast Fourier Transform (FFT) unit 110 refers to an electronic component typically used in digital communications that is responsible for converting the received signal from the time domain to the frequency domain. In multicarrier modulation schemes such as UFMC modulation scheme, the signals are often processed in the frequency domain for efficient manipulation of subcarriers and spectral properties. The FFT unit 110 takes the time-domain signal received through the antenna as input and transforms the time-domain signal into the frequency-domain signal, which involves various mathematical operations such as sampling, and other operations. Examples of the FFT unit 110 may include but are not limited to, hardware implementations within digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and the like.

[0044] The filter bank 112 refers to a set of digital filters used to process different sub-bands of the signal in Universal Filtered Multicarrier (UFMC) modulation. In the UFMC modulation, subcarriers are grouped into sub-bands, and each sub-band is passed through a corresponding filter in the filter bank 112. The filters, implemented as Finite Impulse Response (FIR) filters, are designed to improve spectral containment and reduce out-of-band emissions, allowing for more efficient spectrum usage. In an implementation, the filter bank 112 is configured to process the sub-bands of the signal in both the frequency domains and the time domains, facilitating the conversion between the OTFS and the DR-UFMC modulations. Examples of the filter bank 112 include hardware implementations in digital signal processors (DSPs), application-specific integrated circuits (ASICs), or field-programmable gate arrays (FPGAs) designed to handle UFMC sub-band filtering.

[0045] The pilot signal generator 114 refers to a component responsible for generating pilot signals that are used for channel estimation in the DR-UFMC modulation. In an implementation, the pilot signal generator 114 is configured to generate pre-distorted pilot signals that account for transmission distortion due to Doppler shifts. The pilot signals are designed to enhance the accuracy of channel estimation, even in high-mobility environments. The pilot signal generator 114 creates a pre-distorted pilot signal matrix based on the OTFS pilot signal, ensuring that the receiver perceives the same pattern as with traditional OTFS modulation, thus improving the overall performance of the apparatus 102. Examples of the pilot signal generator 114 include hardware components integrated into DSPs or ASICs within communication systems.

[0046] The transmission interface 116 refers to a hardware module responsible for managing the transmission of the pilot signals from the apparatus 100 to external devices, such as base stations or user equipment in a wireless network. The transmission interface 116 handles the wireless link, ensuring that the pilot signals are transmitted efficiently and with minimal distortion. The transmission interface 116 supports communication in environments where the Doppler shifts are significant, such as highspeed vehicular networks or satellite communications. The transmission interface 116 may include radio frequency (RF) components, antennas, and other communication modules necessary for transmitting the UFMC-modulated signals. Examples of the transmission interface 116 include RF transmitters, network interface cards in mobile devices, and the like.

[0047] The modulation unit 118 refers to a component responsible for modulating data using the DR-UFMC modulation scheme. In an implementation, the modulation unit 118 combines OTFS modulation with the UFMC modulation to create a signal resilient to the Doppler shifts. The modulation unit 118 processes data through a two-dimensional IFFT and then applies UFMC subband filtering, ensuring the data is modulated efficiently for transmission in high-mobility environments. Examples of the modulation unit 118 include implementations in DSPs, FPGAs, or ASICs used in wireless communication devices such as user equipment or base stations.

[0048] The demodulation unit 120 refers to a component responsible for converting received DR-UFMC signals into data by reversing the modulation. In an implementation, the demodulation unit 120 applies Fast Fourier Transform (FFT) and UFMC demodulation techniques to the received signals, converting the DR-UFMC signals from the time domain to the frequency domain and then processing the DR-UFMC signals to recover original data. The demodulation unit 120 ensures that the DR-UFMC signals distorted by the Doppler shifts during transmission are corrected and the data can be accurately decoded. Examples of the demodulation unit 120 include hardware modules in DSPs or FPGAs within wireless communication systems. In an implementation, the apparatus 102 includes a memory. The memory may include suitable logic, circuitry, interfaces and / or code that is configured to store machine code and / or instructions executable by the processor 104. Examples of implementation of the memory may include, but are not limited to, an Electrically Erasable Programmable Read-Only Memory (EEPROM), Random Access Memory (RAM), Read Only Memory (ROM), Hard Disk Drive (HDD), Flash memory, a Secure Digital (SD) card, Solid-State Drive (SSD), a computer readable storage medium, and / or CPU cache memory. The memory may store data matrices, pilot signal patterns (e.g., OTFS and DR-UFMC pilot matrices), and other necessary software instructions. The memory would also support oversampling factors and perform FFT / IFFT operations.

[0049] In operation, the apparatus 102 is configured to generate one or more DR-UFMC pilot signals (SDR_UFMC) based on OTFS pilot signals (SOTFS). The one or more DR-UFMC pilot signals (SDR_UFMC) are generated by pre-distorting the OTFS pilot signals before transmission to account for the distortion caused by the DR-UFMC modulation scheme. In an implementation, the one or more DR-UFMC pilot signals (SDR_UFMC) are generated by taking the OTFS pilot signal (SOTFS), represented as a matrix of the OTFS pilot signals (SOTFS), and modifying the OTFS pilot signals (SOTFS) using a pre-distortion algorithm embedded in the pilot signal generator 114. The pre-distorted SOTFSis then transmitted through the UFMC transmitter 106, which applies subband filtering to enhance spectral containment. The one or more DR-UFMC pilot signals (SDR_UFMC) are generated to ensure that the received signal in the Doppler-delay domain (DD domain) is less affected by the Doppler shifts, which occur in high-mobility environments. By pre-distorting the SOTFS, the apparatus 102 mitigates transmission distortions, allowing for more accurate channel estimation and improving the reliability of communication in scenarios such as vehicular or satellite communication.

[0050] In accordance with an embodiment, the apparatus 102 is further configured to generate the DR-UFMC pilot signals (SDR_UFMC) in a way that concentrates a received power around the delays and the Doppler shifts associated with the propagation paths of a channel over which the DR-UFMC pilot signals (SDR_UFMC) are transmitted. The received power is concentrated by leveraging the pre-distortion algorithm / mechanism in the pilot signal generator 114, which alters the OTFS pilot signal (SOTFS) to compensate for channel characteristics like delays and the Doppler shifts. The filter bank 112 then applies sub-band filtering to refine the OTFS pilot signal (SOTFS) for transmission, ensuring that it is structured to concentrate power in areas corresponding to the relevant Doppler shifts. The received power is concentrated to improve the accuracy of channel estimation by focusing signal power on the key propagation paths, ensuring that the receiver, such as a base station, can detect the signal more effectively, even in environments with significant movements, such as high-speed vehicles or aircraft. Furthermore, concentrating signal power on relevant delays and the Doppler shifts minimizes noise and enhances communication reliability.

[0051]

[0052] In accordance with an embodiment, the DR-UFMC apparatus is further configured to generate the one or more DR-UFMC pilot signals (SDR_UFMC) as in equation:

[0053] SDR-UFMC=FKPUFMCWK, OS FK SOTFS, where,

[0054] Os is an integer representing the oversampling factor, I

[0055] 8

[0056] SOTFSis a (K x \j-diinensional matrix of the transmitted symbols in case of OTFS modulation, where K represents the dimensionality of the delay domain and N represents the dimensionality of the Doppler domain (number of subcarriers), SDR-UFMC is a(X’X V)-dimensional matrix of the transmitted symbols in case of DR-UFMC modulation,

[0057] WK,Ois (K x KOs)-dimensional matrix representing the oversampled FFT,

[0058] FKis (K x K)-dimensional FFT matrix whose (m,n)-th element is written as

[0059]

[0060] PUFMCis a (K x K)-dimensional matrix describing the UFMC processing, i.e. the combination of the per-subband IFFT and subband filtering.

[0061] In an implementation, the sDR_UFMCis generated by the FFT unit 110 and the pilot signal generator 114. TheFFT unit 110 applies the necessary Fast Fourier Transform to generate the FK and WK, OSdimensional matrices. The pilot signal generator 114 then multiplies these matrices with the SOTFSand applies the UFMC processing matrix to create the pre-distorted pilot signal. The apparatus 102 ensures that the sDR-UFMCis adapted to the UFMC modulation scheme while maintaining the same performance as OTFS modulation in terms of Doppler resilience. By using the equation, the apparatus 102 ensures efficient and robust signal transmission, minimizing errors during high-mobility communication.

[0062] In another implementation, the apparatus 102 uses an oversampling factor (Os) greater than 1 to simulate higher granularity in multicarrier modulation, improving the resolution and precision of signal transmission. In such an implementation, the pilot signal generator 114 and the FFT unit 110 are configured to handle the oversampled FFT, which increases the size of the frequency grid, providing finer detail in the signal representation. For example, Os= 8 may be used to divide each subcarrier further for more precise modulation. The oversampling factor is used to more accurately model the signal and account for Doppler shifts, reducing noise and interference in high-mobility environments. The oversampling factor enables more detailed processing of each sub-band, improving the fidelity of the transmitted signals.

[0063] Further, the matrix WK, OS which is (K x Kos)-dimensional matrix represents the oversampled FFT. The (l,m)thentry of the matrix WK, Ois expressed as:

[0064]

[0065] In yet another implementation, PUFMC represents a (K x K)-dimensional matrix that describes the UFMC processing. In such an implementation, the apparatus 102 splits K subcarriers into B disjoint sub-bands of D subcarriers each so that K=BD, allowing each subband to be processed individually through filtering. The filter bank 112 applies passband FIR filtering to each subband, effectively isolating groups of subcarriers and improving spectral containment. For example, if there are 64 subcarriers and 4 subbands, each subband would contain 16 subcarriers. The structure of the PUFMC matrix allows for better control over out-of-band emissions, reducing interference between adjacent subbands and improving spectral efficiency. The mathematical expression of the PUFMC matrix can be expressed by adding few notations: Let ®

[0066]

[0067] be the L-dimensional vector representing the prototype low-pass filter and let

[0068]

[0069] denote the normalized frequency shift of the filter tuned to the bthsubband.

[0070]

[0071] dimensional matrix describing the discrete convolution operation with the filtert“’, whose f th ' element is defined as:

[0072]

[0073] Additionally, the selection matrices Pi, i = 0,..., B-1 are defined as:

[0074] Pi= diag(...) i = 0,..., B - 1.

[0075]

[0076] Based on the above notations, the present disclosure define the (K+L-1) x K matrix as:

[0077]

[0078] Finally, the matrix PUFMCis a K x K dimensional matrix obtained by removing the last L — 1 rows from P̃UFMC.

[0079] Thus, the apparatus 102 applies the prototype low-pass filter to each subband, ensuring that the signal maintains its integrity across the frequency spectrum. Additionally, frequency shifts are applied to tune each subband to its corresponding frequency band. The filter bank 112 implements the L-dimensional low-pass filter and adjusts the subbands using frequency shifts, defined mathematically by the Toeplitz matrix for discrete convolution with the filter, allowing precise control over the signal's spectral properties. The L-dimensional low-pass filter is implemented to reduce interference between subbands and to ensure that the filtered signal retains its spectral containment. The frequency shift ensures that the subbands are properly aligned within the transmission spectrum.

[0080] In another implementation, the apparatus 102 uses a pilot design codebook that generates pre-distorted pilot signals for transmission. The pilot signal generator 114 computes the pilot signal matrix based on the equation sDR-UFMC= FKPUFMC WK, OS FK SOTFS, adjusting the signal structure to mimic the OTFS pilot pattern at the receiver. The codebook ensures that the pilot signal is modified according to the DR-UFMC modulation scheme. The apparatus 102 uses the pilot design codebook to allow for channel estimation using existing OTFS methods, while adapting the signal for DR-UFMC modulation, ensuring compatibility with both modulation schemes.

[0081] SOTFS

[0082] In such an implementation, the pilot design codebook is defined for DR-UFMC, assuming that SOTFScontains the pilot SOTFS

[0083] used in OTFS modulation. Otherwise stated, is an all-zero matrix containing only one symbol equal to 1 at the centre. In order to ensure that the pilot used in DR-UFMC produces at the receiver the same patterns as that produced in the case of OTFS, it is ensured that the pilot pattern matrix fulfils the following relation:

[0084] T? aOTFSpH > P -p QDR-UFMCT H

[0085] K, O.,kK T N — MPMC K T N

[0086] From the equation, the present disclosure discloses the following expression for the pilot signal to be used in DR-UFMC:

[0087]

[0088] The above expression is to be properly scaled in order to ensure that the pilot signal is transmitted with the desired level of power. The matrix 1 shows a representation of the pilot pattern for OTFS (i.e. just one non-zero symbol) for a 64 x 16 grid:

[0089]

[0090] Matrix 1

[0091] The matrix 2 shows the disclosed pilot pattern for DR-UFMC:

[0092]

[0093] Matrix 2 The effect of the pilot pre-distortion with many non-zero symbols with respect to the previous case of the OTFS pilot where only one symbol was non-zero. The pre-distorted pilot has the capability to produce at the receiver in the DD grid a pattern similar to that observed in case of OTFS modulation and that permits the use of channel estimation methods developed for OTFS.

[0094] In another embodiment, the pilot signal pattern of the apparatus 102 is generalized to other modulation schemes like Generalized-Frequency Division Multiplexing (GFDM) and Filter Bank Multicarrier (FBMC). In an implementation, the pilot signal generator 114 and the modulation unit 118 are adapted to use the pilot pre-distortion and filtering techniques with modulation schemes that include a two-dimensional IFFT block, as in GFDM and FBMC. The pilot signal pattern of the apparatus 102 is generalized to allow the apparatus 102 to be applied across various modulation techniques, enhancing its versatility and ensuring better performance in a wider range of communication systems.

[0095] In accordance with an embodiment, the apparatus 102 is further configured to generate one or more pilot signals for more than one transmission channel, wherein a set of one or more pilot signals is generated for each of the transmission channels, wherein the apparatus 102 is further configured to shift a pilot symbol of one set of one or more pilot signals to not overlap a pilot symbol of another set of one or more pilot signals. In an implementation, the pilot signal generator 114 generates distinct pilot signal patterns for each of the transmission channels. The pilot signal generator 114 shifts the pilot symbols in the delay-Doppler grid such that the pilot symbols do not interfere with one another, ensuring that each of the transmission channels has a clear and distinct set of pilot signals. The non-overlapping of the pilot symbols is essential for multi-channel communication in scenarios where multiple users or devices share the same frequency band. By preventing the overlap, the apparatus 102 improves the accuracy of channel estimation and minimizes interference between users, ensuring efficient communication across multiple transmission channels.

[0096] In another embodiment, the apparatus 102 multiplexes multiple users’ pilot signals by assigning distinct pilot patterns to each user and separating the associated signals in the spatial domain. Using multiple antennas and spatial domain processing, the apparatus 102 assigns different pilot signals to each user. The pilot signal generator 114 shifts pilot symbols in the delay-Doppler domain to prevent overlap between users’ signals. The multiplexing of the multiple users’ pilot signals is performed to allow for multi-user communication in the same frequency band, enabling the use of multi-user MIMO (Multiple Input, Multiple Output) systems in environments like mobile or satellite networks.

[0097] In accordance with an embodiment, the apparatus 102 is further configured to shift a guard zone of one set of one or more pilot signals to not overlap a guard zone of another set of one or more pilot signals. In an implementation, the pilot signal generator 114 is responsible for positioning the guard zones around each pilot symbol. The guard zones are shifted in the delay-Doppler grid to ensure that the guard zones remain distinct and non-overlapping. The shifting process is coordinated with the modulation unit 118 and the filter bank 112 to ensure the correct placement of the guard zones.

[0098] The shifting of the guard zones prevents interference between adjacent pilot signals, ensuring clearer signal reception and more accurate channel estimation. By maintaining distinct guard zones, the apparatus 102 avoids signal distortion and improves the clarity of the received data, especially in multi-channel or multi-user environments.

[0099] In accordance with an embodiment, the OTFS pilot is arranged in a (K x N) dimensional matrix, K representing the delay domain and N representing the Doppler domain, wherein a pilot symbol is placed in position (fcp, np) of this (K x lV)-matrix and wherein the pilot symbol is surrounded by guard symbols, Ak and An.. In an implementation, the dimensional matrix arrangement is handled by the pilot signal generator 114, which places the pilot symbols at specific positions (fcp, np) in the (K x lV)-dimensional matrix. The surrounding guard symbols \t- and An are managed to provide adequate spacing, reducing interference. The (K x lV)-dimensional matrix is processed through the modulation unit 118 for transmission via the UFMC transmitter 106. The (K x lV)-dimensional matrix arrangement ensures that the pilot signal is well-structured and resilient to Doppler effects, making it easier to detect at the receiver. The use of guard symbols At and \,(prevents overlapping and interference, leading to more reliable communication in high-mobility scenarios.

[0100] In accordance with an embodiment, the apparatus 102 is a communications network terminal. The communications network terminal may include user equipment in mobile devices, wireless base stations, vehicular communication systems, and the like. The communications network terminal involves the components, such as the UFMC transmitter 106, the processor 104, the pilot signal generator 114, and the FFT unit 110, to perform the necessary modulation and signal processing tasks. The communications network terminal enables the apparatus 102 to function in mobile networks, providing enhanced performance in high-mobility environments where traditional modulation schemes might fail.

[0101] In accordance with an embodiment, the apparatus 102 is a processing chip, designed to handle the computational tasks required for DR-UFMC modulation and pilot signal generation. The UFMC transmitter 106, the processor 104, the pilot signal generator 114, and the FFT unit 110 are integrated into a hardware architecture, such as an ASIC or FPGA, enabling high-performance signal processing within the compact and efficient processing chip. The processing chip allows for deployment in a variety of communication devices, providing the same robustness against Doppler effects while minimizing size and power consumption, ideal for portable or embedded systems.

[0102] FIG. 2 is a diagram that illustrates a DR-UFMC transmitter-channel-receiver chain, in accordance with an embodiment of the present disclosure. FIG. 2 is described in conjunction with elements from FIG. 1. With reference to FIG. 2, there is shown a DR-UFMC transmitter-channel-receiver chain 200. The DR-UFMC transmitter-channel-receiver chain 200 comprises DR Preprocessing Stage 202, UFMC Modulator Stage 204, UFMC Demodulator Stage 206, and DR Post-processing Stage 208. At the DR Pre-processing Stage 202, the DR-UFMC transmitter-channel-receiver chain 200 begins with an input signal matrix XDD(delay-Doppler domain signal) with K x N dimensions received and processed by the IFFT unit 108 (also referred to as Inverse Symplectic Finite Fourier Transform (ISFFT) unit). The IFFT unit 108 converts the input signal matrix XDDfrom the delay-Doppler domain into the frequency-time domain, generating XFTwith K xN dimensions. Such a conversion is performed to the Doppler-resilient characteristics of the apparatus 102, as it ensures robustness against Doppler effects by manipulating the input signal in the delay-Doppler grid.

[0103] At the UFMC Modulator Stage 204, once the signal is in the frequency domain, the UFMC transmitter 106 modulates the input signal by splitting it into B subbands and applying oversampled IFFT 210 to each subband individually. The subband filtering is performed using the filter bank 112, which provides enhanced spectral containment by isolating the subbands and reducing out-of-band emissions. The subbands are then summed 212 to create Si,..., SB, which are the filtered and modulated signals represented as K Os + L - 1 x N. The filtered and modulated signals are then arranged in an overlapping manner with the P / S (parallel-to-serial) conversion 214 and are transmitted as s, the time-domain signal. The UFMC modulation is performed for improving spectral efficiency and minimizing interference in adjacent frequency bands.

[0104] The modulated signal s is transmitted through a wireless channel, which is assumed to be time-varying, especially in high-mobility environments. The wireless channel introduces noise, delay, Doppler shifts, and other distortions to the signal, represented by r, the received signal.

[0105] At the UFMC Demodulator Stage 206, the received signal r undergoes a Serial-to-Parallel (S / P) conversion 216 to prepare the received signal r for further processing in the demodulation unit 120. In the UFMC Demodulator Stage 206, the last symbols from the time-domain waveform are removed, and the remaining symbols are processed by the oversampled Fast Fourier Transform 218. Such processing brings the signal back from the time domain to the frequency domain YFT, and the subband structure is reconstructed for further processing.

[0106] At the DR Post-processing Stage 208, after the UFMC demodulation, the frequency-domain signal YFTis passed through the FFT unit 110 (also referred to as Symplectic Finite Fourier Transform (SFFT)) to revert the frequency-domain signal YFTfrom the frequency-time domain back to the delay-Doppler domain, yielding YDD. A Symbol Detection unit 220 then performs channel estimation and symbol detection on the processed signal YDD, retrieving the original data from the distorted received signal.

[0107] The pilot codebook is superimposed on the data during the transmission process. The pilot signals, generated by the pilot signal generator 114, are embedded into the input signal matrix XDDduring the DR Pre-processing Stage 202. The pre-distorted pilot signals allow the receiver to perform accurate channel estimation, compensating for the effects of the time-varying channel, and enabling efficient symbol detection at the receiver.

[0108] FIG. 3 is a flow chart that illustrates a method for pilot signal generation in the DR-UFMC apparatus, in accordance with an embodiment of the present disclosure. FIG. 3 is described in conjunction with elements from FIGs. 1 and 2. With reference to FIG. 3, there is shown a flowchart of a method 300 for operating the apparatus 102. The method 300 includes a step 302. At step 302, the method 300 includes generating one or more DR-UFMC pilot signals (SDR_UFMC) based on OTFS, pilot signals (SOTFS), wherein the OTFS, pilot signals (SOTFS) are distorted prior to transmission to account for DR-UFMC transmission distortion. In an implementation, the one or more DR-UFMC pilot signals (SDR_UFMC) are generated by taking the OTFS pilot signal (SOTFS), represented as a matrix of the OTFS pilot signals (SOTFS), and modifying the OTFS pilot signals (SOTFS) using a pre-distortion algorithm embedded in the pilot signal generator 114. The pre-distorted SOTFSis then transmitted through the UFMC transmitter 106, which applies sub-band filtering to enhance spectral containment. The one or more DR-UFMC pilot signals (SDR_UFMC) are generated to ensure that the received signal in the Doppler-delay domain (DD domain) is less affected by the Doppler shifts, which occur in high-mobility environments. By pre-distorting the SOTFS, the apparatus 102 mitigates transmission distortions, allowing for more accurate channel estimation and improving the reliability of communication in scenarios such as vehicular or satellite communication.

[0109] The step 302 is only illustrative, and other alternatives can also be provided where one or more steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein.

[0110] There is further provided, a computer program product comprising program instructions for performing the method 300 when executed by the apparatus 102. The computer program product is implemented as an algorithm, embedded in a software stored in a non-transitory computer-readable storage medium. The non-transitory computer-readable storage means may include but are not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. Examples of implementation of computer-readable storage medium, but are not limited to, Electrically Erasable Programmable Read-Only Memory (EEPROM), Random Access Memory (RAM), Read Only Memory (ROM), Hard Disk Drive (HDD), Flash memory, a Secure Digital (SD) card, Solid-State Drive (SSD), a computer-readable storage medium, and / or CPU cache memory.

[0111] The apparatus 102 designed for Doppler-resilient Universal Filtered Multicarrier (DR-UFMC) modulation is useful for wireless communication in high-mobility environments. The apparatus 102 significantly mitigates the effects of Doppler shifts, which are a common challenge in environments where there is rapid relative motion between the transmitter and receiver, such as vehicular communications, satellite links, or high-speed rail systems. The use of OTFS modulation, integrated with the UFMC, ensures that apparatus 102 retains its performance even under conditions where traditional modulation schemes, such as OFDM, would suffer from severe performance degradation due to time-frequency selective fading.

[0112] The apparatus utilizes the UFMC transmitter 106, which applies subband filtering through the filter bank 112, offering improved spectral containment, reducing out-of-band emissions (OOB), minimising interference with neighbouring frequency bands, and increasing spectral efficiency. The introduction of subband oversampling further enhances spectral localization and minimizes distortions caused by Doppler effects. By breaking down the signal into subbands, the apparatus 102 can better manage interference and provide more precise control over signal transmission.

[0113] The pilot signal generator 114 of the apparatus 102 allows for the generation of pilot signals that are superimposed onto the data. The pilot signals are crucial for channel estimation in the DR-UFMC environment. The ability to perform effective channel estimation using the pilot signals improves the accuracy of the received signal's interpretation, leading to more reliable data recovery, which is important in high-mobility scenarios where the wireless channel can change rapidly due to varying Doppler shifts and multipath effects.

[0114] Moreover, the apparatus 102 benefits from the IFFT unit 108 in the transmission chain and the FFT unit 110 in the receiver chain. The IFFT unit 108 and the FFT unit 110 ensure that the signal can be processed efficiently in the delay-Doppler domain, making the signals more resilient to time-varying channel conditions, enhancing communication performance, with a reduced error rate and greater robustness in terms of maintaining signal integrity.

[0115] Finally, the apparatus 102 is designed to handle real-world wireless environments where the communication channel is not static, thereby improving overall performance, reliability, and efficiency in both uplink (user equipment to base station) and downlink communication scenarios. Such an improvement is especially evident in terms of better spectral utilization, reduced interference, and increased data throughput, which are required for modem wireless communication systems such as 5G and beyond.

[0116] Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe, and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be constmed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.

Claims

CLAIMS1. A Doppler-resilient Universal Filtered Multicarrier Modulation, DR-UFMC, apparatus (102) configured to:generate one or more DR-UFMC pilot signals (SDR-UFMC) based on Orthogonal Time Frequency Space, OTFS, pilot signals (SOTFS), wherein the OTFS, pilot signals (SOTFS) are distorted prior to transmission to account for transmission distortion from the DR-UFMC modulation scheme.

2. The DR-UFMC apparatus (102) according to claim 1, wherein the DR-UFMC apparatus (102) is further configured to generate the one or more DR-UFMC pilot signals (SDR-UFMC) to concentrate a received power around delays and Doppler shifts associated to the propagation paths of a channel over which the one or more DR-UFMC pilot signals (SDR-UFMC) are transmitted.

3. The DR-UFMC apparatus (102) according to claim 1 or 2, wherein the DR-UFMC apparatus (102) is further configured to utilize OTFS modulation and to transmit the one or more DR-UFMC pilot signals (SDR-UFMC) utilizing a UFMC transmitter in place of an OFDM transmitter according to the OTFS modulation.

4. The DR-UFMC apparatus (102) according to any preceding claim, wherein the DR-UFMC apparatus (102) is further configured to generate the one or more DR-UFMC pilot signals (SDR-UFMC) as inSDR-UFMC=FKPUFMCWK, OS FK SOTFS, where,PUFMC is a (K x 0-dimensional matrix describing the UFMC processing, i.e. the combination of the per-subband IFFT and subband filtering.

5. The DR-UFMC apparatus (102) according to any preceding claim, wherein the DR-UFMC apparatus (102) is further configured to generate one or more pilot signals for more than one transmission channel, wherein a set of one or more pilot signals is generated for each of the transmission channels, wherein the DR-UFMC apparatus (102) is further configured to:shift a pilot symbol of one set of one or more pilot signals to not overlap a pilot symbol of another set of one or more pilot signals.

6. The DR-UFMC apparatus (102) according to claim 5, wherein the DR-UFMC apparatus (102) is further configured to:shift a guard zone of one set of one or more pilot signals to not overlap a guard zone of another set of one or more pilot signals.

8. The DR-UFMC apparatus (102) according to any of claims 1 to 7, wherein the apparatus (102) is a communications network terminal.

9. The DR-UFMC apparatus (102) according to any of claims 1 to 7, wherein the apparatus (102) is a processing chip.

10. A method (300) for a DR-UFMC apparatus, the method comprising generate one or more DR-UFMC pilot signals (SDR_UFMC) based on Orthogonal Time Frequency Space, OTFS, pilot signals (SOTFS), wherein the OTFS, pilot signals (SOTFS) are distorted prior to transmission to account for DR-UFMC transmission distortion.

11. The method (300) according to claim 10, further comprises: generate the one or more DR-UFMC pilot signals (SDR_UFMC) to concentrate a received power around delays and Doppler shifts associated to the propagation paths of a channel over which the one or more DR-UFMC pilot signals (SDR-UFMC) are transmitted.

12. The method (300) according to claim 10 or 11, further comprises: utilize OTFS modulation and to transmit the one or more DR-UFMC pilot signals (SDR-UFMC) utilizing a UFMC transmitter in place of an OFDM transmitter according to the OTFS modulation.

13. The method (300) according to any one of claims 10 to 12, further comprises: generate the one or more DR-UFMC pilot signals (SDR-UFMC) as inSDR-UFMC=FKPUFMCWK, OS FK SOTFS, where,Os is an integer representing the oversampling factor,SOTFSis a (K x V)-dimensional matrix of the transmitted symbols in case of OTFS modulation, where K represents the dimensionality of the delay domain and N represents the dimensionality of the Doppler domain (number of subcarriers) SDR-UFMC is a(X’X \)-dimensional matrix of the transmitted symbols in case of DR-UFMC modulation, WK / A is (K x K O0-dimensional matrix representing the oversampled FFT,FKIS (K x 70-dimensional FFT matrix whose (m,w)-th element is written asPuFMcis a (K x 70-dimensional matrix describing the UFMC processing, i.e. the combination of the per-subband IFFT and subband filtering.

14. The method (300) according to any one of claims 10 to 13, further comprises: generate one or more pilot signals for more than one transmission channel, wherein a set of one or more pilot signals is generated for each of the transmission channels, andshift a pilot symbol of one set of one or more pilot signals to not overlap a pilot symbol of another set of one or more pilot signals.

15. A computer program product comprising program instructions for performing the method (300) according to any one of claims 10 to 14, when executed by one or more processors in a DR-UFMC system.

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