A device and method for generating an affine frequency division multiplexing signal

Abstract

The disclosure relates to sensing and / or communication in a network. The disclosure proposes a wireless transmitter, a network device, and corresponding methods for operating said devices. The wireless transmitter is configured to obtain M symbols, precode the M symbols based on an M-point discrete Fourier-based transform, and generate an oversampled first set of chirp carriers based on Np pilot sequences and the M precoded symbols. Further, the wireless transmitter is configured generate an affine frequency division multiplexing signal comprising the first set of chirp carriers that are orthogonal in a discrete affine Fourier transform domain.

Description

[0001] A DEVICE AND METHOD FOR GENERATING AN AFFINE FREQUENCY DIVISION MULTIPLEXING SIGNAL

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to sensing and / or communication in a network. The disclosure proposes a wireless transmitter, a network device, a corresponding method for operating the wireless transmitter, and a corresponding method for operating the network device. The wireless transmitter generates an affine frequency division multiplexing signal in a new kind of way.

[0004] BACKGROUND

[0005] In the context of integrated sensing and communication (ISAC) systems, nonlinear distortions introduced by practical power amplifiers, for example, those used in mobile terminals and high-frequency devices, are becoming a matter of significant importance. These distortions, which occur when the input power level exceeds a certain threshold, significantly compromise the quality of the transmitted signal To mitigate this, waveforms with low peak-to-average power ratio (PAPR) values may be employed. This requirement is even more critical for the sensing component of ISAC systems, where optimal PAPR performance is more important A low PAPR ensures that the sensing signal can be transmitted with sufficient power to overcome the two-way attenuation caused by echoes from targets, thereby enhancing the system's overall efficiency and reliability in both its communications and sensing functions

[0006] Affine frequency division multiplexing (AFDM) has emerged as potential waveform candidate for ISAC due to its multi-chirp nature. In AFDM signals, each individual chirp carrier is distinguished by its excellent PAPR performance, making it an ideal candidate for a sensing pilot in ISAC systems. However, an inherent characteristic of AFDM chirp is its full-bandwidth occupation, BW = — , with Tsdenoting the sample period for signal generation This full-bandwidth utilization poses

[0007] A challenges for efficiently managing bandwidth

[0008] Zadoff-Chu (Z-C) sequences, with their chirp-like properties, are recognized for their excellent PAPR and are utilized in generating certain uplink reference signals within Third Generation Partnership Project (3GPP) Long-Term Evolution (LTE) and Fifth Generation (5G) standards. These sequences hold potential for sensing applications due to their inherent chirp-like characteristics The integration of Z-C sequences into orthogonal frequency division multiplexing (OFDM) systems is facilitated by their Discrete Fourier Transform (DFT), which is a scaled conjugate version of the original sequence, adjusted by a constant factor. This mathematical relationship simplifies their implementation within OFDM's framework However, Z- C sequences can only be multiplexed with communication signals either in time or frequency domains, a limitation which can result in diminished sensing performance More critically, such multiplexing inevitably compromises the desirable PAPR properties of the Z-C sequences. This degradation is a key challenge, as the maintenance of good PAPR is vital for ensuring signal integrity and efficient sensing operations in integrated communication and sensing systems.

[0009] Frequency modulated continuous wave (FMCW) signals are distinguished by their notably low PAPR, making them excellent for sensing applications. The advantage of FMCW signals is their consistent power output, which ensures reliable sensing operations. Nevertheless, multiplexing these signals with data for communication purposes remains a complex challenge, and existing methods have only achieved suboptimal results. For instance, the integration of frequency shift keying (FSK) with FMCW enables joint communication and sensing, which allows data transmission within FMCW systems with only low bit- rate. SUMMARY

[0010] In view of the above, an objective of this disclosure is to provide an improved AFDM signal Another objective is to provide an AFDM signal that can be generated with any arbitrary sample rate that exceeds the bandwidth. Another objective is to reduce the complexity of the transmitter that generates an AFDM signal. Another objective is to adapt the above for any (c) AFDM configuration and provide seamless multiplexing with sensing pilots

[0011] These and other objectives are achieved by this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

[0012] The solutions of this disclosure are based on the following considerations.

[0013] Moreover, when single-chirp sensing pilots are transmitted along with data carrying chirp carriers from the same antenna, the good PAPR property of the single chirps might undergo degradation. The critical question then becomes how to maintain this low PAPR benefit of the sensing pilot signal while integrating a data / control communications signal within the ISAC intervals

[0014] Thus, in this disclosure AFDM pilot and communications generation schemes may be designed with low PAPR and with a BW disconnected from the sample rate of the DAC

[0015] An AFDM-based pilot and data signal may be flexibly generated with the following features:

[0016] • The bandwidth of the sensing and communications signal can be any arbitrary value below the sample rate.

[0017] • It should be possible for the signal generation and detection to be implemented with low complexity.

[0018] • It should be possible to generate mixed pilot and communications signals with low PAPR

[0019] A first aspect of this disclosure provides a wireless transmitter, the wireless transmitter is configured to: obtain M symbols, wherein M is an integer equal to or larger than 1; precode the M symbols based on a M-point discrete Fourier-based transform (DFBT) or precode the M symbols after spectrally shaping based on a DFBT, generate an oversampled first set of chirp carriers based on Nppilot sequences and the M precoded symbols, wherein the first set of chirp carriers is oversampled by a factor K / N, wherein N is an integer larger than a sum of M and Np, wherein Npis an integer larger than or equal to 1, wherein K is an integer larger than N; and generate an affine frequency division multiplexing (AFDM) signal comprising the first set of chirp earners that are orthogonal in a discrete affine Fourier transform (DAFT) domain.

[0020] Thus, a bandwidth (BW) of the AFDM signal can be a factor K / N below the sample rate and / or low PAPR may be achieved

[0021] For example, the M-point DFBT may be applied to the M symbols

[0022] The AFDM signal may have a chirped single-carrier component. The wireless transmiter may be an ISAC device.

[0023] The wireless transmitter may obtain the Nppilot sequences.

[0024] The first set of chirp carriers are orthogonal in a DAFT domain.

[0025] The M-point DFBT may be a transform that generates the chirped single carrier signal. The M-point DFBT may be an M-point chirped Fourier processing.

[0026] The wireless transmiter may be or comprise an ISAC signal generator module

[0027] In an implementation form of the first aspect, the wireless transmiter is configured to: generate the oversampled first set of chirp carriers based on the Nppilot sequences and a K-point inverse discrete Fourier transform (IDFT) of at least the M precoded symbols.

[0028] For example, the K-point IDFT may be applied to the M precoded symbols.

[0029] The Nppilot sequences may be oversampled. For example, the Nppilot sequences may be K-long

[0030] In a further implementation form of the first aspect, the M-point DFBT is a M-point DAFT, wherein the wireless transmitter is configured to: generate a second set of chirp carriers based on an N-point inverse discrete affine Fourier transform (IDAFT) using the M precoded symbols and the Np pilot sequences, and generate the oversampled first set of chirp carriers based on at least the second set of chirp carriers.

[0031] For example, the wireless transmiter may be configured to generate the oversampled first set of chirp carriers based on the second set of chirp carriers and a K-Point IDFT.

[0032] For example, the N-point IDAFT may be applied to the M precoded symbols and the Nppilot sequences to generate the second set of chirp carriers.

[0033] In a further implementation form of the first aspect, wireless transmiter is configured to: generate a set of N DFT outputs based on an N-point DFT by using the second set of chirp carriers, generate the oversampled first set of chirp earners based on a K- Point IDFT by using the set of N DFT outputs.

[0034] For example, the N-point DFT may be applied to the second set of chirp carriers to generate the set of N DFT outputs.

[0035] For example, the K-Point IDFT may be applied to the set of N DFT outputs to generate the oversampled first set of chirp carriers.

[0036] In a further implementation form of the first aspect, wireless transmitter is configured to: map the set of N DFT outputs to N inputs of the K-point IDFT that correspond to a set of frequency sub-bands, for example, a predetermined set of frequency subbands.

[0037] In a further implementation form of the first aspect, wireless transmiter is configured to: generate a set of IDFT outputs based on the K-point IDFT using the M precoded symbols, apply one or more K-long chirps to the set of IDFT outputs based on one or more discrete time chirps to generate a third set of chirp carriers, multiplex Nppilot sequences, for example, K-long Np pilot sequences, and the third set of chirp carriers to generate the first set of chirp carriers

[0038] Thus, the generation of the AFDM signal can be implemented with a low complexity wireless transmitter

[0039] For example, the K-Point IDFT may be applied to the set of N DFT outputs to generate the set of IDFT outputs.

[0040] According the above the first set of chirp carriers may be generated based on the Nppilot sequences, for example, the K-long Nppilot sequences, and the K-Point IDFT.

[0041] In a further implementation form of the first aspect, the M-point DFBT is a M-point DFT, wherein the wireless transmitter is configured to: digitally chirp the M symbols or the M spectrally shaped symbols, generate M DFT outputs based on the M- point DFT using the M digitally chirped symbols, and apply a linear phase shift on the M DFT outputs to obtain the M precoded symbols.

[0042] For example, the M symbols may be spectrally shaped before digitally chirping said M symbols.

[0043] According to the above the M symbols may be precoded based on an M-point DFBT.

[0044] For example, the linear phase shift may be defined as:

[0045] In a further implementation form of the first aspect, wireless transmitter is configured to: obtain one or more continuous-time versions of the one or more discrete time chirps, wherein the one or more continuous-time versions are sampled at a rate equal to the bandwidth of the AFDM signal multiplied by K / N, apply the one or more continuous-time versions of the one or more discrete time chirps to the set of IDFT outputs to generate the third set of chirp carriers.

[0046] For example, the sample rate may be given by:

[0047] 1 > BW Ts ~ ~N / K

[0048] In a further implementation form of the first aspect, wireless transmitter is configured to: spectrally shape the M symbols by input nulling, precode the spectrally shaped M symbols based on the M-point DFBT to obtain the precoded M symbols.

[0049] For example, the M symbols may be spectrally shaped before precoding said M symbols.

[0050] In a further implementation form of the first aspect, the AFDM signal comprises a communication signal part and a pilot signal part, wherein the communication signal part is a pointwise product between a discrete-time chirp and a pre-chirping signal that is a single-carrier waveform centered at zero frequency, wherein the pre-chirping signal comprises the M symbols.

[0051] In a further implementation form of the first aspect, the first set of chirp carriers comprises M chirp earners for data transmission corresponding to the M symbols and Npchirp carriers that are pilot signals for sensing or channel estimation. The M chirp carriers and Npchirp carriers may be multiplexed.

[0052] In a further implementation form of the first aspect, the first set of chirp carriers comprises one or more chirp carriers that are nulled.

[0053] Thus, sufficient number of guard symbols for each chirp carrier for sensing and / or communication of the first set of chirp carriers can be implemented. For example, the number of guard symbols may be sufficient such that AFDM signals of the wireless transmitter and other wireless transmitters in a network may not interfere with each other

[0054] In a further implementation form of the first aspect, wireless transmitter is configured to: frequency shift the first set of chirp carriers, wherein the AFDM signal comprises the frequency shifted first set of chirp carriers that are orthogonal in a DAFT domain.

[0055] For example, the first set of chirp carriers may be frequency shifted Vsens, for example, the center of an ISAC frequency band.

[0056] In a further implementation form of the first aspect, the wireless transmitter is configured to oversample the AFDM signal by oversampling the entire AFDM signal or oversampling the pre-chirping signal and the time-domain chirping signal separately

[0057] In a further implementation form of the first aspect, the pre-chirping signal is oversampled by using a K-point IDFT, and / or wherein the discrete-time chirp is oversampled by sampling a continuous-time version of a chirp carrier at a rate equal to the bandwidth of the AFDM signal multiplied by K / N.

[0058] A second aspect of this disclosure provides a network device for coordinating a network of a plurality of wireless sensing devices, wherein the network device is configured to: receive an AFDM signal from one or more wireless sensing devices of the plurality of wireless sensing devices, wherein the AFDM signal is over-sampled by a factor of K / N, wherein K is an integer larger than N and N is an integer equal to or larger than 2; obtain at least one reference chirp; de-chirp the AFDM signal by using the at least one reference chirp; and obtain one or more sets of signals based on the de-chirped signal by using a K-point DFT and selecting from the N lowest-frequency outputs of the K-point DFT.

[0059] The plurality of wireless sensing devices may comprise one or more wireless transmitter according to the first aspect or its implementation forms The plurality of wireless sensing devices may comprise one or more ISAC devices

[0060] The network device may comprise wireless transmitter according to the first aspect or its implementation forms.

[0061] The two or more wireless sensing devices may be coordinated

[0062] In an implementation form of the second aspect, the one or more sets of signals comprise one or more sets of pilot signals of the one or more wireless sensing device and / or one or more sets of communication signals of the one or more wireless sensing device

[0063] In a further implementation form of the second aspect, the network device is configured to: determine one or more waveform parameters, and transmit the one or more waveform parameters to the two or more wireless sensing devices. In a further implementation form of the second aspect, the network device is configured to: determine one or more sets of pilot indexes, and transmit the one or more sets of pilot indexes to the two or more wireless sensing devices, wherein the one or more sets of pilot indexes respectively indicate a set of indexes of pilot signals in an oversampled AFDM signal

[0064] In a further implementation form of the second aspect, the network device is configured to: determine one or more sets of OFDM symbol indexes and / or one or more sets of resource block indexes for ISAC signals, and transmit the one or more sets of OFDM symbol indexes and / or one or more sets of resource block indexes to the two or more wireless sensing devices.

[0065] In a further implementation form of the second aspect, the network device is configured to: determine a number of guard symbols such that AFDM signals of the plurality of wireless sensing devices do not interfere with each other.

[0066] The network device of the second aspect may have implementation forms that correspond to the implementation forms of the wireless transmitter of the first aspect. The network device of the second aspect and its implementation forms may achieve the advantages and effects described above for the wireless transmitter of the first aspect and its respective implementation forms

[0067] A third aspect of this disclosure provides a method of operating a wireless transmitter, wherein the method comprises: obtaining M symbols, wherein M is an integer equal to or larger than 1; preceding the M symbols based on a M-point DFBT; generating an oversampled first set of chirp carriers based on Nppilot sequences and the M precoded symbols, wherein the first set of chirp carriers is oversampled by a factor K / N, wherein N is an integer larger than a sum of M and Np, wherein Npis an integer larger than or equal to 1, wherein K is an integer larger than N; and generating an AFDM signal comprising the first set of chirp carriers that are orthogonal in a DAFT domain.

[0068] The method of the third aspect may have implementation forms that correspond to the implementation forms of the wireless transmitter of the first aspect. The method of the third aspect and its implementation forms achieve the advantages and effects described above for the wireless transmitter of the first aspect and its respective implementation forms.

[0069] A fourth aspect of this disclosure provides a method of operating a network device for coordinating a network of a plurality of wireless sensing devices, wherein the method comprises: receiving an AFDM signal from one or more wireless sensing devices of the plurality of wireless sensing devices, wherein the AFDM signal is over-sampled by a factor of K / N, wherein K is an integer larger than N and N is an integer equal to or larger than 2; obtaining at least one reference chirp; de-chirping the AFDM signal by using the at least one reference chirp; and obtaining one or more sets of signals based on the de-chirped signal by using a K-point DFT and selecting from the N lowest-frequency outputs of the K-point DFT.

[0070] The method of the fourth aspect may have implementation forms that correspond to the implementation forms of the network device of the second aspect. The method of the fourth aspect and its implementation forms achieve the advantages and effects described above for the network device of the second aspect and its respective implementation forms.

[0071] A fifth aspect of this disclosure provides a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of the third aspect or the fourth aspect.

[0072] The computer program of the fifth aspect may have implementation forms that correspond to the implementation forms of the method of the third aspect and / or the method of the fourth aspect. The computer program of the fifth aspect and its implementation forms achieve the advantages and effects described above for the method of the third aspect and its respective implementation forms and / or the method of the fourth aspect and its respective implementation forms. Further, in this disclosure the phrase “transmitter” and “wireless transmitter” may be used interchangeably.

[0073] Further, in this disclosure the phrase “receiver” and “wireless receiver” may be used interchangeably.

[0074] It has to be noted that all devices, elements, units and means described in the disclosure 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 disclosure 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.

[0075] 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 which 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.

[0076] BRIEF DESCRIPTION OF DRAWINGS

[0077] The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

[0078] FIG 1 shows a wireless transmitter according to this disclosure

[0079] FIG 2 shows a network device according to this disclosure.

[0080] FIG 3 shows an orthogonal multiplexing DAFT-s-AFDM with single-chirp AFDM carriers.

[0081] FIG 4 shows sampling a chirped DFT-s-OFDM generated with an oversampled chirp according to this disclosure

[0082] FIG 5 shows an exemplary wireless communications system according to this disclosure.

[0083] FIG 6 shows an exemplary ISAC terminal according to this disclosure.

[0084] FIG 7 shows an exemplary network device according to this disclosure.

[0085] FIG 8 shows an exemplary ISAC signal generator module according to this disclosure.

[0086] FIG 9 shows an exemplary ISAC signal generator module that centers an ISAC signal at a frequency according to this disclosure.

[0087] FIG 10 shows implementing a DAFT-s-AFDM using a chirped DFT-s-OFDM architecture according to this disclosure.

[0088] FIG 11 shows low-complexity simultaneous chirping and up-sampling for the communication signals according to this disclosure.

[0089] FIG 12 sows an exemplary ISAC signal generator module according to this disclosure. FIG 13 sows an exemplary ISAC signal generator module according to this disclosure.

[0090] FIG 14 shows a time-frequency representation of two AFDM chirps, the de-chirping process, and a signal after down-sampling according to this disclosure.

[0091] FIG 15 shows an exemplary low-complexity receiver according to this disclosure

[0092] FIG 16 shows integration of data and pilot symbols with guard symbols according to this disclosure.

[0093] FIG 17 shows time domain multiplexing of an ISAC signal with OFDM according to this disclosure

[0094] FIG 18 shows frequency domain multiplexing of an ISAC signal with OFDM according to this disclosure.

[0095] FIG 19 shows mixed time-frequency domain multiplexing of an ISAC signal with OFDM according to this disclosure

[0096] FIG 20 shows a method according to this disclosure.

[0097] FIG 21 shows a method according to this disclosure

[0098] DETAILED DESCRIPTION OF EMBODIMENTS

[0099] FIG 1 shows a wireless transmitter 100 according to this disclosure. The wireless transmitter 100 is configured to obtain M symbols 101, precode the M symbols 101 based on a M-point DFBT 102 to obtain M precoded symbols 103, generate an oversampled first set of chirp carriers 105 based on Np pilot sequences 104 and the M precoded symbols 103, and generate an AFDM signal 106 comprising the first set of chirp carriers 105.

[0100] Generally, M is an integer equal to or larger than 1, Npis an integer larger than or equal to 1, N is an integer larger than a sum of M and Np, and K is an integer larger than N. The first set of chirp carriers 105 is oversampled by a factor K / N. The first set of chirp carriers 105 are orthogonal in a DAFT domain.

[0101] FIG 2 shows a network device 200 according to this disclosure. The network device 200 is for coordinating a network of a plurality of wireless sensing devices 202. FIG. 2 further shows a plurality of wireless sensing devices 202.

[0102] The network device 200 is configured to receive an AFDM signal 106 from one or more wireless sensing devices 201 of the plurality of wireless sensing devices 202, obtain at least one reference chirp 203, de-chirp the AFDM signal 106 by using the at least one reference chirp 203 to obtain a de-chirped signal 204, and obtain one or more sets of signals 206 based on the dechirped signal 204 by using a K-point DFT 205 and selecting from the N lowest-frequency outputs of the K-point DFT 205.

[0103] Generally, the AFDM signal 106 is over-sampled by a factor of K / N, wherein K is an integer larger thanN andN is an integer equal to or larger than 2

[0104] An N’ -point DFT may be defined as a mathematical transformation used to convert a finite sequence of equally-spaced samples of a function into a same-length sequence of equally-spaced samples of its frequency spectrum. In this disclosure, the term "N’-point" may refer to the number of samples in the time-domain sequence, where "N’" is a positive integer. For example, the DFT may be defined as follows:

[0105] For a given sequence x[n], where n=0,l,. ,,N’-1, the DFT X[k] may be computed as: for k=0,l,...,N’-l, where j is the imaginary unit, and e is the base of the natural logarithm. The result X[k] represents the frequency spectrum of the original sequence, with each k corresponding to a specific frequency component.

[0106] This transformation may allow for the analysis of the frequency components within a signal.

[0107] Based on this disclosure, an AFDM signal may be generated with any arbitrary sample rate that exceeds the bandwidth, maintaining low complexity Furthermore, the signal generation can be adapted for any (c) AFDM configuration and seamlessly multiplexed with sensing pilots, thereby expanding its applicability to diverse integrated communication and sensing scenarios

[0108] Given that a low-PAPR AFDM signal 106 is confined to a finite set of indices within the DAFT domain, it is amenable to orthogonal multiplexing with single-chirp AFDM carriers This capability enables the concurrent execution of communication and sensing tasks as shown in FIG. 3, a feature particularly beneficial in the realm of ISAC systems.

[0109] FIG 3 shows an orthogonal multiplexing DAFT-s-AFDM 106 with single-chirp AFDM carriers.

[0110] The DAFT-spread-AFDM (DAFT-s-AFDM) signal 106 of a transmission assigned the DAFT domain indexes can be written as the pointwise product between a pre-chirping signal that is a single-carrier waveform centered at zero frequency and a discrete-time chirp:

[0111] The first method may involve oversampling the entire signal by some up-sampling module, for example, as described for the ISAC signal generator module shown in FIG. 8.

[0112] For example, the sequence of samples 0mo(^s)maY generated according to one of the following methods

[0113] The above approaches may result in a signal with a bandwidth exceeding the nominal bandwidth as shown in FIG. 4b Unique spectral shaping of this signal may be possible by selectively nulling some inputs in the pre-DAFT domain as shown in FIG

[0114] 4c, which can allow for precise adjustments to the frequency characteristics of the output It may be an advantage of DAFT-s- AFDM signals that the DAFT pre-coding allows for precise manipulation of spectral properties.

[0115] FIG 4 shows sampling a chirped DFT-s-OFDM generated with an oversampled chirp according to this disclosure.

[0116] FIG 4a shows sampling the chirped DFT-s-OFDM generated with a discrete chirp without oversampling.

[0117] FIG 4b shows oversampling the chirped DFT-s-OFDM without spectral shaping.

[0118] FIG 4c shows oversampling the chirped DFT-s-OFDM with spectral shaping.

[0119] An ISAC signal thus obtained can be multiplexed with OFDM signals, providing the flexibility to do so either in the time domain or the frequency domain. Furthermore, this multiplexing can be achieved using a numerology that is distinct from the conventional OFDM parameters, allowing for customization and optimization based on specific system requirements and operational environments.

[0120] FIG 5 shows an exemplary wireless communications system according to this disclosure. The system may comprise a plurality of ISAC terminals 202, for example, as shown in FIG. 6, and a network device 200, for example, as shown in FIG. 7. The network devices 200 may themselves have integrated sensing and communications capabilities.

[0121] FIG 6 shows an exemplary ISAC terminal 100, 201 according to this disclosure.

[0122] FIG 7 shows an exemplary network device 200 according to this disclosure The terminal device 100, 201 may comprise one or more of the following modules

[0123] The following shows two examples for implementing this multiplexing and how the resulting ISAC signal may be up-sampled to a desired sample rate before transmission.

[0124] FIG 8 shows an exemplary ISAC signal generator module according to this disclosure

[0125] The ISAC signal generator module may be configured to obtain M symbols 101, precode the M symbols 101 based on an M- pointDFBT 102 to obtain M precoded symbols 103, wherein the M-point DFBT 102 may be a M-point DAFT

[0126] If the ISAC signal is to be made to occupy a specific sub-band that may not necessarily be centered at zero within the ISAC system total bandwidth of 1 / TSHz, e.g., to allow for frequency domain or mixed time-frequency multiplexing with OFDM signals for integration in a wireless communications system, then the ISAC signal generator module of the wireless transmitter 100 shown in FIG 8 can be modified by using a DFT-based up-sampling as the K / N up-sampling method at the output of the N -point ID AFT module and by mapping the N outputs of the N -point DFT module of the up-sampler to the N inputs corresponding to the desired frequency sub-band of the If -point IDFT module of the up-sampler, for example, as shown in FIG 9

[0127] FIG 9 shows an exemplary ISAC signal generator module that centers an ISAC signal 106 at a frequency according to this disclosure. Here it is assumed the desired frequency sub-band is centered at frequency vsens, for example, in digital frequencies

[0128] To lower the complexity related to the up-sampling module shown in FIG 8 and 9, the pilots and communications parts may be separated from each other.

[0129] FIG 10 shows implementing a DAFT-s-AFDM using a chirped DFT-s-OFDM architecture according to this disclosure.

[0130] For the communications signal part, to achieve a low-complexity architecture capable of generating the DAFT-s-AFDM signal 106, one that can support an arbitrary sample rate and arbitrary parameters (c, c) where c may not necessarily equal c. the equivalence between the DAFT-s-AFDM modulator and a modified version of the DFT-s-OFDM modulator followed by discrete-time chirping is exemplary shown in FIG. 10. This chirping process may introduce the necessary variances in frequency that characterize the DAFT-s-AFDM signal 106.

[0131] FIG 11 shows low-complexity simultaneous chirping and up-sampling for the communication signals according to this disclosure.

[0132] The output of the communications signal generation part may next be multiplexed with pilot sequences 104, which may be taken from a sequence codebook generation module, as shown in FIG 12

[0133] FIG 12 sows an exemplary ISAC signal generator module according to this disclosure

[0134] For example, the ISAC signal generator module may be configured to generate a set of IDFT outputs based on the K-point IDFT using the M precoded symbols 103. Further, one or more K-long chirps may be applied to the set of IDFT outputs based on one or more discrete time chirps to generate a third set of chirp carriers 108, Further, the ISAC signal generator module may be configured multiplex the Np pilot sequences 104 and the third set of chirp carriers 108 to generate the first set of chirp carriers 105.

[0135] FIG 13 shows an exemplary ISAC signal generator module according to this disclosure

[0136] If the ISAC signal 106 is to be made to occupy a specific sub-band, not necessarily centered at zero, within the ISAC system total bandwidth of 1 / 7) Hz, e.g., to allow for frequency domain or mixed time-frequency multiplexing with OFDM signals for integration in a wireless communications system, then the ISAC signal generator module FIG. 12 may be modified by applying a linear-phase shift to the oversampled chirp samples. In FIG 13, this is shown assuming the desired center frequency, for example, in digital frequencies, is denoted vsens

[0137] A network device 200 may comprise one or more of the following modules.

[0138] FIG 14 shows a time-frequency representation of two AFDM chirps, the de-chirping process, and a signal after down-sampling according to this disclosure.

[0139] FIG 14 shows a chirp with DAFT domain index mi , and a zero-th chirp as the reference chirp 203 of an AFDM at the transmitter 100, 201 (on top), after dechirping with an over-sampled version of the zeroth-th chirp at the receiver (on bottom left) and after down-sampling the outcome of that de-chirping (on bottom right). For example, a network device 200 may comprise an ISAC signal receiver module A low-complexity receiver may achieve de-chirping by using a reference chirp 203 that is over-sampled by a factor of K / N. The reference chirp 203 may also be pulseshaped and may be generated with low complexity from a codebook generation module.

[0140] The ISAC signal 106 can be seen as a liner combination of chirp signals, each corresponding to one input of the ID AFT module of the ISAC signal generator 100, 201. The ISAC signal 106 at the input to the ISAC signal receiver may also be a linear combination of chirps Following the de-chirping step using the reference chirp 203, the resulting signal may be a linear combination of tone signals that exhibit each jumps in their instantaneous frequency, as illustrated in FIG. 14, due to the fact that the de-chirping reference chirp 203 is oversampled with a factor of K / N.

[0141] This de-chirping may be followed by a K-point DFT 205. There may be no requirement for explicit complex down-sampling; instead, down-sampling can occur implicitly by selecting from the IV-lowest-frequency outputs of the If -point DFT 205. After this implicit down-sampling, the de-chirped desired signal 204 may not have any frequency jumps due to spectrum folding as shown in FIG 14

[0142] FIG 15 shows an exemplary low-complexity receiver according to this disclosure.

[0143] FIG 15 shows, at the output of the K-point DFT module 205 of the network device 200, the data detection, channel estimation and sensing blocks corresponding to one of the terminal devices 100, 201. To perform data detection, channel estimation and sensing for the signals 106 received from the other transmitting terminal devices 100, 201 these blocks may be duplicated and connected to the specific outputs of the K-point DFT module 205 that correspond to those other transmitting devices 100, 201

[0144] The network device 200 may assign the indices m0,ml,m2, —,mNto each ISAC terminal, ensuring that each signal is allocated a sufficient number of guard symbols.

[0145] Generally, the network device 200 is configured to obtain one or more sets of signals 206 based on the de-chirped signal 204 by using a K-point DFT 205 and selecting from the N lowest-frequency outputs of the K-point DFT 205.

[0146] FIG 16 shows integration of data and pilot symbols with guard symbols according to this disclosure. another resource information that may be determined and signaled to the terminals is the indexes of the frames, slots, OFDM symbols and the resource blocks of these symbols within which the disclosed ISAC signal 106 can be transmitted.

[0147] With regards to this integration, the following presents three examples.

[0148] FIG 17 shows time domain multiplexing of an ISAC signal 106 with OFDM according to this disclosure

[0149] A first example may be based on time domain multiplexing of an ISAC signal with OFDM The network device 200 might instruct the terminals to transmit the ISAC signal 106 only within some OFDM symbols of some slots or frames of the communications system frame structure Outside of these assigned symbols, the same ISAC-compatible terminal devices 100, 201 and other non-ISAC pure-communications terminal devices can transmit OFDM signals

[0150] FIG 18 shows frequency domain multiplexing of an ISAC signal 106 with OFDM according to this disclosure.

[0151] A second example may be based on frequency domain multiplexing of an ISAC signal 106 with OFDM The network device 200 may assign a dedicated frequency sub-band for ISAC signal 106 uplink transmission. Outside of this sub-band, other terminal devices 100, 201 can transmit OFDM signals.

[0152] FIG 19 shows mixed time-frequency domain multiplexing of an ISAC signal with OFDM according to this disclosure

[0153] A third example may be based on mixed time-frequency domain multiplexing of the disclosed ISAC signal 106 with OFDM The network device might assign only a frequency sub-band within some OFDM symbols of some slots or frames to the ISAC signals 106.

[0154] An ISAC resource setting information may be transmitted in an augmented downlink control information (DCI) message or another resource assignment signaling message of that type or in a dedicated signaling message.

[0155] A network device 200 may comprise a waveform parameter setting module. The waveform parameters may include at least one of: a sampling rate Ts, an AFDM parameter cl, a number of data symbols in DAFT-s-AFDM scheme, a bandwidth BW, a type of continuous chirp generation scheme, and the frequency sub-band centered at frequency vsensfor the frequency multiplexing

[0156] These parameters may be transmitted in an augmented DCI message or another signaling message of that type or in a dedicated signaling message. In case of integration with an OFDM-based communications system, some of these parameters may be constrained by the way the ISAC signals 106 are multiplexed with the OFDM signal in time and frequency

[0157] In one example, the parameters may be set in the case of time domain and mixed time-frequency domain multiplexing of the ISAC signal 106 with OFDM. For example, the ISAC signal symbols being aligned in the time domain with the OFDM frame structure may impose constraints on the values that N and K can take. For example, K should be chosen from the same FFT sizes table used for OFDM. This table typically contain only power-of-two values. As for N, it may be set such that — equals the bandwidth BW assigned to the ISAC signal 106, in which case IV may not be a power-of-two integer or IV may be set to the largest power of 2 such that — < BW, for example, in the case of strict inequality full spectral efficiency not being achieved.

[0158] In the case of frequency domain multiplexing or of mixed time-frequency domain multiplexing of the ISAC signal with OFDM, the signaling of the parameter vsens(or of an equivalent parameter such as, for example, a frequency range parameter) may not be left void in the parameter setting message.

[0159] Another example for the ISAC signal 106 generation process may utilize a low-complexity approach that simultaneously combines chirping and up-sampling to generate its communications signal component, for example, the chirped DFT-s-OFDM signal, incorporating low-complexity spectral shaping techniques and the seamless integration of the resulting over-sampled communications signal with over-sampled sensing chirp pilots generated, for example, using conventional methods.

[0160] The over-sampled chirp sequences used in both generating the chirped DFT-s-OFDM communications signal component and the chirp sensing pilots may be shifted in frequency for positioning the ISAC signal 106 in a specific frequency bandwidth of a wireless system.

[0161] A network device may 200 include a low-complexity receiver and may leverage an over-sampled reference chirp 203 by a factor of K / N for de-chirping, subsequently applying a K-point DFT. Among the DFT outputs, some outputs may be aligned with the pilot indexes m1,m2, ... , mNpand guard intervals designated for each terminal device 100, 201, facilitating channel estimation or bi-static wireless sensing at the network device 200. Additionally, other outputs may correspond to the index ranges m„ ... m0+ M — 1 of the communications signals from the different terminal devices 100, 201, including their guard intervals, if present, serving data detection purposes

[0162] The network device 200 may include a waveform parameter setting module that assigns the waveform parameters (for example, a sampling rate, an AFDM parameter a number of data symbols in DAFT-s-AFDM scheme, a bandwidth, a type of continuous chirp generation and frequency shifting parameter) and may signal them to the terminal 100, 201.

[0163] The network device 200 may include an ISAC resources assignment module that assigns pilot indexes and signals them to the terminal 100, 201. The ISAC resources assignment module may also assign (and / or signal to the terminal) OFDM symbol indexes for ISAC signal transmission that is multiplexed in time domain within the communications system frame structure.

[0164] The ISAC resources assignment module may also assign and / or signal to the terminal 100, 201 OFDM resource blocks indexes for ISAC signal transmission that is multiplexed in frequency domain within the communications system frame structure.

[0165] The wireless transmitter 100 may comprise a first processor.

[0166] Generally, the first processor may be configured to perform, conduct or initiate the various operations of the transmitter 100 described herein. The first processor may comprise hardware and / or may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The transmitter 100 may further comprise memory circuitry, which stores one or more instruction(s) that can be executed by the first processor, in particular under control of the software For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the first processor, causes the various operations of the transmitter 100 to be performed. In one embodiment, the transmitter 100 may comprises one or more first processors and a non-transitory memory connected to the one or more first processors The non-transitory memory may carry executable program code which, when executed by the one or more first processors, causes the transmitter 100 to perform, conduct or initiate the operations or methods described herein

[0167] The network device 200 may comprise a second processor.

[0168] FIG 20 shows a method 300 according to this disclosure. The method 300 is a method of operating a wireless transmitter 100 The method 300 comprises a step 301 of obtaining M symbols 101. Further, the method 300 comprises a step 302 of precoding the M symbols 101 based on an M-point DFBT Further, the method 300 comprises a step 303 of generating an oversampled first set of chirp carriers 105 based on Nppilot sequences 104 and the M precoded symbols 103. Further, the method 300 comprises a step 304 of generating an AFDM signal comprising the first set of chirp carriers 105 that are orthogonal in a DAFT domain.

[0169] Generally, the first set of chirp carriers is oversampled by a factor K / N, M is an integer equal to or larger than 1 , N is an integer larger than a sum of M and Np, Npis an integer larger than or equal to 1 , and K is an integer larger than N. FIG 21 shows a method 400 according to this disclosure The method 400 is a method of operating a network device 200 for coordinating a network of a plurality of wireless sensing devices 202. The method 400 comprises a step 401 of receiving an AFDM signal from one or more wireless sensing devices of the plurality of wireless sensing devices 202. Further, the method 400 comprises a step 402 of obtaining at least one reference chirp 203. Further, the method 400 comprises a step 403 of de- chirping the AFDM signal 106 by using the at least one reference chirp 203. Further, the method 400 comprises a step 404 of obtaining one or more sets of signals 206 based on the de-chirped signal 204 by using a K-point DFT and selecting from the N lowest-frequency outputs of the K-point DFT 205.

[0170] Generally, the AFDM signal 106 is over-sampled by a factor of K / N, wherein K is an integer larger than N and N is an integer equal to or larger than 2

[0171] The disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1 A wireless transmiter (100), wherein the wireless transmitter (100) is configured to: obtain M symbols (101), wherein M is an integer equal to or larger than 1; precode the M symbols (101) based on an M-point discrete Fourier-based transform, DFBT (102), generate an oversampled first set of chirp carriers (105) based onNp pilot sequences (104) and the M precoded symbols (103), wherein the first set of chirp carriers (105) is oversampled by a factor K / N, wherein N is an integer larger than a sum of M and Np, wherein Np is an integer larger than or equal to 1 , wherein K is an integer larger than N; and generate an affine frequency division multiplexing, AFDM, signal comprising the first set of chirp carriers (105) that are orthogonal in a discrete affine Fourier transform, DAFT, domain.2 The wireless transmitter (100) according to claim 1, configured to: generate the oversampled first set of chirp carriers (105) based on the Np pilot sequences (104) and a K-point inverse discrete Fourier transform, IDFT, of at least the M precoded symbols (103)3 The wireless transmitter (100) according to claim 1 or 2, wherein the M-point DFBT (102) is a M-point DAFT, wherein the wireless transmitter (100) is configured to: generate a second set of chirp carriers (107) based on an N-point inverse discrete affine Fourier transform, ID AFT, using the M precoded symbols (103) and the Np pilot sequences (104), and generate the oversampled first set of chirp carriers (105) based on at least the second set of chirp carriers (107).4 The wireless transmitter (100) according to claim 3, configured to: generate a set of N discrete Fourier transform, DFT, outputs based on a N-point DFT by using the second set of chirp carriers (107), generate the oversampled first set of chirp carriers (105) based on a K-Point IDFT by using the set of N DFT outputs.5 The wireless transmitter (100) according to claim 4, configured to: map the set of N DFT outputs to N inputs of the K-point IDFT that correspond to a set of frequency sub-bands6 The wireless transmitter (100) according to claim 2, configured to: generate a set of IDFT outputs based on the K-point IDFT using the M precoded symbols (103), apply one or more -long chirps to the set of IDFT outputs based on one or more discrete time chirps to generate a third set of chirp carriers (108),multiplex Np pilot sequences (104) and the third set of chirp carriers (108) to generate the first set of chirp carriers (105)7 The wireless transmitter (100) according to claim 6, wherein the M-point DFBT (102) is a M-point DFT, wherein the wireless transmitter (100) is configured to: digitally chirp the M symbols (101), generate M DFT outputs based on the M-point DFT using the M digitally chirped symbols, and apply a linear phase shift on the M DFT outputs to obtain the M precoded symbols (103).8 The wireless transmitter (100) according to claim 6 or 7, configured to: obtain one or more continuous-time versions of the one or more discrete time chirps, wherein the one or more continuous-time versions are sampled at a rate equal to the bandwidth of the AFDM signal (106) multiplied by K / N, apply the one or more continuous-time versions of the one or more discrete time chirps to the set of IDFT outputs to generate the third set of chirp carriers (108).9 The wireless transmitter (100) according to any one of the preceding claims, configured to: spectrally shape the M symbols (101) by input nulling, precode the spectrally shaped M symbols (101) based on the M-point DFBT (102) to obtain the precoded M symbols (101)10 The wireless transmitter (100) according to any one of the preceding claims, wherein the AFDM signal (106) comprises a communication signal part and a pilot signal part, wherein the communication signal part is a pointwise product between a discrete-time chirp and a pre-chirping signal that is a single-carrier waveform centered at zero frequency, wherein the pre-chirping signal comprises the M symbols (101)11. The wireless transmitter (100) according to any one of the preceding claims, wherein the first set of chirp carriers (105) comprises M chirp carriers for data transmission corresponding to the M symbols (101 ) and Npchirp carriers that are pilot signals for sensing or channel estimation.

12. The wireless transmitter (100) according to any one of the preceding claims, wherein the first set of chirp carriers (105) comprises one or more chirp carriers that are nulled.

13. The wireless transmiter (100) according to any one of the preceding claims, configured to: frequency shift the first set of chirp carriers (105), wherein the AFDM signal (106) comprises the frequency shifted first set of chirp carriers (105) that are orthogonal in a DAFT domain.

14. A network device (200) for coordinating anetwork of a plurality of wireless sensing devices (202), wherein the network device (200) is configured to: receive an affine frequency division multiplexing, AFDM, signal from one or more wireless sensing devices of the plurality of wireless sensing devices (202), wherein the AFDM signal (106) is over-sampled by a factor of K / N, wherein K is an integer larger than N and N is an integer equal to or larger than 2: obtain at least one reference chirp (203); de-chirp the AFDM signal (106) by using the at least one reference chirp (203); and obtain one or more sets of signals (206) based on the de-chirped signal (204) by using a K-point discrete Fourier transform, DFT, and selecting from the N lowest-frequency outputs of the K-point DFT (205).

15. The network device (200) according to claim 14, wherein the one or more sets of signals (206) comprise one or more sets of pilot signals of the one or more wireless sensing device and / or one or more sets of communication signals of the one or more wireless sensing device16 The network device (200) according to claim 14 or 15, configured to: determine one or more waveform parameters, and transmit the one or more waveform parameters to the two or more wireless sensing devices17 The network device (200) according to any one of the claims 14 to 16, configured to: determine one or more sets of pilot indexes, and transmit the one or more sets of pilot indexes to the two or more wireless sensing devices, wherein the one or more sets of pilot indexes respectively indicate a set of indexes of pilot signals in an oversampled AFDM signal (106).

18. The network device (200) according to any one of the claims 14 to 17, configured to: determine one or more sets of orthogonal frequency division multiplexing, OFDM, symbol indexes and / or one or more sets of resource block indexes for integrated sensing and communication, ISAC, signals, and transmit the one or more sets of OFDM symbol indexes and / or one or more sets of resource block indexes to the two or more wireless sensing devices.

19. The network device (200) according to any one of the claims 14 to 18, configured to: determine a number of guard symbols such that AFDM signals (106) of the plurality of wireless sensing devices (202) do not interfere with each other.

20. A method of operating a wireless transmitter (100), wherein the method comprises: obtaining M symbols (101), wherein M is an integer equal to or larger than 1 ; precoding the M symbols (101) based on an M-point discrete Fourier-based transform, DI 'BT: generating an oversampled first set of chirp carriers (105) based on Np pilot sequences (104) and the M precoded symbols (103), wherein the first set of chirp carriers (105) is oversampled by a factor K / N, wherein N is an integer larger than a sum of M and Np, wherein Npis an integer larger than or equal to 1 , wherein K is an integer larger than N; and generating an affine frequency division multiplexing, AFDM, signal comprising the first set of chirp carriers (105) that are orthogonal in a discrete affine Fourier transform, DAFT, domain.

21. A method of operating a network device (200) for coordinating a network of a plurality of wireless sensing devices (202), wherein the method comprises: receiving an affine frequency division multiplexing, AFDM, signal from one or more wireless sensing device of the plurality of wireless sensing devices (202), wherein the AFDM signal (106) is over-sampled by a factor of K / N, wherein K is an integer larger than N and N is an integer equal to or larger than 2: obtaining at least one reference chirp (203); de-chirping the AFDM signal (106) by using the at least one reference chirp (203); and obtaining one or more sets of signals (206) based on the de-chirped signal (204) by using a K-point discrete Fourier transform, DFT, and selecting from the N lowest-frequency outputs of the K-point DFT (205).

22. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of claim 20 or 21.

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