Device and method for AFDM-based pilot signals generation

Abstract

The present disclosure relates to a network entity for chirp-based pilot signal generation, configured to: obtain a first set of parameters from a core network device, wherein the first set of parameters includes: a number, a time-domain chirp rate, and a frequency-domain chirp rate, of the to-be-generated pilot sequence; obtain N pilot sequences based on the first set of parameters, wherein each pilot sequence comprises a set of K pilot chirp carrier samples, and K is an integer not less than N; determine, for each antenna port of the network entity, a subset of the N pilot sequences, and synthesize a pilot signal to be transmitted from that antenna port by forming a new set of K samples each of which is obtained by summing corresponding samples from the K samples of each pilot sequences from the determined subset of the N pilot sequences.

Description

[0001] DEVICE AND METHOD FOR AFDM-BASED PILOT SIGNALS GENERATION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to the field of wireless communications and radar sensing, specifically focusing on techniques and systems within the Integrated Sensing and Communication (ISAC) paradigm. More particularly, the disclosure proposes a network entity and corresponding methods for chirp-based pilot signal generation in wireless communication networks.

[0004] BACKGROUND

[0005] The convergence of wireless communications and radar sensing into the ISAC paradigm marks a pivotal shift in the field, driven by objectives like reduced power consumption, increased spectral efficiency, and lowered hardware costs. This integration challenges traditional paradigms and necessitates novel approaches in system design and signal processing.

[0006] Chirp-based Frequency Modulated Continuous Wave (FMCW) radar, known for its sensing proficiency and processing simplicity, faces integration challenges within the ISAC framework, especially in the context of evolving 6G technologies Conventional integration methods, such as Time-Division Multiplexing (TDM), have shown limited efficiency, prompting the need for more innovative solutions.

[0007] Emerging multi-chirp waveforms, notably Orthogonal Chirp Division Multiplexing (OCDM) and Affine Frequency Division Multiplexing (AFDM), have been identified as promising candidates for 6G communications. OCDM employs the discrete Fresnel transform, while AFDM is based on the discrete affine Fourier transform (DAFT), which includes the discrete Fresnel transform as a specific case. AFDM, in particular, is notable for its potential to exploit the diversity of linear time-varying channels with minimal pilot signal overhead.

[0008] A distinctive feature of AFDM is its effective channel estimation using chirp pilots, differing significantly from pilots in Long- Term Evolution (LTE) and New-Radio (NR) systems. These pilots provide a complete delay-Doppler channel representation, essential in sensing and radar applications for extracting precise range-velocity target information.

[0009] Nonetheless, AFDM faces a significant challenge due to the bandwidth occupancy of its chirps, which span the entire bandwidth from -fs / 2 to fs / 2, with fs representing the sampling rate. This poses a limitation in adjusting the signal bandwidth, thereby creating practical challenges in implementing AFDM within the 6G ISAC framework.

[0010] SUMMARY

[0011] To address these challenges, the present disclosure proposes a novel method for designing AFDM pilot generation schemes This method aims to enable flexible spectral shaping of AFDM-based pilots without the need to change the sampling rate of the Digital-to-Analog Converter (DAC). The proposed solution promises to enhance the applicability and performance of AFDM technology in various communication and sensing scenarios within the 6G ISAC space, addressing a critical gap in current technology

[0012] These and other objectives are achieved by the solution of the present disclosure as provided in the enclosed independent claims. Advantageous implementations are further defined in the dependent claims.

[0013] This disclosure proposes AFDM pilot generation schemes to meet any spectral mask requirements without having to change the sampling rate of the DAC The bandwidth designated for sensing and channel estimation via the pilot signal is configurable to any selected value that does not exceed the sampling rate. The architecture for pilot signal generation and detection is engineered to be inherently simple, facilitating ease of implementation and operational efficiency without compromising the system's efficacy.

[0014] It may be understood that a “pilot sequence” is one of the N pilot chirp carriers. When transmitting a pilot signal through one of the antenna ports, the transmitted signal could be either a single pilot sequence or a composite signal formed by the summation of a select group of these sequences. Practically, the chosen subset of sequences does not encompass the entire set, as numerous chirp carriers within the set are intentionally left unutilized, thereby creating a “pilot guard interval” to mitigate interference. Additionally, the composition of this subset may vary between different antenna ports, allowing for a customized transmission strategy that optimizes the use of the spectral resources and enhances the robustness of the channel estimation process.

[0015] In an implementation form of the first aspect, the forming the new set of K samples each of which is obtained by summing corresponding samples from the K samples of each pilot sequence from the determined subset of the N pilot sequences comprising: for each pilot sequence, applying a weight to each sample of the K pilot chirp carrier samples to produce K weighted pilot chirp carrier samples, wherein each of the new set of K samples of the pilot signal is formed by summing corresponding weighted pilot chirp carrier samples from the K samples of each pilot sequence from the determined subset of the N pilot sequences.

[0016] Optionally, before summing corresponding pilot chirp carrier samples, a weighting function may be applied to the samples, the weighted pilot chirp carrier samples are summed to form the sample for the pilot signal.

[0017] In an implementation form of the first aspect, the network entity is configured to obtain N pilot sequences based on the first set of parameters and based on a second set of parameters, wherein the second set of parameters comprises a bandwidth of the to- be-generated pilot sequences and a sample period (7s) for obtaining the set of K pilot chirp carrier samples for each to-be- generated pilot sequence.

[0018] In the process of generating pilot sequences, it may be necessary to employ additional parameters from the pilot codebook beyond the primary ones initially considered For example, the bandwidth, or the sample period of the to-be-generated pilot sequences may be considered.

[0019] In an implementation form of the first aspect, the network entity is configured to determine a continuous-time chirp carrier function based on a discrete-time pilot chirp carrier, wherein the discrete-time pilot chirp carrier is parameterized with the first set of parameters; and obtain a set of pilot chirp carrier samples by sampling the continuous-time chirp carrier function with a sample rate of l / 7s.

[0020] In an implementation form of the first aspect, the second set of parameters further comprises a type of continuous-time chirp carrier function, wherein when the type of continuous-time chirp carrier function is a first type, the network entity is configured to determine the continuous-time chirp carrier function based on the discrete-time pilot chirp carrier using a complex exponential function whose instantaneous frequency is a chirp carrier specific step function; and when the type of continuoustime chirp carrier function is a second type, the network entity is configured to determine the continuous-time chirp carrier function by applying an interpolation formula to samples of the discrete-time pilot chirp carrier.

[0021] In an implementation form of the first aspect, the network entity is configured to obtain the set of K pilot chirp earner samples based on a look-up table using the first set of parameters and the second set of parameters.

[0022] In an implementation form of the first aspect, the network entity is configured to obtain a reference pilot chirp carrier from the look-up table using the first set of parameters and the second set of parameters, wherein the look-up table is a reduced-size look-up table; generate a sequence of pilot chirp carrier samples by cyclically shifting the reference pilot chirp carrier; and obtain the set of K pilot chirp carrier samples for a pilot chirp carrier from the sequence of K pilot chirp carrier samples.

[0023] Other than online computing the samples using the above-mentioned formulas, another way is to retrieve the required samples from look-up tables computed “off-line” with different combinations of the pilot parameters.

[0024] In an implementation form of the first aspect, the network entity is configured to shift the synthesized pilot signal to a predefined frequency by applying a linear-phase shift to the obtained N pilot sequences

[0025] Possibly, pilot sequences can be shifted in frequency, for instance, for frequency domain multiplexation of the AFDM pilot signal with OFDM.

[0026] In an implementation form of the first aspect, the second set of parameters further comprises a type of window function, and one or more window parameters corresponding to the type of window function.

[0027] In an implementation form of the first aspect, the network entity is configured to pulse-shape an wi-Lli pilot sequence of the N pilot sequences by applying a window function on the K pilot chirp carrier samples of the m-th pilot sequence based on the first set of parameters, the second set of parameters, and a value of m, wherein m is an index of the pilot sequence among the N pilot sequences.

[0028] Optionally, pulse-shaping may be applied for the AFDM chirps against both fractional delay and fractional Doppler and for reducing out-of-band emission (OOBE) levels. In an implementation form of the first aspect, the type of window function comprises a global window function type and / or a section window function type, wherein the network entity is further configured to: when the type of window function is the global window function type, apply a global window function on each pilot chirp carrier sample of the K pilot chirp carrier samples, and / or when the type of window function is the section window function type, apply a section window function on each pilot chirp carrier sample within a chirp section of the K pilot chirp carrier samples

[0029] Notably, to mitigate leakage due to fractional Doppler shifts in the channel, a “global” pulse-shaping i e., a pulse shape applied to the whole AFDM symbol, may be applied For a pulse shaping that attenuates the sharp transitions around time instances, the window function of the pulse shape may be applied on a per-section basis

[0030] In an implementation form of the first aspect, the network entity is configured to append the K pilot chirp carrier samples of the pilot signal with a prefix and / or a suffix of samples, wherein the prefix of samples comprises one of the following: a chirp periodic prefix, a periodic prefix, or a zero-valued prefix, and / or the suffix of samples comprises one of the following: a chirp periodic suffix, a periodic suffix, or a zero- valued suffix.

[0031] Optionally, the pilot signal may be generated with a prefix of duration Tpreflxseconds and / or a suffix of duration Tsuf n>. seconds

[0032] In an implementation form of the first aspect, the network entity is implemented in a terminal device, wherein the network entity is further configured to obtain the second set of parameters from a radio access network (RAN) device, wherein the first set of parameters is obtained from the core network device via the RAN device.

[0033] In a particular embodiment, the network entity may be an IS AC terminal. The IS AC terminal obtains the first set of parameters and the second set of parameters from the RAN device.

[0034] In an implementation form of the first aspect, the network entity is implemented in a RAN device, wherein the network entity is further configured to determine the second set of parameters

[0035] In another embodiment, the network entity may be a RAN device, the second set of parameters may be determined by the RAN device

[0036] A second aspect of the disclosure provides a core network device, which is configured to provide a first set of parameters to one or more network entities for chirp-based pilot sequence generation, wherein the first set of parameters includes: a number (TV) of to-be-generated pilot sequences, a time-domain chirp rate (cl) of the to-be-generated pilot sequence, and a frequencydomain chirp rate (c2) of the to-be-generated pilot sequence, wherein N is a positive integer.

[0037] This disclosure further proposes a core network device for providing parameters that are necessary to the chirp-based pilot signal generation to the network entity.

[0038] In an implementation form of the second aspect, the time-domain chirp rates (cl) assigned to different network entities are chosen to have different values.

[0039] The parameter cl is a cell-specific parameter. The network assigns different values of cl to different cells i e., to different network entities, to reduce inter-cell pilot interference.

[0040] This disclosure further proposes a RAN device for providing parameters that are necessary to the chirp-based pilot signal generation to the network entity.

[0041] In an implementation form of the third aspect, the second set of parameters further comprises a type of window function, and one or more window parameters corresponding to the type of window function, wherein the type of window function comprises a global window function type and / or section window function type.

[0042] A fourth aspect of the disclosure provides a method performed by a network entity for chirp-based pilot sequence generation, the method comprises: obtaining a first set of parameters from a core network device, wherein the first set of parameters includes: a number N of to-be-generated pilot sequences, a time-domain chirp rate (cl ) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be-generated pilot sequence, wherein TV is a positive integer; obtaining TV pilot sequences based on the first set of parameters, wherein each pilot sequence comprises a set of K pilot chirp carrier samples, and K is an integer not less than TV; applying a weight to each set of the TV sets of pilot carrier samples to produce TV sets of weighted pilot carrier samples; and determining, for each antenna port of the network entity, a subset of the TV pilot sequences, and synthesizing a pilot signal to be transmitted from that antenna port by forming a new set of K samples each of which is obtained by summing corresponding samples from the K samples of each pilot sequence from the determined subset of the TV pilot sequences.

[0043] In an implementation form of the fourth aspect, the method comprises: for each pilot sequence, applying a weight to each sample of the K pilot chirp carrier samples to produce K weighted pilot chirp carrier samples, wherein each of the K samples of the pilot signal is formed by summing corresponding weighted pilot chirp carrier samples from the K samples of each pilot sequence from the determined subset of the N pilot sequences.

[0044] In an implementation form of the fourth aspect, the method comprises: obtaining TV pilot sequences based on the first set of parameters and based on a second set of parameters, wherein the second set of parameters comprises a bandwidth of the to-be- generated pilot sequences and a sample period (Ts) for obtaining a set of pilot chirp carrier samples for each to-be-generated pilot sequence.

[0045] In an implementation form of the fourth aspect, the method comprises: determining a continuous-time chirp carrier function based on a discrete-time pilot chirp carrier, wherein the discrete-time pilot chirp carrier is parameterized with the first set of parameters; and obtaining a set of pilot chirp carrier samples by sampling the continuous-time chirp carrier function with a sample rate of l / 7s.

[0046] Implementation forms of the method of the fourth aspect may correspond to the implementation forms of the network entity of the first aspect described above. The method of the fourth aspect and its implementation forms achieve the same advantages and effects as described above for the network entity of the first aspect and its implementation forms. A fifth aspect of the disclosure provides a method performed by a core network device, the method comprises: providing a first set of parameters to one or more network entities for chirp-based pilot sequence generation, wherein the first set of parameters includes: a number (TV) of to-be-generated pilot sequences, a time-domain chirp rate (cl) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be-generated pilot sequence, wherein TV is a positive integer.

[0047] Implementation forms of the method of the fifth aspect may correspond to the implementation forms of the core network device of the second aspect described above. The method of the fifth aspect and its implementation forms achieve the same advantages and effects as described above for the core network device of the second aspect and its implementation forms

[0048] A sixth aspect of the disclosure provides a method performed by a RAN device, the method comprises: forwarding a first set of parameters, received from a core network device, to one or more network entities for chirp-based pilot sequence generation, wherein the first set of parameters includes: a number (TV) of to-be-generated pilot sequences, a time-domain chirp rate (cl ) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be-generated pilot sequence, wherein TV is a positive integer; and providing a second set of parameters to the one or more network entities, wherein the second set of parameters comprises a bandwidth of the to-be-generated pilot sequence and a sample period (7s) for obtaining a set of pilot carrier samples for each to-be-generated pilot sequence, and a type of continuous-time chirp carrier function.

[0049] Implementation forms of the method of the sixth aspect may correspond to the implementation forms of the RAN device of the third aspect described above The method of the sixth aspect and its implementation forms achieve the same advantages and effects as described above for the RAN device of the third aspect and its implementation forms.

[0050] A seventh aspect of the disclosure provides a computer program product comprising a program code for carrying out, when implemented on a processor, the method according to the third aspect and any implementation forms of the third aspect, or the fourth aspect and any implementation forms of the fourth aspect.

[0051] A sixth aspect of the disclosure provides a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to cany out, the fourth aspect and any implementation forms of the fourth aspect, the method according to the fifth aspect and any implementation forms of the fifth aspect, or the method according to the sixth aspect and any implementation forms of the sixth aspect.

[0052] It has to be noted that all devices, elements, units, and means described in the present application could be implemented in software or hardware elements or any kind of combination thereof. All steps that 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

[0053] BRIEF DESCRIPTION OF DRAWINGS

[0054] The above-described aspects and implementation forms of the present disclosure will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

[0055] FIG 1 shows a network entity according to an embodiment of this disclosure; FIG 2 shows a time-frequency representation of two DAFT symbols;

[0056] FIG 3 shows shows the generation of over-sampled chirp pilots according to an embodiment of this disclosure;

[0057] FIG 4 shows a general block diagram of the proposed system according to an embodiment of this disclosure;

[0058] FIG 5 shows a general block diagram of the network entity according to an embodiment of this disclosure;

[0059] FIG 7 shows the frequency shifting of the over-sampled chirp pilots according to an embodiment of this disclosure;

[0060] FIG 8 shows the pulse-shaping of the AFDM chirps according to an embodiment of this disclosure;

[0061] FIG 9 shows a core network device according to an embodiment of this disclosure;

[0062] FIG 10 shows a RAN device according to an embodiment of this disclosure;

[0063] FIG 11 shows a method according to an embodiment of this disclosure;

[0064] FIG 12 shows a method according to an embodiment of this disclosure; and

[0065] FIG 13 shows a method according to an embodiment of this disclosure

[0066] DETAILED DESCRIPTION OF EMBODIMENTS

[0067] Illustrative embodiments of a network entity for chirp-based pilot signal generation, a core network device, a RAN, and corresponding methods are described in the following with reference to the figures Although this description provides a detailed example of possible implementations, it should be noted that the details are intended to be exemplary and in no way limit the scope of the application.

[0068] Moreover, an embodiment or example may refer to other embodiments or examples. For example, any description including but not limited to terminology, element, process, explanation, and / or technical advantage mentioned in one embodiment or example may also apply to the other embodiments or examples.

[0069] FIG 1 shows a network entity 100 for chirp-based pilot signal generation according to an embodiment of the disclosure

[0070] The network entity 100 may comprise processing circuitry (not shown) configured to perform, conduct, or initiate the various operations of the network entity 100 described herein. The processing circuitry may comprise hardware and software. The hardware may comprise analog circuitry 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 network entity 100 may further comprise memory circuitry, which stores one or more instruction(s) that can be executed by the processor or by the processing circuitry, in particular under the 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 processor or the processing circuitry, causes the various operations of the network entity 100 to be performed In one embodiment, the processing circuitry comprises one or more processors and a non-transitory memory connected to one or more processors. The non-transitory memory may carry executable program code which, when executed by one or more processors, causes the network entity 100 to perform, conduct, or initiate the operations or methods described herein.

[0071] The goal of the present disclosure is to address the above-mentioned challenges by designing AFDM pilot generation schemes to meet any spectral mask requirements without having to change the sampling rate of the DAC. The solution proposed in this disclosure aims to provide flexible spectral shaping of AFDM-based pilots with the following features:

[0072] 1 The bandwidth designated for sensing and channel estimation via the pilot signal is configurable to any selected value that does not exceed the sampling rate. Conversely, the sampling rate can be set to any value that surpasses the nominal bandwidth of the pilot signal, thus offering substantial versatility in bandwidth utilization.

[0073] 2 The architecture for pilot signal generation and detection is engineered to be inherently simple, facilitating ease of implementation and operational efficiency without compromising the system's efficacy.

[0074] 3 The design ensures that the pilot signals are generated with a low peak-to-average power ratio (P PR), thereby reducing the power demands and enhancing the signal's resilience to nonlinear distortions. Additionally, the pilot signals exhibit minimal leakage, which is instrumental in augmenting the accuracy of delay-Doppler detection and estimation, critical for robust and reliable sensing in diverse operational environments

[0075] This disclosure addresses a critical gap in the AFDM technology within the 6G ISAC space, offering a solution to enhance its applicability and performance in a variety of communication and sensing scenarios It may be understood that the network entity 100, which generates the chirp-based pilot signal 103, may be any network devices such as advanced base stations, an edge computing node, or backhaul network equipment equipped with ISAC capabilities, or any ISAC terminal devices such as connected vehicles, a smartphone, a smart home device, wearable ISAC device, an industrial ISAC sensor, etc.

[0076] For ease of understanding of this application, the AFDM signal is first introduced here. FIG. 2 illustrates the principle of an AFDM signal structure. AFDM utilizes the DAFT for its signal construction. The DAFT is a linear transformation characterized by parameters (cx, c2), making it a more generalized form that includes the discrete Fresnel transform (DFnT) as a special case

[0077] The bandwidth of the AFDM signal, denoted as 1 / At, remains constant across each chirp, ensuring that the entire bandwidth is utilized efficiently. This is crucial for 6G applications, which demand high spectral efficiency.

[0078] AFDM’s ability to exploit the diversity of linear time- varying (LTV) channels, while keeping the pilot signal overhead low, makes it a promising candidate for future wireless communication systems. Its structure allows for robust performance in various channel conditions, making it especially suitable for the complex environments expected in 6G networks.

[0079] According to an embodiment of this disclosure, when forming the new set of K samples for the pilot signal 103, the network entity 100 may be configured to: for each pilot sequence 102 with index m, apply a weight x[m] to each sample of the K pilot chirp carrier samples to produce K weighted pilot chirp carrier samples, and each of the new set of K samples of the pilot signal 103 is formed by summing corresponding weighted pilot chirp carrier samples from the K samples of each pilot sequence 102 from the determined subset of the N pilot sequences 102.

[0080] According to an embodiment of this disclosure, the network entity may be configured to append the K pilot chirp carrier samples of the pilot signal 103 with a prefix and / or a suffix of samples Notably, the prefix of samples comprises one of the following: a chirp periodic prefix, a periodic prefix, or a zero-valued prefix, and / or the suffix of samples comprises one of the following: a chirp periodic suffix, a periodic suffix, or a zero-valued suffix.

[0081] FIG 4 shows a wireless communications system according to an embodiment of the disclosure The system is composed of a plurality of network devices including at least one core network node 200, at least one network node 300, and a number of network entities 100 capable of communications and sensing, i.e., ISAC terminals. The network devices could themselves have integrated sensing and communications capabilities The core network node 200 is used to assign the cell-specific pilot parameters (most importantly the value of parameters N and c, which need to be coordinated among neighboring cells to keep inter-cell pilot interference at low levels) to the different network devices. Notably, each ISAC terminal may be the network entity 100 shown in FIG. 1. The network entity 100 may obtain the first set of parameters 101 and an additional second set of parameters 104 from a network node, e.g., a RAN device 300. In particular, the first set of parameters 101 is obtained from the core network device 200 via the RAN device 300

[0082] It may be worth mentioning that in a different embodiment of the disclosure, the network entity 100 may be implemented in the RAN device 300. In this case, the network entity 100 is configured to obtain the first set of parameters 101 from the core network device, and, the network entity 100 may be further configured to determine the second set of parameters 104

[0083] According to an embodiment of the disclosure, the network entity 100 may be configured to obtain N pilot sequences 102 based on the first set of parameters 101 and based on a second set of parameters 104, wherein the second set of parameters 104 comprises a bandwidth (BW) of the to-be-generated pilot sequences and a sample period (Ts) for obtaining the set of K pilot chirp carrier samples for each to-be-generated pilot sequence.

[0084] FIG 5 shows a block diagram of a transmitter in the network entity 100 according to an embodiment of this disclosure. In this particular embodiment, the network entity 100 comprises a sequence generator block that is responsible for producing pilot sequences.

[0085] The Analog-to-Digital Converter (ADC) blocks are connected to both pilot signal generators. It digitizes the analog pilot signals generated by the pilot signal generators, converting them into a digital format that can be processed or transmitted by digital systems

[0086] The Antenna Sub-system interfaces with the ADC and is responsible for transmitting the digitized pilot signal via antennas. It includes a plurality of transmit antennas

[0087] The pilot parameters assignment signaling represents a control signal path that sends parameter assignments to various blocks within the network entity 100. It ensures that the pilot signal is generated with the correct settings.

[0088] Sequence generator

[0089] At the sequence generator block of the network entity 100, the samples <(> (kTs) can be either computed online when needed, or stored in look-up tables for different combinations of the pilot codebook parameters This disclosure proposes two types of continuous-time chirp carrier functions for online generation of the continuous-time

[0090] For the first type, the network entity 100 is configured to determine the continuous-time chirp carrier function based on the discrete-time pilot chirp carrier using a complex exponential function whose instantaneous frequency is a chirp carrier-specific step function.

[0091] For the second type, the network entity 100 is configured to determine the continuous-time chirp carrier function by applying an interpolation formula to samples of the discrete-time pilot chirp carrier.

[0092] In particular, the continuous-time version of the discrete-time chirp >m[fc] is to interpolate its samples using their DFT coefficients 4>m[fc] as follows

[0093] It may be understood that one possible continuous-time chirp formula to be used for generating the up-sampled discrete-time chirp pilots is the formula of an exact analog chirp version of the discrete-time AFDM chirp carrier (Type 1 ). Another possible continuous-time formula version is the interpolation formula of the samples of the discrete-time 7V-point AFDM chirp carriers using their W-point DFT coefficients (Type 2).

[0094] Considering the prefix and the suffix of the pilot signal, one possible way to sample the formula is the “online” computation of the above K + Kpreflx+ Ksu fflxsamples from the formulas.

[0095] According to another embodiment of the disclosure, the network entity 100 may be configured to obtain the set of K pilot chirp carrier samples based on a look-up table using the first set of parameters 101 and the second set of parameters 104. Optionally, the network entity 100 may be configured to obtain a reference pilot chirp carrier from the look-up table using the first set of parameters 101 and the second set of parameters 104, wherein the look-up table is a reduced-size look-up table. The network entity 100 may be configured to generate a sequence of pilot chirp carrier samples by cyclically shifting the reference pilot chirp carrier; and obtain the set of K pilot chirp carrier samples for a pilot chirp carrier from the sequence of K pilot chirp carrier samples.

[0096] Integrating these considerations, the total quantity of unique entries within the pilot codebook, which is utilized for the efficient transmission of pilot signals, is estimated to not exceed a few thousand. This estimate presumes that the FFT sizes are commensurate with those employed in extant 5G NR systems. Such a codebook size is conducive to maintaining a balance between system complexity and the flexibility required to accommodate varying channel conditions and operational requirements.

[0097] Frequency-domain multiplexing of the AFDM pilot signal with other waveforms

[0098] The pilot signal can be multiplexed in the frequency domain with other signals possibly having different waveforms e g., within the OFDM-based frame structure of the wireless system. This can be achieved by applying a linear-phase shift to the pilot samples generated using the disclosed method to center their signal in a given frequency of a sub-band. This operation is illustrated in FIG 7 where the center frequency (normalized with respect to the sub-carrier spacing) is denoted as vsFIG 7 shows frequency shifting the over-sampled chirp pilots to vs(the center of the ISAC frequency band)

[0099] According to this embodiment of the disclosure, the network entity 100 is further configured to shift the synthesized pilot signal 103 to a predefined frequency by applying a linear-phase shift to the obtained N pilot sequences 102.

[0100] Pulse-shaping AFDM chirps against both fractional delay and fractional Doppler and for reducing out-of-band emission (OOBE) levels

[0101] FIG 9 shows a core network device 200 according to an embodiment of this disclosure. The core network device 200 is configured to provide a first set of parameters 101 to one or more network entities 100 for chirp-based pilot sequence generation, wherein the first set of parameters 101 includes: a number (N) of to-be-generated pilot sequences, a time-domain chirp rate (<q) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be-generated pilot sequence, wherein N is a positive integer

[0102] In one implementation, the network entity 100 may be the network entity shown in FIG. 1, FIG. 4, or FIG. 5. The core network device 200 may be the core network device 200 shown in FIG. 1 or FIG 4. In one implementation, the network entity 100 may be the network entity shown in FIG. 1 or FIG. 4 The core network device 200 may be the core network device 200 shown in FIG. 1 or FIG. 4. The RAN device 300 may be the RAN device 300 shown in FIG 4.

[0103] Optionally, the second set of parameters 104 further comprises a type of window function, and one or more window parameters corresponding to the type of window function, wherein the type of window function comprises a global window function type and / or section window function type.

[0104] In one particular embodiment, the RAN device 300 may also be the network entity 100. In this case, the RAN device determines the second set of parameters 104, and performs the chirp-based pilot signal generation based on the first set of parameters 101 and the second set of parameters 104

[0105] FIG 11 shows a method 1100 according to an embodiment of the disclosure, particularly for chirp-based pilot sequence generation In a particular embodiment, the method 1500 is performed by the network entity 100 shown in one of FIG. 1, FIG 4, FIG 5, FIG 9, or FIG 10 The method 1100 comprises a step 1101 of obtaining a first set of parameters 101 from a core network device 200, wherein the first set of parameters 101 includes: a number (A) of to-be-generated pilot sequences, a timedomain chirp rate (ct) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be-generated pilot sequence, wherein V is a positive integer. Further, the method 1100 comprises a step 1102 of obtaining N pilot sequences 102 based on the first set of parameters 101, wherein each pilot sequence 102 comprises a set of K pilot chirp carrier samples, and K is an integer not less than N. The method 1100 further comprises a step 1103 of determining, for each antenna port of the network entity 100, a subset of the N pilot sequences 102, and a step 1104 of synthesizing a pilot signal 103 to be transmitted from that antenna port by forming a new set of K samples each of which is obtained by summing corresponding samples from the K samples of each pilot sequence 102 from the determined subset of the N pilot sequences 102

[0106] Possibly, the core network device 200 may be the core network device 200 shown in FIG 1 , FIG. 4, or FIG. 9.

[0107] Optionally, before the step of summing corresponding samples from the K samples of each pilot sequence, the method 1100 further comprises: for each pilot sequence 102, applying a weight to each sample of the K pilot chirp carrier samples to produce K weighted pilot chirp carrier samples. In this way, each of the K samples of the pilot signal 103 is formed by summing corresponding weighted pilot chirp carrier samples from the K samples of each pilot sequence 102 from the determined subset of the V pilot sequences 102

[0108] Optionally, the step 1102 of obtaining A pilot sequences 102 based on the first set of parameters 101, may specifically comprise: obtaining N pilot sequences 102 based on the first set of parameters 101 and based on a second set of parameters 104, wherein the second set of parameters 104 comprises a bandwidth of the to-be-generated pilot sequences and a sample period (7s) for obtaining a set of pilot chirp carrier samples for each to-be-generated pilot sequence.

[0109] Optionally, the method 1100 may further comprise: determining a continuous-time chirp carrier function based on a discretetime pilot chirp carrier, wherein the discrete-time pilot chirp carrier is parameterized with the first set of parameters 101 ; and obtaining a set of pilot chirp carrier samples by sampling the continuous-time chirp carrier function with a sample rate of 1 / 7’s.

[0110] FIG 12 shows a method 1200 according to an embodiment of the disclosure. In a particular embodiment, the method 1200 is performed by the core network device 200 shown in FIG. 1 , FIG. 4, or FIG. 9.

[0111] FIG 13 shows a method 1300 according to an embodiment of the disclosure. In a particular embodiment, the method 1300 is performed by the RAN device 300 shown in FIG. 4 or FIG. 10

[0112] Possibly, the network entity 100 may be the network entity 100 shown in one of FIG. 1, FIG. 4, FIG. 5, FIG. 9, or FIG. 10. The core network device 200 may be the core network device 200 shown in FIG. 1 , FIG. 4, or FIG. 9

[0113] To summarize, embodiments of the present application propose:

[0114] A network entity (which may be a network device or a terminal device) and corresponding methods for generating up to N AFDM-based pilot sequences of an arbitrary length K > N of certain parameters (such as: (bandwidth BW, center digital

[0115] A core network node: which assigns different chirp rate parameters c, and other cell-specific parameters e.g., N and c2. to different network entities to be signaled to their respective terminal devices deployed within their respective cell areas

[0116] A RAN device, which signals pilot codebook parameters to terminal devices (i e., network entities) connected with it.

[0117] The present 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 embodiments of the disclosure, 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 mutually different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation

[0118] Furthermore, any method according to embodiments of the disclosure may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer-readable medium of a computer program product The computer-readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive

[0119] Moreover, it is realized by the skilled person that embodiments of the network entity 100, the core network device 200, or the RAN device 300 comprise the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the solution. Examples of other such means, units, elements, and functions are processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, trellis-coded modulation (TCM) encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the solution.

[0120] Especially, the processor(s) of the network entity 100, the core network device 200, or the RAN device 300 may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression “processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some, or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like

Claims

CLAIMS1 A network entity (100) for chirp-based pilot signal generation, configured to: obtain a first set of parameters (101) from a core network device (200), wherein the first set of parameters (101) includes: a number (N) of to-be-generated pilot sequences, a time-domain chirp rate (c 1 ) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be-generated pilot sequence, wherein N is a positive integer; obtain N pilot sequences (102) based on the first set of parameters (101), wherein each pilot sequence (102) comprises a set of K pilot chirp carrier samples, and K is an integer not less than N; and determine, for each antenna port of the network entity (100), a subset of the N pilot sequences (102), and synthesize a pilot signal (103) to be transmitted from that antenna port by forming a new set of K samples each of which is obtained by summing corresponding samples from the K samples of each pilot sequence from the determined subset of the N pilot sequences (102)2 The network entity (100) according to claim 1, wherein the forming the new set of K samples each of which is obtained by summing corresponding samples from the K samples of each pilot sequence from the determined subset of the N pilot sequences (102) comprises: for each pilot sequence (102), applying a weight to each sample of the K pilot chirp carrier samples to produce K weighted pilot chirp carrier samples, wherein each of the new set of K samples of the pilot signal (103) is formed by summing corresponding weighted pilot chirp earner samples from the K samples of each pilot sequence (102) from the determined subset of the N pilot sequences (102).3 The network entity (100) according to claim 1 or 2, configured to: obtain N pilot sequences (102) based on the first set of parameters (101) and based on a second set of parameters (104), wherein the second set of parameters (104) comprises a bandwidth of the to-be-generated pilot sequences and a sample period (Ts) for obtaining the set of K pilot chirp carrier samples for each to-be-generated pilot sequence.4 The network entitv (100) according to claim 3, configured to: determine a continuous-time chirp carrier function based on a discrete-time pilot chirp carrier, wherein the discretetime pilot chirp carrier is parameterized with the first set of parameters (101); and obtain a set of pilot chirp carrier samples by sampling the continuous-time chirp earner function with a sample rate of 1 / Ts.5 The network entity (100) according to claim 4, wherein the second set of parameters (104) further comprises a type of continuous-time chirp carrier function, wherein when the type of continuous-time chirp carrier function is a first type, the network entity (100) is configured to determine the continuous-time chirp carrier function based on the discrete-time pilot chirp carrier using a complex exponential function whose instantaneous frequency is a chirp carrier specific step function; and when the type of continuous-time chirp carrier function is a second type, the network entity (100) is configured to determine the continuous-time chirp carrier function by applying an interpolation formula to samples of the discretetime pilot chirp carrier.6 The network entity (100) according to claim 3, configured to: obtain the set of K pilot chirp carrier samples based on a look-up table using the first set of parameters (101) and the second set of parameters (104)7 The network entity (100) according to claim 6, configured to: obtain a reference pilot chirp carrier from the look-up table using the first set of parameters (101) and the second set of parameters (104), wherein the look-up table is a reduced-size look-up table; generate a sequence of pilot chirp carrier samples by cyclically shifting the reference pilot chirp carrier; and obtain the set of K pilot chirp carrier samples for a pilot chirp carrier from the sequence of K pilot chirp carrier samples8 The network entity (100) according to one of the claims 1 to 7, configured to: shift the synthesized pilot signal ( 103 ) to a predefined frequency by applying a linear-phase shift to the obtained N pilot sequences (102)9 The network entity (100) according to one of the claims 3 to 8, wherein the second set of parameters (104) further comprises a type of window function, and one or more window parameters corresponding to the type of window function.

10. The network entity (100) according to claim 9, configured to: pulse-shape a m-th pilot sequence (102) of the N pilot sequences (102) by applying a window function on the K pilot chirp carrier samples of the m-th pilot sequence (102) based on the first set of parameters (101), the second set of parameters (104), and a value of m, wherein m is an index of the pilot sequence (102) among the N pilot sequences (102)11. The network entity (100) according to claim 10, wherein the type of window function comprises a global window function type and / or a section window function type, wherein the network entity (100) is further configured to: when the type of window function is the global window function type, apply a global window function on each pilot chirp carrier sample of the K pilot chirp carrier samples, and / or when the type of window function is the section window function type, apply a section window function on each pilot chirp carrier sample within a chirp section of the K pilot chirp carrier samples.

12. The network entity (100) according to one of the claims 1 to 11, configured to: append the K pilot chirp carrier samples of the pilot signal (103) with a prefix and / or a suffix of samples, wherein the prefix of samples comprises one of the following: a chirp periodic prefix, a periodic prefix, or a zero- valued prefix, and / or the suffix of samples comprises one of the following: a chirp periodic suffix, a periodic suffix, or a zero-valued suffix.

13. The network entity (100) according to one of the claims 1 to 12, wherein the network entity (100) is implemented in a terminal device (400), wherein the network entity (100) is further configured to: obtain the second set of parameters (104) from a radio access network device (300), wherein the first set of parameters ( 101 ) is obtained from the core network device (200) via the radio access network device (300).

14. The network entity (100) according to one of the claims 1 to 12, wherein the network entity (100) is implemented in a radio access network device (300), wherein the network entity (100) is further configured to: determine the second set of parameters (104).

15. A core network device (200), configured to: provide a first set of parameters (101) to one or more network entities (100) for chirp-based pilot sequence generation, wherein the first set of parameters (101) includes: a number (N) of to-be-generated pilot sequences, a time-domainchirp rate (cl) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be-generated pilot sequence, wherein N is a positive integer.

16. The core network device (200) according to claim 15, wherein the time-domain chirp rates (cl) assigned to different network entities (100) are chosen to have different values.

17. A radio access network device (300), configured to: forward a first set of parameters (101), received from a core network device (200), to one or more network entities(100) for chirp-based pilot sequence generation, wherein the first set of parameters (101) includes: a number (N) of to- be-generated pilot sequences, a time-domain chirp rate (cl) of the to-be-generated pilot sequence, and a frequencydomain chirp rate (c2) of the to-be-generated pilot sequence, wherein N is a positive integer; and provide a second set of parameters (104) to the one or more network entities (100), wherein the second set of parameters (104) comprises a bandwidth of the to-be-generated pilot sequences, a sample period (Ts) for obtaining a set of pilot chirp carrier samples for each to-be-generated pilot sequence, and a type of continuous-time chirp carrier function.

18. The radio access network device (300) according to claim 17, wherein the second set of parameters (104) further comprises a type of window function, and one or more window parameters corresponding to the type of window function, wherein the type of window function comprises a global window function type and / or section window function type.

19. A method (1100) performed by a network entity (100) for chirp-based pilot sequence generation, comprising: obtaining (1101) a first set of parameters (101) from a core network device (200), wherein the first set of parameters(101) includes: a number N of to-be-generated pilot sequences, a time-domain chirp rate (cl) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be-generated pilot sequence, wherein N is a positive mteger; obtaining (1102) N pilot sequences (102) based on the first set of parameters (101), wherein each pilot sequence (102) comprises a set of K pilot chirp carrier samples, and K is an integer not less than N; and determining (1103), for each antenna port of the network entity (100), a subset of the N pilot sequences (102), and synthesizing (1104) a pilot signal (103) to be transmitted from that antenna port by forming a new set of K samples each of which is obtained by summing corresponding samples from the K samples of each pilot sequence (102) from the determined subset of the N pilot sequences (102).

20. The method (1100) according to claim 19, comprising: for each pilot sequence (102), applying a weight to each sample of the K pilot chirp carrier samples to produce K weighted pilot chirp carrier samples, wherein each of the K samples of the pilot signal (103) is formed by summing corresponding weighted pilot chirp carrier samples from the K samples of each pilot sequence (102) from the determined subset of the N pilot sequences(102)21. The method (1100) according to claim 19 or 20, comprising: obtaining N pilot sequences (102) based on the first set of parameters (101) and based on a second set of parameters (104), wherein the second set of parameters (104) comprises a bandwidth of the to-be-generated pilot sequences and a sample period (Ts) for obtaining a set of pilot chirp carrier samples for each to-be-generated pilot sequence.

22. The method (1100) according to claim 21, comprising: determining a continuous-time chirp carrier function based on a discrete-time pilot chirp carrier, wherein the discretetime pilot chirp carrier is parameterized with the first set of parameters (101); and obtaining a set of pilot chirp carrier samples by sampling the continuous-time chirp carrier function with a sample rate of 1 / Ts.

23. A method (1200) performed by a core network device (200), comprising: providing (1201) a first set of parameters (101) to one or more network entities (100) for chirp-based pilot sequence generation, wherein the first set of parameters (101) includes: a number (N) of to-be-generated pilot sequences, a timedomain chirp rate (cl) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be- generated pilot sequence, wherein N is a positive integer24. A method (1300) performed by a radio access network device (300), comprising: forward (1301) a first set of parameters (101), received from a core network device (200), to one or more network entities (100) for chirp-based pilot sequence generation, wherein the first set of parameters (101) includes: a number (N) of to-be-generated pilot sequences, a time-domain chirp rate (cl) of the to-be-generated pilot sequence, and a frequency-domain chirp rate (c2) of the to-be-generated pilot sequence, wherein N is a positive integer; and providing (1302) a second set of parameters (104) to the one or more network entities, wherein the second set of parameters (104) comprises a bandwidth of the to-be-generated pilot sequence and a sample period (Ts) for obtaining a set of pilot carrier samples for each to-be-generated pilot sequence, and a type of continuous-time chirp carrier function.

25. A computer program product comprising a program code for carrying out, when implemented on a processor, the method according to claim 22, 23 or 24.

Images