Methods and systems for inter-symbol interference cancellation in ultra-long latency air-to-ground communication scenarios

Abstract

This application discloses a method and system for inter-symbol interference cancellation in ultra-long-delay air-to-ground communication scenarios, comprising: calculating the required guard interval length before signal transmission; acquiring a received signal; wherein the received signal includes an improved data frame; the improved data frame includes a pre-group training sequence and a post-group training sequence with consistent unit sequence length, and a guard interval; calculating a direct path Doppler frequency offset estimate based on the pre-group training sequence; calculating a reflection path Doppler frequency offset estimate based on the post-group training sequence; determining a reflection path delay estimate based on the reflection path Doppler frequency offset estimate and the guard interval length; and eliminating inter-symbol interference based on the calculated estimates to obtain orthogonal frequency division multiplexing symbols. This application can stably and efficiently eliminate inter-symbol interference in high-mobility, high-delay, and high-speed air-to-ground patrol scenarios, and can be widely applied in the field of communication technology.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to a method and system for eliminating inter-symbol interference in ultra-long latency air-to-ground communication scenarios. Background Technology

[0002] Due to the ever-increasing demand for airborne data services, high-speed air-to-ground communication (A2G) has attracted widespread research interest in recent years. Compared with terrestrial channels, A2G channels exhibit higher Doppler frequency shift and greater multipath delay, thus complicating the design of high-speed airborne wireless communication systems. In A2G channels, radio signals experience significant Doppler frequency offsets (DFO), leading to severe inter-carrier interference (ICI). Related techniques propose a maximum likelihood detection method to reduce state interference. This method jointly detects subcarriers surrounding the target subcarrier in the current and previous symbols to mitigate ISI caused by insufficient extended cyclic prefix (CP). Another CP-free OFDM system iteratively extrapolates received symbols, classifying some symbols as less susceptible to ISI to recover the received signal. However, the above methods cannot handle ISI caused by channel delays exceeding the duration of one OFDM symbol. Summary of the Invention

[0003] The main objective of this application is to propose a method and system for eliminating inter-symbol interference in ultra-high latency air-to-ground communication scenarios, aiming to stably and efficiently eliminate inter-symbol interference in high-mobility, high-latency A2G cruise scenarios.

[0004] To achieve the above objectives, one aspect of this application proposes a method for inter-symbol interference cancellation in ultra-long latency air-to-ground communication scenarios, the method comprising:

[0005] Calculate the required guard interval length before signal transmission;

[0006] Acquire a received signal; wherein the received signal includes an improved data frame; the improved data frame includes a pre-group training sequence and a post-group training sequence with consistent unit sequence length, as well as a guard interval;

[0007] Based on the aforementioned pre-group training sequence, calculate the direct-path Doppler frequency shift estimate;

[0008] Based on the aforementioned post-group training sequence, the estimated value of the Doppler frequency shift of the reflection path is calculated;

[0009] The estimated reflection path delay is determined by combining the estimated reflection path Doppler frequency offset and the protection interval length.

[0010] Inter-symbol interference is eliminated based on the direct path Doppler frequency offset estimate, the reflection path Doppler frequency offset estimate, and the reflection path time delay estimate to obtain orthogonal frequency division multiplexing symbols.

[0011] In some embodiments, calculating the required protection interval length includes:

[0012] The reflection path delay estimate is determined based on the first distance, the second distance, the link angle, and the speed of light; wherein, the first distance is the distance between the airborne user equipment and the ground base station equipment; the second distance is the distance between the reflector and the ground base station; and the link angle is the angle between the link between the ground base station and the reflector and the link between the ground base station and the airborne user equipment.

[0013] Based on the estimated reflection path delay, the size of the fast Fourier transform, and the sampling interval of the communication system, the length of the guard interval is determined, thus obtaining the guard interval length.

[0014] In some embodiments, calculating the direct-path Doppler frequency shift estimate by combining the pre-group training sequence includes the following steps:

[0015] The direct path signal sample is determined based on the unit sequence length of the pre-group training sequence and the received signal;

[0016] Calculate the first phase of the direct-path signal sample;

[0017] Based on the first phase, the estimated value of the direct-path Doppler frequency shift is obtained.

[0018] In some embodiments, calculating the reflection path Doppler frequency shift estimate by combining the post-group training sequence includes the following steps:

[0019] The reflection path signal sample is determined based on the unit sequence length of the post-group training sequence, the size of the fast Fourier transform, and the received signal.

[0020] Calculate the second phase of the reflected path signal sample;

[0021] Based on the second phase, the estimated value of the Doppler frequency shift of the reflection path is obtained.

[0022] In some embodiments, determining the reflection path delay estimate by combining the reflection path Doppler frequency offset estimate and the guard interval length includes the following steps:

[0023] Using the unit sequence and the estimated reflection path Doppler frequency offset, the received signal is compensated for the reflection path Doppler frequency offset within the guard interval to obtain the compensated signal.

[0024] Based on the time-domain transmitted and received signals, an autocorrelation function is constructed according to two cascaded unit sequences and the compensated signal.

[0025] The communication scenario to which the reflection path delay belongs is determined based on the autocorrelation function; wherein, the communication scenario is determined based on the number of unit sequences included when the post-group training sequence falls into the sampling window;

[0026] The estimated reflection path delay is determined based on the communication scenario.

[0027] In some embodiments, eliminating inter-symbol interference based on the direct path Doppler frequency offset estimate, the reflected path Doppler frequency offset estimate, and the reflected path time delay estimate to obtain orthogonal frequency division multiplexing symbols includes the following steps:

[0028] The time-domain transmitted signal is calculated based on the direct path Doppler frequency offset estimate, the reflection path Doppler frequency offset estimate, and the reflection path time delay estimate.

[0029] Construct temporary variables based on the time-domain transmitted signal;

[0030] The temporary variable is processed sequentially by Fast Fourier Transform, Symbolic Demapping, Symbolic Mapping, and Inverse Fast Fourier Transform to obtain the transformation result;

[0031] The time-domain transmitted signal is updated according to the transformation result until the data frame processing is completed, and an orthogonal frequency division multiplexing symbol after eliminating inter-symbol interference is obtained.

[0032] In some embodiments, the expression for calculating the direct-path Doppler frequency shift is:

[0033] ,

[0034] The expression for calculating the Doppler frequency shift of the reflection path is:

[0035]

[0036] in, This represents the estimated Doppler frequency shift along the direct path; Operations indicate how to obtain The phase; Indicates the received signal; Indicates the first At that moment; Indicates the length of a unit sequence; Indicates the size of the Fast Fourier Transform; This represents the number of sampling points in the time-domain transmitted signal frame.

[0037] To achieve the above objectives, another aspect of this application proposes an inter-symbol interference cancellation system for ultra-long latency air-to-ground communication scenarios, the system comprising:

[0038] The first module is used to calculate the required guard interval length before signal transmission;

[0039] The second module is used to acquire the received signal; wherein the received signal includes an improved data frame; the improved data frame includes a pre-group training sequence and a post-group training sequence with consistent unit sequence length, as well as a guard interval;

[0040] The third module is used to calculate the direct-path Doppler frequency shift estimate by combining the pre-group training sequence;

[0041] The fourth module is used to calculate the estimated value of the Doppler frequency shift of the reflection path by combining the post-group training sequence.

[0042] The fifth module is used to determine the estimated reflection path delay by combining the estimated reflection path Doppler frequency offset and the protection interval length.

[0043] The sixth module is used to eliminate inter-symbol interference based on the direct path Doppler frequency offset estimate, the reflection path Doppler frequency offset estimate, and the reflection path delay estimate to obtain orthogonal frequency division multiplexing symbols.

[0044] To achieve the above objectives, another aspect of this application provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described above.

[0045] To achieve the above objectives, another aspect of the embodiments of this application proposes a computer-readable storage medium storing a computer program that, when executed by a processor, implements the methods described above.

[0046] The embodiments of this application include at least the following beneficial effects: This application provides a method and system for eliminating inter-symbol interference in ultra-long-delay air-to-ground communication scenarios. This scheme improves data frames by processing the received signals of data frames containing pre-group training sequences, post-group training sequences, and guard intervals. The reflection path Doppler frequency shift and direct path Doppler frequency shift can be estimated using the pre-group and post-group training sequences. Furthermore, by utilizing the guard interval length and combining it with the time-domain cross-correlation of the received signals, the reflection path delay can be accurately estimated. Based on the various estimates obtained above, inter-symbol interference in high-mobility, high-delay, high-speed air-to-ground communication scenarios can be eliminated stably and efficiently. Attached Figure Description

[0047] The accompanying drawings are used to provide a further understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0048] Figure 1 This is a flowchart of an inter-symbol interference cancellation method for ultra-high latency air-to-ground communication scenarios provided in this application embodiment;

[0049] Figure 2 This is a data processing flowchart for inter-symbol interference cancellation in ultra-high latency air-to-ground communication scenarios provided in this application embodiment;

[0050] Figure 3 This is a schematic diagram of a cruise scenario provided in an embodiment of this application;

[0051] Figure 4 This is a schematic diagram of the OFDM symbol sequence at the receiver under different maximum multipath test scenarios provided in the embodiments of this application;

[0052] Figure 5 This is a schematic diagram of the frame structure under different L values ​​in a two-path A2G cruise channel provided in the embodiments of this application;

[0053] Figure 6 This is a flowchart of the receiving end signal processing provided in an embodiment of this application;

[0054] Figure 7 This is the probability density function of two scenarios under different SNRs in the simulation experiment provided in this application embodiment. and A schematic diagram of the intersection points;

[0055] Figure 8 This is a schematic diagram of the mean square error of the NLOS path delay estimation value in the simulation experiment provided in the embodiments of this application;

[0056] Figure 9This is a schematic diagram of the block error rate performance of the method in this application embodiment under different GI lengths selected according to the NLOS path delay in the simulation experiment provided in the embodiment of this application;

[0057] Figure 10 This is a schematic diagram of the block error rate performance of increasing the number of intra-frame OFDM symbols in the simulation experiment provided in the embodiments of this application;

[0058] Figure 11 (a) is a comparison chart of the block error rate of this method and other methods in the simulation experiment provided in the embodiments of this application;

[0059] Figure 11 (b) is a comparison chart of the normalized effective spectral efficiency of this method and other methods in the simulation experiment provided in the embodiments of this application;

[0060] Figure 12 This is a schematic diagram of the inter-symbol interference cancellation system for ultra-high latency air-to-ground communication scenarios provided in this application embodiment;

[0061] Figure 13 This is a schematic diagram of the hardware structure of the electronic device provided in the embodiments of this application. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0063] Although functional modules are divided in the system diagram and a logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the system or the order in the flowchart. The terms "first / S100," "second / S200," etc., in the specification, claims, and the aforementioned figures are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0064] It is understood that the terms “first,” “second,” etc., used in this application may be used herein to describe various concepts, but unless otherwise stated, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the words “if,” “when,” or “in response to a determination” as used herein may be interpreted as “when…” or “when…” or “in response to a determination.”

[0065] As used in this application, the terms "at least one", "multiple", "each", "any", etc., "at least one" includes one, two or more, "multiple" includes two or more, "each" refers to each of the corresponding multiples, and "any" refers to any one of the multiples.

[0066] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0067] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0068] Compared to terrestrial channels, high-speed air-to-ground (A2G) channels have higher Doppler shift and greater multipath delay, which complicates the design of high-speed airborne wireless communication systems.

[0069] Orthogonal Frequency-Division Multiplexing (OFDM) systems are widely used in 4G and 5G communication systems due to their ability to improve spectral efficiency and combat frequency-selective fading. In low-mobility scenarios, the channel can be considered approximately invariant within one OFDM symbol period. However, in A2G channels, the radio signal experiences significant Doppler Frequency Offsets (DFOs), leading to severe inter-carrier interference (ICI). Related technologies have proposed several solutions, such as DFO estimation based on repetitive or patterned training sequences, joint DFO estimation and channel coefficient estimation for A2G communication scenarios, and DFO estimation schemes applicable to low signal-to-noise ratio scenarios employing a coarse estimation and fine correction process based on the maximum likelihood principle. However, the above methods only consider single-path DFO and neglect the more realistic multipath DFO situation.

[0070] In real-world A2G scenarios with multipath delays, a basis expansion model (BEM) and extended cyclic prefix (CP) aided by prior delay information are employed to address significant channel delays. Furthermore, OFDM systems using equally spaced pilots have developed channel estimation and delay estimation schemes based on orthogonal matching pursuit (OMP). Other schemes propose a maximum likelihood detection method to reduce states, which jointly detects subcarriers surrounding the target subcarrier in the current and previous symbols to mitigate inter-symbol interference (ISI) caused by insufficient CP. Another OFDM system without CP iteratively extrapolates received symbols, classifying some symbols as less susceptible to ISI to recover the received signal. However, the above methods cannot handle ISI caused by channel delays exceeding the duration of one OFDM symbol.

[0071] In view of this, this application provides a method and system for inter-symbol interference cancellation (ISI) in ultra-high latency air-to-ground communication scenarios. This method is a two-path serial ISI cancellation (TSIC) approach capable of handling challenging high-mobility, high-latency A2G cruise scenarios. Ultra-high latency refers to multipath latency exceeding one OFDM symbol period. This application proposes a novel frame structure, including Grouped Training Sequences (GTSs), OFDM symbols, and Guard Interval (GI). Based on this new frame structure, the latency of non-line-of-sight (NLOS) paths (i.e., reflection paths) and the DFO (Depth Forecast Optimization) of line-of-sight (LOS) paths (i.e., direct paths) and NLOS paths can be estimated using GTSs. This application further designs a novel NLOS path latency estimation method. Most existing solutions employ frequency domain delay estimation methods, while the embodiments of this application utilize GI to provide a window containing only NLOS path signals, which is unaffected by LOS path signals. Then, the NLOS path delay is accurately estimated based on the time domain cross-correlation of GTS and received signals, thereby eliminating inter-symbol interference in ultra-long delay air-to-ground communication scenarios.

[0072] The inter-symbol interference cancellation method for ultra-high latency air-to-ground communication scenarios provided in this application relates to the field of communication technology. This method can be applied to terminals, servers, or software running on either a terminal or a server. In some embodiments, the terminal can be a smartphone, tablet, laptop, desktop computer, smart speaker, smartwatch, or vehicle-mounted terminal, but is not limited to these. The server can be configured as an independent physical server, a server cluster or distributed system composed of multiple physical servers, or a cloud server providing basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communication, middleware services, domain name services, security services, CDN, and big data and artificial intelligence platforms. The server can also be a node server in a blockchain network. The software can be an application implementing the inter-symbol interference cancellation method for ultra-high latency air-to-ground communication scenarios, but is not limited to the above forms.

[0073] This application can be used in a wide variety of general-purpose or special-purpose computer system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices. This application can be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform specific tasks or implement specific abstract data types. This application can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0074] Figure 1 This is an optional flowchart of an inter-symbol interference cancellation method for ultra-high latency air-to-ground communication scenarios provided in this application embodiment. Figure 1 The method may include, but is not limited to, steps S100 to S600.

[0075] Step S100: Calculate the required protection interval length before signal transmission;

[0076] Step S200: Acquire the received signal; wherein the received signal includes an improved data frame; the improved data frame includes a pre-group training sequence and a post-group training sequence with consistent unit sequence length, as well as a guard interval.

[0077] Step S300: Calculate the direct-path Doppler frequency shift estimate by combining the pre-group training sequence.

[0078] Step S400: Calculate the estimated Doppler frequency shift of the reflection path by combining the post-group training sequence.

[0079] Step S500: Combine the estimated Doppler frequency offset of the reflection path with the length of the protection interval to determine the estimated reflection path delay.

[0080] Step S600: Eliminate inter-symbol interference based on the direct path Doppler frequency offset estimate, the reflection path Doppler frequency offset estimate, and the reflection path delay estimate to obtain orthogonal frequency division multiplexing symbols.

[0081] Steps S100 to S600, as illustrated in the embodiments of this application, improve the data frame by processing the received signal of the data frame containing the pre-group training sequence, the post-group training sequence, and the guard interval. The reflection path Doppler frequency shift and the direct path Doppler frequency shift can be estimated using the pre-group training sequence and the post-group training sequence. Furthermore, by utilizing the guard interval length and combining it with the time-domain cross-correlation of the received signal, the reflection path delay can be accurately estimated. Based on the various estimates obtained above, inter-symbol interference in high-mobility, high-delay, high-speed air-to-ground cruise scenarios can be stably and efficiently eliminated.

[0082] In some embodiments, step 100 may include, but is not limited to, steps S110 to S120:

[0083] Step S110: Determine the reflection path delay estimate based on the first distance, the second distance, the link angle, and the speed of light; wherein, the first distance is the distance between the air user equipment and the ground base station equipment; the second distance is the distance between the reflector and the ground base station; and the link angle is the angle between the link between the ground base station and the reflector and the link between the ground base station and the air user equipment.

[0084] Step S120: Determine the length of the protection interval based on the estimated reflection path delay, the size of the fast Fourier transform, and the sampling interval of the communication system, thus obtaining the protection interval length.

[0085] In some embodiments, step S300 includes, but is not limited to, the following steps S310~S330:

[0086] Step S310: Determine the direct path signal sample based on the unit sequence length of the pre-group training sequence and the received signal.

[0087] Step S320: Calculate the first phase of the direct path signal sample.

[0088] Step S330: Based on the first phase, obtain the direct-path Doppler frequency offset estimate.

[0089] In some embodiments, step S400 includes, but is not limited to, the following steps S410~S430:

[0090] Step S410: Determine the reflection path signal sample based on the unit sequence length of the post-group training sequence, the size of the fast Fourier transform, and the received signal.

[0091] Step S420: Calculate the second phase of the reflection path signal sample.

[0092] Step S430: Based on the second phase, obtain the estimated value of the Doppler frequency shift of the reflection path.

[0093] In some embodiments, step S500 includes, but is not limited to, the following steps S510~S540:

[0094] Step S510: Using the unit sequence and the estimated reflection path Doppler frequency offset, the received signal is compensated for the reflection path Doppler frequency offset within the guard interval to obtain the compensated signal.

[0095] Step S520: Based on the time-domain transmitted and received signals, an autocorrelation function is constructed according to the two cascaded unit sequences and the compensated signal.

[0096] Step S530: Determine the communication scenario to which the reflection path delay belongs based on the autocorrelation function; wherein, the communication scenario is determined based on the number of unit sequences included when the post-group training sequence falls into the sampling window.

[0097] Step S540: Determine the estimated reflection path delay value based on the communication scenario.

[0098] In some embodiments, step S600 includes, but is not limited to, the following steps S610 to S640:

[0099] Step S610: Calculate the time-domain transmitted signal based on the direct path Doppler frequency offset estimate, the reflection path Doppler frequency offset estimate, and the reflection path time delay estimate.

[0100] Step S620: Construct temporary variables based on the time-domain transmitted signal.

[0101] Step S630: Perform Fast Fourier Transform, Symbolic Demapping, Symbolic Mapping and Inverse Fast Fourier Transform on the temporary variable in sequence to obtain the transformation result.

[0102] Step S640: Update the time-domain transmitted signal according to the transformation result until the data frame processing is completed, and obtain the orthogonal frequency division multiplexing symbol after eliminating inter-symbol interference.

[0103] In some embodiments, the expression for calculating the direct-path Doppler frequency shift is:

[0104] ,

[0105] The expression for calculating the Doppler frequency shift of the reflection path is:

[0106]

[0107] in, This represents the estimated Doppler frequency shift along the direct path; Operations indicate how to obtain The phase; Indicates the received signal; Indicates the first At that moment; Indicates the length of a unit sequence; Indicates the size of the Fast Fourier Transform; This represents the number of sampling points in the time-domain transmitted signal frame.

[0108] The following section provides a detailed introduction and explanation of the solutions in this application embodiment, using specific examples of ultra-high latency air-to-ground communication scenarios:

[0109] This application provides a method for eliminating inter-symbol interference (ISI) in ultra-long-latency air-to-ground communication scenarios. This method can be applied to eliminate ISI in ultra-long-latency air-to-ground communication scenarios. The overall data processing flow of the interference elimination process based on this application embodiment is as follows: Figure 2 As shown, the focus of this application embodiment is on the frequency offset estimation, time delay estimation, and inter-symbol elimination parts of the processing flow.

[0110] Furthermore, the system model constructed and applied in the embodiments of this application includes a channel model and a frame structure, such as... Figure 3 In the A2G cruise scenario shown, It is the distance between the air user equipment (AUE) and the ground base station (BS). It is the distance between the reflector and the AUE. It is the distance between the reflector and BS. It is the altitude of AUE flight. This is the angle between the BS-reflector link and the BS-AUE link. In this embodiment, the receiver and transmitter have achieved perfect synchronization through a specific signal.

[0111] The Channel Impulse Response (CIR) of the A2G cruise channel consists of a LOS (Low-Side Response) component and a NLOS (Non-Standard-Side Response) component, and can be expressed as:

[0112]

[0113] in, It is absolute time. It is a variable representing the additional time delay. and These represent the CIR values ​​for the LOS and NLOS parts, respectively.

[0114] The calculation formula is:

[0115]

[0116] in Represents Rice factor, It is the imaginary unit. Represents the Dirac delta function. It is the relative LOS path delay. DFO representing the LOS path, This indicates the phase of the LOS path.

[0117] The calculation formula is:

[0118]

[0119] Indicates the first ( DFO of the diffuse reflection path, Indicates the first ( The phase of the diffuse reflection path, It is the number of diffuse reflection paths. It is the time delay of the NLOS path relative to the LOS path in the continuous time domain. It is the maximum time delay of the diffuse path relative to the LOS path, which is related to the height of the AUE. and Represented as:

[0120]

[0121] in, It is the flight speed of AUE. It's the speed of light. It is the carrier frequency. and Representing the LOS path and the first The angle between the NLOS sub-path and the AUE flight direction, Uniformly distributed within a 3.5° interval. Because The values ​​are similar, and considering that the cell radius in an A2G scenario can reach hundreds of kilometers, ( They are approximately equal.

[0122] Based on this, we have:

[0123]

[0124] in, This indicates a unified NLOS path DFO.

[0125] Furthermore, in A2G cruise scenarios, The streaked reflection path can be considered as a unified NLOS path, and its time delay is related to... They are approximately equal. Let the sampling interval of the communication system be... In the discrete time domain, the NLOS delay is... for:

[0126]

[0127] When both the LOS path and NLOS path delays are integer multiples of the sampling interval, the A2G channel's first... The discrete form of the channel coefficients at each time point can be expressed as:

[0128]

[0129] in, It is the second plural number. Let be the first complex number, represented as:

[0130]

[0131] In A2G channels, extremely high DFO will lead to severe ICI. Furthermore, if the multipath delay is greater than the duration of an OFDM symbol, CP cannot eliminate ISI. Therefore, embodiments of this application utilize two sets of GTS and GI to estimate the LOS / NLOS path DFO and NLOS delay, and then use the estimated values ​​of the above parameters to help the receiver eliminate ISI caused by the NLOS path.

[0132] Furthermore, such as Figure 4 As shown, Figure 4 This is a schematic diagram of the received signal sequence in a traditional OFDM system under a two-path A2G channel model. Specifically, one data frame can be transmitted... OFDM symbols ( Each OFDM symbol contains a length of CP of sampling points and One frequency-domain modulated data symbol, of which It is the size of the Fast Fourier Transform (FFT). When Even if ISI cannot be eliminated by CP, some existing solutions can address this type of problem. However, when At that time, these solutions will no longer be effective, such as Figure 4 As shown in scenario 2.

[0133] To solve Figure 4To address the problem in scenario 2, this application provides an improved frame structure, such as... Figure 5 As shown, Scenario 1: Scenario 2: ; Modulus Operators. This frame structure consists of 2 GTS groups. It consists of OFDM symbols and GI. More specifically, it consists of two identical Zadoff-Chu (ZC) sequences. Leading GTS (L-GTS) formed by tandem It is added to the beginning of each frame. Its length is... Unit Sequence (US) It can be expressed in the following forms:

[0134]

[0135] in It is related to the sequence length Coprime prime numbers. Additionally, there is the Ending-GTS (E-GTS), which consists of 4 USs. Placed in the After one OFDM symbol. Between L-GTS and E-GTS, there exists Discrete-time OFDM symbols ( ), and has the following forms of expression:

[0136]

[0137] in, For the first The first OFDM symbol on Each time-domain sample, For the first The first OFDM symbol on Frequency domain symbols on subcarriers.

[0138] Next, in the process of... , ( )and The end of the frame is inserted with a length of The GI of each sampling point is used to prevent the signal of the current frame from affecting the signal of the next frame. The transmitted signal in the time domain... It can be expressed in the following forms:

[0139]

[0140] in, The number of sampling points in a frame. , This is the floor operator.

[0141] exist Figure 5 In this scenario, the received signal consists of two parts, when At that time, the length of the first segment was Part of it is unaffected by ISI, and the length of the second segment is Part of it is affected by ISI. Combining equations (7) and (11), the received signal It can be represented as:

[0142]

[0143] in, The variance is Additive white Gaussian noise. Then, based on equation (12), the goal is to... , and Recover OFDM symbols in unknown situations. Furthermore, in equation (8)... It remains unchanged within a frame.

[0144] Furthermore, in the ISI elimination scheme of this application embodiment, the GI length is determined before the transmission signal is transmitted. And at the receiving end, it is used to estimate the DFO of the NLOS path. . use and The time delay of the NLOS path can be estimated. After estimating the LOS path DFO Then, the received signal is subjected to ICI and ISI cancellation and OFDM symbol recovery using the parameters estimated above. This involves the following four steps, where steps 2 and 3 are not in any particular order:

[0145] 1. Calculation of the length G of GI.

[0146] The magnitude of G is determined before signal transmission. Figure 3 In A2G cruise scenarios, due to The value can be very large, and is always much greater than 0. You can get and Then we have:

[0147]

[0148] in This can be obtained by AUE through radar or sensors. It should be noted that the calculation here... This is a rough value used to determine the size of G.

[0149] Due to the length of GI It should be greater than the NLOS latency. Only then can ISI be eliminated at the receiving end. Combining equations (6) and (13), we can obtain:

[0150]

[0151] in, .

[0152] 2. Estimate the NLOS path DFO, NLOS delay, and NLOS CIR.

[0153] GI can be used to estimate the time delays of DFO and NLOS paths. An appropriate GI length was chosen. The GI window at the receiving end contains only the NLOS path signal. For example... Figure 5 middle The two cases are shown. The length on the NLOS diameter is... The E-GTS portion of the sequence falls within the GI. As the NLOS path delay increases, a larger GI length is required to accommodate the E-GTS portion of the NLOS path, thus maintaining the relationship with equation (14). Conditions to avoid inter-frame ISI. Specifically, the E-GTS portion of the NLOS path that falls into GI refers to the condition in equation (11). ,in satisfy .

[0154] EGTS consists of four USs, and its total length is Therefore, any length extracted from E-GTS is The partial sequences all consist of two cyclically shifted USs, so the DFO of the NLOS path is estimated using the repeatability of the partial sequences. Then, based on the received signal... ( ), can estimate the DFO value of the NLOS path Represented as:

[0155]

[0156] in, express phase, * " indicates the conjugate operator.

[0157] In obtaining Then, further utilization ( The characteristics of E-GTS and EGTS are used to estimate the NLOS path delay. More specifically, in the NLOS path, E-GTS falls within... A portion of the window may contain 2 or 3 US, that is Figure 5 Two scenarios:

[0158] Scenario 1: Contains 2 USs, ;

[0159] Scenario 2: Contains 3 USs, .

[0160] Using known US and estimated The orthogonality of the US, which was destroyed by the DFO, can be restored by compensating the received signal for the NLOS path DFO in the GI. Therefore, based on equations (11) and (12), the orthogonality of the US, which was destroyed by the DFO, can be restored by using two cascaded USs and the received signal after compensating for the NLOS path DFO. Construct an autocorrelation function :

[0161]

[0162] in, .

[0163] According to equation (16), in Figure 5 In scenario 1, exist There is a peak value at that time. There is a half-peak at that time. Figure 5 In scenario 2, exist There is a peak value at that time. Another peak appears at that time. Therefore, it is necessary to find The maximum and second largest values ​​are used to determine whether it is belong Figure 5 Which scenario? and They represent If we find the indices of the maximum and second largest values, then we have:

[0164]

[0165] in, Based on this, we can obtain To determine To determine which scenario it belongs to, we first need to use equation (14):

[0166]

[0167] Then, combining equations (16)-(18), It can be estimated as:

[0168]

[0169] in Let it be a random variable. The optimal value of the decision threshold. It can be obtained by the following method. Apply equation (16) to... Figure 5 In scenario 1, we have:

[0170]

[0171] Since a linear combination of Gaussian random variables is also a Gaussian random variable, it can be considered that... and If they are all Rice random variables, then , ,Right now Follows the variance The non-central parameter is Rice distribution, Follows the variance The non-central parameter is Rice distribution. and It is independent, and the following formula (21) can be used to calculate the value of scene 1. The probability density function (PDF) :

[0172]

[0173] in This represents a zeroth-order modified Bessel function of the first kind. Similarly, in scenario 2... PDF for:

[0174]

[0175] Based on the definitions of Scenario 1 and Scenario 2, the probabilities of both scenarios occurring are equal. Then, according to the minimum average error probability criterion, The following conditions must be met:

[0176]

[0177] Since equations (21) and (22) are complex, equation (23) can be solved using the integral function in MATLAB. This function can perform high-precision numerical integration of the objective function within a specified interval.

[0178] Next, using equations (7) and (12), the DFO estimation window can be used to estimate... :

[0179]

[0180] Finally, we can calculate using equations (7) and (15) to obtain the result. .

[0181] 3. Estimate the LOS path DFO.

[0182] like Figure 5 As shown, when At that time, the preceding LOS path signal Each sample is unaffected by the NLOS path signal, and L-GTS It consists of two US connected in series, similar to equation (15), and the DFO of the LOS path can be calculated. :

[0183]

[0184] Based on equations (7) and (12), we can obtain:

[0185]

[0186] therefore, .

[0187] 4. Eliminate inter-symbol interference in NLOS paths.

[0188] like Figure 5 As shown, OFDM symbols are affected by interference from L-GTS or the previous OFDM symbol. This interference is estimated in... and Then, based on equation (12), ICI and ISI cancellation can be performed on the received signal, that is:

[0189]

[0190] exist Under these conditions, the received signal is only affected by ICI interference; Under these conditions, the received signal is subject to interference from ICI and ISI. Based on equation (27), all OFDM symbols can be recovered serially.

[0191] In general, the methods of the embodiments of this application can be summarized as follows:

[0192] 1. Input receive signal ;

[0193] 2. Calculate according to formula (15) Equation (19) is used to calculate Equation (24) is used to calculate Equation (25) is used to calculate Equation (26) is used to calculate And make .

[0194] 3. Repeat the calculation according to formula (27). , , Define temporary variables ;right Perform an FFT, then perform symbol demapping in the frequency domain, and then remap to obtain intermediate variables. ;right Perform an inverse FFT to obtain the updated ;make ,renew The steps continue until the data frame processing is complete, and the estimated OFDM symbols are obtained. .

[0195] In summary, at the receiving end, the signal processing flow is as follows: Figure 6 As shown.

[0196] The following simulation analysis and results, combined with specific embodiments, further illustrate the beneficial effects of the proposed solution:

[0197] Unless otherwise specified, the simulation parameters for this simulation experiment are shown in Table 1:

[0198] Table 1

[0199]

[0200] Simulations were performed using the simulation parameters in Table 1, and the probability density function was calculated according to formula (23). The results are as follows: Figure 7 As shown, Figure 7 The probability density functions of the two scenarios under different SNRs are plotted in the figure. and The intersection of the two points shows that the optimal decision threshold can be approximated as 0.75. Figure 8 NLOS path delay estimation through simulation The minimum mean squared error (MSE) verifies the above results, that is, in When this is achieved, the lowest MSE can be reached, and this parameter will also be used in subsequent simulations.

[0201] Figure 9 According to The block error rate (BLER) performance of the TSIC algorithm under different selected GI sizes was compared. It can be observed that at larger GI sizes... Under conditions of greater NLOS path delay, fewer OFDM symbols are interfered with by the NLOS path signal, thus improving BLER performance. Furthermore, as... Figure 10As shown, the number of OFDM symbols within a frame is increased. Error propagation can reduce BLER performance, where an estimation error in the current OFDM symbol can affect the next OFDM symbol.

[0202] Next, under the same system bandwidth, the method of this application embodiment will be compared with a series of comparative schemes, including:

[0203] 1. LS-Linear / LS-Average-1 / LS-Average-2: These schemes use the Least Squares (LS) algorithm for channel estimation (CE) and equalization. For CE within an OFDM symbol, LS-Linear applies linear interpolation to the frequency domain channel estimate at the pilot, while LS-Average-1 and LS-Average-2 apply the average channel estimate from all pilots to all data subcarriers. The time-domain and frequency-domain pilots and their spacing for these three schemes are as follows: .

[0204] 2. Ogbe / MCE-PBEM: Because the Ogbe and MCE-PBEM schemes are only used in... Effective at the time, while This is invalid. Therefore, the subcarrier spacing is halved and the FFT points are multiplied by 2 to maintain... .

[0205] Figure 11 (a) shows the BLER performance under different schemes, where all comparative schemes use the ideal LOS path DFO. The method proposed in this application... Under the simulation parameters, both the ideal LOS path DFO and the estimated LOS path DFO were used. It can be seen that even using the estimated LOS path DFO, this method outperforms all comparative schemes. Without the ISI elimination module, BLER performance degrades significantly, which also proves the effectiveness of ISI elimination in the embodiments of this application. Furthermore, Figure 11 (b) evaluated the Normalized Effective Spectral Efficiency (NESE). This shows that even with some redundancy, this application still has an advantage in effective spectral efficiency. The simulation results above show that this application can... The solution effectively eliminated ISI interference under challenging conditions, while the comparative solution suffered significant performance degradation.

[0206] Finally, the computational complexity of different schemes is shown in Table 2, where the complexity calculation of the proposed scheme (TSIC) includes parameter estimation and ICI / ISI elimination. It can be seen that compared with the comparative schemes, the method of this application has a moderate computational complexity.

[0207] Table 2

[0208]

[0209] In summary, the embodiments of this application have at least the following beneficial effects:

[0210] 1. A novel frame structure is proposed, including grouped training sequences, OFDM symbols, and guard intervals. Based on the new frame structure, the DFO of the LOS path and the DFO and delay of the NLOS path can be estimated using GTS.

[0211] 2. A novel NLOS path delay estimation scheme is designed. Although most existing schemes employ frequency domain delay estimation methods, this application utilizes GI to provide a window containing only the NLOS path signal, which is unaffected by the LOS path signal. Then, using the numerically calculated optimal decision threshold, the NLOS path delay can be accurately estimated based on the time-domain cross-correlation between the GTS and the received signal.

[0212] 3. For OFDM systems in A2G cruise scenarios, a novel interference cancellation method is proposed, which utilizes estimated DFO and NLOS path delays to eliminate ISI. Simulation results show that the proposed algorithm works well even with large delays of several OFDM symbol durations.

[0213] Please see Figure 12 This application also provides an inter-symbol interference cancellation system for ultra-long latency air-to-ground communication scenarios, which can implement the above-mentioned inter-symbol interference cancellation method for ultra-long latency air-to-ground communication scenarios. The system includes:

[0214] The second module 101 is used to calculate the required guard interval length before signal transmission;

[0215] The first module 102 is used to acquire the received signal; wherein the received signal includes an improved data frame; the improved data frame includes a pre-group training sequence and a post-group training sequence with consistent unit sequence length, as well as a guard interval;

[0216] The third module 103 is used to calculate the direct-path Doppler frequency shift estimate by combining the pre-group training sequence;

[0217] The fourth module 104 is used to calculate the estimated value of the Doppler frequency shift of the reflection path by combining the post-group training sequence.

[0218] The fifth module 105 is used to determine the estimated reflection path delay by combining the estimated reflection path Doppler frequency offset and the protection interval length.

[0219] The sixth module 106 is used to eliminate inter-symbol interference based on the direct path Doppler frequency offset estimate, the reflection path Doppler frequency offset estimate, and the reflection path delay estimate to obtain orthogonal frequency division multiplexing symbols.

[0220] It is understood that the content of the above method embodiments is applicable to this system embodiment. The specific functions implemented in this system embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0221] This application also provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the aforementioned inter-symbol interference cancellation method for ultra-long latency air-to-ground communication scenarios. This electronic device can be any smart terminal, including tablet computers, in-vehicle computers, etc.

[0222] It is understood that the content of the above method embodiments is applicable to this device embodiment. The specific functions implemented by this device embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0223] Please see Figure 13 , Figure 13 The hardware structure of an electronic device according to another embodiment is illustrated. The electronic device includes:

[0224] The processor 201 can be implemented using a general-purpose CPU (Central Processing Unit), microprocessor, application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this application.

[0225] The memory 202 can be implemented as a read-only memory (ROM), static storage device, dynamic storage device, or random access memory (RAM). The memory 202 can store the operating system and other applications. When the technical solutions provided in the embodiments of this specification are implemented through software or firmware, the relevant program code is stored in the memory 202 and is called and executed by the processor 201 to execute the inter-symbol interference cancellation method for ultra-high latency air-to-ground communication scenarios according to the embodiments of this application.

[0226] Input / output interface 203 is used to implement information input and output;

[0227] The communication interface 204 is used to enable communication and interaction between this device and other devices. Communication can be achieved through wired means (such as USB, network cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.).

[0228] Bus 205 transmits information between various components of the device (e.g., processor 201, memory 202, input / output interface 203, and communication interface 204);

[0229] The processor 201, memory 202, input / output interface 203 and communication interface 204 are connected to each other within the device via bus 205.

[0230] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described inter-symbol interference cancellation method for ultra-high latency air-to-ground communication scenarios.

[0231] It is understood that the content of the above method embodiments is applicable to this storage medium embodiment. The specific functions implemented in this storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0232] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, memory may optionally include memory remotely located relative to the processor, and these remote memories can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0233] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0234] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0235] The system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0236] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0237] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0238] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0239] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the system embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interfaces, apparatuses, or units, and may be electrical, mechanical, or other forms.

[0240] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0241] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0242] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes multiple instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing programs, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0243] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A method for eliminating inter-symbol interference in ultra-long latency air-to-ground communication scenarios, characterized in that, Includes the following steps: Calculate the required guard interval length before signal transmission; Acquire a received signal; wherein the received signal includes an improved data frame; the improved data frame includes a pre-group training sequence and a post-group training sequence with consistent unit sequence length, as well as a guard interval; Based on the aforementioned pre-group training sequence, calculate the direct-path Doppler frequency shift estimate; Based on the aforementioned post-group training sequence, the estimated value of the Doppler frequency shift of the reflection path is calculated; The estimated reflection path delay is determined by combining the estimated reflection path Doppler frequency offset and the protection interval length. Inter-symbol interference is eliminated based on the direct path Doppler frequency offset estimate, the reflection path Doppler frequency offset estimate, and the reflection path time delay estimate to obtain orthogonal frequency division multiplexing symbols.

2. The method according to claim 1, characterized in that, The required protection interval length for the calculation includes: The reflection path delay estimate is determined based on the first distance, the second distance, the link angle, and the speed of light; wherein, the first distance is the distance between the airborne user equipment and the ground base station equipment; the second distance is the distance between the reflector and the ground base station; and the link angle is the angle between the link between the ground base station and the reflector and the link between the ground base station and the airborne user equipment. Based on the estimated reflection path delay, the size of the fast Fourier transform, and the sampling interval of the communication system, the length of the guard interval is determined, thus obtaining the guard interval length.

3. The method according to claim 1, characterized in that, The step of calculating the direct-path Doppler frequency shift estimate by combining the pre-group training sequence includes the following steps: The direct path signal sample is determined based on the unit sequence length of the pre-group training sequence and the received signal; Calculate the first phase of the direct-path signal sample; Based on the first phase, the estimated value of the direct-path Doppler frequency shift is obtained.

4. The method according to claim 1, characterized in that, Based on the aforementioned post-group training sequence, the estimated Doppler frequency shift of the reflection path is calculated, including the following steps: The reflection path signal sample is determined based on the unit sequence length of the post-group training sequence, the size of the fast Fourier transform, and the received signal. Calculate the second phase of the reflected path signal sample; Based on the second phase, the estimated value of the Doppler frequency shift of the reflection path is obtained.

5. The method according to claim 1, characterized in that, The step of determining the estimated reflection path time delay by combining the estimated reflection path Doppler frequency offset and the guard interval length includes the following steps: Using the unit sequence and the estimated reflection path Doppler frequency offset, the received signal is compensated for the reflection path Doppler frequency offset within the guard interval to obtain the compensated signal. Based on the time-domain transmitted and received signals, an autocorrelation function is constructed according to two cascaded unit sequences and the compensated signal. The communication scenario to which the reflection path delay belongs is determined based on the autocorrelation function; wherein, the communication scenario is determined based on the number of unit sequences included when the post-group training sequence falls into the sampling window; The estimated reflection path delay is determined based on the communication scenario.

6. The method according to claim 1, characterized in that, The process of eliminating inter-symbol interference and obtaining orthogonal frequency division multiplexing symbols based on the direct path Doppler frequency offset estimate, the reflected path Doppler frequency offset estimate, and the reflected path time delay estimate includes the following steps: The time-domain transmitted signal is calculated based on the direct path Doppler frequency offset estimate, the reflection path Doppler frequency offset estimate, and the reflection path time delay estimate. Construct temporary variables based on the time-domain transmitted signal; The temporary variable is processed sequentially by Fast Fourier Transform, Symbolic Demapping, Symbolic Mapping, and Inverse Fast Fourier Transform to obtain the transformation result; The time-domain transmitted signal is updated according to the transformation result until the data frame processing is completed, and an orthogonal frequency division multiplexing symbol after eliminating inter-symbol interference is obtained.

7. The method according to claim 1, characterized in that, The expression for calculating the direct-path Doppler frequency shift is as follows: ， The expression for calculating the Doppler frequency shift of the reflection path is: in, This represents the estimated Doppler frequency shift along the direct path; Operations indicate how to obtain The phase; Indicates the received signal; Indicates the first At that moment; Indicates the length of a unit sequence; Indicates the size of the Fast Fourier Transform; This represents the number of sampling points in the time-domain transmitted signal frame.

8. An inter-symbol interference cancellation system for ultra-long latency air-to-ground communication scenarios, characterized in that, include: The first module is used to calculate the required guard interval length before signal transmission; The second module is used to acquire the received signal; wherein the received signal includes an improved data frame; the improved data frame includes a pre-group training sequence and a post-group training sequence with consistent unit sequence length, as well as a guard interval; The third module is used to calculate the direct-path Doppler frequency shift estimate by combining the pre-group training sequence; The fourth module is used to calculate the estimated value of the Doppler frequency shift of the reflection path by combining the post-group training sequence. The fifth module is used to determine the estimated reflection path delay by combining the estimated reflection path Doppler frequency offset and the protection interval length. The sixth module is used to eliminate inter-symbol interference based on the direct path Doppler frequency offset estimate, the reflection path Doppler frequency offset estimate, and the reflection path delay estimate to obtain orthogonal frequency division multiplexing symbols.

9. An electronic device, characterized in that, Including the processor and memory; The memory is used to store programs; The processor executes the program to implement the method as described in any one of claims 1 to 7.

10. A computer storage medium storing a processor-executable program, characterized in that, The processor-executable program, when executed by the processor, is used to implement the method as described in any one of claims 1 to 7.

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