Adaptive frame design method for asymmetrically protected band AFDM system
By using an adaptive asymmetric guard band design to dynamically adjust the frame structure of the AFDM system, the problems of bit error rate and spectral efficiency under high dynamic channels are solved, achieving higher spectral efficiency and robustness.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2025-11-14
- Publication Date
- 2026-06-26
AI Technical Summary
Existing AFDM system frame structure designs struggle to simultaneously balance receiver bit error rate and spectral efficiency in high-dynamic channels. Conservative pilot configuration leads to resource waste, insufficient adaptability, leakage interference, and high bit error rate.
An adaptive asymmetric guard band design is adopted. The width and shape of the guard band are dynamically adjusted through frame-level reliability determination and pilot position mapping relationship. The asymmetric configuration is carried out according to the Doppler energy distribution, and the guard band length is optimized by combining Doppler energy directionality prior and smoothing factor.
While ensuring detection performance and robustness, it improves the proportion of available data subcarriers and system spectral efficiency, reduces bit error rate and leakage interference, and enhances spectral efficiency.
Smart Images
Figure CN121509172B_ABST
Abstract
Description
Technical Field
[0001] This application relates to a frame structure design method for an AFDM system based on adaptive asymmetric guard bands, belonging to the field of information and communication technology. Background Technology
[0002] In highly dynamic communication scenarios involving space and ground integration, the high relative speed of the link, significant frequency offset and Doppler spread, and rapid changes in the channel over time make it difficult for traditional systems to simultaneously guarantee bit error rate performance and spectral efficiency. OFDM systems, represented by Orthogonal Frequency Division Multiplexing (OFDM), are prone to severe inter-carrier and inter-symbol interference under strong Doppler conditions, leading to increased bit error rate, decreased robustness, and requiring higher pilot overhead.
[0003] As a novel modulation scheme for high-dynamic scenarios, AFDM systems utilize chirp-related orthogonal bases and map information to the discrete affine Fourier domain via affine Fourier transform. This results in a sparse and banded distribution of the signal after passing through a linear time-varying channel, naturally suited for detection and estimation under Doppler conditions. However, from a systems engineering perspective, existing AFDM schemes still have significant shortcomings in frame structure design: Firstly, pilots are often embedded with fixed patterns and fixed power, and the guard bands surrounding the pilots typically employ static, symmetrical, and conservative widths to suppress Doppler leakage. To cover worst-case scenarios, most designs are forced to maintain large guard bands, resulting in the consumption of significant data resources and a substantial reduction in spectral efficiency. Conversely, narrowing the guard band can easily lead to leakage interference and a decrease in bit error rate under strong Doppler or highly directional conditions, making it difficult to achieve a balance. Secondly, existing research still falls short in frame-level adaptation: it generally uses static pilot and protection configurations, which limits the utilization of cross-frame Doppler statistical information and makes it difficult to form an effective closed loop; adaptive triggering often relies on fixed thresholds, which are not robust under low signal-to-noise ratio or rapid fluctuation conditions; the protection band shape is mostly symmetrical and conservative, which results in low resource utilization when facing directional Doppler spread; at the same time, the robustness of leakage measurement and noise assessment is limited, which can easily lead to criterion fluctuations and slow convergence, increasing the difficulty of engineering implementation. Summary of the Invention
[0004] To address the challenge of simultaneously balancing receiver bit error rate and spectral efficiency in AFDM system frame structure design under high dynamic channel conditions, this application provides an AFDM system frame structure design method based on adaptive asymmetric guard band.
[0005] This application discloses a frame structure design method for an AFDM system based on adaptive asymmetric guard bands, comprising:
[0006] S1. Obtain the demodulation result vector of the current frame in the AFDM downlink system, and perform frame-level reliability determination based on the demodulation result vector of the current frame. When the corresponding threshold is met, the current frame admission adaptive update process is initiated.
[0007] S2. In the frame of the admission adaptive update process, single-point path detection is performed by using the pilot position and AFDM geometric mapping relationship to obtain candidate pairs of time delay index and Doppler index, and effective paths are selected. Combined with the complex gain estimation of the effective paths, the effective path set of the current frame is formed.
[0008] S3. Based on the effective path set of the current frame, extract the maximum Doppler spread prior and the Doppler energy directionality prior. Based on the maximum Doppler spread prior, obtain the total protection width of the next frame. Based on the Doppler energy directionality prior, construct a cross-frame smoothing direction factor. Based on the total protection width of the next frame, asymmetrically allocate the length of the protection band on the left and right sides of the pilot, so that the protection band is relatively wider on the side with dense Doppler energy and relatively shorter on the side with sparse energy, and generate the adaptive asymmetric protection band and data area layout for the next frame.
[0009] As a preferred embodiment, in S3, a Doppler energy directionality prior is constructed based on the effective path set and the bias of the Doppler energy on both sides of the positive and negative indices.
[0010] Amplitude limiting is applied to the Doppler energy directionality prior to prevent oversaturation of the direction factor;
[0011] The directionality prior of the Doppler energy after clipping is linearly combined with the smoothed value of the direction factor of the previous frame to obtain the direction factor of the current frame.
[0012] Based on the total protection width of the next frame, the lengths of the left and right protection bands of the pilot in the next frame are asymmetrically allocated using the direction factor of the current frame:
[0013]
[0014]
[0015] in and These represent the lengths of the guard bands on the left and right sides of the pilot signal in the next frame, respectively.
[0016] The total protection width for the next frame;
[0017] This is the direction factor for the current frame.
[0018] As a preferred option, Doppler energy directionality prior. for:
[0019]
[0020] in, Symbols representing the Doppler index;
[0021] For the first The energy of a path;
[0022] The prior to the Doppler energy directionality after clipping is:
[0023]
[0024] in ;
[0025] This is a constant that limits the saturation of the direction factor;
[0026] Direction factor of the current frame for:
[0027]
[0028] in, For smoothing coefficients;
[0029] This is the direction factor of the previous frame.
[0030] Preferably, in S3, the Doppler index of the most valid path set in the current frame is used as the maximum Doppler spread prior. ;
[0031] Guard band parameters for the next frame for:
[0032]
[0033] Total protection width of the next frame for:
[0034]
[0035] in, For the maximum delay index, is a system constant.
[0036] Preferably, S1 includes:
[0037] Frame-level reliability metrics are calculated based on the demodulation result vector, including the bit error rate of this frame, the guard band residual ratio, and the out-of-bounds truncation rate of the noise estimation region.
[0038] If the frame-level reliability metrics for the predetermined number of frames all meet the joint threshold of signal-to-noise ratio adaptation, then the current frame will be admitted to the adaptive update process.
[0039] Preferably, the median amplitude is calculated within the noise estimation region of the demodulated result vector of the current frame. According to the median amplitude The noise power baseline was obtained based on the Rayleigh median relation. For any set of indices, net energy is defined as the energy exceeding the noise power baseline. The energy is used to obtain the guard band residual ratio based on the guard band index set and the net energy of the noise estimation region;
[0040] Based on the sparse band equivalent mapping relationship, the proportion of observation pairs that are not covered by the effective path structure or fall outside the structure is used as the out-of-bounds truncation rate of the noise estimation region.
[0041] As a preferred option, the joint threshold for adaptive signal-to-noise ratio is:
[0042]
[0043] in, This is the bit error rate for this frame;
[0044] To protect the residual ratio of the belt;
[0045] The cutoff rate for the noise estimation region;
[0046] For adaptive bit error rate threshold:
[0047]
[0048] For the adaptive protection band residual ratio threshold:
[0049]
[0050] For adaptive out-of-bounds cutoff rate threshold:
[0051]
[0052] Equivalent signal-to-noise ratio;
[0053] , , , , This is an empirical constant.
[0054] Preferably, S2 includes:
[0055] In the admission adaptive update process, single-point path detection is performed on the frames using the pilot position and AFDM geometric mapping relationship to obtain the delay index. And Doppler Index candidate pairings Get each candidate pair Complex gain estimation ,by As a candidate energy measure;
[0056] Based on a unified noise scale and a single-candidate false alarm upper limit, an energy decision threshold is constructed according to the correspondence between exponential energy distribution and false alarm constraints. ;
[0057] satisfy candidate pairings For multiple candidate delay indices mapped to the same Doppler index, the candidate pair corresponding to the one with the largest candidate energy metric is retained as a valid path. ;
[0058] If all candidate pairs All below Then retain the candidate pairings corresponding to the candidate energy measurers. ;
[0059] Valid path set of the current frame , For the first Delay index of the path, For the first Each path corresponds to an integer Doppler index. For lightweight shrinkage or normalization treatment of the first Complex gain estimation for each path.
[0060] Preferably, in S2, single-point path detection is performed within a restricted Doppler search window using the mapping relationship between pilot positions and AFDM geometry to obtain the time delay index. And Doppler Index candidate pairings The restricted Doppler search window is:
[0061]
[0062] in, This is the current search radius;
[0063]
[0064] The maximum Doppler shift estimated from the previous frame;
[0065] This is a fixed search margin;
[0066] This is the theoretical upper limit determined by the orthogonality constraints of AFDM;
[0067] This is for rounding up.
[0068] As a preferred option, the energy decision threshold for:
[0069]
[0070] in, Pilot power;
[0071] Calculate the median amplitude within the noise estimation region of the demodulated vector of the current frame. According to the median amplitude The noise power baseline was obtained based on the Rayleigh median relation. ;
[0072] Single candidate false alarm limit , To preset the total false alarm probability, This represents the total number of candidates within the search window of the current frame.
[0073] The beneficial effects of this application are to construct a frame structure design based on adaptive asymmetric guard band in AFDM downlink system, especially to set an adaptive shrink guard band. Specifically, the total width of the guard band and the left and right asymmetric allocation are determined by the joint use of maximum Doppler spread and directional prior, so that the guard resources shrink gradually and are directionally configured according to the actual channel, which significantly improves the proportion of available data subcarriers and system spectrum efficiency while ensuring detection performance and robustness.
[0074] In addition, this application uses SNR adaptive three thresholds to control the access of guard band shrinkage, ensuring that structural adjustment is initiated only under reliable conditions where bit error rate, leakage and out-of-bounds are all under control;
[0075] This application also employs a restricted Doppler search window driven by the previous frame's Doppler prior and a total false alarm constraint to achieve low-complexity effective path extraction. Attached Figure Description
[0076] Figure 1 This is a design diagram of the adaptive asymmetric protection band frame structure for this application;
[0077] Figure 2 This is a comparison chart of the bit error rates of the adaptive asymmetric guard band AFDM system of this application and the conventional AFDM system;
[0078] Figure 3 This is a comparison of the spectral efficiency of the adaptive asymmetric protection band AFDM system of this application and the conventional AFDM system;
[0079] Figure 4 This is a comparison diagram of the protection intervals of the adaptive asymmetric protection belt AFDM system and the conventional AFDM system in this application. Detailed Implementation
[0080] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.
[0081] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.
[0082] The present application will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the application.
[0083] The AFDM system frame structure design method based on adaptive asymmetric guard band in this embodiment includes:
[0084] Step 1, Frame-level reliability and adaptive admission assessment:
[0085] In the AFDM downlink system, an initial frame structure containing pilot symbols, guard bands, and data areas is constructed. The received signal is deprecated and demodulated using AFDM to obtain the demodulated result vector.
[0086] The demodulation result vector of the current frame in the AFDM downlink system is obtained. Frame-level reliability is determined based on the demodulation result vector of the current frame. When the corresponding threshold is met, the current frame admission adaptive update process is initiated. Specifically, a unified-scale SNR adaptive three-threshold admission mechanism is adopted.
[0087] In the demodulated result vector noise estimation region Take the median of the amplitude:
[0088]
[0089] Based on the Rayleigh median relation, the noise energy baseline is obtained:
[0090]
[0091] For any set of indices, net energy is defined as the energy exceeding the noise power baseline. The energy is used to obtain the guard band residual ratio based on the guard band index set and the net energy of the noise estimation region; specifically, the noise energy baseline is used as a unified scale for subsequent energy subtraction and threshold comparison to ensure comparability under different SNRs. For any index set The net energy for noise removal is defined as:
[0092]
[0093] in, ;
[0094] This means that only energy exceeding the noise energy baseline is counted, avoiding the misidentification of pure noise as effective components. Based on this, the guard band residual ratio is defined as:
[0095]
[0096] in, To protect indexed collections, For noise estimation region, To find a local minimum value greater than zero, avoid having a denominator of 0. The meaning is the proportion of energy that should not appear in the protection zone to the effective energy of the noise estimation area. It is used to characterize the proportion of leakage energy that should not appear in the protection zone. The smaller the value, the less leakage.
[0097] Based on the sparse banded equivalent mapping relationship, the proportion of observations not covered by the effective path structure or falling outside the structure is used as the out-of-bounds truncation rate of the noise estimation region. Specifically, to evaluate whether the banded observation structure is complete, the number of data columns in this frame is denoted as... The number of valid paths is Theoretically, the total number of pairs that can be formed from data columns to observation rows is:
[0098]
[0099] After out-of-bounds removal and duplicate merging, the number of pairs that actually fall within the valid observation row and are retained is denoted as . The out-of-bounds cutoff rate for the noise estimation region is:
[0100]
[0101] The smaller the value, the more complete the strip mapping and the fewer out-of-bounds errors.
[0102] The joint threshold setting method for adaptive signal-to-noise ratio includes:
[0103] After defining the guard band residual ratio and the out-of-bounds truncation rate, adaptive thresholds are set for both and the bit error rate, and the equivalent signal-to-noise ratio is denoted as . The adaptive bit error rate threshold is set as follows:
[0104]
[0105] The adaptive guard band residual ratio threshold is:
[0106]
[0107] in , , The adaptive out-of-bounds cutoff rate threshold is an empirical constant:
[0108]
[0109] in , For an empirical constant, when Lower thresholds to increase robustness, when High-time thresholds are tightened to free up more data resources.
[0110] After obtaining the above three adaptive thresholds, let The bit error rate for this frame is given if and only if Continuous satisfaction Only when the frame is in use does it enter the retractable guard band state. This is the set value.
[0111] Step 2, Selecting an effective path:
[0112] First, in the frames of the admission adaptive update process, single-point path detection is performed using the pilot position and AFDM geometric mapping relationship to obtain candidate pairs of delay index and Doppler index;
[0113] Specifically, after confirming the current link stability through the three adaptive threshold admission mechanisms in step 1, this application no longer uses a full-domain blind search method for AFDM pilot observations of each frame. Instead, it constructs a restricted Doppler search window by combining the Doppler statistics or initial Doppler priors obtained from the previous frame, and makes a decision within this window by combining a unified noise scale and total false alarm constraints. Specifically, for the first frame... A frame, i.e., the current frame, is defined within a given set of maximum latency indices. Based on the Doppler index, only Search for integer Doppler indexes within a range, where the current search radius is... Maximum Doppler shift estimated from the previous frame Adaptive settings:
[0114]
[0115] in, A fixed search margin is provided to accommodate Doppler drift. This is the theoretical upper limit determined by the orthogonality constraints of AFDM, used to ensure that the search range does not exceed the constraints of the system design. This is for rounding up.
[0116] The restricted Doppler search window design of this application allows the search to focus on the vicinity of the existing prior frame, significantly reducing the search time of traditional blind search methods while ensuring robustness to actual channel changes.
[0117] Then, effective paths are selected from candidate pairs of time delay index and Doppler index, and combined with the complex gain estimation of the effective paths, a set of effective paths for the current frame is formed. Specifically, single-point path detection is performed within a restricted Doppler search window using the pilot mapping relationship of the AFDM system to obtain the time delay index. And Doppler Index candidate pairings For each candidate pairing Its pilot observation index in the demodulation domain can be determined. and the corresponding phase compensation factor Let the pilot symbol be . The corresponding observation is The complex gain of the candidate path The estimation using the single-point least squares form is as follows:
[0118]
[0119] by It serves as a candidate energy metric for subsequent screening.
[0120] Based on a unified noise scale and a single-candidate false alarm upper limit, an energy decision threshold is constructed using the correspondence between exponential energy distribution and false alarm constraints. Specifically, to ensure a consistent interpretation of the screening threshold across different SNRs, the noise scale approach from step 1 is used here, calculating the median amplitude within the noise estimation region of the demodulated vector of the current frame. According to the median amplitude The noise power baseline was obtained based on the Rayleigh median relation. ;
[0121] Let the total number of candidates within the constrained Doppler search window of the current frame be . The system presets the total false alarm probability for the entire candidate set. If we divide it equally among all candidates, we obtain the upper limit of false alarms per candidate:
[0122]
[0123] in To prevent the threshold from being too small when the number of candidates is low, a lower bound is set. Based on the correspondence between exponential energy distribution and false alarm constraints, an energy decision threshold is constructed:
[0124]
[0125] in Pilot power, used for normalization To a unified signal-to-noise ratio scale.
[0126] Beneficial for energy decision threshold Candidate paths are filtered, and the effective path set for the current frame is formed by deduplication and merging based on location. Specifically:
[0127] satisfy candidate pairings Paths are considered valid and sorted by energy from largest to smallest. For multiple candidate delay indices mapped to the same Doppler index, the candidate pair corresponding to the one with the largest candidate energy metric is retained. ;
[0128] If all candidate pairs All below Then retain the candidate pairings corresponding to the candidate energy measurers. .
[0129] Based on this, the energy decision threshold is used... of Simplified shrinkage can be used to suppress noise; specifically, lightweight shrinkage or normalization can be employed. It's important to note that this only enhances numerical robustness, not alters the decision logic. The final set of valid paths for the current frame is denoted as:
[0130]
[0131] in For the first Delay index of the path, For the corresponding integer Doppler index, This is a robustly processed complex gain estimate. This set of effective paths is used to construct the strip observation matrix and iterative equalization, and also directly provides the Doppler priors required for subsequent frame-level adaptive guard band control.
[0132] Step 3, Frame-level adaptive asymmetric protection band:
[0133] First, based on the set of valid paths in the current frame, the maximum Doppler spread prior is extracted, and the total protection width of the next frame is obtained based on the maximum Doppler spread prior; specifically, the maximum Doppler spread obtained from the set of valid paths in the current frame... The guard band parameters are obtained by superimposing a preset safety margin. Based on the orthogonality and geometric relationship of the AFDM system, the total width of the guard band in the next frame is calculated. If the total width exceeds the system's allowable range, the guard band parameters are adjusted to ensure that structural constraints such as limited inter-symbol interference and invertible transformation matrix in AFDM are met. Specifically, after obtaining the effective path set... Then, the maximum Doppler extension prior is extracted first from this set:
[0134]
[0135] Considering this as the current channel's requirement for guard band width, and under the condition that step 1 allows for shrinking, the guard band parameters for the next frame... This application sets its value as follows:
[0136]
[0137] That is, ensuring that it is not lower than the standard set by the relevant authorities. Given the minimum safety protection band, a progressive update is performed based on the value from the previous frame. Then, according to the geometric structure of the AFDM system, [the update is then performed]. Calculate the total protection width for the next frame:
[0138]
[0139] in For the maximum delay index, is a system constant.
[0140] As can be seen from the above formula, the total width of the protective strip is determined by the actual Doppler extension and the structural constraints of the AFDM, which effectively avoids the situation of excessively long protective strips.
[0141] In total width Once determined, this application further introduces a priori Doppler energy directionality to asymmetrically configure the guard bands on both sides of the pilot.
[0142] Then, based on the prior knowledge of Doppler energy directionality, a cross-frame smoothing direction factor is constructed. The length of the guard band on both sides of the pilot is asymmetrically allocated according to the total guard width of the next frame, making the guard band relatively wider on the side with dense Doppler energy and relatively shorter on the side with sparse energy. This generates an adaptive asymmetric guard band and data area layout for the next frame, used for subsequent AFDM downlink transmission and reception. This improves the proportion of available data resources and spectral efficiency while ensuring bit error rate performance and controlled leakage. Specifically,
[0143] Specifically, the Doppler energy directionality prior is constructed based on the effective path set:
[0144]
[0145] in Symbols representing Doppler indexes, For the energy of this path, Numerical values reflect the bias of the Doppler energy on both the positive and negative indices.
[0146] To avoid severe oscillations in the guard band shape caused by single-frame anomalous path estimation, a priori Doppler energy directionality is first established. Limiting the amplitude:
[0147]
[0148] in, , To limit the constant of the direction factor saturation, the implementation can take the value of... To prevent the directional factor from becoming oversaturated.
[0149] Then, when allocating the guard band, the orientation factor of the current frame is obtained by using cross-frame first-order smoothing. The direction factor of the current frame is obtained by linearly combining the current frame's clipping result with the smoothed value of the previous frame's direction factor.
[0150]
[0151] in For smoothing coefficients;
[0152] Using the orientation factor from the previous frame, this step is designed to ensure that the orientation decision is supported by statistics from multiple frames, avoiding drastic fluctuations in the shape of the guardrail due to estimation errors in a single frame. Then, based on the already determined total width... Below, using the direction factor For the first The lengths of the guard bands on the left and right sides of the frame pilot are asymmetrically allocated:
[0153]
[0154]
[0155] in and They represent the first Length of the guard bands on the left and right sides of the frame pilot;
[0156] when When this occurs, it indicates that the high-energy path is more concentrated on the positive Doppler side, and a larger proportion of the protection band is allocated to the corresponding leakage-sensitive side to enhance the suppression capability;
[0157] when When the Doppler distribution is approximately symmetrical, then weighted protection is applied to the other side; when the Doppler distribution is approximately symmetrical, The natural property approaches zero, and the protection belt automatically returns to an approximately symmetrical configuration.
[0158] The AFDM frame structure configured with adaptive asymmetric guard band is as follows: Figure 1 As shown, by Figure 2 and Figure 3 Simulation results show that this application can significantly improve spectral efficiency without significantly sacrificing bit error rate performance. Figure 4 This is a schematic diagram showing the change of the protection interval of this application and the traditional conventional AFDM method with the number of frames in actual simulation.
[0159] Step 3 of this application constructs a Doppler directivity statistic based on the energy difference of the effective path on the positive and negative Doppler indices, performs amplitude limiting and cross-frame first-order smoothing to obtain a direction factor, and, under the determined total guard band width, adjusts the length of the guard band on the left and right sides of the pilot linearly or proportionally according to the direction factor, so that the side with concentrated Doppler energy obtains a wider guard band and the side with sparse energy obtains a narrower guard band, so as to directionally suppress the main leakage path and recover long-term redundant guard band resources.
[0160] While this application has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of this application. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of this application as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.
Claims
1. A frame structure design method for an AFDM system based on adaptive asymmetric guard bands, characterized in that, include: S1. Obtain the demodulation result vector of the current frame in the AFDM downlink system, and perform frame-level reliability determination based on the demodulation result vector of the current frame. When the corresponding threshold is met, the current frame admission adaptive update process is initiated. S2. In the frame of the admission adaptive update process, single-point path detection is performed by using the pilot position and AFDM geometric mapping relationship to obtain candidate pairs of time delay index and Doppler index, and effective paths are selected. Combined with the complex gain estimation of the effective paths, the effective path set of the current frame is formed. S3. Based on the effective path set of the current frame, extract the maximum Doppler spread prior and the Doppler energy directionality prior. Obtain the total protection width for the next frame based on the maximum Doppler spread prior. Construct a cross-frame smoothing direction factor based on the Doppler energy directionality prior. Asymmetrically allocate the length of the protection bands on both sides of the pilot signal according to the total protection width of the next frame, making the protection bands relatively wider on the side with dense Doppler energy and relatively shorter on the side with sparse energy, thus generating the adaptive asymmetric protection band and data area layout for the next frame. In S3, the Doppler energy directionality prior is constructed based on the effective path set and the bias of the Doppler energy on both sides of the positive and negative indices. Amplitude limiting is applied to the Doppler energy directionality prior to prevent oversaturation of the direction factor; The directionality prior of the Doppler energy after clipping is linearly combined with the smoothed value of the direction factor of the previous frame to obtain the direction factor of the current frame. Based on the total protection width of the next frame, the lengths of the left and right protection bands of the pilot in the next frame are asymmetrically allocated using the direction factor of the current frame: ； ； in and These represent the lengths of the guard bands on the left and right sides of the pilot signal in the next frame, respectively. The total protection width for the next frame; The direction factor for the current frame; Doppler energy directionality prior for: ； in, Symbols representing the Doppler index; For the first The energy of a path; The prior to the Doppler energy directionality after clipping is: ； in ; This is a constant that limits the saturation of the direction factor; Direction factor of the current frame for: ； in, For smoothing coefficients; This is the direction factor of the previous frame.
2. The AFDM system frame structure design method based on adaptive asymmetric guard band according to claim 1, characterized in that, In S3, the largest Doppler index in the set of valid paths in the current frame is used as the maximum Doppler spread prior. ; Guard band parameters for the next frame for: ； Total protection width of the next frame for: ； in, For the maximum delay index, is a system constant.
3. The AFDM system frame structure design method based on adaptive asymmetric guard band according to claim 1, characterized in that, S1 includes: Frame-level reliability metrics are calculated based on the demodulation result vector, including the bit error rate of this frame, the guard band residual ratio, and the out-of-bounds truncation rate of the noise estimation region. If the frame-level reliability metrics for the predetermined number of frames all meet the joint threshold of signal-to-noise ratio adaptation, then the current frame will be admitted to the adaptive update process.
4. The AFDM system frame structure design method based on adaptive asymmetric guard band according to claim 3, characterized in that, Calculate the median amplitude within the noise estimation region of the demodulated vector of the current frame. According to the median amplitude The noise power baseline was obtained based on the Rayleigh median relation. For any set of indices, net energy is defined as the energy exceeding the noise power baseline. The energy is used to obtain the guard band residual ratio based on the guard band index set and the net energy of the noise estimation region; Based on the sparse band equivalent mapping relationship, the proportion of observation pairs that are not covered by the effective path structure or fall outside the structure is used as the out-of-bounds truncation rate of the noise estimation region.
5. The AFDM system frame structure design method based on adaptive asymmetric guard band according to claim 4, characterized in that, The joint threshold for adaptive signal-to-noise ratio is: ； in, This is the bit error rate for this frame; To protect the residual ratio of the belt; The cutoff rate for the noise estimation region; For adaptive bit error rate threshold: ； For the adaptive protection band residual ratio threshold: ； For adaptive out-of-bounds cutoff rate threshold: ； Equivalent signal-to-noise ratio; , , , , This is an empirical constant.
6. The AFDM system frame structure design method based on adaptive asymmetric guard band according to claim 1, characterized in that, S2 include: In the admission adaptive update process, single-point path detection is performed on the frames using the pilot position and AFDM geometric mapping relationship to obtain the delay index. And Doppler Index candidate pairings Get each candidate pair Complex gain estimation ,by As a candidate energy measure; Based on a unified noise scale and a single-candidate false alarm upper limit, an energy decision threshold is constructed according to the correspondence between exponential energy distribution and false alarm constraints. ; satisfy candidate pairings For multiple candidate delay indices mapped to the same Doppler index, the candidate pair corresponding to the one with the largest candidate energy metric is retained as a valid path. ; If all candidate pairs All below Then retain the candidate pairings corresponding to the candidate energy measurers. ; Valid path set of the current frame , For the first Delay index of the path, For the first Each path corresponds to an integer Doppler index. For lightweight shrinkage or normalization treatment of the first Complex gain estimation for each path.
7. The AFDM system frame structure design method based on adaptive asymmetric guard band according to claim 6, characterized in that, In S2, single-point path detection is performed within a restricted Doppler search window using the mapping relationship between pilot positions and AFDM geometry to obtain the time delay index. And Doppler Index candidate pairings The restricted Doppler search window is: ； in, This is the current search radius; ； The maximum Doppler shift estimated from the previous frame; This is a fixed search margin; This is the theoretical upper limit determined by the orthogonality constraints of AFDM; This is for rounding up.
8. The AFDM system frame structure design method based on adaptive asymmetric guard band according to claim 6, characterized in that, Energy decision threshold for: ； in, Pilot power; Calculate the median amplitude within the noise estimation region of the demodulated vector of the current frame. According to the median amplitude The noise power baseline was obtained based on the Rayleigh median relation. ; Single candidate false alarm limit , To preset the total false alarm probability, This represents the total number of candidates within the search window of the current frame.