Pulse shaping ODDM combined timing and frequency synchronization method based on symmetric double pilot

Abstract

The application belongs to the technical field of wireless communication, and discloses a pulse shaping ODDM joint timing and frequency synchronization method based on symmetric double pilot. The method sets up double pilot rows symmetrically upward and downward in a pulse shaping ODDM frame, constructs a double pilot cross ambiguity function timing metric based on a matched filtering ODDM waveform at a receiving end, obtains a main path timing offset estimation by aggregating pilot matching responses under different timing assumptions in a frequency domain, uses pilot observations corresponding to two pilot rows to perform coarse carrier frequency offset estimation, refines residual frequency offset by short baseline phase accumulation of adjacent delay-time samples, and further corrects the frequency offset by using phase relationships of longer time intervals under phase coherent conditions. The application can configure a non-ambiguous frequency offset capture range according to a pilot row spacing, reduce frequency offset search complexity, and improve timing capture reliability and frequency synchronization accuracy of a pulse shaping ODDM system under high-speed movement and double selective channels.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology and relates to the synchronization processing of delay-Doppler domain modulation receivers for high-mobility dual-selective channels. In particular, it relates to a method for joint timing and frequency synchronization based on pulse shaping orthogonal delay-Doppler division multiplexing (ODDM) with symmetrical dual pilots. Background Technology

[0002] Wireless communication systems designed for high-mobility scenarios such as low-Earth orbit satellites, high-speed railways, unmanned platforms, and vehicle-to-everything (V2X) communication suffer from both significant propagation delay spread and Doppler shift. These delays and Doppler effects complicate synchronization, channel estimation, and data detection processes in traditional time-frequency domain receivers. Delay-Doppler domain modulation, capable of describing a biselective channel in the delay-Doppler plane, has thus become a key candidate technology for high-mobility communications.

[0003] Orthogonal Time-Frequency Space (OTFS) synchronization methods are typically built upon rectangular pulse or discrete grid observation models, often estimating time offset and carrier frequency offset through pilot periodicity, correlation peaks, or discrete delay-time grid metrics. In contrast, pulse shaping (ODDM) performs sample-by-sample pulse shaping using delay-Doppler plane orthogonal pulses, followed by matched filtering at the receiver. Its synchronization front-end actually observes continuous waveform samples after matched filtering, where timing offset, carrier frequency offset, fractional delay, multipath Doppler, transmitter pulse shaping, and receiver matched filtering are coupled together.

[0004] Directly using the OTFS discrete grid synchronization metric can lead to several problems: First, large-scale uncompensated carrier frequency offsets can disrupt single-point correlation accumulation; second, fractional time delays and pulse shaping can result in concentrated spectral shapes in local weak responses, affecting the decision of the normalized correlation metric; and third, it is difficult to simultaneously balance the carrier frequency offset acquisition range and estimation accuracy. Therefore, a joint timing and frequency synchronization method for pulse-shaped ODDM matched filter waveforms is needed. Summary of the Invention

[0005] The purpose of this invention is to provide a pulse shaping ODDM joint timing and frequency synchronization method based on symmetrical dual pilots. This method starts with the matched filter waveform at the receiver, constructs a dual pilot mutual ambiguity function timing metric using two symmetrical pilot lines, and utilizes the pilot line spacing and pilot observation phase relationship to achieve coarse estimation of carrier frequency offset within a configurable acquisition range and fine refinement of residual frequency offset, thereby establishing a reliable principal path timing and frequency reference for subsequent channel estimation and data detection.

[0006] The technical solution adopted in this invention is as follows:

[0007] A pulse-shaping ODDM joint timing and frequency synchronization method based on symmetrical dual-pilot frequency is applied to a pulse-shaping orthogonal delay-Doppler multiplexing ODDM receiver. The method includes the following steps:

[0008] S1, in the ODDM delay-Doppler two-dimensional frame, an upper pilot line and a lower pilot line are set. The upper pilot line and the lower pilot line are located at different delay indices and are expanded along the Doppler dimension. A predetermined line interval is set between the upper pilot line and the lower pilot line.

[0009] S2, the transmitting end performs ODDM modulation and pulse shaping on the ODDM delay-Doppler two-dimensional frame including the upper pilot line, lower pilot line, guard line and data symbols to generate the transmitted ODDM waveform; the receiving end performs matched filtering on the received ODDM waveform and obtains the oversampled matched filter output;

[0010] S3. For each candidate timing position of the oversampled signal of the matched filter output, generate local matched filter pilot reference waveforms corresponding to the upper and lower pilot lines respectively, and multiply the matched filter output with the local matched filter pilot reference waveforms by conjugate to obtain the matched product sequence of the upper and lower pilot branches.

[0011] S4. Perform Discrete Fourier Transform on the matched product sequences of the upper and lower pilot branches respectively, map the phase increment caused by frequency offset to the frequency index dimension, and coherently merge the Discrete Fourier Transform results of the two pilot branches to construct a dual-pilot mutual ambiguity timing metric.

[0012] S5. Select the candidate timing position that maximizes the mutual ambiguity timing metric of the dual pilots from the oversampled signal output by the matched filter, and use it as the estimated value of the main diameter timing offset.

[0013] S6, based on the estimated principal path timing offset, align the oversampled signal output by the overmatched filter to the ODDM delay-time grid, and extract the pilot observations corresponding to the upper and lower pilot lines;

[0014] S7. Use the phase difference between the upper and lower pilot lines to perform coarse carrier frequency offset estimation on the pilot observations corresponding to the upper and lower pilot lines.

[0015] S8. After compensating for the coarse carrier frequency offset, the residual carrier frequency offset is refined by using the phase relationship between adjacent delay-time sampling points to obtain the estimated value of the main diameter equivalent carrier frequency offset.

[0016] S9, based on the estimated timing offset of the main path and the estimated equivalent carrier frequency offset of the main path, performs time and frequency synchronization compensation on the received ODDM waveform.

[0017] Furthermore, the upper and lower pilot lines are full Doppler pilot lines that span all Doppler dimensions, and the upper and lower pilot lines use different known pilot sequences; the guard line is set in the adjacent area of ​​the upper and lower pilot lines to reduce the interference of data symbols on pilot observation.

[0018] Furthermore, ODDM modulation in S2 includes: performing an inverse discrete Fourier transform along the Doppler dimension on the ODDM time-delay-Doppler two-dimensional frame to obtain a time-delay-time domain sampling sequence; and indexing the global base rate according to the global base rate time index. The time-delay-time domain sampling sequence is serialized; and the serialized sampling sequence is pulse-shaped sample by sample using a square root Nyquist pulse or a root raised cosine pulse; wherein For delay index, For local time sampling index, The length of the delay dimension.

[0019] Furthermore, in S3, for any candidate timing position... and any pilot branch Matching product sequences for:

[0020]

[0021] in, For oversampled matched filter output, This is the conjugate of the local matched filter pilot reference waveform corresponding to the pilot branch. For the sampling index within the reference window, and These are the upper pilot branch and the lower pilot branch, respectively.

[0022] Furthermore, in S4, the discrete Fourier transforms are performed on the matched product sequences of the upper and lower pilot branches respectively to obtain:

[0023] ;

[0024] And construct the dual-pilot mutual ambiguity timing metric according to the following expression. :

[0025]

[0026] in, and The upper and lower pilot branches are respectively located at the frequency index. The discrete Fourier transform result at the point, For multipath pilot merging range, The length of the upper and lower pilot lines after oversampling.

[0027] Furthermore, in S7, let the delay index of the upper pilot line be... The delay index of the lower pilot line is The line spacing between the two is Construct the phase product based on the pilot observations corresponding to the upper and lower pilot rows at the same index at the same time. :

[0028] ;

[0029] And the phase product is accumulated along the time index:

[0030] ;

[0031] in, For local time sampling index, For Doppler dimension length, and These represent the lower pilot waveform signal and the upper pilot waveform signal, respectively.

[0032] This yields the coarse carrier frequency offset estimate. The unambiguous capture range of the coarse carrier frequency offset estimate is determined by the line spacing. control.

[0033] Furthermore, the coarse carrier frequency offset estimate satisfy:

[0034] ;

[0035] in, The length of the delay dimension, The length is the Doppler dimension; the normalized unambiguous acquisition interval corresponding to the coarse carrier frequency offset estimate is:

[0036] .

[0037] Furthermore, in S8, after compensating for the coarse carrier frequency offset, conjugate multiplication is performed on adjacent delay-time sampling points on the candidate delay line to obtain short-interval residual frequency offset phase observations:

[0038]

[0039]

[0040] and These are the lower and upper pilot waveforms after coarse frequency offset compensation. The value is selected based on the channel coherence length, and the range is: The reliability weights are determined based on the energy and phase consistency of each candidate delay. and Weighted accumulation of short-interval residual frequency offset phase observations from multiple reliable time-delay lines:

[0041]

[0042] And by The phase is used to obtain the estimated value of the equivalent carrier frequency offset of the main path.

[0043] The advantages of this invention compared to the prior art are:

[0044] (1) The present invention constructs a synchronization metric based on the matched filtering waveform of the pulse-shaped ODDM receiver, avoiding model mismatch caused by directly applying the synchronization rules of the rectangular pulse OTFS discrete grid.

[0045] (2) The present invention forms a DualCAF timing metric by using two symmetrical pilot branches, which can achieve main path timing acquisition without pre-compensation for large carrier frequency offset, thereby improving timing robustness under low signal-to-noise ratio and dual-selective channel conditions.

[0046] (3) The present invention utilizes the symmetrical pilot line spacing to control the unambiguous acquisition range of coarse carrier frequency offset estimation, and can make a trade-off between acquisition range and phase sensitivity by configuring the pilot position, without introducing exhaustive frequency offset search.

[0047] (4) The present invention forms a hierarchical frequency offset estimation structure by using inter-row coarse estimation, short-interval residual refinement and optional long baseline correction. Under the multipath phase disturbance caused by mobility, robust short-interval estimation can be used, and under the condition of phase coherence, long baseline can be used to further improve the accuracy.

[0048] (5) The main path timing and frequency reference output by the present invention can provide stable initialization for subsequent effective channel estimation and data detection, which is beneficial for building a complete pulse shaping ODDM receiver. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the ODDM delay-Doppler frame structure of the present invention; wherein the upper and lower symmetrical pilot lines occupy the entire line along the Doppler dimension, and a guard line is set near the pilot. Detailed Implementation

[0050] The embodiments of the present invention will now be described with reference to the accompanying drawings. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art can adjust the pilot sequence, pilot line spacing, guard line width, oversampling factor, reliable line selection criteria, and long baseline correction enable criteria without departing from the concept of the present invention.

[0051] A pulse-shaping ODDM joint timing and frequency synchronization method based on symmetrical dual-pilot frequency is applied to a pulse-shaping orthogonal delay-Doppler multiplexing ODDM receiver. The method includes the following steps:

[0052] S1, in the ODDM delay-Doppler two-dimensional frame, an upper pilot line and a lower pilot line are set. The upper pilot line and the lower pilot line are located at different delay indices and are expanded along the Doppler dimension. A predetermined line interval is set between the upper pilot line and the lower pilot line.

[0053] like Figure 1 As shown, in a size of In the ODDM delay-Doppler 2D resource grid, an upper pilot row and a lower pilot row are set, located at the delay index respectively. and And it occupies the entire row along the Doppler dimension. The row spacing between the two pilot rows is... Guard lines are set above and below the pilot line, and other resource positions are used to carry data signals;

[0054] The two pilot lines are located at different positions along the time delay dimension, preferably arranged symmetrically with respect to the data region or frame center. A known pilot sequence is placed along the Doppler dimension in each pilot line, and several guard lines are set above and below the pilot lines to reduce interference from data to pilot observations.

[0055] S2, the transmitting end performs ODDM modulation and pulse shaping on the ODDM delay-Doppler two-dimensional frame including the upper pilot line, lower pilot line, guard line and data symbols to generate the transmitted ODDM waveform; the receiving end performs matched filtering on the received ODDM waveform and obtains the oversampled matched filter output;

[0056] The ODDM modulation includes: performing an inverse discrete Fourier transform along the Doppler dimension on the ODDM delay-Doppler two-dimensional frame to obtain a delay-time domain sampling sequence; and indexing the global base rate according to the global base rate time index. The time-delay-time domain sampling sequence is serialized; and the serialized sampling sequence is pulse-shaped sample by sample using a square root Nyquist pulse or a root raised cosine pulse; wherein For delay index, For local time sampling index, The length of the delay dimension.

[0057] S3. For each candidate timing position of the oversampled signal of the matched filter output, generate local matched filter pilot reference waveforms corresponding to the upper and lower pilot lines respectively, and multiply the matched filter output with the local matched filter pilot reference waveforms by conjugate to obtain the matched product sequence of the upper and lower pilot branches.

[0058] For any candidate timing position and any pilot branch Matching product sequences for:

[0059]

[0060] in, For oversampled matched filter output, This is the conjugate of the local matched filter pilot reference waveform corresponding to the pilot branch. For the sampling index within the reference window, and These are the upper pilot branch and the lower pilot branch, respectively.

[0061] S4. Perform Discrete Fourier Transform on the matched product sequences of the upper and lower pilot branches respectively, map the phase increment caused by frequency offset to the frequency index dimension, and coherently merge the Discrete Fourier Transform results of the two pilot branches to construct a dual-pilot mutual ambiguity timing metric.

[0062] The following results were obtained by performing discrete Fourier transforms on the matched product sequences of the upper and lower pilot branches respectively:

[0063] ;

[0064] And construct the dual-pilot mutual ambiguity timing metric according to the following expression. :

[0065]

[0066] in, and The upper and lower pilot branches are respectively located at the frequency index. The discrete Fourier transform result at the point, For multipath pilot merging range, The length of the upper and lower pilot lines after oversampling.

[0067] S5. Select the candidate timing position that maximizes the mutual ambiguity timing metric of the dual pilots from the oversampled signal output by the matched filter, and use it as the estimated value of the main diameter timing offset.

[0068] S6, based on the principal path timing offset estimate, align the oversampled signal output by the overmatched filter to the ODDM delay-time grid, and extract the pilot observations corresponding to the upper and lower pilot lines.

[0069] S7. Use the phase difference between the upper and lower pilot lines to perform coarse carrier frequency offset estimation on the pilot observations corresponding to the upper and lower pilot lines.

[0070] Let the delay index of the upper pilot line be... The delay index of the lower pilot line is The line spacing between the two is Construct the phase product based on the pilot observations corresponding to the upper and lower pilot rows at the same index at the same time. :

[0071] ;

[0072] And the phase product is accumulated along the time index:

[0073] ;

[0074] in, For local time sampling index, For Doppler dimension length, and These represent the lower pilot waveform signal and the upper pilot waveform signal, respectively.

[0075] This yields the coarse carrier frequency offset estimate. The unambiguous capture range of the coarse carrier frequency offset estimate is determined by the line spacing. control;

[0076] The coarse carrier frequency offset estimate satisfy:

[0077] ;

[0078] in, The length of the delay dimension, The length is the Doppler dimension; the normalized unambiguous acquisition interval corresponding to the coarse carrier frequency offset estimate is:

[0079] .

[0080] S8. After compensating for the coarse carrier frequency offset, the residual carrier frequency offset is refined by using the phase relationship between adjacent delay-time sampling points to obtain the estimated value of the main diameter equivalent carrier frequency offset.

[0081] After compensating for the coarse carrier frequency offset, conjugate multiplication is performed on adjacent delay-time sampling points on the candidate delay line to obtain short-interval residual frequency offset phase observations:

[0082]

[0083]

[0084] and These are the lower and upper pilot waveforms after coarse frequency offset compensation. The value is selected based on the channel coherence length, and the range is: The reliability weights are determined based on the energy and phase consistency of each candidate delay. and Weighted accumulation of short-interval residual frequency offset phase observations from multiple reliable time-delay lines:

[0085]

[0086] And by The phase is used to obtain the estimated value of the equivalent carrier frequency offset of the main path.

[0087] S9, based on the estimated timing offset of the main path and the estimated equivalent carrier frequency offset of the main path, performs time and frequency synchronization compensation on the received ODDM waveform.

Claims

1. A method for combined timing and frequency synchronization of pulse shaping ODDM based on symmetrical dual-pilot frequency, characterized in that, The method, applied to a pulse-shaping quadrature delay-Doppler multiplexing (ODDM) receiver, includes the following steps: S1, in the ODDM delay-Doppler two-dimensional frame, an upper pilot line and a lower pilot line are set. The upper pilot line and the lower pilot line are located at different delay indices and are expanded along the Doppler dimension. A predetermined line interval is set between the upper pilot line and the lower pilot line. S2, the transmitting end performs ODDM modulation and pulse shaping on the ODDM delay-Doppler two-dimensional frame including the upper pilot line, lower pilot line, guard line and data symbols to generate the transmitted ODDM waveform; the receiving end performs matched filtering on the received ODDM waveform and obtains the oversampled matched filter output; S3. For each candidate timing position of the oversampled signal of the matched filter output, generate local matched filter pilot reference waveforms corresponding to the upper and lower pilot lines respectively, and multiply the matched filter output with the local matched filter pilot reference waveforms by conjugate to obtain the matched product sequence of the upper and lower pilot branches. S4. Perform Discrete Fourier Transform on the matched product sequences of the upper and lower pilot branches respectively, map the phase increment caused by frequency offset to the frequency index dimension, and coherently merge the Discrete Fourier Transform results of the two pilot branches to construct a dual-pilot mutual ambiguity timing metric. S5. Select the candidate timing position that maximizes the mutual ambiguity timing metric of the dual pilots from the oversampled signal output by the matched filter, and use it as the estimated value of the main diameter timing offset. S6, based on the estimated principal path timing offset, align the oversampled signal output by the overmatched filter to the ODDM delay-time grid, and extract the pilot observations corresponding to the upper and lower pilot lines; S7. Use the phase difference between the upper and lower pilot lines to perform coarse carrier frequency offset estimation on the pilot observations corresponding to the upper and lower pilot lines. S8. After compensating for the coarse carrier frequency offset, the residual carrier frequency offset is refined by using the phase relationship between adjacent delay-time sampling points to obtain the estimated value of the main diameter equivalent carrier frequency offset. S9, based on the estimated timing offset of the main path and the estimated equivalent carrier frequency offset of the main path, performs time and frequency synchronization compensation on the received ODDM waveform.

2. The method for combined timing and frequency synchronization of pulse shaping ODDM based on symmetrical dual-pilot frequency according to claim 1, characterized in that, The upper and lower pilot lines are full Doppler pilot lines that span all Doppler dimensions, and the upper and lower pilot lines use different known pilot sequences. The guard line is set in the adjacent area of ​​the upper and lower pilot lines to reduce the interference of data symbols on pilot observation.

3. The method for combined timing and frequency synchronization of pulse shaping ODDM based on symmetrical dual-pilot frequency according to claim 1, characterized in that, ODDM modulation in S2 includes: performing an inverse discrete Fourier transform along the Doppler dimension on the ODDM time-delay-Doppler two-dimensional frame to obtain a time-delay-time domain sampling sequence; and indexing the global base rate according to the global base rate time index. The time-delay-time domain sampling sequence is serialized; and the serialized sampling sequence is pulse-shaped sample by sample using a square root Nyquist pulse or a root raised cosine pulse; wherein For delay index, For local time sampling index, The length of the delay dimension.

4. The method for combined timing and frequency synchronization of pulse shaping ODDM based on symmetrical dual-pilot frequency according to claim 1, characterized in that, In S3, for any candidate timing position and any pilot branch Matching product sequences for: in, For oversampled matched filter output, This is the conjugate of the local matched filter pilot reference waveform corresponding to the pilot branch. For the sampling index within the reference window, and These are the upper pilot branch and the lower pilot branch, respectively.

5. The method for combined timing and frequency synchronization of pulse shaping ODDM based on symmetrical dual-pilot frequency according to claim 4, characterized in that, In S4, the discrete Fourier transforms of the matched product sequences of the upper and lower pilot branches are performed respectively to obtain: ； And construct the dual-pilot mutual ambiguity timing metric according to the following expression. : in, and The upper and lower pilot branches are respectively located at the frequency index. The discrete Fourier transform result at the point, For multipath pilot merging range, The length of the upper and lower pilot lines after oversampling.

6. The method for combined timing and frequency synchronization of pulse shaping ODDM based on symmetrical dual-pilot frequency according to claim 1, characterized in that, In S7, let the delay index of the upper pilot line be... The delay index of the lower pilot line is The line spacing between the two is Construct the phase product based on the pilot observations corresponding to the upper and lower pilot rows at the same index at the same time. : ； And the phase product is accumulated along the time index: ； in, For local time sampling index, For Doppler dimension length, and These represent the lower pilot waveform signal and the upper pilot waveform signal, respectively. This yields the coarse carrier frequency offset estimate. The unambiguous capture range of the coarse carrier frequency offset estimate is determined by the line spacing. control.

7. The method for combined timing and frequency synchronization of pulse shaping ODDM based on symmetrical dual-pilot frequency according to claim 6, characterized in that, The coarse carrier frequency offset estimate satisfy: ； in, The length of the delay dimension, The length is the Doppler dimension; the normalized unambiguous acquisition interval corresponding to the coarse carrier frequency offset estimate is: 。 8. The method according to claim 1, characterized in that, In S8, after compensating for the coarse carrier frequency offset, conjugate multiplication is performed on adjacent delay-time sampling points on the candidate delay line to obtain short-interval residual frequency offset phase observations: and These are the lower and upper pilot waveforms after coarse frequency offset compensation. The value is selected based on the channel coherence length, and the range is as follows: The reliability weights are determined based on the energy and phase consistency of each candidate delay. and Weighted accumulation of short-interval residual frequency offset phase observations from multiple reliable time-delay lines: And by The phase is used to obtain the estimated value of the equivalent carrier frequency offset of the main path.

Images