A method and system for improving timing synchronization performance of an LTE receiver

Abstract

This invention relates to a method and system for improving the timing synchronization performance of an LTE receiver, comprising the following steps: after coarse timing synchronization (STO), fine synchronization of the received signal is performed using a secondary synchronization signal (SSS) to obtain an estimated STO value; the estimated STO value is decomposed into an integer STO component and a fractional STO component; based on the integer STO component, the starting point determined by coarse synchronization is shifted by the entire sampling point to compensate for the integer STO; based on the fractional STO component, cubic spline interpolation is used to interpolate the signal after integer STO compensation by a fractional multiple of the sampling points to compensate for the fractional STO. This invention obtains an accurate timing synchronization position, minimizes inter-symbol interference (ISI) between adjacent symbols, improves the EVM performance of the LTE receiver, enhances the stability of EVM measurements, and reduces fluctuations in measurement results.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and in particular to a method and system for improving the timing synchronization performance of an LTE receiver. Background Technology

[0002] When an LTE receiver uses the standard sampling mode for reception, the STO synchronization accuracy is not high because no sampling is performed at both the transmitting and receiving ends. The maximum error can be close to ±1 sample. LTE EVM measurement systems generally only compensate for integer multiples of STO, and do not compensate for fractional multiples of STO or only perform simple interpolation. They do not consider the performance of endpoints and interpolation methods, resulting in poor EVM measurement results with large fluctuations.

[0003] In OFDM systems, IFFT and FFT are fundamental functions of transmitter modulation and receiver demodulation, respectively. To perform an N-point FFT at the receiver, accurate sampling of the transmitted signal is required within the OFDM symbol period. STO (Simultaneous Start-of-Track) occurs because of clock offsets between the transmit and receive signals, leading to sampling timing differences and consequently, a degraded received signal. To eliminate this effect, symbol timing synchronization must be performed, which helps achieve accurate sampling. Depending on the estimated position of the OFDM symbol start point, STO has different effects, such as… Figure 3 As shown.

[0004] 1) When the estimated OFDM symbol start point coincides with the precise timing, the orthogonality between the subcarrier frequency components can be maintained. In this case, the OFDM symbol can be perfectly recovered without any interference.

[0005] 2) When the estimated OFDM symbol start point is before the precise timing point, but after the end of the channel response of the previous OFDM symbol. In this case, the first symbol will not overlap with the (l-1)th symbol, i.e., there is no ISI caused by the previous symbol.

[0006] 3) When the estimated OFDM symbol start point is earlier than the end of the channel response of the previous OFDM symbol, the symbol timing is too early to avoid ISI. In this case, the orthogonality between subcarriers is disrupted by ISI (from the previous symbol), and ICI occurs simultaneously.

[0007] 4) When the estimated OFDM symbol start point lags behind the precise timing point. In this case, within the FFT interval, the signal consists of a portion of the current OFDM symbol and a portion of the next OFDM symbol.

[0008] Generally, due to the presence of noise, accurate STO estimation is difficult to obtain. When a residual decimal STO remains, depending on its positive or negative direction, it leads to two scenarios: case 2 and case 4. In the latter case, the distortion (including phase deviation) is so severe that it cannot be compensated for. This illustrates that a refined symbol timing scheme is necessary to prevent STOs in this situation.

[0009] When performing timing synchronization, existing solutions typically only estimate and compensate for STO values ​​that are integer multiples of the original timing value. This method is relatively simple and generally works without problems. However, since STO is random, when the fractional part of STO is negative and close to -0.5, meaning the current starting point lags behind the precise timing point by 0.5 samples, the first 0.5 samples of the next OFDM symbol will be mixed into the FFT window, forming severe ISI and causing a significant deterioration in SNR. This interference is particularly noticeable for narrowband signals with a small number of FFT points, and this interference cannot be compensated for by channel estimation, ultimately leading to a severe deterioration in EVM measurement results.

[0010] In view of the above-mentioned shortcomings, the designer has actively researched and innovated in order to create a method and system for improving the timing synchronization performance of LTE receivers, making them more valuable for industrial applications. Summary of the Invention

[0011] To address the aforementioned technical problems, the purpose of this invention is to provide a method and system for improving the timing synchronization performance of an LTE receiver.

[0012] To achieve the above objectives, the present invention adopts the following technical solution: One of the objectives of this invention is: A method for improving the timing synchronization performance of an LTE receiver includes the following steps: Step 1: After STO coarse synchronization, use the secondary synchronization signal SSS to perform STO fine synchronization on the received signal to obtain the STO estimate. Step 2: Decompose the STO estimate into integer STO components and fractional STO components; Step 3: Based on the integer STO components, move the starting point determined by coarse synchronization by the entire sampling point to compensate for the integer STO; Step 4: Based on the fractional STO component, use cubic spline interpolation to perform fractional sampling point interpolation on the signal after compensating for the integer STO, in order to compensate for the fractional STO.

[0013] As a further improvement of the present invention, before performing step 4, the following steps are also included in sequence: The signal sequence after compensation integer STO is extended from beginning to end to obtain the boundary data points required for cubic spline interpolation. After completing cubic spline interpolation, discard the extended data and extract the intermediate valid data for output.

[0014] As a further improvement of the present invention, the length d of the first and last extensions is matched with the number of boundary points required for cubic spline interpolation, wherein d is 2, so as to support the cubic spline interpolation to obtain a complete set of 4 interpolation support points at the endpoints.

[0015] As a further improvement of the present invention, step 1 specifically includes: Step 11: Extract the SSS symbols of the received signal based on the STO coarse synchronization result, and perform Fast Fourier Transform (FFT) to obtain the received SSS frequency domain sequence. Step 12: Perform conjugate multiplication between the received SSS frequency domain sequence and the local reference SSS sequence to eliminate the phase difference between the sequences; Step 13: Calculate the STO estimate based on the phase difference between the previous and next sampling points.

[0016] As a further improvement of the present invention, step 12 specifically includes: Step 121: Extract the first to Nth subcarriers of the received SSS frequency domain sequence and perform conjugate multiplication with the corresponding subcarriers of the local SSS sequence; Step 122: Extract the 2nd to N+1th subcarriers of the received SSS frequency domain sequence and perform conjugate multiplication with the corresponding subcarriers of the local SSS sequence; where N is the length of the SSS sequence minus 1; Step 123: Multiply the results of the two conjugate multiplications by corresponding points to obtain the product sequence; Step 124: Calculate the phase difference between adjacent sampling points in the product sequence, and calculate the STO estimate based on the phase difference.

[0017] As a further improvement of the present invention, the signals after compensation for integer STO and compensation for fractional STO are used by the output value error vector amplitude EVM measurement unit to obtain the EVM measurement result.

[0018] As a further improvement of the present invention, step 3 specifically includes the following steps: Step 31: Convert the integer STO components to offsets in integer sample point units; Step 32: Move the starting point determined by coarse synchronization by an offset to obtain the corrected starting point; Step 33: Move the corrected starting point forward by an extension length of d units, and move the data ending point backward by an extension length of d units, as the input data window for interpolation processing.

[0019] The second objective of this invention is: A system for improving the timing synchronization performance of an LTE receiver, comprising: The STO fine synchronization unit is used to perform STO fine synchronization on the received signal using the secondary synchronization signal SSS after STO coarse synchronization, so as to obtain the STO estimate. STO decomposition unit, used to decompose STO estimates into integer STO components and fractional STO components; The integer STO compensation unit is used to move the starting point determined by coarse synchronization across the entire sampling point according to the integer STO component in order to compensate for the integer STO. The fractional STO compensation unit is used to perform fractional sampling point interpolation on the signal after integer STO compensation based on the fractional STO component using cubic spline interpolation, in order to compensate for the fractional STO.

[0020] As a further improvement of the present invention, the fractional STO compensation unit includes: The beginning and end extension module is used to extend the signal sequence after compensation integer STO before performing cubic spline interpolation on the signal, so as to obtain the boundary data points required for cubic spline interpolation. The cubic spline interpolation module is used to interpolate the extended signal sequence using a cubic spline interpolation algorithm with a fractional number of sampling points. The data extraction module is used to discard the extended data after interpolation and extract the intermediate valid data for output.

[0021] As a further improvement of the present invention, the system is set in an LTE receiver, which also includes an error vector amplitude (EVM) measurement unit. The system outputs the synchronized signal to the error vector amplitude (EVM) measurement unit to obtain the EVM measurement result.

[0022] By means of the above-described solution, the present invention has at least the following advantages: This invention obtains accurate timing synchronization position, eliminates ISI between adjacent symbols to the greatest extent, improves the EVM performance of LTE receivers, enhances the stability of EVM measurement, and reduces fluctuations in measurement results.

[0023] 1. Improve timing synchronization accuracy and achieve subsampling-level synchronization. This invention employs an adjacent subcarrier phase difference estimation algorithm for the SSS (Sequential Segmentation of Subcarriers) to extract the corresponding points of the 1st to Nth and 2nd to N+1th subcarriers of the received SSS frequency domain sequence and multiply them by the conjugate of the local SSS sequence. The phase difference between adjacent sampling points is then calculated to obtain a floating-point precision STO estimate. Compared to traditional integer multiple STO estimation based on cross-correlation peak detection, this estimation method can accurately identify fractional multiple STO components (such as 0.3 sampling points and -0.5 sampling points), providing a precise input basis for subsequent fractional STO compensation and achieving sub-sampling level timing synchronization accuracy.

[0024] 2. Effectively eliminates severe inter-sign interference (ISI) caused by negative decimal STO. This invention addresses the problems left over from existing technologies that only compensate for integer STOs, specifically solving the FFT window aliasing problem caused by negative decimal STOs. When the decimal STO component is negative and close to -0.5 sampling points, traditional methods cause the first sampling point of the next OFDM symbol to be mixed into the FFT window of the current OFDM symbol, resulting in severe ISI. This invention decomposes the STO estimate into integer and decimal parts, and uses cubic spline interpolation to accurately compensate for the decimal part, thus avoiding the sampling of the next OFDM symbol from being mixed into the current FFT window and minimizing ISI interference between adjacent symbols.

[0025] 3. Improve EVM measurement performance and stability This invention applies an improved timing synchronization method to the EVM measurement system of an LTE receiver. Through the coordinated use of cubic spline interpolation and end-to-end extension (d=2), the accuracy of the interpolation endpoints is ensured while compensating for fractional STOs. Experimental results show that, compared to the traditional scheme that only compensates for integer STOs, this invention can improve EVM measurement performance by more than 7dB, while reducing measurement fluctuations and improving the stability and reliability of EVM measurements. This performance improvement is particularly significant for narrowband signals with a small number of FFT points.

[0026] 4. Achieve the optimal balance between accuracy and complexity This invention employs a differentiated compensation strategy, decomposing the STO estimate into integer and fractional parts for separate processing: the integer part is compensated by shifting the coarse synchronization starting point (coarse-grained, low complexity), while the fractional part is compensated using cubic spline interpolation (fine-grained, high precision). This scheme ensures compensation accuracy while avoiding the excessively high computational complexity associated with full-precision interpolation, achieving an optimal balance between accuracy and complexity.

[0027] 5. Ensure endpoint interpolation accuracy to form a complete data processing closed loop. Before performing cubic spline interpolation, this invention extends the signal sequence after integer STO compensation by d=2 at both ends to ensure that all four interpolation support points are obtained even when the interpolation point is at the endpoint, thus guaranteeing the continuity and smoothness of the second derivative of cubic spline interpolation at the endpoints. After interpolation, the extended data is discarded, and the intermediate valid data is extracted for output. Simultaneously, during the integer compensation stage, the corrected starting point is moved forward by d units, and the data ending point is moved backward by d units, forming a complete data processing closed loop of "expanding window → interpolation → shrinking window," ensuring that the interpolation operation does not introduce additional data offset and guaranteeing the temporal alignment accuracy of the output data.

[0028] 6. It has good scalability and versatility. This invention is designed based on improving the EVM measurement performance of LTE receivers, but its application is not limited to this. The STO fine synchronization method and compensation mechanism proposed in this invention are also applicable to the design of timing synchronization systems in receivers of other OFDM systems such as LTE, WiFi, and 5G NR, and have good scalability and versatility.

[0029] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the following are preferred embodiments of the present invention described in detail with reference to the accompanying drawings. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a block diagram of the LTE receiver EVM measurement principle of the present invention; Figure 2 This is a block diagram illustrating the STO fine synchronization principle of the present invention; Figure 3 This is a diagram illustrating the impact of STO; Figure 4 It is a constellation diagram that only compensates for the integer part of the STO using existing technology; Figure 5 This is a schematic diagram illustrating the optimization of the fractional part of STO compensation according to the method described herein. Detailed Implementation

[0032] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0034] First embodiment of the present invention: This embodiment of a method for improving the timing synchronization performance of an LTE receiver includes the following steps: Step 1: After STO coarse synchronization, use the secondary synchronization signal SSS to perform STO fine synchronization on the received signal to obtain the STO estimate.

[0035] Step 1 specifically includes: Step 11: Extract the SSS symbols of the received signal based on the STO coarse synchronization result, and perform Fast Fourier Transform (FFT) to obtain the received SSS frequency domain sequence. Step 12: Perform conjugate multiplication between the received SSS frequency domain sequence and the local reference SSS sequence to eliminate the phase difference between the sequences; Step 13: Calculate the STO estimate based on the phase difference between the previous and next sampling points.

[0036] Step 12 specifically includes: Step 121: Extract the first to Nth subcarriers of the received SSS frequency domain sequence and perform conjugate multiplication with the corresponding subcarriers of the local SSS sequence; Step 122: Extract the 2nd to N+1th subcarriers of the received SSS frequency domain sequence and perform conjugate multiplication with the corresponding subcarriers of the local SSS sequence; where N is the length of the SSS sequence minus 1; Step 123: Multiply the results of the two conjugate multiplications by corresponding points to obtain the product sequence; Step 124: Calculate the phase difference between adjacent sampling points in the product sequence, and calculate the STO estimate based on the phase difference.

[0037] Specifically, in one embodiment, the length of the SSS sequence in the LTE system is 62, therefore N is set to 61. This means that the first to 61 subcarriers of the received SSS frequency domain sequence are extracted and multiplied conjugately with the corresponding subcarriers of the local SSS sequence, and simultaneously, the second to 62 subcarriers are extracted and multiplied conjugately with the corresponding subcarriers of the local SSS sequence. It should be noted that the N value of this invention can be adjusted according to the length of the synchronization signal sequence in different OFDM systems. For example, in a WiFi system, the corresponding N value can be set according to the length of its synchronization signal sequence.

[0038] An explanation of the improvement to fine synchronization using the secondary synchronization signal SSS in step 1: Conventional approach: Cross-correlate the received SSS with the local SSS, detect timing points by peak position, and output integer sampling point positions.

[0039] Invention solution: 1. Extract subcarriers 1-61 and 2-62 of the received SSS frequency domain sequence, and multiply them by the conjugate of the local SSS sequence respectively; 2. Multiply the results of the two conjugate multiplications by corresponding points to obtain the product sequence; 3. Calculate the phase difference between adjacent sampling points in the product sequence, and calculate the STO estimate based on the phase difference.

[0040] Technical benefits: This scheme outputs floating-point precision STO estimates (e.g., 0.3 sampling points, -0.5 sampling points), rather than just integer sampling point positions. This "adjacent subcarrier phase difference" estimation algorithm is not publicly available in existing technologies or conventional SSS synchronization. Its physical significance lies in transforming the timing problem into a phase estimation problem, achieving sub-sampling level precision, and providing an input basis for subsequent fractional STO compensation.

[0041] Step 2: Decompose the STO estimate into integer STO components and fractional STO components.

[0042] Improved explanation of dividing STO into integer and decimal parts in step 2: Common knowledge only discloses the operation of "decomposition", but does not disclose "how to compensate separately after decomposition".

[0043] This invention is formed as follows: Integer part: Moving coarse synchronization start point compensation (coarse-grained, low complexity) Decimal part: Cubic spline interpolation compensation (fine-grained, high-precision) This differentiated combination creates a technological synergy: it ensures compensation accuracy while avoiding the excessive computational complexity caused by full-precision interpolation.

[0044] Step 3: Based on the integer STO component, move the starting point determined by coarse synchronization to the entire sampling point to compensate for the integer STO.

[0045] Step 3 specifically includes the following steps: Step 31: Convert the integer STO components to offsets in integer sample point units; Step 32: Move the starting point determined by coarse synchronization by an offset to obtain the corrected starting point; Step 33: Move the corrected starting point forward by an extension length of d units, and move the data ending point backward by an extension length of d units, as the input data window for interpolation processing.

[0046] Before proceeding to step 4, the following steps are also included in sequence: The signal sequence after compensation integer STO is extended from beginning to end to obtain the boundary data points required for cubic spline interpolation. After completing cubic spline interpolation, discard the extended data and extract the intermediate valid data for output.

[0047] The length d of the first and last extensions is matched with the number of boundary points required for cubic spline interpolation, where d is set to 2 to support cubic spline interpolation to obtain a complete set of 4 interpolation support points at the endpoints.

[0048] Step 4: Based on the fractional STO component, use cubic spline interpolation to perform fractional sampling point interpolation on the signal after compensating for the integer STO, in order to compensate for the fractional STO.

[0049] Improvements to the cubic spline interpolation in step 4: Applying cubic spline interpolation to fractional STO compensation in LTE receivers and solving the ISI problem caused by negative fractional STO has specific application scenario innovations.

[0050] The inventiveness of this invention is reflected in: 1. Specific application scenario: Specifically designed to solve the FFT window aliasing problem caused by negative decimal STO (such as -0.5 sampling points); 2. Completeness of supporting mechanisms: Cubic spline interpolation is not used in isolation, but forms a complete technical loop with end-to-end extension (d=2) and dynamic window adjustment (moving forward and backward by d units); 3. Unpredictability of technical effects: Cubic spline interpolation improves EVM performance by more than 7dB compared to linear interpolation, an effect that cannot be predicted by those skilled in the art.

[0051] Improvements to the beginning and end extensions in step 4: The extensions of this invention have specific technical objectives and parameter constraints.

[0052] Conventional endpoint extension is a general concept, but this invention has the following unique characteristics: 1. The Mathematical Necessity of the Extension Length: d=2 is not an empirical value, but is determined by the mathematical principles of cubic spline interpolation. Cubic spline interpolation requires constructing a cubic polynomial for each interval, needing function value information from the endpoints and neighboring points of that interval, requiring a total of 4 data points. When the interpolation point is located at the endpoint of the original sequence, it is necessary to extend outward by 2 points to obtain a complete 4-point support set. This is a mathematical necessity, not an experimental optimization result.

[0053] 2. End-to-end integrity design: The extension and subsequent "discarding the extension part" form a closed loop, ensuring that the interpolated data is aligned with the original data window and does not introduce additional offset.

[0054] Improvements to integer STO compensation and window management in step 4: The moving coarse synchronization start point compensation integer STO is a routine operation of OFDM receivers, but it is an essential component of the overall scheme.

[0055] Its collaborative relationship with the decimal compensation module: In particular, "moving the corrected starting point forward by d units and the data ending point backward by d units" and "discarding the extended part" form a complete window management mechanism, which is a pairing relationship between dynamic window adjustment and cubic spline interpolation.

[0056] The signals after compensation for integer STO and compensation for fractional STO are used by the output value error vector amplitude EVM measurement unit to obtain the EVM measurement results.

[0057] The coordination between multiple steps in this embodiment: 1. Synergistic Effect 1: Complete closed loop of SSS adjacent subcarrier phase difference estimation → STO decomposition → differential compensation: The first step: SSS adjacent subcarrier phase difference estimation: The output STO estimate is a floating-point number (such as 0.3, -0.5), which retains the precision of the decimal part, which is a prerequisite for subsequent decimal compensation.

[0058] The second step: STO decomposition: decompose the floating-point number STO into an integer part and a fractional part.

[0059] Three stages: Differentiated compensation: The integer part is compensated using window movement (coarse-grained, low complexity), and the decimal part is compensated using cubic spline interpolation (fine-grained, high precision).

[0060] Synergistic effect: It forms a complete closed loop of "estimation → decomposition → compensation". If only integer compensation is used, decimal STO remains, leading to ISI; if only interpolation compensation is used without separating integers, the computational complexity is too high and may introduce accumulated errors. This scheme achieves the optimal balance between accuracy and complexity.

[0061] 2. Synergistic Effect 2: Paired Synergy of Cubic Spline Interpolation and End-to-End Extension: Cubic spline interpolation: requires four data points around the interpolation point to ensure the continuity and smoothness of the second derivative.

[0062] End-to-end extension (d=2): Extend the sequence by 2 points at each end to ensure that 4 data points can also be obtained at the endpoints.

[0063] Discard the extension after interpolation: restore the original data window boundaries to avoid increased data volume and window offset.

[0064] Synergistic effect: If only cubic spline interpolation is used without extension, the interpolation accuracy at the endpoints decreases, leading to a deterioration in the EVM measurement results at the beginning and end of the data block; if only extension is used without cubic spline interpolation, the higher-order smoothing characteristics cannot be utilized. The two form an accuracy guarantee mechanism.

[0065] 3. Synergistic Effect 3: Paired Synergy between Dynamic Window Adjustment and Interpolated Data Truncation: After integer compensation, the starting point is moved forward by d units.

[0066] Move the data end point backward by d units: ensure that the extended data window contains complete information.

[0067] Discard the first and last d data points after interpolation: restore the original window boundaries and avoid data offset.

[0068] Synergistic effect: The data processing paradigm of "expanding the window → interpolation → shrinking the window" ensures that the interpolation operation does not introduce additional data offset, and the temporal alignment accuracy of the output data is guaranteed. Without dynamic window adjustment, the extended data cannot be correctly aligned; without the discard step, the output data volume will increase and an offset will be introduced.

[0069] 4. Synergistic Effect 4: Identification and Targeted Compensation for Negative Decimal STOs Floating-point STO estimation: It can identify negative decimal STOs (such as -0.5 sampling points).

[0070] Cubic spline interpolation compensation: Accurate resampling of negative decimal STOs to prevent the next OFDM symbol sample from being mixed into the current FFT window.

[0071] Synergistic effect: It solves the specific technical problem pointed out in the background technology that "when the decimal part is negative and close to -0.5, the first 0.5 samples of the next OFDM symbol will be mixed into the FFT window, forming a serious ISI".

[0072] The second embodiment of the present invention: This embodiment of a system for improving the timing synchronization performance of an LTE receiver includes: The STO fine synchronization unit is used to perform STO fine synchronization on the received signal using the secondary synchronization signal SSS after STO coarse synchronization, so as to obtain the STO estimate. STO decomposition unit, used to decompose STO estimates into integer STO components and fractional STO components; The integer STO compensation unit is used to move the starting point determined by coarse synchronization across the entire sampling point according to the integer STO component in order to compensate for the integer STO. The fractional STO compensation unit is used to perform fractional sampling point interpolation on the signal after integer STO compensation based on the fractional STO component using cubic spline interpolation, in order to compensate for the fractional STO.

[0073] The fractional STO compensation unit includes: The beginning and end extension module is used to extend the signal sequence after compensation integer STO before performing cubic spline interpolation on the signal, so as to obtain the boundary data points required for cubic spline interpolation. The cubic spline interpolation module is used to interpolate the extended signal sequence using a cubic spline interpolation algorithm with a fractional number of sampling points. The data extraction module is used to discard the extended data after interpolation and extract the intermediate valid data for output.

[0074] The system is installed in the LTE receiver, which also includes an error vector amplitude (EVM) measurement unit. The system outputs the synchronized signal to the error vector amplitude (EVM) measurement unit to obtain the EVM measurement result.

[0075] Experimental examples of the present invention: The purpose of this experimental example is to improve the quality of the received signal by adding fractional STO detection and compensation to the SSS detection part in time-domain fine synchronization, thereby eliminating ISI of adjacent symbols caused by fractional STO and improving the performance and stability of EVM measurement.

[0076] The block diagram of the LTE receiver EVM measurement system in this experimental example is as follows: Figure 1 As shown. Before entering the FFT, coarse synchronization and fine synchronization of STO need to be performed separately. Coarse synchronization mainly involves estimating and compensating for STOs that are multiples of integers, while fine synchronization involves estimating and compensating for STOs that are fractional to the coarse synchronization. This article mainly describes the implementation process of STO fine synchronization.

[0077] In this experimental example, STO fine synchronization is mainly achieved through the secondary synchronization signal SSS in LTE, which is a 62-m sequence in the frequency domain. First, the SSS signal of the received signal is extracted using the coarse synchronization result and multiplied with the local reference SSS signal using a conjugate multiplication to eliminate phase differences between sequences. Then, the phase difference between the previous and subsequent samples is used to calculate the phase deviation caused by STO, and the time-domain STO is calculated from the deviation. The STO is then divided into integer and fractional parts for compensation. First, the integer STO is compensated by shifting the starting point of the coarse synchronization by an integer number of samples. Then, the previous signal is interpolated by a fractional factor; here, cubic spline interpolation is used. The interpolation method has a significant impact on performance; using other first-order interpolation methods (such as linear interpolation) yields limited performance improvement. Since cubic spline interpolation requires sampling data from four points around the interpolation point, the original synchronization sequence needs to be extended at both ends to ensure the accuracy of the endpoint interpolation. d is the extension length, whose value depends on the interpolation method; here, it is set to 2. The interpolated received signal eliminates the influence of STO. The above block diagram for precise synchronization is as follows: Figure 2 As shown.

[0078] STO is a floating-point number caused by the sampling frequency deviation between the transmitter and receiver during initial synchronization. Many existing technologies only compensate for the integer part of the STO, neglecting the fractional part. However, when the fractional part of the STO is negative, it introduces the CP of the next symbol into the current symbol, causing significant interference. This interference is more pronounced for symbols with fewer FFT points (narrowband). The following explanation uses the parameter settings of RMCDL R4 FDD mode in LTE to illustrate its impact on EVM performance.

[0079] Figure 4 The EVM performance is compensated only for integer STOs (PSS_EVM=-29.79, PBCH_EVM=-24.43). Figure 5 To compensate for the performance issues of integer and decimal STO (PSS_EVM=-37.18, PBCH_EVM=-34.77), a performance improvement of over 7dB is evident.

[0080] This invention is based on improving the performance of LTE EVM measurement, but its application is not limited to this. It can also be applied to the design of timing synchronization systems in receivers of other common OFDM systems such as LTE and WIFI.

[0081] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0082] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of improving timing synchronization performance of an LTE receiver, characterized by, The steps are as follows: Step 1: After STO coarse synchronization, use the secondary synchronization signal SSS to perform STO fine synchronization on the received signal to obtain the STO estimate. Step 2: Decompose the STO estimate into integer STO components and fractional STO components; Step 3: Based on the integer STO component, move the starting point determined by coarse synchronization by the entire sampling point to compensate for the integer STO; Step 4: Based on the fractional STO component, use cubic spline interpolation to perform fractional sampling point interpolation on the signal after compensating for the integer STO, in order to compensate for the fractional STO.

2. The method of improving timing synchronization performance of an LTE receiver of claim 1, wherein, Before proceeding to step 4, the following steps are also included in sequence: The signal sequence after compensation integer STO is extended from beginning to end to obtain the boundary data points required for cubic spline interpolation. After completing cubic spline interpolation, discard the extended data and extract the intermediate valid data for output.

3. The method of improving timing synchronization performance of an LTE receiver of claim 2, wherein, The length d of the first and last extensions is matched with the number of boundary points required for cubic spline interpolation, where d is 2, to support cubic spline interpolation to obtain a complete set of 4 interpolation support points at the endpoints.

4. The method of improving timing synchronization performance of an LTE receiver of claim 1, wherein, Step 1 specifically includes: Step 11: Extract the SSS symbols of the received signal based on the STO coarse synchronization result, and perform Fast Fourier Transform (FFT) to obtain the received SSS frequency domain sequence. Step 12: Perform conjugate multiplication between the received SSS frequency domain sequence and the local reference SSS sequence to eliminate the phase difference between the sequences; Step 13: Calculate the STO estimate based on the phase difference between the previous and next sampling points.

5. The method for improving the timing synchronization performance of an LTE receiver as described in claim 4, characterized in that, Step 12 specifically includes: Step 121: Extract the first to Nth subcarriers of the received SSS frequency domain sequence and perform conjugate multiplication with the corresponding subcarriers of the local SSS sequence; Step 122: Extract the 2nd to N+1th subcarriers of the received SSS frequency domain sequence and perform conjugate multiplication with the corresponding subcarriers of the local SSS sequence; where N is the length of the SSS sequence minus 1; Step 123: Multiply the results of the two conjugate multiplications by corresponding points to obtain the product sequence; Step 124: Calculate the phase difference between adjacent sampling points in the product sequence, and calculate the STO estimate based on the phase difference.

6. The method for improving the timing synchronization performance of an LTE receiver as described in claim 1, characterized in that, The signals after compensation for integer STO and compensation for fractional STO are used by the output value error vector amplitude EVM measurement unit to obtain the EVM measurement result.

7. The method for improving the timing synchronization performance of an LTE receiver as described in claim 1, characterized in that, Step 3 specifically includes the following steps: Step 31: Convert the integer STO component into an offset in whole integer sampling point units; Step 32: Move the starting point determined by coarse synchronization by the offset to obtain the corrected starting point; Step 33: Move the corrected starting point forward by an extension length of d units, and move the data ending point backward by an extension length of d units, as the input data window for interpolation processing.

8. A system for improving the timing synchronization performance of an LTE receiver, characterized in that, include: The STO fine synchronization unit is used to perform STO fine synchronization on the received signal using the secondary synchronization signal SSS after STO coarse synchronization, so as to obtain the STO estimate. STO decomposition unit, used to decompose the STO estimate into integer STO components and fractional STO components; An integer STO compensation unit is used to move the starting point determined by coarse synchronization by the entire sampling point according to the integer STO component in order to compensate for the integer STO. The fractional STO compensation unit is used to perform fractional sampling point interpolation on the signal after integer STO compensation using cubic spline interpolation based on the fractional STO component, so as to compensate for the fractional STO.

9. The system for improving the timing synchronization performance of an LTE receiver as described in claim 8, characterized in that, The fractional STO compensation unit includes: The beginning and end extension module is used to extend the signal sequence after compensation integer STO before performing cubic spline interpolation on the signal, so as to obtain the boundary data points required for cubic spline interpolation. The cubic spline interpolation module is used to interpolate the extended signal sequence using a cubic spline interpolation algorithm with a fractional number of sampling points. The data extraction module is used to discard the extended data after interpolation and extract the intermediate valid data for output.

10. A system for improving the timing synchronization performance of an LTE receiver as described in any one of claims 8 to 9, characterized in that, The system is installed in an LTE receiver, which also includes an error vector amplitude (EVM) measurement unit. The system outputs the synchronized signal to the error vector amplitude (EVM) measurement unit to obtain the EVM measurement result.

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