A processing method, receiver and system for narrowband LTE receiver EVM

Abstract

This invention relates to a method, receiver, and system for processing the EVM (Electronic Virtual Machine) of a narrowband LTE receiver, comprising the following steps: Step 1: Obtaining the bandwidth mode of the OFDM signal to be transmitted; Step 2: Performing analog-to-digital conversion sampling on the received signal at a first sampling rate or a second sampling rate; Selecting a synchronization processing strategy based on the bandwidth mode of the received signal. This invention reduces the complexity of AD / DA control, decreasing the number of sampling frequencies from six to two, and eliminating the original fractional STO (Small Unit Tolerance) estimation and interpolation compensation modules. It improves the EVM performance of the LTE receiver in narrowband mode, 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 for processing EVM in a narrowband LTE receiver, a receiver, and a system. Background Technology

[0002] Existing LTE EVM measurement systems generally need to adapt to sampling rates under all bandwidths. If the sampling rate is adjusted according to the bandwidth, it will lead to complex RF front-end and AD control processes, and the subsequent timing synchronization will have low synchronization accuracy due to the lack of prior sampling. The maximum error can be close to ±1 sample. When performing fine synchronization later, it is necessary to estimate and compensate for a fraction of the STO, which will increase the processing delay.

[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. In other words, to detect the start point of each (CP-deprecated) OFDM symbol, symbol timing synchronization must be performed, which helps to obtain accurate sampling. The STO (Segment Time Occurrence) has different effects depending on the estimated position of the OFDM symbol start point.

[0004] When the estimated OFDM symbol start point coincides with the precise timing, the orthogonality between subcarrier frequency components can be maintained. In this case, the OFDM symbol can be perfectly recovered without any interference. However, when the estimated OFDM symbol start point lags behind the precise timing, the signal consists of a portion of the current OFDM symbol and a portion of the next OFDM symbol within the FFT interval. In this case, the distortion (including phase deviation) is too severe to be compensated for. The impact of this error varies depending on the bandwidth under the LTE protocol. With larger bandwidths, the number of FFT points is greater, and the influence of the first part of the next OFDM symbol is distributed across all subcarriers, thus having a smaller impact. However, for smaller bandwidths, this impact is very significant, causing a substantial deterioration in the measurement performance of narrowband EVMs. This demonstrates that a proper symbol timing scheme is necessary to prevent STO in this situation.

[0005] In view of the above-mentioned shortcomings, the designer has actively researched and innovated in order to create a processing method, receiver and system for narrowband LTE receiver EVM, so as to make it more valuable for industrial use. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a method, receiver, and system for processing EVM in a narrowband LTE receiver.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: One of the objectives of this invention is: A method for processing a narrowband LTE receiver EVM includes the following steps: Step 1: Obtain the bandwidth mode of the OFDM signal to be transmitted: If the signal is in bandwidth mode or narrowband mode, then the signal is interpolated by a factor of L to increase the sampling rate to the preset first sampling rate. If the bandwidth mode is wideband mode, then the original sampling rate, i.e., the second sampling rate, is maintained. Step 2: Perform analog-to-digital conversion sampling on the received signal at either the first or second sampling rate; select a synchronization processing strategy based on the bandwidth mode of the received signal. Coarse synchronization processing: After L-fold decimation of the received signal in narrowband mode, correlation operations are performed with the local master synchronization sequence to obtain the coarse synchronization position; Fine synchronization processing: Centered on the coarse synchronization position, 2i+1 timing candidate channels are opened in parallel. Each channel is correlated with the local auxiliary synchronization sequence, and the channel with the largest correlation peak is selected as the fine synchronization output. Remove the cyclic prefix from the precise synchronization output and perform an FFT transformation; Symbols are extracted from the signal after FFT transformation, channel estimation and normalization are performed, and the error vector magnitude is calculated.

[0008] As a further improvement of the present invention, the first sampling rate is 15.36MHz, the second sampling rate is 30.72MHz; the bandwidth corresponding to the wideband mode is ≥10MHz; the bandwidth corresponding to the narrowband mode is <10MHz; the L-fold interpolation or decimation factor L is determined according to the bandwidth of the narrowband mode: L=8 when the bandwidth is 1.4MHz, L=4 when the bandwidth is 3MHz, L=2 when the bandwidth is 5MHz, and L=1 when the bandwidth is ≥10MHz.

[0009] As a further improvement of the present invention, in the fine synchronization processing step, i in the number of parallel channels 2i+1 is determined according to the bandwidth mode: when the bandwidth is 1.4MHz, i=4 and the number of channels is 9; when the bandwidth is 3MHz, i=2 and the number of channels is 5; when the bandwidth is 5MHz, i=1 and the number of channels is 3; when the bandwidth is ≥10MHz, i=0 and the number of channels is 1. The fine synchronization processing step directly outputs the coarse synchronization position.

[0010] As a further improvement of the present invention, the coarse synchronization processing step specifically includes: decimating the narrowband mode received signal by a factor of L to reduce the sampling rate to match the sampling rate of the local master synchronization sequence; performing a time-domain sliding cross-correlation operation on the decimated signal and the local master synchronization sequence; and outputting the position corresponding to the peak value as the coarse synchronization position when the correlation peak value meets the preset conditions.

[0011] As a further improvement of the present invention, the fine synchronization processing step specifically includes: taking the coarse synchronization position as the center, selecting i timing points before and after it to generate 2i+1 parallel timing candidate channels; performing FFT transformation on the signal of each channel after L-fold decimation; performing frequency domain point multiplication and cumulative correlation operation on the FFT result of each channel and the local auxiliary synchronization sequence; comparing the correlation peaks of all channels, and selecting the timing point corresponding to the channel with the largest peak as the fine synchronization output; the fine synchronization processing step does not require fractional symbol timing offset estimation and interpolation compensation.

[0012] The second objective of this invention is: A receiver, comprising: An analog-to-digital converter is used to sample the received signal at a preset first sampling rate or a second sampling rate; A bandwidth mode detection unit is used to detect the bandwidth mode of the received signal. Synchronization unit, including: The coarse synchronization processing module is used to perform correlation operations with the local master synchronization sequence after L-fold decimation of the received signal when the bandwidth mode is narrowband mode, in order to obtain the coarse synchronization position; when the bandwidth mode is wideband mode, it directly outputs the original received signal as the coarse synchronization position. The fine synchronization processing module is used to open 2i+1 timing candidate channels in parallel with the coarse synchronization position as the center. Each channel performs correlation calculations with the local auxiliary synchronization sequence and selects the channel with the largest correlation peak as the fine synchronization output. When the bandwidth mode is wideband mode, this module bypasses the output of the coarse synchronization result. The decyclic prefix and FFT unit is used to remove the cyclic prefix and perform FFT transformation based on the fine synchronization output; The EVM computation unit is used to extract symbols, estimate the channel, normalize, and calculate the error vector magnitude.

[0013] As a further improvement of the present invention, the precision synchronization processing module includes: The parallel channel generation submodule is used to select i timing points before and after the coarse synchronization position to generate 2i+1 parallel timing candidate channels. The decimation and FFT submodule is used to perform FFT transformation on the signal of each channel after L-fold decimation. The frequency domain correlation submodule is used to perform frequency domain correlation operations between the FFT results of each channel and the local auxiliary synchronization sequence; The comparison output submodule is used to compare the relevant peak values ​​of all channels and select the timing point corresponding to the channel with the largest peak value as the fine synchronization output. The fine synchronization processing module does not include a fractional sign timing offset estimation unit and an interpolation compensation unit.

[0014] As a further improvement of the present invention, the first sampling rate is 15.36MHz, and the second sampling rate is 30.72MHz; the bandwidth corresponding to the wideband mode is ≥10MHz, and the bandwidth corresponding to the narrowband mode is <10MHz; the value of L is: L=8 when the bandwidth is 1.4MHz, L=4 when the bandwidth is 3MHz, L=2 when the bandwidth is 5MHz, and L=1 when the bandwidth is ≥10MHz; the value of i is: i=4 when the bandwidth is 1.4MHz, i=2 when the bandwidth is 3MHz, i=1 when the bandwidth is 5MHz, and i=0 when the bandwidth is ≥10MHz.

[0015] The third objective of this invention: A processing system for a narrowband LTE receiver EVM includes a transmitter and a receiver as described above; The transmitter includes: The transmission processing unit is used to perform L-fold interpolation processing on the narrowband mode signal according to the bandwidth mode of the signal to be transmitted, so that the sampling rate is unified to the first sampling rate, and to maintain the original sampling rate, i.e. the second sampling rate, for the wideband mode signal. A digital-to-analog converter is used to convert processed digital signals into analog signals; The radio frequency (RF) transmitter front end is used to upconvert analog signals to RF and transmit them.

[0016] As a further improvement of the present invention, the L-fold interpolation and L-fold decimation in the transmitter and receiver share the same L value, which is uniquely determined by the bandwidth mode; the coarse synchronization processing module and the fine synchronization processing module are implemented using field-programmable gate arrays, and 2i+1 parallel timing candidate channels are processed in parallel in the FPGA, with the overall synchronization processing delay being less than one OFDM symbol period.

[0017] By means of the above-described solution, the present invention has at least the following advantages: This invention reduces the complexity of AD / DA control, decreasing the number of sampling frequencies from six to two, and eliminating the original fractional STO estimation and interpolation compensation modules. It improves the EVM performance of the LTE receiver in narrowband mode, enhances the stability of EVM measurements, and reduces fluctuations in measurement results.

[0018] 1. Reduce AD / DA control complexity and simplify RF front-end design. This invention distinguishes between wideband (≥10MHz) and narrowband (<10MHz) modes. It performs L-fold interpolation on the narrowband signal at the transmitting end and L-fold decimation on the receiving end, unifying the six different sampling rates (1.92MHz, 3.84MHz, 7.68MHz, 15.36MHz, 23.04MHz, 30.72MHz) specified in the LTE protocol into two sampling frequencies: 15.36MHz and 30.72MHz. The AD / DA converter only needs to support these two sampling rates, eliminating the need for frequent switching of sampling clocks and filter parameters based on bandwidth. This significantly reduces the control complexity between the RF front-end and the digital baseband, minimizing system configuration time and potential control error risks.

[0019] 2. Eliminate the decimal sign timing offset estimation and interpolation compensation modules to reduce processing latency. In existing technologies, narrowband signals suffer from insufficient timing synchronization accuracy due to their low sampling rate, requiring estimation of a fractional STO and interpolation compensation. This process necessitates buffering a large amount of data to obtain the STO estimate, resulting in significant processing delays. This invention addresses this by performing L-fold oversampling on the narrowband signal, limiting the timing error to ±1 / L of the original sampling points. Furthermore, it employs a fine synchronization structure centered on a coarse synchronization point and using 2i+1 parallel candidate channels. By directly comparing the relevant peak values ​​of each channel, the optimal timing point is selected, eliminating the need for fractional STO estimation and interpolation compensation. This design not only saves interpolation filter and buffer resources but also reduces the fine synchronization processing delay to within one OFDM symbol period, making it particularly suitable for high real-time processing implemented on FPGAs.

[0020] 3. Improve the EVM measurement performance of LTE receivers in narrowband mode. In LTE narrowband modes (1.4MHz, 3MHz, 5MHz), the subcarrier spacing is small, and the symbol timing offset (STO) is more sensitive to the disruption of orthogonality. In traditional schemes, a timing error of ±1 sampling point can lead to a significant deterioration in EVM measurement results. This invention improves the timing accuracy to ±1 / L sampling points (±1 / 8 sampling points accuracy at 1.4MHz bandwidth) through L-fold oversampling, and precisely locks the optimal timing position through parallel multi-channel fine synchronization, making the EVM measurement results in narrowband mode more accurate and stable, with a significantly reduced fluctuation amplitude. Experiments show that this invention ensures the consistency of EVM measurement performance under different bandwidths.

[0021] 4. Improve the stability and repeatability of EVM measurement results Because the synchronization module of this invention adopts a deterministic parallel comparison structure (2i+1 channels processing simultaneously), the randomness introduced by fractional STO estimation error in traditional schemes is eliminated, and the measurement results are less affected by noise and channel fluctuations. The variance of EVM results from multiple measurements of the same device under test is significantly reduced, meeting the stringent requirements of high-precision test instruments for measurement repeatability.

[0022] 5. Clear architecture, easy to implement in parallel on FPGA, and high system real-time performance. Both the coarse synchronization and fine synchronization modules of this invention adopt a structured design: coarse synchronization narrows the synchronization search range to a local level by extracting and correlating with PSS; fine synchronization processes 2i+1 fixed-number candidate channels (maximum not exceeding 9 channels) in parallel with the coarse synchronization point. This architecture avoids serial traversal or iterative estimation, has no data dependencies between channels, can be fully parallelized and pipelined in an FPGA, has fixed and predictable processing delays, and meets the requirements of real-time EVM measurement.

[0023] 6. Suitable for setting up LTE EVM test systems with clearly defined parameters. This invention is particularly suitable for LTE device EVM testing scenarios where parameters such as cell ID (Ncell ID), reference channel type (RC in RMC DL), duplex mode (FDD / TDD), and sampling rate (Fs) are known. It can serve as the core receiver architecture for communication test instruments, simplifying instrument design and improving testing efficiency. For situations where the parameters of the device under test are unclear, this invention can be applied after adding a parameter blind detection module at the front end, demonstrating good scalability.

[0024] 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

[0025] 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.

[0026] Figure 1 This is a block diagram illustrating the EVM measurement principle of the LTE transmitter and receiver of this invention; Figure 2 This is a block diagram illustrating the STO coarse synchronization processing principle of the present invention; Figure 3 This is a block diagram illustrating the STO (Simultaneous Time-to-Synchronization) precision synchronization processing principle of the present Detailed Implementation

[0027] 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.

[0028] 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.

[0029] First embodiment of the present invention: This embodiment of a method for processing a narrowband LTE receiver EVM includes the following steps in sequence: Step 1: Obtain the bandwidth mode of the OFDM signal to be transmitted: If the signal is in bandwidth mode or narrowband mode, then the signal is interpolated by a factor of L to increase the sampling rate to the preset first sampling rate. If the bandwidth mode is wideband mode, then the original sampling rate, i.e., the second sampling rate, is maintained.

[0030] Specifically, the first sampling rate is 15.36MHz, and the second sampling rate is 30.72MHz; the bandwidth corresponding to the wideband mode is ≥10MHz; the bandwidth corresponding to the narrowband mode is <10MHz; the L-fold interpolation or decimation factor L is determined according to the bandwidth of the narrowband mode: L=8 when the bandwidth is 1.4MHz, L=4 when the bandwidth is 3MHz, L=2 when the bandwidth is 5MHz, and L=1 when the bandwidth is ≥10MHz.

[0031] Step 2: Perform analog-to-digital conversion sampling on the received signal at either the first or second sampling rate; select a synchronization processing strategy based on the bandwidth mode of the received signal. Coarse synchronization processing: After L-fold decimation of the received signal in narrowband mode, correlation operations are performed with the local master synchronization sequence to obtain the coarse synchronization position.

[0032] Specifically, the coarse synchronization processing steps include: decimating the narrowband mode received signal by a factor of L to reduce the sampling rate to match the sampling rate of the local master synchronization sequence; performing a time-domain sliding cross-correlation operation between the decimated signal and the local master synchronization sequence; and outputting the position corresponding to the peak value as the coarse synchronization position when the correlation peak value meets the preset conditions.

[0033] Fine synchronization processing: Centered on the coarse synchronization position, 2i+1 timing candidate channels are opened in parallel. Each channel is correlated with the local auxiliary synchronization sequence, and the channel with the largest correlation peak is selected as the fine synchronization output.

[0034] Specifically, the fine synchronization processing steps include: selecting i timing points before and after the coarse synchronization position to generate 2i+1 parallel timing candidate channels; performing FFT transformation on the signal of each channel after L-fold decimation; performing frequency domain point multiplication and cumulative correlation operation on the FFT result of each channel and the local auxiliary synchronization sequence; comparing the correlation peaks of all channels and selecting the timing point corresponding to the channel with the largest peak as the fine synchronization output; the fine synchronization processing steps do not require fractional symbol timing offset estimation and interpolation compensation.

[0035] Specifically, in the fine synchronization processing step, the number of parallel channels 2i+1 is determined according to the bandwidth mode: when the bandwidth is 1.4MHz, i=4 and the number of channels is 9; when the bandwidth is 3MHz, i=2 and the number of channels is 5; when the bandwidth is 5MHz, i=1 and the number of channels is 3; when the bandwidth is ≥10MHz, i=0 and the number of channels is 1. The fine synchronization processing step directly outputs the coarse synchronization position.

[0036] Remove the cyclic prefix from the precise synchronization output and perform an FFT transformation.

[0037] Symbols are extracted from the signal after FFT transformation, channel estimation and normalization are performed, and the error vector magnitude is calculated.

[0038] The core of this technical solution lies in unifying the six sampling rates into two by interpolation at the transmitter and decimation at the receiver, and combining this with a two-level synchronization architecture with bandwidth adaptation (coarse synchronization + PSS, fine synchronization + parallel multi-channel SSS), thereby eliminating fractional STO estimation and interpolation compensation and improving narrowband EVM measurement performance.

[0039] I. Improvements to individual steps in this embodiment: 1. Interpolation / Extraction Steps: Existing technologies only disclose the implementation of interpolation / decimation filters, without revealing the design concept of "using interpolation / decimation as a tool to simplify the system architecture and linking it with bandwidth classification." This solution addresses the technical problem of "multiple sampling rates leading to complex AD / DA control," rather than the sampling rate conversion itself.

[0040] The innovation of this solution lies not in "whether to use interpolation / decimation", but in "deeply binding interpolation / decimation with bandwidth classification strategies to simplify system-level sampling rate specifications".

[0041] Specifically: The six sampling rates were reduced to two, 15.36M and 30.72M, which significantly reduced the complexity of AD / DA control. The interpolation factor L is not chosen arbitrarily, but is uniquely determined by the "uniform target sampling rate / original sampling rate" (L = 15.36M / original sampling rate), which is mathematically necessary.

[0042] 2. Coarse synchronization steps (L-fold extraction + PSS related) In existing technologies, PSS correlation is often used independently or only for coarse timing, without clearly forming a cascade with "oversampling factor L" and "parallel multi-channel SSS fine synchronization". In this scheme, the functional division of coarse and fine synchronization is clear: coarse synchronization is responsible for reducing the uncertainty window, while fine synchronization is responsible for local fine-tuning. While this two-level architecture is known, this scheme further links the coarse synchronization decimation factor L to the bandwidth, and the decimated sampling rate precisely matches the local sequence sampling rate of the PSS. This "parameter matching design" has not been disclosed.

[0043] In the coarse synchronization of this scheme, the correspondence between the decimation factor L and the bandwidth, as well as the precise matching between the decimated sampling rate and the local PSS sequence sampling rate, ensure that related operations do not require any additional resampling or interpolation, thus reducing computational complexity. Moreover, the purpose of coarse synchronization is not merely to complete synchronization, but to "narrow the search range of fine synchronization to a local area (±i sampling points)," creating conditions for subsequent parallel multi-channel fine synchronization.

[0044] 3. Fine synchronization steps (parallel multi-channel + SSS frequency domain correlation) The existing technology does not disclose the design concept of "replacing fractional STO estimation and compensation with parallel multi-channel search". In the existing technology, fractional STO estimation is considered necessary (such as using CP correlation to estimate frequency / time offset in the existing technology). However, this embodiment finds that as long as the transmitter performs L-fold interpolation on the narrowband signal (i.e., the receiver oversamples), the timing error is limited to integer multiples of the sampling points, and fractional compensation is not required. This technical insight is itself creative, and parallel multi-channel is just a specific means to realize this insight.

[0045] 4. EVM Calculation Steps The improvement of the EVM calculation module in this scheme lies in its coordination with the front-end synchronization module. Since the precision synchronization module directly outputs high-precision integer multiple sampling point synchronization results (without fractional compensation), the input signal quality of EVM calculation (especially in narrowband mode) is significantly better than that of traditional schemes, and the measurement results are more stable and have less fluctuation.

[0046] The innovation of the EVM calculation module should not be evaluated in isolation, but rather the entire receiving link should be considered as a whole. This solution addresses the specific problem of "STO sensitivity leading to EVM measurement performance degradation in narrowband mode," and its beneficial effect (improved narrowband EVM measurement stability) is the result of the combined effect of front-end synchronization and back-end EVM calculation.

[0047] II. Improvement points for coordination among multiple steps in this embodiment; 1. Coordination Point 1: Uniform sampling rate at the transmitter + parallel fine synchronization at the receiver, eliminating the need for a fractional STO compensation module. Transmitter: Narrowband signal L-fold interpolation, uniformly 15.36M; Receiver: Oversampled signal (15.36M or 30.72M), timing error is limited to ±1 / L original sampling points (i.e. less than 1 original sampling point interval).

[0048] Receiver: Parallel multi-channel fine synchronization (2i+1 channels); the optimal timing point is directly selected through parallel search, without the need to estimate fractional offset or interpolation compensation.

[0049] In traditional schemes, fractional STO estimation and interpolation compensation are considered essential (because timing errors can exceed half a sampling point at low sampling rates). This scheme completely eliminates these two modules through a joint design of "active interpolation at the transmitter + parallel search at the receiver." This not only reduces processing latency (eliminating the need to buffer data while waiting for estimation) but also saves hardware resources (interpolation filters, multipliers). No existing literature teaches a way to completely "bypass" fractional STO compensation; the effect of this "module removal" is revolutionary, not simply a matter of adding the functions of individual modules.

[0050] 2. Collaboration Point 2: Bandwidth classification + adaptive parallel channel number, optimal matching of resources and performance. The smaller the narrowband bandwidth and the smaller the subcarrier spacing, the more sensitive it is to STO (Simultaneous Transmission Tolerance), and the higher the required synchronization accuracy. This scheme achieves the opposite: the smaller the bandwidth, the larger L (higher oversampling factor), the more parallel channels (more refined search), and the higher the synchronization accuracy. This coordinated design of "bandwidth-oversampling factor-number of parallel channels-synchronization accuracy-resource consumption" is not the conventional "one-size-fits-all" optimization in this field, but a precise adaptation to the physical characteristics of different LTE bandwidths. In existing technologies, synchronization modules typically use fixed parameters (such as fixed oversampling factor or fixed search window), which cannot simultaneously meet the performance and resource requirements of all bandwidths. This scheme achieves the dual goals of optimal narrowband performance and minimum broadband resource consumption through adaptive parameter configuration, using a non-linear resource allocation strategy that is negatively correlated with bandwidth.

[0051] 3. Coordination Point 3: Coarse synchronization narrows the search range + fine synchronization ensures parallel local search, guaranteeing real-time performance. Coarse synchronization: By using PSS correlation, the synchronization uncertainty is reduced from the entire frame range (e.g., tens of thousands of sampling points within a 10ms frame) to ±i sampling points (i is at most 4).

[0052] Fine synchronization: Parallel processing of 2i+1 channels (up to 9), with no data dependency. Fine synchronization can be completed in a fixed, extremely short time (e.g., within one OFDM symbol period), without the need for serial traversal or iterative estimation.

[0053] In traditional solutions, coarse synchronization alone results in insufficient accuracy; while fine synchronization (global search) alone leads to excessive computational complexity, making real-time execution impossible. This solution narrows the search range to a local area through coarse synchronization, and performs parallel searches of that local area through fine synchronization. This makes the overall synchronization latency controllable and predictable, making it particularly suitable for FPGA pipeline implementations. This two-stage linkage architecture of "significant dimensionality reduction through coarse synchronization + parallel processing through fine synchronization" reduces processing latency by at least an order of magnitude compared to "coarse synchronization + serial fine synchronization" (e.g., point-by-point traversal of candidate points) (because it's parallel rather than serial). Although the two-stage synchronization itself is known, the design of precisely matching the parallel processing range with the coarse synchronization range (i.e., the number of parallel channels is exactly equal to the number of points within the uncertain interval of coarse synchronization) ensures waste-free parallelism.

[0054] The second embodiment of the present invention: A receiver according to this embodiment includes: An analog-to-digital converter is used to sample the received signal at a preset first sampling rate or a second sampling rate; A bandwidth mode detection unit is used to detect the bandwidth mode of the received signal. Synchronization unit, including: The coarse synchronization processing module is used to perform correlation operations with the local master synchronization sequence after L-fold decimation of the received signal when the bandwidth mode is narrowband mode, in order to obtain the coarse synchronization position; when the bandwidth mode is wideband mode, it directly outputs the original received signal as the coarse synchronization position. The fine synchronization processing module is used to open 2i+1 timing candidate channels in parallel with the coarse synchronization position as the center. Each channel performs correlation calculations with the local auxiliary synchronization sequence and selects the channel with the largest correlation peak as the fine synchronization output. When the bandwidth mode is wideband mode, this module bypasses the output of the coarse synchronization result. The decyclic prefix and FFT unit is used to remove the cyclic prefix and perform FFT transformation based on the fine synchronization output; The EVM computation unit is used to extract symbols, estimate the channel, normalize, and calculate the error vector magnitude.

[0055] Specifically, the fine synchronization processing module includes: The parallel channel generation submodule is used to select i timing points before and after the coarse synchronization position to generate 2i+1 parallel timing candidate channels. The decimation and FFT submodule is used to perform FFT transformation on the signal of each channel after L-fold decimation. The frequency domain correlation submodule is used to perform frequency domain correlation operations between the FFT results of each channel and the local auxiliary synchronization sequence; The comparison output submodule is used to compare the relevant peak values ​​of all channels and select the timing point corresponding to the channel with the largest peak value as the fine synchronization output. The fine synchronization processing module does not include a fractional sign timing offset estimation unit and an interpolation compensation unit.

[0056] Specifically, the first sampling rate is 15.36MHz, and the second sampling rate is 30.72MHz; the bandwidth corresponding to the wideband mode is ≥10MHz, and the bandwidth corresponding to the narrowband mode is <10MHz; the value of L is: L=8 when the bandwidth is 1.4MHz, L=4 when the bandwidth is 3MHz, L=2 when the bandwidth is 5MHz, and L=1 when the bandwidth is ≥10MHz; the value of i is: i=4 when the bandwidth is 1.4MHz, i=2 when the bandwidth is 3MHz, i=1 when the bandwidth is 5MHz, and i=0 when the bandwidth is ≥10MHz.

[0057] The third embodiment of the present invention: This embodiment of a narrowband LTE receiver EVM processing system includes a transmitter and a receiver as described above. The transmitter includes: The transmission processing unit is used to perform L-fold interpolation processing on the narrowband mode signal according to the bandwidth mode of the signal to be transmitted, so that the sampling rate is unified to the first sampling rate, and to maintain the original sampling rate, i.e. the second sampling rate, for the wideband mode signal. A digital-to-analog converter is used to convert processed digital signals into analog signals; The radio frequency (RF) transmitter front end is used to upconvert analog signals to RF and transmit them.

[0058] Specifically, the L-fold interpolation and L-fold decimation in the transmitter and receiver share the same L value, which is uniquely determined by the bandwidth mode; the coarse synchronization processing module and the fine synchronization processing module are implemented using field-programmable gate arrays, and 2i+1 parallel timing candidate channels are processed in parallel in the FPGA, with the overall synchronization processing delay being less than one OFDM symbol period.

[0059] Experimental examples of the present invention: The purpose of this experiment is to achieve high real-time fine synchronization of received signals by implementing different sampling rate processing strategies in the transmitter and receiver for wideband (20M, 15M, 10M) and narrowband (5M, 3M, 1.4M) signals respectively. This maintains the original sampling rate for wideband signals and performs L-fold interpolation and decimation, as well as corresponding synchronization processing, for narrowband signals. It requires little or no buffering, making it particularly suitable for multi-channel parallel processing on FPGAs. This improves the performance and stability of EVM measurements.

[0060] The block diagram of the LTE receiver EVM measurement system is as follows: Figure 1 As shown in the table below, the relationship between transmission bandwidth and sampling rate according to the LTE protocol is as follows: The aforementioned multiple modes require the measurement system to adapt to various sampling rates, resulting in complex control of the DA, AD, and RF front-end. Designing the transceiver system according to the corresponding sampling rate leads to a decrease in timing synchronization accuracy, necessitating STO estimation and compensation during STO fine synchronization. Since a large amount of data needs to be buffered before compensation to obtain the STO estimate, this method consumes significant buffer space and has high latency. This solution addresses this by differentiating between wideband (>=10M) and narrowband (<10M) scenarios. In wideband mode, using the standard sampling rate for transmission and reception, the 15M bandwidth has an FFT point count of 1536 that is not a power of 2, causing processing difficulties. Typically, zeros are padded to expand the FFT point count to 2048, and the sampling rate becomes 30.72M. In narrowband mode, a uniform sampling rate of 15.36M is used, reducing the total system sampling rate options from six to two: 15.36M and 30.72M. An interpolation filtering module is added to the transmitter, where L is the interpolation factor; a decimation module is added to the receiver synchronization module, where L is the decimation factor. The correspondence between bandwidth, sampling rate, and L is shown in the table below: This system offers high synchronization accuracy, particularly in narrowband mode, significantly reducing the impact of STO timing errors on EVM performance. Before entering the FFT, coarse and fine synchronization of the STO are performed separately. For wideband signals, coarse synchronization directly uses the received signal at the original rate (L=1) for correlation calculation to obtain the accurate starting point position. For narrowband signals, the received oversampled signal is decimated by a factor of L, and then correlated with the time-domain PSS sequence. Based on the result, an approximate synchronization position is obtained, and the signal is output at the original rate. Therefore, the received signal rate is not changed. This module primarily aims to narrow the calculation range for fine synchronization. The block diagram of the coarse synchronization processing is shown below. Figure 2 As shown.

[0061] The STO fine synchronization module directly takes the coarse synchronization point position for wideband signals and outputs it directly via bypass. For narrowband signals, STO fine synchronization is mainly achieved through the secondary synchronization signal SSS in LTE, which is a 62m-sequence in the frequency domain. Narrowband signals use L-fold oversampling, requiring detailed comparisons of ±i points around the coarse timing point, transforming these starting point data into parallel 2... The system uses i+1 channels, performs frequency domain correlation operations on each channel with the local SSS sequence, and then selects the channel containing the maximum correlation peak. The data from that channel is output as the result of fine synchronization. This parallel processing structure is particularly suitable for FPGA processing due to its low latency. It effectively solves the problem of frequent switching between AD and DA sampling rates in existing systems, and also eliminates the need to estimate the fractional STO and perform interpolation compensation, thus reducing processing latency. The block diagram of fine synchronization processing is shown below. Figure 3 As shown.

[0062] This invention proposes a transceiver architecture based on LTE EVM measurement, which reduces the complexity of front-end AD control and improves the real-time performance of the system. It is suitable for building LTE EVM test systems with clearly defined parameters such as RC, Ncell ID, FDD / TDD, and Fs.

[0063] 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.

[0064] 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.

[0065] 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 processing narrowband LTE receiver EVM, characterized by, The steps are as follows: Step 1: Obtain the bandwidth mode of the OFDM signal to be transmitted: If the signal is in bandwidth mode or narrowband mode, then the signal is interpolated by multiple L to increase the sampling rate to the preset first sampling rate. If the bandwidth mode is wideband mode, then the original sampling rate, i.e., the second sampling rate, is maintained. Step 2: Perform analog-to-digital conversion sampling on the received signal at the first sampling rate or the second sampling rate; select a synchronization processing strategy based on the bandwidth mode of the received signal. Coarse synchronization processing: After L-fold decimation of the received signal in narrowband mode, correlation operations are performed with the local master synchronization sequence to obtain the coarse synchronization position; Fine synchronization processing: Centered on the coarse synchronization position, 2i+1 timing candidate channels are opened in parallel. Each channel is correlated with the local auxiliary synchronization sequence, and the channel with the largest correlation peak is selected as the fine synchronization output. Remove the cyclic prefix from the precise synchronization output and perform an FFT transformation; Symbols are extracted from the signal after FFT transformation, channel estimation and normalization are performed, and the error vector magnitude is calculated.

2. The method of claim 1, wherein the EVM is measured for a narrowband LTE receiver. The first sampling rate is 15.36MHz, and the second sampling rate is 30.72MHz; the bandwidth corresponding to the wideband mode is ≥10MHz; the bandwidth corresponding to the narrowband mode is <10MHz; the L-fold interpolation or decimation factor L is determined according to the bandwidth of the narrowband mode: L=8 when the bandwidth is 1.4MHz, L=4 when the bandwidth is 3MHz, L=2 when the bandwidth is 5MHz, and L=1 when the bandwidth is ≥10MHz.

3. The method of claim 1, wherein the EVM is measured for a narrowband LTE receiver. In the fine synchronization processing step, the number of parallel channels 2i+1 is determined according to the bandwidth mode: when the bandwidth is 1.4MHz, i=4 and the number of channels is 9; when the bandwidth is 3MHz, i=2 and the number of channels is 5; when the bandwidth is 5MHz, i=1 and the number of channels is 3; when the bandwidth is ≥10MHz, i=0 and the number of channels is 1. The fine synchronization processing step directly outputs the coarse synchronization position.

4. The method of claim 1, wherein the EVM is measured for a narrowband LTE receiver. The coarse synchronization processing steps specifically include: decimating the narrowband mode received signal by a factor of L to reduce the sampling rate to match the sampling rate of the local master synchronization sequence; performing a time-domain sliding cross-correlation operation on the decimated signal and the local master synchronization sequence; and outputting the position corresponding to the peak value as the coarse synchronization position when the correlation peak value meets a preset condition.

5. The method of claim 1, wherein the EVM is measured for a narrowband LTE receiver. The fine synchronization processing steps specifically include: selecting i timing points before and after the coarse synchronization position as the center, generating 2i+1 parallel timing candidate channels; performing FFT transformation on the signal of each channel after L-fold decimation; performing frequency domain point multiplication and cumulative correlation operation on the FFT result of each channel and the local auxiliary synchronization sequence; comparing the correlation peaks of all channels, and selecting the timing point corresponding to the channel with the largest peak as the fine synchronization output; the fine synchronization processing steps do not require fractional symbol timing offset estimation and interpolation compensation.

6. A receiver, characterized by include: An analog-to-digital converter is used to sample the received signal at a preset first sampling rate or a second sampling rate; A bandwidth mode detection unit is used to detect the bandwidth mode of the received signal. Synchronization unit, including: The coarse synchronization processing module is used to perform correlation operations with the local master synchronization sequence after L-fold decimation of the received signal when the bandwidth mode is narrowband mode, in order to obtain the coarse synchronization position; when the bandwidth mode is wideband mode, it directly outputs the original received signal as the coarse synchronization position. The fine synchronization processing module is used to open 2i+1 timing candidate channels in parallel with the coarse synchronization position as the center. Each channel performs correlation calculations with the local auxiliary synchronization sequence and selects the channel with the largest correlation peak as the fine synchronization output. When the bandwidth mode is wideband mode, this module bypasses the output of the coarse synchronization result. The decyclic prefix and FFT unit is used to remove the cyclic prefix and perform FFT transformation based on the fine synchronization output; The EVM computation unit is used to extract symbols, estimate the channel, normalize, and calculate the error vector magnitude.

7. A receiver as described in claim 6, characterized in that, The precise synchronization processing module includes: The parallel channel generation submodule is used to select i timing points before and after the coarse synchronization position to generate 2i+1 parallel timing candidate channels. The decimation and FFT submodule is used to perform FFT transformation on the signal of each channel after L-fold decimation. The frequency domain correlation submodule is used to perform frequency domain correlation operations between the FFT results of each channel and the local auxiliary synchronization sequence; The comparison output submodule is used to compare the relevant peak values ​​of all channels and select the timing point corresponding to the channel with the largest peak value as the fine synchronization output. The precise synchronization processing module does not include a fractional sign timing offset estimation unit and an interpolation compensation unit.

8. A receiver as described in claim 6, characterized in that, The first sampling rate is 15.36MHz, and the second sampling rate is 30.72MHz; the bandwidth corresponding to the wideband mode is ≥10MHz, and the bandwidth corresponding to the narrowband mode is <10MHz; the value of L is: L=8 when the bandwidth is 1.4MHz, L=4 when the bandwidth is 3MHz, L=2 when the bandwidth is 5MHz, and L=1 when the bandwidth is ≥10MHz; the value of i is: i=4 when the bandwidth is 1.4MHz, i=2 when the bandwidth is 3MHz, i=1 when the bandwidth is 5MHz, and i=0 when the bandwidth is ≥10MHz.

9. A processing system for a narrowband LTE receiver EVM, characterized in that, Includes a transmitter and a receiver as described in any one of claims 6 to 8; The transmitter includes: The transmission processing unit is used to perform L-fold interpolation processing on the narrowband mode signal according to the bandwidth mode of the signal to be transmitted, so that the sampling rate is unified to the first sampling rate, and to maintain the original sampling rate, i.e. the second sampling rate, for the wideband mode signal. A digital-to-analog converter is used to convert processed digital signals into analog signals. The radio frequency (RF) transmitter front end is used to upconvert analog signals to RF and transmit them.

10. The processing system for a narrowband LTE receiver EVM as described in claim 9, characterized in that, The L-fold interpolation and L-fold decimation in the transmitter and receiver share the same L value, which is uniquely determined by the bandwidth mode. The coarse synchronization processing module and the fine synchronization processing module are implemented using field-programmable gate arrays. 2i+1 parallel timing candidate channels are processed in parallel in the FPGA, and the overall synchronization processing delay is less than one OFDM symbol period.

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