CN113794666B - Method and system for analyzing large frequency offset data by comprehensive tester - Google Patents
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Abstract
The invention provides a method and a system for analyzing large frequency offset data by a comprehensive tester, and belongs to the technical field of wireless signal analysis. The method for analyzing the large frequency offset data by the comprehensive tester comprises the following steps: coarsely synchronizing a power window; pre-estimating frequency offset; pre-compensating frequency offset; the long training sequence LTS is precisely synchronized, and the precise frame head position is obtained; estimating the short training sequence STS coarse frequency offset to obtain a coarse frequency offset value; STS frequency offset compensation; LTS fine frequency offset estimation; and (3) signal frequency offset compensation: and obtaining a final frequency offset value according to the coarse frequency offset value and the fine frequency offset value, and finishing signal frequency offset compensation according to the frequency offset value. The beneficial effects of the invention are as follows: and the large frequency offset signal is analyzed in an auxiliary way, so that the problem of synchronization failure of the large frequency offset signal is avoided.
Description
Technical Field
The invention relates to a frequency offset estimation method, in particular to a method and a system for analyzing large frequency offset data by a comprehensive tester.
Background
OFDM is a special multi-carrier transmission technique that can be regarded as either a modulation technique or a multiplexing technique. OFDM can reduce the influence of frequency selective fading of a broadband system by parallelizing high-rate information symbols into low-rate symbols and then transmitting the low-rate symbols on a plurality of orthogonal subcarriers in parallel; by adding a Guard Interval (GI), the individual intersymbol interference is effectively avoided. At the receiving end, the fading of the channel can be compensated by using a simple frequency domain equalizer, so that the implementation of the OFDM receiver becomes very simple.
Over the entire transmit-receive link, the transmitter up-converts the baseband signal to a radio frequency signal by carrier modulation and the receiver down-converts the signal to baseband by using the same frequency local carrier. However, during the transceiving process, the crystal oscillator caused by unstable components of the transmitter and the receiver, or the carrier frequency deviation (Carrier Frequency Offset) caused by Doppler frequency shift, also called frequency deviation, is used as f t And f r The carrier frequencies of the transmitter and receiver, respectively, the difference Δf=f between the two r -f t Then it is the frequency offset carried by the receiver baseband data. If the subcarrier spacing of the baseband signal is f c Then the ratio of the carrier frequency deviation to the subcarrier spacing is recorded asIn general, when |ρ| > 1, it can be referred to asLarge frequency offset.
When the comprehensive tester tests the DUT, carrier frequency deviation exists in signals sent by the DUT due to errors introduced in the design of physical devices and circuits of the DUT. The integrated meter processes the baseband signal with frequency offset, which is generally calculated based on the phase difference of the time domain repetition part of the long training sequence LTS and the short training sequence STS.
The subcarrier spacing of Wi-Fi standard (802.11 a/g/n/ac/ax/be) is 312.5KHz, which long training sequence duration Deltat=3.2 us, frequency offset estimation capability Wherein, the sampling rate Fs multiplied by the training sequence duration deltat is the number of sampling points N, and arg is the range of the arctangent angle (-pi). Likewise, the short training sequence duration Δt=0.8 us, and the frequency offset estimation capability Δf= (-245 KHz 625 KHz), i.e. the short training sequence frequency offset estimation capability exceeds the subcarrier spacing 312.5KHz. Then for frequency offsets |Δf| > 156.25KHz, a short training sequence must be used to estimate and compensate for the frequency offset.
However, when a large frequency offset exists, the LTS fine synchronization module before frequency offset estimation is damaged due to the fact that the received signal has a large frequency offset. After the frequency offset causes the fine synchronization failure, intersymbol interference is introduced due to incorrect frame head position selection. After synchronization failure, the STS and LTS have incorrect position selection, and their use as frequency offsets becomes incorrect, and the reception of the entire signal is problematic.
Disclosure of Invention
The invention provides a method and a system for analyzing large frequency offset data by a comprehensive tester, which aim to solve the technical problems that the DUT possibly has larger frequency offset due to component problems when the comprehensive tester issues Wi-Fi standard (802.11 a/g/n/ac/ax/be) test to the DUT of equipment to be tested and the frequency offset influences the synchronization and detection of signals and has analysis errors in the prior art.
The method for analyzing the large frequency offset data by the comprehensive tester comprises the following steps:
s1: coarse synchronization of power windows: the method comprises the steps of searching a rough starting point and a rough end point of each frame of data, determining a rough synchronization point and performing rough synchronization on signals;
s2: frequency offset pre-estimation: the method comprises the steps of estimating a pre-frequency offset value of data after coarse synchronization;
s3: frequency offset pre-compensation: pre-compensating the received signal according to the estimated pre-frequency offset value;
s4: LTS fine synchronization: performing sliding correlation operation on the data subjected to the pre-compensation frequency offset by adopting a long training sequence LTS to obtain an accurate frame head position;
s5: STS coarse frequency offset estimation: based on the correct frame head position, a short training sequence STS is adopted to obtain a coarse frequency offset value;
s6: STS frequency offset compensation: performing frequency offset compensation on the signal after the fine synchronization according to the coarse frequency offset value;
s7: LTS fine frequency offset estimation: a long training sequence LTS is adopted to obtain a fine frequency offset value;
s8: and (3) signal frequency offset compensation: and (3) obtaining a final frequency offset value according to the coarse frequency offset value obtained in the step (S5) and the fine frequency offset value obtained in the step (S7), and finishing signal frequency offset compensation according to the frequency offset value.
The invention is further improved, in the step S1, the double sliding window algorithm is adopted for coarse synchronization, and the specific processing method is as follows:
s11: calculating the power of each sampling point of the received signal;
s12: calculating the power value difference of adjacent double windows and the power value difference of the double windows:
s13: and acquiring the frame start and end positions according to the change of the power value difference value of the double window.
The invention is further improved, and the specific processing method of the step S2 is as follows:
s21: the frequency offset is calculated by a blind estimation method based on the preamble of the received signal,
the interval duration selects STS sequence length 0.8us, and the interval sampling point is N 1 =fs 0.8us, the duration of the frequency offset calculation is selected to be 0.1us, i.e. the continuous sampling point is N 2 =fs 0.1us, the calculation formula is:
wherein f (n) represents an average frequency offset sequence of backup data with the n-th segment of duration of 0.1us data, G (n) is a calculation process intermediate quantity, arctan is an arctangent, superscript is a complex conjugate of a complex signal, n takes a value from 1 to 239 under a value range of 24us, fs is a sampling rate,
s22: frequency offset sequence differential calculation
The differential calculation after calculating the frequency offset based on f (n) is expressed as:
g(n)＝f(n)-f(n-1)
when the absolute value of g (n) is smaller than the first set value and the continuous number m of absolute values smaller than the first set value is larger than the set threshold, indicating that the pre-frequency offset calculation is successful, recording the continuous starting point as k and the pre-frequency offset value f pre And (3) setting the average value of m frequency offsets f (n) from k to above a threshold value.
The invention is further improved, in step S3, the pre-frequency offset f is calculated pre Then, the formula of the compensation received signal z (t) is:where j is an imaginary unit.
The invention is further improved, in step S4, the accurate frame start position is obtained by sliding correlation of the local long training sequence and the received signal, and in step S3, the data z after the pre-frequency offset is compensated * (t) is described in complex form as z * (t)＝z I (t)+j*z Q (t), t=1 …, N, n=fs×28us, the ideal long training sequence LTS time domain signal is denoted as x (t) =x I (t)+j*x Q (t), t=1, …, M, m=fs×3.2us, the correlation operation is defined as
The synchronization process adopts the data z after compensating the pre-frequency offset * (t) performing sliding correlation operation with the local known training sequence x (t), judging the similarity degree, if z * And (t) the correlation value between the moment i and x (t) is marked as C (i), then:
C(i)＝correl(z I (i+t)，x I (t))+correl(z I (i+t)，x Q (t))+correl(z Q (i+t)，x I (t))+correl(z Q (i+t)，x Q (t))
based on the characteristics of the correlation operation, if z * If x (t) is present on (t), then 2 distinct peaks appear at C (i) when the sliding correlation is to the corresponding starting point, and the two peaks are separated by the LTS duration, if the first peak appears at i 1 The second peak occurs at i 2 And i 2 -i 1 =fs×3.2us, then fine synchronization is successful, and the frame start position t is updated StartNew ＝i 1 -Fs*9.6us。
The invention is further improved in step S5, according to the new frame start position t StartNew Processing the re-backup data, wherein the backup mode is z 1 (t)＝y(t)，t∈[t StartNew t StartNew +16us*Fs]I.e. backup with fine synchronization point t StartNew Based on the standard, the total length is 16us, and the coarse frequency offset f is calculated based on STS sts Is shown as follows:
wherein arctan is the inverse tangent and superscript is the complex conjugate of the complex signal.
The invention is further improved, in step S6, after the coarse frequency offset is obtained, the backup signal z is compensated 1 Mode (t) is
The invention is further improved, in step S7, the starting position of LTS is t lts ＝t StartNew +8us fs, interval length N 2 =fs×3.2us, lts frequency offset calculates the start position t lts2 ＝t lts +0.2us Fs, fine frequency offset f of LTS lts The calculation method of (1) is as follows:
the invention is further improved, in step S8, the frequency offset Δf=f of the whole received signal sts +f lts Performing frequency offset compensation on the received signal y (t) in a mode of y * (t)＝y(t)*e -j2πΔft 。
The invention also provides a system for realizing the method for analyzing the large frequency offset data by the comprehensive tester, which comprises the following steps:
and a power window coarse synchronization module: the method comprises the steps of searching a rough starting point and a rough end point of each frame of data, determining a rough synchronization point and performing rough synchronization on signals;
the frequency offset pre-estimation module: the method comprises the steps of estimating a pre-frequency offset value of data after coarse synchronization;
frequency offset precompensation module: the pre-compensation unit is used for pre-compensating the received signal according to the estimated pre-frequency offset value;
LTS fine synchronization module: performing sliding correlation operation on the data subjected to the pre-compensation frequency offset by adopting a long training sequence LTS to obtain an accurate frame head position;
STS coarse frequency offset estimation module: the method is used for acquiring a coarse frequency offset value by adopting a short training sequence STS based on the correct frame head position;
STS frequency offset compensation module: the method is used for carrying out frequency offset compensation on the signals after the fine synchronization according to the coarse frequency offset value;
LTS fine frequency offset estimation module: the method is used for acquiring a fine frequency offset value by adopting a long training sequence LTS;
and the signal frequency offset compensation module: the method is used for obtaining a final frequency offset value according to the coarse frequency offset value and the fine frequency offset value, and finishing signal frequency offset compensation according to the frequency offset value.
Compared with the prior art, the invention has the beneficial effects that: a frequency offset precompensation module is added in the comprehensive tester for assisting in analyzing the large frequency offset signal and avoiding the problem of synchronization failure of the large frequency offset signal, so that the added module ensures that the large frequency offset signal is accurately synchronized, and then the accurate large frequency offset is estimated by combining a short training sequence and a long training sequence, and after frequency offset compensation is carried out, signal analysis is completed according to a signal analysis flow. The invention overcomes the influence caused by large frequency offset and improves the accuracy and stability of the comprehensive tester for analyzing the DUT signal performance of the equipment to be tested.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a schematic diagram of a dual power window energy variation;
FIG. 3 is a schematic diagram of a frequency offset scenario of a backup sequence;
FIG. 4 is a schematic diagram showing the difference between the frequency offsets of the backup sequences;
FIG. 5 is a graph of LTS sliding-related energy distribution without pre-frequency offset compensation;
FIG. 6 is a graph showing LTS sliding-related energy distribution for pre-frequency offset compensation;
FIG. 7 is a schematic diagram of the result of analyzing large frequency offset data by the comprehensive tester before improvement;
FIG. 8 is a schematic diagram of the result of the comprehensive tester analyzing large frequency offset data by the method of the invention.
Detailed Description
The invention will be described in further detail with reference to the drawings and examples.
As shown in FIG. 1, the method for analyzing large frequency offset data by the comprehensive tester comprises the following steps:
s1: coarse synchronization of power windows: the method comprises the steps of searching a rough starting point and a rough end point of each frame of data, determining a rough synchronization point and performing rough synchronization on signals;
s2: frequency offset pre-estimation: the method comprises the steps of estimating a pre-frequency offset value of data after coarse synchronization;
s3: frequency offset pre-compensation: pre-compensating the received signal according to the estimated pre-frequency offset value;
s4: LTS fine synchronization: performing sliding correlation operation on the data subjected to the pre-compensation frequency offset by adopting a long training sequence LTS to obtain an accurate frame head position;
s5: STS coarse frequency offset estimation: based on the correct frame head position, a short training sequence STS is adopted to obtain a coarse frequency offset value;
s6: STS frequency offset compensation: performing frequency offset compensation on the signal after the fine synchronization according to the coarse frequency offset value;
s7: LTS fine frequency offset estimation: a long training sequence LTS is adopted to obtain a fine frequency offset value;
s8: and (3) signal frequency offset compensation: and (3) obtaining a final frequency offset value according to the coarse frequency offset value obtained in the step (S5) and the fine frequency offset value obtained in the step (S7), and finishing signal frequency offset compensation according to the frequency offset value.
The invention is based on the comprehensive tester testing DUT to issue Wi-Fi standard (802.11 a/g/n/ac/ax/be) signals, so that based on protocol standards, the test DUT has the same short training sequence STS and long training sequence LTS. The STS and the LTS are used for standard compatibility, synchronization, frequency offset estimation and compensation, and the invention is based on the process of synchronization, frequency offset estimation and compensation under the scene of large frequency offset, and the subsequent analysis is carried out according to the conventional analysis of various Wi-Fi modes.
The invention will now be described in detail with reference to the accompanying drawings, it being understood that the description is only for the purpose of illustrating and explaining the invention, and not for the purpose of limiting the same.
Assuming that an ideal signal transmitted by the DUT is x (t), a signal received by the comprehensive tester as a receiving end is y (t), t is a time domain sampling point sequence number, and due to the influences of factors such as components, channels, noise and the like, the signal y (t) received by the comprehensive tester has a frequency offset delta f which is larger than 312.5KHz of a subcarrier interval, and if only the influence of the frequency offset is considered, a receiving model is y (t) =x (t) ×e j2 πΔft Where j is an imaginary unit.
Step S1: coarse synchronization of power windows
Finding an approximate estimate of the starting point of the data is the first step of the instrumentation receiver. By detecting whether new data arrives at the channel, searching a rough starting point and a rough ending point of each frame of data, gaps exist among a plurality of data frames of the Wi-Fi signal, and coarse synchronization is performed by adopting a double sliding window algorithm. A schematic diagram of a double sliding window algorithm is shown in fig. 2.
The received signal y (t) is a complex signal, denoted y (t) =y I (t)+j*y Q (t), t is the sampled data sequence number point, y I (t) is the real part of y (t), y Q (t) is the imaginary part of y (t), j is the imaginary unit.
Step S11: calculating the power of each sampling point of the received signal
Each sample point of the baseband signal y (t) has been represented as an analog-to-digital sampled voltage value, which is calculated as power
pwr(t)＝y I (t) 2 +y Q (t) 2
Step S12: calculating window power values
The window duration is chosen to be τ=1us, and at a sampling rate Fs (greater than the signal bandwidth), the window power continues with a sampling point number n=fs τ. Where window a is the accumulation of signal power from time t to (t+τ), denoted WA (t), window B is the accumulation of signal power from time τ (N samples) to time t, denoted WB (t), and window C is the window B power minus the window a power, denoted WC (t).
Step S13: determining frame start and end positions
From the curve of window C, it can be seen that when the top point is reached, window B has energy, but window a has no energy, and when window a has energy, curve C gradually descends until it is flat, so it is considered that the energy data arrives when curve C reaches the top point, which is the start point of the frame. Similarly, when curve C reaches the next negative vertex, it is considered the end of the frame.
Using threshold method determination, the frame start set framestartset=k×max (WC (t)), and the frame end set frameendset=k×min (WC (t)), first find a frame start t Start Find an end of frame t End The threshold K is empirically determined to be 15dB, combined into one frame.
Step S2: frequency offset pre-estimation
Backing up the leading part, processing by using backup data in a mode of z (t) =y (t), and t epsilon [ t ] Start -4us*Fs t Start +20us*Fs]I.e. the backup takes place at the coarse synchronization point t obtained in step S1 Start The back-off is 4us, and the total length is 24us.
The initial position obtained by coarse synchronization in step 1 is coarse, and a local ideal training sequence is needed to be used for sliding correlation on a backup signal, and when the sliding correlation peak value is maximum, the initial position is the fine synchronization position.
But the accuracy of the sliding correlation calculation is greatly affected by the presence of large frequency offsets. Therefore, the frequency offset of the backup data needs to be calculated first, and after the frequency offset is compensated, the related operation precision is not affected.
LTS cannot estimate frequency offset, but DUT signal STS always has an inaccurate part related to power amplifier lifting, so that the frame head is blind at this time, the initial position of frequency offset is also blind, and the frequency offset is calculated by using a sliding calculation post-frequency offset difference method, which is called a frequency offset blind estimation method. The short training sequence STS has a sequence length of 0.8us in the time domain and a total repetition duration of 10 times of 8us, and frequency offset is calculated by taking 0.1us as a unit, and because frequency offset based on STS is almost the same, in the STS signal, the frequency offset value is close to 0 after subtraction, but not belongs to the part of the STS signal, and the frequency offset value is completely irregular after subtraction. The frequency offset value difference calculation is followed by 0, then the STS effectively calculates the frequency offset, and then reads the frequency offset value of the corresponding position, and then the frequency offset value is the pre-estimated frequency offset.
Step S21 calculates frequency offset based on z (t) blind estimation method
The interval time length selects STS sequence length 0.8us, then the sampling point is spacedIs N 1 =fs 0.8us. The duration of the frequency offset calculation is selected to be 0.1us, namely the duration sampling point is N 2 ＝Fs*0.1us。
Wherein f (n) represents an average frequency offset sequence of backup data with the n-th segment of duration of 0.1us, G (n) represents an intermediate quantity in the calculation process, arctan represents an arctangent, superscript represents complex conjugate of complex signals, and n takes values from 1 to 239 in a value range of 24us.
Step S22 frequency offset sequence differential calculation
Differential calculation after frequency offset is calculated based on f (n) is expressed as
g(n)＝f(n)-f(n-1)
The frequency offset values calculated from STS are almost identical, then g (n) is close to 0 at the STS signal position. Setting rules, when the absolute value of g (n) is smaller than 5KHz and the continuous number m is larger than 50, indicating that the pre-frequency offset calculation is successful, recording the continuous starting point as k and the pre-frequency offset value f pre For the mean value of the frequency offsets f (n) corresponding to the 50 consecutive g (n),fig. 3 shows the frequency offset result of the backup sequence f (n), in Hz, with a distinct and steady value over the range of n=50 to 120, the remainder being irregular. As shown in fig. 4, g (n) is a differential value of f (n), and from g (n), a steady state of n=50 to 120 can be determined, and the pre-frequency offset value f of f (n) is found in this interval pre Approximately at around 430 KHz.
Step S3: frequency domain precompensation
Calculating to a pre-frequency offset f pre Then, the mode of compensating the received signal z (t) is as follows
Step S4: LTS fine synchronization
The step 1 power window synchronization scheme can only obtain a near frame start position, and the accurate frame start position is obtained through sliding correlation between a local training sequence and a received signal.
Step S3, compensating the data z after the pre-frequency offset * (t) is described in complex form as:
z * (t)＝z I (t)+j*z Q (t)，t＝1…，N，N＝Fs*28us
since STS is a frame open part, there is generally a power climbing process, and the synchronization length is only 0.8us, so the local training sequence selects LTS, the duration of LTS is 3.2us, and ideal LTS time domain signal expressed as x (t) =x is generated in the receiving module according to the protocol I (t)+j*x o (t), t=1, …, M, m=fs×3.2us. The correlation operation is defined as:
the synchronization process adopts the data z after compensating the pre-frequency offset * And (t) performing sliding correlation operation with the local known training sequence x (t), judging the similarity degree of the sliding correlation operation, wherein the specific operation is to respectively and crossly correlate IQ paths, and taking the square accumulated value after correlation.
If z * And (t) the correlation value between the moment i and x (t) is marked as C (i), then:
C(i)＝correl(z I (i+t)，x I (t))+correl(z I (i+t)，x Q (t))+correl(z Q (i+t)，x I (t))+correl(z Q (i+t)，x Q (t))
based on the characteristics of the correlation operation, if z * If x (t) is present on (t), then when the sliding correlation reaches the corresponding starting point, a distinct peak will appear at C (i), and then there will be two peaks according to twice the repetition periodicity of LTS, with a spacing of 3.2us. If the first peak occurs at i 1 The second peak occurs at i 2 And i 2 -i 1 =fs×3.2us, then fine synchronization is successful, update t StartNew ＝i 1 -Fs 9.6us. If the fine synchronization detection fails, t StartNew ＝t Start 。
Fig. 5 is an energy distribution diagram of the LTS sliding correlation C (i) without the pre-frequency offset compensation, and fig. 6 is an energy distribution diagram of the LTS sliding correlation C (i) under the pre-frequency offset compensation condition, where it is obvious that the pre-frequency offset compensation is performed to find out the correlation peak normally and find out the normal frame head position.
Step S5: STS coarse frequency offset estimation
Step S4 determines a new frame header, according to which t StartNew Processing the re-backup data, wherein the backup mode is z 1 (t)＝y(t)，t∈[t StartNew t StartNew +16us*Fs]I.e. backup with fine synchronization point t StartNew For reference, the total length is 16us.
Considering STS as the frame start part, some cases will have a power ramp up procedure, thus discarding the first 4 repetition periods. STS sequence length 0.8us, interval sampling point is N 1 =fs 0.8us. Calculating coarse frequency offset f based on STS sts The method of (2) is as follows:
wherein arctan is the arctangent and superscript is the complex conjugate of the complex signal.
Step S6: STS coarse frequency offset compensation
Calculating coarse frequency offset f sts After that, the backup signal z is compensated 1 Mode (t) is
Step S7: LTS fine frequency offset estimation
LTS has a starting position t lts ＝t StartNew +8us fs, interval length N 2 =fs 3.2us, the complete LTS signal is a GI of 1.6us and two repeated sequences of 3.2us, where the GI of 1.6us is the second half repeat of the 3.2us sequence, taking into account t StartNew With the possibility of inaccuracy, move backwards by 02us enters the GI, and LTS frequency offset calculates the initial position t lts2 ＝t lts +0.2us fs, superscript is the complex conjugate of the complex signal. LTS fine frequency offset f lts The calculation method of (1) is as follows:
step S8: signal frequency offset compensation
Step S5 calculates a coarse frequency offset f sts Step S7 calculates the fine frequency offset f based on step S5 lts The frequency offset of the whole received signal Δf=f sts +f lts . And (3) carrying out frequency offset compensation on the received signal y (t), wherein the compensation mode is as follows:
y * (t)＝y(t)*e -j2πΔft
the steps determine that the signal still calculates to the accurate synchronous position t under the influence of the large frequency offset StartNew And the frequency offset delta f, thus finishing the preliminary processing of the signals and finishing the signals of synchronization and frequency offset compensation, and analyzing each test index according to the normal protocol flow.
And (3) experimental verification:
the situation that the comprehensive tester does not perform frequency offset pre-estimation and compensates for the comprehensive tester to analyze large frequency offset data is shown in fig. 7, and the data cannot be normally analyzed due to the fact that the frame head positioning is 2us away from the power window to cause synchronization failure and intersymbol interference is introduced.
The condition that the comprehensive tester adopts the method to pre-estimate the frequency offset and compensate the comprehensive tester to analyze the large frequency offset data is shown in figure 8, the frame synchronization is successful from the power window, the data analysis is finished based on the result, and the frequency offset is estimated to be 433.35KHz.
According to the scheme and analysis, the method can ensure that the precise synchronization of the large frequency offset signals is finished, and after the accurate large frequency offset is estimated by combining the short training sequence and the long training sequence and the frequency offset compensation is carried out, each index of the signals can be normally analyzed. The invention overcomes the influence caused by large frequency offset and improves the accuracy and stability of the comprehensive tester for analyzing the DUT signal performance.
The invention also provides a system for realizing the method for analyzing the large frequency offset data by the comprehensive tester, which comprises the following steps:
and a power window coarse synchronization module: the method comprises the steps of searching a rough starting point and a rough end point of each frame of data, determining a rough synchronization point and performing rough synchronization on signals;
the frequency offset pre-estimation module: the method comprises the steps of estimating a pre-frequency offset value of data after coarse synchronization;
frequency offset precompensation module: the pre-compensation unit is used for pre-compensating the received signal according to the estimated pre-frequency offset value;
LTS fine synchronization module: performing sliding correlation operation on the data subjected to the pre-compensation frequency offset by adopting a long training sequence LTS to obtain an accurate frame head position;
STS coarse frequency offset estimation module: the method is used for acquiring a coarse frequency offset value by adopting a short training sequence STS based on the correct frame head position;
STS frequency offset compensation module: the method is used for carrying out frequency offset compensation on the signals after the fine synchronization according to the coarse frequency offset value;
LTS fine frequency offset estimation module: the method is used for acquiring a fine frequency offset value by adopting a long training sequence LTS;
and the signal frequency offset compensation module: the method is used for obtaining a final frequency offset value according to the coarse frequency offset value and the fine frequency offset value, and finishing signal frequency offset compensation according to the frequency offset value.
The above embodiments are preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, which includes but is not limited to the embodiments, and equivalent modifications according to the present invention are within the scope of the present invention.
Claims (10)
1. The method for analyzing the large frequency offset data by the comprehensive tester is characterized by comprising the following steps of:
s1: coarse synchronization of power windows: the method comprises the steps of searching a rough starting point and a rough end point of each frame of data, determining a rough synchronization point and performing rough synchronization on signals;
s2: frequency offset pre-estimation: the method comprises the steps of estimating a pre-frequency offset value of data after coarse synchronization;
s3: frequency offset pre-compensation: pre-compensating the received signal according to the estimated pre-frequency offset value;
s4: LTS fine synchronization: performing sliding correlation operation on the data subjected to the pre-compensation frequency offset by adopting a long training sequence LTS to obtain an accurate frame head position;
s5: STS coarse frequency offset estimation: based on the correct frame head position, a short training sequence STS is adopted to obtain a coarse frequency offset value;
s6: STS frequency offset compensation: performing frequency offset compensation on the signal after the fine synchronization according to the coarse frequency offset value;
s7: LTS fine frequency offset estimation: a long training sequence LTS is adopted to obtain a fine frequency offset value;
s8: and (3) signal frequency offset compensation: and (3) obtaining a final frequency offset value according to the coarse frequency offset value obtained in the step (S5) and the fine frequency offset value obtained in the step (S7), and finishing signal frequency offset compensation according to the frequency offset value.
2. The method for analyzing large frequency offset data by using a comprehensive tester according to claim 1, wherein: in step S1, coarse synchronization is performed by adopting a double sliding window algorithm, and the specific processing method comprises the following steps:
s11: calculating the power of each sampling point of the received signal;
s12: calculating the power value difference of adjacent double windows and the power value difference of the double windows:
s13: and acquiring the frame start and end positions according to the change of the power value difference value of the double window.
3. The method for analyzing large frequency offset data by using a comprehensive tester according to claim 1, wherein: the specific processing method of the step S2 is as follows:
s21: frequency offset is calculated with a blind estimation algorithm based on the preamble of the received signal,
the interval duration selects STS sequence length 0.8us, and the interval sampling point is N 1 =fs 0.8us, the duration of the frequency offset calculation is selected to be 0.1us, i.e. holdThe continuous sampling point is N 2 =fs 0.1us, the calculation formula is:
wherein f (n) represents an average frequency offset sequence of backup data with the n-th segment of duration of 0.1us data, G (n) is a calculation process intermediate quantity, arctan is an arctangent, superscript is a complex conjugate of a complex signal, n takes a value from 1 to 239 under a value range of 24us, fs is a sampling rate,
s22: frequency offset sequence differential calculation
The differential calculation after calculating the frequency offset based on f (n) is expressed as:
g(n)＝f(n)-f(n-1)
when the absolute value of g (n) is smaller than the first set value and the continuous number m of absolute values smaller than the first set value is larger than the set threshold, indicating that the pre-frequency offset calculation is successful, recording the continuous starting point as k and the pre-frequency offset value f pre And (3) setting the average value of m frequency offsets f (n) from k to above a threshold value.
4. The method for analyzing large frequency offset data by using a comprehensive tester according to claim 3, wherein: in step S3, a pre-frequency offset f is calculated pre Then, the formula of the compensation received signal z (t) is:where j is an imaginary unit.
5. The method for analyzing large frequency offset data by using a comprehensive tester according to claim 4, wherein: in step S4, the accurate frame start position is obtained by sliding correlation between the local long training sequence and the received signal, and in step S3, the data z after the pre-frequency offset is compensated * (t) is described in complex form as z * (t)＝z I (t)+j*z Q (t), t=1 …, N, n=fs×28us, the ideal long training sequence LTS time domain signal is denoted as x (t) =x I (t)+j*x Q (t), t=1, …, M, m=fs×3.2us, the correlation operation is defined as
The synchronization process adopts the data z after compensating the pre-frequency offset * (t) performing sliding correlation operation with the local known training sequence x (t), judging the similarity degree, if z * And (t) the correlation value between the moment i and x (t) is marked as C (i), then:
C(i)＝correl(z I (i+t)，x I (t))+correl(z I (i+t)，x Q (t))+correl(z Q (i+t)，x I (t))+correl(z Q (i+t)，x Q (t))
based on the characteristics of the correlation operation, if z * If x (t) is present on (t), then 2 distinct peaks appear at C (i) when the sliding correlation is to the corresponding starting point, and the two peaks are separated by the LTS duration, if the first peak appears at i 1 The second peak occurs at i 2 And i 2 -i 1 =fs×3.2us, then fine synchronization is successful, and the frame start position t is updated StartNew ＝i 1 -Fs*9.6us。
6. The method for analyzing large frequency offset data by using a comprehensive tester according to claim 5, wherein: in step S5, the new frame start position t is used StartNew Processing the re-backup data, wherein the backup mode is z 1 (t)＝y(t)，t∈[t StartNew t StartNew +16us*Fs]I.e. backup with fine synchronization point t StartNew Based on the standard, the total length is 16us, and the coarse frequency offset f is calculated based on STS sts Is shown as follows:
wherein arctan is the inverse tangent and superscript is the complex conjugate of the complex signal.
7. The method for analyzing large frequency offset data by using a comprehensive tester according to claim 6, wherein: in step S6, after obtaining the coarse frequency offset, the backup signal z is compensated 1 Mode (t) is
8. The method for analyzing large frequency offset data by using a comprehensive tester according to claim 7, wherein: in step S7, the starting position of the LTS is t lts ＝t StartNew +8us fs, interval length N 2 =fs×3.2us, lts frequency offset calculates the start position t lts2 ＝t lts +0.2us Fs, fine frequency offset f of LTS lts The calculation method of (1) is as follows:
9. the method for analyzing large frequency offset data by using a comprehensive tester according to claim 8, wherein: in step S8, the frequency offset Δf=f of the entire received signal sts +f lts Performing frequency offset compensation on the received signal y (t) in a mode of y * (t)＝y(t)*e -j2πΔft 。
10. A system for implementing the method for analyzing large frequency offset data of the comprehensive testing machine according to any one of claims 1 to 9, comprising:
and a power window coarse synchronization module: the method comprises the steps of searching a rough starting point and a rough end point of each frame of data, determining a rough synchronization point and performing rough synchronization on signals;
the frequency offset pre-estimation module: the method comprises the steps of estimating a pre-frequency offset value of data after coarse synchronization;
frequency offset precompensation module: the pre-compensation unit is used for pre-compensating the received signal according to the estimated pre-frequency offset value;
LTS fine synchronization module: performing sliding correlation operation on the data subjected to the pre-compensation frequency offset by adopting a long training sequence LTS to obtain an accurate frame head position;
STS coarse frequency offset estimation module: the method is used for acquiring a coarse frequency offset value by adopting a short training sequence STS based on the correct frame head position;
STS frequency offset compensation module: the method is used for carrying out frequency offset compensation on the signals after the fine synchronization according to the coarse frequency offset value;
LTS fine frequency offset estimation module: the method is used for acquiring a fine frequency offset value by adopting a long training sequence LTS;
and the signal frequency offset compensation module: the method is used for obtaining a final frequency offset value according to the coarse frequency offset value and the fine frequency offset value, and finishing signal frequency offset compensation according to the frequency offset value.
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