CN113093163A - High-speed target speed measurement method based on effective OFDM communication subcarrier detection - Google Patents

High-speed target speed measurement method based on effective OFDM communication subcarrier detection Download PDF

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CN113093163A
CN113093163A CN202110305487.4A CN202110305487A CN113093163A CN 113093163 A CN113093163 A CN 113093163A CN 202110305487 A CN202110305487 A CN 202110305487A CN 113093163 A CN113093163 A CN 113093163A
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frequency offset
index
fft
frequency
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CN113093163B (en
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余小游
余苗
赵旺兴
余晨箫
余俐嘉
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Hunan University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S11/00—Systems for determining distance or velocity not using reflection or reradiation
    • G01S11/02—Systems for determining distance or velocity not using reflection or reradiation using radio waves
    • G01S11/10—Systems for determining distance or velocity not using reflection or reradiation using radio waves using Doppler effect
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S11/00—Systems for determining distance or velocity not using reflection or reradiation
    • G01S11/02—Systems for determining distance or velocity not using reflection or reradiation using radio waves
    • G01S11/04—Systems for determining distance or velocity not using reflection or reradiation using radio waves using angle measurements

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Abstract

The invention discloses a high-speed target speed measurement method based on effective OFDM communication subcarrier detection, which comprises the steps of firstly utilizing two sections of same leader sequences to carry out cross-correlation estimation to obtain decimal times subcarrier interval frequency offset, and then carrying out decimal times frequency offset compensation on a receiving sequence. On the premise of accurate time synchronization, a SIGNAL field OFDM symbol or a load OFDM symbol is found, FFT is carried out on the SIGNAL field OFDM symbol or the load OFDM symbol, a modulus is carried out on the SIGNAL field OFDM symbol or the load OFDM symbol to obtain an amplitude-frequency response sequence, the subcarrier index with the amplitude larger than 2 times and smaller than 16 times of average amplitude is found to be an effective subcarrier index without interference, and the range is within (1, FFTSIZE). The indexes are segmented into index subsets according to continuity, and in four possible cases, the average value of the index subsets and the offset of FFTSIZE/2 are calculated to estimate the integral multiple frequency offset. The method can greatly reduce the calculation complexity, and the speed measurement precision reaches the magnitude of centimeter per second under the condition of ensuring decimal frequency multiplication offset compensation.

Description

High-speed target speed measurement method based on effective OFDM communication subcarrier detection
Technical Field
The invention belongs to the technical field of 6G mobile communication, and particularly relates to a high-speed target speed measurement method based on effective OFDM communication subcarrier detection.
Background
The high-speed moving target refers to a target with the flight speed reaching the kilometer per second, such as a low-orbit satellite in a future 6G mobile communication scene, a supersonic aircraft which runs in the opposite direction and the like. The traditional high-speed target speed measurement problem is generally carried out by adopting a method that radar equipment transmits a linear frequency modulation signal, then echo reflected signals are captured and tracked and detected according to a radar receiver, and the Doppler frequency shift of the reflected signals needs to be detected; however, due to the limited signal receiving surface of the target reflected signal and the diversity of the reflected objects, a high requirement is placed on the receiving sensitivity of the radar. In addition, the radar reception signal processing requires a complex clutter suppression technique (CFAR constant false alarm processing) to eliminate the interference detection of the false target, and also requires Low Noise Amplification (LNA) on the real target signal, so that the signal processing complexity is high. Therefore, general radar high-speed measurement equipment is expensive and is widely used in the military communication field.
In the field of civil communication, speed measurement and positioning are mostly used in high-speed rail scenes in the existing 4G/5G base station communication, the relative speed is at most hundred meters per second magnitude generally, and in addition, 4G/5G radio frequency signals are mostly at 2-6 GHz frequency, so that Doppler frequency offset is mostly dozens of Hz to hundred Hz magnitude, in OFDM baseband waveform, frequency offset tracking can be carried out only by adopting a simple decimal subcarrier interval frequency offset estimation method, thereby ensuring that subsequent channel estimation finishes decoding to carry out communication. In the field of 6G in the future, radio frequency signals of millimeter wave level or even terahertz level are used for communication, the radio frequency domain is at least dozens of GHz level, and compatible scenes including satellites can be used for communication even when the speed requirement reaches several kilometers per second, and at the moment, mobile communication and speed measurement positioning based on the OFDM baseband waveform become a very troublesome problem.
According to the calculation formula of Doppler frequency offset
Figure BDA0002983313250000011
Let fc be 100Ghz, c be 3 × 108m/s, v 3000m/s, in this caseThe doppler shift is calculated as fd 1 Mhz. For such a large doppler frequency offset, the conventional estimation method, such as the LCR (level crossing) method, has a level observation period of only ten or more points, and thus, a large calculation error is caused. And the decimal frequency offset can be accurately estimated by using a Cyclic Prefix (CP) time domain estimation method, and the method has no effect on the integral multiple frequency offset.
In the field of 4G communication, for example, the baseband sampling rate of an FDD-LTE system is only 30.72MHz, the number of subcarriers is generally 1024, the subcarrier interval at this time is 30KHz, even if the baseband sampling rate is expanded to 122.88MHz in a 5G-NR scene, the number of subcarriers is expanded to 4096, the subcarrier interval is also 30KHz, so that for 1MHz Doppler frequency offset, the frequency offset is equivalent to nearly 33 integer frequency offsets plus a decimal frequency offset of 0.333 times, the traditional integer frequency offset detection algorithm adopts maximum likelihood to traverse at least-50 to 50, namely at least one hundred times of cross-correlation detection, the complexity is very high, no good method for detecting large integer frequency offset exists at present, and no method for measuring the speed of a high-speed moving target based on 6G mobile communication and OFDM baseband communication waveforms is available.
Disclosure of Invention
The embodiment of the invention aims to provide a high-speed target speed measurement method based on effective OFDM communication subcarrier detection, aiming at Doppler frequency offset of a large integer times of subcarrier intervals, the calculation complexity is greatly reduced, the detection speed is greatly improved, and the speed measurement precision reaches the magnitude of centimeter per second under the condition of ensuring decimal frequency offset compensation.
The technical scheme adopted by the invention is that the high-speed target speed measurement method based on effective OFDM communication subcarrier detection is carried out according to the following steps:
s1, firstly, two sections of leader sequences with the same length and adjacent sequences are used for carrying out cross-correlation estimation to obtain decimal subcarrier spacing frequency offset of the OFDM baseband signal, wherein the decimal subcarrier spacing frequency offset comprises a decimal frequency offset estimation part and an integral frequency offset estimation part;
s2, performing decimal frequency multiplication offset compensation on the received sequence;
s3, finding out a SIGNAL field OFDM symbol or a load OFDM symbol on the premise of accurate time synchronization, performing FFT and modulus to obtain an amplitude-frequency response sequence, and finding out a subcarrier index with the amplitude more than 2 times and less than 16 times of average amplitude as an effective subcarrier index without interference, wherein the range is within (1, FFTSIZE); and segmenting the index into index subsets according to the continuity, under four possible conditions, calculating the average value of the index subsets and the offset of FFTSIZE/2 to estimate integral frequency offset, adding the integral multiple and the decimal multiple to obtain the final frequency offset estimation size, using the obtained frequency offset estimation as the estimated value of Doppler frequency offset, estimating the target speed by using a Doppler frequency offset formula, and judging the acceleration and deceleration states of the target according to positive and negative offsets.
The invention can be applied to the relative speed measurement problem of a high-speed moving target in the 6G mobile communication field, the air-space-ground integration and perception communication integration technology, and particularly relates to the problem of performing signal processing on the OFDM baseband physical layer waveform so as to perform megahertz (MHz) Doppler frequency offset estimation. The method is suitable for OFDM signal field symbols and load symbols containing virtual subcarriers and effective subcarriers, and Doppler frequency offset reaches the megalevel situation in a high-speed scene.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart of an embodiment of the present invention;
FIG. 2 is a schematic diagram of a possible situation 1 of effective subcarrier positions under large frequency offset;
FIG. 3 is a schematic diagram of a possible situation 2 of effective subcarrier positions under large frequency offset;
FIG. 4 is a schematic diagram of a possible situation 3 of effective subcarrier positions under large frequency offset;
FIG. 5 is a schematic diagram of a possible situation 4 of effective subcarrier locations under large frequency offset;
FIG. 6 is a diagram of fractional frequency offset variation with signal-to-noise ratio in a simulation environment;
FIG. 7 is a diagram illustrating a variation of integer frequency offset with signal-to-noise ratio in a simulation environment;
fig. 8 is a flowchart of the algorithm steps of the integer multiple frequency offset estimation method.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The OFDM baseband frequency offset is mainly caused by two aspects: the Doppler frequency shift and the oscillation frequency shift of a down-conversion device, the latter is generally in the magnitude of thousands of hertz, and the speed error estimated by an OFDM baseband is within one thousandth of the Doppler frequency shift far less than a few megahertz, so the default large Doppler frequency shift is the OFDM baseband frequency shift.
In the frequency domain of the OFDM baseband signal, subcarriers are divided into two types, namely, effective subcarriers and virtual subcarriers. The effective sub-carriers refer to sub-carriers loaded with information symbols (generally pilot symbols and data BPSK/QPSK/16QAM/64QAM symbols) in a sub-carrier frequency range of some specific width; the virtual sub-carriers are not loaded with any information symbols, and thus the amplitude of the virtual sub-carriers is 0. Before the base band waveform transmitting end is subjected to IFFT modulation, proper virtual subcarriers are inserted, which is mainly used for reducing the peak-to-average ratio of OFDM symbols, otherwise, all subcarriers load information symbols, the peak-to-average ratio is increased sharply, and the unacceptable degree of a system is easily reached.
In the time domain frame structure of the baseband OFDM symbol, a preamble sequence is generally used for time synchronization or initial frequency offset estimation before a load symbol, a block pilot frequency (used for tracking a frequency selective fading channel) OFDM symbol, a service information SIGNAL field OFDM symbol and a data information load OFDM symbol are used behind the load symbol, and FFT spectrum detection is carried out from the block pilot frequency OFDM symbol, so that the FFT spectrum detection can be seenOnly the active subcarrier symbols have signal energy and the virtual subcarrier energy is noise energy. If no frequency offset exists, according to the base band physical layer resource allocation principle, the effective subcarrier energy is distributed in a one-dimensional symmetrical mode relative to a position (or a half FFT size point) of half the total number of subcarriers, and when the frequency offset exists, the middle point of the effective subcarrier is properly offset relative to the point. By using the principle, the offset can be determined by detecting the energy of the effective subcarriers and finding the position index, so that the integral multiple frequency offset is calculated. In order to accurately estimate the frequency deviation, the invention provides that the number of virtual subcarriers in the middle section of amplitude-frequency response is 0 or the number of virtual subcarriers in the middle section is less than the number of virtual subcarriers on two sides, and simultaneously, in order to avoid virtual detection, the invention provides that the range of the estimated frequency deviation is 0
Figure BDA0002983313250000041
Fs is the baseband signal sampling rate.
The specific flow of the high-speed target speed measurement method based on effective OFDM communication subcarrier detection is shown in FIG. 1.
Firstly, two sections of same leader sequences are utilized to carry out cross-correlation estimation to obtain decimal times subcarrier interval frequency offset of an OFDM baseband signal, wherein the decimal times frequency offset and integral multiple frequency offset estimation are included; then, decimal frequency multiplication deviation compensation is carried out on the received sequence. On the premise of accurate time synchronization, a SIGNAL field OFDM symbol or a load OFDM symbol is found, FFT is carried out on the SIGNAL field OFDM symbol or the load OFDM symbol, a modulus is carried out on the SIGNAL field OFDM symbol or the load OFDM symbol to obtain an amplitude-frequency response sequence, the subcarrier index with the amplitude larger than 2 times and smaller than 16 times of average amplitude is found to be an effective subcarrier index without interference, and the range is within (1, FFTSIZE). The indexes are segmented into index subsets according to continuity, and in four possible cases, the average value of the index subsets and the offset of FFTSIZE/2 are calculated to estimate the integral multiple frequency offset.
Aiming at OFDM baseband signals, the invention firstly utilizes a preamble method to calculate initial frequency offset, and deduces the frequency offset size to be decimal times of subcarrier interval frequency offset size.
Two sections of preamble sequences which are completely consistent and have the length of L and are close to each other are transmitted, the sampling rate of a baseband symbol is set as Fs, the time domain expression containing frequency offset is as follows,
Figure BDA0002983313250000042
pimeans of (1) a leader sequence (q)iMeans of preamble sequence 2, x (i) means time domain symbol of the transmitting end of preamble sequence 1 or 2, i means ith symbol of total length, e means natural constant or euler number representing euler's formula, Δ f means frequency offset size, and j means imaginary unit representing complex number.
The two sequences are cross-correlated and summed,
Figure BDA0002983313250000043
Figure BDA0002983313250000044
meaning that the preamble 2 symbols are conjugated;
wherein
Figure BDA0002983313250000045
Is the subcarrier spacing, Δ ffictionFrequency offset of decimal times subcarrier spacing, m0Is an integer multiple of the interval frequency offset multiple of the sub-carrier, the angle is calculated by the above formula (2),
Figure BDA0002983313250000051
the angle is periodically rotated about 2 pi, so angling this equation can estimate the fractional subcarrier spacing offset as,
Figure BDA0002983313250000052
here the received sequence is also noisy and the summation is to reduce the noise effect.
Secondly, the invention carries out time domain decimal frequency offset compensation on all the receiving sequences Frame aiming at the OFDM baseband signals, and only integral multiple frequency offset estimation is remained in the follow-up process after the decimal frequency offset compensation is finished.
The formula for the compensation is described as follows,
Figure BDA0002983313250000053
FrameLength is the frame length.
Finally, the invention introduces a method for estimating the interval frequency offset of integer times of subcarriers aiming at OFDM baseband signals. And after the decimal frequency multiplication offset compensation is completed, assuming that time synchronization is accurately completed, finding a subsequent SIGNAL field OFDM symbol or a load OFDM symbol, performing FFT on the subsequent SIGNAL field OFDM symbol or the load OFDM symbol to obtain a frequency domain sequence, and then performing modulus calculation to obtain an amplitude-frequency response sequence.
Due to the difference of the resource allocation methods of the physical layer of the transmitting terminal, when the effective subcarriers are selected, the virtual subcarriers may appear in the middle of the virtual subcarriers on both sides although the effective subcarriers are symmetrical about the center. Therefore, under a large frequency offset, four different situations may occur when a receiving end detects an effective subcarrier, see fig. 2 to 5 in the specification.
Setting the FFT length to be N for the amplitude-frequency response sequenceFFTDescribed in detail according to the energy threshold detection algorithm as an amplitude-frequency response sequence X (n)fft)，nfft＝1，2，...，NFFTBy amplitude threshold detection, if
Figure BDA0002983313250000054
In order to obtain an average value, the right side of the inequality needs to be provided with NFFTAnd (5) secondary detection.
Then the effective sub-carrier is determined, and the corresponding effective sub-carrier index is found, the range is (1, N)FFT) Within.
In addition, strong interference may be contained within the OFDM baseband spectrum, so the energy detection threshold ceiling,
Figure BDA0002983313250000061
for eliminating interference.
No matter how the noise is affected, the effective sub-carriers are distributed continuously, and then the indexes are divided into several different continuous index subsets according to the continuity detection, and the average value of the index subsets and N are usedFFTThe offset value of/2 obtains integral frequency deviation delta fInteger. The estimation of the integral multiple frequency offset is discussed in four different cases with reference to graphs, and the principle is to estimate the offset of the average value of the index subset relative to the central point. In calculating the index subset average, as discussed in more detail below,
2) with reference to FIG. 2, if there is only one segment of consecutive index (x)1，x2，...xm) Taking the average of these indices
Figure BDA0002983313250000062
Then
Figure BDA0002983313250000063
The positive and negative biases are common.
ΔfIntegerMeaning an estimate of the magnitude of the integer frequency offset, and m meaning the length of the first segment of consecutive indices.
2) If only two consecutive indexes (x) are provided, as described in connection with FIG. 3 of the drawings1，x2，...，xm) And (y)1，y2，...，yn) And m is n, the average value of the first segment is taken
Figure BDA0002983313250000064
And second segment mean value
Figure BDA0002983313250000065
Then
Figure BDA0002983313250000066
The positive and negative biases are common. n means the length of the second segment consecutive index.
3) If only two consecutive indexes (x) are provided, as described in connection with FIG. 4 of the specification1，x2，...，xm) And (y)1，y2，...，yn) And m < n, if yn＜x1Then it is determined as negative bias and the first segment is subtracted by NFFTThen calculating the average value with the second stage
Figure BDA0002983313250000067
x _ Ave2 means the equivalent average of two consecutive indices in this case;
if y1＞xmThen the method is judged to be positive bias, and N is added to the first segmentFFTThen calculating the average value with the second stage
Figure BDA0002983313250000071
Then
Figure BDA0002983313250000072
4) When there are three consecutive indexes (x) in conjunction with the description of FIG. 51，x2，...，xm) And (y)1，y2，...，yn) And (z)1，z2，...，zl) And m + l ═ n, xm＜z1(ii) a If y1-xm＜z1-ynThen the negative bias is judged, and the third segment is subtracted by NFFTThen calculating the average value with the first section
Figure BDA0002983313250000073
x _ Ave3 means the equivalent average of consecutive indices of the first segment and the third segment in this case; the meaning of l is the length of the third segment consecutive index in this case;
if z is1-yn＜y1-xmJudging the error to be positive, adding N to the third segmentFFTThen calculating the average value with the first section
Figure BDA0002983313250000074
While calculating the second segment mean
Figure BDA0002983313250000075
Then
y _ Ave3 means the average of the second segment consecutive indices in this case;
Figure BDA0002983313250000076
for the OFDM baseband signal, after the integral multiple frequency offset and the decimal frequency offset are estimated, the total frequency offset estimation size is delta f-delta ffiction+ΔfIntegerThis estimate is approximately equal to the doppler shift estimate as described above. Finally, according to the calculation formula of Doppler frequency offset,
Figure BDA0002983313250000077
and estimating the speed value, wherein c is the speed of light, fd is the Doppler frequency offset, and fc is the frequency offset caused by oscillation of the device when the frequency is converted from radio frequency to baseband. Since fc is typically much smaller than fd on the order of megahz on the order of a few KHz, the speed error estimated by Δ f is within one thousandth, and therefore fd is approximately equal to the OFDM baseband frequency offset Δ f.
Compared with the traditional maximum likelihood detection algorithm, the method greatly reduces the calculated amount, the performance of the estimation method mainly depends on integral frequency offset estimation, the key for influencing the integral frequency offset estimation performance is decimal frequency offset compensation, the integral frequency offset is hardly influenced by noise, and the high signal-to-noise ratio estimation speed precision is in the centimeter per second level.
Examples
In the embodiment, interference detection brought by narrow-band strong interference to effective subcarrier detection is not considered, and device frequency offset brought by a down-conversion process is not considered in OFDM baseband frequency offset.
Under a certain simulation environment, the sampling rate of an OFDM baseband signal is set to be 30.72MHz, the number of subcarriers or the FFT length is set to be 1024, the interval of the subcarriers is 30KHz, a PN sequence containing 1024 points of two leading symbols is used for estimating decimal frequency offset, an OFDM data symbol frequency domain adopts BPSK mapping, the CP length is 128, and the time domain symbol bit width is set to be 2^ 10. Loading gaussian noise sets the signal-to-noise ratio to 0 to 30 dB.
The signal-to-noise ratio is set to be 30dB, the Doppler frequency offset is set to be-64X 30KHz + 0.4X 30 KHz-1.908 MHz, the effective subcarrier sequence is set to be [448: 512513: 576], and the amplitude-frequency response of the receiver after decimal frequency multiplication offset compensation is shown in the attached figure 2 of the specification.
The signal-to-noise ratio is set to be 30dB, the Doppler frequency offset is set to be-64X 30KHz + 0.4X 30 KHz-1.908 MHz, the effective subcarrier sequence is set to be [384: 448577: 640], and the amplitude-frequency response of the receiver after decimal frequency multiplication offset compensation is shown in the attached figure 3 of the specification.
The Doppler frequency offset is set to be-404 x 30KHz +0.4 x 30 KHz-12.108 MHz, the signal-to-noise ratio is set to be 30dB, the effective subcarrier sequence is set to be [448: 512513: 576], and the amplitude-frequency response of the receiver after decimal frequency multiplication offset compensation is shown in the attached figure 4 of the specification.
The Doppler frequency offset is set to be-404 x 30KHz +0.4 x 30 KHz-12.108 MHz, the signal-to-noise ratio is set to be 30dB, the effective subcarrier sequence is set to be [384: 448577: 640], and the amplitude-frequency response of the receiver after decimal frequency multiplication offset compensation is shown in the attached figure 5 of the specification.
The decimal frequency multiplication offset compensation formula is shown in formula (5).
The preamble position and the data OFDM symbol after the CP segment can be correctly found under the condition of accurate time synchronization. The estimated relative frequency deviation error is calculated by the formula
Figure BDA0002983313250000081
As the specification, the attached figure 6 is a graph of the change of the decimal frequency offset with the signal-to-noise ratio under the environment, and a calculation formula is shown in a formula (4). The graph shows that the fractional frequency offset estimation error is below 10^ (-3) when the signal-to-noise ratio reaches above 30 dB.
The algorithm steps of the integer multiple frequency offset estimation method combined with the contents of the invention in the embodiment of the invention are described in the attached figure 8 of the specification.
As shown in fig. 7, which is a graph showing variation of integer frequency offset estimation with signal-to-noise ratio after decimal frequency offset compensation in the environment, simulation result graphs are the same in four cases considering the contents of the invention, and one of the graphs is listed. The figure shows that the integral frequency deviation is not affected by noise after decimal frequency doubling deviation compensation, so that the frequency deviation error is below 10 < -6 > under high signal-to-noise ratio under large Doppler frequency deviation, and the estimation accuracy of the speed error is below centimeter level.
The invention aims at a large Doppler velocity measurement method, and in an actual velocity measurement scene, when a target is far away from and close to and accelerates and decelerates, the index value of integral frequency offset estimation detection can be changed as follows by combining the contents of the invention:
in the first case, in combination with equation (8), the target is away from the calculated Δ fIntegerNegative, when the target approaches Δ fIntegerPositive value, at target acceleration, x1～xmAll will increase, xm-x1The length remains the same so that x _ Ave1 increases, and when the target decelerates, x1～xmAll will decrease, xm-x1The length remains unchanged and x _ Ave1 decreases.
In the second case, equation (9) is combined, the target moves away from the calculated Δ fIntegerNegative, when the target approaches Δ fIntegerPositive, x _ Ave1 and y _ Ave1 both increase during target acceleration and x _ Ave1 and y _ Ave1 both decrease during target deceleration.
For the third case, combining equations (10), (11), (12), the target distance calculated Δ fIntegerNegative, when the target approaches Δ fIntegerPositive, x _ Ave2 increases when the target accelerates, and x _ Ave2 decreases when the target decelerates.
For the fourth case, combining equations (13), (14), and (15), the target distance is calculated as Δ fIntegerNegative, when the target approaches Δ fIntegerPositive, x _ Ave3 and y _ Ave3 both increase at target acceleration, and x _ Ave3 and y _ Ave3 both decrease at target acceleration.
All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the system embodiment, since it is substantially similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims (5)

1. The high-speed target speed measurement method based on effective OFDM communication subcarrier detection is characterized by comprising the following steps of:
s1, firstly, two sections of leader sequences with the same length and adjacent sequences are used for carrying out cross-correlation estimation to obtain decimal subcarrier spacing frequency offset of the OFDM baseband signal, wherein the decimal subcarrier spacing frequency offset comprises a decimal frequency offset estimation part and an integral frequency offset estimation part;
s2, performing decimal frequency multiplication offset compensation on the received sequence;
s3, finding out a SIGNAL field OFDM symbol or a load OFDM symbol on the premise of accurate time synchronization, performing FFT and modulus to obtain an amplitude-frequency response sequence, and finding out a subcarrier index with the amplitude more than 2 times and less than 16 times of average amplitude as an effective subcarrier index without interference, wherein the range is within (1, FFTSIZE); and segmenting the index into index subsets according to the continuity, under four possible conditions, calculating the average value of the index subsets and the offset of FFTSIZE/2 to estimate integral frequency offset, adding the integral multiple and the decimal multiple to obtain the final frequency offset estimation size, using the obtained frequency offset estimation as the estimated value of Doppler frequency offset, estimating the target speed by using a Doppler frequency offset formula, and judging the acceleration and deceleration states of the target according to positive and negative offsets.
2. The method for measuring speed of a high speed target based on effective OFDM communication subcarrier detection according to claim 1, wherein the S1 specifically comprises:
two sections of preamble sequences which are completely consistent and have the length of L and are close to each other are transmitted, the sampling rate of a baseband symbol is set as Fs, the time domain expression containing frequency offset is as follows,
Figure FDA0002983313240000011
pimeans of (1) a leader sequence (q)iThe meaning of (a) is preamble sequence 2, x (i) is time domain symbol of the transmitting end of preamble sequence 1 or 2, i is the ith symbol of the total length, e is the natural constant or euler number representing euler formula, Δ f is frequency offset, j is the imaginary unit representing complex number;
the two sequences are cross-correlated and summed,
Figure FDA0002983313240000012
Figure FDA0002983313240000013
meaning that the preamble 2 symbols are conjugated;
wherein
Figure FDA0002983313240000014
Figure FDA0002983313240000015
Is the subcarrier spacing, Δ ffictionFrequency offset of decimal times subcarrier spacing, m0Frequency offset for integer times subcarrier spacingMultiple, calculating the angle of the above formula (2),
Figure FDA0002983313240000021
the angle is periodically rotated about 2 pi, so angling this equation can estimate the fractional subcarrier spacing offset as,
Figure FDA0002983313240000022
3. the method for measuring the speed of a high-speed target based on the detection of the effective OFDM communication subcarriers according to claim 1 or 2, wherein the S2 specifically includes:
the compensation formula is as follows,
Figure FDA0002983313240000023
FrameLength is the frame length.
4. The method for measuring speed of a high speed target based on effective OFDM communication subcarrier detection according to claim 1, wherein the S3 specifically comprises:
setting the FFT length to be N for the amplitude-frequency response sequenceFFTDescribed in detail according to the energy threshold detection algorithm as an amplitude-frequency response sequence X (n)fft),nfft＝1,2,...,NFFTBy amplitude threshold detection, if
Figure FDA0002983313240000024
Then the effective sub-carrier is determined, and the corresponding effective sub-carrier index is found, the range is (1, N)FFT) The content of the compound is less than the content of the compound;
in addition, strong interference may be contained in the OFDM baseband spectrum, so the energy detection threshold is limited;
dividing the index into several different continuous index subsets according to the continuity detection, and using the average value of these index subsets and NFFTThe offset value of/2 obtains integral frequency deviation delta fInteger(ii) a In four different cases, the number of the cases,
1) if there is only one segment of consecutive index (x)1,x2,...xm) Taking the average of these indices
Figure FDA0002983313240000025
Then
Figure FDA0002983313240000026
The positive and negative biases are universal; Δ fIntegerMeaning an integral multiple frequency deviation size estimated value, and m meaning the length of the first section continuous index;
2) if there are only two consecutive indexes (x)1,x2,...,xm) And (y)1,y2,...,yn) And m is n, the average value of the first segment is taken
Figure FDA0002983313240000031
And second segment mean value
Figure FDA0002983313240000032
Then
Figure FDA0002983313240000033
The positive and negative biases are universal; n means the length of the second segment consecutive index;
3) if there are only two consecutive indexes (x)1,x2,...,xm) And (y)1,y2,...,yn) And m < n, if yn＜x1Then it is determined as negative bias and the first segment is subtracted by NFFTThen averaged with the second stageValue of
Figure FDA0002983313240000034
x _ Ave2 means the equivalent average of two consecutive indices in this case;
if y1＞xmThen the method is judged to be positive bias, and N is added to the first segmentFFTThen calculating the average value with the second stage
Figure FDA0002983313240000035
Then
Figure FDA0002983313240000036
4) If there are three consecutive indexes (x)1,x2,...,xm) And (y)1,y2,...,yn) And (z)1,z2,...,zl) And m + l ═ n, xm＜z1(ii) a If y1-xm＜z1-ynThen the negative bias is judged, and the third segment is subtracted by NFFTThen calculating the average value with the first section
Figure FDA0002983313240000037
x _ Ave3 means the equivalent average of consecutive indices of the first segment and the third segment in this case; the meaning of l is the length of the third segment consecutive index in this case;
if z is1-yn＜y1-xmJudging the error to be positive, adding N to the third segmentFFTThen calculating the average value with the first section
Figure FDA0002983313240000038
While calculating the second segment mean
Figure FDA0002983313240000041
y _ Ave3 means the average of the second segment consecutive indices in this case; then
Figure FDA0002983313240000042
The total frequency offset estimation size is delta f ═ delta ffiction+ΔfIntegerThe Doppler frequency offset is calculated according to a formula,
Figure FDA0002983313240000043
and estimating the speed value, wherein c is the speed of light, fd is the Doppler frequency offset, and fc is the frequency offset caused by oscillation of the device when the frequency is converted from radio frequency to baseband.
5. The method for measuring the speed of a high-speed target based on the effective OFDM communication sub-carrier detection as claimed in claim 4, wherein the energy detection threshold is limited by the method of,
Figure FDA0002983313240000044
for eliminating interference.
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