CN108055058B - High-precision measurement method for carrier Doppler and change rate thereof - Google Patents
High-precision measurement method for carrier Doppler and change rate thereof Download PDFInfo
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- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
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- H04B1/70751—Synchronisation aspects with code phase acquisition using partial detection
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7073—Synchronisation aspects
- H04B1/7085—Synchronisation aspects using a code tracking loop, e.g. a delay-locked loop
Abstract
The invention discloses a high-precision measurement method for carrier Doppler and change rate thereof. The high-precision measuring method is high in measuring precision and capable of shortening frequency searching time. The invention is realized by the following technical scheme: the main control unit divides the measurement flow of the carrier Doppler and the change rate thereof into three states of coarse frequency measurement, primary fine frequency measurement and secondary fine frequency measurement, and the carrier Doppler and change rate compensation unit adopts the carrier Doppler and the Doppler change rate of the main control unit to complete double compensation of the carrier Doppler and the change rate thereof on the sampling data; the sampled data after frequency compensation sequentially passes through a mode identification and control unit, a frequency measurement unit, a peak search unit and a frequency calculation unit to complete carrier recovery and FFT operation; obtaining a primary measured value of carrier Doppler and Doppler change rate; the secondary fine frequency measurement state repeats the operation flow of the last fine frequency measurement state, so that carrier Doppler, Doppler change rate and search time information are obtained.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and relates to a high-precision measurement method for carrier Doppler and change rate thereof.
Technical Field
The received signal under the high dynamic environment contains larger Doppler frequency and change rate thereof, and because the signal dynamic is high, the carrier wave can not be regarded as a single-frequency signal in the capturing process, and can be regarded as a linear frequency modulation signal in a short time generally, and parameters such as the Doppler frequency, the frequency change rate and the like of the linear frequency modulation signal are estimated. The doppler carrier and the received carrier do not coincide and the coherent integration amplitude of the following code loop will be attenuated. The traditional carrier tracking method is difficult to obtain a good compromise between high dynamic stress and tracking precision. The key to high dynamic weak signal acquisition is the estimation of the doppler and doppler change rate of the carrier signal. The high dynamic weak signal environment puts higher requirements on the reliability of the receiver. Conventional carrier loops include phase-locked loops and frequency-locked loops. The fundamental difference between the two is the difference in the discriminators and the corresponding characteristic differences that result. When the Doppler frequency offset with larger amplitude is processed, if the loop bandwidth is not increased, the Doppler frequency offset can enable the carrier wave to exceed the capture frequency band of the phase-locked loop; the increase of the loop bandwidth will introduce more noise to reduce the accuracy, and when the level of the introduced noise is close to or exceeds the threshold voltage of the loop, the loss of lock is caused; meanwhile, for Doppler frequency offset with a large change rate, the response speed of the phase-locked loop cannot keep up. Since the sampling rate is usually high, the sampled data rate is high, so that the subsequent processing speed is difficult to keep up or unnecessary waste is caused. Particularly, for some synchronous demodulation algorithms, the complexity is high, the calculation amount is large, and the throughput rate of data cannot be too high under the condition of meeting the requirement of system real-time performance, so that the data needs to be slowed down. The phase-locked loop can more closely track the carrier phase measurement of the signal output with a narrow noise bandwidth, and the demodulated data bit error rate is low but less tolerant to dynamic stress. When the noise is strong or the required loop bandwidth is wide, the phase locked loop may have difficulty locking the signal. The frequency-locked loop has good dynamic performance by adopting a wider noise bandwidth, can more robustly tolerate the high dynamic stress of a user and the interference of radio frequency, multipath, ionospheric scintillation and the like, can track a signal with lower signal-to-noise ratio, is less sensitive to data bit jump, is slightly less compact in signal tracking, has higher loop noise, is less accurate in output carrier phase measurement value, and has higher bit error rate in the data demodulation process. A phase-locked loop with the aid of a frequency-locked loop is a rather common combination in which the frequency-locked loop and the phase-locked loop operate simultaneously. The frequency difference signal output by the frequency-locked loop filter is integrated to become the phase difference output by the phase-locked loop filter. In a spread spectrum receiver, in order for a tracking loop to successfully track a received signal, a carrier frequency initially copied inside the spread spectrum receiver must match the received signal to a certain extent, otherwise, if a frequency error between the copied signal and the received signal exceeds a pull-in range of the tracking loop, the tracking loop usually cannot be locked. Therefore, the spread spectrum receiver performs signal acquisition before starting signal tracking to estimate a coarse carrier doppler estimation value of a received signal, but in a high-dynamic weak signal scene, the carrier doppler estimation value estimated by signal acquisition has a large error with a real carrier doppler, and the received signal has a large doppler change rate, so that a tracking loop cannot be locked quickly and stably.
In a traditional measurement method, a measurement subsystem performs down-sampling processing on a received signal, then performs rough frequency measurement processing on sampled data, and then performs fine frequency measurement processing on the sampled data. In order to improve the measurement accuracy of carrier Doppler and Doppler change rate, more frequency slots need to be opened for the carrier Doppler and Doppler change rate in the coarse frequency measurement stage and the fine frequency measurement stage, so that the search time is greatly prolonged, and the requirement of a system on the measurement time cannot be met; in order to meet the requirement of the system on the measurement time, the number of frequency slots opened for the carrier doppler and the doppler change rate is limited, which reduces the measurement accuracy of the carrier doppler and the doppler change rate. Therefore, this processing method cannot simultaneously improve the accuracy of measurement of carrier doppler and doppler change rate and shorten the search time.
Disclosure of Invention
In order to overcome the defects of the traditional measuring method, the invention provides the high-precision measuring method of the carrier Doppler and the change rate thereof, which has high measuring precision and can shorten the frequency searching time.
The above object of the present invention can be achieved by the following introduction, a method for measuring carrier doppler and its variation rate with high accuracy, comprising the steps of:
in a spread spectrum receiver measurement system, a starting signal of upper-layer software is transmitted to a main control unit connected with an initialization unit, the main control unit divides a measurement flow of carrier Doppler and a change rate thereof into three states of coarse frequency measurement, primary fine frequency measurement and secondary fine frequency measurement, and controls a first-stage down-sampling unit to complete first-stage down-sampling processing on a received signal according to an information rate of the received signal and a carrier Doppler range; in a coarse frequency measurement state, the carrier Doppler and change rate compensation unit generates a local composite carrier by adopting the carrier Doppler and Doppler change rate of each frequency slot, and samples data stored in the first-stage storage unit after first-stage down sampling completes double compensation of the carrier Doppler and Doppler change rate; the sampling data after frequency compensation sequentially passes through a mode identification and control unit, a frequency measurement unit, a peak search unit and a frequency calculation unit to obtain rough measurement values of carrier Doppler and Doppler change rate; in a primary fine frequency measurement state, a carrier Doppler and change rate compensation unit firstly generates a local composite carrier according to a coarse measurement value in a coarse frequency measurement state, frequency pre-compensation is carried out on sampling data in a first-stage storage unit, the sampling data subjected to secondary down-sampling processing by a second-stage down-sampling unit is stored in a second-stage storage unit, then the sampling data in the second-stage storage unit is subdivided into a plurality of frequency slots according to the coarse measurement value in the coarse frequency measurement state, frequency compensation is carried out on the sampling data in the second-stage storage unit, and the sampling data subjected to frequency compensation sequentially passes through a mode identification and control unit, a frequency measurement unit, a peak search unit and a frequency calculation unit to obtain a primary fine measurement value of the carrier Doppler and the Doppler change rate; the secondary fine frequency measurement state repeats the operation flow of the last fine frequency measurement state, so that carrier Doppler, Doppler change rate and search time information are obtained.
Compared with the traditional measuring method, the invention has the following beneficial effects:
the measurement precision is high. The invention divides the fine frequency measurement state into a primary fine frequency measurement state and a secondary fine frequency measurement state, adopts the measurement information of the last frequency measurement state to carry out frequency pre-compensation on the sampling data of a first-stage storage unit, has small error between the estimated carrier Doppler rough estimation value and the real carrier Doppler error, and a first-stage down-sampling unit completes first-stage down-sampling processing on the received signal according to the information rate and the carrier Doppler range of the received signal; the second-stage down-sampling unit completes second-stage down-sampling processing on the sampling data subjected to frequency pre-compensation; the measurement accuracy of carrier Doppler and Doppler change rate can be further improved; the defect that a tracking loop in the prior art can not be locked generally is overcome.
The frequency search time can be shortened. The invention carries out frequency precompensation before the fine frequency measurement state, shortens the processing time of a single frequency slot, carries out frequency precompensation and two rounds of fine frequency measurement before the fine frequency measurement in the environment of high dynamic state (the maximum Doppler change rate is +/-15 kHz/s) and weak signals (the carrier-to-noise ratio is 40dB), measures the measurement precision of carrier Doppler and the change rate thereof, and completes carrier recovery and fast Fourier transform FFT operation on the signals after the frequency compensation according to the frequency measurement state of the main control unit through the mode identification and control unit and the frequency measurement unit; and the peak searching unit and the frequency calculating unit perform peak judgment on the FFT operation result to find a maximum peak value and a frequency slot corresponding to the peak value, so as to complete searching and calculating of the carrier Doppler and the change rate thereof. The search time of the frequency is shortened. The search time of carrier Doppler and Doppler change rate can be further reduced, and compared with the traditional measurement method, the carrier Doppler can be further improved under the condition that the hardware resource overhead is not increased.
Drawings
FIG. 1 is a schematic diagram of the structure of the measuring system of the present invention.
Fig. 2 is a schematic diagram of the ID integration filter of the first stage down-sampling unit.
Fig. 3 is a schematic diagram of the local composite carrier generation principle of the carrier doppler and its rate of change compensation unit.
Fig. 4 is a schematic diagram of the structural principle of the pattern recognition and control unit.
FIG. 5 is a schematic diagram of a current measurement subsystem.
The invention is further described with reference to the following figures and examples.
Detailed Description
See fig. 1. According to the invention, in a spread spectrum receiver measurement system, a starting signal of upper-layer software is transmitted to a main control unit connected with an initialization unit, and the main control unit divides the measurement flow of carrier Doppler and the change rate thereof into three states of coarse frequency measurement, primary frequency measurement and secondary frequency measurement; in a coarse frequency measurement state, the first-stage down-sampling unit completes first-stage down-sampling processing on the received signal according to the information rate and the carrier Doppler range of the received signal; in a coarse frequency measurement state, the carrier Doppler and change rate compensation unit generates a local composite carrier by adopting the carrier Doppler and Doppler change rate of each frequency slot, and the dual compensation of the carrier Doppler and Doppler change rate is completed on sampling data which is subjected to first-stage down sampling and then stored in the first-stage storage unit; the sampling data after frequency compensation sequentially passes through a mode identification and control unit, a frequency measurement unit, a peak search unit and a frequency calculation unit to obtain rough measurement values of carrier Doppler and Doppler change rate; in a primary fine frequency measurement state, a carrier Doppler and change rate compensation unit firstly generates a local composite carrier according to a coarse measurement value in a coarse frequency measurement state, frequency pre-compensation is carried out on sampling data in a first-stage storage unit, the sampling data subjected to secondary down-sampling processing by a second-stage down-sampling unit is stored in a second-stage storage unit, then the sampling data in the second-stage storage unit is subdivided into a plurality of frequency slots according to the coarse measurement value in the coarse frequency measurement state, frequency compensation is carried out on the sampling data in the second-stage storage unit, and the sampling data subjected to frequency compensation sequentially passes through a mode identification and control unit, a frequency measurement unit, a peak search unit and a frequency calculation unit to obtain a primary fine measurement value of the carrier Doppler and the Doppler change rate; the secondary fine frequency measurement state repeats the operation flow of the last fine frequency measurement state, so that carrier Doppler, Doppler change rate and search time information are obtained.
In the rough frequency measurement state, the mode identification and control unit divides the signal after frequency compensation into a single-frequency mode for processing, and carrier recovery is completed on the signal after frequency compensation according to the frequency measurement state of the main control unit; the frequency measurement unit configures the number of FFT operation points according to the frequency measurement state of the main control unit and completes FFT operation on the signal after carrier recovery; the peak value searching unit carries out peak value judgment on the fast Fourier transform FFT operation result output by the frequency measuring unit, finds the maximum peak value and a frequency slot corresponding to the peak value, and completes frequency searching of the received signal; the frequency calculating unit completes the search calculation of the carrier Doppler and the change rate thereof according to the frequency slot corresponding to the peak value to obtain the carrier Doppler, the Doppler change rate and the search time information; in the primary and secondary fine frequency measurement states, the mode identification and control unit divides the biphase phase shift keying BPSK signal into a double frequency mode according to the modulation type of the received signal, and divides the biphase phase shift keying QPSK and the coherent quadrature phase shift keying SQPSK two modulation signals into a quadruple frequency mode; and completing carrier recovery of the signal after frequency compensation.
The measurement subsystem comprises the following steps:
in the step 1, a first-stage down-sampling unit performs first down-sampling processing on a received signal according to the information rate and the carrier Doppler range of the received signal, and stores sampling data subjected to the first down-sampling into a first-stage storage unit;
in step 2, the main control unit subdivides a plurality of frequency slots according to the ranges of the carrier Doppler and the Doppler change rate to be searched, the carrier Doppler and change rate compensation unit generates a local composite carrier by adopting the carrier Doppler and the Doppler change rate of each frequency slot, and double compensation of the carrier Doppler and the Doppler change rate is completed on the sampled data.
And 2, the carrier Doppler and the change rate compensation thereof complete the double compensation of the carrier Doppler and the Doppler change rate on the sampled data. The main control unit subdivides a plurality of frequency slots according to the range of the carrier Doppler and Doppler change rate to be searched, and the carrier Doppler control word K can be obtained by the following formula calculation according to the carrier Doppler and Doppler change rate of each frequency slotfAnd a Doppler change rate control word Kr，
Kf＝fdop/fs·232
Kr＝fr/fs 2·232
Wherein f isdoplCarrier Doppler, f, requiring compensation for the current frequency binrDoppler rate of change, f, to be compensated for the current frequency binsIs the signal sampling frequency that needs frequency compensation;
in step 3, the carrier Doppler and change rate compensation unit adopts the measurement information of the last frequency measurement state to perform frequency pre-compensation on the sampling data of the first-stage storage unit, and the second-stage down-sampling unit performs second down-sampling processing on the frequency-compensated signal according to the frequency measurement state of the main control unit and stores the second down-sampled sampling data into the second-stage storage unit;
the down-sampling processing in step 1 and step 3 adopts an ID integral filter structure. The ID integral filter mainly comprises a DDS part and an integral zero clearing part, an integral frequency control word is determined according to the frequency measurement state of a main control unit, zero clearing pulses are generated by the DDS to carry out integral zero clearing operation on input data so as to complete ID integral filtering, and finally integral filtering data are sent to a storage unit. The carrier Doppler and Doppler change rate compensation unit generates two local carriers by adopting carrier Doppler control words and Doppler change rate control words through address mapping and table lookup respectively, generates a local composite carrier through complex multiplication operation, and then performs complex multiplication operation on the sampled data and the local composite carrier to complete double compensation of carrier Doppler and Doppler change rate of the sampled data.
In the step 4, the whole process of the main control unit is divided into three states of coarse frequency measurement, primary fine frequency measurement, secondary fine frequency measurement and the like, and in the coarse frequency measurement state, the mode identification and control unit divides the signal after frequency compensation into a single-frequency mode for processing; in the primary and secondary fine frequency measurement states, the mode identification and control unit completes carrier recovery on the signal after frequency compensation according to the modulation type of the received signal, wherein the BPSK signal is divided into a double frequency mode, and the QPSK, SQPSK and UQPSK signals are divided into a quadruple frequency mode;
and 4, the mode identification and control unit determines a control state according to the frequency measurement state of the main control unit and the modulation type of the received signal. In the coarse frequency measurement state, dividing a received signal into a single-frequency mode for processing; in the fine frequency measurement state, the carrier recovery of the signals is completed according to the modulation type of the received signals, BPSK signals are divided into a frequency doubling mode, and QPSK, SQPSK and UQPSK signals are divided into a frequency quadrupling mode;
in step 5, the frequency measurement unit configures the number of FFT operation points according to the frequency measurement state of the main control unit, and completes FFT operation on the signal after carrier recovery, the mode identification and control unit completes carrier recovery on the signal after frequency compensation according to the frequency measurement state of the main control unit, the peak search unit performs peak judgment on the FFT operation result output by the frequency measurement unit, finds the maximum peak value and the frequency slot corresponding to the peak value, and completes frequency search of the received signal, and the frequency calculation unit completes search calculation of signal carrier Doppler and the change rate thereof according to the frequency slot corresponding to the peak value, and obtains information such as carrier Doppler, Doppler change rate, search time and the like.
And 5, configuring the FFT operation point number according to the frequency measurement state of the main control unit by the frequency measurement operation. Adopting 2048 operation points in a coarse frequency measurement state and a primary fine frequency measurement state; in the secondary fine frequency measurement state, 4096 operation points are adopted, and finally FFT operation is completed on the signal after carrier recovery.
The whole process of the whole step is divided into three states of coarse frequency measurement, primary accurate frequency measurement, secondary accurate frequency measurement and the like. In the rough frequency measurement state, subdividing a plurality of frequency slots according to the range of carrier Doppler and Doppler change rate to be searched, performing frequency compensation on the sampled data in the first-stage storage unit, and obtaining rough measurement values of the carrier Doppler and the Doppler change rate through units such as pattern recognition and control, frequency measurement, peak value search, frequency calculation and the like; in a primary fine frequency measurement state, a carrier Doppler and change rate compensation unit firstly generates a local composite carrier according to a coarse measurement value in the coarse frequency measurement state, frequency pre-compensation is carried out on sampling data in a first-stage storage unit, the sampling data are stored in a second-stage storage unit after being processed by a second-stage down-sampling unit, then a plurality of frequency slots are subdivided according to the coarse measurement value in the coarse frequency measurement state, frequency compensation is carried out on the sampling data in the second-stage storage unit, and primary fine measurement values of the carrier Doppler and the Doppler change rate are obtained through units of mode identification and control, frequency measurement, peak value search, frequency calculation and the like; the secondary fine frequency measurement state repeats the operation flow of the primary fine frequency measurement state, so that information such as carrier Doppler, Doppler change rate, search time and the like is obtained.
Setting the received signal to BPSK signal, information rate Rb1kbps, system clock fclk90MHz, carrier doppler range f of the received signaldopl+ -100 kHz, Doppler Rate of change range frate15kHz/s, first stage down-sampling clock fsample256kHz, sample time t of the received signals＝0.512s。
In the coarse frequency measurement state, the main control unit slots with the carrier Doppler of zero, the initial Doppler change rate of zero and the Doppler change rate search step length of 250Hz/s, subdivides the carrier Doppler and the Doppler change rate into 60 frequency slots,
see fig. 2. For adapting information rate and carrier Doppler of received signalSampling clock fsampleSetting the carrier-to-noise ratio of the received signal to be 40dB in consideration of a weak signal scene, wherein the received signal is completely submerged in background noise, and in order to detect the carrier wave of the received signal which is suppressed, the first-stage down-sampling unit needs to increase the integral gain by prolonging the integral time, and then setting the sampling time t of the received signals＝0.512s。
The first-stage down-sampling unit adopts an ID integral filter which mainly comprises a direct digital frequency synthesizer DDS (direct digital synthesizer) for generating a zero clearing pulse by adopting an integral frequency control word, and the ID integral filter generates a down-sampling clock f according to the first-stage down-sampling unitsampleGenerating an integral frequency control word, generating a zero clearing pulse by a direct digital frequency synthesizer DDS (direct digital synthesizer) by adopting the integral frequency control word, continuously performing integral-zero clearing operation on input data by the zero clearing pulse, and when the sampling time t issAnd finishing storing the sampling data into the first-stage storage unit when the time reaches 0.512 s.
The local carrier generation unit generates a local composite carrier according to the carrier Doppler and Doppler change rate of each frequency slot, the carrier Doppler and Doppler change rate compensation unit adopts the local composite carrier to perform frequency compensation on the sampled data in the first-stage storage unit, the mode identification and control unit divides the received signal into a single-frequency mode to be processed, the frequency measurement unit, the peak search unit, the frequency calculation unit and other units are used for obtaining rough measurement values of the carrier Doppler and Doppler change rate, and the search time t of the rough measurement state can be calculated according to the following formulap1，
tp1＝N1×(fsample×ts/fclk)＝87.381ms
In a primary fine frequency measurement state, a carrier Doppler and change rate compensation unit generates a local composite carrier according to a coarse measurement value in a coarse frequency measurement state, the carrier Doppler and change rate compensation unit performs frequency pre-compensation on sampling data in a first-stage storage unit by adopting the local composite carrier, an ID integral filter in a second-stage down-sampling unit selects 4, and the sampling data subjected to second-stage down-sampling processing is stored in a second-stage storage unit; then the main control unit takes the carrier Doppler rough measurement value asCarrier Doppler, initial Doppler change rate is Doppler change rate rough measurement value, Doppler change rate search step length is 32.0Hz/s to refine carrier Doppler and Doppler change rate, the carrier Doppler and change rate are divided into at least 100 frequency slots, local composite carrier is generated according to the carrier Doppler and Doppler change rate of each frequency slot, a carrier Doppler and change rate compensation unit adopts the local composite carrier to perform frequency compensation on sampling data in a second-stage storage unit, a mode identification and control unit divides a received signal into a double-frequency mode to complete carrier recovery, a primary accurate measurement value of the carrier Doppler and Doppler change rate is obtained through units of frequency measurement, peak value search, frequency calculation and the like, and the main control unit can calculate search time t of a primary accurate measurement state according to the following formulap2＝fsample×ts/fclk+N2×(fsample/4×ts/fclk)＝37.865ms
In the secondary fine frequency measurement state, frequency pre-compensation is completed by using a primary fine measurement value of the primary fine frequency measurement state, the order of an ID integral filter in the second-stage down-sampling unit is selected 16, and sampling data after the second-stage down-sampling processing is stored in a second-stage storage unit; then the main control unit takes the primary accurate measurement value of the carrier Doppler as the carrier Doppler, the initial Doppler change rate as the primary accurate measurement value of the Doppler change rate, the search step length of the Doppler change rate is 4.0Hz/s to refine the carrier Doppler and the Doppler change rate, the carrier Doppler and the change rate thereof are divided into 100 frequency slots, other operation flows of the primary accurate frequency measurement state are repeated, and the main control unit can calculate the search time t of the secondary accurate frequency measurement state according to the following formulap3，
tp3＝fsample×ts/fclk+N3×(fsample/16×ts/fclk)＝6.007ms
After three states of coarse frequency measurement, primary accurate frequency measurement, secondary accurate frequency measurement and the like, the main control unit can obtain carrier Doppler accuracy f by the following calculationdopl_resDoppler rate of change accuracy frate_resTime of search tp，
fdopl_res＝fsample/16/2/FFT＝1.953Hz
frate_res＝4.0Hz/s
tp＝tp1+tp2+tp3＝131.253ms
In the traditional measurement method, carrier Doppler accuracy f 'can be obtained by calculating by a main control unit according to the following formula through two states of coarse frequency measurement and fine frequency measurement'dopl_resDoppler change rate accuracy f'rate_resTime t 'is searched'p，
f′dopl_res＝fsample/4/2/FFT＝15.625Hz
frate_res＝32.0Hz/s
t′p＝(N1+N2)×(fsample×ts/fclk)＝233.017ms
Therefore, the two-round precision frequency measurement method and the method for frequency pre-compensation before precision frequency measurement provided by the invention provide a feasible scheme of the carrier Doppler and change rate measurement method thereof in the environment of high dynamic state (maximum Doppler change rate +/-15 kHz/s) and weak signals (carrier-to-noise ratio 40 dB).
See fig. 3. The carrier doppler and rate of change compensation unit comprises a local composite carrier generation unit connected to the control unit. In order to complete the dual compensation of carrier Doppler and Doppler change rate for the received signal, the local composite carrier generating unit of the carrier Doppler and Doppler change rate compensation unit needs to subdivide the range of the carrier Doppler and Doppler change rate to be searched into a plurality of frequency slots, and the main control unit can calculate and generate carrier Doppler control words and Doppler change rate control words K according to the carrier Doppler and Doppler change rate of each subdivided frequency slot of the local composite carrier generating unit by the following formulafAnd a Doppler change rate control word Kr，
Kf＝fdop/fs·232
Kr＝fr/fs 2·232
Wherein f isdoplCarrier Doppler, f, requiring compensation for the current frequency binrDoppler rate of change, f, to be compensated for the current frequency binsIs the signal sampling frequency that needs frequency compensation;
the local composite carrier generation unit acquires the carrier Doppler control word K generated by the main control unitfAfter one-time integral operation, generating a path of local carrier Doppler carrier through address mapping and sine table lookup; the Doppler change rate control word KrAfter two times of integral operation, generating another path of local Doppler change rate carrier wave through address mapping and sine table lookup; and the two local Doppler change rate carriers can generate local composite carriers through complex multiplication operation of a combiner multiplier. And the carrier Doppler and change rate compensation unit performs complex multiplication operation on the sampled data and the local composite carrier to complete double compensation of the carrier Doppler and the Doppler change rate of the sampled data of the second-stage down-sampling unit.
See fig. 4. The mode identification and control unit can divide the signal into different modes according to the modulation type of the received signal to complete carrier recovery. The sampling data after the frequency compensation of the carrier Doppler and the change rate compensation unit thereof firstly completes the carrier recovery according to a single-frequency mode, a double-frequency mode and a quadruple-frequency mode, the main control unit selects the carrier recovery mode according to the frequency measurement mode, wherein, in the primary precise frequency measurement state and the secondary precise frequency measurement state, the binary phase shift keying BPSK signal is divided into the double-frequency mode, and the binary phase shift keying QPSK, the offset quaternary phase shift keying SQPSK, the binary phase shift keying and the QPSK three modulation signals are divided into the quadruple-frequency mode; and inputting the sampling data subjected to carrier recovery into a frequency measurement unit.
Claims (10)
1. A high-precision measurement method for carrier Doppler and change rate thereof is characterized by comprising the following steps:
in a spread spectrum receiver measurement system, a starting signal of upper-layer software is transmitted to a main control unit connected with an initialization unit, the main control unit divides a measurement flow of carrier Doppler and a change rate thereof into three states of coarse frequency measurement, primary fine frequency measurement and secondary fine frequency measurement, and controls a first-stage down-sampling unit to complete first-stage down-sampling processing on a received signal according to an information rate of the received signal and a carrier Doppler range; in a coarse frequency measurement state, the carrier Doppler and change rate compensation unit generates a local composite carrier by adopting the carrier Doppler and Doppler change rate of each frequency slot, and samples data stored in the first-stage storage unit after first-stage down sampling completes double compensation of the carrier Doppler and Doppler change rate; the sampling data after frequency compensation sequentially passes through a mode identification and control unit, a frequency measurement unit, a peak search unit and a frequency calculation unit to obtain rough measurement values of carrier Doppler and Doppler change rate; in a primary fine frequency measurement state, a carrier Doppler and change rate compensation unit firstly generates a local composite carrier according to a coarse measurement value in a coarse frequency measurement state, frequency pre-compensation is carried out on sampling data in a first-stage storage unit, the sampling data subjected to secondary down-sampling processing by a second-stage down-sampling unit is stored in a second-stage storage unit, then the sampling data in the second-stage storage unit is subdivided into a plurality of frequency slots according to the coarse measurement value in the coarse frequency measurement state, frequency compensation is carried out on the sampling data in the second-stage storage unit, and the sampling data subjected to frequency compensation sequentially passes through a mode identification and control unit, a frequency measurement unit, a peak search unit and a frequency calculation unit to obtain a primary fine measurement value of the carrier Doppler and the Doppler change rate; the secondary fine frequency measurement state repeats the operation flow of the last fine frequency measurement state, so that carrier Doppler, Doppler change rate and search time information are obtained.
2. A method for high accuracy measurement of carrier doppler and its rate of change as claimed in claim 1 wherein: in the rough frequency measurement state, the mode identification and control unit divides the signal after frequency compensation into a single-frequency mode for processing, and carrier recovery is completed on the signal after frequency compensation according to the frequency measurement state of the main control unit; the frequency measurement unit configures the number of fast Fourier transform FFT operation points according to the frequency measurement state of the main control unit, and completes FFT operation on the signal after carrier recovery.
3. A method for high accuracy measurement of carrier doppler and its rate of change as claimed in claim 2 wherein: the peak value searching unit carries out peak value judgment on the fast Fourier transform FFT operation result output by the frequency measuring unit, finds the maximum peak value and a frequency slot corresponding to the peak value, and completes frequency searching of the received signal; and the frequency calculating unit completes the search calculation of the carrier Doppler and the change rate thereof according to the frequency slot corresponding to the peak value to obtain the carrier Doppler, the Doppler change rate and the search time information.
4. A method for high accuracy measurement of carrier doppler and its rate of change as claimed in claim 1 wherein: in the primary and secondary fine frequency measurement states, the mode identification and control unit divides the biphase phase shift keying BPSK signal into a double frequency mode according to the modulation type of the received signal, and divides the biphase phase shift keying QPSK and the coherent quadrature phase shift keying SQPSK two modulation signals into a quadruple frequency mode; and completing carrier recovery of the signal after frequency compensation.
5. A method for high accuracy measurement of carrier doppler and its rate of change as claimed in claim 1 wherein: the first-stage down-sampling unit performs first down-sampling processing on the received signal according to the information rate and the carrier Doppler range of the received signal, and stores the sampled data after the first down-sampling into the first-stage storage unit; the main control unit subdivides a plurality of frequency slots according to the range of carrier Doppler and Doppler change rate to be searched, the carrier Doppler and change rate compensation unit generates local composite carriers by adopting the carrier Doppler and Doppler change rate of each frequency slot, and double compensation of the carrier Doppler and Doppler change rate is completed on sampling data.
6. A method for high accuracy measurement of carrier doppler and its rate of change as claimed in claim 1 wherein: the carrier Doppler and change rate compensation unit adopts the measurement information of the last frequency measurement state to carry out frequency pre-compensation on the sampling data of the first-stage storage unit, and the second-stage down-sampling unit carries out secondary down-sampling processing on the signals after frequency compensation according to the frequency measurement state of the main control unit and stores the sampling data after secondary down-sampling into the second-stage storage unit.
7. A method for high accuracy measurement of carrier doppler and its rate of change as claimed in claim 1 wherein: the peak value searching unit carries out peak value judgment on an FFT operation result output by the frequency measuring unit, finds a maximum peak value and a frequency slot corresponding to the peak value, completes frequency searching of a received signal, and the frequency calculating unit completes searching and calculating of signal carrier Doppler and change rate thereof according to the frequency slot corresponding to the peak value, and obtains carrier Doppler, Doppler change rate and searching time information.
8. A method for high accuracy measurement of carrier doppler and its rate of change as claimed in claim 1 wherein: the first-stage down-sampling unit adopts an ID integral filter which mainly comprises a direct digital frequency synthesizer DDS (direct digital synthesizer) for generating a zero clearing pulse by adopting an integral frequency control word, and the ID integral filter generates a down-sampling clock f according to the first-stage down-sampling unitsampleGenerating an integral frequency control word, generating a zero clearing pulse by a direct digital frequency synthesizer DDS (direct digital synthesizer) by adopting the integral frequency control word, continuously performing integral-zero clearing operation on input data by the zero clearing pulse, and when the sampling time t issAnd finishing storing the sampling data into the first-stage storage unit when the time reaches 0.512 s.
9. A method for high accuracy measurement of carrier doppler and its rate of change as claimed in claim 1 wherein: the main control unit obtains a carrier Doppler control word K through calculation according to the carrier Doppler and the Doppler change rate of each frequency slot by the following formulafAnd a Doppler change rate control word Kr，
Kf＝fdop/fs·232
Kr＝fr/fs 2·232
Wherein f isdopIs required for the current frequency slotCompensated carrier Doppler, frDoppler rate of change, f, to be compensated for the current frequency binsIs the signal sampling frequency that requires frequency compensation.
10. A method for high accuracy measurement of carrier doppler and its rate of change as claimed in claim 1 wherein: the carrier Doppler and change rate compensation unit comprises a local composite carrier generation unit connected with the control unit, the main control unit subdivides a plurality of frequency slots according to the range of the carrier Doppler and Doppler change rate to be searched, and the main control unit can calculate and generate a carrier Doppler control word K according to the carrier Doppler and Doppler change rate of each subdivided frequency slot of the local composite carrier generation unit by the following formulafAnd a Doppler change rate control word Kr，
Kf＝fdop/fs·232
Kr＝fr/fs 2·232
Wherein f isdopCarrier Doppler, f, requiring compensation for the current frequency binrDoppler rate of change, f, to be compensated for the current frequency binsIs the signal sampling frequency that requires frequency compensation.
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