CN101179545B - Doppler frequency cancellation based full digital main carrier tracking method - Google Patents

Abstract

The invention relates to an all-digital main carrier tracking method based on a Doppler frequency cancellation which belongs to a measurement and control communications field. The invention is characterized in that: by using a characteristic of a frequency spectrum which is dual-modulated by the main carrier and a vice-carrier of a USB measurement and control signal, in the signal of carrying out the main carrier capture and removing most of Doppler frequency difference, a FIR lowpass filter is used for extracting the main carrier signal carrying a negative Doppler rest frequency difference information, a positive-negative cancellation of the Doppler rest frequency difference is completed, and a purpose of tracking the main carrier is reached. The invention overcomes problems of trouble in a ring road structure and parameter design, a Doppler residual error not able to be removed completely in a traditional way of using a phase-locked loop, and thus the invention is suitable for tracking the main carrier in the USB measurement and control system.

Description

The full digital main carrier tracking method that offsets based on Doppler frequency

Technical field

The present invention relates to a kind of full digital main carrier tracking method that offsets based on Doppler frequency, (Unified S-band, USB) main carrier of measurement and control signal is followed the tracks of to be applicable to unified S-band.This method need not feedback control loop, just can realize eliminating the purpose of Doppler frequency deviation preferably.This scheme is specially adapted to the tracking Control of main carrier under big Doppler's frequency change rate situation.This method belongs to the telemetry communication field.

Background technology

In communication process owing to often there is radially movement velocity (along the speed of communication object rectilinear direction) between the communication object, cause received signal and transmit between Doppler effect appears, make it have Doppler frequency difference; In addition, in most of the cases, the motion of communication object is not at the uniform velocity, and the variation that this causes the received signal Doppler frequency again makes signal receive difficulty more.In ground communication, owing to be subjected to the restriction of movement velocity, Doppler effect is not too obvious.But in space flight measurement and control communication, because the high-speed motion of observing and controlling object (as satellite, guided missile, carrier rocket etc.), Doppler effect is obvious, makes signal receiving quality worsen, even can't normally receive.For example, certain spacecraft carries out observing and controlling in the flight of deep space high speed with the USB TT﹠C system, and the information rate of its subcarrier communication is 1Kbps, and the maximum Doppler frequency difference and the doppler changing rate that may reach are respectively ± 150KHz and 50KHz/s, and it is extremely difficult that this will cause that signal receives.Therefore, seek the research focus that the method for resisting Doppler effect becomes the telemetry communication field.

The USB TT﹠C system adopts the dual modulation mode, and promptly each drive test control baseband signal is at first carried out sub-carrier modulation such as PSK, FSK, lumps together the PM modulation of carrying out main carrier again, main carrier and subcarrier is arranged, as shown in Figure 1 in the signal spectrum after the modulation.For Doppler frequency and frequency change rate to the Chinese People's Anti-Japanese Military and Political College, many researchers have done a large amount of work, study and design a series of method.The process that these methods are eliminated Doppler frequency difference mainly is divided into catching of main carrier signal and follows the tracks of two parts.Identification that the catching of main carrier mainly finished main carrier and the roughly location in frequency domain are to eliminate most Doppler frequency difference; The elimination to the residue Doppler frequency difference is mainly finished in the tracking of main carrier, thereby finishes the rectification of all Doppler frequency differences in the measurement and control signal.In the prior USB TT﹠C system, the method that main carrier is caught employing mainly contains frequency sweep method, declares the frequency spectrum balanced method, spectrum mask matching method, spectrum energy center method and to the frequency spectrum pre-setting method under the situation of observing and controlling object motion state precognition etc.; And the tracking of main carrier all is the mode that adopts phase-locked loop basically, follow the tracks of remaining Doppler frequency difference by the phase-locked loop closed loop, difference between different designs person's method is that mainly purpose all is to reduce the remaining frequencies residual error as far as possible in the selection to the structural design of loop and loop parameter.Follow the tracks of remaining Doppler frequency difference with phase-locked loop, simple in structure, it is few to take resource, but has certain frequency residual error all the time, and Doppler frequency difference can't be eliminated fully; When doppler changing rate is big, in order to follow the tracks of the variation of Doppler frequency, need to adopt the high-order phase-locked loop, and the design of high-order phase-locked loop relates to the stability problem of loop, implement very difficulty.

Summary of the invention

The present invention provides a kind of full digital main carrier tracking method that offsets based on Doppler frequency according to the problems referred to above.This method has been utilized the frequency spectrum characteristic of USB measurement and control signal main carrier and subcarrier dual modulation, in having carried out the complex signal of main carrier after having caught, eliminated most Doppler frequency difference, extract the main carrier signal that carries negative Doppler frequency difference information, Doppler frequency difference is carried out positive and negative offseting, reach thorough elimination Doppler frequency difference, finish the purpose that main carrier is followed the tracks of.This method is intuitively easy, can increase the elimination fully that realizes under few situation Doppler frequency difference at hardware resource, and is not subjected to the restriction of doppler changing rate size.

The invention is characterized in that described method contains following steps successively:

Step (1): the logical analog signal of the USB observing and controlling band that has Doppler frequency difference that receives is at first passed through analog to digital converter, changes digital signal into.

Step (2): the USB observing and controlling band that has Doppler frequency difference that step (1) is obtained leads to digital signal through a quadrature down converter, obtains having the complex baseband signal of Doppler frequency difference, and its real part and imaginary part are used I respectively ₁, Q ₁The two paths of data information representation.

Step (3): the baseband complex signal that has Doppler frequency difference that step (2) is obtained is eliminated most Doppler frequency difference through a main carrier acquisition equipment.The I that this main carrier acquisition equipment is exported step (2) earlier ₁, Q ₁Two paths of data is respectively as real part and imaginary part, merge into plural number, do the fast fourier transform of N (selection of N is relevant with the resource of the sample rate of analog to digital converter and hardware) point again, the spectrum mask that the result after the conversion is taken absolute value again and preset in advance carries out related operation, in the maximum Doppler scope of setting, search for relevant peaks, the frequency location of relevant peaks correspondence is the position of main carrier in frequency domain, again with the sinusoidal and cosine complex oscillation frequency of main carrier positional information control digital controlled oscillator output, then with the baseband complex signal of importing that has Doppler frequency difference (by I ₁, Q ₁The two paths of data merging forms) do complex multiplication, finish most Doppler frequency difference and eliminate, and the output complex signal, its real part and imaginary part are used I respectively ₂, Q ₂The two paths of data information representation.Wherein, preset the amplitude spectrum that spectrum mask is the individual pulse that adopts of known transmitter; Related operation refers to two discrete signals that will have different relative time delaies and carries out the computing that the correspondence position sampled point multiplies each other and sues for peace; The maximum Doppler scope is generally ± 300kHz by the radial velocity decision of spacecraft; If the distance of the position deviation zero-frequency of main carrier in frequency domain is D (Hz), then the frequency of two-way oscillator signal is K*D (Hz), and wherein K is the modulation sensitivity of digital controlled oscillator, is generally 1; Big Doppler frequency difference is often referred to and satisfies the situation of frequency difference elimination back maximum residual frequency deviation less than 16kHz.

Step (4): the complex signal that step (3) is obtained forms device through a spectrum symmetric signal, forms frequency spectrum and becomes symmetrical two-way complex signal X about zero-frequency ₁And X ₂This spectrum symmetric signal forms device the complex signal of importing is divided into two-way, and one the tunnel is left intact, and directly X is used in output ₁Expression, one tunnel imaginary part that will import complex signal (is Q ₂) multiply by-1, then and real part (be I ₂) merge into plural number output together, use X ₂Expression.

Step (5): the two-way complex signal step (4) obtains, offset preprocessor through Doppler frequency, form two-way complex signal Y ₁And Y ₂Output.This Doppler frequency offsets the complex signal X of preprocessor to step (4) output ₂(output has the main carrier complex signal of negative Doppler frequency information, uses Y for Finite Impulse Response, FIR) low-pass filtering to carry out finite impulse response ₂Expression; Complex signal X to step (4) output ₁Carry out delay process, output Y ₁Expression is to guarantee that signal is by X ₂To Y ₂Needed time and by X ₁To Y ₁The needed time equates.

Step (6): by the Doppler frequency canceller, the USB observing and controlling baseband complex signal of the Doppler frequency difference that has been eliminated is finished the tracking of main carrier the two-way complex signal of step (5) output.This Doppler frequency canceller multiplies each other the two-way complex signal of step (5) output, realizes that Doppler frequency offsets.

The full digital main carrier tracking method that offsets based on Doppler frequency that the present invention proposes, its major advantage comprises: method is intuitively easy, can increase the elimination fully that realizes under few situation Doppler frequency difference than conventional phase locked loops method hardware resource, and not be subjected to the restriction of doppler changing rate size.

Description of drawings

Fig. 1 is a USB measurement and control signal baseband frequency spectrum schematic diagram.

Fig. 2 is based on the main carrier tracking method that Doppler frequency offsets and totally realizes block diagram.

Fig. 3 is the quadrature frequency conversion block diagram.

Fig. 4 is a main carrier acquisition equipment block diagram.

Fig. 5 is that the spectrum symmetric signal forms the device block diagram.

Fig. 6 is that Doppler frequency offsets the preprocessor block diagram.

Fig. 7 is a Doppler frequency canceller block diagram.

Embodiment

Below in conjunction with accompanying drawing, introduce content of the present invention in detail:

Fig. 2 is based on the overall realization block diagram of the main carrier tracking method that Doppler frequency offsets.As shown in Figure 2.Receiver receives the logical analog signal of the USB observing and controlling band that has Doppler frequency difference, earlier successively through behind the devices such as analog to digital converter, quadrature down converter, main carrier acquisition equipment, and the USB observing and controlling of most of Doppler frequency difference that has been eliminated numeral complex baseband signal.This complex baseband signal forms device through spectrum signal, obtains the two-way frequency spectrum and becomes symmetrical complex signal about zero-frequency; When this two-way complex signal offseted preprocessor through Doppler frequency, the one tunnel through time-delay output, and one the tunnel through exporting after the FIR low-pass filtering.This two-way output signal is eliminated the USB observing and controlling numeral complex baseband signal of Doppler frequency difference fully through the Doppler frequency canceller at last.

Below be the arthmetic statement and the specific implementation method thereof of each several part:

At first, the logical analog signal of the USB observing and controlling band that has Doppler frequency difference that receives is through analog to digital converter, and finishing sample rate is f _sAnalog-to-digital conversion, be digital signal with analog-signal transitions.F wherein _sThe selection and the maximum information speed of the maximum Doppler frequency offset of USB measurement and control signal and subcarrier signal relevant, f in general _sAt least be greater than above-mentioned both peaked 2 times.For example maximum Doppler frequency offset is 1Kbps for the maximum information speed of ± 150KHz, subcarrier signal, then f _sShould select 300KHz at least, generally select more than the 600KHz.

Fig. 3 is the quadrature frequency conversion block diagram.As shown in Figure 3, through the logical digital signal process of the USB observing and controlling band that has Doppler frequency difference after analog-to-digital conversion quadrature down converter, obtain having the USB observing and controlling baseband digital signal of Doppler frequency difference, the specific implementation method is: with the signal of input respectively with the homophase road of digital controlled oscillator and positive cross-channel signal multiplication, export I respectively ₁And Q ₁

Fig. 4 is a main carrier acquisition equipment block diagram.As shown in Figure 4, catch main carrier through the main carrier acquisition equipment, export after eliminating most Doppler frequency difference through the baseband signal behind the quadrature frequency conversion; The specific implementation method is:

(1) earlier will be through the input baseband signal I behind the quadrature frequency conversion ₁And Q ₁Be converted to plural number through the real/complex conversion device, do the fast fourier transform that N is ordered again, be transformed into frequency domain.Precision P after wherein doing the selection of fast fourier transform points N and being transformed into frequency domain has relation, P=f _s/ N can make N big under the situation that hardware resource allows as far as possible.For example, at f _sUnder the situation of=800KHz/s, can select N=4096.

(2) frequency spectrum after the fast fourier transform is taken absolute value obtain amplitude spectrum, and carry out related operation with the spectrum mask that presets of storage in advance with the skew of different relative frequencies, the relative frequency skew of said two devices, the just position of relevant peaks when finding out the correlation maximum; Promptly find the main carrier position thus, finish acquisition procedure.Wherein, preset spectrum mask and be the amplitude spectrum of the individual pulse that known transmitter adopts, related operation refers to two discrete signals that will have different relative time delaies and carries out the computing that the correspondence position sampled point multiplies each other and sues for peace.

(3) be converted to the complex oscillation signal with the residing spectrum position information Control of the main carrier digital controlled oscillator output homophase and the quadrature two-way oscillator signal of catching, and through the real/complex conversion device.If the distance of the position deviation zero-frequency of main carrier in frequency domain is D (Hz), then the frequency of two-way oscillator signal is K*D (Hz), and wherein K is the modulation sensitivity of digital controlled oscillator, is generally 1.

(4) complex baseband signal of complex oscillation signal that oscillator is exported and input is (by I ₁And Q ₁Through the real number complex conversion) do complex multiplication, finish the elimination of big Doppler frequency difference, and the result is converted to two-way real number I ₂And Q ₂Output.Wherein, big Doppler frequency difference is often referred to and satisfies the situation of frequency difference elimination back maximum residual frequency deviation less than 16kHz.

Fig. 5 is that the spectrum symmetric signal forms the device block diagram.As shown in Figure 5, eliminated complex baseband signal (I behind the most Doppler frequency difference ₂And Q ₂Be respectively its real part and imaginary part), behind spectrum symmetric signal formation device, form the two-way complex signal X of frequency spectrum about the zero-frequency symmetry ₁And X ₂The specific implementation method is:

(1) elimination that will import the complex baseband signal (I behind the most Doppler frequency difference ₂And Q ₂Be respectively its real part and imaginary part) output, obtain complex signal X ₁

(2) with the signal Q that imports ₂Multiply by-1 as imaginary part, input signal I ₂As real part, closing the road is complex signal X ₂Output.

The complex baseband signal of having eliminated behind most of Doppler frequency difference can be expressed as:

$S_T=e^{i(w_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Psi;}}_n)}=\cos (w_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Psi;}}_n)+i\sin (w_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Psi;}}_n)={\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H2007101799740E00011.png"\; state="\{\{state\}\}">I</figure-callout>}}_2+\mathrm{<figure-callout\; id="2"\; label="i\; Q"\; filenames="H2007101799740E00011.png"\; state="\{\{state\}\}">i</figure-callout>}{Q}_{}{}_2$

W wherein _DsFor having eliminated the residue frequency difference behind the most Doppler frequency difference, m is the number of subcarrier in the USB system, Ψ _nBe n modulated subcarrier signal, T is the discrete sampling time, Expression Ψ ₁+ Ψ ₂+ Ψ _m

Signal S _TBehind spectrum symmetric signal formation device, output X ₁And X ₂For:

${\mathrm{<figure-callout\; id="1"\; label="X"\; filenames="H2007101799740E00011.png,H2007101799740E00022.png"\; state="\{\{state\}\}">X</figure-callout>}}_1={\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H2007101799740E00011.png"\; state="\{\{state\}\}">I</figure-callout>}}_2+\mathrm{<figure-callout\; id="2"\; label="i\; Q"\; filenames="H2007101799740E00011.png"\; state="\{\{state\}\}">i</figure-callout>}{Q}_{}{}_2=\cos (w_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Psi;}}_n)+i\sin (w_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Psi;}}_n)=e^{i(w_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Psi;}}_n)}$

${\mathrm{<figure-callout\; id="2"\; label="X"\; filenames="H2007101799740E00011.png"\; state="\{\{state\}\}">X</figure-callout>}}_2=I_2-\mathrm{<figure-callout\; id="2"\; label="i\; Q"\; filenames="H2007101799740E00011.png"\; state="\{\{state\}\}">i</figure-callout>}{Q}_{}{}_2=\cos (w_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Psi;}}_n)-i\sin (w_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Psi;}}_n)=e^{-i(w_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&Psi;}}_n)}$

Fig. 6 is that Doppler frequency offsets the preprocessor block diagram.As shown in Figure 6, the complex signal X of frequency spectrum symmetry ₁And X ₂After the process Doppler frequency offsets preprocessor, the pre-complex baseband signal Y that eliminates the residue Doppler frequency difference of one tunnel output ₁, the negative Doppler frequency difference complex signal Y that one tunnel output extracts ₂The specific implementation method is:

(1) with the complex signal X of frequency spectrum symmetry of input ₁Through a delayer time-delay, the size of time-delay will equate with the time-delay of FIR low pass filter.

(2) with the complex signal X that imports ₂Through the filtering of a FIR low pass filter, output comprises the complex signal Y of negative Doppler frequency difference information ₂The selection of FIR low pass filter need be satisfied two conditions, the one, filter bandwidht can not be less than the maximum residual frequency deviation after eliminating through big Doppler frequency deviation, the 2nd, filter bandwidht can not greater than in the USB measurement and control signal frequency spectrum from the sub-carrier modulation frequency of a nearest subcarrier of main carrier.

Complex signal X ₁And X ₂After the process Doppler frequency offsets preprocessor, output complex signal Y ₁And Y ₂,

Wherein T ' for T through the time-delay after the discrete sampling time.

Fig. 7 is a Doppler frequency canceller block diagram.As shown in Figure 7, the Doppler frequency canceller will be eliminated the complex baseband signal Y of residue Doppler frequency difference in advance ₁With the negative Doppler frequency difference complex signal Y that extracts ₂Do complex multiplication, finish the elimination of remaining Doppler frequency difference, output signal Z.

$Z={\mathrm{<figure-callout\; id="1"\; label="Y"\; filenames="H2007101799740E00011.png,H2007101799740E00022.png"\; state="\{\{state\}\}">Y</figure-callout>}}_1*{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="H2007101799740E00011.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2=e^{i\left(\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&psi;}}_n\right)}.$

By above step, finally finished catching and following the tracks of of main carrier, eliminated Doppler frequency difference fully.

As previously mentioned, according to the present invention, the full digital main carrier tracking method that offsets based on Doppler frequency avoided existing various USB main carrier tracking method need design phase-locked loop, need be according to the problem of Doppler's characteristic Design loop structure and adjustment loop parameter, method realizes simple; Its tracking performance to Doppler frequency is compared with traditional phase-locked loop method, does not stay residual error, can eliminate Doppler frequency deviation fully, and be not subjected to the influence of doppler changing rate size; In USB telemetry communication field, this method has very big novelty at main carrier track side mask, meets the developing direction of USB telemetry communication art.

Claims (1)

1. the full digital main carrier tracking method that offsets based on Doppler frequency is characterized in that, contains following steps successively:

Step (1): the logical analog signal of the unified S-band USB observing and controlling band that has Doppler frequency difference that receiver is received changes digital signal into through analog to digital converter;

Step (2): the USB observing and controlling band that has Doppler frequency difference that step (1) is obtained leads to digital signal through a quadrature down converter, obtains having the complex baseband signal of Doppler frequency difference, and its real part and imaginary part are used I respectively ₁, Q ₁Two paths of data is represented;

Step (3): the baseband complex signal that has Doppler frequency difference that step (2) is obtained is eliminated most of Doppler frequency difference according to the following steps through a main carrier acquisition equipment:

Step (3.1): the described complex baseband signal I of step (2) ₁, Q ₁Be converted to plural number with a real/complex conversion device, remake the conversion of N point fast Fourier and take absolute value;

Step (3.2): the spectrum mask that presets of amplitude spectrum after the fast fourier transform that step (3.1) is obtained and storage in advance carries out related operation, search for relevant peaks in the maximum Doppler scope of setting, the frequency location of relevant peaks correspondence is the position of main carrier in frequency domain; Wherein, preset spectrum mask and be the amplitude spectrum of the individual pulse that known transmitter adopts, related operation refers to two discrete signals that will have different relative time delaies and carries out the computing that the correspondence position sampled point multiplies each other and sues for peace, the maximum Doppler scope is by the decision of the radial velocity of spacecraft, for ± 300kHz;

Step (3.3): with the residing spectrum position information of main carrier that step (3.2) is caught the homophase of digital controlled oscillator output and the frequency of quadrature two-way oscillator signal are controlled: wherein, if the distance of the position deviation zero-frequency of main carrier in frequency domain is D (Hz), then the frequency of two-way oscillator signal is K*D (Hz), wherein K is the modulation sensitivity of digital controlled oscillator, is 1; The two-way oscillator signal of controlled oscillator output is converted to the complex oscillation signal through the real/complex conversion device;

Step (3.4): complex oscillation signal that step (3.3) is obtained and input by described I ₁, Q ₁The two paths of data signal is through real/complex conversion and the complex baseband signal that obtains multiplies each other as plural number in a multiplier, finishes the elimination of most of Doppler frequency difference and the result is converted to the two-way real number I of complex signal with a plural number/real number transducer ₂, Q ₂Output; Wherein, most of Doppler frequency difference refers to satisfy the situation of frequency difference elimination back maximum residual frequency deviation less than 16kHz;

Step (4): the complex signal that step (3) is obtained forms device through a spectrum symmetric signal, obtains its frequency spectrum according to the following steps and becomes symmetrical two-way complex signal X about zero-frequency ₁And X ₂:

Step (4.1): the input elimination behind the most Doppler frequency difference, I ₂And Q ₂Be respectively the complex baseband signal output of its real part and imaginary part, obtain complex signal X ₁

Step (4.2): the signal Q of input ₂Multiply by-1, as imaginary part, the signal I of input ₂As real part, closing the road is complex signal output:

Wherein, $X_1=I_2+Q_2=\cos ({\mathrm{\&omega;}}_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&psi;}}_n)+i\sin ({\mathrm{\&omega;}}_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&psi;}}_n)=e^{i({\mathrm{\&omega;}}_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&psi;}}_n)}$

$X_2=I_2-{\mathrm{iQ}}_2=\cos ({\mathrm{\&omega;}}_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&psi;}}_n)-i\sin ({\mathrm{\&omega;}}_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&psi;}}_n)=e^{-i({\mathrm{\&omega;}}_{\mathrm{ds}}T+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{\&psi;}}_n)}$

Wherein, ω _DsFor having eliminated the residue frequency difference behind the most Doppler frequency difference,

M is the number of subcarrier in the USB system,

ψ _nBe n modulated subcarrier signal,

T is the discrete sampling time;

Step (5): the complex signal X of the frequency spectrum symmetry that step (4) obtains ₁And X ₂After the process Doppler frequency offsets preliminary treatment, divide two-way output following signal according to the following steps: the pre-complex baseband signal Y that eliminates the residue Doppler frequency difference ₁, and Doppler frequency difference complex signal Y ₂:

Step (5.1): the complex signal X of input ₂Through the filtering of a finite impulse response FIR low pass filter, output only comprises the complex signal Y of Doppler frequency difference information ₂: should T ' for T through the time-delay after the discrete sampling time, maximum residual frequency deviation after the bandwidth of described FIR low pass filter will be equal to or greater than and eliminate through most of Doppler frequency deviation, and described bandwidth should be less than or equal in the USB measurement and control signal frequency spectrum modulating frequency from a nearest subcarrier of main carrier simultaneously;

Step (5.2): the complex signal X of input ₁Through a delayer time-delay, the time-delay of FIR low pass filter described in the size of time-delay and the step (5.1) equates:

T ' for T through the time-delay after the discrete sampling time;

Step (6): with a Doppler frequency canceller the complex baseband signal Y of step (5) output ₁With complex signal Y ₂Multiply each other as plural number, finish remaining Doppler frequency difference and eliminate, output signal Z,

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