CN110278170A - Short wave communication frequency deviation estimating method based on maximum likelihood - Google Patents
Short wave communication frequency deviation estimating method based on maximum likelihood Download PDFInfo
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- CN110278170A CN110278170A CN201910631108.3A CN201910631108A CN110278170A CN 110278170 A CN110278170 A CN 110278170A CN 201910631108 A CN201910631108 A CN 201910631108A CN 110278170 A CN110278170 A CN 110278170A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2649—Demodulators
- H04L27/265—Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
- H04L2027/0024—Carrier regulation at the receiver end
- H04L2027/0026—Correction of carrier offset
Abstract
The invention discloses a kind of the short wave communication frequency deviation estimating method based on maximum likelihood, the specific steps of this method are as follows: transmitting terminal emits user's data to be transmitted, the synchronizing sequence formation data frame structure of user's data to be transmitted and its front end；Data frame structure is handled by Digital Up Convert, obtains transmission of data sequences；Transmission of data sequences is transmitted by short wave channel and synchronized sampling, obtains receiving data sequence in receiving end；Offset estimation is carried out to receiving data sequence using maximum-likelihood criterion, obtains the offset estimation value of receiving data sequence.The present invention solves larger by error and causes that the rotation of signal phase, generate can not error correction mistake, system performance the problems such as sharply deteriorating；It does not need to carry out channel estimation while improving estimated accuracy, greatly reduces computation complexity；Meanwhile frequent change to receiver crystal oscillator frequency is avoided, without increasing equipment cost.
Description
Technical field
The invention belongs to New Technology Of Shortwave Communication field more particularly to a kind of short wave communication offset estimations based on maximum likelihood
Method.
Background technique
Short wave communication refer to wavelength between 100 meters -10 meters, a kind of radio communication of frequency range 3MHz--30MHz
Technology.The electric wave of short wave communication transmitting will get to receiving end through the reflection in ionosphere, and communication distance is telecommunication farther out
Main means.Although novel radio electrical communication system continues to bring out, this ancient and traditional communication party of short wave communication
Formula nevertheless suffers from global most attention, not only without eliminating, instead also in continuous fast development, because it has other lead to
The advantages of letter system does not have: firstly, shortwave is unique telecommunication means not restricted by network and relaying.Such as it fights
It strives or disaster, when satellite is under attack, the capability to resist destruction and autonomous communication ability of shortwave are that other communication equipments can not match in excellence or beauty；
Secondly, the communication of the remote districts such as mountain area, gobi and ocean is mainly by shortwave；Finally, cheap communication cost is but also shortwave has
There is wide market.
When carrying out short wave communication in order to facilitate information transmission, transmitting terminal usually will be on the low frequency signal that carry information
Frequency conversion is high-frequency signal of the frequency range in 3MHz-30MHz, this process needs a high frequency carrier.After channel transmission, connect
Receiving end needs the high-frequency signal that will be received to downconvert to low frequency signal, this process needs one to extract useful information
With the identical high frequency carrier of transmitting terminal frequency.However due to the manufacture craft of electronic component, circuit board wiring etc. because
Element influences, so that the carrier frequency for sending and receiving both ends generation can not be identical, is constantly present an error.When this mistake
When difference is smaller, although receiver can normally receive and demodulated signal, its performance is enough greatly reduced；When this error is larger
When, will result in signal phase rotation, will generate can not error correction miss so that communication system performance sharply deteriorates.
Application No. is CN201010608140.9, the patents of entitled " a kind of method and device of offset estimation "
In, frequency deviation pre-compensation is carried out to data are received by history frequency deviation value；Channel estimation is carried out to compensated data and frequency deviation is estimated
Meter, obtains the first offset estimation value of current subframe；Using the first offset estimation value of current subframe to frequency deviation pre-compensation after
Data carry out secondary frequency offset compensation.The estimation method needs to carry out channel estimation, brings the increasing of calculation amount in offset estimation
Add.Application No. is CN201310283549.1, in the patent of entitled " a kind of offset estimation be the method compensated ", when
It receives whether the radio frames second half section crystal oscillator adjustment period reaches, then adjusts crystal oscillator frequency with present frame estimation frequency deviation Δ f, from
And eliminate frequency deviation.Although this method is not required to channel estimation, but need to be constantly changing the crystal oscillator frequency of receiver to reach
The purpose of frequency deviation, it is controllable vibration device that this, which just needs crystal oscillator, and the requirement to vibrator is very high, increases equipment cost.
Summary of the invention
To solve the above-mentioned problems, the short wave communication offset estimation based on maximum likelihood that the purpose of the present invention is to propose to a kind of
Method, solve it is larger by error and cause the rotation of signal phase, generate can not error correction mistake, system performance sharply deteriorate etc. and to ask
Topic；It does not need to carry out channel estimation while improving estimated accuracy, greatly reduces computation complexity；Meanwhile avoiding docking
The frequent change of receipts machine crystal oscillator frequency, without increasing equipment cost.
Technical principle of the invention: for as receive and dispatch both ends frequency error (abbreviation frequency deviation) brought by penalty,
Before not demodulated also after down coversion, offset estimation is carried out to signal using maximum-likelihood criterion, it is artificial by this frequency deviation from
It is removed in the signal of down coversion, and then the data into demodulator is made to be no frequency deviation data.
In order to achieve the above object, the present invention is resolved using following technical scheme.
Short wave communication frequency deviation estimating method based on maximum likelihood, comprising the following steps:
Step 1, transmitting terminal emits user's data to be transmitted, the synchronizing sequence shape of user's data to be transmitted and its front end
At data frame structure；Data frame structure is handled by Digital Up Convert, obtains transmission of data sequences；
Step 2, the transmission of data sequences obtains in receiving end by short wave channel transmission and synchronized sampling and receives data
Sequence；
Step 3, offset estimation is carried out to receiving data sequence using maximum-likelihood criterion, obtains the frequency of receiving data sequence
Inclined estimated value.
Further, the synchronizing sequence C is by the modulated generation of pseudo-random sequence；And C=(c0,…,cj,…,cn-1), cj
Indicate j-th of data of synchronizing sequence, n is the length of synchronizing sequence.
Further, the short wave channel has p+q+1 rank, wherein has p rank before main diameter, there is q rank after main diameter；It is described short
Wave channel is H (j Δ t)=[h in the characteristic of jth time Δt-p(jΔt),…,h0(jΔt),…,hq(j Δ t)], h-p(jΔ
T) the characteristic of-p rank in j time Δt of short wave channel is indicated, Δ t is the time interval of two transmission symbols,
RsymFor the transmission baud rate of transmitting terminal.
Further, the receiving data sequence R=(r0,…,rj,…,rn-1),0≤j<n；Its
In, r'z=h-p(zΔt)xp+z+…+h-1(zΔt)x1+z+h0(zΔt)xz+h1(zΔt)x-1+z+…+hq(zΔt)x-q+z+wz,
(- p≤z < n+q), as z > 0, r'z=r'j；xjFor j-th of data of pseudo-random sequence, and xj=0,
1}；wzIt is 0 to obey mean value, variance σ2Normal distribution two-dimentional noise samples value.
Further, described that offset estimation is carried out to receiving data sequence using maximum-likelihood criterion, the specific steps are that:
3.1, set the likelihood function of offset estimation as
3.2, solution likelihood will be converted into the problem of receiving data sequence progress offset estimation using maximum-likelihood criterion
FunctionOffset estimation value f when maximumbias；Obtain the offset estimation formula based on likelihood function are as follows:
3.3, prior probability and the posterior probability for setting each offset estimation value are equal, then the frequency deviation based on likelihood function is estimated
Meter formula can be written as following form:
The offset estimation formula based on likelihood function is solved, the offset estimation value f of receiving data sequence is obtainedbias；
Wherein, Indicate the prior probability of frequency deviation, p (R) expression receives reception
The probability of data sequence R,For the posterior probability of frequency deviation.
Further, the offset estimation formula of the solution based on likelihood function, follows the steps below to implement:
(a) frequency resolution D is calculated, and m equal part is carried out to it, obtains frequency stepping length d:
Wherein, N is the points of Fast Fourier Transform (FFT)；
(b) enabling i is index variables, and is initialized with i=0；
(c) i-th section of frequency deviation is calculated；
Firstly, calculating offset sequenceWherein
Secondly, using synchronizing sequence C and Fourier transform to RiOffset estimation is carried out, i-th section of frequency deviation is obtainedAnd its
Corresponding amplitude Vi；
Finally, index variables i adds 1, the size of i and m are judged；If i < m gos to step c)；Otherwise (d) is entered step；
(d) amplitude vector V=(V is found0,…Vi,…Vm-1) in the corresponding index number I of maximum value and index number I
Corresponding offset estimation value
(e) it calculatesAnd it willAs the offset estimation value f for receiving sequencebias。
Further, described to use synchronizing sequence C and quickly diaphragm filter to RiOffset estimation is carried out, it is specific
Are as follows:
Firstly, according to offset sequenceWith synchronizing sequence C=(c0,…,cj,…,cn-1), construction
Quasi sine signal sequence:Wherein
Secondly, alignment sinusoidal signal sequenceThe Fast Fourier Transform of N point is carried out, and in frequency offset estimation range [- fmax,
fmax] in, find amplitude maximum ViAnd its corresponding frequency
Further, the alignment sinusoidal signalCarry out the Fast Fourier Transform of N point are as follows: as n >=N, interception is quasi-
Sinusoidal signal sequenceTop n data carry out Fast Fourier Transform；As n < N, in quasi sine signal sequenceEnd
(N-n) a data 0 are added, obtain the quasi sine signal sequence that length is N, then carry out to the quasi sine signal sequence that length is N
Fast Fourier Transform.
Compared with prior art, the invention has the benefit that
(1) present invention is solved through maximum-likelihood criterion in the case where not increasing Fast Fourier Transform (FFT) (FFT) points
The larger problem of offset estimation error caused by as discrete spectrum, greatly improves frequency resolution, reduces offset estimation and misses
Difference, and do not need to carry out channel estimation, computation complexity is substantially reduced, under the premise of not increasing hardware complexity, is greatly improved
Estimated accuracy.
(2) present invention estimates frequency deviation using maximum-likelihood criterion, the concept of frequency stepping length is introduced, to not
Offset sequence with stepping length carries out offset estimation, applied widely；It can reached according to the stock number of Shortwave Communication System
It is required that selecting lesser FFT to count, to save system resources space under the premise of frequency resolution.
Detailed description of the invention
The present invention is described in further details in the following with reference to the drawings and specific embodiments.
Fig. 1 is implementation flow chart of the invention；
Fig. 2 is the data frame structure schematic diagram in the present invention；
Fig. 3 is that fading parameter is 2ms/1Hz short wave channel time-varying characteristics figure in embodiment；
Fig. 4 is the corresponding spectral contrast figure of difference frequency deviation value in the embodiment of the present invention；
Fig. 5 is the schematic diagram for carrying out m equal part in the embodiment of the present invention to frequency resolution；
Fig. 6 is intermediate waves baseband signal power spectrogram of the embodiment of the present invention；
Fig. 7 the method for the present invention and offset estimation value of the conventional fast Fourier transform method at Signal to Noise Ratio (SNR)=- 5dB
Statistic histogram；
Fig. 8 is the standard deviation and signal-to-noise ratio curve graph of evaluated error under difference etc. point parameter in the embodiment of the present invention；
Fig. 9 is the frequency offset estimation result figure that difference FFT counts in the embodiment of the present invention.
Specific embodiment
The embodiment of the present invention and effect are described in further detail with reference to the accompanying drawing.
Referring to Fig.1, based on a kind of flow diagram of the short wave communication frequency deviation estimating method based on maximum likelihood of the present invention,
The specific implementation steps are as follows for it:
Step 1, transmitting terminal emits user's data to be transmitted, the synchronizing sequence shape of user's data to be transmitted and its front end
At data frame structure；Data frame structure is handled by Digital Up Convert, obtains transmission of data sequences；
The data frame of maximum likelihood frequency deviation estimating method suitable for short wave communication has structure as shown in Figure 2.Wherein,
Synchronizing sequence is formed by pseudo-random sequence is modulated, and data segment is user's information to be transmitted.The effect of synchronizing sequence is same
The determination of beans-and bullets shooter, offset estimation, channel estimation etc..Below with binary phase shift keying (Binary Phase Shift Key,
BPSK it) is described in detail for the baseband communication system modulated to how carrying out offset estimation.
Specifically, it is assumed that pseudo-random sequence X=(x0,…,xj,…,xn-1),xj={ 0,1 } obtains same after BPSK is modulated
Step sequence C=(c0,…,cj,…,cn-1), wherein cj=1-2 × xj.Send baud rate (symbol numbers that the unit time sends)
For RsymA symbol/second, the time interval for sending adjacent-symbol areSecond；In synchronizing sequence followed by identical modulation methods
The data segment of formula.
Step 2, the transmission of data sequences obtains in receiving end by short wave channel transmission and synchronized sampling and receives data
Sequence；
The information for obeying frame format in step 1 is transmitted through short wave channel, in the received receiving data sequence in receiving end
For the receiving data sequence R=(r0,…,rj,…,rn-1),0≤j<n；Wherein, r'z=h-p(zΔt)
xp+z+…+h-1(zΔt)x1+z+h0(zΔt)xz+h1(zΔt)x-1+z+…+hq(zΔt)x-q+z+wz, (- p≤z < n+q), as z >
When 0, r'z=r'j；xjFor j-th of data of pseudo-random sequence, and xj={ 0,1 }；wzIt is 0 to obey mean value,
Variance is σ2Normal distribution two-dimentional noise samples value.
Above-mentioned short wave channel has p+q+1 rank, wherein has p rank before main diameter, there is q rank after main diameter；The short wave channel is
The characteristic of j time Δt is H (j Δ t)=[h-p(jΔt),…,h0(jΔt),…,hq(j Δ t)], h-p(j Δ t) indicates shortwave
For-p the rank of channel in the characteristic of j time Δt, Δ t is the time interval of two transmission symbols,RsymFor transmitting
The transmission baud rate at end.
Shortwave transmission channel has the characteristics that change over time and change, and this variation not only causes to decline to signal, together
When can also generate Doppler frequency spectrum.As shown in figure 3, giving two diameter fading parameters in figure is 2ms/1Hz short wave channel (real part)
Performance plot, the average decline of each path is 0dB.Two diameter of parameter refers to that there are two paths, when 2ms refers to two paths
Between be spaced, 1Hz refer to the Doppler spectrum bandwidth due to caused by sending and receiving stations relative motion and multi-angle remission be 1Hz, can also
It is faster to be simply interpreted as the bigger channel conversion of numerical value.
Step 3, offset estimation is carried out to receiving data sequence using maximum-likelihood criterion, obtains the frequency of receiving data sequence
Inclined estimated value.Specifically include following sub-step:
3.1, set the likelihood function of offset estimation as
3.2, solution likelihood will be converted into the problem of receiving data sequence progress offset estimation using maximum-likelihood criterion
FunctionOffset estimation value f when maximumbias；Obtain the offset estimation formula based on likelihood function are as follows:
3.3, prior probability and the posterior probability for setting each offset estimation value are equal, then the frequency deviation based on likelihood function is estimated
Meter formula can be written as following form:
The offset estimation formula based on likelihood function is solved, the offset estimation value f of receiving data sequence is obtainedbias；
Wherein, Indicate the prior probability of frequency deviation, p (R) expression receives reception
The probability of data sequence R,For the posterior probability of frequency deviation.
Specifically, the offset estimation formula based on likelihood function is solved, is followed the steps below to implement:
(a) frequency resolution D is calculated, and m equal part is carried out to it, obtains frequency stepping length d:
Wherein, N is the points of Fast Fourier Transform (FFT)；
(b) enabling i is index variables, and is initialized with i=0；
(c) i-th section of frequency deviation is calculated；
Firstly, calculating offset sequenceWherein
Secondly, using synchronizing sequence C and Fourier transform to RiOffset estimation is carried out, i-th section of frequency deviation is obtainedAnd its
Corresponding amplitude Vi；
Finally, index variables i adds 1, the size of i and m are judged；If i < m gos to step c)；Otherwise (d) is entered step；
(d) amplitude vector V=(V is found0,…Vi,…Vm-1) in the corresponding index number I of maximum value and index number I
Corresponding offset estimation value
(e) it calculatesAnd it willAs the offset estimation value f for receiving sequencebias。
Further, described to use synchronizing sequence C and quickly diaphragm filter to RiOffset estimation is carried out, it is specific
Are as follows:
Firstly, according to offset sequenceWith synchronizing sequence C=(c0,…,cj,…,cn-1), construction
Quasi sine signal sequence:Wherein
Secondly, alignment sinusoidal signal sequenceThe Fast Fourier Transform of N point is carried out, and in frequency offset estimation range [- fmax,
fmax] in, find amplitude maximum ViAnd its corresponding frequency
Wherein, as n >=N, quasi sine signal sequence is interceptedTop n data carry out Fast Fourier Transform；As n < N
When, in quasi sine signal sequenceEnd add (N-n) a data 0, obtain the quasi sine signal sequence that length is N, then it is right
The quasi sine signal sequence that length is N carries out Fast Fourier Transform.
The pros and cons of traditional FFT method and the method for the present invention are exemplified below:
For traditional FFT method, it is simple and quick that FFT is that the common method of field of signal processing has the advantages that,
Essence is the discrete spectrum of the sequence of calculation.The concrete analysis of its frequency offset estimation accuracy is as follows:
Assuming that being based on receiving data sequence R=(r0,…,rj,…,rn-1) and C=(c0,…,cj,…,cn-1) construction standard is just
String signalWhereinIt is directed at sinusoidal signalAfter carrying out N point FFT, frequency
Rate resolution ratioObservable frequency range is-fFFTHz~fFFTHz, whereinThat is
After FFT transform only it is observed that kD (k be betweenInteger) frequency component, or can only approximately reflect base
The probability size of each possible frequency deviation value kD is obtained in receiving data sequence R, i.e.,If true frequency deviation
fbias≠ kD then will appear evaluated error after FFT transform.
For example, certain Shortwave Communication System Rsym=2.048 × 103Symbol/second, points N=128 FFT, then its frequency discrimination
Rate D=16Hz.When true frequency deviation value is respectively 80H, 88Hz, the frequency spectrum after FFT transform is as shown in Figure 4.
As can see from Figure 4 when frequency deviation value is 80Hz (i.e. frequency deviation value be frequency resolution integral multiple), in 80Hz
Locate the peak value of existence anduniquess, other Frequency points are 0, i.e.,It is maximum, then it is assumed that estimator 80Hz；And work as
When frequency deviation value is 88Hz (i.e. frequency deviation value is the non-integral multiple of frequency resolution), there is the different peak of amplitude in multiple Frequency points
Value, and the corresponding amplitude maximum of 96Hz, then it is assumed thatMaximum, therefore select 96Hz as offset estimation value, this
There are the errors of 8Hz between estimated value 96Hz and true value 88Hz.
It generally, can be using the method for the points for increasing FFT in order to reduce evaluated error (i.e. raising frequency resolution)
To realize.However it is limited in practical applications since the objective condition such as calculation amount, memory space and arithmetic speed restrict
The upper limit of FFT points, therefore the error of estimation cannot be reduced in actual offset estimation simply by this method.
The frequency offset estimation accuracy concrete analysis of the method for the present invention is as follows:
Assuming that true frequency deviation is kD+id, (0≤i < m).When the deviation frequency artificially added is (m-i) × d, sequence is deviated
It arranges the total frequency deviation for being included and is exactly (k+1) D.Utilize the frequency excursion algorithm based on Fourier transform that can accurately estimate at this time
Count out total frequency deviation and corresponding peak value V(m-i)×d；The offset component artificially added is then subtracted with total offset to obtain
The former true frequency offset of sequence.(such as (m-i+1) × d) if the deviation frequency artificially added is near (m-i) × d,
It is (k+1) D and corresponding peak-peak that total frequency deviation can be also estimated using the frequency excursion algorithm based on Fourier transform
For V(m-i+1)×d(can have multiple peak values in this case, as shown in Figure 4), but V(m-i+1)×d<V(m-i)×d, the method for the present invention meeting
Selecting Index serial number I=m-i and the corresponding estimated value of serial number IThen finally estimated by step 5
ValueAs a result as shown in Figure 5.
It is seen from fig 5 that the method for the present invention is substantially reduced compared to the offset estimation method error of conventional Fourier Transform,
Deng dividing, the bigger precision of parameter m is higher, and the frequency excursion algorithm as m=1 based on maximum-likelihood criterion is degenerated for based on Fourier
The frequency excursion algorithm of leaf transformation.
In addition, the method for the present invention is suitable for various modulation systems: such as QPSK, 8PSK, QAM, the present embodiment is in order to intuitive
Show the method for the present invention process, using BPSK modulation entire estimation procedure is described.
Emulation experiment
In order to verify the performance of the method for the present invention, the base band that modulation system is BPSK is carried out and has emulated, wherein BPSK is modulated
Pulse-shaping afterwards chooses the raised cosine pulse function that coefficient is 0.4.
Short wave channel parameter are as follows: the average decline of double diameter 2ms/1Hz, each path are 0dB；Sending baud rate is
2400Baud/S；Signal-to-noise ratio is defined as in emulationUnit is dB, wherein EsFor the symbol received
Energy,σ2For the dimensional Gaussian white noise variance being superimposed upon on channel.Fig. 6 is to generate according to parameter as above
Shortwave baseband signal power spectrogram.
Emulation 1
The offset estimation of the method for the present invention and traditional quickly diaphragm filter at Signal to Noise Ratio (SNR)=- 5dB is respectively adopted
Performance.Two methods are carried out with 10000 emulation respectively, wherein Fast Fourier Transform points are, wait and divide parameter m at 128 points
=8, each frequency deviation is set at random within the scope of [- 100,100] Hz, by the frequency offset estimation result of two methods and true frequency deviation
Error be depicted as histogram, as a result as shown in Figure 7.
As can see from Figure 7, the error that two methods provide all is swung near 0Hz, and is based on fast Flourier
The amplitude of fluctuation of converter technique is greater than the method for the present invention.Simultaneously as can also be seen from Figure the estimated result of two methods be similar to be in
Existing Gaussian Profile, therefore the superiority and inferiority of estimation can be assessed with the parameter (mean value and standard deviation) for portraying Gaussian Profile.Its
In, mean value embodies the order of accuarcy of estimated data from statistics angle, and standard deviation then embodies the degree of scatter of estimated data, mark
Quasi- difference shows that more greatly the result estimated is more dispersed.Such as the result provided in emulation 1 has: (1) based on Fast Fourier Transform
Method: error mean is -0.2812Hz, standard deviation 5.8291Hz.I.e. error is fallen within the scope of -0.2812 ± 3 × 5.8291Hz
Probability be 0.9974.(2) the method for the present invention: error mean is -0.1453Hz, standard deviation 2.8576Hz, i.e. error fall in -
Probability within the scope of 0.1453 ± 3 × 2.8576Hz is 0.9974.By being analyzed above as it can be seen that the frequency deviation value that two methods estimate
Mean value and true value it is essentially identical, but the intensity of error that the method for the present invention estimates will be significantly larger than quick Fourier
Leaf transformation method.
Emulation 2
Influence when investigating parameter m difference value to the method for the present invention estimation performance.Fast Fourier Transform is arranged to count
It is 128 points, m=1,2,4 and 8 is taken to be emulated under different signal-to-noise ratio respectively.The mean value and true value base of the frequency deviation estimated
This is identical, counts to the standard deviation of evaluated error, curve is as shown in Figure 8.As can see from Figure 8, no matter divisions is waited to join
What value number m takes, and the method for the present invention can fast convergence；In low signal-to-noise ratio range, with the increase of signal-to-noise ratio, the mistake that estimates
Poor standard deviation is reduced rapidly；And in high s/n ratio range, the increase of signal-to-noise ratio can not be effectively reduced standard deviation.In identical letter
It makes an uproar than under, with equal increase for dividing parameter m, the error to standard deviation estimated is decreased.
Emulation 3
When using the method for the present invention to offset estimation, in order to obtain the estimated result more concentrated under high s/n ratio
(higher concentration degree/lesser standard deviation), can hardware condition allow in the case where using increase FFT points method come
It realizes.Here it simulates mutually same parameter m=8, the difference FFT of dividing and counts () at 128 points and 512 points under different state of signal-to-noise
Influence to estimated result, simulation result are as shown in Figure 9.
From the figure, it can be seen that when the increase that mono- timing of m is counted with FFT, the error to standard deviation estimated also subtracts therewith
It is small, that is to say, that the frequency deviation value estimated is increasingly concentrated.Such as m=8, signal-to-noise ratio be when being 0dB, FFT be respectively 128,
256 and 512 points in the case where the error to standard deviation that estimates be respectively 2.605Hz, 1.311Hz and 0.953Hz.Illustrate the present invention
Lesser FFT can be selected to count according to the stock number of Shortwave Communication System, under the premise of reaching requirement frequency resolution, from
And save system resources space.
Those of ordinary skill in the art will appreciate that: realize that all or part of the steps of above method embodiment can pass through
The relevant hardware of program instruction is completed, and program above-mentioned can be stored in a computer readable storage medium, the program
When being executed, step including the steps of the foregoing method embodiments is executed；And storage medium above-mentioned includes: ROM, RAM, magnetic disk or light
The various media that can store program code such as disk.
The above description is merely a specific embodiment, but scope of protection of the present invention is not limited thereto, any
Those familiar with the art in the technical scope disclosed by the present invention, can easily think of the change or the replacement, and should all contain
Lid is within protection scope of the present invention.Therefore, protection scope of the present invention should be based on the protection scope of the described claims.
Claims (8)
1. the short wave communication frequency deviation estimating method based on maximum likelihood, which comprises the following steps:
Step 1, transmitting terminal emits user's data to be transmitted, and user's data to be transmitted and the synchronizing sequence of its front end form number
According to frame structure；Data frame structure is handled by Digital Up Convert, obtains transmission of data sequences；
Step 2, the transmission of data sequences obtains in receiving end by short wave channel transmission and synchronized sampling and receives data sequence
Column；
Step 3, offset estimation is carried out to receiving data sequence using maximum-likelihood criterion, the frequency deviation for obtaining receiving data sequence is estimated
Evaluation.
2. the short wave communication frequency deviation estimating method according to claim 1 based on maximum likelihood, which is characterized in that step 1
In, the synchronizing sequence C is by the modulated generation of pseudo-random sequence；And C=(c0..., cj..., cn-1), cj indicates synchronizing sequence
J-th of data, n are the length of synchronizing sequence.
3. the short wave communication frequency deviation estimating method according to claim 1 based on maximum likelihood, which is characterized in that step 2
In, the short wave channel has p+q+1 rank, wherein has p rank before main diameter, there is q rank after main diameter；The short wave channel is in jth Δ t
The characteristic at moment is H (j Δ t)=[h-p(j Δ t) ..., h0(j Δ t) ..., hq(j Δ t)], h-p(j Δ t) indicates short wave channel
- p rank j time Δt characteristic, Δ t be two transmission symbol time intervals,RsymFor the hair of transmitting terminal
Send baud rate.
4. the short wave communication frequency deviation estimating method according to claim 1 based on maximum likelihood, which is characterized in that step 2
In, the receiving data sequence R=(r0..., rj..., rn-1),0≤j < n；Wherein, r 'z=h-p(zΔ
t)xp+z+…+h-1(zΔt)x1+z+h0(zΔt)xz+h1(zΔt)x-1+z+…+hq(zΔt)x-q+z+wz, (- p≤z < n+q), when
When z > 0, r 'z=r 'j；xjFor j-th of data of pseudo-random sequence, and xj={ 0,1 }；wzIt is to obey mean value
0, variance σ2Normal distribution two-dimentional noise samples value.
5. the short wave communication frequency deviation estimating method according to claim 1 based on maximum likelihood, which is characterized in that step 3
In, it is described that offset estimation is carried out to receiving data sequence using maximum-likelihood criterion, the specific steps are that:
Step 3.1, set the likelihood function of offset estimation as
Step 3.2, the problem of carrying out offset estimation to receiving data sequence using maximum-likelihood criterion, is converted into solution likelihood
FunctionOffset estimation value f when maximumbias；Obtain the offset estimation formula based on likelihood function are as follows:
Step 3.3, prior probability and the posterior probability for setting each offset estimation value are equal, then the frequency deviation based on likelihood function is estimated
Meter formula can be written as following form:
The offset estimation formula based on likelihood function is solved, the offset estimation value f of receiving data sequence is obtainedbias；
Wherein, Indicate the prior probability of frequency deviation, p (R) expression, which receives, receives data sequence
The probability of R is arranged,For the posterior probability of frequency deviation.
6. the short wave communication frequency deviation estimating method according to claim 5 based on maximum likelihood, which is characterized in that described to ask
Offset estimation formula of the solution based on likelihood function, follows the steps below to implement:
(a) frequency resolution D is calculated, and m equal part is carried out to it, obtains frequency stepping length d:
Wherein, N is the points of Fast Fourier Transform (FFT)；
(b) enabling i is index variables, and is initialized with i=0；
(c) i-th section of frequency deviation is calculated；
Firstly, calculating offset sequenceWherein
Secondly, using synchronizing sequence C and Fourier transform to RiOffset estimation is carried out, i-th section of frequency deviation is obtainedAnd its it is corresponding
Amplitude Vi；
Finally, index variables i adds 1, the size of i and m are judged；If i < m gos to step c)；Otherwise (d) is entered step；
(d) amplitude vector V=(V is found0... Vi... Vm-1) in the corresponding index number I of maximum value it is corresponding with index number I
Offset estimation value
(e) it calculatesAnd it willAs the offset estimation value f for receiving sequencebias。
7. the short wave communication frequency deviation estimating method according to claim 6 based on maximum likelihood, which is characterized in that described to adopt
With synchronizing sequence C and quickly diaphragm filter to RiOffset estimation is carried out, specifically:
Firstly, according to offset sequenceWith synchronizing sequence C=(c0..., cj..., cn-1), construction is quasi- just
String signal sequence:Wherein
Secondly, alignment sinusoidal signal sequenceThe Fast Fourier Transform of N point is carried out, and in frequency offset estimation range [- fmax, fmax]
It is interior, find amplitude maximum ViAnd its corresponding frequency
8. the short wave communication frequency deviation estimating method according to claim 7 based on maximum likelihood, which is characterized in that described right
Quasi sine signalCarry out the Fast Fourier Transform of N point are as follows: as n >=N, intercept quasi sine signal sequenceTop n number
According to progress Fast Fourier Transform；As n < N, in quasi sine signal sequenceEnd add (N-n) a data 0, grown
Degree is the quasi sine signal sequence of N, then carries out Fast Fourier Transform to the quasi sine signal sequence that length is N.
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