CN103117980B - For the fast digital auto frequency control method of OFDM receiver - Google Patents
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Abstract
The present invention relates to a kind of fast digital auto frequency control method for OFDM receiver, the method comprises the following steps: 1) frequency deviation estimation, 2) frequency deviation judgement and 3) frequency deviation control, frequency deviation estimating step is based on data-aided, the leading training sequence received is carried out thin synchronous and thick synchronous, estimate fractional frequency offset and integer frequency offset respectively; Frequency deviation decision steps judgement current frequency offset is the need of carrying out frequency deviation control; Frequency deviation rate-determining steps revised version ground temperature mends pressuring controlling oscillator frequency, controls frequency deviation.The present invention, by short training sequence time domain correlation estimated score times frequency deviation, decreases operand; By receiving and the frequency domain differential demodulation computing correlation estimation integer frequency offset of the leading training sequence in this locality, improve the robustness of integer frequency offset estimation, also eliminating the impact of timing offset; Control to overcome by self adaptation frequency deviation the frequency drift that components and parts individual difference and environmental change cause, avoid and calibrate with standard signal source.
Description
Technical field
The invention belongs to wireless communication technique field, be specifically related to a kind of be applicable to ofdm system wireless receiver automatic frequency controller and AutomaticFrequencyController be called for short implementation method and the software flow of AFC.
Background technology
Because orthogonal frequency division multiplexi and OrthogonalFrequencyDivisionMultiplexing are hereinafter referred to as OFDM, this technology has higher band efficiency and good Effect of Carrier Frequency Offset, has been widely used in wired and wireless communication system.But OFDM is very responsive for frequency departure, frequency departure is divided into again mark overtones band deviation relative to subcarrier spacing and integer multiple frequency deviation, wherein fractional part of frequency offset can cause inter-carrier interference, integer frequency offset can cause the cyclic shift receiving data symbol, so frequency deviation estimation and frequency deviation control problem are related to correctness and the reliability of transfer of data.Current mostly depends on autocorrelation value based on data-aided frequency excursion algorithm, and its frequency offset estimation range is less, is difficult to the integer frequency offset tackled in a big way, does not also consider that timing offset is on estimating to obtain impact simultaneously.
Receiver receives and sends signal, receives signal with local oscillator signals frequency conversion, and process is through the transmission data of the signal recuperation transmitter of frequency multiplication.Receiver performs automatic frequency control conventional method analog-and digital-two kinds of methods, and analogy method is portable poor, and circuit is complicated, and digital method is generally the frequency error rectification error of estimating local frequency.Because the individual difference of components and parts and environmental factor cause the drift of system parameters, traditional control method must use standard signal source to local oscillator calibration again and again.If harsh to frequency requirement, frequency deviation controls there is challenge.
Summary of the invention
The present invention is just for the technical problem existed in prior art, provide a kind of Frequency Estimation and the auto frequency deviation control method that are applicable to OFDM receiver, the method can be accomplished in larger frequency deviation region, realize accurate frequency deviation to estimate and automatic frequency control, can be controlled within minimum scope via the receiving signal frequency offset after the process of this technological system, ensure that subsequent treatment can normally be carried out.
In order to achieve the above object, technical scheme of the present invention is as follows, a kind of fast digital auto frequency control method for OFDM receiver, the method comprises the following steps: 1) frequency deviation estimation, 2) frequency deviation judgement and 3) frequency deviation control, 1) described frequency deviation estimating step arranges the training sequence being used for frequency deviation and estimating at transmitting terminal, receive these training sequences successively at receiving terminal, concrete grammar is: 11) get the time domain preamble training sequence latter half received and negative obtain P
r(k), 0≤k≤N, N=256, and carry out thin synchronous in time domain, obtain the fractional frequency offset estimated value of subcarrier spacing
Described is carefully synchronously the correlation window choosing 64 length, carries out related operation, obtain correlation calculation result R, thus obtain a point estimated value for several times carrier wave frequency deviation the conjugation of first 64 sample value and 64 sample values of its delay 128 receiving leading training sequence
2) described frequency deviation decision steps adjudicates described step 1) middle gained frequency deviation estimated value is the need of carrying out frequency deviation control, and concrete grammar is:
21) obtaining step 1) gained frequency deviation estimated value, P point is averaged, and obtains frequency deviation average
22) require to arrange the frequency deviation control objectives scope that receiver normally works according to Communication System Design
wherein f
srepresent the maximum frequency deviation value of system requirements, judge frequency deviation average
whether meet this target zone, satisfied then do not carry out frequency deviation control, otherwise frequency deviation control is carried out to it;
3) described frequency controlling step adjusts the control voltage of temperature complement voltage-control oscillator TCXO adaptively thus revises frequency deviation, stores control coefrficient s and control voltage v ' simultaneously, and to increase the efficiency automatically controlled after system power failure, concrete grammar is:
31) control coefrficient initial value s is calculated: the frequency deviation obtained due to frequency deviation estimating step
be the deviation of corresponding radio-frequency carrier, if carrier frequency is p times of TCXO frequency, then described frequency deviation average is converted to the frequency difference of TCXO frequency
voltage controlled oscillator control voltage v is directly proportional to frequency of oscillation f, i.e. f=av+b, and wherein a, b are constant, obtains Δ f=a Δ v, obtains
32) to above-mentioned steps 2) judgement gained need the frequency deviation average of carrying out frequency deviation control to carry out frequency deviation adjustment, by 31) formula
calculate the difference DELTA v that voltage controlled oscillator control voltage v should adjust, adjustment voltage controlled oscillator control voltage is v '=v+ Δ v, and wherein v ' is the control voltage value after adjustment,
33) to step 32) step control after effect judge, control after frequency deviation meet
then store this control voltage v ', if frequency deviation does not still meet after controlling, after Corrective control coefficient s, repeat 32).
As a modification of the present invention, described a kind of fast digital auto frequency control method for OFDM receiver, is characterized in that described step 1 frequency deviation is further comprising the steps of in estimating, 12) to P
rk the compensate of frequency deviation of () row point several times, obtains the training sequence P ' after fractional frequency offset compensation
rk (), described compensate of frequency deviation obtains fractional frequency offset estimated value
after, utilize estimated value
in time domain, frequency compensation is carried out to training sequence, as follows:
13) at frequency domain to P '
rk () carries out thick synchronous, obtain the integer frequency offset estimation value of subcarrier spacing
Described frequency domain is synchronously slightly first to P '
r(k) and local transmission training sequence P
tk () is Fourier transform FFT and is obtained its frequency domain data R (k) and P
trk (), respectively to frequency domain data R (k) and P
trk () carries out calculus of differences, definition calculus of differences:
R
diff(k)＝R
*(k)·R(k+8)
R
diff(k) and ref
diffk () represents frequency domain data R (k) and P respectively
trk () carries out the data after calculus of differences;
Then to difference sequence R
diff(k) and ref
diffk () is in sliding cross-correlation calculating, the displacement when cross correlation value reaches maximum is the size of integer frequency offset, integer frequency offset estimation value
be calculated as follows and obtain:
Wherein-3≤i≤3, it comes relevant with training sequence in the spacing of the non-zero points of frequency domain, and the scope of integer frequency offset estimation is [-3,3], exceeds the integer frequency offset estimation that can make the mistake;
As a modification of the present invention, described step 11) send the subcarrier transmission data that leading training sequence uses the integral multiple of 4 on frequency domain, other subcarrier is empty, therefore it comprises 4 64 short training sequences in time domain, first short training sequence A represents, second short training sequence is the repetition of first short training sequence, and third and fourth short training sequence is the negative value of first short training sequence, is expressed as A, A ,-A ,-A.
As a modification of the present invention, described step 12) in definition related operation be:
Wherein, represent and get sequence conjugate, s (k) represents the time-domain training sequence sent, and n (k) represents additive white Gaussian noise, and its average is zero, variance
ε represents with the normalized carrier wave frequency deviation ε=ε of subcarrier spacing
p+ ε
i, N=256, M=64, L=4, m=2.
As a modification of the present invention, described step 21) frequency deviation estimating step gained frequency deviation P point gets average, and more the more accurate control effects of large Doppler estimation is more accurate for P value, but consuming time more of a specified duration, ageing reduction.P value is required by system frequency deviation control precision and ageing requirement compromise is chosen.This method frequency deviation estimating step gained frequency deviation P point gets average, and P is 1.
As a modification of the present invention, described step 31) in voltage controlled oscillator control voltage v to be directly proportional to frequency of oscillation f f=av+b, wherein a, b are constant.The value of a, b is provided by voltage controlled oscillator manufacturer information handbook, and different components and parts individualities can be variant; Control coefrficient
p is frequency, because the individual different a value that can cause of envirment factor and components and parts is drifted about to some extent, needs self adaptation to correct s.
As a modification of the present invention, described step 33) in frequency deviation control coefrficient s is calibrated, method is:
wherein Δ v is the difference of control voltage,
for the frequency deviation average before frequency deviation control,
for the frequency deviation average after frequency deviation control.
As a modification of the present invention, described step 33) in, carry out storage for the control voltage v ' meeting system frequency deviation requirement and adopt majority decision method, repeated storage is in multiple address, read the magnitude of voltage of this position after system reboot, will occur that the maximum value of ratio is as control voltage initial value.
Relative to prior art, the present invention has the following advantages: the inventive method only utilizes the autocorrelation performance that in leading training sequence, short training sequence A is good, carries out related operation obtain fractional frequency offset accurately by the data that the conjugation of first 64 sample value is less with 64 sample values of its delay 128; Introduce the calculus of differences of a leading training sequence frequency domain simultaneously, the autocorrelation performance utilizing it good completes the estimation of integer frequency offset, improve the robustness of integer frequency offset estimation, also eliminate the impact of timing offset on this algorithm, emulation to show under different timing offset all can be correct estimate integer frequency offset; Self-adaptative adjustment frequency deviation control coefrficient overcomes frequency deviation that environmental factor, components and parts individual difference and time drift cause in the outer phenomenon constantly fluctuated up and down of target zone; For the real-time update of control voltage initial value avoid system because of environment difference cause using before must use standard signal source calibration, improve system effectiveness simultaneously.
Accompanying drawing explanation
Fig. 1 sends pilot training sequence block diagram;
Fig. 2 is fractional frequency offset algorithm for estimating block diagram;
Fig. 3 is integer frequency offset estimation algorithm block diagram;
Fig. 4 is that auto frequency deviation controls the software flow pattern of frequency deviation judgement and frequency deviation control fast;
Fig. 5 is integer frequency offset estimation analogous diagram under different timing deviation;
Fig. 6 is the overall flow chart of steps of the present invention.
Embodiment
In order to deepen the understanding of the present invention and understanding, below in conjunction with the drawings and specific embodiments, the present invention is further illustrated and introduce.
Embodiment 1:
See Fig. 6, a kind of fast digital auto frequency control method for OFDM receiver, the method comprises the following steps: 1) frequency deviation is estimated, 2) frequency deviation judgement and 3) frequency deviation control, described frequency deviation estimating step arranges the training sequence being used for frequency deviation and estimating at transmitting terminal, these training sequences are received successively at receiving terminal, see Fig. 1, for the leading training sequence structure that frequency deviation is estimated, send leading training sequence uses the subcarrier of the integral multiple of 4 to transmit data on frequency domain, other subcarrier is empty, therefore it comprises 4 64 short training sequences in time domain, first short training sequence A represents, then leading training sequence can be expressed as [A, A, – A, – A], as Fig. 1 shows.
See Fig. 2, fractional frequency offset is estimated and compensate of frequency deviation: after frequency deviation estimates to occur in Timing Synchronization, when synchronous point d being detected
maxtime, extract N (N is 256) point data subsequently, to rear N/2 point symbol position negate, obtain time domain preamble training sequence P
r(k):
Utilize periodicity and the correlation of leading training sequence, choose the correlation window of 64 length, related operation is carried out, definition to the conjugation of first 64 sample value of leading training sequence and 64 sample values of its delay 128:
Wherein, represent and get sequence conjugate, s (k) represents the time-domain training sequence sent, and n (k) represents additive white Gaussian noise, and its average is zero, variance
ε represents with the normalized carrier wave frequency deviation (ε=ε of subcarrier spacing
p+ ε
i), N=256, M=64, L=4, m=2
Based on above formula, when | ε
p| during < L/2m, fractional frequency offset can be estimated as:
Estimate to obtain fractional part of frequency offset
after, utilize estimated value
in time domain, compensate of frequency deviation is carried out to signal, as follows:
Wherein, P
rk () is compensate of frequency deviation front signal, P '
rk () is signal after compensate of frequency deviation.
See Fig. 3, integer frequency offset estimation:
After time domain fractional part of frequency offset is estimated and compensated, essentially eliminate the ICI brought by carrier wave frequency deviation, but system still may also exist integer frequency offset ε
iand timing offset τ, integer frequency offset estimation is by frequency domain training sequence R (k) received and the training sequence P of transmission at frequency domain
tk () is done displacement cross-correlation and is completed, the displacement when cross correlation value reaches maximum is the size of integer frequency offset.Timing offset τ is then by reception frequency domain data R (k) and sends frequency domain training sequence P
trk () carries out difference respectively, thus eliminate the impact of timing offset.
First to P '
r(k) and P
tk () is Fourier transform FFT and is obtained its frequency domain data R (k) and P
trk (), respectively to frequency domain data R (k) and P
trk () carries out calculus of differences, definition calculus of differences:
R
diff(k)＝R
*(k)·R(k+8)
R
diff(k) and ref
diffk () represents frequency domain data R (k) and P respectively
trk () carries out the data after calculus of differences.
, then to difference sequence R
diff(k) and ref
diffk () is in sliding cross-correlation calculating, the shift value when cross correlation value reaches maximum is the size of integer frequency offset, integer frequency offset estimation value
be calculated as follows and obtain:
Wherein-3≤i≤3, it comes relevant with training sequence in the spacing of the non-zero points of frequency domain, and the scope of integer frequency offset estimation is [-3,3], exceeds the integer frequency offset estimation that can make the mistake.
Be there is no integer frequency offset estimation analogous diagram under timing frequency deviation and different timing deviation, can finding out see Fig. 5, Fig. 5, owing to employing calculus of differences, correctly can estimate integer frequency offset, eliminate the impact of timing frequency deviation completely.
Comprehensively, the total estimated value of frequency deviation ε can be obtained
for:
To an above-mentioned gained P frequency deviation estimated value
be averaged and obtain frequency deviation average
p value choose by ageing to compromise with accuracy choose, P value is larger, and frequency deviation controls more accurate, causes control ageing poorer simultaneously.The present embodiment is burst System, being 1, carrying out frequency deviation judgement, control at once after namely estimating frequency deviation for guaranteeing that timeliness that frequency deviation controls gets P,
See Fig. 4, judge frequency deviation estimated value
whether meet
wherein f
sbe the positive frequency deviation of maximum permission meeting Communication System Design requirement, this frequency deviation sets by during overall system design.If meet
then communication system can normally work, and does not need to adjust frequency deviation, so do not adjust frequency deviation.If do not meet
then now communication system work is abnormal, needs to adjust frequency deviation, this frequency deviation is reported frequency deviation rate-determining steps, adjusts system frequency deviation.
The temperature complement voltage-control oscillator TCXO available register that the present embodiment adopts controls its control voltage, thus adjustment self-oscillation is frequent.Chip data handbook obtains formula f=av+b, and wherein f is concussion frequency, and v is control voltage, and a, b are constants.System frequency multiplier frequency is 175, obtains radio frequency carrier frequency f '=175f=175 (av+b), Δ f '=175a Δ v; Wherein Δ f ' be radio frequency carrier frequency difference, i.e. above-mentioned frequency deviation
calculate system initial frequency deviation control coefrficient
according to carrier frequency computing system initial control voltage v, write temperature complement voltage-control oscillator register.
Calculate control voltage v difference
, changing control voltage v by amendment register value is v '=v+ Δ v, changes the concussion frequency of local temperature complement voltage-control oscillator thus revises radio frequency carrier frequency, reducing frequency deviation.After carrying out above-mentioned control, the frequency deviation estimated value that frequency deviation estimating step obtains is judged, if frequency deviation meets after controlling
then the above-mentioned frequency deviation control coefrficient s calculated is accurately in applied environment, storage control coefrficient s and now control voltage v '.Otherwise must revise s.The modification method of frequency deviation control coefrficient s is
wherein Δ v is the difference of control voltage,
for the frequency deviation average before frequency deviation control,
for the frequency deviation average after frequency deviation control.
Repeat after correcting frequency deviation control coefrficient s that above-mentioned frequency deviation judges, control flow, judge whether frequency deviation meets system frequency deviation requirement, satisfied then storage control voltage and control coefrficient, satisfiedly then again carry out control coefrficient s correction.Iteration correction s, meets until control frequency deviation
then now control voltage v and control coefrficient s is only the correct temperature complement voltage-control oscillator control voltage of system under current operating environment and control coefrficient, and store, after facilitating system reboot, next time directly calls.Storage method uses majority decision, be stored in 10 addresses simultaneously, when next time calls, read the value of this address, occur that maximum values is control voltage and control coefrficient, avoid because the unexpected storage errors caused, after causing system reboot, frequency deviation excessive causing cannot work.
Above-mentioned auto frequency deviation controls to continue to perform in system operation, effectively avoids system parameters running status of drifting about in time to change the frequency drift caused.
It should be noted that above-described embodiment is only preferred embodiment of the present invention; be not used for limiting protection scope of the present invention; the equivalent replacement made on the basis of the above or substitute all fall into protection scope of the present invention, protection scope of the present invention is as the criterion with claims.
Claims (5)
1. for a fast digital auto frequency control method for OFDM receiver, the method comprises the following steps: 1) frequency deviation estimation, 2) frequency deviation judgement and 3) frequency deviation control, it is characterized in that:
1) described frequency deviation estimating step arranges the training sequence being used for frequency deviation and estimating at transmitting terminal, and receive these training sequences successively at receiving terminal, concrete grammar is:
11), after frequency deviation estimates to occur in Timing Synchronization, the time domain preamble training sequence latter half received is got and negative obtains P
r(k), 0≤k≤N, N=256, and carry out thin synchronous in time domain, obtain the fractional frequency offset estimated value of subcarrier spacing
utilize periodicity and the correlation of leading training sequence, choose the correlation window of 64 length, related operation is carried out, definition to the conjugation of first 64 sample value of leading training sequence and 64 sample values of its delay 128:
Wherein,
*represent and get sequence conjugate, s (k) represents the time-domain training sequence sent, and n (k) represents additive white Gaussian noise, and its average is zero, variance
ε represents with the normalized carrier wave frequency deviation of subcarrier spacing and ε=ε
f+ ε
i, N=256, M=64, L=4, m=2, wherein ε
ffor fractional frequency offset estimated value, ε
ifor integer frequency offset estimation value; Based on above formula, when | ε
f| during < L/2m, fractional frequency offset can be estimated as:
12) to P
rk () carries out the compensate of frequency deviation of point several times, obtain the training sequence P after fractional frequency offset compensation
r' (k),
Described compensate of frequency deviation obtains fractional frequency offset estimated value
after, utilize estimated value
in time domain, frequency compensation is carried out to training sequence, as follows:
P
r' (k)=P
r(k) e
-j α; In formula
13) at frequency domain to P
r' (k) carry out thick synchronous, obtains the integer frequency offset estimation value of subcarrier spacing
Described frequency domain is synchronously slightly first to P
r' (k) and local transmission training sequence P
tk () is Fourier transform FFT and is obtained its frequency domain data R (k) and P
trk (), respectively to frequency domain data R (k) and P
trk () carries out calculus of differences, definition calculus of differences:
R
diff(k)＝R
*(k)·R(k+8)
R
diff(k) and ref
diffk () represents frequency domain data R (k) and P respectively
trk () carries out the data after calculus of differences;
Then to difference sequence R
diff(k) and ref
diffk () is in sliding cross-correlation calculating, the displacement when cross correlation value reaches maximum is the size of integer frequency offset, integer frequency offset estimation value
be calculated as follows and obtain:
Wherein-3≤i≤3, it comes relevant with training sequence in the spacing of the non-zero points of frequency domain, and the scope of integer frequency offset estimation is [-3,3], exceeds the integer frequency offset estimation that can make the mistake;
2) described frequency deviation decision steps adjudicates described step 1) middle gained frequency deviation estimated value is the need of carrying out frequency deviation control, and concrete grammar is:
21) obtaining step 1) the total estimated value of gained carrier wave frequency deviation ε
to P frequency deviation estimated value
be averaged and obtain frequency deviation average
22) require to arrange the frequency deviation control objectives scope that receiver normally works according to Communication System Design
wherein f
srepresent the maximum frequency deviation value of system requirements, judge frequency deviation average
whether meet this target zone, satisfied then do not carry out frequency deviation control, otherwise frequency deviation control is carried out to it;
3) described frequency controlling step adjusts the control voltage of temperature complement voltage-control oscillator TCXO adaptively thus revises frequency deviation, store control coefrficient s and control voltage v' simultaneously, to increase the efficiency automatically controlled after system power failure, concrete grammar is: 31) calculate control coefrficient initial value s: the frequency deviation obtained due to frequency deviation estimating step
be the deviation of corresponding radio-frequency carrier, if carrier frequency is p times of TCXO frequency, then described frequency deviation average is converted to the frequency difference of TCXO frequency
voltage controlled oscillator control voltage v is directly proportional to frequency of oscillation f, i.e. f=av+b, and wherein a, b are constant, obtains Δ f=a Δ v, obtains
32) to above-mentioned steps 2) judgement gained need the frequency deviation average of carrying out frequency deviation control to carry out frequency deviation adjustment, by
calculate the difference DELTA v that voltage controlled oscillator control voltage v should adjust, adjustment voltage controlled oscillator control voltage is v'=v+ Δ v, and wherein v' is the control voltage value after adjustment,
33) to step 32) frequency deviation control after effect judge, control after frequency deviation meet
then store this control voltage v', if frequency deviation does not still meet after controlling, after Corrective control coefficient s, repeat 32).
2. a kind of fast digital auto frequency control method for OFDM receiver according to claim 1, it is characterized in that described step 11) send the subcarrier transmission data that leading training sequence uses the integral multiple of 4 on frequency domain, other subcarrier is empty, therefore it comprises 4 64 short training sequences in time domain, first short training sequence A represents, second short training sequence is the repetition of first short training sequence, third and fourth short training sequence is the negative value of first short training sequence, is expressed as A, A ,-A ,-A.
3. a kind of fast digital auto frequency control method for OFDM receiver according to claim 1, it is characterized in that, described P point is averaged, and P is 1.
4. a kind of fast digital auto frequency control method for OFDM receiver according to claim 1, is characterized in that described step 3) in frequency deviation control coefrficient s is calibrated, method is:
wherein Δ v is the difference of control voltage,
for the frequency deviation average before frequency deviation control,
for the frequency deviation average after frequency deviation control.
5. a kind of fast digital auto frequency control method for OFDM receiver according to claim 1, it is characterized in that described step 3) in, storage is carried out for the control voltage v' meeting system frequency deviation requirement and adopts majority decision method, repeated storage is in multiple address, read the magnitude of voltage of this position after system reboot, will occur that the maximum value of ratio is as control voltage initial value.
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| CN103647739A (en) * | 2013-10-28 | 2014-03-19 | 上海大学 | OFDM-PON uplink frame synchronization method |
| CN104702554B (en) * | 2013-12-09 | 2017-12-15 | 瑞昱半导体股份有限公司 | Offset correction of carrier frequency method |
| CN106330315B (en) * | 2015-06-15 | 2019-02-05 | 深圳市中兴微电子技术有限公司 | A kind of data processing method and device |
| CN109391580B (en) * | 2017-08-04 | 2021-06-15 | 安立股份有限公司 | Synchronization device and synchronization method |
| CN110113285B (en) * | 2019-05-05 | 2021-06-11 | 东南大学 | OFDM system closed-loop time-frequency synchronization method and device |
| CN110417701B (en) * | 2019-07-23 | 2021-09-07 | 东南大学 | Method and device for identifying OFDM (orthogonal frequency division multiplexing) equipment based on preamble differential spectrum |
| CN117014279A (en) * | 2023-10-07 | 2023-11-07 | 成都国恒空间技术工程股份有限公司 | Differential integer frequency offset estimation method of OFDM system |
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| Title |
|---|
| Hyungu Hwang;Daeho Kim.Automatic Frequency Control in Packet Based OFDM Systems.《2011 17th Asia-Pacific Conference on Communications (APCC)》.2011,259 - 263. * |
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| Publication number | Publication date |
|---|---|
| CN103117980A (en) | 2013-05-22 |
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