CN102420793A - Tracking control method of digital communication receiver time and carrier frequency synchronization - Google Patents

Abstract

The invention belongs to the field of digital communication receivers, and relates to a tracking control method of digital communication receiver time and carrier frequency synchronization. The tracking control method comprises the following steps of: selecting a parameter of a PID (Proportion Integration Differentiation) controller; obtaining a decimal time deviation R(k) between the carrier frequency and a symbol; obtaining a residual deviation E(k) subjected to former deviation correction; carrying out following clinical value regulation on the decimal time deviation R(k): calculating a deviation correction value U(k) of the tracking control; and judging whether the U(k) is in the specified range, if not, resetting the parameter of the PID controller, if yes, carrying out carrier frequency and symbol time synchronization by using the correction value. The invention can better eliminate influences of steady-state errors, and is not sensitive to influence of quality of the tracking control to the control coefficient, thereby ensuring that the control coefficient is determined more simply and easily.

Description

The tracking and controlling method of a kind of digital communication receiver time and carrier frequency synchronization

Affiliated technical field

The invention belongs to the digital communication receiver field, particularly a kind of digital audio broadcasting receiver that meets the DRM standard.

Background technology

The DRM digital broadcasting is a kind of global digital audio broadcast standard of being formulated by european telecommunication alliance (ETSI).This standard is present unique in the world digital audio broadcast standard of supporting amplitude modulation and fm band simultaneously, is applicable to the frequency range below the 174MHz frequency, can be used for the digital improvement of intermediate waves analog AM and VHF wave band analog fm broadcasting.Because itself and case of conventional analog broadcast have high degree of compatibility aspect bandwidth occupancy, and can make full use of existing transmitter, make its development very fast, the multinational DRM broadcasting of having started broadcasting separately in Europe.

The modulation system that the broadcasting of DRM digital audio is adopted is OFDM (OFDM).OFDM (Orthogonal Frequency Division Multiplexing) is an orthogonal frequency division multiplexi, is a kind of of multi-carrier modulation (Multi-Carrier Modulation).The basic principle of OFDM technology is to be the plurality of sub channel with whole channel distribution, uses a number of sub-carrier to modulate on each subchannel, and these subcarriers are mutually orthogonal, thereby subchannel is also mutually orthogonal each other.The highspeed serial data stream of in whole channel, transmitting has like this become the low-speed parallel data of in each subchannel, transmitting, and makes that the symbol time of corresponding data is elongated.Thereby strengthened opposing multipath interference capability, improved the ability of channel transmission data.

The major advantage of OFDM technology is: enhancing signal opposing multipath interference capability, improved bandwidth utilization, and under band-limited situation, make the transmission rate of data be greatly improved.The major defect of OFDM technology comprises two aspects: extremely strong frequency sensitivity and very high peak-to-average power ratio.Extremely strong frequency sensitivity is presented as very strict synchronous requirement aspect digital receiver.

In DRM digital audio broadcasting receiver, OFDM mainly comprises following aspect synchronously: the frequency of carrier wave and Phase synchronization; Sample frequency and sampling time are synchronous; Symbol time synchronously and the DRM transmission frame synchronously.Wherein, the synchronous whether accurate performance to whole DRM digital receiver of carrier frequency and symbol time has very big influence.Present synchronization and estimation technology basically all with being divided into synchronously of carrier frequency and symbol time thick synchronously with thin two parts synchronously, the acquisition phase that slightly is otherwise known as synchronously, tracking phase synchronously carefully is otherwise known as.For carrier frequency synchronization, thick mainly is synchronously in order to obtain the subcarrier spacing frequency deviation of integral multiple, then is in order to obtain the subcarrier spacing frequency deviation of little several times synchronously carefully.And synchronous for symbol time, slightly be in order to obtain the sampling time interval skew of integral multiple synchronously, carefully be in order to obtain the sampling time interval skew of little several times synchronously.

In DRM digital audio broadcasting receiver, it is synchronous to obtain accurate carrier frequency and symbol time.Carrier frequency and symbol time should comprise estimation of deviation and tracking Control two parts synchronously.In the present simultaneous techniques, very ripe for the estimation technique of integer frequency offset and the skew of integral multiple sampling time interval, and corresponding correcting method is also very simple.But, then not very perfect for the research of the method for synchronous of fractional part of frequency offset and decimal sampling time interval skew, particularly there is bigger defective in tracking control technology.A kind of tracking control technology commonly used is that the weighted value that this decimal times estimation of deviation is worth the correction value of the same once time synchronization is subtracted each other, with the difference that obtains as this subsynchronous correction value.The major defect that this technology exists is following: owing to receive the influence of the factors such as frequency selective fading of multipath effect, Doppler effect and channel, make the signal that receives be difficult to represent with precise math model, in this case; Definite comparison difficulty that just can become of weights coefficient, coefficient is too small, can make that lock in time is elongated; Coefficient is excessive; Then can make the correction value inaccuracy, influence synchronous precision, can there be the steady-state error that is difficult to eliminate in this control technology.

Summary of the invention

The objective of the invention is to overcome the above-mentioned deficiency of prior art, provide a kind of can the fine influence that must eliminate steady-state error, the tracking and controlling method of the digital audio broadcasting receiver that is easy to realize.The present invention is to provide a kind of automatic tracking control method of the PID of employing control; This method can the fine influence that must eliminate steady-state error; And the quality of tracking Control is very inresponsive to the influence of control coefrficient, thereby makes control coefrficient must confirm to become fairly simple, realizes easily.Technical scheme of the present invention is following:

The tracking and controlling method of a kind of digital communication receiver time and carrier frequency synchronization comprises the following steps:

1), chooses three parameters of PID controller: proportionality coefficient K according to the characteristic that receives signal _P, integral coefficient K _IWith differential coefficient K _D, set up DRM digital audio broadcasting receiver isochronous controller based on PID control;

The sequence number of 2) establishing the OFDM symbol is k, and carrier frequency or symbol time deviation are estimated, obtains carrier frequency and intersymbol decimal times deviation R (k);

3) the estimated bias R (k) that calculates current acquisition subtracts each other with previous bias correction value, obtains through the residual deviation E (k) after the preceding bias correction;

4) decimal times deviation R (k) is carried out following critical value adjustment:

$\left\{\begin{array}{cc}R\left(k\right)=R\left(k\right),& -0.5\&le;R\left(k\right)\&le;0.5\\ R\left(k\right)=R\left(k\right)-1,& R\left(k\right)>0.5\\ R\left(k\right)=R\left(k\right)+1,& R\left(k\right)<-0.5\end{array}\right.$

5) proportional parts Δ P (the k)=K in the calculating correction value increment _P* E (k);

6) integral part Δ I (the k)=K in the calculating correction value increment _I* ∑ E (k), ∑ E (k) sues for peace to a preceding k+1 residual deviation;

7) differential part Δ D (the k)=K in the calculating correction value increment _D* [E (k)-E (k-1)], wherein, E (k-1) is the residual deviation that obtains in the last secondary tracking control procedure;

8) calculate the correction value increment,, obtain incremental portion Δ U (k)=Δ P (k)+Δ I (the k)+Δ D (k) of this correction three part additions of the correction value increment that obtains in above-mentioned three steps;

9), obtained the bias correction value U (k) of this tracking Control with the correction value increment addition of previous bias correction value and acquisition in the last step;

10) judge that U (k) whether in the scope of regulation, if not in prescribed limit, then need reset the PID controller parameter; If the regulation scope in, then use this correction value carry out carrier frequency and symbol time synchronous.

Adopt DRM digital audio broadcast software receiver of the present invention on PC platform and embedded platform, all to realize.The application platform of the embedded-type ARM platform of Windows CE 6.0 operating systems as DRM digital audio broadcast software receiver is equipped with in employing, and the DRM signal source file that adopts the generation of DRM signal source software transmitter is as the test source file.Through acceptance test; Adopt DRM digital audio broadcast software receiver of the present invention can receive continuously voice signal clearly in real time; Explain that the present invention not only can realize the automatic tracking Control of carrier frequency and symbol time accurately; And realizing simply, consumes resources is few, can be in the very limited embedded platform use down of resource.

Description of drawings

Fig. 1 is a FB(flow block) of the present invention.

Fig. 2 is PID control principle figure, and R (k) is a decimal times estimation of deviation value, and E (k) is a residual deviation, K _PBe PID controller proportionality coefficient, K _IBe PID controller integral coefficient, K _DBe PID controller differential coefficient, U (k-1) is a preceding bias correction value, and U (k) is this bias correction value.

Embodiment

As shown in Figure 1, the present invention includes three key steps: the obtaining of pid control parameter, carrier frequency and the decimal times estimation of deviation of symbol time and the calculating of bias correction value.Concrete scheme is following:

One, pid control parameter obtains

PID control is meant ratio, integration, differential control.When the structure and parameter of controlled device can not be on top of, or when can not get precise math model, other technology of control theory is difficult to adopt, and the structure and parameter of system controller must rely on experience and field adjustable to confirm.At this moment the thereof using PID control technology is the most convenient, and this also is the main cause that the present invention adopts this method.Below the basic principle of concise and to the point narration PID control technology:

1. ratio (P) control section.

Proportional control is the simplest a kind of control mode.The output of its controller and the proportional relation of error originated from input signal.When proportional control only, there is steady-state error in system's output.Implementation method as shown in the formula:

U(t)＝K _p*E(t) (1)

K in the formula _PBe proportionality coefficient.

2. integration (I) control section.

In order to eliminate steady-state error, in controller, must introduce integral.Integral is to the integration of error seeking time, and along with the increase of time, integral can increase.Add the proportional control part, proportional+integral (PI) controller can make system after getting into stable state, not have steady-state error.The integral control implementation method as shown in the formula:

$U\left(t\right)=\frac{1}{T_I}{\&Integral;}_0^{t}E\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}---\left(2\right)$

T wherein _IBe the time of integration.

3. differential (D) control section.

Differential control can reduce overshoot, overcomes vibration, and the stability of system is improved, and accelerates the dynamic responding speed of system simultaneously, reduces the adjustment time, thereby improves the dynamic property of system.Implementation method as shown in the formula:

$U\left(t\right)=T_D\frac{\mathrm{dE}\left(t\right)}{\mathrm{dt}}---\left(3\right)$

4. implementation.

Can adopt forms such as PI, PD or PDI.The universal expression formula of PID control model is:

$U\left(t\right)=K_p*E\left(t\right)+K_p*\frac{1}{T_I}{\&Integral;}_0^{t}E\left(\mathrm{\&tau;}\right)\mathrm{d\&tau;}+K_p*T_D\frac{\mathrm{dE}\left(t\right)}{\mathrm{dt}}---\left(4\right)$

Under numeric field, replace integration with summation, replace difference quotient with difference coefficient, formula 4 becomes:

$U\left(k\right)=K_{p}E\left(k\right)+K_I\underset{j=0}{\overset{k}{\mathrm{\&Sigma;}}}E\left(j\right)+K_D[E\left(k\right)-E(k-1)]+U_0---\left(5\right)$

U in the formula ₀Be the base value of controlled quentity controlled variable, i.e. the value of U (k) during k=0.Make K _I=K _P* T _S/ T _I, K _D=K _P* T _D/ T _S, T _SBe the sampling period, just can obtain PID control principle figure, like Fig. 2.

5.PID the parameter tuning of controller

The parameter tuning of PID controller is a size of confirming proportionality coefficient, the time of integration and the derivative time of PID controller according to the characteristic of controlled process.The present invention adopt engineering adjust in aritical ratio method method commonly used, directly examination is gathered and is obtained parameter.The step of adjusting of examination method of gathering is " first ratio, integration again, last differential ".

1) proportional control of adjusting

The proportional control effect is big by changing to for a short time, observe each secondary response, until obtaining reacting fast, the little response curve of overshoot.

2) integral element of adjusting

Earlier the proportionality coefficient of selecting in the step 1) is reduced to originally 50～80%, will puts a higher value, observed responses curve the time of integration again.Reduce the time of integration then, strengthen integral action, and corresponding resize ratio coefficient, examination is gathered to obtaining satisfied response repeatedly, confirms the parameter of ratio and integration.

3) differentiation element of adjusting

After the parameter of ratio and integration obtains, the differentiation element of just can adjusting.The differentiation element of adjusting is in order to accelerate the dynamic responding speed of system.If less demanding to dynamic process in practical application, simple in order to realize, also can cast out differentiation element.The PID controller just has been simplified to the PI controller like this.

Two, the decimal of carrier frequency and symbol time times estimation of deviation

The present invention is not directed against the decimal times bias estimation method of particular carrier wave frequency and symbol time.In the present invention, the fractional part of frequency offset difference of carrier frequency adopts the frequency domain algorithm for estimating; The decimal of symbol time times deviation adopts the related algorithm in the channel equalization to estimate.

1. the carrier frequency fractional part of frequency offset is estimated

The fractional part of frequency offset of supposing carrier frequency is Δ f, and an OFDM symbol time is spaced apart T _S, then per elapsed time T _S, the phase increment Φ that produces on each subcarrier _kEqual Δ f and T _SProduct.And all have three pilot value in the middle of each OFDM symbol of DRM signal, and these three pilot tones are at an OFDM mark space T _SThe interior phase increment that produces can be calculated at receiving terminal easily, so just can calculate the fractional part of frequency offset of carrier frequency according to above-mentioned relation.

2. the decimal of symbol time times estimation of deviation

The decimal of symbol time times deviation delta t is to adopt a kind of time deviation method of estimation based on channel estimating to estimate.This method is included into the decimal times deviation of the symbol time part as channel latency in the process of channel estimating.At first, the expression formula of channel is postponed to handle, the delay of channel is increased Δ t; Then, the sampled value that obtains after the channel estimating is carried out zero padding, the data after the zero padding are added the Hamming window processing; Then, the data after the windowing are carried out IFFT (inverse fast fourier transform), the delay-energy spectrum that has so just obtained channel is estimated; At last, obtain the decimal times deviation delta t of symbol time through the peak value of search delay-energy spectrum.

Three, the calculating of bias correction value

The calculating of bias correction value is on the basis of the decimal times deviation of known PID controller parameter and carrier frequency and symbol time, to carry out.Wherein the PID controller parameter can reconfigure before the bias correction value is calculated, thereby can make whole synchronous tracking Control process can carry out real-time adjustment, made whole tracking Control process have higher flexibility.After obtaining each parameter of PID controller; At first; Need carry out critical value adjustment with the symbol time deviation to the carrier frequency of the little several times estimating to obtain; Because the influence of factors such as multidiameter fading channel, phase noise, estimation quantization error possibly make estimated value generation phase hit, promptly estimate deviate generation phase hit; Then, carrier frequency and the symbol time deviation and the preceding bias correction value that once calculates of the little several times of estimating to obtain are subtracted each other, obtain passing through the residual deviation after correction last time; Then; Utilize each calculation of parameter of this residual deviation and PID controller to go out the incremental portion of this bias correction value than a preceding bias correction value, concrete grammar is that the ratio, integration and the differential coefficient that utilize PID respectively calculate proportional parts, integral part and differential part in the correction value increment; At last, with correction value incremental portion that obtains and the addition of previous bias correction value, obtain this bias correction value.It should be noted that each correction value incremental portion should be controlled within the scope for the wrong estimation effect of concussion of minimizing system and elimination burst.So, if the correction value that obtains not within control range, then need be obtained the PID controller parameter again, repeat the aforesaid operations step, up to the bias correction value of obtaining in control range, and this bias correction value is applied to synchronous correction.

Accomplish after above-mentioned three steps, just accomplished the synchronous tracking Control of time and carrier frequency.Below demodulation, during an OFDM symbol, repeat aforesaid operations, just can dynamically realize the automatic tracking Control of time and carrier frequency synchronization.

Be a specific embodiment of the present invention below:

1), sets the parameter of PID controller according to the PID controller parameter middle method of adjusting.Simple for what realize, can cast out calculating, because the differential part is very little to the influence of whole tracking Control process to differential coefficient.For the carrier frequency synchronization tracking Control, the preset proportion COEFFICIENT K _PBe 0.5, integral coefficient K _IBe 0.001; For the time synchronized tracking Control, the preset proportion COEFFICIENT K _PBe 0.1, integral coefficient K _IBe 0.0003.Above-mentioned parameter remains unchanged in whole synchronous tracking Control process.

2) sequence number of pilot frequency carrier wave is 16,48,64.Hamming window W (n) equals 0.54+0.46*cos (2* π * n/N), when | when n| is not more than N/2/; W under other situation (n) equals 0, wherein N=512.Counting of IFFT conversion is 512.

3) when carrying out the synchronous tracking Control of symbol time, if the bias correction value that calculates is greater than 2; Perhaps when carrying out the carrier frequency synchronization tracking Control, if the bias correction value that calculates greater than 1, must be adjusted the parameter of PID controller.

Claims (1)

1. the tracking and controlling method of digital communication receiver time and carrier frequency synchronization comprises the following steps:

1), chooses three parameters of PID controller: proportionality coefficient K according to the characteristic that receives signal _P, integral coefficient K _IWith differential coefficient K _D, set up DRM digital audio broadcasting receiver isochronous controller based on PID control;

The sequence number of 2) establishing the OFDM symbol is k, and carrier frequency or symbol time deviation are estimated, obtains carrier frequency and intersymbol decimal times deviation R (k);

3) the estimated bias R (k) that calculates current acquisition subtracts each other with previous bias correction value, obtains through the residual deviation E (k) after the preceding bias correction;

4) decimal times deviation R (k) is carried out following critical value adjustment:

$\left\{\begin{array}{cc}R\left(k\right)=R\left(k\right),& -0.5\&le;R\left(k\right)\&le;0.5\\ R\left(k\right)=R\left(k\right)-1,& R\left(k\right)>0.5\\ R\left(k\right)=R\left(k\right)+1,& R\left(k\right)<-0.5\end{array}\right.$

5) proportional parts Δ P (the k)=K in the calculating correction value increment _P* E (k);

6) integral part Δ I (the k)=K in the calculating correction value increment _I* ∑ E (k), ∑ E (k) sues for peace to a preceding k+1 residual deviation;

7) differential part Δ D (the k)=K in the calculating correction value increment _D* [E (k)-E (k-1)], wherein, E (k-1) is the residual deviation that obtains in the last secondary tracking control procedure;

8) calculate the correction value increment,, obtain incremental portion Δ U (k)=Δ P (k)+Δ I (the k)+Δ D (k) of this correction three part additions of the correction value increment that obtains in above-mentioned three steps;

9), obtained the bias correction value U (k) of this tracking Control with the correction value increment addition of previous bias correction value and acquisition in the last step;

10) judge that U (k) whether in the scope of regulation, if not in prescribed limit, then need reset the PID controller parameter; If the regulation scope in, then use this correction value carry out carrier frequency and symbol time synchronous.

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