CN101471726B - Digitalized automatic frequency correction method based on true frequency reference signal - Google Patents

Abstract

The invention discloses a digital automatic frequency correction method based on real frequency reference signals, which relates to the technical field of frequency synchronization of a transiting side and a receiving side in communication. The method comprises the following steps: sampling a channel of real received signals; under the condition that the real frequency reference signal exists in the received signals, calculating the frequency error function of the local frequency source signal and the received frequency reference signal; correcting the frequency of the local frequency source according to the frequency error function, thereby achieving the frequency synchronization between the transiting side and the receiving side. Compared with the prior frequency correction method based on complex frequency reference signals, the digital automatic frequency correction method doesn't need to acquire the mutually-orthogonal complex frequency reference signals of the channel I and the channel Q; overcomes the problem of imbalance compensation of the channel I and the channel Q; and therefore, greatly reduces the complexity of system implementation on the premise of ensuring the frequency correction accuracy.

Description

Digitlization automatic frequency correcting method based on the real frequency reference signal

[technical field]

The present invention relates to the Frequency Synchronization system in the field of communication transmission, relate in particular to a kind of digitlization automatic frequency correcting method based on the real frequency reference signal.

[background technology]

In telecommunication transmission system, the frequency source signal frequency of receiving terminal need be consistent with the frequency source signal frequency of transmitting terminal usually.In order to accomplish this point, a kind of method that can adopt is to adopt high-precision crystal oscillator at transmitting-receiving two-end.It is expensive that but high-precision crystal oscillator compares usually, and meeting occurrence frequency drift after long-time the use, need regularly carry out manual frequency and proofread and correct.

The another kind of method that can adopt is to send a frequency reference signal (being called calibrating frequency signal or pilot signal again) by transmitting terminal to receiving terminal; Receiving terminal carries out from dynamic(al) correction the frequency of local frequency source signal according to the frequency reference signal that receives; Make the frequency of local frequency source signal in the scope that precision allows, follow the tracks of frequency, thereby reach the purpose of receiving-transmitting sides Frequency Synchronization in frequency reference signal.This method is called automatic frequency tracking or automatic frequency correction.

Sometimes frequency reference signal is not to exist always, but intermittently send.Must detect in the received signal whether have frequency reference signal earlier this moment before implementing automatic frequency correction.Only under the prerequisite that frequency reference signal exists, just can implement automatic frequency correction.

In automatic frequency correction, only need a common voltage controlled oscillator (VCO) and some control circuits just can realize high-precision Frequency Synchronization usually, not only less expensive, and frequency correction is to accomplish automatically, does not need regularly to carry out artificial calibrating frequency.

An exemplary of automatic frequency correction is the frequency correction between base station and travelling carriage or the repeater in the gsm mobile communication system.The base station every sent a duration at a distance from about 46ms or 51ms and is about the calibrating frequency burst packets (FCB) of 577s in the downlink broadcast channel, i.e. frequency reference signal, and travelling carriage or repeater can be according to the frequency source frequencies of these FCB corrections oneself.

Automatic frequency correcting method is divided into analog and digital two kinds.Analog automatic frequency correcting method obtains to be used for the adjustment signal of frequency correction through the processing to analog signal; Digital automatic frequency correcting method is then first with analog signal digital, and then through digital signal being handled the adjustment signal that obtains to be used for frequency correction.

Common digital automatic frequency correcting method is that the plural form (being the mutually orthogonal real frequency reference signal of I, Q two-way) according to the receive frequency reference signal is implemented, for example United States Patent (USP) bulletin US 6226336B1 and US2005/0129149A1.This digital automatic frequency based on the complex frequency reference signal detects and the handled sampled data of bearing calibration is a plural number, and its real part and imaginary part are respectively the real number sample values that I, the mutually orthogonal real frequency reference signal sampling of Q two-way is obtained at synchronization.

Yet the digital automatic frequency correcting method based on the complex frequency reference signal has higher complexity.The I, the Q two-way frequency reference signal that obtain plural form need carry out the quadrature frequency conversion to be realized through road frequency reference signal to real number form, and this is much more complicated than the road frequency reference signal that obtains real number form; In addition; It is unbalance in the process that obtains I, Q two-way frequency reference signal, may to introduce some again; Comprise amplitude imbalance (I, Q two-way amplitude different), phase imbalance (I, Q two-way phase place non-orthogonal) etc., these are unbalance can to influence the precision of automatic frequency correcting method.Need to compensate unbalance in order addressing this problem, but to do and can make the complexity increase that system realizes like this.

[summary of the invention]

The object of the invention is exactly for overcoming the above-mentioned higher shortcoming of digital automatic frequency correcting method complexity based on the complex frequency reference signal, a kind of digitlization automatic frequency correcting method based on the real frequency reference signal being provided.

For this reason, the present invention takes following technical scheme to realize:

The present invention's the digitlization automatic frequency correcting method based on the real frequency reference signal, its frequency reference signal are from transmitting terminal, and acquiescence exists or confirms to exist through frequency detecting, comprising:

One road intermediate frequency or the baseband analog real signal of the end of spontaneous emission in the future sampled, analog-to-digital conversion is the step of digital signal;

Calculate the step of the frequency error function of local frequency source signal and transmitting terminal frequency source signal with this reality sampled data;

There is or when frequency detecting is confirmed marking signal set that frequency reference signal exists the result of calculation of the gating frequency error function step of line data conversion of going forward side by side with the adjustment increment that obtains the frequency of this locality is adjusted at the said frequency reference signal of acquiescence;

Said adjustment increment is added up to obtain the step of local frequency source numeral adjustment signal;

This numeral adjustment signal is converted to the step of simulation adjustment signal;

This simulation adjustment signal is carried out the step that filtering forms local frequency source control voltage;

Realize that with the local frequency source of this frequency source control voltage control local frequency adjustment makes it the step with the Frequency Synchronization of transmitting terminal.

In said sampling, the analog-to-digital step; Sampling clock is obtained through frequency division/frequency multiplication by local frequency source signal; According to transmitting-receiving frequency difference allowed bands different in the practical application; Sample frequency is got the different preset value with the ratio of local frequency source signal frequency, and sample frequency changes along with the adjustment of local frequency source.

In the step of said calculated rate error function; The frequency error function by 2 times of the difference of the product of two groups of said signal real sampled datas through the acquisition of level and smooth back; Wherein every group all comprises two real sampled datas; In one group in the sampling instant sum of two real sampled datas and another group the sampling instant sum of two real sampled datas equate that the difference of the sampling instant of two real sampled datas is the odd in sampling time in every group.

In the step of said calculated rate error function; More specifically; In said two groups of real sampled datas, after two real sampled datas of every group multiply each other through multiplier, two groups of real sampled datas product all export subtracter to and calculate both poor; Then it is carried out smoothing processing, obtain said frequency error function.

In the step of said acquisition adjustment increment, the marking signal that is existed by said mark frequency reference signal triggers a gate, makes its result of calculation that allows said frequency error function carry out data conversion through a converter, with the said adjustment increment of final acquisition.

The said data conversion that the frequency error function is carried out is monotonic transformation.Monotone increasing still is that monotone decreasing was determined by the selected sampling time.

Compared with prior art, the invention has the advantages that:

At first; Only need are directly handled the real sampled data of the frequency reference signal signal (i.e. one road real frequency reference signal) of real number form; Just can calculate the required adjustment amount of frequency correction, and the frequency reference signal of plural form sampled and handle and want much simple;

Secondly,, also do not have the imbalance compensation problem, so the present invention has reduced the complexity that system realizes greatly under the prerequisite of guaranteeing the frequency correction precision owing to need not to obtain I, the mutually orthogonal frequency reference signal of Q two-way of plural form;

Moreover the present invention is convenient to adopt dsp chip, fpga chip or asic chip to wait to realize.

[description of drawings]

Fig. 1 is the theory diagram of the system that is the basis of the digitlization automatic frequency correcting method based on the real frequency reference signal with the present invention;

Fig. 2 is a parameter A in the embodiment of the invention ²The algorithm structure sketch map of [n], C [n], S [n];

Fig. 3 is a parameter A in the embodiment of the invention ² _L[n], C _M[n], S _NThe algorithm structure sketch map of [n];

Fig. 4 is the algorithm structure sketch map that calculates local frequency source adjustment signal in the embodiment of the invention;

Fig. 5 is in the embodiment of the invention, when frequency reference signal existence and noiseless, and detection metric C _M[n] and frequency error function S _NThe relation curve of [n] and sampling time τ.

[embodiment]

Below in conjunction with accompanying drawing, specific embodiment of the present invention and principle are done detailed explanation:

As shown in Figure 1; The present invention's the digitlization automatic frequency correcting method based on the real frequency reference signal in another application, protects simultaneously with the applicant and the open in this application digitlization automatic frequency detection method based on real signal is realized therein, comprises A/D converter (also being A-D converter) 102, automatic frequency and correcting algorithm module 104, D/A converter (also being digital-to-analog converter) 106, low pass filter 108, voltage controlled oscillator 110 and frequency division/frequency multiplier 112.

In Fig. 1, the simulation real signal r (t) of reception comes from the intermediate frequency or the base band output of transmitting terminal.R (t) is through the sampling and the analog to digital conversion of A/D converter 102, and the digital real signal r [n] that obtains dispersing sends into automatic frequency and correcting algorithm module 104.

The sampling clock of A/D converter 102 is provided by the local frequency source that voltage controlled oscillator 110 and frequency division/frequency multiplier 112 constitute.If the frequency of the frequency reference signal of the real signal that is received is f; The frequency of local frequency source signal is f+ Δ f; Frequency error between then local frequency source signal and the said frequency reference signal is Δ f, and the relation of sampling time τ and local frequency source signal frequency f+ Δ f does

$\mathrm{\τ}=\frac{4k+1}{4(f+\mathrm{\Δf})},$

Or

$\mathrm{\τ}=\frac{4k+3}{4(f+\mathrm{\Δf})}.$

Wherein k is a design parameter, and k ∈ 0,1,2 ... }, can choose according to the needs of practical application.

Because there is frequency error Δ f in local frequency source, the sampling time τ that therefore chooses according to above-mentioned relation is uncertain, and in the present invention, its scope that allows to change does

$\frac{k}{f}<\mathrm{\&tau;}<\frac{2k+1}{2f},$

Or

$\frac{2k+1}{2f}<\mathrm{\&tau;}<\frac{k+1}{f}.$

The permission excursion of corresponding frequency error does with it

$-\frac{f}{4k+2}<\mathrm{\&Delta;f}<\frac{f}{4k},$

Or

$-\frac{f}{4k+4}<\mathrm{\&Delta;f}<\frac{f}{4k+2}.$

That is to say,,, then can realize that with the present invention automatic frequency detects and proofreaies and correct if frequency error Δ f is within the above-mentioned permission excursion in case selected sampling time τ according to above-mentioned relation; , can't realize frequency error Δ f that automatic frequency detects and proofreaies and correct otherwise will exceeding correcting range of the present invention.

The algorithm structure of automatic frequency and correcting algorithm module 104 inside such as Fig. 2, Fig. 3, shown in Figure 4.This algorithm at first in Fig. 2 according to following formula

A ²[n]＝r ²[n]+r ²[n-1]，

C[n]＝2(r[n]r[n-4]-r[n-1]r[n-3])，

S[n]＝2(r[n]r[n-3]-r[n-1]r[n-2])；

Accomplish A respectively ²The calculating of [n], C [n], S [n]; Then in Fig. 3 according to following formula

$A_L^2\left[n\right]=\frac{1}{L}\underset{m=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{A}^2[n-m],$

$C_M\left[n\right]=\frac{1}{M}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}C[n-m],$

$S_N\left[n\right]=\frac{1}{N}\underset{m=0}{\overset{N-1}{\mathrm{\&Sigma;}}}S[n-m].$

To A ²[n], C [n], S [n] carry out respectively smoothly obtaining A ² _L[n], C _M[n], S _N[n].Wherein L, M, N are design parameter, and L, M, N ∈ 1,2,3 ... }, can choose according to the needs of application scenario.

A ² _LThe physical meaning of [n] is for receiving the estimated value of real signal power (or its 2 times), the decision threshold benchmark whether the real signal medium frequency reference signal that is received as detection exists here; C _MThe physical meaning of [n] is for detecting the detection metric whether the real signal medium frequency reference signal that received exists in certain frequency error range; S _NThe physical meaning of [n] is the frequency error function of local frequency source signal and frequency reference signal.

Only comprise 4 kinds of rudimentary algorithm unit among Fig. 2 and Fig. 3, they are delayer 202, multiplier 204, adder 206 and amplifier 208.

In Fig. 4, A ² _L[n] is as detecting the decision threshold benchmark whether frequency reference signal exists, through obtaining decision threshold α A after the amplifier 208 ² _L[n], wherein α is a design parameter, and α ∈ (0,1), can choose according to the needs of practical application.

C _M[n] as detect detection metric that whether frequency reference signal exist in threshold compataror 402 with decision threshold α A ² _L[n] compares, if

C _M[n]＞αA ² _L[n]，

Judge that then frequency reference signal exists,, trigger and open gate 404, allow S through producing a prearranged signal _N[n] passes through; Otherwise judge that frequency reference signal does not exist, produce another signal at stop gate 404, forbid S _N[n] passes through.

It is pointed out that above-mentioned to A ²[n], C [n], A ² _L[n], C _MThe calculating of [n], and utilize A ² _L[n], C _MWhether [n] exists the detection of being carried out to frequency reference signal is unwanted under the occasion that the given frequency reference signal exists always.

S _N[n] if frequency reference signal exists, then is added to converter 406 enterprising line translations through gate 404 as the frequency error function, obtains the adjustment increment of local frequency source.This adjustment increment is adjusted signal through the numeral that accumulator (being made up of delayer 202 and adder 206) obtains local frequency source afterwards, is sent to the D/A converter 106 among Fig. 1.

If the selected sampling time does

$\mathrm{\&tau;}=\frac{4k+1}{4(f+\mathrm{\&Delta;f})},$

Then work as

S _N[n]＞0

The time, sampling time τ is bigger than normal in expression, and the frequency of promptly local frequency source signal can be adjusted local frequency source signal this moment its frequency is increased less than the frequency of frequency reference signal.When

S _N[n]＜0

The time, sampling time τ is less than normal in expression, and the frequency of promptly local frequency source signal is greater than the frequency of frequency reference signal, and can adjust local frequency source signal this moment reduces its frequency.

If the selected sampling time does

$\mathrm{\&tau;}=\frac{4k+3}{4(f+\mathrm{\&Delta;f})},$

Then work as

S _N[n]＞0

The time, sampling time τ is less than normal in expression, and the frequency of promptly local frequency source signal is greater than the frequency of frequency reference signal, and can adjust local frequency source signal this moment reduces its frequency.When

S _N[n]＜0

The time, sampling time τ is bigger than normal in expression, and the frequency of promptly local frequency source signal can be adjusted local frequency source signal this moment its frequency is increased less than the frequency reference signal frequency.

For obtaining adjusting increment to S _NThe conversion that [n] implements can be ± ρ sign{S _N[n] } or ± ρ S _NForms such as [n], wherein

$\mathrm{sign}\left\{x\right\}=\left\{\begin{array}{cc}-1& x<0\\ 0& x=0,\\ 1& x>0\end{array}\right.\mathrm{\&rho;}>0;$

The choosing of positive and negative number and ρ depended on the symbol and the size with the voltage-controlled slope of curve of VCO of choosing in sampling time.

In Fig. 1; The numeral adjustment signal transformation that D/A converter 106 is calculated automatic frequency and correcting algorithm module 104 becomes simulation adjustment signal; Carry out forming voltage controlled oscillator 110 control voltages after the loop filtering through low pass filter 108 again; Control is by the local frequency source that voltage controlled oscillator 110 and frequency division/frequency multiplier 112 constitute, and makes the frequency-tracking of local frequency source signal in the frequency of receive frequency reference signal.

What more than describe is embodiment of the present invention, is further described in the face of principle of the present invention down.

Receiving real signal can be expressed as

Wherein Asin (2 π ft+ φ) is a frequency reference signal, and A, f, φ are respectively amplitude, frequency and the initial phase of frequency reference signal, and η (t) is a noise, and s (t) is other signal, and it is a random process.

This is to the explanation of inventive principle for ease, can make adjustment before VCO control voltage remain unchanged, promptly τ is constant the sampling time; And ignore the influence of noise η (t) for the time being; The sample sequence s [n] that supposes s (t) simultaneously is ergodic independent same distribution discrete random sequence, and average is 0, and variance is D ²/ 2.

When frequency reference signal does not exist, have

A ²[n]＝s ²[n]+s ²[n-1]，

C[n]＝2(s[n]s[n-4]-s[n-1]s[n-3])，

S[n]＝2(s[n]s[n-3]-s[n-1]s[n-2])；

$A_L^2\left[n\right]=\frac{1}{L}\underset{m=0}{\overset{L-1}{\mathrm{\&Sigma;}}}\left(s^2\right[n-m]+s^2[n-m-1\left]\right),$

$C_M\left[n\right]=\frac{1}{M}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}2\left(s\right[n-m\left]s\right[n-m-4]-s[n-m-1\left]s\right[n-m-3\left]\right),$

$S_N\left[n\right]=\frac{1}{N}\underset{m=0}{\overset{N-1}{\mathrm{\&Sigma;}}}2\left(s\right[n-m\left]s\right[n-m-3]-s[n-m-1\left]s\right[n-m-2\left]\right).$

When L, M, N → ∞, have

A ² _L[n]→D ²，

C _M[n]→0，

S _N[n]→0。

Adjudicate relational expression for certain given α ∈ (0,1) this moment

C _M[n]＞αA ² _L[n]

Be false, so when L, M, N choose enough greatly, C _M[n] can be used as the non-existent detection metric of judgement frequency reference signal.

When frequency reference signal exists, have

A ²[n]＝A ²-A ²cos(2πfτ))cos(2πf(2n-1)τ+2φ)，

C[n]＝A ²(cos(8πfτ)-cos(4πfτ))，

S[n]＝A ²(cos(6πfτ)-cos(2πfτ))；

$A_L^2\left[n\right]=A^2-{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="H2008101849759E00012.png,H2008101849759E00021.png"\; state="\{\{state\}\}">A</figure-callout>}}^2\cos \left(2\mathrm{\&pi;f\&tau;}\right)\frac{1}{L}\underset{m=0}{\overset{L-1}{\mathrm{\&Sigma;}}}\cos (2\mathrm{\&pi;f}(2n-2m-1)\mathrm{\&tau;}+2\mathrm{\&phi;}),$

C _M[n]＝A ²(cos(8πfτ)-cos(4πfτ))，

S _N[n]＝A ²(cos(6πfτ)-cos(2πfτ))。

When L, M, N → ∞, have

A ² _L[n]→A ²，

C _M[n]≡A ²(cos(8πfτ)-cos(4πfτ))，

S _N[n]≡A ²(cos(6πfτ)-cos(2πfτ))。

It is thus clear that C _M[n] and S _N[n] be the function of sampling time τ just, and irrelevant with sampling instant n, and the relation curve of they and τ is as shown in Figure 5.

Under the situation that frequency reference signal exists, if sampling time τ is chosen for

$\mathrm{\&tau;}=\frac{1}{4(f+\mathrm{\&Delta;f})},$

Then the permission excursion of sampling time τ does

$0<\mathrm{\&tau;}<\frac{1}{2f},$

The permission excursion that is frequency error Δ f does

$-\frac{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="H2008101849759E00012.png,H2008101849759E00021.png"\; state="\{\{state\}\}">f</figure-callout>}}{2}<\mathrm{\&Delta;f}<\&infin;.$

As can beappreciated from fig. 5, interval (0,1/2f) in, C _M[n] is even function with respect to τ=1/4f.As Δ f=0, promptly during τ=1/4f, C _M[n]=A ², reach maximum.F departs from 0 when Δ, when promptly τ departs from 1/4f, and C _M[n] diminishes gradually.Always exist the neighborhood δ (α) of τ=1/4f for certain given α ∈ (0,1) this moment, as τ ∈ δ (α), and when promptly frequency error Δ f is less than certain value of confirming, the judgement relational expression

C _M[n]＞αA ² _L[n]

Set up, so when L, M, N choose enough greatly, C _M[n] can be used as the detection metric that the judgement frequency reference signal exists in certain frequency error range.

It can also be seen that from Fig. 5, interval (0,1/2f) in, S _N[n] is odd function with respect to τ=1/4f.As Δ f=0, promptly during τ=1/4f, S _N[n]=0.When Δ f＜0, promptly during τ＞1/4f, S _N[n]＞0; Otherwise, when Δ f＞0, promptly during τ＜1/4f, S _N[n]＜0.Therefore known or detect under the situation that frequency reference signal exists, when L, M, N choose enough greatly, S _N[n] can be used as the frequency error function of local frequency source signal and frequency reference signal.

Through to S _N[n] carries out suitable conversion, can obtain the adjustment increment of local frequency source.The voltage-controlled curve of supposing VCO has positive slope, to S _NThe conversion of [n] can be ρ sign{S _N[n] }.If τ is near the scope of the relative narrower of 1/4f, then S _N[n] is approximately linear relationship with the relation of τ, and this moment is to S _NThe conversion of [n] also can be ρ S _N[n].Certainly, to S _NThe conversion of [n] can also have other form.

The adjustment increment of local frequency source is sent to the D/A converter and removes to produce VCO control voltage through after adding up.If Δ f＜0, i.e. τ＞1/4f, then adjust increment on the occasion of, VCO control voltage is increased, the frequency of local frequency source signal increases thereupon, thereby causes Δ f to increase; Otherwise, if Δ f＞0, i.e. τ＜1/4f, then adjusting increment is negative value, and VCO control voltage is reduced, the frequency of local frequency source signal reduces thereupon, thereby causes Δ f to reduce.Therefore, through above-mentioned corrective action, Δ f will be round 0 fluctuation up and down, thereby makes the frequency-tracking of local frequency source signal in the frequency of receive frequency reference signal, realizes the function of automatic frequency correction.

Under the situation that frequency reference signal exists, if sampling time τ is chosen for

$\mathrm{\&tau;}=\frac{3}{4(f+\mathrm{\&Delta;f})},$

Then the permission excursion of sampling time τ does

$\frac{1}{2f}<\mathrm{\&tau;}<\frac{1}{f},$

The permission excursion that is frequency error Δ f does

$-\frac{\mathrm{<figure-callout\; id="4"\; label="f"\; filenames="H2008101849759E00012.png"\; state="\{\{state\}\}">f</figure-callout>}}{4}<\mathrm{\&Delta;f}<\frac{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="H2008101849759E00012.png,H2008101849759E00021.png"\; state="\{\{state\}\}">f</figure-callout>}}{2}.$

As can beappreciated from fig. 5, interval (1/2f, the C in 1/f) _M[n] and S _N[n] respectively with interval (0, the C in 1/2f) _M[n] and S _N[n] shape is identical, but S _NThe opposite in sign of [n] is promptly at τ=S of 1/4f place _N[n] passes zero point with positive slope, and at τ=S of 3/4f place _N[n] passes zero point with negative slope.Therefore, identical with above-mentioned principle, when L, M, N choose enough greatly, C _M[n] still can be used as the detection metric that the judgement frequency reference signal exists in certain frequency error range, S _N[n] still can be used as the frequency error function of local frequency source signal and frequency reference signal, but when calculating local frequency source adjustment increment to S _NIn the conversion that [n] done, S _N[n] will use-S _N[n] replaces.

Above-mentioned conclusion is promoted.Under the situation that frequency reference signal exists, if sampling time τ is chosen for

$\mathrm{\&tau;}=\frac{4k+1}{4(f+\mathrm{\&Delta;f})},$

Then the permission excursion of sampling time τ does

$\frac{k}{f}<\mathrm{\&tau;}<\frac{2k+1}{2f},$

The permission excursion that is Δ f does

$-\frac{f}{4k+2}<\mathrm{\&Delta;f}<\frac{f}{4k}.$

If sampling time τ is chosen for

$\mathrm{\&tau;}=\frac{4k+3}{4(f+\mathrm{\&Delta;f})},$

Then the permission excursion of sampling time τ does

$\frac{2k+1}{2f}<\mathrm{\&tau;}<\frac{k+1}{f},$

The permission excursion that is Δ f does

$-\frac{f}{4k+4}<\mathrm{\&Delta;f}<\frac{f}{4k+2}.$

Wherein, k ∈ 0,1,2 ... }.For above two kinds of situation, when L, M, N choose enough greatly, C _M[n] can be as the detection metric of judgement frequency reference signal existence in certain frequency error range, S _N[n] can be as the frequency error function of local frequency source signal and frequency reference signal.But with regard to the calculating of local frequency source adjustment increment; Before the adjustment increment that calculates under a kind of situation can directly be used for adding up of frequency adjustment amount, the adjustment increment that calculates under then a kind of situation must just can be used for adding up of frequency adjustment amount after the symbol negate.

More than be to provide ignoring under the situation of noise to the explanation of the principle of the invention.If the influence of consideration of noise η (t), the performance of above method will worsen to some extent.The sample sequence η [n] that supposes η (t) is 0 for average, and variance is σ ²/ 2 white noise sequence, and ergodic does not then exist and L, M, N → during ∞, has when frequency reference signal

A ² _L[n]→D ²+σ ²，

C _M[n]→0，

S _N[n]→0。

When the existence of receive frequency reference signal and L, M, N → ∞, have

A ₂ ^L[n]→A ²+σ ²，

C _M[n]→A ²(cos(8πfτ)-cos(4πfτ))，

S _N[n]→A ²(cos(6πfτ)-cos(2πfτ))。

Therefore, under the enough big situation of L, M, N, said method is still set up, and the deterioration of performance can be controlled within the scope of permission.

Need to prove; In said method, after the detection threshold factor-alpha was given, sampling time τ must be near the scope of the relative narrower of (2k+1)/4f; Be that frequency error must be limited in the small range, frequency reference signal just can be detected.In order to enlarge detection range, promptly enlarge the allowed band of frequency error, can adopt some measures.For example, can use

Replaced C _M[n] also can add a sawtooch sweep voltage at the voltage-controlled end of the past VCO of detection-phase and carry out frequency scanning at a slow speed as detection metric.In addition, in order to enlarge the range of linearity of frequency error function, can use arctg (S _N[n]/C _M[n]) replacement S _N[n] is as the frequency error function.But adopting above measure is to be cost with the complexity that increase to realize.

The present invention is specially adapted to those only need be in the system that real number field is handled to received signal.The frequency-shift repeater in the gsm mobile communication system for example; It only need forward one road radio frequency receiving signal of real number form at the real number field shift frequency, after amplifying, and need a road of real number form not received processing such as on complex field, carrying out demodulates information after the I, Q two-way orthogonal signalling of signal transformation pluralize again.But; This method does not receive this limitation, and also promptly, the present invention utilizes the application of the method for digitization frequencies reference signal emending frequency; As long as there is a frequency reference signal in some occasions and need carries out frequency correction with it, then just can be those skilled in the art and differentiate that back is applied mechanically.

In the gsm system frequency-shift repeater; Adopt above-mentioned digital automatic frequency to detect and the descending calibrating frequency signal (being frequency reference signal) of bearing calibration tracking base stations based on the real frequency reference signal; Only need a common VCXO (VCXO); Add that simple algorithm realizes circuit; Just can make the relative error of the frequency of frequency-shift repeater and base station remain on desired ± 5 * 10 of GSM standard (ETSI EN 300609-4, YD/T 1337-2005) for frequency-shift repeater provides high-precision local frequency source ^-8In.Provide the method for local frequency source to compare with adopting expensive constant-temperature crystal oscillator, both reduced cost, do not need regularly to carry out artificial calibrating frequency again.Compare with bearing calibration based on the digital automatic frequency detection of complex frequency reference signal with employing; Owing to need not to obtain I, the mutually orthogonal frequency reference signal of Q two-way of plural form; There is not the imbalance compensation problem yet, therefore under the prerequisite of guaranteeing the frequency correction precision, reduced the complexity that system realizes greatly.

Claims (5)

1. digitlization automatic frequency correcting method based on the real frequency reference signal, this real frequency reference signal are from transmitting terminal, and acquiescence exists or confirms to exist through frequency detecting, it is characterized in that, comprising:

One road intermediate frequency or the baseband analog real signal of the end of spontaneous emission in the future sampled, analog-to-digital conversion is the step of digital signal;

Calculate the step of the frequency error function of local frequency source signal and transmitting terminal frequency source signal with the digital signal after this analog-to-digital conversion; Be specially: the frequency error function by two groups of through the difference of the product of the said digital signal after the analog-to-digital conversion 2 times through the acquisition of level and smooth back; Wherein every group all comprises two said digital signals; In one group in the sampling instant sum of two said digital signals and another group the sampling instant sum of two said digital signals equate that the difference of the sampling instant of two said digital signals is the odd in sampling time in every group;

There is or when frequency detecting is confirmed marking signal set that the real frequency reference signal exists the result of calculation of the gating frequency error function step of line data conversion of going forward side by side with the adjustment increment that obtains the frequency of this locality is adjusted in the said real frequency reference signal of acquiescence;

Said adjustment increment is added up to obtain the step of local frequency source numeral adjustment signal;

This numeral adjustment signal is converted to the step of simulation adjustment signal;

This simulation adjustment signal is carried out the step that filtering forms local frequency source control voltage;

Realize that with the local frequency source of this frequency source control voltage control local frequency adjustment makes it the step with the Frequency Synchronization of transmitting terminal;

The sampling time of wherein, said intermediate frequency or base band real signal being sampled is confirmed as follows:

If the frequency of the real frequency reference signal of the real signal that is received is f; The frequency of local frequency source signal is f+ Δ f; Frequency error between then local frequency source signal and the said real frequency reference signal is Δ f, and the relation of sampling time τ and local frequency source signal frequency f+ Δ f does

Or

Wherein k is a design parameter, and k ∈ 0,1,2 ... }, can choose according to the needs of practical application;

The scope that the sampling time τ that chooses according to above-mentioned relation allows to change does

Or

The permission excursion of corresponding frequency error does with it

Or

2. the digitlization automatic frequency correcting method based on the real frequency reference signal according to claim 1 is characterized in that:

In said sampling, the analog-to-digital step; Sampling clock is obtained through frequency division/frequency multiplication by local frequency source signal; According to transmitting-receiving frequency difference allowed bands different in the practical application; Sample frequency is got the different preset value with the ratio of local frequency source signal frequency, and sample frequency changes along with the adjustment of local frequency source.

3. the digitlization automatic frequency correcting method based on the real frequency reference signal according to claim 1 is characterized in that:

In the step of said calculated rate error function; In the digital signal after said two groups of analog-to-digital conversion; After digital signal after two analog-to-digital conversion of every group multiplies each other through multiplier; The product of the digital signal after two groups of analog-to-digital conversion all exports subtracter to and calculates both poor, then it is carried out smoothing processing, obtains said frequency error function.

4. the digitlization automatic frequency correcting method based on the real frequency reference signal according to claim 1 and 2 is characterized in that:

In the step of said acquisition adjustment increment; The marking signal that is existed by said sign real frequency reference signal triggers a gate; Make its result of calculation that allows said frequency error function carry out data conversion, with the said adjustment increment of final acquisition through a converter.

5. the digitlization automatic frequency correcting method based on the real frequency reference signal according to claim 4 is characterized in that: the said data conversion that the frequency error function is carried out is monotonic transformation.

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