CN1801794A - Frequency automatic correction method and apparatus - Google Patents

Abstract

Said invention provides frequency autocorrection method and device. It contains A, proceeding frequency correction to receiver output complex form outburst signal r(i), i= 1,..., 155, according to relevant frequency departure estimated value delta omega frequency departure B, proceeding channel estimate and equalization processing to frequency corrected outburst signal to obtain multiple channel estimated value h(n)and time delay regulation volume TOA, C, calculating frequency departure frequency departure of next outburst signal delta omega for next outburst signal frequency signal frequency correction. Said device includes said frequency departure correction module, normal demodulation module and frequency departure estimate module. Said method and device can estimate and compensate frequency departure generated by Doppler Effect in mobile terminal high-speed moving relative to base station.

Description

A kind of frequency automatic correction method and device

Technical field

The present invention relates to the gsm wireless communications field, refer to frequency automatic correction method and device under the high-speed moving state of the relative base station of a kind of portable terminal especially.

Background technology

Wave point in the gsm system combines frequency division multiple access and tdma.The basic conception of GSM on wireless transmission is: the unit of transmission is the sequence of 156 modulation bit, and it is called a burst (burst).Burst takies the frequency bandwidth of 200kHz, and the duration is 0.577ms (15/26ms).Its 200kHz that takies is called as crack frequently.The band resource of GSM is that base unit is divided according to 200kHz.With the 900MHz frequency band is example, and this baseband comprises the sub-band of two 25MHz: 890-915Mhz and 935-960Mhz.Frequently the centre frequency in crack evenly distributes from interval, frequency band border 200kHz in these frequency bands.Therefore 124 different cracks are frequently arranged in 25MHz.Frequently the crack is exactly the radio-frequency channel of stipulating in the gsm protocol.Characteristics of fdma system are: the normal communication between travelling carriage and base station depends on the radio-frequency channel of the same frequency of both sides' negotiation.

Exist under the situation of relative motion in base station and portable terminal, portable terminal receives the frequency of base station signal and the frequency generation deviation of expection, and this offset frequency can be described with Doppler's model:

$\mathrm{\Δf}=\frac{v}{\mathrm{\λ}}=\frac{v\·f}{c}$ (formula 1)

In the formula 1, Δ f represents offset frequency, and v represents the translational speed of portable terminal, and f represents signal frequency, and c represents electromagnetic wave transfer rate (being the light velocity).

Because the frequency source of portable terminal need lock base station frequency, this moment, there was a frequency shift (FS) in the frequency source of portable terminal.Same, also there is a same frequency shift (FS) in the signal frequency that the base station receives portable terminal.So the actual frequency offset of base station received signal is:

$\mathrm{\Δf}=2\·\frac{v}{\mathrm{\λ}}=2\·\frac{v\·f}{c}$ (formula 2)

With speed is 50km/h, and frequency is that 900Mhz is an example, and then the frequency deviation according to formula 2 portable terminal received signals is:

$\mathrm{\Δf}=2\·\frac{v\·f}{c}=\frac{2\×50\×{10}^3\×900{\×10}^6}{3600\×3\×{10}^8}=83.4\mathrm{Hz}$

When high-speed motion, for example speed is 200km/h, and when frequency was 1800Mhz, frequency deviation was 667Hz.Therefore, exist between base station and the travelling carriage under the high-speed motion situation, frequency shift (FS) is to being that the gsm system performance of characteristics exists and has a strong impact on time-division/frequency division multiplexing.

Be conceived to low-speed motion at the beginning of the gsm system development and use, do not consider and concrete regulation, it is generally acknowledged that the movement velocity of the relative base station of travelling carriage is less than 150km/h for doing in the application of high-speed motion system such as train etc.Existing gsm system is not taked solution to the frequency departure under the high-speed motion.As shown in Figure 1, in the burst demodulating system of general base station, be to adopt conventional equalizing demodulation technology.Comprise receiver, demodulator and decoder.Receiver receives wireless signal from wireless mouth, after frequency conversion and filtering, the base band burst of the digital form that obtains is sent to demodulator.Demodulator is sent to decoder after with the demodulation of base band burst and deciphers.This demodulation techniques are not considered the influence of the frequency shift (FS) that the relative velocity between base station and the travelling carriage causes, so the situation of the relative base station of incompatibility travelling carriage high-speed motion.

Along with the development of gsm system, the application of deriving of high speed kinematic systems such as railway has appearred being specifically designed to.Train speed usually at 200km/h between the 400km/h.Because the Doppler frequency deviation effect of the relative motion between portable terminal (on the train) and base station (the fixing) makes to there are differences between effect frequency and the nominal frequency.This difference can be ignored under the low-speed motion situation, and under the high-speed motion environment, will exert an influence to systematic function: descend as speech quality, and dropped calls, conversation can not be set up etc.

Summary of the invention

The invention provides a kind of frequency automatic correction method and device, estimate with compensation when the high-speed motion of the relative base station of portable terminal because the frequency departure of Doppler effect generation.

The inventive method comprises the following steps:

A: with the burst r (i) of the plural form of receiver output, i=0 ... 155, according to its correspondent frequency estimation of deviation value Δ ω, carry out frequency correction;

B: the burst after the frequency correction is carried out channel estimating and equilibrium treatment, obtain complex channel estimated value h (n) and time delay adjustment amount TOA;

C: estimate h (n) and time delay adjustment amount TOA by described complex channel, calculate the frequency deviation ω of next burst, be used for next burst frequency correction.

According to said method of the present invention, the burst frequency departure estimated value of first time slot is set at 0.

According to said method of the present invention, the concrete grammar that carries out frequency correction in the described steps A is:

A1: calculate 156 I, the Q two-way correction factor:

e ^jkΔω＝cos(kΔω)+jsin(kΔω)k＝0，...，155；

A2: carry out frequency correction, the burst after obtaining proofreading and correct with the complex multiplication of gripping altogether of the correction factor with burst r (i): $\hat{r}\left(i\right)=r\left(i\right)\×e^{-\mathrm{jk\Δ\ω}},i=0,...,155.$

The computational methods of the described correction factor are look-up table.

The method of described step C calculating frequency deviation delta ω is:

C1: calculate 4 complex channels and estimate h (n) and corresponding time delay adjustment amount TOA;

C2: utilize 4 complex channels to estimate that h (n) and training sequence calculate a skew phase place;

C3: the skew phase place that will calculate adds the frequency offseting value of current burst, as the frequency departure estimated value Δ ω of next burst.

Described step C2 comprises the steps:

C21: utilize 4 complex channels to estimate that h (n) carries out convolution algorithm to training sequence;

C22: grip plural number altogether with what the relevant position training sequence in the burst multiply by training sequence after the convolution;

C23: the result of calculation of step C22 is set the interval by one carry out the cross product computing, the each point cross product that adds up result;

C24: the cross product result's that will add up out phase place is as the skew phase place.

Set described in the step C23 and be spaced apart 16.

The present invention provides a kind of frequency automatic correction device in addition, comprising: a frequency departure correction module, a standard demodulation module and a frequency departure estimation module;

The burst of the plural form of described frequency departure correction module reception base station receiver output and the exemplary frequency deviation values of frequency departure estimation module output are carried out frequency correction to current burst;

Described standard demodulation module receives the burst after proofreading and correct, and carries out channel estimating and equilibrium treatment, obtains complex channel estimated value and time delay adjustment amount, exports to the frequency departure estimation module; And demodulated output data is given decoder;

Described frequency departure estimation module estimates the exemplary frequency deviation values of next burst according to the complex channel estimated value and the time delay adjustment amount that obtain, exports to described frequency departure correction module, is used for next burst frequency correction.

Frequency automatic correction method of the present invention can effectively compensate because the frequency departure that the relative motion Doppler effect of travelling carriage and base station brings improve the performance of gsm system under high-speed motion state, and implementation method is simple, and is with low cost.

Description of drawings

Fig. 1 is a burst demodulation flow chart of the prior art;

Fig. 2 is frequency automatic correction device of the present invention and signal flow graph thereof.

Embodiment

Below in conjunction with Fig. 2, the present invention program is described in detail.

The invention provides a kind of frequency departure means for correcting, comprising: a frequency departure correction module, a standard demodulation module and a frequency departure estimation module.

The burst of the plural form of described frequency departure correction module reception base station receiver output and the exemplary frequency deviation values of frequency departure estimation module output are carried out frequency correction to current burst;

Described standard demodulation module receives the burst after proofreading and correct, and carries out channel estimating and equilibrium treatment, obtains complex channel estimated value and time delay adjustment amount, exports to the frequency departure estimation module; And demodulated output data is given decoder;

Described frequency departure estimation module estimates the exemplary frequency deviation values of next burst according to the complex channel estimated value and the time delay adjustment amount that obtain, exports to described frequency departure correction module, is used for next burst frequency correction.

Adopt above-mentioned means for correcting of the present invention, realize carrying out from the concrete grammar of dynamic(al) correction as follows the frequency of input signal:

Receiver receives signal from wireless mouth, after frequency conversion and filtering, has formed the burst r (i) of plural form, i=0 ... 155.The frequency deviation ω that r (i) is corresponding with it (Δ ω initial value is made as 0) is input to the frequency departure correction module in the frequency departure means for correcting of the present invention, carries out frequency correction.Concrete grammar is:

At first, calculate 156 I, the Q two-way correction factor: e ^{Jk Δ ω}=cos (k Δ ω)+jsin (k Δ ω), k=0 ..., 155; Concrete computational methods can adopt look-up table, promptly store 0-360 ° sin and cos value in advance in a tables of data;

Then, grip complex multiplication, the burst after obtaining proofreading and correct altogether with burst and the correction factor $\hat{r}\left(i\right)=r\left(i\right)\×e^{-\mathrm{jk\Δ\ω}},i=0,...,155;.$

Burst after proofreading and correct is delivered to the standard demodulation module carry out channel estimating and equilibrium treatment, the output demodulation result is given decoder, obtain complex channel simultaneously and estimate h (n), and time delay adjustment amount TOA (complex channel is estimated and the concrete computational methods of time delay adjustment amount are prior art, is omitted at this).

Complex channel estimation and time delay side-play amount are sent to frequency departure estimation module of the present invention the frequency departure of next burst are estimated.The exemplary frequency deviation values that estimates is delivered to frequency correction module the burst of next time slot is carried out frequency correction.

The concrete grammar that the frequency departure estimation module is carried out the frequency departure estimation is:

1, the complex channel of acceptance criteria demodulation module output is estimated h (n), and time delay adjustment amount TOA;

Utilize 4 complex channels to estimate training sequence is carried out convolution algorithm (standard agreement GSM05.02 is consulted in the training sequence definition):

2, the training sequence that the relevant position training sequence in the burst be multiply by after the convolution is gripped altogether;

3, carry out cross product computing (concrete space-number is relevant with the computational methods of h (n), and 16 is preferred values) by interval 16;

$\mathrm{CrossP}\left(j\right)=\widetilde{\mathrm{Tr}}\left(j\right)\×\widetilde{\mathrm{Tr}}*(j-16),i=19,...,25$

Obtain 7 cross product results altogether.

4, these cross products result is added up;

$\mathrm{CrossP}=\underset{j=19}{\overset{25}{\mathrm{\Σ}}}\mathrm{CrossP}\left(j\right),$

And the phase place of calculating accumulation result:

$\mathrm{\Δ}\widetilde{\mathrm{\ω}}=\mathrm{arctg}(\mathrm{Re}\left(\mathrm{CrossP}\right),\mathrm{Im}\left(\mathrm{CrossP}\right));$

5, upgrade estimation, and output to the frequency correction that the frequency departure correction module is used for next burst frequency;

$\mathrm{\Δ\ω}=\mathrm{\Δ\ω}+K\×\mathrm{\Δ}\widetilde{\mathrm{\ω}};$ Wherein K is a coefficient, its typical value K=0.0003.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claims.

Claims (8)

1, a kind of frequency automatic correction method is characterized in that comprising the following steps:

A: with the burst r (i) of the plural form of receiver output, i=0 ... 155, according to its correspondent frequency estimation of deviation value Δ ω, carry out frequency correction;

B: the burst after the frequency correction is carried out channel estimating and equilibrium treatment, obtain complex channel estimated value h (n) and time delay adjustment amount TOA;

C: estimate h (n) and time delay adjustment amount TOA by described complex channel, calculate the frequency deviation ω of next burst, be used for next burst frequency correction.

2, the method for claim 1 is characterized in that: the burst frequency departure estimated value of first time slot is set at 0.

3, method as claimed in claim 2 is characterized in that: the concrete grammar that carries out frequency correction in the described steps A is:

A1: calculate 156 I, the Q two-way correction factor:

e ^jkΔω＝cos(kΔω)+jsin(kΔω) k＝0，...，155；

A2: carry out frequency correction, the burst after obtaining proofreading and correct with the complex multiplication of gripping altogether of the correction factor with burst r (i): $\hat{r}\left(i\right)=r\left(i\right){\×e}^{-\mathrm{jk\Δ\ω}},i=0,...,155.$

4, method as claimed in claim 3 is characterized in that: the computational methods of the described correction factor are look-up table.

5, as claim 3 or 4 described methods, it is characterized in that: the method for described step C calculating frequency deviation delta ω is:

C1: calculate 4 complex channels and estimate h (n) and corresponding time delay adjustment amount TOA;

C2: utilize 4 complex channels to estimate that h (n) and training sequence calculate a skew phase place;

C3: the skew phase place that will calculate adds the frequency offseting value of current burst, as the frequency departure estimated value Δ ω of next burst.

6, method as claimed in claim 5 is characterized in that: described step C2 comprises the steps:

C21: utilize 4 complex channels to estimate that h (n) carries out convolution algorithm to training sequence;

C22: grip plural number altogether with what the relevant position training sequence in the burst multiply by training sequence after the convolution;

C23: the result of calculation of step C22 is set the interval by one carry out the cross product computing, the each point cross product that adds up result;

C24: the cross product result's that will add up out phase place is as the skew phase place.

7, method as claimed in claim 6 is characterized in that: set described in the step C23 and be spaced apart 16.

8, a kind of frequency automatic correction device is characterized in that comprising: a frequency departure correction module, a standard demodulation module and a frequency departure estimation module;

The burst of the plural form of described frequency departure correction module reception base station receiver output and the exemplary frequency deviation values of frequency departure estimation module output are carried out frequency correction to current burst;

Described standard demodulation module receives the burst after proofreading and correct, and carries out channel estimating and equilibrium treatment, obtains complex channel estimated value and time delay adjustment amount, exports to the frequency departure estimation module; And demodulated output data is given decoder;

Described frequency departure estimation module estimates the exemplary frequency deviation values of next burst according to the complex channel estimated value and the time delay adjustment amount that obtain, exports to described frequency departure correction module, is used for next burst frequency correction.

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