CN1585289A - Method for compensating frequency offset in wireless mobile communication system - Google Patents

Abstract

The method is to intercept the training sequences of maximum in the received digital spread spectrum signal, insert the pre-configured frequency bias to the local training sequence to coordinate with the intercepted training sequence, select the maximum value in the coordinated data to determine the frequency bias of the time slot. Smooth and rectify the frequency bias, the impulse response mixed channel is obtained by the channel estimation, the spread spectrum code, the harass code and the weight. Process the impulse response of the mixed channel of each customer with frequency bias compensation to improve the performance of the unspreading.

Description

The method that in the mobile radio system frequency deviation is compensated

Technical field:

The present invention relates to field of wireless communication, be specifically related to the compensate of frequency deviation problem of radio mobile communication field the signal of reception.

Background technology:

In mobile communication system, there is a difference on the frequency in the signal of signal that receiver receives and transmitter emission, is commonly referred to frequency shift (FS).The frequency shift (FS) that Doppler causes can reach the hundreds of hertz, and the maximum frequency difference of being introduced by carrier wave can reach KHz, so receiving terminal must carry out frequency correction.Frequency calibration function is finished by the frequency correction loop, device commonly used has automatic frequency control (AFC, Auto FrequencyControl) and phase-locked loop (PLL, Phase Lock Loop), in money acute hearing, Chen Yingmei " Electronic Circuit of Communication " (People's Telecon Publishing House's in January, 2004 version), introduction is arranged.

The frequency correction loop is to come contrary frequency skew, the frequency shift (FS) that can effectively proofread and correct follow-up bursty data by adjusting local frequency.But this correction can't have any improvement to current reception data.Therefore, need carry out the frequency difference compensating operation to current reception data.

Be 97115151.2 in China Patent No., name is called patent of invention, US5303257, WO9524086A and " channel estimating and the equilibrium " of " carrier wave recovers and the method and the device thereof of compensation in the spread spectrum communication system "

(Georgios B.Giannakis etc., People's Telecon Publishing House's in November, 2002 version) technical scheme below having introduced in: the data hard decision demodulation of coming out by despreading, again carry out QPSK (Quadrature Phase Shift Keying then, the strong control of four phase places) modulation, ask for the bit of readjustment and the phase difference between the unsentenced bit, ask frequency deviation with following formula again:

${\mathrm{cita}}^{\left(k_{\mathrm{VRU}}\right)}=\frac{1}{2M}\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}(\frac{{\mathrm{cita}}_{2,i}^{\left(k_{\mathrm{VRU}}\right)}}{4.5+i}-\frac{{\mathrm{cita}}_{\mathrm{1,21}-i}^{\left(k_{\mathrm{VRU}}\right)}}{5.5+i})---\left(1\right)$

Obtain after the frequency deviation data being carried out compensate of frequency deviation, its implementation as shown in Figure 1a.

The phase place frequency offset calculation that following formula is represented can be represented by Fig. 1 b, in Fig. 1 b:

$\mathrm{\Δf}=\frac{{\mathrm{\θ}}_0-{\mathrm{\θ}}_1}{{\mathrm{\Δt}}_1}=\frac{{\mathrm{\θ}}_2-{\mathrm{\θ}}_0}{{\mathrm{\Δt}}_2}---\left(3\right)$

Here think 4.5+i and 5.5+i approximately equal in (1) formula.After (1) formula of utilization is tried to achieve frequency deviation, be converted into phase place again and refill each symbol, give the decoding unit of back as soft output information.

In the prior art, when frequency shift (FS) is bigger, at TD-SCDMA (Time Division-Synchronous Code Division Multiple Access) in burst time, the subscriber channel environment is constant in the time of no longer can being assumed to be, and the channel impulse response h (t) that obtains by training sequence no longer is applicable to whole burst.Therefore, after carrying out joint-detection, utilize unknown user data to declare demodulation firmly, obtain compensate of frequency deviation, there are the following problems: when frequency shift (FS) is bigger, at TD-SCDMA in burst time, the subscriber channel environment is constant in the time of no longer can being assumed to be, and the channel impulse response h (t) that obtains by training sequence no longer is applicable to whole burst, therefore, the decreased performance of joint-detection, thus error rates of data increases after causing despreading.Because error rates of data increases after the despreading, thereby cause demodulation performance to descend.Declare demodulation firmly owing to adopt, inevitably introduced and declared loss firmly.When the integral multiple variation appearred in phase place, this scheme can't effectively compensate.Under some error situation, declare back demodulation planisphere firmly and appear at round dot, can bring bigger error.

Summary of the invention

The technical problem to be solved in the present invention is, proposes a kind of new technical scheme that can overcome the prior art defective, can improve overall performance.

Technical scheme of the present invention is: the training sequence that intercepts out maximum diameter in the digital spread spectrum signal that receives; In local training sequence, add after the default frequency deviation and to carry out relevantly, select maximum to determine the frequency deviation of current time slots in the data after relevant with the training sequence of intercepting; Frequency deviation is smoothly revised; By channel estimating, spreading code, scrambler, weights, obtain the mixed channel impulse response; Compensate of frequency deviation is carried out in each user's mixed channel impulse response.

Preset described the adding in local training sequence, and its method can be that the possible range of selective reception sequence frequency difference is [f _Max, f _Max], be located at and carry out λ estimation in this scope, then frequency difference is spaced apart $f_d=\frac{{2f}_{\max }}{\mathrm{\λ}};$ At different frequency difference point f={0, ± f _d, ± 2f _d.., ± f _MaxDefault compensate of frequency deviation value e ^{-j2 π fi}

Select maximum in the described data after relevant, its method can be, selects the peak value of mould of the correlated results of each frequency deviation after relevant respectively, selects maximum from a plurality of correlation peaks.

Described frequency deviation is smoothly revised, its method can be, preserves last time slot frequency offset estimation result and to its weighting, to current frequency offset estimation result weighting, both handle by the adder addition.Specifically be level and smooth to the frequency deviation of current time slots and former time slot, carry out phase estimation again with the weighting forgetting factor:

${\stackrel{\‾}{f}}_{\mathrm{correct}}^{k,n}=(1-p){\stackrel{\‾}{f}}_{\mathrm{correct}}^{k,n-1}+{\mathrm{pf}}_{\mathrm{correct}}^{k,n}$

${\stackrel{\‾}{\mathrm{\θ}}}_{\mathrm{correct}}^{k,n}=2\mathrm{\π}{\stackrel{\‾}{f}}_{\mathrm{correct}}^{k,n}\·t$

Wherein, p is the weighting forgetting factor, is made as between 0.75～0.9.

The present invention has carried out compensate of frequency deviation before joint-detection, do not need to carry out demodulation and declare firmly, and the loss of having avoided demodulation to declare has firmly improved the performance of joint-detection; Owing to adopt the method for frequency deviation traversal, therefore as long as in the frequency deviation of setting, just can effectively compensate to frequency deviation; Bigger frequency deviation there is compensating action preferably; Can effectively improve system signal noise ratio-bit error rate performance; Owing to only need and maximum diameter carries out relevantly, so amount of calculation is little, and is practical.

Description of drawings:

Fig. 1 a is that the compensate of frequency deviation scheme realizes schematic diagram in the prior art;

Fig. 1 b is that frequency deviation is repaid phase place frequency offset calculation schematic diagram in the scheme in fact in the prior art;

Fig. 2 is the flow process of one embodiment of the present of invention and implements module diagram;

Fig. 3 is a frequency deviation smoothing processing schematic diagram.

Embodiment

In the TD-SCDMA system, no matter in the uplink synchronous process, still in the traffic channel transmission process, the known array effective length is 128chips in a time slot.The present invention utilizes this known array to carry out Frequency Estimation exactly.

Introduce basic ideas of the present invention below earlier:

If known transmission sequence is

S＝{s ₁，s ₂，...，s _n} (4)

Through air traffic channel, corresponding receiving terminal sequence is

R＝{r ₁，r ₂，...，r _n，...，r _n+W} (5)

Wherein W is the multidiameter window width.Consider interference such as noise, frequency deviation, receiving chip in the formula (5) can be expressed as:

$r_n=(1+e^{j{\mathrm{\φ}}_n})S_n+n_n---\left(6\right)$

φ wherein _nBecause frequency offset interference causes.

If the possible range of this receiving sequence frequency difference is f=[-f _Max, f _Max], suppose that carrying out λ time in this scope estimates that then frequency difference is spaced apart $f_d=\frac{{2f}_{\max }}{\mathrm{\λ}},$ The frequency difference point of traversal is

f＝{0，±f _d，±2f _d，..，± _fmax} (7)

Default compensate of frequency deviation value is e ^{-j2 π fi}, f _i∈ f.

At different frequency difference points local training sequence is carried out frequency difference prebias, though there is multi-path problem in each user, for a certain multipath of same subscriber, its frequency deviation is consistent, therefore only need to wherein the training sequence of strong multipath be correlated with.Then the correlated results of certain frequency deviation of certain user is:

${\mathrm{\Ω}}^{i,k}=\{{\mathrm{\Ω}}_1^{i,k},{\mathrm{\Ω}}_2^{i,k}\mathrm{\Λ},{\mathrm{\Ω}}_{2n-1}^{i,k}\}i=1,\mathrm{\Λ},\mathrm{\λ}---\left(8\right)$

Wherein i is an i frequency traversal point, and k is k user.To formula (8) delivery, and search for its peak value, as follows:

${\mathrm{\Ω}}_{\mathrm{peak}}^{i,k}=\mathrm{peak}\left(\right\{\left|\right|{\mathrm{\Ω}}_1^{i,k}\left|\right|,\left|\right|{\mathrm{\Ω}}_2^{i,k}\left|\right|,\mathrm{\Λ}\left|\right|{\mathrm{\Ω}}_{2n-1}^{i,k}\left|\right|\left\}\right)---\left(9\right)$

Each compensate of frequency deviation point is carried out traversal search, and the set of k user's training sequence correlation peak point is Ω ^k:

${\mathrm{\Ω}}^k=\{{\mathrm{\Ω}}_{\mathrm{peak}}^{-f_{\max },k},\mathrm{\Λ},C_{\mathrm{peak}}^{0,k},\mathrm{\Λ}{C}_{\mathrm{peak}}^{f_{\max },k}\}---\left(10\right)$

Wherein the peak value of best compensate of frequency deviation point is:

${\mathrm{\Ω}}_f^k=\max \left({\mathrm{\Ω}}^k\right)---\left(11\right)$

K user in the frequency offset estimating value of n time slot is:

${\mathrm{\θ}}_{\mathrm{correct}}^{k,n}={2\mathrm{\πf}}_{\mathrm{correct}}^k\·t---\left(12\right)$

Wherein t is a slot length, f _Correct ^kIt is the best estimate frequency difference of k user's correspondence.

After estimating the best frequency deviation of current time slots,, need smoothly revise the frequency offset estimating of current time slots for effectively utilizing frequency deviation information in the past and reducing amount of calculation.Adopt the weighting forgetting factor that the frequency offset estimating value of current time slots and former time slot is smoothly revised:

${\stackrel{\‾}{\mathrm{\θ}}}_{\mathrm{correct}}^{k,n}=(1-p){\stackrel{\‾}{\mathrm{\ρ}}}_{\mathrm{correct}}^{k,n-1}+{\mathrm{p\θ}}_{\mathrm{correct}}^{k,n}---\left(13\right)$

Wherein p is the weighting forgetting factor, generally is made as between 0.75～0.9.

In order to prevent that phase place from 2 π upset taking place, therefore, formula (12), (13) order to be adjusted, promptly advanced line frequency is level and smooth partially, carries out phase estimation again, suc as formula (14) and (15):

${\stackrel{\‾}{f}}_{\mathrm{correct}}^{k,n}=(1-p){\stackrel{\‾}{f}}_{\mathrm{correct}}^{k,n-1}+{\mathrm{pf}}_{\mathrm{correct}}^{k,n}---\left(14\right)$

${\stackrel{\‾}{\mathrm{\θ}}}_{\mathrm{correct}}^{k,n}=2\mathrm{\π}{\stackrel{\‾}{f}}_{\mathrm{correct}}^{k,n}\·t---\left(15\right)$

After obtaining revised frequency offset estimating, before joint-detection, compensate of frequency deviation is carried out in the mixed channel impulse response.

According to above thinking, the present invention's design module as shown in Figure 2, comprise that mainly frequency deviation presets device 22, multiplier 23, intercepting training sequence module (comprising the maximum diameter search) 24, correlation module 25 is selected peak value module (comprising delivery) 26, local training sequence module 27, peak-peak judging module 28, the level and smooth correcting process 29 of frequency deviation, frequency deviation estimating modules 210, spreading code, scrambler, weights generator 211, channel estimation module 212, mix impulse response module 213, joint-detection module 214, demodulation module 215.

Workflow of the present invention is: according to design objective and requirement, can obtain the possible range of receiving sequence frequency deviation in advance, set frequency difference and be spaced apart $f_d=\frac{2f_{\max }}{\mathrm{\λ}}.$ Using the default 22 pairs of local training sequences 27 of device of multiplier 23 and frequency deviation to carry out frequency deviation presets.During reception, can obtain receiving data 21, carry out the maximum diameter search, and from receive data, intercept the training sequence 217 of maximum diameter by intercepting block 24 from antenna end.Use correlation module 25 to carry out relevant with the local training sequence 216 that carries out after frequency deviation is preset from the training 217 of intercepting.Select result's 218 deliverys after 26 pairs of modules are correlated with and select peak-peak with peak value.Peak-peak 219 is sent into peak-peak judging module 28, obtain each user largest peaks 220 after the frequency deviation traversal in current time slots.Obtain peak-peak 220 corresponding preset frequency deviation values in the level and smooth correcting process 29 of frequency deviation, and utilize formula (14) to carry out the frequency deviation smoothing processing.Result after the frequency deviation smoothing processing 221 is sent into frequency deviation estimating modules 210, obtain each user's of current time slots phase deviation estimated value 222.

By channel estimator 212, spreading code, scrambler, weights generator 211 and multiplier 23 obtain mixed channel impulse response 213; With the frequency offset estimating value 222 after level and smooth, carry out compensate of frequency deviation by 23 pairs of mixed channel impulse responses of multiplier 223, the mixed channel impulse response 224 after being compensated; Obtain data 225 after the despreading through joint-detection module 214, carry out demodulation and deliver to decoder through 214 pairs of data of demodulation module 225.

Referring to Fig. 3, the frequency deviation smoothing processing is described, the frequency deviation smoothing processing comprises current time slots frequency offset estimation result 31, weighting P34, weighting (1-P) 32, the last time slot frequency deviation result 33 of preservation is to the last time slot frequency offset estimation result of preserving, weighting (1-P), to the current time slots frequency offset estimation result, weighting P, both are by adder 35 additions, utilize formula 14, calculate the level and smooth revised frequency offset estimating 36 of current time slots.

In sum, the outstanding feature of this patent is to adopt the method for frequency deviation traversal, and the maximum diameter training sequence with intercepting after the frequency deviation that adding is preset in local training sequence carries out relevant.To different frequency deviations, its correlated results difference is selected maximum in the data after a series of being correlated with, and determines the frequency deviation of current time slots.Adopt the method for weighting correction, the frequency offset estimating of current time slots is revised.Owing to the line frequency offset compensation that advances in joint-detection, therefore can improve the despreading performance, and the error diffusion of having avoided the laggard line frequency offset compensation of despreading to bring.Improved the performance and the entire system performance of joint-detection, had higher breakthrough.

Claims (5)

1, the method that in a kind of mobile radio system frequency deviation is compensated comprises:

1.1 in the digital spread spectrum signal that receives, intercept out the training sequence of maximum diameter;

Carry out relevantly 1.2 in local training sequence, add after the default frequency deviation with the training sequence of intercepting, select maximum to determine the frequency deviation of current time slots in the data after relevant;

1.3 frequency deviation is smoothly revised;

1.4, obtain the mixed channel impulse response by channel estimating, spreading code, scrambler, weights;

1.5 compensate of frequency deviation is carried out in each user's mixed channel impulse response.

2, the method that in the described mobile radio system of claim 1 frequency deviation is compensated is characterized in that, preset described the adding in local training sequence, and its method is that the possible range of selective reception sequence frequency difference is [f _Max, f _Max], be located at and carry out λ estimation in this scope, then frequency difference is spaced apart $f_d=\frac{{2f}_{\max }}{\mathrm{\λ}};$ At different frequency difference point f={0, ± f _d, ± 2f _d.., ± f _MaxDefault compensate of frequency deviation value e ^{-j2 π fi}

3, the method that in the described mobile radio system of claim 1 frequency deviation is compensated, it is characterized in that select maximum in the described data after relevant, its method is, select the peak value of mould of the correlated results of each frequency deviation after relevant respectively, from a plurality of correlation peaks, select maximum.

4, the method that in the described mobile radio system of the arbitrary claim of claim 1 to 3 frequency deviation is compensated, it is characterized in that, described frequency deviation is smoothly revised, its method is, preserve last time slot frequency offset estimation result and to its weighting, to current frequency offset estimation result weighting, both handle by the adder addition.

5, the method that in the described mobile radio system of claim 4 frequency deviation is compensated, it is characterized in that, weighted factor to last time slot frequency offset estimation result is 1-p, weighted factor to the current time slots frequency offset estimation result is p, level and smooth to the frequency deviation of current time slots and former time slot earlier, carry out phase estimation again:

${\stackrel{\‾}{f}}_{\mathrm{correct}}^{k,n}=(1-p){\stackrel{\‾}{f}}_{\mathrm{correct}}^{k,n-1}+p{f}_{\mathrm{correct}}^{k,n}$

${\stackrel{\‾}{\mathrm{\θ}}}_{\mathrm{correct}}^{k,n}=2\mathrm{\π}{\stackrel{\‾}{f}}_{\mathrm{correct}}^{k,n}\·t$

Wherein, p is the weighting forgetting factor, is made as between 0.75～0.9.

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