CN1671064A - Method of frequency compensation for Direct Sequence Spread Spectrum (DSSS) mobile communication system - Google Patents
Method of frequency compensation for Direct Sequence Spread Spectrum (DSSS) mobile communication system Download PDFInfo
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Abstract
This invention refers to a frequency deviation compensation method for separating RAKE receiver, which contains making independent frequency compensation to Doppler shift in each RAKE signal, generating base band feedback control signal according to RAKE shift and making uniform frequency compensation to RF and IF. Said method can quick and accurately estimate the frequency shift of tracked route, speed up AFC convergence rate and greatly raise the tracking range of frequency shift variation.
Description
Technical field
The present invention relates to automatic frequency control (AFC) method of travelling carriage separating multiple diameter (Rake) receiver in direct sequence spread spectrum (DSSS) mobile communication system, more particularly, relate in inherent each the road multipath signal of travelling carriage separating multiple diameter (Rake) receiver the method that Doppler frequency shift is on a large scale carried out the independent frequency compensation.
Background technology
The mobile communication system of the employing direct sequence spread spectrum communication technology faces the problem of signal multipath transmisstion usually.Multipath transmisstion causes owing to there are many transmission paths in signal between transmitter and receiver, the mobile communication system that adopts various modulation techniques is all had a negative impact, and for example the intersymbol interference (ISI) that causes of multipath transmisstion has limited the maximum information transmission rate of system.For overcoming the interference that multipath transmisstion causes, the general Rake receiver that adopts in the mobile communication system of direct sequence spread spectrum is realized the diversity reception of multipath signal.The multipath signal that separating multiple diameter (Rake) receiver exceeds a chip (chip) to the relative delay is distinguished by coherent detection, and carry out the merging of multipath energy, broken the influence of multipath transmisstion, and utilized the naturally occurring diversity energy that multipath transmisstion brought the rate of information throughput.
For the diversity of utilizing separating multiple diameter (Rake) receiver merges performance, at first to realize the Frequency Synchronization between the transmitter and receiver.And the Doppler effect that mobile communication system itself is had produces frequency shift (FS) between transmitter and receiver, influence Frequency Synchronization between the two.The accuracy and the stability of receiving-transmitting sides crystal oscillator also exert an influence to Frequency Synchronization, because the frequency of radio frequency and intermediate frequency is to be realized by frequency multiplication by the output frequency of crystal oscillator, the accuracy of crystal oscillator and stability directly determine the accuracy and the stability of radio frequency and intermediate frequency, and the absolute value of frequency shift (FS) amplifies because of frequency multiplication, rf frequency is high more, and the frequency shift (FS) between the transmitter and receiver is big more.
The Doppler frequency shift that relative motion between the transmitter and receiver produces can be calculated by following formula:
In the formula (1), v is a motion velocity of mobile station, and λ is a carrier wavelength, and θ is the angle of the incident wave direction and the travelling carriage direction of motion.
In the prior art, mobile communication system is used QPSK or is under the basic improved modulation technique situation with QPSK, and travelling carriage generally carries out the estimation of frequency shift (FS) with pilot tone (pilot) signal of base station.Specifically, because the travelling carriage frequency pilot sign that it received in each synchronizing process is changeless, therefore do not having under the situation of Doppler frequency shift, this frequency pilot sign should be steady state value through the CF signal phase place that produces after phase modulated, promptly receiver receive the angle phi of I+jQ complex signal should be constant.After frequency pilot sign is carried out integration, can utilize additive phase skew the carrying out Doppler frequency deviation of introducing between the adjacent pilot symbols to estimate, as shown in the formula:
In the formula (2), Δ φ is between the I, Q complex signal of adjacent pilot symbols because the additive phase skew that Doppler effect causes, this phase deviation is the additive phase rotation between the frequency pilot sign that is caused by frequency shift (FS), and Δ t is the cycle of frequency pilot sign.Formula (2) shows, the estimated performance of Δ f is decided by phase place is rotated fully the estimated performance of Δ φ.
The normalization phase information of frequency pilot sign complex signal I+jQ can be expressed as
Δφ＝φ
n-φ
n-1。(4)
In formula (3), (4), φ
nAnd φ
N-1, represent the phase place of n frequency pilot sign and n-1 frequency pilot sign complex signal respectively.
Can derive following formula by formula (3) and (4):
| Δ φ | under the very little situation, conventional evaluation method adopts following formula approximate calculation Δ φ:
Δφ≈sinΔφ (6)
The compensation method of above-mentioned prior art is adjusted the local oscillator of travelling carriage according to the Δ φ numerical value that calculates, thereby realizes the compensation to Doppler frequency shift.Because above-mentioned formula (6) only is only applicable to the very little scope of Δ φ numerical value, it is only comparatively accurate under the less situation of Doppler frequency deviation to adopt this conventional method to carry out compensate of frequency deviation.When motion velocity of mobile station was higher, the approximate compensation method of this routine had bigger deviation, influenced the convergence rate of the accurate and AFC of compensate of frequency deviation.
In addition, conventional separating multiple diameter (RAKE) receiver frequency compensation method can only be unified the voltage controlled oscillator (VCO) of compensated receiver according to frequency deviation in each path of multipath signal, and can not refer to that to each peak device (finger) carries out frequency compensation separately according to the frequency deviation in each path.The frequency compensation method of conventional RAKE receiver is specially, and every multipath has different frequency shift (FS)s, and each refers to that the peak device provides the frequency offset estimating in footpath separately.Need refer to that the frequency offset estimating of peak device carries out suitable average and filtering based on all, generate one tunnel feedback signal, the frequency of radio frequency and intermediate frequency be unified FEEDBACK CONTROL by regulating local voltage controlled oscillator.This method can compensate at radio frequency and the intermediate frequency averaged frequency offset composition to many multipaths, but can not make every multipath all obtain good frequency compensation, thereby can not make each demodulation performance that refers to the peak device all reach optimum.
Therefore, need a kind of improved frequency bias compensation method accurately to estimate and can be to Doppler frequency deviation in a big way to each refers to that peak device (finger) carries out the independent frequency compensation in the RAKE receiver.
Summary of the invention
The purpose of this invention is to provide a kind of frequency bias compensation method that is used for separating multiple diameter (Rake) receiver, this method is carried out the independent frequency compensation to Doppler frequency shift in each road multipath signal, frequency deviation according to each paths generates the baseband feedback control signal again, radio frequency (RF) and intermediate frequency (IF) are carried out the unified frequency compensation, thereby improve the overall frequency compensation performance of Rake receiver.
A kind of frequency bias compensation method that is used for direct sequence spread spectrum mobile communication system travelling carriage separating multiple diameter (Rake) receiver of the present invention comprises referring to peak device independent frequency compensation and two basic steps of receiver overall average compensation, it is characterized in that:
In referring to peak device independent frequency compensation process, further comprise step:
By integration/cleaning module the complex signal that refers to the frequency pilot sign that the peak device is received is carried out integration;
Carry out normalization by the frequency pilot sign complex signal of normalization module after, and obtain sine value, the cosine value of frequency pilot sign complex signal phase n despreading;
By the multiplication cross module sine value and the cosine value of adjacent pilot symbols complex signal phase n and φ n-1 are carried out the multiplication cross computing, obtain sine value and the cosine value of phase deviation Δ between the adjacent pilot symbols;
This phase deviation vector is mapped to-one of eight subintervals of π to π according to sine and the cosine value of phase deviation Δ by interval mapping block, the width in each subinterval is π/4;
In the subinterval of being shone upon according to the sine value of the phase deviation Δ that converts with cosine value calculates this phase deviation vector and near the phase place angle Δ θ sine value between the reference axis;
Phase place angle Δ θ is estimated by curve compensation by the curve compensation module;
To be estimated by phase conversion that the phase place angle Δ θ that obtains converts according to the interval at place reverts to phase deviation Δ between the actual frequency pilot sign complex signal;
Calculate the frequency shift (FS) Δ f that this refers to peak device institute track path pilot symbol signal by the frequency offset calculation module according to phase deviation Δ between the frequency pilot sign and frequency pilot sign cycle Δ t;
The frequency shift (FS) Δ f of the finger peak device that will be calculated by the appraising frequency bias module feeds back to the frequency correction module that refers in the peak device as feedback signal;
By frequency correction module input is referred to that the chip signal of peak device carries out frequency correction;
In receiver overall average frequency compensation step, further comprise step:
Carry out energy or signal-to-noise ratio (snr) estimation by energy or the signal-to-noise ratio (SNR) estimation module frequency pilot sign after to integration;
By the thresholding comparison module energy or signal-to-noise ratio (snr) estimation value and predetermined threshold are compared, when energy or signal-to-noise ratio (snr) estimation value are higher than predetermined threshold, produce and merge the feasible switch conduction that merges of control signal, cause referring to measure in the peak device calculating that the frequency shift (FS) of estimating participates in the frequency shift (FS) of RAKE receiver overall average, otherwise when energy or signal to noise ratio are lower than predetermined threshold, produce the merging control signal and make that merging switch disconnects, cause this to refer to that frequency shift (FS) of estimating in the peak device does not participate in the calculating of RAKE receiver overall average frequency shift (FS);
By combiner each frequency shift (FS) that refers to that the peak device produces that participates in the frequency shift (FS) of calculating RAKE receiver overall average is merged addition;
By averager the frequency shift (FS) of average acquisition overall average is asked in each frequency shift (FS) of addition;
By low pass filter the overall average frequency shift (FS) is carried out smoothly;
To be converted to the voltage signal that voltage controlled oscillator is controlled through level and smooth overall average frequency shift (FS) by D/A;
Voltage controlled oscillator controlled adjustment institute output frequency, thus local intermediate frequency of receiver and rf frequency regulated.
Said method of the present invention, refer to that at each peak device automatic frequency controls before the fine convergence, in the estimated value and predetermined threshold step relatively by described pilot symbol energies that refers to threshold compataror execution in the peak device and signal to noise ratio, predetermined threshold is provided with low value, after each referred to that peak device automatic frequency is controlled fine convergence, this predetermined threshold was provided with high value.
Said method of the present invention in the multiplication cross step performed by the multiplication cross module, adopts following formula
Carry out the multiplication cross computing, wherein Δ is the phase deviation between adjacent pilot symbols complex signal phase n and the φ n-1.
Said method of the present invention, in the interval mapping step performed by interval mapping block, adopt the following step to carry out subinterval mapping and the calculating of phase place angle Δ θ sine value:
Will [π, π) the phase deviation interval is divided into 8 subintervals, is respectively: [π ,-3 π/4), [3 π/4,-pi/2), [pi/2 ,-π/4), [π/4,0), [0, π/4), [π/4, pi/2), [pi/2,3 π/4) and [3 π/4, π), number consecutively is subinterval 0 to 7;
In the 1st, 2,5,6 subintervals, sin Δ θ=| ± cos Δ φ |,
In the 0th, 3,4,7 subintervals, sin Δ θ=| ± sin Δ φ |.
Said method of the present invention, in the Δ θ estimation steps performed by the curve compensation module, adopt fore-telling row formula to carry out curve compensation and the estimation of the phase place angle of cut:
f(sinΔθ)＝O．21(sinΔθ)
2+1
Said method of the present invention, in the phase transition step performed by phase conversion, adopt following formula to carry out phase transition:
The 0th subinterval, Δ φ=-π+Δ θ,
The 1st subinterval, Δ φ=-pi/2-Δ θ,
The 2nd subinterval, Δ φ=-pi/2+Δ θ,
The 3rd subinterval, Δ φ=-Δ θ,
The 4th subinterval, Δ φ=Δ θ,
The 5th subinterval, Δ φ=pi/2-Δ θ,
The 6th subinterval, Δ φ=pi/2+Δ θ,
The 7th subinterval, Δ φ=π-Δ θ.
Said method of the present invention, in the frequency offset calculation step performed by the frequency offset calculation module, adopt following formula to carry out frequency offset calculation:
Said method of the present invention, in the frequency deviation independent compensation step, frequency correction module will be used the complex conjugate frequency e of this frequency offset estimating value that refers to that peak device measurement estimates in the finger peak device performed by frequency correction module
-2 π Δ ftCarry out complex multiplication operation with baseband complex signal I+jQ, thus baseband complex signal is applied a reverse phase place and rotate the phase deviation of eliminating or weaken the complex signal vector that frequency displacement causes.
Adopt above-mentioned frequency bias compensation method of the present invention, can make every Lu Zhifeng device estimate the frequency deviation of institute's track path separately fast and accurately, thereby accelerate the convergence rate of AFC, and improve the following range that frequency deviation is changed greatly.
Description of drawings
Fig. 1 is the schematic diagram that phase deviation vector between the frequency pilot sign complex signal is mapped in eight subintervals that the inventive method adopted;
Fig. 2 is the compensated curve schematic diagram that the inventive method adopted;
Fig. 3 is the error precision and the art methods error precision line curve chart relatively of the inventive method evaluation phase skew in a subinterval;
Fig. 4 carries out frequency compensated general structure schematic diagram for the RAKE receiver tracking/merging multipath signal that the inventive method adopted;
Fig. 5 is the schematic diagram of the RAKE receiver middle finger shown in Figure 4 peak device structure that the inventive method adopted;
Fig. 6 is the schematic diagram of multiplication cross modular structure in the finger shown in Figure 5 peak device that the inventive method adopted.
Embodiment
Describe the specific embodiment of the inventive method in detail below in conjunction with accompanying drawing.
For the prior art appraising frequency bias method range of linearity that solves formula (6) representative is too little, to appraising frequency bias poor accuracy and the slow problem of convergence on a large scale, the inventive method adopts improved frequency deviation measurement method.As shown in Figure 1, receive in pilot tone complex signal I, the Q signal phase deviation polar plot at travelling carriage, on unit circle with [π, π) the phase deviation interval is divided into 8 subintervals, is respectively: [π ,-3 π/4), [3 π/4,-pi/2), [pi/2,-π/4), [π/4,0), [0, π/4), [π/4, pi/2), [pi/2,3 π/4) and [3 π/4, π), number consecutively is subinterval 0 to 7.Among Fig. 1, in the subinterval of numbering 5, shown the I of two frequency pilot signs, the phase deviation vector between the Q complex signal with band arrow line segment table, the phase deviation angle of this phase deviation vector as shown is Δ φ.On subinterval schematic diagram shown in Figure 1, the phase deviation vector between the frequency pilot sign can be used following formulate:
e
jΔφ＝cosΔφ+jsinΔφ (7)
In the residing interval of phase deviation vector, the present invention does not directly measure calculating to phase deviation Δ φ, but the angle Δ θ between this phase deviation vector and the immediate reference axis is measured calculating, be phase deviation vector and the angle between reference axis upward in this angle the 5th subinterval shown in Figure 1.For any Δ φ numerical value in-π to the π scope, through being mapped in some subintervals, its pairing Δ θ numerical value is all in 0 to π/4 scope.In the 5th subinterval example shown in Figure 1, the relation of Δ θ and Δ φ is as follows:
The mapping relations in all the other seven subintervals are discussed in the back to some extent.Method of the present invention is by being divided into the phase deviation vector space in eight subintervals, thereby expanded the valuation scope of Δ φ to π between-the π from-pi/2 to pi/2, because the estimation of Δ φ is converted into estimation to Δ θ, and the valuation scope of Δ θ is limited in [0 in any subinterval, π/4] in, thereby the accuracy of assurance estimation.When in each subinterval, carrying out Δ θ estimation, nonlinearity erron when adopting formula (6) between sin Δ θ and the Δ θ in order further to eliminate art methods, method of the present invention adopts specific compensated curve that sin Δ θ is compensated, thereby obtains the very little estimation of linearity error of Δ θ.The compensated curve that the present invention adopts obtains based on following formula:
In interval [0, π/4], can with one section parabola as Δ θ/sin Δ θ be similar to and as the compensated curve of the actual employing of the present invention, this parabola expression formula is as follows:
f(sinΔθ)＝0.21(sinΔθ)
2+1 (10)
The relation of the compensated curve of formula (10) and Δ θ/sin Δ θ curve as shown in Figure 2.In corresponding Δ θ was 0 to π/4 scope, sin Δ θ number range was between 0 to 0.7071 among Fig. 2.As shown in Figure 2, the compensated curve of formula (10) and Δ θ/sin Δ θ curve is approximate substantially.
Adopt formula (10) compensated curve substitution formula (9), the valuation expression formula of the Δ θ that obtains can be expressed as:
The inventive method further adopts formula (11) to carry out the phase deviation estimation on basis, division phase offset vector subinterval, and its error adopts formula (6) to compare with conventional method, and the error of measuring estimation reduces greatly.Figure 3 shows that the present invention adopts formula (11) to measure and estimates that the estimation precision that adopts formula (6) to measure estimation with prior art compares, as can be seen from Figure 3 in 0 to π/4 scope, the estimation curve (11) that adopts measurement evaluation method of the present invention to be obtained has favorable linearity, the worst error of this estimation curve only is about 0.001 π, to improve greatly than art methods precision.
The RAKE receiver general structure schematic diagram that the inventive method of representing Fig. 4 adopts.As shown in Figure 4, method of the present invention is adopting on the basis of accurately measuring evaluation method calculating Doppler frequency deviation, the Doppler frequency deviation estimated value that further each Lu Zhifeng device (finger) is provided merges through combiner (Combiner), again each frequency deviation that participates in merging is carried out calculating mean value by averager, this mean value is undertaken smoothly by a low pass filter (LPF), the filtering result is through the feedback control signal of D/A conversion back as voltage controlled oscillator (VCO), regulate the output frequency of VCO, this output frequency is through will using as the local intermediate frequency and the radio-frequency signal source of receiver after the frequency conversion.With reference to the structure in every Lu Zhifeng device shown in Figure 5, method of the present invention is utilizing specific accurate measurement evaluation method to estimate each frequency offset estimating value that refers to that the peak device follows the tracks of the road warp simultaneously, also energy or the signal to noise ratio (SIR) according to frequency pilot sign provides the merging control signal, and whether the frequency offset estimating value that is used to control this Lu Zhifeng device participates in the calculating of feedback control signal.
Explained later merges the concrete steps of control: as shown in Figure 4, the baseband I that the travelling carriage RAKE receiver receives and demodulates, Q complex signal are sent to each and refer to peak device (Fingerl to FingerN), each refers to the specific multipath signal of peak device tracking, and provides related offset estimation Δ fl to Δ fn.With reference to Fig. 5, frequency pilot sign through integration is transferred into energy (Energy) or signal to noise ratio (SIR) estimator, calculate energy or signal-to-noise ratio (SNR) estimation value, this estimated value compares with predetermined threshold in threshold compataror, when comparative result when being higher than predetermined threshold, the merging control signal control K switch conducting shown in Figure 4 of threshold compataror output disconnects otherwise then merge control signal control switch K.Like this, each refers to that the measured frequency deviation that estimates of finger peak device of having only energy or signal to noise ratio to be higher than predetermined threshold in the peak device could merge by adder among Fig. 4.Frequency offset signal after the merging is through the averager calculating mean value, and this mean value is sent to low pass filter (LPF) and carries out smoothly then, and the output of LPF is through the FEEDBACK CONTROL voltage of D/A (D/A) conversion formation to local voltage controlled oscillator (VCO).The above-mentioned FEEDBACK CONTROL that the overall frequency deviation of RAKE receiver is carried out that is feedback controlled to, can be implemented in the averaged frequency offset composition of each road multipath of compensation in radio frequency and the intermediate-freuqncy signal thus, under the situation of each road multipath frequency deviation direction unanimity, this overall compensate of frequency deviation can reduce each Lu Zhifeng device and carry out frequency compensated pressure in base band.The merging control signal that method of the present invention utilizes every Lu Zhifeng device to produce especially makes and only utilizes the high relatively path of the quality of reception in total FEEDBACK CONTROL, makes total FEEDBACK CONTROL more effective than the mode in whole all paths of utilization of prior art.
Moreover, as shown in Figure 4, method of the present invention also refers to each that the frequency offset estimation result Δ f of peak device directly feeds back to this and refers to peak device self, is used for the frequency deviation of its track path is carried out independent compensation.Figure 5 shows that and refer to that peak device (Finger) inside carries out the structural representation of frequency separate compensation.Among Fig. 5, after baseband complex signal I, the Q that a certain Lu Zhifeng device is received enters and refers to the peak device, at first carry out the frequency correction compensation according to this frequency deviation feedback signal that refers to the peak device by frequency correction module, frequency correction module will be used the complex conjugate frequency e of this frequency offset estimating value that refers to that peak device measurement estimates
-j2 π Δ fiCarry out complex multiplication operation with baseband complex signal I+jQ, equal that like this baseband complex signal is applied a reverse phase place and rotate the phase deviation of eliminating or weaken the complex signal vector that frequency displacement causes.It is pointed out that the operation of receiver starting stage, do not estimate the frequency shift (FS) Δ f that refers to peak device institute track path owing to measure as yet, so this frequency correction module is inoperative.
Describe the inventive method is carried out the frequency deviation measurement estimation in referring to the peak device step in detail below in conjunction with Fig. 5.As shown in Figure 5, through after the correction of frequency correction module, I, Q baseband complex signal enter integration/cleaning (I/D) module, by this module frequency pilot sign are carried out integration.Then, the frequency pilot sign complex signal behind the integration is carried out normalization by the normalization module, to make things convenient for phase calculation.Subsequently, in multiplication cross (Cross Product) module, utilize phase n and the sine value of φ n-1 and the sine and the cosine value that cosine value calculates the phase deviation Δ φ that is caused by frequency shift (FS) of adjacent pilot symbols, these computational methods specifically can adopt structure shown in Figure 6 to realize by formula (5) expression.The sine value sin Δ of the phase deviation Δ φ that calculates and cosine value cos Δ are imported into interval mapping block, numerical value according to cos Δ φ and sin Δ φ in this module is mapped to one of 0 to 7 work song interval with the phase deviation vector, and determines the value of sin Δ θ according to the subinterval of being shone upon.Calculate by following formula group (12) particularly:
In the 1st, 2,5,6 subintervals, sin Δ θ=| ± cos Δ φ |,
In the 0th, 3,4,7 subintervals, sin Δ θ=| ± sin Δ φ |, (12)
Interval mapping block is also determined the conversion relation between Δ θ and the Δ φ, is determined by following formula group (13) particularly:
The 0th subinterval, Δ φ=-π+Δ θ,
The 1st subinterval, Δ φ=-pi/2-Δ θ,
The 2nd subinterval, Δ φ=-pi/2+Δ θ,
The 3rd subinterval, Δ φ=-Δ θ,
The 4th subinterval, Δ φ=Δ θ, (13)
The 5th subinterval, Δ φ=pi/2-Δ θ,
The 6th subinterval, Δ φ=pi/2+Δ θ,
The 7th subinterval, Δ φ=π-Δ θ.
The formula (8) that aforesaid the 5th subinterval example shown in Figure 1 is adopted only is a kind of situation in formula group (12), (13).
After above-mentioned interval mapping, the sin Δ θ numerical value that is obtained is between 0 value 0.707.This sin Δ θ numerical value compensates sin Δ θ according to formula (11) through the curve compensation module, finishes the approximate estimation to Δ θ by sin Δ θ.The Δ θ estimation numerical value that is obtained is between 0 to π/4, and the numerical value Δ θ that this estimation draws is comparatively accurate.Phase conversion is input with the estimated value of Δ θ, after this vector that interval mapping block provides belongs to the information in subinterval, converses Δ φ numerical value according to the different mining in subinterval with formula group (13).The frequency offset calculation module utilizes formula (2) to calculate actual frequency shift (FS) Δ f according to the Δ φ numerical value that converses.This frequency shift (FS) Δ f directly feeds back to the frequency correction module that refers in the peak device, makes this refer to that the peak device obtains the independent frequency compensation.Like this, method of the present invention refers to each outside unified radio frequency of regulating RAKE receiver of peak device overall average frequency offset signal, the intermediate frequency VCO adopting, also utilize frequency shift (FS) Δ f baseband I, the Q complex signal to input in referring to the peak device that refers to the measured estimation of peak device to carry out the independent frequency compensation, obtain to be better than the Doppler frequency deviation compensation effect of prior art thus.
Because each refers to that the peak device is before the fine convergence of AFC, Doppler frequency deviation weakens the storage effect of frequency pilot sign, the pilot symbol energies that obtains when producing the merging control signal and the estimation of signal to noise ratio are all on the low side, so initial time of RAKE receiver work, the predetermined threshold that refers to the threshold compataror in the peak device can be provided with lower slightlyly, treat that RAKE receiver slightly improves this predetermined threshold after working properly again.
Adopt method of the present invention, can produce under the situation of Doppler frequency shift on a large scale at the travelling carriage high-speed motion, carry out frequency compensation quickly and effectively, making the direct spreading sequence spread spectrum can be applied to travelling carriage needs in the mobile communication environment of high-speed motion.
Claims (8)
1. a frequency bias compensation method that is used for direct sequence spread spectrum mobile communication system travelling carriage separating multiple diameter (Rake) receiver comprises referring to peak device independent frequency compensation and two basic steps of receiver overall average compensation, it is characterized in that:
In referring to peak device independent frequency compensation process, further comprise step:
By integration/cleaning module the complex signal that refers to the frequency pilot sign that the peak device is received is carried out integration;
Carry out normalization by the frequency pilot sign complex signal of normalization module after, and obtain sine value, the cosine value of frequency pilot sign complex signal phase n despreading;
By the multiplication cross module sine value and the cosine value of adjacent pilot symbols complex signal phase n and φ n-1 are carried out the multiplication cross computing, obtain sine value and the cosine value of phase deviation Δ between the adjacent pilot symbols;
This phase deviation vector is mapped to-one of eight subintervals of π to π according to sine and the cosine value of phase deviation Δ by interval mapping block, the width in each subinterval is π/4;
In the subinterval of being shone upon according to the sine value of the phase deviation Δ that converts with cosine value calculates this phase deviation vector and near the phase place angle Δ θ sine value between the reference axis;
Phase place angle Δ θ is estimated by curve compensation by the curve compensation module;
To be estimated by phase conversion that the phase place angle Δ θ that obtains converts according to the interval at place reverts to phase deviation Δ between the actual frequency pilot sign complex signal;
Calculate the frequency shift (FS) Δ f that this refers to peak device institute track path pilot symbol signal by the frequency offset calculation module according to phase deviation Δ between the frequency pilot sign and frequency pilot sign cycle Δ t;
The frequency shift (FS) Δ f of the finger peak device that will be calculated by the appraising frequency bias module feeds back to the frequency correction module that refers in the peak device as feedback signal;
By frequency correction module input is referred to that the chip signal of peak device carries out frequency correction;
In receiver overall average frequency compensation step, further comprise step:
Carry out energy or signal-to-noise ratio (snr) estimation by energy or the signal-to-noise ratio (SNR) estimation module frequency pilot sign after to integration;
By the thresholding comparison module energy or signal-to-noise ratio (snr) estimation value and predetermined threshold are compared, when energy or signal-to-noise ratio (snr) estimation value are higher than predetermined threshold, produce and merge the feasible switch conduction that merges of control signal, cause referring to measure in the peak device calculating that the frequency shift (FS) of estimating participates in the frequency shift (FS) of separating multiple diameter (RAKE) receiver overall average, otherwise when energy or signal to noise ratio are lower than predetermined threshold, produce the merging control signal and make that merging switch disconnects, cause this to refer to that frequency shift (FS) of estimating in the peak device does not participate in the calculating of separating multiple diameter (RAKE) receiver overall average frequency shift (FS);
By combiner each frequency shift (FS) that refers to that the peak device produces that participates in the frequency shift (FS) of calculating separating multiple diameter (RAKE) receiver overall average is merged addition;
By averager the frequency shift (FS) of average acquisition overall average is asked in each frequency shift (FS) of addition;
By low pass filter the overall average frequency shift (FS) is carried out smoothly;
To be converted to the voltage signal that voltage controlled oscillator is controlled through level and smooth overall average frequency shift (FS) by D/A;
Voltage controlled oscillator controlled adjustment institute output frequency, thus local intermediate frequency of receiver and rf frequency regulated.
2. frequency bias compensation method according to claim 1, refer to that at each peak device automatic frequency controls before the fine convergence, in the estimated value and predetermined threshold step relatively by described pilot symbol energies that refers to threshold compataror execution in the peak device and signal to noise ratio, predetermined threshold is provided with low value, after each referred to that peak device automatic frequency is controlled fine convergence, this predetermined threshold was provided with high value.
3. frequency bias compensation method according to claim 1 in the multiplication cross step performed by the multiplication cross module, adopts following formula
Carry out the multiplication cross computing, wherein Δ is the phase deviation between adjacent pilot symbols complex signal phase n and the φ n-1.
4. frequency bias compensation method according to claim 1, in the interval mapping step performed by interval mapping block, adopt the following step to carry out subinterval mapping and the calculating of phase place angle Δ θ sine value:
Will [π, π) the phase deviation interval is divided into 8 subintervals, is respectively: [π ,-3 π/4), [3 π/4,-pi/2), [pi/2 ,-π/4), [π/4,0), [0, π/4), [π/4, pi/2), [pi/2,3 π/4) and [3 π/4, π), number consecutively is subinterval 0 to 7;
In the 1st, 2,5,6 subintervals, sin Δ θ=| ± cos Δ φ |,
In the 0th, 3,4,7 subintervals, sin Δ θ=| ± sin Δ φ |.
5. frequency bias compensation method according to claim 1, in the Δ θ estimation steps performed by the curve compensation module, adopt following formula to carry out curve compensation and the estimation of the phase place angle of cut:
f(sinΔθ)＝0.21(sinΔθ)
2+1
6. frequency bias compensation method according to claim 1, in the phase transition step performed by phase conversion, adopt following formula to carry out phase transition:
The 0th subinterval, Δ φ=-π+Δ θ,
The 1st subinterval, Δ φ=-pi/2-Δ θ,
The 2nd subinterval, Δ φ=-pi/2+Δ θ,
The 3rd subinterval, Δ φ=-Δ θ,
The 4th subinterval, Δ φ=Δ θ,
The 5th subinterval, Δ φ=pi/2-Δ θ,
The 6th subinterval, Δ φ=pi/2+Δ θ,
The 7th subinterval, Δ φ=π-Δ θ.
7. frequency bias compensation method according to claim 1, in the frequency offset calculation step performed by the frequency offset calculation module, adopt following formula to carry out frequency offset calculation:
8. frequency bias compensation method according to claim 1, in the frequency deviation independent compensation step, frequency correction module will be used the complex conjugate frequency e of this frequency offset estimating value that refers to that peak device measurement estimates in the finger peak device performed by frequency correction module
-j2 π Δ ftCarry out complex multiplication operation with baseband complex signal I+jQ, thus baseband complex signal is applied a reverse phase place and rotate the phase deviation of eliminating or weaken the complex signal vector that frequency displacement causes.
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