JP3419361B2 - Spread spectrum receiver - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum receiver having a function of correcting the frequency of a carrier wave.

[0002]

2. Description of the Related Art Conventionally, in a communication system using a code division multiple access (CDMA) system, in quasi-coherent detection used in a receiver, if a carrier wave reproduced by an oscillator has a frequency offset, an error characteristic is deteriorated. A correction circuit that corrects the frequency of the carrier wave is required.

An example of a spread spectrum receiver equipped with this correction circuit is disclosed in Japanese Patent No. 2672769. In this system, the baseband signal output from the quasi-synchronous detection circuit is delayed, the baseband signals before and after the delay are respectively correlated with the spread code to obtain the partial correlation value, and then the delayed partial correlation value After multiplying the complex conjugate number by the partial correlation value before delay and separating the imaginary part of the multiplied value, the integrator integrates for a certain period to obtain the information indicating the frequency error, and based on that value, the carrier frequency I am trying to make corrections.

[0004]

In the above-mentioned conventional apparatus, the carrier frequency is corrected based on the information indicating the frequency error obtained from the correlation value between the baseband signal and the spread code. For this reason, frequency synchronization cannot be performed until the synchronization acquisition is completed, such as when the power is turned on (when the power is turned on) or when the device returns from an out-of-service area. Since the frequency correction can be performed, there is a problem that the frequency correction is delayed.

The present invention has been made in view of the above problems, and an object thereof is to enable frequency correction even before synchronization is achieved.

[0006]

In order to achieve the above-mentioned object, in the invention described in claim 1, as the correction means for correcting the frequency of the carrier wave, the calculation of the correlation output from the quasi-synchronous detection means (10) is performed. A matched filter (31) that outputs a block correlation vector obtained by dividing a complex correlation vector that is correlated with a spread code into a plurality of blocks within one symbol for the baseband signal before being performed, and is output from this matched filter. Means (32, 33) for obtaining information indicating the frequency error of the carrier based on the block correlation vector for each block, and the matched filter
Is configured to output the correlation vector for each symbol
And the integration means uses the phase output from the matched filter.
Integrate when the magnitude of the function vector exceeds the threshold
And is characterized in that the frequency of the carrier wave is corrected based on the information indicating the frequency error integrated by the integrating means .

By using the improved matched filter (31) as described above, a complex correlation vector that is correlated with a spread code is obtained.
A block that divides the kutru into multiple blocks within one symbol.
The frequency error of the carrier based on the clock correlation vector
Get information and output from matched filter
Carry at the timing when the magnitude of the correlation vector exceeds the threshold
Information indicating the frequency error of the transmitted wave is integrated, and the integrated frequency
Correct the carrier frequency based on the information indicating the wave number error
Because in the so that, it is possible to perform even frequency correction before synchronization can be established.

[0008]

[0009]

The information indicating the above-mentioned frequency error is
As in the invention described in claim 2 , it is possible to use a frequency error vector obtained from a block correlation vector for each block. Further, as in the third aspect of the invention, the phase angle of the frequency error vector can be used.

According to the fourth aspect of the invention, the quasi-synchronous detection means (10) is used as the correction means for correcting the frequency of the carrier wave.
The first means (31 to 36) for outputting the information indicating the frequency error of the carrier wave based on the baseband signal before being subjected to the calculation of the correlation, which is obtained by the calculation of the correlation. and second means you outputs information indicating the frequency error of the carrier wave based on the correlation vector (15 to 18), in the state that are not synchronized on the basis of the calculation result of the correlation, the output frequency from the first means A third means (19) for correcting the frequency of the carrier wave based on the information indicating the error and, in a synchronized state, correcting the frequency of the carrier wave based on the information indicating the frequency error output from the second means. , 20,
And 23 and 24), only contains the first means, baseband
The complex correlation vector that is correlated with the spreading code
A block obtained by dividing the tor into multiple blocks within one symbol.
A matched filter that outputs a correlation vector (31)
And for each block output from this matched filter
Frequency error of carrier based on block correlation vector
Means (32, 33) for obtaining information indicating
Integration means (34) for integrating the indicated information,
The chid filter also outputs a correlation vector for each symbol.
And the integrating means comprises a matched filter
Thais in which the magnitude of the output correlation vector exceeds the threshold
And the information indicating the frequency error is output.
The feature is that it is designed to do.

According to the present invention, when synchronization is not achieved, frequency correction is performed from the baseband signal before correlation, and when synchronization is achieved and stable, a correlation vector obtained by calculation of correlation is obtained. The frequency correction method can be switched so that the frequency correction is performed based on the above, and appropriate frequency correction can be performed. The state of being in sync includes the state of being in clock synchronization and the state in which the base station is captured and correlated.

According to the fifth aspect of the invention, the quasi-synchronous detection means (10) is used as the correction means for correcting the frequency of the carrier wave.
A first means (31 to 36) for obtaining information indicating the frequency error of the carrier based on the baseband signal before being subjected to the correlation calculation, and the carrier based on the correlation vector obtained by the correlation calculation. Second means (15 to 18) for obtaining the information indicating the frequency error of No. 1, third means (23) for detecting the magnitude of the correlation vector, and first means when the magnitude of the correlation vector is smaller than a predetermined value. The frequency of the carrier wave is corrected based on the information indicating the frequency error output from the means, and based on the information indicating the frequency error output from the second means when the magnitude of the correlation vector is equal to or larger than a predetermined value. Fourth means for correcting the frequency of the carrier wave (19,
And 20, 24), only contains the first means, baseband
The complex correlation vector that is correlated with the spreading code
A block obtained by dividing the tor into multiple blocks within one symbol.
A matched filter that outputs a correlation vector (31)
And for each block output from this matched filter
Frequency error of carrier based on block correlation vector
Means (32, 33) for obtaining information indicating
Integration means (34) for integrating the indicated information,
The chid filter also outputs a correlation vector for each symbol.
And the integrating means comprises a matched filter
Thais in which the magnitude of the output correlation vector exceeds the threshold
And the information indicating the frequency error is output.
The feature is that it is designed to do.

Also in the present invention, as in the invention described in claim 4 , it is possible to perform appropriate frequency correction by switching the frequency correction method depending on whether the synchronization is established or not. .

In the invention according to claim 4 or 5 , the second means is the same as the invention according to claim 6 ,
The information indicating the frequency error of the carrier can be obtained based on the block correlation vector for each block.

The reference numerals in parentheses of the above-mentioned means are for showing the correspondence with the concrete means described in the embodiments described later.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention shown in the drawings will be described.

FIG. 1 shows the configuration of a spread spectrum receiver according to an embodiment of the present invention.

In the figure, the spread spectrum received signal is input to the quasi-coherent detection circuit 10 and quasi-coherently detected using the carrier signal from the oscillator 11. This quasi-synchronous detection circuit may have the same configuration as that disclosed in Japanese Patent No. 2672769, and its specific configuration is not shown, but a multiplier, a π / 2 phase shifter, and a low-pass filter are used. , A / D converter, etc., and outputs digital orthogonal baseband signals (complex baseband signals).

The correlator 12 correlates the output baseband signal with the spreading code from the spreading code generator 13. As this spreading code, the same spreading code as that used for spread spectrum of the received signal is used. As the spreading code, a PN code, a Walsh code, or a combination of both is used.

The output from the correlator 12 is integrated for each block by the block correlation circuit 14 and output as a block correlation vector. In this embodiment, as shown in FIG. 2, one symbol (consisting of n chips) is divided into two blocks, and the output vector φ from the correlator 12 is
The first half block correlation vector φ ₁ integrated by the first half n / 2 chip section (block 1 section) and the second half block correlation vector φ ₂ integrated by the second half n / 2 chip section (block 2 section) are output. In the present specification, arrows attached to φ, φ ₁ , φ _2, etc. shown in the drawings are omitted.

Here, the block correlation vector is a vector consisting of two elements of a real part α and an imaginary part β of the correlation value, and can be considered as a complex number represented by φ = α + jβ, and the first half block correlation vector φ ₁ and the latter half block correlation vector φ ₂ are the angles θ ₁ and θ ₂ as shown in FIG.
Each is represented by a vector with ₂ .

The first half block correlation vector φ ₁ is delayed by the delay circuit 15 by ½ of the symbol period T _sym .
Further, the complex conjugate calculator 16 obtains the complex conjugate vector φ ₁ ^* of the first half block correlation vector. Then, in the complex multiplier 17, the complex conjugate vector φ ₁ ^* of the delayed first half block correlation vector and the complex multiplication of the latter half block correlation vector φ ₂ are performed. The vector represented by this complex multiplication becomes the frequency error vector Δφ (= φ ₁ ^* × φ ₂ ) as shown in FIG. The phase angle Δθ (= θ ₂ −θ ₁ ) of this frequency error vector indicates the amount of phase rotation between block 1 and block 2, that is, the frequency error. The phase angle Δθ of the frequency error vector can be obtained from the frequency error vector Δφ by using Expression 1.

[0024]

## EQU00001 ## .DELTA..theta. = Arg (.DELTA..phi.) In this embodiment, the frequency error vector .DELTA..phi. Output from the complex multiplier 17 is integrated by the integrator 18 for a predetermined integration interval over several symbols. By performing this integration, the frequency error vector Δφ is averaged and the S / N ratio can be improved.

The output of the integrator 18 is input to the frequency error detection circuit 19 via the switching circuit 24. In the frequency error detector 19, the phase difference Δθ (frequency error) is obtained from the integrated frequency error vector Δφ using the above-mentioned mathematical expression 1. Then, based on this phase difference Δθ, the frequency correction value determination circuit 20 determines the frequency correction value using, for example, a table of the phase difference Δθ and the frequency correction value, and supplies the oscillator 11 with a control signal corresponding to the frequency correction value. Output.
The oscillator 11 is composed of a VCO or the like, and the frequency of the carrier wave in the oscillator 11 is corrected by the control signal output from the frequency correction value determination circuit 20.

As described above, in this embodiment, the baseband signal output from the quasi-synchronous detection circuit 10 is 1
Block correlation vectors φ ₁ and φ ₂ that are correlated with the spreading code are obtained for each block divided into two in the symbol, and the first half block correlation vector φ ₁ is delayed to obtain its complex conjugate vector φ ₁ ^* . The complex error vector Δφ is obtained by performing complex multiplication of the complex conjugate vector φ ₁ ^* and the latter half block correlation vector φ _2.
After integrating φ, the phase difference Δθ is obtained to correct the carrier frequency. As a result, the oscillator 11
It is possible to perform frequency correction so that the frequency offset amount of the carrier wave output from is close to zero.

Note that the number of divisions within one symbol is not limited to 2, and can be larger than that. Now, let the number of divisions be k, and let the frequency offset amount (frequency deviation amount) be Δω.
Then, the phase difference Δθ is expressed by Equation 2.

[0028]

## EQU00002 ## .DELTA..theta. =. DELTA..omega..multidot.T _sym / k where _{-.pi..ltoreq..DELTA..theta..ltoreq..pi} .

[0029]

[Expression 3] | Δω | ≦ π · k / T _{sym From} Expression 3, it can be seen that the detectable frequency offset amount can be increased by increasing the block division number k.

Further, as shown in FIG. 1, the former half block correlation vector φ ₁ obtained through the delay circuit 15 and the latter half block correlation vector φ ₂ output from the block correlation circuit 14 are added by the adder 21. It By this addition, it is possible to obtain the same correlation vector as in the normal case where the above block division is not performed. Then, the demodulation processing circuit 22 performs demodulation processing based on the correlation vector, and demodulated data is output.

The above-mentioned carrier frequency correction is performed in a stable state where the spread signal is synchronized. Since the synchronization is not established at the initial stage, such as when the power is turned on (when the power is turned on) or when the vehicle returns from the outside of the service area, frequency correction is performed if the signal after the above correlation calculation (despreading process) is used. It is not possible.

Therefore, in this embodiment, the power calculation circuit 23, the switching circuit 24, and the initial carrier frequency correction circuit 100 are provided so that the frequency of the carrier wave can be corrected even at the initial stage. That is, the power calculation circuit 23 obtains the magnitude of the block correlation vector in one symbol output from the block correlation circuit 14 (for example, the power obtained by squaring the real part and the imaginary part of the vector and adding them). When the magnitude of the block correlation vector is equal to or larger than a predetermined value, the switching circuit 24 is controlled so that the integrator 18 and the frequency error detection circuit 19 are connected, assuming that they are synchronized and stable. Also,
When the magnitude of the block correlation vector is smaller than a predetermined value, the initial carrier wave frequency correction circuit 100 and the frequency error detection circuit 19 are determined to be in an initial state where synchronization is not achieved.
The switching circuit 24 is controlled so as to connect.

The initial carrier frequency correction circuit 100 will be specifically described below.

The initial carrier frequency correction circuit 100 is
The matched filter 31, the complex conjugate calculator 32, the complex multiplier 33, the integrator 34, the power calculator 35,
It is composed of a comparator 36.

The baseband signal output from the quasi-coherent detection circuit 10 is input to the matched filter 31. The matched filter is generally used for synchronization supplement and measurement of delay profile by pilot symbols. The matched filter 31 used in this embodiment has an improved configuration of the normally used matched filter. FIG. 4 shows its specific configuration.

The matched filter 31 is composed of a transversal filter. The input baseband signal is sequentially delayed by a plurality of delay lines 311, and the signal at the connection point (tap) of each delay line 311 has a tap coefficient (set according to the spread code) 312 a ₁ , A ₂ ,
..., each multiplied by a _N. The correlation vector can be obtained by adding the values multiplied by the tap coefficient.

In this embodiment, the tap is divided into the first half and the second half, and the first half block correlation vector of one symbol is obtained from the adder 313, and the second half block correlation vector is obtained from the adder 314. Also, the adder 315
A correlation vector for each symbol is obtained from Here, the first half block correlation vector, the second half block correlation vector, and the correlation vector correspond to the first half block correlation vector φ ₁ , the second half block correlation vector φ ₂ , and the output vector φ output from the block correlation circuit 14 described above. Therefore, in the following description, the same symbols are attached.

From the first half block correlation vector φ ₁ output from the matched filter 31, the complex conjugate calculator 32
Then, the complex conjugate vector φ ₁ ^* is obtained, and the complex multiplier 17 performs complex multiplication of the complex conjugate vector φ ₁ ^* and the latter half block correlation vector φ ₂ to obtain the frequency error vector Δφ.
(= Φ ₁ ^* × φ ₂ ) is required. The frequency error vector Δφ is integrated by the integrator 34 in a plurality of symbol intervals.

The integration of the integrator 34 is performed on the basis of the timing signal obtained by the power calculation circuit 35 and the comparator 36. That is, the magnitude of the correlation vector φ is obtained by the power calculation circuit 35 from the correlation vector φ output from the matched filter 31, and the magnitude of the correlation vector φ is compared with the threshold value by the comparator 36. When the magnitude of the correlation vector φ is equal to or larger than the threshold value, it is determined that the correlation is obtained, the timing signal is output from the comparator 36 to the integrator 34, and the integrator 34 integrates the frequency error vector Δφ.

The integrated value of the frequency error vector Δφ thus obtained is input to the frequency error detection circuit 19 via the switching circuit 24. Then, the frequency error detection circuit 19 determines the phase difference Δθ, the frequency correction value determination circuit 20 determines the frequency correction value, and the oscillator 11 outputs a control signal corresponding to the frequency correction value. As a result, the frequency of the carrier wave in the oscillator 11 is corrected.

By providing the initial carrier wave frequency correction circuit 100 using the matched filter 31 as shown in this embodiment, the carrier wave frequency is corrected even in the initial stage where synchronization is not achieved such as at power-on. be able to.

Then, in a synchronized and stable state,
By stopping the operation of the matched filter 31 and performing frequency correction based on the block correlation vector from the block correlation circuit 14, it is possible to reduce current consumption.

Further, according to the above embodiment,
It is possible to perform frequency correction based on received signals from a plurality of base stations as well as received signals from one base station. That is, as shown in FIG. 5, when the received signals A to D are sequentially input, the power calculation circuit 35 obtains peaks A to D of the magnitudes of the respective correlation vectors. Of these, when the peak is above the threshold,
The integrator 34 integrates the frequency error vector. In the case of FIG. 5, since the peak A, the peak C, and the peak D are equal to or more than the threshold value, the frequency error vector obtained from each peak is integrated by the integrator 34. As a result, as shown in FIG. 6, a frequency error vector obtained by synthesizing the frequency error vectors obtained from the peaks A, C, and D can be obtained, and the frequency correction is performed on the basis of the frequency error vector. It can be performed accurately and at high speed.

Further, by using such an initial carrier frequency correction circuit 100, even when intermittent packet data is received as in packet communication, chip synchronization and frequency correction are performed within a given fixed time. Can be completed.

The number of divisions in one symbol in the initial carrier frequency correction circuit 100 is not limited to 2, and may be more than that.

Further, in the above-mentioned embodiment, the frequency error vector is used as the information indicating the frequency error of the carrier wave obtained based on the block correlation vector divided into a plurality of blocks. It may be a corner.

In the above-described embodiment, the correlation between the baseband signal and the spread code is calculated, then the integration is performed for each block, and then the first-half block correlation vector is delayed, but Japanese Patent No. 2672769 is disclosed. As described in the publication, the baseband signal may be delayed, and the baseband signal before and after the delay may be correlated with the spreading code.

Note that the constituent elements of the above-described spread spectrum receiver shown in FIG. 1 are not limited to those configured by hardware, but may be configured by software, so that each constituent element has its own function. It is understood as a means to realize.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a spread spectrum receiver according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram for explaining a relationship between a first half block correlation vector and a second half block correlation vector when one symbol is divided into two blocks.

FIG. 3 is a diagram for explaining a first half block correlation vector, a second half block correlation vector, and a frequency error vector.

FIG. 4 is a diagram showing a specific configuration of a matched filter 31.

FIG. 5 is a diagram for explaining that when received signals are sequentially input from a plurality of base stations, peaks of magnitudes of respective correlation vectors are sequentially obtained.

FIG. 6 is a diagram for explaining that frequency error vectors based on received signals from a plurality of base stations are combined to obtain a combined frequency error vector.

[Explanation of symbols]

10 ... Quasi-synchronous detection circuit, 11 ... Oscillator, 12 ... Correlator,
13 ... Spread code generator, 14 ... Block correlation circuit, 15
... delay circuit, 16 ... complex conjugate calculator, 17 ... complex multiplier, 18 ... integrator, 19 ... frequency error detector, 20 ... frequency correction value determination circuit, 21 ... adder value, 22 ... demodulation processing circuit, 23 ... power calculation circuit, 24 ... switching circuit, 31 ...
Matched filter, 32 ... Complex conjugate operator, 33 ... Complex multiplier, 34 ... Integrator, 35 ... Power operation circuit, 36 ...
Comparator, 100 ... Initial carrier frequency correction circuit.

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04J 13/00-13/06 H04B 1/69-1/713 H04L ⁷ /00-7/10

Claims (6)

(57) [Claims] 1. A quasi-synchronous detection means for quasi-coherently detecting a received signal using a carrier wave and outputting a baseband signal.
0) and the correlation calculation means (12 to 1) for calculating the correlation between the baseband signal output from the quasi-synchronous detection means and the spread code.
4) and a spread spectrum receiver configured to perform demodulation processing based on an output from the correlation calculation means, comprising a correction means for correcting the frequency of the carrier wave, wherein the correction means comprises the quasi-synchronization A matched filter that outputs a block correlation vector obtained by dividing a complex correlation vector obtained by correlation with a spreading code into a plurality of blocks with respect to the baseband signal output from the detection means before the calculation of the correlation is performed. (31), means (32, 33) for obtaining information indicating the frequency error of the carrier wave based on the block correlation vector for each block output from the matched filter, and integration for integrating the information indicating the frequency error. Means (34)
And the matched filter includes a correlation vector for each symbol.
Is also configured to output the
Magnitude of the correlation vector output from the Tide filter
The integration is performed at the timing when is above the threshold.
The spread spectrum receiver is configured to correct the frequency of the carrier wave based on the information indicating the frequency error integrated by the integrating means . 2. The spread spectrum receiver according to claim 1 , wherein the information indicating the frequency error is a frequency error vector obtained from a block correlation vector for each block. 3. The spread spectrum receiver according to claim 1 , wherein the information indicating the frequency error is a phase angle of a frequency error vector obtained from a block correlation vector for each block. 4. A quasi-coherent detection means (1) for quasi-coherently detecting a received signal using a carrier wave and outputting a baseband signal.
0) and the correlation calculation means (12 to 1) for calculating the correlation between the baseband signal output from the quasi-synchronous detection means and the spread code.
4) and a spread spectrum receiver configured to perform demodulation processing based on an output from the correlation calculation means, comprising a correction means for correcting the frequency of the carrier wave, wherein the correction means comprises the quasi-synchronization first means you outputs information indicating the frequency error of the carrier on the basis of the baseband signal before computation of the correlation output from the detection means is carried out (31-3
6), wherein the second means you outputs information indicating the frequency error of the carrier on the basis of the correlation vector obtained by the correlation computation (15 to 18), wherein the synchronization is based on the calculation result of the correlation In the non-state, the frequency of the carrier is corrected based on the information indicating the frequency error of the carrier output from the first means, and in the synchronized state, the frequency is output from the second means. Third means (19, 2) for correcting the frequency of the carrier based on the information indicating the frequency error of the carrier.
And 0,23,24), only contains the first means, with respect to the base band signal, spread
The complex correlation vector that is correlated with the sign within one symbol
Output block correlation vector divided into multiple blocks
Matched filter (31) and this matched fill
To the block correlation vector for each block output from
On the basis of how to obtain the information indicating the frequency error of the carrier wave.
Integrate the stage (32, 33) and the information indicating the frequency error
An integrating means (34) for
Is designed to output the correlation vector for each symbol.
And the integrating means outputs from the matched filter.
The magnitude of the applied correlation vector is greater than or equal to a threshold value.
Information indicating the frequency error by performing the integration in imming
A spread spectrum receiver characterized by being designed to output . 5. A quasi-coherent detection means (1) for quasi-coherent detection of a received signal using a carrier wave and outputting a baseband signal.
0) and the correlation calculation means (12 to 1) for calculating the correlation between the baseband signal output from the quasi-synchronous detection means and the spread code.
4) and a spread spectrum receiver configured to perform demodulation processing based on an output from the correlation calculation means, comprising a correction means for correcting the frequency of the carrier wave, wherein the correction means comprises the quasi-synchronization first means you outputs information indicating the frequency error of the carrier on the basis of the baseband signal before computation of the correlation output from the detection means is carried out (31-3
6), third detecting said second means you outputs information indicating the frequency error of the carrier on the basis of the correlation vector obtained by the correlation computation (15 to 18), the magnitude of the correlation vector Means of (2
3) and the frequency of the carrier wave based on the information indicating the frequency error of the carrier wave output from the first means when the magnitude of the correlation vector detected by the third means is smaller than a predetermined value. The frequency of the carrier wave is corrected based on the information indicating the frequency error of the carrier wave output from the second means when the magnitude of the correlation vector detected by the third means is equal to or larger than a predetermined value. and fourth means for correcting (19,20,24), viewed including the said first means, to said baseband signal, spreading
The complex correlation vector that is correlated with the sign within one symbol
Output block correlation vector divided into multiple blocks
Matched filter (31) and this matched fill
To the block correlation vector for each block output from
On the basis of how to obtain the information indicating the frequency error of the carrier wave.
Integrate the stage (32, 33) and the information indicating the frequency error
An integrating means (34) for
Is designed to output the correlation vector for each symbol.
And the integrating means outputs from the matched filter.
The magnitude of the applied correlation vector is greater than or equal to a threshold value.
Information indicating the frequency error by performing the integration in imming
A spread spectrum receiver characterized by being designed to output . 6. The correlation calculating means outputs a block correlation vector obtained by dividing a complex correlation vector correlated with a spread code into a plurality of blocks within one symbol, and the second means comprises: The spread spectrum receiver according to claim 4 or 5 , wherein the spread spectrum receiver is configured to obtain information indicating a frequency error of the carrier based on a block correlation vector for each block.