JPH11261443A - Spread modulation signal receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain quick synchronization acquisition by applying Fourier transform to a base band spread modulation signal and a reference signal, generating a multiplication signal between a complex conjugate signal of the reference signal that is Fourier-transformed and the base band spread modulation signal that is Fourier-transformed, generating a correlation signal by applying inverse Fourier transform to the multiplication signal so as to limit each frequency band width of the Fourier-transformed signal. SOLUTION: An input terminal of a reception section 1 consisting of a base band signal generating section 13, an analogue/digital converter section 14 and a 2nd memory 15 is connected to an antenna 11, and its output terminal is connected to an input terminal of a 1st Fourier transform section 2. An input terminal of a 1st filter means 3 is connected to an output terminal of the 1st Fourier transform section 2, and its output terminal is connected to a 1st input terminal of a multiplier section 7. An output terminal of a reference signal generating section 4 is connected to an input terminal of a 2nd Fourier transform section 5. An input terminal of a 2nd filter means 6 is connected to an output terminal of the 2nd Fourier transform section 5 and its output terminal is connected to a 2nd input terminal of the multiplier section 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread-spectrum modulated signal receiving apparatus, and more particularly, to multiplying a Fourier-transformed baseband spread-spectrum modulated signal by a Fourier-transformed reference signal, and performing inverse Fourier transform on the multiplied signal to obtain a correlation signal. The present invention relates to a spread-modulated signal receiving apparatus capable of achieving a quick synchronization acquisition by reducing the amount of calculation required until a signal is generated.

[0002]

2. Description of the Related Art Conventionally, a moving object tracking method using radio waves has been used to track the current position of a moving object that appropriately moves within a predetermined area. In this mobile object tracking method, a transmitter that transmits radio waves to a mobile object is carried, and a base station that receives the radio waves radiated from the transmitter is provided near a required area. The current position of the moving object is known based on the arrival direction of the vehicle. In this mobile object tracking method, various signal modulation methods can be used as a signal modulation method transmitted / received between a transmitter carried by the mobile object and a base station. A spread modulation method using a PN code is known.

[0003] In the spread modulation system using a PN code, a primary modulation signal such as PSK (pulse shift keying) is formed on the transmission side by transmission data, and then a PN (pseudo-modulation) signal is added to the primary modulation signal. Forming a spread modulation signal (secondary modulation signal) multiplied by a random noise) code,
Next, the spread modulation signal is converted into a transmission signal and transmitted on radio waves. On the other hand, on the receiving side, a baseband spread modulated signal is extracted from the received radio wave, and the product sum of the baseband spread modulated signal and a reference signal formed using the same PN code as the PN code multiplied on the transmitting side is calculated. Thus, a correlation signal is generated. Then, this correlation signal is converted to PS
K demodulation is performed to obtain received data.

FIG. 13 is a waveform diagram showing an example of a signal waveform used in the spread modulation system using the PN code, wherein A shows a primary (PSK) modulated signal. Indicates a PN code, and C indicates a spread modulation signal obtained by multiplying A and B by the illustrated waveform.

As shown in FIG. 13, primary (PSK)
The relationship between the modulation signal and the PN code is such that a plurality of chip sections Tc of the PN code are allocated to each bit section T of the primary (PSK) modulation signal, and is usually selected such that T≫Tc.

FIG. 14 is a characteristic diagram showing a frequency spectrum of a signal used in the spread modulation method using the PN code. A curve A shows a frequency spectrum of a primary (PSK) modulated signal. Indicates the frequency spectrum of the spread modulation signal.

As shown in FIG. 14, primary (PSK)
The relationship between the frequency spectrum distribution of the modulated signal and the spread modulated signal is that the frequency spectrum of the primary (PSK) modulated signal is distributed within a relatively narrow range, whereas the frequency spectrum of the spread modulated signal is distributed over a wide range. I do.

In FIG. 14, when the frequency spectrum of the spread modulation signal causes interference, it is necessary to limit the frequency spectrum as shown by curve B and the frequency band as shown by curve C. is there. At this time, as shown in FIG. 13, the waveform of the spread modulation signal indicated by the curve C is band-limited, and becomes a waveform indicated by the curve d.

Next, FIG. 15 is a block diagram showing an example of a main part configuration of a known spread modulation signal receiving apparatus of a spread modulation system using a PN code.

As shown in FIG. 15, a spread modulation signal receiving apparatus includes a receiving section 41, a first Fourier transform section 42,
A reference signal generator 43, a second Fourier transformer 44, a multiplier 45, an inverse Fourier transformer 46, a demodulator 47,
It comprises a control unit 48, an antenna 49, and a signal output terminal 50. In this case, the receiving unit 41 includes a baseband signal generating unit 51, an analog-digital (A / D) converting unit 52, and a memory 53.

The receiving section 41 has an input end connected to the antenna 49 and an output end connected to an input end of the first Fourier transform section 42. The output terminal of the reference signal generator 43 is connected to the input terminal of the second Fourier transformer 44. Multiplication unit 4
Reference numeral 5 denotes a first input terminal connected to the output terminal of the first Fourier transform unit 42, a second input terminal connected to the output terminal of the second Fourier transform unit 44, and an output terminal connected to the input terminal of the inverse Fourier transform unit 46. Connected to. The demodulation unit 47 has an input terminal connected to the output terminal of the inverse Fourier transform unit 46, and an output terminal connected to the signal output terminal 50.
Connected to. The control unit 48 includes a reception unit 41, a first Fourier transformation unit 42, a reference signal generation unit 43, a second Fourier transformation unit 44, a multiplication unit 45, an inverse Fourier transformation unit 46, and a demodulation unit 4.
7 respectively. In the receiving unit 41,
The baseband signal generator 51 has an input terminal connected to the input terminal of the receiver 41 and an output terminal connected to an input terminal of the A / D converter 52. The input terminal of the memory 53 is the A / D converter 5.
2, and the output terminal is connected to the output terminal of the receiver 41.

Here, FIG. 2 shows the P used on the transmitter side.
FIG. 16 is a signal waveform diagram illustrating an example of an N code and a reference signal generated by the reference signal generation unit 43. FIG. 16 illustrates a transform obtained by performing a Fourier transform on the reference signal illustrated in FIG. It is a signal waveform diagram of a signal.

FIG. 3 is a signal waveform diagram showing an example of a baseband spread modulation signal output from the receiving section 41.
The dots (black diamonds) shown in FIG. 3 indicate sample points sampled by the A / D converter 52. FIG. 17 is a characteristic diagram of a converted signal obtained after Fourier-transforming the baseband spread-spectrum modulated signal illustrated in FIG. 3 by the first Fourier transformer 42. Here, the receiving unit 41, as shown by a curve C in FIG.
The transmitter receives a radio signal including a spread modulated signal whose band is limited.

FIG. 18 is a signal waveform diagram showing a correlation signal output from the inverse Fourier transform unit 46 when the frequency spectrum shown in FIGS. 16 and 17 is input to the multiplier 45. The dots (black diamonds) shown in FIG. 18 indicate the correlation values at discrete times.

The operation of the spread-modulated signal receiving apparatus having the above configuration will be described below with reference to FIGS. 2, 3, and 16 to 18.

On the transmitter side, PN as shown in FIG.
When the signal radio wave spread and modulated by the code and band-limited is captured by the antenna 49, the baseband signal generation unit 51 of the reception unit 41, as well known, amplifies the reception signal and frequency. By performing processing such as conversion, an analog baseband spread modulation signal is extracted and supplied to the A / D converter 52. The A / D converter 52 converts the analog baseband spread modulation signal into a digital baseband spread modulation signal as shown in FIG.
A fixed number of samples are temporarily stored in the memory 53. Next, the baseband spread modulation signal read from the memory 53 is Fourier-transformed in the first Fourier transform unit 42 to be converted into a frequency domain signal as shown in FIG. It is supplied to the input end.
Further, the reference signal generation unit 43 generates, as a reference signal, the same code as the PN code generated on the transmitter side as shown in FIG. The reference signal is Fourier-transformed by the second Fourier transform unit 44, converted into a reference frequency domain signal as shown in FIG. 16, and supplied to the second input terminal of the multiplier 45. At this time, the multiplication unit 4
5 for the supplied complex conjugate signal of the reference frequency domain signal and the similarly supplied frequency domain signal,
Multiplication is performed for each of the same frequency components to generate a frequency domain multiplication signal, which is supplied to the inverse Fourier transform unit 46. The frequency domain multiplied signal is subjected to inverse Fourier transform in the inverse Fourier transform unit 46, and the frequency domain multiplied signal is converted into a time domain multiplied signal as shown in FIG. This time domain multiplied signal is, as is well known, FIG.
2 is a correlation signal between a baseband spread modulation signal as shown in FIG. 2 and a reference signal as shown in FIG. The correlation signal is supplied to the demodulation unit 47, and when PSK demodulation is performed to determine the data at the time when the correlation value becomes maximum, reception data corresponding to the transmission data is obtained. It is supplied to a utilization circuit (not shown) via the output terminal 50. Note that these series of operations are performed by the control unit 48.
Is performed under the control of

In a known spread modulation signal receiving apparatus, as a means for obtaining a correlation signal output by the inverse Fourier transform unit 46, one baseband spread modulation signal is used.
2. Description of the Related Art A matched filter is known in which a sample is temporally shifted and a sum of products with a reference signal is calculated to obtain a correlation signal. In this case, assuming that the number of samples of the baseband spread modulation signal for one cycle of the reference signal is N,
In order to obtain one correlation value, the sum is obtained by multiplying the N samples of the reference signal and the N samples of the baseband spread modulation signal, so that N times of product-sum calculations are required. In the above calculation, the baseband spread modulation signal is temporally shifted from 0 to (N−1) samples to obtain a correlation value.
The total is N ² times of sum of products. Further, when the data transmitted by spread modulation is multi-level PSK modulated, it is necessary to calculate the correlation value for each of the in-phase channel and the orthogonal channel, so the number of times of product sum is 2N ² times.

On the other hand, as shown in FIG. 15, the number of times of product sum when the correlation is obtained by using the Fourier transform and the inverse Fourier transform is as follows. The number of samples N
Is a power of 2 raised to an integer power, and the Fourier transform and the inverse Fourier transform include a well-known fast Fourier transform (FFT; FFT).
ast Fourier Transform). First, the first Fourier transform unit 42 and the second Fourier transform unit 44 respectively use Nlog
₂ N times (converted into complex numbers), the multiplication unit 45 takes N times (converted into complex numbers), and the inverse Fourier transform unit 46 takes Nlog ₂ N times (converted into complex numbers). The sum is (N + 3Nlog ₂ N) times in complex number conversion, and (28N + 12Nlo) in real number conversion as in the case of the matched filter.
g ₂ N) times. Note that the same number of product-sum times is obtained even when multi-level PSK modulation is performed. When obtaining a correlation using the Fourier transform and the inverse Fourier transform, if N is large, a correlation signal can be obtained with a smaller number of product-sum times than with a matched filter.
There is an advantage that synchronization acquisition can be performed faster.

[0019]

By the way, the above-mentioned known spread modulation signal receiving apparatus which obtains a correlation by using Fourier transform, uses a frequency band (conversion) used when Fourier transforms a baseband spread modulation signal or a reference signal. The correlation is obtained using the total number of samples in the frequency band. Therefore, when the baseband spread modulation signal is band-limited as shown in FIG. 17, even if samples other than the occupied frequency band are not multiplied by the Fourier-transformed reference signal, the correlation signal is converted. I couldn't ask.

Since the number of sums of products until the correlation signal is obtained is determined by the number of data (N) in the conversion frequency band, the baseband spread modulation signal is band-limited as described above. However, it was difficult to perform synchronization acquisition by reducing the number of times of product summation.

The present invention has been made in view of such a background, and an object of the present invention is to obtain a correlation by using a Fourier transform, thereby effectively using a sample to be transformed, thereby obtaining a product-sum number. It is an object of the present invention to provide a spread-spectrum signal receiving apparatus that reduces the number of signals and performs quick synchronization acquisition.

[0022]

To achieve the above object, a spread modulation signal receiving apparatus according to the present invention comprises: a receiving section for generating a baseband spread modulated signal; a reference signal generating section for generating a reference signal; First and second Fourier transform units for performing Fourier transform on the spread modulation signal and the reference signal,
A multiplication unit that generates a multiplication signal of the Fourier-transformed baseband spread modulation signal and one of the complex conjugate signals of the Fourier-transformed reference signal, and an inverse Fourier transformation unit that performs an inverse Fourier transform of the multiplication signal to generate a correlation signal. A first and a second for limiting each frequency bandwidth of the Fourier-transformed baseband spread modulation signal and the Fourier-transformed reference signal
Means provided with a filter unit are provided.

According to the above means, the first filter unit limits the frequency bandwidth of the Fourier-transformed baseband spread modulated signal, the second filter unit limits the frequency bandwidth of the Fourier-transformed reference signal, and the multiplication unit When calculating the correlation between the baseband spread-spectrum modulated signal subjected to Fourier transform and the complex conjugate signal of one of the Fourier-transformed reference signals, the number of data samples is reduced by limiting the frequency bandwidth of these signals. Therefore, the number of samples used in the multiplication unit and the inverse Fourier transform unit is also reduced, so that the number of sums of products of the multiplication unit and the inverse Fourier transform unit is reduced, so that quick synchronization acquisition can be performed.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an embodiment of the present invention, a spread modulation signal receiving apparatus receives a radio wave including a spread modulation signal spread-modulated by a PN code and generates a baseband spread modulation signal. , A reference signal generating section for generating a reference signal having a correlation with the PN code, first and second Fourier transform sections for Fourier transforming the baseband spread modulated signal and the reference signal, and a baseband spread modulated signal and a Fourier transformed Fourier transform. A first multiplying unit that multiplies any one of the converted reference signals by a complex conjugate signal to generate a multiplied signal, and an inverse Fourier transform unit that generates a correlation signal by performing an inverse Fourier transform of the multiplied signal; Between the second Fourier transform unit and the multiplying unit, a fourth band that limits the frequency bandwidths of the Fourier-transformed baseband spread modulation signal and the Fourier-transformed reference signal, respectively. And in which it is provided a second filter unit.

In one embodiment of the present invention, the spread-modulated signal receiving apparatus includes a first filter provided on the output side of the second filter means.
A memory is provided.

In a specific example of the embodiment of the present invention, the spread modulation signal receiving apparatus uses a PN code or a PN code as a reference signal.
It consists of one of the signals whose code frequency band is restricted.

In a preferred example of the embodiment of the present invention, in the spread modulation signal receiving apparatus, the first and second filter means are low-pass filters, and the lower limit of the pass frequency bandwidth is the baseband spread modulation signal. 1 / of signal rate
2 has been selected.

In another embodiment of the present invention,
The spread modulation signal receiving apparatus includes an analog-to-digital converter in which a receiving section generates a baseband spread modulation signal.

In another specific example of the embodiment of the present invention, the spread-spectrum modulated signal receiving apparatus includes a receiving unit including a second memory for temporarily storing a baseband spread-spectrum modulated signal.

According to these embodiments of the present invention, first, the first filter section limits the frequency band of the baseband spread modulated signal that has been Fourier transformed by the first Fourier transform section. The frequency band of the reference signal subjected to Fourier transform by the Fourier transform unit is similarly limited by the second filter unit. Next, following the Fourier transform, the baseband spread-spectrum modulated signal whose band has been limited and the reference signal are multiplied by a multiplier. Finally, the inverse Fourier transform unit inverse Fourier transforms the multiplied signal output from the multiplication unit to obtain a correlation signal. In such a series of operation steps, since the number of data samples is reduced by limiting the signal band in each of the first filter unit and the second filter unit, the number of samples used in the multiplication unit and the inverse Fourier transform unit is reduced. Is also reduced, the number of times of multiplication and summation in the multiplication unit and the inverse Fourier transform unit is reduced, and quick synchronization acquisition can be performed.

[0031]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a main configuration of a first embodiment of a spread modulation signal receiving apparatus according to the present invention.

As shown in FIG. 1, the spread modulation signal receiving apparatus according to the present embodiment includes a receiving section 1 and a first Fourier transform section 2.
, A first filter means 3, a reference signal generation section 4, and a second
Fourier transform unit 5, second filter means 6, multiplication unit 7
, Inverse Fourier transform unit 8, demodulation unit 9, control unit 10
, An antenna 11, and a signal output terminal 12. The receiving unit 1 includes a baseband signal generating unit 13
, An analog-digital (A / D) converter 14 and a second memory 15.

The receiving section 1 has an input terminal connected to the antenna 1.
1 and an output terminal is connected to an input terminal of the first Fourier transform unit 2. The first filter means 3 has an input terminal connected to the output terminal of the first Fourier transform unit 2 and an output terminal connected to the multiplication unit 7.
Is connected to the first input terminal of The output terminal of the reference signal generator 4 is connected to the input terminal of the second Fourier transformer 5. Second
The filter unit 6 has an input terminal connected to the output terminal of the second Fourier transform unit 5, and an output terminal connected to the second input terminal of the multiplication unit 7. The output of the multiplier 7 is connected to the input of the inverse Fourier transformer 8. The demodulation unit 9 has an input terminal connected to the output terminal of the inverse Fourier transform unit 8 and an output terminal connected to the signal output terminal 12.
Connected to. The control unit 10 includes a receiving unit 1, a first Fourier transform unit 2, a reference signal generating unit 4, a second Fourier transform unit 5,
The multiplier 7, the inverse Fourier transformer 8, and the demodulator 9 are connected to each other. In the receiving unit 1, the baseband signal generating unit 13 has an input terminal connected to the input terminal of the receiving unit 1,
The output terminal is connected to the input terminal of the A / D converter 14. Second
The memory 15 has an input terminal connected to the output terminal of the A / D converter 14 and an output terminal connected to the output terminal of the receiving unit 1.

FIG. 4 is a characteristic diagram of a converted signal obtained after Fourier transforming the baseband spread modulated signal shown in FIG. 3 by the first Fourier transform unit 2. Are also shown together with the frequency bandwidth of the. FIG. 5 is a characteristic diagram of a converted signal obtained after Fourier transform is performed by the first Fourier transform unit 5 when the reference signal generating unit 4 generates a PN code as shown in FIG. 2 as a reference signal. And the frequency bandwidth of the second filter means 6 is also shown. further,
FIG. 6 is a waveform diagram showing the correlation signal output from the inverse Fourier transform unit 8 when the frequency spectrum shown in FIGS. The dots (black diamonds or white circles) shown in FIG. 6 indicate correlation values at discrete times.

The operation of the first embodiment having the above configuration will be described with reference to FIG.
The description will be made with reference to FIGS.

First, from a transmitter carried by a mobile body or the like, FIG.
Are spread-modulated with a PN code as shown in (1), band-limited, transmitted on a radio wave, and the signal radio wave is captured by the antenna 11. As is well known, the baseband signal generating section 13 of the receiving section 1 performs amplification of the received signal, frequency conversion using a local oscillation frequency, and other processing to convert the analog baseband spread modulated signal. The extracted data is supplied to the A / D converter 14. The A / D conversion unit 14 converts the analog baseband spread modulation signal into a digital baseband spread modulation signal as shown in FIG. 3 and temporarily stores a predetermined number of samples in the second memory 15. I do. Next, the baseband spread modulated signal read from the second memory 15 is Fourier-transformed in the first Fourier transform unit 2 and is converted into a frequency domain signal as shown in FIG.
Supplied to Next, the frequency band of this frequency domain signal is limited by the first filter means 3,
Is supplied to the first input terminal.

In this case, as shown in FIG. 4, in the first filter means 3, if the number of effective samples is limited to N / 4 with respect to the total number N of samples in the conversion frequency band, the frequency The first filter means 3 having a bandwidth A is used, and the first filter means 3 having a frequency bandwidth B when the number of effective samples is limited to N / 8.

On the other hand, the reference signal generating section 4 generates a reference signal having a correlation with the PN code generated on the transmitter side, for example, as shown in FIG.
Is generated as a reference signal.
The reference signal is subjected to Fourier transform in the second Fourier transform unit 5, converted into a reference frequency domain signal as shown in FIG. 5 and supplied to the second filter unit 6. Subsequently, the frequency band of the reference frequency domain signal is limited by the second filter means 6 and is supplied to the second input terminal of the multiplier 7.

In this case, in the second filter means 6, as shown in FIG. 5, when the number of effective samples is limited to N / 4 with respect to the total number N of samples in the conversion frequency band, the frequency When the second filter means 6 having a bandwidth of A 'is used, and when the number of effective samples is limited to N / 8, the second filter means 6 having a frequency bandwidth of B' is used. Used.

The first filter means 3 and the second filter means 6 have the same frequency bandwidth. When the frequency bandwidth of the first filter means 3 is A, the second filter means 6 is used. If the frequency bandwidth is A ', the frequency bandwidth of the first filter means 3 is B. If the frequency bandwidth of the first filter means 3 is B, the frequency bandwidth of the second filter means 6 is also B'.

Next, the multiplying unit 7 performs a complex operation on the frequency domain signal supplied to the first input terminal with the restricted frequency band and the reference frequency domain signal supplied to the second input terminal with the restricted frequency band. The signal is multiplied by a conjugate signal to generate a frequency domain multiplication signal, which is supplied to the inverse Fourier transform unit 8. This frequency domain multiplied signal is subjected to inverse Fourier transform in the inverse Fourier transform unit 8, converted into a correlation signal as shown in FIG. 6, and supplied to the demodulation unit 9.

Here, in FIG. 6, a curve A indicates that the frequency bandwidth of the first filter means 3 is A, and the second filter means 6
Shows the correlation signal when the frequency bandwidth of the first filter means 3 is A ', and the curve B shows that the frequency bandwidth of the first filter means 3 is B,
7 shows a correlation signal when the frequency bandwidth of the filter means 6 is B ′.

The dots (black diamonds or white circles) on these curves indicate correlation values in discrete time, and the smaller the number of effective samples extracted by the first filter means 3 and the second filter means 6, the smaller the number of effective samples. The number of dots is also shown small. Compared with the correlation signal curve according to the conventional example shown in FIG. 18, the correlation value becomes maximum at the same time, but the number of samples used for outputting the correlation signal in the inverse Fourier transform unit 8 is reduced. The number of samples of the correlation signal also decreases.

When such a correlation signal is input to the demodulation unit 9, PSK demodulation similar to that of the demodulation unit 47 shown in FIG. 15 is performed, and reception data corresponding to transmission data is output to the signal output terminal 12. Is output. These series of operations are performed under the control of the control unit 10.

The number of times of product sum according to the first embodiment is as follows. The total number of samples is N, and the number of effective samples extracted by the first filter means 3 and the second filter means 6 is Ns.
(However, Ns <N), and both are numbers of integer powers of 2.

First, the product-sum times of the first Fourier transform unit 2 and the second Fourier transform unit 5 are N
It becomes log ₂ N times (complex number conversion). Next, in the multiplication unit 7, the number of samples to be input is determined by the first filter unit 3 and the second
Since the number of products and sums is reduced to Ns by the filter means 6, the number of product sums here is Ns (converted into a complex number). Similarly, the inverse Fourier transform unit 8 performs Nslog ₂ Ns times (converted into a complex number). In total, 2Nlog ₂ N + Ns + Nslo
g ₂ Ns times (converted to complex number) or 16N + 8Nlog
₂ N + 12Ns + 4Nslog ₂ Ns times the (real terms).

As described above, in the first embodiment, since the number of times of product sum in the multiplication unit 7 and the inverse Fourier transform unit 8 can be reduced, the synchronous acquisition can be performed accordingly.

FIG. 7 is a characteristic diagram showing the relationship between the total number of samples and the number of product-sum calculations in the first embodiment.

In FIG. 7, the curve A represents the number N of effective samples.
s is reduced to Ns = N / 2, and curve B is the characteristic when the number of samples Ns is reduced to Ns = N / 8. Curve C shows the characteristic of a known spread modulation signal receiving apparatus which does not use the first filter means 3 and the second filter means 6 mentioned for comparison, and curve D shows the matched signal also shown for comparison. The characteristics of a known spread modulation signal receiving device using a filter.

As shown by the curve A in FIG. 7, the spread modulation signal receiving apparatus according to the first embodiment in which the number Ns of effective samples is reduced to Ns = N / 2 is the known spread signal shown by the curve C. A first embodiment in which the amount of calculation indicating the number of product sums is reduced to about 81% as compared with the modulation signal receiving apparatus, and the number of effective samples Ns is reduced to Ns = N / 8, as shown in curve B. In the spread-spectrum modulated signal receiving apparatus of the example, the amount of calculation indicating the number of sums of products is reduced to about 68% as compared with the known spread-spectrum modulated signal receiving apparatus indicated by curve C.

FIG. 8 is a block diagram showing a main part of a spread modulation signal receiving apparatus according to a second embodiment of the present invention. In FIG. 8, the same constituent elements as those shown in FIG. 1 are shown. Are given the same reference numerals.

When the second embodiment is compared with the first embodiment, the second embodiment is such that the output of the second filter means 6 is supplied to the multiplier 7 via the first memory 16; The control unit 17 is different from the first embodiment in that the control unit 17 also controls the first memory 16 in addition to the components controlled by the control unit 10 shown in FIG. There is no difference.

The operation of the second embodiment shown in FIG. 8 will be described while referring to differences from the operation of the first embodiment shown in FIG.

First, the control unit 17 operates the reference signal generation unit 4 and the second Fourier transform unit 5 to generate a reference frequency domain signal. As a result, the band is limited via the second filter unit 6. Valid samples are output to the first memory 16. At this time, the controller 17 controls the first memory 16 to write the sample output from the second filter means 6 to the first memory 16 and output the same sample from the multiplier 7 at the same time. Subsequently, the operations of the multiplication unit 7 and the inverse Fourier transform unit 8 are the same as the operations in the first embodiment, so that the inverse Fourier transform unit 8 outputs the same correlation signal as the correlation signal obtained in the first embodiment. Is done. The control unit 17 repeats the above control until one cycle of the reference signal is output. The number of times of product sum in this case is the same as the number of times of product sum in the first embodiment.

When the same reference signal is used after the output of the reference signal for one cycle, the control unit 17 stops the operations of the reference signal generation unit 4 and the second Fourier transform unit 5, and then the first The valid samples stored in the memory 16 are output to the multiplier 7. At this time, the sample output from the first memory 16 is the same as the sample output from the second filter means 6 when the reference signal generation unit 4 and the second Fourier transform unit 5 are operated. The Fourier transform unit 8 outputs the same correlation signal as the correlation signal obtained in the first embodiment. At this time, since the second Fourier transform unit 5 is not operating, the number of times of sum of products for this is smaller than the number of times of sum of products in the first embodiment. In this case, the total sum of product times is Nlog ₂ N + Ns + Nslog ₂ Ns times (in terms of complex numbers) or 8N + 4Nlog ₂ N + 12N
s + 4Nslog ₂ Ns times (real number conversion).

FIG. 9 is a characteristic diagram showing the relationship between the total number of samples and the number of product sums in the second embodiment.
This corresponds to FIG. 7 in the embodiment. Note that FIG.
The reference numerals of the respective curves in FIG. 7 are the same as those of the respective curves shown in FIG.

When valid samples are output from the first memory 16 as in the second embodiment, when Ns = N / 2, as shown by the curve A, the effective sample is shown by the curve C. As compared with the known spread modulation signal receiving apparatus, the number of times of product sum is reduced to about 72%, and when Ns = N / 8 as shown in the curve B, it is shown in the curve C. Compared with the known spread modulation signal receiving apparatus, the number of times of product sum is reduced to about 54%.

In the first and second embodiments, the reference signal generator 4 generates a PN code generated on the transmitter side as a reference signal. However, as shown in FIG. May be generated as a reference signal. Here, the reference signal as shown in FIG.
When input to the Fourier transform unit 5, a reference frequency domain signal as shown in FIG. 11 is output. Subsequently, as in the case of the first embodiment, the frequency bandwidth of the second filter
When the apparatus is set and operated so as to be within the range A ′ or B ′ shown in FIG. 11, the inverse Fourier transform unit 8 outputs
Are output as shown in FIG. FIG.
The reference numerals of the respective curves in FIG. 6 are the same as those of the respective curves shown in FIG. Even if such a band-limited PN code is used for the reference signal, a correlation signal as shown in FIG. 6 is obtained, as in the case where the PN code is used.

In the above embodiment, a PN code generated on the transmitter side or a PN code whose band is limited is used as the reference signal. However, the reference signal according to the present invention is such a code or signal. However, the present invention is not limited to this, and other codes or signals may be used as long as the codes or signals have a high correlation with the PN code used on the transmitter side.

In the first and second embodiments, the frequency band is limited by the first filter means 3 and the second filter means 6 as shown in FIGS. Has been extracted. At this time, the first
As described in the description of the second embodiment, even if the pass frequency bandwidth around the direct current is narrowed down to 1 / Tc to extract effective samples, the same applies as shown in FIG. 6 or FIG. A correlation signal having a maximum correlation value with time is obtained.
As is well known, a filter such as described above is one half the rate of the baseband spread modulated signal and the reference signal.
(= １ ／ Tc) as the lower limit of the pass frequency bandwidth.

In the above embodiment, an example in which PSK modulation is used as the primary modulation method has been described. However, the primary modulation method according to the present invention is not limited to PSK modulation. It is needless to say that the digital modulation method of the above may be used.

[0063]

As described above, according to the present invention, the frequency band of the baseband spread modulated signal subjected to Fourier transform by the first Fourier transform unit is limited by using the first filter means. The frequency band of the reference signal subjected to Fourier transform by the two-Fourier transform unit is similarly limited using the second filter means, and the baseband spread modulated signal subjected to the Fourier transform and the frequency band is limited by the multiplying unit; Since the multiplication signal is multiplied by the complex conjugate signal of the reference signal whose frequency band has been limited by the conversion, and the inverse Fourier transform unit inversely Fourier-transforms the multiplied signal output from the multiplication unit, a correlation signal is obtained. At the time of generation of a multiplied signal at the time of generation and at the time of generation of a correlation signal by inverse Fourier transform of the multiplied signal at the inverse Fourier transform unit Is greatly reduced, as a result, so that the calculation amount for obtaining a correlation signal is reduced, there is an effect that it is possible to perform rapid synchronization acquisition.

According to the present invention, the first memory is provided in the second filter means, so that when the same reference signal is used repeatedly, the reference signal which has been subjected to the Fourier transform and the frequency band of which is limited is used. This makes it possible to read out from the first memory, whereby the amount of calculation of the sum of products of the second Fourier transform unit is further reduced, and there is an effect that it is possible to perform synchronization acquisition more quickly.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main configuration of a spread modulation signal receiving apparatus according to a first embodiment of the present invention.

FIG. 2 shows a PN code used on the transmitter side and a PN code used as a reference signal on the side of the spread modulation signal receiving apparatus of the present invention.
It is a waveform diagram which shows an example of a code | symbol.

FIG. 3 is a signal waveform diagram illustrating an example of a baseband spread modulation signal output from a receiving unit.

FIG. 4 is a characteristic diagram showing a frequency spectrum showing an example of a baseband spread modulated signal Fourier-transformed by a first Fourier transform unit and a frequency bandwidth of a first filter unit.

FIG. 5 is a frequency spectrum showing an example of a reference signal (PN code) Fourier-transformed by a second Fourier transform unit;
FIG. 9 is a characteristic diagram showing the frequency bandwidth of the second filter means.

FIG. 6 is a characteristic diagram showing an example of a correlation signal obtained at the output of the inverse Fourier transform unit when the reference signal generation unit generates a reference signal (PN code).

FIG. 7 is a characteristic diagram showing a relationship between the total number of samples and the number of product-sum calculations in the first embodiment shown in FIG. 1;

FIG. 8 is a block diagram showing a configuration of a main part of a second embodiment of the spread modulation signal receiving apparatus according to the present invention.

FIG. 9 is a characteristic diagram showing a relationship between the total number of samples and the number of product-sum calculations in the second embodiment shown in FIG.

FIG. 10 is a signal waveform diagram illustrating an example of a signal when a reference signal generation unit generates a PN code of which band is limited as a reference signal.

FIG. 11 is a characteristic diagram showing a frequency spectrum showing an example of a reference signal (band-limited PN code) Fourier-transformed by the second Fourier transformer and a frequency bandwidth of the second filter means.

FIG. 12 is a characteristic diagram illustrating an example of a correlation signal obtained at the output of the inverse Fourier transform unit when the reference signal generation unit generates a reference signal (a PN code with band limitation).

FIG. 13 is a signal waveform diagram showing an example of a signal waveform used in a spread modulation method using a PN code.

FIG. 14 is a characteristic diagram showing a frequency spectrum distribution of a primary (PSK) modulation signal, a spread modulation signal, and a band-limited spread modulation signal.

FIG. 15 is a block diagram showing a main configuration of a known spread modulation signal receiving apparatus of a spread modulation system using a PN code.

FIG. 16 is a characteristic diagram showing a frequency spectrum showing an example of a reference signal (PN code) that has been Fourier-transformed by a second Fourier transformer in a known spread-modulated signal receiving apparatus.

FIG. 17 is a characteristic diagram illustrating a frequency spectrum showing an example of a baseband spread modulation signal that has been Fourier-transformed by a first Fourier transformer in a known spread-modulation signal receiving apparatus.

FIG. 18 is a signal waveform diagram showing an example of a correlation signal obtained at an inverse Fourier transform unit and an output in a known spread modulation signal receiving apparatus.

[Explanation of symbols]

 Reference Signs List 1 receiving unit 2 first Fourier transform unit 3 first filter unit 4 reference signal generating unit 5 second filter unit 6 second Fourier transform unit 7 multiplying unit 8 inverse Fourier transform unit 9 demodulation unit 10, 17 control unit 11 antenna 12 signal Output terminal 13 Baseband signal generator 14 Analog-digital (A / D) converter 15 Second memory 16 First memory

Claims (6)

[Claims] A receiving unit that receives a radio wave including a spread modulation signal spread-modulated by a PN code and generates a baseband spread modulation signal; and a reference signal generation unit that generates a reference signal correlated with the PN code. A first and a second Fourier transform unit for Fourier transforming the baseband spread modulation signal and the reference signal, and a complex conjugate signal of one of the Fourier transformed baseband spread modulated signal and the Fourier transformed reference signal; A multiplication unit that multiplies the other signal to generate a multiplied signal; and an inverse Fourier transform unit that generates an inverse Fourier transform of the multiplied signal to generate a correlation signal. The first and second Fourier transform units include: First and second filters for limiting the frequency bandwidths of the Fourier-transformed baseband spread modulated signal and the Fourier-transformed reference signal between the multiplier and the multiplier; A spread-modulation signal receiving apparatus, comprising a filter means. 2. The spread modulation signal receiving apparatus according to claim 1, wherein a first memory is provided on an output side of said second filter means. 3. The spread modulation signal receiving apparatus according to claim 1, wherein the reference signal is one of the PN code and a signal in which a frequency band of the PN code is limited. 4. The low-pass filter wherein the first and second filter means are selected so that a lower limit of a pass frequency bandwidth is の of a rate of the baseband spread modulated signal and the reference signal. 4. The spread modulation signal receiving apparatus according to claim 1, wherein: 5. The spread modulation signal receiving apparatus according to claim 1, wherein the reception section includes an analog-to-digital conversion section that generates the baseband spread modulation signal. 6. The spread modulated signal receiving apparatus according to claim 1, wherein the receiving unit includes a second memory for temporarily storing the baseband spread modulated signal.