JP2002353856A - Spread spectrum signal receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spread spectrum signal receiver that can reduce a capturing and tracking error of a received signal even when the spread spectrum received signal is subjected to band limit and a PN code in the received signal is unsharpened. SOLUTION: A PN code sequence coincident with a PN code sequence superimposed on a received spread spectrum signal is generated at an optional code phase and code frequency, waveform correction is applied to the waveform of the replica PN code so that it matches with the deteriorated waveform of the PN code in the received signal and then the correlation processing is conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a spread spectrum signal receiving apparatus for capturing and tracking a received signal which has been spread with a pseudo noise code (hereinafter, referred to as a PN code).

[0002]

2. Description of the Related Art In a spread spectrum signal receiving apparatus for receiving a signal spread in spectrum by a PN code, the same PN code as that on the transmitting side is generated in the receiving apparatus to despread the received signal spread in spectrum. Demodulates information included in the superimposed signal. In this case, in order to capture the phase and frequency of the PN code and demodulate the information continuously, a method of tracking the received signal using a coat phase locked loop is general.

FIG. 5 is a diagram showing a configuration of a conventional spread spectrum signal receiving apparatus.
0, an A / D converter 30, a signal controller 40, and a controller 50.

In FIG. 1, a spread spectrum signal transmitted from a transmitting station is received by an antenna 10, subjected to frequency conversion and signal amplification processing by a frequency conversion section 20, and converted into an intermediate frequency signal. In the process of performing the frequency conversion, though not shown, it is general to pass a band-limited filter having appropriate characteristics to limit the noise band.

The A / D converter 30 quantizes the intermediate frequency signal at a predetermined sampling frequency, converts the quantized digital signal into a digital signal, and supplies the digital signal to a signal processor 40.

The signal processing unit 40 includes a plurality of N signal tracking units 41, 4111,.
41-n. Each of the signal tracking units 41, 41-11,..., 41-n is composed of a baseband conversion unit 42 and a despreading unit 43 that operate independently of each other.
0 controls carrier phase synchronization and code phase synchronization. The despreading unit 43 is a PN code generating unit 4
4, a correlation section 45 and an accumulation section 46.

The baseband converter 42 mixes the orthogonal baseband signals I and Q with local frequencies having an orthogonal relationship in order to remove the intermediate frequency carrier component supplied from the A / D converter 30. It is supplied to the despreading unit 43.

A replica PN code generator 44 generates a PN code identical to the PN code superimposed on the received signal (hereinafter referred to as replica PN code) at an arbitrary phase and at an arbitrary frequency. P-phase replica PN code that matches on axis, this P-phase replica PN
An E-phase replica PN code which is advanced from the code on the time axis by a predetermined phase difference and an L-phase replica PN code which is delayed from the P-phase replica PN code by a predetermined phase difference on the time axis are generated. The I and Q signals supplied from the baseband converter 42 and the above three types of replica PN codes are independently subjected to a correlation process by a correlator 45, and each is processed for a predetermined time, for example, for one cycle of the PN code. By integrating the correlation values in the time and integrating section 46, the integrated correlation values Rpi, Rpq, Rei, Req, Rli, Rl
Get q.

[0009] Integrated correlation values Rpi, Rpq for P phase
The control unit 50 controls the baseband conversion unit 40 so that carrier phase synchronization is established based on the correlation value of.

On the other hand, the integrated correlation values Rei, Req, Rli, and Rlq relating to the E phase and the L phase are generally represented by a code-phase discrimination signal DＲｅD = (Rei ²⁰十 Req ² ) ^1/2 −
(Rli ² + Rlq ² ) ^1/2 ｝ is performed, and the control unit 50 controls the PN code generation unit 44 so that the code phase discrimination signal D becomes 0, thereby establishing code phase synchronization.

FIG. 6 is a diagram showing a configuration of another conventional spread spectrum signal receiving apparatus. 6 differs from the configuration diagram of the spread spectrum signal receiving apparatus of FIG.
The difference is that a replica PN code differentiator 47 is provided.
The PN code differentiator 47 performs a differentiating process on the replica PN code output from the PN code generator 44, and converts the differentiated E-phase replica PN code E ″ and the differentiated L-phase replica PN code L ″ into a correlator. 45.

[0012]

By the way, in a conventional spread spectrum signal receiving apparatus as shown in FIGS. 5 and 6, a band filter is generally inserted in the process of frequency conversion. In order to improve the anti-interference characteristic and reduce the noise band, it is necessary to employ a filter having a narrow band castle pass characteristic. However, limiting the frequency to a narrower band causes dullness in the received signal, and as a result, generates an error component in the process of despreading due to the correlation between the PN code and the replica PN code in the received signal. Will be.

[0013] Therefore, the present invention provides a method for controlling a spread spectrum of a received signal by subjecting the received signal to PN
It is an object of the present invention to provide a spread spectrum signal receiving apparatus in which errors in capturing and tracking a received signal are reduced even when the code is dull.

[0014]

According to a first aspect of the present invention, there is provided a spread spectrum signal receiving apparatus comprising: a baseband converting means for removing a carrier component from a spread spectrum received signal to convert the signal into a baseband signal; Replica PN code generating means for generating a PN code string coincident with the PN code string superimposed on the spread spectrum signal at an arbitrary code phase and code frequency, and a replica PN code output from the replica PN code generating means. Replica PN code correction means for performing waveform correction on the waveform and outputting a replica PN code subjected to the waveform correction processing; received spread spectrum signal output from the baseband conversion means and output from the replica PN code correction means Replica P that has undergone waveform correction processing
A correlation / integration means for performing a correlation process on the N code and an obtained correlation result for at least one period of the PN code to obtain an integrated correlation value, and based on the integrated correlation value of the correlation / integration means And control means for controlling the replica PN code generating means.

According to the spread spectrum signal receiving apparatus of the present invention, the waveform of the replica PN code is subjected to the waveform processing so as to match the waveform deterioration of the PN code in the received signal, and then the correlation processing is performed. Therefore, even if the PN code waveform in the received signal is dull due to band limitation,
It is possible to reduce an error in capturing and tracking a received signal.

According to a second aspect of the present invention, there is provided the spread spectrum signal receiving apparatus as set forth in the first aspect, wherein the replica PN code generating means includes a PN code superimposed on the received signal and a time axis. The P-phase replica PN code and the E-phase replica PN code and the P-phase replica P that are advanced by a predetermined phase difference on the time axis with respect to the P-phase replica PN code.
L which is delayed from the N code by a predetermined phase on the time axis
A phase replica PN code or an EL phase replica PN code which is a difference between the E phase replica PN code and the L phase replica PN code is generated, and the replica PN code correcting means generates the E phase replica PN code and the L phase replica PN code. The waveform correction is performed on a phase replica PN code or the EL phase replica PN code.

According to the spread spectrum signal receiving apparatus of the present invention, the E-phase replica PN code and the L-phase replica PN code or the E-L phase replica PN code further include a waveform of the PN code in the received signal. Since the waveform is corrected so as to match the deterioration, the code phase can be simply and accurately synchronized.

According to a third aspect of the present invention, there is provided a spread spectrum signal receiving apparatus, comprising: a baseband converting means for removing a carrier component from a spread spectrum received signal to convert the carrier signal into a baseband signal; and superimposing the baseband signal on the received spread spectrum signal. PN code generating means for generating a PN code sequence that matches the PN code sequence being performed at an arbitrary code phase and code frequency, and adding a baseband signal to the waveform of the replica PN code output from the replica PN code generating means. Replica PN code adaptive differential processing means for adaptively performing differential processing in accordance with the dullness of the output, and a spread spectrum signal received from the baseband conversion means and output from the replica PN code adaptive differential processing means. The replica PN code that has been adaptively differentiated. A correlation / integration means for performing an integration process on the obtained correlation result over at least one cycle of the PN code to obtain an integrated correlation value, and the replica PN code based on the integrated correlation value of the correlation / integration means. Control means for controlling the generation means.

According to the spread spectrum signal receiving apparatus of the present invention, the replica PN code waveform is subjected to the adaptive differentiation process so as to match the waveform deterioration of the PN code in the received signal, and then the correlation process is performed. Even if the PN code waveform in the received signal is dull due to band limitation,
An error in tracking the received signal can be reduced, and the received signal can be tracked stably.

According to a fourth aspect of the present invention, there is provided a spread spectrum signal receiving apparatus according to the third aspect, wherein the replica PN code generating means includes a PN code superimposed on a received signal and a time axis. The P-phase replica PN code and the E-phase replica PN code and the P-phase replica P that are advanced by a predetermined phase difference on the time axis with respect to the P-phase replica PN code.
L which is delayed from the N code by a predetermined phase on the time axis
A phase replica PN code or an EL phase replica PN code which is a difference between the E phase replica PN code and the L phase replica PN code is generated. The L-phase replica PN code, or the E-L
The phase replica PN code is adaptively differentiated according to the dullness of the baseband signal, and then supplied to the correlation / integration means.

According to the spread spectrum signal receiving apparatus of the present invention, the PN code in the received signal is further compared with the E phase replica PN code and the L phase replica PN code or the EL phase replica PN code. Since the adaptive differentiation processing is performed so as to match the waveform deterioration of the above, the code phase can be simply and accurately synchronized.

[0022]

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

FIG. 1 is a diagram showing a configuration of a spread spectrum signal receiving apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a state in which the waveform of the PN code in the received signal is blunted as an ideal model (conventional method) as a waveform model.

In the spread spectrum signal receiving apparatus, as described above, as a result of inserting the filter for limiting the band into the path of the received signal, the input signal becomes dull and the PN code of the received signal is reduced. The waveform is
It deteriorates from the original rectangular waveform. The degree of the deterioration has various waveform shapes depending on the pass characteristics of the filter. When this waveform shape is represented as a model, a waveform that rises in a step shape (rectangular shape) like an input signal S0 (t) shown as an ideal model in FIG.
FIG. 2C shows a linear model such as an input signal S1 (t) that rises in a straight line, FIG. 2C shows a curve model that rises in a curve like an input signal S2 (t), or those of them. Various waveforms depending on the degree of inclination and shape of the composite can be assumed. Note that FIG.
In the figure, only the rising portion of the PN code waveform is shown, but the same applies to the falling portion.

In a conventional spread spectrum signal receiving apparatus,
Even when the waveform of the PN code in the received signal is dull,
As the replica PN code, a rectangular code waveform as shown as an ideal model in FIG. 2A is generated.
If the correlation between the PN code having the deteriorated waveform shape and the replica PN code having the rectangular shape is taken, an error component is generated in the process of despreading by the correlation.

In the first embodiment, the replica PN
P phase replica PN generated by code generation section 44
E leads the code by a predetermined phase difference on the time axis
L-phase replica PN delayed by a predetermined phase on the time axis with respect to the phase replica PN code and the P-phase PN code
The code is subjected to an appropriate waveform correction process by the replica PN code correction unit 48 so as to match the waveform deterioration of the PN code in the received signal, so that the PN code waveform in the received signal is dull due to band limitation. Even in this case, the error in tracking the received signal is reduced.

FIG. 1 is different from the configuration of the conventional spread spectrum signal receiving apparatus of FIG. 5 in that a PN code corrector 48 is newly added, and the PN code corrector 48 generates the PN code in the PN code generator 44. Replica PN
The waveform of the code is corrected, and the replica PN code whose waveform has been corrected is supplied to the correlation unit 45A. The despreading unit 4
3A, the correlation unit 45A, the integration unit 46A, and the control unit 50A
Each of them is functionally the same as the conventional one shown in FIG. 5, but has a suffix A because it may be partially changed in a specific configuration with the addition of the PN code correction unit 48.

Now, in FIG. 1, the PN code generator 4
4 and the P-phase replica PN code that coincides on the time axis with the PN code superimposed on the received signal and the orthogonal baseband signals I and Q from the baseband converter 42 (that is, the received PN code). Code) and the correlation unit 4
5A to obtain the correlation values Pi and Pq.
i and Pq are accumulated in the integrating section 46A for a predetermined time, for example, PN
Integrates the time for one code cycle, and the integrated values Rpi, R
pq is input to the carrier phase synchronization control unit of the control unit 50A, and the local frequency is controlled so as to synchronize with the carrier phase.

Next, the E-phase replica PN code and the L-phase replica PN code generated by the PN code generation section 44 are rectangularly shaped by the PN code correction section 48 so as to match the waveform deterioration of the PN code in the received signal. Is subjected to appropriate waveform correction processing, and the corrected E phase replica P
N code Ea and corrected L phase replica PN code L
a is supplied to the correlation unit 45A. In the correlator 45A, the received PN code and the corrected E phase replica PN code E
a, the corrected L-phase replica PN code La is multiplied by the correlation value Eia, Eqa and the correlation value Lia, L
qa, the correlation values Eia, Eqa and the correlation value Li
a and Lqa are accumulated by the integrating unit 46A for a predetermined time, for example, P
Integrates the time for one cycle of N code, and the integrated value Rei
a, Reqa and integrated values Rlia, Rlqa
It is input to the code phase synchronization control unit of 0A.

Then, the code phase synchronization control section of the control section 50A determines the integrated values Reia and Reqa and the integrated value Rli
Based on a and Rlqa, the phase of the replica PN code generated by the replica PN code generation section 44 is tracked so as to be always synchronized with the received PN code.

In order to accurately track the phase of the replica PN code so as to always synchronize with the received PN code, the corrected E-phase replica PN code Ea and the corrected L-phase replica PN code La It is important that the code is properly corrected to match the waveform of the code.

For this reason, when the waveform of the received PN code is specified, the PN code correction section 48 may fix the degree of correction in accordance with the specified PN code, or the received PN code may be fixed.
A plurality of waveform models can be prepared so as to correspond to the assumed waveform of the code, and can be selected and used according to the received PN code. In addition, it is possible to adopt a configuration in which waveform processing is adaptively performed using, for example, an integrated value so as to automatically match the received PN code. The configuration of the PN code correction unit 48 is desirably formed of a digital logic circuit in order to perform various correction processes in accordance with control signals. For example, a necessary type of look-up table Can be configured.

Although the first embodiment has been described as using the E phase signal and the L phase signal independently, the replica PN signal is used to obtain a later phase discrimination signal.
The E-L phase signal may be first used at the code stage.

Further, in the first embodiment, the PN code correction unit 4 adds the E-phase and L-phase replica PN codes to each other.
8 is performed, the replica correction PN code of P phase may be similarly subjected to the waveform correction processing by the PN code correction unit. In this case, the accuracy of the carrier phase synchronization control is improved. Can be expected.

FIG. 3 is a diagram showing a configuration of a spread spectrum signal receiving apparatus according to a second embodiment of the present invention.
FIG. 4 is a diagram showing a state in which the waveform of the PN code in the received signal has been blunted, as an ideal model (conventional method) as a waveform model, and showing each differential signal waveform of each waveform model. .

FIG. 3 is different from the configuration diagram of the spread spectrum signal receiving apparatus of FIG. 1 according to the first embodiment in that the replica PN code correcting section 48 of FIG.
The point is that an N-code adaptive differential processing unit 49 is provided. The adaptive differential processing unit 49 controls the rectangular PN code output from the PN code generation unit 44 by applying appropriate control to the code phase synchronization control unit in the control unit 50B according to the dullness of the baseband signal. E phase replica PN after adaptive differentiation processing by adaptively performing waveform correction processing and differentiation processing
The code Ea ″ and the L-phase replica PN code La ″ are supplied to the correlation unit 45B.

The despreading section 43B, correlating section 45B, integrating section 46B, and control section 50B are functionally the same as those in FIG. Since there is a possibility that the configuration may be partially changed, a suffix B is added to each.

Now, referring to FIG.
Phase replica PN code Ea ″ and adaptive differentiated L
The phase replica PN code La ″ is supplied from the adaptive differentiation processing unit 49 to the correlation unit 45B. The correlation unit 45B receives the received PN code and the adaptive differentiation-processed E phase replica PN.
Code Ea ″ and adaptive differential processed L-phase replica PN
And the correlation value Eia ″, E
qa "and the correlation values Lia" and Lqa "are taken, and the correlation values Eia" and Eqa "and the correlation values Lia" and Lqa "are integrated by the integration unit 46B for a predetermined time, for example, the time of one cycle of the PN code. And the integrated value Reia ″, Req
a "and the integrated values Rlia", Rlqa ".
To the code phase synchronization control unit.

Then, in the code phase synchronization control section of the control section 50B, the integrated values Reia "and Reqa" and the integrated value Rl
Based on ia "and Rlqa", the phase of the replica PN code generated by the replica PN code generation unit 44 is tracked so as to always be synchronized with the received PN code, and the adaptive differentiation processing unit 49 is controlled.

In order to accurately track the phase of the replica PN code so as to always synchronize with the received PN code, the adaptive differential processing E phase replica PN code E
a ″ and L phase replica PN code L after adaptive differentiation processing
It is important that a ″ is properly processed so as to match the waveform of the received PN code.

For this reason, as shown in FIG. 4, when the shape of the waveform of the PN code in the received signal is modeled, it is used in the conventional example shown in FIG. 4A as an ideal model. The signal rising in a step shape (rectangular shape) like the input signal S0 (t), the signal rising in a straight line like the input signal S1 (t) shown as a linear model in FIG. Various waveforms corresponding to the degree of inclination and shape can be assumed for a signal that rises in a curve like an input signal S2 (t) shown as a curve model in FIG. Then, each signal model S0
1 for each of (t), S1 (t), and S2 (t)
The differential signals S0 '(t), S1' (t), S2 '
(T) Second derivative signal S0 "(t), S1" (t), S
2 "(t) is formed, and the quantized signal r0" is formed.
(T), r1 "(t), and r2" (t) are obtained by quantizing each second-order differential signal. In this figure, P
Although only the rising portion of the N code waveform is shown, the same applies to the falling portion.

When the waveform of the received PN code is specified, the adaptive differentiation processing unit 49 may fix the degree of differentiation in accordance with the specified waveform, or may correspond to the assumed waveform of the received PN code. It is also possible to prepare a plurality of waveform models so that they can be selected and used according to the received PN code. Also, the received PN
It can be configured to perform waveform processing adaptively using, for example, an integrated value so as to automatically match the code. Further, the adaptive differential processing unit 49 outputs the second-order differential signal S ″ (t) or further outputs a quantized signal r ″ (t). Although the amplitude is ± 1 and ± 0.5 in the figure as the form of quantization, it is needless to say that the same effect can be obtained by quantizing using other numerical values.

The configuration of the adaptive differential processing section 49 is desirably formed of a digital logic circuit in order to perform various correction processes according to control signals. More specifically, the second-order differential signal S ″ (t) corresponding to the waveform model or the quantized signal r ″ (t) corresponding to the waveform model is made to correspond to a required type of waveform using a storage unit. It is preferable that the data is stored in a look-up table format and output by one-stage digital signal processing.

It should be noted that, depending on the waveform model used in the adaptive differentiating section 49, the relative relationship between the E phase and the L phase becomes asymmetric, and an offset may occur in the obtained phase discrimination signal, but this offset can be grasped in advance. From
The correction as the specified value does not affect the tracking operation.

Although the description has been given of the case where the second-order differentiation processing is performed, the present invention is not limited to this, and the first-order differentiation processing may be performed.

In each of the above embodiments, application to tracking of a received signal has been described. However, the present invention can be similarly applied to capturing of a received signal.

[0047]

According to the spread spectrum signal receiving apparatus of the present invention, the waveform of the replica PN code is subjected to the waveform processing so as to match the waveform deterioration of the PN code in the received signal, and then the correlation processing is performed. Therefore, even when the PN code waveform in the received signal is dull due to the band limitation, it is possible to reduce an error in capturing and tracking the received signal.

According to the second aspect of the present invention, the E-phase replica PN code and the L-phase replica PN code or the E-L phase replica P
Since the N code is subjected to waveform correction so as to match the waveform deterioration of the PN code in the received signal, the code phase can be simply and accurately synchronized.

According to the third aspect of the present invention, the waveform of the replica PN code is subjected to the adaptive differentiation processing so as to match the waveform deterioration of the PN code in the received signal, and then the correlation processing is performed. Even when the PN code waveform in the received signal is dull due to band limitation, errors in tracking the received signal can be reduced, and the received signal can be tracked stably.

According to the fourth aspect of the present invention, there is further provided an E-phase replica PN code and an L-phase replica PN code, or an E-L phase replica P
Since adaptive differentiation processing is performed on the N code so as to match the waveform deterioration of the PN code in the received signal, the code phase can be simply and accurately synchronized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a spread spectrum signal receiving apparatus according to a first embodiment.

FIG. 2 is a diagram showing a waveform model of a PN code in a received signal.

FIG. 3 is a configuration diagram of a spread spectrum signal receiving apparatus according to a second embodiment.

FIG. 4 is a view showing a waveform model of a PN code in a received signal and its differential waveform.

FIG. 5 is a configuration diagram of a conventional spread spectrum signal receiving apparatus.

FIG. 6 is a configuration diagram of another conventional spread spectrum signal receiving apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Antenna 20 Frequency conversion part 30 A / D conversion part 40 Signal processing part 41 Signal tracking part 42 Baseband conversion part 43 Despreading part 44 PN code generation part 45 Correlation part 46 Accumulation part 47 PN code differentiation part 48 PN code correction part 49 Adaptive differential processing unit 50 Control unit

Claims (4)

[Claims] 1. A baseband conversion means for removing a carrier component from a spread-spectrum received signal and converting the carrier signal into a baseband signal, and a PN code sequence coincident with a PN code sequence superimposed on the received spread-spectrum signal. A replica PN code generating means for generating the code at an arbitrary code phase and code frequency; applying a waveform correction to the waveform of the replica PN code output from the replica PN code generating means; Replica PN
Code correction means, and performs correlation processing on the received spread spectrum signal output from the baseband conversion means and the waveform-corrected replica PN code output from the replica PN code correction means, and obtains the obtained correlation result. Correlation / integration means for performing integration processing at least over one cycle of the PN code to obtain an integrated correlation value, and control means for controlling the replica PN code generation means based on the integrated correlation value of the correlation / integration means. A spread spectrum signal receiving apparatus, comprising: 2. The spread spectrum signal receiving apparatus according to claim 1, wherein said replica PN code generating means comprises:
A P-phase replica PN code that coincides on the time axis with the PN code superimposed on the received signal; and an E-phase replica PN code and a P-phase code that advance the P-phase replica PN code by a predetermined phase difference on the time axis. An L phase replica PN code which is delayed by a predetermined phase on the time axis with respect to the phase replica PN code, or an EL phase replica PN code which is a difference between the E phase replica PN code and the L phase replica PN code is generated. A spread spectrum signal receiving apparatus, wherein the replica PN code correcting means performs the waveform correction on the E-phase replica PN code and the L-phase replica PN code or the EL-phase replica PN code. 3. A baseband conversion means for removing a carrier component from a spread spectrum received signal and converting the carrier signal into a baseband signal, and a PN code sequence coincident with a PN code sequence superimposed on the received spread spectrum signal. Replica PN code generating means for generating at an arbitrary code phase and code frequency; and adaptively differentiating the waveform of the replica PN code output from the replica PN code generating means in accordance with the dullness of the baseband signal. Replica PN code adaptive differential processing means to output; a received spread spectrum signal output from the baseband conversion means; and an adaptively differentiated replica PN code output from the replica PN code adaptive differential processing means. And the obtained correlation result is at least the PN code Correlation / integration means for performing an integration process over a period to obtain an integrated correlation value, and control means for controlling the replica PN code generation means based on the integrated correlation value of the correlation / integration means. Spread spectrum signal receiving apparatus. 4. The spread spectrum signal receiving apparatus according to claim 3, wherein said replica PN code generating means comprises:
A P-phase replica PN code that coincides on the time axis with the PN code superimposed on the received signal; and an E-phase replica PN code and a P-phase code that advance the P-phase replica PN code by a predetermined phase difference on the time axis. An L phase replica PN code which is delayed by a predetermined phase on the time axis with respect to the phase replica PN code, or an EL phase replica PN code which is a difference between the E phase replica PN code and the L phase replica PN code is generated. The replica PN code adaptive differentiating means adaptively differentiates the E-phase replica PN code and the L-phase replica PN code or the EL-phase replica PN code in accordance with the dullness of the baseband signal. A spread-spectrum signal receiving apparatus that supplies the spread spectrum signal to the correlation / integration means.