JPH09261123A - Spread spectrum receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely acquire the synchronization with a simple circuit configuration and also to perform the accurate inverse spreading of spectrum by setting the free running frequency of a VCO in the prescribed conditional ranges. SOLUTION: The received spread spectrum signal is converted into the low frequency by a frequency conversion circuit 1 and then multiplied by the spreading code received from a spreading code generation circuit 15 by a multiplier 2. The output of the multiplier 2 undergoes the phase comparison with the output of a VCO 13 via a phase comparison circuit 4. The output of the circuit 4 is applied to the VCO 13 as a control signal via an LPF 6. The free running frequency of the VCO 13 is set in such ranges as fc1<f0+δf<fc2 or fc2<f0-δ$<fc1 and δfs<δf respectively. In such cases, fc1 shows the frequency that decides the minimum capture range within ±1 chip of a self-correlation point together with fc2 showing the frequency that decides a capture range at the extreme autocorrelation point, and δfs showing the frequency difference which can secure the sliding correlation respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct sequence spread spectrum receiving apparatus, which is an improvement of synchronization supplement and a transmitting side P when a phase locked loop is used for acquisition and holding of synchronization.
The present invention relates to a spread spectrum receiver that prevents the occurrence of a phase error between an N code and a PN code on the receiving side.

[0002]

2. Description of the Related Art Conventionally, as one of wireless communication systems,
Spread spectrum communication systems are widely known. In this spread spectrum system, a carrier side is modulated with an information signal such as voice or data on the transmitting side, and M is added to the information modulated signal.
Spread spectrum is performed by multiplying by a spreading code such as a sequence. Then, the spread spectrum signal is transmitted from the antenna. On the other hand, on the receiving side, the received spread spectrum signal is multiplied by the same spreading code as on the transmitting side to perform despreading, and further information demodulation is performed to obtain an information signal.

In such a spread spectrum communication system, when despreading on the receiving side, the spreading code created on the receiving side and the spreading code in the received signal must be synchronized and multiplied. Therefore, conventionally, as shown in FIG. 2, a spread spectrum receiving apparatus has been proposed which maintains the synchronization relationship between the spreading code created on the receiving side and the spreading code in the received signal. In FIG. 2, the received spread spectrum signal is a frequency conversion circuit (1).
After the frequency is converted to a low frequency so that it can be easily processed by the circuit in the subsequent stage, the spread code generation circuit (3) is applied to the multiplier (2).
Is multiplied by the spreading code generated from The output signal of the multiplier (2) is compared in phase with the output signal of the VCO (voltage controlled crystal oscillator circuit) (5) in the phase comparison circuit (4). The output signal of the phase comparison circuit (4) corresponding to the result of the phase comparison is smoothed by the LPF (6) and then applied to the VCO (5) as a control signal, and the VCO (5) is supplied in response to the control signal.
The oscillation frequency of is changed. The output signal of the VCO (5) is applied to the phase comparison circuit (4), frequency-divided by the frequency division circuit (7) and then applied to the spread code generation circuit (3). Here, the multiplier (2), the phase comparison circuit (4), the VCO (5), the LPF (6), and the frequency dividing circuit (7).
The spread code generation circuit (8) constitutes a so-called PLL (Phase Locked Loop), and the phase comparison circuit (4)
Of the PLL so that the phase difference between the two input signals of
Works. Therefore, the generation timing of the spread code from the spread code generation circuit (3) changes according to the change of the oscillation frequency of the VCO (5), and the PLL causes the phases of the two input signals of the phase comparison circuit (4) to change. Operate in synchronism with each other, the phases of the output signal of the multiplier (2) and the output signal of the VCO (5) are synchronized.

After the PLL is locked, a spread code synchronized with the spread spectrum signal is generated, and the spread spectrum signal and the spread code are multiplied by the multiplier (2) to perform despreading. Then, the output signal of the multiplier (2) generated by despreading is passed through the BPF (8),
An information signal can be obtained by being applied to the demodulation circuit (9) and demodulated.

[0005]

By the way, the synchronization acquisition must be performed before the synchronization is held. In the conventional circuit of FIG. 2, the synchronization supplement detection circuit (10) and the DC voltage source (1) are used.
1) and the switch (12) were added. When performing the synchronous acquisition, the switch (12) selects the DC voltage source (11), so that a predetermined oscillation frequency signal is generated from the VCO (5) and the synchronous acquisition of the PLL is performed. The predetermined oscillation frequency is set so as to have a desired lock frequency. Then, the synchronization acquisition detection circuit (10) detects the correlation between the spread code in the spread spectrum signal and the spread code of the spread code generation circuit (3), and when the correlation becomes equal to or higher than a predetermined level, the synchronization of the PLL is achieved. Is detected. In response to the output signal of the synchronization acquisition detection circuit (13) indicating synchronization acquisition, the switch (12) switches to LP.
The output signal of F (6) is selected. Therefore, VC is set so that the phase difference between the two input signals of the phase comparison circuit (4) becomes zero.
The oscillation frequency of O (5) is changed, and the synchronization of the PLL is maintained. However, since a special circuit must be added to supplement the synchronization, the circuit configuration becomes complicated.

In the synchronization holding operation, the phase of the spreading code created on the receiving side does not exactly match the phase of the spreading code in the spread spectrum signal due to the delay of the elements constituting the circuit of FIG. , Couldn't do accurate despreading.

[0007]

SUMMARY OF THE INVENTION The present invention is a spread spectrum receiving apparatus for receiving a spread spectrum signal, comprising a despreading circuit for despreading the spread spectrum signal with a spread code, and a free run frequency having a reverse spread spectrum. A VCO set apart from the carrier frequency f0 of the signal by a predetermined frequency δf; an output signal of the first despreading circuit;
A phase comparison circuit that compares the phase with the output signal of the VCO, a control signal generation circuit that generates a control signal of the VCO according to the output signal of the phase comparison circuit, and a spread code according to the output signal of the VCO. And a spread code generating circuit for generating the VCO, wherein the free-run frequency of the VCO is fc1 <f
0 + δf <fc2 or fc2 <f0−δf <fc1
And a range of δfs <δf. However, fc1: frequency that determines the minimum capture range within ± 1 chip of the correlation point of autocorrelation. fc2: frequency that determines the capture range at the maximum point of autocorrelation. δfs: Frequency difference that allows sliding correlation.

A spread spectrum receiver for receiving a spread spectrum signal, comprising a despreading circuit for despreading the spread spectrum signal with a spread code, and a free-run frequency for a carrier frequency f0 of the spread spectrum signal. A VCO set to be separated by a predetermined frequency δf, a phase comparison circuit for comparing the phases of the output signal of the first despreading circuit and the output signal of the VCO, and the VCO according to the output signal of the phase comparison circuit. Control signal generating circuit for generating a control signal of the VCO and a spreading code generating circuit for generating a spreading code according to the output signal of the VCO, and the free-run frequency of the VCO is fc3 <f0 + δf <fc4 or fc4 <. f0-δf <fc3 range and δfs <δ
It is set according to the range of f. However, fc3: a frequency that determines the capture range at the second-order maximum point of autocorrelation. fc4: frequency that defines the capture range at the first-order maximum point of autocorrelation. δfs: Frequency difference that allows sliding correlation.

Further, a spread spectrum receiver for receiving a spread spectrum signal, wherein the spread spectrum circuit is a despreading circuit for despreading the spread spectrum signal, and a free-run frequency is for a carrier frequency f0 of the spread spectrum spread signal. A VCO set to be separated by a predetermined frequency δf,
A phase comparison circuit that compares the phase of the output signal of the first despreading circuit and the output signal of the VCO, and a control signal generation circuit that generates a control signal of the VCO in accordance with the output signal of the phase comparison circuit, And a spread code generating circuit that generates a spread code according to an output signal of the VCO, wherein the VCO has a free-run frequency in a range of fc5 <f0 + δf <fc6 or fc6 <f0−δf <fc5 and δfs <.
It is set according to the range of δf. However, fc1: frequency that determines the capture range at the maximum maximum point of cross-correlation. fc2: frequency that determines the capture range at the maximum point of autocorrelation. δfs: Frequency difference that allows sliding correlation.

Further, a solid-state oscillator or a SAW oscillator is used as an oscillator forming the VCO. Furthermore, a receiving electric field strength detecting circuit for detecting the receiving electric field strength and a switching signal generating circuit for generating a switching signal when the receiving electric field strength is equal to or lower than a predetermined strength are provided, and the VCO free-run frequency is changed according to the switching signal. It is characterized in that the frequency is switched to a frequency close to the carrier frequency f0.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment of the present invention, in which (13) is a VCO in which the free-run frequency is set δf away from the carrier frequency and the oscillation frequency is variable, (14) is a frequency dividing circuit that serves as a clock signal generating circuit for generating a spread code, and (15) is a first to third spread code P1 according to the spread code P0 from the first spread code generation circuit (3). A second spreading code generating circuit for generating one of the first to third spreading codes P1 to P3, and a selection circuit for selecting one spreading code from the first to third spreading codes P1 to P3.
7) is a second multiplier that serves as a second despreading circuit for multiplying the spread spectrum signal by the output signal of the selection circuit (16);
Reference numeral 8) is a correlation detection circuit for detecting the correlation between the spread spectrum signal and the spread code, and (19) controls the selection circuit (16). ) Is a control circuit for controlling. The same circuits as those in the conventional example shown in FIG. 2 are designated by the same reference numerals as those in the conventional example shown in FIG.

In FIG. 1, when reception is started, first, an operation of capturing the synchronization between the output signal of the first multiplier (2) and the output signal of the VCO (13) is performed. The received spread spectrum signal is frequency-converted into a low frequency by the frequency conversion circuit (1), and then the first multiplier (2) (first despreading circuit)
It is multiplied with the spreading code generated from the second spreading code generating circuit (15) described later. Then, the output signal of the first multiplier (2) is applied to the VCO (13) in the phase comparison circuit (4).
Is compared with the output signal. The output signal of the phase comparison circuit (4) corresponding to the result of the phase comparison is smoothed by the LPF (6) and then applied to the VCO (13) as its control signal.

Further, the output signal of the VCO (13) is applied to the phase comparison circuit (4) and at the same time the frequency division circuit (1
It is also applied to 4) and divided by m. Then, the spreading code P0 is generated from the first spreading code generation circuit (3) based on the frequency division output signal of the frequency division circuit (14). Further, according to the spread code, the second spread code generator circuit (15) serves as a reference first spread code P1, a second spread code P2 advanced from the first spread code P1 by a predetermined phase, and the second spread code P2. A third spreading code P3 which is delayed from the one code P1 by a predetermined phase is generated.

Here, the first spreading code generating circuit (3) is
For example, it is a well-known circuit that is composed of a shift register and an exclusive OR gate and that generates an M-sequence code according to the output signal of the VCO (13) that is a clock signal. Further, the second spreading code generating circuit (15), for example, uses the spreading code P0 of the first spreading code generating circuit (3).
Is used as data, and the output signal of the VCO (13) is used as a clock signal, and the spread code P0 is sequentially transmitted to the shift registers of the first to third stages. The output signal of the second-stage shift register is set to the first spreading code P1, and the VCO (1
The second spreading code P2, which advances from the first spreading code by one clock of the output signal of 3), is output from the first-stage shift register, and the third spreading code P3 delayed by one clock is output from the third-stage shift register. It will be generated.

Further, since the free-run frequency of the VCO (13) is set to a frequency separated by δf from the carrier signal of the spread spectrum signal, a phase difference between the two input signals of the phase comparison circuit (4) occurs, The PLL operation can be surely performed so that the phase difference between the output signal of the first multiplier (2) and the output signal of the VCO (13) becomes zero. Further, the spread code from the second spread code generation circuit (15) is applied to the first multiplier (2). Therefore, since the generation timing of the spreading code generated from the first spreading code generation circuit (3) changes according to the change in the oscillation frequency of the VCO (5), the PLL outputs the output signal of the first multiplier (2). VCO
It operates so that the phase difference from the output signal of (13) becomes zero. That is, the first multiplier (2), the phase comparison circuit (4), L
The PF (6) and the VCO (13) form a PLL, and the PLL operates so that the phase difference between the two input signals of the phase comparison circuit (4) becomes zero.

Therefore, by using a widely known PLL method, the synchronization between the output signal of the first multiplier (2) and the output signal of the VCO (13) can be reliably captured. By the way, the free-run frequency of the VCO (13) is set to be separated from the carrier frequency of the spread code by δf. Phase comparison circuit (4), LPF (6) and VCO
In the PLL composed of (13), when the lockup time is t, the time required for sliding two autocorrelation chips in FIG. 3 can be expressed as t ≦ (2 / f).

[0017]

[Equation 1]

## EQU1 ## Here, f is a frequency. When the spreading code is an M-sequence code, the autocorrelation as shown in FIG. 3A is obtained. By the way, the relationship between the correlation level and the capture range of the PLL is shown in FIG. 4, and the capture range is shown inside the curve in FIG. From FIG. 4 (a), the capture range at the correlation level distant from ± 1 chip from the maximum point shown in FIG. 3 (a) is within the range of fcm1 and fcm1 ′, and the correlation level corresponding to the maximum point of correlation is obtained. The PLL capture range is fcm2 and f
It is within the range of cm2 '. Then, from FIG.
When the correlation level is between the maximum point and the levels of the ± 1 chips, the PLL synchronizes with the output signal of the first multiplier (2). Therefore, if the carrier frequency of the spreading code is f0,
The upper limit of the capture range is

[0019]

[Equation 2]

And the lower limit of the capture range is

[0021]

(Equation 3)

Δf is set so that In addition to these conditions, the condition set by the equation (1) is added. If the spreading code is a non-M sequence code such as a Gold code, the autocorrelation as shown in FIG. 3B is obtained.
From FIG. 4B, the capture range of the correlation level corresponding to the secondary maximum point is within the range of fcn1 and fcn1 ', and the capture range of the PLL of the correlation level corresponding to the primary maximum point is fcn2 and fcn2'. It is within the range of and.
From FIG. 3B, the correlation level is 2
Δf that the PLL locks when it is between the next maximum point
When set to, there is no accidental synchronization with the secondary maximum. Therefore, if the carrier frequency of the spreading code is f0,
The upper limit of the capture range is

[0023]

(Equation 4)

And the lower limit of the capture range is

[0025]

(Equation 5)

Δf is set so that In addition to these conditions, the condition set by the equation (1) is added. Further, when a spread spectrum signal of another transmitter having a different spread code is received, a cross correlation as shown by the solid line in FIG. 3C is obtained. The autocorrelation is as shown by the dotted line in FIG. From FIG. 4C, the capture range of the correlation level corresponding to the maximum maximum point of the cross correlation is fcc1 and fc.
It is within the range of c1 ', and the capture range of the correlation level corresponding to the self maximum point is within the range of fcc2 and fcc2'. Then, from FIG. 3C, if δf is set so that the PLL locks when the correlation level is between the maximum point of the autocorrelation and the maximum point of the cross-correlation, it is erroneously synchronized with the maximum point. Never. Therefore, if the carrier frequency of the spreading code is f0, the upper limit of the capture range is

[0027]

(Equation 6)

And (f0 + δf) is the lower limit of the capture range,

[0029]

(Equation 7)

Δf is set so that In addition to these conditions, the condition set by the equation (2) is added. Therefore, if δf is set according to the system in which the spreading code is the M-sequence or the non-M-sequence, or the system in which the cross-correlation occurs due to the plurality of spreading codes, the first multiplier (2) can be used without pseudo lock. Output signal and VCO (1
Accurate synchronization with the output signal of 3) can be reliably captured.

Here, as the oscillator of the VCO (13),
By using the solid-state oscillator, the free-run frequency can be set with high accuracy, and a stable free-run frequency can be obtained. Therefore, it is possible to eliminate the adjustment of the VCO (13) at the time of manufacturing the receiver or aging. Furthermore, by using a SAW oscillator, VC
Since the variable range of the frequency of O (13) can be made relatively wide, the free-run frequency of the VCO (13) can be accurately and arbitrarily set within the predetermined range.

When the synchronization acquisition is completed, the control circuit (19)
The output signal of VCO (13) is applied to VCO (1
According to the output signal of 3), the first control signal is the control circuit (1
9) is applied from the selection circuit (16) to the selection circuit (1
6) performs the selection operation. Then, the correlation between the received spread spectrum signal and the selected spread code is detected by the correlation detection circuit (18). The control circuit (19) determines whether the phase of the spread code is behind or ahead of the phase of the spread spectrum signal according to the detected correlation output, and the second control signal outputs the control circuit ( 19) occurs. Then, according to the second control signal,
The output generation timing of the frequency dividing circuit (14) is variable.
That is, when it is determined that the phase of the spread code is behind the phase of the spread spectrum signal according to the comparison result, the output generation timing of the frequency dividing circuit (14) is advanced by the second control signal, and as a result, The phase of the spreading code advances. Conversely, if it is determined that the phase of the spread code is ahead of the phase of the spread spectrum signal, the output generation timing of the frequency dividing circuit (14) is delayed, so that the phase of the spread code is delayed. By controlling the output generation timing of the frequency dividing circuit (14) according to the detected autocorrelation, the spread code in the received spread spectrum signal and the spread code created by the receiver can be synchronized, and The synchronization can be maintained.

Therefore, by the above operation, the spread code synchronized with the spread code in the spread spectrum signal is generated,
Accurate despreading is performed by multiplying the spread spectrum signal and the spread code by the first multiplier (2). The output signal of the first multiplier (2) is the BPF.
An information signal can be obtained by applying to the demodulation circuit (9) via (8) and demodulating the output signal.

Even when the synchronization is acquired, the output generation timing of the frequency dividing circuit (14) is controlled, but the frequency dividing circuit (1
Since the change in the output phase of 4) is small with respect to the change in the frequency of the VCO (13), the control of the output generation timing of the frequency dividing circuit (14) does not adversely affect the synchronization acquisition operation. Also,
Specific circuit examples of the correlation detection circuit (18) and the control circuit (19) are described in Japanese Patent Application No. 7-68263 filed before the patent application of the present invention, and thus the description of the operation is omitted. Furthermore, the correlation detection circuit (18) and the control circuit (19) are not limited to the circuit shown in FIG.
-73972, Japanese Patent Application 7-73973 and Japanese Patent Application 7
It can also be realized by the circuit described in No. 73974.

In the circuit of FIG. 1, an electric field strength detection circuit (20) for detecting the received electric field strength according to the output signal of the frequency conversion circuit (1), and a switching signal is generated when the received electric field strength is below a reference level. The switching signal generating circuit is connected. If the received electric field strength is higher than the reference level, no switching signal is generated and the free-run frequency of the VCO (13) is set to a frequency δf away from the carrier signal of the spread code. When the received electric field strength drops below the reference level, a switching signal is generated from the switching signal generating circuit (21) and the VCO
The free-run frequency of (13) switches to δf ′ which is closer to the carrier signal. Therefore, it is possible to increase the sensitivity of the spread spectrum receiver when the electric field is weak.

[0036]

As described above, according to the present invention, V
Since the free-run frequency of CO is set within a predetermined condition range, it is not necessary to add a special circuit, and it is possible to reliably obtain synchronization with a simple circuit configuration. Further, since the correlation output between the spread code and the spread spectrum signal is detected and the spread code and the spread spectrum signal are synchronized according to the detection result, the spread code on the transmission side and the spread side are synchronized. , Accurate spectrum despreading can be performed.

Furthermore, in the process of generating the input signal of the spread code generating circuit, the generation timing of the input signal is adjusted to adjust the phase of the spread code, so that temperature change, power supply voltage change, time change, VCO change. It is possible to always carry out accurate spectrum despreading regardless of variations in the free-running frequency and without limiting the adjustment range.
Also, if the phase of the spreading code is adjusted in a unit that is sufficiently smaller than the chip period of the spreading code, synchronization can be achieved with high accuracy.

Furthermore, since the correlation between the spread code and the spread spectrum signal is detected and held by time division, the circuit can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a correlation diagram for explaining the present invention.

FIG. 4 is a characteristic diagram showing a relationship between a correlation and a capture range.

[Explanation of symbols]

 13 VCO 14 Frequency Dividing Circuit 15 Second Spread Code Generating Circuit 16 Selection Circuit 17 Second Multiplier 18 Correlation Detection Circuit 19 Control Circuit

Claims (5)

[Claims] 1. A spread spectrum receiving apparatus for receiving a spread spectrum signal, comprising: a despreading circuit for despreading the spread spectrum signal with a spread code; and a free-run frequency for a carrier frequency f0 of the spread spectrum spread signal. V set apart by a predetermined frequency δf
CO, a phase comparison circuit that compares the output signal of the first despreading circuit and the output signal of the VCO, and a control signal generator that generates a control signal of the VCO according to the output signal of the phase comparison circuit And a spread code generation circuit that generates a spread code according to the output signal of the VCO, wherein the free-run frequency of the VCO is fc1 <f0 + δf
A spread spectrum receiving apparatus, which is set according to a range of <fc2 or fc2 <f0-δf <fc1 and a range of δfs <δf. However, fc1: frequency that determines the minimum capture range within ± 1 chip of the correlation point of autocorrelation. fc2: frequency that determines the capture range at the maximum point of autocorrelation. δfs: Frequency difference that allows sliding correlation. 2. A spread spectrum receiver for receiving a spread spectrum signal, comprising a despreading circuit for despreading the spread spectrum signal with a spread code, and a free-run frequency for a carrier frequency f0 of the spread spectrum spread signal. V set apart by a predetermined frequency δf
CO, a phase comparison circuit that compares the output signal of the first despreading circuit and the output signal of the VCO, and a control signal generator that generates a control signal of the VCO according to the output signal of the phase comparison circuit And a spreading code generating circuit for generating a spreading code according to the output signal of the VCO, wherein the free-run frequency of the VCO is fc3 <f0 + δf
<Sp4 or fc4 <f0-δf <fc3 and a range of δfs <δf. However, fc3: a frequency that determines the capture range at the second-order maximum point of autocorrelation. fc4: frequency that defines the capture range at the first-order maximum point of autocorrelation. δfs: Frequency difference that allows sliding correlation. 3. A spread spectrum receiver for receiving a spread spectrum signal, comprising a despreading circuit for despreading the spread spectrum signal with a spread code, and a free-run frequency for a carrier frequency f0 of the spread spectrum spread signal. V set apart by a predetermined frequency δf
CO, a phase comparison circuit that compares the output signal of the first despreading circuit and the output signal of the VCO, and a control signal generator that generates a control signal of the VCO according to the output signal of the phase comparison circuit And a spread code generation circuit that generates a spread code according to the output signal of the VCO, wherein the free-run frequency of the VCO is fc5 <f0 + δf.
A spread spectrum receiving apparatus, which is set according to a range of <fc6 or fc6 <f0-δf <fc5 and a range of δfs <δf. However, fc1: frequency that determines the capture range at the maximum maximum point of cross-correlation. fc2: frequency that determines the capture range at the maximum point of autocorrelation. δfs: Frequency difference that allows sliding correlation. 4. A spread spectrum receiver according to claim 1, 2 or 3, wherein a solid-state oscillator or a SAW oscillator is used as an oscillator constituting the VCO. 5. A reception field strength detection circuit for detecting a reception field strength and a switching signal generation circuit for generating a switching signal when the reception field strength is equal to or lower than a predetermined strength, and a VCO free-run according to the switching signal. The frequency is the carrier frequency f
The spread spectrum receiving apparatus according to claim 1, wherein the frequency is switched to a frequency approaching zero.