JPH0918445A - Spread spectrum receiver - Google Patents

Abstract

PURPOSE: To provide a spread spectrum receiver capable of accurately matching spread codes on a transmission side and a reception side one with another. CONSTITUTION: The spread code is generated from a spread code generation circuit 16 corresponding to the output signal of VCO 14 generated synchronously with the output signal of a first inverse spread circuit 11. The spread code performs the inverse spread of a spread spectrum signal in the first inverse spread circuit 11. Also, the output signal of the VCO 14 is multiplied by the spread spectrum signal in a multiplication circuit 17, and a reproduced spread code is obtained at the output terminal of an LPF 18 by applying the output signal of the multiplication circuit 17 to an LPF 18. The reproduced spread code inversely spreads the spread spectrum signal in a second inverse spread circuit 19.

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 receiver, and a spread spectrum receiver for preventing the occurrence of a phase error between a PN code on the transmitting side and a PN code on the receiving side when a phase locked loop is used. Regarding

[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 phase-compared with the output signal of the VCO (voltage controlled oscillator circuit) (5) in the phase comparison circuit (4). The output signal of the phase comparison circuit (4) according to the result of the phase comparison is
After being smoothed by the LPF (6), it is applied as a control signal to the VCO (5), and the oscillation frequency of the VCO (5) is changed according to the control signal. 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), the frequency dividing circuit (7) and the spreading code generating circuit (8) form a so-called PLL (phase locked loop), and the two input signals of the phase comparison circuit (4) are connected. The PLL operates so that the phase difference becomes zero. Therefore, the generation timing of the spread code from the spread code generation circuit (3) changes in accordance with the change in the oscillation frequency of the VCO (5), and the PLL has the phase comparison circuit (4) 2
Since the two input signals operate so as to be synchronized in phase, 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]

In FIG. 2, since the PLL operates so that the phases of two input signals of the phase comparison circuit (4) are synchronized, the output signal of the multiplier (2) and the VCXO ( The phase difference with the output signal of 5) becomes zero. However, the phase of the spread code created on the receiving side does not exactly match the phase of the spread code in the spread spectrum signal due to the delay of the elements constituting the circuit of FIG. I couldn't.

[0006]

The present invention has been made in view of the above points, and is a spread spectrum receiving apparatus for receiving a spread spectrum signal, wherein the spread spectrum signal is despread with a spread code. A first despreading circuit, a phase synchronization circuit that generates an output signal synchronized with the phase of the output signal of the despreading circuit, and a spreading code generation that generates a first spreading code according to the output signal of the phase synchronization circuit A circuit, a spread code reproducing circuit for reproducing a second spread code according to the spread spectrum signal and an output signal of the phase synchronization circuit, and a second spread code reproducing circuit for despreading the spread spectrum signal with the reproduced second spread code. And two despreading circuits.

The spread code reproduction circuit comprises a multiplication circuit for multiplying the spread spectrum signal by the output signal of the phase synchronization circuit, and a removal circuit for removing high frequency components of the output signal of the multiplication circuit. It is characterized by Furthermore, a spread spectrum receiver for receiving a spread spectrum signal, wherein a first despreading circuit for despreading the spread spectrum signal with a spreading code and an output signal synchronized with the phase of the output signal of the despreading circuit are generated. A phase synchronization circuit for generating a first spreading code according to an output signal of the phase synchronization circuit, an output signal of the first despreading circuit, an output signal of the phase synchronization circuit and the first A spread code reproducing circuit for reproducing the second spread code according to the first spread code, and a second spread code and a spread spectrum signal for the second spread code.
And a despreading circuit.

Furthermore, a comparison circuit for comparing the levels of the output signals of the first and second despreading circuits, and one of the output signals of the first and second comparison circuits is selected according to the output signal of the comparison circuit. And a selection circuit.

[0009]

According to the present invention, the spread code is generated from the spread code generating circuit in response to the output signal of the phase locked loop circuit which is generated in synchronization with the output signal of the first despreading circuit. The spreading code despreads the spread spectrum signal in the first despreading circuit. Further, the output signal of the phase synchronization circuit is multiplied by the spread spectrum signal in the multiplication circuit, and by applying the output signal of the multiplication circuit to the low pass filter, the spread code reproduced at the output end of the low pass filter can be obtained. The reproduced spreading code despreads the spread spectrum signal in the second despreading circuit. Therefore, since the spread code is reproduced from the received spread spectrum signal, it is possible to establish the synchronization relationship between the spread code on the transmitting side and the spread code on the receiving side, and to perform accurate spectrum despreading.

[0010]

FIG. 1 is a diagram showing an embodiment of the present invention,
(10) is a frequency conversion circuit for frequency-converting the received spread spectrum signal, (11) is a first despreading circuit for despreading the output signal of the frequency conversion circuit (10), and (12) is a first despreading circuit (11). ) And a VCO output signal to be described later are compared in phase with each other, (13) is an LPF (low-pass filter) that smoothes the output signal of the phase comparison circuit (12), and (14) is an LPF ( VCO (voltage controlled oscillator circuit) whose frequency is variable according to the output signal of 13), (15) is a frequency divider circuit for dividing the output signal of VCO (14), and (16) is a frequency divider circuit (15). (17) is a multiplication circuit for multiplying the output signal of the frequency conversion circuit (10) and the output signal of the VCO (14), and (18) is a multiplication circuit. In the output signal of the circuit (18) LPF for cutting high frequency components, (19) a second despreading circuit for spectrum despreading the output signal of the frequency conversion circuit (10) by the output signal of the LPF (18), and (20) a second despreading circuit (19)
Is a BPF (band-pass filter) for limiting the output signal of BPF to a predetermined frequency band, and (21) is a demodulation circuit for demodulating the output signal of the BPF (20). In FIG. 1, the spread spectrum signal received is frequency-converted by a frequency conversion circuit (10) to a low frequency so that it can be easily processed by a circuit in a subsequent stage, and then a spread code generation circuit described later by a first despreading circuit (11). It is despread by the spreading code generated from (16). Then, the output signal of the first despreading circuit (11) is applied to the phase comparison circuit (12) and phase-compared with the output signal of the VCO (14). The output signal of the phase comparison circuit (12) corresponding to the result of the phase comparison is smoothed by the LPF (13) and then applied to the VCO (10) as its control signal. The oscillation frequency of the VCO (14) is variable according to the output signal of the LPF (13). The output signal of the VCO (14) is applied to the phase comparison circuit (12). Here, the phase comparison circuit (12), LPF (13) and VCO (14)
Constitutes a phase synchronization circuit, so-called PLL, and the PLL operates so that the phase difference between the two input signals of the phase comparison circuit (12) becomes zero.

The output signal of the VCO (14) is applied to the phase comparison circuit (12) and the frequency divider circuit (1).
It is also applied to 5) and the frequency is divided. A spreading code is generated from the spreading code generation circuit (16) based on the frequency division output signal of the frequency division circuit (15) and applied to the first despreading circuit (11).
Therefore, the generation timing of the spread code generated from the first spread code generation circuit (3) also changes according to the change in the oscillation frequency of the VCO (5), so that the PLL outputs the output of the first despread circuit (11). It operates so that the phase of the signal and the output signal of the VCO (14) are synchronized. Therefore, it is possible to maintain the synchronization between the output signal of the first despreading circuit (11) and the output signal of the VCO (14) by using a widely known PLL method.

The output signal of the VCO (14) is applied to the multiplication circuit (17) and is multiplied by the output signal of the frequency conversion circuit (17). Here, the spread code in the received spread spectrum signal is m (t), and the carrier signal is COS (ωt + θ).
i), ignoring the modulated signal, the received spread spectrum signal SS is

[0013]

[Equation 1]

## EQU1 ## The output signal generated from the VCO (14) is COS (ωt + θo). Where θ
o is the phase difference between the received signal and the output signal of the VCO 14. Therefore, the output signal S1 of the multiplication circuit (17) is

[0015]

[Equation 2]

## EQU1 ## The output signal of the multiplication circuit (17) has its high frequency component removed by the LPF (18).
The output signal S2 of the LPF (18) is

[0017]

(Equation 3)

Then, the spread code is reproduced. Where C
OS (θi−θo) becomes a constant, and k = COS (θi−
θo). Further, in the second despreading circuit (19), the output signal of the frequency conversion circuit (10) is LPF (1
Despreading is performed by the spreading code generated from 8). Therefore, the output signal S3 of the second despreading circuit (19) is given by the following equations (1) and (3):

[0019]

(Equation 4)

And becomes a component of the modulation signal. Where m
(T) · m (t) = 1. Then, the output signal of the second despreading circuit (19) is limited to a predetermined frequency bandwidth by the BPF (20), the interfering signal is removed, and then demodulated by the demodulation circuit (21). FIG. 3 shows another embodiment of the present invention, in which (22) is a multiplication circuit for multiplying the spread code from the spread code generation circuit (16) by the output signal of the VCO (14), and (23) is a first circuit. A multiplication circuit that multiplies the output signal of the despreading circuit (11) and the output signal of the multiplication circuit (22), (2
4) is an LPF for removing high frequency components of the output signal of the multiplication circuit (23), and (25) is the first despreading circuit (11).
A first envelope detection circuit for detecting the output signal of
6) is a second envelope detection circuit for performing envelope detection of the output signal of the second despreading circuit (19), and (27) is output signals of the first and second envelope detection circuits (25) and (26). A comparison circuit for comparison, (28) is a first and second despreading circuit (11)
And a selection circuit for selecting one of the output signals of (19).

In FIG. 3, the phase comparison circuit (12), L
As in FIG. 1, the PF (13) and the VCO (14) operate so that the phase difference between the two input signals of the phase comparison circuit (12) becomes 0, so that the first despreading circuit (11) operates. The phase of the output signal and the output signal of the VCO (14) become synchronized. Therefore, by using a widely known PLL method, it is possible to maintain the synchronization between the output signal of the first despreading circuit (11) and the output signal of the VCO (14), as in FIG.

On the other hand, the output signal of the VCO (14) and the spread code generated by the spread code generation circuit (16) are multiplied by the multiplication circuit (22). If the spreading code from the spreading code generation circuit (16) is m '(t), the multiplication circuit (22)
Output signal S4 of

[0023]

(Equation 5)

## EQU1 ## Further, in the first despreading circuit (11), the output signal SS of the frequency conversion circuit (10) is despread by the spreading code from the spreading code generating circuit (16). The output signal S5 of the spreading circuit (11) is

[0025]

(Equation 6)

## EQU1 ## Further, since the output signals of the first despreading circuit (11) and the multiplication circuit (22) are multiplied in the multiplication circuit (23), the output signal S6 of the multiplication circuit (23) is obtained.
From equation (5) and equation (6),

[0027]

(Equation 7)

## EQU1 ## However, m ′ (t) · m ′ (t) =
It is one. The output signal of the multiplication circuit (23) is the LPF (2
In 4), the high frequency component therein is removed. Therefore, LP
The output signal S7 of F (24) is

[0029]

(Equation 8)

Then, as is clear from the equation (8), the spread code is reproduced. Then, in the second despreading circuit (19), the output signal of the frequency conversion circuit (10) is spectrum despread by the regenerated spreading code, and the second despreading circuit (1
The output signal S8 of 9) is obtained from the equations (1) and (8).

[0031]

[Equation 9]

## EQU1 ## Further, the output signals of the first despreading circuit first and second despreading circuits (11) and (19) are applied to the selection circuit (28), and at the same time, the first and second envelope detection circuits (25), respectively. ) And (26).
In the first and second envelope detection circuits (25) and (26), the output signals of the first and second despreading circuits (11) and (19) are subjected to envelope detection. By the envelope detection, the correlation between the spread spectrum signal and the spread code is detected. First
And the output signals of the second envelope detection circuits (25) and (26) are applied to the comparison circuit (27) and compared. The output signal of the comparison circuit (27) corresponding to the comparison result is applied to the selection circuit (28), and the selection circuit (28) outputs the first and second despreading circuits (11) and (19) according to the comparison result. A signal having a good correlation is selected from the output signals. For that reason,
Of the first and second despreading circuits (11) and (19),
The one with good despreading is selected. Selection circuit (2
The output signal of 8) is limited to a predetermined frequency bandwidth by the BPF (20) and then demodulated by the demodulation circuit (21).

Also in the first embodiment, as shown in FIG. 3, the correlation between the output signals of the first and second despreading circuits (11) and (19) is compared and a signal having a good correlation is selected. If so, the interference characteristic can be improved. Further, FIG. 4 shows another embodiment of the present invention, in which (29) is a multiplication circuit for multiplying the output signal of the first despreading circuit (11) and the output signal of the VCO (14), and (30) is a spreading circuit. Code generation circuit (1
A multiplication circuit for multiplying the spread code from 6) by the output signal of the multiplication circuit (29), and (31) is an LPF for removing high frequency components of the output signal of the multiplication circuit (30).

In FIG. 4, the phase comparison circuit (12), L
As in FIG. 1, the PF (13) and the VCO (14) operate so that the phase difference between the two input signals of the phase comparison circuit (12) becomes 0, so that the first despreading circuit (11) operates. The phase of the output signal and the output signal of the VCO (14) become synchronized. Therefore, by using a widely known PLL method, it is possible to maintain the synchronization between the output signal of the first despreading circuit (11) and the output signal of the VCO (14), as in FIG.

On the other hand, the output signal of the first despreading circuit (11) is multiplied by the output signal of the VCO (14) in the multiplication circuit (29), and the output signal S9 of the multiplication circuit (29) is
From equation (6),

[0036]

(Equation 10)

Is as follows. Then, the output signal S9 of the multiplication circuit (29) is multiplied by the spreading code generated from the spreading code generation circuit (16) in the multiplication circuit (30), and the output signal S10 of the multiplication circuit (30) is given by the expression (7). ). In the output signal of the multiplication circuit (30), the high frequency component is removed by the LPF (31), and the spread code is reproduced as shown in equation (8). The spread code reproduced by the LPF (31) is transferred to the frequency conversion circuit (1) by the second despreading circuit (19).
The output signal of (0) is spectrum despread, and the output signal of the second despreading circuit (19) is as shown in equation (9), and is only the carrier signal component. The output signal of the second despreading circuit (19) is limited to a predetermined band by the BPF (20) and then demodulated by the demodulation circuit (21).

Further, instead of the method of reproducing the spread code in the embodiments of FIGS. 3 and 4, the output signal of the first despreading circuit (11) and the spread code from the spread code generating circuit (16) are used first. Then, the multiplication result is multiplied by the output signal of the VCO (14), and the multiplication result of the second time is multiplied by the LPF.
The spread code can be reproduced by applying a high frequency component to the signal to remove the high frequency component.

[0039]

As described above, according to the present invention, since the spread code is reproduced from the spread spectrum signal, the spread code synchronized with the spread spectrum signal can be obtained.
The spreading codes of the transmitting side and the receiving side are synchronized, and accurate spectrum despreading can be performed. In addition, spread spectrum can be performed with a simple circuit.

Further, the correlation outputs of the signal despread by the spreading code created on the receiving side and the signal despread by the reproduced spreading code are compared to select the best signal. As a result, the interference characteristic can be improved.

[Brief description of the drawings]

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

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

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a block diagram showing another embodiment of the present invention.

[Explanation of symbols]

10 frequency conversion circuit 11 first despreading circuit 12 phase comparison circuit 13, 18, 24, 31 LPF 14 VCO 15 frequency dividing circuit 16 spreading code generation circuit 17, 22, 23, 29, 30 multiplication circuit 19 second despreading circuit 20 BPF 21 demodulation circuit 25 first envelope detection circuit 26 second envelope detection circuit 27 comparison circuit 28 selection circuit

Claims (5)

[Claims] 1. A spread spectrum receiver for receiving a spread spectrum signal, comprising: a first despreading circuit for despreading the spread spectrum signal with a first spreading code; and a phase of an output signal of the first despreading circuit. A phase synchronization circuit for generating an output signal in synchronization with the phase synchronization circuit, a spread code generation circuit for generating the first spread code according to the output signal of the phase synchronization circuit, the spread spectrum signal and the output signal of the phase synchronization circuit And a second despreading circuit for despreading the spread spectrum signal with the regenerated second spreading code. Receiver. 2. The spread code reproduction circuit comprises a multiplication circuit for multiplying the spread spectrum signal and an output signal of the phase locked loop circuit, and a removal circuit for removing a high frequency component of the output signal of the multiplication circuit. The spread spectrum receiving apparatus according to claim 1, wherein 3. A first and second correlation detection circuit for detecting a correlation between output signals of the first and second despreading circuits, and a comparison circuit for comparing output signals of the first and second correlation detection circuits. 2. The spread spectrum receiving apparatus according to claim 1, further comprising: a selection circuit that selects one of the output signals of the first and second despreading circuits according to the output signal of the comparison circuit. 4. A spread spectrum receiver for receiving a spread spectrum signal, comprising: a first despreading circuit for despreading the spread spectrum signal with the first spreading code; and an output signal of the first despreading circuit. A phase synchronization circuit for generating an output signal synchronized with the phase; a spreading code generation circuit for generating the first spreading code according to the output signal of the phase synchronization circuit; an output signal of the first despreading circuit; A spread code reproduction circuit for reproducing a second spread code according to the output signal of the phase synchronization circuit and the first spread code; and a second despread circuit for despreading the spread spectrum signal with the second spread code. A spread spectrum receiving apparatus comprising: 5. A first and second correlation detection circuit for detecting a correlation between output signals of the first and second despreading circuits, and a comparison circuit for comparing output signals of the first and second correlation detection circuits, 5. The spread spectrum receiving apparatus according to claim 4, further comprising: a selection circuit that selects one of the output signals of the first and second despreading circuits according to the output signal of the comparison circuit.