JPH03220933A - Spread spectrum signal demodulation circuit and demodulator using same - Google Patents

Abstract

PURPOSE:To prevent mis-discrimination of synchronization by discriminating the synchronization state based on a ratio of outputs passing through a 1st filter means having a nearly equal pass band width to a band width of an information signal and a 2nd filter means having a broader band width respectively. CONSTITUTION:A 1st filter means 7 having a nearly equal pass band width to a band width of an information signal and a 2nd filter means 8 having a wider band width than the pass band width of the 1st filter means 7 are connected to an output terminal of a multiplier means 5. Then a discrimination means 11 discriminates the synchronization state based on the ratio of outputs from the 1st filter means 7 and the 2nd filter means 8. Thus, even when a fluctuation of an input level or a change in the synchronization state takes place, no mis-discrimination takes place. Moreover, since the AGC (automatic gain control) is automatically switched in response to synchronization or asynchronization, the circuit design is implemented independently and the degree of freedom of the design is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a spread spectrum signal demodulation circuit and a demodulation device using the same.

(b) Conventional technology Conventionally, the spectrum width is sufficiently wider than that of the information signal1.
For example, binary pseudo noise code (Pseudo No1se
A carrier modulated with a PN code (hereinafter referred to as a PN code) is transmitted, and the receiving side uses the same P
So-called spread spectrum communication is known in which the original information is demodulated by multiplying the received signal by an N code (see, for example, the November 1978 issue of Denshi Kagaku).

In such spread spectrum communication, the information signal is modulated using a PN code with wide spectrum transmission as mentioned above, so in order to accurately demodulate the information signal, the code generated on the receiving side must be synchronized with the code on the transmitting side. It is necessary to do so.

Generally, a multiplier is provided on the receiving side to multiply the received signal by the receiving side code, and the output of this multiplier is passed through a filter having approximately the same bandwidth as the information signal. The level of the signal is detected, and when the level of the signal exceeds a predetermined level, it is determined that the state is close to synchronization. This utilizes the fact that the level of the multiplication output when the code phases match is higher than the level of the multiplication output when the code phases do not match.

Note that when the level of the signal that has passed through the filter is lower than a predetermined level, the phase of the code on the receiving side is changed little by little, and the phase changing operation continues until the level reaches the predetermined level or higher. be done.

(c) Problems to be Solved by the Invention In general, in wireless communications, and in mobile wireless communications in particular, the amplitude of the received signal fluctuates significantly due to factors such as the distance between the transmitter and receiver and the surrounding topography. The dynamic range must be expected to be approximately 60 to 90 dB.

One way to absorb this fluctuation is to pass the received signal through a limiter to make it constant amplitude, but in this case, the anti-jamming performance, which is one of the characteristics of spread spectrum communication, will deteriorate by more than 6 dB ( For example, Jaticic Publishing “
(See page 236 of ``Spread Spectrum Communication System'').

Therefore, automatic gain control (AGC'I) is usually used, but in wireless circuits, the control width per amplifier stage is 20~
Since it is about 30 dB, it is necessary to apply AGC in multiple stages.

In addition, the responsiveness of AGC is determined in the synchronization pull-in process.
In order to detect the change in amplitude that occurs when the code phases go from mismatched to matched, the amplitude must be slow enough to not follow such sudden changes, while after synchronization , it must be fast enough to quickly optimize the signal amplitude.

Furthermore, when there is no desired signal, interference waves and noise
It is desirable to prevent excessive manpower from being applied to the multiplier (correlation circuit) and the subsequent demodulation circuit, and to control the level of the desired wave component input to the multiplier to be constant when a desired wave is present. .

However, an AGC that satisfies the above conditions has a very complex groove bottom, and it is difficult to predict the transient response of the amplitude of the signal controlled by the AGC, making it difficult to optimally detect the multiplier output for determining the synchronization state. This made level setting difficult, and erroneous synchronization judgments were likely to occur.

(d) Means for Solving the Problems In view of the above points, the present invention multiplies the received spread spectrum signal and the code output from the code generation means by the multiplication means, thereby changing the spectrum of the received spread spectrum signal. a spread spectrum signal demodulation circuit for despreading, the first filter means being connected to the output end of the multiplication means and having a passband width substantially equal to the bandwidth of the information signal; and also connected to the output end of the multiplication means. and a second filter means having a bandwidth wider than the bandwidth of the first filter means, and outputs that have passed through the first filter means and the second filter means are supplied, and the ratio of the magnitudes of both outputs is supplied. determining means for determining the synchronization state based on the output of the first filter means; and when the output of the first filter means is supplied, and a signal indicating that the synchronization state is present is supplied from the determination means, the determination means determines the synchronization state based on the output of the first filter means. The present invention is characterized by further comprising a control means for supplying to the code generation means a code phase correction signal for correcting the output phase of the code output from the code generation means.

Further, the present invention includes a receiving means that includes an active element and receives a spread spectrum signal, a multiplication means that multiplies the received spread spectrum signal received by the receiving means and a code output from the code generating means, and a first filter means connected to the output end of the multiplication means and having a passband width substantially equal to the bandwidth of the information signal; and also connected to the output end of the multiplication means and wider than the bandwidth of the first filter means. second filter means having a bandwidth; and an automatic means for providing a gain control signal to the active element of the receiving means based on the output of the multiplier means or the first filter means; gain control means;
outputs that have passed through the first filter means and the second filter means are supplied, and determination means for determining a synchronization state based on the ratio of the magnitudes of both outputs; When a signal indicating a synchronized state is supplied from the determining means, the code generating means generates a code phase correction signal for correcting the output phase of the code output from the code generating means based on the output of the first filter means. and control means for supplying a control signal to the automatic gain control means in order to perform an automatic gain control operation based on the output of the first filter means.

(E) Effect According to the present invention, the first filter means having a pass band width substantially equal to the bandwidth of the information signal and a bandwidth wider than the pass band width of the first filter means are provided at the output end of the multiplication means. The synchronization state is determined according to the ratio of the magnitude of the output from the first filter means and the output from the second filter means.

(F) Embodiment FIG. 1 is a diagram showing an embodiment of the present invention. In FIG. 1, (1) is an antenna, and (2) is a front end that converts a high frequency signal from the antenna (1) into a predetermined intermediate frequency signal, and includes an active element for amplifying the high frequency signal. (3) is an intermediate frequency amplification circuit including an active element for amplifying an intermediate frequency signal, (4) is a bandpass filter with a passband width W, and (5) is a bandpass filter (4).
A multiplier (7) for multiplying the signal passed through by the code from the code generator (6) is connected to the output terminal of the multiplier (5) and has a passband width F) which is approximately equal to the bandwidth of the information signal. A first filter, (8) with l is also connected to the output of the multiplier (5) and a second filter, (9) has a bandwidth Fw wider than the passband width FN of the first filter (7). is the first
The first detector performs envelope detection on the output of the filter (7), the second detector (10) performs envelope detection on the output of the second filter (8), and the output from the first detector (9) (11) and the output of the second wave detector (10), and a determination circuit (12) that determines the synchronization state based on the ratio of the magnitudes of both outputs is connected to the output end of the first filter (7). The demodulation circuit (13) is supplied with the output of the first filter (7), and when the determination circuit (11) supplies a signal indicating that the synchronization state is present, the demodulation circuit (13) operates based on the output of the first filter (7). A code phase correction signal that corrects the output phase of the code output from the code generator (6) is sent to the code generator (6).
a second code phase correction signal that sequentially changes the output phase of the code output from the code generator (6) when the determination circuit (11) does not supply a signal indicating that the synchronization state is present; A control circuit (14) supplies the output of the multiplier (5) and the output of the first filter (7) to the code generator (6), and operates the multiplier based on the control signal from the control circuit (13). The AGC circuit selects AGC based on the output of (5) or <AGC based on the output of the first filter (7), and the active elements of the front end (2) and intermediate frequency amplification circuit (3) are Control gain.

Next, the principle of the present invention will be explained with reference to FIG.

Now, the spectrum of the information signal is a rectangle with a bandwidth B as shown in Fig. 2(a), and this is transmitted to the transmitting side with a bandwidth W=ηB (η is the spreading factor and η>1−). It is assumed that the signal is spread over a rectangular spectrum.

Now, when only the desired wave signal is received as shown in FIG. 2(b), if the code phase on the receiving side matches the code phase on the transmitting side, the signal passing through the first filter (7) Since the magnitude of the signal passing through the second filter (8) is equal to the magnitude of the signal passing through the second filter (8), the ratio r becomes 1.

On the other hand, if the code phases do not match, the spectrum will be doubly spread and nearly flat, so the second filter (
8) passband width Fw is Fw=aF.

If (α>1), the ratio r will be approximately α (provided that α is not very large).

In addition, when receiving a signal spread with another code [see Figure 2 (c)], and when receiving a white random noise [see Figure 2 (c)],
d)], when a narrowband interference wave is received [see Figure 2 (e)
), etc., the ratio r is approximately α as in the case described above.

By the way, when the desired wave is received synchronously and multiple interference waves and noises are included as shown in FIG. 2(f), the ratio r becomes 1 depending on the magnitude of the interference waves and noises. It grows from The demodulation circuit (12) includes a first filter (
7) is input, but assuming that noise up to twice as much as the carrier wave is allowed in that signal, the ratio r under the worst condition is r = (1+K a )/(1+
K). However, the passband FN of the first filter (7)
It is assumed that the spectrum after multiplication is approximately flat except for the information signal. Also, 1<(α to 1+)/(1+
It is assumed that the relationship K)<α holds true.

Therefore, by setting an appropriate threshold between (1+α)/(1+K) and α for r, it is possible to determine when the desired wave is being received in a synchronous state and when it is not. I can do something.

Next, the operation of the circuit shown in FIG. 1 will be explained.

The signal received by the antenna (1) passes through a front end (2) and an intermediate frequency amplification circuit (3), and then is sent to a multiplier (5).
) and is multiplied by the code from the code generator (6) in such a multiplier (5).

The multiplication outputs are supplied to a first filter (7) and a second filter (8), then subjected to envelope detection, respectively, and supplied to a determination circuit (11). In the determination circuit (11),
The synchronization state is determined based on the principle described above.

As a result of such a determination, if the synchronization state is not established, a signal indicating the state is supplied to the control circuit (13), and the control circuit (13) generates a second code phase correction signal that sequentially changes the code phase based on this signal. is output to the code generator (6).

The second code phase correction signal is supplied to the determination circuit (11
) continues until the synchronization status is determined.

After that, when the determination circuit (11) determines that it is in the synchronous state, it supplies a signal indicating the state to the control circuit (13), and the control circuit (13) controls the first filter (7) based on this signal. The code phase correction signal based on the output of the code generator (
6) to maintain synchronization.

Moreover, when the AGC circuit (14) is in an asynchronous state,
The gain of the front end (2) and intermediate frequency amplification circuit (3) is controlled based on the output of the multiplier (5>), and when in the synchronized state, the gain of the first one is controlled based on the control signal from the control circuit (13).
The state is switched to control the gains of the front end (2) and intermediate frequency amplification circuit (3) based on the output of the filter (7).

Note that the determination operation in the determination circuit (11) may be either an analog method that directly uses the envelope output or a digital method that first converts it into a digital signal and processes it.
Although various circuit configurations can be considered, it can be easily realized using a microcomputer.

(G) Effects of the Invention According to the present invention, there is no possibility of erroneous determination even if the input level fluctuates or the synchronization state changes.

Furthermore, since the AGC can be automatically switched depending on whether it is synchronous or asynchronous, circuit design can be done independently, increasing the degree of freedom in design.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 (a) to (
f) is a diagram for explaining the principle of the present invention. (1,)(2)(3)... An antenna serving as a receiving means,
Front end and intermediate frequency amplification circuit, (5)...multiplier, (6)...code generator, (7)...first filter, (8)...second filter, (11) ...determination circuit, (12) ... demodulation circuit, (13) ... control circuit, (14) ... AGC circuit.

Claims (4)

[Claims] (1) A spread spectrum signal demodulation circuit that despreads the spectrum of the received spread spectrum signal by multiplying the received spread spectrum signal and the code output from the code generation means by the multiplication means, the multiplication means comprising: a first filter means connected to the output end and having a pass band width substantially equal to the bandwidth of the information signal; and a first filter means also connected to the output end of the multiplication means and having a bandwidth wider than the bandwidth of the first filter means a second filter means having a second filter means, a determining means to which outputs having passed through the first filter means and the second filter means are supplied, and for determining a synchronization state based on a ratio of the magnitudes of both outputs; a code phase for correcting the output phase of the code output from the code generation means based on the output of the first filter means when the output of the first filter means is supplied and a signal indicating a synchronized state is supplied from the determination means. A spread spectrum signal demodulation circuit comprising: control means for supplying a modified signal to the code generation means. (2) The control means generates a second code phase correction signal that sequentially changes the output phase of the code output from the code generation means when a signal indicating that the synchronization state is not supplied from the determination means. 2. The spread spectrum signal demodulation circuit according to claim 1, wherein said spread spectrum signal demodulation circuit is configured to supply said code generation means to said code generation means. (3) receiving means that includes an active element and receives a spread spectrum signal; multiplication means that multiplies the received spread spectrum signal received by the receiving means by the code output from the code generation means; and the multiplication means a first one connected to the output end of the first
filter means, second filter means also connected to the output of the multiplication means and having a wider bandwidth than the bandwidth of the first filter means, the outputs of the multiplication means and the first filter means being supplied; The multiplication means or the first
automatic gain control means for supplying a gain control signal to the active element of the receiving means based on the output of the filter means;
a determining means that is supplied with the outputs that have passed through the filter means and the second filter means, and determines a synchronization state based on the ratio of the magnitudes of both outputs; and a determining means that is supplied with the output of the first filter means; When a signal indicating a synchronized state is supplied, a code phase correction signal for correcting the output phase of the code output from the code generation means based on the output of the first filter means is supplied to the code generation means. A spread spectrum signal demodulating apparatus, further comprising: control means for supplying a control signal to the automatic gain control means in order to perform an automatic gain control operation based on the output of the first filter means. (4) The control means includes a second code phase correction signal that sequentially changes the output phase of the code output from the code generation means when a signal indicating that the synchronization state is not supplied from the determination means. 4. The spread spectrum signal demodulating device according to claim 3, wherein said spread spectrum signal demodulating device is configured to supply said code generating means to said code generating means.