JPH07240701A - Spread spectrum circuit and inverse spread spectrum circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit without using spread codes like PN codes by spreading the output signal, which is obtained by linearly modulating a carrier by an information signal, with a spread signal consisting of an analog signal having a prescribed frequency and inversely spreading and demodulating a reception signal by an inverse spread signal. CONSTITUTION:The information signal is applied to a linear modulation circuit 15 through an input terminal 23. Meanwhile, the carrier signal from a VCO 16 is inputted to the circuit 15 and a programmable divider 17. The carrier signal inputted to the divider 17 has the frequency divided by a variable frequency division ratio, and the output signal has the phase compared with a reference signal by a phase comparator 19, and the output signal is inputted to the VCO 16 as a control signal through an LPF 20. The carrier signal is modulated in the circuit 15 by the information signal to generate a modulated signal, and this signal is inputted to a multiplier 22 and is multiplied by the analog sine wave signal from an oscillator 21, and the spread spectrum signal is transmitted from an antenna. Meanwhile, the reception signal is inversely spread and demodulated in a spectrum inverse spread circuit by the inverse spread signal to obtain the information signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum circuit and a reverse spread circuit which perform spread spectrum and despread using a spread signal of a predetermined frequency.

[0002]

2. Description of the Related Art Conventionally, various wireless signal systems have been proposed, and among them, there is a spread spectrum communication system. In this spread spectrum communication system (particularly, direct spread system), the transmission side multiplies the primary modulation signal modulated by the information signal by a spread code to obtain a spread spectrum signal. Then, the spectrum-spread signal is wirelessly transmitted. On the other hand, on the receiving station side, the received signal is despread by multiplying it by a spreading code, the received signal is returned to a primary modulated signal, and this is demodulated to obtain an information signal. As described above, in the spread spectrum communication method, since the spread spectrum signal is wirelessly communicated, it is possible to perform communication while eliminating interference with radio communication by radio waves of a predetermined frequency.

FIG. 3 shows a conventional spread spectrum circuit.
In FIG. 3, a primary modulation signal is generated by the primary modulation circuit (1), and an output signal of the primary modulation circuit (1) is generated by a multiplier (2) from a PN (pseudo spread) code generator (3). PN
It is multiplied by the code and spread spectrum is performed. And the spectrum despreading is the PN generated at the receiving side.
This is done by multiplying the code by the PN code in the received signal in synchronism. As such a spectrum despreading circuit, a DLL (delay lock loop) as shown in FIG. 4 is used.
There is something called. In FIG. 4, the received signal whose frequency has been converted by the frequency conversion circuit (4) is applied to the multipliers (5) and (6), and the first P signal from the PN code generator (7) is applied.
The N code and the second PN code which is 1 bit before the first PN code are respectively multiplied. The outputs of the multipliers (5) and (6) are detected by the envelope detectors (8) and (9), respectively, and then applied to the comparator (10) for comparison. An output corresponding to the comparison result of the comparator (10) is applied to a VCXO (voltage controlled crystal oscillator) (12) via an LPE (low pass filter) (11). In addition, VCXO
The output signal of (12) is applied to the PN code generator (7). Further, the first PN code is T / T in the delay circuit (13).
After being delayed by two, it is applied to a multiplier (14) and multiplied by the received signal to perform spectrum despreading. Incidentally, T is a time corresponding to one bit of the PN code.

By the way, envelope detectors (8) and (9)
The output of is as shown in Fig. 5 (a) and (b), respectively.
The output of the comparator (10) to which the high level is output when synchronized and the output is 0 when deviated by 1 bit or more, and the output of the comparator (10) has a waveform as shown in FIG. Becomes The point (a) in FIG. 5C is an intermediate point between the two output synchronization points of the PN code generator (7). Therefore, FIG.
In the circuit of FIG. 5, the VCXO (1) is set so that the output level of the LPF (11) becomes 0 level such as the point (a) of FIG.
The frequency of the output signal of 2) changes, and it will be in a lock state.

[0005]

However, since the spread spectrum circuit of FIG. 3 spreads using a spread code such as a PN code, perfect synchronization is not achieved between the spread spectrum signal and the spread code at the time of spectrum despreading. If not taken, there is a problem that the amount of synchronization shift becomes a noise component in the form of white noise and the S / N of the primary demodulated signal deteriorates.

Further, in the spectrum despreading circuit, the outputs of the envelope detectors (8) and (9) become 0 when the synchronization is out of sync for 1 bit or more, so that the input signal of the VCXO (12) disappears. It took a long time for the circuit of No. 4 to be in the synchronous state. Therefore, since a circuit such as a sliding correlator is added so that the circuit of FIG. 4 is brought into a synchronized state in a short time, there is a problem that the circuit becomes complicated.

Further, as shown in FIG. 4, since two loops using two multipliers (5) and (6) are formed, if the loop gains are different, the output of the comparator (10) There is an offset in the signal. Therefore, the DLL of FIG.
Even if is locked, the point (a) in FIG. 5C is not positioned in the middle of the two output sync points of the PN code generator (7).
The PN code was not synchronized with the received signal and could not perform correct spectrum despreading.

Further, when a received signal having a strong electric field strength is received, the outputs of the envelope detectors (8) and (9) are shown in FIG.
The waveform becomes as shown in (d), and it becomes difficult to detect the synchronization point.
Therefore, it is necessary to provide an AGC circuit in order to adjust the electric field strength of the received signal to an appropriate level so that the output becomes a triangular output. Therefore, there is a problem that the circuit of FIG. 4 becomes complicated.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and a carrier generation circuit for generating a plurality of carrier signals of a predetermined frequency, and a primary modulation of the carrier signal with an information signal 1 A spectrum comprising a secondary modulation circuit, a spread signal generation circuit for generating an analog signal having a predetermined frequency as a spread signal, and a spread circuit for spreading the output signal of the primary modulation circuit with the spread signal. Spreading circuit.

Further, a despread signal generation circuit for generating a despread signal from the received signal, a despread circuit for despreading the received signal by the despread signal, and a demodulation for generating demodulated signals of a plurality of predetermined frequencies. It is characterized by comprising a signal generation circuit and a primary demodulation circuit which demodulates the output signal of the despreading circuit by the demodulation signal and generates an information signal.

The despread signal generation circuit further includes a spread signal detection circuit for detecting a spread signal from a received signal and a PLL for generating a despread signal whose phase matches that of the spread signal.
And a circuit.

[0012]

In the spread spectrum circuit according to the present invention, 1
In the next modulation circuit, the carrier signal generated by the carrier generation circuit is modulated with the information signal. The output signal of the primary modulation circuit is spectrum-spread by an analog signal which is a spread signal having a predetermined frequency. Since the frequency of the carrier signal is selected from one of the multiple frequencies,
The primary modulated signal can be different depending on the selection and will have its own distinctiveness.

In the spectrum despreading circuit according to the present invention, the received signal is applied to the despread signal generating circuit,
A despread signal is generated from the received signal. In the despreading circuit, the despread signal despreads the spectrum-spread signal. The output signal of the despreading circuit is applied to the primary demodulation circuit, demodulated by the demodulation signal from the demodulation signal generation circuit,
An information signal is obtained. Here, if the demodulated signal of the primary demodulation circuit has the same frequency as the carrier signal at the time of modulation,
A correct information signal is obtained.

[0014]

1 is a diagram showing an embodiment of a spread spectrum circuit of the present invention, in which (15) is a primary modulation circuit and (16) is a primary modulation circuit.
Is a VCO (voltage controlled oscillator) that generates a carrier signal,
(17) is a programmable divider that divides a carrier wave signal, (18) is a reference oscillator that generates a reference signal, (1
9) is a phase comparator for phase comparison between the output signal of the programmable divider (17) and the reference signal, (20) is LPF (low pass filter) for smoothing the output signal of the phase comparator (19), and (21) is spreading. An oscillator for generating a fixed frequency signal as a signal, and (22) a multiplier as a spreading circuit.

In FIG. 1, an information signal is applied to the primary modulation circuit (15) via an input terminal (23). Also,
The carrier signal from the VCO (16) is a primary modulation circuit (1
5) and the programmable divider (17). The carrier wave signal applied to the programmable divider (17) is divided by a variable division ratio. The output signal of the programmable divider (17) is phase-compared with the reference signal in the phase comparator (19). The output signal of the phase comparator (19) is smoothed by the LPF (20) and then applied to the VCO (16) as a control signal. And VCO (16)
The frequency of the carrier signal from is changed in response to the control signal. Therefore, if only one of the frequency division ratios of the programmable divider (17) is selected, a carrier signal having a frequency corresponding to the selected frequency division ratio is generated.

In the primary modulation circuit (15), the carrier signal is modulated by the information signal to generate a modulated signal.
Here, an angle modulation method such as FM modulation, a PSK modulation method, an FSK modulation method, or the like is used for the primary modulation circuit (15). The modulated signal is applied to the multiplier (22) and is multiplied by an analog signal such as a sine wave signal which is a spread signal generated from the oscillator (21). Here, the frequency of the sinusoidal signal is a single frequency that is much higher than the frequency of the modulating signal. Then, the signal spectrum-spread by the multiplier (22) is transmitted from the antenna. The multiplier (2
In 2), instead of the output signal of the oscillator (21),
The output signal of the reference oscillator (18) may be used.

Therefore, in the circuit of FIG. 1, if one carrier signal is generated from a plurality of frequencies corresponding to the receiver,
You will have the discriminating power of yourself and others. FIG. 2 is a diagram showing an embodiment of the spectrum despreading circuit of the present invention. In FIG. 2, (24) is a spread signal detection circuit, (25) is a first divider, (26) is a first phase comparator, and (27) is a first phase comparator.
LPF, (28) is VCXO, (29) is a second divider, (30) is a despreader multiplier, and (31) is 1
Next demodulation circuit, (32) VCO, (33) programmable divider, (34) reference oscillator, (35) second phase comparator, (36) second LPF.

In FIG. 2, the received signal is applied to the spread signal detection circuit (24) and the multiplier (30) via the antenna. The received signal is a signal that has been spread spectrum by the spread spectrum circuit of FIG. Spread signal detection circuit (2
In 4), the spread signal is detected from the received signal. Since the sine wave signal is used for spread spectrum, the detected spread signals are "0", "1", "0",
It becomes a signal that repeats "1". The detected spread signal is frequency-divided by the first divider (25) and the first phase comparator (2
6) is applied. The output signal of the VCXO (28) is divided by the second divider (29) at a fixed division ratio and then applied to the first phase comparator (26). First
In the phase comparator (26), the output signals of the first and second diverters (25) and (29) are compared in phase, and an output signal corresponding to the phase difference is generated. The output signal is the first L
It is smoothed by PF (27) and then applied to VCXO (28). Then, the output frequency of the VCXO (28) is controlled according to the output signal of the first LPF (27) so that the phase of the input signal of the first phase comparator (26) is synchronized.

On the other hand, the output signal of the VCXO (28) is applied to the multiplier (30) as a despread signal. In the multiplier (30), the receiver signal and the despread signal are multiplied, and spectrum despreading is performed. Here, since the despread signal is a sine wave signal synchronized with the spread signal detected by the spread signal detection circuit (24), the spectrum despread can be correctly performed.

The output signal of the multiplier (30) is applied to the primary demodulation circuit (31) and demodulated by the demodulated signal generated from the VCO (32) to generate an information signal at the output terminal (37). Further, the VCO (32), the programmable divider (33), the reference oscillator (34), the second phase comparator (35) and the second LPF (36) form a PLL circuit, and divide the dividing ratio of the programmable divider (34). If changed, the frequency of the carrier signal changes. The spectrum can be correctly despread only when the frequency of the demodulated signal of the primary demodulation circuit (31) is equal to the frequency of the carrier signal at the time of primary modulation. As the demodulation signal of the primary demodulation circuit (31), instead of the output signal of the PLL circuit, for example, a signal having a predetermined single frequency using the output signal of the reference oscillator (34) may be used. . In this case, the receiver using the spectrum despreading circuit corresponds to only one of the frequencies of the carrier signal of the primary modulation.

Further, since a widely known PLL method is used to synchronize the received signal and the spread signal, the circuit configuration of the spectrum despreading circuit can be simplified. Further, by shortening the lockup time of the PLL circuit, the time until the two signals are synchronized can be shortened. Here, as the first phase comparator (26), a digital phase comparator that produces an error output linearly with respect to a phase difference of -π / 2 to π / 2 is suitable, and a VCXO (28) Since the output frequency is corrected linearly, the despread signal synchronizes with the received signal in a short time.

FIG. 6 shows a specific example of the configuration of the spread signal detection circuit (24). Since the structure is the same as the conventional one, the description thereof will be omitted. In FIG. 6, the received signal is applied to the comparator (38) and compared with a predetermined level. A signal of "1" is generated when the level of the received signal is higher than a predetermined level, and a signal of "0" is generated when the level is lower than the predetermined level. The output signal of the comparator (38) is the direct coincidence determination circuit (3
9) and after being delayed by the delay circuit (40) for a predetermined time, they are applied to the coincidence determination circuit (40). In the coincidence determination circuit (39), a signal "0" is generated when the two input signals match, and a signal "1" is generated when the two input signals do not match. Furthermore, the output signal of the coincidence determination circuit (39) is applied to the clock input terminal of the D-FF (41). Since the inverted Q output terminal and the D input terminal of the D-FF (41) are connected, the output state of the D-FF (41) is inverted at the falling edge of the clock input signal. As a result, a spread signal is generated at the Q output terminal of the D-FF (41).

[0023]

According to the spread spectrum circuit of the present invention, the fixed frequency signal is used as the spread signal, but one is selected from a plurality of carrier signals and the primary modulation signal is changed according to the selection. If they do, they can identify themselves. Since a fixed frequency analog signal is used as the spread signal, a complicated circuit for generating the PN code is not required, and the circuit for generating the spread signal can be simplified. Furthermore, since the received signal and the analog signal are multiplied at the time of spectrum despreading, the occurrence of white noise-like noise is reduced even if there is a synchronization shift between the two signals. The deterioration of S / N is prevented.

Further, in the spectrum despreading circuit according to the present invention, since the detected spread signal and the despread signal are phase-synchronized with each other, the received signal and the despread signal are synchronized with each other. In addition, the received signal and the despread signal can be synchronized, and the circuit configuration can be simplified. Since there is only one loop that synchronizes the phase of the received signal and the despread signal, the problem of offset caused by the loop gain difference can be solved, and the phase can be properly synchronized.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional example of a spread spectrum circuit.

FIG. 4 is a block diagram showing a conventional example of a spectrum despreading circuit.

FIG. 5 is a waveform diagram showing output waveforms of respective parts of FIG.

FIG. 6 is a block diagram showing a main part of FIG.

[Explanation of symbols]

 15, primary modulation circuit 16, 32 VCO 17, 33 programmable divider 18, 24 reference oscillator 19, 26, 35 phase comparator 20, 27, 36 LPF 21 oscillator 22, 30 multiplier 24 spread signal detection circuit 25, 29 divider 28 VCXO 31 Primary demodulation circuit

Claims (3)

[Claims] 1. A carrier generation circuit for generating a plurality of carrier signals of a predetermined frequency, a primary modulation circuit for primary-modulating the carrier signal with an information signal, and a spreader for generating an analog signal having a predetermined frequency as a spread signal. A spread spectrum circuit comprising: a signal generation circuit; and a spreader circuit for spreading the output signal of the primary modulation circuit with the spread signal. 2. A despread signal generation circuit for generating a despread signal from a spread signal in the received signal, a despread circuit for despreading the received signal by the despread signal, and a demodulated signal of a plurality of predetermined frequencies. And a primary demodulation circuit that demodulates the output signal of the despreading circuit with the demodulated signal to generate an information signal. 3. The despread signal generating circuit detects a spread signal from a received signal, and a despread signal generating a despread signal in phase with the spread signal.
3. A spectrum despreading circuit according to claim 2, comprising an LL circuit.