JP2781947B2 - Direct spread spectrum spread communication equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a spread spectrum communication apparatus using direct spreading.

[0002]

2. Description of the Related Art In a direct spread spectrum spread communication apparatus, a transmission system spread-modulates a digital information signal with a pseudo-noise spreading code having a bit rate sufficiently faster than the digital information signal, and a reception system performs spreading modulation equivalent to the transmission system. Demodulate by despreading with code.

In the receiving system of this communication system, a received signal synchronized with a spread code is despread from a spread modulation band to a baseband modulation bandwidth. Received signals that are not synchronized with the spreading code are spread over at least the entire spread modulated bandwidth. With the mechanism as described above, the process gain of this communication method can be obtained.

[0004] Therefore, if the process gain is sufficiently large with respect to the interference of the interfering wave, the effect of the interfering wave does not appear at all. However, a strong interfering wave that invalidates the process gain is greatly affected by data demodulation similarly to a general wireless communication system.

[0005] Therefore, in such a case, means for reducing the interference of some interference waves is required. As the interference reducing means, a method of further increasing the process gain can be considered. To increase the process gain, it is conceivable to increase the bandwidth of the spread spectrum or reduce the bit rate of the digital information signal.

However, in reality, the frequency band set for the communication of the own station is defined and finite,
The bandwidth of the spread modulation cannot be increased. Therefore, the only way to increase the process gain is to reduce the bit rate of the digital information signal.However, to eliminate the effects of strong interference that would invalidate the process gain, the bit rate of the digital information signal must be reduced. Must be significantly reduced.

Therefore, it is more effective to use other interference mitigation means in order to prevent the bit rate of the digital information signal from being greatly reduced. Therefore, conventionally, a method has been proposed in which an interference wave is removed by using a variable notch filter or a variable bandpass filter in a receiving system.

FIG. 9 is a block diagram showing an example of a conventional direct spread spectrum spread communication apparatus using a variable notch filter.

In the communication apparatus shown in FIG. 9, a transmission system and a reception system are switched by a transmission / reception switch 2 connected to an antenna 1. The receiving system includes a low noise amplifier 3, a down converter 4, a variable notch filter 16, an IF amplifier 6, and an interference wave detection circuit 7 and a control circuit 8 connected to the variable notch filter 16 from the output side of the IF amplifier 6 in this order. And is connected to a demodulation circuit (not shown).

The transmission system is an exclusive logic of the digital information signal from the high power amplifier 13, the PSK modulation circuit 12 and the digital information signal generation circuit (not shown) and the spread code from the spread code generation circuit 15 which are connected in sequence. It is composed of an addition circuit 11 and the like for obtaining the sum.

Phased lock oscillator (PL)
O) The oscillation signal of 17 is output from the down converter 4 and the PS
The spread code supplied to the K modulation circuit 12 and generated by the spread code generation circuit 15 is also supplied to a demodulation circuit by despreading of the receiving system.

The reception operation of the communication device will be described. Before starting communication, the transmission / reception switch 2 is set to the reception side, the notch frequency of the variable notch filter 16 is set outside the communication band, and the reception circuit is operated. And
The interfering wave detection circuit 7 is used to detect whether or not another station is communicating, and if so, the own station stands by without performing communication. If another station is not communicating, similarly, the presence or absence of an interference wave is detected by the interference wave detection circuit 7. If not, the control circuit 8 communicates the notch frequency of the variable notch filter 16. Control to be out of band,
If an interfering wave exists, the control circuit 8 controls the variable notch filter 16 so that the notch frequency is at a position where the interfering wave exists. By starting communication through the above procedure, interference of an interfering wave can be removed.

[0013]

As described above, in the case where a strong interfering wave that invalidates the process gain is considered, the variable notch filter or the variable band-pass filter as described above is used as the interference reducing means. However, the variable band-pass filter has a complicated structure, so that a small and inexpensive direct spread spectrum communication device cannot be realized. There is a problem that some of them are removed. Although the configuration of the variable notch filter is simple, there is a problem that, similar to the variable bandpass filter, the filter removes an interference wave and also removes a part of a desired wave.

[0014]

SUMMARY OF THE INVENTION A direct spread spectrum spread communication apparatus according to the present invention comprises: an interference wave detection circuit for detecting an interference wave from a received directly spread spectrum spread signal; and a digital signal from the interference wave detection circuit. A control circuit for generating a control signal by converting the transmission frequency into an occupied frequency band of a transmission radio wave in which the interference from the control circuit is reduced by a signal from the control circuit when an interference wave exists. A down-converter for a receiving circuit and a PSK modulation circuit for a transmission circuit to which a local oscillation signal is supplied from the synthesizer; a spreading code generation circuit and a digital information signal circuit connected to the PSK modulation circuit ing. The spread code generation circuit can change the chip rate so as to correspond to the occupied frequency band changed so as not to be disturbed by making the chip rate variable by the control signal. Further, the digital information signal circuit is provided with a bit rate variable circuit for varying a bit rate by a control signal, and changes a bit rate so as to correspond to an occupied frequency band changed so as not to be disturbed.

[0015]

According to the present invention, the occupied frequency band of the transmission wave is controlled so that the interference wave and the transmission wave do not overlap according to the detection output of the interference wave detection circuit. Accordingly, the chip rate of the spreading code and the bit rate of the digital information signal can be changed, so that it is possible to remove strong interference of an interference wave that invalidates the process gain.

[0016]

FIG. 1 is a block diagram showing an embodiment of the present invention. Parts similar to those in the conventional example of FIG. 9 are denoted by the same reference numerals. The difference from the apparatus of FIG. 9 is that the bandpass filter 5 is provided instead of the
Instead of O17, for example, a synthesizer 9 capable of changing the oscillation frequency of the PLL system is provided, and the control circuit 8 is connected to the synthesizer 9 and to the spreading code generation circuit 10. This spread code generating circuit 10 is adapted to change the chip rate of the spread code.

The operation of the receiving system of the apparatus shown in FIG. 1 will be described below. The signal received by the antenna 1 is input to the low noise amplifier 3 of the receiving system by the transmission / reception switch 2.
The low-noise amplifier 3 amplifies the received signal with low noise, and inputs the received signal and the local oscillation signal of the synthesizer 9 to the down-converter 4. The received signal frequency-converted by the down converter 4 is input to a band-pass filter 5 that passes only a desired intermediate frequency. Bandpass filter 5
Is filtered by the IF amplifier 6 and output to the demodulation circuit.

The transmission system operates as follows. The addition circuit 11 performs an exclusive OR operation on the spread code generated by the spread code generation circuit 10 with the variable chip rate and the digital information signal in the addition circuit 11, and uses the local oscillation signal of the synthesizer 9 at the output thereof to generate a PSK modulation circuit 12. PSK modulation is performed. The PSK-modulated signal is power-amplified by the high power amplifier 13, output to the antenna 1 via the transmission / reception switch 2, and transmitted.

In the receiving system, the output of the IF amplifier 6 is
A part thereof is input to the interference wave detection circuit 7. The control circuit 8 changes the local oscillation frequency of the synthesizer 9 and the chip rate of the spread code generation circuit 10 having a variable chip rate according to the detection output of the interference wave detection circuit 7. Therefore, P
The occupied frequency band of the transmission radio wave formed by the SK modulation circuit 12 can be controlled so as to reduce interference according to the interference radio wave.

Next, a procedure for determining the occupied band of the transmission radio wave will be described. FIG. 2 is a block diagram of an example of an interference wave detection circuit used in the device according to the present invention. Received signal input terminal 1
An FM detection circuit 20 and an A / D converter 21 are connected between 8 and an output terminal 19 of the detection output.

FIG. 3 is a flowchart of a procedure for controlling the occupied frequency band of the transmission radio wave when the interference wave detection circuit of FIG. 2 is used. Hereinafter, this flowchart will be described with reference to FIGS.
This will be described with reference to the spectral distribution diagram of FIG.

FIG. 4 shows the communication frequency band set for the own station.
And the frequency f ₁ to f ₂ as shown in (a). at first,
By operating the receiving system try a data demodulation (Fig. 3 step S1), the other station judges whether or not the communication using the frequency band from the frequency f ₁ to f ₂ (FIG. 3 step S2).
If another station is communicating, the communication procedure is interrupted (step S3 in FIG. 3), and the communication procedure is resumed after waiting for a certain time.

If the other station is not communicating, it is checked whether or not an interference wave exists using the interference wave detection circuit shown in FIG. 2 (step S4 in FIG. 3). If disturbance is not present, communicates with the communication bandwidth whole of f ₂ from the frequency f ₁ in the band occupied by the transmission radio wave as shown in FIG. 4 (a) (FIG. 3 step S5).

If there is an interfering wave, the interfering frequency is digitized by the FM detection circuit 20 and the A / D converter 21 shown in FIG. The frequency of the wave is determined (step S6 in FIG. 3). Therefore, if there is an interfering wave as shown in FIG. 4B, the oscillation frequency of the synthesizer 9 is changed, the chip rate of the spread code generating circuit 10 having a variable chip rate is reduced, and the occupied band of the transmission radio wave is reduced. Is set as shown in FIG. 4C (step S in FIG. 3).
7) If there is an interfering wave as shown in FIG. 4 (d), the oscillation frequency of the synthesizer 9 is changed, the chip rate of the spread code generation circuit 10 with a variable chip rate is reduced, and the transmission radio wave is occupied. The band is set as shown in FIG. 4E (step S7 in FIG. 3). In this way, it is possible to perform favorable communication by removing the influence of the interference wave.

FIG. 5 is a block diagram of another example of the interference wave detection circuit used in the device according to the present invention. This is designed on the assumption that the transmission path characteristics are grasped in advance, and there is a possibility that an interference wave may exist only in a certain band. Between the input terminal 18 and output terminal 19, a low-pass filter 22 for passing only the frequency f ₃ or less of the frequency of FIG. 7 described later
When the first carrier sense circuit 24 is connected, it is connected to the high-pass filter 23 for passing only the frequency f ₃ or more frequency second carrier sense circuit 25 is provided between the input terminal 18 and output terminal 19-1 I have.

FIG. 6 is a flowchart of a procedure for determining the occupied band of the transmission radio wave when the interference wave detection circuit shown in FIG. 5 is used. Hereinafter, this procedure will be described with reference to the spectrum distribution diagram of FIG. 7 and FIG.

[0027] and the communication bandwidth set in the own station from the frequency f ₁ shown in FIG. 7 (a) to f _2, interferes so the band from the frequency f ₁ as shown in FIG. 7 (b) to f ₃ It is assumed that the transmission path characteristics in which only a significant interference wave may exist are known in advance.

First, communication is started (step S1 in FIG. 6).
0). First, the band f ₂ performs carrier sense from a frequency f ₃ (FIG. 6 step S11), and determines whether the detection output (FIG. 6 step S12). If there is a detection output, it is determined that another station is communicating, and the communication procedure is interrupted and waits (step S13 in FIG. 6).

[0029] it is judged that there is no detection output from other station is not communicating, performs carrier sense from the frequency f ₁ in the band of f ₃ (FIG. 6 step S14). If there is a detection output here, the occupied band of the transmission radio wave is determined as shown in FIG. 7C assuming that an interference wave as shown in FIG. 7B exists (step S17 in FIG. 6).

If there is no detection output, it is determined that no interfering wave exists, and the occupied frequency band of the transmission radio wave is set as shown in FIG. 7A (step S16 in FIG. 6).

By using the low-pass filter 22 and the high-pass filter 23 as band-pass filters having frequencies f _{1 to} f ₃ and band-pass filters having frequencies f _{3 to} f ₂ , more accurate carrier sensing can be performed. .

FIG. 8 is a block diagram showing another embodiment of the direct spread spectrum communication apparatus according to the present invention. The difference from the apparatus of FIG. 1 is that a bit rate variable circuit 14 is provided before the digital information signal is supplied to the adder circuit 11, and this is controlled by the control circuit 8, and the spread code generating circuit 15 has a variable chip rate. That is not to be done.

The operation of the apparatus shown in FIG. 8 is substantially the same as the operation of the apparatus shown in FIG. 1, and therefore detailed description thereof will be omitted, and only different points will be described.

According to the detection output of the interference wave detection circuit 7,
The control circuit 8 changes the local oscillation frequency of the synthesizer 9 and changes the bit rate of the digital information signal by the bit rate variable circuit 14. Therefore, unlike the embodiment of FIG. 1, a spread code generation circuit 15 having a fixed chip rate is used. However, the occupied band of the transmission radio wave formed by the PSK modulation circuit 12 is a desired band which is less affected by jamming radio waves. Can be controlled so that For example, with reference to FIGS. 7A to 7C, when another station is not communicating and there is no interfering wave,
The local oscillation frequency of the synthesizer 9 is set between f ₁ and f ₂ , and the bit rate of the digital information signal is set to the maximum by using the bit rate variable circuit 14, and all communication is performed as shown in FIG. Let the band be the occupied band of the transmission radio wave. If multiple stations are not communicating and an interfering wave as shown in FIG. 7B exists, the local oscillation frequency of the synthesizer 9 is set to f
₃ and f ₂ , the bit rate of the digital information signal is reduced by using the variable bit rate circuit 14,
As shown in FIG. 7C, the occupied band of the transmission radio wave is controlled.

[0035]

As described above, according to the present invention, it is possible to obtain an inexpensive and compact direct-sequence spread-spectrum communication apparatus which can maintain a good reception state even when a strong interfering wave exists. it can.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating an example of an interference wave detection circuit.

FIG. 3 is a flowchart when the interference wave detection circuit of FIG. 2 is used.

FIG. 4 is a spectrum distribution diagram for explaining FIG. 3;

FIG. 5 is a block diagram of another embodiment of the interference wave detection circuit.

FIG. 6 is a flowchart when the circuit of FIG. 5 is used.

FIG. 7 is a spectrum distribution diagram for explaining FIG. 6;

FIG. 8 is a block diagram of another embodiment of the present invention.

FIG. 9 is a block diagram of an example of a conventional direct spread spectrum communication apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 Transmission / reception switch 3 Low noise amplifier 4 Down converter 5 Band pass filter 6 IF amplifier 7 Interference wave detection circuit 8 Control circuit 9 Synthesizer 10, 15 Spread code generation circuit 11 Addition circuit 12 PSK modulation circuit 13 High power amplifier 14 Bit rate Variable circuit

Continuation of the front page (56) References JP-A-4-81151 (JP, A) JP-A-5-68017 (JP, A) JP-A-2-1822045 (JP, A) JP-A-2-192238 (JP) JP-A-3-195132 (JP, A) JP-A-4-3535 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04J 13/00

Claims (3)

(57) [Claims] An interference wave detection circuit for detecting an interference wave from a received directly spread spectrum spread signal; a control circuit for digitizing a signal from the interference wave detection circuit to generate a control signal; When a control signal from the control circuit is supplied, a synthesizer whose transmission frequency is controlled so that the frequency band is occupied by the transmitted radio wave so that the disturbance of the interference wave is reduced, and a local transmission signal from the synthesizer are supplied. A direct spread spectrum communication apparatus comprising: a down converter for a receiving circuit; a PSK modulation circuit for a transmission circuit; a spread code generation circuit and a digital information signal circuit connected to the PSK modulation circuit. 2. A spread code generation circuit, wherein a chip rate is changed by a control signal from a control circuit. When an interfering wave is present, the chip rate is changed by a synthesizer controlled by the control signal. 2. The direct spread spectrum spread communication apparatus according to claim 1, wherein the chip rate is changed so as to correspond to the occupied frequency band of the transmitted radio wave. 3. The digital information signal circuit has a bit rate variable circuit for changing a bit rate by a control signal from a control circuit, and when an interfering wave is present, the digital information signal circuit is changed by a synthesizer controlled by the control signal. 2. The direct spread spectrum spread communication apparatus according to claim 1, wherein the bit rate is changed so as to correspond to the occupied frequency band of the transmitted radio wave.