JPH0730515A - Direct spread spectrum communication equipment - Google Patents

Abstract

PURPOSE:To control an occupied frequency band of a transmission radio wave at spread modulation corresponding to a detection output of a disturbing wave detection circuit by providing a BPF, a synthesizer and a spread code generating circuit to the equipment. CONSTITUTION:A signal received by an antenna 1 is inputted to a BPF 5 passing through only a desired intermediate frequency signal via a transmission reception changeover switch 2, a low noise amplifier 3 and a down-converter 4 and a reception signal filtered by the BPF 5 is amplified by an IF amplifier 6 and outputted to a demodulation circuit. Then part of the output of the amplifier 6 is inputted to a disturbing wave detection circuit 7, and a control circuit 8 varies a tip rate of a variable tip rate spread code generating circuit 10 and a local oscillation frequency of a synthesizer 9 corresponding to a detection output from the circuit 7. Thus, the occupied frequency band of the transmission radio wave generated by a PSK modulation circuit 12 is controlled to receive less disturbance of a disturbing radio wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a spread spectrum communication device by direct spread.

[0002]

2. Description of the Related Art In a direct sequence spread spectrum communication apparatus, a transmission system spread-modulates a digital information signal with a pseudo-noise spreading code having a bit rate sufficiently higher than the digital information signal, and a reception system spreads the signal equivalent to the transmission system. Despread with a code and demodulate.

In the receiving system of this communication system, the received signal synchronized with the spreading code is despread from the band of spread modulation to the bandwidth of baseband modulation. Received signals that are out of sync with the spreading code are spread over at least the entire spread modulated bandwidth. With the above mechanism, the process gain of this communication method can be obtained.

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 will be greatly affected by the data demodulation as in a general wireless communication system.

Therefore, in such a case, a means for reducing the interference of some kind of interfering wave 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 spread spectrum bandwidth or decrease the bit rate of the digital information signal.

However, in reality, the frequency band set for the communication of the own station is regulated and finite,
The bandwidth of 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, but in order to remove the effect of a strong interfering wave that invalidates the process gain, the bit rate of the digital information signal should be reduced. Must be significantly reduced.

Therefore, in order not to significantly reduce the bit rate of the digital information signal, it is more effective to use other interference reducing means together. Therefore, conventionally, there has been proposed a method of removing an interfering wave by using a variable notch filter or a variable bandpass filter in the receiving system.

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

In the communication device of FIG. 9, a transmission system and a reception system are switched by a transmission / reception changeover switch 2 connected to an antenna 1. The reception system includes a low noise amplifier 3, a down converter 4, a variable notch filter 16, an IF amplifier 6, and an interfering 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 order. And a demodulation circuit (not shown).

The transmission system is the 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 configured by an adder circuit 11 for summing and the like.

Phased Rock Oscillator (PL
O) 17 oscillation signal is generated by the down converter 4 and PS.
The spread code supplied to the K modulation circuit 12 and generated by the spread code generation circuit 15 is also supplied to the demodulation circuit by despreading in the receiving system.

A reception operation of this communication device will be described. Before starting communication, the transmission / reception changeover switch 2 is set to the receiving side, the notch frequency of the variable notch filter 16 is set to outside the communication band, and the receiving system 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 station waits without communicating. If other stations are not communicating, the interference wave detection circuit 7 similarly detects whether or not an interference wave exists. If not, the control circuit 8 communicates the notch frequency of the variable notch filter 16. Control to be out of band,
When the interfering wave exists, the control circuit 8 controls the notch frequency of the variable notch filter 16 so that the notch frequency is at the position where the interfering wave exists. By starting the communication through the above procedure, the interference of the interfering wave can be removed.

[0013]

As described above, when a strong interfering wave that invalidates the process gain is considered, the variable notch filter or the variable bandpass filter as described above is conventionally used as the interference reducing means. However, since the variable bandpass filter has a complicated configuration, a small and inexpensive direct spread spectrum communication device cannot be realized. There is a problem that some of them are also removed. The variable notch filter has a simple structure, but similarly to the variable bandpass filter, there is a problem that the filter removes the interference wave and at the same time removes a part of the desired wave.

[0014]

A communication device according to the present invention comprises an interfering wave detection circuit, a control circuit, a synthesizer, and a circuit for varying the chip rate of a spread code or a circuit for varying the bit rate of a digital information signal. By doing so, it becomes possible to control the occupied frequency band of the transmission radio wave at the time of spread modulation in accordance with the detection output of the interference wave detection circuit.

[0015]

According to the present invention, the occupied frequency band of the transmission radio wave is controlled so that the interference wave and the transmission radio wave do not overlap with each other in accordance with the detection output of the interference wave detection circuit. It becomes possible to eliminate the interference of strong interfering waves.

[0016]

FIG. 1 is a block diagram of an embodiment of the present invention. The same parts as those in the conventional example of FIG. 9 are denoted by the same reference numerals. 9 is different from the device of FIG. 9 in that a bandpass filter 5 is provided instead of the variable notch filter 16,
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 the spread code generating circuit 10. The spread code generation 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 changeover switch 2.
The received signal is low-noise amplified by the low noise amplifier 3, and the received signal and the local oscillation signal of the synthesizer 9 are input to the down converter 4. The received signal whose frequency has been converted by the down converter 4 is input to the bandpass filter 5 that passes only the desired intermediate frequency. Bandpass filter 5
The received signal filtered by is amplified by the IF amplifier 6 and output to the demodulation circuit.

The transmission system operates as follows. The adder circuit 11 performs an exclusive OR operation on the spread code and the digital information signal generated by the spread code generator circuit 10 of the variable chip rate in the adder circuit 11, and outputs the output from the local oscillation signal of the synthesizer 9 in the PSK modulation circuit 12. PSK modulation. The PSK-modulated signal is power-amplified by the high power amplifier 13 and 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
Part of it 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 generating circuit 10 having a variable chip rate in response to the detection output of the interfering 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 the interference according to the interference radio wave.

Next, the procedure for determining the occupied band of the transmitted 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 the output terminal 19 of the detection output.

FIG. 3 is a flow chart 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. This flowchart will be described below with reference to FIG.
This will be described with reference to the spectrum distribution chart of (e) and FIG.

FIG. 4 shows the communication frequency band set in the own station.
The frequencies are f ₁ to f ₂ shown in (a). at first,
The receiving system is operated to demodulate data (step S1 in FIG. 3), and it is determined whether another station is communicating in the frequency band from frequency f ₁ to f ₂ (step S2 in FIG. 3).
If another station is communicating, the communication procedure is interrupted (step S3 in FIG. 3), the communication procedure is restarted after waiting for a certain period of time.

If another station is not communicating, the interfering wave detection circuit shown in FIG. 2 is used to check whether or not an interfering wave exists (step S4 in FIG. 3). If no interfering wave exists, communication is performed with the entire communication band of frequencies f ₁ to f ₂ as the occupied band of the transmission radio wave as shown in FIG. 4A (step S5 in FIG. 3).

If an interfering wave exists, the interfering frequency is digitized by the FM detection circuit 20 and the A / D converter 21 shown in FIG. 2, and the interfering frequency is determined from the correspondence table of the digital value and the frequency built in the control circuit 8. The frequency of the wave is known (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 transited to reduce the chip rate of the variable chip rate spread code generating circuit 10 to occupy the occupied band of the transmission radio wave. Is set as shown in FIG. 4C (step S in FIG. 3).
7) If there is an interfering wave as shown in FIG. 4D, the oscillation frequency of the synthesizer 9 is transited to reduce the chip rate of the variable chip rate spread code generating circuit 10 to occupy the transmitted radio wave. The band is set as shown in FIG. 4E (step S7 in FIG. 3). In this way, it becomes possible to remove the influence of the interfering wave and perform good communication.

FIG. 5 is a block diagram of another example of the interference wave detection circuit used in the device according to the present invention. It was devised on the assumption that the transmission path characteristics are known in advance and there is a possibility that the interference wave exists only in a certain band. Between the input terminal 18 and the output terminal 19, a low-pass filter 22 that allows only frequencies below frequency f _{3 in} FIG.
And a first carrier sense circuit 24 are connected, and a high-pass filter 23 and a second carrier sense circuit 25 that pass only a frequency of frequency f ₃ or higher are connected between the input terminal 18 and the output terminal 19-1. There is.

FIG. 6 is a flow chart 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. This procedure will be described below with reference to the spectrum distribution chart of FIG. 7 and FIG.

The communication band set in the own station is set to frequencies f ₁ to f ₂ shown in FIG. 7 (a) so that it interferes with the band from frequencies f ₁ to f ₃ shown in FIG. 7 (b). It is assumed that the transmission line characteristics in which only such disturbing waves may exist are known in advance.

First, communication is started (step S1 in FIG. 6).
0). First, carrier sensing is performed in the frequency band from f ₃ to f ₂ (step S11 in FIG. 6), and the presence or absence of detection output is determined (step S12 in FIG. 6). If there is a detection output, it is determined that another station is communicating, the communication procedure is interrupted, and the process waits (step S13 in FIG. 6).

If there is no detection output, it is determined that the other station is not communicating, and carrier sensing is performed in the band of frequencies f ₁ to f ₃ (step S14 in FIG. 6). If there is a detection output here, it is determined that there is an interfering wave as shown in FIG. 7B, and the occupied band of the transmission radio wave is determined as shown in FIG. 7C (step S17 in FIG. 6).

If there is no detection output, it is determined that there is no interfering wave, and the occupied frequency band of the transmitted 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 a band-pass filter of frequencies f _{1 to} f _{3 and} a band-pass filter of frequencies f _{3 to} f ₂ , respectively, more accurate carrier sensing can be performed. .

FIG. 8 is a block diagram of another embodiment of the direct spread spectrum communication apparatus of the present invention. 1 is different from the device of FIG. 1 in that a bit rate variable circuit 14 is provided in a stage before supplying the digital information signal to the adder circuit 11 and is controlled by the control circuit 8, and the spread code generation circuit 15 has a variable chip rate. It is that it is not done.

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

Corresponding 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, the spread code generating 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 in which the influence of the interference radio wave is small. Can be controlled to be 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 to an intermediate value 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, so that all communication is performed as shown in FIG. The band is the occupied band of the transmitted radio wave. If multiple stations are not communicating and there is an interfering wave as shown in FIG. 7B, the local oscillation frequency of the synthesizer 9 is changed to f
_It is set between ₃ and f ₂ , and the bit rate variable circuit 14 is used to reduce the bit rate of the digital information signal.
As shown in FIG. 7C, the occupied band of the transmitted radio wave is controlled.

[0035]

As described above, according to the present invention, it is possible to obtain an inexpensive and compact direct spread spectrum communication device which can maintain a good reception state even in the presence of a strong interference wave. it can.

[Brief description of drawings]

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

FIG. 2 is a block diagram of 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.

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 device.

[Explanation of symbols]

 1 Antenna 2 Transmission / Reception Switch 3 Low Noise Amplifier 4 Down Converter 5 Band Pass Filter 6 IF Amplifier 7 Interfering Wave Detection Circuit 8 Control Circuit 9 Synthesizer 10, 15 Spread Code Generation Circuit 11 Adder Circuit 12 PSK Modulation Circuit 13 High Power Amplifier 14 Bit Rate Variable circuit

Claims (3)

[Claims] 1. An interference wave detection circuit, a synthesizer, and a control circuit for changing an oscillation frequency of the synthesizer in response to a detection signal of the interference wave detection circuit to control an occupied frequency band of a transmission electric wave at the time of spread modulation. A direct sequence spread spectrum communication device characterized by the above. 2. A synthesizer controlled by a control circuit and a spreading code generating circuit with a variable chip rate, and the oscillation frequency of the synthesizer and the chip rate of the spreading code generating circuit are changed in response to a detection signal of an interference wave detecting circuit. The direct spread spectrum spread communication apparatus according to claim 1, wherein the occupied frequency band of the transmitted radio wave is controlled by controlling the transmission. 3. A synthesizer controlled by a control circuit and a bit rate variable circuit for a digital information signal, wherein the oscillation frequency of the synthesizer and the bit rate of the digital information signal are changed in response to a detection signal of an interference wave detection circuit. The direct-spread-spectrum spread communication device according to claim 1, wherein the occupied frequency band of the transmitted radio wave is controlled.