JPS58162144A - Detecting system of interference wave - Google Patents

Abstract

PURPOSE:To detect interference without errors by using a receiving signal from which level fluctuation due to fading is removed and also using level fluctuation at the time of no modulation. CONSTITUTION:A receiving signal (in) is applied to an amplifying circuit 1 whose gain is automatically controlled, so that amplitude variation due to fading is removed. The output of the amplifying circuit 1 is applied to an amplitude detecting circuit 2 and a beat waveform is extracted. The level of the beat waveform is applied to a level measuring circuit 3 and the measured result is applied to an analog gate 6. On the other hand, the output of the amplifying circuit 1 is demodulated by a PM (or FM) demodulator 4. The demodulated output is applied to a call detecting circuit 5, and if the input signal is modulated, the modulation display signal is applied to an analog gate 6 to close the gate 6. Thus the level fluctuation at calling or the level fluctuation due to fading is prevented from being wrongly detected as the level fluctuation due to an interference wave, so that precise detection output (out) can be obtained.

Description

[Detailed Description of the Invention] This invention relates to a method for detecting whether or not there is interference waves from other sources with respect to wavelength waves, and is particularly applicable to mobile radio communication systems that perform multi-frequency switching connections without providing a central control station. This invention relates to a suitable interference wave detection method.

In the cordless telephone system, which is an example of this type of mobile radio communication system. As I will explain in detail later, there are multiple telephones each connected to a telephone line.

Each is connected to a corresponding wireless telephone by a wireless line. In this case, if different frequencies are assigned to each radio line, mutual interference will not occur under normal conditions. However, as a practical matter, in order to utilize frequencies effectively, it is necessary to use a small number of frequencies in common. However, when a small number of frequencies are shared in this way, if two carrier waves assigned the same frequency approach each other.

The two carrier waves cause interference, and the difference between the frequencies of the two carrier waves becomes a beat, which appears in the received signal as an envelope signal of the carrier wave, and when this is amplitude-detected, it is detected as a beat.

Therefore, normal communication becomes impossible, and it becomes necessary to switch the line frequency to an available frequency.

Conventionally, the above-mentioned frequency switching was performed by the caller listening to a beat sound and operating a switch. However, in order to hear the beat sound, you need to listen for a certain amount of time.

This was not only uncomfortable, but also had the disadvantage that it was impossible to make a phone call during that time.

Therefore, a first object of the present invention is to detect beats caused by interference between two carrier waves designated with the same frequency as electrical signals without error.

Another object of the present invention is to obtain the above-mentioned beat detection signal within as short a time as possible.

According to the present invention, there is provided an amplifier circuit that amplifies a received carrier in an automatic gain controllable manner but does not output a component whose amplitude fluctuates slowly, and an amplitude detector that detects the amplitude fluctuation component that remains in the output of this amplifier circuit. a level measuring circuit for measuring the level of the detected output of the amplitude detector; a determining means for determining whether or not the received carrier is modulated from the output of the amplifier circuit; , an analog gate 8 which cuts off the received carrier when the discriminating means determines that the received carrier is modulated and passes it when it determines that the received carrier is not modulated; and a low-pass filter that stabilizes the output of the analog boot. An interference wave detection method is obtained which is characterized by comprising: and a comparison circuit that detects an interference wave when the output value of the low-pass filter reaches a certain value.

- Next, a detailed explanation will be given with reference to the drawings.

FIG. 1 is a block diagram of a cordless telephone system shown as an example of a mobile radio communication system without a central control station.

As shown in FIG. 1, wireless connection devices A, B. C are each connected to separate telephone lines.

It is connected to corresponding wireless telephones A', B', and C' through wireless lines, respectively. As mentioned earlier, if individual frequencies are assigned to each of these wireless lines, in principle, mutual interference will not occur.

(5) In order to make effective use of frequencies, it will be necessary to share a small number of frequencies.

Anyway, now the above 3! There are two sets of transmitting/receiving frequencies (f+) for the combination of Ii's wireless connection device and wireless telephone.

It is assumed that the configuration is such that only f'+, fl, fl) are allocated so that any device can utilize these two sets of frequencies. Then, when wireless connection device A and wireless telephone I are using frequencies fl and fl, and wireless connection device B and wireless telephone B' start using frequencies, it can be seen that frequencies f1 and f'+ are being used. and. Automatically switch to another frequency f21f'2 and set up a wireless line.

At this time, when the wireless connection device C and the wireless telephone C' try to start using it, it is detected that the image frequencies ft+f/1 and fl 1 7"2 are in use, and the line connection becomes impossible. You will have to wait until it becomes vacant.

If a large number of the above-mentioned systems are installed at the terminals of the public fish communication network, the wireless connection device D and the wireless telephone D belonging to different groups
' may set the line (6) using the frequency fl+f'l. There is no problem if this is a far place where it does not cause interference, but when wireless telephone I moves and approaches the wireless connection device, the wireless connection device receives waves from wireless telephone X as well as wireless telephone D'. , as explained above, mutual interference occurs. At this time, the wireless connection device and the wireless telephone D' are switched to other available frequencies. The method of the present invention, which will be described later, is capable of reliably obtaining the necessary interference wave detection signal in a short time in order to electrically switch between the two without manual intervention.

Generally, when two carrier waves designated with the same frequency cause interference, the difference between the two carrier wave frequencies appears as a beat in the received signal. This becomes the envelope signal of the carrier wave, so
This beat can be detected by amplitude detection of the signal received by the radio receiver. However, in reality, reliable detection is impossible simply by detecting the received signal. Namely.

Even if PM modulation or FM modulation method is used.

Due to the frequency four-phase characteristics of the transmission path, PM-+AM conversion (or FM
-) AM conversion) occurs, so not only the phase plane but also the amplitude direction fluctuates. For this reason.

Merely measuring the level of amplitude fluctuations risks detecting amplitude fluctuations during one conversation and erroneously detecting them, even though the interference waves are strong. Alternatively, since it is a mobile object such as a cordless telephone, it is affected by fading, and the ratio of the desired wave to the interference wave may change rapidly, causing the beat sound to suddenly become stronger, which can be detected and falsely detected. There is also danger.

The present invention is designed to detect interference without error while paying attention to the above points.

FIG. 2 is a block diagram showing the configuration of an embodiment of the interference wave detection method according to the present invention. As an amplifier circuit 1 in which gain control is automatically performed.

As for its response characteristics, gain control is performed to follow amplitude fluctuations to the extent of fading.

A value is selected so that gain control cannot be performed for fast amplitude fluctuations such as beats when there is interference. That is, slow fluctuations in amplitude such as fading are removed from the output of the amplifier circuit 1.

When there is an interference wave in the received carrier in addition to the desired wave, beat fluctuations corresponding to the difference frequency occur.

The amplitude detection circuit 2 extracts a beat waveform appearing as an amplitude variation of the carrier remaining in the output of the amplifier circuit 1. The level measurement circuit 3 is a level measurement circuit that measures the level of the beat waveform output from the amplitude detection circuit 2.

Even if there is no interference wave and only one carrier wave is received,
If modulation is applied to an audio signal or the like, level fluctuations will occur in the received carrier, so it is necessary to separate the signals for this reason.

Since the level of the demodulated output of the PM (or FM) demodulator 4 becomes high when a call is in progress, this is measured by the busy detection circuit 5 to determine whether one call is in progress or not.

Determine whether or not the carrier is modulated. If modulated, a modulation indication signal (for example, "1") is emitted, and if no modulation is applied, a non-modulation indication signal (in this case, "o") is issued. Emits.

The analog gate 6 is the output of the alarm circuit 5 during the second talk. When I decide that it is.

The output of the circuit 3 is directly sent to the nonlinear filter low-pass filter 7. When the output of the nonlinear low-pass filter 7 becomes higher than the value vc of the reference power source 8, the comparator circuit 9 outputs a detection signal indicating that there is an interference wave. That is, the demodulator 4 and the busy detection circuit 5 determine whether or not the received carrier is modulated, and when it is determined that the carrier is modulated, the analog gate 6 is turned off to detect an interference wave. is prevented.

By the way, beat fluctuations when there is an interference wave also affect the phase (or frequency) of the carrier, so as a result of demodulating this to PM (or FM), a beat sound is heard and degrades the call quality. .

In particular, when the ratio of the desired wave to the interference wave changes significantly due to the influence of fading, this beat sound suddenly becomes louder, so the interference wave must be detected as quickly as possible. Also, if the desired wave (io) becomes larger than the interference wave, the demodulation result of the interference wave will appear in the PM (or FM) demodulation output.
There is a risk of crosstalk occurring.

Care must be taken when detecting interference waves due to the influence of such fading. Therefore, in FIG. 2, a nonlinear band-pass filter 7 is provided so that the response to high-level beats becomes faster. In other words, the beat level is low.

When the input value of the nonlinear low-pass filter 7 is small, the diode Xt does not become conductive, and the resistance R1 + capacitance C1
It operates based on the time constants R and c of the first circuit. When the beat level is high and the input value of the nonlinear low-pass filter 7 is high, the diode Xl also conducts,
Capacitor C1 is charged not only by resistor R1 but also by R2, and the response of the two circuits becomes faster. Note that the nonlinear low-pass filter 7 operates as a nonlinear filter even without the resistor R2. - In the explanation of Fig. 2 above, the detection response for high-level beats is made faster by making the second circuit 7 nonlinear, but the same effect can be obtained by making the level measurement circuit 3 nonlinear instead. It will be done.

FIG. 3 is a diagram showing a specific structure of the level measuring circuit 3 in FIG. 2. The circuit shown in FIG. 3 includes a nonlinear circuit 10 that allows a beat waveform with a high input level to easily pass through.
It consists of a rectifier circuit 11 and a smoothing circuit. When the input level is high, the diode ' x 2 and
3 becomes conductive and rectifies and smooths it, resulting in faster response of the 2 circuits.

As can be seen from the above explanation, by using the nonlinear filter 7 shown in Fig. 2 or the level measurement circuit shown in Fig. 3, even if the beat sound of the interference wave suddenly becomes louder due to fading, the interference wave can be detected. The response speed is much faster, so loud beats don't reach your ears for a long time.

As described above, according to the second aspect of the present invention, a system is provided that can automatically detect the occurrence of interference based on the beat fluctuation of a carrier received by a radio receiving device. In particular, it has excellent protection against erroneous detection of interference waves during a single call, and response characteristics against changes in beat level and motion due to fading. If automatic switching between two frequencies is controlled based on the detection output of this system, a mobile radio system that can automatically and reliably avoid interference can be obtained.

The system of the present invention is particularly effective when implemented in combination with an automatic frequency switching device in a cordless telephone.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of the configuration of a cordless telephone system, Figure 2 is a block diagram showing the configuration of an interference wave detection system that is an embodiment of the present invention, and Figure 3 is a diagram showing interference wave detection according to the present invention. FIG. 3 is a diagram showing an example of a level detection circuit used in the method. Explanation of symbols = 1 is an amplifier circuit capable of automatic gain control, 2 is an amplitude detection circuit, 3 is a level measurement circuit, 4 is a demodulator, 5 is a busy detection circuit, 6 is an analog gate, 7 is a nonlinear low pass Filter, 8 is reference power supply. 9 is a comparison circuit, 10 is a nonlinear circuit, 11 is a rectifier circuit, 1
2 is a smoothing circuit. (13) Figure 1

Claims (1)

[Claims] 1. An amplifier circuit that amplifies the received carrier in an automatic gain controllable manner but does not output components whose amplitudes fluctuate slowly, and an amplitude detector that detects the amplitude fluctuations remaining in the output of this amplifier circuit. a detector, a level measuring circuit for measuring the level of the detected output of the amplitude detector, a determining means for determining whether or not the received carrier is modulated from the output of the amplifier circuit; an analog gate that cuts off the output when the discriminating means determines that the received carrier is modulated, and allows the output to pass when the discriminating means determines that the received carrier is not modulated; An interference wave characterized by comprising a low-pass filter that stabilizes the output of this analog gate, and a comparison circuit that detects that there is an interference wave when the output value of this low-pass filter reaches a certain value. Detection method. 2. In claim 1, the low-pass filter is a nonlinear low-pass filter that responds slowly when the level of the amplitude detection output is low and responds quickly when the level of the amplitude detection output is high. This interference detection method is characterized by: 3. The low-pass filter of the second term was connected in parallel to a primary circuit consisting only of a resistor and a capacitor, and across both ends of the resistor. 3. The interference wave detection method according to claim 2, which comprises a resistive circuit including a diode, and has a fast response to large fluctuations in the output of the level measuring circuit. 4. The interference device according to claim 1, wherein the level measuring circuit comprises a nonlinear circuit that easily passes through high input levels, and means for rectifying and smoothing the output of this circuit. Wave detection method. 5 In claim 1, the determining means:
An interference wave detection system characterized in that the method is a means for detecting whether or not a level of a result of FM or PM demodulation of the carrier is above a value.