JPS6238620A - Circuit of detecting interference wave - Google Patents

Abstract

PURPOSE:To prevent mis-detection due to beatlevel fluctuation caused by fading and mis-detection caused due to large angular modulation at talking by providing a high pass filter between an AM detector and a level detector and using a busy state detection circuit and a gate circuit. CONSTITUTION:The output of the detector 1 is a superimposed waveform between the amplitude fluctuation of a low frequency component due to fading and the beat component due to an interference wave. Thus, in order to eliminate the amplitude fluctuation of the low frequency component due to fading, the high pass filter 3 is used. On the other hand, the busy state detection circuit 5 detecting the output level demodulated by an amplitude device 7 and a demodulator 6 decides whether a demodulated output level is a prescribed level or over or below, and when the level is the prescribed level or over, a gate circuit 4 applies gating so as to prevent mis-detection due to the amplitude fluctuation of a carrier caused by it that the angular modulation caused by too large modulation at busy state is large.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for detecting whether or not there is an interference wave from another with respect to a desired wave among signals received by a radio receiver.

In particular, the present invention relates to an interference wave detection circuit suitable for an angle modulation type mobile radio communication system that performs multi-frequency switching connections.

〔overview〕

The present invention is a circuit that detects the presence of interference by detecting beats with interference waves from a radio receiver, which cuts off the low frequency components of the beats and further stops detection when the degree of modulation of the communication signal is high. This prevents false detection due to carrier wave amplitude fluctuations caused by fading that varies at low frequencies and deep angular modulation.

[Conventional technology]

In conventional mobile radio communication systems, in order to make effective use of frequencies, each radio device has multiple common radio lines, and calls are made by selecting an empty line from among them, which is called multi-channel access. Systems applying this method are widely used.

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. When a small number of frequencies are shared in this way, the carrier waves may cause interference due to the same frequency, and the difference between the carrier waves may appear as a beat in the received signal. In such a case, normal communication becomes impossible and it becomes necessary to switch the line frequency to an available frequency.

Conventionally, a beat detection circuit was provided for each radio, and this circuit detected the beat by, for example, detecting the amplitude of the intermediate frequency signal and determining the magnitude of its output level. Attempts have been made to detect the occurrence of radio interference and switch to another free line.

FIG. 3 shows a conventional interference detection method in which a beat output level from which an amplitude modulated wave is detected by a detector 1 is detected by a level detector 2, and a comparator 8 determines whether the level is larger or smaller than a reference level. It is something that does. The amplifier 7 has a function of amplifying a received carrier or an intermediate frequency carrier, and the demodulator 6 has a function of demodulating a modulated wave angle-modulated by an audio signal, a data signal, or the like.

[Problem that the invention seeks to solve]

However, the conventional interference wave detection method causes the following problems. In other words, reliable detection is not possible by simply amplitude-detecting the received signal, and even if phase modulation or frequency modulation is used, due to the frequency-phase characteristics of the transmission path, when a call is busy, only one carrier wave is present. Since amplitude fluctuations of the carrier wave occur due to large angle modulation, fluctuations occur not only in the phase plane but also in the amplitude.

Amplitude fluctuations also occur due to fluctuations in the desired wave level due to fading. For this reason, simply measuring the level of the beat with the interfering wave by amplitude detection may lead to false detection during a busy state or during fading even though there is no interfering wave, which is a practical problem.

The present invention aims to improve the above-mentioned drawbacks, and aims to provide an interference detection method that can detect interference without error when it occurs.

[Means for solving problems]

The present invention includes an input terminal for inputting a carrier wave of an angle-modulated received signal, an amplitude detector for amplitude-detecting the signal at this input terminal, and a level detector for detecting the beat level of the output of the amplitude detector. In an interference wave detection circuit equipped with a comparator that compares the detection level of the level detector with a reference level, a high-pass filter is inserted in the output circuit of the amplitude detector, and angle modulation of the signal appearing at the input terminal is performed. A circuit for detecting that the degree of modulation of is equal to or greater than a predetermined value, and a gate circuit for blocking a circuit from the input of the amplitude detector to the output of the comparator using the detection output of this circuit. shall be.

[Effect]

The effects of the present invention are as follows: +l) By installing a high-pass filter between the AM detector 1 and the level detector 2, it is possible to sufficiently remove low frequency amplitude fluctuations due to fading, (2 ) By using a busy detection circuit and a gate circuit, detection is not performed when the degree of modulation exceeds a predetermined level during a busy time, resulting in false detection due to carrier wave amplitude fluctuations caused by deep angular modulation during a busy time. can be prevented.

〔Example〕

Next, embodiments of the present invention will be described with reference to the accompanying drawings.

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

Similar parts corresponding to those in FIG. 3 (prior art) are given the same reference numerals.

An AM detector l is connected between the input (IN) and the output (OUT).
, a high-pass filter 3, a gate circuit 4, a level detector 2, and a comparator 8 are successively connected in cascade, and an amplifier 7, a demodulator 6, and a busy detection circuit 5 are further connected between the input and the gate circuit 4. A series of cascaded circuits is provided.

The detector 1 has a detection function for amplitude modulation, and for example, a so-called LOG AMP, which generates an output voltage proportional to the rdB value of the input electric field level, is often used. As shown in FIG. 2(a), the output of the detector 1 is a superimposed waveform of the amplitude fluctuation of the low frequency component due to fading and the beat component due to the interference wave. Therefore, a high-pass filter 3 is used to remove amplitude fluctuations of low frequency components due to fading. This results in Figure 2 (C
As shown in Fig. 1, only the beat component due to interference waves can be extracted.

The reason why the beat amplitude value in FIG. 2(C) is not constant is due to fading, and the reason is that the ratio between the desired wave level and the interference wave level, the so-called D/V value, is not constant.

On the other hand, a busy detection circuit 5 that detects the output level demodulated by the amplifier 7 and the demodulator 6 determines whether the demodulated output level is above or below a predetermined level, and if it is above the predetermined level, the gate circuit 4 This prevents erroneous detection due to carrier wave amplitude fluctuations caused by large angular modulation caused by a modulating person during a gate call.

〔Effect of the invention〕

As described above, according to the present invention, a system is provided that can automatically detect the occurrence of interference waves based on the B1 fluctuation of the carrier received by the radio receiving device. In particular, it is possible to prevent erroneous detection due to carrier wave amplitude fluctuations caused by large angular modulation during a call, and erroneous detections due to beat level fluctuations due to fading.

By controlling automatic frequency switching using the detection output of this method, a mobile radio system that can automatically and reliably avoid interference can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block configuration circuit diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is an operational waveform diagram of each part of the apparatus according to the embodiment of the present invention. FIG. 3 is a block configuration circuit diagram of the conventional method. 1...AM detector, 2...level detector, 3...
High-pass filter, 4... Gate circuit, 5... Busy detection circuit, 6... Demodulator, 7... Amplifier, 8... Comparator. Patent applicant: NEC Corporation, -8- Agent: Patent attorney Takashi Ide, OUT Shoulder: 1 time M2: Tsuta: 3 times

Claims (1)

[Claims] (1) An input terminal that inputs the carrier wave of the angle-modulated received signal, an amplitude detector that amplitude-detects the signal at this input terminal, a level detector that detects the beat level of the output of this amplitude detector, and this In an interference wave detection circuit equipped with a comparator that compares the detection level of the level detector with a reference level, a high-pass filter is inserted in the output circuit of the amplitude detector, and the angular modulation of the signal appearing at the input terminal is The present invention is characterized by comprising a circuit that detects that the degree of modulation is greater than or equal to a predetermined value, and a gate circuit that uses the detection output of this circuit to shut off a circuit from the input of the amplitude detector to the output of the comparator. interference wave detection circuit.