JPS6366098B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field to which the Invention Pertains] The present invention relates to a method for detecting mutual interference between a plurality of transmitting devices using the same channel in a wireless communication method. . especially,
A wireless communication system suitable for mobile radio communication systems or cordless telephones in which frequencies are allocated so that a small number of channels are commonly used for a large number of transmitting devices. The present invention relates to a channel interference detection method suitable as a detection method for a receiving device to detect channel interference and reconfigure a channel when a transmitting device attempts to start communication.

[Description of prior art]

In wireless communication systems, in order to use frequencies efficiently, a small number of channels are commonly assigned to many devices, and when interference occurs on the same channel, this is automatically detected and the channel is reconfigured. The method is widely used. In such a method, it is necessary for the receiving device to accurately detect the occurrence of channel interference in a short period of time, and for this reason, beat detection methods have been widely used.

FIG. 1 shows a block diagram of a receiver for a conventional beat detection method. In FIG. 1, a signal received by an antenna is converted into an intermediate frequency signal by a high frequency circuit 1, amplified by an intermediate frequency amplifier 2, and passed through a band limiting filter 3 to remove out-of-band noise. The output signal of the filter 3 is amplified by a limiter amplifier 4 and envelope fluctuations are removed, and a modulated signal is demodulated by a frequency detector 5.

To detect a beat signal generated by channel interference, the output of the filter 3 is branched and sent to an envelope detector 6.
is applied to the AC signal, its output is amplified by an amplifier 7, its beat frequency component is selected by a low-pass filter 8, and the average level of the AC signal is detected by a rectifier circuit 9.

Such a detection method is based on the premise that there is a frequency difference between the transmission carrier frequencies of the two transmitting devices that are causing the interference that generates a detectable frequency beat. When the difference in the carrier frequencies of the two transmitting devices becomes 10 Hz or less, the envelope detector 6, amplifier 7, and low-pass filter 8 are
It becomes difficult to accurately detect beats. For example, when a large number of devices, such as cordless telephones, are mass-produced to the same standard, the carrier wave frequencies of the transmitting devices appear to be very close to each other, and the frequency fluctuation factors are also the same, so the detectable frequency beat may not occur. On the other hand, in the conventional method shown in FIG. 1, if the upper limit of the pass frequency of the low-pass filter 8 is set high, it becomes susceptible to noise, so if the upper limit of the pass frequency is set low, the carrier waves of the two transmitters If the frequency difference is large, the beat cannot be detected. Therefore, since the upper limit of the pass frequency of this filter is set to a certain degree high, this conventional method has the disadvantage that beat detection is susceptible to the influence of noise.

If channel interference cannot be detected correctly when a channel is set and communication is started, the channel is not reset and so-called interference occurs. When the level of a new interference wave generated during communication is higher than the level of the desired wave during communication, the communicating device will be unable to continue communication.

[Purpose of the invention]

An object of the present invention is to provide a detection method that can detect channel interference with high sensitivity even when the transmission carrier frequencies of two transmitting devices that cause interference are very close. Another object of the present invention is to provide a channel interference detection method that is less affected by noise.

[Features of the invention]

The present invention is a method that is applied to a device that transmits and receives frequency modulated (including phase modulated) wireless communication signals, and the wireless communication signal receiving device is provided with channel interference detection means for detecting interference of received carrier waves. In this method, the transmitting device for wireless communication signals is equipped with means for changing the transmitting carrier frequency at a constant low frequency (f ₀ ), and the channel interference detecting means in the receiving device is equipped with a limiter circuit that limits the amplitude of the signal obtained at the output of the limiter circuit, and a frequency discrimination circuit that detects frequency changes in the signal obtained at the output of the limiter circuit, and the output signal of the frequency discrimination circuit has a frequency that is a natural number multiple of the constant low frequency. It is characterized by detecting whether or not the frequencies (f ₀ , 2f ₀ , 3f ₀ . . . ) are included.

[Effect]

Suppose that while a receiving device is receiving a frequency-modulated wireless communication signal transmitted from a transmitting device, a carrier wave transmitted by a transmitting device different from the transmitting device interferes for some reason. At this time,
A frequency corresponding to the difference between the wireless communication signals transmitted by the two transmitting devices, that is, a beat component occurs in the received signal of the receiving device. This causes amplitude modulation in the received signal due to the nonlinear characteristics of the receiving circuit,
It is obtained from the output of the envelope detection circuit provided in the receiver.

In the method of the present invention, the carrier wave of the wireless communication signal transmitted from the transmitting device is fluctuated at a constant low frequency (f ₀ ), so the beat component obtained in the output of the envelope detection circuit is at this low frequency. The frequency is fluctuating at the frequency (f ₀ ). A limit circuit is connected to the output of the envelope detection circuit, and the beat component itself disappears in this limiter circuit, but the frequency fluctuation caused by the frequency f ₀ that occurs in this beat component remains in the output of the limiter circuit.
This frequency fluctuation is identified by a frequency discrimination circuit (note that this frequency discrimination circuit is a separate circuit from the circuit that detects the frequency-modulated information of the wireless communication signal).

The fluctuation that remains in the output of this frequency discrimination circuit is
In reality, in addition to the frequency f ₀ mentioned above, various frequencies that are natural number multiples of the frequency f ₀ occur. In other words, if the above-mentioned another transmitting device that caused the interference is a conventional device in which the present invention is not implemented, the carrier wave of the wireless communication signal transmitted by that other transmitting device will have a fluctuation of frequency f ₀ . There isn't. Therefore, in the output of the frequency discrimination circuit, fluctuations in the frequency f ₀ given to the carrier wave of the wireless communication signal generated from the transmitting device with which the communication is being performed are mainly detected. Furthermore, if the other transmitting device that caused the interference is also a device in which the present invention is implemented, the beat component obtained in the output of the envelope detection circuit has at least two frequencies f ₀ with different phases. There is fluctuation in the frequency due to the nonlinear characteristics of each part of the receiving device, which causes the generation of beat components.
In addition to f ₀ , fluctuation components of frequencies that are natural number multiples of frequency f ₀ , such as frequencies 2f ₀ , 3f ₀ , . . . , occur.

Therefore, by detecting one of these frequencies f ₀ , 2f ₀ , 3f ₀ , etc. from the output signal of the frequency discrimination circuit, it is detected that a beat is detected due to interference. be able to. Even if the carrier waves of the signals being transmitted by two interfering transmitters happen to be very close together, and the beat frequency generated by the interference is too low to be detected by normal circuits, The output signal of this frequency discrimination circuit includes the frequencies f ₀ , 2f ₀ , 3f ₀ , . . . and can be detected.

[Explanation based on examples]

FIG. 2 is a block diagram of a transmitter according to an embodiment of the present invention, and FIG. 3 is a block diagram of a receiver according to an embodiment of the present invention.

The transmitter shown in FIG. 2 is configured such that an audio signal applied to an input terminal 11 is frequency modulated by a frequency modulation circuit 12, amplified by a transmitter circuit 13, and transmitted from an antenna. The feature of the present invention is that a low frequency oscillator 15 is connected to the input of this frequency modulation circuit 12, and is configured to generate a predetermined constant low frequency f ₀ and change the carrier wave frequency at this frequency. It's where it was.

In the receiving device shown in FIG. 3, the same parts as those of the conventional circuit explained in FIG. 1 are denoted by the same symbols. That is, a high frequency signal received by an antenna is amplified and frequency converted by a high frequency circuit 1 to become an intermediate frequency signal, which is amplified by an intermediate frequency amplifier 2, and out-of-band noise is removed by a band limiting filter 3. The output of the filter 3 is amplified by a limiter amplifier 4 to remove the envelope component, and frequency demodulated by a frequency detection circuit 5 to obtain a signal output.

On the other hand, the output of the filter 3 is branched, the envelope of the received signal is detected by the envelope detector 6, the output is amplified by the amplifier 7, and the frequency necessary for beat detection is selected by the low-pass filter 8. be done. Here, the feature of the present invention is that the output of the low-pass filter 8 is given to the limiter amplifier 21 and amplified, and the envelope component of the signal that has passed through the low-pass filter 8 is removed. The signal is applied to the circuit 22 and its frequency change is detected, and its output is applied to the rectifier circuit 24 via the bandpass filter 23. The bandpass filter 23 is set to pass a certain low frequency f ₀ generated by the oscillator 15 added to the transmitting device and a harmonic frequency 2f ₀ twice that frequency. Rectifier circuit 2
The beat detection output is obtained as the output of 4.

In a device configured in this way, the carrier frequency of the transmitting device is constantly changing at a constant low frequency f ₀ . This frequency f ₀ is suitably a low frequency that does not affect the communication audio signal, and is preferably set to 1 to 30 Hz. Also, this frequency f ₀ of the transmitting device
The deeper the modulation depth, the higher the detection effect.
A fraction to a few tenths of that of a communication voice signal
It is appropriate to set the depth sufficiently shallow. In this example device, the maximum modulation frequency deviation of the audio signal was 5 kHz, and the frequency deviation due to this frequency f ₀ was set to 0.5 kHz.

FIG. 4 shows a signal waveform diagram when the transmission signals of two such transmitting devices interfere with each other. Figures 4a and 4b show the output signal waveforms of the oscillators 15 of the two transmitters. When the transmission signals of these two transmitters interfere, a signal with a waveform as shown in FIG. 4c, for example, results. FIG. 4c shows only the upper half of the signal. This signal corresponds to the output signal of the filter 3 of the receiving device shown in FIG. When this signal is detected by the envelope detector 6, Fig. 4d
becomes the signal. Although this signal contains high-frequency noise components, it passes through the low-pass filter 8 and becomes the signal shown in FIG. 4e. This signal is amplified and amplitude limited by the limiter amplifier 21, and its envelope component is removed, resulting in the signal shown in FIG. 4f. When this signal is detected by a frequency discrimination circuit for a signal corresponding to a frequency change, a signal shown in FIG. 4g is obtained. Generally, the frequency of the signal g is the output frequency f ₀ of the oscillator 15 of the transmitting device or its twice frequency 2f ₀ . That is, if one of the two interfering transmitting devices is the device of the present invention shown in FIG. 2 and the other device is a conventional device with a constant carrier frequency, the beat frequency due to the mutual interference is: Output frequency f ₀ of the oscillator 15 of the transmitting device
is equal to However, when the two transmitting devices that interfere with each other are both devices of the present invention shown in FIG. 2, their carrier frequencies are each frequency f ₀
Therefore, in addition to the difference f ₀ between the two carrier frequencies, the harmonics 2f ₀ , 3f ₀ , etc. generated by the nonlinear characteristics of the receiving device are included.

Therefore, in the receiver shown in FIG.
3 sets its passing frequency to the frequency f ₀ generated by the oscillator 15 of the transmitting device or its harmonic 2f ₀ ,
Furthermore, the passband width can be set extremely narrow. That is, even if there is amplitude noise in the envelope-detected beat frequency, this is removed by the limiter amplifier 21 and does not affect beat detection. Furthermore, since the bandpass filter 23 can be set to an extremely narrow band, the influence of noise is reduced.

In the method of the present invention, even if the carrier frequencies of two transmitting devices that interfere with each other are extremely close, it is extremely rare for the changes in the carrier frequencies to be synchronized, and the presence of channel interference can be accurately detected. can be detected.

In the method of the present invention, the envelope component is detected once from the received signal in the receiving device, and the frequency change is detected from the envelope detection output, so that the signal generated from one transmitting device and without interference beats is detected. This will not be mistakenly detected as channel interference.

Furthermore, in the method of the present invention, even if the low-pass filter 8 that limits the frequency band of the envelope detection output widens its pass band, band limiting and frequency discrimination are performed at the subsequent stage, so amplitude noise Channel interference detection is no longer affected. Therefore, the passband of the low-pass filter 8 can be set wider than in the conventional system, and the carrier frequencies of the two transmitting devices that cause channel interference can be set to
This can be effectively detected even when the distance is quite far.

FIG. 5 shows an example of the configuration of the frequency discrimination circuit 22. As shown in FIG.
That is, in this embodiment device, the frequency discrimination circuit 22
, the output signal of the limiter amplifier 21 is applied to a trigger circuit 31 that differentiates, and this output pulse is applied to the trigger input of a mono-multi vibrator 32,
Further, the output of the monomulti-vibrator 32 is smoothed by a CR low-pass filter 33. In this frequency discrimination circuit 22, the rise of the output rectangular wave of the limiter amplifier 21 is detected by the trigger circuit 31 and a short pulse is output, and this pulse causes the monomulti vibrator 32 to transmit a rectangular wave with a constant pulse width. By smoothing this with the CR low-pass filter 33, a voltage signal proportional to the input frequency can be obtained.

FIG. 6 shows an example of the configuration of the bandpass filter 23. For this bandpass filter 23, a ready-made integrated circuit R5609 manufactured by RETICON was used. This integrated circuit is TRIG
When a signal with a frequency of 1536 Hz is applied to IN, it operates as a 1-octave bandpass filter with a center frequency of 14.1 Hz.

FIG. 7 is a diagram showing the test results of the method according to the embodiment of the present invention. This test was conducted on a cordless telephone with a frequency spacing of 25 kHz between adjacent channels. The frequency band used by this cordless telephone is 250 MHz, and the output transmission power of the transmitter is approximately 5 mW. The frequency deviation due to frequency modulation of the audio signal is up to 5 kHz, the carrier frequency of the transmitter is lower than the frequency f ₀ is 14 Hz, this frequency
The frequency deviation for varying f ₀ is 0.5kHz.

In FIG. 7, the horizontal axis shows the frequency difference between two transmitting devices that interfere with each other, and the vertical axis shows the level ratio of two carrier waves, which is the channel interference detection limit. The horizontal axis is a logarithmic scale, and the vertical axis is expressed in dB.

In this FIG. 7, A is the characteristic measured for the method according to the present invention shown in FIGS. 2 and 3, and B
are the characteristics of a comparative example in which the same measurements were made for the conventional method shown in FIG. The method according to the embodiment of the present invention has higher detection sensitivity than the conventional method. That is,
The frequency difference between the two carrier waves is from 1Hz to 1kHz,
It is possible to detect a level difference of up to approximately 40 dB between two carrier waves. In particular, when the carrier frequencies of two transmitting devices are close to each other, the detection limit level ratio is high, indicating a significant improvement over the conventional method.

〔application〕

In the above description, the low frequency f ₀ signal that changes the carrier wave of the transmitting device is a sine wave, but this may be a rectangular wave, a sawtooth wave, or any other type of waveform. When this signal is not a sine wave, the detected output frequency obtained at the output of the frequency discrimination circuit provided after the envelope detection circuit of the receiving device is not necessarily 2f ₀ , but is a higher-order multiple such as 3f ₀ or 4f ₀ . It may be harmonic. Therefore, the pass frequency of the bandpass filter provided at the output of this frequency discrimination circuit is determined whether to be f ₀ or a harmonic of f ₀ depending on the output signal waveform of the low frequency f ₀ oscillator of the transmitting device. It is better to set

The frequency discrimination circuit provided after the envelope detection circuit described above may be any type of circuit other than the circuit explained in the above example, and the frequency discrimination circuit referred to herein also includes a phase discrimination circuit.

Further, as the filter inserted into the output circuit of this frequency discrimination circuit, any filter other than the one explained in the above example may be used. This filter can be replaced by a low-pass filter instead of a bandpass filter. Furthermore, depending on the characteristics of the frequency discrimination circuit, it is possible to obtain an equivalent output signal without necessarily requiring this filter.

Further, in the above description, this communication method is a method of transmitting an audio signal by frequency modulation, but the content of the modulated signal is not limited to an audio signal, but may be data information, image information, or any other signal. Further, regarding the modulation method, the present invention is not limited to frequency modulation, and the present invention can be similarly implemented using PCM modulation, various pulse modulations, various angle modulations, and the like.

〔Effect of the invention〕

As explained above, according to the method of the present invention,
A system can be obtained that can detect with high sensitivity the occurrence of channel interference even when the carrier frequencies of two interfering transmitters are very close. The method of the present invention is less affected by noise and has fewer detection errors. According to the system of the present invention, fast cycle fading that occurs in mobile radio communication systems will not be mistaken as a beat due to interference.

The method of the present invention is implemented in cordless telephones that do not have a function to perform channel control in common with systems installed adjacently, and are configured so that channel interference is detected by the receiving device and the channel is reset. The effect is remarkable.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional receiver. FIG. 2 is a block diagram of a transmitter according to an embodiment of the present invention. FIG. 3 is a block diagram of a receiving device according to an embodiment of the present invention. FIG. 4 is a signal waveform diagram for explaining operation. FIG. 5 is a diagram showing an example of the configuration of the frequency discrimination circuit of the above embodiment device. FIG. 6 is a diagram showing an example of the configuration of the low-pass filter of the apparatus of the above embodiment. FIG. 7 is a diagram showing actually measured characteristics of channel interference detection sensitivity according to the method according to the present invention and the conventional method.

Claims (1)

[Claims] 1. A receiving device for a frequency-modulated wireless communication signal includes: an envelope detection circuit for detecting an envelope of a received carrier wave; and means for detecting a signal obtained as an output of the envelope detection circuit. In a wireless communication channel interference detection method that detects interference in a channel in use by detecting a signal of a predetermined level in the detection means, the wireless communication signal transmitting device includes: The detecting means of the receiving device includes means for changing the transmission carrier frequency at a constant low frequency, and the detecting means of the receiving device includes a limiter circuit that limits the amplitude of the signal obtained at the output of the envelope detection circuit; 1. A channel interference detection method for wireless communication, comprising: a frequency discrimination circuit that detects a frequency change that is a natural number multiple of the constant low frequency from a signal obtained as an output. 2. The wireless communication channel interference detection method according to claim 1, wherein the detecting means includes a filter that passes the output signal of the frequency discrimination circuit. 3. The filter according to claim 2, wherein the filter that passes the output signal of the frequency discrimination circuit is a bandpass filter that detects the certain low frequency and the harmonic frequency of this frequency from the output signal. Wireless communication channel interference detection method.