JPS6072420A - System for detecting channel interference of radio communication - Google Patents

Abstract

PURPOSE:To detect channel interference with high sensitivity by providing a transmitter with a means for changing a transmission carrier frequency at a prescribed low frequency and providing a signal detecting means with a limiter circuit limiting the amplitude of a signal and a frequency discriminating circuit detecting the frequency change of the signal. CONSTITUTION:An output of a low pass filter 8 is given to a limiter amplifier 21, where the said output is amplified and the envelope component of the signal passing through the low pass filter 8 is eliminated, the result is applied to a frequency discriminating circuit 22 so as to allow the frequency change to be detected, and its output is given to a rectifier circuit 24 via a band pass filter 23. The band pass filter 23 is set so that a prescribed low frequency f0 generated from an oscillator 15 added to the transmitter and a double harmonic frequency 2f0 twice the f0 are passed therethrough. A beat detection output is obtained at the output of the rectifier circuit 24. The carrier frequency of the transmitter is changed always at the prescribed low frequency f0 in the device constituted in this way. A low frequency not giving any effect on a communication voice signal is suitable for this frequency f0 and preferably 1-30Hz.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a method for detecting mutual interference in a wireless communication system in which a plurality of transmitting devices use the same channel. . In particular, it is 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, and it is a wireless communication system that is suitable for mobile radio communication systems or cordless telephones. 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 another transmitting device attempts to start communication on a channel.

[Description of prior art]

In wireless communication systems, in order to use frequencies efficiently,
A widely used method is to allocate a small number of channels to a large number of devices in common, and when interference occurs on the same channel, this is automatically detected and the channel is reconfigured. In such a system, 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, the beat detection method has been widely used.

FIG. 1 shows a block diagram of a receiving device for a conventional beat detection method. In FIG. 1, the signal received by the antenna is converted into an intermediate frequency signal by a high frequency circuit, 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 this 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 fed to the envelope detector 6, the output is amplified by the amplifier 7, and the beat frequency component is selected by the low-pass filter 8. However, the rectifier circuit 9 is configured to detect the average level of the AC signal.

Such a detection method is based on the premise that there is a frequency nose that generates a detectable frequency beat between the transmitted carrier frequencies of two transmitting devices that are causing interference. When the carrier waves of the two transmitting devices become 10 Hz or less, it becomes difficult to detect a pupil test with the above configuration. For example, when many devices, such as cordless telephones, are mass-produced on the same small scale, the general transmission frequencies of the transmitting devices appear to be very close to each other, and the frequency fluctuation factors are also the same, making it possible to detect them. Beats at certain frequencies may not occur. On the other hand, in the conventional case shown in FIG. If the difference in carrier frequency is large, the beat cannot be detected. Therefore, since the upper limit of the passing frequency of this filter is set to a certain degree, 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 will not be reset and so-called interference will occur. When the level of the interference wave newly generated during communication is the level K2 of the desired wave during communication, the device currently communicating becomes 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]

In the present invention, the transmitting device is equipped with means for changing the transmitting carrier frequency at a constant low frequency, and the channel interference detection circuit of the receiving device is configured to detect the amplitude of the beat signal obtained at the output of the envelope detection circuit of the received signal. A limiter circuit that limits
The present invention is characterized by comprising a frequency discrimination circuit that detects a frequency change in a signal obtained as an output of the limiter circuit.

It is preferable that the output of each frequency discrimination circuit is provided with a bandpass filter for detecting the above-mentioned fixed low frequency or a harmonic frequency of this frequency from this output signal.

[Explanation based on an example] 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.

In the transmitting device shown in FIG. 2, an audio signal received at an input terminal 11 is frequency modulated by a frequency modulation circuit 12, and multiplied by a transmitting circuit 13. IF and transmitted from the antenna. The feature of the present invention is +7. A low frequency oscillator 15 is connected to the J-wave number modulation circuit I2 and generates a predetermined low frequency fo, which is configured to avoid changing the IM transmission frequency at this frequency. be.

In the receiving device shown in FIG. 3, the same parts as those of the conventional circuit explained in FIG. 1 are shown with the same symbols.

That is, the high frequency signal received by the antenna is increased by +17. l and frequency converted to become an intermediate frequency signal, which is amplified by an intermediate frequency amplifier 2, and a band-limiting filter 3 removes the out-of-band signal X11i''1.
The output of the detector 3 is amplified by limiter amplification 2:44 to remove the envelope component, and frequency demodulated by the frequency detection circuit 5 to obtain a signal output as IU.

On the other hand, the output of the filter 3 is branched to the envelope detector 6.
The envelope of the received signal is detected, the output thereof is amplified by the amplifier 7, and the frequency necessary for heat detection is selected by the low-pass filter 8. The features of the present invention are as follows:
The output of the low-pass filter 8 (is given to the I limiter amplifier 21 and increased by 1%3, and the envelope component of the signal that has passed through the low-pass filter 8 is removed, and the signal is output to the frequency discrimination circuit 22.
The frequency change is detected by 1]-1, and its output is given to the rectifier circuit 24 via the bandpass filter 23 at i', ll'+. )
1: Pass-pass filter 23 It is set to pass a constant low frequency ro generated by the oscillator 15 added to the transmitting device and a harmonic frequency 2fo twice that frequency.

A beat detection output is obtained as the output of the rectifier circuit 24.

υJ, transmitting device ffl:
The general transmission frequency of is constantly changing at a constant low frequency fo. This frequency fo affects the communication audio signal λj::
A low frequency that does not give l is appropriate, and 1 to 3011z
It is recommended to set it to . Also, this frequency f of the transmitting device
The deeper the modulation depth by o, the better the detection effect will be.However, it is appropriate to set the modulation depth to be very shallow, to about one to several tenths of that of the communication audio signal. , the i1d frequency deviation of the audio signal is up to 5 k
Ilz, and the frequency deviation due to this frequency fo is 0.
5k 117. It was set to

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 output signal waveforms of the oscillators 15 of the two transmitters. When the transmission signals of these two transmitters interfere, for example, a signal with a fourth waveform, lc4, becomes a signal. FIG. 4C is a diagram showing 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, it becomes the signal shown in FIG. 4d. The current signal contains a matching component of a high frequency, but when it passes through a low-frequency wave relaxer), it becomes a signal shown in the 41st line 1e. This signal is amplified by the amplifier 21 and subjected to amplitude limitation, 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 this signal g is the output frequency fo of the oscillator 15 of the transmitting device or its twice frequency 2r1]. One of the two interfering transmitting devices: y1' is the device of the present invention shown in FIG. For a certain device, the beat frequency due to mutual interference will be equal to the output frequency fo of the oscillator 15 of the sender 1-1 device.

However, two transmitting devices interfere with each other;? When I: are both devices of the present invention shown in FIG. 2, their carrier frequencies each change at the frequency fo, so the difference between the two carrier frequencies is 2r, ).

Therefore, in the receiving device shown in FIG.
Set it to the frequency fo or its harmonic 2fo, and pass through it! The width of one area can be set extremely narrow. In other words, even if there is amplitude noise in the envelope-detected beat frequency, it will be removed by the limiter amplifier 21.
Lj is removed and has no effect on beat detection. moreover,
Since the bandpass filter 23 can be set to an extremely narrow band, the noise of 15 jJP becomes small.

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 the interference beam 1 generated from one transmitting device is
A signal that does not cause - will not be erroneously detected as channel interference.

Furthermore, in the method of the present invention, even if the low-pass filter 8 which sinusoidizes the frequency band of the envelope detection output has a wide passband, 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 this 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
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, the frequency discrimination circuit 22 is applied to a single trigger circuit 31 that differentiates the output signal of the limiter amplifier 21, and this output pulse is applied to the mono-multi pie flake 32.
, and the output of this mono-multi pie break 32 is further smoothed by a CR low-pass filter 33. In this frequency discrimination circuit 22, the rise of the rectangular wave output from the IJ mitter amplifier 21 is detected by the trigger circuit 31, and a °C short pulse is output, and this pulse causes the monoilch piebreak 32 to transmit a rectangular wave with a constant pulse width. Ru. Is this smoothed out by CR low pass filter 33? By I-'t-J', it is possible to obtain a voltage signal proportional to the input frequency by 1:#.

FIG. 6 shows the configuration i+++ of the bandpass filter 23. The shell bandpass filter is equipped with a ready-made integrated circuit made by RETICON.
III5R5609 was used. This integrated circuit is a TRI
When a signal with a frequency of 153611z is given to G IIN,
It operates as a 1-octave band cutter with a center frequency of 14.1+12.

FIG. 7 is a diagram showing the test results of the method according to the embodiment of the present invention.

This test is performed with a frequency spacing of 25 k between adjacent channels.
This was done regarding the cordless telephone assigned to llz. The frequency band used by this cordless telephone is 250 Mllz, and the output transmission power of the transmitter is approximately 5 mW. The maximum frequency shift due to frequency modulation of the audio signal is 5kllz, the carrier frequency of the transmitter is lowered to a lower frequency fo, 1411z, and the frequency shift to change this frequency by several fo is 0.5... ::: In Figure 7, the horizontal axis shows the frequency difference between the two that interfere with each other, and the vertical axis shows the level ratio of the two II waves, which is the channel dryness inspection limit. The horizontal axis is a logarithmic scale, and the vertical axis is expressed in dB. :This seventh
In the figure, A refers to the characteristics measured in Figures 2 and 3.
7a6. *Q'riJaa, 11ka crystals: □ Its detection sensitivity is higher than the Beiju style. That is, when the frequency difference between two carrier waves is from 1112 to l k fiz, the level difference between two carrier waves can be detected up to about 4 (MB).Especially when the carrier wave frequencies of two transmitting devices are close to each other, The detection limit level ratio has increased, and a significant improvement has been achieved compared to 1: conventional method.

〔application〕

In the above explanation, the low frequency fo signal that changes the carrier wave of the transmitting device was a sine wave, but this is a square wave.
The properties of sawtooth waves and other waveforms are consistent. 1 When this signal is not a sine wave, the detection output same wave number obtained at the output of the frequency discriminator circuit provided after the interference line detection circuit of the communication device is not necessarily 2fo, but 3fo or 4fo.
f, o f,; It may become a high-order inertia weak wave. Therefore: A small band A! is provided for the output of this frequency discrimination circuit. : The passing frequency of the wave transmitter is set to fo or rl depending on the power signal waveform of the oscillator of the low frequency jo of the transmitting device.
, ' times " = Uni = Nini Engineering risk: 't'l" + hi
':r) a, 1jJj.

The discrimination circuit may be any type of circuit of the circuits explained in the ten examples, and the frequency discrimination circuit referred to here also includes a phase filter circuit.

Further, the filter inserted in the output circuit of this frequency discrimination circuit may be a filter similar to that described in the above example. This filter does not have to be a bandpass filter, but can be replaced by a low-frequency filter. Also 11-1
Depending on the nature of the wave number discriminator circuit, it may not necessarily be possible to exceed this value: /g
Equivalent cutting signals can be obtained without the need for an L device.

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 a signal such as data information, image information, or the like. In addition, regarding modulation methods, it is limited to frequency modulation, PCM modulation, various pulse modulations, and various angular velocity Kl! The present invention can be similarly implemented using if and the like.

〔Effect of the invention〕

As explained above, the method of the present invention has the ability to detect channel interference with high sensitivity even when the carrier frequencies of two interfering transmitters are very close. Ni gets 111. The method of the present invention is less affected by Jiff sound and has fewer detection errors. According to the system of the present invention, rapid periodic fading that occurs in a mobile radio communication system will not be mistaken as B1- due to interference.

The system of the present invention is configured to perform channel control in common with threads installed adjacent to -C, and to detect channel interference with a receiving device and perform channel +lf setting>jf. When applied to cordless telephones, the effect is remarkable.

[Brief explanation of the drawing]

FIG. 1 shows a conventional receiver block llt'+. FIG. 2 is a block diagram of a transmitter block III according to an embodiment of the present invention. FIG. 3 is a block diagram of a receiving apparatus 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 a low-pass filter of the device according to the second embodiment. FIG. 7 is a diagram that does not show actually measured characteristics of channel interference detection sensitivity according to the method according to the present invention and the conventional method. Nippon Telegraph and Telephone Public Corporation: ('Nia,
i.

Claims (3)

[Claims] (1) A receiving device for wireless communication includes an envelope detection circuit for detecting the envelope of a received carrier wave, and means for detecting a signal obtained from the output of the envelope detection circuit, and a predetermined method for detecting the signal obtained from the output of the envelope detection circuit. In a method for detecting interference in a channel in use by detecting a signal at a level of The detecting means includes a limiter circuit that limits the amplitude of the signal obtained at the output of the envelope detection circuit, and a frequency discrimination circuit that detects a frequency change of the signal obtained at the output of the limiter circuit. A wireless communication channel interference detection method characterized by: (2) The radio communication channel interference detecting power type according to claim (1), wherein the detecting means includes a filter that passes the output signal of the frequency discrimination circuit. (3) 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 or a harmonic frequency of this frequency from the output signal. (1) Channel interference detection method for line communications and communications.