JPS6243615B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting whether or not there is interference waves from other sources with respect to a desired wavelength wave among signals received by a radio receiver, and in particular, the present invention relates to a method for detecting whether or not there is interference waves from other sources with respect to a desired wavelength wave among signals received by a radio receiver. The present invention relates to an interference detection method suitable for a mobile radio communication system that performs multi-frequency switching connections without interruption.

In the cordless telephone system, which is an example of this type of mobile radio communication system, as will be explained in detail later, multiple telephones each individually 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 circuit, 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 sharing a small number of frequencies like this, when two carrier waves assigned the same frequency approach each other, two
The two carrier waves cause interference, and the difference between the frequencies of the two carrier waves becomes a bead, 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 bead. 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, it is necessary to listen for a certain amount of time, which is not only uncomfortable, but also has the disadvantage that it becomes impossible to talk 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, an amplifier circuit that amplifies a received carrier with a controllable gain, a first level measurement circuit that measures the level of the output of this amplifier circuit,
means for sending the result of the level measurement to the amplifier circuit to control the gain to keep the output level of the amplifier circuit constant; and a second level measurement for measuring output fluctuations of the first level measurement circuit. a comparison circuit that outputs a signal when the output value of the second level measurement circuit reaches a certain value, and a determining means that determines whether or not the received carrier is modulated based on the output of the amplifier circuit. , any output signal from the output of the first level measurement circuit to the output of the comparison circuit is cut off when the discrimination means determines that the received carrier is modulated; An interference wave detection method is obtained, which is characterized in that it includes a gate means for passing and outputting when it is determined that this is the case, and uses the finally obtained output signal as an interference wave detection signal.

Next, a detailed description 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, and C are each connected to separate telephone lines,
They are connected to corresponding radio telephones A', B', and C' by radio circuits, respectively. As mentioned earlier, if individual frequencies are assigned to each of these wireless lines, mutual interference will not occur in principle, but in order to make effective use of frequencies, it is necessary to share a small number of frequencies. become.

Now, for the above three combinations of wireless connection devices and wireless telephones, two reception frequencies ( ₁ ,
₁ ' and ₂ , ₂ '), and all devices are configured to be able to use these two sets of frequencies. Then, when wireless connection device A and wireless telephone A' are using frequencies ₁ and ₁ ', and wireless connection device B and wireless telephone B' are about to start using frequencies 1 and 1', frequencies ₁ and ₁ ' are being used. automatically selects another frequency.
₂ , ₂ ' and set up the wireless circuit.

At this time, when wireless connection device C and wireless telephone C' try to start using the wireless connection device C and wireless telephone C', both frequencies
It is detected that ₁ , ₁ ' and ₂ , ₂ ' are in use, and line connection becomes impossible, and the user waits until one becomes free.

If a large number of the above-mentioned methods are installed on terminals of the public communication network, wireless connection device D belonging to another group
and wireless telephone D' may set up a line using frequencies ₁ and ₁ '. There is no problem if this is a far-field force that does not cause interference, but wireless telephones
When A' moves and approaches wireless connection device D, wireless connection device D receives a wireless phone in addition to wireless telephone D'.
Since it also receives the wave A′, as explained earlier,
Mutual interference occurs. At this time, the wireless connection device D and the wireless telephone D' are switched to other vacant frequencies. The method of the present invention, which will be described later, is capable of reliably and quickly obtaining the interference wave detection signal necessary to electrically perform this switching 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. Since this becomes an envelope signal of the carrier wave, this beat can be detected by amplitude-detecting the received signal of the radio receiver. However, reliable detection is not possible simply by detecting the received signal. That is, P.M.
Even if modulation or FM modulation is used, due to the frequency and phase characteristics of the transmission path, 1.
Even in the case of only one carrier wave, PM→AM conversion (or FM→AM conversion) occurs, which causes fluctuations not only in the phase plane but also in the amplitude direction. For this reason,
If you simply measure the level of amplitude fluctuations, there is a risk that amplitude fluctuations during a busy time will be detected, even though there is no interference wave, resulting in erroneous detection. Alternatively, since it is a mobile object such as a cordless telephone, it may be 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. There is also a risk of doing so.

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. The output level of the amplifier circuit 1 whose gain is controllable is measured by a first level measuring circuit 2, and gain control is performed based on the measurement result so that the output level of the amplifier circuit 1 is constant. That is, the control voltage of the output of the first level measuring circuit 2 is set in the direction of decreasing the gain of the amplifier circuit 1 when the level of the received carrier is high, and on the contrary, the direction of increasing the gain of the amplifier circuit 1 when the level of the received carrier is low. Work at. Therefore, when there is a bead fluctuation in the amplitude of the received input carrier due to the influence of interference waves, etc., a beat waveform will be extracted at the output of the first level measurement circuit 2 in order to suppress it. . The second step is to measure the level of the extracted beat waveform.
This is the level measuring circuit 3.

When the output of the second level measuring circuit 3 becomes higher than the voltage V _c , it is compared by the comparator 4 and it is determined that the amplitude fluctuation of the received input carrier has reached a certain value.

Even if there is no interference wave and a single carrier wave is received, if it is modulated by an audio signal or the like, a level fluctuation will occur in the received carrier, so it is necessary to separate the received carrier.

Since the demodulated output of the PM (or FM) demodulator 5 has a high level during a busy time, this is measured by the busy detection circuit 6 to determine whether the busy state is active or not.
It is determined whether there is a modulation in the carrier. When the busy detection circuit 6 determines that the bus is busy, the output of the comparison circuit 4 does not necessarily rise due to interference, so the gate circuit 7 applies a gate to prevent false detection of interference waves. Preventing.

FIG. 3 is a diagram showing the configuration of a second embodiment of the present invention. 1 to 6 in the figure are all the same as in FIG. 2, but the difference is that an analog gate 8 is incorporated on the input side of the second level measuring circuit 3 instead of the gate circuit 7 in FIG. be. That is, when the busy detection circuit 6 determines that the carrier is modulated, even if the output of the first level measurement circuit 2 changes slightly, the analog gate 8
is turned off to prevent the output of the second level measuring circuit 3 from rising, thereby preventing erroneous detection of interference waves.

Beat fluctuations when there is an interference wave also affect the phase (or frequency) of the carrier, so as a result of PM (or FM) demodulation, a beat sound is heard, degrading call quality. In particular, when the ratio of the desired wave to the interference wave changes significantly due to the influence of fading, the beat sound suddenly becomes louder, so the interference wave must be detected quickly. Furthermore, if the interference wave becomes larger than the desired wave, the demodulation result of the interference wave will appear in the PM (or FM) demodulation output, so there is a risk of crosstalk occurring. It is necessary to be careful in detecting interference waves due to the influence of such fading, which will be explained next.

Both FIG. 4 and FIG. 5 are diagrams showing the specific configuration of the second level measurement circuit devised to quickly detect interference waves when high beat fluctuations occur, and FIG. and corresponds to circuit 3 used in FIG.

The level measuring circuit shown in FIG. 4 includes a nonlinear circuit 10 that easily passes high-level fluctuations in the input.
A rectifier circuit, a smoothing circuit 12, and this smoothing circuit 12
A filter 13 is provided to stabilize the output. In other words, when the input level is high, diode X ₁ or X ₂ becomes conductive, so as a result of rectifying and smoothing this, the output rises faster, and the response of the level output (level out) to the level input (level in) is It has the effect of speeding up.

In FIG. 5, both the rectifier circuit 11 and the smoothing circuit 12 are the same as those in FIG. 4, and a nonlinear filter 14 for stabilizing the output of the smoothing circuit 12 is added thereto. In the level measurement circuit shown in Figure 5, when the amplitude of the level input is small, the smoothed value is also small, so the diode
X ₃ does not become conductive and operates with time constant R ₃ C. When the level input is high, the smoothed output by the smoothing circuit 12 also shows a large value, so the diode _X3 becomes conductive and the capacitor C is charged not only from the resistor _R3 but also from _R3 , and the response of the circuit becomes faster.

In other words, as described with respect to Figures 4 and 5,
In the present invention, even if the interference beat sound suddenly becomes louder due to fading, it rises more quickly in the level measurement circuit, so the loud beat sound will not reach the human ear for a long time.

As described above, according to the present invention, a method can be obtained that can automatically detect the occurrence of interference based on the carrier beat fluctuations received by a radio receiving device. In particular, it is excellent in protection against erroneous detection of interference waves during a call and response characteristics against beat level fluctuations due to fading. If automatic frequency switching is controlled using 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]

FIG. 1 is a diagram showing an example of the configuration of a cordless telephone system, FIG. 2 is a configuration block diagram of a first embodiment of the present invention, and FIG. 3 is a configuration diagram of a second embodiment of the present invention.
FIG. 4 shows a first example of the level detection circuit used in the interference detection method according to the invention, and FIG. 5 shows a second example of the level detection circuit used in the interference detection method according to the invention. It is a diagram. Explanation of symbols: 1 is an amplifier circuit, 2 is a first level detection circuit, 3 is a second level detection circuit, 4 is a comparison circuit, 5 is a demodulator, 6 is a busy detection circuit, 7 is a gate circuit, 8 10 represents an analog gate circuit, 10 represents a nonlinear circuit, 11 represents a rectifier circuit, 12 represents a smoothing circuit, 13 represents a filter, and 14 represents a nonlinear filter.

Claims (1)

[Claims] 1. An amplifier circuit that amplifies a received carrier in a controllable gain manner, a first level measurement circuit that measures the level of the output of this amplifier circuit, and a first level measurement circuit that measures the level of the output of this amplifier circuit, and transmits the result of the level measurement to the amplifier circuit. means for controlling the gain of the feed to make the output level of the amplifier circuit constant; a second level measuring circuit for measuring output fluctuations of the first level measuring circuit; a comparison circuit that outputs a signal when the output value reaches a certain value; a determination means that determines whether the received carrier is modulated based on the output of the amplifier circuit; and an output of the first level measurement circuit. gate means for blocking any output signal from to the output of the comparison circuit when the discriminating means determines that the received carrier is modulated, and for passing and outputting when determining that the received carrier is not modulated; An interference wave detection method characterized in that the finally obtained output signal is used as an interference wave detection signal. 2. The interference wave detection method according to claim 1, wherein the second level measuring circuit has a characteristic of slow response when the input level is low and fast response when the input level is high. . 3. A patent characterized in that the second level measuring circuit set forth in item 2 is formed by connecting in series a nonlinear circuit that easily passes high-level inputs, a rectifier circuit, and a smoothing circuit. An interference wave detection method according to claim 2. 4. The second level measuring circuit in the above item 2 is a low level measuring circuit having a rectifying circuit, a smoothing circuit, a primary circuit composed of a resistor and a capacitor, and a resistive circuit including a diode connected in parallel to both ends of the resistor. It consists of a bandpass filter connected in series,
The interference wave detection method according to claim 2, characterized in that the response to high levels is increased.