JPH0568896B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting that a beat of two carrier waves is included in a received signal of a radio receiver. In particular, the present invention relates to an interference wave detection method suitable for a mobile radio communication system that performs multi-frequency switching connections without providing a central control station.

An example of this type of mobile radio communication system is the cordless telephone system. As illustrated in FIG. 1, wireless connection devices A, B, and C are each connected to a telephone set, and are coupled to corresponding wireless telephones A', B', and C', respectively, by a radio line. If individual frequencies are assigned to each of these radio lines, mutual interference will not occur in principle, but in order to make effective use of frequencies, it is necessary to use a small number of frequencies in common.

Now, for these three sets of wireless connection devices and wireless telephones, two sets of transmitting/receiving frequencies ( ₁ , ₁ ' and ₂ ,
₂ '), and all devices are configured so that they can use these two sets of frequencies. While wireless connection device A and wireless telephone A' are using frequencies ₁ and ₁ ', when wireless connection device B and wireless telephone B' try to start using frequencies,
Knowing that frequencies ₁ and ₁ ′ are used,
Automatically switches to another frequency ₂ , ₂ ' and sets up a wireless line.

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

If a large number of such systems are installed at terminals in a public communication network, wireless connection devices D and wireless telephones D' belonging to different groups may establish lines using frequencies ₁ and ₁ '. There is no problem if this is a far place where it does not cause interference, but if wireless telephone A' moves and approaches wireless connection device D, mutual interference will occur. At this time, it is desirable that the wireless connection device D automatically detect interference and switch to another available frequency. This requires a method for automatically and accurately detecting the occurrence of interference.

The present invention was made against this background, and it is an object of the present invention to provide a method that can automatically detect the occurrence of interference from the reception output of a radio receiving device.

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 demodulating the received signal of the radio receiver. Generally, when a received signal is demodulated and the received signal is not receiving a communication signal (for example, during a call), noise appears in the received signal. This noise is, for example, background noise on the transmitting side, and as another example, noise generated in a wireless device or a wireless line. Therefore, it is not possible to distinguish between noise and the beat by simply measuring the level of this received signal, but from the demodulated signal of this received signal,
By providing a short time lag and detecting the correlation between signals during that time, noise and beats can be distinguished. That is, since a beat is basically a continuous signal of a sine wave, the same state continues before and after a short period of time, but since noise is random, there is no correlation before and after a short period of time. The present invention detects beats by detecting this correlation, and detects that carrier frequencies are causing interference.

Demodulation of the received signal here refers to amplitude demodulation, which of course can obtain the envelope signal of the carrier wave as its output, but if the type of demodulation circuit of the receiver is frequency modulation FM demodulation or phase modulation PM Even with demodulation, the beat of the interference wave is often obtained in the demodulated output, and this can be used to detect interference.

That is, the present invention provides means for obtaining a pulse signal corresponding to an envelope signal of a carrier wave detected from a received signal, means for detecting that a communication signal is modulated from the received signal to the carrier wave, and a detection output of this means. means for counting the pulse signal at a time other than the time when the communication signal is modulated using the pulse signal; and means for clearing the counting contents of the means at each specific time;
The present invention is characterized by comprising means for determining that the count content of the counting means is less than a certain value when a clear signal is sent from the means.

Preferably, the specific time is a time when the cumulative amount of time other than the time during which the communication signal is modulated reaches a certain value.

Hereinafter, the present invention will be explained in more detail using embodiment drawings.

FIG. 2 is a circuit configuration diagram of an embodiment according to the method of the present invention. The signal given to the left end in the figure is a signal in the audio frequency band that has been received by the wireless receiver and demodulated. This input signal is applied to a pulse forming circuit 1 to be pulsed, and its output is applied to an input IN of a counter 5 via an AND circuit 3. Since the carry output OUT of this counter is fed back to its own inhibit input CI, once the output rises, the output is held until a signal is input to the clear input CL. This output is applied to the input D of the D-type flip-flop 7, and its inverted output becomes the interference detection output out.

On the other hand, the signal at the input in is branched and applied to the busy detection circuit 8. This busy detection circuit 8 includes a peak detection circuit 9 and a resistor voltage divider circuit 1 which outputs its output level.
Comparison circuit 11 that compares with a reference value given from 0
When the peak level of the signal in the audio frequency band exceeds a certain value, the call is considered busy.

The output of this busy detection circuit 8 is given to the inputs of AND circuits 3 and 12. A clock signal _H is applied to the other input of the AND circuit 12.
This output is given to the input IN of the counter 13,
Its output is applied to the clock input CK of the flip-flop 7 and to the input D of the flip-flop 14. A clock signal _H is applied to the clock input CK of this flip-flop 14, and its output Q is the clear input CL of the counters 5 and 13.
given to.

Corresponding this configuration with the claims, the means for obtaining the pulse signal is the pulse generator 1, the means for detecting that the communication signal is modulated is the busy detection circuit 8, and the means for detecting that the communication signal is modulated is the busy detection circuit 8. The means are a gate circuit 3 and a counter 5, and the means for clearing at specific times is a counter 13 and a flip-flop 14. Further, the determining means is a flip-flop 7 which receives the carry output of the counter 5 as an input.

The operation of the circuit configured as described above will be explained with reference to the operation waveform diagrams shown in FIGS. 3 and 4. The leftmost symbols in FIGS. 3 and 4 are waveform diagrams of points with corresponding symbols indicated by crosses in FIG. 2. FIG. 3 shows a case where no interference occurs, and FIG. 4 shows a case where interference occurs.

First, in the case of Figure 3, if there is no interference, input
The in signal 0 includes background noise and communication device noise, and when this is compared with the zero level by the pulse generator 1, fine random pulses are obtained as shown in FIG. 3. In Fig. 3, from P ₁ to P ₂ , the call voice is modulated, and the output 8 of the busy detection circuit 8 (“0” when detected, “1” when not detected)
), AND circuits 3 and 12 are in a disconnected state. Therefore, although the period from P ₁ to P ₂ is interrupted, the output 1 of the pulse generation circuit 1 is counted by the counter 5 and counted up to P ₃ to output the output signal 5.
is sent.

On the other hand, counter 13 similarly counts clock signal _H over time T ₁ +T ₂ and sends out output signal 13 when it counts up. At this time, flip-flop 7
When it is determined whether the signal 5 is present or not and it is found that the counter 5 has already counted up, the signal 7 is not sent to its output.

Next, in the case of Figure 4, when interference occurs, there is a periodic beat in the input in signal 0,
This is pulsed by the pulsing circuit 1 and becomes a signal with a long period as shown in FIG. 4. Even if this is counted by the counter 5 over the time T ₃ +T ₄ , it will take a considerable time to count up, and the counter 13 counts up first and sends out the output 13. At this time, since there is no signal at input D of flip-flop 7, flip-flop 7
is inverted and outputs a signal 7 to notify that interference has occurred.

As described above, according to the present invention, a method can be obtained that can automatically detect the occurrence of interference from the reception output of a radio reception device. This method has a relatively simple configuration and is suitable for implementation in mobile devices. By controlling automatic frequency switching using the detection output according to the present invention, a mobile radio system that can automatically 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 circuit configuration diagram of an embodiment of the present invention. FIGS. 3 and 4 are operational waveform diagrams. 1...pulsing circuit (means for obtaining a pulse signal),
5... Counter (means for counting), 7... Flip-flop (means for determining), 8... Busy detection circuit (means for detecting that the communication signal is modulated), 13... Counter, 14... Flip-flop (means of clearing).

Claims (1)

[Claims] 1. In a method for detecting interference between carrier waves by detecting that a received signal of a radio receiver includes a beat due to two carrier frequencies, the carrier wave detected from the received signal; means for obtaining a pulse signal corresponding to an envelope signal; means for detecting that a communication signal is modulated from the received signal to a carrier wave; and a time period during which the communication signal is modulated using the detection output of the means. means for counting the pulse signals at a time other than the above; means for clearing the count of the means at specific time intervals; and means for clearing the counts of the means at specific time intervals; An interference wave detection method comprising means for determining whether there is an interference wave. 2. The interference wave detection method according to claim 1, wherein the specific time is the time when the accumulation of times other than the time when the communication signal is modulated reaches a certain value. 3. The interference wave detection method according to claim 1, wherein the envelope signal is an envelope signal of an intermediate frequency signal. 4. The interference wave detection method according to claim 1, wherein the envelope signal is a demodulated audio signal.