JPH0312807B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a radio interference detection method for a radio telephone system to which a multi-channel access method is applied.

[Technical background of the invention and its problems]

In recent years, in wireless telephone equipment such as cordless telephone equipment, which consists of a fixed device and a mobile device that form a set, each set has a plurality of common wireless lines in order to make effective use of frequencies. A system has been proposed that applies a so-called multi-channel access method, in which a vacant line is selected from among them and a call is made. However, in this type of system, if the call areas are far apart at the start of a call, there is a possibility that a plurality of adjacent sets may select the same radio line to make a call. For this reason, if, for example, a mobile device of one set moves during a call and enters the call area of the other set, interference will occur on the same line, causing a problem in which the call will be interrupted.

Conventionally, a beat detection circuit is provided for each set, and this circuit detects a beat by, for example, AM detecting an intermediate frequency signal and determining the magnitude of its output level. Attempts have been made to recognize the occurrence of radio interference and switch the line in use to another vacant line.

However, in recent years, in order to use frequencies even more effectively, the frequency interval of the line has been narrowed, for example from 25kHz to 12.5kHz, and in such cases the beat frequency has been reduced to a few Hz, for example. It tends to be extremely low. The reason is as follows. That is, in order to narrow the frequency interval of a radio line, it is necessary to reduce the transmission frequency deviation of each device. However, when the transmission frequency deviation of each device is reduced in this way, the difference in transmission frequency when different sets use the same radio line also becomes small. Therefore, the beat frequency that occurs when two different sets use the same radio link and cause interference will be lower. When the beat frequency becomes low in this manner, it becomes extremely difficult to detect beats in the conventional interference detection method that only includes a beat detection circuit due to the detection accuracy of the beat detection circuit, and it is not suitable for practical use.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a radio interference detection method that can reliably detect the occurrence of interference even if the frequency interval of lines is small, and can quickly and accurately respond to the occurrence of interference. [Summary of the Invention] In order to achieve the above object, the present invention provides a beat detection means and a means for varying the transmission frequency of the communication line in each set, and by this means, the transmission frequency does not affect the transmission/reception operation. A frequency shift of a predetermined width is applied to make the frequency difference between each transmission frequency noticeable at the time of interference, thereby increasing the beat frequency and making it possible to detect the beat reliably.

[Embodiments of the invention]

The figure is a block configuration diagram of a radio device to which a radio interference detection method is applied in an embodiment of the present invention.
Note that this figure shows the moving device side, and the portions related to the present invention on the fixed device side (not shown) have the same structure as the moving device. In the figure, 1 is the receiving section, 2
1 and 2 indicate transmitting units, respectively.

The receiving section 1 amplifies a received signal received by an antenna 11 with a high frequency amplification circuit 12, mixes it with a local oscillation signal generated from a local oscillation circuit (LO) 3 in a mixing circuit (MIX) 13, and then amplifies it with a band pass filter. (BPF) 14 to obtain the intermediate frequency,
The intermediate frequency signal is FM-detected by an FM detection circuit 15 and is provided as a baseband signal to an audio amplification circuit (not shown).

On the other hand, in the transmitter 2, a modulation circuit (MOD) 21 converts a baseband signal output from an audio amplification circuit (not shown) into an FM modulated wave in an intermediate frequency band, and a mixing circuit (MIX) 22 converts the baseband signal into an FM modulated wave in a local oscillation circuit (LO). ) 3 to obtain a transmission frequency signal, which is amplified by a high frequency amplification circuit 23 and then transmitted from an antenna 24.

Here, the local oscillator circuit (LO) 3 is composed of a synthesizer using a PLL circuit, and selectively generates a plurality of radio line frequencies at intervals of, for example, 12.5 kHz according to a command signal from the control circuit 4. ing.

Now, the receiving section 1 is provided with a beat detection circuit 5. The beat detection circuit 5 performs AM detection on the intermediate frequency signal output of the bandpass filter (BPF) 14 and then rectifies it, and when the rectified output exceeds a predetermined level and the rectified output is equal to the detected output from the FM detection circuit 15. When it is greater than the rectification level,
It generates a detection output. Here, the reason for setting the condition that the AM detection rectification output is larger than the FM detection rectification output when generating the detection output is as follows. In other words, in FM and PM receivers, bandpass filters are generally not ideal, so even if no interference is occurring, the arrival of angle-modulated signals may cause interference. As a result, a relatively high level amplitude modulated wave component is output. If this phenomenon occurs, the amplitude modulated wave component will be detected as if it were generated by interference, which is undesirable. However, if the detection output is generated only when the AM detection output becomes larger than the FM detection output, then when audio is arriving,
Even if the AM detection output is at a high level, it can be prevented from being immediately detected as interference, so accurate interference detection is always possible.

On the other hand, the local oscillation circuit 3 is provided with a random period generator 6 for giving a slight frequency deviation to its oscillation frequency. This random period generator 6
is configured to waveform-shape and output a signal with an irregular period generated from a pseudo-random circuit in which, for example, a random oscillator or a flip-flop circuit is connected in multiple stages. The random period generator 6 operates when a drive signal is supplied from the control circuit 4 to generate the irregular signal, and changes the oscillation frequency of the local oscillation circuit 3 to a predetermined frequency according to the period of this signal. The width can be varied in steps. here,
The variable width of the above frequency, that is, the width of the frequency deviation, is
A very small amount that does not affect call quality, e.g.
It is set to around 100Hz.

Next, the wireless interference detection method of this embodiment will be explained based on the above structure. First, when starting a call, the wireless device outputs a command signal from the control circuit 4 to the local oscillation circuit 3 to designate an idle line, sets the oscillation frequency of the oscillation circuit 3, and thereafter uses the line based on this frequency. Make a call. That is,
The audio signal is FM modulated in a modulation circuit 21, mixed with a local oscillation signal from a local oscillation circuit 3 in a mixing circuit 22, and sent out from an antenna 24. On the other hand, the signal received by the antenna 11 is mixed with the local oscillation signal from the local oscillation circuit 3 in the combining circuit 13, and then leaked in the band pass filter 14 to become an intermediate frequency signal, which is then sent to the FM detection circuit. 15, the signal is FM detected and supplied to the audio amplification circuit.

By the way, the intermediate frequency signal is led to the beat detection circuit 5, where it is determined whether or not there is a beat.

If it is assumed that the beat detection circuit 5 is now generating a judgment output indicating that there is no beat, then the control circuit 4
issues a drive signal to the random period generator 6, which causes the generator 6 to generate a signal in which "1" and "0" are inverted irregularly. Then, from the local oscillation circuit 3, a signal whose frequency changes stepwise according to the level of the above-mentioned irregular signal with a maximum width of 100 Hz, that is, a local oscillation signal, is given a minute frequency deviation at irregular intervals. A signal is generated, so that the transmission frequency at the mobile device changes in accordance with the frequency deviation. This operation is similar for fixed devices, and the transmission frequency on the fixed device side is also changing.

In this state, if the line frequency of another wireless telephone set and the line frequency used by your own set are interfering with each other by a difference of a few Hz, the frequency shift imparted to the transmitting and receiving frequencies will cause the The difference between each line frequency is expanded to, for example, about 100 Hz. Therefore, beats that could not be detected by the beat detection circuit 5 because the frequency was too low can now be easily detected by increasing the frequency to 100 Hz.

When a beat is detected as described above and a detection output is generated from the beat detection circuit 5, the control circuit 4 selects another idle line that has been detected and stored in advance during the standby period, and selects this idle line. A command is issued to the local oscillation circuit 3 to change the transmission/reception frequency of the line to switch the communication line. Thereafter, the detection output of the beat detection circuit 5 is monitored in the same way, and if this detection output corresponds to no beat, a frequency shift is applied at irregular intervals to the transmission frequency after the above switching. do. Note that the fixed device also performs this detection operation, so the side that detects it early starts the operation of selecting another idle line. Then, the lines are switched through mutual exchange of control signals.

In this way, with the method of this embodiment, beat detection is performed by giving a frequency deviation to the transmission frequency of the telephone line, so even if the beat frequency is extremely low, for example, several Hz or less, the above-mentioned beat can be detected. The frequency can be increased, and as a result, beats can be detected reliably. Therefore, it becomes possible to respond quickly and reliably to the occurrence of interference. Furthermore, since the frequency shift is applied at irregular intervals, interference can be detected quickly. In other words, the two sets involved in the interference may have caused frequency shifts with similar periods.
Even if the periods are generally not the same, it takes a long time for the occurrence time of a beat at a high frequency to exceed the detection time required by the beat detection circuit 5, but if it is irregular, there is a probability that it can be detected immediately. interference can be detected early after it occurs.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, a random period generator is used to provide a frequency shift at irregular periods, but the frequency shift may be provided at a constant period. Of course, in that case, it is better to have the same cycle for each set. Alternatively, a signal having an irregular period may be generated by controlling a program of a microprocessor used in the control circuit. If you do this,
Since no new circuit components are required, a device with a simple configuration can be provided. Further, in the embodiment described above, a frequency shift is given to the oscillation frequency of the local oscillation circuit, but the frequency shift may also be given by an FM modulation circuit. Further, the means for applying a frequency shift may be provided only on one of the moving device and the fixed device, and the means for detecting beats may be provided only on the other. Further, when the transmitting frequency and the receiving frequency are the same, means for applying a frequency shift and means for detecting beats may be provided only to the mobile devices of each set. In addition, the operation of the control circuit, the configuration of the beat detection circuit, the configuration for providing frequency shift, etc. can be modified in various ways without departing from the gist of the present invention.

〔Effect of the invention〕

As described in detail above, in the present invention, each set is provided with a beat detection means and means for varying the transmission frequency of the communication line, and this means provides a frequency deviation to the transmission frequency.

Therefore, according to the present invention, it is possible to provide a radio interference detection method that can reliably detect even low frequency beats and can quickly and accurately respond to the occurrence of interference.

[Brief explanation of drawings]

The figure is a block configuration diagram of a radio device to which a radio interference detection method is applied in an embodiment of the present invention. 1... Receiving section, 2... Transmitting section, 3... Local oscillation circuit, 4... Control circuit, 5... Beat detection circuit,
6...Random period generator.

Claims (1)

[Scope of Claims] 1 A plurality of sets consisting of a fixed device and a mobile device that are paired with each other are made to each have a plurality of common wireless lines, and when a given set starts a call, an unused wireless line of each other set is disconnected. In a system that selectively performs calls using the angle modulation method, each set is provided with means for detecting beats from the received signal and means for applying a frequency shift to the transmission frequency of the radio line during the call, and this means A radio interference detection method characterized in that beat detection is performed while applying a frequency shift to the frequency. 2. The radio interference detection method according to claim 1, wherein the means for imparting a frequency shift to the transmission frequency provides a frequency shift of a predetermined width at irregular intervals. 3. The radio interference detection system according to claim 1, wherein the means for imparting a frequency shift to the transmission frequency is provided in both the fixed device and the mobile device.