JPH01152844A - Transmission disconnection detecting circuit for digital radio communication system - Google Patents

Abstract

PURPOSE:To detect disconnection of a corresponding transmitter accurately by detecting a transmission center frequency and an intermediate frequency corresponding to the frequency deviated to both sides by a prescribed frequency from the center frequency and interrupting the transmission output when the amplitude difference of adjacent detection output signal strings is a prescribed value or below. CONSTITUTION:A frequency control circuit 72a generates a signal varying the frequency sequentially and periodically being the center frequency f'0 corresponding to the transmission frequency f2 of the transmitter and frequencies f'-, f'+ deviated to both sides of the center frequency by DELTAf in the order of lower frequency. A judging circuit 74a synchronizes a detection output S71 by a timing signal S72B from a frequency control circuit 72a and uses an AD converter 741 to convert it into a digital value. A comparator circuit 743 compares the preceding digital conversion value latched by a latch circuit 742 with the present digital conversion value from the AD converter 741 synchronously with the 2nd internal timing signal S74B. Thus, even with the presence of adjacent channel interference, the transmission disconnection of the corresponding transmitter is detected accurately.

Description

[Detailed Description of the Invention] [Summary] ゛Regarding a circuit that detects the interruption of a transmission signal in a digital wireless communication system, the existence of an AGC in a receiving device amplifies the leakage of the transmission signal of an adjacent channel when the transmission signal is interrupted. The aim is to detect transmission signal disconnection even if interference waves occur, and is provided at a stage subsequent to the automatic gain control circuit of a digital wireless receiving device, and is designed to detect transmission center frequency of a transmitting device corresponding to the receiving device and the corresponding frequency. Means for detecting intermediate frequencies corresponding to first and second frequencies shifted from the center frequency by a predetermined frequency on both sides, and an amplitude difference between adjacent detection outputs from the detection means is outside a certain range. and determining means for outputting a disconnection of the transmission output of the transmitting device, and is configured to detect a signal disconnection of the corresponding transmitting device.

[Industrial application field]

The present invention relates to a digital wireless communication system,
More specifically, in a digital wireless communication system, the transmission signal of a corresponding transmitter is cut off, the modulation spectrum of an adjacent channel is leaked, and the leakage is detected by an automatic gain control device (
The present invention relates to a transmission interruption detection circuit provided in a receiving device that is capable of detecting interference signals in the normal pupil without depending on the generation of interference signals due to gain adjustment in AGC.

FIG. 7 shows a block diagram of a digital wireless communication system to which the transmission interruption detection circuit of the present invention is applied. multiple on the sending side,
In the illustrated example, two transmitters 1.2 are provided, each with a center frequency f0.2 as shown in FIG. A digital modulated signal is sent out via antenna 3 at ft. On the other hand, on the receiving side, receiving devices 5 and 6 corresponding to each of the transmitting devices 1 and 2 are provided to receive corresponding transmission signals via antennas 4, respectively.

In the above-mentioned digital wireless communication system, the transmitting device, for example, the transmitting device 2 may be disconnected, and the transmitting signal of the center frequency f2 as shown by the broken line in FIG. 8 may not be output. The receiving device 6 needs to detect such a transmission interruption.

[Conventional technology]

FIG. 9 shows a configuration diagram of a conventional receiving device. The receiving device 6 includes a duplexer 61, a low noise amplifier 62, a down converter 63, a filter 64, an AGC 65, a demodulator 66, and a detector 67 connected after the AGC 65. Here, the detector 67 detects the output of the AGC 65 and checks its amplitude, and if it is below a certain level, outputs an alarm signal ALM indicating that the corresponding transmitter 2 has lost its transmission, and functions as a transmission interruption detection circuit. ing.

The down converter 63 converts the microwave with the center frequency f2 to an intermediate frequency (IF) f'2, and the AGC
65, the detector 67 and the demodulator 66 have an intermediate frequency f1
It operates in 2.

[Problem that the invention seeks to solve]

As shown in FIG. 8, if the transmitting device 2 is disconnected and the transmitted signal of the center frequency f2 is lost, the original state is that the receiving device 6 does not receive the signal of the center frequency f2. However, since the data spectrum is wide in digital wireless communication, the modulation spectrum of frequencies around the center frequency f of an adjacent channel may leak to the channel side of the center frequency f2 where transmission is interrupted.

Although the amplitude of the leakage signal is small, the amplitude value is the same as that achieved by gain control of the AGC 65. Therefore, when the wave is detected by the wave detector 67, the amplitude value of the detected signal also becomes a certain value. Since this detected amplitude is generally small, it is possible to output an alarm signal ALM as a defective state.

However, it is unclear whether the cause is due to disconnection of the transmitter.
It is not possible to determine whether the problem is due to other causes, and this poses a problem in terms of maintenance and inspection. Furthermore, in some cases, when the detected amplitude exceeds a certain level, the alarm signal ALM may not be able to be output.

Under these circumstances, it is desired to be able to accurately detect disconnection of the corresponding transmitter.

[Means for solving problems]

A block diagram of the principle of the transmission interruption detection circuit of the present invention is shown in FIG.

The transmission interruption detection circuit is provided at a stage after the AGC 65 and before the demodulator 66 in the receiving device. The transmission interruption detection circuit is
It consists of a detection means 71 and a judgment means 74.

Since the transmission detection circuit is provided after the down converter, it operates at the intermediate frequency IF. The detection means 71 detects a transmission center frequency f0 of a transmitting device corresponding to the receiving device, and first and second frequencies f- and f shifted from the center frequency by a predetermined frequency on both sides. , the intermediate frequency f′ corresponding to . .

Detect fL-, fl. The determining means 74 inputs the detected output S71 from the detecting means in response to the output timing of the intermediate frequency, and when the amplitude difference between adjacent input detected output signal sequences is less than a certain value, the transmitting device Outputs transmission output disconnection.

[For production]

A normal reception spectrum is shown in FIG. 2(a).

That is, the central intermediate frequency f'. f'-, f' which shows the maximum amplitude at and is shifted by Δf on both sides thereof.

The amplitude of is the same as V', and f'. smaller than the amplitude of Or a frequency f'-, f' whose amplitude is smaller than the amplitude of flo by Δa, for example, 10 dB.

may be determined. On the other hand, leakage from the adjacent channel causes AG
As shown in FIGS. 2(b) and 2(C), the interference received spectrum whose gain has been adjusted by C65 is not only generally smaller in amplitude than in FIG. 2(a), but also has an intermediate frequency f'-,f'. The amplitude distribution at , f' is shown in Figure 2 (
As shown in a), the center intermediate frequency f'. It is not symmetrical with the left and right sides being the maximum.

Sequentially r'-, r'. , f', and periodic intermediate frequencies are detected. In the case of a normal reception spectrum as shown in FIG. 2(a), the detection output of the detection means 71 yields successively large and small signal sequences as shown in FIG. 3(a). For other interference reception spectra, see Figure 3 (b) and (C).
The detected output is as shown in the figure. The determining means 74 determines that it is normal when the amplitude difference between adjacent detection output sequences is equal to or greater than a certain value as shown in FIG. .

Also, not necessarily three intermediate frequencies f'-.

It is not necessary to sequentially detect flo, fl, etc., and a disconnection on the transmitting side can be detected by monitoring the shape of the spectrum.

Note that the determining means 74 may additionally confirm that the amplitude is equal to or greater than the threshold value TH in order to improve credibility.

〔Example〕

A transmission interruption detection circuit according to an embodiment of the present invention will be described with reference to FIG.

The transmission interruption detection circuit is provided within the receiving device, and is connected to the AGC65.
It is installed later in the process. The branching filter 61 to the demodulator 66 in the receiving device are the same as the conventional ones.

A digital radio wave radiated from a transmitter (not shown) at a center frequency ft is received by the antenna 4 and converted to an intermediate frequency by the down converter 63.

Therefore, the circuits after filter 64 operate at intermediate frequencies.

The transmission interruption detection circuit consists of an envelope detector 71a, a frequency control circuit 72a, a VCO 73a, and a judgment circuit 74a connected as shown. The envelope detector 71a, the frequency control circuit 72a, and the VCO 73a constitute the detection means 71.

The judgment circuit 74a, as shown in FIG.
41, latch circuit 742, comparison circuit 743, output circuit 7
44 and a timing circuit 745.

It may also include a level determination circuit 746.

The frequency control circuit 72a controls the transmission center frequency f of the transmitting device.
The center frequency f' of the intermediate frequency corresponding to 2.

and f'-, f' shifted by Δf on both sides thereof.

, periodically in descending order of frequency, that is, f'-, f'. (1, f/-, fl.

It generates a signal that changes the frequency such as f'and;...

The signals for changing the frequency from the frequency control circuit 72a include f'- and f'. , f′ and the voltage signal 5 corresponding to
72A to the VCO 73a, and a change timing signal 372B (FIG. 6(a)) to the determination circuit 74a.

The VCO 73a inputs the voltage signal 572A and outputs f'- and f' depending on the voltage level. , f′, and oscillates at a frequency corresponding to , f′. These oscillation frequency signals S73 are detected by the detection circuit 71.
a, and the detection circuit 71a sequentially outputs an envelope-detected output signal 571 in response to these variable frequencies.

The determination circuit 74a outputs the detected output S71 to the frequency control circuit 7.
Timing signal 372B from 2a (Figure 6(a))
The signals are synchronized and converted into digital values by an AD converter 741. Therefore, the values converted into digital values become time-series data as shown in FIGS. 3(a) to 3(C). The timing circuit 745 outputs the timing signal 372B to 1
The first internal timing signal 574A is generated by thinning out the signal every third time (FIG. 6(b)).

The latch circuit 742 latches the output of the AD converter 741 in synchronization with this timing signal 574A. Therefore, the latch circuit 742 has fL in FIG. 3(a).

A digital value corresponding to f'- or f' is latched.

The multi-timing circuit 745 receives the first internal timing signal 5
A second internal timing signal 374B (which has an opposite phase relationship and is thinned out every other time at a different timing from that of 74A) is output (FIG. 6(C)). The comparison circuit 743 compares the previous digital conversion value latched by the latch circuit 742 and A in synchronization with the second internal timing signal 374B.
The current digital conversion value from the D converter 741 is compared. That is, taking FIG. 3(a) as an example, f'. Compare the amplitudes of the signal and the signal (r, The device is assumed to be normal, and nothing is output to the output circuit 744.

On the other hand, in the case of a signal train as shown in FIGS. 3(b) and 3(c), there is no guarantee that the absolute value of the amplitude difference between the time-series signals will be greater than a certain value A, and will often be less than A. In this case, the comparator circuit 743 determines that transmission is interrupted and outputs an interruption detection signal to the output circuit 744. As a result, the output circuit 744 outputs an alarm signal ALM, and notifies the downstream circuit or maintenance panel that the transmitting device has stopped transmitting.

Note that the determination circuit 74a determines the output of the AD converter 741 in the level determination circuit 74b using a threshold value TH (FIG. 3(a)).
Figure 3(b) compared to ~(C)).

As shown in (C), if there is a signal smaller than the threshold value TH, an alarm signal ALM can be outputted via the output circuit 744.

The level determination circuit 746 can also directly input the detection output 371 before the AD converter 741 to determine the level in an analog manner.

The determination circuit shown in FIG. 5 compares and determines the amplitudes of adjacent signals arriving in time series relatively easily, so although we have described the case of digital processing, it is also possible to perform analog processing. .

Although the above embodiments have described typical detection examples, in order to detect a disconnection on the transmitting side, it is sufficient to monitor the shape of the spectrum, so it is not necessary to sequentially detect intermediate frequency components. Therefore, the detection means can be configured to use three filters, three detectors, and three comparators so that amplitude differences can be identified from each other.

〔Effect of the invention〕

As described above, according to the present invention, even if there is interference between adjacent channels, transmission interruption of a corresponding transmitter can be accurately detected.

[Brief explanation of the drawing]

FIG. 1 is a principle block diagram of the transmission interruption detection circuit of the present invention, and FIGS. 2(a) to (C) and 3(a) to (c) illustrate the operation of the transmission interruption detection circuit of FIG. 4 and 5 are circuit diagrams related to the transmission interruption detection circuit of the embodiment of the present invention. FIGS. 6(a) to (C) are timing signal waveform diagrams of FIG. FIG. 7 is a block diagram of a digital wireless communication system to which the transmission interruption detection circuit of the present invention is applied, FIG. 8 is a waveform diagram of the transmitted signal shown in FIG. Figure 10 is the 9th
It is an AGC output waveform diagram of the figure. (Explanation of symbols) 1.2... Transmitting device, 3, 4... Antenna, 5
．． 6... Receiving device, 61... Duplexer, 62...
Low noise amplifier, 63... Down converter, 64... Filter, 65... AGC166.
... Demodulator, 71 ... Detection means, 74 ... Judgment means.

Claims (1)

[Scope of Claims] 1. Provided at a stage subsequent to the automatic gain control circuit (65) of a digital radio receiving device, the transmitting center frequency (f) of a transmitting device corresponding to the receiving device
_0), and first and second frequencies (f_-, f_+) shifted from the center frequency by a predetermined frequency on both sides,
intermediate frequency (f'0, f'_-, f'_+) corresponding to
means (71) for detecting a component of the detection means (71); and determination means (74) for outputting a transmission output disconnection of the transmitter when the amplitude difference between adjacent detection outputs (S71) from the detection means is outside a certain range. ) A transmission interruption detection circuit for a digital wireless communication system. 2. The detection means includes a frequency control circuit (72a) that outputs a voltage corresponding to the intermediate frequency (f'_-, f'_0, f'_+), and a variable frequency control circuit (72a) that outputs a voltage corresponding to the intermediate frequency (f'_-, f'_0, f'_+); A patent claim comprising: an oscillation circuit (72b) that outputs an intermediate frequency signal; and a detection circuit (71a) that detects the output from the automatic control circuit in response to the variable intermediate frequency signal from the variable frequency oscillation circuit. The transmission interruption detection circuit according to item 1. 3. The variable frequency oscillator circuit is a voltage controlled oscillator (VC
The transmission interruption detection circuit according to claim 2, comprising: O). 4. The transmission interruption detection circuit according to any one of claims 1 to 3, wherein the detection means performs envelope detection of the output from the automatic control circuit. 5. The determining means (74) includes an AD converter (741) that converts the detected signal (S71) from the detecting means into a digital signal, and an intermediate frequency output timing corresponding to the transmission center frequency to convert the digital signal into a digital signal. or a storage circuit (742, 745) that stores data only at other intermediate frequency output timings, and inputs the output of the storage circuit and the output of the AD converter, and compares digital signal conversion values that are adjacent in time series. However, if the mutual value is less than a predetermined value, a failure signal (ALM
) A transmission interruption detection circuit according to any one of claims 1 to 4, comprising a comparison output circuit (743, 744) that outputs a signal. 6. Claim 5, wherein the determining means (74) outputs the transmission interruption signal only when the AD conversion value is below a predetermined threshold and the comparison value is below a predetermined value. Transmission interruption detection circuit described in .