JP2679710B2 - Transmission disconnection detection circuit for digital wireless communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] A circuit for detecting transmission signal disconnection in a digital wireless communication system, in which interference is generated by amplifying transmission signal leakage of an adjacent channel at the time of transmission signal disconnection due to the presence of AGC in the receiving device. Even if a wave is generated, the transmission center frequency of the transmitter corresponding to the receiver is provided after the automatic gain control circuit of the receiver of the digital radio system for the purpose of detecting transmission signal loss, and the center of the transmission. When the amplitude difference between the means for detecting the intermediate frequency corresponding to the first and second frequencies deviated from the frequency by a predetermined frequency on both sides and the adjacent detection outputs from the detection means is outside a certain range A determination unit that outputs a transmission output cutoff of the transmission device, and is configured to detect a signal cutoff of the corresponding transmission device. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital wireless communication system, and more specifically, disconnection of a transmission signal of a corresponding transmission device in the digital wireless communication system can prevent a modulation spectrum of an adjacent channel from leaking. The present invention relates to a transmission disconnection detection circuit provided in a receiving device, which is capable of accurately detecting the leakage without depending on generation of an interference signal due to gain adjustment by an automatic gain control device (AGC). FIG. 74 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 example shown in the figure, two transmitters 1 and 2 are provided, each of which transmits a digitally modulated signal via an antenna 3 at center frequencies f ₁ and f ₂ as shown in FIG. On the other hand, the receiving side is provided with receiving devices 5 and 6 respectively corresponding to the transmitting devices 1 and 2 via the antenna 4 so as to receive the corresponding transmission signals. In the above digital wireless communication system, the transmission device, for example, the transmission device 2 may be disconnected and the transmission signal having the center frequency f ₂ as indicated by the broken line in FIG. The receiving device 6 needs to detect such a transmission interruption. [Prior Art] FIG. 9 shows a block diagram of a conventional receiving apparatus. Receiving device 6
Is a demultiplexer 61, low noise amplifier 62, 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 is the AG
The output of C65 is detected and its amplitude is checked. When the output is below a certain level, an alarm signal ALM indicating the transmission interruption of the corresponding transmission device 2 is output, and it functions as a transmission interruption detection circuit. The down converter 63 converts the microwave of the center frequency f ₂ into the intermediate frequency (IF) f ′ ₂ , and the AGC 65,
Detector 67 and the demodulator 66 operates at intermediate frequency f _'2. [Problems to be Solved by the Invention] As shown in FIG. 8, if the transmission device 2 is disconnected and the transmission signal of the center frequency f ₂ is lost, the reception device 6 does not receive the signal of the center frequency f _2. Is the original state. However, since the spectrum of data is wide in the digital radio signal, the center frequency of the adjacent channel is
The modulation spectrum of frequencies around f ₁ may leak to the channel side of the center frequency f ₂ where transmission is interrupted. Although the amplitude of the leakage signal is small, the AGC 65 controls the gain to provide a certain amplitude value. Therefore, when the wave is detected by the wave detector 67, the amplitude value of the detected signal also becomes a certain value. Generally this detection amplitude is usually small, so
For the time being, it is possible to output the alarm signal ALM as a defective state. However, it is not possible to identify whether the cause is due to the disconnection of the transmitter or other causes,
There is a problem in maintenance. In some cases, the alarm signal ALM may not be output when the detected amplitude exceeds a certain level. Under such circumstances, it is required to be able to accurately detect the disconnection of the corresponding transmitting device. [Means for Solving the Problems] FIG. 1 shows a principle block diagram of a transmission disconnection detection circuit of the present invention. The transmission disconnection detection circuit is in a stage after the AGC65 in the receiving device,
It is provided before the demodulator 66. The transmission interruption detection circuit includes a detection means 71 and a determination means 74. Since the transmission interruption detection circuit is provided in the subsequent stage of the down converter, it operates at the intermediate frequency IF. The detection means 71 includes a transmission center frequency f ₀ of the transmission device corresponding to the reception device, and a first frequency offset from the center frequency by a predetermined frequency on both sides.
And intermediate frequencies f ′ ₀ , f ′ ₋ , f ′ ₊ corresponding to the second frequencies f ₋ , f ₊ , are detected. The determination means 74 inputs the detection output S71 from the detection means in response to the output timing of the intermediate frequency, and if the amplitude difference between the adjacent ones of the input detection output signal trains is less than a certain value, the transmitter The transmission output cutoff of is output. [Operation] The normal reception spectrum is shown in Fig. 2 (a). That is, the maximum amplitude is shown at the center intermediate frequency f ′ ₀ ,
Both sides Δf shifted by f _'-, f' ₊ amplitude Ho Isuzu the same, moreover, f _'0 is smaller than the amplitude. Or, '.DELTA.a than the amplitude of _0, for example 10 dB, only a small amplitude frequency f' f _-, may define f _'+. On the other hand, the interference reception spectrum leaked from the adjacent channel and gain-adjusted by the AGC 65 has generally smaller amplitudes than those in FIG. 2 (a) as illustrated in FIGS. 2 (b) and 2 (c). not only intermediate frequency f _'-, f' _0, f _'+ in the amplitude distribution as shown in FIG. 2 (a), the center intermediate frequency f' ₀ is not left-right ho Isuzu symmetry as the maximum. Sequentially _{f '-, f' 0,} f '+ and periodic intermediate frequency is detected. In the case of the normal reception spectrum as shown in FIG. 2 (a), the detection output of the detection means 71 is a sequence of large and small signals as shown in FIG. 3 (a). In the case of the interference reception spectrum other than that, the detection output is as shown in FIGS. 3 (b) and 3 (c). The judging means 74 normalizes when the amplitude difference between adjacent ones of the detection output trains is equal to or more than a certain value as shown in FIG. 3 (a), and otherwise outputs the alarm signal ALM by interrupting the transmission of the transmitting device. . Also, necessarily, three intermediate frequency _{f '-, f' 0,} f '+
Is not required to be detected in order, but the disconnection on the transmission side can be detected by monitoring the shape of the spectrum. In addition, the determination means 74 can be added to confirm that the amplitude is equal to or more than the threshold value TH in order to improve reliability. [Embodiment] 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 in the reception device and is provided after the AGC 65. Demultiplexer 61 in receiver ~ Demodulator
Up to 66 is the same as before. The digital radio wave radiated from the transmitter (not shown) at the center frequency f ₂ is received by the antenna 4 and converted into the intermediate frequency by the down converter 63. Therefore, the circuit after the filter 64 operates at the intermediate frequency. The transmission break detection circuit is configured by connecting an envelope detector 71a, a frequency control circuit 72a, a VCO 73a, and a determination circuit 74a as shown in the figure. The envelope detector 71a, the frequency control circuit 72a, and the VCO 73a constitute the detecting means 71. As shown in FIG. 5, the judgment circuit 74a includes an AD converter 741,
It is composed of a latch circuit 742, a comparison circuit 743, an output circuit 744 and a timing circuit 745. Further, the level determination circuit 746 may be provided. The frequency control circuit 72a controls the transmission center frequency f ₂ of the transmitter.
The center frequency f ′ ₀ of the intermediate frequency corresponding to the frequency f ′ ₋ , f ′ ₊ , which is deviated by Δf on both sides of the center frequency f ′ ₋ , f ′ ₀ , f from the lowest frequency to the lower frequency sequentially. ′ ₊ ;
f ′ ₋ , f ′ ₀ , f ′ ₊ ; ... and a signal for changing the frequency are generated. As a result, the baseband envelope signal corresponding to each of the intermediate frequencies is sequentially and selectively obtained. The signal for changing the frequency from the frequency control circuit _{72a, f '-, f'} 0, the voltage signal S7 corresponding to f _'+
Output 2A to VCO73a and change timing signal S72B
(Fig. 6 (a)) is output to the determination circuit 74a. VCO73a inputs the voltage signal S72A, f according to the voltage level _'-, f' _0, oscillates at a frequency corresponding to f _'+. These oscillation frequency signals S73 are applied to the detection circuit 71a, and the detection circuit 71a sequentially outputs the envelope-detected output signal S71 in response to these variable frequencies. The determination circuit 74a synchronizes the detection output S71 with the timing signal S72B (FIG. 6 (a)) from the frequency control circuit 72a, and the AD converter 741 converts it into a digital value. Therefore,
The values converted into digital values are shown in FIGS. 3 (a) to (c).
As shown in the figure, it becomes time series data. The timing circuit 745 thins out every other timing signal S72B,
To generate the internal timing signal S74A (FIG. 6 (b)). The latch circuit 742 latches the output of the AD converter 741 in synchronization with this timing signal S74A. Therefore, the latch circuit 742, 'digital value corresponding to _0, or, f' f of FIG. 3 (a) _- a digital value corresponding to or f _'+ is latched. The timing circuit 745 outputs the second internal timing signal S74B which is thinned out every other timing (in an antiphase relationship) at a timing different from that of the first internal timing signal S74A (FIG. 6 (c)). Comparison circuit
The 743 compares the previous digital conversion value latched by the latch circuit 742 with the current digital conversion value from the AD converter 741 in synchronization with the second internal timing signal S74B. That is, taking Fig. 3 (a) as an example, f '
The amplitude of the ₀ signal and that of the f ' ₊ signal are compared. When the absolute value of the amplitude difference between these signal sequences is equal to or greater than a constant value A,
That is, in the case of the signal train shown in FIG. 3A, the transmission device is normal and outputs nothing to the output circuit 744. On the other hand, in the case of the 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 is a fixed value A or more, and it is often A or less. In this case, the comparison circuit 743 determines that the transmission is disconnected and outputs a disconnection detection signal to the output circuit 744. As a result, the output circuit 744 outputs the alarm signal ALM, and notifies the circuit or the maintenance panel in the subsequent stage of the transmission interruption of the transmission device. The decision circuit 74a outputs the output of the AD converter 741 in the level decision circuit 746 to the threshold value TH (FIGS. 3A to 3C).
Compared with each other, as shown in FIGS. 3 (b) and 3 (c),
When there is a signal smaller than the threshold value TH, the alarm signal ALM can be output via the output circuit 744. The level determination circuit 746 can also directly input the detection output S71 before the AD converter 741, that is, to determine the level in an analog manner. The decision circuit of FIG. 5 has described the case of digital processing in order to make comparative judgments of the amplitudes of adjacent signals arriving in time series relatively easily, but it is also possible to carry out analog processing. .. Although the above-mentioned embodiments describe typical detection examples,
Since it is sufficient to monitor the shape of the spectrum in order to detect the disconnection on the transmission side, it is not necessary to detect the intermediate frequency components in order. Therefore, as the detection means, three filters, three detectors, and three comparators can be used so that the amplitude differences can be discriminated from each other. [Effects of the Invention] As described above, according to the present invention, even if there is interference in an adjacent channel, it is possible to accurately detect the transmission interruption of the corresponding transmission device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the principle of a transmission interruption detection circuit according to the present invention, and FIGS. 2 (a) to (c) and FIGS. 3 (a) to (c) are shown in FIG. A signal waveform diagram for explaining the operation of the transmission interruption detection circuit, FIGS. 4 and 5 are circuit diagrams relating to the transmission interruption detection circuit of the embodiment of the present invention, and FIGS. 6 (a) to 6 (c) are FIG. 7 is a block diagram of a digital wireless communication system to which the transmission interruption detecting circuit of the present invention is applied, FIG. 8 is a transmission signal waveform diagram of FIG. 7, and FIG. 9 is a conventional receiver. Fig. 10 is a circuit configuration diagram of Fig. 10, and Fig. 10 is an AGC output waveform diagram of Fig. 9. (Explanation of symbols) 1,2 …… Transmitter, 3,4 …… Antenna, 5,6 …… Receiver, 61 …… Splitter, 62 …… Low noise amplifier, 63 …… Down converter, 64 …… Filter, 65 ... AGC, 66 ... Demodulator, 71 ... Detection means, 74 ... Judgment means.

Claims (1)

(57) [Claims] It is provided after the automatic gain control circuit (65) of the digital radio receiver, and has a transmission center frequency (f ₀ ) of the transmitter corresponding to the receiver, and is deviated from the center frequency by a predetermined frequency on both sides. Detection means (71) for detecting the components of the intermediate frequencies (f ′ ₀ , f ′ ₋ , f ′ ₊ ) corresponding to the first and second frequencies (f ₋ , f ₊ ) and the detection means (71). Among the components of the intermediate frequencies (f ′ ₀ , f ′ ₋ , f ′ ₊ ) which are the detection output (S71), those adjacent to each other (f ′ ₋ and f ′ ₀ , and f ′ ₀ and f ′). ₊ ), A determination means (74) for outputting a transmission output disconnection of the transmitter when each amplitude difference is out of a fixed range. A transmission disconnection detection circuit of digital wireless communication system. 2. Variable to _{- ( ', f' 0,} f '+ f) a frequency control circuit for outputting a voltage corresponding to the (72a), in response to the voltage from the frequency control circuit wherein the detecting means (71) comprises an intermediate frequency A variable frequency oscillating circuit (73a) that outputs an intermediate frequency signal, and a detection circuit (71a) that detects the output from the automatic control circuit (65) in response to the variable intermediate frequency signal from the variable frequency oscillating circuit. The transmission disconnection detection circuit according to claim 1, which is provided. 3. The transmission interruption detection circuit according to claim 2, wherein the variable frequency oscillation circuit (73a) includes a voltage controlled oscillator (VCO). 4. The first to third claims, wherein the detection means (71) performs envelope detection of the output from the automatic control circuit (65).
The transmission disconnection detection circuit according to any one of items. 5. The judging means (74) is an AD converter (741) for converting the detection signal (S71) from the detection means (71) into a digital signal, and outputs the digital signal to an intermediate frequency output corresponding to the transmission center frequency. A memory circuit (742, 745) that stores only at the timing or other intermediate frequency output timing, and inputs the output of the memory circuit and the output of the AD converter,
Each intermediate frequency component _{f '-, f' 0,} f '+ a digital signal conversion values of the adjacent signals respectively inputted as a time series signal corresponding to the repeating sequences compared to each other, between said each other more than a predetermined value If the comparison output circuit (7
43, 744), The transmission interruption detection circuit according to any one of claims 1 to 4. 6. The determination means (74) outputs the transmission interruption signal only when the value obtained by the AD converter is less than or equal to a predetermined threshold value and the value obtained by the comparison is less than a predetermined value. The transmission interruption detection circuit according to the item.