JP2550759B2 - Line delay change detection system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a system for detecting a change in transmission delay amount of a communication line, and more specifically to transmitting data from a central station to a base station. The present invention relates to a system for detecting a change in the transmission delay amount of a communication line. The present invention
In particular, the present invention relates to a system for detecting a change in transmission delay of a communication line in a system that uses a communication line such as a telephone line for carrying data among wireless transmission systems having a simulcast function.

[Conventional technology and problems to be solved]

In order to widen the service area of the paging system (radio call system), it is necessary to have a plurality of transmission base stations. In order to effectively use radio waves and increase the efficiency of the system (increase in subscriber capacity per wave), it is necessary to emit radio waves of the same frequency from each transmitting base station at the same time with the same calling signal. In other words, it is a method called multi-station transmission or simulcasting.

As illustrated in FIG. 1, a paging system having a simulcast function basically comprises a central station 12, a plurality of transmission base stations 16 to 18, and transmission lines 13 to 15 such as a ground line connecting them. . The central office 12 manages the overall operation of the system and receives pages from subscribers. The paging information is distributed to each transmission base station under its control, and the signal phase synchronization for surely performing simulcast is managed and executed. Central office
12 receives a call request from a subscriber and, after confirming the validity of the call, converts the call data into an appropriate signal format for transferring to each transmitting base station, and is necessary for signal phase synchronization described later. It is sent to each transmission base station together with the delay information. The ground lines 13 to 15 have different transmission delay amounts. Each transmitting base station decodes the data signal from the central station, converts it into a calling signal (paging code), and emits it from the transmitting section with a predetermined delay time.

In this case, in the radio wave interference area where the electric field strengths from multiple transmission base stations are close to each other, the ringing signals from those transmission base stations are received at almost the same level, so that each received signal may differ due to the difference in the line delay amount. If the phases of the data are deviated from each other, they interfere with each other, the paging reception identification is not correctly performed, and the calling rate is reduced. For example, FIG. 2 illustrates the phase relationship of received signals. When the received signal phase of a data signal from a certain transmitting base station shown in FIG. 2 (a) is used as a reference, the receiving signal phase from another transmitting base station is (b).
With the same phase as shown in FIG. 6, reception identification can be performed without any problem even in the radio interference region. However, as shown in (c), when the phase is shifted by 180 degrees with respect to the reference received signal phase, reception identification becomes impossible due to interference.

As a measure against this, a variable delay circuit etc. is provided in each transmitting base station (Fig. 1), and the phase shift of the data signal emitted from each transmitting base station is compensated so as to be within 1/4 bit and the same. Phase synchronization is performed so that data is simultaneously emitted from each transmitting base station.

However, when the communication line used for the connection between the central station 12 and each transmission base station 16-18 is a metallic line,
A fixed equalization circuit may be provided in the central office 12, but if a carrier line with a large service area such as a wireless relay line is used, line switching by line service providers may occur for various reasons, causing delays in the past. Since the time changes, the delay compensation time has to be reset. For that purpose, it is necessary to immediately detect that the transmission delay amount of the line has changed.

In order to detect this delay amount change, conventionally, there has been a system in which a high-precision oscillator is provided in each transmitting base station to create a reference phase, and the phase difference of the data transmitted from the central station with respect to the reference phase is detected. However, this requires a high-precision oscillator, and thus has a drawback of high cost.

As another conventional solution, there is a turnback detection system as shown in FIG. This detection system 20 is
A phase comparator 27 is provided in 21 and each transmitting base station 29
The folding circuit 25 is provided inside. The call data from the paging switch 22 of the central office 21 is sent out through the phase comparator 27 and goes through the downlink telephone line 24 to each transmitting base station 29.
Transferred to. In each transmitting base station, the transferred data is added to the transmitting unit 38 through the loopback circuit 25 and the variable delay circuit 36, modulated, frequency converted, amplified, etc., and emitted from the antenna 39. Transfer data is also returned to the loopback circuit 25.
Some or all of them are turned back by the
It is transferred to the central office 21 via. This return data is compared with the output data from the paging switch 22 in the phase comparator 27 to detect the phase difference, and when the phase difference changes, an error signal 28 is supplied to the paging switch 22. It is a thing.

However, in order to transmit the call data signal, the downlink 24
Although this is sufficient, this conventional technique also requires the upstream line 26, resulting in high cost. Further, originally, only the change in the transmission delay amount of the downlink 24 from the central station 21 to each transmitting base station 29 should be detected, but in this conventional method, it is detected as a change including the delay amount of the uplink 26. There is a drawback that it does.

It is an object of the present invention to solve the above problems and provide an inexpensive system that automatically detects a change in the amount of transmission delay using only the downlink.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a system for detecting a change in transmission delay amount of a communication line in a communication system for transmitting data from a central station to a base station. In the present system, the central station mixes the reference signal having a constant frequency that does not substantially affect the data transmission with the transmission data and sends it. Then, the base station separates the reference signal from the received data, and detects whether the phase change of the separated reference signal exceeds a predetermined range. Thereby, the change in the transmission delay amount of the communication line is detected.

〔Example〕

Examples of the present invention will be described below. FIG. 4 shows a schematic block diagram of a transmission delay amount change detection system for a communication line, which is an embodiment of the present invention. Throughout the drawings, the same or similar members are denoted by the same reference numerals.

The change detection system 30 according to the present invention basically comprises a central office 41, each transmitting base station 32, and a communication line 24 connecting them. The communication line 24 is a ground line, a wired line,
It includes all lines that transmit data, such as wireless lines and carrier lines. Central office 41 is paging switch 22
Manages the entire system 30 and accepts actual pages. The paging switch 22 accepts the call request from the subscriber, confirms the validity of the call, and then sends to the mixer 35 the call data signal converted into an appropriate signal format for transfer to each transmitting base station. Supply. Oscillator
34 generates a continuous sinusoidal reference signal having a constant frequency of, for example, 300 Hz and supplies it to the mixer 35. Mixer
The 35 mixes (superimposes) a 300 Hz reference signal with the data signal from the paging switch 22 and sends it to each transmission base station. The transmitted data signal is transmitted to each transmitting base station 32 (only one station is shown) via the communication line 24. The data signal is typically an FSK or PSK signal having a carrier wave in the band 1K to 3.4KHz.

Each transmission base station 32 includes a delay amount change detection device 40. The data signal transmitted from the central office 41 first passes through the change detection device 40, and then is sent to the transmission unit 38 via the variable delay circuit 36 that provides the required delay. The transmitter 38 decodes the data signal, converts it into a calling signal (paging code), and emits it from the antenna 39.

The change detection device 40 separates the low frequency reference signal mixed with the data signal and monitors the phase of the reference signal. When the transmission delay amount changes due to the line switching of the communication line 24, etc., the phase of the reference signal received by the transmitting base station changes abruptly.By detecting it, the change in the line delay amount can be known. it can. The change detection device 40 constantly monitors the phase of the reference signal, detects a change in the phase, and outputs an error signal. The error signal is reported to the central office 41 by dial-up, wireless communication or other communication means, and in response thereto, the central office 41 starts the delay compensation time correction procedure. The change detection device 40 continues to monitor the phase of the reference signal.

In FIG. 5, a block diagram of a more specific circuit example of the change detection device 40 is shown.

The data signal 26 including the reference signal from the communication line 24 is filtered by the bandpass filter 42 to remove 300 Hz, and only the carrier signal for data transfer (1 KHz to 3.4 KHz) is extracted and supplied to the variable delay circuit 36 as in the conventional case. Then, it is transmitted to the transmitting unit 38 and processed. On the other hand, the signal 26 is simultaneously input to the bandpass filter 44 of 300 Hz, where the carrier signal for data transfer is removed, and only the reference signal of 300 Hz is output. This output is waveform-shaped by the amplifier 45 and the switching circuit 46 and converted into a rectangular wave 46s of 300 Hz. The output 45s of the amplifier 45 and the rectangular wave 46s which is the output of the switching circuit 46 are shown in FIG.

The signal 48 is a 76.8 KHz clock pulse obtained by frequency division from an oscillator (not shown) built in the transmitter 38, and is supplied to the engine detection circuit 47. The edge detection circuit 47 outputs a HIGH signal 47s for one clock immediately after the rise of the 300Hz rectangular wave 46s according to the clock signal 48. A circuit example of the edge detection circuit 47 and its timing are shown in FIGS. The clock signal 48 is supplied to the clock inputs of the D flip-flops 47A and 47B. 300Hz
Square wave 46s enters the D input of the flip-flop 47A, and its Q output 48As enters the D input of the flip-flop 47B.
The Q output of the flip-flop 47A and the Q output of the flip-flop 47B are respectively input to the AND circuit 47C, from which an output 47s for one clock of the edge detection circuit is obtained.

The clock signal 48 is also supplied to the count input of the preloadable 8-bit counter 49. Clock signal
The frequency of 48 is 76.8KHz, which is just 300Hz x 25
Is 6. Therefore, this counter 49 counts exactly 300 Hz when counting once. The 8-bit output of the counter 49 is connected in parallel to the 8-bit decoder 50.
The decoder 50 outputs the hexadecimal "EF" decoded output 53 and 16
It outputs a gate signal (window signal) 54 which becomes HIGH for 16 clocks from "FO" to "FF" (see Fig. 9). Since the gate signal or window signal 54 is for 16 clocks, 16/7
The pulse width (window width) is 6800 seconds (about 208 μs).

When the rising edge detection signal of 300Hz rectangular wave 47s comes while this 54 gate signal is HIGH (see Fig. 9), AND-OR
A preload signal 52s is output from the circuit 52 to the counter 49, and the counter 49 is preloaded with hexadecimal "F8". F8
Is the center value from FO to FF, which is the window width, and starts counting again from that center value, so that the next rising edge of the normal rectangular wave 47s should fall into the next window.
Therefore, this preload causes the counter 49 to be synchronized with the 300 Hz reference signal every time. That is, 300Hz
As long as the phase of the reference signal of
The 0 degree phase of s (rising edge after waveform shaping) is synchronized with the count value F8 of the counter 49, and 1 cycle (about 3.3ms)
The counter 49 is synchronized with the reference signal every time.

On the other hand, the decoder output 53 is connected to the count input of the 4-bit error counter 51, and the counter 49 displays the hexadecimal "E".
When F "is counted, the output value 53 from the decoder 50 causes the count value of the error counter 51 to change from 0 to 1.
By the way, the preload signal 52s is also connected to the clear input of the error counter 51. Therefore, as shown in FIG. 9, when the rectangular wave signal 47s of 300 Hz is input during the HIGH period of the gate signal 54, the error counter 51 outputs the signal 53
Although the count value is increased to 1, the signal 52s immediately resets it to 0. That is, as long as the phase of the reference signal of 300 Hz does not change and is continuous, the error counter 51 is cleared every time, and therefore does not take a value larger than "1".

The gate signal 54 determines the pull-in range time for synchronizing the reference signal of 300 Hz and the counter 49. That is, in this embodiment, a jitter of about ± 104 μs is allowed.

Next, if the transmission delay amount changes due to switching of the line, the reference signal of 300 Hz becomes discontinuous. In this case, the 300 Hz rectangular wave signal 47s, which has been included in the gate width until now, is no longer required in the gate width. Then, nothing is output from the AND-OR circuit 52, the counter 49 self-runs and the reference signal does not come into it even if the gate is opened every cycle, and the count value of the error counter 51 is +1 every 3.3 ms. Will be done.
As a result, the count value of the error counter 51 is "15" (16
Carry output 51s becomes HIGH when it becomes F). This signal 51s indicates that the 300 Hz reference signal has not been synchronized with the counter 49 in the present apparatus 15 times consecutively, which means that there is some discontinuity in the input reference signal.
That is, this is an error output that detects a change in the transmission delay amount of the communication line. The error output 51s is, for example, the transmission unit 3
The control system of the central station, which is notified via 8 or directly to the central station, recognizes this and starts the delay compensation time correction procedure. At the same time, the compulsory lock signal 57 is set to HIGH in order to synchronize the counter 49 with the reference signal according to the new line delay amount. As a result, the next 300Hz signal 47s
At the rising edge of, the output 52s of the AND-OR circuit 52 becomes HIGH, the counter 49 is forcibly preloaded to F8, the error counter 51 is also cleared, and the normal mode is restored. After that, the control system returns the signal 57 to LOW, and the next change in delay amount can be detected again.

Although this embodiment is composed of a logic circuit, it is of course possible to replace it with a microprocessor and control it by a program.

As described above, according to the present embodiment, the delay amount change exceeding ± 100 μs can be reliably detected, and the delay amount change detectable range is about 0.1 to 3.2 ms. Moreover, in the present embodiment, even if there is a change in the delay amount of 3.4 ms or more, this can also be detected from the periodicity of 300 Hz. As a result, 3.3ms × n ± 1
Only the change in the delay amount of 00 μs (n = 0, 1, 2 ...) Can not be detected, and all other changes can be detected. Since the delay amount of a normal telephone line is 1 to 2 ms, the present invention can sufficiently perform its intended function. Further, by changing the setting of the decoder 50 and changing the window width of the gate signal 54, the threshold value for detecting the delay amount change can be freely set.

Further, even if noise is carried on the communication line, it is ignored when the noise is within the LOW period of the gate signal 54 and has no adverse effect. If the gate signal 54
Even if noise is mixed in during the HIGH period, if there is no noise during the next gate signal period, it will not affect. In addition, even if there is a momentary disconnection in the communication line, if it is restored before the count value of the counter 51 reaches 15, it is automatically ignored. Further, by changing the content of the decoder 50 to change the value that gives the signal 53, or changing the number of bits of the counter 51, or by adding the decoder 58 and outputting an error signal with an arbitrary count value, The integration time for detecting the delay amount change can be set arbitrarily.

Furthermore, while the gate signal 54 is LOW, the 300Hz signal 47s
If a circuit for reading the count value of the counter 49 at the time of occurrence of is added, the amount of delay change itself can be measured.

〔The invention's effect〕

Since the detection system according to the present invention is configured as described above, it can be operated only by the downlink communication line, so the line usage of the system is reduced. Since the change in the delay amount of the communication circuit can be automatically detected by the relatively simple hardware, the simulcast wireless system can be realized more easily and at a lower cost. Since a low-frequency reference signal that does not affect data transmission is used, this device can be added without affecting the conventional system.

In addition, this system does not detect the difference between the reference signal phase and the absolute phase of the local oscillator, but detects the change in the phase of the reference signal itself, and pulls in the reference phase at each cycle to synchronize the device. Therefore, the accuracy does not depend on the oscillator, and high detection accuracy can be obtained easily at low cost.

Since it is composed entirely of digital circuits, temperature characteristics and the like are stable, and the change detection threshold level can be freely set.

Even for disturbances such as line noise, erroneous detection will not occur due to the integration effect. Further, the width of this integration effect (integration time) can be set arbitrarily.

It is possible to measure not only the change in the delay amount but also the change amount itself.

The change in delay amount can be automatically detected and the delay time can be automatically compensated, and the reliability and maintenance of the entire system can be improved.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a simulcast paging system to which the detection system of the present invention can be applied. FIG. 2 is an explanatory diagram of reception phases of data signals from a plurality of transmission base stations. FIG. 3 is a block diagram showing a conventional loopback detection system for detecting a change in line delay amount. FIG. 4 is a block diagram showing a line delay amount change detection system which is an embodiment of the present invention. FIG. 5 is a circuit block diagram of the change detection device 40 shown in FIG. FIG. 6 is a diagram explaining output waveforms of the amplifier 45 and the switching circuit 46 shown in FIG. FIG. 7 is a block diagram of a circuit example of the edge detection circuit 47 shown in FIG. FIG. 8 is a diagram for explaining the output of the edge detection circuit 47 of FIG. 9 and 10 are timing charts for explaining the relationship between the output waveforms in the circuit of FIG. [Explanation of main symbols] 24 …… Communication line 30 …… Line delay amount change detection system 32 …… Transmission base station 34 …… Oscillator 35 …… Mixer 36 …… Variable delay circuit 38 …… Transmission unit 39 …… Antenna 40 …… Delay amount change detector 41 …… Central office 42,44 …… Filter 45 …… Amplifier 46 …… Switching circuit 47 …… Edge detection circuit 47s …… 300Hz rectangular wave based on the reference signal 48 …… Clock signal 49 …… 8-bit counter 50 …… Decoder 51 …… Error counter 51s …… Error signal 52 …… AND-OR circuit

Claims (1)

(57) [Claims] 1. A system for detecting a change in a transmission delay amount of a communication line in a communication system for transmitting data from a central station to a base station via the communication line: A reference signal having a constant frequency that does not have a negative influence on the transmission data and transmitting the mixture; the base station separates the reference signal from the received data; a separating unit; and a predetermined relationship with the reference signal frequency. A local oscillator that oscillates a frequency signal having: a monitoring unit that periodically monitors whether or not the phase shift of the separated reference signal is within a predetermined width set based on the local oscillator frequency signal; When the displacement of the signal phase is within the predetermined width,
Retracting means for moving the reference signal phase so that the reference signal phase is located substantially in the center of the predetermined width; the number of consecutive occurrences of the event when the reference signal phase displacement is outside the predetermined width. A delay amount change detection system comprising: a counting unit that counts and outputs an error signal when the count value exceeds a predetermined value.