JPH0486029A - System for detecting change of line delay amount - Google Patents

Abstract

PURPOSE:To automatically detect a change in the transmission delay amount of a communication line by detecting whether a change in the phase of a separated reference signal exceeds a prescribed range or not. CONSTITUTION:A change detector 40 separates the low frequency reference signal mixed in a data signal and monitors the phase of the reference signal. In this case, the phase of the reference signal is monitored at all times. When the phase is changed, it is detected and an error signal is outputted. The error signal is reported to a central station 41 by a communicating means such as dial-up, radio communication or others, and the central station 41 starts the process of correcting delay compensation time while responding to the error signal. Then, the change detector 40 continuously monitors the phase of the reference signal. Thus, high detection accuracy can be easily obtained at low cost.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a system for detecting changes in the amount of transmission delay in a communication line, and more specifically, relates to a system for detecting changes in the amount of transmission delay in a communication line, and more specifically, to a system for detecting changes in the amount of transmission delay in a communication line. The present invention relates to a system for detecting changes in the amount of transmission delay of a communication line. The present invention particularly relates to a system for detecting a change in the amount of transmission delay of a communication line in a wireless transmission system having a simulcast function that uses a communication line such as a telephone line for transmitting data.

[Conventional technology and issues to be solved]

In order to widen the service area of a paging system (wireless paging system), it is necessary to install multiple transmitting base stations. In order to effectively utilize radio waves and improve system efficiency (increase subscriber capacity per wave), it is necessary to simultaneously emit radio waves of the same frequency with the same paging signal from each transmitting base station. In other words, it is a method called multi-station transmission or simulcasting.

As illustrated in FIG. 1, a paging system with a simulcast function basically consists of a central station 12, multiple transmitting base stations 16-18, and communication lines 13-15 such as terrestrial lines connecting them. Become. The central station 12 is
It manages the overall operation of the system and accepts pages from subscribers. It distributes paging information to each transmitting base station under its control, and manages and executes signal phase synchronization to ensure simulcasting. After receiving a call request from a subscriber and confirming the validity of the call, the central station 12 converts the call data into an appropriate signal format for transfer to each transmitting base station, and performs signal phase synchronization as described below. It is sent to each transmitting base station along with the delay information necessary for the transmission.

The terrestrial lines 13 to 15 each have a different amount of transmission delay. Each transmitting base station decodes the data signal from the central station, converts it into a paging signal (bathing code), and transmits it from the transmitter after a predetermined delay time.

In this case, in a radio wave interference area where the electric field strengths from multiple transmitting base stations are close to each other, the paging signals from those transmitting base stations are received at almost the same level, so each received signal is If the data are out of phase, they will interfere with each other, and paging reception identification will not be performed correctly, resulting in a decrease in call rate. For example, FIG. 2 illustrates the phase relationship of received signals. When the received signal phase of the data signal from the transmitting base station shown in FIG. 2(a) is taken as a reference, if the received signal phase from another transmitting base station is the same phase as shown in FIG. 2(b), Reception identification is possible without problems even in radio wave interference areas. However, as shown in (c), when the phase is shifted by 180 degrees with respect to the reference received signal phase, reception becomes impossible to identify due to interference.

As a countermeasure for this, a variable delay circuit, etc. is installed in each transmitting base station (Figure 1) to compensate for the phase shift of the data signals emitted from each transmitting base station to within 1/4 bit, so that the same Phase synchronization is used to simultaneously transmit data from each transmitting base station.

However, if the communication line used for connection between the central station 12 and each transmitting base station 16 to 18 is a metallic line, a fixed equalization circuit may be provided in the central station 12, but the service area is large and the wireless When using a carrier line such as a trunk line, line switching by the line service provider occurs for various reasons, which causes a change in the conventional delay time, so the delay compensation time must be reset.

For this purpose, it is necessary to immediately detect a change in the amount of transmission delay of the line.

In order to detect this change in delay amount, there has conventionally been a system in which a highly accurate oscillator is provided in each transmitting base station to create a reference phase, and a phase difference between the data transmitted from the central station and the reference phase is detected.

However, this requires a highly accurate oscillator, which has the disadvantage of increasing cost.

Another conventional solution was a fold-back detection system as shown in FIG. This detection system 20 includes a phase comparator 27 in the central station 21 and a folding circuit 25 in each transmitting base station 29. Central station 2
Call data from one paging exchange 22 is sent out through a phase comparator 27 and transferred to each transmitting base station 29 via a downlink telephone line 24. At each transmitting base station, the transferred data is applied to a transmitter 38 through a folding circuit 25 and a variable delay circuit 36, subjected to modulation, frequency conversion, amplification, etc., and then emitted from an antenna 39. The transferred data is also partially or completely returned by a return circuit 25 and sent to the central office 21 via an uplink telephone line 26.
will be forwarded to.

This return data is compared with the data sent from the paging exchanger 22 in the phase comparator 27 to detect a phase difference, and when a change occurs in the phase difference, an error signal 28 is supplied to the paging exchanger 22. It is something.

However, in order to transmit the paging data signal, the downlink 24
However, in this conventional technology, uplink 26
This also results in high costs. Furthermore, although 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, this conventional method detects the change as including the delay amount of the uplink 26. It has the disadvantage that it does.

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

[Means to solve the problem]

In order to achieve the above object, the present invention provides a system for detecting changes in the amount of transmission delay of a communication line in a communication system that transmits data from a central station to a base station via a communication line. In this system, a reference signal having a fixed frequency that does not substantially affect data transmission is mixed with transmission data and sent out at the central station. The base station then separates the reference signal from the received data and detects whether a change in phase of the separated reference signal exceeds a predetermined range. This detects changes in the amount of transmission delay in the communication line.

〔Example〕

Examples of the present invention will be described below. FIG. 4 shows a schematic block diagram of a system for detecting changes in transmission delay of a communication line, which is an embodiment of the present invention. Identical or similar members are given the same reference numerals throughout the figures.

The change detection system 30 according to the invention basically consists of a central station 41, each transmitting base station 32, and a communication line 24 connecting them. The communication line 24 includes all lines for transmitting data, such as terrestrial lines, wired lines, wireless lines, and carrier lines. The central office 41 manages the entire system 30 by the basing exchanger 22,
Perform the actual page reception. The basing exchanger 22 is
After receiving a call request from a subscriber and confirming the validity of the call, a mixer 35 converts the call data signal into an appropriate signal format for transfer to each transmitting base station.
supply to. An oscillator 34 generates a continuous sinusoidal reference signal with a constant frequency of, for example, 300 Hz and feeds it to a mixer 35 . The mixer 35 mixes a 300 Hz reference signal with the data signal from the paging exchanger 22 (
) and sends it to each transmitting base station. The sent 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 using a carrier wave in the band IK to 3.4 KHz.

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

The change detection device 40 separates the low frequency reference signal mixed into the data signal and monitors the phase of the reference signal. When the amount of transmission delay changes due to switching of the communication line 24, etc., a sudden change occurs in the phase of the reference signal received by the transmitting base station, so if this is detected, it is possible to know the change in the amount of delay of the line. 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, the central office 41 initiates a delay compensation time correction procedure. 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
The band pass filter 42 removes 300 Hz and extracts only the carrier signal for data transfer (IKHz to 3.4 KHz), which is supplied to the variable delay circuit 36 as before, and transmitted to the transmitter 38 for processing. On the other hand, signal 26
is simultaneously input to a 300Hz bandpass filter 44, where the carrier signal for data transfer is removed,
Only the reference signal of 300H2 is output. This output is waveform-shaped by an amplifier 45 and a switching circuit 46 and converted into a 300 Hz rectangular wave 46s.

The output 45s of the amplifier 45 and the rectangular wave 4.6s 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 edge detection circuit 47.

According to the clock signal 48, the edge detection circuit 47
A HIGH signal 47s is output for one clock immediately after the rise of the 0Hz rectangular wave 46s. Edge detection circuit 47
A circuit example and its timing are shown in FIGS. 7 and 8. The clock signal 48 is applied to the D flip-flops 47A, 4
7B clock input. A 300 Hz rectangular wave 46s enters the D input of the flip-flop 47A, and its Q output 47As enters the D input of the flip-flop 47B. The Q output of the flip-flop 47A and the Q-bar output of the flip-flop 47B are input to an AND circuit 47C, from which an output 47s for one clock of the edge detection circuit is obtained.

Clock signal 48 is also provided to the count input of a preloadable 8-bit counter 49. The frequency of clock signal 48 is 76.8 KHz, which is exactly 300 Hz x 256. Therefore, this counter 49
If you count one round, you will be counting exactly 300Hz. The 8-bit output of the counter 49 is connected in parallel to an 8-bit decoder 50. The decoder 50 outputs an output 53 obtained by decoding hexadecimal "EF" and hexadecimal + IF
HI for 16 clocks from Or+ to t+FF
Outputs the dito signal (window signal) 54 that becomes GH (9th
(see figure).

Since the digital signal or window signal 54 is for 16 clocks, the pulse width is 16/76800 seconds (approximately 208 μs).
window width).

While this 54 DIT signal is HIGH, the rising detection signal of the 300H2 rectangular wave 47s comes (see FIG. 9), and the preload signal 52s is sent from the AND-OR circuit 52.
is output to the counter 49, and the counter 49 is preloaded with hexadecimal "F8".

F8 is the center value of the window width from FO to FF,
Since counting starts again from the center value, the next rising edge of the normal rectangular wave 47s should fall within the next window. Therefore, with this preload, the counter 4
9 will be synchronized with the 300Hz reference signal every time.

That is, as long as the phase of the 300Hz reference signal does not change and is continuous, the 0 degree phase of the signal 47s (the rising edge after waveform shaping) is synchronized with the count value F8 of the counter 49, and lasts for one period (approximately 3.5 degrees). counter 49 every 3ms)
is synchronized to the reference signal.

On the other hand, the decoder output 53 is the 4-bit error counter 51
is connected to the count input of the counter 49.
When counting the sum T+E p++, the decoder 5
The count value of the error counter 51 changes from 0 to 1 due to the output 53 from 0. By the way, the preload signal 52
s is also connected to the clear input of the error counter 51. Therefore, as shown in FIG. 9, when the 300 Hz rectangular wave signal 47s is input during the HIGH period of the gate signal 54, the error counter 51 is counted up to a count value of 1 by the signal 53, but the signal 52
s will immediately reset it to 0.

That is, as long as the phase of the 300 Hz reference signal does not change and is continuous, the error counter 51 is cleared every time, so it does not take a value larger than 1'°.

The digital signal 54 is a 300Hz reference signal and a counter 4.
This means that the pull-in range time is determined for synchronization with 9. That is, in this embodiment, a jitter of approximately ±104 μS is allowed.

Next, when the amount of transmission delay changes due to line switching or the like, the reference signal of 300 Hz becomes discontinuous.

In this case, the 300 Hz rectangular wave signal 47s, which has been included in the det width, is no longer needed in the det width. Then, nothing is output from the AND-OR circuit 52, and the counter 49 continues to run freely, and even if the DET is opened every period, the reference signal comes into it, but the count value of the error counter 51 changes every 3.3 ms. +1 will be added. As a result, when the count value of the error counter 51 reaches "15" (F in hexadecimal), the carry output 51s becomes HIGH.

This signal 51s consists of 15 consecutive 300Hz reference signals.
This indicates that synchronization with the counter 49 in the device could not be achieved at this time, which means that there was some kind of discontinuity in the input reference signal. In other words, this is an error output that detects a change in the amount of transmission delay of the communication line. Error output 51s
is reported to the central station, for example, via the transmitter 38 or directly, and the control system of the central station that recognizes this starts a procedure for correcting the delay compensation time. At the same time, the counter 49 is synchronized with the reference signal according to the new line delay 2, and the forced lock signal 57 is set to HIGH. As a result, at the next rising edge of the 300 Hz signal 47s, the output 52s of the AND-OR circuit 52 becomes HIGH, the counter 49 is forcibly preloaded to F8, and the error counter 51 is also cleared, returning to normal mode. return. 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 constructed using a logic circuit, it is of course possible to replace this with a microprocessor and control it by a program.

As described above, according to this embodiment, it is possible to reliably detect a delay amount change exceeding ±100 μs, and the detectable width of the total delay change is about 0.1 to 3.2 rn s. However, in this embodiment, even if there is a change in delay amount of 3.4 ms or more, this can also be detected from the periodicity of 300 Hz. As a result, 3.3ms Xn±100μs (n=
o, 1.2, etc.) cannot be detected, and all others can be detected.

Since the amount of delay in a typical telephone line is 1 to 2 ms, the present invention fully performs its intended function. Also, by changing the settings of the decoder 50 and changing the window width of the gate signal 54,
The threshold value for detecting a change in delay amount can be freely set.

Furthermore, even if noise is added to the communication line 1-, as long as the noise is within the LOW period of the gate signal 54, it is ignored and has no adverse effect at all.

Even if noise is mixed in during the period when the gate signal 54 is I]IGH, if there is no noise during the next DIT signal period, there will be no effect. Furthermore, even if there is a momentary interruption of the communication line, if it is restored before the count value of the counter 51 reaches 15, it will be automatically ignored. Also, by changing the content of the decoder 50 to change the value that produces the signal 53, or by changing the number of bits in the counter 51, or by adding a decoder 58 and outputting an error signal with an arbitrary count value, The integration time for detecting a change in delay amount can be set arbitrarily.

Further, while the gate signal 54 is LOW, 300H
By adding a circuit that reads the count value of the counter 49 at the time when the z signal 47s is generated, the amount of delay change itself can be measured.

〔Effect of the invention〕

Since the detection system according to the present invention is configured as described above, it can operate using only a downlink communication line, so that the line usage of the system is reduced.

Relatively simple hardware can automatically detect changes in communication line delay, making it easier to implement a simulcast wireless system at a lower cost. Since it uses a low-frequency reference signal that does not affect data transmission, 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 instead detects changes in the phase of the reference signal itself, and synchronizes the equipment by pulling in the reference phase at each cycle. Since the accuracy is independent of the oscillator,
High detection accuracy can be obtained easily and inexpensively.

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

Even with disturbances such as line noise, there is no false detection due to the integral effect. Also, the width of this integral effect (integral time)
can also be set arbitrarily.

In addition to detecting changes in the amount of delay, it is also possible to measure the amount of change itself.

Automatic detection of delay amount changes and automatic delay time compensation become possible, and the reliability and maintainability of the entire system can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of a simulcast vaping 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 multiple transmitting base stations. FIG. 3 is a block diagram showing a conventional loopback detection system that detects changes in line delay. 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. 4. FIG. 6 is a diagram illustrating output waveforms of the amplifier 45 and switching circuit 46 shown in FIG. 5. FIG. 7 is a block diagram of an example of the edge detection circuit 47 shown in FIG. 5. FIG. 8 is a diagram illustrating the output of the edge detection circuit 47 of FIG. 7. 9 and 10 are timing diagrams illustrating the relationship between each output waveform in the circuit of FIG. 5. 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 section 39...Antenna 40...Delay amount change detection device 41...Central station 42.44...Filter 45...Amplifier 46...Switching circuit 47...Edge detection circuit 47s... ...Based on reference signal < 300Hz square wave 48
... Clock signal 49 ... 8-bit counter 50 ... Decoder 51 ... Error counter 51s ... Error signal 52 ... AND-OR circuit

Claims (2)

[Claims] (1) A system that detects changes in the amount of transmission delay of a communication line in a communication method that transmits data from a central station to a base station via a communication line, which has a substantial effect on data transmission at the central station. A reference signal having a constant frequency that does not give a signal is mixed with transmission data and transmitted, and the base station separates the reference signal from the received data, and the phase change of the separated reference signal exceeds a predetermined range. A system characterized by detecting changes in the amount of transmission delay of a communication line by detecting. (2) A system for detecting changes in the amount of transmission delay of a communication line in a communication method that transmits data from a central station to a base station via a communication line, which has a substantial effect on data transmission at the central station. An oscillator that generates a reference signal with a constant frequency that does not give any noise is provided, a mixer is provided that mixes the reference signal from the oscillator with transmission data, and the data mixed with the reference signal is sent out and received at the base station. separation filter means for separating the reference signal from the separated data; monitoring means for periodically monitoring the phase of the separated reference signal and outputting a signal when the displacement of the phase is within a predetermined range; Detecting changes in the amount of transmission delay in a communication line, comprising: counting means that counts the absence of an output signal from the means and outputs an error signal when the counted value exceeds a predetermined value. system.