JPS6348466B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a modem device (hereinafter referred to as MODEM) that communicates via a line, and in particular, even when a momentary interruption of an incoming signal occurs due to a momentary interruption of the line, it is possible to receive a signal before the momentary interruption. It maintains the conditions and enables data demodulation immediately upon recovery from momentary interruption.
Regarding demodulation control method of MODEM.

BACKGROUND ART Conventionally, communication means for transmitting and receiving data in high-speed data transmission, or signal formats during communication, have been standardized and have a certain predetermined format.

For example, Figure 1 shows MODEM based on the means of communication.
FIG. 2 is an explanatory diagram of a typical communication data format during the period, and shows a communication procedure at the start of communication.

In the figure, 1 means the start of communication and is a tone signal that foretells the arrival of received data, 2 is a predetermined no-signal time, that is, a pause, 3 is a training signal for setting reception conditions for transmitted data,
4 indicates actual transmission data, and 5 indicates no signal indicating completion of data transmission.

A block of communication data assumed in the present invention usually arrives in the format shown in Figure 1, and on the receiving side of the MODEM that receives the incoming signal, the arrival of the signal is detected by carrier detection means, and the incoming signal is detected. Detecting whether or not it is a tone signal with a tone detection means,
If the incoming signal is a tone signal, the following conditions for reception are based on the incoming training signal: Equalizer frequency characteristics, phase characteristics settings, carrier frequency and phase settings, amplitude range, etc. reception of actual data. Set the conditions on the MODEM side for this, then receive the actual data that comes in, and when the actual data is completed, the carrier detection signal will no longer be detected, so it will stop.

The above is the procedure and operation from the start of reception to the completion of reception of the actual data block, but the problem here is that there are momentary interruptions in the line. In other words, if there is a momentary interruption in the line while receiving real data, the incoming signal will naturally be silent for a certain period of time, and the carrier signal cannot be received either, so the no-signal time will exceed the fall time of the carrier detection circuit for a certain period of time or more. If this continues, the carrier detection signal will drop, and the device will judge this no-signal state as a completion of reception of received data or a pause after the tone, and the device will recognize the restarted incoming signal as a training signal to start communication. , tries to reset the conditions for reception, but since what is actually arriving is the continuation of the actual data, the conditions set for reception are broken, and subsequent actual data cannot be correctly configured. There was a problem that the conditions for reception could not be restored.

As a method to deal with this, even if the incoming signal becomes non-signal, the setting conditions for reception before the incoming signal becomes non-signal are maintained, and whether the next incoming incoming signal is a training signal or the continuation of the actual reception after restarting. It has been considered to add a means to determine whether data is data to MODEM, but the determination must be made even in the case of a short momentary interruption, and the restart of actual data reception is delayed by the judgment time every momentary interruption. This method has the disadvantage that the number of implementation circuits increases in proportion to the addition of the determination function.

The present invention has been made in view of this background, and its purpose is to detect whether the arriving signal after no signal is real data or not a training signal in order to detect an instantaneous interruption. Rather than making a determination based on the signal, we focus on the distribution of the duration of instantaneous interruptions and determine the occurrence of an instantaneous interruption based on the duration of no signal.

A feature of the present invention is that in demodulation control of a modem that communicates via a line, the detection operation of a carrier detection circuit that detects all incoming signals that arrive at the receiving side of the modem is changed when a signal arrives. This is achieved by configuring the falling time when the signal disappears to be longer than the rising time, and setting the falling time to a shorter time length than the pause between the tone signal and the training signal in the communication method. It is in.

EXAMPLES In order to explain the present invention more specifically, the present invention will be described in detail based on Examples.

FIG. 2 is an explanatory diagram according to an embodiment of the present invention, and is an example of a distribution diagram of the instantaneous line interruption occurrence distribution probability and duration time.

These characteristics, of course, vary depending on the line situation, and although the occurrence of instantaneous interruptions is stochastic,
It can be seen that instantaneous interruptions of longer duration are less likely to occur, and the frequency of their occurrence decreases rapidly.

FIG. 3 is an explanatory diagram of a carrier detection circuit according to an embodiment of the present invention. In the figure, 11 is a rectifier circuit that full-wave rectifies the incoming signal, 12 is a resistor, 13 is a diode, 14 is a resistor, 15 is a capacitor, and 16
is a comparison circuit, and 12, 13, 14, and 15 constitute a pseudo-integrator circuit with a rise time t ₁ and a fall time t _2. The time constant on the side is C・(1/R ₁₂ +1/R ₁₄ ) ^-1 , and the falling time is C・
This shows that they have become as specified in R ₁₄ . Further, the alphanumeric characters attached to each wiring section indicate the signals at the respective locations.

Note that FIG. 4 is a supplementary diagram of FIG. 3 and shows signal waveforms at each part.

As shown in the figure, if there is an instantaneous interruption (no signal) at _t0 , which is shorter than the post-tone pause time _t3 in Figure 1, in the middle of the incoming input a, the output after rectification is b.
The output that passes through the pseudo-integrator circuit becomes c or c', and the output that is sliced and shaped by the comparison level d of the comparator circuit is e or c'.
e′, which becomes the output of the carrier detection circuit.

Note that c′ and e′ are response examples of the conventional circuit, and t ₁ = t ₂
The state when <t ₀ <t ₃ is shown, and c and e are response examples of the circuit of the embodiment and are response examples when t ₁ <t ₀ <t ₂ <t ₃ .

If carrier detection is performed using _a carrier detection circuit operating under the conditions described above, the output of the carrier detection circuit _will be Since the receiving side of MODEM can accept and receive the actual data signal as soon as the reception actual data signal resumes as reception of non-signal data without changing the receiving mode.

By treating a disconnection of t ₂ or longer as a pause signal, it is possible to accept training signals in the communication procedure without violating conventional regulations.

Even if the line is momentarily interrupted, the transmitting side continues to transmit, so the line characteristics (frequency characteristics, delay time, phase distortion, etc.) do not change significantly before and after the momentary line interruption, so the receiving side If the equalization conditions (frequency equalization, phase equalization, synchronization) etc. set at the beginning of the communication are saved during a series of communications, the incoming data can be received correctly when the incoming signal resumes.

Furthermore, the probability that an instantaneous interruption of t ₂ or more will occur is rare, but not zero, and in this case, a data error will occur due to an equalization error similar to the engagement example, but in practice, the pause time t ₃ is within the communication standard. 75 ⁺ 25ms from the point of view. On the other hand, considering the current situation where most of the instantaneous interruption times _t0 are less than 10ms, we set _t2 under the condition of _t3 > _t2 > _t0 to distinguish between _t3 and _t0 . Although this is an extremely simple means, the effects are extremely large.

Note that the falling time _t2 is created by making the time constants of the pseudo-integrator circuits of R and C asymmetric, and creating slice 2.
Although the description has been made by converting it into a value, this is just one example, and the present invention can create the fall time regardless of the specific means, such as using a time delay means, using a pseudo-integrator circuit as an integrating circuit, or realizing it by programming. would be included in the scope.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a typical communication data format based on the communication procedure, FIG. 2 is a distribution diagram of the number of instantaneous interruptions and their duration, and FIG. An explanatory diagram of a carrier detection circuit according to an embodiment of the present invention. FIG. 4 is a signal waveform at each part of FIG. 3. In the figure, t ₃ is a pause time, t ₂ is a fall time of the carrier detection circuit, and t ₀ is the instantaneous interruption time of the line, _t1 is the start-up time of the carrier detection circuit, 11 is the rectifier circuit,
12 to 15 are pseudo-integrator circuits, 16 is a comparison circuit, a
is the incoming input.

Claims (1)

[Claims] 1. In demodulation control of a modem that communicates via a line, the detection operation of the carrier detection circuit that detects all incoming signals that arrive at the reception side of the modem is changed from the rise time at the time of signal arrival to the time at which the signal disappears. 1. A demodulation control method for a signal including an instantaneous interruption, characterized in that the falling time is configured to be long, and the falling time is set to a shorter time length than a pause between a tone signal and a training signal in a communication method.