JPS61161042A - Digital transmission system - Google Patents

Abstract

PURPOSE:To attain transmission with high quality by controlling a pulse width of a digital main signal to any of T,T-DELTA1 and DELTA2 for digital supervisory signal transmis sion. CONSTITUTION:A digital main signal (a) is inputted from a terminal 15 and a digital supervisory signal (b) is inputted from a terminal 17 and a clock signal is inputted from a terminal 17 to a pulse width selection circuit 18 selectively. The circuit 18 transmits each pulse of a pulse width T when the signal (a) is logical 1 and the signal (b) is logical 0, of a pulse width T-DELTA1(DELTA1<T/2) when the signals (a), (b) are logical 1, of pulse width DELTA2/T/2 when the signal (a) is logical 0 and the signal (b) is logical 1 and 0 when both signals (a), (b) are logical 0. An output of the circuit 18 drivers a light source 21 via a light source driving circuit 19 and the light output is transmitted to a photodetector 28 via an optical fiber. A part of output light of the light source 21 controls the circuit 19 via an automatic output control circuit 24 to make the output pulse constant. The element 28 converts a light signal into an electric signal and outputs a main signal to a terminal 33 via an equalizing amplifier 29 and an identification device 31. A supervisory signal is detected from the output of the identifi cation device 31 and the amplifier 29 via a subtractor, a rectifier and an LPF.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a digital transmission method C2 in which a digital monitoring signal is transmitted superimposed on a digital king signal.

``Prior Art'' Conventionally, in relay transmission systems such as optical communications, wireless communications, and coaxial cable communications, composite modulation or superimposed modulation, which modulates the amplitude of the digital main signal, has been known as a method for transmitting digital monitoring signals. There is. This amplitude modulation method includes performing amplitude modulation using all time slots (two) of the digital main signal, or inserting a small number of auxiliary codes into the digital signal sequence of the main signal, and using these auxiliary codes as the digital supervisory control signal. There is a method that performs more amplitude modulation.

[Problems to be Solved by the Invention] These conventional methods have the disadvantage that strict linearity is required of the transmitter. In particular, when a semiconductor laser is used as a source of light in an optical communication device (-), the relationship between the current applied to the semiconductor laser and the oscillation output is
As shown by a curve 11 in FIG. 8, when the input current I exceeds the oscillation threshold It, the oscillation output increases linearly with respect to the input current IC2. The semiconductor laser input current subjected to complex modulation (modulation degree △) for monitoring signal transmission is shown by curve 12 in Fig. 1.
As shown, the main signal “1” (mark), the monitoring signal “
It is considered as a pulse with amplitude 1 at θ″′ (space), and the main signal″
0'', the amplitude is zero (no pulse) when the monitoring signal is ``0'', the main signal +!1# is a pulse with amplitude (1-△) when the monitoring signal is ``1'', the main signal is ``0'', the monitoring signal is "1" is considered as a pulse with amplitude.For this complex modulated human input signal 12 (2), the semiconductor laser output optical pulse intensity appears as shown in Fig. While modulation is performed, there is a problem in that amplitude modulation cannot be performed sufficiently for 0'' (space) signals.

In order to solve this problem (2), the relationship between the oscillation threshold current It of the semiconductor laser and the bias current factor 8 of the input current should be made almost equal. However, the oscillation threshold It of the semiconductor laser , changes over time, etc., and it is necessary to accurately track the bias current IB against this fluctuation, which requires a complicated control circuit.

[Means for Solving the Problems] According to the present invention (2), a digital signal and a digital supervisory signal are manually generated on the transmitting side, and the digital main signal is 1", the digital supervisory signal is 0#, and the pulse width is Send out a pulse of T, the digital main signal is @131, the digital monitoring signal is 1", send out a pulse of pulse width (T-△1), the digital main signal is II O#, the digital monitoring signal is 1". The digital main signal is lIO#, the digital supervisory signal is 0'', and a pulse with a pulse width of 0 is sent out.On the receiving side, the digital main signal (the two are normal pulse modulation (on-off modulation) Signal (2) is demodulated using the same method (2), digital monitoring signal (2) is equalized and amplified the received signal to convert changes in pulse width into amplitude changes, and demodulates from the amplitude changes. △1 and △2 are equal to or less than T/2, and △1=△2 may be satisfied.

Embodiment FIG. 1 shows an embodiment of the present invention, in which a digital main signal from the main signal input terminal 15 and a digital supervisory signal from the supervisory signal input terminal 16 are input at the transmitter side 14C; , digital main signal "1', digital monitoring signal lIO" sends a pulse with pulse width T, digital main signal "0", digital monitoring signal *O#, does not send a pulse, digital main signal "1", The digital monitoring signal "'1" sends out a pulse with a pulse width (T-.DELTA.1), and the digital main signal 11O" and the digital monitoring signal "1" send out a pulse with a pulse width .DELTA.2.

For example, the digital main signal from the main signal input terminal 15,
The clock signal of the digital main signal from the clock terminal 17 and the digital monitoring signal from the terminal 16 are input to the pulse width selection circuit 18, and the pulse width selection circuit 18 selects the C pulse as follows depending on the input state (: In other words, when the digital main signal a is shown in Fig. 2a, and the digital monitoring signal is shown in Fig. 2b (2) (when the monitoring signal is 0'', the main signal 1'', A pulse with a pulse width of T and 0 (zero) is output for each,
When the monitoring signal is “L”, C2 is the main signal @1111,
@Q” sign (two pairs each to T-, △(△1=△
In case 2), a pulse with a pulse width is output. The output pulse of this pulse width selection circuit 18 causes the light source drive circuit 1 to
A light source 21 is driven through the terminal 9, and the light source output is sent to the receiving side 23 from the output terminal 22. A part of the output light of the light source 21 is input to the automatic output control circuit 24, and the light source drive circuit 19 is controlled by the output of the automatic output control circuit 24, so that the optical output power of the light source 21 is kept almost constant C:.

The pulse selection circuit 181- has an output pulse width of T, for example.
There are three monostable multivibrators, △ and △.
, IIQ", one of the three monostable multivibrators is selected, and the selected one is connected to terminal 1.
7 clock. △ is below T/2J2, preferably about T/10 to T/20, so that pulses with a pulse width (to T-) and pulses with a pulse width can be relatively easily distinguished on the receiving side (2). You will be beaten.

In this way, the pulse width of the drive current pulse for the light source 21 varies depending on the input information, but the pulse amplitude is constant, so the input current is As shown by curve 25, the output pulse light intensity becomes a C constant amplitude pulse as shown by curve 26.Therefore, there is no risk of insufficient modulation by the monitoring signal as described in connection with FIG. current I
It is not necessary to strictly control B, and the input current C- can be stably outputted with a pulse width approximately proportional to the output optical pulse C-4 and whose amplitude is approximately constant.

In reception (111123, the received optical signal input to the reception input terminal 27 is converted into two electrical signals by the light receiving element 28, and the electrical signals are equalized and amplified by the equalization amplifier 29 (two noise components). is removed to obtain a waveform as shown in FIG. As shown in FIG. With such an envelope detection circuit, only the waveform shown in FIG. 2(d) is obtained, and the monitoring signal cannot be extracted as is.

In this embodiment, the output of the amplifier 29 is branched and supplied to a supervisory signal extraction circuit 34. In the monitoring signal extraction circuit 34, the subtraction circuit 35 (output waveform of the second amplifier 29 (second
d) and the output waveform of the discriminator 31 (FIG. 2e) is subtracted to obtain the waveform shown in FIG. 2f. This signal is passed through two rectifier circuits 36C to form a waveform shown in the second [Jg, and is further smoothed by a low-pass filter 37 as shown in the second figure. 2b) is extracted at the receiving side 23 (-) and output to the monitoring signal output terminal 38. The output of the amplifier 29 is also supplied to the timing circuit 32 (2), and a timing signal equal to the pulse period is extracted and the timing signal is The signal is supplied to the output terminal 39.

As explained above, in this embodiment, in order to send a monitoring signal at the transmitting side 14C2, the C pulse width T, (to T-),
By selecting △ and zero, a stable composite modulation circuit is realized.
On the receiving side 23, the pulse width modulated received waveform is converted into an amplitude change by the equalizing amplifier 22ζ due to the band-limiting characteristics of the transmission medium and the receiving circuit. It is possible to extract and transmit high-quality monitoring signals.

In the embodiment shown in FIG. 1, all of the main signals are modulated by the supervisory signal, and one supervisory signal is sent from C2. An auxiliary code is inserted as a transmission path code.
B I M (m binary wifi:1 m
arkinsertion) code or m B I
C(m binary w, i, thl compl
element 'm5ertion) code, DmBIM
(differential m binary, w
ith l mark "1" sertion) codes, and an embodiment in which the present invention is applied to a case where one main signal is transmitted using these codes will be described.

Example of FIG. 4 FIG. 4 shows an embodiment of the present invention for mBIM code C2, and FIG. 5 is a waveform time chart for explaining its operating principle. In this example, m=2. That is, the signal applied to the main signal input terminal 151 in FIG. 4 (2) is 2 bits of random information as shown in FIG.
The code is inserted once as an auxiliary code. In this example, unlike the embodiment shown in FIG. 1, the main signal modulated by the supervisory signal (2) is only this auxiliary code C two times in a row. have

FIG.
1, a block synchronization pulse (FIG. 5b) synchronized with time slot C of the auxiliary code is extracted. The monitoring signal from the terminal 16 (FIG. 5d) and the block synchronization signal from the block synchronization circuit 41 (FIG. 5b) are connected to the AND gate 4.
2, and the pulse width control pulse shown in FIG.
Clock waveform generated by slice circuit 43 + two people from 7 (
The slice voltage in Figure 5C) is increased.

Therefore, the output of the slice circuit 43 is as shown in FIG. The width is the “work” of the monitoring signal.

A waveform having a pulse width of T-Δ and T corresponding to 0'' is obtained.The output of this slice circuit 43 and the terminal 1
The main signal of FIG.
A composite modulated optical waveform is obtained in which only the auxiliary code "1" is pulse width modulated by the monitoring signal as shown in C.

On the receiving side 23, the received optical signal is passed through a light receiving element 27 and an amplifier 28.
, the discriminator 31 (= the main signal is regenerated and obtained from the terminal 33 (2). In the monitoring signal extraction circuit 34, the discriminator 3
The branch output of 1 is input to the block synchronization circuit 45, and a block synchronization pulse (FIG. 5i) is detected. The output waveform of the equalizing amplifier 29 (Fig. 5 h) is supplied to the analog gate 46, and the analog gate 46 is controlled by the block synchronization pulse (Fig. 5 1), and the time slot of the auxiliary code "1" in the main signal is Only the received waveform (Fig. 5g) is extracted. The output of this analog gate 46 is passed through a low-pass filter 47.
, an inverting amplifier 48, respectively.
The waveform is as shown in FIG. 1, and the monitoring signal is correctly reproduced at the output terminal 38 of the monitoring signal extraction circuit 34. Note that the information codes Il and I'2 in the main signal in Fig. 5g are 11" IIQ
” can take a random C, so the fifth diagram is 11.I2
are shown on the assumption that each of the waveforms is 1"1.IIQ", and is therefore similar to a so-called eye pattern waveform.

In the m81c code and the DmBIM code C, the relationship between the auxiliary code and the information bit immediately before it is that of the auxiliary code, so the auxiliary code and the information bit immediately before it are "11".
The code pattern ζ is limited to "O" or "0" and "1". Therefore, this 2-bit pattern appears periodically, and if we consider this as one periodic pattern, we can see the pattern shown in Figure 4C.
If the monitoring signal is pulse-width modulated in the same way as in the case of the ``mBIM'', it is possible to send one monitoring signal.
and mBlc, DmBIM code (2) In contrast, in the embodiment of the present invention in which complex modulation is performed only on the auxiliary code or the auxiliary code and the bit immediately before it, the supervisory signal can be transmitted for the remaining information bits without causing quality deterioration. In addition, in the embodiment of the present invention, composite modulation is applied so that the pulse width is T or T-Δ only when the main signal "'1" (mark) code is used. Like △
It has the advantage that there is no need to create narrow pulses and high-speed modulation is possible.

Example of Fig. 6 Fig. 6 shows an embodiment of the present invention, and is an example in which complex modulation is performed only on the auxiliary code of m81c or DmBIM code, and Fig. 7 shows the waveform time to explain the operation. It is a chart. The main signal from terminal 15 is shown in Figure 7 ai.
As shown in FIG. 2, the information code C is 11-, I2, and the auxiliary code T2 is subsequently inserted into the code string. From this code string, the block synchronization circuit 41 extracts a block synchronization pulse as shown in FIG. 42+2, and the pulse width selection circuit 49 is controlled based on its output≦2.The output pulse width of this pulse width selection circuit 49 is determined by the 1", 0" states of the auxiliary code and the "1", 0 state of the monitoring signal. "Depending on the state, it takes either T, T-, △, or 0 (zero) in Figure 1 (as explained in Figure 1). The waveform passing through the light source drive circuit 19 and light source 21 is shown in Figure 7 d. In other words, only when the monitoring signal is 1'' (mark), the auxiliary code is T-Δ corresponding to 1'' and 0'', respectively.

The optical pulse becomes an optical signal with a pulse width of Δ, and the optical pulse corresponding to the information code (2) in the main signal becomes a waveform that is not modulated by the monitoring signal (Y), and is guided to the transmission output terminal 22.

On the receiving side 23, a block synchronization pulse is detected from the block synchronization circuit 45 (2) from the code string reproduced by the discriminator 31, and the waveform shown in FIG. e) and the output delayed by the delay element 51 for one time slot (g) in FIG. From the subtracted output waveform, only the time slot of the block synchronization pulse (FIG. 7f) is punched out by the analog gate 46 as shown in FIG. 37, passes through the inverting amplifier 48 to the monitoring signal receiving terminal 38ζ
Yu is guided. The received supervisory signal waveform is correctly transmitted as shown in FIG. 7 (-).

In this embodiment, only the waveform of the auxiliary code in the main signal is transmitted as one supervisory signal by C-composite pulse width modulation, so there is no quality deterioration in the transmission of the information code in the main signal.
It has the advantage of being able to transmit high-quality supervisory signals.

"Effects of the Invention" As explained above, according to the present invention, the pulse width of the main signal is T, (T-Δ1) for monitoring signal transmission.

By controlling either △2 or O (zero), it becomes possible to send a message of higher quality than that of 2, and it is especially useful for communication devices that use a light source element with large nonlinearity such as a semiconductor laser. For example, there is no need to control the bias current IB, and the configuration can be relatively simple, which is highly effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform time chart for explaining the operating principle of the system shown in FIG. A diagram showing an example of input/output characteristics, input current, and output light. Fig. 4 is a block diagram showing an example in which this invention is used as the main signal of mBIM code (dual use). Fig. 5 shows the operation of the method shown in Fig. 4. FIG. 6 is a block diagram showing an example in which the present invention is applied to the main signal of the m131C code. FIG. 7 is a waveform time chart to explain the principle of operation. FIG. 8 is a waveform time chart for explaining the principle of operation. is a diagram showing an example of input/output characteristics, input current, and output light of a semiconductor laser to explain conventional composite modulation. 14: Transmission side, 15: Main signal input terminal, 16: Monitoring signal input terminal, 17 : Clock input terminal, 18: Pulse width selection circuit, 19: Light source drive circuit, 21: Light source, 22: Light source output terminal, 23: Receiving side, 24: Automatic output control circuit, 2
7: Reception input terminal, 28: Photodetector, 29: Equalization amplifier, 31: Discriminator, 32: Timing circuit, 33: Reception main signal output terminal, 34: Monitoring signal extraction circuit, 36: Rectifier circuit, 37: Low Band pass filter, 38: Reception monitoring signal output terminal, 39: Reception timing output terminal, 41.45 Ni block synchronization circuit, 43 Ni slice circuit, 48: Inverting amplifier. Patent Applicant: Representative of Nippon Telegraph and Telephone Public Corporation Person: Takuda Kusano 1 Kenshi 1 Cow 2 Figures 3 Times 40 L---1------11 −
---” 6 times 111111-1o o (J'
■ in the mouth Φ = ・−・−
E - Offshore 7 tu 8 solid

Claims (1)

[Claims] (1) Digital main signal of “1” and “0” on the transmitting side,
The above digital main signal is “1” and the digital monitoring signal is “0”.
”, the width of the sending pulse is T, and the digital main signal is “1”.
”, the width of the sending pulse is T when the digital monitoring signal is “1”.
-Δ_1 (Δ_1<T/2), the digital main signal is "0", the digital monitoring signal is "1", the width of the sending pulse is Δ_2 (Δ_2<T/2), the digital main signal is "0", When the digital monitoring signal is "0", the sending pulse is set to zero, and the receiving side equalizes and amplifies the received signal, converts the change in pulse width into an amplitude change, demodulates the digital monitoring signal from the amplitude change, and converts the received signal to A digital transmission method that identifies and demodulates the digital main signal by demodulating the pulse modulated signal.