JPS60232749A - Digital repeating transmission system - Google Patents

Abstract

PURPOSE:To cancel jitters of the same pattern mutually which are generated in respective reproducing repeaters and to reduce the generation of jitters without adding a specific circuit to each reproducing repeater by connecting the inverted output of an identification decoder to the post stage. CONSTITUTION:Plural reproducing repeaters 4 connected through cables 3 are arranged between a transmitter 1 and a receiver 2 of a digital repeating transmission system. A signal from an input terminal 11 of each repeater 4 is branched into two signals through an identification equalizer 12 and respective branched signals are inputted to a decoder 13 and a timing signal extracting circuit 14. The output of the circuit 14 is amplified by an amplifier 15 and the amplified signal is inputted to the decoder 13 and a converter 16. The decoder 13 inverts all the output signals and applies its output Q to the converter 16, which converts a ''NON RETURN TO ZERO'' signal from the decoder 13 into a ''RETURN TO ZERO'' signal. The converted RZ signal is sent from a transmitting circuit 17 to an output terminal 18 to connect the output of each repeater 4 to the post stage. Thus, the jitters of the same pattern are mutually cancelled without adding a specific circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a relay transmission system for transmitting digital communication signals. The present invention is applied to a digital relay transmission system in which a regenerator extracts a timing signal from a received signal and regenerates output digital information in synchronization with the timing signal. It can be applied to any wired optical signal transmission method, electrical signal transmission method, or wireless transmission method.

[Conventional technology]

When the distance between a transmitting device and a receiving device is large, a method is widely used in which relay devices are inserted in series in a transmission medium that couples the transmitting device and receiving device to regenerate and relay the transmitted signal. In this method, when each regenerative repeater extracts a timing signal from its received signal, jitter occurs in the timing signal. When this jitter passes through many regenerative repeaters, it is good if its occurrence is random, but since the circuit of each regenerative repeater is generally the same, the cause of its occurrence is the same, and the jitter has the same pattern. is generated in each regenerative repeater, and is added to one form each time regenerative repeating is repeated.

When the number of regenerative repeaters between the transmitting device and the receiving device is small, this added jitter is not much of a problem, but when the number of regenerative repeaters increases, it becomes a problem, for example in transoceanic submarine relay systems. The compensation method was researched. A conventional method is to insert a high-Q timing circuit including an automatic phase control loop for each predetermined number of relays, but its suppression effect on low-frequency components of jitter is small, and the circuit for this purpose is It is complex and large,
It cannot be constructed economically as it requires electricity.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION An object of the present invention is to provide an efficient and economical method for suppressing jitter that occurs in a digital relay transmission line including a large number of regenerative repeaters and that adds up in the same pattern.

[Means for solving problems]

The present invention includes a transmitting device that transmits a digital signal, a transmission medium having one end coupled to an output terminal of the transmitting device, and a receiving device having an input terminal coupled to the other end of the transmission medium.
a plurality of regenerative repeaters inserted in series in the middle of the transmission medium; the regenerative repeater includes means for extracting a timing signal from a digital signal received at the input terminal; In the digital relay transmission system, the digital relay transmission system includes means for reproducing digital information in synchronization with the timing signal extracted by the above means, and means for transmitting the digital information reproduced by the means to an output terminal. All or part of the device is characterized in that it is configured to transmit to its output a complementary code which is an inversion of the digital signal received at its input.

When the number of regenerative repeaters that transmit complementary codes is even, the signal transmitted by the transmitting device and the signal received by the receiving device are the same, but when the number is odd, the signal transmitted by the transmitting device or the receiving device is inverted. good. However, even if the output of the receiving device is the complementary code of the output of the transmitting device, the information is the same, so inversion is not necessarily necessary depending on the form of use at the subsequent stage.

[Effect]

When the digital signal is inverted for each regenerative repeater, the coarseness and fineness of the code will be swapped for each regenerative repeater, and the phase fluctuation of the timing signal that occurs as the code changes from coarse to fine and the change from fine to coarse will be affected. Since the directions of the accompanying phase fluctuations of the timing signal are reversed, when they are added, the phase fluctuations cancel each other out.

〔Example〕

FIG. 1 is a block diagram of a digital relay transmission system according to an embodiment of the present invention. A cable 3 is installed as a transmission medium between the transmitter I and the receiver 2, and a large number of regenerative repeaters 4 are inserted in series in the cable 3. A binary digital signal is transmitted through this relay transmission path.

Here, the feature of the present invention is that each regenerator 4 extracts a timing signal from the received signal and uses this timing signal to regenerate the transmitted signal, and the transmitted signal is the same as the received signal. It is exactly where the complementary sign is inverted. That is, if the digital signal transmitted from the transmitter 1 is, for example, 01100110, when it is relayed by one regenerative repeater 4, it is inverted and becomes 10011001. This is indicated in FIG. 1 by Q and d.

In this way, the sparseness and density of the codes are exchanged for each regenerative repeater, and the timing signal phase fluctuation, that is, jitter, that occurs as the code changes from coarse to fine, and the timing signal that occurs as the code changes from fine to coarse. Since the direction of the phase fluctuation, that is, the jitter, is switched, when this jitter is added, this phase fluctuation cancels each other out.If the duty ratio is 50% in a binary code, the sick is essentially It will disappear.

FIG. 2 shows a configuration diagram of a regenerative repeater used in an embodiment of the present invention. The signal at input terminal 11 is sent to decoder 13 via equalizer 12. Further, the output of the equalizer 12 is branched and inputted to the timing signal extraction circuit 14, and the output thereof is amplified by the amplifier 15 and given to the identification decoder 13. The output of the identification decoder 13 is NRZ (non turn
RZ (return to zero) signal.

The signal is transmitted from the transmitting circuit 17 to the output terminal 18 via the converting circuit 16 that converts the signal into

The feature of the present invention is that the output signal of the identification decoder 13 is sent out after being completely inverted from its input signal. That is, in FIG. 2, the output signal of the identification decoder 13 is shown so that d, not Q, is connected to the subsequent stage.

FIG. 3 is a diagram showing the main part of the output circuit of this identification decoder 13. In other words, since a typical output circuit is composed of two active pair transistors as shown in Figure 3,
One of the collector outputs becomes an inverted output, and by utilizing this, there is no need to particularly design a new circuit to implement the present invention.

Next, we will explain in detail why the shifters are canceled by sending out complementary codes that invert the output signals in such a large number of cascaded regenerative repeaters.

FIG. 4 is a diagram showing a model of a transmission path in which N regenerative repeaters 4 are connected in cascade. Let H(ω) be the transfer function of the timing signal of each regenerative repeater 4 (specifically, the transfer function of the tuned circuit that constitutes the timing signal extraction circuit 14 shown in the above embodiment), and Assuming that the electric waste vector of the added jitter is the same for each regenerative repeater and is denoted by Φ(ω), the electric waste vector of the jitter with respect to the timing of the signal passing through the N regenerative repeaters 4 is ΦN (ω) becomes ・・・・・・・・・(1). ω is the angular frequency. In particular, if the timing signal extraction circuit 14 is composed of a single tuning circuit, then the equation (1) becomes: (3). Here B is the effective bandwidth of the tuned circuit.

From this equation (3), it can be seen that the shifter operates according to the number N of regenerative repeaters.

Here, the present invention is a regenerative repeater whose output signal is the complementary code of the input signal, so the model of jitter addition of the transmission line is as shown in Fig. 5, and for even numbered regenerative repeaters,
The frequency spectrum θ(ω) of the added jitter has a negative sign. Therefore, regarding the timing of the signal passing through the N regenerative repeaters 4, the frequency spectrum of the jitter is as follows (4). Assuming that the timing signal extraction circuit is a single-tuned circuit, equations (2) to (4) become as follows, and therefore, the jitter electric current vector φN(ω) after N relays is ΦN(ω)=1 #N(jω)1z (5)

As described above, in the present invention, the addition of jitter is reduced, and in particular, the addition of jitter of low frequency components is reduced. for example(
In equation 3), if ω=0, the jitter of the even number of relayed timing signals becomes zero.

Also, regarding the frequency ω within the effective band of the tuning circuit, for example, if ω/B = 1/100, then by comparing equations (2) and (3),
It can be seen that in the present invention, the jitter is reduced by a factor of 2.5 Xl0-'.

Next, to explain the test results of the method according to the embodiment of the present invention, this test cannot be performed without using a multi-relay transmission line, but by connecting the cable in a loop using one relay, We conducted a round experiment. FIG. 6 is a block diagram of this test device.

In this test, an optical fiber cable 21 with a total length of 15 km is connected between the output terminal 18 and the input terminal U of one regenerative repeater, so that the signal from the output terminal 18 is returned to the input terminal 11. The connection between the conversion circuit 16 and the transmission circuit 17 is cut, a switch 22 is connected here, and the output of the conversion circuit 16 and the PN signal given from the outside are selectively input to the input of the transmission circuit 17. Configure it as follows. Further, the input of the conversion circuit 16 is configured to select one of the two outputs Q of the identification/decoding circuit 13. At this time,
The timing signal is monitored at the monitor terminal 24.

In this test equipment, switch 22 is first connected to the PN signal side of the lower switch in the diagram, and a PN signal shorter than the transmission delay time of +n is input to 15.
is connected to the top of the diagram, ie, to the output of the conversion circuit 16, to circulate this PN signal into this loop. First, the switch 23 was set to the upper side of the diagram, that is, the state in which the present invention was not implemented, and the jitter observed at that time was as shown in FIG. 7A. Next, when the switch 23 was connected to the lower side of the diagram, that is, the state of the present invention, the jitter at that time was as shown in FIG. 7B. In FIG. 7, the horizontal axis represents the number of signal cycles, and the vertical axis represents jitter in terms of voltage. That is,
It can be seen that when the present invention is not implemented, jitter is added each time the signal circulates, but when the present invention is implemented, there is almost no addition of jitter even when the signal circulates.

In the above example, the method of transmitting the 2 (! code) with a duty ratio of 50% was explained, but even if the duty ratio deviates from 50%, the corresponding effect is achieved.Also, for multilevel digital signals, , when extracting a timing signal with a regenerative repeater, similar implementations can be made.

However, the logic for creating complementary codes is one-to-one like binary
, it is necessary to set a predetermined logic according to which the complementary codes are uniform for each fraction.

[Effects of the Invention] As explained above, according to the present invention, the jitters generated in the same pattern in each regenerative repeater cancel each other out when they are added, and the jitter is substantially reduced to 4. Mouth; v) 5 Shimo 612 Shimo 7112

Claims (5)

[Claims] (1) A transmitting device that transmits a digital signal, a transmission medium whose one end is connected to the output terminal of this transmitting device, a receiving device whose input terminal is connected to the other end of this transmission medium, and a part of the above transmission medium. a plurality of regenerative repeaters inserted in cascade into the regenerative repeater, the regenerative repeater comprising: a means for extracting a timing signal from a digital signal received at an input terminal; and a means for extracting a timing signal from a digital signal received at an input terminal; In a digital relay transmission system including means for reproducing in synchronization with a timing signal extracted by the means and means for transmitting the digital information reproduced by the means to an output terminal, all or one of the plurality of regenerative repeaters A digital relay transmission system, characterized in that the unit is configured to transmit a complementary code of the digital signal received at its input terminal to its output terminal. (2) All of the regenerative repeaters are configured to transmit to their output terminals the complementary code of the digital signal received at their input terminals, and the number of regenerative repeaters is an even number. Digital relay transmission method described in . (3) All of the regenerative repeaters are configured to transmit to their output terminals the complement of the digital signal received at their input terminals, the number of regenerative repeaters is an odd number, and either the transmitting device or the receiving device One of them includes means for converting a transmitted digital signal into a complementary code.
The digital relay transmission method described in item 1. (4) A claim in which a portion of the regenerative repeater is configured to transmit to an output terminal the complementary code of a digital signal received at its input terminal, and the number of the portion of the regenerative repeater is an even number. The digital relay transmission method according to item fi1. (5) Some of the regenerative repeaters are configured to transmit the complementary code of the digital signal received at the input terminal to the output terminal, and the number of the regenerative repeaters is an odd number, and the transmitting device or the receiving device Any one of the above includes means for converting the transmitted digital signal into a complementary code.
The digital relay transmission method described in item 1).