GB2217944A - "Optical repeater supervisory system" - Google Patents

Abstract

An in-service optical repeater supervising system uses mBIP code (in which date is assembled into blocks of M data bits plus 1 parity bit), and a carrier signal S5 of the supervising signal for supervising an optical repeater Y is generated from the frame frequency by causing a parity bit Pb to be repeatedly inverted between an even parity bit Pb2 and an odd parity bit Pb1 in successive frames. With this supervising system, even when the error ratio of the line code is degraded, the optical repeater Y can respond to a supervisory command signal, since the carrier frequency level of the supervising signal does not decrease. <IMAGE>

Description

OPTICAL. REPEATER SUPERVISORY SYSTEM FIELD OF THE INVENTION This invention relates to an optical repeater supervisory system for monitoring an optical repeater in in-service remote-control using with mBlP line code.

DESCRIPT10N OF TIIE PRIOR ART In an optical submerged repeater system with an optical fiber cable laid on the sea bed, the operation of optical repeaters provided on the optical fiber cable can be supervised controlled only from a ground station. Further, for system operation it is necessary to be able to supervise the optical repeaters at all time without interrupting the communication service. Therefore, in such an in-service supervisory system, a mB1P code is widely used as a line code.

The mBlP code consists of m-bit data Db and one parity bit Pb determined by m bits. In this system, a command signal is transmitted to each optical repeater by making use of the even and odd property of the parity bit Pb. The parity violation which means that even parity is normally used and parity is occasionally changed to odd in order to send the information of the command.

The construction of a prior art repeater and a method of demodulation of a carrier signal of a supervisory singal in the optical repeater will now be explained with reference to Figs. 5 and 6.

Fig. 5 shows the prior art optical repeater R.

Reference numeral 1 designates an O/E converter for converting an optical signal L1 from an optical fiber cable 7 to an electric signal S1. Numeral 2 designates a decision circuit for regenerating the reccived signal. Numeral 3 designates an E/O converter for convcrtiny the regenerated singal S2 reproduced as electric signal from the decision circuit 2 to optical signal L2. Numeral 4 designates a timing circuit for generating a clock signal S3 providing a timing of regeneration of the electric signal S1.Numeral 5 designates a T-f I ip-f lop for detecting the inversion of the parity bit Pb by inputting the regenerated signal S2 and clock signal 53. Numeral 6 designates a band-pass filter for passing the output signal S4 of the T-flip-flop 5 and having a pass frequency equal to one-half of the repetition of the parity inversion. The T-flip-flop 5 and band-pass fiter 6 constitute a demodulation circuit A on for demodulating the carrier signal S5 of the supervisoring singal in the optical repeater R.

Figs. 6(a) to 6(c) are views illustrating the process of demodulation of the carrier signal S5 of the supervisoring signal in the demodulation circuit A of Fig. 5.

Fig. 6(a) shows the B1P code transmitted from a sea sore tc'rmiial equipment. Each frame of this code consists of n blocks BL each consisting of m-bit mBlP code data Ob and one parity bit Pb. Of each frame F, the parity bit Pb of a cerlain particular block BL, for instance the first block Bt in the case of Fig. 6(a), is set as an odd parity bit Pb, while the parity bits Pb of the remaininy blocks BL are set as even parity bits Pb2.Using the frame cycle F as a carrier signal, a supervisoring command singal provided from a supervisoring signal generator (not stlown) in the terminal equipment modulates this carrier signal before being sent out to each optical repeater R.

In the optical repeater R, as shown in Fig. 5, when regenerated signal S2 is input to the parity of the output parity bit, the T-flip-flop 5 is inverted very time the party bit Pb is odd parity bit Pbl as shown in Fig. 6(b). When mark signals M1 and space signals M2, in the information bits corresponding to m-bit data Db, are equiprobable, the Dc level of the output signal 54 of Fig. 6(b) is changed with the frequency of odd parity, i. e. the frequency of the frame F. Shown at C1 and C2 are respectively marks and spaces of parity bits Pb.Thus, by passing the output signal S4 from the T-flip-flop 5 through a band-pass filter 6 with one-half of the frame repetition frequency as the pass frequency, a component at one-falf the frame repetition frequency as shown in Fig. 6(c) is demodulated.

In the prior art, such a frequency component is used as a carrier frequency of the supervisoring signal to pulsewidth modulale a baseband signal. By so doing, each optical repeater R is localized through code designation for transmission of commands, reading-out of the status of the optical repeater R and detection of the bit error rate.

With the prior art supervisoring system, however, the rule of parity bits Pb is lost when the terror rate of the transmission channel increases. in such a case, at the time when an error bit Eb occurs in the regenerated signal S2, by being generated from the output singal S4 of the r- flip-flop 5, the phase of the carrier signal S5 from the band-pass filter 6 is inverted as shown in Fig. 7. In other words, an error bit modulate the phase of the supervisory carrier. In consequence, the frequency spectrum of the carricr generated by the odd parity bit Pbl is spread by phase modulation due to error bits, so that the level of the demodulated supervisoring singal decreases.

Fig. 8 shows the S/N ratio of the prior art supervisoring signal as a function of bit error rate of the transmission channel. This curve is obtained by the experiments conducted with the supervisoring singal carrier frequency set to 26.4 klji, bandwidth of the band-pass filter 6 set to 2 kz, transmission speed set to 295.6 M bits/sec., data bit Db per block Bl set to 24 bits and with a psuedo random signal of 239-1 used as a test pattern. As is seen from the figure, the S/N is suddenly degraded with the decrease of the level of the supervisoring signal around error ratio 10-6 ~ 10-5. Thus, with the prior art sulervisorins system the supervisoring of the optical repeater R becomes impossible when the error rate exceeds 10-6.

The present invention is intended in order to solve the above problems inherent in the prior art, and it seeks to provide an optical repeater supervisoring system, which can effect supervisoring of optical repeater even when the error ratio is degraded.

SUMMARY OF THE INVENTION According to the invention, there is provided an inservice optical repeater supervisoring system, which uses mB1P code, and in which a carrier signal of the supervisoring signal for supervisoring an optical repeater is generated by causing a parity bit to be repeatedly inverted to an even parity and an odd parity for every frame consisting of n (n) 2) blocks.

With the supervisoring system according to the invention, even when the error ratio of the transmission channel is degraded, the optical repeater can respond to a supervisory command signal for the carrier frequency level of the monitoring signal does not decrease.

BRIEF DESCRIPTION OF TIIE DRAl[NGS Fig. 1 is a block diagram showing an optical repeater including a supervisoring singal demodulation circuit according to the invention; Figs. 2 and 3 are timing charts showing signals at different points of the optical repeater in case of a normal status and in case when an error bit occurs, respectively, with (a) being a mBlP code regenerated signal S2, (b) being a T-flip-flop output signal S4, (c) being an exclusive OR gate output signal S6, and (d) being a band-pass filter output carrier signal S5; Fig. 4 is a figure showing the S/N ratio of the supervisoring signal as a function of bit error rate of the transmission channel;; Fig. 5 is a block diagram showing an optictIl repeater including a supervisoring signal demodulation circuit in the prior art; Figs. 6 and 7 are timing charts showing signals at different points in case of a normal status and in case when an error bit occurred respoctivelty, with (a) being mB1P code regenerated signal S2, (b) being T-flip-flop output signal S4, and (c) being a band-pass filter output carrier signal S5; and Fig. 8 is a figure showing the S/N ratio of the supervisoring signal in the optical repeater of Fig. 5 as a function of the bit error rate.

DESCRIPTION OF IHE PREFERRED EHBODIHENT Now, an embodiment of the invention will be described with reference to Figs. 1 to 4.

Fig. 1 is a block diagram showing an optical repeater Y including a supervisoring signal carrier signal demodula tion circuit B. The circuit according to the invention is different from the prior art circuit shown in Fig. 5 in that an m-bit shift register 8 and an exclusive OR gate 9 are provided between T-flip-flop 5 and band-pass filter 6. Fig.

2 shows waveforms of signals appearing in various parts of tie circuit according to the invention. The operation will now be described with reference to this waveform timing chart.

Fig. 2(a) shows the waveform of mB1P code regenerated signal S2. Parity bits Pb are odd parity bits Pbl for one frame F (consisting of 9 blocks BL for instance) and even parity bits Pb2 for the next frame, and so on. That is, the parity bits are inverted to be even or odd for every frame.

rhus, the r-flip-flop 5 provides an output signal S4 as shown in Fig. 2(b). As is shown, in a frame F including even parity bits Pb2, the parity bits Pb2 fixedly provide spaces C1. In a frame F including odd parity bits Pbi, the parity bits Pbl provide sPaces C2 and marks C1 alternately.

The polarity of the signal is thus inverted for every odd parity bit Pbl. As shown in Fig. 1, this output signal S4 is supplied to a shift register 8 of m+1 bits, for instance, to provide a delay of mF1 bits, while it is also supplied to an exclusive OR gate 9. The output of the shift register 8 is also supplied to the exclusive OR gate 9. The exclusive OR gate S6 provides an output signal S6. Fig. 2(c) shows the waveform of tlie output signal S6 of tie exclusive OR gate 9. As is shown, in a frame F including even parity bits PI)2 only marks C1 are provided, while in a frame F including odd parity bits Pbl spaces C2 are provided at all time.Thus, by passing tie signal S6 through band-pass fitter 6 with pass frequency equal lo one-falf of the frame repetition frequency, a frequency component equal to one-falf the frame frequency is obtained like the prior art supervisoring singal. -this signal is used as carrier frequency to transmit the supervisory command signal.

Now, operation when an error occurs in the transmission channel signal will be described with reference to Fig.

3. When an error bit Eb occurrs in a frame F as shown in Fig. 3(a), the output signal S4 of the T-flip-flop 5 provides a space C2 in correspondence to a block BL in which the error occurrs. Furlher, the exclusive OR gate 9 provides an output signal S6 as shown in Fig. 3(c). Unlike the prior art supervisoring system, inversion of parity bit Pb occurs only in the block BL in which an error occurrs.

Ihus, in the carrier signal S5 from the band-pass filter 6 only a missing pulse portion is produced in a frame F, in which the error occurrs, as shown in Fig. 3(d).

Thus, according to the invention unlike the prior art, the carrier frequency of the carrier signal S5 is not subject to any phase modulation even when the first error rate is degraded. It is thus possible to maintain the level of the carrier frequency up to an error rate, with which the missing putse portion is extremely increased.

Fig 4 shows the S/N ratio of the supervisoring signal according to the invention as a function of bit error rate. Tie figure is obtained as a result of calculation under the same conditions as in the case of Fig. 8. It will be seen from tie figure that the S/N ratio is not degraded until the error ratio increases to 10 -2 rhis means that supervisory of the optical repeater Y can be obtained even when the error rate is degraded.

As has been described in the foregoing, according to the invention even with degraded error ratio of the transmisson channel signal the supervisory command signal (or supervisoring signal) can be correctly demodulated. It is thus possible to avoid erroneous operation of the optical repeater and provide a highly reliable supervisoring singal.

The invention is thus applicable to a system using mB1P code as supervisory signal as well, so that it is very beneficial for the operation and maintenance of such systems.

Claims (4)

1. An optical repeater supervisory system for monitoring an optical repeater with in-service mode by using a supervising signal transmitted from a supervising signal set, wherein a carrier signal for said supervising signal is provided by forming each frame of a plurality of blocks each consisting of a mBIP code and providing even and odd parities for alternate frames and is transmitted to said optical repeater.

2. An optical repeater supervisory system for monitoring an optical repeater with in-service mode by using a supervising signal transmitted from a supervising signal set, wherein said optical repeater extracts a mBIP code and inverts it in a T-flip-flop, said inverted mBIP being supplied to a first input of an exclusive OR gate and also through a shift register providing a delay for M+1 bits to a second input of said exclusive OR gate, said exclusive OR gate providing a low frequency component of said mBIP code, said low frequency component being passed through a bandpass filter having a pass frequency equal to one-half of a predetermined frequency for demodulating the carrier signal of said supervising signal.

13. An optical repeater supervisory system for monitoring an optical repeater with in-service mode by using a supervising signal transmitted from a supervising signal set, wherein a carrier signal for said supervising signal is provided by forming each frame of a plurality of blocks each consisting of a mBIP code and providing even and odd parities for alternate frames and is transmitted to said optical repeater, and said optical repeater extracts said mBIP code and inverts it in a T-flip-flop, said inverted mBIP being supplied to a first input terminal of an exclusive OR gate and also through a shift register providing a delay for m+l bits to a second input of said exclusive OR gate, said exclusive OR gate providing a low frequency component of said mBIP code, said low frequency component being passed through a bandpass filter having a pass frequency equal to one-half of a predetermined frequency for demodulating the carrier signal of said supervising signal.

4. An optical repeater supervisory system substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.