RU2349039C2 - Method of probability detection increase of radiation coupling from optical fiber - Google Patents

Abstract

FIELD: physics, communication.

SUBSTANCE: invention concerns methods of detection of infringement of working capacity of the protected fiber-optical systems of transmission (FOTS) information of restricted access and can be used as an expedient of the constant control of a fiber-optical transmission line (FOTL) from leakage on the optical channel. In the method, consisting in reception, detection of optical signals from a fiber-optical line, amplification, integration and analogue-digital transformation of the gained analogue electrical signals which in the numeral shape are compared to control value in such a manner that in case of decrease in amplitude of a signal below control value on the given quantity the alarm signal is shaped. That through each quantity of readout N making a j-th cycle set by the timer, medial sampling value

which is calculated is new the gained quantity Faugh is remembered and used in the subsequent cycles for evaluation of a control signal under the formula

after the termination of each j cycles remembered and subtracted from the value calculated in the j-7, j-k1, j-k2…j-km cycles, the gained difference is compared to in advance given thresholds of detection Φ_d and alarms Φ_a and in case one of requirements

that is carried out the alarm signal is shaped, in a case if one of requirements

that for quantity of medial sampling value in a j+1 cycle is carried out quantity calculated either in j-k1-1, or in j-k2-1 is accepted, either in j-k3-7 or … in j-km - depending on what of requirements (4) is carried out, otherwise the value is accepted, used in y cycle, and k1/k2, k12/k…km-1/km≥Φ_a/Φ_d.

EFFECT: increase of the signal/noise relation at decision-making for signals pickup of any shape, amplitude and duration, and also an error exception at decision-making at the expense of the account of slow changes of a signal in definition of control value.

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Description

The invention relates to methods for detecting a malfunction of protected fiber-optic transmission systems (FOTS) of limited access information and can be used as a method of continuous monitoring of a fiber-optic transmission line (FOCL) from leakage through an optical channel.

A known method of controlling FOCLs from the patent "Device that controls the operation of fiber-optic communication, and a receiver that includes the mentioned device" (French Patent No. 2568431 from 1988 on application No. 8411970 from 1984).

The method consists in the fact that the optical signals received from the fiber optic line are detected and amplified to the required value. After that, to eliminate impulse noise and reduce the influence of noise, the signal is integrated and converted from analog to digital form using analog-to-digital conversion. Analog-to-digital conversion is performed periodically with a given frequency. The resulting value is compared with one or more previous values. If the difference exceeds the set value, an alarm is triggered. The comparison reveals a violation in the operation of the communication system, since it is believed that sudden changes indicate a deliberate violation, and slow changes are caused by external and internal factors.

The control device that implements the method operates as follows. Optical signals received from a fiber optic line are detected by a photodetector and amplified by a photocurrent amplifier. Next, the signals are fed to the output driver and integrator. Thus, at the output of the shaper output information signals are generated. From the output of the integrator, the sequence of signals is converted in such a way that a low-frequency control signal is formed at the output of the integrator, the amplitude of which is proportional to the attenuation of the optical signal in the fiber-optic communication line. Next, the control signal is converted into digital form using an analog-to-digital converter (ADC), which is clocked by a generator. The signals from the output of the ADC are fed to random access memory (RAM) and to the input of a digital comparator. The comparator compares the value of the received signal with one or more previous values retrieved from RAM. If the amplitude of the received signal is less than that of one or more of the previous ones by a predetermined value, an ALARM signal is generated.

The disadvantages of this method of controlling FOCL include the following facts.

1. Low noise immunity due to the fact that the control uses a once-measured signal value, which can be distorted by impulse noise or noise emission.

2. High probabilities of signal skipping and false alarm due to the small signal processing base (product of the signal frequency band and its processing time).

The well-known "Method for detecting a slow output of optical radiation through the side surface of a fiber-optic communication line" (Russian Patent No. 2251810 dated 01/20/2003 according to the application No. 2003101467/09), which is closest to the claimed method and therefore adopted as a prototype.

The method consists in the fact that the optical signals received from the fiber optic line are detected and amplified to the required value. After that, the signal is integrated and converted from analog form to digital form using the ADC. After that, the sum of the deviations of the current signal values from the control value is calculated taking into account the sign during the time specified by the timer. After that, the obtained current values of the sums are compared with a predetermined reference signal, and an alarm is generated if the difference in the current value of the sum exceeds the reference signal by the value of the specified threshold value. Moreover, the threshold value is periodically adjusted.

A device that implements the method operates as follows. Optical signals from a fiber optic line are detected by a photodetector, amplified by a photocurrent amplifier, and fed to the output through an output signal shaper. The signals from the output of the photocurrent amplifier go to the input of the integrator, from the output of which - to the input of the ADC, where they are converted from analog form to digital form. The ADC is clocked by a generator, the signals from which are fed to the timer input. The timer counts the time during which the total is calculated. From the output of the ADC, the signals are sent to an arithmetic logic unit (ALU), which sums (taking into account the sign) the obtained value with the previously received sum. The amount is stored in RAM. The digital comparator compares the current values of the signal received from the ADC output with the previous one (or several previous ones), as well as the received amount with a given threshold value. If the current value is lower than the previous (previous) by a limit value or the amount reaches a predetermined value, the alarm device generates an alarm. The timer counts down the period of time after which the zero amount is set in RAM. Thus, slow changes in attenuation that occur during a time longer than the storage time of the current values will be detected, since they will lead to a constant increase in the sum (with a negative sign) and, ultimately, to achieve the response value of the alarm device.

The disadvantages of this detection method include the following.

1. The method meets the criterion of optimal signal isolation against a background of noise (the most possible signal-to-noise ratio when making a decision) only for a constant amplitude pick-up signal. This leads to the fact that for pickup signals that vary during the calculation of the sum, the extremely low values of the probabilities of skipping the signal and false alarm are not achieved.

2. The maximum duration of the detected signal is limited by the period of time through which the zero amount is set in RAM.

3. The method does not allow to detect a very slow smooth output of the optical signal.

The technical problem to be solved is an increase in the probability of detecting a covert attempt to pick up an optical signal from the side surface of an optical fiber.

The technical result is to increase the signal-to-noise ratio when making decisions for pick-up signals of any shape, amplitude and duration, as well as to increase the probability of detection when making decisions by taking into account slow signal changes in determining the control value.

This technical result is achieved by a method of increasing the probability of detecting the output of radiation from an optical fiber, which consists in receiving, detecting optical signals from a fiber optic line, amplifying, integrating and analog-to-digital converting the obtained analog electrical signals, which are digitally compared with a control value in this way that in the case of a decrease in the signal amplitude below the control value by a predetermined value, an alarm is generated.

What is new is that after each number of samples N that make up the j-th cycle specified by the timer, the average sample value is calculated

which is remembered and used in subsequent cycles to calculate the control signal according to the formula

after the end of each j-th cycle, the obtained value Ф _{j is} stored and subtracted from the value calculated in j-1, j-k1, j-k2 ... j-km cycles, the obtained difference is compared with the predetermined detection thresholds Ф _о and alarm Ф _m and if one of the conditions

then an alarm is generated if one of the conditions

then for the value of the average sample value in the j + 1 cycle, the value calculated either in j-k1-1, or j-k2-1, or in j-k3-1, ... or in j-km, depending on which from conditions (4) is fulfilled, otherwise the quantity used in the j cycle is taken, moreover, k1 / k2, kl2 / k ... km-1 / km≥Ф _m / Ф _o .

The set of essential features of the proposed method allows to increase the signal-to-noise ratio when making decisions for signals of any shape, amplitude and duration, since when calculating the most probable signal amplitude, the absolute value of the implementation at a given time is taken. In addition, a detection threshold has been introduced, upon exceeding which a pickup signal of any duration is detected.

The drawing shows a functional diagram of a photodetector that implements the inventive method: 1 - optical fiber (S); 2 - receiving optoelectronic module (PROM); 3 - amplifier-limiter (UO); 4 - linear amplifier (LU); 5 - amplitude detector (HELL); 6 - integrator (INT); 7 - ADC; 8 - clock generator (TG); 9 - device for calculating the average (UVS); 10 - average RAM; 11 - device for calculating the squared deviation (UVCO); 12 - adder (SUM); 13 - RAM amounts; 14 - subtraction device (SUB); 15 - digital comparator (KOM 1); 16 - digital comparator (KOM 2).

A device that implements the inventive method works as follows. A permanently received optical information signal with an OB (1) is fed to the input pole of the PROM (2), where it is converted into an electrical signal. From the PROM output, the signal goes to the input of the UO (3), which forms a digital information signal. The same signal is fed to the input of the amplifier (4), which amplifies the amplitude of the signal to the desired level. After that, HELL (5) converts the signal amplitude to a constant control level (KU), which is fed to the input of INT (6). INT limits the frequency band of the control signal and accordingly reduces noise.

After that, the analog signal is converted into a digital Kotelnikov series using the ADC (7), which is clocked by the TG (8) (the clock period is Δt). A sample of the input implementation Yi arrives at the UVS (9), which calculates the average sample value for a given period of time T (the number of samples N = T / Δt). The obtained average sample is written in one of the registers of RAM average (10), from which the values are fed to the first input of the UVCO (11), to the second input of which the sample of the input implementation Yi is received. UVCO calculates the square of the deviations ΔYi ² received at the input of the SUM (12), which calculates the sum of the squares of the deviations Фj.

After the end of each cycle (N samples), the signal Ф _{j is} supplied to the CONTRACT (14), which calculates the modulus of the difference of two values Ф _j -Ф _jk , the last of which is stored in one of the RAM registers of the sums (13). The obtained value / ΔФ _jk / is compared using the COM (16) with the detection threshold Ф _o and using the COM (15) with the alarm threshold Ф _m .

If the difference between the compared values / ΔФjk / -Ф _{о is} greater than zero, a signal is generated to prohibit overwriting the average sample value in the corresponding RAM register (10).

If the difference of the compared values / ΔФjk / -Ф _{m is} greater than zero, an alarm is generated.

In the prototypes of the converters FOBOS-100M and FOBOS-100S that implement the inventive method, the following elements and devices were used: receiving optoelectronic modules PROM-364-155 and HFBR-2316T; amplifier limiter K500LP116; linear amplifier K500LP116; amplitude detector 2BC523VM; Integrator OPA177GS; ADC, clock generator, mean calculation device, average value RAM, deviation squared calculator, adder, sum RAM, subtraction device, digital comparators are implemented in the PIC16C717 microcontroller with specially developed DEMOS software.

Tests of the samples showed the following results: at a detection threshold of 0.01 dB, an alarm threshold of 0.05 dB, three-stage control at k1 = 1, k2 = 8, k3 = 64, signals of almost any duration were detected.

Claims (1)

A method of increasing the probability of detecting the output of radiation from an optical fiber, which consists in receiving, detecting optical signals from a fiber optic line, amplifying, integrating and analog-to-digital converting the received analog electrical signals, which are digitally compared with a control value in such a way that the signal amplitude decreases below the control value by a predetermined amount an alarm is generated, characterized in that after each quantity set by the timer, accounts N, making up the j-th cycle, the average sample value is calculated

which is remembered and used in subsequent cycles to calculate the control signal according to the formula

after the end of each j-th cycle, the obtained value Ф _{j is} stored and subtracted from the value calculated in j-1, j-k1, j-k2 ... j-km cycles, the obtained difference is compared with the predetermined detection thresholds Ф _o and alarm Ф _m and if one of the conditions

then an alarm is generated if one of the conditions

then the value calculated either in j-k1-1, or in j-k2-1, or in j-k3-1 ... or in j-km is taken as the average sample value in the j + 1 cycle, depending on which of conditions (4) is fulfilled, otherwise the quantity used in the j cycle is taken, moreover, k1 / k2, k12 / k ... km-1 / km≥Ф _m / Ф _o .