Hello,
Today I am going to share with you an example of error handling before error correction on SF16E single board with Raman and BPA transmission.
Problem Description
The client signal flow is: (Station B) SF16E---BA---RPC01--------------RPC02—PA-DCU-SF16E (Station A), and the reverse signals are consistent.
Trouble phenomenon: After the customer reported that the signal adjustment on both sides was passed, it was found at station A that the bit error rate before error correction was 6, and there was a BEFFEC_EXC error code limit warning before error correction.
Alarm
The BEFFEC_EXC alarm is reported on the SF16E board at site A
Processing ideas:
1- Insufficient dispersion compensation
2- Non-linearity or signal-to-noise ratio problems cause
Process:
1- Consider the problem of bit errors before error correction caused by insufficient dispersion compensation. The transmission distance of stations A and B is 303 kilometers, and the span attenuation is about 60db. The SF16E single board is used. Check the product documentation. The dispersion limited distance of the single board is 120 kilometers. The customer uses a two-way for a DCU of 80 kilometers and a DCU of 40 kilometers in one direction, the compensation distance is 200 kilometers. According to the dispersion calculation formula:
dispersion compensation distance = transmission distance - limited distance + 10~30, dispersion compensation is sufficient, and the cause of dispersion is eliminated.
2- Consider the error before error correction caused by nonlinear reasons. The transmitting end is BA+RPC01 dual-stage amplification, and the receiving end receives light about -33dbm. According to the span attenuation of about 60db, the transmitting end power is about 27dbm. If the incoming light power is too strong, it will cause non-linearity, which will lead to bit errors and non-linear processing. The common idea of the problem is to add optical attenuation at the originating end to lower the optical power of the incoming fiber, but the unmanned station at site B does not have this condition.
3- After confirmation, the incoming fiber power can be reduced by reducing the forward Raman pump power. First try to reduce 0.5db. It is found that the error rate before error correction becomes 8 and the error code over-limit alarm disappears before error correction. Decrease 0.5db again and find that the bit error rate is 0 before error correction.
Root cause & Solution
1- When dealing with long-distance transmission errors, if the errors caused by nonlinearity or signal-to-noise ratio are considered, it can be solved by adjusting the optical power of the Raman pump source. If it is a signal-to-noise ratio problem, the pump source light can be increased. Try the power, if it is due to non-linearity, reduce the pump power and reduce the input power to avoid non-linearity caused by excessive optical power. After this problem reduces the transmitter power, the error disappears. From the debugging experience, when the BA fiber input power is large, the forward Raman should not be turned on too much. Usually, the equivalent fiber input power after the forward Raman is guaranteed to be around +23dB.
2- When adjusting the optical power of the pump source, it is not advisable to adjust it too much at one time, and gradually adjust and observe in steps of 0.5db.
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