Page 544 - Fiber Optic Communications Fund

Digital Signal Processing 525

11.5 Write a computer program to compensate for CD of a fiber-optic system with the following param-
2
eters: =−22 ps /km, transmission distance = 1000 km, symbol rate = 25 GSym/s, modulation =
2
NRZ-QPSK. Determine the number of taps required for the time domain technique using a FIR fil-
ter. Also, write a program to compensate for CD in the frequency domain using FFTs. Compare the
computational costs associated with time and frequency domain techniques.

11.6 Provide the algorithms of an adaptive equalizer based on the constant-modulus algorithm (CMA).
11.7 Explain the principles of digital back propagation (DBP). Can DBP compensate for the impairments
due to interaction between fiber nonlinearity and ASE?
11.8 Explain the differences between symmetric and asymmetric split-step Fourier schemes.

11.9 Write a computer program to simulate a single-span fiber-optic system using the symmetric
split-step Fourier scheme. The parameters of the system are as follows: symbol rate = 25 GSym/s,
2
−1
NRZ-QPSK, span length L = 80 km, =−22 ps /km, loss = 0.2dB/km, = 1.1W −1 km , launch
2
power = 10 dBm. At the receiver, introduce DBP with (a) step size = L, (b) step size = L/2. Compare
the constellation diagrams with and without DBP. Ignore laser phase noise.

Further Reading
R. Chassaing and D. Reay, Digital Signal Processing. John Wiley & Sons, New York 2008.
S. Haykin, Adaptive Filter Theory, 4th edn. Prentice-Hall, Englewood ciffs, NJ, 2001.
S. Haykin, Communication System, 4th edn. John Wiley & Sons, New York 2001.
J.G. Proakis, Digital Communications, 4th edn., McGraw-Hill, New York, 2001.
H. Meyr, M. Molenclaey, and S. Fechtel, Digital Communication Receivers, Synchronization, Channel Estimation, and
Signal Processing. John Wiley & Sons, New York, 1998.

References

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