Module 11
Digital Signal Processing
(1) Use the Existing Modules / Components for Your Research Papers, Research Projects, Theses and Lab Simulation Experiments.
(2) Modify the Modules / Components to the Next Level for Your Research Papers, Research Projects and Theses.
(3) Integrate Different Modules / Components in the OCSim Package to Realize Your Own Fiber Optic Communication Systems.
(4) Modify the Modules for Co-Simulations with the Third Party Commercial Optical Communication Systems Softwares.
Source Code: coherent_rx_phase_comp.m
Compensation of laser phase noise in a coherent QPSK system.
This source code calls the following functions:
(1) phase_noise.m: This function introduces laser phase noise as a Wiener process. Laser linewidth should be provided.
(2) up_sample.m: This function introduces the same phase over the entire symbol interval.
(3) fiber_prop.m: This function describes the fiber propagation.
(4) amp.m: This function describes optical amplifier.
(5) gauss.m: The receiver is modeled as a low pass second order gaussian filter.
(6) down_sample.m: This function gets one sample per symbol.
(7) ph_noise_comp_viterbi.m: This function compensates for phase noise using Viterbi-Viterbi algorithm.
Explore Further this Module:
11.1 Change the linewidths of Tx laser and LO from 25 kHz to 1 MHz and observe the constellation diagrams before and after the phase compensation. Write a program to calculate the phase variance. Plot the phase variance before and after the phase compensation.
11.2 Set the linewidths to 0 Hz and observe the constellation diagrams before and after the phase compensation. Can the laser phase noise compensator compensate for amplifier noise? Explain.
11.3 Set the linewidths to 100 kHz. Change the transmission distance from 200 km and 1000 km. Find the optimum block size in each case.
11.4 Design and simulate following coherent QPSK fiber optic system links with digital signal processing:
28 GBaud, 20 span coherent QPSK fiber optic system link
10 GBaud, 60 span coherent QPSK fiber optic system link
28 GBaud, 20 span Nyquist pulse coherent QPSK fiber optic system link
10 GBaud, 60 span Nyquist pulse coherent QPSK fiber optic system link
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n GBaud, N span coherent QPSK fiber optic system link
n GBaud, N span Nyquist pulse coherent QPSK fiber optic system link
Choose the desired values of n and N for simulations.
Simulate more:
Modify to DP-QPSK optical Communication systems. Scientific and Programing support is available for modifying to DP-QPSK optical systems.
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Selected Simulated Results
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Source Code: fiber_prop_CD_comp.m
Compensation of fiber chromatic dispersion in a coherent QPSK system.
This source code calls the following functions:
(1) phase_noise.m: This function introduces laser phase noise as a Wiener process. Laser linewidth should be provided.
(2) up_sample.m: This function introduces the same phase over the entire symbol interval.
(3) fiber_prop.m: This function describes the fiber propagation.
(4) amp.m: This function describes optical amplifier.
(5) down_sample_CD.m: This function does down-sampling with number of sample per symbol = down_sample_factor. For example, if down_sample_factor = 4, it means the number of samples per symbol at the receiver after down-sampling = 4.
(6) CD_comp.m: This function provides CD compensation in digital domain.
(7) ph_noise_comp_viterbi.m: This function compensates for phase noise using Viterbi-Viterbi algorithm.
Explore Further this Module:
11.5 Turn off the laser phase noise (by setting the line widths of transmitter laser and LO to zero) and observe the constellation diagrams. Compare this with the constellation diagram when the linewidths are non-zero.
11.6 Introduce the phase noise compensator (ph_noise_comp_viterbi.m) when the laser linewidth ranges from 100 kHz to 1MHz and observe the constellation diagrams before and after the phase compensation and CD compensation blocks.
11.7 Increase the number of spans to 20 and calculate the number of taps required. Observe the constellation diagram before and after the CD compensation.
11.8 Design and simulate following coherent QPSK fiber optic system links with digital signal processing:
28 GBaud, 20 span coherent QPSK fiber optic system link
10 GBaud, 60 span coherent QPSK fiber optic system link
28 GBaud, 20 span Nyquist pulse coherent QPSK fiber optic system link
10 GBaud, 60 span Nyquist pulse coherent QPSK fiber optic system link
– – –
– – –
n GBaud, N span coherent QPSK fiber optic system link
n GBaud, N span Nyquist pulse coherent QPSK fiber optic system link
Choose the desired values of n and N for simulations.
Simulate more:
Modify to DP-QPSK optical Communication systems. Scientific and Programing support is available for modifying to DP-QPSK optical systems.
.
Selected Simulated Results
.
.
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