Module 13
Nonlinear Coherent QPSK Fiber Optic Communication Systems
(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: fiber_prop_nonlinear_coherent_qpsk.m
Compensation of Chromatic Dispersion (CD) and Self Phase Modulation (SPM) in a Long Haul Nonlinear Coherent QPSK Fiber Optic Communication System through Digital Signal Processing (DSP).
This source code calls the following functions:
(1) power_meter.m : Calculates the average power in dBm.
(2) constellation_diagram.m : Plots the constellation.
(3) tx_nrz_psk.m : The cw signal is modulated by an PSK data. To realize QPSK modulation, tx_nrz_psk.m is called twice, for the in-phase and quadrature components.
(4) fiber_prop.m : solves the NLSE using a split-step Fourier scheme.
(5) amp.m : Inline amplifier is realized using this function.
(6) gauss.m: A Gaussian bandpass filter is introduced. The half-bandwidth (‘bw’) should be specified. This could also be used as a low pass filter and in this case, ‘bw’ is the 3-dB bandwidth.
(7) raised_cosine.m: Raised cosine function in time domain
(8) 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.
(9) ber_calc_qpsk.m: calculates the BER by comparing the received bit pattern with the transmitted bit pattern.
Explore Further this Module:
13.1 Turn off the nonlinearity (set ‘gam’=0) and plot the BER as a function of transmission distance. Choose the launch power (av_power_dBm = -6 dBm). Change the transmission distance from 120X80 km to 240X80 km. Change the number of bits, if needed. Observe that BER increases with distance.
13.2 Repeat 13.1 at a higher launch power (say – 3 dBm). Observe that BER is lower than that in 13.1 since higher launch power implies better performance in a linear system.
13.3 Turn on the nonlinearity (set ‘gam’=1.1
). Fix the transmission distance as 150X80 km. Change the launch power from -8 dBm to 3 dBm (with an increment of 2 dBm) and plot the BER vs launch power. Observe that the BER decreases initially (linear regime) and then starts to increase (nonlinear regime).
13.4 Repeat 13.3 for a different transmission distance say 100X80 km. Adjust the number of bits to get a reliable estimate of BER.
13.5 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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