Performance of coherent optical OFDM transmission through dispersive optical fibers with four-wave mixing | |
| Author | Phan Bach Khoa |
| Call Number | AIT Thesis no.TC-08-06 |
| Subject(s) | Orthogonal frequency division multiplexing Laser communication systems |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Telecommunications, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. TC-08-06 |
| Abstract | Orthogonal Frequency Division Multiplexing (OFDM) is a special form of multicarrier modulation (MCM). High spectral efficiency, efficient elimination of intersymbol interference (ISI), robustness to channel fading, and immunity to dispersion are prominent properties of OFDM. A combination of OFDM and coherent lightwave communication system called coherent optical OFDM (CO-OFDM) has been proposed for long distance optical communications to combat dispersion in optical fibers. CO-OFDM system is affected by chromatic dispersion, laser phase noise, four-wave mixing crosstalk (FWM), additive white Gaussian noise (A WGN) and so on. In this thesis, the performance of CO-OFDM transmission through dispersive optical fiber with FWM is considered. The effects of chromatic dispersion and laser phase noise are first considered. After transmission through the CO-OFDM system, the signal constellation is rotated due to chromatic dispersion and laser phase noise. Dispersion compensation is applied in order to rotate the signal constellation back to the origin. However, dispersion compensation is not perfect. FWM crosstalk, which is the dominant nonlinear effect in multichannel optical communication systems, is considered. In order to mitigate the FWM nonlinear effects, a design method called random carrier selection is proposed. In this method, a higher bit-rate signal constellation is used, resulting in a lower number of OFDM channels used. The selection of channels is done randomly so that channel frequencies are spaced unequally. We focus on two types of modulation schemes: phase-shift keying (BPSK, QPSK, 8-PSK) and optimal 8-QAM. The comparisons among these modulation schemes are subject to the same bit error rate (BER), available optical bandwidth, signal degradation parameters, and bit rate. We first demonstrate an improvement in the BER performance by using QPSK modulation with half of the channels and unequal spacing instead of BPSK modulation with all channels. Then we demonstrate the BER improvement by using the optimal 8-QAM modulation with two-third of channels and unequal spacing instead of QPSK modulation with all channels. |
| Year | 2008 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-08-06 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Poompat Saengudomlert |
| Examination Committee(s) | Rajatheva, R. M. A. P.;Ahmed, Kazi M. |
| Scholarship Donor(s) | Electricity of Vietnam |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2008 |