Simulation tool development for optical OFDM transmitter and receiver
Tutor / director / evaluatorGene Bernaus, Joan M.
Document typeMaster thesis
Rights accessOpen Access
OFDM has become an important issue within the optical field during the last two decades. For this reason, for a better understanding of the impact from transmitter and receiver, the full system (modulator and demodulator) has been implemented using Matlab. The different components of the transmitter and receiver have been coded in a modular way. Thus, the different parts of the transmitter are the sequence generator, the amplitude and phase modulator (BPSK, QPSK, 16QAM and 64QAM), the OFDM modulator and the optical up-converter. While the parts of the receiver are the optical down-converter, the OFDM demodulator, the amplitude and phase demodulator (BPSK, QPSK, 16QAM and 64QAM) and the estimator of sequences. Besides, there are two modules to analyse the system, one to measure the EVM and another one to calculate the BER using the Monte Carlo method. Finally, the channel can be noiseless of with AWGN. The analysed factors that influence the modulation and demodulation are the constellation calculation (mainly 16QAM and 64QAM), the ADC of the receiver (number of quantization bits) and the optical up and down conversion (the rate between the input electrical signal to the optical up-converter and Vpi). These parameters introduce an error that affects the performance of the full modulation and demodulation. The simulations has been done with a bit sequence with a length around 262.000 bits. The results were analysed from multiple simulations, studying individually the different parameters. To summarize, the ADC is the parameter that affects most the system introducing errors. For a BPSK and QPSK modulation, 4 quantization bits are enough to get a very good result. For a 16QAM, 5 quantization bits are required. Finally, for a 64QAM, 6 quantization bits are necessary. In addition, the optical conversion practically doesn?t affect to the BPSK and QPSK modulation, but the introduced error is more relevant for the 16QAM and very important for the 64QAM. The constellation calculation also affect the system (in a slighter way) due to the limited number of bits, with a longer sequence this error can be mitigated.
Investigadion on OFDM Superchannels for Fiber-optic Communications