P. Chathuranga Weeraddana, Masters Thesis

Abstract

Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation scheme that achieves high spectral efficiency by using minimally densely spaced orthogonal subcarriers without increasing the transmitter and receiver complexities. Despite its promises OFDM systems are vulnerable to the carrier frequency offset (CFO) arising from transceiver oscillator mismatches andor Doppler shifts.

The principle motive behind this thesis study is to investigate the performance degradation in OFDM systems due to CFO induced by transmitterreceiver oscillator frequency mismatches. Our derivations are distinct from the other existing results and derivations available in the open literature as most of them considered CFO to be a constant, in contrast we treat it as a random parameter which is the case in reality.

We begin with a derivation of new approximated intercarrier interference (ICI) expression which enables us to carry out the subsequent derivations associated with new bit error rate (BER) and symbol error rate (SER) expressions for binary phase shift keying (BPSK) and 4-quadrature amplitude modulation (QAM) OFDM systems with random CFO or random residual CFO.

Those derived results can be classified into two parts based on the correlation between the residual CFO or CFO and the channel, i.e., performance analysis with channel independent residual CFO or CFO and performance analysis with channel dependent residual CFO. The BERSER expressions in BPSK4-QAM OFDM systems with uniformly distributed CFO and Gaussian distributed residual CFO are obtained under the channel independent case and additive white Gaussian (AWGN), frequencyflat and selective Rayleigh fading channels are considered separately. Moreover, in the case of channel dependent scenario, we derive BERSER expressions in BPSK4-QAM OFDM systems with frequency-flat Rayleigh fading where the residual CFO is Gaussian distributed conditioned on the channel parameters. The simulation results are provided to verify the accuracy of the new BER/SER expressions.

Keywords

carrier frequency offset, OFDMA

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Thesis: Performance Analysis of OFDM Systems with Random Residual Frequency Offset

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