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<p>In this thesis, the effect of Doppler shift on adaptive orthogonal frequency-division multiplex (OFDM) modulation in a cognitive radio (CR) application is investigated. We present Monte Carlo simulations of OFDM modulation in which a group or groups of subcarriers are modulated using quadrature phase-shift keying (QPSK) modulation and 16-ary quadrature amplitude modulations (16QAM). We show that turning off some subcarriers does not affect the performance as long as the effective Eb/No remains the same. We also present Monte Carlo simulations where the power ratio of two sets of subcarriers is changed while maintaining the same total power in order to investigate the effect on performance. Finally, we consider a two-user CR scenario and investigate the performance effect on a primary user by a secondary user in terms of various Doppler shift offsets where both the primary user and secondary user use OFDM modulations.
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<br>Subjects: Cognitive Radio (CR); Signal-to-Noise Ratio (SNR); Signal-to-Interference Ratio (SIR); Adaptive Orthogonal Frequency Division Multiplexing (AOFDM); Frequency Offset; Doppler shift; Quadrature Phase Shift Keying (QPSK); Quadrature Amplitude Modulations (QAM); Subcarrier Allocation Scheme</div>
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Ahn, Byunghyun</div>
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