A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 2002

Orthogonal Frequency Division Multiplexing or OFDM is a form of multi-carrier modulation technique. High spectral efficiency, robustness to channel fading, immunity to impulse interference, uniform average spectral density, capability of handling very strong echoes and less non linear distortion are among the favorite properties of OFDM. Even though there are many advantages of OFDM, it has two main drawbacks: high Peak to Average Power Ratio (PAPR) and frequency offset. In this thesis, the issue of PAPR reduction in OFDM is discussed. The effect of modulation schemes on PAPR is illustrated at the beginning of the thesis. Two new algorithms are proposed to reduce the PAPR. The first algorithm, Lookup Table Approach, is carried out by selecting the input sequences properly using a lookup table. The second algorithm, Envelope Scaling Approach, is to scale the input envelope for some subcarriers before they are transformed to the time domain by Inverse Fast Fourier Transform (IFFT). Simulation results show that PAPR can be reduced significantly with both schemes. The BER performance for multipath fading channel of the proposed schemes is insignificantly different when comparing to adaptive Partial Transmitted Sequence (PTS). The costs of the proposed schemes are information rate in the Lookup Table approach and the complexity in the Envelope Scaling Approach respectively.