Enhanced Peak-to-Average Power Ratio Reduction Technique In 0fdm Communication Systems

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Addis Ababa University


The Orthogonal Frequency Division Multiplexing (OFDM) is a strong candidate for the current and future wireless communications system due to its high data rates transmission capability and robustness against multi-path fading effects. A major drawback of OFDM is its high peak to average power ratio (PAPR). Since most practical transmission systems are peak power limited, the average transmit power should be reduced for linear operation over the full dynamic range, which degrades the received signal power. In this thesis we review the most popular OFDM PAPR-reduction techniques and demonstrate in detail that Selected Mapping (SLM) scheme is a particularly promising reduction technique. In a SLM system, an OFDM symbol is mapped to a set of independent but equivalent symbols and then the lowest-PAPR symbol is selected for transmission. The tradeoff for PAPR reduction in SLM is computational complexity as each mapping requires an additional inverse fast Fourier transform (IFFT) operation in the transmitter. An enhanced SLM method is proposed for computational complexity reduction. The proposed SLM scheme transforms an input symbol sequence into a set of OFDM signals by multiplying the phase sequences by the signal after a certain intermediate stage of inverse fast Fourier transform (IFFT). The enhanced SLM technique reduces computational complexity by 48% while it shows almost the same performance of PAPR reduction as that of the conventional SLM OFDM scheme.



Electrical Engineering