Optimization of PAPR in OFDM using Orthogonal Selective Level Mapping (SLM)
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Abstract— To optimize the PAPR in conventional OFDM, Low Complexity Selective Level Mapping (SLM) is considered in this paper as it reduces PAPR significantly without loss of information. Orthogonal Frequency Division Multiplexing (OFDM) is the multicarrier modulation techniques, and it provides the provides the high spectral efficiency, low complication in implementation, less sensitivity to echoes and distortion. Due to these advantages of OFDM system is vastly used in various communication systems. But the major drawback of OFDM system is increase in peak power due to coherent addition of sub carriers. OFDM signal is the sum of many independently modulated sinusoidal waves and the amplitude is almost Rayleigh distribution. Amplitude of OFDM signal shows strong fluctuations and the resultant high Peak-to Average. Several techniques have been proposed to reduce PAPR, Low Complexity SLM can be employed in this paper to reduce PAPR in an OFDM system. In Low complexity SLM, PAPR can be reduced by multiplying the original signal with Orthogonal vector and generate statistically independent sequences which represent the same information before IFFT operation in OFDM system. The resulting independent data blocks are then forwarded into IFFT operation simultaneously and generate OFDM signal sequences.
After that compute the PAPR for all the OFDM signal sequences. Finally, the one sequence with the smallest PAPR will be selected for transmission. The proposed SLM scheme achieves similar PAPR reduction performance with much lower computational complexity compared with the conventional SLM scheme. The performance of the proposed SLM scheme is verified with various modulation schemes. The results are simulated using MATLAB.
Keywords— Selective Level Mapping (SLM), OFDM, Peak to Average Power Ratio
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