A Bit-Wise XOR Method to Reduce Peak-to-Average Power Ratio for OFDM Systems

• Main Authors: Vuyan Huang, 黃富源
• Other Authors: 吳靜雄
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/83288013664599655105

碩士 === 國立臺灣大學 === 電信工程學研究所 === 93 === A wireless channel has some bad characteristics, such as large attenuation, interference, multi-path, noise, and so on. Orthogonal frequency division multiplexing (OFDM) is a good solution for the high data rate wireless transmission. With the advancement of digital circuits, the complex modulator can be implemented by inverse fast Fourier transform (IFFT). It also can resist multi-path interference by adding cyclic prefix (CP). Though it has many advantages, the primary drawback is its large envelope fluctuation, which is quantified by the parameters called Peak to Average Power ratio (PAPR) or Crest Factor (CF). The high PAPR of transmission system causes low power efficiency. Thus, it needs a high linearity power amplifier to avoid distortion. In practice, most transmission systems must meet their power constraint. In this thesis, we propose a multiple signal representation (MSR) method to reduce the PAR. We exclusive or the original data bit sequence with different pseudo binary sequences to get different new data bit sequences which represent the same data bit sequence, and then we transmit the lowest PAR data bit sequence among them. This method is easier and simpler than the other methods, and the performance of this method emulates the performance of Tone Injection and Tone Reservation with moderated complexity. For 128-tones 16-QAM OFDM system, our proposed method achieves 5 dB PAR reduction with 32 iterations, while Tone Injection and Tone Reservation can achieve 5-6 dB with moderated complexity. We also evaluate the BER of this system under the Additive White Gaussian Noise (AWGN) channel and utilize the side information as training sequence to implement a comb-type equalizer to decrease BER under Rayleigh fading channel. In our simulation results, we find that for 128-tones OFDM system with 8 iterations applied by our proposed PAR reduction method perform well under the Soft Limiter clipping model when input back-off is 8 dB (IBO=8 dB). Index Terms— Comb-type Equalizer, orthogonal frequency division multiplexing (OFDM), peak to average ratio (PAR or PAPR), Pilot Symbol Assist Modulation (PSAM).