PAPR Reduction Of OFDM System Using Tone Reservation Algorithm

Orthogonal Frequency Division Multiplexing (OFDM) is one of the most cheering developments of modern broadband wireless networks. By dividing the total channel into a lot of small overlapping frequency sub-channels, OFDM can handle multi-path propagation efficiently and the robustness against frequency selective fading interference is increased. The precious spectrum is made full use of at the same time. To avoid the interference between sub-carriers so as to keep the orthogonality, the cyclic prefix is introduced.However, in OFDM system, the signals have a large dynamic range which tends to arouse nonlinear distortion when the signals go through the amplifier. A large PAPR (Peak to Average Power Ratio) will need power back-off of the power amplifier, so the efficiency of the power amplifier is reduced. A large PAPR also increases the complexity of the analog-to-digital (A/D) and digital-to-analog (D/A) converters. In addition, the nonlinear distortion can deteriorate the bit error rate (BER) of OFDM system. The PAPR problem is the bottleneck of the application of OFDM system.The paper summarizes the conventional algorithms and fully discusses the tone reservation (TR) methods. After that we present a TR method based on FFT/IFFT and its modified scheme. Significant PAPR reduction can be achieved and only a few iterative operations are needed. Different from the TR method studied above, we abstract the reserved tones'data randomly after the FFT. The new abstract way outperforms the existing scheme. And then we propose to replace FFT by the fast discrete cosine transform (FDCT) which could reduce the computational complexity. Moreover, the experiments prove that the BER will not be affected and higher PAPR reduction can be achieved. Multiple input multiple output techniques combined with OFDM (MIMO-OFDM) also has the drawback of large PAPR. Instead of reducing the PAPR at each transmitter separately, a peak canceling signal is generated at one antenna by using the DCT/IFFT structure and is then applied to the other antennas with simple modifications according to the STBC (Space Time Block Code) property. The simulation result shows the effectivity as well as the practicability.