Research On PAPR Reduction Algorithm In OFDM Systems

Orthogonal frequency division multiplexing(OFDM) system has been widely used in many mobile communication realms with the advantage of high spectral efficiency, simple accommodation to multiple users and capability of combating multi-path fading. Nowadays, it has been adopted in various wireless communication standards, such as IEEE 802.11a/g, IEEE 802.16, and Digital Video Broadcasting(DVB), and played a key role in the fourth generation(4G) mobile communication system. However, there are two main drawbacks of OFDM, the high peak to average power ratio(PAPR) and its sensitivity to the carrier frequency offset. High PAPR requires that power amplifier(PA) has wide linear dynamic range. When the transmitted data with large peaks are passing through PA, the signal may suffer from significant in band distortion, spectral spreading and consequently deteriorating the BER performance. PAPR problem of OFDM has restricted it from widespread adoption in future mobile communication system.Nowadays, the existing PAPR reduction algorithms can be divided into three types: coding, signal preliminary distortion and probabilistic methods. Probabilistic methods won't affect the BER performance of system, which is one of the main hot issues in the research of PAPR reduction. In this paper, we conducted research on PAPR reduction algorithms based on probabilistic methods. This thesis is structured around Tone Injection(TI) and Tone reservation(TR), and the main contents are as follows:On the basis of the traditional tone injection(TI) technique, a new dual-mode TI(DTI) method is proposed for 16 QAM in this paper. In DTI, the whole constellation is firstly divided into two parts, then each part performs its TI operation respectively, and two parts use the same equivalent points as extended points where the part with lower peak power is selected as the DTI plan. DTI takes the idea of dividing and conquering to decrease the dimension of problem and the peak power of signals. In order to get better PAPR reduction performance, the modified Taguchi algorithm with sigmoid limiting transformation is employed to seek the solutions which meets the needs of DTI. Besides, a restorable clipping-complement(CC) method is introduced to further reduce the PAPR of OFDM signals. CC is a tradeoff between BER performance and PAPR performance. Simulation reveals the effectiveness of the proposed method.To avoid the frequent IFFT/FFT operations brought by frequency-domain filtering, an improved filter free TKM-TR method is proposed on the basis of existing arithmetic. The improved TKM-TR method optimizes the scaling vector, which makes TKM-TR method suitable in lower CR situation. Besides, Intelligent Algorithm is employed to promote the performance of proposed method, PSO and ABC are devoted to seek the optimal CR threshold of TKM-TR method. Simulation results demonstrate that hybrid algorithm can further optimize the PAPR reduction performance.