A Systematic Approach Of The PAPR Reduction In OFDM Wireless Communication Systems

Frequency spectrum becomes a more and more scarce resource day by day, along with the arrival of the so-called information society and the booming of wireless communications, especially mobile communications. In order to make the best use of the spectrum, many technical methods are proposed. Among many multi-carrier signal processing techniques for the next generation mobile communications, Orthogonal Frequency Division Multiplexing (OFDM) and the correlative technology by its high band-width efficiency, its robustness to multi-path and pulse noise, its high transmission speed, its ability of flexible modulation on sub-carriers in accordance with the channel conditions, its lower implementation cost, and so on, has obtained the widespread application in the multitudinous domains, been adopted as one of the key transmission technologies of the forthcoming fourth-generation (4G) multimedia mobile communication systems.One of the main disadvantages of OFDM systems is its large magnitude fluctuation of time domain signal, thereby occurs the high Peak-to-Average Power Ratio (PAPR) problem. Compared with the conventional single carrier transmission methods, high PAPR leads to a necessity for increasing the dynamic range of amplifier and Digital-to-Analog converter/Analog-to-Digital converter (D/A or A/D). If the linearity range of the system cannot fit the dynamic range of the signal, it will incur signal distortion, change the spectrum of the superposed signal, thus distort the orthogonality of sub-channels, result in mutual interference and worsen the Bit Error Rate (BER) performance of the system.This dissertation has thoroughly researched on this crucial problem of OFDM technology based on the proposed mathematical solution model.As the premise and foundation, a mathematical solution model on PAPR is proposed firstly. According to the above reasoning, some new algorithms are proposed from three aspects, i.e., the method of 'component modification', the method of 'new component injection', and the method of 'change of operational rule'. The method of 'component modification' changes the summing results by modifying operating component. The prejudge technique, the adaptive technique, the code restriction technique and the partial clipping algorithm are proposed in this dissertation. Some algorithms such as Clipping, Companding and Coding are analyzed firstly. Clipping is a nonlinear process and may cause significant in-band distortion, which degrades the BER performance, and induces out-of-band noise, which reduces the spectral efficiency. Companding Transform is an efficient method to reduce the PAPR by compressing large signals while enhancing small ones, whereas similarly has high BER problem. So, some new algorithms are proposed. The prejudge technique decides whether PAPR reduction methods should be adopted or not based on the prospective criteria. When the prejudge technique is used in conjunction with other PAPR reduction algorithms like Clipping, Companding and so on, PAPR reduction performance will be improved and the deleterious effects may be significantly reduced. By adopting adaptive algorithm, the adaptive technique automatically adjusts the parameters of PAPR suppression methods based on the prospective criteria and the actual communication conditions, and enables effective tradeoff between reduction in PAPR and other performance of the OFDM system automatically. Prejudge and adaptive technique can be applied to all other PAPR reduction algorithms, moreover these two algorithms can be combined to be employed. The code restriction technique is adopted to constrain every constellation point in certain region which approaches to the unclipped constellation point, thus reduces PAPR to fit the system's request and improves the BER performance. The partial Clipping algorithm first divides an OFDM signal into several blocks, then applies Clipping process to each block separately, finally merges these blocks and transmits it. This algorithm reduces linear dynamic range of the signal, avoids serious nonlinear distortion, and improves the system BER performance simultaneously.The method of 'new component injection' reduces PAPR by inpouring of new operating components. Since this kind of method has the problem with transmission and examination of side information, a novel scheme to deal with the transmission of side information and two simple and reliable algorithms on the examination of side information are proposed. Examples of existing algorithms include Partial Transmit Sequence (PTS), Selective Mapping (SLM), and Tone Reservation (TR). Their main difficulties lie in the transmission and examination of side information as well as high computational complexity. Whether the receiver can correctly recover the original information or not depends on the quality of transmission and examination of side information. Concerning the transmission of side information, as existing algorithms had not considered the problem of peak regrowth after inserting side information, a novel scheme to deal with the transmission of side information is proposed in this dissertation. This scheme not only solves the problem of peak regrowth and the problem of managing side information uniformly , but also helps to achieve frame synchronization. Making use of Coding theory, two simple and reliable algorithms on the examination of side information are proposed. These two algorithms are suitable for M-PSK (Phase Shift Keying), and show lower computational complexity and higher reliability.The method of 'change of operational rule' which solves the PAPR problem with changing the orthogonal transform pair of OFDM is proposed. The summary review on this method is proposed based on some related works. Also, it is the main direction for further research.In summary, this dissertation investigated the PAPR problem of OFDM systems, and proposed a mathematical solution model. Based on the analytical model, some new techniques and algorithms, such as the prejudge technique, adaptive technique, the code restriction technique, the partial Clipping algorithm, the novel scheme on transmission of side information, as well as two more simple and reliable algorithms on examination of side information, are proposed. Numerical experiments based on MATLAB affirmed the validity of these algorithms. The efficiency and versatility of some algorithms have high practical value. The further development and consummation of the algorithm system will be helpful to a comprehensive solution to the PAPR problem.