Ofdm Peak To Average, Than The Suppression Of Critical Technology Research

With the rapid development of mobile communications business from traditional voice services to those video transmission and other multimedia services, how to use the limited available wireless spectrum resources to provide mobile broadband multimedia services has become a challenge to mobile communications technologies. Compared to the traditional single carrier technology, OFDM, with the advantages of high spectral efficiency and immunity to multipath fading, has been the physical layer technology in many wireless communication systems, such as 802.16e, LTE and 4G..However, High Peak-to-Average Power Ratio is a main problem in OFDM systems. Reducing PAPR efficiently is important to reduce the linear range requirements to D/A (Digital-to-Analog converter) and high power amplifier, also to lower power consumption and cut operating costs for mobile networks. That's a key topic for OFDM research. In this paper, two signal re-distortion methods-Constrained clipping and Active Constellation Extension- has been studied.The third part of this paper proposed Repeated Constrained Clipping (RCC) method and Variable Clipping Threshold and Distortion Area Value Repeated Con- strained Clipping (VTDA-RCC). RCC improves performance of PAPR reduction by increasing computational complexity. In different iterations, VTDA-RCC gets different values of clipping threshold and Distortion Area, implements the allocation of lower computation and less EVM resources for those OFDM symbols to easily reduce PAPR, and higher computation and more EVM resources for those OFDM symbols to hard reduce PAPR. On the conditions of 10 MHz bandwidth, 1024 sub-carriers, 16QAM constellation mapping, and the largest iteration number I_max= 10, when CCDF equals 10^-4 , VTDA-RCC method could reduce all the OFDM symbols'PAPR to 6.5 dB below, which is lower 2.3 dB than Constrained Clipping .The fourth part proposed Distortion-Controlling Active Constellation Extension (DC-ACE) method and the Re-Modifying Constellation Points Active Constellation Extension (RMCP-ACE) method. Compared to the original ACE, DC-ACE extends the Constellation Point Expanding Area. DC-ACE weights the constellation points being in the periphery of Constellation diagram by more than one times, and then goes to ACE or DC-ACE algorithm. On the conditions of 5 MHz bandwidth, 256 sub-carriers, QPSK constellation mapping, and the largest iteration number I_max= 5, when CCDF equals 10^-4 , After Re-Modifying Constellation Points, ACE could reduce by 1.2 dB more than the original ACE, and DC-ACE could reduce by 0.73 dB more than the original DC-ACE. Furthermore, because of Re-Modifying Constellation Points, CCDF cure of the output signal declines faster and the distribution of peak power points is closer.In the fifth part of this paper, two methods studied above were integrated to a new method, and was applied to IEEE 802.16e system in the simulation. The new method is based on ACE, uses the noise out of band to reduce PAPR, and in different iterations, gets different values of clipping threshold and Distortion Area, while, for the points in the interior of Constellation diagram, adopts the same algorithm as Constrained Clipping method.Constrained Clipping and Active Constellation Extension studied in this paper, is with good PAPR reduction ability and compatibility with the present protocols, could be implemented easily, and could be applied to IEEE 802.16e and other OFDM systems.