Wimax Papr Inhibition Of Key Technologies

As a new member of the 3rd Generation mobile communication, WiMAX (World Interoperability for Microwave Acess) has aroused widespread concerns, because of its wide coverage and high-speed data access.Orthogonal Frequency Division Multiplexing (OFDM) is one of the core technologies of WiMAX's physical layer. OFDM has advantages of anti multipath interference and easy equalization; however, it also has inherent drawaback: high Peak-to-Average Power Ratio (PAPR). The high PAPR needs amplifier has wide linear dynamic range, which is hard and expensive to implement, so high PAPR has become the bottleneck of its commercial application. This thesis is interested in this problem.First of all, this thesis focuses on the PAPR reduction technology based on clipping method. By introducing the concept of Error Vector Magnitude (EVM) and comparing the difference between signal PAPR and effective PAPR, this paper proposes a novel PAPR reduction algorithm, named Adaptive EVM Clipping. This algorithm adjusts each symbol's EVM according to the input signal's initial PAPR, in the assurance that the average EVM meets the requirement of the specific system. That is to say, the higher input signal's PAPR, the larger EVM is adopted and vice versa. The simulation results show that with the condition of 2048 subcarriers, 64QAM modulation,EVM≤2% and CCDF=1×10?4, the processed signal's PAPR is no more than 6.5dB, and the BER performance loss is less than 0.3dB at level of BER = 1×10?2.Secondly, considering WiMAX's flexible bandwidth allocation, this thesis puts forward the concept of Multi-band OFDM, which is a superimposed multi-channel OFDM signal with different carrier frequencies and different bandwidths. Then, this paper studies the method of compositing the multi-band OFDM signals together and presents a novel compositing algorithm based on the subcarriers'orthogonal property and IFFT's linear superposition property. As all the compositing process is done in baseband, so it's easy and low-cost to implement compared with traditional IF or RF composting methods.Thirdly, this paper studies the multi-band OFDM's PAPR problems. Compositing multi-channel OFDM signals will induce peak regrowth; so in order to suppress the peak regrowth, this paper presents a Multi-band Adaptive EVM Clipping algorithm, which combines multi-band OFDM compositing process with PAPR reduction. By using IFFT compositing algorithm, the multi-band OFDM's PAPR problem can be changed into the larger single-band OFDM's PAPR problem. The simulation results show that with 64QAM modulation, EVM no more than 2%, the processed multi-band OFDM's PAPR is less than 6.2dB and the loss of BER performance is less than 0.5dB at the level of BER = 1×10?3.The research results of WiMAX's PAPR reduction can be directly applied to not only WiMAX's implementation but also other communication systems, which adopt OFDM as transmission technology, such as Digital Audio Broadcast (DAB), Digital Video Broadcast (DVB), and Wireless LAN and so on.