Research On Peak To Average Power Ratio Technology In OFDM System

OFDM (Orthogonal Frequency Division Multiplexing) is a parallel transmission scheme of MCM (Multi-Carriers Modulation). It transmits information through orthogonal multiple sub-carriers and has high utilization of frequency spectrum, good capability of countering multi-path interference. It is also adaptive to high-rate data transmission and multimedia data transmission. This technology has been regarded as the core technology of 4G wireless communications system in the future. However, a major drawback of OFDM signals is their high PAPR (Peak to Average Power Ratio), which makes the inter-modulation distortion occur. The distortion severely deteriorates the performance of the OFDM systems. So, how to effectively reduce the PAPR of the input OFDM signal is an important issue, which needs to be solved in OFDM systems. According to the problem mentioned above, this dissertation focuses on reducing PAPR algorithms design for OFDM systems, and being testified with MATLAB simulations. Around all these aspects, makes such efforts as the followings below:1. The principle of DFT-based OFDM system, key techniques, advantages and disadvantages of OFDM technology are analyzed in this thesis.2. The reason of high PAPR is deduced in this paper, the definition and distribution of PAPR is presented in detail. On the basis, the paper makes deep analysis on simulation, and summarizes the most popular three kinds of PAPR reducing techniques, including pre-distorting technology, coding technology and scrambling technology. Also, the paper makes thorough compare of these methods. Particularly, strong emphasis is cast on PTS (partial transmit sequences), which belongs to the scrambling technology. Though, the PTS method possesses the advantages of anti distortion, not being limited by the number of carriers, less loss of frequency spectrum. However, the most serious flaw of PTS is the heavy complexity of computation, which strongly restricts the application of PTS method. Thus, it is very significant to propose improved methods, which could not only reduce the PAPR of OFDM systems effectively, but also possess low complexity of computation.3. A deep discussion is presented around the issue of how to reduce the calculation complexity in PAPR reducing methods. From different angles, several well accepted improved schemes are deeply analyzed and researched, which could not only reduce the computational complexity, but also keep good performance of OFDM systems. The improved methods include: (1) Considering of the particular characteristic of interleaved partition method, it can be used to reduce the PTS's complexity. (2) Iterative PTS is proposed from the point of assistant weighed index, which reduced computation complexity by a long way. (3)Synthesize the PAPR performance and system complexity, double PTS is proposed, which has a structural innovation to optimize assistant weighed index. The paper makes deep simulation and analysis using MATLAB software. Simulation result shows that these schemes, which are less complex and more easily implemented, suffer little PAPR performance degradation.In the end, makes a thorough summarization of the efforts in this dissertation, and analyzes the achievements and insufficiencies that need to be improved later. Besides, makes an expectation of the further work.