Research On Key Technologies Of Physical Layer In 4G System

As the rapid development in wireless communication, higher and higher data transmission was required in many services. The conventional communication system with single carrier is hard to meet the desired performance of the system. We have to find other techniques to replace it to greatly satisfy user's needs for high-speed data transfer rate. Because of its good performance on anti multi-path interference and optimum spectrum efficiency, Orthogonal Frequency Division Multiplexing (OFDM) is regarded as the key technology of the physical layer in the fourth generation mobile communication system and plays an important role. So far, many communication systems have actively made use of this technology. However, a major drawback of OFDM technology is its high Peak-to-Average Power Ratio (PAPR), which makes the inter-modulation distortion and severely deteriorates the performance of systems. As so, how to effectively reduce the higher PAPR of the OFDM signals is rather an important issue. In the thesis the research is mainly around this problem.In the dissertation, firstly, the OFDM system including some fundamental theories and its key technologies are introduced. Then, the definition and distribution of PAPR is presented in detail. The paper summarizes the most popular three kinds of PAPR reducing techniques, including coding technique, clipping technique, and probability technique.In this paper, by analyzing the Partial Transmit Sequence (PTS) algorithm and sub-optimal PTS algorithm, two improved partial transmit sequence algorithms (Half-IPTS and Threshold IPTS) are presented. The Half-IPTS algorithm based on IPTS vastly reduces the computational complexity by giving the values of half the factors. The Threshold PTS algorithm weakens the amount of computation of traditional PTS algorithm through setting a fitted threshold. The paper makes deep simulations and analyses using Matlab software, The Matlab simulation results show that the proposed algorithms reduce the computational complexity with slight PAPR performance degradation compared with the traditional PTS algorithm.