Research On The PAPR Reducing Techniques In The OFDM Underwater Acoustic Communication System

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier parallel transmit technique. It has been a research hotspot in wireless communication field because of its remarkable anti-multipath performance and full bandwidth utilization in recent years.Due to multi-path propagation, and high temporal and spatial variability of the channel conditions, the acoustic signal distortion is very serious. The related problems of OFDM were studied in this thesis. Performance and feasibility of this technique were proved through simulation and OFDM-based acoustic communication trial.The main content of this thesis are as follows:1. The orthogonality of OFDM and realization principle of OFDM system based on IFFT/FFT was discussed and analysed. Researching on the impact of OFDM system caused by frequency offset, and a method utilizing cyclic prefix (CP) is presented.2. One major drawback of OFDM is high peak-to-average power ratio (PAPR). Reducing the peak-to-average power ratio (PAPR) technique was detailedly studied from pre-distorting technique and non-distorting two aspects of the algorithms. Limiting, C transforming, partial transmit sequence (PTS), selected mapping (SLM) and a new detection algorithms were discussed. The related improvement was realized after simulating and comparing.3. The algorithms which for reducing the PAPR were proved through pool trial. A graphical interface acoustic communication system was realized by using LabView. The performance of system was proved by the results of simulation study and lake trial.