The Application Study Of Orthogonal Frequency Division Multiplexing Technique In UWA Communication

Narrow bandwidth and strong interference introduced by multipath are the main obstacle of the underwater signal's credible and high-speed transmission. Orthogonal frequency division multiplexing (OFDM) technique has both high spectrum efficiency and good ability to confront the multipath fading. Multiple input multiple output (MIMO) technique can increase spectrum efficiency and improve the system's transmit rate farther, but it is helpless for the frequency selection deep fading channel. If combine OFDM with MIMO, it will have two effect. First, realize high transfer rate. Second, realize strong reliability through diversity. OFDM and MIMO-OFDM are studied in this dissertation.The main content about OFDM is as follows.1. About the peak-to-average power ratio (PAPR) problem, the method of disturbing codes and adding a window to cut the peak value is brought forward and combined in this dissertation.2. About the synchronization problem, time-domain synchronization arithmetic and frequency-domain synchronization arithmetic are proposed, and some simulations are completed.3. About the channel estimation problem, kinds of schemes based on pilot are proposed, such as LS, linearity interpolation, Choi S I interpolation, Cubic interpolation, Lagrange interpolation, the interpolation method based on transform domain. And some simulations are completed.4. About the frequency deflection problem, another arithmetic called ICI self-cancellation is proposed, and the corresponding channel estimation method is given. The communication system about the method is simulated.5. Do experimentation in Song Hua Lake.The main content about MIMO-OFDM is as follows.1. About the coding technique, Space-time Block Coding (STBC) scheme is studied. The two transmitter one receiver STBC-OFDM system is adopted. 2. About the system synchronization, the special synchronization signal based on the improved back to back signal is brought forward. Then the coarse timing synchronization and fine timing synchronization are studied and some simulations are completed.3. About the channel estimation problem, the special pilot design scheme which is different from the SISO-OFDM's system is given, such as the overlap pilot design method, the interlaced pilot design method and the improved interpolation arithmetic based on DFT.In all, the study about OFDM technique is in the in-depth research phase, thestudy about MIMO-OFDM is on the basic research stage.