Research And Implementation Of OFDM Adaptive Modulation And Coding Underwater Acoustic Communication Technology

Along with the increasing proportion of today’s social communication needs inthe military as well as civilian areas, the users’ requirements for the communicationquality and the communication efficiency are improving, this prompted largelybooming with the rapid development of new technologies in the field ofcommunication. At the same time, however, it also makes the growing tension on thelimited spectrum resources,so Orthogonal Frequency Division Multiplexing (OFDM)communication technology occupy an increasingly important position in the field ofcommunications because of its efficient use of the spectrum and superior performancein fighting against multipath propagation interference.In underwater acoustic communications, channel at different aquaticenvironment, different depths, different seasons have the different characteristics,.Andeven in the same channel environment,fading characteristics corresponding todifferent frequencies are different. This leads to a fixed modulation mode andparameter is difficult to meet the requirements of the different channel conditions. Sothe research on adaptive coding and modulation communication technology based onthe real-time channel feedback is particularly necessary.Firstly, the performance of OFDM technology with varied parameters wasdiscussed basing on simulations. Secondly, a set of OFDM communication scheme ofadaptive code modulation was designed which is based on channel environmentestimation of ray acoustics, SNR estimation algorithm of receiver, and adaptivescheme of bit allocation. In view of the different channel fading condition inmulti-carrier transmission, this scheme selects schemes of every subcarrier adaptively,which premises the high efficiency of channel with reliably transmission quality. Theperformance of transmission system was discussed in simulation environment andverified by experiment in lake. After that, a realizable adaptive modulation and codingscheme with hardware implementation was proposed, that is no longer take subcarrieras adaptive object, but consider overall quality of channel as the standard, and switchmodulation and coding method of all subcarriers adaptively. At last, theimplementation and experimental results was introduced, after which, problems andfuture improvement ideas were summarized.