Research On Underwater Acoustic Adaptive OFDM Communication Technology

With the advancement of technology, development of marine resources, offshore oil exploration, environmental monitoring and disaster warning and other underwater acoustic communication technology have been developing rapidly. Networking of underwater acoustic communication is becoming an important trend of development. Underwater acoustic communication network is designed to achieve high throughput, low energy consumption,and to maximize the use of channel with the fixed transmit power or a fixed bit error rate, that the underwater acoustic adaptive link became the hotspot. Orthogonal Frequency Division Multiplexing (OFDM) has a high spectrum efficiency and strong anti-multipath capabilities.The combination of OFDM and adaptive link technology can give full play to their technical superiority.This article increases the throughput of the communication system within certain bit error rate, using adaptive modulation and coding techniques. This article selected convolution coding as the channel coding scheme and analyzed it’s performance via theoretical derivation.Meanwhile, use MATLAB to study the improvement of performance to OFDM underwater communication.Firstly, proposed a suitable channel mode for adaptive communication system. The model turn the Doppler factor into linear variable within a period of time to keep the channel stable on tens of milliseconds after Doppler compensation (residual Doppler is negligible).Adaptive transmission technique adjusts the parameters of the transmitting terminal adaptively according to the channel status. This paper studied reasonable and effective criteria according to the assessment criteria that has been proposed. This paper chooses orthogonal matching pursuit (OMP) algorithm to estimate the contribution of a larger path of the channel to obtain channel state information (CSI). OMP algorithm can restore time-domain channel information and greatly reduce the complexity of the receiver design and energy waste with few observations.Secondly, the paper studies the adaptive modulation and coding (AMC) technology using in the adaptive link technique. Select the modulation and coding scheme (MCS) for each subcarrier according to the channel status appropriately which can improve the performance of OFDM system effectively. Three adaptive coding modulation switching algorithms were proposed and each of them were studied and simulated.Finally, the entire communication system was designed as a closed-loop. The paper introduced an SBLA (Simple Bites Loading Algorithm) in adaptive wireless communication to reduce the amount of data of feedback information. The tank experiments verified the reliabilities of the entire communication system and proven that the adaptive technology can greatly improve the conventional system on the bandwidth efficiency.