Research On Several Key Issues For Video Adaptive Transmissions Over Underwater Acoustic Channels

With the development of marine economy,video transmissions over underwater channels have become one of the important issues both in industry and academic world.However,as the main medium for underwater middle-long range transmissions,the acoustic channels are featured with hostile characteristics,and have been an essential pain spot,which undermines the transmission performance.As a consequence,scholars have done a lot of work to tackle the bandwidth limitation,Doppler spread,etc.In order to transmit data more efficiently,a feasi-ble way is to introduce adaptive technologies.Therefore,this thesis dedicates effort to several key issues for the designs of underwater acoustic video adaptive transmissions.And the main research emphases are listed as follows:(1)Study the channel sounding and predicting technologies for underwater acoustic over-spread channels.To address the ineffectiveness of traditional channel sounding method on the overspread channels,this paper proposes a dynamic sliding sounding approach.Compared with the traditional method,the dynamic sliding sounding approach has a wider Doppler observation window,and avoids the aliasing phenomenon in the Doppler power spectrum.Once the channels are sounded,making full use of the cross-path covariance of the channel,a time series model based Kalman filter algorithm is used to predicte the channel response at future time.Furthermore,the information criterion of model selec-tion theory is adopted to find the optimal model order,which achieves a balance between model accuracy and computing complexity.(2)Study the adaptive designs of pseudo-analog video transmssions based on both channel state information and the importance of video content.Pseudo-analog video transmis-sions have graceful degradation property inherited from analog video transmissions,can be deployed using digital circuits on the market,and provide the potential to take into account the importance of video content.ECast is one of the few considering both the importance of video content and the channel state information in the designs,however it can not be applied directly in the underwater area.Therefore,this paper adopts OFDM block transmssion mechanism against underwater acoustic channels,does not ignore the interference between subcarriers,and tries to find the optimal precoding unitary matrix,power loading matrix and subcarrier matching matrix under the feedback of perfect and imperfect channel state information.(3)Study the adaptive designs of digital video transmissions based on channel state informa-tion.Video will be compressed into bitstreams by HEVC/H.265 encoder before transmis-sions,and then be encoded by error-control coding technique,where the rate is adaptively determined by the channel conditions.Based on two different types of feedback informa-tion,i.e.,full CSI and the second-order statistics of the CSI,this paper obtains the signal to interference ratio of each subcarrier through theoretical derivations.Then,an adaptive bit loading and power loading algorithm is proposed along with the optimal precoding design,which tries to maximum the transmission rate.