High Efficient Underwater Acoustic Spread Spectrum Communication Telemetry Research

Sound wave is the only information carrier of long range transmission underwater.As a result,underwater acoustic(UWA)communication telemetry becomes the main technology of underwater information interaction.UWA channels are special and variable according to the inhomogeneous distributed of sea medium,bubble,marine animals,ocean current,internal wave and surface wave.The particularity of UWA communication relies on the specific characteristics of UWA channels.The available bandwidth is quite limited for the sake of the severe attenuation of sea medium to high frequency signal and the high level ambient noise of sea in low frequency.Furthermore,the limitation of transducer craft has lessened or degraded the utilization and efficiency of UWA bandwidth.The central frequency and bandwidth are variable function according to the range between the transducer and the receiver.Generally,the optimal central frequency and bandwidth will decease as the increasing of range.The UWA commun ication has faced huge challenging duing its doppler,multipath spread,time varying,frequency varying and space varying.UWA spread spectrum communication telemetry exchanges realiability with efficiency,which performs steady and reliable over intense time varying and fading channels.It is applied in robust UWA communication,middle and long range UWA communication,power limited UWA communication,security UWA communication and low detection probability UWA communication.Spread spectrum also provides multiple access ability for multiple user communication.But the conventional UWA spread spectrum communication occupies low data rate,and it can't meet the need of UWA large scale information interaction.This paper focuses high data rate UWA spread spectrum communication telemetry,and the article will discuss the probalility of high data rate spread spectrum UWA communication from the four aspects:generalized M-ary spread spectrum,multiple channel spread spectrum,multi-carrier spread spectrum,and UWA spre ad spectrum based on different sequences.Conventional M-ary spread spectrum and CSK spread spectrum are elements which consisits of generalized M-ary UWA spread spectrum.They can both ameliorate the limitation of spread spetrum gain to data rate to some extent as compared to DSSS telemetry.In another way,it can improve the data rate as equal to anti-noise ability.M-ary CSK spread spectrum UWA communication telemetry is proposed as a combined method in this paper.It can perform better in ameliorating the limitation of spread spectrum gain to data rate as compared with M-ary spread spectrum and CSK through the combination.Furthermore,self correlation and cross correlation properties of sequences are both utilized,and the data rate of UWA communication systme is enhanced.Multiple channel spread spectrum telemetry can enhance the data rate of UWA communication system multiple times.Quadrature double channel telemetry and multiple channel M-ary telemetry are discussed in this paper.It is proposed that quadrature double telemetry based on msequences which can combine code phase information in this paper.It is adpoted in CSK and M-ary CSK.The results indicate that it can enhance data rate efficiently in the condition of minimizing interference through quadrat ure double channel and combining code phase information.Multi-carrier telemetry can enhance frequency spectrum efficiency.High efficiency signal processing and equalization algorithm in frequency domain,flexible frequency spectrum designing and power allocation according to channel situation can be available.It will be explored that MFSK with lag carriers,frequency spread spectrum UWA communication system and generalized multi-carrier UWA communication in this paper.The results indicate that multi-carrer system can perform better with the same power.Every kind of UWA spread spectrum communication scheme owns its corresponding optimal pseudo sequences.First,aiming at the problem that CSK system based on sequences can't utilize code phase information fully,this paper has proposed CSK UWA spread spectrum based on Lengendre sequences from the aspect of improving sequences,and it has been evaluated effectively.Second,PPM UWA spread spectrum communication system based on N-H sequences is proposed since it utilizes aperiodic self correlation property.Furthermore,virtual time reverse mirror technology is adopted.Then,the influence of different code phase to UWA spread spectrum communication is studied,and a variable data rate UWA communication system based on different code sets is discussed.