Research On The Method Of OFDM To Improve The Performance Of Underwater Long-distance Current Communication

The fixed-point observation platform based on inductive coupling transmission technology is the most important,reliable and stable method for long-term in real time observation of the ocean.With the development of marine biological information monitoring technology,higher requirements have been placed on the transmission performance of collected data.Among them,the influence of seawater channels on the transmission of electrical signals is crucial.Current transmission in seawater has the advantages of low probability of refraction and reflection,small path loss,fast transmission speed,and low underwater electrical noise.However,the physical characteristics of seawater medium and the infinite nature of the water space cause problems such as multipath effects and frequency selective fading in underwater current transmission,which limits the rate and reliability of long-distance transmission of current signals.The OFDM technology has the advantages of resisting multipath and frequency selective fading of seawater channels,improving bandwidth utilization and channel capacity.This paper analyzes the performance of underwater long-distance current communication system from four aspects:channel modeling,algorithm design,algorithm optimization and Peak-to Average Power Ratio of inhibition.Firstly,the vertical distribution characteristics and frequency characteristics of seawater conductivity were analyzed.Based on the conductivity characteristics,COMSOL was used to establish electrical signal transmission models of different depths.The simulation results show that the transmission of underwater long-distance current signals has the problems of multipath effect and frequency selective fading.Based on the simulation results,a 10-path transmission mathematical model is established.Second,OFDM technology is used to overcome the problems of multipath effects and frequency selective fading in signal transmission.In this paper,the long-distance underwater current communication system based on OFDM algorithm is simulated and analyzed from three depths of 300m,1000m and 2000m,and the transmission bandwidths of 2MHz,1MHz and 700k Hz are determined respectively.The OFDM algorithm combines channel estimation and compensation and bit allocation based on the principle of water injection to determine the optimal transmission scheme for the system,which can effectively resist multipath effects and frequency selective fading,and improve system performance.Simulation results show that the bit error rate at different depths can be reduced below 10^-4,and the channel capacity can be increaed by a maximun of 2.57bps/Hz compared with a single carrier system.Finally,the iterative limiting filter method is used to suppress the excessive PAPR of the signal.The simulation is carried out from two aspects:the effect of suppressing the PAPR and impact on the system reliability.The results show that the iterative limiting filtering method with 4d B and 4 iterations can reduce the PAPR to less than 6.6d B.The bit error rate can be maintained at a level of 10^-4.The results of this paper provide a theoretical basis for improving the performance of long-distance current transmission,and have practical research significance.