MIMO Spread Spectrum Underwater Acoustic Communication

Underwater acoustic channel is a complex wireless channel with time varying and spatial variation,and it is also a random channel with serious multipath effect,which will cause some loss of sound waves energy during transmission.These characteristics of underwater acoustic channel greatly limit the information transmission capacity of underwater acoustic communication system and seriously affect the performance of the system.Therefore,robust and high quality underwater acoustic communication has been faced with severe challenges.The spread spectrum communication system has the character of strong anti-jamming ability and anti multipath capability.It has multiple access capability to work under the low SNR condition.However,it is an obvious disadvantage that the system's transmission rate is too low in application.MIMO technology is a new communication technology in recent years,which can make use of space resources to improve the system capacity without increasing the spectrum resources and the transducer transmission power.In order to improve the quality of spread spectrum underwater acoustic communication,this paper will combine MIMO technology and spread spectrum technology to develop the MIMO spread spectrum underwater acoustic communication system.First of all,the basic principle of spread spectrum underwater acoustic communication technology and spread spectrum receiver algorithm for energy detectoris are studied in this paper,focusing on the research of the M-ary spread spectrum underwater acoustic communication system and combination spread spectrum underwater acoustic communication system.The combination spread spectrum system developed from M-ary spread spectrum system on the application of R-Complexity mapping mode in mathematics,compared with other spread spectrum communication,have multiplied transmission capacity.On the basis of these systems,this paper uses the differential energy detector and M-ary differential energy detector to overcome the gain loss caused by the carrier phase hopping interference,and time reversal mirror technique to reduce the impact of multipath interference on the spread spectrum communication system.The interference effect of energy detector and time reversal mirror technology is verified by simulation,which contribute to a stable and reliable spread spectrum communication system.Secondly,study the principle of MIMO underwater acoustic communication system and combine it with spread spectrum communication.The LS,MMSE and MP algorithms in MIMO channel estimation are studied to improve the performance of time reversal mirror in MIMO system.However,the simulation results show that in same combination condition the increase of transmission elements can lead to the decrease of the system performance.It is proposed to reduce the number of transmission transducers and reduce the number of devices by using the high-order combined spread spectrum based on the R-Complexity,which can achieve low error rate communication system.Then,it can further improve the communication rate of MIMO spread spectrum acoustic communication system.Finally,the communication coding mode,signal processing technology and communication system proposed in this paper are tested by river test,and the application details of the algorithm are explained in the actual data processing.By using the spread spectrum acoustic communication algorithm and MIMO spread spectrum acoustic communication technology proposed in this paper,the high quality MIMO spread acoustic communication is successfully completed in the experiment,and the feasibility of the coding mode and algorithm is verified.