Research On Underwater Wireless Optical Communication Based On Analog Digital Signal

With the progress of science and technology in marine resources exploration and development, our country has made some achievements in seabed resources detection, underwater sensor networks, Underwater Unmanned Aerial Vehicle(UAV) and nuclear submarine. These achievements are inseparable from the information of underwater wireless transmission. At present, underwater wireless communication can be divided into three types, which are long wave communication, underwater acoustic communication and optical communication. Optical communication transmits information with the blue-green laser as vehicle, Compared to other means of communication, it can carry more capacity, big communication bandwidth, being confidential and small volume, which not only can overcome the shortcomings of the long wave communication as well as underwater acoustic communication’s disadvantages of large volume, poor secrecy and so on. But also can through the water air interface to accomplish the air against underwater wireless information transmission. Therefore, it has important significance to study the underwater wireless optical communication system.This paper firstly analyzes the water channel of light attenuation effect. Test the laboratory transmission channel attenuation coefficients by using a power meter. And compare the measured attenuation coefficient of the same wave against that in different ocean. Basing on the analysis of the transmission channel attenuation coefficient, slot error rate, information transmission capacity and bandwidth requirements were compared and analyzed, which are from different modulations for optical wireless communication emission power under water. The above promotes that the hardware implementation based on OOK(on-off keying) modulation is the simplest and most available about bandwidth. Especially the PPM(pulse position modulation) modulation optical transmitter power and slot error rate were the lowest.Secondly, according to the completion of a theoretical analysis, we designed the underwater wireless optical communication system with the technology of OOK. It is programmed by LABVIEW software programming environment. It accomplished the lossless transmission of text information in the condition of the laboratory transport.And then, after the realization of OOK modulation underwater wireless transmission, we continue to take the FPGA(Field-Programmable Gate Array) development board, basing on the PPM modulation, to transmit the text messages under the water accurately. We succeed to touch the emitted light average power about the two modulation, in the same transmission rate, interval and contents. Conclude that the transmit power based on the PPM is far less than the OOK. Furthermore, the anti-interference ability of the pulse position modulation(PPM) is much larger than the OOK modulation.Finally, we acquired the methods of voice signal underwater transmission based on both the analog modulation and the pulse width modulation(PWM). When sending the same message from the transmitter to the receiver, we analyzed the light emission power of the sender and the received waveform of the receiver and prove that the PWM modulation than the analog modulation has higher anti-interference ability and higher optical power utilization. In addition to, based on the analog modulation, we come true the underwater real time wireless optical transmission for the analog video signal.