Underwater And Underground Current Field Communication System Design

Into the21st century, underwater and underground resources development has drawnincreasing attention. However, in the process of developing will encounter a variety ofcommunication difficulties. For example, how to make underwater salvage divers todetermine the target location, after the mine collapse, mine survivors how to get in touch withthe ground. All of these indicate particularly the importance to develop a wirelesselectromagnetic communications device that can be used underwater and underground. Themain task in this paper is to design an underwater and underground electromagneticcommunications system based on the current field theory, including a set of analog voicecommunication system and a digital communication system.Firstly the current field of communication theory is introduced in this paper, andhorizontal electric dipole is selected as a transmission antenna based on the current fieldtheory, the two plates of the antenna is infinite lossy medium in a region as a launch site area,to form a large equivalent loop antenna. The antenna matching circuit chooses matchingtransformer, whose design is according to the antenna impedance. Due to underwater andunderground communications frequency is limited in the VLF band, and the design of analogvoice communication system directly convert the voice signal to electrical signal transmissionwhich does not require the modulation and demodulation process, the short-range real-timevoice transmission using this method is quite effective. The digital communication systems inthis paper use the idea of software radio, modulation and demodulation and filtering processis completed internally in the DSP software. Modulation mode uses π/4DQPSK which hasadvantages of narrow band, high power utilization, fading, etc. The digital system hardware isbased on DSP, FPGA is used to configure the connection between TR600voice codec chipand PCM chip TLV320AIC10, meanwhile aid DSP performs to control TR600, as well as theoperation of the AD and DA. Digital system has SMS communication, and voicecommunications, voice communications can not transmit real-time voice signal, the signalmust be cached for some time first and then sent out which would have resulted in acommunication delay, but the TR600compresses the speech signal before transmission,making the delay time greatly shortened. Digital system has the PC software which cancommunicate with DSP via USB. The PC software is written by VC, including the sender and receiver two interfaces, which can set the parameters, including carrier frequency, symbol rate,the structure of the MAC frame, the transmitter power and receiver front end magnification,etc., the use of the software settings increases the flexibility of the system, it alsodemonstrated the advantages of software radio method. There are a variety of ways to loadDSP-start the program, USB boot loader mode is chosen in this paper, the load operation isdirectly integrated in the PC software, modify, debug, and download of the firmware hasbecome extremely convenient.