Research On Underwater Acoustic Fax Communication

Underwater acoustic channel is a complex time-, space- and frequency-variant channel, which is restricted by numbers of negative factors, e.g. narrow band, high ambient noise, multipath distortion and deep fading. Based on this most difficult wireless channel, underwater acoustic communication therefore becomes one of the most complex and challenging research directions in the field of underwater acoustic technology.Underwater acoustic Fax communication is a new application of using Fax communication into underwater acoustic area. This paper makes a primary exploration into this new application field.Fax machine is a widely-used electronic equipment in offices. The significance of Fax lies in the transmission of multi-page text pages and the accurate reconstruction in receiver. Besides this classic significance of Fax, underwater acoustic Fax communication has its own special significance: Under bad channel conditions, pure data communication is hardly to be implemented. In this case, Fax communication, which is based on the principle of serial image scanning transmission, provides an alternative method of data communication by the way of text reconstruction in receiver.This paper constructs an underwater acoustic Fax communication system and implements the design of PC Fax software and the design of underwater acoustic Fax modem.Taking account of the multipath of underwater acoustic channel and the special redundancy of Fax files, this paper designs special compression/decompression and modulation/demodulation algorithms. The programming of Fax software is realized on the platform of Borland O+ BuilderS.O, with the application of a large amount of VCL components and Win32 API functions.This paper adapts TI's DSP TMS320C542 as the core of underwater acoustic Fax modem to realize the digital frequency synthesizer, modulation, and Goertzel spectral analysis demodulation. TLC320AC01 is used to realize the interface of DSP and analog signals. As to the communication between DSP's synchronous serial port and PC's asynchronous serial port, the paper designs a special DSP algorithm to realize this compatible communication with a software interface.