Realization Of The Maritime Mobile Communications System Based On The Ad Hoc Network

Wireless Mobile Ad Hoc Network(Ad Hoc) is built on specific occasions. It's a temporary system composed by mobile nodes with wireless receiving and sending functions. It also can constitute arbitrary network topology through wireless communication. VHF communication system is widely used in Offshore and Inland Water Transport. It is one important component of the vessel in distress and security communication system, also it's an indispensable communication methods in Navigation Administration and Maritime Search and Rescue. With the development of the shipping industry, the amount of data transmission demand increases, the capacity of VHF channel becomes more congested, and the interval of channel becomes smaller. Thereby it's necessary to reduce the bandwidth for the sake of saving the precious channel resource and improving the availability of the communication system channel. The technology of speech coding plays an important role in carrying out this target. In this thesis, a kind of low-rate voice compression/decompression communication system is designed and realized, which can be used in maritime VHF communication system.First of all, the basic theory of voice coding/decoding is introduced in this thesis. Then it introduces several typical voice coding/decoding algorithms and theirs respective advantages as well as theirs application conditions are proposed. It also illustrates the reason for choosing Multi-band Excitation Vocoder as the research objects. The basic theory,parameter pick-up and voice synthesized of the multi-band excitation is mainly analyzed. Also, it gives a brief introduction for advanced multi-band excitation algorithms.Secondly, a hardware voice compression/decompression system is designed and realized in this thesis. The idea of the hardware and software of system are particularly introduced. The hardware part of system considers the voice compression/decompression chip AMBE-2000 and SCM chip C8051F020 as the core, the other function chips comprises the external circuit, which can realize the function of voice signal sampling, compression/decompression coding, signal transmission and so on. In the software part of system, we chooses the SCM chip C8051F020 as the manipulative core. C8051F020 receives the 2.0kbps compressed voice data from AMBE-2000, extracts the effective data , combines into the system data stream, sends over the transmission path.Lastly, this thesis gives the experimental results, also it gives the waveform trajectory map , which measured at using voice compression/decompression chip several major pins normal working by oscilloscope. The experiment results indicates that this voice system can provide a good voice transmit, also the voice can be heard clearly. The future work is how to perfect the voice compression/decompression system.