Research And Implementation On The Scheme Of Anti-jamming For Hydrologic Cableway Deepwater Communication Channel

Hydrological forecast provides reliable information assurance that is required tocontrol the floods and manage the water resource. In the recent years, with the technicalimprovements of hydrologic systems, the methods and technologies of hydrologicalforecast have been developed greatly. In order to solve the problem that the hydrologysampler invented by the research group of the Yangtze River upstream hydrologicalbureau has poor anti-jamming capacity, this thesis starts around the anti-jammingscheme of the hydrologic cableway deep communication system and the focus is mainlyon the half-duplex communication, the design of the launched chip, automatic gaincontrol, symbol synchronization and data de-spreading. Meanwhile, we put forward thecorresponding algorithm, the solution which utilizes the M-ary Spread Spectrum System,and the whole scheme of the hydrologic cableway deep communication system.Moreover, it succeed in software stimulations, hardware tests and field tests.This thesis analyzes the theory of anti-jamming, describes some kinds ofanti-jamming technology in brief, and discusses the features and the rationale of directsequence spread spectrum communication and the key performance indicators of spreadspectrum system. The description which involves the principle and the technology ofthe digital matched filter and the M-ary spreading and de-spreading provides the designof the system with a theoretical basis. For discontinuous communication, a kind of pilotsequence is designed to realize automatic gain control and quick synchronization easily.A data frame consists of the AGC sequence, the synchronization spread spectrumsequence and the message spread spectrum sequence and these three different sequencesare used for automatic gain control, synchronization and spreading and de-spreading ofthe message respectively. The scheme of quick and stable automatic gain control isdesigned to keep the signal amplitude at a certain extent. The matched filter is utilizedto realize rapid PN code acquisition, the acquisition time of which is much shortercompared to that of the traditional PN code acquisition based on sliding correlation, andit satisfies the requirement of the system which is to synchronize quickly. The timingenable signal indicates the de-spreading process of the message spread spectrumsequence and the method used for de-spreading is to search the phase in multi-channelwhich means that the16groups of local spread spectrum PN code are searched in themeantime to find the group whose phase is same as that of the received message spread spectrum sequence, and the original message is get through the original phase of thisgroup of PN code. What is more, we make the shoreside host machine and theunderwater machine transform their states between transmission and reception properlyto realize the half-duplex communication, which ensures the normal communication.Finally, Verilog HDL is used for hardware programming on the FPGA, timingstimulation is used to stimulate and analyze every module of the hydrologic cablewaydeep communication system and SignalTapⅡ Logic Analyzer which is an onlinedebugging tool of QuartusⅡ is used to test the overall performance of the system on thehardware platform and the results of the field tests taken in the hydrological stationconfirm the correctness of the scheme.