Design And Realization Of Digital Modulator In Underwater Acoustic Communication

Modern communication system is a land-sea-space three-dimensional communication network whose realization is mainly restrained by underwater communication. Acoustic is the only effective means available in underwater communication at present. The marine relaying communication platform that relay communication among under-water and above-water parts is an important component of it, which includes wireless communication subsystem and underwater acoustic communication subsystem. This paper mainly carries on the research of the digital modulator in underwater acoustic communication subsystem of this platform.This paper firstly introduces basic principles, development state and achievements of underwater acoustic communication. Then proceed from main factors that influence the system design, the paper explains the basic principles of FSK and Pattern Time-Delay Coding applied in our system and analyzes signal characteristics and realization of each method in detail. These discuss offers definite basis for the design of the digital modulator.Next, this paper discusses design of the digital modulator and especially analyzes design of modulating circuit. Common frequency synthetic technology is discussed briefly and basic principle and characteristic of direct digital frequency synthesize technology adopted in out design is investigated in detail. Then the scheme of modulating circuit is put forward, the structure that PC and the modulating circuit cooperate through serial connection is adopted, and module function is partitioned.Finally hardware and software are carried on to realize function of each module and embedded operate system μC/OS-II is utilized to support the software develop. Many laboratory-scale testing proves that the performance of the modulator has attained the design requirement and satisfied need of system. Moreover, to some questions existing while testing, some advices have been proposed.