| HF communication plays an extremely important role in marine radio communications. Ships at sea maintain contacts with outside world through short-wave radio. The emergence and raise of the Inmarsat once let people have a question about the presence on the short-wave communication, but with the exposure of the limitation of the Inmarsat and the inherent characteristics of HF communication, people are convinced of the necessity of the HF communication. Since the 1980s, marine HF communication technology has greatly developed.Due to the increasing requirements of shipping business and communication, the maritime HF communication has gradually developed from traditional Morse telegraph to the Narrow Band Direct Printing telegraph and the high-speed data transmission. Since 02nd January 1992, when GMDSS started to be in the transition progress, all shipping enterprises have installed the NBDP equipment, in order to meet such a significant reform. The NBDP equipment, which is combined by the technology of digital communication and of computer science, joins with radio stations to form one of the main terminal equipments of earth communication system for GMDSS.This article firstly analyzes the development and the main characteristics of the maritime radio communication, and briefly introduces the concept and the main functions of GMDSS and NBDP. Then the components of NBDP equipment, encoding method, error correction technique and the two work mode ARQ and FEC are introduced respectively, in particular, the work principle and work process of ARQ and FEC in detail. The principle is the theoretical basis for the software design.Based on the working characteristics and process of ARQ and FEC propose a solution of software realization, including using server and client of SOCKET network simulates as the terminal of information sending station and information receiving station, using MFC for display and widget design to show the communication process clearly. On the basis of the theoretical principle and the solution, complete the encoding and decoding program of ARQ and FEC including phasing process, recognition process, communication process and ending process. Programmed by C++ and simulated in VS2005 environment, a good result is obtained by simulating the work process of the two modes on the SOCKET server and client network interface. |
