摘要
奈伏泰斯(NAVTEX)系统是以窄带直接印字电报方式发送和自动接收海上安全信息的系统，为保证船舶航行安全发挥着极其重要的作用，也是全球海上遇险与安全系统(GMDSS)中重要的组成部分。
近几十年来各种新技术的迅速发展为通信领域注入了新的活力，随着超大规模集成电路(VLSI)技术和计算机技术的飞速发展，数字信号处理(DSP)技术在通信领域中已经有了广泛的应用。
本论文研究的内容是基于DSP技术的汉字奈伏泰斯接收机的实现。
根据系统设计的性能要求，依据带通采样定理，本设计采用模数转换电路对奈伏0泰斯射频信号直接采样，采样值送DSP处理，通过数字带通滤波器获得低频端信号，再对该低频信号的采样值进行抽取、定时检测，从而完成对奈伏泰斯射频信号的解调译码过程。本设计采用了一种较新颖的译码方法，即基于快速傅立叶变换(FFT)算法检测2FSK信号的方法，简化了信息接收的过程，是论文的创新点。同时运用Matlab软件对奈伏泰斯系统进行性能仿真，以验证算法实现的可行性。独立完成了DSP目标板的设计与调试，实现了对汉字奈伏泰斯信号的正确接收。
本文所研究的内容适应当前海上移动通信技术的发展与更新，采用软件无线电(Soft Radio)技术，为汉字奈伏泰斯接收机的进一步研制提供了一定的理论依据，具有一定的实用价值。本设计的意义在于采用DSP技术和数字化电路设计，满足对接收机低功耗、高集成度和性能稳定的要求，以尽量简单的硬件平台完成系统的性能。
NAVTEX (NAVIGATION TELEX) is an international automated direct-printing service for promulgation of navigational and meteorological warnings and urgent information to ship. It will fulfill an integral role in the GMDSS (Global Maritime Distress and Safety System) developed by the International Maritime Organization and is already contributing to safety at sea.
The development of new technology accelerates the progress of communication. Along with the rapid growth of VLSI (Very Large Scale Integration) technology and computer technology, DSP (Digital Signal Processor) has been used widely in communications areas.
In this paper, the Chinese NAVTEX receiver based on DSP are studied and implemented.
Based on the performance requirement of the system, an analog-to-digital conversion circuit is adopted to sample the NAVTEX signal directly according as band-pass sampling theorem, and the samples are processed in DSP. Through a digital band-pass filter, the signal in low frequency is obtained and taken out. The whole process of demodulation and decoding is completed after the samples are timed and detected. A novel algorithm to detect the 2FSK (Frequency-Shift Keying) signal is adopted to make the signal receiving simple, that is the Fast Fourier Transform algorithm, and this is the innovation of the paper. At the same time, the paper simulates NAVTEX system's performances using Matlab to validate the feasibility of the algorithm. The design and debug of a DSP target board is finished all alone to implement the receiving of the NAVTEX signal.
The study in this paper is adapted to the development and change of current maritime communication technology and provides some theoretic foundation for more develop of Chinese NAVTEX receiver by using the Soft Radio technology. It is
provided with definite practicality. The significance of the paper is that it adopts the advanced digital technology and digital circuit design to meet the needs about low power consumption, high integration and steady performance of the system. That is to accomplish the system performance with the hardware as more simple as possible.
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