The Research And Implementation Of OFDM Technology In NAVDAT Receiver System

Based on the research of GMDSS modernization trends and E-Navigation development strategies, a new high-speed digital broadcast system, called NAVDAT that proposed from the development of maritime communication is intensive studied in this paper, which focus on the study of its core technology - orthogonal frequency division multiplexing (OFDM). Meanwhile, combined with the software radio concept, the signal receiving and demodulation part of NAVDAT system based on ARM STM32 Cortex-M4 is designed in this paper.NAVDAT system use the similar operation mode with NAVTEX, which is the existing maritime communication system. NAVDAT working mode is that all the coast stations share a 10kHz channel with a special time slot, and a large number of sub carriers are modulated by OFDM and 16-QAM in the 500kHz band. Compared to NAVTEX system that used FSK, NAVDAT use OFDM to convert high-speed serial data into low-speed parallel data, which could improve the bandwidth utilization and the speed of data transmission.Through the research of the structure of NAVDAT system and OFDM principle, a signal demodulation algorithm, including the signal processing of training sequence, pilot signal and 16-QAM, is given in this paper. In this system, data extraction is designed with the technology of FATFS file system, USB HOST. And the DSP use the STM32F4 library for its FFT algorithm. At the end of this paper, a series of work is summarized including the introduction of the development platform and simulation and verification of the system.The conclusion of this paper will be helpful to the manufacture of NAVDAT receiver in the future, and the ideology based on the development trend of maritime communication will be useful to the modernization process of GMDSS.