Design And Realization Of The Control Unit For VHF Radiotelephone

VHF radiotelephone (Very High Frequency Radiotelephone) is a short-range communications tool on maritime mobile communications; it is also an important component of the Vessel Traffic Management System (VTS,Vessel Traffic Servises). It plays an important role on the ships' communications on the sea. It can make a call when in distress,urgency,safety communications or daily business communication. In accordance with the requirements of the SOLAS Convention, ships in any of the voyages should be equipped with the VHF radiotelephone after implementation of the GMDSS.Traditional VHF radiotelephone communicates with other ships in analog method, it is simple, but the communication quality is poor and is difficult to be controlled. With the development of semiconductor technology, the VHF communication is digitalized gradually.This paper proposed digital VHF radiotelephone communications system based on that,improved the VHF radiotelephone circuit of control unit based on the existing RF front-end circuitry, some parts of the analog circuit was integrated into DSP. The main idea of this paper is: the sampled speech signal is encoded with excited linear prediction (CELP, Code Excited Linear Predictive) and then is modulated in FSK signal in the transmit circuit.In the receive circuit, the corresponding FSK demodulating algorithm and CELP decoding algorithm is used to reconstruct the speech signal . Meanwhile, some analog baseband voice processing circuit (such as audio muting, pre-emphasis, de-emphasis etc.) is integrated into DSP in order to simplify the hardware circuit through software programming methods.Not only local VHF radiotelephone control unit is designed but also USB communication interface and Ethernet communication interface are added in this paper.They are designed for exchanging data with the ship's voyage data recorder (VDR) which is useful to analyze the cause of the accident or maritime disputes by calling back the data stored in VDR.The ADI's latest dual-core DSP ADSP-BF609 is used as he main controller of the VHF radiotelephone control unit in this paper.At first, some voice processing knowledge is briefly introducted, and make a choice by comparing the various voice codec algorithm. Then make a lot of work on the CELP codec algorithm and FSK modulation and demodulation algorithm theory which is suitable for my design, and some related formulas were deduced.After designing the hardware circuit schematic and PCB circuit board,hardware debugging should be done. CELP speech codec algorithm, FSK demodulation algorithm, CODEC, audio AD DDS and related voice processing program are written in the integrated development environment CCES (Cross Core Embedded Studio) based on the hardware platform. Finally,debugg the system and analysis the results,the feasibility of the design is verified.