Study On OFDM Technology Based On27.5-39.5MHz Frequency Band

OFDM(Orthogonal Frequency Division Multiplexing) is a high-speed transmission technology in wireless environment, the main idea is let the given channel into many sub channels in the frequency domain, hen use of the sub carrier modulation in each sub channel, and each sub carrier transmission in parallel mode. It belongs to the multi carrier modulation (Multi—Carrier Modulation, MCM) technology, but it strengthens the ability to resist frequency selective fading and narrowband interference, it also use the power control and adaptive modulation to coordination work. Channel27.5-39.5MHz band is fishing communication channel, with the development of fishery industry, the requirements for communication quality improved, so need to strengthen the construction of the frequency band signal. This paper based on the "fishing ship VHF FM radio telephone based general technical specifications", and the OFDM modulation as a tool to realize communication more convenient and safe.This paper takes TI Company DSP (Digital Signal Processing) chip TMS320VC5502as the hardware carrier, around the realization of OFDM system and the G.729speech coding, according to the parameters of IEEE802.11a and IEEE802.16to definition the design parameters.The first part is the first chapter of content. Introduce the speech coding and OFDM modulation, and declare the research institutions and significance.The second part is the second chapter to the third chapter of contents. First introduced the fishing channel and the necessity of the fishery radio can be fast and convenient communication. Then introduced the G.729speech coding standards and principles, analysis the pretreatment of the encoding process, the target signal calculation and fixed codebook search module, then analyzed the decoding module functions. Described the demodulation and modulation principle of OFDM, and describes the characteristics of wireless channel. At last analysis the OFDM system synchronization and channel estimation and other key technologies.The third part includes the fourth chapter and the fifth chapter. Declare the implementation process of OFDM and G.729speech coding on DSP in details. Give the principle diagram and software flow chart of the hardware implementation to realize OFDM and speech coding function, and introduced each device on hardware function, and also given the connection between components and DSP. Analysis the source code in speech coding part, and introduce the chip dedicated software development tools. At last use the software to come true each OFDM module.