The Research And Realization Of Multi-Carrier Modulation Method Based On The Low-Frequency Elastic Wave Channel

The theme mainly focused on the problem how to apply Orthogonal Frequency Division Multiplexing modulation technology to the low-frequency elastic wave through-the-earth communication system which takes the layered earth for transmission medium. Through the OFDM modulation technology, the binary message is modulated to the low-frequency elastic wave.After the modulation, the signal can resist attenuation characteristics of the earth channel effectively and multipath effect caused by reflection and refraction when elastic wave transfer over the channel.This paper first introduced the related principles of OFDM and digital modulation mapping technology, etc. Then the system frame of OFDM modulation system is given. This paper emphatically introduces the basic principle of Key link such as serial to parallel converter (parallel to serial converter), IFFT/FFT transform, Adding Cycle Prefix (Removing Cycle Prefix). Basic principle of three kinds of digital modulation mapping way is introduced, and the signal space between them is compared.According to the information, channel model is established. The related parameters of OFDM modulation technology for low-frequency elastic wave channel is obtained according to the model, meanwhile, the corresponding digital modulation mode is selected. Then the Rayleigh multipath channel model is established in MATLAB simulation environment through the OFDM related parameters based on the conclusion above. By means of simulations analysis which is based on the OFDM modulation technology for low frequency signal, the feasibility of OFDM modulation technology in the low-frequency elastic wave channel is confirmed.Based on the above-mentioned study, the hardware design and software design based on ARM9 core2440 is carried out under the condition available in laboratory.Then the system structure of hardware and framework of the software is also discussed. Finally the D/A Circuit design based on the MAX-530 and the algorithm in C language of the key modules are realized. In this theme, the modulation scheme of the low-frequency elastic wave through-the-earth communication system and the realization related to the system for hardware and software is a great platform for the further work. The result provides available experience in future to use the technique.