The Research Modulation Technology Of Elastic Wave Through-the-earth Communication Based On Ofdm

In this paper, the importance of the elastic wave modulation technique in the through-the-earth communication system is analyzed, based on a number of related references. The present development situation of wireless communication and modulation technology in complex environment are presented. The elastic wave through-the-earth communication system aiming at the transmission characteristics and attenuation in the earth channel is designed, with the analysis and studies on OFDM modulation technology of elastic wave.This paper mainly studies on how to suppress PAPR, selecting OFDM modulation parameters, dividing subcarrier, selecting subcarrier modulation modes, subcarriers'bit allocation merger, and channel coding. After analyzing and comparing encoding method, scrambling code method and amplitude clipping method, the amplitude clipping and peak window technologies are chosen to suppress elastic wave's PAPR problem, so that the complexity of the through-the-earth communication system and the impact on the transmission rate will be reduced. The multipath time delay is analyzed according to elastic wave transmitting track in the earth channel. And guard interval length and OFDM signal circle length are established to ensure the system transfer rate and spectrum availability ratio. After analyzing and comparing MQAM and MPSK modulation, according to the earth channel's attenuation specification, MPSK modulation is slected which has better ability in anti-noise. On the basis of calculating OFDM modulation parameters and frequency band suitable for elastic wave through-the-earth transition, subcarrier intervals are figured out and the elastic wave frequency band is divided into ten subcarriers. On the subcarrier's modulation and number, Fischer algorithm with less bit error rate is selected as subcarrier bit allocation algorithm. Combining with OFDM modulation, Turbo encoding is as the channel encoding scheme which can ensure high transfer rate under lower SNR circumstances. Finally the simulation is made and the simulation results are analyzed.OFDM modulation technology in the elastic wave through-the-earth communication is studied in this paper, which lays foundations for the application of elastic wave through-the-earth communication. However, because of the complex earth channel, the elastic wave modulation needs further research.