Research Of Multi-carriers Communication Technology Applied To Long Distance Single Cable

With slight cable core, convenient application in logging and low price, the single-core cable has been widely used in oil field logging as the medium connecting groundand down-hole instruments, both for transmitting data and providing electricity.However, as a result of its structure and length, the single-core cable only has a narrowtransmission bandwidth. Besides, due to its slow transmission speed and thecomplicated logging environment, data accuracy of single-core cable transmission canbe hardly reached. With the development of information processing and sensortechnology, the data volume delivered of logging is on the rise, which presents higherrequirements for cable transmission. Therefore, it becomes a significant issue to studycable transmission technology with high capacity, high efficiency and high accuracy.Against such a background, this thesis makes a model with PSpice for5000-kilometer-long single-core cable and analyzes the signal channel transmissioncharacteristics and noise features of the cable. Thus, it uses100kHz bandwidth toconduct convolutional encoding and error control coding of Viterbi coding to datadelivered, in the hope of enhancing error correcting capability of transferred data. As thehigh-band signal of the transmission cable weaken seriously, this thesis compares threedifferent digital modulation methods and employs OFDM multi-carrier modulationscheme to allocate the data to several sub-bands to improve band efficiency andtransmission speed.As the cable has a rather narrow channel bandwidth, symbol disturbance willfrequently occur, when it becomes serious, even destroying the orthogonality of the sub-carrier. This research studies signal channel estimation and symbol timing estimation.Since synchronization is an essential step of the OFDM system, this thesis usesmaximum likelihood estimation method of cyclic prefix, so as to ensure accuracy andavoiding inserting pilot frequency and occupying available bandwidth. The signalchannel estimation is based on training sequence estimation to obtain the power of eachsub-channel. Then, self-adaptive bit allocation, which uses water-filling algorithm, can be used on the basis of the estimated results. Signal channels with higher improvementwill carry more information bits on their sub-carriers. The results of bit allocation willbe applied in the future data transmission and the self-adaptive bit loading efficientlyimproves data transmission speed.