Research Of High Speed Cabel Transmission System Based On Orthogonal Basis Multiplexing

Orthogonal frequency division multiplexing(OFDM)has been widely used in wireless transmission.It has become a hotpot to improve the transmission rate of logging and measurement while drilling(MWD)by applying OFDM in cable transmission system.This paper focuses mostly on the researches on cable channel modeling,peak to average power ratio(PAPR)suppression and orthogonal basis modulation.Applying electromagnetic theory and wave equation this paper has built a 7-conductor cable transmission modeling,introducing mutual resistance,mutual capacitance and mutual inductance.The transmission matrix and wave equation of 7-conductor cable has beed solved out.The black box analysis theory on cable is proposed and parameter A-matrix is introduced.The transmission characteristics of whole cable could be calculated with the input impedances measured with open-circuit and short-circuit.To suppress PAPR an improved realization method based on partial transfer sequence(PTS)is proposed.The range of phase factors could be predicted by calculating the difference of phases of adjacent data.A partial companding method based on tone reservation is proposed and implemented.The fomula of patial companding coefficient has beed developed in this paper.By comparing the suppression effect,error rate and outside bandwith radiation spectrum feature,the overall performance of patial companding superior to PTS.Patial companding leads to lower computational complexity than tone reservation,and is especially pertinent to high PAPR.The cable channel is narrow-band.In order to communicate at high transmission rate,it is necessary that either to improve the modulation method,or to expand the bandwidth.By introducing time-frequency analysis,multi-resolution modulation is proposed,which could make full used of each cycle waveform in each subcarrier to modulate signal,compared to OFDM which could only modulate one signal in each subcarrier.For the adjacent subcarriers the high frequency is twice higher than the low one.The scaling function in V0 sapce and wavelet function in Wj space are used to modulate the coefficient in the correspongding subcarrier.The orthogonality between the scaling function and wavelet function could ensure that the data of different subcarriers would not interference with each other and the data could be demodulated with an upper veracity.For cable channel,the fundamental frequency is set to 1 kHz,and the maximum usable frequency is 256 kHz.The number of subcarriers in OFDM is 256,and it is 511 adopting multi-resolution modulation.For OFDM the transmission is at speed up to 1 Mbps with quadrature amplitude modulation(QAM)modulation.For multi-resolution system the speed could be 2 Mbps when the coefficients are modulated with the same modulation method.The pilot structure and bit error rate(BER)of multi-resolution system also are studied in this paper.The multi resolution othogonal time-frequency multiplexing(MR-OTFM)scheme is proposed in this paper,which has simpler algorithm and lower amount of computions than the multi-resolution modulation.The coefficient of could be moudulated with two orthogonal basis functions.For 256 kHz bandwidth there are 511 waveforms modulated with 16-QAM,and the transmission speed could be up to 2Mbps.The transmission system which is moudulated with db4 wavelet packet has a good stability,and is especially permanent for the severe channel environments.For the cyclic prefix(CP)is not necessary for wavelet packet modulation,the transfer efficiency is as 1.1 times as OFDM.In order to expand the cabel bandwidth the Chebyshev amplitude equalizer and all-pass phase equalizer have beed designed for OFDM.The amplitude attenuation and phase shift can be effectively compensated.