Patent ID: 6175599
Filing Date: 2001-01-16
Classification: H04L

Abstract:
A method of transmitting digital data acquired in an oil well logging operation from the downhole logging instrumentation to the surface over a logging cable, comprising the steps of:acquiring the digital data downhole from one or more downhole logging instruments at a symbol rate;modulating an analog carrier waveform with the acquired digital data using a quadrature amplitude modulation technique comprising the substeps ofmapping the acquired digital data as a series of symbols at a symbol rate where a unique sequence of digital bits is represented by a symbol and each symbol is indicative of a point in signal space,outputting the symbols as two streams at a sample rate representing the x and y coordinates in signal space of the symbols, the sample rate being an integer multiple greater than 1 of the symbol rate,multiplying a first carrier signal by the x coordinate stream to obtain a first product,multiplying a second carrier signal, orthogonal to the first carrier signal, by the y coordinate stream to obtain a second product, andadding the first and second products to produce a sampled waveform;converting the sampled waveform to an analog QAM waveform; andtransmitting the analog QAM waveform over the logging cable to a surface receiver.