Method and apparatus to train telemetry system for optimal

Abstract

A telemetry system employs a periodic pseudorandom training sequence to effectively initialize an adaptive digital FIR filter-equalizer for optimal communications between a surface modem and downhole measuring equipment, without requiring any changes to the normal logging configuration or any special operator intervention. In a 'training mode', an electronic source in a downhole sonde transmits a predetermined training sequence to a surface modem via a cable. The source preferably transmits the training sequence continuously until the surface modem has acclimated itself to the characteristics of the multiconductor cable by adaptively configuring the filter-equalizer, thereby enabling the surface modem to accurately interpret data received from the sonde despite attenuation, noise, or other distortion on the cable. The filter-equalizer adjusts itself in response to an error signal generated by comparing the filter-equalizer's output with a similar training sequence provided by a training generator. After the surface modem is trained, the system operates in an 'operational mode,' in which the sonde transmits data corresponding to downhole measurements, and the filter-equalizer's error signal is generated by comparing the filter-equalizer's output to a sliced version of the filter-equalizer's output. In this mode, the filter-equalizer continually adjusts itself to most accurately receive and interpret the data.