QAM-based Study Of Cable Telemetry System

The high-speed cable telemetry system is an important component of imaging well logging that is used for the high-speed, real-time and accurate data transmission and is the"throat"of collection, transmission and controlling of data. The cable telemetry system has developed at full speed in recent years. In the l 980's Manchester coding is used in most cable telemetry system. while in the 1990's the information from the underground instrument is larger and larger with the appearance of perfect equipment and imaging well logging and the baseband system does not adapt to high speed transmission.In order to meet the requirements of imaging logging technology and a large number of underground information to upload, transmission adopted carrier transmission approach. After comparing several commonly used modulation, This design used an efficient QAM (quadrature amplitude modulation) modulation. On the base of this, according to the data flow analysis of cable telemetry system, the data protocol of high-speed cable telemetry system based on the QAM modulation has been designed. Adopt DSP, FPGA technology in the system, not merely improve the precision measured, improves systematic dependability, stability, and the one that has realized the data is real-time and dealing with at a high speed. Surface unit and host computer interface design of front with when use by CAN the buses, USB and RS232 at the same time. Before designing high speed transmitter system, the modulation process and demodulation process of QAM is simulated by MATLAB. Then C language and assembly language is used to design several programs such as QAM program, CRC verification program, control programs of DSP and so on.It has been proved that this new kind of telemetry tool is feasible and can be put into use.