A frequency-domain propagation model of bypass downlink system with transfer matrix method

Although many patents have introduced the principle of bypass downlink system for automatic drilling, and the downlink systems have been used to communicate from the surface equipment to the bottom-hole-assembly (BHA) for thousands of meters, there are few literature reports of propagation theory of the downlink telemetry. In order to increase the transmission rate of downlink system, it is necessary to study mathematical model of the downlink communication channel. In this paper, a frequency-domain model of the downlink communication for the bypass downlink system is established based on the transfer matrix method, which describes the relationships between the transmitted flow rate pulses from the downlink equipment on the surface and the received voltage signals from downhole turbine generator, and can be used to predict downhole signal waveform. The prediction result is compared to that of the method of characteristic (MOC) algorithm and validated by the experiments. Simulation and experimental results show that the proposed model is correct and feasible.