On the Investigation of Achievable Links for VLC based Wireless Downhole Telemetry Systems

In this study, the use of visible light communications (VLC) is discussed as a wireless telemetry solution for the gas pipeline downhole monitoring systems. A gas pipeline environment is emulated using Zemax software where we model a cylinder of 7 inches diameter along with a light source at the beginning of the pipeline and a detector on the other end with one-inch spacing from the pipeline’s edge. The coating material of the pipeline is specified as carbon steel, and properties of methane gas are considered in the simulation as similar to the real field conditions. We then perform a non-sequential ray-tracing method on the system with varying link distances, half viewing angles, and cut-off frequencies in order to investigate the effect of these parameters on the detected rays and the power received. Through MATLAB, we derived the channel impulse responses (CIRs) of the system, and according to these values, channel characterization is made by calculating the channel DC gain, path loss, root-mean-square (RMS) delay spread, and mean excess delay spread. Based on the investigations and results, at a certain bit-error-rate (BER), the maximum achievable link distances are observed for different modulation orders.