A Channel Model Suitable for Employing Efficient Beam Steering on Tropospheric Communication Links

Abstract

Tropospheric communication systems find extensive use in both civil and military applications for long distance point to point communication. 21^st century warfare requires high performance tropo systems capable of supporting high data rates for real time communication between various fighting elements. Most of the research and development for enhancing performance of tropo systems, has been in minimizing propagation loss due to fast-fading of channel. Limited progress has been made to overcome slow, diurnal and seasonal, changes in troposphere, which lead to considerable signal attenuation. Beam steering can be used to minimize slow fading loss in tropospheric links, enhancing their performance. Transmitter and receiver antenna beams should be dynamically steered in order to point to the tropospheric heights that are most conducive for propagation at any given time, for receiving maximum power. This paper discusses prominent tropospheric channel models and examines their suitability for beam steering. Dinc’s ray-based model can be used for employing beam steering in tropospheric links. It employs a ray-based approach for determining powers received due to signal propagation at different tropospheric heights using real world data of atmospheric parameters obtained from NASA’s LIDAR experiment. However, Dinc’s model needs certain modifications for exact representation of tropospheric turbulence and its propagation characteristics. A modified ray-based channel model has been presented in this paper, derived by making required changes in Dinc’s model. Simulation results, showing a comparison of transmission loss obtained from modified model and Dinc’s model with widely used ITU-R P.2001 model, are presented in the paper for validation. The paper also presents calculation of received power for different heights using modified model, validating its suitability for beam steering. Real world atmospheric parameters have been obtained from Indian Meteorological Department (IMD) for validation process. Received powers obtained for different heights using modified model have been compared to determine the most favourable heights for signal propagation. Knowledge of favourable heights for different times of a day in different seasons, can be used to steer transmit and receive antenna beams towards the favourable heights, at any given time and day, resulting in efficient beam steering.