Measured Antenna Pointing Errors for Frequency Coordination of SATCOM On-the-Move Terminals

We analyze the pointing accuracy of two different antenna types of Satellite Communications (SATCOM)-on-the-Move (SOTM) terminals. We measured the antenna de-pointing in azimuth and elevation in a laboratory environment with the SOTM terminal mounted on a motion emulator fed with the terrain profile of the famous Churchville test track of the Aberdeen Proving Ground. Based on the measurements, we model the motion induced antenna de-pointing statistically by a stable distribution with parameters according to a Levy distribution. The parameters are dependent on the antenna type and tracking algorithm. Moreover, for both terminals we determine the effective isotropic radiated power (EIRP) density projected on the geostationary arc in dependence on the antenna de-pointing. We compare these off-axis EIRP densities with coordinated limits of the International Telecommunications Union (ITU) and determine the probability of exceeding the off-axis EIRP density limit. Large de-pointing values occur only for small fractions of time but force the SOTM terminal operator to significantly reduce the EIRP to stick to the ITU limits. As an alternative we propose a change of the frequency coordination process, suggesting a probability based approach that allows ITU mask violations for a predefined percentage of time in favor of an efficient usage of the available terminal EIRP.