A method for evaluating coexistence of LTE and radar altimeters in the 4.2–4.4 GHz band

In response to presidential level directives to make additional spectrum available for commercial use, the United States National Telecommunication and Information Administration (NTIA) identified several government bands for consideration. One of the bands identified with potential for sharing with commercial users was the 4.2–4.4 GHz band. This paper examines the current use of this spectrum as a function of time and location and presents a methodology for evaluation of concepts for sharing between the primary and secondary users. The current incumbent use is aircraft Frequency Modulated Continuous Wave (FMCW) radar altimeters; whereas the proposed commercial secondary users are presumed to be small-cell commercial networks employing LTE technology. Since the performance of the radar altimeter is safety-of-life critical, a deep understanding of co-existence between these systems is necessary to evaluate whether sharing is feasible. This paper presents a method for evaluation of the potential for spectrum sharing between the ground-based LTE systems and commercial radar altimeters. The proposed harmful interference assessment strategy uses MATLAB TM and its associated LTE Toolbox along with aircraft location data obtained by monitoring the Automatic Dependent Surveillance Broadcast (ADS-B) signals which are available in real time from the airplanes to perform the assessment.