A Cognitive Module for Secondary Radios Operating at the 2.5 GHz LTE Band on Indoor Environments

The 2.5 GHz band is allocated to licensed systems of the LTE. Due to the propagation characteristics in this band, the signal is severely degraded by walls and other similar obstacles, making coverage in indoor environments difficult. While this is an issue for the purpose of providing LTE indoor coverage, it may also produce spectrum opportunities for secondary users. In this paper, we introduce a design of a cognitive module for secondary radios to operate on this band alongside the primary LTE users. This module leverages both statistical and Machine Learning methods to detect idle channel periods and to estimate for how long the secondary user may use the band. Based on real data of LTE channel usage in indoor environments, we propose a mathematical model for the length of idle periods and show that a small set of narrow-band energy sensors is enough to detect transmission opportunities.