Coordination of allocation measurements in OFDM based ad hoc overlay systems

With an increasing demand for mobile communications an efficient usage of the available spectral resources gains importance, since suitable frequency bands are limited. Although nearly all frequency bands are assigned to specified services and users causing a frequency shortage, measurements show that nevertheless there are a lot of unused spectrum holes in the time frequency domain, leading to an overall low spectral efficiency (M.A. McHenry et al., 2006). In this paper we consider an overlay scenario with an OFDM (orthogonal frequency division multiple access) based additional ad hoc overlay system operating in the same frequency band as the licensed system and exploiting the spectrum holes. Since spectrum sensing is a key issue for the coexistence of both systems we propose a method in the MAC (medium access control) layer for frame synchronization, enabling the coordination of allocation measurements. Furthermore, we point out some signal processing aspects regarding overlay systems.