I. Introduction
Spectrum sensing to detect the presence of primary user transmissions is a crucial task for a cognitive radio system, which opportunistically accesses the spectrum once an empty subband is detected. Two basic approaches to spectrum sharing have been considered [1]: spectrum overlay and spectrum underlay. According to the spectrum overlay approach, the secondary users sense and identify unused frequency bands and use them for communication purposes. Thus, the secondary users (SU) are responsible for detecting the unused bands and they should vacate the spectrum as soon as the primary user begins its activities [2]. The underlay approach imposes constraints on the secondary users' transmission power level so that it can operates below the noise floor of primary users. In this paper we focus on the experimental evaluation of the overlay spectrum sharing.