In this paper, we present a software defined radio (SDR) based cognitive radio implementation and demonstration. Using GNU Radio and USRP SDR boards, we implement and demonstrate a cognitive radio that detects spectrum holes in the FM band and exploits the available spectrum holes to transmit digital and analog data without interfering the existing FM transmission. Moreover, we demonstrate that when a primary user's transmission starts over the original spectrum holes, the cognitive radio automatically adapts its transmission to avoid interference to the newly coming primary user. Additionally, we have implemented and demonstrated a frequency hopping over multiple spectrum holes to support multiple secondary users with minimum interference to each other.

In this paper, we present a software-defined radio (SDR) based cognitive radio (CR) implementation and demonstration over the frequency modulation (FM) band. Using GNU Radio as the software platform and USRP (Universal Software Radio Peripheral) SDR boards as the hardware solution, we implement and demonstrate a CR that autonomously senses the entire FM band, detects all the active FM stations (occupied bands) as well as the spectrum holes (non-occupied bands), exploits the available spectrum holes to transmit secondary users' data without interference with the existing FM transmission. Moreover, we demonstrate that when a primary user's transmission returns to its allocated spectrum band after a period of absence, the CR automatically adapts its transmission and hands off to a different spectrum hole that is available to avoid interference with the returning primary user. Moreover, we have proposed, implemented, and demonstrated a frequency hopping scheme over multiple spectrum holes to support multiple secondary users while attaining the minimum interference among the users.to the fact that spectrum congestion is mainly caused by the inefficient use of spectrum rather than the scarcity of spectrum [1]. Therefore, new technologies are needed to exploit the vacant spectrum bands and to improve the spectrum utilization in dynamically changing environments. Cognitive Radio (CR) [2] has arisen to be an appealing solution to the spectral crowding problem by enabling the opportunistic use of frequency bands that are not heavily occupied by licensed users [3].