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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.

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Cooperative coherent systems are well-known in radar and countermeasures communities where the transmitter and receiver antennas are co-located on the same platform; hence, the radio frequency (RF) sources are synchronized and the physical separation of coherent systems is limited or confined within the same platform. To improve the effectiveness of cooperative countermeasure systems, it is highly desired to significantly increase the physical separation between cooperative elements. In this paper, we study a non-coherent cooperative RF system where the cooperative elements are located on two separate platforms without hard-line connections to them. Hence, the cooperative signal exchange among multiple cooperative elements has to be transmitted via an RF link and the non-coherent cooperative system would allow the RF source to be located on a separate platform, thus increasing the physical separation. The two cooperative elements are operated with two separate local oscillators, which leads to large non-coherency between multiple platforms.