  In this paper we propose a novel adaptive scheme for full duplex
communication of secondary users (SUs) in a cognitive radio network. The
secondary network operates in three modes; Cooperative Sensing (CS), Full
Duplex Transmit and Sensing (FDTS), and Full Duplex Transmit and Receive
(FDTR). In the CS mode, the secondary nodes detect the activity of primary
users (PUs) through a novel cooperative MAC protocol and will decide the
systems mode of operation in the subsequent spectrum hole. In the FDTS mode one
of the SUs senses the PUs activity continuously whilst transmitting to another
node. In the FDTR mode, the SUs would communicate bidirectionally in an
asynchronous full duplex (FD) manner, with decreased maximum and average
collision durations. Analytical closed forms for probability of collision,
average collision duration and cumulative collision duration, as well as
throughput of the SU network are derived, and performance of the proposed
protocol in terms of above-mentioned metrics, its effectiveness, and advantages
over conventional methods of sensing and transmission are verified via
simulations
