  We consider a cognitive radio network where primary users (PUs) employ
network coding for data transmissions. We view network coding as a spectrum
shaper, in the sense that it increases spectrum availability to secondary users
(SUs) and offers more structure of spectrum holes that improves the
predictability of the primary spectrum. With this spectrum shaping effect of
network coding, each SU can carry out adaptive channel sensing by dynamically
updating the list of the PU channels predicted to be idle while giving priority
to these channels when sensing. This dynamic spectrum access approach with
network coding improves how SUs detect and utilize temporal spectrum holes over
PU channels. Our results show that compared to the existing approaches based on
retransmission, both PUs and SUs can achieve higher stable throughput, thanks
to the spectrum shaping effect of network coding.
