  In this letter, the problem of optimal resource power allocation and relay
selection for two way relaying cognitive radio networks using half duplex
Decode and Forward (DF) and Amplify and Forward (AF) systems are investigated.
The primary and secondary networks are assumed to access the spectrum at the
same time, so that the interference introduced to the primary network caused by
the secondary network should be below a certain interference threshold. In
addition, a selection strategy between the AF and DF schemes is applied
depending on the achieved secondary sum rate without affecting the quality of
service of the primary network. A suboptimal approach based on a genetic
algorithm is also presented to solve our problem. Selected simulation results
show that the proposed suboptimal algorithm offers a performance close to the
performance of the optimal solution with a considerable complexity saving.
