Deploying cognitive radio femtocell network
(CRFN) inside a macrocell network can significantly increase
the utilization of the available macrocell bandwidth and
increase the capacity of the macrocell. However, the success of
this deployment in terms of performance degradation of the
macrocell and the acceptable throughput for the CRFN is not
well defined. In this paper, we propose a time division duplex
(TDD) operation of a CRFN and investigate its performance
inside a macrocell operating in frequency division duplex
(FDD) mode. It is shown that with a proper sensing and
transmission scheme the capacity of the CRFN can be increased
by simultaneous transmissions on multiple channels, water-filling
further improves the result when interference from the macrocell
basestation is large. The proposed scheme is applicable to full
duplex networks, such as LTE and GSM.