  In this paper, we present the case of utilizing interference temperature (IT)
as a dynamic quantity rather than as a fixed quantity in an orthogonal
frequency division multiple access (OFDMA) based spectrum sharing systems. The
fundamental idea here is to reflect the changing capacity demand of primary
user (PU) over time in setting the interference power threshold for secondary
user (SU). This type of dynamic IT will allow the SU to opportunistically have
higher transmit power during relaxed IT period, thereby resulting in higher
network capacity. The cognitive radio network (CRN) considered in this paper
has an underlay network configuration in which the available spectrum of the PU
is accessed concurrently by SU provided that the interference power at the PU
receiver from SU is under a certain power threshold. This power threshold is
set to maintain and guarantee a certain level of quality of service (QoS) for
PU network. Theoretical expressions for outage probability and mean capacity
for SU network are derived, and validated with simulation results, and it is
observed that utilizing dynamic IT results in high network performance gains as
compared to utilizing a fixed IT in cognitive radio system.
