  In this letter, the coexisting success probability and throughput of a
wireless network consisting of multiple subnetworks of different radio access
technologies (RATs) is investigated. The coexisting success probability that is
defined as the average of all success probabilities of all subnetworks is found
in closed-form and it will be shown to have the concavity over the number of
channels in the unlicensed band. The optimal deployment densities of all
different RATs access points (APs) that maximize the coexisting success
probability are shown to exist and can be found under the derived constraint on
network parameters. The coexisting throughput is defined as the per-channel sum
of all spectrum efficiencies of all subnetworks and numerical results show that
it is significantly higher than the throughput of the unlicensed band only
accessed by WiFi APs.
