  We characterize a multi tier network with classical macro cells, and multi
radio access technology (RAT) small cells, which are able to operate in
microwave and millimeter-wave (mm-wave) bands. The small cells are assumed to
be deployed along roads modeled as a Poisson line process. This
characterization is more realistic as compared to the classical Poisson point
processes typically used in literature. In this context, we derive the
association and RAT selection probabilities of the typical user under various
system parameters such as the small cell deployment density and mm-wave antenna
gain, and with varying street densities. Finally, we calculate the signal to
interference plus noise ratio (SINR) coverage probability for the typical user
considering a tractable dominant interference based model for mm-wave
interference. Our analysis reveals the need of deploying more small cells per
street in cities with more streets to maintain coverage, and highlights that
mm-wave RAT in small cells can help to improve the SINR performance of the
users.
