Coverage in Networks with Hybrid Terahertz, Millimeter Wave, and Microwave Transmissions

In this paper, a three-tier heterogeneous network (HetNet) is considered, where access points (APs), small-cell base stations (SBSs) and macrocell BSs (MBSs) transmit in terahertz (THz), millimeter wave (mmWave), microwave frequency bands, respectively. Distinguishing features of transmission in each frequency band are taken into account, including the blockage model, path loss, beamforming and small-scale fading. Path loss based association criterion is considered for user equipments (UEs). By using tools from stochastic geometry, the complementary cumulative distribution function (CCDF) of the received signal power, the Laplace transform of the aggregate interference, and the SINR coverage probability are investigated, and general expressions are obtained. Finally, numerical results show that making the THz APs more densely distributed can enhance the received signal power but decrease the SINR coverage probability.