Analysis of user association in multi-tier, multi-band heterogeneous cellular networks

In this paper, the impact of the three-tier, multi-band heterogeneous networks (Het-Nets) performance, comprising of Terahertz (THz) tier, Sub-Terahertz (Sub-THz) tier, and millimeter wave (mmWave) tier has been modeled using stochastic geometry and analyzed under different network conditions. THz-enabled Het-Nets are expected to provide ultra-wide bandwidth and high data rates for next-generation applications. However, due to the inherent characteristics of the THz band such as high path loss, molecular absorption, and line-of-sight (LOS) blockage, THz communications can only offer limited coverage and may remain underutilized in an indoor environment. The coexistence of multi-band communication is considered the main requirement of future communication networks to improve coverage in indoor and outdoor environments. Moreover, the analytical expressions derived for the tier-wise user association probabilities have been validated using Monte-Carlo simulations and the results are found in agreement. The results obtained through this investigation provide a comprehensive insight into the dependency of user association on network parameters like antenna array size, transmit power, and cell range expansion (CRE) bias. Furthermore, this investigation establishes the significance of network and environmental conditions in particular the impact of CRE bias and antenna array sizes on the utilization of THz tier for serving the indoor user.