Downlink coverage performance of 2-tier closed access heterogeneous cellular networks

Cellular networks are becoming heterogeneous due to the deployment of various low-powered base stations (BSs) within the macro cells. This introduces different classes of BSs and increases the BS density which creates complexity in interference analysis. Recent heterogeneous cellular network models consider Poisson Point Process (PPP) distribution for all BSs within the network for performance analysis. Although this type of consideration can lead to unrealistically close deployment of BSs, it is argued to still provide a close lower bound with a realistic scenario. In this work, we consider a grid-based deployment for macro BSs to ensure a minimum separation between them and randomly distributed low-powered BSs within the macro cells. We analyze the co-channel interference in such network for a macro cell user and evaluate coverage performance for downlink transmission under closed access. Instead of considering the actual distance of every user for network performance evaluation, we use a average user distance based on the user distribution. This simplifies the analysis while mostly providing a higher coverage probability than the PPP distributed models.