Coverage and capacity analysis of relay-based device-to-device communications underlaid cellular networks

Coverage and capacity are the key parameters of 4G and beyond wireless networks. These parameters of Long Term Evolution Advanced (LTE-A) networks can be greatly enhanced by enabling device-to-device (D2D) communication. In this paper, full duplex amplify and forward (FDAF) relay nodes (RNs) have been introduced to assisting cellular and D2D communications. The coverage probability (CP) and transmission capacity (TC) for both the cellular and D2D communications have been analyzed with FDAF relay based network. The D2D users can communicate directly or via relaying with FDAF RNs. Cellular users, D2D users and RNs in the network have been modeled using homogeneous spatial poisson point process (SPPP). The closed-form expressions of CP and TC for cellular as well as D2D communications have been derived by using stochastic geometry. The pairing of D2D users is decided by the shortest distance reduced path loss and formed pair either directly or via RN assistance. The approximate complementary cumulative distribution function (CCDF) of the signal to interference plus noise ratio (SINR) for both the cellular users and the D2D users have been derived. The closed form expressions of CP and TC show that coverage and capacity of both the cellular and D2D communications are influenced by various parameters such as D2D user density, relay node density and the distance of D2D pair. Results show the improvement of CP and TC for cellular and D2D communications with the help of RNs.