Modeling SCMA in D2D underlaid cellular network

Sparse code multiple access (SCMA) has been recently proposed as an efficient multiple access scheme, which allows non-orthogonal spectrum resource sharing and enables system overloading. In this paper, we apply SCMA into device-to-device (D2D) communication underlaid cellular network, targeting at using the overload feature of SCMA to increase device connectivity and expand network capacity. In particular, we develop a stochastic geometry based framework to analyze the influence of SCMA on the signal-to-interference ratio (SIR) statistics of a typical cellular uplink and a typical D2D link. Based on the results, we analytically compare SCMA with orthogonal frequency-division multiple access (OFDMA) using area spectral efficiency (ASE) and quantify the closed-form ASE gain of SCMA over OFDMA. Notably, it is numerically shown that system ASE can be significantly improved using SCMA, asymptotically 38% increase over OFDMA under typical system settings. In addition, we enable interference management by allowing D2D users to use slotted ALOHA and derive the optimal multiple access probability (MAP) in order to maximize the proportional fairness utility function. The results are helpful in the implementation of SCMA in D2D underlaid cellular network.