On the Average Sum-Rate of the 3D Single-Cell SCMA Systems

Two-dimensional (2D) models for performance analysis of wireless networks are inappropriate for high-rise buildings and city central business districts, particularly when massive connectivity is required. In practice, wireless systems operate in three-dimensional (3D) environments, so modeling and analyzing them in 3D space makes sense. In this letter, we first derive the analytical expression average sum-rate of the 3D sparse code multiple access (SCMA) system. Then, the lower and upper bounds of the average sum-rate are derived in terms of the relevant design parameters, which provide new insights into the 3D single-cell SCMA systems. It is found that the average sum-rate is a strictly and monotonically increasing function w.r.t. the number of resource blocks (RBs) and the overloading factor, respectively. Monte Carlo simulations confirm the precision of our theoretical results. Moreover, a comparison of the SCMA average sum-rate with two new versions of code-domain non-orthogonal multiple access (CD-NOMA) schemes, i.e., random multiple access (RMA) oriented SCMA and dense code multiple access (DCMA), is evaluated.