Rate-splitting multiple access (RSMA) is a flexible interference management technique in which a part of the message of each user is carried by a common stream that is decoded by all users. This paper analyzes the downlink coverage probability of one-layer RSMA in an ultra-dense network where the base stations (BSs) follow a Poisson point process and the signal power is attenuated according to the stretched path loss model. The decoding of the common and the private streams is described by two equivalent channel gain thresholds, which are then combined into a single condition for the successive interference cancellation chain to succeed. Based on this observation, closed-form approximations of the common stream and the user coverage probabilities are derived by means of Gauss-Laguerre quadratures. The analytical results, which are confirmed by Monte Carlo simulations, show that the power splitting ratio must stay below a threshold that depends on the required common-stream rate, and that the coverage probability reaches a peak before decreasing when the density of BSs grows.

Rate-splitting multiple access, ultra dense network, coverage probability, Poisson point process, stochastic geometry.