  Rate-Splitting multiple access (RSMA) has emerged as a key enabler in
improving the performance of the beyond fifth-generation (5G) cellular
networks. The existing literature has typically considered the sum rate of the
users to evaluate the performance of RSMA. However, it has been shown in the
existing works that maximizing the sum rate can result in asymmetric user
performance. It significantly enhances one user's rate at the cost of the rate
of another RSMA user. Further, imperfections can reduce the performance of
successive interference cancellation (SIC)-based RSMA. Therefore, in this
letter, we consider the imperfection in SIC and derive suitable bounds on
fractions of the power allocated for common and private messages and the
fraction of common message intended for each user in an RSMA pair such that
their individual RSMA rates are greater than their respective orthogonal
multiple access (OMA) rates. Through simulations, we validate the derived
bounds. We show that they can be used to appropriately select the RSMA
parameters resulting in users' RSMA rates being better than their respective
OMA rates.

Signal Processing