A Lemma for Capacity Analysis in General Fading Channels With Applications to EGC, RSMA and IRS-Assisted Systems

This letter presents a new expression for evaluating the ergodic capacity in general fading channels. Its broad applicability is validated by applying it to various communication systems, including: (i) systems with equal gain combining (EGC) diversity, (ii) multi-user rate-splitting multiple access (RSMA) systems with EGC, and (iii) intelligent reflecting surface (IRS)-assisted systems employing EGC with arbitrary numbers of IRS elements and diversity branches. The IRS is considered under different transmission schemes such as intelligent transmission, transmission with imperfect phase shifts, and blind transmission. Subsequently, the preciseness of the expression in various fading channels is verified through numerical and simulation results.