Amirkabir University of Technology AUT Journal of Electrical Engineering 2588-2910 58 Special Issue 1 2026 05 01 The Upper-Bound of the Average Achievable Rate of Non Orthogonal Multiple Access 51 58 5914 10.22060/eej.2025.24031.5647 EN Mina Baghani PhD, Faculty of Technical and Engineering, Imam Khomeini International University, Qazvin, Iran 0000-0001-5806-6043 Journal Article 2025 04 04 The Non Orthogonal Multiple Access (NOMA) is a popular candidate for the next generation of wireless networks. Two advantages of NOMA are that it can achieve a higher rate and support more users compared to orthogonal multiple access (OMA). By increasing the number of users occupied a subchannel in NOMA, the achievable rate and the number of supported users of the system have been increased. Thus, we can assume there are infinite users in the system wanting to share one subchannel to derive the upper bound of the achievable rate of NOMA. In this article, the optimal power allocation function of infinite users in NOMAis derived, which maximizes the average achievable rate of the system under the maximum power constraint. The performances of the proposed power allocation strategy are compared with the simple case with only two users in NOMA. The simulation results show the gap between the average achievable rate and the outage probability of infinite users and two users in the NOMA system. https://eej.aut.ac.ir/article_5914_dd5bfdeb57f7c75d400de61e99d78e2e.pdf