In this work, we study the resource allocation problem for downlink in5G New Radio (NR) mobile networks in the case of orthogonal frequency-division multiple access (OFDMA). One of the key features of 5G mobile networks is the usage of antenna arrays that allows them to form beams in a specific direction and send data to several users at the same transmission time interval (TTI) via the same carrier or resource block (RB). Antenna arrays usually contain up to 64 single antennas. We modeled the process of the data transmission from the cell to the user device or user equipment (UE), formulated mathematical abstraction of the resource allocation problem, and proposed a lightweight algorithm that uses a proportional fair metric.