Abstract: This article presents a dynamic random access scheme for orthogonal frequency division multiple access (OFDMA) systems. The key features of the proposed scheme are: it is a combination of both the distributed and the centralized schemes, it can accommodate several delay sensitivity classes, and it can adjust the number of random access channels in a media access control (MAC) frame and the access probability according to the outcome of Mobile Terminals access attempts in previous MAC frames. For floating populated packet-based networks, the proposed scheme possibly leads to high average user satisfaction.

Key words: random access scheme;RACH;OFDMA;dynamic access probability