Abstract: Disclosed herein are a multiple access hierarchical cellular network and a multiple access mobile communication terminal using the multiple access hierarchical cellular network. The multiple access hierarchical cellular network includes a macrocell that is served by Frequency Hopping-Orthogonal Frequency Division Multiple Access (FH-OFDMA), and microcells that are served by Orthogonal Frequency Division Multiple Access (OFDMA). The multiple access mobile communication terminal accesses a macrocell, which is served by FH-OFDMA, using FH-OFDMA when it moves at a speed higher than a predetermined speed, and a microcell, which is served by OFDMA, using OFDMA when it moves at a speed lower than the predetermined speed.

Abstract: Disclosed is an upstream access method in an Orthogonal Frequency Division Multiple Access (OFDMA)-based mobile communication system in which a random access method in an OFDMA network includes randomly selecting, by each subscriber device, one of a plurality uplink random access channels, if a random access request to the OFDMA network is transmitted by each subscriber device, accessing through the selected channel if a collision has not occurred in the selected channel, randomly selecting one of the uplink random access channels, if a collision has occurred in the selected channel, and if the number of retries for channel selection is less than a predetermined value, and determining whether a has collision has occurred, accessing through a finally selected channel, if it is determined that a collision has occurred; and randomly selecting one of the uplink random access channels if it is determined that a collision has occurred.