An OFDM based multiple access system provides strong persistence against selective frequency fading and further provides suppression of inter-cell interference by using cell differentiating scrambling codes. Thus, the OFDM system maximizes frequency reuse rate. The present invention includes an OFDM modulator frequency-division-multiplexing data to be transmitted, a code division unit multiplexing the frequency-division-multiplexed data with a prescribed code, and an RF end converting the data multiplexed by the code division unit to a radio frequency signal to transmit. Accordingly, the present invention raises the degree of freedom (frequency division, time division, code division) of system implementation in the multiple access system. The OFDM system includes the scrambling of the downlink data by different scrambling codes by a cell unit for base stations within at least two neighboring cells to identify the respective cells and transmitting the spread downlink data.