Performance analysis of adaptive downlink modulation using OFDM and MC-CDMA for future mobile communications system

To meet the strong demand for broadband multimedia services by both nomadic and mobile users, it is important to increase the bit rate of future mobile communications systems. To enhance system capacity, novel technologies or new concepts for improving system capacity are indispensable. Performance analysis for adaptive downlink modulation using orthogonal frequency division multiplexing (OFDM) and multicarrier CDMA (MC-CDMA) is presented. The basic concept of the proposal method is that a time frame is divided into two sub-frames, one is for OFDM and the other is for MC-CDMA, and the base station (BS) allocates the preferred modulation scheme to each user in each time slot in accordance with their service requirements and link conditions such as the received signal strength indication (RSSI) level and interference signal strength. Simulation results show that the throughput performance of the proposed system is better than that of the system using OFDM or MC-CDMA only.