System-level study of OFDM and CDMA with adaptive modulation/coding for a 5 MHz channel

In this paper, the downlink performance of OFDM and CDMA cellular systems is investigated for deployment scenarios similar to those envisioned by the 3GPP. In particular, the system-level performance characteristics are studied for packet data oriented systems with adaptive modulation and coding (AMC), operating on a 5 MHz channel with one-cell frequency reuse. For the CDMA case, both Rake and MMSE receivers are considered. Three link adaptation scenarios are considered: ideal (fast) time-only adaptation, slow link adaptation (based on average C/(I+N)), and ideal time-frequency adaptation (only for OFDM). Performance is evaluated using indicators such as total throughput and data rate profile, for five propagation environments (pedestrian A and B, Vehicular A and B, and GSM typical urban) and for single antenna systems as well as space-time transmit diversity (STTD) systems. Results show a significant performance benefit for fast link adaptation in all systems, and also indicate that OFDM provides a performance benefit that depends on the channel delay spread.