CDMA vs. OFDM for Cellular

Speaking of CDMA vs. OFDM (see last blog entry), there is a major debate in the industry as to whether OFDM has inherent advantages over CDMA in cellular networks. IEEE 802.16 (as supported by the WiMAX Forum) has chosen Orthogonal Frequency Division Multiplexing as the basis of its radio technology. OFDM is also used in IEEE 802.11a, IEEE 802.11g and IEEE 802.11n, as well as in Flarion???s Flash OFDM system. As reported in an in-depth study of how cellular technologies will evolve beyond current 3G systems that I recently completed for Datacomm Research, one advantage is that with wider radio channels, OFDM effectively combats a radio effect called intersymbol interference. ISI is a consequence of the ???slowness??? of the speed of light, where reflected signals interfere with successive symbols (modulated waveforms). However, for current 3G systems with radio channels up to 5 MHz, it???s not clear that OFDM provides that much of an advantage. But with next generation systems that will deliver throughput rates in the 10 Mbps to 100 Mbps range, the advantages could start becoming significant, especially when combined with multiple input multiple output (MIMO). 3GPP has a work group studying how current cellular technologies might best evolve, including looking at OFDM. OFDM, however is not the only option. Another option is multi-carrier CDMA where multiple CDMA channels are combined for higher throughputs. While the cellular community is studying this, the mobile WiMAX community is racing forward as quickly it can to try and complete their technology. Needless to say, there is a huge amount at stake and its very hard at this stage to predict winners and losers, especially as it may be several years before any of these systems start to be deployed. And what will we call these new networks? 3.5G? 4G? Advanced 3G? Brilliant 3G?