CDMA versus OFDM, a performance comparison in selective fading channels

CDMA (code division multiple access) and OFDM (orthogonal frequency division multiplexing) are two well known air interface technologies in modern mobile communication. A performance comparison of CDMA and OFDM systems in selective fading channels is presented. The comparison proceeds in two steps. First, simple OFDM and CDMA systems with the same bandwidth are considered. A comparable bit rate is transmitted over both systems and the bit error rate in selective fading channels is observed. Second, two existing standards (DVB and UTRA FDD) are compared. We concentrate on the downlink and simulate the two systems in rural and typical urban channels. Simulations with a very high mobile velocity (350 km/h) are also conducted on both systems. We use a RAKE receiver for the CDMA system and compare its performance with a coherent and differential OFDM detector. We conclude that OFDM achieves better BER results than CDMA using a RAKE receiver for the same bandwidth efficiency.