Complexity Comparison of OFDM and CDMA for Wideband Communication Systems

It is commonly believed that OFDM systems have a complexity advantage over CDMA. We show that there are two ways for CDMA complexity to remain competitive with OFDM: a multi-channel approach, in which a wideband system is composed of multiple narrow-band systems; and a frequency-domain equalization approach, where the CDMA receiver is based on the same efficient FFT technique used in OFDM. By making some assumptions on receiver design and wireless channel characteristics, we find simple formulas for the required number of complex multiplications per second. MIMO and broadcast systems are considered as special cases.