ABSTRACT
In OFDMA systems, several users share a spectrum simultaneously by modulating exclusive sets of orthogonal subcarriers; thus each user’s signal can be easily separated in the frequency domain. OFDMA allows straightforward dynamic channel assignment, and, furthermore, multiuser and frequency diversities can be easily exploited. On the other hand, in OFDM spatial multiplexing systems, independent data from several users are transmitted on the same set of subcarriers simultaneously, thus promising higher spectral efficiency.The combination of multiple-input multiple-output (MIMO) architecture and OFDM basically turns a frequency-selective MIMO channel to a set of frequency-flat MIMO channels. This makes all the MIMO techniques in a flat-fading channel also applicable in a frequency-selective fading channel.
