Antenna Diversity for an OFDM System in a Fading Channel

This paper explores antenna diversity issues for Orthogonal Frequency Division Multiplexing (OFDM) in frequency flat and selective fading environment using three combining methods – maximal ratio combining (MRC), equal gain combining (EGC), and selection combining (SC). For OFDM, diversity combining can be done on individual subcarriers (narrowband combining) or on the entire OFDM symbol (wideband combining). For narrowband combining, OFDM diversity performance in frequency selective can be predicted using flat fading analytic formulas, given that subchannels are sufficiently narrowband. For wideband combining, an equivalent channel model based on the number of rays in the channel is formulated and an analytic expression for wideband SC is derived. Computer simulation is used to verify these expressions and methods to improve the three combining techniques are discussed, including metric filtering, selection grouping, and higher order selection diversity.