Diversity Management in MIMO-OFDM Systems

Over the last decade, a large degree of consensus has been reached within the research community regarding the physical layer design that should underpin state-of-the-art and future wireless systems (e.g., IEEE 802.11a/g/n, IEEE 802.16e/m, 3GPP-LTE, LTE-Advanced). In particular, it has been found that the combination of multicarrier transmission and multiple-input multiple-output (MIMO) antenna technology leads to systems with high spectral efficiency while remaining very robust against the hostile wireless channel environment. The vast majority of contemporary wireless systems combat the severe frequency selectivity of the radio channel using orthogonal frequency diversity multiplexing (OFDM) or some of its variants. The theoretical principles of OFDM can be traced back to (Weinstein & Ebert, 1971), however, implementation difficulties delayed the widespread use of this technique well until the late 80s (Cimini Jr., 1985). It is well-known that the combination of OFDM transmission with channel coding and interleaving results in significant improvements from an error rate point of view thanks to the exploitation of the channel frequency diversity (Haykin, 2001, Ch. 6). Further combination with spatial processing using one of the available MIMO techniques gives rise to a powerful architecture, MIMO-OFDM, able to exploit the various diversity degrees of freedom the wireless channel has to offer (Stuber et al., 2004).