  A contemporary perspective on the tradeoff between transmit antenna diversity
and spatial multiplexing is provided. It is argued that, in the context of most
modern wireless systems and for the operating points of interest, transmission
techniques that utilize all available spatial degrees of freedom for
multiplexing outperform techniques that explicitly sacrifice spatial
multiplexing for diversity. In the context of such systems, therefore, there
essentially is no decision to be made between transmit antenna diversity and
spatial multiplexing in MIMO communication. Reaching this conclusion, however,
requires that the channel and some key system features be adequately modeled
and that suitable performance metrics be adopted; failure to do so may bring
about starkly different conclusions. As a specific example, this contrast is
illustrated using the 3GPP Long-Term Evolution system design.
