  Multiple antenna (MIMO) devices are widely used to increase reliability and
information bit rate. Optimal error rate performance (full diversity and large
coding gain), for unknown channel state information at the transmitter and for
maximal rate, can be achieved by approximately universal space-time codes, but
comes at a price of large detection complexity, infeasible for most practical
systems. We propose a new coded modulation paradigm: error-correction outer
code with space-only but time-varying precoder (as inner code). We refer to the
latter as Ergodic Mutual Information (EMI) code. The EMI code achieves the
maximal multiplexing gain and full diversity is proved in terms of the outage
probability. Contrary to most of the literature, our work is not based on the
elegant but difficult classical algebraic MIMO theory. Instead, the relation
between MIMO and parallel channels is exploited. The theoretical proof of full
diversity is corroborated by means of numerical simulations for many MIMO
scenarios, in terms of outage probability and word error rate of LDPC coded
systems. The full-diversity and full-rate at low detection complexity comes at
a price of a small coding gain loss for outer coding rates close to one, but
this loss vanishes with decreasing coding rate.
