Although MIMO techniques are significantly ‘younger’ than OFDM, they also reached a
state of maturity and hence the family of recent wireless standards includes the optional employment of
MIMO techniques, which motivates the joint study of OFDM and MIMO techniques in this volume.
The research of MIMO arrangements was motivated by the observation that the MIMO capacity
increases linearly with the number of transmit antennas, provided that the number of receive antennas
is equal to the number of transmit antennas. With the further proviso that the total transmit power is
increased proportionately to the number of transmit antennas, a linear capacity increase is achieved upon
increasing the transmit power. This is beneficial since, according to the classic Shannon–Hartley law,
the achievable channel capacity increases only logarithmically with the transmit power. Thus MIMOOFDM
may be considered a ‘green’ transceiver solution.