Average Transmit Power Gain of MIMO Fading Channels Over SISO AWGN Channels

This paper is concerned with the average transmit power under adaptive transmission for multiple-input multiple-output (MIMO) antenna systems with multi-beams in fading environments when the channel-state information at both the transmitter and the receiver is available. The transmitter is supposed to be capable of spatiotemporal subchannel selection and power control as eigenvalues of channel matrix changes. Our focus is on an eigenvalue-inversion based optimization transmission scheme. With the scheme, we first introduce a concept of average transmit power gain (ATPG) of MIMO fading channels over single-input single-output additive white Gaussian noise channels in order to analyze deeply relationship between the average transmit power, the number of transmit antennas, the number of receive antennas, and fading channel characterizations. Then in Rayleigh fading we derive several insightful ATPG expressions for single-beam and multi-beam transmissions, respectively. Based on these expressions, the potential amounts of transmit power savings are further estimated in several cases when the underlying MIMO system is very large. Moreover, consideration of extending ATPG is also given in the presence of spatial correlation.