Energy-Efficient Power Loading for a MIMO-SVD System and Its Performance in Flat Fading

In this paper we formulate a power loading problem for the spatial subchannels (parallel channels) of a single-carrier MIMO-SVD system. The power loading solution is designed to minimize the energy-per-goodbit (EPG) of the MIMO-SVD system. The optimum power loading obtained by solving a nonlinear fractional program, has a closed-form expression and is found by applying a water-filling procedure. It is observed that the optimum total transmit power (water level) depends not only on the MIMO channel realization, but also on the ratio of circuit power cost (which depends on the number of antennas) to transmit power cost (which depends on path loss and other factors). We study the statistical performance (using simulation) of the solution in Rayleigh and Rician flat-fading channels. Using outage EPG as a measure of performance, we determine the MIMO configuration (from a set of allowed configurations) that yields the minimum outage EPG. It is observed that the average number of spatial subchannels utilized (which indicates preference for diversity or multiplexing) depends on the ratio of circuit power cost to transmit power cost and fading type (Rayleigh or Rician). For both cases, the results show that both multiplexing and diversity obtained by MIMO systems are critical for energy efficiency.