On Optimum Power Allocation for Multi-Antenna Wideband Helicopter-to-Ground Communications

This paper introduces a generalized version of time-reversed, space-time block codes (TR-STBCs), called GTRSTBCs that operates with non-equal power allocation between two inter-symbol interference (ISI) channels in a 2 transmit, 1 receive antenna helicopter-to-ground radio link. The power allocation is parameterized by ρ, the portion of the total available power allocated to channel 1. The criteria for selecting the optimum ρ is minimizing the residual mean-squared error at the MMSE equalizer output. GTR-STBC is applied to measured channel impulse responses and a simple statistical channel model. The results show that 1) the optimum value of ρ gives the best tradeoff between signal-to-noise ratio and ISI; 2) equal power allocation may not be the optimum power allocation when channel side information is available; and 3) the optimum profile of ρ over measured channels channels is significantly different than from that in statistical channel models.