Differential services in HSR communication systems: Power allocation and antenna selection

In the downlink of high-speed railway communication systems equipped with distributed transmit antennas, high mobility leads to fast time-varying received signal to noise ratios. In this case, dynamic time-domain power allocation and antenna selection could be jointly optimized to improve the system energy efficiency. This paper considers this problem in such a simple way where dynamic switching between multiple-input-multiple-output and single-input-multiple-output is allowed and exclusively utilized, while the sparse scattering terrains and delay-sensitive traffic flows are taken into account. The original optimization problem is a typical mixed integer nonlinear programming (MINLP) problem. Instead of conventional iteration based methods, such as the extended cutting plane method, we propose a low-complexity and direct solution by exploiting the physical nature of original problem, which can be utilized in real time. Theoretical results show that our proposed method can be viewed as the generalization of channel-inversion associated with transmit antenna selection. Also, compared with methods without dynamic antenna selection, our method significantly decreases the average transmit power.