Adaptive Beamforming and Modulation Design for 5G V2I Networks

This paper proposes adaptive beamforming, power allocation, and modulation designs for 5G V2I networks. We consider a scenario where a base station (BS) equipped with multiple antennas is serving a single antenna vehicular equipment (VE). We employ a two stage design approach; the first stage considers the beamforming design, and the second stage considers adaptive power allocation, and modulation designs for fixed beamforming. For the beamforming design, we apply the maximum ratio transmission (MRT) due to its optimality. And for fixed beamforming, the proposed design problem turns out to be a power and modulation adaptation problem which can be solved when the distribution of the signal to noise ratio (SNR) is known. For this reason, we propose a novel and general approach to derive the statistical distribution of SNR by exploiting the structure of the array, the beamforming type and slow fading channel coefficients, and utilize the derived SNR distribution to design the power and modulation adaptation strategies. It is shown that the proposed design requires different power adaptation policies for continuous and discrete M-QAM modulations. All the analytical expressions have been verified by performing extensive simulations. Furthermore, we have examined the effect of different channel parameters on the proposed adaptation policies. We have observed that the proposed power allocation is very useful when the number of scatterers Ls and modulation order are very low. In all other cases, we have found that a constant power allocation is an optimal strategy for a medium to large Ls and modulation order.