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This letter proposes a budgeted combinatorial multi-armed bandit (BC-MAB)-based two-stage beamforming scheme for an energy-constrained unmanned aerial vehicle MIMO system. The proposed scheme learns the pre-beamformer from the historical data which reduces the pilot overhead and uses the bangperbuck ratio to address the energy constraint. In the first stage, the pre-beamformer is designed using a reinforcement learning method based on BC-MAB to maximize spectral efficiency. The total energy and the energy consumption are set as the budget and the cost, respectively. Consider the energy constraint, the bangperbuck ratio is introduced to represent the trade-off between the received energy per slot and the number of communication slots. A pre-beamforming algorithm is proposed to maximize the bangperbuck ratio to achieve a good trade-off and reduce the dimension of instantaneous CSI (ICSI). In the second stage, a multi-user beamforming algorithm is designed to maximize spectral efficiency using the reduced ICSI, where the problem is transformed to convex using Lagrangian transformation and fractional programming. Simulations validate the superiority of the proposed scheme.

The author presents a new comprehensive evaluation method based on uncertainty theory in this paper. According to this kind of method, the evaluation quality of each evaluated index given by every expert is regarded as an uncertain variable. Then a comparison rule of uncertain comprehensive evaluation is proposed by means of expected value of uncertain variable. Some properties about the comparison rule are discussed. At last, an example about the comparison of urban environment quality is given to illustrate the uncertain comprehensive evaluation method.

Abstract: This paper derives an asymptotic average symbol error probability (SEP) expression for multipleinput multiple-output (MIMO) two-hop amplify-and-forward (AF) relay systems with optimal beamforming. The analysis at high signal-to-noise ratio (SNR) quantifies the diversity order and array gain, which are valid for any antenna numbers of the terminals and arbitrary channel fading models. It is also proved that the system performance is dominated by the relatively degraded one of the two-hop channels. Our results based on the simple expressions provide valuable insights into the performance and practical design considerations of MIMO AF networks.