UAV-MIMO Under Wobbling: A Comparative Analysis of Centralized and Distributed Implementations

In this paper, we investigate the impact of random wobbling on the performance of unmanned aerial vehicle (UAV) communications. We consider two practical implementation forms of UAV-multiple input multiple output (MIMO) system, namely 1) centralized implementation, where a compact multi-antenna array is deployed on a single UAV platform and hence wobbling directly has impact on the entire array; 2) distributed implementation, where a virtual MIMO system is formed via cooperative UAV swarm, and wobbling occurs independently for every single transmit antenna. For both cases, we define and analyze the beamforming gain loss-factor as the performance metric to evaluate the adverse effect caused by wobbling. Based on derived analytical expressions, the centralized and distributed implementations are compared to show their preferable operating scenarios, respectively, considering different system and implementation parameters including the carrier frequency, wobbling variance, user position, antenna number, and inter-antenna spacing, etc. It is revealed that the distributed MIMO implementation could be more robust to wobbling, especially when the number of antennas is large. Simulations verify the accuracy of derived analytical expressions, and confirm the corresponding conclusions.