Over-the-Air Computation Strategy Using Space-Time Line Code for Data Collection by Multiple Unmanned Aerial Vehicles

In this study, we investigated a data collection system for multiple unmanned aerial vehicles (UAVs) in the sky. To reduce the required data collection time for a time-division multiple access (TDMA)-based protocol, an over-the-air computation (OAC) strategy was employed, and the average values of data computed. In this method, multiple single-antenna sensing UAVs (sUAVs) report the sensing data to a two-antenna data-collection UAV (dUAV) through the OAC strategy. To this end, we propose an efficient OAC strategy using a space-time line code (STLC) scheme that can achieve a full spatial diversity gain. Using the efficient data collection protocol of the proposed STLC-OAC strategy, the overall operation time for data collection can be significantly reduced relative to s TDMA-based strategy. Furthermore, the proposed STLC-OAC strategy can reduce the normalized mean square error (NMSE) of the estimated average value of the data relative to that of the TDMA-based method. As the gap in the NMSEs between TDMA- and STLC-OAC-based strategies was observed to increase as the number of sUAVs increased, it can be concluded that the proposed STLC-OAC strategy is advantageous for UAV-based data collection systems, especially when a large number of sUAVs report the sensing data.