Orthogonal Space-Time Block Code Based Over-the-Air Computation in Backscatter Sensor Networks

In backscatter sensor networks, performing over-the-air computation (AirComp) is challenging, because backscatter devices are impossible to accomplish channel estimation and precoding operations to offset the distortions caused by wireless channels. In this letter, we propose an orthogonal space-time block code based AirComp scheme for a monostatic backscatter AirComp network. To minimize the computation mean square error while satisfying energy harvesting constraints, we also propose a Rayleigh quotient based globally optimal power splitting ratios. Simulation results are provided to show that our proposed optimal power splitting ratios outperform the maximum, channel inversion, and random power splitting ratios.