Gaining from Multiple Ambient Sources: Signaling Matrix for Multi-Antenna Backscatter Devices

The backscatter device (BD) in ambient backscatter communication (AmBC) systems is often illuminated by multiple ambient sources in reality. Although multiple ambient sources can benefit the AmBC systems, this scenario has been rarely studied. This letter gives an answer to the overlooked question of how to effectively obtain the gain from multiple ambient sourcesusing a proper signaling matrix on a multi-antenna BD. We optimize the BD signaling matrix based on the criterion of minimizing the AmBC system bit-error-rate (BER) performance. The derived signaling matrices combine the ambient signals and steer the backscatter signal toward the receiver to increase the received signal strength. The simulation results show that the multi-antenna BD effectively uses multiple ambient sources, and the derived BD signaling matrices robustly achieve a larger communication range or a higher datarate of AmBC systems.