Automated Electronic Mode Stirring in Reverberant Cavities to Optimize Backscatter Link Margins

Abstract

The usage of backscatter communications in metal-rich environments is limited by the deep nulls present due to dense multipath. With the round-trip path losses incurred by backscatter communication links, the system link budget is very sensitive to these nulls. Real-world applications require a strategy to mitigate this path loss actively in a wireless uplink, while conforming to the size, weight, and power constraints of the system. Past research has shown that electronic mode stirring can mitigate the effects of multipath in a static scenario. This work presents an automated reconfiguration strategy that can search through a set of electronic mode stirring states to optimize for improved link margins. The experiments are performed with a 2.4~GHz dual-polarized electronic mode stirring system designed for use within metal animal cages used in neurological research. Path loss measurements represent the spatially dependent multipath, with an animal motion model to simulate a real-time system. Measurements indicate that the system can reduce worst-case one-way path loss by 26~dB in static scenarios. Then, the simulation measures the number of path loss samples which exceed a nominal threshold for reliable communication. The percentage of samples that exceed this path loss threshold in the un-stirred system is 32%, regardless of simulated velocity. Under slow moving conditions, automated reconfiguration improves that percentage of samples exceeding the path loss threshold to 8%, a reduction of 75%. The improvement is less pronounced with fast motion, which results in a percentage of 26%-28% that exceed the path loss threshold. Given a sufficient update rate, this simple reconfiguration strategy could be used to mitigate multipath for backscatter communication.-