Multi-carrier backscatter communication system for concurrent wireless and batteryless sensing

Wireless and batteryless sensing has recently attracted significant attention of researchers in IoT and WSN applications. It turns out to be more challenging when simultaneous data acquisition from multiple sensors is required. This paper introduces a non-orthogonal multiple access technique MSMA, using extremely simple wireless and batteryless sensor tags and a reader to support concurrent streaming from multiple sensors. By simultaneously handling non-orthogonal subcarriers, produced either by multiple or single sensor tag, it can realize concurrent sensor data streaming, which can be used in health monitoring of machinery and civil structures. The paper explains the two primary challenges in MSMA, the optimal assignment of subcarrier frequencies and the unavoidable harmonics from one subcarrier to others. Since the mutual interference among subcarriers is unevenly distributed over the available frequency band, random allocation of subcarrier frequencies may result in degraded system performance. Results show that the interference can be canceled out with the signal processing technique and the system communication capacity can be increased significantly with a proposed heuristic approach compared to random allocation of subcarrier frequencies to the sensor tags.