Zero-Padding Space-Time Block Code for Dual-Antenna Backscatter Tag

Backscatter communications is receiving increasing attention in Internet of Things (IoT), while one major challenge for backscatter communications is that the circuit complexity for high performance tag is also high. In this article, for dual-antenna backscatter tag, we propose a zero-padding space-time block code (ZPSTBC) that can simultaneously improve the tag performance and reduce the complexity of the tag circuit. An interesting thing is that padding zero into space-time block code (STBC) is not beneficial in conventional multi-input-multi-output (MIMO) channels, but may lead to performance improvement in MIMO backscatter channels, from perspectives of error rate and energy harvesting, and also reduce the circuit complexity of the tag. This is due to characteristic of the MIMO structures and tag circuit of backscatter communications. We provide rigorous mathematical analysis and numerical simulations to illustrate the performance improvement and the tag complexity reduction caused by the proposed ZPSTBC.