Adaptive Transmission Repetition and Combining in Bistatic WiFi Backscatter Communications

Extracting data bits from bistatic-backscattered WiFi signals by threshold-based decoding is challenging due to severe fluctuation of OFDM signals. We propose adaptive transmission repetition to combat this problem. The key idea is to let a backscatter transmitter repeat transmissions and a receiver combines those so that signal fluctuation is filtered out due to its time-changing patterns, as observed in our testbed experiments, thus reducing bit error rate. However, excessive transmission repetitions lead to the waste of channel time, thus we propose an algorithm to adapt the number of repetitions so as to maximize the effective throughput in the present communication condition. We demonstrate via testbed experiments that the proposed algorithm adapts well to various communication conditions and achieves near-best throughput performance.