Ambient backscatter communication enables passive sensors to convey sensing data on ambient RF signals in the air at ultralow power consumption. To extract data bits from such signals, threshold-based decoding has generally been considered, but suffers against Wi-Fi signals due to severe fluctuation of OFDM signals. In this paper, we propose a pattern-matching-based decoding algorithm for Wi-Fi backscatter communications. The key idea is the identification of unique patterns of signal samples that arise from the inevitable smoothing of Wi-Fi signals to filter out noisy fluctuation. We provide the mathematical basis of obtaining the pattern of smoothed signal samples as the slope of a line expressed in a closed-form equation. Then, the new decoding algorithm was designed to identify the pattern of received signal samples as a slope rather than classifying their amplitude levels. Thus, it is more robust against signal fluctuation and does not need tricky threshold configuration. Moreover, for even higher reliability, the pattern was identified for a pair of adjacent bits, and the algorithm decodes a bit pair at a time rather than a single bit. We demonstrate via testbed experiments that the proposed algorithm significantly outperforms conventional threshold-based decoding variants in terms of bit error rate for various distances and data rates.
Cognitive radio is widely expected to be a promising technology to efficiently exploit underutilized spectrum. Regulatory committees in many countries are taking into account the spectrum policy of dynamic spectrum access using this technology. The TV band is under consideration as a first step to share the spectrum resource. As a result, many activities to specify a standard using this band have been shown. In this paper, an overview on the physical layer of Ecma-392 standard and IEEE 802.11af draft standard is presented together with software simulated performance results. Furthermore, the effect of the frequency diversity on different number of subcarriers and channel bandwidth is analyzed and discussed.
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