Reducing Phase Cancellation Effect with ASK-PSK Modulated Stamp in Augmented UHF RFID Indoor Localization System

In this paper, we propose exploiting ASK-PSK modulated stamp in receiving path selection technique to lessen the phase cancellation effect in augmented ultra-high-frequency (UHF) radio frequency identification (RFID) indoor localization system (AURIS). In AURIS, a tag-like semi-passive RFID component (referred as sensatag) can capture backscatter signal of other proximal tags with presence of RF source. According to the principle of backscatter radio link, the received signal at sensatag antenna is the superposition of backscatter signal of tags and continuous carrier wave (CW) from RF source. However, due to phase difference between tag's backscatter signal and RF CW, the modulated backscatter signal could be cancelled. We refer this effect as phase cancellation effect. Exploiting the spatial diversity of dual-antenna's two receiving paths, the likelihood of phase cancellation occurrence could be reduced. But the developed technique with two co-operating paths is not energy efficient. Therefore, this paper proposes to inject a ASK-PSK modulated stamp sequence in the pilot tone of backscatter signal as a signature of phase cancellation for ASK modulated data frame, which could be identified by the receiving sensatag. With the knowledge of occurrence of phase cancellation, sensatag could activate the alternative receiving path. This technique fully exploits the space diversity of dual-antenna, and also reduces the power consumption by reducing one receiving path in operation. We demonstrate the performance of stamp based receiving path selection technique with data obtained from computer simulation.