A Passive Bidirectional BLE Tag Demonstrating Battery-Free Communication in Tablet/Smartphone-to-Tag, Tag-to-Tablet/Smartphone, and Tag-to-Tag Modes

Wireless connectivity in loT devices must be low power and compatible with the widely-deployed commodity hardware such as BLE-embedded tablets/smartphones. However, conventional loT transceivers (TRXs) consume several milliwatts of active power, such as 4.1 mW BLE TX and 3.6mW BLE RX [1]. As a result, most of the current loT devices require either wall power, or bulky/frequently-recharged batteries (Fig. 31.5.1, top, first). Near-field communication (NFC) is compatible with smartphones, but the operating range is limited to less than 10cm, which hinders pragmatic deployment of most loT applications (Fig. 31.5.1, top, second). Far-field radiative RFID realizes battery-less communication through tens of centimeters to several meters [2], but it can only be read by dedicated RFID hardware instead of a commodity tablet/smartphone (Fig. 31.5.1, top, third). As a result, far-field RFID readers contradict the target of cost-effective loT deployment leveraging ubiquitous standards such as BLE. Recently, codeword-translation backscatter enables a low-power loT tag to be more compatible with existing infrastructures [3] (Fig. 31.5.1, top, fourth), while there are several shortcomings: 1) The tag still relies on wall power or battery, leading to bulky size or limited lifetime. 2) An additional decoder is required to compare the codeword-translation backscatter signal with incident BLE packets from the original access point (AP), so the backscatter signal cannot be directly demodulated by a commodity device. 3) The existing far-field backscatter chips realized a communication range less than 35m [3], which were not practical for most outdoor applications. 4) Each tag can only backscatter data unidirectionally towards the AP, while the tag can only detect the advertising (ADV) events instead of recovering the data coming from a commodity device [3], [4]. 5) Tag-to-tag communication has not been realized, so it's not able to construct a network for loT applications.