Enabling Efficient Passive RFID SystemsThrough Modulation Silencing
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RFID technology has attracted much attention due to its wide range of applications, such as inventory control and object tracking. Passive RFID tags are battery-less, mobile and lack intercommunication. Hence, they require a central node (the reader) to power them up, organize their replies, and read their data. In the last decade, several proposals have targeted the channel efficiency in RFID systems to improve time and power efficiencies. While such proposals achieve significant performance improvements, they are limited by the backscattering half-duplex channel in which the reader has to wait for the tag to finish its reply (even if the reply is corrupt or redundant). In this thesis, the Modulation Silencing Mechanism (MSM) is proposed as a novel full-duplex-like communication over half-duplex RFID links. With a simple additional circuit at the tag and upgraded software algorithms at the reader, the reader is capable of terminating the tag's non-useful transmissions. Consequently, we propose three schemes that utilize MSM in key application domains where the tag-reader transaction contains a considerable amount of non-useful transmissions. MSM is utilized to enhance tag identification, tag count estimation and tag authentication. First, we propose a Modulation Silencing Anti-collision (MSA) scheme that targets collision time reduction in time slotted anti-collision protocols. In MSA, the time requirements of state of the art identification protocols are significantly reduced. Moreover, we establish a backward compatibility procedure for proper identification of legacy and MSM-enabled tags. Secondly, a Variance- Modulation Silencing Estimation (VMSE) scheme is proposed to increase tag estimation accuracy and to minimize overall estimation time. Variance-to-mean ratio estimator is proposed to determine the most accurate tag count estimate. VMSE combines both, the accuracy of the variance-to-mean ratio estimator and the time efficiency of MSM and delivers rapid, accurate, and anonymous tag estimation that outperform recent estimation schemes for small and large scale tag deployment. Finally, we propose Unique Hash Sequence Authentication (UHSA) scheme for efficient tag authentication. The UHSA is based on hashed key prefetching algorithm at the reader augmented by the MSM circuitry at the tag. UHSA scheme provides higher time efficiency and robustness against tracking and compromising attacks.