Probabilistic optimal tree hopping for RFID identification

Abstract

Radio Frequency Identification (RFID) systems are widely used in various applications such as supply chain management, inventory control, and object tracking. Identifying RFID tags in a given tag population is the most fundamental operation in RFID systems. While the Tree Walking (TW) protocol has become the industrial standard for identifying RFID tags, little is known about the mathematical nature of this protocol and only some ad-hoc heuristics exist for optimizing it. In this paper, first, we analytically model the TW protocol, and then using that model, propose the Tree Hopping (TH) protocol that optimizes TW both theoretically and practically. The key novelty of TH is to formulate tag identification as an optimization problem and find the optimal solution that ensures the minimal average number of queries. With this solid theoretical underpinning, for different tag population sizes ranging from 100 to 100K tags, TH significantly outperforms the best prior tag identification protocols on the metrics of the total number of queries per tag, the total identification time per tag, and the average number of responses per tag by an average of 50%, 10%, and 30%, respectively, when tag IDs are uniformly distributed in the ID space, and of 26%, 37%, and 26%, respectively, when tag IDs are non-uniformly distributed.

Fairness Matters: Identification of Active RFID Tags with Statistically Guaranteed Fairness

“…We implemented and compared the performance of FRIP with nine prior tag identification protocols, namely the 3 nondeterministic (Aloha [21], BS [22], and ABS [23]), the 4 deterministic (TH [17], TW [24], ATW [25], and STT [26]), and the 2 hybrid protocols (MAS [27] and ASAP [28]). We did not compare FRIP with FNFRA [29] because the two protocols address different problems: FNFRA focuses on making reader scheduling process fair while FRIP focuses on making the tag identification process fair.…”

“…Existing RFID identification protocols mostly focus on minimizing identification time and are unfair because in each round of identification, the same set of tags has to transmit more times compared to the other tags. In [17], Shahzad and Liu evaluated the fairness of their TH protocol along with other RFID identification protocols, and showed that TH achieves the highest fairness among all existing protocols. However, TH is not designed to achieve any required fairness; its design objective is to just minimize the identification time without fairness constraints.…”

“…For evaluation and comparison, we implemented FRIP and nine RFID identification protocols, which represent the stateof-the-art, in Matlab. These nine protocols are Aloha [21], BS [22], ABS [23], TH [17], TW [24], ATW [25], STT [26], MAS [27], and ASAP [28]. We performed side-byside comparisons of FRIP with these protocols using tag populations ranging in sizes from a hundred tags to a million tags and following different distributions.…”

“…Therefore, the batteries of the tags that experience more collisions in each round deplete at a faster rate compared to the batteries of the tags that experience less collisions. Although several protocols such as STT [26], ATW [25], and TH [17], have been proposed to reduce the number of collisions, they focus on reducing the identification time and do not address the fairness issue. Token-MAC is a deterministic protocol, not based on TW, in which a reader provides tokens, i.e., permission to transmit, to tags such that tags with lower historical success rate receive more tokens [30].…”

“…The objective function in this case is E[T ], given by Equation (15), and the inequality constraint is k − m ≤ 0. Equations (17) to (20) give the four KKT conditions that must be satisfied to obtain the optimal solution. (19) µ ≥ 0, Dual feasibility (20) where µ is called KKT multiplier.…”