Dheeraj K. Klair

A Survey and Tutorial of RFID Anti-Collision Protocols

RFID technologies have revolutionized the asset tracking industry, with applications ranging from automated checkout to monitoring the medication intakes of elderlies. In all these applications, fast, and in some cases energy efficient, tag reading is desirable, especially with increasing tag numbers. In practice, tag reading protocols face many problems. A key one being tag collision, which occurs when multiple tags reply simultaneously to a reader. As a result, an RFID reader experiences low tag reading performance, and wastes valuable energy. Therefore, it is important that RFID application developers are aware of current tag reading protocols. To this end, this paper surveys, classifies, and compares state-of-the-art tag reading protocols. Moreover, it presents research directions for existing and future tag reading protocols.

On the energy consumption of Pure and Slotted Aloha based RFID anti-collision protocols

A recent development in wireless sensor networks (WSNs) research is to equip sensor nodes with an RFID reader so that they can be used to track animate or in-animate RFID tagged objects. A key problem in such networks, however, is the energy efficiency of current RFID anti-collision protocols. Specifically, the energy cost incurred by a RFID reader to read and monitor n tags.This paper, therefore, aims to identify the most energy efficient variant among 12 Pure and Slotted Aloha based RFID anti-collision protocols. We present an analytical methodology that evaluates the energy consumed in the following phases: (i) success, (ii) collision, and (iii) idle listening. We first calculate the delay of each phase and then use it to formulate the energy consumption, battery lifetime, and battery wastage of all variants. We found that the Pure Aloha with fast mode consumes the lowest energy and is suitable for tag identification. However, none of the protocols promises energy efficient monitoring of identified tags. In other words, the reader is required to re-read all tags every time to sense their presence; a process that consumes a significant amount of energy.

An Investigation into thie Energy Eficiency of Pure and Slotted Aloha Based REID Anti-Collision Protocols

This paper investigates the energy efficiency of RFID anti-collision protocols and their suitability for use in RFID-enhanced wireless sensor networks (WSNs). We present a detailed analytical methodology and an in-depth qualitative and quantitative energy consumption analysis of Pure and Slotted Aloha anti-collision protocols and their variants. We find that Slotted Aloha variants that employ muting with early-end are the most energy efficient, but are computationally expensive. Overall, for all Aloha variants we investigated, if the offered load is very high, tag responses cause a bottleneck at the reader. Thereby, resulting in no tags being identified and incur significant identification delays ¿ thus severely impacting a sensor nodes battery life.

On the Suitability of Framed Slotted Aloha based RFID Anti-collision Protocols for Use in RFID-Enhanced WSNs

This paper studies the energy consumption of frame slotted Aloha (FSA) based anti-collision protocols. Specifically, we investigate twelve FSA variants using a detailed qualitative and quantitative methodology to evaluate their energy efficiency with varying tag population. Our results show that the variant that adjusts its frame size in accordance with tag population and incorporates the muting and early-end feature has the lowest energy consumption, hence most suited for RFID-enhanced WSNs.

On the Accuracy of RFID Tag Estimation Functions

Dynamic framed slotted Aloha (DFSA) based tag reading protocols rely on a tag estimation function to calculate the best frame size to use for a given tag set. An inaccurate estimate results in high identification delays and unnecessary energy wastage. This is particularly serious when DFSA based tag reading protocols are used in RFID-enhanced wireless sensor networks (WSNs), where nodes are battery constrained. To this end, this paper presents qualitative and quantitative analysis of five tag estimation functions using Monte Carlo simulations. We iteratively estimate a given set of tags and evaluate the mean error, variability, skew and Kurtosis of each functions error distribution. Lastly, we compare and identify the most efficient tag estimation function that is suitable for RFID-enhanced WSNs.

A Novel Anti-Collision Protocol for Energy Efficient Identification and Monitoring in RFID-Enhanced WSNs

This paper presents a dynamic framed slotted Aloha (DFSA) protocol that is energy efficient, and more importantly, is the first protocol capable of monitoring tags. Our protocol uses three separate frames: 1) reservation, 2) body, and 3) monitor. The reservation and body frame are used to identify tags, whereas the monitor frame is used to keep track of identified tags. We have performed extensive simulation studies on all three frames, and compared our protocol with existing framed Aloha protocols. From our results, we confirm that our protocol is suitable for use in RFID-enhanced wireless sensor networks (WSNs).

E2MAC: An energy efficient MAC for RFID-enhanced wireless sensor networks

The primary aim of any anti-collision protocols is to identify tags quickly, as doing so ensures that a Radio Frequency IDentification (RFID) reader incurs minimal energy wastage and achieves high identification rate. To date, researchers have proposed various protocols to minimize tag collisions and idle slots-key factors that determine a readers read rate and energy expenditure. Most of these protocols, however, are designed for single reader systems. To this end, we propose E^2MAC, an energy efficient, distributed Medium Access Control (MAC) protocol for identifying and monitoring tags in RFID-enhanced wireless sensor networks. E^2MAC exploits the low power capability of a ultra-wideband transceiver and distinct pulses to address the reader collision problem. In addition, it uses ResMon, an enhanced dynamic frame slotted Aloha protocol to read and monitor tags. Lastly, E^2MAC uses a novel load balancing algorithm to amortize the cost of reading and monitoring tags to multiple readers. These E^2MAC features ensure that the contention level at each reader is kept at a minimum and distributed fairly. As a result, E^2MAC has a high reading rate and low energy consumption. In addition, E^2MAC helps in minimizing the impact of the tag orientation problem, where a tag becomes unreadable if its antenna is parallel to a readers field lines. In particular, the use of multiple readers increases spatial diversity and hence increases the likelihood that a tag is readable by at least one reader. Our simulation results show E^2MAC to have very low energy consumption, reading delay and per-reader collision. More importantly, system designers have the flexibility to lower these metrics further with additional readers, bigger frame sizes, or by dividing tags into small groups.

A Simulation Study on the Energy Efficiency of Pure and Slotted Aloha Based RFID Tag Reading Protocols

This paper studies the energy efficiency of twelve Pure and Slotted Aloha tag reading protocol variants via simulation. We compare their energy consumption in three collision resolution phases: 1) success, 2) collision, and 3) idle. Our extensive simulation results show that Pure Aloha with fast mode and muting has the lowest energy consumption, and hence is most suited for deployment in energy-constrained environments.