A survey of RFID readers anticollision protocols

International audienceWhile RFID technology is gaining increased attention from industrial community deploying different RFID-based applications, it still suffers from reading collisions. As such, many proposals were made by the scientific community to try and alleviate that issue using different techniques either centralized or distributed, monochannel or multichannels, TDMA or CSMA. However, the wide range of solutions and their diversity make it hard to have a clear and fair overview of the different works. This paper surveys the most relevant and recent known state-of-the-art anti-collision for RFID protocols. It provides a classification and performance evaluation taking into consideration different criteria as well as a guide to choose the best protocol for given applications depending on their constraints or requirements but also in regard to their deployment environments

Energy Efficient Protocols for Active RFID

Radio frequency identification (RFID) systems come in different flavours; passive, active, semi-passive, or semi-active. Those different types of RFID are supported by different, internationally accepted protocol standards as well as by several accepted proprietary protocols. Even though the diversity is large between the flavours and between the standards, the RFID technology has evolved to be a mature technology, which is ready to be used in a large variety of applications. This thesis explores active RFID technology and how to develop and apply data communication protocols that are energy efficient and which comply with the different application constraints. The use of RFID technology is growing rapidly, and today mostly “passive” RFID systems are used because no onboard energy source is needed on the transponder (tag). However, the use of “active” RFID-tags with onboard power sources adds a range of opportunities not possible with passive tags. Besides that Active RFID offers increased working distance between the interrogator (RFID-reader) and tags, the onboard power source also enables the tags to do sensor measurements, calculations and storage even when no RFID-reader is in the vicinity of the tags. To obtain energy efficiency in an Active RFID system the communication protocol to be used should be carefully designed. This thesis describes how energy consumption can be calculated, to be used in protocol definition, and how evaluation of protocols in this respect can be made. The performance of such a new protocol, in terms of energy efficiency, aggregated throughput, delay, and number of collisions in the radio channel is evaluated and compared to an existing, commercially available protocol for Active RFID, as well as to the IEEE standard 802.15.4 (used, e.g., in the Zigbee medium-access layer). Simulations show that, by acknowledging the payload and using deep sleep mode on the tag, the lifetime of a tag is increased. For all types of protocols using a radio channel, when arbitrating information, it is obvious that the utilization of that channel is maximized when no collisions occur. To avoid and minimize collisions in the media it is possible to intercept channel interference by using carrier sense technology. The knowledge that the channel is occupied should result in a back-off and a later retry, instead of persistently listening to the channel which would require constant energy consumption. We study the effect on tag energy cost and packet delay incurred by some typical back-off algorithms (constant, linear, and exponential) used in a contention based CSMA/CA (Carrier Sense Multiple Access/ Collision Avoidance) protocol for Active RFID communication. The study shows that, by selecting the proper back-off algorithm coefficients (based on the number of tags and the application constraints), i.e., the initial contention window size and back-off interval coefficient, the tag energy consumption and read-out delays can be significantly lowered. The initial communication between reader and tag, on a control channel, establishes those important protocol parameters in the tag so that it tries to deliver its information according to the current application scenario in an energy efficient way. The decision making involved in calculating the protocol parameters is conducted in the local RFID-reader for highest efficiency. This can be done by using local statistics or based on knowledge provided by the logistic backbone databases. As the CMOS circuit technology evolves, new possibilities arise for mass production of low price and long life active tags. The use of wake-up radio technology makes it possible for active tags to react on an RFID-reader at any time, in contrast to tags with cyclic wake-up behaviour. The two main drawbacks with an additional wake-up circuit in a tag are the added die area and the added energy consumption. Within this project the solution is a complete wake-up radio transceiver consisting of only one hi-frequency very low power, and small area oscillator. To support this tag topology we propose and investigate a novel reader-tag communication protocol, the frequency binary tree protocol

TriSense: RFID, radar, and USRP-based hybrid sensing system for enhanced sensing and monitoring

This thesis presents a comprehensive approach to contactless human activity recognition (HAR) using the capabilities of three distinct technologies: radio frequency identification (RFID), Radar, and universal software-defined radio peripheral (USRP) for capturing and processing Wi-Fi-based signals. These technologies are then fused to enhance smart healthcare systems. The study initially utilises USRP devices to analyse Wi-Fi channel state information (CSI), choosing this over received signal strength for more accurate activity recognition. It employs a combination of machine learning and a hybrid of deep learning algorithms, such as the super learner and LSTM-CNN, for precise activity localisation. Subsequently, the study progresses to incorporate a transparent RFID tag wall (TRT-Wall) that employs a passive ultra-high frequency (UHF) RFID tag array. This RFID system has proven highly accurate in distinguishing between various activities, including sitting, standing, leaning, falling, and walking in two directions. Its effectiveness and non-intrusiveness make it particularly suited for elderly care, achieved using a modified version of the Transformer model without the use of a decoder. Furthermore, a significant advancement within this study is the creation of a novel fusion (RFiDARFusion) system, which combines RFID and Radar technologies. This system employs a long short-term memory networks variational autoencoder (LSTM-VAE) fusion model, utilising RFID amplitude and Radar RSSI data. This fusion approach significantly improves accuracy in challenging scenarios, such as those involving long-range and non-line-of-sight conditions. The RFiDARFusion system notably improves the detection of complex activities, highlighting its potential to reduce healthcare costs and enhance the quality of life for elderly patients in assisted living facilities. Overall, this thesis highlights the significant potential of radio frequency technologies with artif icial intelligence, along with their combined application, to develop robust, privacy-conscious, and cost-effective solutions for healthcare and assisted living monitoring systems